Sample records for pressure gradient induced
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Relationship between exercise pressure gradient and haemodynamic progression of aortic stenosis.
Ringle, Anne; Levy, Franck; Ennezat, Pierre-Vladimir; Le Goffic, Caroline; Castel, Anne-Laure; Delelis, François; Menet, Aymeric; Malaquin, Dorothée; Graux, Pierre; Vincentelli, André; Tribouilloy, Christophe; Maréchaux, Sylvestre
We hypothesized that large exercise-induced increases in aortic mean pressure gradient can predict haemodynamic progression during follow-up in asymptomatic patients with aortic stenosis. We retrospectively identified patients with asymptomatic moderate or severe aortic stenosis (aortic valve area<1.5cm 2 or<1cm 2 ) and normal ejection fraction, who underwent an exercise stress echocardiography at baseline with a normal exercise test and a resting echocardiography during follow-up. The relationship between exercise-induced increase in aortic mean pressure gradient and annualised changes in resting mean pressure gradient during follow-up was investigated. Fifty-five patients (mean age 66±15 years; 45% severe aortic stenosis) were included. Aortic mean pressure gradient significantly increased from rest to peak exercise (P<0.001). During a median follow-up of 1.6 [1.1-3.2] years, resting mean pressure gradient increased from 35±13mmHg to 48±16mmHg, P<0.0001. Median annualised change in resting mean pressure gradient during follow-up was 5 [2-11] mmHg. Exercise-induced increase in aortic mean pressure gradient did correlate with annualised changes in mean pressure gradient during follow-up (r=0.35, P=0.01). Hemodynamic progression of aortic stenosis was faster in patients with large exercise-induced increase in aortic mean pressure gradient (≥20mmHg) as compared to those with exercise-induced increase in aortic mean pressure gradient<20mmHg (median annualised increase in mean pressure gradient 19 [6-28] vs. 4 [2-10] mmHg/y respectively, P=0.002). Similar results were found in the subgroup of 30 patients with moderate aortic stenosis. Large exercise-induced increases in aortic mean pressure gradient correlate with haemodynamic progression of stenosis during follow-up in patients with asymptomatic aortic stenosis. Further studies are needed to fully establish the role of ESE in the decision-making process in comparison to other prognostic markers in asymptomatic patients with aortic stenosis. Copyright © 2017 Elsevier Masson SAS. All rights reserved.
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An analysis of induced pressure fields in electroosmotic flows through microchannels.
Zhang, Yonghao; Gu, Xiao-Jun; Barber, Robert W; Emerson, David R
2004-07-15
Induced pressure gradients are found to cause band-broadening effects which are important to the performance of microfluidic devices, such as capillary electrophoresis and capillary chromatography. An improved understanding of the underlying mechanisms causing an induced pressure gradient in electroosmotic flows is presented. The analysis shows that the induced pressure distribution is the key to understanding the experimentally observed phenomena of leakage flows. A novel way of determining the static pressures at the inlet and outlet of microchannels is also presented that takes account of the pressure losses due to flow contraction and expansion. These commonly neglected pressure losses at the channel entrance and outlet are shown to be important in accurately describing the flow. The important parameters that define the effect of induced pressure on the flows are discussed, which may facilitate the design of improved microfluidic devices. The present model clearly identifies the mechanism behind the experimentally observed leakage flows, which is further confirmed by numerical simulations. Not only can the leakage flow occur from the electric-field-free side channel to the main channel, but also the fluid in the main channel can be attracted into the side channel by the induced pressure gradient. Copyright 2004 Elsevier Inc.
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Kim, Yong Joon; Jo, Sungkil; Moon, Daruchi; Joo, Youngcheol; Choi, Kyung Seek
2014-05-01
To comprehend the mechanism of focal chorioretinal damage by analysis of the pressure distribution and dynamic pressure induced by infused air during fluid-air exchange. A precise simulation featuring a model eye and a fluid circuit was designed to analyze fluid-air exchange. The pressure distribution, flow velocity, and dynamic pressure induced by infusion of air into an air-filled eye were analyzed using an approach based on fluid dynamics. The size of the port and the infusion pressure were varied during simulated iterations. We simulated infusion of an air-filled eye with balanced salt solution (BSS) to better understand the mechanism of chorioretinal damage induced by infused air. Infused air was projected straight toward a point on the retina contralateral to the infusion port (the "vulnerable point"). The highest pressure was evident at the vulnerable point, and the lowest pressure was recorded on most retinal areas. Simulations using greater infusion pressure and a port of larger size were associated with elevations in dynamic pressure and the pressure gradient. The pressure gradients were 2.8 and 5.1 mm Hg, respectively, when infusion pressures of 30 and 50 mm Hg were delivered through a 20-gauge port. The pressure gradient associated with BSS infusion was greater than that created by air, but lasted for only a moment. Our simulation explains the mechanism of focal chorioretinal damage in numerical terms. Infused air induces a prolonged increase in focal pressure on the vulnerable point, and this may be responsible for visual field defects arising after fluid-air exchange. Copyright 2014 The Association for Research in Vision and Ophthalmology, Inc.
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NASA Astrophysics Data System (ADS)
Semenov, Semen; Schimpf, Martin
2004-01-01
The movement of molecules and homopolymer chains dissolved in a nonelectrolyte solvent in response to a temperature gradient is considered a consequence of temperature-induced pressure gradients in the solvent layer surrounding the solute molecules. Local pressure gradients are produced by nonuniform London van der Waals interactions, established by gradients in the concentration (density) of solvent molecules. The density gradient is produced by variations in solvent thermal expansion within the nonuniform temperature field. The resulting expression for the velocity of the solute contains the Hamaker constants for solute-solvent and solute-solute interactions, the radius of the solute molecule, and the viscosity and cubic coefficient of thermal expansion of the solvent. In this paper we consider an additional force that arises from directional asymmetry in the interaction between solvent molecules. In a closed cell, the resulting macroscopic pressure gradient gives rise to a volume force that affects the motion of dissolved solutes. An expression for this macroscopic pressure gradient is derived and the resulting force is incorporated into the expression for the solute velocity. The expression is used to calculate thermodiffusion coefficients for polystyrene in several organic solvents. When these values are compared to those measured in the laboratory, the consistency is better than that found in previous reports, which did not consider the macroscopic pressure gradient that arises in a closed thermodiffusion cell. The model also allows for the movement of solute in either direction, depending on the relative values of the solvent and solute Hamaker constants.
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Markham, Larry W; Knecht, Sandra K; Daniels, Stephen R; Mays, Wayne A; Khoury, Philip R; Knilans, Timothy K
2004-11-01
Often, the lack of systemic arterial hypertension and the lack of a resting arm-leg blood pressure gradient are used to assess the adequacy of the anatomic result after intervention for coarctation of the aorta (CoA). Some patients with no arm-leg gradient at rest may develop a gradient with exercise, leading caregivers to question the success of the repair. It is not clear what the prevalence is of patients who have undergone a successful intervention for CoA and have no arm-leg gradient at rest but develop a significant gradient with exercise and which factors may predict the development of an arm-leg gradient with exercise. This study evaluates the prevalence and predictors of an exercise-induced arm-leg gradient in subjects who have undergone an apparently successful intervention for CoA.
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Bed failure induced by internal solitary waves
NASA Astrophysics Data System (ADS)
Rivera-Rosario, Gustavo A.; Diamessis, Peter J.; Jenkins, James T.
2017-07-01
The pressure field inside a porous bed induced by the passage of an Internal Solitary Wave (ISW) of depression is examined using high-accuracy numerical simulations. The velocity and density fields are obtained by solving the Dubreil-Jacotin-Long Equation, for a two-layer, continuously stratified water column. The total wave-induced pressure across the surface of the bed is computed by vertically integrating for the hydrostatic and nonhydrostatic contributions. The bed is assumed to be a continuum composed of either sand or silt, with a small amount of trapped gas. Results show variations in pore-water pressure penetrating deeper into more conductive materials and remaining for a prolonged period after the wave has passed. In order to quantify the potential for failure, the vertical pressure gradient is compared against the buoyant weight of the bed. The pressure gradient exceeds this weight for weakly conductive materials. Failure is further enhanced by a decrease in bed saturation, consistent with studies in surface-wave induced failure. In deeper water, the ISW-induced pressure is stronger, causing failure only for weakly conductive materials. The pressure associated with the free-surface displacement that accompanies ISWs is significant, when the water depth is less than 100 m, but has little influence when it is greater than 100 m, where the hydrostatic pressure due to the pycnocline displacement is much larger. Since the pore-pressure gradient reduces the specific weight of the bed, results show that particles are easier for the flow to suspend, suggesting that pressure contributes to the powerful resuspension events observed in the field.
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NASA Technical Reports Server (NTRS)
Rose, W. C.
1973-01-01
The results of an experimental investigation of the mean- and fluctuating-flow properties of a compressible turbulent boundary layer in a shock-wave-induced adverse pressure gradient are presented. The turbulent boundary layer developed on the wall of an axially symmetric nozzle and test section whose nominal free-stream Mach number and boundary-layer thickness Reynolds number were 4 and 100,000, respectively. The adverse pressure gradient was induced by an externally generated conical shock wave. Mean and time-averaged fluctuating-flow data, including the complete experimental Reynolds stress tensor and experimental turbulent mass- and heat-transfer rates are presented for the boundary layer and external flow, upstream, within and downstream of the pressure gradient. The mean-flow data include distributions of total temperature throughout the region of interest. The turbulent mixing properties of the flow were determined experimentally with a hot-wire anemometer. The calibration of the wires and the interpretation of the data are discussed. From the results of the investigation, it is concluded that the shock-wave - boundary-layer interaction significantly alters the turbulent mixing characteristics of the boundary layer.
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Dynamic variation in sapwood specific conductivity in six woody species
Jean-Christophe Domec; Frederick C. Meinzer; Barbara Lachenbruch; Johann Housset
2008-01-01
Our goals were to quantify how non-embolism inducing pressure gradients influence trunk sapwood specific conductivity (ks) and to compare the impacts of constant and varying pressure gradients on ks with KCl and H20 as the perfusion solutions. We studied six woody species (three conifers and three...
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Cardiovascular Pressures with Venous Gas Embolism and Decompression
NASA Technical Reports Server (NTRS)
Butler, B. D.; Robinson, R.; Sutton, T.; Kemper, G. B.
1995-01-01
Venous gas embolism (VGE) is reported with decompression to a decreased ambient pressure. With severe decompression, or in cases where an intracardiac septal defect (patent foramen ovale) exists, the venous bubbles can become arterialized and cause neurological decompression illness. Incidence rates of patent foramen ovale in the general population range from 25-34% and yet aviators, astronauts, and deepsea divers who have decompression-induced venous bubbles do not demonstrate neurological symptoms at these high rates. This apparent disparity may be attributable to the normal pressure gradient across the atria of the heart that must be reversed for there to be flow potency. We evaluated the effects of: venous gas embolism (0.025, 0.05 and 0.15 ml/ kg min for 180 min.) hyperbaric decompression; and hypobaric decompression on the pressure gradient across the left and right atria in anesthetized dogs with intact atrial septa. Left ventricular end-diastolic pressure was used as a measure of left atrial pressure. In a total of 92 experimental evaluations in 22 dogs, there were no reported reversals in the mean pressure gradient across the atria; a total of 3 transient reversals occurred during the peak pressure gradient changes. The reasons that decompression-induced venous bubbles do not consistently cause serious symptoms of decompression illness may be that the amount of venous gas does not always cause sufficient pressure reversal across a patent foramen ovale to cause arterialization of the venous bubbles.
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NASA Astrophysics Data System (ADS)
Ouyed, Amir; Ouyed, Rachid; Jaikumar, Prashanth
2018-02-01
We simulate and study the microphysics of combustion (flame burning) of two flavored quark matter (u,d) to three flavored quark matter (u,d,s) in a trapped neutrino regime applicable to conditions prevailing in a hot proto-neutron star. The reaction-diffusion-advection equations for (u,d) to (u,d,s) combustion are coupled with neutrino transport, which is modeled through a flux-limited diffusion scheme. The flame speed is proportional to initial lepton fraction because of the release of electron chemical potential as heat, and reaches a steady-state burning speed of (0.001-0.008)c. We find that the burning speed is ultimately driven by the neutrino pressure gradient, given that the pressure gradient induced by quarks is opposed by the pressure gradients induced by electrons. This suggests, somewhat counter-intuitively, that the pressure gradients that drive the interface are controlled primarily by leptonic weak decays rather than by the quark Equation of State (EOS). In other words, the effects of the leptonic weak interaction, including the corresponding weak decay rates and the EOS of electrons and neutrinos, are at least as important as the uncertainties related to the EOS of high density matter. We find that for baryon number densities nB ≤ 0.35 fm-3, strong pressure gradients induced by leptonic weak decays drastically slow down the burning speed, which is thereafter controlled by the much slower burning process driven by backflowing downstream matter. We discuss the implications of our findings to proto-neutron stars.
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Tidally influenced alongshore circulation at an inlet-adjacent shoreline
Hansen, Jeff E.; Elias, Edwin P.L.; List, Jeffrey H.; Erikson, Li H.; Barnard, Patrick L.
2013-01-01
The contribution of tidal forcing to alongshore circulation inside the surfzone is investigated at a 7 km long sandy beach adjacent to a large tidal inlet. Ocean Beach in San Francisco, CA (USA) is onshore of a ∼150 km2 ebb-tidal delta and directly south of the Golden Gate, the sole entrance to San Francisco Bay. Using a coupled flow-wave numerical model, we find that the tides modulate, and in some cases can reverse the direction of, surfzone alongshore flows through two separate mechanisms. First, tidal flow through the inlet results in a barotropic tidal pressure gradient that, when integrated across the surfzone, represents an important contribution to the surfzone alongshore force balance. Even during energetic wave conditions, the tidal pressure gradient can account for more than 30% of the total alongshore pressure gradient (wave and tidal components) and up to 55% during small waves. The wave driven component of the alongshore pressure gradient results from alongshore wave height and corresponding setup gradients induced by refraction over the ebb-tidal delta. Second, wave refraction patterns over the inner shelf are tidally modulated as a result of both tidal water depth changes and strong tidal flows (∼1 m/s), with the effect from currents being larger. These tidally induced changes in wave refraction result in corresponding variability of the alongshore radiation stress and pressure gradients within the surfzone. Our results indicate that tidal contributions to the surfzone force balance can be significant and important in determining the direction and magnitude of alongshore flow.
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Gao, Chan; Zhang, Xueyong; Zhang, Chuanchao; Sui, Zhilei; Hou, Meng; Dai, Rucheng; Wang, Zhongping; Zheng, Xianxu; Zhang, Zengming
2018-05-17
Herein, pressure-induced phase transitions of RDX up to 50 GPa were systematically studied under different compression conditions. Precise phase transition points were obtained based on high-quality Raman spectra with small pressure intervals. This favors the correctness of the theoretical formula for detonation and the design of a precision weapon. The experimental results indicated that α-RDX immediately transformed to γ-RDX at 3.5 GPa due to hydrostatic conditions and possible interaction between the penetrating helium and RDX, with helium gas as the pressure-transmitting medium (PTM). Mapping of pressure distribution in samples demonstrates that the pressure gradient is generated in the chamber and independent of other PTMs. The gradient induced the first phase transition starts at 2.3 GPa and completed at 4.1 GPa. The larger pressure gradient promoted phase transition in advance under higher pressures. Experimental results supported that there existed two conformers of AAI and AAE for γ-RDX, as proposed by another group. δ-RDX was considered to only occur in a hydrostatic environment around 18 GPa using helium as the PTM. This study confirms that δ-RDX is independent of PTM and exists under non-hydrostatic conditions. Evidence for a new phase (ζ) was found at about 28 GPa. These 4 phases have also been verified via XRD under high pressures. In addition to this, another new phase (η) may exist above 38 GPa, and it needs to be further confirmed in the future. Moreover, all the phase transitions were reversible after the pressure was released, and original α-RDX was always obtained at ambient pressure.
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Delaunois, A; Gustin, P; Dessy-Doize, C; Ansay, M
1994-01-01
1. The modulatory role of neuropeptide Y (NPY) on pulmonary oedema induced by acetylcholine and capsaicin was investigated. The effects of NPY on the haemodynamic response to acetylcholine, phenylephrine and substance P were also investigated. 2. Isolated, ventilated, exsanguinated lungs of the rabbit were perfused with a constant flow of recirculating blood-free perfusate. The double/arterial/venous occlusion method was used to partition the total pressure gradient (delta Pt) into four components: the arterial gradient (delta Pa), the pre- and post-capillary gradients (respectively delta Pa' and delta Pv') and the venous pressure gradient (delta Pv). Endothelial permeability was evaluated by measuring the capillary filtration coefficient (Kf,c). 3. Acetylcholine (10(-8) M to 10(-4) M) and substance P (SP, 10(-10) M to 10(-6) M) induced a concentration-dependent increase in the Kf,c. Capsaicin (10(-4) M) and 5-hydroxytryptamine (5-HT) (10(-4) M) also increased this parameter. NPY (10(-8) M) completely inhibited the effects of acetylcholine and capsaicin on the Kf,c, without preventing the effects of substance P and 5-HT. 4. Acetylcholine induced concentration-dependent vasoconstriction in the precapillary segment. The effect was inhibited by NPY and aspirin, an inhibitor of cyclo-oxygenase, while ketanserin, a 5-HT2 receptor antagonist, and SR140333, a new NK1 antagonist, had no protective effect. Phenylephrine increased delta Pa at high concentration, an effect also inhibited by NPY and aspirin. Substance P had no significant haemodynamic effect. When injected together with NPY, substance P (10(-6) M) induced a significant increase in the total pressure gradient.(ABSTRACT TRUNCATED AT 250 WORDS) Images Figure 2 Figure 3 PMID:7532083
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A wet/wet differential pressure sensor for measuring vertical hydraulic gradient.
Fritz, Brad G; Mackley, Rob D
2010-01-01
Vertical hydraulic gradient is commonly measured in rivers, lakes, and streams for studies of groundwater-surface water interaction. While a number of methods with subtle differences have been applied, these methods can generally be separated into two categories; measuring surface water elevation and pressure in the subsurface separately or making direct measurements of the head difference with a manometer. Making separate head measurements allows for the use of electronic pressure sensors, providing large datasets that are particularly useful when the vertical hydraulic gradient fluctuates over time. On the other hand, using a manometer-based method provides an easier and more rapid measurement with a simpler computation to calculate the vertical hydraulic gradient. In this study, we evaluated a wet/wet differential pressure sensor for use in measuring vertical hydraulic gradient. This approach combines the advantage of high-temporal frequency measurements obtained with instrumented piezometers with the simplicity and reduced potential for human-induced error obtained with a manometer board method. Our results showed that the wet/wet differential pressure sensor provided results comparable to more traditional methods, making it an acceptable method for future use.
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NASA Technical Reports Server (NTRS)
Throckmorton, D. A.
1975-01-01
An experimental investigation was performed to determine the effect of pressure gradient on the heat transfer to space shuttle reusable surface insulation (RSI) tile array gaps under thick, turbulent boundary layer conditions. Heat transfer and pressure measurements were obtained on a curved array of full-scale simulated RSI tiles in a tunnel wall boundary layer at a nominal freestream Mach number of 10.3 and freestream unit Reynolds numbers of 1.6, 3.3, and and 6.1 million per meter. Transverse pressure gradients were induced over the model surface by rotating the curved array with respect to the flow. Definition of the tunnel wall boundary layer flow was obtained by measurement of boundary layer pitot pressure profiles, and flat plate wall pressure and heat transfer. Flat plate wall heat transfer data were correlated and a method was derived for prediction of smooth, curved array heat transfer in the highly three-dimensional tunnel wall boundary layer flow and simulation of full-scale space shuttle vehicle pressure gradient levels was assessed.
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Smit, C A J; Haverkamp, G L G; de Groot, S; Stolwijk-Swuste, J M; Janssen, T W J
2012-08-01
Ten participants underwent two electrical stimulation (ES) protocols applied using a custom-made electrode garment with built-in electrodes. Interface pressure was measured using a force-sensitive area. In one protocol, both the gluteal and hamstring (g+h) muscles were activated, in the other gluteal (g) muscles only. To study and compare the effects of electrically induced activation of g+h muscles versus g muscles only on sitting pressure distribution in individuals with a spinal cord injury (SCI). Ischial tuberosities interface pressure (ITs pressure) and pressure gradient. In all participants, both protocols of g and g+h ES-induced activation caused a significant decrease in IT pressure. IT pressure after g+h muscles activation was reduced significantly by 34.5% compared with rest pressure, whereas a significant reduction of 10.2% after activation of g muscles only was found. Pressure gradient reduced significantly only after stimulation of g+h muscles (49.3%). g+h muscles activation showed a decrease in pressure relief (Δ IT) over time compared with g muscles only. Both protocols of surface ES-induced of g and g+h activation gave pressure relief from the ITs. Activation of both g+h muscles in SCI resulted in better IT pressure reduction in sitting individuals with a SCI than activation of g muscles only. ES might be a promising method in preventing pressure ulcers (PUs) on the ITs in people with SCI. Further research needs to show which pressure reduction is sufficient in preventing PUs.
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Observations of wave-induced pore pressure gradients and bed level response on a surf zone sandbar
NASA Astrophysics Data System (ADS)
Anderson, Dylan; Cox, Dan; Mieras, Ryan; Puleo, Jack A.; Hsu, Tian-Jian
2017-06-01
Horizontal and vertical pressure gradients may be important physical mechanisms contributing to onshore sediment transport beneath steep, near-breaking waves in the surf zone. A barred beach was constructed in a large-scale laboratory wave flume with a fixed profile containing a mobile sediment layer on the crest of the sandbar. Horizontal and vertical pore pressure gradients were obtained by finite differences of measurements from an array of pressure transducers buried within the upper several centimeters of the bed. Colocated observations of erosion depth were made during asymmetric wave trials with wave heights between 0.10 and 0.98 m, consistently resulting in onshore sheet flow sediment transport. The pore pressure gradient vector within the bed exhibited temporal rotations during each wave cycle, directed predominantly upward under the trough and then rapidly rotating onshore and downward as the wavefront passed. The magnitude of the pore pressure gradient during each phase of rotation was correlated with local wave steepness and relative depth. Momentary bed failures as deep as 20 grain diameters were coincident with sharp increases in the onshore-directed pore pressure gradients, but occurred at horizontal pressure gradients less than theoretical critical values for initiation of the motion for compact beds. An expression combining the effects of both horizontal and vertical pore pressure gradients with bed shear stress and soil stability is used to determine that failure of the bed is initiated at nonnegligible values of both forces.
Plain Language SummaryThe pressure gradient present within the seabed beneath breaking waves may be an important physical mechanism transporting sediment. A large-scale laboratory was used to replicate realistic surfzone conditions in controlled tests, allowing for horizontal and vertical pressure gradient magnitudes and the resulting sediment bed response to be observed with precise instruments. Contrary to previous studies, the pore pressure gradient exhibited a range of values when erosion occurred, which indicates that erosion is the result of multiple physical mechanisms competing to secure or destabilize the sediment bed. The observations provide a better understanding of the forces acting within the sediment, and could improve parameters used in coastal sediment transport models to better predict coastal change.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28029367','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28029367"><span>On the feasibility to conduct gradient liquid chromatography separations in narrow-bore columns at pressures up to 2000bar.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>De Pauw, Ruben; Swier, Tim; Degreef, Bart; Desmet, Gert; Broeckhoven, Ken</p> <p>2016-11-18</p> <p>The limits in operating pressures are extended for narrow-bore columns in gradient elution up to 2000bar. As the required pumps for these pressures are incompatible with common chromatographic solvents and are not suitable to apply a mobile phase composition gradient, a mobile phase delivery and injection system is described and experimentally validated which allows to use any possible chromatographic solvent in isocratic and gradient elution. The mobile phase delivery and injection system also allows to perform multiple separations without the need to depressurize the column. This system consists out of 5 dual on/off valves and two large volume loops in which the gradient and equilibration volume of initial mobile phase are loaded by a commercial liquid chromatography pump. The loops are then flushed toward the column at extreme pressures. The mobile phase delivery and injection system is first evaluated in isocratic elution and shows a comparable performance to a state-of-the-art commercial flow-through-needle injector but with twice the pressure rating. Distortion of the loaded gradient by dispersion in the gradient storage loop is studied. The effect of the most important parameters (such as flow rate, pressure and gradient steepness) is experimentally investigated. Different gradient steepnesses and volumes can be applied at different flow rates and operating pressures with a good repeatability. Due to the isobaric operation of the pumps, the gradient is monitored in real-time by a mass flow meter installed at the detector outlet. The chromatograms are then converted from time to volume-base. A separation of a 19-compound sample is performed on a 300×2.1mm column at 1000bar and on a 600×2.1mm column at 2000bar. The peak capacity was found to increase from 141 to 199 and thus scales with L as is predicted by theory. This allows to conclude that the inlet pressure for narrow-bore columns in gradient elution can be increased up to 2000bar without fundamental pressure-induced limitations. Copyright © 2016 Elsevier B.V. All rights reserved.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25597807','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25597807"><span>Rapid concentration of deoxyribonucleic acid via Joule heating induced temperature gradient focusing in poly-dimethylsiloxane microfluidic channel.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ge, Zhengwei; Wang, Wei; Yang, Chun</p> <p>2015-02-09</p> <p>This paper reports rapid microfluidic electrokinetic concentration of deoxyribonucleic acid (DNA) with the Joule heating induced temperature gradient focusing (TGF) by using our proposed combined AC and DC electric field technique. A peak of 480-fold concentration enhancement of DNA sample is achieved within 40s in a simple poly-dimethylsiloxane (PDMS) microfluidic channel of a sudden expansion in cross-section. Compared to a sole DC field, the introduction of an AC field can reduce DC field induced back-pressure and produce sufficient Joule heating effects, resulting in higher concentration enhancement. Within such microfluidic channel structure, negative charged DNA analytes can be concentrated at a location where the DNA electrophoretic motion is balanced with the bulk flow driven by DC electroosmosis under an appropriate temperature gradient field. A numerical model accounting for a combined AC and DC field and back-pressure driven flow effects is developed to describe the complex Joule heating induced TGF processes. The experimental observation of DNA concentration phenomena can be explained by the numerical model. Copyright © 2014 Elsevier B.V. All rights reserved.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AIPC.1113..403L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AIPC.1113..403L"><span>Therapeutic Ultrasound Enhancement of Drug Delivery to Soft Tissues</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lewis, George; Wang, Peng; Lewis, George; Olbricht, William</p> <p>2009-04-01</p> <p>Effects of exposure to 1.58 MHz focused ultrasound on transport of Evans Blue Dye (EBD) in soft tissues are investigated when an external pressure gradient is applied to induce convective flow through the tissue. The magnitude of the external pressure gradient is chosen to simulate conditions in brain parenchyma during convection-enhanced drug delivery (CED) to the brain. EBD uptake and transport are measured in equine brain, avian muscle and agarose brain-mimicking phantoms. Results show that ultrasound enhances EBD uptake and transport, and the greatest enhancement occurs when the external pressure gradient is applied. The results suggest that exposure of the brain parenchyma to ultrasound could enhance penetration of material infused into the brain during CED therapy.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li class="active"><span>1</span></li> <li><a href="#" onclick='return showDiv("page_2");'>2</a></li> <li><a href="#" onclick='return showDiv("page_3");'>3</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_1 --> <div id="page_2" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_1");'>1</a></li> <li class="active"><span>2</span></li> <li><a href="#" onclick='return showDiv("page_3");'>3</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="21"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.usgs.gov/of/2012/1062/','USGSPUBS'); return false;" href="https://pubs.usgs.gov/of/2012/1062/"><span>Migration rates and formation injectivity to determine containment time scales of sequestered carbon dioxide</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Burke, Lauri</p> <p>2012-01-01</p> <p>Additionally, this research establishes a methodology to calculate the injectivity of a target formation. Because injectivity describes the pressure increase due to the introduction of fluids into a formation, the relevant application of injectivity is to determine the pressure increase, due to an injection volume and flow rate, that will induce fractures in the reservoir rocks. This quantity is defined mathematically as the maximum pressure differential between the hydrostatic gradient and the fracture gradient of the target formation. Injectivity is mathematically related to the maximum pressure differential of the formation, and can be used to determine the upper limit for the pressure increase that an injection target can withstand before fracturing.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.fs.usda.gov/treesearch/pubs/42121','TREESEARCH'); return false;" href="https://www.fs.usda.gov/treesearch/pubs/42121"><span>Persistent wind-induced enhancement of diffusive CO2 transport in a mountain forest snowpack</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.fs.usda.gov/treesearch/">Treesearch</a></p> <p>D. R. Bowling; W. J. Massman</p> <p>2011-01-01</p> <p>Diffusion dominates the transport of trace gases between soil and the atmosphere. Pressure gradients induced by atmospheric flow and wind interacting with topographical features cause a small but persistent bulk flow of air within soil or snow. This forcing, called pressure pumping or wind pumping, leads to a poorly quantified enhancement of gas transport beyond the...</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27165887','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27165887"><span>Bernoulli's Principle Applied to Brain Fluids: Intracranial Pressure Does Not Drive Cerebral Perfusion or CSF Flow.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Schmidt, Eric; Ros, Maxime; Moyse, Emmanuel; Lorthois, Sylvie; Swider, Pascal</p> <p>2016-01-01</p> <p>In line with the first law of thermodynamics, Bernoulli's principle states that the total energy in a fluid is the same at all points. We applied Bernoulli's principle to understand the relationship between intracranial pressure (ICP) and intracranial fluids. We analyzed simple fluid physics along a tube to describe the interplay between pressure and velocity. Bernoulli's equation demonstrates that a fluid does not flow along a gradient of pressure or velocity; a fluid flows along a gradient of energy from a high-energy region to a low-energy region. A fluid can even flow against a pressure gradient or a velocity gradient. Pressure and velocity represent part of the total energy. Cerebral blood perfusion is not driven by pressure but by energy: the blood flows from high-energy to lower-energy regions. Hydrocephalus is related to increased cerebrospinal fluid (CSF) resistance (i.e., energy transfer) at various points. Identification of the energy transfer within the CSF circuit is important in understanding and treating CSF-related disorders. Bernoulli's principle is not an abstract concept far from clinical practice. We should be aware that pressure is easy to measure, but it does not induce resumption of fluid flow. Even at the bedside, energy is the key to understanding ICP and fluid dynamics.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006PhDT........47E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006PhDT........47E"><span>Supersonic turbulent boundary layers with periodic mechanical non-equilibrium</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ekoto, Isaac Wesley</p> <p></p> <p>Previous studies have shown that favorable pressure gradients reduce the turbulence levels and length scales in supersonic flow. Wall roughness has been shown to reduce the large-scales in wall bounded flow. Based on these previous observations new questions have been raised. The fundamental questions this dissertation addressed are: (1) What are the effects of wall topology with sharp versus blunt leading edges? and (2) Is it possible that a further reduction of turbulent scales can occur if surface roughness and favorable pressure gradients are combined? To answer these questions and to enhance the current experimental database, an experimental analysis was performed to provide high fidelity documentation of the mean and turbulent flow properties along with surface and flow visualizations of a high-speed (M = 2.86), high Reynolds number (Retheta ≈ 60,000) supersonic turbulent boundary layer distorted by curvature-induced favorable pressure gradients and large-scale ( k+s ≈ 300) uniform surface roughness. Nine models were tested at three separate locations. Three pressure gradient models strengths (a nominally zero, a weak, and a strong favorable pressure gradient) and three roughness topologies (aerodynamically smooth, square, and diamond shaped roughness elements) were used. Highly resolved planar measurements of mean and fluctuating velocity components were accomplished using particle image velocimetry. Stagnation pressure profiles were acquired with a traversing Pitot probe. Surface pressure distributions were characterized using pressure sensitive paint. Finally flow visualization was accomplished using schlieren photographs. Roughness topology had a significant effect on the boundary layer mean and turbulent properties due to shock boundary layer interactions. Favorable pressure gradients had the expected stabilizing effect on turbulent properties, but the improvements were less significant for models with surface roughness near the wall due to increased tendency towards flow separation. It was documented that proper roughness selection coupled with a sufficiently strong favorable pressure gradient produced regions of "negative" production in the transport of turbulent stress. This led to localized areas of significant turbulence stress reduction. With proper roughness selection and sufficient favorable pressure gradient strength, it is believed that localized relaminarization of the boundary layer is possible.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19870033194&hterms=coulomb+law&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dcoulomb%2Blaw','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19870033194&hterms=coulomb+law&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dcoulomb%2Blaw"><span>Beam-induced pressure gradients in the early phase of proton-heated solar flares</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Tamres, David H.; Canfield, Richard C.; Mcclymont, A. N.</p> <p>1986-01-01</p> <p>The pressure gradient induced in a coronal loop by proton beam momentum deposition is calculated and compared with the thermal pressure gradient arising from nonuniform deposition of beam energy; it is assumed that the transfer of momentum and energy from beam to target occurs via the Coulomb interaciton. Results are presented for both a low mean energy and a high mean energy proton beam injected at the loop apex and characterized by a power-law energy spectrum. The present treatment takes account of the breakdown of the cold target approximation for the low-energy proton beam in the corona, where the thermal speed of target electrons exceeds the beam speed. It is found that proton beam momentum deposition plays a potentially significant role in flare dynamics only in the low mean energy case and only in the corona, where it may dominate the acceleration of target material for as long as several tens of seconds. This conclusion suggest that the presence of low-energy nonthermal protons may be inferred from velocity-sensitive coronal observations in the early impulsive phase.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018NucFu..58e6004C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018NucFu..58e6004C"><span>Kinetic electromagnetic instabilities in an ITB plasma with weak magnetic shear</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chen, W.; Yu, D. L.; Ma, R. R.; Shi, P. W.; Li, Y. Y.; Shi, Z. B.; Du, H. R.; Ji, X. Q.; Jiang, M.; Yu, L. M.; Yuan, B. S.; Li, Y. G.; Yang, Z. C.; Zhong, W. L.; Qiu, Z. Y.; Ding, X. T.; Dong, J. Q.; Wang, Z. X.; Wei, H. L.; Cao, J. Y.; Song, S. D.; Song, X. M.; Liu, Yi.; Yang, Q. W.; Xu, M.; Duan, X. R.</p> <p>2018-05-01</p> <p>Kinetic Alfvén and pressure gradient driven instabilities are very common in magnetized plasmas, both in space and the laboratory. These instabilities will be easily excited by energetic particles (EPs) and/or pressure gradients in present-day fusion and future burning plasmas. This will not only cause the loss and redistribution of the EPs, but also affect plasma confinement and transport. Alfvénic ion temperature gradient (AITG) instabilities with the frequency ω_BAE<ω<ω_TAE and the toroidal mode numbers n=2{-}8 are found to be unstable in NBI internal transport barrier plasmas with weak shear and low pressure gradients, where ω_BAE and ω_TAE are the frequencies of the beta- and toroidicity-induced Alfvén eigenmodes, respectively. The measured results are consistent with the general fishbone-like dispersion relation and kinetic ballooning mode equation, and the modes become more unstable the smaller the magnetic shear is in low pressure gradient regions. The interaction between AITG activity and EPs also needs to be investigated with greater attention in fusion plasmas, such as ITER (Tomabechi and The ITER Team 1991 Nucl. Fusion 31 1135), since these fluctuations can be enhanced by weak magnetic shear and EPs.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/8160828','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/8160828"><span>Intramyocardial pressure gradients in working and nonworking isolated cat hearts.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Mihailescu, L S; Abel, F L</p> <p>1994-03-01</p> <p>This study presents an improved method for the measurement of intramyocardial pressure (IMP) using the servo-nulling mechanism. Glass micropipettes (20-24 microns OD) were used as transducers, coated to increase their mechanical resistance to breakage, and placed inside the left ventricular wall with a micropipette holder and manipulator. IMP was measured at the base of the left ventricle in working and nonworking isolated cat hearts that were perfused with Krebs-Henseleit buffer. In working hearts a transmural gradient of systolic IMP oriented from endocardium toward the epicardium was found; the endocardial values for systolic IMP were slightly higher than systolic left ventricular pressure (LVP), by 11-18%. Increases in afterload induced increases in IMP, without changing the systolic IMP-to-LVP ratio. In nonworking hearts with drained left ventricles, the systolic transmural gradient for IMP described for working hearts persisted, but at lower values, and was directly dependent on coronary perfusion pressure. Systolic IMP-to-LVP ratios were always > 1. The diastolic IMP of both working and nonworking hearts exhibited irregular transmural gradients. Our results support the view that generated systolic IMP is largely independent of LVP development.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFMOS23A1991O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFMOS23A1991O"><span>Alongshore Momentum Balance Over Shoreface-Connected Ridges, Fire Island, NY</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ofsthun, C.; Wu, X.; Voulgaris, G.; Warner, J. C.</p> <p>2016-12-01</p> <p>he momentum balance of alongshore flows over straight, uniform shelfs has been analyzed extensively over the last few decades. More recently, the effect of coastline curvature and how this might alter the relative significance of the momentum terms has received additional attention. In this contribution, the alongshore momentum over shelves with straight coastline, but non-uniform bathymetry is examined. Hydrodynamic and hydrographic data collected by the US Geological Survey (Fire Island Coastal Change project) on the inner shelf of Fire Island, NY over a region of shore-face connected ridges (SFCRs) are used to describe wind-induced circulation and the terms of the alongshore momentum balance equation. Analysis of the data revealed a predominantly alongshore circulation, under westward wind forcing, with localized offshore (onshore) current veering over the ridge crests (troughs). Momentum balance analysis hinted that local acceleration, advective acceleration, and bottom stress are balanced by wind stress and regional (>100 km) pressure gradient force. In addition, a numerical model using an idealized SFCR bathymetry, forced by our observed winds, was employed to compare the momentum balance relationships identified by the data and those under steady-state conditions published earlier (Warner et al., 2014). A synthesis of the numerical and experimental data revealed that the true pressure gradient force results from the sum of local pressure gradient force, which maintains a Bernoulli-like relationship with alongshore advective acceleration, and regional pressure gradient force, which maintains a strong, negative relationship with wind stress. The differences between steady-state and realistic conditions is mainly on the contributions of regional scale pressure gradients that develop under realistic conditions, and the reduced contribution of local scale pressure gradients which develop best under steady-state conditions. Our analysis indicates that current veering over ridge crests, a consistent occurrence, is a combination of a cross-shore gradient in the inconsistent relationship between local advective acceleration and pressure gradient and frictional-torque with the latter being the dominant mechanism under realistic forcing.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70034727','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70034727"><span>Pressure-gradient-driven nearshore circulation on a beach influenced by a large inlet-tidal shoal system</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Shi, F.; Hanes, D.M.; Kirby, J.T.; Erikson, L.; Barnard, P.; Eshleman, J.</p> <p>2011-01-01</p> <p>The nearshore circulation induced by a focused pattern of surface gravity waves is studied at a beach adjacent to a major inlet with a large ebb tidal shoal. Using a coupled wave and wave-averaged nearshore circulation model, it is found that the nearshore circulation is significantly affected by the heterogeneous wave patterns caused by wave refraction over the ebb tidal shoal. The model is used to predict waves and currents during field experiments conducted near the mouth of San Francisco Bay and nearby Ocean Beach. The field measurements indicate strong spatial variations in current magnitude and direction and in wave height and direction along Ocean Beach and across the ebb tidal shoal. Numerical simulations suggest that wave refraction over the ebb tidal shoal causes wave focusing toward a narrow region at Ocean Beach. Due to the resulting spatial variation in nearshore wave height, wave-induced setup exhibits a strong alongshore nonuniformity, resulting in a dramatic change in the pressure field compared to a simulation with only tidal forcing. The analysis of momentum balances inside the surf zone shows that, under wave conditions with intensive wave focusing, the alongshore pressure gradient associated with alongshore nonuniform wave setup can be a dominant force driving circulation, inducing heterogeneous alongshore currents. Pressure-gradient- forced alongshore currents can exhibit flow reversals and flow convergence or divergence, in contrast to the uniform alongshore currents typically caused by tides or homogeneous waves.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003JCli...16.3723S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003JCli...16.3723S"><span>Numerical Simulation of Atmospheric Response to Pacific Tropical Instability Waves(.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Small, R. Justin; Xie, Shang-Ping; Wang, Yuqing</p> <p>2003-11-01</p> <p>Tropical instability waves (TIWs) are 1000-km-long waves that appear along the sea surface temperature (SST) front of the equatorial cold tongue in the eastern Pacific. The study investigates the atmospheric planetary boundary layer (PBL) response to TIW-induced SST variations using a high-resolution regional climate model. An investigation is made of the importance of pressure gradients induced by changes in air temperature and moisture, and vertical mixing, which is parameterized in the model by a 1.5-level turbulence closure scheme. Significant turbulent flux anomalies of sensible and latent heat are caused by changes in the air sea temperature and moisture differences induced by the TIWs. Horizontal advection leads to the occurrence of the air temperature and moisture extrema downwind of the SST extrema. High and low hydrostatic surface pressures are then located downwind of the cold and warm SST patches, respectively. The maximum and minimum wind speeds occur in phase with SST, and a thermally direct circulation is created. The momentum budget indicates that pressure gradient, vertical mixing, and horizontal advection dominate. In the PBL the vertical mixing acts as a frictional drag on the pressure-gradient-driven winds. Over warm SST the mixed layer deepens relative to over cold SST. The model simulations of the phase and amplitude of wind velocity, wind convergence, and column-integrated water vapor perturbations due to TIWs are similar to those observed from satellite and in situ data.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/20080041567','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20080041567"><span>Some Simple Solutions to the Problem of Predicting Boundary-Layer Self-Induced Pressures</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bertram, Mitchel H.; Blackstock, Thomas A.</p> <p>1961-01-01</p> <p>Simplified theoretical approaches are shown, based on hypersonic similarity boundary-layer theory, which allow reasonably accurate estimates to be made of the surface pressures on plates on which viscous effects are important. The consideration of viscous effects includes the cases where curved surfaces, stream pressure gradients, and leadingedge bluntness are important factors.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017APS..DFDG17004W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017APS..DFDG17004W"><span>Low-frequency dynamics of pressure-induced turbulent separation bubbles</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Weiss, Julien; Mohammed-Taifour, Abdelouahab; Lefloch, Arnaud</p> <p>2017-11-01</p> <p>We experimentally investigate a pressure-induced turbulent separation bubble (TSB), which is generated on a flat test surface through a combination of adverse and favorable pressure gradients imposed on a nominally two-dimensional, incompressible, turbulent boundary layer. We probe the flow using piezo-resistive pressure transducers, MEMS shear-stress sensors, and high-speed, 2D-2C, PIV measurements. Through the use of Fourier analysis of the wall-pressure fluctuations and Proper Orthogonal Decomposition of the velocity fields, we show that this type of flow is characterized by a self-induced, low-frequency contraction and expansion - called breathing - of the TSB. The dominant Strouhal number of this motion, based on the TSB length and the incoming velocity in the potential flow, is of the order of 0.01. We compare this motion to the low-frequency dynamics observed in laminar separation bubbles (LSBs), geometry-induced TSBs, and shock-induced separated flows.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/biblio/21027788-thermal-gradient-induced-forces-geodesic-reference-masses-lisa','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/21027788-thermal-gradient-induced-forces-geodesic-reference-masses-lisa"><span></span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Carbone, L.; Ciani, G.; Dolesi, R.</p> <p></p> <p>The low frequency sensitivity of space-borne gravitational wave observatories will depend critically on the geodesic purity of the trajectories of orbiting test masses. Fluctuations in the temperature difference across the enclosure surrounding the free-falling test mass can produce noisy forces through several processes, including the radiometric effect, radiation pressure, and outgassing. We present here a detailed experimental investigation of thermal gradient-induced forces for the Laser Interferometer Space Antenna (LISA) gravitational wave mission and the LISA Pathfinder, employing high resolution torsion pendulum measurements of the torque on a LISA-like test mass suspended inside a prototype of the LISA gravitational reference sensormore » that will surround the test mass in orbit. The measurement campaign, accompanied by numerical simulations of the radiometric and radiation pressure effects, allows a more accurate and representative characterization of thermal-gradient forces in the specific geometry and environment relevant to LISA free-fall. The pressure dependence of the measured torques allows clear identification of the radiometric effect, in quantitative agreement with the model developed. In the limit of zero gas pressure, the measurements are most likely dominated by outgassing, but at a low level that does not threaten the current LISA noise estimate, which assumes a maximum net force per degree of temperature difference of 100(pN/K) for the overall thermal gradient-induced effects.« less</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/biblio/22210558-light-induced-cross-transport-phenomena-single-component-gas','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/22210558-light-induced-cross-transport-phenomena-single-component-gas"><span>Light-induced cross transport phenomena in a single-component gas</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Chermyaninov, I. V.; Chernyak, V. G., E-mail: Vladimir.Chernyak@usu.ru</p> <p>2013-07-15</p> <p>The cross transport processes that occur in a single-component gas in a capillary and are caused by resonance laser radiation and pressure and temperature gradients are studied. An expression for entropy production is derived using a system of kinetic Boltzmann equations in a linear approximation. The kinetic coefficients that determine the transport processes are shown to satisfy the Onsager reciprocal relations at any Knudsen numbers and any character of the elastic interaction of gas particles with the capillary surface. The light-induced baro- and thermoeffects that take place in a closed heat-insulated system in the field of resonance laser radiation aremore » considered. Analytical expressions are obtained for the Onsager coefficients in an almost free-molecular regime. The light-induced pressure and temperature gradients that appear in a closed heat-insulated capillary under typical experimental conditions are numerically estimated.« less</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29753461','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29753461"><span>Hepatic venous pressure gradient after portal vein embolization: An accurate predictor of future liver remnant hypertrophy.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Mohkam, Kayvan; Rode, Agnès; Darnis, Benjamin; Manichon, Anne-Frédérique; Boussel, Loïc; Ducerf, Christian; Merle, Philippe; Lesurtel, Mickaël; Mabrut, Jean-Yves</p> <p>2018-05-09</p> <p>The impact of portal hemodynamic variations after portal vein embolization on liver regeneration remains unknown. We studied the correlation between the parameters of hepatic venous pressure measured before and after portal vein embolization and future hypertrophy of the liver remnant after portal vein embolization. Between 2014 and 2017, we reviewed patients who were eligible for major hepatectomy and who had portal vein embolization. Patients had undergone simultaneous measurement of portal venous pressure and hepatic venous pressure gradient before and after portal vein embolization by direct puncture of portal vein and inferior vena cava. We assessed these parameters to predict future liver remnant hypertrophy. Twenty-six patients were included. After portal vein embolization, median portal venous pressure (range) increased from 15 (9-24) to 19 (10-27) mm Hg and hepatic venous pressure gradient increased from 5 (0-12) to 8 (0-14) mm Hg. Median future liver remnant volume (range) was 513 (299-933) mL before portal vein embolization versus 724 (499-1279) mL 3 weeks after portal vein embolization, representing a 35% (7.4-83.6) median hypertrophy. Post-portal vein embolization hepatic venous pressure gradient was the most accurate parameter to predict failure of future liver remnant to reach a 30% hypertrophy (c-statistic: 0.882 [95% CI: 0.727-1.000], P < 0.001). A cut-off value of post-portal vein embolization hepatic venous pressure gradient of 8 mm Hg showed a sensitivity of 91% (95% CI: 57%-99%), specificity of 80% (95% CI: 52%-96%), positive predictive value of 77% (95% CI: 46%-95%) and negative predictive value of 92.3% (95% CI: 64.0%-99.8%). On multivariate analysis, post-portal vein embolization hepatic venous pressure gradient and previous chemotherapy were identified as predictors of impaired future liver remnant hypertrophy. Post-portal vein embolization hepatic venous pressure gradient is a simple and reproducible tool which accurately predicts future liver remnant hypertrophy after portal vein embolization and allows early detection of patients who may benefit from more aggressive procedures inducing future liver remnant hypertrophy. (Surgery 2018;143:1-2.). Copyright © 2018 Elsevier Inc. All rights reserved.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015APS..DFDH36002E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015APS..DFDH36002E"><span>Pressure gradient induced generation of microbubbles</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Evangelio, Alvaro; Campo-Cortes, Francisco; Gordillo, Jose Manuel</p> <p>2015-11-01</p> <p>It is well known that the controlled production of monodisperse bubbles possesses uncountable applications in medicine, pharmacy and industry. Here we provide with a detailed physical description of the bubble formation processes taking place in a type of flow where the liquid pressure gradient can be straightforwardly controlled. In our experiments, a gas flow rate discharges through a cylindrical needle into a pressurized chamber. The pressure gradient created from the exit of the injection needle towards the entrance of a extraction duct promotes the stretching of the gas ligament downstream. In our analysis, which is supported by an exhaustive experimental study in which the liquid viscosity is varied by three orders of magnitude, different regimes can be distinguished depending mainly on the Reynolds number. Through our physical modeling, we provide closed expressions for both the bubbling frequencies and for the bubble diameters as well as the conditions under which a monodisperse generation is obtained in all regimes found. The excellent agreement between our expressions and the experimental data fully validates our physical modeling.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.S23C0825P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.S23C0825P"><span>Geothermal Gradient impact on Induced Seismicity in Raton Basin, Colorado and New Mexico</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pfeiffer, K.; Ge, S.</p> <p>2017-12-01</p> <p>Since 1999, Raton Basin, located in southeastern Colorado and northern New Mexico, is the site of wastewater injection for disposing a byproduct of coal bed methane production. During 1999-2016, 29 wastewater injection wells were active in Raton Basin. Induced seismicity began in 2001 and the largest recorded earthquake, an M5.3, occurred in August 2011. Although most injection occurs in the Dakota Formation, the majority of the seismicity has been located in the crystalline basement. Previous studies involving Raton Basin focused on high injection rates and high volume wells to determine their effect on increased pore pressure. However, the geothermal gradient has yet to be studied as a potential catalyst of seismicity. Enhanced Geothermal Systems throughout the world have experienced similar seismicity problems due to water injection. Raton's geothermal gradient, which averages 49± 12°C/km, is much higher then other areas experiencing seismicity. Thermal differences between the hot subsurface and cooler wastewater injection have the potential to affect the strength of the rock and allow for failure. Therefore, we hypothesis that wells in high geothermal gradient areas will produce more frequent earthquakes due to thermal contrast from relatively cold wastewater injection. We model the geothermal gradient in the surrounding areas of the injection sites in Raton Basin to assess potential spatial relationship between high geothermal gradient and earthquakes. Preliminary results show that the fluid pressure increase from injecting cool water is above the threshold of 0.1MPa, which has been shown to induce earthquakes. In addition, temperatures in the subsurface could decrease up to 2°C at approximately 80 m from the injection well, with a temperature effect reaching up to 100 m away from the injection well.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/biblio/6882348-holographic-interferometry-ultrasmall-pressure-induced-curvature-changes-bilayer-lipid-membranes','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/6882348-holographic-interferometry-ultrasmall-pressure-induced-curvature-changes-bilayer-lipid-membranes"><span>Holographic interferometry of ultrasmall-pressure-induced curvature changes of bilayer lipid membranes</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Picard, G.; Schneider-Henriquez, J.E.; Fendler, J.H.</p> <p></p> <p>Two-exposure interferometric holograms have been shown to sensitively report ultrasmall-pressure (10 natm)-induced curvature changes in glyceryl monooleate (GMO) bilayer lipid membranes (BLMs). The number of concentric fringes observed, and hence the lateral distance between the plane of the Teflon and the BLM, increased linearly with increasing transmembrane pressure and led to a value of 1.1 {plus minus} 0.05 dyn/cm for the surface tension of the BLM. BLMs with appreciable Plateau-Gibbs borders have been shown to undergo nonuniform deformation; the bilayer portion is distorted less than the surrounding Plateau-Gibbs border upon the application of a transmembrane pressure gradient.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24436580','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24436580"><span>Calf pump activity influencing venous hemodynamics in the lower extremity.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Recek, Cestmir</p> <p>2013-03-01</p> <p>Calf muscle pump is the motive force enhancing return of venous blood from the lower extremity to the heart. It causes displacement of venous blood in both vertical and horizontal directions, generates ambulatory pressure gradient between thigh and lower leg veins, and bidirectional streaming within calf perforators. Ambulatory pressure gradient triggers venous reflux in incompetent veins, which induces ambulatory venous hypertension in the lower leg and foot. Bidirectional flow in calf perforators enables quick pressure equalization between deep and superficial veins of the lower leg; the outward (into the superficial veins) oriented component of the bidirectional flow taking place during calf muscle contraction is no pathological reflux but a physiological centripetal flow streaming via great saphenous vein into the femoral vein. Calf perforators are communicating channels between both systems making them conjoined vessels; they are not involved in the generation of pathological hemodynamic situations, nor do they cause ambulatory venous hypertension. The real cause why recurrences develop has not as yet been cleared. Pressure gradient arising during calf pump activity between the femoral vein and the saphenous remnant after abolition of saphenous reflux triggers biophysical and biochemical events, which might induce recurrence. Thus, abolition of saphenous reflux removes the hemodynamic disturbance, but at the same time it generates precondition for reflux recurrence and for the comeback of the previous pathological situation; this chain of events has been called hemodynamic paradox.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19750020309','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19750020309"><span>Pressure gradient effects on heat transfer to reusable surface insulation tile-array gaps</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Throckmorton, D. A.</p> <p>1975-01-01</p> <p>An experimental investigation was performed to determine the effect of pressure gradient on the heat transfer within space shuttle reusable surface insulation (RSI) tile-array gaps under thick, turbulent boundary-layer conditions. Heat-transfer and pressure measurements were obtained on a curved array of full-scale simulated RSI tiles in a tunnel-wall boundary layer at a nominal free-stream Mach number and free-stream Reynolds numbers. Transverse pressure gradients of varying degree were induced over the model surface by rotating the curved array with respect to the flow. Definition of the tunnel-wall boundary-layer flow was obtained by measurement of boundary-layer pitot pressure profiles, wall pressure, and heat transfer. Flat-plate heat-transfer data were correlated and a method was derived for prediction of heat transfer to a smooth curved surface in the highly three-dimensional tunnel-wall boundary-layer flow. Pressure on the floor of the RSI tile-array gap followed the trends of the external surface pressure. Heat transfer to the surface immediately downstream of a transverse gap is higher than that for a smooth surface at the same location. Heating to the wall of a transverse gap, and immediately downstream of it, at its intersection with a longitudinal gap is significantly greater than that for the simple transverse gap.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_1");'>1</a></li> <li class="active"><span>2</span></li> <li><a href="#" onclick='return showDiv("page_3");'>3</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_2 --> <div id="page_3" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_1");'>1</a></li> <li><a href="#" onclick='return showDiv("page_2");'>2</a></li> <li class="active"><span>3</span></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="41"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMOS51A1148G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMOS51A1148G"><span>Resolving the Role of the Dynamic Pressure in the Burial, Exposure, Scour, and Mobility of Underwater Munitions</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gilooly, S.; Foster, D. L.</p> <p>2017-12-01</p> <p>In nearshore environments, the motion of munitions results from a mixture of sediment transport conditions including sheet flow, scour, bedform migration, and momentary liquefaction. Incipient motion can be caused by disruptive shear stresses and pressure gradients. Foster et al. (2006) incorporated both processes into a single parameter, indicating incipient motion as a function of the bed state. This research looks to evaluate the role of the pressure gradient in positional state changes such as burial, exposure, and mobility. In the case of munitions, this may include pressure gradients induced by vortex shedding or the passing wave. Pressure-mapped model munitions are being developed to measure the orientation, rotation, and surface pressure of the munitions during threshold events leading to a new positional state. These munitions will be deployed in inner surf zone and estuary environments along with acoustic Doppler velocimeters (ADVs), pore water pressure sensors, a laser grid, and a pencil beam sonar with an azimuth drive. The additional instruments allow for near bed and far field water column and sediment bed sampling. Currently preliminary assessments of various pressure sensors and munition designs are underway. Two pressure sensors were selected; the thin FlexiForce A201 sensors will be used to indicate munition rolling during threshold events and diaphragm sensors will be used to understand changes in surrounding pore water pressure as the munition begins to bury/unbury. Both sensors are expected to give quantitative measurements of dynamic pressure gradients in the flow field surrounding the munition. Resolving the role of this process will give insight to an improved incipient motion parameter and allow for better munition motion predictions.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PhRvA..93d3825Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PhRvA..93d3825Z"><span>Electromagnetically-induced-transparency intensity-correlation power broadening in a buffer gas</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zheng, Aojie; Green, Alaina; Crescimanno, Michael; O'Leary, Shannon</p> <p>2016-04-01</p> <p>Electromagnetically-induced-transparency (EIT) noise correlation spectroscopy holds promise as a simple, robust method for performing high-resolution spectroscopy used in optical magnetometry and clocks. Of relevance to these applications, we report on the role of buffer gas pressure and magnetic field gradients on power broadening of Zeeman-EIT noise correlation resonances.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/15104807','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/15104807"><span>Confocal Raman microscopy of morphological changes in poly(ethylene terephthalate) film induced by supercritical CO(2).</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Fleming, Oliver S; Kazarian, Sergei G</p> <p>2004-04-01</p> <p>Poly(ethylene terephthalate) (PET) film was exposed to supercritical (sc) CO(2) and confocal Raman microscopy was used to investigate the morphological changes induced. The study evaluates the use of oil and dry objectives in confocal mode to obtain depth profiles of PET film. These results were compared with the data obtained by mapping of the film cross-section. A significant gradient of degree of crystallinity normal to the surface of PET film down to 60 microm has been observed. The gradient of the degree of morphological changes are functions of exposure time and pressure.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014cosp...40E1591K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014cosp...40E1591K"><span>Thermospheric neutral density estimates from heater-induced ion up-flow at EISCAT</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kosch, Michael; Ogawa, Yasunobu; Yamazaki, Yosuke; Vickers, Hannah; Blagoveshchenskaya, Nataly</p> <p></p> <p>We exploit a recently-developed technique to estimate the upper thermospheric neutral density using measurements of ionospheric plasma parameters made by the EISCAT UHF radar during ionospheric modification experiments. Heating the electrons changes the balance between upward plasma pressure gradient and downward gravity, resulting in ion up-flow up to ~200 m/s. This field-aligned flow is retarded by collisions, which is directly related to the neutral density. Whilst the ion up-flow is consistent with the plasma pressure gradient, the estimated thermospheric neutral density depends on the assumed composition, which varies with altitude. Results in the topside ionosphere are presented.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018GeoJI.tmp..167E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018GeoJI.tmp..167E"><span>Increased likelihood of induced seismicity in highly overpressured shale formations</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Eaton, David W.; Schultz, Ryan</p> <p>2018-05-01</p> <p>Fluid-injection processes such as disposal of saltwater or hydraulic fracturing can induce earthquakes by increasing pore pressure and/or shear stress on faults. Natural processes, including transformation of organic material (kerogen) into hydrocarbon and cracking to produce gas, can similarly cause fluid overpressure. Here we document two examples from the Western Canada Sedimentary Basin where earthquakes induced by hydraulic fracturing are strongly clustered within areas characterized by pore-pressure gradient in excess of 15 kPa/m. Despite extensive hydraulic-fracturing activity associated with resource development, induced earthquakes are virtually absent in the Montney and Duvernay Formations elsewhere. Statistical analysis suggests a negligible probability that this spatial correlation developed by chance. This implies that, in addition to known factors such as anthropogenic pore-pressure increase and proximity to critically stressed faults, high in-situ overpressure of shale formations may also represent a controlling factor for inducing earthquakes by hydraulic fracturing. On a geological timescale, natural pore-pressure generation may lead to fault-slip episodes that regulate magnitude of formation-overpressure.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016NatCo...713860S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016NatCo...713860S"><span>Suppressed ion-scale turbulence in a hot high-β plasma</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schmitz, L.; Fulton, D. P.; Ruskov, E.; Lau, C.; Deng, B. H.; Tajima, T.; Binderbauer, M. W.; Holod, I.; Lin, Z.; Gota, H.; Tuszewski, M.; Dettrick, S. A.; Steinhauer, L. C.</p> <p>2016-12-01</p> <p>An economic magnetic fusion reactor favours a high ratio of plasma kinetic pressure to magnetic pressure in a well-confined, hot plasma with low thermal losses across the confining magnetic field. Field-reversed configuration (FRC) plasmas are potentially attractive as a reactor concept, achieving high plasma pressure in a simple axisymmetric geometry. Here, we show that FRC plasmas have unique, beneficial microstability properties that differ from typical regimes in toroidal confinement devices. Ion-scale fluctuations are found to be absent or strongly suppressed in the plasma core, mainly due to the large FRC ion orbits, resulting in near-classical thermal ion confinement. In the surrounding boundary layer plasma, ion- and electron-scale turbulence is observed once a critical pressure gradient is exceeded. The critical gradient increases in the presence of sheared plasma flow induced via electrostatic biasing, opening the prospect of active boundary and transport control in view of reactor requirements.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5187751','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5187751"><span>Suppressed ion-scale turbulence in a hot high-β plasma</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Schmitz, L.; Fulton, D. P.; Ruskov, E.; Lau, C.; Deng, B. H.; Tajima, T.; Binderbauer, M. W.; Holod, I.; Lin, Z.; Gota, H.; Tuszewski, M.; Dettrick, S. A.; Steinhauer, L. C.</p> <p>2016-01-01</p> <p>An economic magnetic fusion reactor favours a high ratio of plasma kinetic pressure to magnetic pressure in a well-confined, hot plasma with low thermal losses across the confining magnetic field. Field-reversed configuration (FRC) plasmas are potentially attractive as a reactor concept, achieving high plasma pressure in a simple axisymmetric geometry. Here, we show that FRC plasmas have unique, beneficial microstability properties that differ from typical regimes in toroidal confinement devices. Ion-scale fluctuations are found to be absent or strongly suppressed in the plasma core, mainly due to the large FRC ion orbits, resulting in near-classical thermal ion confinement. In the surrounding boundary layer plasma, ion- and electron-scale turbulence is observed once a critical pressure gradient is exceeded. The critical gradient increases in the presence of sheared plasma flow induced via electrostatic biasing, opening the prospect of active boundary and transport control in view of reactor requirements. PMID:28000675</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012APS..DFDA30008S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012APS..DFDA30008S"><span>Experimental Nanofluidics in an individual Nanotube</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Siria, Alessandro; Poncharal, Philippe; Biance, Anne Laure; Fulcrand, Remy; Purcell, Stephen; Bocquet, Lyderic</p> <p>2012-11-01</p> <p>Building new devices that benefit from the strange transport behavior of fluids at nanoscales is an open and worthy challenge that may lead to new scientific and technological paradigms. We present here a new class of nanofluidic device, made of individual Boron-Nitride (BN) nanotube inserted in a pierced membrane and connecting two macroscopic reservoirs. We explore fluidic transport inside a single BN nanotube under electric fields, pressure drops, chemical gradients, and combinations of these. We show that in this transmembrane geometry, the pressure-driven streaming current is voltage gated, with an apparent electro-osmotic zeta potential raising up to one volt. Further, we measured the current induced by ion concentration gradients and show its dependency on the surface charge.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26716691','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26716691"><span>Effects of Hydrostatic Pressure on Carcinogenic Properties of Epithelia.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Tokuda, Shinsaku; Kim, Young Hak; Matsumoto, Hisako; Muro, Shigeo; Hirai, Toyohiro; Mishima, Michiaki; Furuse, Mikio</p> <p>2015-01-01</p> <p>The relationship between chronic inflammation and cancer is well known. The inflammation increases the permeability of blood vessels and consequently elevates pressure in the interstitial tissues. However, there have been only a few reports on the effects of hydrostatic pressure on cultured cells, and the relationship between elevated hydrostatic pressure and cell properties related to malignant tumors is less well understood. Therefore, we investigated the effects of hydrostatic pressure on the cultured epithelial cells seeded on permeable filters. Surprisingly, hydrostatic pressure from basal to apical side induced epithelial stratification in Madin-Darby canine kidney (MDCK) I and Caco-2 cells, and cavities with microvilli and tight junctions around their surfaces were formed within the multi-layered epithelia. The hydrostatic pressure gradient also promoted cell proliferation, suppressed cell apoptosis, and increased transepithelial ion permeability. The inhibition of protein kinase A (PKA) promoted epithelial stratification by the hydrostatic pressure whereas the activation of PKA led to suppressed epithelial stratification. These results indicate the role of the hydrostatic pressure gradient in the regulation of various epithelial cell functions. The findings in this study may provide clues for the development of a novel strategy for the treatment of the carcinoma.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4696811','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4696811"><span>Effects of Hydrostatic Pressure on Carcinogenic Properties of Epithelia</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Tokuda, Shinsaku; Kim, Young Hak; Matsumoto, Hisako; Muro, Shigeo; Hirai, Toyohiro; Mishima, Michiaki; Furuse, Mikio</p> <p>2015-01-01</p> <p>The relationship between chronic inflammation and cancer is well known. The inflammation increases the permeability of blood vessels and consequently elevates pressure in the interstitial tissues. However, there have been only a few reports on the effects of hydrostatic pressure on cultured cells, and the relationship between elevated hydrostatic pressure and cell properties related to malignant tumors is less well understood. Therefore, we investigated the effects of hydrostatic pressure on the cultured epithelial cells seeded on permeable filters. Surprisingly, hydrostatic pressure from basal to apical side induced epithelial stratification in Madin-Darby canine kidney (MDCK) I and Caco-2 cells, and cavities with microvilli and tight junctions around their surfaces were formed within the multi-layered epithelia. The hydrostatic pressure gradient also promoted cell proliferation, suppressed cell apoptosis, and increased transepithelial ion permeability. The inhibition of protein kinase A (PKA) promoted epithelial stratification by the hydrostatic pressure whereas the activation of PKA led to suppressed epithelial stratification. These results indicate the role of the hydrostatic pressure gradient in the regulation of various epithelial cell functions. The findings in this study may provide clues for the development of a novel strategy for the treatment of the carcinoma. PMID:26716691</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29498569','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29498569"><span>Fifty shades of gradients: does the pressure gradient in venous sinus stenting for idiopathic intracranial hypertension matter? A systematic review.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>McDougall, Cameron M; Ban, Vin Shen; Beecher, Jeffrey; Pride, Lee; Welch, Babu G</p> <p>2018-03-02</p> <p>OBJECTIVE The role of venous sinus stenting (VSS) for idiopathic intracranial hypertension (IIH) is not well understood. The aim of this systematic review is to attempt to identify subsets of patients with IIH who will benefit from VSS based on the pressure gradients of their venous sinus stenosis. METHODS MEDLINE/PubMed was searched for studies reporting venous pressure gradients across the stenotic segment of the venous sinus, pre- and post-stent pressure gradients, and clinical outcomes after VSS. Findings are reported according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. RESULTS From 32 eligible studies, a total of 186 patients were included in the analysis. Patients who had favorable outcomes had higher mean pressure gradients (22.8 ± 11.5 mm Hg vs 17.4 ± 8.0 mm Hg, p = 0.033) and higher changes in pressure gradients after stent placement (19.4 ± 10.0 mm Hg vs 12.0 ± 6.0 mm Hg, p = 0.006) compared with those with unfavorable outcomes. The post-stent pressure gradients between the 2 groups were not significantly different (2.8 ± 4.0 mm Hg vs 2.7 ± 2.0 mm Hg, p = 0.934). In a multivariate stepwise logistic regression controlling for age, sex, body mass index, CSF opening pressure, pre-stent pressure gradient, and post-stent pressure gradient, the change in pressure gradient with stent placement was found to be an independent predictor of favorable outcome (p = 0.028). Using a pressure gradient of 21 as a cutoff, 81/86 (94.2%) of patients with a gradient > 21 achieved favorable outcomes, compared with 82/100 (82.0%) of patients with a gradient ≤ 21 (p = 0.022). CONCLUSIONS There appears to be a relationship between the pressure gradient of venous sinus stenosis and the success of VSS in IIH. A randomized controlled trial would help elucidate this relationship and potentially guide patient selection.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014PhDT.......116P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014PhDT.......116P"><span>Microscale solution manipulation using photopolymerized hydrogel membranes and induced charge electroosmosis micropumps</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Paustian, Joel Scott</p> <p></p> <p>Microfluidic technology is playing an ever-expanding role in advanced chemical and biological devices, with diverse applications including medical diagnostics, high throughput research tools, chemical or biological detection, separations, and controlled particle fabrication. Even so, local (microscale) modification of solution properties within microchannels, such as pressure, solute concentration, and voltage remains a challenge, and improved spatiotemporal control would greatly enhance the capabilities of microfluidics. This thesis demonstrates and characterizes two microfluidic tools to enhance local solution control. I first describe a microfluidic pump that uses an electrokinetic effect, Induced-Charge Electroosmosis (ICEO), to generate pressure on-chip. In ICEO, steady flows are driven by AC fields along metal-electrolyte interfaces. I design and microfabricate a pump that exploits this effect to generate on-chip pressures. The ICEO pump is used to drive flow along a microchannel, and the pressure is measured as a function of voltage, frequency, and electrolyte composition. This is the first demonstration of chip-scale flows driven by ICEO, which opens the possibility for ICEO pumping in self-contained microfluidic devices. Next, I demonstrate a method to create thin local membranes between microchannels, which enables local diffusive delivery of solute. These ``Hydrogel Membrane Microwindows'' are made by photopolymerizing a hydrogel which serves as a local ``window'' for solute diffusion and electromigration between channels, but remains a barrier to flow. I demonstrate three novel experimental capabilities enabled by the hydrogel membranes: local concentration gradients, local electric currents, and rapid diffusive composition changes. I conclude by applying the hydrogel membranes to study solvophoresis, the migration of particles in solvent gradients. Solvent gradients are present in many chemical processes, but migration of particles within these gradients is not well understood. An improved understanding would allow solvophoresis to be engineered (e.g. for coatings and thin film deposition) or reduced (e.g. in fouling processes during reactions and separations). Toward this end, I perform velocity measurements of colloidal particles at various ethanol-water concentrations and gradient strengths. The velocity was found to depend on the mole fraction via the equation u = DSP▿ln X, where u is the velocity, DSP is the mobility, and X is the ethanol mole fraction.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017SPIE10323E..8OW','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017SPIE10323E..8OW"><span>High resolution temperature mapping of gas turbine combustor simulator exhaust with femtosecond laser induced fiber Bragg gratings</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Walker, Robert B.; Yun, Sangsig; Ding, Huimin; Charbonneau, Michel; Coulas, David; Lu, Ping; Mihailov, Stephen J.; Ramachandran, Nanthan</p> <p>2017-04-01</p> <p>Femtosecond infrared (fs-IR) laser written fiber Bragg gratings (FBGs), have demonstrated great potential for extreme sensing. Such conditions are inherent in advanced gas turbine engines under development to reduce greenhouse gas emissions; and the ability to measure temperature gradients in these harsh environments is currently limited by the lack of sensors and controls capable of withstanding the high temperature, pressure and corrosive conditions present. This paper discusses fabrication and deployment of several fs-IR written FBG arrays, for monitoring exhaust temperature gradients of a gas turbine combustor simulator. Results include: contour plots of measured temperature gradients, contrast with thermocouple data.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25000878','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25000878"><span>Induced charge electroosmosis micropumps using arrays of Janus micropillars.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Paustian, Joel S; Pascall, Andrew J; Wilson, Neil M; Squires, Todd M</p> <p>2014-09-07</p> <p>We report on a microfluidic AC-driven electrokinetic pump that uses Induced Charge Electro-Osmosis (ICEO) to generate on-chip pressures. ICEO flows occur when a bulk electric field polarizes a metal object to induce double layer formation, then drives electroosmotic flow. A microfabricated array of metal-dielectric Janus micropillars breaks the symmetry of ICEO flow, so that an AC electric field applied across the array drives ICEO flow along the length of the pump. When pumping against an external load, a pressure gradient forms along the pump length. The design was analyzed theoretically with the reciprocal theorem. The analysis reveals a maximum pressure and flow rate that depend on the ICEO slip velocity and micropillar geometry. We then fabricate and test the pump, validating our design concept by demonstrating non-local pressure driven flow using local ICEO slip flows. We varied the voltage, frequency, and electrolyte composition, measuring pump pressures of 15-150 Pa. We use the pump to drive flows through a high-resistance microfluidic channel. We conclude by discussing optimization routes suggested by our theoretical analysis to enhance the pump pressure.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/16376361','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/16376361"><span>Eddies in a bottleneck: an arbitrary Debye length theory for capillary electroosmosis.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Park, Stella Y; Russo, Christopher J; Branton, Daniel; Stone, Howard A</p> <p>2006-05-15</p> <p>Using an applied electrical field to drive fluid flows becomes desirable as channels become smaller. Although most discussions of electroosmosis treat the case of thin Debye layers, here electroosmotic flow (EOF) through a constricted cylinder is presented for arbitrary Debye lengths (kappa(-1)) using a long wavelength perturbation of the cylinder radius. The analysis uses the approximation of small potentials. The varying diameter of the cylinder produces radially and axially varying effective electric fields, as well as an induced pressure gradient. We predict the existence of eddies for certain constricted geometries and propose the possibility of electrokinetic trapping in these regions. We also present a leading-order criterion which predicts central eddies in very narrow constrictions at the scale of the Debye length. Eddies can be found both in the center of the channel and along the perimeter, and the presence of the eddies is a consequence of the induced pressure gradient that accompanies electrically driven flow into a narrow constriction.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3174066','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3174066"><span>Eddies in a Bottleneck: An Arbitrary Debye Length Theory for Capillary Electroosmosis</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Park, Stella Y.; Russo, Christopher J.; Branton, Daniel; Stone, Howard A.</p> <p>2011-01-01</p> <p>Using an applied electrical field to drive fluid flows becomes desirable as channels become smaller. Although most discussions of electroosmosis treat the case of thin Debye layers, here electroosmotic flow (EOF) through a constricted cylinder is presented for arbitrary Debye lengths (κ−1) using a long wavelength perturbation of the cylinder radius. The analysis uses the approximation of small potentials. The varying diameter of the cylinder produces radially and axially varying effective electric fields, as well as an induced pressure gradient. We predict the existence of eddies for certain constricted geometries and propose the possibility of electrokinetic trapping in these regions. We also present a leading-order criterion which predicts central eddies in very narrow constrictions at the scale of the Debye length. Eddies can be found both in the center of the channel and along the perimeter, and the presence of the eddies is a consequence of the induced pressure gradient that accompanies electrically driven flow into a narrow constriction. PMID:16376361</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017APS..DFDM24007A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017APS..DFDM24007A"><span>Flow Analysis of a Rising Crude Oil Micro-Droplet Affected by Attached Microbial Streamers</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Amaro, Matthew; White, Andrew; Jalali, Maryam; Sheng, Jian</p> <p>2017-11-01</p> <p>Microfluidic experiments show bacteria flowing past a pinned crude oil droplet produce microbial aggregates and streamers on the oil-water interface. High speed DIC microscopy at 1000 fps for 1 sec with a sampling interval of 10 min captures the evolving flow and bacterial motility as well as adhesion, aggregation and streamer events. With bacteria as tracers, velocity measurements are acquired with in-house PIV-assisted PTV software. Flow fields with spatial resolution 2.5 μm are measured around an O(100) μm drop in a 700 ×700 μm window. Full budgets of the 2D Navier-Stokes equation are faithfully resolved to determine pressure gradients by performing the balance over a control volume enclosing the droplet. Pressure gradients are integrated over the border of the control region to obtain pressure profiles at the leading and trailing edges. A momentum balance can be used to determine the drag induced by the drop and any attached streamers. Cases with and without streamers and their differing flow features are presented. Additionally streamers produce nonzero curl in the pressure gradient field providing a tool for identifying the position of otherwise invisible streamers. Ongoing experiments and future applications of the tools presented here will be discussed. Funded by GoMRI, NSF, ARO.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/15178303','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/15178303"><span>Frequency-dependent laminar electroosmotic flow in a closed-end rectangular microchannel.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Marcos; Yang, C; Ooi, K T; Wong, T N; Masliyah, J H</p> <p>2004-07-15</p> <p>This article presents an analysis of the frequency- and time-dependent electroosmotic flow in a closed-end rectangular microchannel. An exact solution to the modified Navier-Stokes equation governing the ac electroosmotic flow field is obtained by using the Green's function formulation in combination with a complex variable approach. An analytical expression for the induced backpressure gradient is derived. With the Debye-Hückel approximation, the electrical double-layer potential distribution in the channel is obtained by analytically solving the linearized two-dimensional Poisson-Boltzmann equation. Since the counterparts of the flow rate and the electrical current are shown to be linearly proportional to the applied electric field and the pressure gradient, Onsager's principle of reciprocity is demonstrated for transient and ac electroosmotic flows. The time evolution of the electroosmotic flow and the effect of a frequency-dependent ac electric field on the oscillating electroosmotic flow in a closed-end rectangular microchannel are examined. Specifically, the induced pressure gradient is analyzed under effects of the channel dimension and the frequency of electric field. In addition, based on the Stokes second problem, the solution of the slip velocity approximation is presented for comparison with the results obtained from the analytical scheme developed in this study. Copyright 2004 Elsevier Inc.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5708728','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5708728"><span>Non-invasive assessment of pulsatile intracranial pressure with phase-contrast magnetic resonance imaging</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Lindstrøm, Erika Kristina; Vatnehol, Svein Are Sirirud; Mardal, Kent-André; Emblem, Kyrre Eeg; Eide, Per Kristian</p> <p>2017-01-01</p> <p>Invasive monitoring of pulsatile intracranial pressure can accurately predict shunt response in patients with idiopathic normal pressure hydrocephalus, but may potentially cause complications such as bleeding and infection. We tested how a proposed surrogate parameter for pulsatile intracranial pressure, the phase-contrast magnetic resonance imaging derived pulse pressure gradient, compared with its invasive counterpart. In 22 patients with suspected idiopathic normal pressure hydrocephalus, preceding invasive intracranial pressure monitoring, and any surgical shunt procedure, we calculated the pulse pressure gradient from phase-contrast magnetic resonance imaging derived cerebrospinal fluid flow velocities obtained at the upper cervical spinal canal using a simplified Navier-Stokes equation. Repeated measurements of the pulse pressure gradient were also undertaken in four healthy controls. Of 17 shunted patients, 16 responded, indicating high proportion of “true” normal pressure hydrocephalus in the patient cohort. However, there was no correlation between the magnetic resonance imaging derived pulse pressure gradient and pulsatile intracranial pressure (R = -.18, P = .43). Pulse pressure gradients were also similar in patients and healthy controls (P = .26), and did not differ between individuals with pulsatile intracranial pressure above or below established thresholds for shunt treatment (P = .97). Assessment of pulse pressure gradient at level C2 was therefore not found feasible to replace invasive monitoring of pulsatile intracranial pressure in selection of patients with idiopathic normal pressure hydrocephalus for surgical shunting. Unlike invasive, overnight monitoring, the pulse pressure gradient from magnetic resonance imaging comprises short-term pressure fluctuations only. Moreover, complexity of cervical cerebrospinal fluid flow and -pulsatility at the upper cervical spinal canal may render the pulse pressure gradient a poor surrogate marker for intracranial pressure pulsations. PMID:29190788</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29190788','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29190788"><span>Non-invasive assessment of pulsatile intracranial pressure with phase-contrast magnetic resonance imaging.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ringstad, Geir; Lindstrøm, Erika Kristina; Vatnehol, Svein Are Sirirud; Mardal, Kent-André; Emblem, Kyrre Eeg; Eide, Per Kristian</p> <p>2017-01-01</p> <p>Invasive monitoring of pulsatile intracranial pressure can accurately predict shunt response in patients with idiopathic normal pressure hydrocephalus, but may potentially cause complications such as bleeding and infection. We tested how a proposed surrogate parameter for pulsatile intracranial pressure, the phase-contrast magnetic resonance imaging derived pulse pressure gradient, compared with its invasive counterpart. In 22 patients with suspected idiopathic normal pressure hydrocephalus, preceding invasive intracranial pressure monitoring, and any surgical shunt procedure, we calculated the pulse pressure gradient from phase-contrast magnetic resonance imaging derived cerebrospinal fluid flow velocities obtained at the upper cervical spinal canal using a simplified Navier-Stokes equation. Repeated measurements of the pulse pressure gradient were also undertaken in four healthy controls. Of 17 shunted patients, 16 responded, indicating high proportion of "true" normal pressure hydrocephalus in the patient cohort. However, there was no correlation between the magnetic resonance imaging derived pulse pressure gradient and pulsatile intracranial pressure (R = -.18, P = .43). Pulse pressure gradients were also similar in patients and healthy controls (P = .26), and did not differ between individuals with pulsatile intracranial pressure above or below established thresholds for shunt treatment (P = .97). Assessment of pulse pressure gradient at level C2 was therefore not found feasible to replace invasive monitoring of pulsatile intracranial pressure in selection of patients with idiopathic normal pressure hydrocephalus for surgical shunting. Unlike invasive, overnight monitoring, the pulse pressure gradient from magnetic resonance imaging comprises short-term pressure fluctuations only. Moreover, complexity of cervical cerebrospinal fluid flow and -pulsatility at the upper cervical spinal canal may render the pulse pressure gradient a poor surrogate marker for intracranial pressure pulsations.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_1");'>1</a></li> <li><a href="#" onclick='return showDiv("page_2");'>2</a></li> <li class="active"><span>3</span></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_3 --> <div id="page_4" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_2");'>2</a></li> <li><a href="#" onclick='return showDiv("page_3");'>3</a></li> <li class="active"><span>4</span></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="61"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EPJP..129..155A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EPJP..129..155A"><span>Interaction of nanoparticles for the peristaltic flow in an asymmetric channel with the induced magnetic field</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Akbar, Noreen Sher; Raza, M.; Ellahi, R.</p> <p>2014-07-01</p> <p>In the present investigation, we examined the interaction of nanoparticle copper with the base fluid water in an asymmetric channel in the presence of an induced magnetic field. The complexity of equations describing the flow of the nanofluid is reduced by applying the low-Reynolds number and long-wavelength approximations. The resulting equations are solved exactly. The obtained expressions for the velocity and temperature phenomenon are sketched in graphs. The resulting relations for pressure gradient and pressure rise are plotted for various pertinent parameters. The streamlines are drawn for some physical quantities to discuss the trapping phenomenon.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25178834','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25178834"><span>Induced groundwater flux by increases in the aquifer's total stress.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Chang, Ching-Min; Yeh, Hund-Der</p> <p>2015-01-01</p> <p>Fluid-filled granular soils experience changes in total stress because of earth and oceanic tides, earthquakes, erosion, sedimentation, and changes in atmospheric pressure. The pore volume may deform in response to the changes in stress and this may lead to changes in pore fluid pressure. The transient fluid flow can therefore be induced by the gradient in excess pressure in a fluid-saturated porous medium. This work demonstrates the use of stochastic methodology in prediction of induced one-dimensional field-scale groundwater flow through a heterogeneous aquifer. A closed-form of mean groundwater flux is developed to quantify the induced field-scale mean behavior of groundwater flow and analyze the impacts of the spatial correlation length scale of log hydraulic conductivity and the pore compressibility. The findings provided here could be useful for the rational planning and management of groundwater resources in aquifers that contain lenses with large vertical aquifer matrix compressibility values. © 2014, National Ground Water Association.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5316482','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5316482"><span>Broadening of Analyte Streams due to a Transverse Pressure Gradient in Free-Flow Isoelectric Focusing</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Dutta, Debashis</p> <p>2017-01-01</p> <p>Pressure-driven cross-flows can arise in free-flow isoelectric focusing systems (FFIEF) due to a non-uniform electroosmotic flow velocity along the channel width induced by the pH gradient in this direction. In addition, variations in the channel cross-section as well as unwanted differences in hydrostatic heads at the buffer/sample inlet ports can also lead to such pressure-gradients which besides altering the equilibrium position of the sample zones have a tendency to substantially broaden their widths deteriorating the separations. In this situation, a thorough assessment of stream broadening due to transverse pressure-gradients in FFIEF devices is necessary in order to establish accurate design rules for the assay. The present article describes a mathematical framework to estimate the noted zone dispersion in FFIEF separations based on the method-of-moments approach under laminar flow conditions. A closed-form expression has been derived for the spatial variance of the analyte streams at their equilibrium positions as a function of the various operating parameters governing the assay performance. This expression predicts the normalized stream variance under the chosen conditions to be determined by two dimensionless Péclet numbers evaluated based on the transverse pressure-driven and electrophoretic solute velocities in the separation chamber, respectively. Moreover, the analysis shows that while the stream width can be expected to increase with an increase in the value of the first Péclet number, the opposite trend will be followed with respect to the latter. The noted results have been validated using Monte Carlo simulations that also establish a time/length scale over which the predicted equilibrium stream width is attained in the system. PMID:28081900</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUOSEC14C1017Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUOSEC14C1017Y"><span>Tidally-driven Surface Flow in a Georgia Estuarine Saltmarsh</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Young, D.; Bruder, B. L.; Haas, K. A.; Webster, D. R.</p> <p>2016-02-01</p> <p>Estuarine saltmarshes are diverse, valuable, and productive ecosystems. Vegetation dampens wave and current energy, thereby allowing the estuaries to serve as a nursery habitat for shellfish and fish species. Tidally-driven flow transports nutrients into and out of the estuary, nourishing inshore and offshore vegetation and animals. The effects of vegetation on the marsh hydrodynamics and on the estuary creek and channel flow are, unfortunately, poorly understood, and the knowledge that does exist primarily originates from modeling studies. Field studies addressing marsh surface flows are limited due to the difficulty of accurately measuring the water surface elevation and acquiring concurrent velocity measurements in the dense marsh vegetation. This study partially bridges the gap between the model observations of marsh flow driven by water surface elevation gradients and flume studies of flow through vegetation. Three current meters and three pressure transducers were deployed for three days along a transect perpendicular to the main channel (Little Ogeechee River) in a saltmarsh adjacent to Rose Dhu Island (Savannah, Georgia, USA). The pressure transducer locations were surveyed daily with static GPS yielding highly accurate water surface elevation data. During flood and ebb tide, water surface elevation differences between the marsh and Little Ogeechee River were observed up to 15 cm and pressure gradients were observed up to 0.0017 m of water surface elevation drop per m of linear distance. The resulting channel-to-saltmarsh pressure gradients substantially affected tidal currents at all current meters. At one current meter, the velocity was nearly perpendicular to the Little Ogeechee River bank. The velocity at this location was effectively modeled as a balance between the pressure gradient and marsh vegetation-induced drag force using the Darcy-Weisbach/Lindner's equations developed for flow-through-vegetation analysis in open channel flow.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17547657','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17547657"><span>Comparison between gradient-dependent hydraulic conductivities of roots using the root pressure probe: the role of pressure propagations and implications for the relative roles of parallel radial pathways.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Bramley, Helen; Turner, Neil C; Turner, David W; Tyerman, Stephen D</p> <p>2007-07-01</p> <p>Hydrostatic pressure relaxations with the root pressure probe are commonly used for measuring the hydraulic conductivity (Lp(r)) of roots. We compared the Lp(r) of roots from species with different root hydraulic properties (Lupinus angustifolius L. 'Merrit', Lupinus luteus L. 'Wodjil', Triticum aestivum L. 'Kulin' and Zea mays L. 'Pacific DK 477') using pressure relaxations, a pressure clamp and osmotic gradients to induce water flow across the root. Only the pressure clamp measures water flow under steady-state conditions. Lp(r) determined by pressure relaxations was two- to threefold greater than Lp(r) from pressure clamps and was independent of the direction of water flow. Lp(r) (pressure clamp) was two- to fourfold higher than for Lp(r) (osmotic) for all species except Triticum aestivum where Lp(r) (pressure clamp) and Lp(r) (osmotic) were not significantly different. A novel technique was developed to measure the propagation of pressure through roots to investigate the cause of the differences in Lp(r). Root segments were connected between two pressure probes so that when root pressure (P(r)) was manipulated by one probe, the other probe recorded changes in P(r). Pressure relaxations did not induce the expected kinetics in pressure in the probe at the other end of the root when axial hydraulic conductance, and probe and root capacitances were accounted for. An electric circuit model of the root was constructed that included an additional capacitance in the root loaded by a series of resistances. This accounted for the double exponential kinetics for intact roots in pressure relaxation experiments as well as the reduced response observed with the double probe experiments. Although there were potential errors with all the techniques, we considered that the measurement of Lp(r) using the pressure clamp was the most unambiguous for small pressure changes, and provided that sufficient time was allowed for pressure propagation through the root. The differences in Lp(r) from different methods of measurement have implications for the models describing water transport through roots and the potential role of aquaporins.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26283413','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26283413"><span>Pressure and shear stress in trabecular bone marrow during whole bone loading.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Metzger, Thomas A; Schwaner, Stephen A; LaNeve, Anthony J; Kreipke, Tyler C; Niebur, Glen L</p> <p>2015-09-18</p> <p>Skeletal adaptation to mechanical loading is controlled by mechanobiological signaling. Osteocytes are highly responsive to applied strains, and are the key mechanosensory cells in bone. However, many cells residing in the marrow also respond to mechanical cues such as hydrostatic pressure and shear stress, and hence could play a role in skeletal adaptation. Trabecular bone encapsulates marrow, forming a poroelastic solid. According to the mechanical theory, deformation of the pores induces motion in the fluid-like marrow, resulting in pressure and velocity gradients. The latter results in shear stress acting between the components of the marrow. To characterize the mechanical environment of trabecular bone marrow in situ, pore pressure within the trabecular compartment of whole porcine femurs was measured with miniature pressure transducers during stress-relaxation and cyclic loading. Pressure gradients ranging from 0.013 to 0.46 kPa/mm were measured during loading. This range was consistent with calculated pressure gradients from continuum scale poroelastic models with the same permeability. Micro-scale computational fluid dynamics models created from computed tomography images were used to calculate the micromechanical stress in the marrow using the measured pressure differentials as boundary conditions. The volume averaged shear stress in the marrow ranged from 1.67 to 24.55 Pa during cyclic loading, which exceeds the mechanostimulatory threshold for mesenchymal lineage cells. Thus, the loading of bone through activities of daily living may be an essential component of bone marrow health and mechanobiology. Additional studies of cell-level interactions during loading in healthy and disease conditions will provide further incite into marrow mechanobiology. Copyright © 2015 Elsevier Ltd. All rights reserved.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29878071','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29878071"><span>Flow-related Right Ventricular - Pulmonary Arterial Pressure Gradients during Exercise.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wright, Stephen P; Opotowsky, Alexander R; Buchan, Tayler A; Esfandiari, Sam; Granton, John T; Goodman, Jack M; Mak, Susanna</p> <p>2018-06-06</p> <p>The assumption of equivalence between right ventricular and pulmonary arterial systolic pressure is fundamental to several assessments of right ventricular or pulmonary vascular hemodynamic function. Our aims were to 1) determine whether systolic pressure gradients develop across the right ventricular outflow tract in healthy adults during exercise, 2) examine the potential correlates of such gradients, and 3) consider the effect of such gradients on calculated indices of right ventricular function. Healthy untrained and endurance-trained adult volunteers were studied using right-heart catheterization at rest and during submaximal cycle ergometry. Right ventricular and pulmonary artery pressures were simultaneously transduced, and cardiac output was determined by thermodilution. Systolic pressures, peak and mean gradients, and indices of chamber, vascular, and valve function were analyzed offline. Summary data are reported as mean ± standard deviation or median [interquartile range]. No significant right ventricular outflow tract gradients were observed at rest (mean gradient = 4 [3-5] mmHg), and calculated effective orifice area was 3.6±1.0 cm2. Right ventricular systolic pressure increases during exercise were greater than that of pulmonary artery systolic pressure. Accordingly, mean gradients developed during light exercise (8 [7-9] mmHg) and increased during moderate exercise (12 [9-14] mmHg, p < 0.001). The magnitude of the mean gradient was linearly related to cardiac output (r2 = 0.70, p < 0.001). In healthy adults without pulmonic stenosis, systolic pressure gradients develop during exercise, and the magnitude is related to blood flow rate.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23737171','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23737171"><span>Distribution of perfusion.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Glenny, Robb; Robertson, H Thomas</p> <p>2011-01-01</p> <p>Local driving pressures and resistances within the pulmonary vascular tree determine the distribution of perfusion in the lung. Unlike other organs, these local determinants are significantly influenced by regional hydrostatic and alveolar pressures. Those effects on blood flow distribution are further magnified by the large vertical height of the human lung and the relatively low intravascular pressures in the pulmonary circulation. While the distribution of perfusion is largely due to passive determinants such as vascular geometry and hydrostatic pressures, active mechanisms such as vasoconstriction induced by local hypoxia can also redistribute blood flow. This chapter reviews the determinants of regional lung perfusion with a focus on vascular tree geometry, vertical gradients induced by gravity, the interactions between vascular and surrounding alveolar pressures, and hypoxic pulmonary vasoconstriction. While each of these determinants of perfusion distribution can be examined in isolation, the distribution of blood flow is dynamically determined and each component interacts with the others so that a change in one region of the lung influences the distribution of blood flow in other lung regions. © 2011 American Physiological Society.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29034403','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29034403"><span>Customised spatiotemporal temperature gradients created by a liquid metal enabled vortex generator.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Zhu, Jiu Yang; Thurgood, Peter; Nguyen, Ngan; Ghorbani, Kamran; Khoshmanesh, Khashayar</p> <p>2017-11-07</p> <p>Generating customised temperature gradients in miniaturised flow-free liquid chambers is challenging due to the dominance of diffusion. Inducing internal flows in the form of vortices is an effective strategy for overcoming the limitations of diffusion in such environments. Vortices can be produced by applying pressure, temperature and electric potential gradients via miniaturised actuators. However, the difficulties associated with the fabrication, integration, maintenance and operation of such actuators hinder their utility. Here, we utilise liquid metal enabled pumps to induce vortices inside a miniaturised liquid chamber. The configuration and rotational velocity of these vortices can be controlled by tuning the polarity and frequency of the energising electrical signal. This allows creation of customised spatial temperature gradients inside the chamber. The absence of conventional moving elements in the pumps facilitates the rapid reconfiguration of vortices. This enables quick transition from one temperature profile to another, and creates customised spatiotemporal temperature gradients. This allows temperature oscillation from 35 to 62 °C at the hot spot, and from 25 to 27 °C at the centre of the vortex within 15 seconds. Our liquid metal enabled vortex generator can be fabricated, integrated and operated easily, and offers opportunities for studying thermo-responsive materials and biological samples.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018CTM....22..131L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018CTM....22..131L"><span>A DNS study of the physical mechanisms associated with density ratio influence on turbulent burning velocity in premixed flames</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lipatnikov, Andrei N.; Chomiak, Jerzy; Sabelnikov, Vladimir A.; Nishiki, Shinnosuke; Hasegawa, Tatsuya</p> <p>2018-01-01</p> <p>Data obtained in 3D direct numerical simulations of statistically planar, 1D weakly turbulent flames characterised by different density ratios σ are analysed to study the influence of thermal expansion on flame surface area and burning rate. Results show that, on the one hand, the pressure gradient induced within a flame brush owing to heat release in flamelets significantly accelerates the unburned gas that deeply intrudes into the combustion products in the form of an unburned mixture finger, thus causing large-scale oscillations of the burning rate and flame brush thickness. Under the conditions of the present simulations, the contribution of this mechanism to the creation of the flame surface area is substantial and is increased by σ, thus implying an increase in the burning rate by σ. On the other hand, the total flame surface areas simulated at σ = 7.53 and 2.5 are approximately equal. The apparent inconsistency between these results implies the existence of another thermal expansion effect that reduces the influence of σ on the flame surface area and burning rate. Investigation of the issue shows that the flow acceleration by the combustion-induced pressure gradient not only creates the flame surface area by pushing the finger tip into the products, but also mitigates wrinkling of the flame surface (the side surface of the finger) by turbulent eddies. The latter effect is attributed to the high-speed (at σ = 7.53) axial flow of the unburned gas, which is induced by the axial pressure gradient within the flame brush (and the finger). This axial flow acceleration reduces the residence time of a turbulent eddy in an unburned zone of the flame brush (e.g. within the finger). Therefore, the capability of the eddy for wrinkling the flamelet surface (e.g. the side finger surface) is weakened owing to a shorter residence time.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19950014629','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19950014629"><span>Statistics of pressure and pressure gradient in homogeneous isotropic turbulence</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Gotoh, T.; Rogallo, R. S.</p> <p>1994-01-01</p> <p>The statistics of pressure and pressure gradient in stationary isotropic turbulence are measured within direct numerical simulations at low to moderate Reynolds numbers. It is found that the one-point pdf of the pressure is highly skewed and that the pdf of the pressure gradient is of stretched exponential form. The power spectrum of the pressure P(k) is found to be larger than the corresponding spectrum P(sub G)(k) computed from a Gaussian velocity field having the same energy spectrum as that of the DNS field. The ratio P(k)/P(sub G)(k), a measure of the pressure-field intermittence, grows with wavenumber and Reynolds number as -R(sub lambda)(exp 1/2)log(k/k(sub d)) for k less than k(sub d)/2 where k(sub d) is the Kolmogorov wavenumber. The Lagrangian correlations of pressure gradient and velocity are compared and the Lagrangian time scale of the pressure gradient is observed to be much shorter than that of the velocity.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20050210229&hterms=Gradient&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3DGradient','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20050210229&hterms=Gradient&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3DGradient"><span>Optimal disturbances in boundary layers subject to streamwise pressure gradient</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Ashpis, David E.; Tumin, Anatoli</p> <p>2003-01-01</p> <p>An analysis of the optimal non-modal growth of perturbations in a boundary layer in the presence of a streamwise pressure gradient is presented. The analysis is based on PSE equations for an incompressible fluid. Examples with Falkner-Scan profiles indicate that a favorable pressure gradient decreases the non-modal growth, while an unfavorable pressure gradient leads to an increase of the amplification. It is suggested that the transient growth mechanism be utilized to choose optimal parameters of tripping elements on a low-pressure turbine (LPT) airfoil. As an example, a boundary layer flow with a streamwise pressure gradient corresponding to the pressure distribution over a LPT airfoil is considered. It is shown that there is an optimal spacing of the tripping elements and that the transient growth effect depends on the starting point.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20020048138&hterms=fap&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dfap','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20020048138&hterms=fap&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dfap"><span>Arterial Pressure Gradients during Upright Posture and 30 deg Head Down Tilt</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sanchez, E. R; William, J. M.; Ueno, T.; Ballard, R. E.; Hargens, A. R.; Holton, Emily M. (Technical Monitor)</p> <p>1997-01-01</p> <p>Gravity alters local blood pressure within the body so that arterial pressures in the head and foot are lower and higher, respectively, than that at heart level. Furthermore, vascular responses to local alterations of arterial pressure are probably important to maintain orthostatic tolerance upon return to the Earth after space flight. However, it has been difficult to evaluate the body's arterial pressure gradient due to the lack of noninvasive technology. This study was therefore designed to investigate whether finger arterial pressure (FAP), measured noninvasively, follows a normal hydrostatic pressure gradient above and below heart level during upright posture and 30 deg head down tilt (HDT). Seven healthy subjects gave informed consent and were 19 to 52 years old with a height range of 158 to 181 cm. A Finapres device measured arterial pressure at different levels of the body by moving the hand from 36 cm below heart level (BH) to 72 cm above heart level (AH) in upright posture and from 36 cm BH to 48 cm AH during HDT in increments of 12 cm. Mean FAP creased by 85 mmHg transitioning from BH to AH in upright posture, and the pressure gradient calculated from hydrostatic pressure difference (rho(gh)) was 84 mmHg. In HDT, mean FAP decreased by 65 mmHg from BH to AH, and the calculated pressure gradient was also 65 mmHg. There was no significant difference between the measured FAP gradient and the calculated pressure gradient, although a significant (p = 0.023) offset was seen for absolute arterial pressure in upright posture. These results indicate that arterial pressure at various levels can be obtained from the blood pressure at heart level by calculating rho(gh) + an offset. The offset equals the difference between heart level and the site of measurement. In summary, we conclude that local blood pressure gradients can be measured by noninvasive studies of FAP.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017APS..DFDA24002Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017APS..DFDA24002Z"><span>Uncertainty based pressure reconstruction from velocity measurement with generalized least squares</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, Jiacheng; Scalo, Carlo; Vlachos, Pavlos</p> <p>2017-11-01</p> <p>A method using generalized least squares reconstruction of instantaneous pressure field from velocity measurement and velocity uncertainty is introduced and applied to both planar and volumetric flow data. Pressure gradients are computed on a staggered grid from flow acceleration. The variance-covariance matrix of the pressure gradients is evaluated from the velocity uncertainty by approximating the pressure gradient error to a linear combination of velocity errors. An overdetermined system of linear equations which relates the pressure and the computed pressure gradients is formulated and then solved using generalized least squares with the variance-covariance matrix of the pressure gradients. By comparing the reconstructed pressure field against other methods such as solving the pressure Poisson equation, the omni-directional integration, and the ordinary least squares reconstruction, generalized least squares method is found to be more robust to the noise in velocity measurement. The improvement on pressure result becomes more remarkable when the velocity measurement becomes less accurate and more heteroscedastic. The uncertainty of the reconstructed pressure field is also quantified and compared across the different methods.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PhFl...28k6101W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PhFl...28k6101W"><span>On the impact of adverse pressure gradient on the supersonic turbulent boundary layer</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Qian-Cheng; Wang, Zhen-Guo; Zhao, Yu-Xin</p> <p>2016-11-01</p> <p>By employing the particle image velocimetry, the mean and turbulent characteristics of a Mach 2.95 turbulent boundary layer are experimentally investigated without the impact of curvature. The physical mechanism with which the streamwise adverse pressure gradient affects the supersonic boundary layer is revealed. The data are compared to that of the concave boundary layer with similar streamwise distributions of wall static pressure to clarify the separate impacts of the adverse pressure gradient and the concave curvature. The logarithmic law is observed to be well preserved for both of the cases. The dip below the logarithmic law is not observed in present investigation. Theoretical analysis indicates that it could be the result of compromise between the opposite impacts of the compression wave and the increased turbulent intensity. Compared to the zero pressure gradient boundary layer, the principal strain rate and the turbulent intensities are increased by the adverse pressure gradient. The shear layer formed due the hairpin packets could be sharpened by the compression wave, which leads to higher principal strain rate and the associated turbulent level. Due to the additional impact of the centrifugal instability brought by the concave wall, even higher turbulent intensities than that of the adverse pressure gradient case are introduced. The existence of velocity modes within the zero pressure gradient boundary layer suggests that the large scale motions are statistically well organized. The generation of new velocity modes due to the adverse pressure gradient indicates that the turbulent structure is changed by the adverse pressure gradient, through which more turbulence production that cannot be effectively predicted by the Reynolds-stress transport equations could be brought.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007PCE....32..421G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007PCE....32..421G"><span>In situ chemical osmosis experiment in the Boom Clay at the Mol underground research laboratory</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Garavito, A. M.; De Cannière, P.; Kooi, H.</p> <p></p> <p>Studies on the compatibility of Boom Clay with large amounts of nitrate- bearing bituminized radioactive waste have recently raised a particular interest for osmosis-induced effects in this reference formation in Belgium. Indeed, water flow and solute transport may be associated with several types of driving forces, or gradients (chemical, electrical, thermal), in addition to the hydraulic forces, resulting in the so-called coupled flows. Fluid flow caused by driving forces different than hydraulic gradients is referred to as osmosis. Chemical osmosis, the water flow induced by a chemical gradient across a semi-permeable membrane, can generate pressure increase. The question thus arises if there is a risk to create high pore pressures that could damage the near-field of medium-level waste (MLW) galleries, if osmotically driven water flows towards the galleries are produced by the release of large amounts of NaNO 3 (750 t) in the formation. To what extent a low-permeability clay formation such as the Boom Clay acts as an osmotic membrane is thus a key issue to assess the relevance of osmosis phenomena for the disposal of medium-level waste. An in situ osmosis experiment has been conducted at the H ADES underground research laboratory to determine the osmotic efficiency of Boom Clay at the field scale. A recently developed chemical osmosis flow continuum model has been used to design the osmosis experiment, and to interpret the water pressure measurements. Experimental data could be reproduced quite accurately by the model, and the inferred parameter values are consistent with independent determinations for Boom Clay. A rapid water pressure increase (but limited to about a 2 m water column) was observed after 12 h in the filter containing the more saline water. Then, the osmotically induced water pressure slowly decays on several months. So, the experimental results obtained in situ confirm the occurrence of non-hydraulic flow phenomena (chemical osmosis) in a low-permeability plastic formation such as the Boom Clay. The osmotic efficiency of Boom Clay is high under undisturbed chemical conditions ( σ = 0.41 at 0.014 M NaHCO 3), but rapidly decreases when the dissolved salts concentration increases ( σ = 0.07 at 0.14 M NaHCO 3). A semi-permeable membrane behaviour of the Boom Clay (high efficiencies) may be expected for the disposal of nitrate-bearing radioactive waste. However, the presently observed osmotically induced pressure is too low to have a significant mechanical impact on the host rock. Finally, the short duration of the osmosis test performed suggests that the shut-in test method used is effective for osmosis testing.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013ThCFD..27..599M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013ThCFD..27..599M"><span>Analytical study of mixed electroosmotic-pressure-driven flow in rectangular micro-channels</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Movahed, Saeid; Kamali, Reza; Eghtesad, Mohammad; Khosravifard, Amir</p> <p>2013-09-01</p> <p>Operational state of many miniaturized devices deals with flow field in microchannels. Pressure-driven flow (PDF) and electroosmotic flow (EOF) can be recognized as the two most important types of the flow field in such channels. EOF has many advantages in comparison with PDF, such as being vibration free and not requiring any external mechanical pumps or moving parts. However, the disadvantages of this type of flow such as Joule heating, electrophoresis demixing, and not being suitable for mobile devices must be taken into consideration carefully. By using mixed electroosmotic/pressure-driven flow, the role of EOF in producing desired velocity profile will be reduced. In this way, the advantages of EOF can be exploited, and its disadvantages can be prevented. Induced pressure gradient can be utilized in order to control the separation in the system. Furthermore, in many complicated geometries such as T-shape microchannels, turns may induce pressure gradient to the electroosmotic velocity. While analytical formulas are completely essential for analysis and control of any industrial and laboratory microdevices, lack of such formulas in the literature for solving Poisson-Boltzmann equation and predicting electroosmotic velocity field in rectangular domains is evident. In the present study, first a novel method is proposed to solve Poisson-Boltzmann equation (PBE). Subsequently, this solution is utilized to find the electroosmotic and the mixed electroosmotic/pressure-driven velocity profile in a rectangular domain of the microchannels. To demonstrate the accuracy of the presented analytical method in solving PBE and finding electroosmotic velocity, a general nondimensional example is analyzed, and the results are compared with the solution of boundary element method. Additionally, the effects of different nondimensional parameters and also aspect ratio of channels on the electroosmotic part of the flow field will be investigated.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27350150','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27350150"><span>Inhaled Beta Agonist Bronchodilator Does Not Affect Trans-diaphragmatic Pressure Gradient but Decreases Lower Esophageal Sphincter Retention Pressure in Patients with Chronic Obstructive Pulmonary Disease (COPD) and Gastroesophageal Reflux Disease (GERD).</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Del Grande, Leonardo M; Herbella, Fernando A M; Bigatao, Amilcar M; Jardim, Jose R; Patti, Marco G</p> <p>2016-10-01</p> <p>Chronic obstructive pulmonary disease (COPD) patients have a high incidence of gastroesophageal reflux disease (GERD) whose pathophysiology seems to be linked to an increased trans-diaphragmatic pressure gradient and not to a defective esophagogastric barrier. Inhaled beta agonist bronchodilators are a common therapy used by patients with COPD. This drug knowingly not only leads to a decrease in the lower esophageal sphincter (LES) resting pressure, favoring GERD, but also may improve ventilatory parameters, therefore preventing GERD. This study aims to evaluate the effect of inhaled beta agonist bronchodilators on the trans-diaphragmatic pressure gradient and the esophagogastric barrier. We studied 21 patients (mean age 67 years, 57 % males) with COPD and GERD. All patients underwent high-resolution manometry and esophageal pH monitoring. Abdominal and thoracic pressure, trans-diaphragmatic pressure gradient (abdominal-thoracic pressure), and the LES retention pressure (LES basal pressure-transdiaphragmatic gradient) were measured before and 5 min after inhaling beta agonist bronchodilators. The administration of inhaled beta agonist bronchodilators leads to the following: (a) a simultaneous increase in abdominal and thoracic pressure not affecting the trans-diaphragmatic pressure gradient and (b) a decrease in the LES resting pressure with a reduction of the LES retention pressure. In conclusion, inhaled beta agonist bronchodilators not only increase the thoracic pressure but also lead to an increased abdominal pressure favoring GERD by affecting the esophagogastric barrier.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20040088235&hterms=Gradient&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3DGradient','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20040088235&hterms=Gradient&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3DGradient"><span>Temporal gradients in shear stimulate osteoblastic proliferation via ERK1/2 and retinoblastoma protein</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Jiang, Guang-Liang; White, Charles R.; Stevens, Hazel Y.; Frangos, John A.</p> <p>2002-01-01</p> <p>Bone cells are subject to interstitial fluid flow (IFF) driven by venous pressure and mechanical loading. Rapid dynamic changes in mechanical loading cause transient gradients in IFF. The effects of pulsatile flow (temporal gradients in fluid shear) on rat UMR106 cells and rat primary osteoblastic cells were studied. Pulsatile flow induced a 95% increase in S-phase UMR106 cells compared with static controls. In contrast, ramped steady flow stimulated only a 3% increase. Similar patterns of S-phase induction were also observed in rat primary osteoblastic cells. Pulsatile flow significantly increased relative UMR106 cell number by 37 and 62% at 1.5 and 24 h, respectively. Pulsatile flow also significantly increased extracellular signal-regulated kinase (ERK1/2) phosphorylation by 418%, whereas ramped steady flow reduced ERK1/2 activation to 17% of control. Correspondingly, retinoblastoma protein was significantly phosphorylated by pulsatile fluid flow. Inhibition of mitogen-activated protein (MAP)/ERK kinase (MEK)1/2 by U0126 (a specific MEK1/2 inhibitor) reduced shear-induced ERK1/2 phosphorylation and cell proliferation. These findings suggest that temporal gradients in fluid shear stress are potent stimuli of bone cell proliferation.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19890030904&hterms=water+pressure&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dwater%2Bpressure','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19890030904&hterms=water+pressure&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dwater%2Bpressure"><span>Modeling of wave-coherent pressures in the turbulent boundary layer above water waves</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Papadimitrakis, Yiannis ALEX.</p> <p>1988-01-01</p> <p>The behavior of air pressure fluctuations induced by progressive water waves generated mechanically in a laboratory tank was simulated by solving a modified Orr-Sommerfeld equation in a transformed Eulerian wave-following frame of reference. Solution is obtained by modeling the mean and wave-coherent turbulent Reynolds stresses, the behavior of which in the turbulent boundary layer above the waves was simulated using a turbulent kinetic energy-dissipation model, properly modified to account for free-surface proximity and favorable pressure gradient effects. The distribution of both the wave-coherent turbulent Reynolds stress and pressure amplitudes and their corresponding phase lags was found to agree reasonably well with available laboratory data.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_2");'>2</a></li> <li><a href="#" onclick='return showDiv("page_3");'>3</a></li> <li class="active"><span>4</span></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_4 --> <div id="page_5" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_3");'>3</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li class="active"><span>5</span></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="81"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EPJP..132..173T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EPJP..132..173T"><span>Electro-osmotic flow of couple stress fluids in a micro-channel propagated by peristalsis</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tripathi, Dharmendra; Yadav, Ashu; Anwar Bég, O.</p> <p>2017-04-01</p> <p>A mathematical model is developed for electro-osmotic peristaltic pumping of a non-Newtonian liquid in a deformable micro-channel. Stokes' couple stress fluid model is employed to represent realistic working liquids. The Poisson-Boltzmann equation for electric potential distribution is implemented owing to the presence of an electrical double layer (EDL) in the micro-channel. Using long wavelength, lubrication theory and Debye-Huckel approximations, the linearized transformed dimensionless boundary value problem is solved analytically. The influence of electro-osmotic parameter (inversely proportional to Debye length), maximum electro-osmotic velocity (a function of external applied electrical field) and couple stress parameter on axial velocity, volumetric flow rate, pressure gradient, local wall shear stress and stream function distributions is evaluated in detail with the aid of graphs. The Newtonian fluid case is retrieved as a special case with vanishing couple stress effects. With increasing the couple stress parameter there is a significant increase in the axial pressure gradient whereas the core axial velocity is reduced. An increase in the electro-osmotic parameter both induces flow acceleration in the core region (around the channel centreline) and it also enhances the axial pressure gradient substantially. The study is relevant in the simulation of novel smart bio-inspired space pumps, chromatography and medical micro-scale devices.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/biblio/22596940-compressible-two-phase-model-dispersed-particle-flows-application-from-dense-dilute-regimes','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/22596940-compressible-two-phase-model-dispersed-particle-flows-application-from-dense-dilute-regimes"><span>A compressible two-phase model for dispersed particle flows with application from dense to dilute regimes</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>McGrath, Thomas P., E-mail: thomas.p.mcgrath@navy.mil; St Clair, Jeffrey G.; Department of Mechanical and Aerospace Engineering, University of Florida, 231 MAE-A, P.O. Box 116250, Gainesville, Florida 32611</p> <p>2016-05-07</p> <p>Multiphase flows are present in many important fields ranging from multiphase explosions to chemical processing. An important subset of multiphase flow applications involves dispersed materials, such as particles, droplets, and bubbles. This work presents an Eulerian–Eulerian model for multiphase flows containing dispersed particles surrounded by a continuous media such as air or water. Following a large body of multiphase literature, the driving force for particle acceleration is modeled as a direct function of both the continuous-phase pressure gradient and the gradient of intergranular stress existing within the particle phase. While the application of these two components of driving force ismore » well accepted in much of the literature, other models exist in which the particle-phase pressure gradient itself drives particle motion. The multiphase model treats all phases as compressible and is derived to ensure adherence to the 2nd Law of Thermodynamics. The governing equations are presented and discussed, and a characteristic analysis shows the model to be hyperbolic, with a degeneracy in the case that the intergranular stress, which is modeled as a configuration pressure, is zero. Finally, results from a two sample problems involving shock-induced particle dispersion are presented. The results agree well with experimental measurements, providing initial confidence in the proposed model.« less</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JESS..126...78D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JESS..126...78D"><span>The role of boundary layer momentum advection in the mean location of the ITCZ</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dixit, Vishal; Srinivasan, J.</p> <p>2017-08-01</p> <p>The inter-tropical convergence zones (ITCZ) form closer to the equator during equinoxes while they form well away from the equator during the boreal summer. A simple three-way balance between the pressure gradients, Coriolis force and effective Rayleigh friction has been classically used to diagnose the location of maximum boundary layer convergence in the near equatorial ITCZ. If such a balance can capture the dynamics of off-equatorial convergence was not known. We used idealized aqua planet simulations with fixed, zonally symmetric sea surface temperature boundary conditions to simulate the near equatorial and off-equatorial ITCZ. As opposed to the convergence of inter-hemispheric flows in the near equatorial convergence, the off-equatorial convergence forms due to the deceleration of cross-equatorial meridional flow. The detailed momentum budget of the off-equatorial convergence zone reveals that the simple balance is not sufficient to capture the relevant dynamics. The deceleration of the meridional flow is strongly modulated by the inertial effects due to the meridional advection of zonal momentum in addition to the terms in the simple balance. The simple balance predicts a spurious near equatorial convergence and a consistent off-equatorial convergence of the meridional flow. The spurious convergence disappears when inertial effects are included in the balance. As cross equatorial meridional flow decelerates to form convergence, the inertial effects cancel the pressure gradient effects near the equator while they add away from the equator. The contribution to the off-equatorial convergence induced by the pressure gradients is significantly larger than the contribution due to the inertial effects and hence pressure gradients appear to be the primary factor in anchoring the strength and location of the off-equatorial convergence.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.fs.usda.gov/treesearch/pubs/34977','TREESEARCH'); return false;" href="https://www.fs.usda.gov/treesearch/pubs/34977"><span>Xylem hydraulic safety margins in woody plants: coordination of stomatal control of xylem tension with hydraulic capacitance</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.fs.usda.gov/treesearch/">Treesearch</a></p> <p>Frederick C. Meinzer; Daniel M. Johnson; Barbara Lachenbruch; Katherine A. McCulloh; David R. Woodruff</p> <p>2009-01-01</p> <p>The xylem pressure inducing 50% loss of hydraulic conductivity due to embolism (P50) is widely used for comparisons of xylem vulnerability among species and across aridity gradients. However, despite its utility as an index of resistance to catastrophic xylem failure under extreme drought, P50 may have no special...</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4995943','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4995943"><span>Intratumoral oxygen gradients mediate sarcoma cell invasion</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Lewis, Daniel M.; Park, Kyung Min; Tang, Vitor; Xu, Yu; Pak, Koreana; Eisinger-Mathason, T. S. Karin; Simon, M. Celeste; Gerecht, Sharon</p> <p>2016-01-01</p> <p>Hypoxia is a critical factor in the progression and metastasis of many cancers, including soft tissue sarcomas. Frequently, oxygen (O2) gradients develop in tumors as they grow beyond their vascular supply, leading to heterogeneous areas of O2 depletion. Here, we report the impact of hypoxic O2 gradients on sarcoma cell invasion and migration. O2 gradient measurements showed that large sarcoma mouse tumors (>300 mm3) contain a severely hypoxic core [≤0.1% partial pressure of O2 (pO2)] whereas smaller tumors possessed hypoxic gradients throughout the tumor mass (0.1–6% pO2). To analyze tumor invasion, we used O2-controllable hydrogels to recreate the physiopathological O2 levels in vitro. Small tumor grafts encapsulated in the hydrogels revealed increased invasion that was both faster and extended over a longer distance in the hypoxic hydrogels compared with nonhypoxic hydrogels. To model the effect of the O2 gradient accurately, we examined individual sarcoma cells embedded in the O2-controllable hydrogel. We observed that hypoxic gradients guide sarcoma cell motility and matrix remodeling through hypoxia-inducible factor-1α (HIF-1α) activation. We further found that in the hypoxic gradient, individual cells migrate more quickly, across longer distances, and in the direction of increasing O2 tension. Treatment with minoxidil, an inhibitor of hypoxia-induced sarcoma metastasis, abrogated cell migration and matrix remodeling in the hypoxic gradient. Overall, we show that O2 acts as a 3D physicotactic agent during sarcoma tumor invasion and propose the O2-controllable hydrogels as a predictive system to study early stages of the metastatic process and therapeutic targets. PMID:27486245</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27486245','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27486245"><span>Intratumoral oxygen gradients mediate sarcoma cell invasion.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Lewis, Daniel M; Park, Kyung Min; Tang, Vitor; Xu, Yu; Pak, Koreana; Eisinger-Mathason, T S Karin; Simon, M Celeste; Gerecht, Sharon</p> <p>2016-08-16</p> <p>Hypoxia is a critical factor in the progression and metastasis of many cancers, including soft tissue sarcomas. Frequently, oxygen (O2) gradients develop in tumors as they grow beyond their vascular supply, leading to heterogeneous areas of O2 depletion. Here, we report the impact of hypoxic O2 gradients on sarcoma cell invasion and migration. O2 gradient measurements showed that large sarcoma mouse tumors (>300 mm(3)) contain a severely hypoxic core [≤0.1% partial pressure of O2 (pO2)] whereas smaller tumors possessed hypoxic gradients throughout the tumor mass (0.1-6% pO2). To analyze tumor invasion, we used O2-controllable hydrogels to recreate the physiopathological O2 levels in vitro. Small tumor grafts encapsulated in the hydrogels revealed increased invasion that was both faster and extended over a longer distance in the hypoxic hydrogels compared with nonhypoxic hydrogels. To model the effect of the O2 gradient accurately, we examined individual sarcoma cells embedded in the O2-controllable hydrogel. We observed that hypoxic gradients guide sarcoma cell motility and matrix remodeling through hypoxia-inducible factor-1α (HIF-1α) activation. We further found that in the hypoxic gradient, individual cells migrate more quickly, across longer distances, and in the direction of increasing O2 tension. Treatment with minoxidil, an inhibitor of hypoxia-induced sarcoma metastasis, abrogated cell migration and matrix remodeling in the hypoxic gradient. Overall, we show that O2 acts as a 3D physicotactic agent during sarcoma tumor invasion and propose the O2-controllable hydrogels as a predictive system to study early stages of the metastatic process and therapeutic targets.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27486576','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27486576"><span>Quantifying Dynamic Changes in Plantar Pressure Gradient in Diabetics with Peripheral Neuropathy.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Lung, Chi-Wen; Hsiao-Wecksler, Elizabeth T; Burns, Stephanie; Lin, Fang; Jan, Yih-Kuen</p> <p>2016-01-01</p> <p>Diabetic foot ulcers remain one of the most serious complications of diabetes. Peak plantar pressure (PPP) and peak pressure gradient (PPG) during walking have been shown to be associated with the development of diabetic foot ulcers. To gain further insight into the mechanical etiology of diabetic foot ulcers, examination of the pressure gradient angle (PGA) has been recently proposed. The PGA quantifies directional variation or orientation of the pressure gradient during walking and provides a measure of whether pressure gradient patterns are concentrated or dispersed along the plantar surface. We hypothesized that diabetics at risk of foot ulceration would have smaller PGA in key plantar regions, suggesting less movement of the pressure gradient over time. A total of 27 participants were studied, including 19 diabetics with peripheral neuropathy and 8 non-diabetic control subjects. A foot pressure measurement system was used to measure plantar pressures during walking. PPP, PPG, and PGA were calculated for four foot regions - first toe (T1), first metatarsal head (M1), second metatarsal head (M2), and heel (HL). Consistent with prior studies, PPP and PPG were significantly larger in the diabetic group compared with non-diabetic controls in the T1 and M1 regions, but not M2 or HL. For example, PPP was 165% (P = 0.02) and PPG was 214% (P < 0.001) larger in T1. PGA was found to be significantly smaller in the diabetic group in T1 (46%, P = 0.04), suggesting a more concentrated pressure gradient pattern under the toe. The proposed PGA may improve our understanding of the role of pressure gradient on the risk of diabetic foot ulcers.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018CSR...153...16Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018CSR...153...16Y"><span>Simulation of river plume behaviors in a tropical region: Case study of the Upper Gulf of Thailand</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yu, Xiaojie; Guo, Xinyu; Morimoto, Akihiko; Buranapratheprat, Anukul</p> <p>2018-02-01</p> <p>River plumes are a general phenomenon in coastal regions. Most previous studies focus on river plumes in middle and high latitudes with few studies examining those in low latitude regions. Here, we apply a numerical model to the Upper Gulf of Thailand (UGoT) to examine a river plume in low latitudes. Consistent with observational data, the modeled plume has seasonal variation dependent on monsoon conditions. During southwesterly monsoons, the plume extends northeastward to the head of the gulf; during northeasterly monsoons, it extends southwestward to the mouth of the gulf. To examine the effects of latitude, wind and river discharge on the river plume, we designed several numerical experiments. Using a middle latitude for the UGoT, the bulge close to the river mouth becomes smaller, the downstream current flows closer to the coast, and the salinity in the northern UGoT becomes lower. The reduction in the size of the bulge is consistent with the relationship between the offshore distance of a bulge and the Coriolis parameter. Momentum balance of the coastal current is maintained by advection, the Coriolis force, pressure gradient and internal stresses in both low and middle latitudes, with the Coriolis force and pressure gradient enlarged in the middle latitude. The larger pressure gradient in the middle latitude is induced by more offshore freshwater flowing with the coastal current, which induces lower salinity. The influence of wind on the river plume not only has the advection effects of changing the surface current direction and increasing the surface current speed, but also decreases the current speed due to enhanced vertical mixing. Changes in river discharge influence stratification in the UGoT but have little effect on the behavior of the river plume.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19900011479','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19900011479"><span>Experimental feasibility of investigating acoustic waves in Couette flow with entropy and pressure gradients</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Parrott, Tony L.; Zorumski, William E.; Rawls, John W., Jr.</p> <p>1990-01-01</p> <p>The feasibility is discussed for an experimental program for studying the behavior of acoustic wave propagation in the presence of strong gradients of pressure, temperature, and flow. Theory suggests that gradients effects can be experimentally observed as resonant frequency shifts and mode shape changes in a waveguide. A convenient experimental geometry for such experiments is the annular region between two co-rotating cylinders. Radial temperature gradients in a spinning annulus can be generated by differentially heating the two cylinders via electromagnetic induction. Radial pressure gradients can be controlled by varying the cylinder spin rates. Present technology appears adequate to construct an apparatus to allow independent control of temperature and pressure gradients. A complicating feature of a more advanced experiment, involving flow gradients, is the requirement for independently controlled cylinder spin rates. Also, the boundary condition at annulus terminations must be such that flow gradients are minimally disturbed. The design and construction of an advanced apparatus to include flow gradients will require additional technology development.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014ExFl...55.1767P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014ExFl...55.1767P"><span>Direct measurements of local bed shear stress in the presence of pressure gradients</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pujara, Nimish; Liu, Philip L.-F.</p> <p>2014-07-01</p> <p>This paper describes the development of a shear plate sensor capable of directly measuring the local mean bed shear stress in small-scale and large-scale laboratory flumes. The sensor is capable of measuring bed shear stress in the range 200 Pa with an accuracy up to 1 %. Its size, 43 mm in the flow direction, is designed to be small enough to give spatially local measurements, and its bandwidth, 75 Hz, is high enough to resolve time-varying forcing. Typically, shear plate sensors are restricted to use in zero pressure gradient flows because secondary forces on the edge of the shear plate caused by pressure gradients can introduce large errors. However, by analysis of the pressure distribution at the edges of the shear plate in mild pressure gradients, we introduce a new methodology for correcting for the pressure gradient force. The developed sensor includes pressure tappings to measure the pressure gradient in the flow, and the methodology for correction is applied to obtain accurate measurements of bed shear stress under solitary waves in a small-scale wave flume. The sensor is also validated by measurements in a turbulent flat plate boundary layer in open channel flow.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19960015858','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19960015858"><span>A Study of the Development of Steady and Periodic Unsteady Turbulent Wakes Through Curved Channels at Positive, Zero, and Negative Streamwise Pressure Gradients, Part 1</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Schobeiri, M. T.; John, J.</p> <p>1996-01-01</p> <p>The turbomachinery wake flow development is largely influenced by streamline curvature and streamwise pressure gradient. The objective of this investigation is to study the development of the wake under the influence of streamline curvature and streamwise pressure gradient. The experimental investigation is carried out in two phases. The first phase involves the study of the wake behind a stationary circular cylinder (steady wake) in curved channels at positive, zero, and negative streamwise pressure gradients. The mean velocity and Reynolds stress components are measured using a X-hot-film probe. The measured quantities obtained in probe coordinates are transformed to a curvilinear coordinate system along the wake centerline and are presented in similarity coordinates. The results of the steady wakes suggest strong asymmetry in velocity and Reynolds stress components. However, the velocity defect profiles in similarity coordinates are almost symmetrical and follow the same distribution as the zero pressure gradient straight wake. The results of Reynolds stress distributions show higher values on the inner side of the wake than the outer side. Other quantities, including the decay of maximum velocity defect, growth of wake width, and wake integral parameters, are also presented for the three different pressure gradient cases of steady wake. The decay rate of velocity defect is fastest for the negative streamwise pressure gradient case and slowest for the positive pressure gradient case. Conversely, the growth of the wake width is fastest for the positive streamwise pressure gradient case and slowest for the negative streamwise pressure gradient. The second phase studies the development of periodic unsteady wakes generated by the circular cylinders of the rotating wake generator in a curved channel at zero streamwise pressure gradient. Instantaneous velocity components of the periodic unsteady wakes, measured with a stationary X-hot-film probe, are analyzed by the phase averaging techniques. The temporal distribution of velocity and Reynolds stress components obtained in a stationary frame of reference are transformed to a spatial distribution in a relative frame of reference. Profiles of phase-averaged velocity and Reynolds stress distributions in the relative frame of reference and similarity coordinates are presented. The velocity defect and Reynolds stress distributions agree with the results of the wake development behind a stationary cylinder in the curved channel at zero streamwise pressure gradient. The phase-averaged third-order correlations, presented in the relative frame of reference and similarity coordinates, show pronounced asymmetric features.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/servlets/purl/897958','SCIGOV-STC'); return false;" href="https://www.osti.gov/servlets/purl/897958"><span>Behavior of Explosives Under Pressure in a Diamond Anvil Cell</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Foltz, M F</p> <p>2006-06-20</p> <p>Diamond anvil cell (DAC) studies can yield information about the pressure dependence of materials and reactions under conditions comparable to shock loading. The pressure gradient across the face of the diamonds is often deliberately minimized to create uniform pressure over much of the sample and a simplified data set. To reach very high pressures (30-40 GPa), however, it may be necessary to use ''softer'', high nitrogen content diamonds that are more susceptible to bending under pressure. The resulting enhanced pressure gradient then provides a view of high-pressure behavior under anisotropic conditions similar to those found at the burn front inmore » a bulk sample. We discuss visual observations of pressure-induced changes relative to variations in burn rate of several explosives (Triaminotrinitrobenzene, Nitromethane, CL-20) in the DAC. The burn rate behavior of both Nitromethane (NM) and Triaminotrinitrobenzene (TATB) were previously reported for pressures up to {approx}40 GPa. Nitromethane showed a near monotonic increase in burn rate to a maximum at {approx}30 GPa after which the burn rate decreased, all without color change. At higher pressures, the TATB samples had shiny (metallic) polycrystalline zones or inclusions where the pressure was highest in the sample. Around the shiny zones was a gradation of color (red to yellow) that appeared to follow the pressure gradient. The color changes are believed related to disturbances in the resonance structure of this explosive as the intermolecular separations decrease with pressure. The color and type of residue found in unvented gaskets after the burn was complete also varied with pressure. The four polymorphs of CL-20 ({alpha}, {beta}, {gamma}, {var_epsilon}-Hexanitrohexaazaisowurtzitane, HNIW) did not change color up to the highest pressure applied ({approx}30 GPa), and each polymorph demonstrated a distinctly different burn rate signature. One polymorph {beta} was so sensitive to laser ignition over a narrow pressure range that the sample could not be aligned with a low power laser without ignition. The burn rate for that one polymorph could only be measured at pressures above and below that unique pressure. This anomalous ignition threshold is discussed with respect to the matrix of possible polymorphs, most of which have not been isolated in the laboratory. The changes in behavior, color and reaction rates of all samples are discussed with respect to possible implications to chemistry at high pressure.« less</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19830021409','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19830021409"><span>Dual laser optical system and method for studying fluid flow</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Owen, R. B.; Witherow, W. K. (Inventor)</p> <p>1983-01-01</p> <p>A dual laser optical system and method is disclosed for visualization of phenomena in transport substances which induce refractive index gradients such as fluid flow and pressure and temperature gradients in fluids and gases. Two images representing mutually perpendicular components of refractive index gradients may be viewed simultaneously on screen. Two lasers having wave lengths in the visible range but separated by about 1000 angstroms are utilized to provide beams which are collimated into a beam containing components of the different wave lengths. The collimated beam is passed through a test volume of the transparent substance. The collimated beam is then separated into components of the different wave lengths and focused onto a pair of knife edges arranged mutually perpendicular to produce and project images onto the screen.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA133127','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA133127"><span>Interactive Mechanisms of Sliding-Surface Bearings.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.dtic.mil/">DTIC Science & Technology</a></p> <p></p> <p>1983-08-01</p> <p>lower, upper) bearing surface V Three-dimensional gradient operator ix Two-dimensional surface gradient operator ( ),. Pertaining to the bearing surface...thermal gradients . The tilt-pad feature required the pad inclination to be determined by the condition of moment equilibrium about the pivot point. This...into the computation of pressure and shear in a fluid film. Incipience Point of Film Rupture On page 93 of Appendix A, pressure gradient and pressure of</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017APS..DFDA16003B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017APS..DFDA16003B"><span>Experimental Study of Unsteady Flow Separation in a Laminar Boundary Layer</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bonacci, Andrew; Lang, Amy; Wahidi, Redha; Santos, Leonardo</p> <p>2017-11-01</p> <p>Flow separation, caused by an adverse pressure gradient, is a major problem in many applications. Reversing flow near the wall is the first sign of incipient separation and can bristle shark scales which may be linked to a passive, flow actuated separation control mechanism. An investigation of how this backflow forms and how it interacts with shark skin is of interest due to the fact that this could be used as a bioinspired means of initiating flow control. A water tunnel experiment aims to study unsteady separation with a focus on the reversing flow development near the wall within a flat plate laminar boundary layer (Re on order of 105) as an increasing adverse pressure gradient is induced by a rotating cylinder. Unsteady reversing flow development is documented using DPIV. Funding was provided by the National Science Foundation under the Research Experience for Undergraduates (REU) program (EEC 1659710) and the Army Research Office.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3493643','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3493643"><span>Molecular reorientation of a nematic liquid crystal by thermal expansion</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Kim, Young-Ki; Senyuk, Bohdan; Lavrentovich, Oleg D.</p> <p>2012-01-01</p> <p>A unique feature of nematic liquid crystals is orientational order of molecules that can be controlled by electromagnetic fields, surface modifications and pressure gradients. Here we demonstrate a new effect in which the orientation of nematic liquid crystal molecules is altered by thermal expansion. Thermal expansion (or contraction) causes the nematic liquid crystal to flow; the flow imposes a realigning torque on the nematic liquid crystal molecules and the optic axis. The optical and mechanical responses activated by a simple temperature change can be used in sensing, photonics, microfluidic, optofluidic and lab-on-a-chip applications as they do not require externally imposed gradients of temperature, pressure, surface realignment, nor electromagnetic fields. The effect has important ramifications for the current search of the biaxial nematic phase as the optical features of thermally induced structural changes in the uniaxial nematic liquid crystal mimic the features expected of the biaxial nematic liquid crystal. PMID:23072803</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PhRvE..96c3114S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PhRvE..96c3114S"><span>Luminescence from cavitation bubbles deformed in uniform pressure gradients</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Supponen, Outi; Obreschkow, Danail; Kobel, Philippe; Farhat, Mohamed</p> <p>2017-09-01</p> <p>Presented here are observations that demonstrate how the deformation of millimetric cavitation bubbles by a uniform pressure gradient quenches single-collapse luminescence. Our innovative measurement system captures a broad luminescence spectrum (wavelength range, 300-900 nm) from the individual collapses of laser-induced bubbles in water. By varying the bubble size, driving pressure, and perceived gravity level aboard parabolic flights, we probed the limit from aspherical to highly spherical bubble collapses. Luminescence was detected for bubbles of maximum radii within the previously uncovered range, R0=1.5 -6 mm, for laser-induced bubbles. The relative luminescence energy was found to rapidly decrease as a function of the bubble asymmetry quantified by the anisotropy parameter ζ , which is the dimensionless equivalent of the Kelvin impulse. As established previously, ζ also dictates the characteristic parameters of bubble-driven microjets. The threshold of ζ beyond which no luminescence is observed in our experiment closely coincides with the threshold where the microjets visibly pierce the bubble and drive a vapor jet during the rebound. The individual fitted blackbody temperatures range between Tlum=7000 and Tlum=11 500 K but do not show any clear trend as a function of ζ . Time-resolved measurements using a high-speed photodetector disclose multiple luminescence events at each bubble collapse. The averaged full width at half-maximum of the pulse is found to scale with R0 and to range between 10 and 20 ns.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20040112441&hterms=adrenergic&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dadrenergic','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20040112441&hterms=adrenergic&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dadrenergic"><span>Estimation of diastolic intraventricular pressure gradients by Doppler M-mode echocardiography</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Greenberg, N. L.; Vandervoort, P. M.; Firstenberg, M. S.; Garcia, M. J.; Thomas, J. D.</p> <p>2001-01-01</p> <p>Previous studies have shown that small intraventricular pressure gradients (IVPG) are important for efficient filling of the left ventricle (LV) and as a sensitive marker for ischemia. Unfortunately, there has previously been no way of measuring these noninvasively, severely limiting their research and clinical utility. Color Doppler M-mode (CMM) echocardiography provides a spatiotemporal velocity distribution along the inflow tract throughout diastole, which we hypothesized would allow direct estimation of IVPG by using the Euler equation. Digital CMM images, obtained simultaneously with intracardiac pressure waveforms in six dogs, were processed by numerical differentiation for the Euler equation, then integrated to estimate IVPG and the total (left atrial to left ventricular apex) pressure drop. CMM-derived estimates agreed well with invasive measurements (IVPG: y = 0.87x + 0.22, r = 0.96, P < 0.001, standard error of the estimate = 0.35 mmHg). Quantitative processing of CMM data allows accurate estimation of IVPG and tracking of changes induced by beta-adrenergic stimulation. This novel approach provides unique information on LV filling dynamics in an entirely noninvasive way that has previously not been available for assessment of diastolic filling and function.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5051935','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5051935"><span>Cell Blebbing in Confined Microfluidic Environments</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Ibo, Markela; Srivastava, Vasudha; Robinson, Douglas N.; Gagnon, Zachary R.</p> <p>2016-01-01</p> <p>Migrating cells can extend their leading edge by forming myosin-driven blebs and F-actin-driven pseudopods. When coerced to migrate in resistive environments, Dictyostelium cells switch from using predominately pseudopods to blebs. Bleb formation has been shown to be chemotactic and can be influenced by the direction of the chemotactic gradient. In this study, we determine the blebbing responses of developed cells of Dictyostelium discoideum to cAMP gradients of varying steepness produced in microfluidic channels with different confining heights, ranging between 1.7 μm and 3.8 μm. We show that microfluidic confinement height, gradient steepness, buffer osmolarity and Myosin II activity are important factors in determining whether cells migrate with blebs or with pseudopods. Dictyostelium cells were observed migrating within the confines of microfluidic gradient channels. When the cAMP gradient steepness is increased from 0.7 nM/μm to 20 nM/μm, cells switch from moving with a mixture of blebs and pseudopods to moving only using blebs when chemotaxing in channels with confinement heights less than 2.4 μm. Furthermore, the size of the blebs increases with gradient steepness and correlates with increases in myosin-II localization at the cell cortex. Reduction of intracellular pressure by high osmolarity buffer or inhibition of myosin-II by blebbistatin leads to a decrease in bleb formation and bleb size. Together, our data reveal that the protrusion type formed by migrating cells can be influenced by the channel height and the steepness of the cAMP gradient, and suggests that a combination of confinement-induced myosin-II localization and cAMP-regulated cortical contraction leads to increased intracellular fluid pressure and bleb formation. PMID:27706201</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/20030062175','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20030062175"><span>Optimal Disturbances in Boundary Layers Subject to Streamwise Pressure Gradient</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Ashpis, David E.; Tumin, Anatoli</p> <p>2003-01-01</p> <p>An analysis of the non-modal growth of perturbations in a boundary layer in the presence of a streamwise pressure gradient is presented. The analysis is based on PSE equations for an incompressible fluid. Examples with Falkner- Skan profiles indicate that a favorable pressure gradient decreases the non-modal growth while an unfavorable pressure gradient leads to an increase of the amplification. It is suggested that the transient growth mechanism be utilized to choose optimal parameters of tripping elements on a low-pressure turbine (LPT) airfoil. As an example, a boundary-layer flow with a streamwise pressure gradient corresponding to the pressure distribution over a LPT airfoil is considered. It is shown that there is an optimal spacing of the tripping elements and that the transient growth effect depends on the starting point. The amplification is found to be small at the LPT s very low Reynolds numbers, but there is a possibility to enhance the transient energy growth by means of wall cooling.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_3");'>3</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li class="active"><span>5</span></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_5 --> <div id="page_6" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li class="active"><span>6</span></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="101"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19900000176&hterms=Electromagnetic+Pulse&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DElectromagnetic%2BPulse','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19900000176&hterms=Electromagnetic+Pulse&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DElectromagnetic%2BPulse"><span>Electromagnetic Meissner-Effect Launcher</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Robertson, Glen A.</p> <p>1990-01-01</p> <p>Proposed electromagnetic Meissner-effect launching apparatus differs from previous electromagnetic launchers; no need for electromagnet coil on projectile. Result, no need for brush contacts and high-voltage commutation equipment to supply current directly to projectile coil, or for pulse circuitry to induce current in projectile coil if brush contacts not used. Compresses magnetic field surrounding rear surface of projectile, creating gradient of magnetic pressure pushing projectile forward.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24318655','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24318655"><span>Blood pressure regulation V: in vivo mechanical properties of precapillary vessels as affected by long-term pressure loading and unloading.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Eiken, Ola; Mekjavic, Igor B; Kölegård, Roger</p> <p>2014-03-01</p> <p>Recent studies are reviewed, concerning the in vivo wall stiffness of arteries and arterioles in healthy humans, and how these properties adapt to iterative increments or sustained reductions in local intravascular pressure. A novel technique was used, by which arterial and arteriolar stiffness was determined as changes in arterial diameter and flow, respectively, during graded increments in distending pressure in the blood vessels of an arm or a leg. Pressure-induced increases in diameter and flow were smaller in the lower leg than in the arm, indicating greater stiffness in the arteries/arterioles of the leg. A 5-week period of intermittent intravascular pressure elevations in one arm reduced pressure distension and pressure-induced flow in the brachial artery by about 50%. Conversely, prolonged reduction of arterial/arteriolar pressure in the lower body by 5 weeks of sustained horizontal bedrest, induced threefold increases of the pressure-distension and pressure-flow responses in a tibial artery. Thus, the wall stiffness of arteries and arterioles are plastic properties that readily adapt to changes in the prevailing local intravascular pressure. The discussion concerns mechanisms underlying changes in local arterial/arteriolar stiffness as well as whether stiffness is altered by changes in myogenic tone and/or wall structure. As regards implications, regulation of local arterial/arteriolar stiffness may facilitate control of arterial pressure in erect posture and conditions of exaggerated intravascular pressure gradients. That increased intravascular pressure leads to increased arteriolar wall stiffness also supports the notion that local pressure loading may constitute a prime mover in the development of vascular changes in hypertension.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19810003848','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19810003848"><span>Experimental analysis of the boundary layer transition with zero and positive pressure gradient</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Arnal, D.; Jullen, J. C.; Michel, R.</p> <p>1980-01-01</p> <p>The influence of a positive pressure gradient on the boundary layer transition is studied. The mean velocity and turbulence profiles of four cases are examined. As the intensity of the pressure gradient is increased, the Reynolds number of the transition onset and the length of the transition region are reduced. The Tollmein-Schlichting waves disturb the laminar regime; the amplification of these waves is in good agreement with the stability theory. The three dimensional deformation of the waves leads finally to the appearance of turbulence. In the case of zero pressure gradient, the properties of the turbulent spots are studied by conditional sampling of the hot-wire signal; in the case of positive pressure gradient, the turbulence appears in a progressive manner and the turbulent spots are much more difficult to characterize.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JPhCS.708a2012B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JPhCS.708a2012B"><span>Large-eddy simulations of adverse pressure gradient turbulent boundary layers</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bobke, Alexandra; Vinuesa, Ricardo; Örlü, Ramis; Schlatter, Philipp</p> <p>2016-04-01</p> <p>Adverse pressure-gradient (APG) turbulent boundary layers (TBL) are studied by performing well-resolved large-eddy simulations. The pressure gradient is imposed by defining the free-stream velocity distribution with the description of a power law. Different inflow conditions, box sizes and upper boundary conditions are tested in order to determine the final set-up. The statistics of turbulent boundary layers with two different power-law coefficients and thus magnitudes of adverse pressure gradients are then compared to zero pressure-gradient (ZPG) data. The effect of the APG on TBLs is manifested in the mean flow through a much more prominent wake region and in the Reynolds stresses through the existence of an outer peak. The pre-multiplied energy budgets show that more energy is transported from the near-wall region to farther away from the wall.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016ApPhA.122..117L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016ApPhA.122..117L"><span>Structural properties of pressure-induced structural phase transition of Si-doped GaAs by angular-dispersive X-ray diffraction</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lin, Kung-Liang; Lin, Chih-Ming; Lin, Yu-Sheng; Jian, Sheng-Rui; Liao, Yen-Fa; Chuang, Yu-Chun; Wang, Chuan-Sheng; Juang, Jenh-Yih</p> <p>2016-02-01</p> <p>Pressure-induced phase transitions in n-type silicon-doped gallium arsenide (GaAs:Si ) at ambient temperature were investigated by using angular-dispersive X-ray diffraction (ADXRD) under high pressure up to around 18.6 (1) GPa, with a 4:1 (in volume ratio) methanol-ethanol mixture as the pressure-transmitting medium. In situ ADXRD measurements revealed that n-type GaAs:Si starts to transform from zinc- blende structure to an orthorhombic structure [GaAs-II phase], space group Pmm2, at 16.4 (1) GPa. In contrast to previous studies of pure GaAs under pressure, our results show no evidence of structural transition to Fmmm or Cmcm phase. The fitting of volume compression data to the third-order Birch-Murnaghan equation of state yielded that the zero-pressure isothermal bulk moduli and the first-pressure derivatives were 75 (3) GPa and 6.4 (9) for the B3 phase, respectively. After decompressing to the ambient pressure, the GaAs:Si appears to revert to the B3 phase completely. By fitting to the empirical relations, the Knoop microhardness numbers are between H PK = 6.21 and H A = 5.85, respectively, which are substantially smaller than the values of 7-7.5 for pure GaAs reported previously. A discontinuous drop in the pressure-dependent lattice parameter, N- N distances, and V/ V 0 was observed at a pressure of 11.5 (1) GPa, which was tentatively attributed to the pressure-induced dislocation activities in the crystal grown by vertical gradient freeze method.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/11062879','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/11062879"><span>Numerical simulation of cavitation bubble dynamics induced by ultrasound waves in a high frequency reactor.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Servant, G; Caltagirone, J P; Gérard, A; Laborde, J L; Hita, A</p> <p>2000-10-01</p> <p>The use of high frequency ultrasound in chemical systems is of major interest to optimize chemical procedures. Characterization of an open air 477 kHz ultrasound reactor shows that, because of the collapse of transient cavitation bubbles and pulsation of stable cavitation bubbles, chemical reactions are enhanced. Numerical modelling is undertaken to determine the spatio-temporal evolution of cavitation bubbles. The calculus of the emergence of cavitation bubbles due to the acoustic driving (by taking into account interactions between the sound field and bubbles' distribution) gives a cartography of bubbles' emergence within the reactor. Computation of their motion induced by the pressure gradients occurring in the reactor show that they migrate to the pressure nodes. Computed bubbles levitation sites gives a cartography of the chemical activity of ultrasound. Modelling of stable cavitation bubbles' motion induced by the motion of the liquid gives some insight on degassing phenomena.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5479527','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5479527"><span>Hemodynamic and metabolic characteristics associated with development of a right ventricular outflow tract pressure gradient during upright exercise</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>van Riel, Annelieke C. M. J.; Systrom, David M.; Oliveira, Rudolf K. F.; Landzberg, Michael J.; Mulder, Barbara J. M.; Bouma, Berto J.; Maron, Bradley A.; Shah, Amil M.; Waxman, Aaron B.</p> <p>2017-01-01</p> <p>Background We recently reported a novel observation that many patients with equal resting supine right ventricular(RV) and pulmonary artery(PA) systolic pressures develop an RV outflow tract(RVOT) pressure gradient during upright exercise. The current work details the characteristics of patients who develop such an RVOT gradient. Methods We studied 294 patients (59.7±15.5 years-old, 49% male) referred for clinical invasive cardiopulmonary exercise testing, who did not have a resting RVOT pressure gradient defined by the simultaneously measured peak-to-peak difference between RV and PA systolic pressures. Results The magnitude of RVOT gradient did not correspond to clinical or hemodynamic findings suggestive of right heart failure; rather, higher gradients were associated with favorable exercise findings. The presence of a high peak RVOT gradient (90th percentile, ≥33mmHg) was associated with male sex (70 vs. 46%, p = 0.01), younger age (43.6±17.7 vs. 61.8±13.9 years, p<0.001), lower peak right atrial pressure (5 [3–7] vs. 8 [4–12]mmHg, p<0.001), higher peak heart rate (159±19 vs. 124±26 beats per minute, p<0.001), and higher peak cardiac index (8.3±2.3 vs. 5.7±1.9 L/min/m2, p<0.001). These associations persisted when treating peak RVOT as a continuous variable and after age and sex adjustment. At peak exercise, patients with a high exercise RVOT gradient had both higher RV systolic pressure (78±11 vs. 66±17 mmHg, p<0.001) and lower PA systolic pressure (34±8 vs. 50±19 mmHg, p<0.001). Conclusions Development of a systolic RV-PA pressure gradient during upright exercise is not associated with an adverse hemodynamic exercise response and may represent a normal physiologic finding in aerobically fit young people. PMID:28636647</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015PhDT.......107G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015PhDT.......107G"><span>Magnetic anisotropy at material interfaces</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Greene, Peter Kevin</p> <p></p> <p>In this dissertation, a comprehensive set of depth dependent magnetic measurements, as well as structural characterizations, were carried out on the Co/Pd multilayer system. The first-order reversal curve (FORC) technique is applied extensively to identify reversal mechanisms and different reversal phases within the material. In particular, the extension of the FORC technique to x-ray magnetic circular dichroism (XMCD) as a surface sensitive technique that identifies reversible magnetization change was performed for the first time. Polarized neutron reflectivity (PNR) was also used to directly measure the magnetization as a function of depth. The effects of deposition pressure grading within the Co/Pd multilayers were investigated. Structures were graded with three distinct pressure regions. FORC analysis shows that not only does increasing the deposition pressure increase the coercivity and effective anisotropy within that region, but also the order in which the pressure is changed also affects the entire structure. Layers grown at high sputtering pressures tend to reverse via domain wall pinning and rotation while those grown at lower pressures reverse via rapid domain wall propagation laterally across the film. Having high pressure layers underneath low pressure layers causes disorder to vertically propagate and lessen the induced anisotropy gradient. This analysis is confirmed by depth dependent magnetization profiles obtain from PNR. Continuously pressure-graded Co/Pd multilayers were then sputtered at two incident angles onto porous aluminum oxide templates with different pore aspect ratios. The effects of pressure grading versus uniform low pressure deposition is studied, as well as the effect of the angle of the incident deposition flux. The coercivity of the pressure graded perpendicular flux sample is compared to the low pressure sample. Additionally the effect of deposition angle and pore sidewall deposition is investigated. It is shown that sidewall deposition strongly affects the reversal behavior. As another way to induce a vertical anisotropy gradient, Co/Pd multilayers were bombarded with Ar+ ions at different energies and fluences. The effects of the depth dependent structural damage as a function of irradiation conditions were investigated. It is shown that the structural damage weakens the perpendicular anisotropy of the surface layers, causing a tilting of the surface magnetic moment into the plane of the film. The surface behavior is explicitly measured and shown to have a significant tilting angle in the top 5 nm depending on irradiation energy and fluence. Continuing the study of vertical anisotropy gradients in Co/Pd multilayers, multilayers with varied Co thickness were studied. Four films with varying Co thickness profiles were created and then patterned into nanodot arrays with diameters between 700 nm and 70 nm. The different films were graded continuously, or in stacks with varying Co thicknesses. An anisotropy gradient is shown to be established in the graded samples, and the switching field is lowered as a result. Furthermore, in the continuously graded samples the magnetization reversal behavior is fundamentally different from all other samples. The thermal energy barriers are measured in the uniform and continuously graded samples, yielding similar results. Finally, the establishment of exchange anisotropy at the ferromagnet / antiferromagnet (FM/AFM) interface in the epitaxial Fe/CoO system is investigated as a function of AFM thickness. The establishment of frozen AFM moments is analyzed using the FORC technique. The FORC technique combined with vector coil measurements also shows the transition from rotatable AFM to pinned AFM moments and suggests a mechanism of winding domain walls within the bulk AFM. (Abstract shortened by UMI.).</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19770026162','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19770026162"><span>Experimental and theoretical investigation of three-dimensional turbulent boundary layers and turbulence characteristics inside an axial flow inducer passage. Final Report. Ph.D. Thesis, Jun. 1971</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Anand, A. K.; Lakshminarayana, B.</p> <p>1977-01-01</p> <p>Analytical and experimental investigations of the characteristics of three dimensional turbulent boundary layers in a rotating helical passage of an inducer rotor are reported. Expressions are developed for the velocity profiles in the inner layer, where the viscous effects dominate, in the outer layer, where the viscous effects are small, and in the interference layer, where the end walls influence the flow. The prediction of boundary layer growth is based on the momentum integral technique. The equations derived are general enough to be valid for all turbomachinery rotors with arbitrary pressure gradients. The experimental investigations are carried out in a flat plate inducer 3 feet in diameter. The mean velocity profiles, turbulence intensities and shear stresses, wall shear stress, and limiting streamline angles are measured at various radial and chordwise locations by using rotating probes. The measurements are in general agreement with the predictions. The radial flows are well represented by an expression which includes the effect of stagger angle and radial pressure gradient. The radial flows in the rotor channel are higher than those on a single blade. The collateral region exists only very near the blade surface. The radial component of turbulence intensity is higher than the streamwise component because of the effect of rotation.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5491223','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5491223"><span>Physiology of Angina and Its Alleviation With Nitroglycerin</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Williams, Rupert; Lockie, Timothy; Khawaja, Muhammed Z.; De Silva, Kalpa; Lumley, Matthew; Patterson, Tiffany; Arri, Satpal; Ihsan, Sana; Ellis, Howard; Guilcher, Antoine; Clapp, Brian; Chowienczyk, Philip J.; Plein, Sven; Perera, Divaka; Marber, Michael S.; Redwood, Simon R.</p> <p>2017-01-01</p> <p>Background: The mechanisms governing exercise-induced angina and its alleviation by the most commonly used antianginal drug, nitroglycerin, are incompletely understood. The purpose of this study was to develop a method by which the effects of antianginal drugs could be evaluated invasively during physiological exercise to gain further understanding of the clinical impact of angina and nitroglycerin. Methods: Forty patients (mean age, 65.2±7.6 years) with exertional angina and coronary artery disease underwent cardiac catheterization via radial access and performed incremental exercise using a supine cycle ergometer. As they developed limiting angina, sublingual nitroglycerin was administered to half the patients, and all patients continued to exercise for 2 minutes at the same workload. Throughout exercise, distal coronary pressure and flow velocity and central aortic pressure were recorded with sensor wires. Results: Patients continued to exercise after nitroglycerin administration with less ST-segment depression (P=0.003) and therefore myocardial ischemia. Significant reductions in afterload (aortic pressure, P=0.030) and myocardial oxygen demand were seen (tension-time index, P=0.024; rate-pressure product, P=0.046), as well as an increase in myocardial oxygen supply (Buckberg index, P=0.017). Exercise reduced peripheral arterial wave reflection (P<0.05), which was not further augmented by the administration of nitroglycerin (P=0.648). The observed increases in coronary pressure gradient, stenosis resistance, and flow velocity did not reach statistical significance; however, the diastolic velocity–pressure gradient relation was consistent with a significant increase in relative stenosis severity (k coefficient, P<0.0001), in keeping with exercise-induced vasoconstriction of stenosed epicardial segments and dilatation of normal segments, with trends toward reversal with nitroglycerin. Conclusions: The catheterization laboratory protocol provides a model to study myocardial ischemia and the actions of novel and established antianginal drugs. Administration of nitroglycerin causes changes in the systemic and coronary circulation that combine to reduce myocardial oxygen demand and to increase supply, thereby attenuating exercise-induced ischemia. Designing antianginal therapies that exploit these mechanisms may provide new therapeutic strategies. PMID:28468975</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28468975','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28468975"><span>Physiology of Angina and Its Alleviation With Nitroglycerin: Insights From Invasive Catheter Laboratory Measurements During Exercise.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Asrress, Kaleab N; Williams, Rupert; Lockie, Timothy; Khawaja, Muhammed Z; De Silva, Kalpa; Lumley, Matthew; Patterson, Tiffany; Arri, Satpal; Ihsan, Sana; Ellis, Howard; Guilcher, Antoine; Clapp, Brian; Chowienczyk, Philip J; Plein, Sven; Perera, Divaka; Marber, Michael S; Redwood, Simon R</p> <p>2017-07-04</p> <p>The mechanisms governing exercise-induced angina and its alleviation by the most commonly used antianginal drug, nitroglycerin, are incompletely understood. The purpose of this study was to develop a method by which the effects of antianginal drugs could be evaluated invasively during physiological exercise to gain further understanding of the clinical impact of angina and nitroglycerin. Forty patients (mean age, 65.2±7.6 years) with exertional angina and coronary artery disease underwent cardiac catheterization via radial access and performed incremental exercise using a supine cycle ergometer. As they developed limiting angina, sublingual nitroglycerin was administered to half the patients, and all patients continued to exercise for 2 minutes at the same workload. Throughout exercise, distal coronary pressure and flow velocity and central aortic pressure were recorded with sensor wires. Patients continued to exercise after nitroglycerin administration with less ST-segment depression ( P =0.003) and therefore myocardial ischemia. Significant reductions in afterload (aortic pressure, P =0.030) and myocardial oxygen demand were seen (tension-time index, P =0.024; rate-pressure product, P =0.046), as well as an increase in myocardial oxygen supply (Buckberg index, P =0.017). Exercise reduced peripheral arterial wave reflection ( P <0.05), which was not further augmented by the administration of nitroglycerin ( P =0.648). The observed increases in coronary pressure gradient, stenosis resistance, and flow velocity did not reach statistical significance; however, the diastolic velocity-pressure gradient relation was consistent with a significant increase in relative stenosis severity (k coefficient, P <0.0001), in keeping with exercise-induced vasoconstriction of stenosed epicardial segments and dilatation of normal segments, with trends toward reversal with nitroglycerin. The catheterization laboratory protocol provides a model to study myocardial ischemia and the actions of novel and established antianginal drugs. Administration of nitroglycerin causes changes in the systemic and coronary circulation that combine to reduce myocardial oxygen demand and to increase supply, thereby attenuating exercise-induced ischemia. Designing antianginal therapies that exploit these mechanisms may provide new therapeutic strategies. © 2017 The Authors.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/20130012776','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20130012776"><span>Computational Modeling of Cephalad Fluid Shift for Application to Microgravity-Induced Visual Impairment</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Nelson, Emily S.; Best, Lauren M.; Myers, Jerry G.; Mulugeta, Lealem</p> <p>2013-01-01</p> <p>An improved understanding of spaceflight-induced ocular pathology, including the loss of visual acuity, globe flattening, optic disk edema and distension of the optic nerve and optic nerve sheath, is of keen interest to space medicine. Cephalad fluid shift causes a profoundly altered distribution of fluid within the compartments of the head and body, and may indirectly generate phenomena that are biomechanically relevant to visual function, such as choroidal engorgement, compromised drainage of blood and cerebrospinal fluid (CSF), and altered translaminar pressure gradient posterior to the eye. The experimental body of evidence with respect to the consequences of fluid shift has not yet been able to provide a definitive picture of the sequence of events. On earth, elevated intracranial pressure (ICP) is associated with idiopathic intracranial hypertension (IIH), which can produce ocular pathologies that look similar to those seen in some astronauts returning from long-duration flight. However, the clinically observable features of the Visual Impairment and Intracranial Pressure (VIIP) syndrome in space and IIH on earth are not entirely consistent. Moreover, there are at present no experimental measurements of ICP in microgravity. By its very nature, physiological measurements in spaceflight are sparse, and the space environment does not lend itself to well-controlled experiments. In the absence of such data, numerical modeling can play a role in the investigation of biomechanical causal pathways that are suspected of involvement in VIIP. In this work, we describe the conceptual framework for modeling the altered compartmental fluid distribution that represents an equilibrium fluid distribution resulting from the loss of hydrostatic pressure gradient.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/11270555','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/11270555"><span>A spinal thecal sac constriction model supports the theory that induced pressure gradients in the cord cause edema and cyst formation.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Josephson, A; Greitz, D; Klason, T; Olson, L; Spenger, C</p> <p>2001-03-01</p> <p>Spinal cord cysts are a devastating condition that occur secondary to obstructions of the spinal canal, which may be caused by congenital malformations, trauma, spinal canal stenosis, tumors, meningitis, or arachnoiditis. A hypothesis that could explain how spinal cord cysts form in these situations has been presented recently. Therefore, a novel spinal thecal sac constriction model was implemented to test various aspects of this hypothesis. Thecal sac constriction was achieved by subjecting rats to an extradural silk ligature at the T8 spinal cord level. Rats with complete spinal cord transection served as a second model for comparison. The animals underwent high-resolution magnetic resonance imaging and histological analysis. Thecal sac constriction caused edema cranial and caudal to the ligation within 3 weeks, and cysts developed after 8 to 13 weeks. In contrast, cysts in rats with spinal cord transection were located predominantly in the cranial spinal cord. Histological sections of spinal cords confirmed the magnetic resonance imaging results. Magnetic resonance imaging provided the specific advantage of enabling characterization of events as they occurred repeatedly over time in the spinal cords of individual living animals. The spinal thecal sac constriction model proved useful for investigation of features of the cerebrospinal fluid pulse pressure theory. Edema and cyst distributions were in accordance with this theory. We conclude that induced intramedullary pressure gradients originating from the cerebrospinal fluid pulse pressure may underlie cyst formation in the vicinity of spinal canal obstructions and that cysts are preceded by edema.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018CSR...160....1C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018CSR...160....1C"><span>Forced wave induced by an atmospheric pressure disturbance moving towards shore</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chen, Yixiang; Niu, Xiaojing</p> <p>2018-05-01</p> <p>Atmospheric pressure disturbances moving over a vast expanse of water can induce different wave patterns, which can be determined by the Froude number Fr. Generally, Fr = 1 is a critical value for the transformation of the wave pattern and the well-known Proudman resonance happens when Fr = 1. In this study, the forced wave induced by an atmospheric pressure disturbance moving over a constant slope from deep sea to shore is numerically investigated. The wave pattern evolves from a concentric-circle type into a triangular type with the increase of the Froude number, as the local water depth decreases, which is in accord with the analysis in the unbounded flat-bottom cases. However, a hysteresis effect has been observed, which implies the obvious amplification of the forced wave induced by a pressure disturbance can not be simply predicted by Fr = 1. The effects of the characteristic parameters of pressure disturbances and slope gradient have been discussed. The results show that it is not always possible to observe significant peak of the maximum water elevation before the landing of pressure disturbances, and a significant peak can be generated by a pressure disturbance with small spatial scale and fast moving velocity over a milder slope. Besides, an extremely high run-up occurs when the forced wave hits the shore, which is an essential threat to coastal security. The results also show that the maximum run-up is not monotonously varying with the increase of disturbance moving speed and spatial scale. There exists a most dangerous speed and scale which may cause disastrous nearshore surge.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA286110','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA286110"><span>International Conference on Hypertonic Resuscitation (6th) (SALT 6), Held in Teton Village, Wyoming on 2-3 Jun 1994. Program and Abstracts</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.dtic.mil/">DTIC Science & Technology</a></p> <p></p> <p>1994-10-01</p> <p>Furthermore, a systemic -wide incrL ase in capillary permeability raises the interstitial colloid osmotic pressure ([’i) and reverses the [’p-H’i gradient in...1:40 Mayuki Aibiki, Medical University of South Carolina Abstract #1 Role of Autonomic Nervous System in Acute Pressor Effects Induced by 3.5...YOUNES 33,36 Zwischenberger 21 Zwissler 35 SALT 6 Teton Village, Wyoming Abstract 1 ROLE OF AUTONOMIC NERVOUS SYSTEM IN ACUTE PRESSOR EFFECTS INDUCED BY</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/20020021649','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20020021649"><span>A Study of Wake Development and Structure in Constant Pressure Gradients</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Thomas, Flint O.; Nelson, R. C.; Liu, Xiaofeng</p> <p>2000-01-01</p> <p>Motivated by the application to high-lift aerodynamics for commercial transport aircraft, a systematic investigation into the response of symmetric/asymmetric planar turbulent wake development to constant adverse, zero, and favorable pressure gradients has been conducted. The experiments are performed at a Reynolds number of 2.4 million based on the chord of the wake generator. A unique feature of this wake study is that the pressure gradients imposed on the wake flow field are held constant. The experimental measurements involve both conventional LDV and hot wire flow field surveys of mean and turbulent quantities including the turbulent kinetic energy budget. In addition, similarity analysis and numerical simulation have also been conducted for this wake study. A focus of the research has been to isolate the effects of both pressure gradient and initial wake asymmetry on the wake development. Experimental results reveal that the pressure gradient has a tremendous influence on the wake development, despite the relatively modest pressure gradients imposed. For a given pressure gradient, the development of an initially asymmetric wake is different from the initially symmetric wake. An explicit similarity solution for the shape parameters of the symmetric wake is obtained and agrees with the experimental results. The turbulent kinetic energy budget measurements of the symmetric wake demonstrate that except for the convection term, the imposed pressure gradient does not change the fundamental flow physics of turbulent kinetic energy transport. Based on the turbulent kinetic energy budget measurements, an approach to correct the bias error associated with the notoriously difficult dissipation estimate is proposed and validated through the comparison of the experimental estimate with a direct numerical simulation result.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017Tectp.703...98T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017Tectp.703...98T"><span>Mechanical models for dikes: A third school of thought</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Townsend, Meredith R.; Pollard, David D.; Smith, Richard P.</p> <p>2017-04-01</p> <p>Geological and geophysical data from continental volcanic centers and giant radial swarms, and from oceanic shield volcanoes and rift zones, indicate that dikes propagate laterally for distances that can be 10 to over 100 times their height. What traps dikes within the shallow lithosphere and promotes these highly eccentric shapes? Gravity-induced stress gradients in the surrounding rock and pressure gradients in the magma are the primary loading mechanisms; pressure gradients due to magma flow are secondary to insignificant, because the flow direction is dominantly horizontal. This configuration of vertical, blade-shaped dikes with horizontal dike propagation and magma flow is fundamentally different from the two dike model configurations described in a recent review paper as two schools of thought for mechanical models of dikes. In School I, a dike is disconnected from its source and ascends under the influence of buoyancy. In School II, a dike is connected to a magma reservoir and is driven upward by magma flux from the source. We review the geological and geophysical data supporting the vertical dike - horizontal flow/propagation configuration and suggest the abundance and veracity of these data in many different geological settings, and the modeling results that address this physical process, warrant adding this as a third school of thought. A new analytical solution for the boundary-value problem of a homogeneous, isotropic, and linear elastic solid with a vertical, fluid-filled crack is used to investigate the effects of gravitationally induced stress and pressure gradients on the aperture distribution, dike-tip stress intensity, and stable height. Model results indicate that in a homogeneous crust, dikes can achieve stable heights greater than a kilometer only if the host rock fracture toughness KIC 100 MPa · m1/2. However, density stratification of the crust is an effective mechanism for trapping kilometer-scale dikes even if the host rock is very weak (KIC = 0). This analysis may explain why vertical dikes propagate laterally for great distances, but reside within a narrow range of depths in the crust.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19830054819&hterms=employment+work&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Demployment%2Bwork','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19830054819&hterms=employment+work&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Demployment%2Bwork"><span>A comparison of methods for computing the sigma-coordinate pressure gradient force for flow over sloped terrain in a hybrid theta-sigma model</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Johnson, D. R.; Uccellini, L. W.</p> <p>1983-01-01</p> <p>In connection with the employment of the sigma coordinates introduced by Phillips (1957), problems can arise regarding an accurate finite-difference computation of the pressure gradient force. Over steeply sloped terrain, the calculation of the sigma-coordinate pressure gradient force involves computing the difference between two large terms of opposite sign which results in large truncation error. To reduce the truncation error, several finite-difference methods have been designed and implemented. The present investigation has the objective to provide another method of computing the sigma-coordinate pressure gradient force. Phillips' method is applied for the elimination of a hydrostatic component to a flux formulation. The new technique is compared with four other methods for computing the pressure gradient force. The work is motivated by the desire to use an isentropic and sigma-coordinate hybrid model for experiments designed to study flow near mountainous terrain.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018EPJP..133..180D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018EPJP..133..180D"><span>A study on the unsteady flow of two immiscible micropolar and Newtonian fluids through a horizontal channel: A numerical approach</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Devakar, M.; Raje, Ankush</p> <p>2018-05-01</p> <p>The unsteady flow of two immiscible micropolar and Newtonian fluids through a horizontal channel is considered. In addition to the classical no-slip and hyper-stick conditions at the boundary, it is assumed that the fluid velocities and shear stresses are continuous across the fluid-fluid interface. Three cases for the applied pressure gradient are considered to study the problem: one with constant pressure gradient and the other two cases with time-dependent pressure gradients, viz. periodic and decaying pressure gradient. The Crank-Nicolson approach has been used to obtain numerical solutions for fluid velocity and microrotation for diverse sets of fluid parameters. The nature of fluid velocities and microrotation with various values of pressure gradient, Reynolds number, ratio of viscosities, micropolarity parameter and time is illustrated through graphs. It has been observed that micropolarity parameter and ratio of viscosities reduce the fluid velocities.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21405577','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21405577"><span>Trapped electron mode turbulence driven intrinsic rotation in Tokamak plasmas.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wang, W X; Hahm, T S; Ethier, S; Zakharov, L E; Diamond, P H</p> <p>2011-02-25</p> <p>Progress from global gyrokinetic simulations in understanding the origin of intrinsic rotation in toroidal plasmas is reported. The turbulence-driven intrinsic torque associated with nonlinear residual stress generation due to zonal flow shear induced asymmetry in the parallel wave number spectrum is shown to scale close to linearly with plasma gradients and the inverse of the plasma current, qualitatively reproducing experimental empirical scalings of intrinsic rotation. The origin of current scaling is found to be enhanced k(∥) symmetry breaking induced by the increased radial variation of the safety factor as the current decreases. The intrinsic torque is proportional to the pressure gradient because both turbulence intensity and zonal flow shear, which are two key ingredients for driving residual stress, increase with turbulence drive, which is R/L(T(e)) and R/L(n(e)) for the trapped electron mode. © 2011 American Physical Society</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li class="active"><span>6</span></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_6 --> <div id="page_7" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li class="active"><span>7</span></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="121"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24008165','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24008165"><span>Radial mean arterial pressure reliably reflects femoral mean arterial pressure in uncomplicated pediatric cardiac surgery.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Cetin, Secil; Pirat, Arash; Kundakci, Aycan; Camkiran, Aynur; Zeyneloglu, Pinar; Ozkan, Murat; Arslan, Gulnaz</p> <p>2014-02-01</p> <p>To see if radial mean arterial pressure reliably reflects femoral mean arterial pressure in uncomplicated pediatric cardiac surgery. An ethics committee-approved prospective interventional study. Operating room of a tertiary care hospital. Forty-five children aged 3 months to 4 years who underwent pediatric cardiac surgery with hypothermic cardiopulmonary bypass. Simultaneous femoral and radial arterial pressures were recorded at 10-minute intervals intraoperatively. A pressure gradient>5mmHg was considered to be clinically significant. The patients' mean age was 14±11 months and and mean weight was 8.0±3.0kg. A total of 1,816 simultaneous measurements of arterial pressure from the radial and femoral arteries were recorded during the pre-cardiopulmonary bypass, cardiopulmonary bypass, and post-cardiopulmonary bypass periods, including 520 (29%) systolic arterial pressures, 520 (29%) diastolic arterial pressures, and 776 (43%) mean arterial pressures. The paired mean arterial pressure measurements across the 3 periods were significantly and strongly correlated, and this was true for systolic arterial pressures and diastolic arterial pressures as well (r>0.93 and p<0.001 for all). Bland-Altman plots demonstrated good agreement between femoral and radial mean arterial pressures during the pre-cardiopulmonary bypass, cardiopulmonary bypass, and post-cardiopulmonary bypass periods. A significant radial-to-femoral pressure gradient was observed in 150 (8%) of the total 1,816 measurements. These gradients occurred most frequently between pairs of systolic arterial pressure measurements (n = 113, 22% of all systolic arterial pressures), followed by mean arterial pressure measurements (n = 28, 4% of all mean arterial pressures) and diastolic arterial pressures measurements (n = 9, 2% of all diastolic arterial pressures). These significant gradients were not sustained (ie, were not recorded at 2 or more successive time points). The results suggested that radial mean arterial pressure provided an accurate estimate of central mean arterial pressure in uncomplicated pediatric cardiac surgery. There was a significant gradient between radial and femoral mean arterial pressure measurements in only 4% of the mean arterial pressure measurements, and these significant gradients were not sustained. Copyright © 2014 Elsevier Inc. All rights reserved.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22986439','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22986439"><span>Normal values for high-resolution anorectal manometry in healthy women: effects of age and significance of rectoanal gradient.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Noelting, Jessica; Ratuapli, Shiva K; Bharucha, Adil E; Harvey, Doris M; Ravi, Karthik; Zinsmeister, Alan R</p> <p>2012-10-01</p> <p>High-resolution manometry (HRM) is used to measure anal pressures in clinical practice but normal values have not been available. Although rectal evacuation is assessed by the rectoanal gradient during simulated evacuation, there is substantial overlap between healthy people and defecatory disorders, and the effects of age are unknown. We evaluated the effects of age on anorectal pressures and rectal balloon expulsion in healthy women. Anorectal pressures (HRM), rectal sensation, and balloon expulsion time (BET) were evaluated in 62 asymptomatic women ranging in age from 21 to 80 years (median age 44 years) without risk factors for anorectal trauma. In total, 30 women were aged <50 years. Age is associated with lower (r=-0.47, P<0.01) anal resting (63 (5) (≥50 years), 88 (3) (<50 years), mean (s.e.m.)) but not squeeze pressures; higher rectal pressure and rectoanal gradient during simulated evacuation (r=0.3, P<0.05); and a shorter (r=-0.4, P<0.01) rectal BET (17 (9) s (≥50 years) vs. 31 (10) s (<50 years)). Only 5 women had a prolonged (>60 s) rectal BET but 52 had higher anal than rectal pressures (i.e., negative gradient) during simulated evacuation. The gradient was more negative in younger (-41 (6) mm Hg) than older (-12 (6) mm Hg) women and negatively (r=-0.51, P<0.0001) correlated with rectal BET but only explained 16% of the variation in rectal BET. These observations provide normal values for anorectal pressures by HRM. Increasing age is associated with lower anal resting pressure, a more positive rectoanal gradient during simulated evacuation, and a shorter BET in asymptomatic women. Although the rectoanal gradient is negatively correlated with rectal BET, this gradient is negative even in a majority of asymptomatic women, undermining the utility of a negative gradient for diagnosing defecatory disorders by HRM.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23003124','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23003124"><span>Diurnal blood pressure variations are associated with changes in distal-proximal skin temperature gradient.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kräuchi, Kurt; Gompper, Britta; Hauenstein, Daniela; Flammer, Josef; Pflüger, Marlon; Studerus, Erich; Schötzau, Andy; Orgül, Selim</p> <p>2012-11-01</p> <p>It is generally assumed that skin vascular resistance contributes only to a small extent to total peripheral resistance and hence to blood pressure (BP). However, little is known about the impact of skin blood flow (SBF) changes on the diurnal variations of BP under ambulatory conditions. The main aim of the study was to determine whether diurnal patterns of distal SBF are related to mean arterial BP (MAP). Twenty-four-hour ambulatory measurements of BP, heart rate (HR) and distal (mean of hands and feet) as well as proximal (mean of sternum and infraclavicular region) skin temperatures were carried out in 51 patients (men/women = 18/33) during a 2-d eye hospital investigation. The standardized ambulatory protocol allowed measurements with minimal interference from uncontrolled parameters and, hence, some conclusive interpretations. The distal minus proximal skin temperature gradient (DPG) provided a measure for distal SBF. Individual cross-correlation analyses revealed that the diurnal pattern of MAP was nearly a mirror image of DPG and hence of distal SBF. Scheduled lunch and dinner induced an increase in DPG and a decline in MAP, while HR increased. Low daytime DPG (i.e. low distal SBF) levels significantly predicted sleep-induced BP dipping (r = -.436, p = .0014). Preliminary path analysis suggested that outdoor air temperature and atmospheric pressure may act on MAP via changed distal SBF. Changes in distal SBF may contribute to diurnal variation in MAP, including sleep-induced BP dipping and changes related to food intake. This finding might have an impact on individual cardiovascular risk prediction with respect to diurnal, seasonal and weather variations; however, the underlying mechanisms remain to be discovered.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017APS..DFD.L9006C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017APS..DFD.L9006C"><span>Role of body surface pressure and kinematics in fish turning</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Costello, John; Costello, Sean; Dabiri, John; Leftwich, Megan C.</p> <p>2017-11-01</p> <p>Experiments on freely swimming zebrafish were conducted to study the relative contributions to angular acceleration from both the induced pressure field in the fluid surrounding the animal as well as changes in the body moment of inertia due bending during turning maneuvers. PIV-based pressure measurements indicated that turning is initiated by subtle changes to body posture that create large pressure gradients at the head and tail of the animal. The angular turning motion that results from this pressure-based torque is amplified by the animal bending, which reduces the body moment of inertia during the turn. The demonstrated ability to decouple torque generation and body kinematics, using a combination PIV-based pressure measurements and image-based inertia measurements, can facilitate exploration of maneuvering dynamics in a broader range of swimming species, including a search for possible convergent maneuvering strategies that might be common among aquatic animals.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28753738','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28753738"><span>Modification of splenic stiffness on acoustic radiation force impulse parallels the variation of portal pressure induced by transjugular intrahepatic portosystemic shunt.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>De Santis, Adriano; Nardelli, Silvia; Bassanelli, Chiara; Lupo, Marinella; Iegri, Claudia; Di Ciesco, Carmela Anna; Forlino, Mariana; Farcomeni, Alessio; Riggio, Oliviero</p> <p>2018-03-01</p> <p>Spleen and liver stiffness (LS) measured by acoustic radiation force impulse (ARFI) imaging has been shown to be useful in identifying patients with portal hypertension. The study aims to establish if the modification of portal pressure induced by a transjugular intrahepatic portosystemic shunt (TIPS) parallels the modification of spleen or LS measured by ARFI in order to understand if ARFI may be used to monitor the modification of portal pressure in patients with cirrhosis. Thirty-eight patients with severe portal hypertension underwent LS and spleen stiffness (SS) before TIPS and 1 week after TIPS. Portal atrial gradient (PAG) was measured before and after the shunt opening. Portal atrial gradient decreased significantly from 19.5 to 6 mmHg (P < 0.001). SS decreased significantly after TIPS (pre-TIPS 3.7 m/s vs post-TIPS 3. 1 m/s; P < 0.001), and LS was also significantly modified by TIPS (pre-TIPS 2.8 m/s vs post-TIPS 2.4 m/s; P = 0.003). PAG and SS values measured before and after TIPS were significantly correlated (r = 0.56; P < 0.001); on the other hand, PAG and LS were not (r = 0.19; P = 0.27). Two patients developed a persistent hepatic encephalopathy refractory to medical treatment and were submitted to the reduction of the stent diameter. The modification of SS was parallel to the modification of PAG. Spleen stiffness is superior to LS in detecting the modification of portal pressure induced by TIPS. This makes SS a potential non-invasive method to monitor the modification of portal hypertension. Further investigations are needed to establish applicability and clinical utility of this promising tool in the treatment of portal hypertension. © 2017 Journal of Gastroenterology and Hepatology Foundation and John Wiley & Sons Australia, Ltd.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/20070021687','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20070021687"><span>Analytic Formulation and Numerical Implementation of an Acoustic Pressure Gradient Prediction</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Lee, Seongkyu; Brentner, Kenneth S.; Farassat, Fereidoun</p> <p>2007-01-01</p> <p>The scattering of rotor noise is an area that has received little attention over the years, yet the limited work that has been done has shown that both the directivity and intensity of the acoustic field may be significantly modified by the presence of scattering bodies. One of the inputs needed to compute the scattered acoustic field is the acoustic pressure gradient on a scattering surface. Two new analytical formulations of the acoustic pressure gradient have been developed and implemented in the PSU-WOPWOP rotor noise prediction code. These formulations are presented in this paper. The first formulation is derived by taking the gradient of Farassat's retarded-time Formulation 1A. Although this formulation is relatively simple, it requires numerical time differentiation of the acoustic integrals. In the second formulation, the time differentiation is taken inside the integrals analytically. The acoustic pressure gradient predicted by these new formulations is validated through comparison with the acoustic pressure gradient determined by a purely numerical approach for two model rotors. The agreement between analytic formulations and numerical method is excellent for both stationary and moving observers case.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/19034481','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/19034481"><span>Physiology of vitreous surgery.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Stefánsson, Einar</p> <p>2009-02-01</p> <p>Vitreous surgery has various physiological and clinical consequences, both beneficial and harmful. Vitrectomy reduces the risk of retinal neovascularization, while increasing the risk of iris neovascularization, reduces macular edema and stimulates cataract formation. These clinical consequences may be understood with the help of classical laws of physics and physiology. The laws of Fick, Stokes-Einstein and Hagen-Poiseuille state that molecular transport by diffusion or convection is inversely related to the viscosity of the medium. When the vitreous gel is replaced with less viscous saline, the transport of all molecules, including oxygen and cytokines, is facilitated. Oxygen transport to ischemic retinal areas is improved, as is clearance of VEGF and other cytokines from these areas, thus reducing edema and neovascularization. At the same time, oxygen is transported faster down a concentration gradient from the anterior to the posterior segment, while VEGF moves in the opposite direction, making the anterior segment less oxygenated and with more VEGF, stimulating iris neovascularization. Silicone oil is the exception that proves the rule: it is more viscous than vitreous humour, re-establishes the transport barrier to oxygen and VEGF, and reduces the risk for iris neovascularization in the vitrectomized-lentectomized eye. Modern vitreous surgery involves a variety of treatment options in addition to vitrectomy itself, such as photocoagulation, anti-VEGF drugs, intravitreal steroids and release of vitreoretinal traction. A full understanding of these treatment modalities allows sensible combination of treatment options. Retinal photocoagulation has repeatedly been shown to improve retinal oxygenation, as does vitrectomy. Oxygen naturally reduces VEGF production and improves retinal hemodynamics. The VEGF-lowering effect of photocoagulation and vitrectomy can be augmented with anti-VEGF drugs and the permeability effect of VEGF reduced with corticosteroids. Starling's law explains vasogenic edema, which is controlled by osmotic and hydrostatic gradients between vessel and tissue. It explains the effect of VEGF-induced vascular permeability changes on plasma protein leakage and the osmotic gradient between vessel and tissue. At the same time, it takes into account hemodynamic changes that affect the hydrostatic gradient. This includes the influence of arterial blood pressure, and the effect oxygen (laser treatment) has in constricting retinal arterioles, increasing their resistance, and thus reducing the hydrostatic pressure in the microcirculation. Reduced capillary hydrostatic pressure and increased osmotic gradient reduce water fluxes from vessel to tissue and reduce edema. Finally, Newton's third law explains that vitreoretinal traction decreases hydrostatic tissue pressure in the retina, increases the pressure gradient between vessel and tissue, and stimulates water fluxes from vessel into tissue, leading to edema.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29153849','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29153849"><span>Cutting balloon and high-pressure balloon dilation for palliative treatment of congenital double-chambered right ventricle and primary infundibular stenosis in a Golden retriever dog.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Schober, Karsten E; Rhinehart, Jaylyn; Kohnken, Rebecca; Bonagura, John D</p> <p>2017-12-01</p> <p>Combined cutting balloon and high-pressure balloon dilation was performed in a dog with a double-chambered right ventricle and severe infundibular stenosis of the right ventricular outflow tract. The peak systolic pressure gradient across the stenosis decreased by 65% after dilation (from 187 mmHg before to 66 mmHg after) affirming the intervention as successful. However, early re-stenosis occurred within 3 months leading to exercise intolerance, exercise-induced syncope, and right-sided congestive heart failure. Cutting balloon followed by high-pressure balloon dilation provided temporary but not long-term relief of right ventricular obstruction in this dog. Copyright © 2017 Elsevier B.V. All rights reserved.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28414348','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28414348"><span>Optical ray tracing method for simulating beam-steering effects during laser diagnostics in turbulent media.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wang, Yejun; Kulatilaka, Waruna D</p> <p>2017-04-10</p> <p>In most coherent spectroscopic methods used in gas-phase laser diagnostics, multiple laser beams are focused and crossed at a specific location in space to form the probe region. The desired signal is then generated as a result of nonlinear interactions between the beams in this overlapped region. When such diagnostic schemes are implemented in practical devices having turbulent reacting flow fields with refractive index gradients, the resulting beam steering can give rise to large measurement uncertainties. The objective of this work is to simulate beam-steering effects arising from pressure and temperature gradients in gas-phase media using an optical ray tracing approach. The ZEMAX OpticStudio software package is used to simulate the beam crossing and uncrossing effects in the presence of pressure and temperature gradients, specifically the conditions present in high-pressure, high-temperature combustion devices such as gas turbine engines. Specific cases involving two-beam and three-beam crossing configurations are simulated. The model formulation, the effects of pressure and temperature gradients, and the resulting beam-steering effects are analyzed. The results show that thermal gradients in the range of 300-3000 K have minimal effects, while pressure gradients in the range of 1-50 atm result in pronounced beam steering and the resulting signal fluctuations in the geometries investigated. However, with increasing pressures, the temperature gradients can also have a pronounced effect on the resultant signal levels.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19880005766','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19880005766"><span>Secondary subharmonic instability of boundary layers with pressure gradient and suction</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>El-Hady, Nabil M.</p> <p>1988-01-01</p> <p>Three-dimensional linear secondary instability is investigated for boundary layers with pressure gradient and suction in the presence of a finite amplitude TS wave. The focus is on principal parametric resonance responsible for a strong growth of subharmonics in a low disturbance environment. Calculations are presented for the effect of pressure gradients and suction on controlling the onset and amplification of the secondary instability.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JChPh.138q4701Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JChPh.138q4701Y"><span>Pressure induced structural phase transition in solid oxidizer KClO3: A first-principles study</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yedukondalu, N.; Ghule, Vikas D.; Vaitheeswaran, G.</p> <p>2013-05-01</p> <p>High pressure behavior of potassium chlorate (KClO3) has been investigated from 0 to 10 GPa by means of first principles density functional theory calculations. The calculated ground state parameters, transition pressure, and phonon frequencies using semiempirical dispersion correction scheme are in excellent agreement with experiment. It is found that KClO3 undergoes a pressure induced first order phase transition with an associated volume collapse of 6.4% from monoclinic (P21/m) → rhombohedral (R3m) structure at 2.26 GPa, which is in good accord with experimental observation. However, the transition pressure was found to underestimate (0.11 GPa) and overestimate (3.57 GPa) using local density approximation and generalized gradient approximation functionals, respectively. Mechanical stability of both the phases is explained from the calculated single crystal elastic constants. In addition, the zone center phonon frequencies have been calculated using density functional perturbation theory at ambient as well as at high pressure and the lattice modes are found to soften under pressure between 0.6 and 1.2 GPa. The present study reveals that the observed structural phase transition leads to changes in the decomposition mechanism of KClO3 which corroborates with the experimental results.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23656146','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23656146"><span>Pressure induced structural phase transition in solid oxidizer KClO3: a first-principles study.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Yedukondalu, N; Ghule, Vikas D; Vaitheeswaran, G</p> <p>2013-05-07</p> <p>High pressure behavior of potassium chlorate (KClO3) has been investigated from 0 to 10 GPa by means of first principles density functional theory calculations. The calculated ground state parameters, transition pressure, and phonon frequencies using semiempirical dispersion correction scheme are in excellent agreement with experiment. It is found that KClO3 undergoes a pressure induced first order phase transition with an associated volume collapse of 6.4% from monoclinic (P2(1)/m) → rhombohedral (R3m) structure at 2.26 GPa, which is in good accord with experimental observation. However, the transition pressure was found to underestimate (0.11 GPa) and overestimate (3.57 GPa) using local density approximation and generalized gradient approximation functionals, respectively. Mechanical stability of both the phases is explained from the calculated single crystal elastic constants. In addition, the zone center phonon frequencies have been calculated using density functional perturbation theory at ambient as well as at high pressure and the lattice modes are found to soften under pressure between 0.6 and 1.2 GPa. The present study reveals that the observed structural phase transition leads to changes in the decomposition mechanism of KClO3 which corroborates with the experimental results.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011APS..DFDS17005B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011APS..DFDS17005B"><span>Puffing flame instability - Part II: Predicting the onset and frequency</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Boettcher, Philipp; Shepherd, Joseph; Menon, Shyam; Blanquart, Guillaume</p> <p>2011-11-01</p> <p>Experiments and simulations have been performed on fuel rich n- hexane air mixtures in a closed vessel. Both experiments and simulations show a distinct cyclic combustion or ``puffing'' mode. The misalignment of buoyancy induced pressure gradients and density gradients across the flame front is responsible for the generation of vorticity and its subsequent roll-up into vortex rings. In the present work, a simplified model is proposed based on the fundamental interactions between fluid mechanical and chemical parameters. This simplified fluid mechanics model is based on dimensional analysis and is used to predict the onset and frequency of the puffing behavior. This work was sponsored by The Boeing Company through CTBA-GTA-1.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1433222','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1433222"><span>Effect of Valsalva's manoeuvre and hyoscinbutylbromide on the pressure gradient across the wall of oesophageal varices.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Hosking, S W; Robinson, P; Johnson, A G</p> <p>1987-01-01</p> <p>To assess whether Valsalva's manoeuvre might cause variceal bleeding, 22 patients with oesophageal varices were studied. In 12 patients who received no previous treatment to their varices the median pressure gradient across the varix wall at rest was 19 (6-36) mmHg, and in 10 patients whose varices were thrombosed at their distal end the median pressure gradient in the proximal patent varix was 8 (1-6) mmHg. In untreated patients groups, the pressure gradient rose by 6-12 mmHg during Valsalva's manoeuvre in four patients, fell by 4-11 mmHg in five patients and was virtually unchanged in the remainder. These changes seem unlikely to cause variceal bleeding. Patients who repeated Valsalva's manoeuvre showed similar changes on each occasion. Six patients in the untreated group also received hyoscinbutylbromide 20 mg iv. No change was seen in the pressure gradient in five patients, suggesting that it is of little value in preventing variceal bleeding. PMID:3500098</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25172821','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25172821"><span>Incorporating high-pressure electroosmotic pump and a nano-flow gradient generator into a miniaturized liquid chromatographic system for peptide analysis.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Chen, Apeng; Lynch, Kyle B; Wang, Xiaochun; Lu, Joann J; Gu, Congying; Liu, Shaorong</p> <p>2014-09-24</p> <p>We integrate a high-pressure electroosmotic pump (EOP), a nanoflow gradient generator, and a capillary column into a miniaturized liquid chromatographic system that can be directly coupled with a mass spectrometer for proteomic analysis. We have recently developed a low-cost high-pressure EOP capable of generating pressure of tens of thousands psi, ideal for uses in miniaturized HPLC. The pump worked smoothly when it was used for isocratic elutions. When it was used for gradient elutions, generating reproducible gradient profiles was challenging; because the pump rate fluctuated when the pump was used to pump high-content organic solvents. This presents an issue for separating proteins/peptides since high-content organic solvents are often utilized. In this work, we solve this problem by incorporating our high-pressure EOP with a nano-flow gradient generator so that the EOP needs only to pump an aqueous solution. With this combination, we develop a capillary-based nano-HPLC system capable of performing nano-flow gradient elution; the pump rate is stable, and the gradient profiles are reproducible and can be conveniently tuned. To demonstrate its utility, we couple it with either a UV absorbance detector or a mass spectrometer for peptide separations. Copyright © 2014. Published by Elsevier B.V.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013APS..DFD.R6006W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013APS..DFD.R6006W"><span>Dissimilar viscosity induced sample pre-concentration in elecrokinetic nanofluidic channels</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wink, Dean; Shelton, Elijah; Pennathur, Sumita; Storey, Brian</p> <p>2013-11-01</p> <p>Nanofluidic analysis systems boast many advantages: portability, small sample handling, short processing times, and potential for integration with mobile electronics. However, such systems face the challenge of detecting increasingly small volumes of sample at low concentrations. In this work, we demonstrate a unique pre-concentration technique in electrokinetic nanofluidic systems based on a viscosity mismatch between two fluids. In nanofluidic electrokinetic systems, finite electric double layers (EDL) lead to non-uniform electric potentials and transverse concentration distributions. Therefore, when the EDL is comparable in size to the channel height, negatively charged ions are repelled from negatively charged walls and preferentially populate the channel centerline. Furthermore, an axial piecewise viscosity distribution induces internal pressure gradients within the channel. These force the ions to move at a different average velocities based on the pressure gradient being favorable or adverse, leading to focusing. To experimentally probe this phenomenon, we electrokinetically inject solutions of borate buffer with and without glycerol (to change the viscosity) and use a fluorescent tracer dye to visualize the flow. We perform the injections in cross-geometry channels of 20 micron, 1 micron, and 250 nanometer depths. We measure fluorescence at 5, 10 and 15 mm distances from junction. Enhancement is characterized by comparing intensities to control measurements for systems with uniform viscosity.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24834936','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24834936"><span>Pressure chamber tests of eustachian tube function document lower efficiency in adults with colds when compared to without colds.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Doyle, William J; Singla, Alok; Banks, Juliane; El-Wagaa, Jenna; Swarts, J Douglas</p> <p>2014-07-01</p> <p>Fractional gradient equilibrated (FGE) for ears with applied positive but not negative middle ear (ME)-ambient pressure gradients is highly sensitive to a cold-like illness (CLI). The sequential development of eustachian tube (ET) dysfunction, ME under-pressure, and otitis media (OM) characterizes many children during a CLI. If linked, OM burden would be lessened by interventions that promote/preserve good ET function during a CLI. Evaluating this requires a quantitative ET function test for MEs with an intact tympanic membrane responsive to a CLI. Pressure chamber testing of ET function was performed at +200 and -200 daPa in 3 groups of adults: group I, 21 subjects with an extant CLI and groups II and III, 14 and 57 adults, respectively, without a CLI. ME-chamber pressure gradient was recorded by tympanometry before and after the subject swallowed twice. ET functional efficiency was quantified as the FGE, which was then compared among groups using a Mann-Whitney U test. At chamber pressures of 200 daPa, the ME-chamber pressure gradient was negative, and FGE was low and not different among groups. At chamber pressures of -200 daPa that gradient was positive, and FGE was significantly higher in groups II and III when compared with group I.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19800009140','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19800009140"><span>First results of a study on turbulent boundary layers in oscillating flow with a mean adverse pressure gradient</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Houdeville, R.; Cousteix, J.</p> <p>1979-01-01</p> <p>The development of a turbulent unsteady boundary layer with a mean pressure gradient strong enough to induce separation, in order to complete the extend results obtained for the flat plate configuration is presented. The longitudinal component of the velocity is measured using constant temperature hot wire anemometer. The region where negative velocities exist is investigated with a laser Doppler velocimeter system with BRAGG cells. The boundary layer responds by forced pulsation to the perturbation of potential flow. The unsteady effects observed are very important. The average location of the zero skin friction point moves periodically at the perturbation frequency. Average velocity profiles from different instants in the cycle are compared. The existence of a logarithmic region enables a simple calculation of the maximum phase shift of the velocity in the boundary layer. An attempt of calculation by an integral method of boundary layer development is presented, up to the point where reverse flow starts appearing.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016APS..DFD.E7004B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016APS..DFD.E7004B"><span>Experimental Study of Unsteady Separation in a Laminar Boundary Layer</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bonacci, Andrew; Lang, Amy; Wahidi, Redha; Santos, Leo</p> <p>2016-11-01</p> <p>Separation, caused by an adverse pressure gradient, can be a major problem to aircraft. Reversing flow occurs in separated regions and an investigation of how this backflow forms is of interest due to the fact that this could be used as a means of initiating flow control. Specifically, backflow can bristle shark scales which may be linked to a passive, flow actuated separation control mechanism. An experiment was conducted in a water tunnel to replicate separation, with a focus on the reversing flow development near the wall within a laminar boundary layer. Using a rotating cylinder, an adverse pressure gradient was induced creating a separated region over a flat plate. In this experiment the boundary layer grows to sizes great enough that the scale of the flow is increased, making it more measurable to DPIV. In the future, this research can be utilized to better understand flow control mechanisms such as those enabled by shark skin. Funding from Army Research Office and NSF REU site Grant EEC 1358991 is greatly appreciated.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016NatSR...637407Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016NatSR...637407Z"><span>How a High-Gradient Magnetic Field Could Affect Cell Life</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zablotskii, Vitalii; Polyakova, Tatyana; Lunov, Oleg; Dejneka, Alexandr</p> <p>2016-11-01</p> <p>The biological effects of high-gradient magnetic fields (HGMFs) have steadily gained the increased attention of researchers from different disciplines, such as cell biology, cell therapy, targeted stem cell delivery and nanomedicine. We present a theoretical framework towards a fundamental understanding of the effects of HGMFs on intracellular processes, highlighting new directions for the study of living cell machinery: changing the probability of ion-channel on/off switching events by membrane magneto-mechanical stress, suppression of cell growth by magnetic pressure, magnetically induced cell division and cell reprograming, and forced migration of membrane receptor proteins. By deriving a generalized form for the Nernst equation, we find that a relatively small magnetic field (approximately 1 T) with a large gradient (up to 1 GT/m) can significantly change the membrane potential of the cell and thus have a significant impact on not only the properties and biological functionality of cells but also cell fate.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li class="active"><span>7</span></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_7 --> <div id="page_8" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li class="active"><span>8</span></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="141"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5114642','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5114642"><span>How a High-Gradient Magnetic Field Could Affect Cell Life</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Zablotskii, Vitalii; Polyakova, Tatyana; Lunov, Oleg; Dejneka, Alexandr</p> <p>2016-01-01</p> <p>The biological effects of high-gradient magnetic fields (HGMFs) have steadily gained the increased attention of researchers from different disciplines, such as cell biology, cell therapy, targeted stem cell delivery and nanomedicine. We present a theoretical framework towards a fundamental understanding of the effects of HGMFs on intracellular processes, highlighting new directions for the study of living cell machinery: changing the probability of ion-channel on/off switching events by membrane magneto-mechanical stress, suppression of cell growth by magnetic pressure, magnetically induced cell division and cell reprograming, and forced migration of membrane receptor proteins. By deriving a generalized form for the Nernst equation, we find that a relatively small magnetic field (approximately 1 T) with a large gradient (up to 1 GT/m) can significantly change the membrane potential of the cell and thus have a significant impact on not only the properties and biological functionality of cells but also cell fate. PMID:27857227</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19790024048','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19790024048"><span>Estimation of tunnel blockage from wall pressure signatures: A review and data correlation</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hackett, J. E.; Wilsden, D. J.; Lilley, D. E.</p> <p>1979-01-01</p> <p>A method is described for estimating low speed wind tunnel blockage, including model volume, bubble separation and viscous wake effects. A tunnel-centerline, source/sink distribution is derived from measured wall pressure signatures using fast algorithms to solve the inverse problem in three dimensions. Blockage may then be computed throughout the test volume. Correlations using scaled models or tests in two tunnels were made in all cases. In many cases model reference area exceeded 10% of the tunnel cross-sectional area. Good correlations were obtained regarding model surface pressures, lift drag and pitching moment. It is shown that blockage-induced velocity variations across the test section are relatively unimportant but axial gradients should be considered when model size is determined.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19960021727&hterms=LUNG+SIMULATION&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DLUNG%2BSIMULATION','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19960021727&hterms=LUNG+SIMULATION&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DLUNG%2BSIMULATION"><span>Regional volume changes in canine lungs suspended in air</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Abbrecht, Peter H.; Kyle, Richard R.; Bryant, Howard J.; Feuerstein, Irwin</p> <p>1995-01-01</p> <p>The purpose of this study was to determine the effect of the absence of a pleural pressure gradient (simulating the presumed condition found in microgravity) upon regional expansion of the lung. We attempted to produce a uniform pressure over the surface of the lung by suspending excised lungs in air. Such studies should help determine whether or not the absence of a pleural pressure gradient leads to uniform ventilation. A preparation in which there is no pleural pressure gradient should also be useful in studying non-gravitational effects on ventilation distribution.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140010664','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140010664"><span>Unilateral Loss of Spontaneous Venous Pulsations in an Astronaut</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mader, Thomas H.; Gibson, C. Robert; Lee, Andrew G.; Patel, Nimesh; Hart, Steven; Pettit, Donald R.</p> <p>2014-01-01</p> <p>Spontaneous venous pulsations seen on the optic nerve head (optic disc) are presumed to be caused by fluctuations in the pressure gradient between the intraocular and retrolaminar venous systems. The disappearance of previously documented spontaneous venous pulsations is a well-recognized clinical sign usually associated with a rise in intracranial pressure and a concomitant bilateral elevation of pressure in the subarachnoid space surrounding the optic nerves. In this correspondence we report the unilateral loss of spontaneous venous pulsations in an astronaut 5 months into a long duration space flight. We documented a normal lumbar puncture opening pressure 8 days post mission. The spontaneous venous pulsations were also documented to be absent 21 months following return to Earth.. We hypothesize that these changes may have resulted from a chronic unilateral rise in optic nerve sheath pressure caused by a microgravity-induced optic nerve sheath compartment syndrome.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70023611','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70023611"><span>An analytical solution for transient flow of Bingham viscoplastic materials in rock fractures</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Amadei, B.; Savage, W.Z.</p> <p>2001-01-01</p> <p>We present below an analytical solution to model the one-dimensional transient flow of a Bingham viscoplastic material in a fracture with parallel walls (smooth or rough) that is subjected to an applied pressure gradient. The solution models the acceleration and the deceleration of the material as the pressure gradient changes with time. Two cases are considered: A pressure gradient applied over a finite time interval and an applied pressure gradient that is constant over time. The solution is expressed in dimensionless form and can therefore be used for a wide range of Bingham viscoplastic materials. The solution is also capable of capturing the transition that takes place in a fracture between viscoplastic flow and rigid plug flow. Also, it shows the development of a rigid central layer in fractures, the extent of which depends on the fluid properties (viscosity and yield stress), the magnitude of the pressure gradient, and the fracture aperture and surface roughness. Finally, it is shown that when a pressure gradient is applied and kept constant, the solution for the fracture flow rate converges over time to a steady-state solution that can be defined as a modified cubic law. In this case, the fracture transmissivity is found to be a non-linear function of the head gradient. This solution provides a tool for a better understanding of the flow of Bingham materials in rock fractures, interfaces, and cracks. ?? 2001 Elsevier Science Ltd. All rights reserved.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/20160011108','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20160011108"><span>Evolution of a Planar Wake in Adverse Pressure Gradient</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Driver, David M.; Mateer, George G.</p> <p>2016-01-01</p> <p>In the interest of improving the predictability of high-lift systems at maximum lift conditions, a series of fundamental experiments were conducted to study the effects of adverse pressure gradient on a wake flow. Mean and fluctuating velocities were measured with a two-component laser-Doppler velocimeter. Data were obtained for several cases of adverse pressure gradient, producing flows ranging from no reversed flow to massively reversed flow. While the turbulent Reynolds stresses increase with increasing size of the reversed flow region, the gradient of Reynolds stress does not. Computations using various turbulence models were unable to reproduce the reversed flow.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19890005997','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19890005997"><span>The influence of free-stream turbulence on turbulent boundary layers with mild adverse pressure gradients</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hoffmann, Jon A.</p> <p>1988-01-01</p> <p>The influence of near isotropic free-stream turbulence on the shape factors and skin friction coefficients of turbulent bounday layers is presented for the cases of zero and mild adverse pressure gradients. With free-stream turbulence, improved fluid mixing occurs in boundary layers with adverse pressure gradients relative to the zero pressure gradient condition, with the same free-stream turbulence intensity and length scale. Stronger boundary layers with lower shape factors occur as a result of a lower ratio of the integral scale of turbulence to the boundary layer thickness, and to vortex stretching of the turbulent eddies in the free stream, both of which act to improve the transmission of momentum from the free stream to the boundary layers.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19890012674','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19890012674"><span>The influence of free-stream turbulence on turbulent boundary layers with mild adverse pressure gradients</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hoffmann, J. A.; Kassir, S. M.; Larwood, S. M.</p> <p>1989-01-01</p> <p>The influence of near isotropic free-stream turbulence on the shape factors and skin friction coefficients of turbulent boundary layers is presented for the cases of zero and mild adverse pressure gradients. With free-stream turbulence, improved fluid mixing occurs in boundary layers with adverse pressure gradients relative to the zero pressure gradient condition, with the same free-stream turbulence intensity and length scale. Stronger boundary layers with lower shape factors occur as a result of a lower ratio of the integral scale of turbulence to the boundary layer thickness, and to vortex stretching of the turbulent eddies in the free-stream, both of which act to improve the transmission of momentum from the free-stream to the boundary layers.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5377364','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5377364"><span>Controlled droplet transport to target on a high adhesion surface with multi-gradients</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Deng, Siyan; Shang, Weifeng; Feng, Shile; Zhu, Shiping; Xing, Yan; Li, Dan; Hou, Yongping; Zheng, Yongmei</p> <p>2017-01-01</p> <p>We introduce multi-gradients including Laplace pressure gradient, wettable gradient and wettable different gradient on a high adhesion surface via special wedge-pattern and improved anodic oxidation method. As a result of the cooperative effect mentioned above, controlled directional motion of a droplet on a high adhesion surface is realized, even when the surface is turned upside down. The droplet motion can be predicted and the movement distances can be controlled by simply adjusting the wedge angle and droplet volume. More interestingly, when Laplace pressure gradient is introduced on a V-shaped wettable gradient surface, two droplets can move toward one another as designed. PMID:28368020</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/12060254','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/12060254"><span>What are the driving forces for water lifting in the xylem conduit?</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Zimmermann, Ulrich; Schneider, Heike; Wegner, Lars H; Wagner, Hans-Jürgen; Szimtenings, Michael; Haase, Axel; Bentrup, Friedrich-Wilhelm</p> <p>2002-03-01</p> <p>After Renner had shown convincingly in 1925 that the transpirational water loss generates tensions larger than 0.1 MPa (i.e. negative pressures) in the xylem of cut leafy twigs the Cohesion Theory proposed by Böhm, Askenasy, Dixon and Joly at the end of the 19th century was immediately accepted by plant physiologists. Introduction of the pressure chamber technique by Scholander et al. in 1965 enforced the general belief that tension is the only driving force for water lifting although substantial criticism regarding the technique and/or the Cohesion Theory was published by several authors. As typical for scientific disciplines, the advent of minimal- and non-invasive techniques in the last decade as well as the development of a new, reliable method for xylem sap sampling have challenged this view. Today, xylem pressure gradients, potentials, ion concentrations and volume flows as well as cell turgor pressure gradients can be monitored online in intact transpiring higher plants, and within a given physiological context by using the pressure probe technique and high-resolution NMR imaging techniques, respectively. Application of the pressure probe technique to transpiring plants has shown that negative absolute pressures (down to - 0.6 MPa) and pressure gradients can exist temporarily in the xylem conduit, but that the magnitude and (occasionally) direction of gradients contrasts frequently the belief that tension is the only driving force. This seems to be particularly the case for plants faced with problems of height, drought, freezing and salinity as well as with cavitation of the tensile water. Reviewing the current data base shows that other forces come into operation when exclusively tension fails to lift water against gravity due to environmental conditions. Possible candidates are longitudinal cellular and xylem osmotic pressure gradients, axial potential gradients in the vessels as well as gel- and gas bubble-supported interfacial gradients. The multiforce theory overcomes the problem of the Cohesion Theory that life on earth depends on water being in a highly metastable state.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3816290','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3816290"><span>Bending-induced electromechanical coupling and large piezoelectric response in a micromachined diaphragm</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Wang, Zhihong; Yao, Yingbang; Wang, Xianbin; Yue, Weisheng; Chen, Longqing; Zhang, Xi Xiang</p> <p>2013-01-01</p> <p>We investigated the dependence of electromechanical coupling and the piezoelectric response of a micromachined Pb(Zr0.52Ti0.48)O3 (PZT) diaphragm on its curvature by observing the impedance spectrum and central deflection responses to a small AC voltage. The curvature of the diaphragm was controlled by applying air pressure to its back. We found that a depolarized flat diaphragm does not initially exhibit electromechanical coupling or the piezoelectric response. However, upon the application of static air pressure to the diaphragm, both electromechanical coupling and the piezoelectric response can be induced in the originally depolarized diaphragm. The piezoelectric response increases as the curvature increases and a giant piezoelectric response can be obtained from a bent diaphragm. The obtained results clearly demonstrate that a high strain gradient in a diaphragm can polarize a PZT film through a flexoelectric effect, and that the induced piezoelectric response of the diaphragm can be controlled by adjusting its curvature. PMID:24185198</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28296135','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28296135"><span>Assessment of trans-aortic pressure gradient using a coronary pressure wire in patients with mechanical aortic and mitral valve prostheses.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kherada, Nisharahmed; Brenes, Juan Carlos; Kini, Annapoorna S; Dangas, George D</p> <p>2017-03-15</p> <p>Accurate evaluation of trans-aortic valvular pressure gradients is challenging in cases where dual mechanical aortic and mitral valve prostheses are present. Non-invasive Doppler echocardiographic imaging has its limitations due to multiple geometric assumptions. Invasive measurement of trans-valvular gradients with cardiac catheterization can provide further information in patients with two mechanical valves, where simultaneous pressure measurements in the left ventricle and ascending aorta must be obtained. Obtaining access to the left ventricle via the mitral valve after a trans-septal puncture is not feasible in the case of a concomitant mechanical mitral valve, whereas left ventricular apical puncture technique is associated with high procedural risks. Retrograde crossing of a bileaflet mechanical aortic prosthesis with standard catheters is associated with the risk of catheter entrapment and acute valvular regurgitation. In these cases, the assessment of trans-valvular gradients using a 0.014˝ diameter coronary pressure wire technique has been described in a few case reports. We present the case of a 76-year-old female with rheumatic valvular heart disease who underwent mechanical aortic and mitral valve replacement in the past. She presented with decompensated heart failure and echocardiographic findings suggestive of elevated pressure gradient across the mechanical aortic valve prosthesis. The use of a high-fidelity 0.014˝ diameter coronary pressure guidewire resulted in the detection of a normal trans-valvular pressure gradient across the mechanical aortic valve. This avoided a high-risk third redo valve surgery in our patient. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3913518','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3913518"><span>Experimental Study on the Flow Regimes and Pressure Gradients of Air-Oil-Water Three-Phase Flow in Horizontal Pipes</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Al-Hadhrami, Luai M.; Shaahid, S. M.; Tunde, Lukman O.; Al-Sarkhi, A.</p> <p>2014-01-01</p> <p>An experimental investigation has been carried out to study the flow regimes and pressure gradients of air-oil-water three-phase flows in 2.25 ID horizontal pipe at different flow conditions. The effects of water cuts, liquid and gas velocities on flow patterns and pressure gradients have been studied. The experiments have been conducted at 20°C using low viscosity Safrasol D80 oil, tap water and air. Superficial water and oil velocities were varied from 0.3 m/s to 3 m/s and air velocity varied from 0.29 m/s to 52.5 m/s to cover wide range of flow patterns. The experiments were performed for 10% to 90% water cuts. The flow patterns were observed and recorded using high speed video camera while the pressure drops were measured using pressure transducers and U-tube manometers. The flow patterns show strong dependence on water fraction, gas velocities, and liquid velocities. The observed flow patterns are stratified (smooth and wavy), elongated bubble, slug, dispersed bubble, and annular flow patterns. The pressure gradients have been found to increase with the increase in gas flow rates. Also, for a given superficial gas velocity, the pressure gradients increased with the increase in the superficial liquid velocity. The pressure gradient first increases and then decreases with increasing water cut. In general, phase inversion was observed with increase in the water cut. The experimental results have been compared with the existing unified Model and a good agreement has been noticed. PMID:24523645</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24523645','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24523645"><span>Experimental study on the flow regimes and pressure gradients of air-oil-water three-phase flow in horizontal pipes.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Al-Hadhrami, Luai M; Shaahid, S M; Tunde, Lukman O; Al-Sarkhi, A</p> <p>2014-01-01</p> <p>An experimental investigation has been carried out to study the flow regimes and pressure gradients of air-oil-water three-phase flows in 2.25 ID horizontal pipe at different flow conditions. The effects of water cuts, liquid and gas velocities on flow patterns and pressure gradients have been studied. The experiments have been conducted at 20 °C using low viscosity Safrasol D80 oil, tap water and air. Superficial water and oil velocities were varied from 0.3 m/s to 3 m/s and air velocity varied from 0.29 m/s to 52.5 m/s to cover wide range of flow patterns. The experiments were performed for 10% to 90% water cuts. The flow patterns were observed and recorded using high speed video camera while the pressure drops were measured using pressure transducers and U-tube manometers. The flow patterns show strong dependence on water fraction, gas velocities, and liquid velocities. The observed flow patterns are stratified (smooth and wavy), elongated bubble, slug, dispersed bubble, and annular flow patterns. The pressure gradients have been found to increase with the increase in gas flow rates. Also, for a given superficial gas velocity, the pressure gradients increased with the increase in the superficial liquid velocity. The pressure gradient first increases and then decreases with increasing water cut. In general, phase inversion was observed with increase in the water cut. The experimental results have been compared with the existing unified Model and a good agreement has been noticed.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19980227788','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19980227788"><span>Boundary-Layer Transition on a Group of Blunt Nose Shapes at a Mach Number of 2.20</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Jackson, Mary W.; Czarnecki, K. R.</p> <p>1961-01-01</p> <p>An investigation has been made to study boundary-layer transition on six axisymmetrical blunt bodies of revolution. Model shapes were selected with respect to the degree of favorable pressure gradient over the model surface. Tests were conducted at a Mach number of 2.20 and over a range of free-stream Reynolds number per foot of about 1.4 x 10(exp 6) to 6.5 x 10(exp 6). The tests were made at an angle of attack of 0 deg. with zero heat transfer. For the hemisphere, the flow remained essentially laminar over the model surface length for the entire pressure range of the tests. For a strong favorable pressure gradient followed by any weak favorable, neutral, or adverse gradient, the tendency was for transition to occur at or immediately behind the shoulder. A single strip of three-dimensional roughness in the region of strong favorable pressure gradient did not fix transition on the models at the roughness location except at the maximum test pressures, whereas a second roughness strip added in a region of neutral or adverse pressure gradient did fix transition. Experimental pressure coefficients agreed closely with modified Newtonian theory except in the shoulder region.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19940028441','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19940028441"><span>Modification of the MML turbulence model for adverse pressure gradient flows. M.S. Thesis - Akron Univ., 1993</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Conley, Julianne M.</p> <p>1994-01-01</p> <p>Computational fluid dynamics is being used increasingly to predict flows for aerospace propulsion applications, yet there is still a need for an easy to use, computationally inexpensive turbulence model capable of accurately predicting a wide range of turbulent flows. The Baldwin-Lomax model is the most widely used algebraic model, even though it has known difficulties calculating flows with strong adverse pressure gradients and large regions of separation. The modified mixing length model (MML) was developed specifically to handle the separation which occurs on airfoils and has given significantly better results than the Baldwin-Lomax model. The success of these calculations warrants further evaluation and development of MML. The objective of this work was to evaluate the performance of MML for zero and adverse pressure gradient flows, and modify it as needed. The Proteus Navier-Stokes code was used for this study and all results were compared with experimental data and with calculations made using the Baldwin-Lomax algebraic model, which is currently available in Proteus. The MML model was first evaluated for zero pressure gradient flow over a flat plate, then modified to produce the proper boundary layer growth. Additional modifications, based on experimental data for three adverse pressure gradient flows, were also implemented. The adapted model, called MMLPG (modified mixing length model for pressure gradient flows), was then evaluated for a typical propulsion flow problem, flow through a transonic diffuser. Three cases were examined: flow with no shock, a weak shock and a strong shock. The results of these calculations indicate that the objectives of this study have been met. Overall, MMLPG is capable of accurately predicting the adverse pressure gradient flows examined in this study, giving generally better agreement with experimental data than the Baldwin-Lomax model.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19850024019','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19850024019"><span>A comparison of experimental and theoretical results for rotordynamic coefficients of four annular gas seals</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Childs, D. W.; Nelson, C. C.; Elrod, D.; Nicks, C.</p> <p>1985-01-01</p> <p>The test facility and initial test program developed to experimentally measure the fluid forces induced by annular gas seals is described. A comparison of theoretically predicted and experimentally obtained data for smooth and honeycomb seals is provided. And a comparison of experimental data from the tests of three smooth-rotor/smooth-stator seals is provided. The leakage of the working fluid through the seal, the pressure gradient along the seal length, entrance pressure-loss data, and rotordynamic coefficients provide a basis for comparison. A short discussion on seal theory is included, and various rotordynamic coefficient identification schemes are described.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19750006501','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19750006501"><span>A model for jet-noise analysis using pressure-gradient correlations on an imaginary cone</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Norum, T. D.</p> <p>1974-01-01</p> <p>The technique for determining the near and far acoustic field of a jet through measurements of pressure-gradient correlations on an imaginary conical surface surrounding the jet is discussed. The necessary analytical developments are presented, and their feasibility is checked by using a point source as the sound generator. The distribution of the apparent sources on the cone, equivalent to the point source, is determined in terms of the pressure-gradient correlations.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/20030062088','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20030062088"><span>Transient Growth Theory Prediction of Optimal Placing of Passive and Active Flow Control Devices for Separation Delay in LPT Airfoils</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Tumin, Anatoli; Ashpis, David E.</p> <p>2003-01-01</p> <p>An analysis of the non-modal growth of perturbations in a boundary layer in the presence of a streamwise pressure gradient is presented. The analysis is based on PSE equations for an incompressible fluid. Examples with Falkner-Skan profiles indicate that a favorable pressure gradient decreases the non-modal growth while an unfavorable pressure gradient leads to an increase of the amplification. It is suggested that the transient growth mechanism be utilized to choose optimal parameters of tripping elements on a low-pressure turbine (LPT) airfoil. As an example, a boundary layer flow with a streamwise pressure gradient corresponding to the pressure distribution over a LPT airfoil is considered. It is shown that there is an optimal spacing of the tripping elements and that the transient growth effect depends on the starting point. At very low Reynolds numbers, there is a possibility to enhance the transient energy growth by means of wall cooling.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA433237','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA433237"><span>Stress Fracture Etiology as Dependent on Mechanically Induced Fluid Flow</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.dtic.mil/">DTIC Science & Technology</a></p> <p></p> <p>2004-08-01</p> <p>polymethylmethacry- 1994: Weinbaum et al., 1994: Hillsley and Frangos , late. Two Steinmann pins, 4nmn in diameter and 92 mm 1994: Frangos et al., 1996...fluorescent labeling analyses, in which new bone ( Frangos et al., 1996, Rubin et al., 1997, Jacobs et al., formation and intracortical remodeling were...components, i.e., been supported by mounting in vitro experimental work pressure gradients, a close source driving fluid velocity ( Frangos et al</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li class="active"><span>8</span></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_8 --> <div id="page_9" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li class="active"><span>9</span></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="161"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2265277','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2265277"><span>Translocation pathways for inhaled asbestos fibers</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Miserocchi, G; Sancini, G; Mantegazza, F; Chiappino, Gerolamo</p> <p>2008-01-01</p> <p>We discuss the translocation of inhaled asbestos fibers based on pulmonary and pleuro-pulmonary interstitial fluid dynamics. Fibers can pass the alveolar barrier and reach the lung interstitium via the paracellular route down a mass water flow due to combined osmotic (active Na+ absorption) and hydraulic (interstitial pressure is subatmospheric) pressure gradient. Fibers can be dragged from the lung interstitium by pulmonary lymph flow (primary translocation) wherefrom they can reach the blood stream and subsequently distribute to the whole body (secondary translocation). Primary translocation across the visceral pleura and towards pulmonary capillaries may also occur if the asbestos-induced lung inflammation increases pulmonary interstitial pressure so as to reverse the trans-mesothelial and trans-endothelial pressure gradients. Secondary translocation to the pleural space may occur via the physiological route of pleural fluid formation across the parietal pleura; fibers accumulation in parietal pleura stomata (black spots) reflects the role of parietal lymphatics in draining pleural fluid. Asbestos fibers are found in all organs of subjects either occupationally exposed or not exposed to asbestos. Fibers concentration correlates with specific conditions of interstitial fluid dynamics, in line with the notion that in all organs microvascular filtration occurs from capillaries to the extravascular spaces. Concentration is high in the kidney (reflecting high perfusion pressure and flow) and in the liver (reflecting high microvascular permeability) while it is relatively low in the brain (due to low permeability of blood-brain barrier). Ultrafine fibers (length < 5 μm, diameter < 0.25 μm) can travel larger distances due to low steric hindrance (in mesothelioma about 90% of fibers are ultrafine). Fibers translocation is a slow process developing over decades of life: it is aided by high biopersistence, by inflammation-induced increase in permeability, by low steric hindrance and by fibers motion pattern at low Reynolds numbers; it is hindered by fibrosis that increases interstitial flow resistances. PMID:18218073</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19880033523&hterms=Hydrostatic+pressure&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DHydrostatic%2Bpressure','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19880033523&hterms=Hydrostatic+pressure&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DHydrostatic%2Bpressure"><span>Accurate pressure gradient calculations in hydrostatic atmospheric models</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Carroll, John J.; Mendez-Nunez, Luis R.; Tanrikulu, Saffet</p> <p>1987-01-01</p> <p>A method for the accurate calculation of the horizontal pressure gradient acceleration in hydrostatic atmospheric models is presented which is especially useful in situations where the isothermal surfaces are not parallel to the vertical coordinate surfaces. The present method is shown to be exact if the potential temperature lapse rate is constant between the vertical pressure integration limits. The technique is applied to both the integration of the hydrostatic equation and the computation of the slope correction term in the horizontal pressure gradient. A fixed vertical grid and a dynamic grid defined by the significant levels in the vertical temperature distribution are employed.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018JPCM...30t5002L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018JPCM...30t5002L"><span>Pressure gradients fail to predict diffusio-osmosis</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Liu, Yawei; Ganti, Raman; Frenkel, Daan</p> <p>2018-05-01</p> <p>We present numerical simulations of diffusio-osmotic flow, i.e. the fluid flow generated by a concentration gradient along a solid-fluid interface. In our study, we compare a number of distinct approaches that have been proposed for computing such flows and compare them with a reference calculation based on direct, non-equilibrium molecular dynamics simulations. As alternatives, we consider schemes that compute diffusio-osmotic flow from the gradient of the chemical potentials of the constituent species and from the gradient of the component of the pressure tensor parallel to the interface. We find that the approach based on treating chemical potential gradients as external forces acting on various species agrees with the direct simulations, thereby supporting the approach of Marbach et al (2017 J. Chem. Phys. 146 194701). In contrast, an approach based on computing the gradients of the microscopic pressure tensor does not reproduce the direct non-equilibrium results.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2001PhDT........46O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2001PhDT........46O"><span>Navier-Stokes solutions of unsteady separation induced by a vortex: Comparison with theory and influence of a moving wall</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Obabko, Aleksandr Vladimirovich</p> <p></p> <p>Numerical solutions of the unsteady Navier-Stokes equations are considered for the flow induced by a thick-core vortex convecting along an infinite surface in a two-dimensional incompressible flow. The formulation is considered as a model problem of the dynamic-stall vortex and is relevant to other unsteady separation phenomena including vorticity ejections in juncture flows and the vorticity production mechanism in turbulent boundary-layers. Induced by an adverse streamwise pressure gradient due to the presence of the vortex above the wall, a primary recirculation region forms and evolves toward a singular solution of the unsteady non-interacting boundary-layer equations. The resulting eruptive spike provokes a small-scale viscous-inviscid interaction in the high-Reynolds-number regime. In the moderate-Reynolds-numbers regime, the growing recirculation region initiates a large-scale interaction in the form of local changes in the streamwise pressure gradient accelerating the spike formation and resulting small-scale interaction through development of a region of streamwise compression. It also was found to induce regions of streamwise expansion and "child" recirculation regions that contribute to ejections of near-wall vorticity and splitting of the "parent" region into multiple co-rotating eddies. These eddies later merge into a single amalgamated eddy that is observed to pair with the detaching vortex similar to the low-Reynolds-number regime where the large-scale interaction occurs, but there is no spike or subsequent small-scale interaction. It is also found that increasing the wall speed or vortex convection velocity toward a critical value results in solutions that are indicative of flows at lower Reynolds numbers eventually leading to suppression of unsteady separation and vortex detachment processes.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018PhPl...25d2115C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018PhPl...25d2115C"><span>On the role and value of β in incompressible MHD simulations</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chahine, Robert; Bos, Wouter J. T.</p> <p>2018-04-01</p> <p>The parameter β, defined as the ratio of the pressure to the square of the magnetic field, is widely used to characterize astrophysical and fusion plasmas. However, in the dynamics of a plasma flow, it is the pressure gradient which is important rather than the value of the pressure itself. It is shown that if one is interested in the influence of the pressure gradient on the dynamics of a plasma, it is not the quantity β which should be considered, but a similar quantity depending on the pressure gradient. The scaling of this newly defined quantity is investigated using incompressible magnetohydrodynamic simulations in a periodic cylinder in the Reversed Field Pinch flow regime.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27689385','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27689385"><span>High-Efficiency Fog Collector: Water Unidirectional Transport on Heterogeneous Rough Conical Wires.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Xu, Ting; Lin, Yucai; Zhang, Miaoxin; Shi, Weiwei; Zheng, Yongmei</p> <p>2016-12-27</p> <p>An artificial periodic roughness-gradient conical copper wire (PCCW) can be fabricated by inspiration from cactus spines and wet spider silks. PCCW can harvest fog on periodic points of the conical surface from air and transports the drops for a long distance without external force, which is attributed to dynamic as-released energy generated from drop deformation in drop coalescence, in addition to both gradients of geometric curve (inducing Laplace pressure) and periodic roughness (inducing surface energy difference). It is found that the ability of fog collection can be related to various tilt-angle wires, thus a fog collector with an array system of PCCWs is further designed to achieve a continuous process of efficient water collection. As a result, the effect of water collection on PCCWs is better than previous results. These findings are significant to develop and design materials with water collection and water transport for promising application in fogwater systems to ease the water crisis.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016Icar..270...67T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016Icar..270...67T"><span>Sun-stirred Kraken Mare: Circulation in Titan's seas induced by solar heating and methane precipitation</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tokano, Tetsuya; Lorenz, Ralph D.</p> <p>2016-05-01</p> <p>Density-driven circulation in Titan's seas forced by solar heating and methane evaporation/precipitation is simulated by an ocean circulation model. If the sea is transparent to sunlight, solar heating can induce anti-clockwise gyres near the sea surface and clockwise gyres near the sea bottom. The gyres are in geostrophic balance between the radially symmetric pressure gradient force and Coriolis force. If instead the sea is turbid and most sunlight is absorbed near the sea surface, the sea gets stratified in warm seasons and the circulation remains weak. Precipitation causes compositional stratification of the sea to an extent that the sea surface temperature can be lower than the sea interior temperature without causing a convective overturning. Non-uniform precipitation can also generate a latitudinal gradient in the methane mole fraction and density, which drives a meridional overturning with equatorward currents near the sea surface and poleward currents near the sea bottom. However, gyres are more ubiquitous than meridional overturning.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018PhRvF...3c4606V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018PhRvF...3c4606V"><span>Determination of wall shear stress from mean velocity and Reynolds shear stress profiles</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Volino, Ralph J.; Schultz, Michael P.</p> <p>2018-03-01</p> <p>An analytical method is presented for determining the Reynolds shear stress profile in steady, two-dimensional wall-bounded flows using the mean streamwise velocity. The method is then utilized with experimental data to determine the local wall shear stress. The procedure is applicable to flows on smooth and rough surfaces with arbitrary pressure gradients. It is based on the streamwise component of the boundary layer momentum equation, which is transformed into inner coordinates. The method requires velocity profiles from at least two streamwise locations, but the formulation of the momentum equation reduces the dependence on streamwise gradients. The method is verified through application to laminar flow solutions and turbulent DNS results from both zero and nonzero pressure gradient boundary layers. With strong favorable pressure gradients, the method is shown to be accurate for finding the wall shear stress in cases where the Clauser fit technique loses accuracy. The method is then applied to experimental data from the literature from zero pressure gradient studies on smooth and rough walls, and favorable and adverse pressure gradient cases on smooth walls. Data from very near the wall are not required for determination of the wall shear stress. Wall friction velocities obtained using the present method agree with those determined in the original studies, typically to within 2%.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/biblio/21088258-remodelling-superior-caval-vein-after-angioplasty-infant-superior-caval-vein-syndrome','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/21088258-remodelling-superior-caval-vein-after-angioplasty-infant-superior-caval-vein-syndrome"><span>Remodelling of the Superior Caval Vein After Angioplasty in an Infant with Superior Caval Vein Syndrome</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Mert, Murat; Saltik, Levent; Gunay, Ilhan</p> <p>2004-08-15</p> <p>An 8-month old girl was presented with superior caval vein syndrome early after cardiac surgery. Angiography showed severe stenosis of the superior caval vein with 50 mmHg pressure gradient. Following balloon angioplasty, the pressure gradient was reduced to 7 mmHg with some residual stenosis of the superior caval vein. When the patient was reevaluated 5 months after the procedure, angiography revealed a normal diameter of the superior caval vein without a pressure gradient.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19890046357&hterms=1087&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3D%2526%25231087','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19890046357&hterms=1087&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3D%2526%25231087"><span>Acoustic waves in gases with strong pressure gradients</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Zorumski, William E.</p> <p>1989-01-01</p> <p>The effect of strong pressure gradients on the acoustic modes (standing waves) of a rectangular cavity is investigated analytically. When the cavity response is represented by a sum of modes, each mode is found to have two resonant frequencies. The lower frequency is near the Viaesaela-Brundt frequency, which characterizes the buoyant effect, and the higher frequency is above the ordinary acoustic resonance frequency. This finding shows that the propagation velocity of the acoustic waves is increased due to the pressure gradient effect.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/19507386','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/19507386"><span>Pulmonary hypertension in dogs with mitral regurgitation attributable to myxomatous valve disease.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Chiavegato, David; Borgarelli, Michele; D'Agnolo, Gino; Santilli, Roberto A</p> <p>2009-01-01</p> <p>Pulmonary hypertension has been associated with mitral insufficiency caused by chronic degenerative valve disease in dogs. Our aim was to search for associations between left atrial to aortic root ratio, end-systolic and end-diastolic volume indices, and changes in the right ventricular to right atrial pressure gradient as estimated by the peak velocity of tricuspid regurgitation in dogs with chronic degenerative valve disease and different classes of heart failure. Dogs, for which follow-up was available were evaluated for changes in the right ventricular to right atrial systolic pressure gradient over time. Three hundred and forty-four dogs were studied; 51 in the International Small Animal Cardiac Health Council class la, 75 in class 1b, 113 in class 2, 97 in class 3a, and 8 in class 3b. The mean values for right ventricular to right atrial systolic pressure gradient, end-systolic volume index, end-diastolic volume index, and left atrial to aortic ratio were 49.2 +/- 17.1 mmHg, 149.12 +/- 60.8 and 37.7 +/- 21.6 ml/m2, and 1.9 +/- 0.5, respectively. A weak positive correlation was found between the right ventricular to right atrial systolic pressure gradient and the left atrial to aorta ratio (r = 0.242, P < 0.0001), end-diastolic volume index (r = 0.242, P < 0.0001), and end-systolic volume index (r = 0.129, P < 0.001). Follow up was available for 49 dogs. Of these, 18 had an increased, 12 a decreased, and 19 a stable right ventricular to right atrial systolic pressure gradient despite therapy. The equivalence point between the sensitivity and specificity curves of about 80% in the coincident point corresponded to a right ventricular to right atrial systolic pressure gradient of 48 mmHg. Our results suggest an association between the progressive nature of chronic degenerative mitral valve disease and pulmonary hypertension. It is of clinical interest that, with a right ventricular to right atrial systolic pressure gradient pressure gradient at or above 48 mmHg, pulmonary hypertension does not appear to improve despite therapy targeted at lowering the left atrial load.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28797477','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28797477"><span>Effects of oxygen on responses to heating in two lizard species sampled along an elevational gradient.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>DuBois, P Mason; Shea, Tanner K; Claunch, Natalie M; Taylor, Emily N</p> <p>2017-08-01</p> <p>Thermal tolerance is an important variable in predictive models about the effects of global climate change on species distributions, yet the physiological mechanisms responsible for reduced performance at high temperatures in air-breathing vertebrates are not clear. We conducted an experiment to examine how oxygen affects three variables exhibited by ectotherms as they heat-gaping threshold, panting threshold, and loss of righting response (the latter indicating the critical thermal maximum)-in two lizard species along an elevational (and therefore environmental oxygen partial pressure) gradient. Oxygen partial pressure did not impact these variables in either species. We also exposed lizards at each elevation to severely hypoxic gas to evaluate their responses to hypoxia. Severely low oxygen partial pressure treatments significantly reduced the gaping threshold, panting threshold, and critical thermal maximum. Further, under these extreme hypoxic conditions, these variables were strongly and positively related to partial pressure of oxygen. In an elevation where both species overlapped, the thermal tolerance of the high elevation species was less affected by hypoxia than that of the low elevation species, suggesting the high elevation species may be adapted to lower oxygen partial pressures. In the high elevation species, female lizards had higher thermal tolerance than males. Our data suggest that oxygen impacts the thermal tolerance of lizards, but only under severely hypoxic conditions, possibly as a result of hypoxia-induced anapyrexia. Copyright © 2017. Published by Elsevier Ltd.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017APS..DFDQ21005P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017APS..DFDQ21005P"><span>Confinement effects in premelting dynamics</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pramanik, Satyajit; Wettlaufer, John</p> <p>2017-11-01</p> <p>We examine the effects of confinement on the dynamics of premelted films driven by thermomolecular pressure gradients. Our approach is to modify a well-studied setting in which the thermomolecular pressure gradient is driven by a temperature gradient parallel to an interfacially premelted elastic wall. The modification treats the increase in viscosity associated with the thinning of films studied in a wide variety of materials using a power law and we examine the consequent evolution of the elastic wall. We treat (i) a range of interactions that are known to underlie interfacial premelting and (ii) a constant temperature gradient wherein the thermomolecular pressure gradient is a constant. The difference between the cases with and without the proximity effect arises in the volume flux of premelted liquid. The proximity effect increases the viscosity as the film thickness decreases thereby requiring the thermomolecular pressure driven flux to be accommodated at larger temperatures where the premelted film thickness is the largest. Implications for experiment and observations of frost heave are discussed.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PhRvE..96e2801P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PhRvE..96e2801P"><span>Confinement effects in premelting dynamics</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pramanik, Satyajit; Wettlaufer, John S.</p> <p>2017-11-01</p> <p>We examine the effects of confinement on the dynamics of premelted films driven by thermomolecular pressure gradients. Our approach is to modify a well-studied setting in which the thermomolecular pressure gradient is driven by a temperature gradient parallel to an interfacially premelted elastic wall. The modification treats the increase in viscosity associated with the thinning of films, studied in a wide variety of materials, using a power law and we examine the consequent evolution of the confining elastic wall. We treat (1) a range of interactions that are known to underlie interfacial premelting and (2) a constant temperature gradient wherein the thermomolecular pressure gradient is a constant. The difference between the cases with and without the proximity effect arises in the volume flux of premelted liquid. The proximity effect increases the viscosity as the film thickness decreases thereby requiring the thermomolecular pressure driven flux to be accommodated at higher temperatures where the premelted film thickness is the largest. Implications for experiment and observations of frost heave are discussed.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19720029443&hterms=Parkin&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DParkin','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19720029443&hterms=Parkin&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DParkin"><span>Induced and permanent magnetism on the moon - Structural and evolutionary implications.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sonett, C. P.; Dyal, P.; Colburn, D. S.; Mihalov, J. D.; Parkin, C. W.; Smith, B. F.; Schubert, G.; Schwartz, K.</p> <p>1971-01-01</p> <p>It is shown that the moon possesses an extraordinary response to induction from the solar wind due to a combination of a high interior electrical conductivity together with a relatively resistive crustal layer into which the solar wind dynamic pressure forces back the induced field. The dark side response, devoid of solar wind pressure, is approximately that expected for the vacuum case. These data permit an assessment of the interior conductivity and an estimate of the thermal gradient in the crustal region. The discovery of a large permanent magnetic field at the Apollo 12 site corresponds approximately to the paleomagnetic residues discovered in both Apollo 11 and 12 rock samples. The implications regarding an early lunar magnetic field are discussed and it is shown that among the various conjectures regarding the early field the most prominent are either an interior dynamo or an early approach to the earth though no extant model is free of difficulties.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70025108','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70025108"><span>Subsurface fluid pressures from drill-stem tests, Uinta Basin, Utah</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Nelson, P.H.</p> <p>2002-01-01</p> <p>High fluid pressures are known to be associated with oil and gas fields in the Uinta Basin, Utah. Shut-in pressure measurements from drill-stem tests show how pressure varies with depth and by area within the basin. The data base used in this report incorporates over 2,000 pressure measurements from drill-stem tests in wells completed prior to 1985. However, the number of useful pressure measurements is considerably less, because many drill-stem tests fail to stabilize at the actual formation pressure if the permeability is low. By extracting the maximum pressure measurements recorded in a collection of wells within an area, the trend of formation pressure within that area can be approximated. Areal compilations of pressures from drill-stem tests show that overpressured rock formations occur throughout much of the northern and eastern areas of the Uinta Basin. In particular, significant overpressuring (0.5 < pressure gradient < 0.8 psi/ft) is found throughout much of the Altamont-Bluebell field at depths ranging from 10,000 to 13,000 ft, equivalent to 5,000 to 8,000 ft below sea level. Limited data indicate that the pressure gradient declines at depths greater than 13,000 ft. An underpressured zone appears to exist in the Altamont-Bluebell field at depths shallower than 5,000 ft. Throughout the eastern Uinta Basin, moderately overpressured zones (0.46 < pressure gradient < 0.5 psi/ft) are common, with local evidence of significantly overpressured zones, but pressure gradients greater than 0.6 psi/ft are rare.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24861781','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24861781"><span>Constant pressure mode extended simple gradient liquid chromatography system for micro and nanocolumns.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Šesták, Jozef; Kahle, Vladislav</p> <p>2014-07-11</p> <p>Performing gradient liquid chromatography at constant pressure instead of constant flow rate has serious potential for shortening the analysis time and increasing the productivity of HPLC instruments that use gradient methods. However, in the constant pressure mode the decreasing column permeability during a long period of time negatively affects the repeatability of retention time. Thus a volume-based approach, in which the detector signal is plotted as a function of retention volume, must be taken into consideration. Traditional HPLC equipment, however, requires quite complex hardware and software modifications in order to work at constant pressure and in the volume-based mode. In this short communication, a low cost and easily feasible pressure-controlled extension of the previously described simple gradient liquid chromatography platform is proposed. A test mixture of four nitro esters was separated by 10-60% (v/v) acetone/water gradient and a high repeatability of retention volumes at 20MPa (RSD less than 0.45%) was realized. Separations were also performed at different values of pressure (20, 25, and 31MPa), and only small variations of the retention volumes (up to 0.8%) were observed. In this particular case, the gain in the analysis speed of 7% compared to the constant flow mode was realized at a constant pressure. Copyright © 2014 Elsevier B.V. All rights reserved.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24370000','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24370000"><span>Very high pressure liquid chromatography using core-shell particles: quantitative analysis of fast gradient separations without post-run times.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Stankovich, Joseph J; Gritti, Fabrice; Stevenson, Paul G; Beaver, Lois A; Guiochon, Georges</p> <p>2014-01-17</p> <p>Five methods for controlling the mobile phase flow rate for gradient elution analyses using very high pressure liquid chromatography (VHPLC) were tested to determine thermal stability of the column during rapid gradient separations. To obtain rapid separations, instruments are operated at high flow rates and high inlet pressure leading to uneven thermal effects across columns and additional time needed to restore thermal equilibrium between successive analyses. The purpose of this study is to investigate means to minimize thermal instability and obtain reliable results by measuring the reproducibility of the results of six replicate gradient separations of a nine component RPLC standard mixture under various experimental conditions with no post-run times. Gradient separations under different conditions were performed: constant flow rates, two sets of constant pressure operation, programmed flow constant pressure operation, and conditions which theoretically should yield a constant net heat loss at the column's wall. The results show that using constant flow rates, programmed flow constant pressures, and constant heat loss at the column's wall all provide reproducible separations. However, performing separations using a high constant pressure with programmed flow reduces the analysis time by 16% compared to constant flow rate methods. For the constant flow rate, programmed flow constant pressure, and constant wall heat experiments no equilibration time (post-run time) was required to obtain highly reproducible data. Copyright © 2013 Elsevier B.V. All rights reserved.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27463696','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27463696"><span>On Localized Vapor Pressure Gradients Governing Condensation and Frost Phenomena.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Nath, Saurabh; Boreyko, Jonathan B</p> <p>2016-08-23</p> <p>Interdroplet vapor pressure gradients are the driving mechanism for several phase-change phenomena such as condensation dry zones, interdroplet ice bridging, dry zones around ice, and frost halos. Despite the fundamental nature of the underlying pressure gradients, the majority of studies on these emerging phenomena have been primarily empirical. Using classical nucleation theory and Becker-Döring embryo formation kinetics, here we calculate the pressure field for all possible modes of condensation and desublimation in order to gain fundamental insight into how pressure gradients govern the behavior of dry zones, condensation frosting, and frost halos. Our findings reveal that in a variety of phase-change systems the thermodynamically favorable mode of nucleation can switch between condensation and desublimation depending upon the temperature and wettability of the surface. The calculated pressure field is used to model the length of a dry zone around liquid or ice droplets over a broad parameter space. The long-standing question of whether the vapor pressure at the interface of growing frost is saturated or supersaturated is resolved by considering the kinetics of interdroplet ice bridging. Finally, on the basis of theoretical calculations, we propose that there exists a new mode of frost halo that is yet to be experimentally observed; a bimodal phase map is developed, demonstrating its dependence on the temperature and wettability of the underlying substrate. We hope that the model and predictions contained herein will assist future efforts to exploit localized vapor pressure gradients for the design of spatially controlled or antifrosting phase-change systems.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015APS..DFDL22008C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015APS..DFDL22008C"><span>Assessment of fluctuating pressure gradient using acceleration spectra in near wall flows</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cadel, Daniel; Lowe, K. Todd</p> <p>2015-11-01</p> <p>Separation of contributions to the fluctuating acceleration from pressure gradient fluctuations and viscous shear fluctuations in the frequency domain is examined in a turbulent boundary layer. Past work leveraging turbulent accelerations for pressure gradient measurements has neglected the viscous shear term from the momentum equation--an invalid assumption in the case of near wall flows. The present study seeks to account for the influence of the viscous shear term and spectrally reject its contribution, which is thought to be concentrated at higher frequencies. Spectra of velocity and acceleration fluctuations in a flat plate, zero pressure gradient turbulent boundary layer at a momentum thickness Reynolds number of 7500 are measured using a spatially resolving three-component laser Doppler velocimeter. This canonical case data is applied for validation of the spectral approach for future application in more complex aerodynamic flows.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li class="active"><span>9</span></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_9 --> <div id="page_10" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li class="active"><span>10</span></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="181"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25068642','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25068642"><span>Computational analysis of microbubble flows in bifurcating airways: role of gravity, inertia, and surface tension.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Chen, Xiaodong; Zielinski, Rachel; Ghadiali, Samir N</p> <p>2014-10-01</p> <p>Although mechanical ventilation is a life-saving therapy for patients with severe lung disorders, the microbubble flows generated during ventilation generate hydrodynamic stresses, including pressure and shear stress gradients, which damage the pulmonary epithelium. In this study, we used computational fluid dynamics to investigate how gravity, inertia, and surface tension influence both microbubble flow patterns in bifurcating airways and the magnitude/distribution of hydrodynamic stresses on the airway wall. Direct interface tracking and finite element techniques were used to simulate bubble propagation in a two-dimensional (2D) liquid-filled bifurcating airway. Computational solutions of the full incompressible Navier-Stokes equation were used to investigate how inertia, gravity, and surface tension forces as characterized by the Reynolds (Re), Bond (Bo), and Capillary (Ca) numbers influence pressure and shear stress gradients at the airway wall. Gravity had a significant impact on flow patterns and hydrodynamic stress magnitudes where Bo > 1 led to dramatic changes in bubble shape and increased pressure and shear stress gradients in the upper daughter airway. Interestingly, increased pressure gradients near the bifurcation point (i.e., carina) were only elevated during asymmetric bubble splitting. Although changes in pressure gradient magnitudes were generally more sensitive to Ca, under large Re conditions, both Re and Ca significantly altered the pressure gradient magnitude. We conclude that inertia, gravity, and surface tension can all have a significant impact on microbubble flow patterns and hydrodynamic stresses in bifurcating airways.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19800024910','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19800024910"><span>Plenum response to simulated disturbances of the model and fan inlet guide vanes in a transonic tunnel</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Gloss, B. B.</p> <p>1980-01-01</p> <p>In order to aid in the design of the National Transonic Facility (NTF) control system, test section/plenum response studies were carried out in a 0.186 scale model of the NTF high speed duct. Two types of disturbances, those induced by the model and those induced by the compressor inlet guide vanes were simulated. Some observations with regard to the test section/plenum response tests are summarized as follows. A resonance frequency for the test section/plenum area of the tunnel of approximately 50 Hz was observed for Mach numbers from 0.40 to 0.90. However, since the plenum is 3.1 times (based on volume) too large for the scaled size of the test section, care must be taken in extrapolating these data to NTF conditions. The plenum pressure data indicate the existence of pressure gradients in the plenum. The test results indicate that the difference between test section static pressure and plenum pressure is dependent on test section flow conditions. Plenum response to inlet guide vane type disturbances appears to be slower than plenum response to test section disturbances.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/1724535','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/1724535"><span>Effects of nitroglycerin and nitroprusside on vascular capacitance of anesthetized ganglion-blocked dogs.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ogilvie, R I; Zborowska-Sluis, D</p> <p>1991-10-01</p> <p>To determine whether changes in vascular capacitance induced by nitroglycerin (NTG) and nitroprusside were due to changes in compliance or unstressed vascular volume, doses producing similar reductions in arterial pressure (Psa) were studied on separate days in six dogs anesthetized and ventilated with pentobarbital after splenectomy during ganglion blockade with hexamethonium. Mean circulatory filling pressure (Pmcf) was determined during transient circulatory arrest induced by acetylcholine at baseline blood volumes and after increases of 5 and 10 ml/kg. Central blood volumes (CBVs, pulmonary artery to aortic root) were determined from transit times, and separately measured cardiac output (CO) was estimated by thermodilution (right atrium to pulmonary artery). NTG and nitroprusside produced similar reductions in Psa and Pmcf without significantly altering right atrial pressure (Pra), pressure gradient for venous return, or CO. Total vascular compliance was not altered, but total vascular capacitance was increased on an average of 4.0 +/- 1.4 ml/kg after NTG and 3.0 +/- 1.3 ml/kg after nitroprusside by increases in unstressed volume. Both drugs caused a variable reduction in CBV, averaging 2 ml/kg. Thus, both drugs produced a large increase in peripheral venous capacitance by increasing unstressed vascular volume without altering total vascular compliance.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/20170004932','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20170004932"><span>Axial Flow Conditioning Device for Mitigating Instabilities</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Ahuja, Vineet (Inventor); Birkbeck, Roger M. (Inventor); Hosangadi, Ashvin (Inventor)</p> <p>2017-01-01</p> <p>A flow conditioning device for incrementally stepping down pressure within a piping system is presented. The invention includes an outer annular housing, a center element, and at least one intermediate annular element. The outer annular housing includes an inlet end attachable to an inlet pipe and an outlet end attachable to an outlet pipe. The outer annular housing and the intermediate annular element(s) are concentrically disposed about the center element. The intermediate annular element(s) separates an axial flow within the outer annular housing into at least two axial flow paths. Each axial flow path includes at least two annular extensions that alternately and locally direct the axial flow radially outward and inward or radially inward and outward thereby inducing a pressure loss or a pressure gradient within the axial flow. The pressure within the axial flow paths is lower than the pressure at the inlet end and greater than the vapor pressure for the axial flow. The invention minimizes fluidic instabilities, pressure pulses, vortex formation and shedding, and/or cavitation during pressure step down to yield a stabilized flow within a piping system.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA247939','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA247939"><span>A Study of the Flow Structure of Tip Vortices on a Hydrofoil</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.dtic.mil/">DTIC Science & Technology</a></p> <p></p> <p>1986-11-28</p> <p>as measured from the flow visualization imager. . . 0 . . . 61 III.10 The vertical location of the tip vortex center as measured from the flow...pressure gra- dients of opposite sign exist on both sides of an airfoil . These gradients induce an inward lateral flow on the suc- tion side and an...And most recently, Cebeci et al. (1986) developed a viscous/inviscid interaction method to calculate the flow around airfoils , emphasizing the</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/biblio/7110368-fabrication-tic-ni-functionally-gradient-materials-mechanical-thermal-properties','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/7110368-fabrication-tic-ni-functionally-gradient-materials-mechanical-thermal-properties"><span></span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Ma, Xiangfeng; Tanihata, Kimiaki; Miyamoto, Yoshinari</p> <p></p> <p>A TiC/Ni functionally gradient material (FGM) fabricated via gas-pressure combustion sintering is presently investigated to establish its mechanical and thermal properties. Attention is given to the FGM's specific thermal conductivities with different thermal cycling conditions; these are found to decrease with thermal cycling in all samples tested, implying that the lateral cracks are generated in the FGM and then propagated by the thermal cycle. High compressive stresses are induced at the TiC surface when this is constrained by a Cu block. 6 refs.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27806903','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27806903"><span>High-pressure balloon dilation in a dog with supravalvular aortic stenosis.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Pinkos, A; Stauthammer, C; Rittenberg, R; Barncord, K</p> <p>2017-02-01</p> <p>A 6-month-old female intact Goldendoodle was presented for diagnostic work up of a grade IV/VI left basilar systolic heart murmur. An echocardiogram was performed and revealed a ridge of tissue distal to the aortic valve leaflets at the sinotubular junction causing an instantaneous pressure gradient of 62 mmHg across the supravalvular aortic stenosis and moderate concentric hypertrophy of the left ventricle. Intervention with a high-pressure balloon dilation catheter was pursued and significantly decreased the pressure gradient to 34 mmHg. No complications were encountered. The patient returned in 5 months for re-evaluation and static long-term reduction in the pressure gradient was noted. Copyright © 2016 Elsevier B.V. All rights reserved.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PhFl...28i2007C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PhFl...28i2007C"><span>Light-induced phenomena in one-component gas: The transport phenomena</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chermyaninov, I. V.; Chernyak, V. G.</p> <p>2016-09-01</p> <p>The article presents the theory of transport processes in a one-component gas located in the capillary under the action of resonant laser radiation and the temperature and pressure gradients. The expressions for the kinetic coefficients determining heat and mass transport in the gas are obtained on the basis of the modified Boltzmann equations for the excited and unexcited particles. The Onsager reciprocal relations for cross kinetic coefficients are proven for all Knudsen numbers and for any law interaction of gas particles with each other and boundary surface. Light-induced phenomena associated with the possible non-equilibrium stationary states of system are analyzed.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19850002186&hterms=planetary+boundaries&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dplanetary%2Bboundaries','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19850002186&hterms=planetary+boundaries&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dplanetary%2Bboundaries"><span>The inducement of planetary boundary layer mass convergence associated with varying vorticity beneath tropospheric wind maximum</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Johnson, D. R.</p> <p>1984-01-01</p> <p>The effects of the vorticity distribution are applied to study planetary boundary layer mass convergence beneath free tropospheric wind maximum. For given forcing by viscous and pressure gradient forces beneath a wind maximum, boundary layer cross stream mass transport is increased by anticyclonic vorticity on the right flank and decreased by cyclonic vorticity on the left flank. Such frictionally forced mass transport induces boundary layer mass convergence beneath the relative wind maximum. This result is related to the empirical rule that the most intense convection and severe weather frequently develop beneath the 500 mb zero relative vorticity isopleth.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19940028717','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19940028717"><span>Numerical simulation of thermally induced near-surface flows over Martian terrain</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Parish, T. R.; Howard, A. D.</p> <p>1993-01-01</p> <p>Numerical simulations of the Martian near-surface wind regime using a mesoscale atmospheric model have shown that the thermally induced near-surface winds are analogous to terrestrial circulations. In particular, katabatic wind displays a striking similarity to flow observed over Antarctica. Introduction of solar radiation strongly perturbs the slope flows; anabatic conditions develop in middle to high latitudes during the daytime hours due to the solar heating of the sloping terrain. There appears to be a rapid transition from the katabatic to the anabatic flow regimes, emphasizing the primary importance of radiative exchanges at the surface in specifying the horizontal pressure gradient force.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/2360680','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/2360680"><span>Measurement of mean circulatory filling pressure and vascular compliance in domestic pigs.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ogilvie, R I; Zborowska-Sluis, D; Tenaschuk, B</p> <p>1990-06-01</p> <p>To measure mean circulatory filling pressure (Pmcf), a balloon was placed in the right atrium of seven pentobarbital sodium-anesthetized open-chest pigs for transient occlusion of flow combined with mechanical transfer of blood from the arterial to the venous circulation. Equilibration occurred within 6-8 s at a pressure at 12.3 +/- 0.3 (SE) mmHg after a 2.9 +/- 0.2 ml/kg transfer of blood. In another group of pentobarbital sodium-anesthetized closed-chest pigs, acetylcholine (ACh) was used to induce cardiac arrest. The Pmcf was 11.6 +/- 1.0 mmHg in the 7:17 pigs that arrested for 6-8 s. In four isoflurane-anesthetized closed-chest pigs, the Pmcf was 12.0 +/- 1.0 mmHg after terminal cardiac arrest induced by KCl. The pressure gradient for venous return [Pmcf--right atrial pressure (Pra)] averaged 5.9 +/- 0.2 mmHg. Total vascular compliance estimated from plots of Pmcf at base line, 5, and 10 ml/kg increases in circulating volume was 2.1 +/- 0.3 and 3.5 +/- 0.9 ml.kg-1.mmHg-1 in the balloon and ACh groups, respectively compared with 2.8 +/- 0.4 ml.kg-1.mmHg-1 using a volume infusion-withdrawal method without circulatory arrest. The use of ACh for the estimate of Pmcf in the pig is not recommended because of failure to consistently induce circulatory arrest and probable failure to achieve sufficient equilibrium of vascular pressures 6-8 s postarrest when it occurs.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22617069','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22617069"><span>[Diagnostic importance of the alveolar-arterial oxygen gradient].</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Weinans, Marije A E; Drost-de Klerck, Amanda M; ter Maaten, Jan C</p> <p>2012-01-01</p> <p>The alveolar-arterial (A-a) oxygen gradient is the difference between the partial pressure of oxygen in the alveoli and the partial pressure of arterial oxygen and can be elevated in the case of pulmonary disease. We describe a 41-year-old patient with pneumonia who presented with abdominal pain, in whom calculation of the A-a gradient could have led to earlier diagnosis. The A-a oxygen gradient is mainly of diagnostic importance and the presented nomogram allows easy and quick interpretation. This might lead to a more frequent use of the A-a oxygen gradient in the future.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/16711923','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/16711923"><span>Statistics of pressure fluctuations in decaying isotropic turbulence.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kalelkar, Chirag</p> <p>2006-04-01</p> <p>We present results from a systematic direct-numerical simulation study of pressure fluctuations in an unforced, incompressible, homogeneous, and isotropic three-dimensional turbulent fluid. At cascade completion, isosurfaces of low pressure are found to be organized as slender filaments, whereas the predominant isostructures appear sheetlike. We exhibit several results, including plots of probability distributions of the spatial pressure difference, the pressure-gradient norm, and the eigenvalues of the pressure-Hessian tensor. Plots of the temporal evolution of the mean pressure-gradient norm, and the mean eigenvalues of the pressure-Hessian tensor are also exhibited. We find the statistically preferred orientations between the eigenvectors of the pressure-Hessian tensor, the pressure gradient, the eigenvectors of the strain-rate tensor, the vorticity, and the velocity. Statistical properties of the nonlocal part of the pressure-Hessian tensor are also exhibited. We present numerical tests (in the viscous case) of some conjectures of Ohkitani [Phys. Fluids A 5, 2570 (1993)] and Ohkitani and Kishiba [Phys. Fluids 7, 411 (1995)] concerning the pressure-Hessian and the strain-rate tensors, for the unforced, incompressible, three-dimensional Euler equations.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..15.2564T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..15.2564T"><span>Microseismicity Induced by Fluid Pressure Drop (Laboratory Study)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Turuntaev, Sergey; Zenchenko, Evgeny; Melchaeva, Olga</p> <p>2013-04-01</p> <p>Pore pressure change in saturated porous rocks may result in its fracturing (Maury et Fourmaintraux, 1993) and corresponding microseismic event occurrences. Microseismicity due to fluid injection is considered in numerous papers (Maxwell, 2010, Shapiro et al., 2005). Another type of the porous medium fracturing is related with rapid pore pressure drop at some boundary. The mechanism of such fracturing was considered by (Khristianovich, 1985) as a model of sudden coal blowing and by (Alidibirov, Panov, 1998) as a model of volcano eruptions. If the porous saturated medium has a boundary where it directly contacted with fluid under the high pressure (in a hydraulic fracture or in a borehole), and the pressure at that boundary is dropped, the conditions for tensile cracks can be achieved at some distance from the boundary. In the paper, the results of experimental study of saturated porous sample fracturing due to pore pressure rapid drop are discussed. The samples (82 mm high, ∅60 mm) were made of quartz sand, which was cemented by "liquid glass" glue with mass fraction 1%. The sample (porosity 35%, uniaxial unconfined compression strength 2.5 MPa) was placed in a mould and saturated by oil. The upper end of the sample contacted with the mould upper lid, the lower end contacted with fluid. The fluid pressure was increased to 10 MPa and then discharged through the bottom nipple. The pressure increases/drops were repeated 30-50 times. Pore pressure and acoustic emission (AE) were registered by transducers mounted into upper and bottom lids of the mould. It was found, that AE sources (corresponded to microfracturing) were spreading from the open end to the closed end of the sample, and that maximal number of AE events was registered at some distance from the opened end. The number of AE pulses increased with every next pressure drop, meanwhile the number of pulses with high amplitudes diminished. It was found that AE maximal rate corresponded to the fluid pressure gradient maximal values. The model of AE relation with the pore pressure gradient was considered based on the following assumptions: AE event occurred when the pore pressure gradient reaches some critical value; the critical value varies and can be described by Weibull distribution. Permeability variation during the fluid pressure drop was estimated by means of fluid pressure data and pore-elastic equation solution for small time intervals (0.01 sec). The study showed possibility to solve both a direct problem of microseismicity variation relation with fluid pressure changes and an inverse problem of defining permeability by registering microseismic activity variation in particular volume of porous medium alongside with pore pressure measurements at some point.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/biblio/22299657-plasmon-excitation-metal-slab-fast-point-charge-role-additional-boundary-conditions-quantum-hydrodynamic-model','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/22299657-plasmon-excitation-metal-slab-fast-point-charge-role-additional-boundary-conditions-quantum-hydrodynamic-model"><span>Plasmon excitation in metal slab by fast point charge: The role of additional boundary conditions in quantum hydrodynamic model</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Zhang, Ying-Ying; Department of Applied Mathematics, University of Waterloo, Waterloo, Ontario N2L 3G1; An, Sheng-Bai</p> <p>2014-10-15</p> <p>We study the wake effect in the induced potential and the stopping power due to plasmon excitation in a metal slab by a point charge moving inside the slab. Nonlocal effects in the response of the electron gas in the metal are described by a quantum hydrodynamic model, where the equation of electronic motion contains both a quantum pressure term and a gradient correction from the Bohm quantum potential, resulting in a fourth-order differential equation for the perturbed electron density. Thus, besides using the condition that the normal component of the electron velocity should vanish at the impenetrable boundary ofmore » the metal, a consistent inclusion of the gradient correction is shown to introduce two possibilities for an additional boundary condition for the perturbed electron density. We show that using two different sets of boundary conditions only gives rise to differences in the wake potential at large distances behind the charged particle. On the other hand, the gradient correction in the quantum hydrodynamic model is seen to cause a reduction in the depth of the potential well closest to the particle, and a reduction of its stopping power. Even for a particle moving in the center of the slab, we observe nonlocal effects in the induced potential and the stopping power due to reduction of the slab thickness, which arise from the gradient correction in the quantum hydrodynamic model.« less</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19730019439','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19730019439"><span>Open forum</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p></p> <p>1973-01-01</p> <p>Some experiments on turbulent free shear layers in pressure gradients are discussed. Topics covered in the discussion include: (1) two dimensional vortex structures, (2) the effect of channel walls, and (3) the case of a mixing layer in pressure gradient.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29761086','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29761086"><span>Aortic-Brachial Pulse Wave Velocity Ratio: A Measure of Arterial Stiffness Gradient Not Affected by Mean Arterial Pressure.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Fortier, Catherine; Desjardins, Marie-Pier; Agharazii, Mohsen</p> <p>2018-03-01</p> <p>Aortic stiffness, measured by carotid-femoral pulse wave velocity (cf-PWV), is used for the prediction of cardiovascular risk. This mini-review describes the nonlinear relationship between cf-PWV and operational blood pressure, presents the proposed methods to adjust for this relationship, and discusses a potential place for aortic-brachial PWV ratio (a measure of arterial stiffness gradient) as a blood pressure-independent measure of vascular aging. PWV is inherently dependent on the operational blood pressure. In cross-sectional studies, PWV adjustment for mean arterial pressure (MAP) is preferred, but still remains a nonoptimal approach, as the relationship between PWV and blood pressure is nonlinear and varies considerably among individuals due to heterogeneity in genetic background, vascular tone, and vascular remodeling. Extrapolations from the blood pressure-independent stiffness parameter β (β 0 ) have led to the creation of stiffness index β, which can be used for local stiffness. A similar approach has been used for cardio-ankle PWV to generate a blood pressure-independent cardio-ankle vascular index (CAVI). It was recently demonstrated that stiffness index β and CAVI remain slightly blood pressure-dependent, and a more appropriate formula has been proposed to make the proper adjustments. On the other hand, the negative impact of aortic stiffness on clinical outcomes is thought to be mediated through attenuation or reversal of the arterial stiffness gradient, which can also be influenced by a reduction in peripheral medium-sized muscular arteries in conditions that predispose to accelerate vascular aging. Arterial stiffness gradient, assessed by aortic-brachial PWV ratio, is emerging to be at least as good as cf-PWV for risk prediction, but has the advantage of not being affected by operating MAP. The negative impacts of aortic stiffness on clinical outcomes are proposed to be mediated through attenuation or reversal of arterial stiffness gradient. Aortic-brachial PWV ratio, a measure of arterial stiffness gradient, is independent of MAP.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20040089321&hterms=lack+exercise&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dlack%2Bexercise','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20040089321&hterms=lack+exercise&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dlack%2Bexercise"><span>Bone tissue engineering: the role of interstitial fluid flow</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hillsley, M. V.; Frangos, J. A.</p> <p>1994-01-01</p> <p>It is well established that vascularization is required for effective bone healing. This implies that blood flow and interstitial fluid (ISF) flow are required for healing and maintenance of bone. The fact that changes in bone blood flow and ISF flow are associated with changes in bone remodeling and formation support this theory. ISF flow in bone results from transcortical pressure gradients produced by vascular and hydrostatic pressure, and mechanical loading. Conditions observed to alter flow rates include increases in venous pressure in hypertension, fluid shifts occurring in bedrest and microgravity, increases in vascularization during the injury-healing response, and mechanical compression and bending of bone during exercise. These conditions also induce changes in bone remodeling. Previously, we hypothesized that interstitial fluid flow in bone, and in particular fluid shear stress, serves to mediate signal transduction in mechanical loading- and injury-induced remodeling. In addition, we proposed that a lack or decrease of ISF flow results in the bone loss observed in disuse and microgravity. The purpose of this article is to review ISF flow in bone and its role in osteogenesis.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/2000753','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/2000753"><span>Noninvasive estimation of left atrial pressure in patients with congestive heart failure and mitral regurgitation by Doppler echocardiography.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Gorcsan, J; Snow, F R; Paulsen, W; Nixon, J V</p> <p>1991-03-01</p> <p>A completely noninvasive method for estimating left atrial pressure in patients with congestive heart failure and mitral regurgitation has been devised with the use of continuous-wave Doppler echocardiography and brachial sphygmomanometry. Of 46 patients studied with mitral regurgitation, 35 (76%) had jets with distinct Doppler spectral envelopes recorded. The peak ventriculoatrial gradient was obtained by measuring peak mitral regurgitant velocity in systole and using the modified Bernoulli equation. This gradient was then subtracted from peak brachial systolic blood pressure, an estimate of left ventricular systolic pressure, to yield left atrial pressure (left atrial pressure = systolic blood pressure - mitral regurgitant pressure gradient). Noninvasive estimates of left atrial pressure from 35 patients were plotted against simultaneous recordings of mean pulmonary capillary wedge pressure resulting in the correlation y = 0.88x + 3.3, r = 0.88, standard error of estimate = +/- 4 mm Hg (p less than 0.001). Therefore, continuous-wave Doppler echocardiography and sphygmomanometry may be used in selected patients with congestive heart failure and mitral regurgitation for noninvasive estimation of left atrial pressure.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010EGUGA..12.8050M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010EGUGA..12.8050M"><span>The composite TTG series: evidence for a non-unique tectonic setting for Archaean crustal growth.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Moyen, Jean-François</p> <p>2010-05-01</p> <p>The geodynamic context of formation of the Archaean TTG (tonalite-trondhjemite-granodiorite) series, the dominant component of the Archaean continental crust, is a matter of debate. The two end-member models for TTG formation are melting of the basaltic slab in a "hot subduction"; and intra-plate melting of basaltic rocks at the base of thick crust (oceanic plateau?). Both models do however predict strikingly different geothermal gradients, as in the modern Earth a typical subduction gradient is less than 10 °C/km compared to > 25-30 °C/km in the case of plateau melting. Using a large database of published TTG compositions, and filtering it to remove rocks that do not match the definition of TTG, it is possible to show that the TTG series is actually composite and made of a range of geochemically identifiable components that can be referred to as low-, medium- and high-pressure groups. The geochemistry of the low-pressure group (low Al, Na, Sr, relatively high Y and Nb) is consistent with derivation from a plagioclase and garnet- amphibolite; the medium-pressure group was formed in equilibrium with a garnet-rich, plagioclase-poor amphibolite, whereas the high pressure group derived from a rutile bearing eclogite. As the temperature of melting of metamafic rocks is largely independent from pressure, this corresponds to melting along a range of contrasting geothermal gradients. The low pressure group requires gradients of 10-12 °C/km, whereas the gradient required for the low pressure group can be as high as 25—30 °C/km. Regardless of the preferred tectonic model for the Archaean, such a range of gradients requires an equally large range of tectonic sites for the formation of the Archaean continental crust.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li class="active"><span>10</span></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_10 --> <div id="page_11" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li class="active"><span>11</span></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="201"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23005554','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23005554"><span>Flow shear stabilization of rotating plasmas due to the Coriolis effect.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Haverkort, J W; de Blank, H J</p> <p>2012-07-01</p> <p>A radially decreasing toroidal rotation frequency can have a stabilizing effect on nonaxisymmetric magnetohydrodynamic (MHD) instabilities. We show that this is a consequence of the Coriolis effect that induces a restoring pressure gradient force when plasma is perturbed radially. In a rotating cylindrical plasma, this Coriolis-pressure effect is canceled by the centrifugal effect responsible for the magnetorotational instability. In a magnetically confined toroidal plasma, a large aspect ratio expansion shows that only half of the effect is canceled. This analytical result is confirmed by numerical computations. When the plasma rotates faster toroidally in the core than near the edge, the effect can contribute to the formation of transport barriers by stabilizing MHD instabilities.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27686700','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27686700"><span>Study of heat transfer on physiological driven movement with CNT nanofluids and variable viscosity.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Akbar, Noreen Sher; Kazmi, Naeem; Tripathi, Dharmendra; Mir, Nazir Ahmed</p> <p>2016-11-01</p> <p>With ongoing interest in CNT nanofluids and materials in biotechnology, energy and environment, microelectronics, composite materials etc., the current investigation is carried out to analyze the effects of variable viscosity and thermal conductivity of CNT nanofluids flow driven by cilia induced movement through a circular cylindrical tube. Metachronal wave is generated by the beating of cilia and mathematically modeled as elliptical wave propagation by Blake (1971). The problem is formulated in the form of nonlinear partial differential equations, which are simplified by using the dimensional analysis to avoid the complicacy of dimensional homogeneity. Lubrication theory is employed to linearize the governing equations and it is also physically appropriate for cilia movement. Analytical solutions for velocity, temperature and pressure gradient and stream function are obtained. The analytical results are numerically simulated by using the Mathematica Software and plotted the graphs for velocity profile, temperature profile, pressure gradient and stream lines for better discussion and visualization. This model is applicable in physiological transport phenomena to explore the nanotechnology in engineering the artificial cilia and ciliated tube/pipe. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19730006564','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19730006564"><span>The turbulent boundary layer on a porous plate: An experimental study of the heat transfer behavior with adverse pressure gradients</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Blackwell, B. F.; Kays, W. M.; Moffat, R. J.</p> <p>1972-01-01</p> <p>An experimental investigation of the heat transfer behavior of the near equilibrium transpired turbulent boundary layer with adverse pressure gradient has been carried out. Stanton numbers were measured by an energy balance on electrically heated plates that form the bottom wall of the wind tunnel. Two adverse pressure gradients were studied. Two types of transpiration boundary conditions were investigated. The concept of an equilibrium thermal boundary layer was introduced. It was found that Stanton number as a function of enthalpy thickness Reynolds number is essentially unaffected by adverse pressure gradient with no transpiration. Shear stress, heat flux, and turbulent Prandtl number profiles were computed from mean temperature and velocity profiles. It was concluded that the turbulent Prandtl number is greater than unity in near the wall and decreases continuously to approximately 0.5 at the free stream.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JFS....40..233D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JFS....40..233D"><span>Unsteady separation and vortex shedding from a laminar separation bubble over a bluff body</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Das, S. P.; Srinivasan, U.; Arakeri, J. H.</p> <p>2013-07-01</p> <p>Boundary layers are subject to favorable and adverse pressure gradients because of both the temporal and spatial components of the pressure gradient. The adverse pressure gradient may cause the flow to separate. In a closed loop unsteady tunnel we have studied the initiation of separation in unsteady flow past a constriction (bluff body) in a channel. We have proposed two important scalings for the time when boundary layer separates. One is based on the local pressure gradient and the other is a convective time scale based on boundary layer parameters. The flow visualization using a dye injection technique shows the flow structure past the body. Nondimensional shedding frequency (Strouhal number) is calculated based on boundary layer and momentum thicknesses. Strouhal number based on the momentum thickness shows a close agreement with that for flat plate and circular cylinder.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4643262','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4643262"><span>Feedback Regulation of Intracellular Hydrostatic Pressure in Surface Cells of the Lens</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Gao, Junyuan; Sun, Xiurong; White, Thomas W.; Delamere, Nicholas A.; Mathias, Richard T.</p> <p>2015-01-01</p> <p>In wild-type lenses from various species, an intracellular hydrostatic pressure gradient goes from ∼340 mmHg in central fiber cells to 0 mmHg in surface cells. This gradient drives a center-to-surface flow of intracellular fluid. In lenses in which gap-junction coupling is increased, the central pressure is lower, whereas if gap-junction coupling is reduced, the central pressure is higher but surface pressure is always zero. Recently, we found that surface cell pressure was elevated in PTEN null lenses. This suggested disruption of a feedback control system that normally maintained zero surface cell pressure. Our purpose in this study was to investigate and characterize this feedback control system. We measured intracellular hydrostatic pressures in mouse lenses using a microelectrode/manometer-based system. We found that all feedback went through transport by the Na/K ATPase, which adjusted surface cell osmolarity such that pressure was maintained at zero. We traced the regulation of Na/K ATPase activity back to either TRPV4, which sensed positive pressure and stimulated activity, or TRPV1, which sensed negative pressure and inhibited activity. The inhibitory effect of TRPV1 on Na/K pumps was shown to signal through activation of the PI3K/AKT axis. The stimulatory effect of TRPV4 was shown in previous studies to go through a different signal transduction path. Thus, there is a local two-legged feedback control system for pressure in lens surface cells. The surface pressure provides a pedestal on which the pressure gradient sits, so surface pressure determines the absolute value of pressure at each radial location. We speculate that the absolute value of intracellular pressure may set the radial gradient in the refractive index, which is essential for visual acuity. PMID:26536260</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19850021620','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19850021620"><span>A Method for Computing the Core Flow in Three-Dimensional Leading-Edge Vortices. Ph.D. Thesis - North Carolina State Univ.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Luckring, J. M.</p> <p>1985-01-01</p> <p>A theory is presented for calculating the flow in the core of a separation-induced leading-edge vortex. The method is based on matching inner and outer representations of the vortex. The inner model of the vortex is based on the quasicylindrical Navier-Stokes equations; the flow is assumed to be steady, axially symmetric, and incompressible and in addition, gradients in the radial direction are assumed to be much larger then gradients in the axial direction. The outer model is based on the three-dimensional free-vortex-sheet theory, a higher-order panel method which solves the Prandtl-Glauert equation including nonlinear boundary conditions pertinent to the concentrated vorticity representation of the leading edge vortex. The resultant flow is evaluated a posteriori for evidence of incipient vortex breakdown and the critical helix angle concept, in conjunction with an adverse longitudinal pressure gradient, is found to correlate well with the occurrence of vortex breakdown at the trailing edge of delta, arrow, and diamond wings.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018JGRC..123.1860R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018JGRC..123.1860R"><span>Variability in Benthic Exchange Rate, Depth, and Residence Time Beneath a Shallow Coastal Estuary</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Russoniello, Christopher J.; Heiss, James W.; Michael, Holly A.</p> <p>2018-03-01</p> <p>Hydrodynamically driven benthic exchange of water between the water column and shallow seabed aquifer is a significant and dynamic component of coastal and estuarine fluid budgets. Associated exchange of solutes promotes ecologically important chemical reactions, so quantifying benthic exchange rates, depths, and residence times constrains coastal chemical cycling estimates. We present the first combined field, numerical, and analytical modeling investigation of wave-induced exchange. Temporal variability of exchange was calculated with data collected by instruments deployed in a shallow estuary for 11 days. Differential pressure sensors recorded pressure gradients across the seabed, and up- and down-looking ADCPs recorded currents and pressures to determine wave parameters, surface-water currents, and water depth. Wave-induced exchange was calculated (1) directly from differential pressure measurements, and indirectly with an analytical model based on wave parameters from (2) ADCP and (3) wind data. Wave-induced exchange from pressure measurements and ADCP-measured wave parameters matched well, but both exceeded wind-based values. Exchange induced by tidal pumping and current-bed form interaction—the other primary drivers in shallow coastal waters were calculated from tidal stage variation and ADCP-measured currents. Exchange from waves (mean = 20.0 cm/d; range = 1.75-92.3 cm/d) greatly exceeded exchange due to tides (mean = 3.7 cm/d) and current-bed form interaction (mean = 6.5 × 10-2 cm/d). Groundwater flow models showed aquifer properties affect wave-driven benthic exchange: residence time and depth increased and exchange rates decreased with increasing hydraulic diffusivity (ratio of aquifer permeability to compressibility). This new understanding of benthic exchange will help managers assess its control over chemical fluxes to marine systems.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/12231794','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/12231794"><span>Direct Demonstration of a Growth-Induced Water Potential Gradient.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Nonami, H.; Boyer, J. S.</p> <p>1993-05-01</p> <p>When transpiration is negligible, water potentials in growing tissues are less than those in mature tissues and have been predicted to form gradients that move water into the enlarging cells. To determine directly whether the gradients exist, we measured water potentials along the radius of stems of intact soybean (Glycine max [L.] Merr.) seedlings growing in vermiculite in a water-saturated atmosphere. The measurements were made in individual cells by first determining the turgor with a miniature pressure probe, then determining the osmotic potential of solution from the same cell, and finally summing the two potentials. The osmotic potentials were corrected for sample mixing in the probe. The measurements were checked with a thermocouple psychrometer that gave average tissue water potentials. In the elongating region, the water potential was highest near the xylem and lowest near the epidermis and in the center of the pith. In the basal, more mature region of the same stems, water potentials were near zero next to the xylem and throughout the tissue. These basal potentials reflected mostly the potential of the xylem, which extended into the elongating tissues. Thus, the high basal potential confirmed the high potential near the xylem in the elongating tissues. The psychrometer measurements for each tissue gave average potentials that agreed with the average of the cell potentials from the pressure probe. We conclude that a radial gradient was present in the elongating region that formed a water potential field in three dimensions around the xylem and that confirmed the predictions of Molz and Boyer (F.J. Molz and J.S. Boyer [1978] Plant Physiol 62: 423-429).</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=158741','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=158741"><span>Direct Demonstration of a Growth-Induced Water Potential Gradient.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Nonami, H.; Boyer, J. S.</p> <p>1993-01-01</p> <p>When transpiration is negligible, water potentials in growing tissues are less than those in mature tissues and have been predicted to form gradients that move water into the enlarging cells. To determine directly whether the gradients exist, we measured water potentials along the radius of stems of intact soybean (Glycine max [L.] Merr.) seedlings growing in vermiculite in a water-saturated atmosphere. The measurements were made in individual cells by first determining the turgor with a miniature pressure probe, then determining the osmotic potential of solution from the same cell, and finally summing the two potentials. The osmotic potentials were corrected for sample mixing in the probe. The measurements were checked with a thermocouple psychrometer that gave average tissue water potentials. In the elongating region, the water potential was highest near the xylem and lowest near the epidermis and in the center of the pith. In the basal, more mature region of the same stems, water potentials were near zero next to the xylem and throughout the tissue. These basal potentials reflected mostly the potential of the xylem, which extended into the elongating tissues. Thus, the high basal potential confirmed the high potential near the xylem in the elongating tissues. The psychrometer measurements for each tissue gave average potentials that agreed with the average of the cell potentials from the pressure probe. We conclude that a radial gradient was present in the elongating region that formed a water potential field in three dimensions around the xylem and that confirmed the predictions of Molz and Boyer (F.J. Molz and J.S. Boyer [1978] Plant Physiol 62: 423-429). PMID:12231794</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4604314','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4604314"><span>Effect of oral nitrate supplementation on pulmonary hemodynamics during exercise and time trial performance in normoxia and hypoxia: a randomized controlled trial</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Bourdillon, Nicolas; Fan, Jui-Lin; Uva, Barbara; Müller, Hajo; Meyer, Philippe; Kayser, Bengt</p> <p>2015-01-01</p> <p>Background: Hypoxia-induced pulmonary vasoconstriction increases pulmonary arterial pressure (PAP) and may impede right heart function and exercise performance. This study examined the effects of oral nitrate supplementation on right heart function and performance during exercise in normoxia and hypoxia. We tested the hypothesis that nitrate supplementation would attenuate the increase in PAP at rest and during exercise in hypoxia, thereby improving exercise performance. Methods: Twelve trained male cyclists [age: 31 ± 7 year (mean ± SD)] performed 15 km time-trial cycling (TT) and steady-state submaximal cycling (50, 100, and 150 W) in normoxia and hypoxia (11% inspired O2) following 3-day oral supplementation with either placebo or sodium nitrate (0.1 mmol/kg/day). We measured TT time-to-completion, muscle tissue oxygenation during TT and systolic right ventricle to right atrium pressure gradient (RV-RA gradient: index of PAP) during steady state cycling. Results: During steady state exercise, hypoxia elevated RV-RA gradient (p > 0.05), while oral nitrate supplementation did not alter RV-RA gradient (p > 0.05). During 15 km TT, hypoxia lowered muscle tissue oxygenation (p < 0.05). Nitrate supplementation further decreased muscle tissue oxygenation during 15 km TT in hypoxia (p < 0.05). Hypoxia impaired time-to-completion during TT (p < 0.05), while no improvements were observed with nitrate supplementation in normoxia or hypoxia (p > 0.05). Conclusion: Our findings indicate that oral nitrate supplementation does not attenuate acute hypoxic pulmonary vasoconstriction nor improve performance during time trial cycling in normoxia and hypoxia. PMID:26528189</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AIPC.1628..901T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AIPC.1628..901T"><span>Thermal transpiration: A molecular dynamics study</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>T, Joe Francis; Sathian, Sarith P.</p> <p>2014-12-01</p> <p>Thermal transpiration is a phenomenon where fluid molecules move from the cold end towards the hot end of a channel under the influence of longitudinal temperature gradient alone. Although the phenomenon of thermal transpiration is observed at rarefied gas conditions in macro systems, the phenomenon can occur at atmospheric pressure if the characteristic dimensions of the channel is less than 100 nm. The flow through these nanosized channels is characterized by the free molecular flow regimes and continuum theory is inadequate to describe the flow. Thus a non-continuum method like molecular dynamics (MD) is necessary to study such phenomenon. In the present work, MD simulations were carried out to investigate the occurance of thermal transpiration in copper and platinum nanochannels at atmospheric pressure conditions. The mean pressure of argon gas confined inside the nano channels was maintained around 1 bar. The channel height is maintained at 2nm. The argon atoms interact with each other and with the wall atoms through the Lennard-Jones potential. The wall atoms are modelled using an EAM potential. Further, separate simulations were carried out where a Harmonic potential is used for the atom-atom interaction in the platinum channel. A thermally insulating wall was introduced between the low and high temperature regions and those wall atoms interact with fluid atoms through a repulsive potential. A reduced cut off radius were used to achieve this. Thermal creep is induced by applying a temperature gradient along the channel wall. It was found that flow developed in the direction of the increasing temperature gradient of the wall. An increase in the volumetric flux was observed as the length of the cold and the hot regions of the wall were increased. The effect of temperature gradient and the wall-fluid interaction strength on the flow parameters have been studied to understand the phenomenon better.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24209296','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24209296"><span>Fast gradient separation by very high pressure liquid chromatography: reproducibility of analytical data and influence of delay between successive runs.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Stankovicha, Joseph J; Gritti, Fabrice; Beaver, Lois Ann; Stevensona, Paul G; Guiochon, Georges</p> <p>2013-11-29</p> <p>Five methods were used to implement fast gradient separations: constant flow rate, constant column-wall temperature, constant inlet pressure at moderate and high pressures (controlled by a pressure controller),and programmed flow constant pressure. For programmed flow constant pressure, the flow rates and gradient compositions are controlled using input into the method instead of the pressure controller. Minor fluctuations in the inlet pressure do not affect the mobile phase flow rate in programmed flow. There producibilities of the retention times, the response factors, and the eluted band width of six successive separations of the same sample (9 components) were measured with different equilibration times between 0 and 15 min. The influence of the length of the equilibration time on these reproducibilities is discussed. The results show that the average column temperature may increase from one separation to the next and that this contributes to fluctuation of the results.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/20090004704','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20090004704"><span>Analytic Formulation and Numerical Implementation of an Acoustic Pressure Gradient Prediction</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Lee, Seongkyu; Brentner, Kenneth S.; Farassat, F.; Morris, Philip J.</p> <p>2008-01-01</p> <p>Two new analytical formulations of the acoustic pressure gradient have been developed and implemented in the PSU-WOPWOP rotor noise prediction code. The pressure gradient can be used to solve the boundary condition for scattering problems and it is a key aspect to solve acoustic scattering problems. The first formulation is derived from the gradient of the Ffowcs Williams-Hawkings (FW-H) equation. This formulation has a form involving the observer time differentiation outside the integrals. In the second formulation, the time differentiation is taken inside the integrals analytically. This formulation avoids the numerical time differentiation with respect to the observer time, which is computationally more efficient. The acoustic pressure gradient predicted by these new formulations is validated through comparison with available exact solutions for a stationary and moving monopole sources. The agreement between the predictions and exact solutions is excellent. The formulations are applied to the rotor noise problems for two model rotors. A purely numerical approach is compared with the analytical formulations. The agreement between the analytical formulations and the numerical method is excellent for both stationary and moving observer cases.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018PhRvE..97a2908E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018PhRvE..97a2908E"><span>Pressure evolution and deformation of confined granular media during pneumatic fracturing</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Eriksen, Fredrik K.; Toussaint, Renaud; Turquet, Antoine Léo; Mâløy, Knut J.; Flekkøy, Eirik G.</p> <p>2018-01-01</p> <p>By means of digital image correlation, we experimentally characterize the deformation of a dry granular medium confined inside a Hele-Shaw cell due to air injection at a constant overpressure high enough to deform it (from 50 to 250 kPa). Air injection at these overpressures leads to the formation of so-called pneumatic fractures, i.e., channels empty of beads, and we discuss the typical deformations of the medium surrounding these structures. In addition we simulate the diffusion of the fluid overpressure into the medium, comparing it with the Laplacian solution over time and relating pressure gradients with corresponding granular displacements. In the compacting medium we show that the diffusing pressure field becomes similar to the Laplace solution on the order of a characteristic time given by the properties of the pore fluid, the granular medium, and the system size. However, before the diffusing pressure approaches the Laplace solution on the system scale, we find that it resembles the Laplacian field near the channels, with the highest pressure gradients on the most advanced channel tips and a screened pressure gradient behind them. We show that the granular displacements more or less always move in the direction against the local pressure gradients, and when comparing granular velocities with pressure gradients in the zone ahead of channels, we observe a Bingham type of rheology for the granular paste (the mix of air and beads), with an effective viscosity μB and displacement thresholds ∇ ⃗Pc evolving during mobilization and compaction of the medium. Such a rheology, with disorder in the displacement thresholds, could be responsible for placing the pattern growth at moderate injection pressures in a universality class like the dielectric breakdown model with η =2 , where fractal dimensions are found between 1.5 and 1.6 for the patterns.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011PhFl...23g3101A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011PhFl...23g3101A"><span>The influence of pressure relaxation on the structure of an axial vortex</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ash, Robert L.; Zardadkhan, Irfan; Zuckerwar, Allan J.</p> <p>2011-07-01</p> <p>Governing equations including the effects of pressure relaxation have been utilized to study an incompressible, steady-state viscous axial vortex with specified far-field circulation. When sound generation is attributed to a velocity gradient tensor-pressure gradient product, the modified conservation of momentum equations that result yield an exact solution for a steady, incompressible axial vortex. The vortex velocity profile has been shown to closely approximate experimental vortex measurements in air and water over a wide range of circulation-based Reynolds numbers. The influence of temperature and humidity on the pressure relaxation coefficient in air has been examined using theoretical and empirical approaches, and published axial vortex experiments have been employed to estimate the pressure relaxation coefficient in water. Non-equilibrium pressure gradient forces have been shown to balance the viscous stresses in the vortex core region, and the predicted pressure deficits that result from this non-equilibrium balance can be substantially larger than the pressure deficits predicted using a Bernoulli equation approach. Previously reported pressure deficit distributions for dust devils and tornados have been employed to validate the non-equilibrium pressure deficit predictions.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3163721','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3163721"><span>Quantification and Compensation of Eddy-Current-Induced Magnetic Field Gradients</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Spees, William M.; Buhl, Niels; Sun, Peng; Ackerman, Joseph J.H.; Neil, Jeffrey J.; Garbow, Joel R.</p> <p>2011-01-01</p> <p>Two robust techniques for quantification and compensation of eddy-current-induced magnetic-field gradients and static magnetic-field shifts (ΔB0) in MRI systems are described. Purpose-built 1-D or 6-point phantoms are employed. Both procedures involve measuring the effects of a prior magnetic-field-gradient test pulse on the phantom’s free induction decay (FID). Phantom-specific analysis of the resulting FID data produces estimates of the time-dependent, eddy-current-induced magnetic field gradient(s) and ΔB0 shift. Using Bayesian methods, the time dependencies of the eddy-current-induced decays are modeled as sums of exponentially decaying components, each defined by an amplitude and time constant. These amplitudes and time constants are employed to adjust the scanner’s gradient pre-emphasis unit and eliminate undesirable eddy-current effects. Measurement with the six-point sample phantom allows for simultaneous, direct estimation of both on-axis and cross-term eddy-current-induced gradients. The two methods are demonstrated and validated on several MRI systems with actively-shielded gradient coil sets. PMID:21764614</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21764614','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21764614"><span>Quantification and compensation of eddy-current-induced magnetic-field gradients.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Spees, William M; Buhl, Niels; Sun, Peng; Ackerman, Joseph J H; Neil, Jeffrey J; Garbow, Joel R</p> <p>2011-09-01</p> <p>Two robust techniques for quantification and compensation of eddy-current-induced magnetic-field gradients and static magnetic-field shifts (ΔB0) in MRI systems are described. Purpose-built 1-D or six-point phantoms are employed. Both procedures involve measuring the effects of a prior magnetic-field-gradient test pulse on the phantom's free induction decay (FID). Phantom-specific analysis of the resulting FID data produces estimates of the time-dependent, eddy-current-induced magnetic field gradient(s) and ΔB0 shift. Using Bayesian methods, the time dependencies of the eddy-current-induced decays are modeled as sums of exponentially decaying components, each defined by an amplitude and time constant. These amplitudes and time constants are employed to adjust the scanner's gradient pre-emphasis unit and eliminate undesirable eddy-current effects. Measurement with the six-point sample phantom allows for simultaneous, direct estimation of both on-axis and cross-term eddy-current-induced gradients. The two methods are demonstrated and validated on several MRI systems with actively-shielded gradient coil sets. Copyright © 2011 Elsevier Inc. All rights reserved.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015SPIE.9326E..0SM','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015SPIE.9326E..0SM"><span>Characterization of nanosecond pulse electrical field shock waves using imaging techniques</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mimun, L. Chris; Ibey, Bennett L.; Roth, Caleb C.; Barnes, Ronald A.; Sardar, Dhiraj K.; Beier, Hope T.</p> <p>2015-03-01</p> <p>Nanosecond pulsed electric fields (nsPEF) cause the formation of small pores, termed nanopores, in the membrane of cells. Current nanoporation models treat nsPEF exposure as a purely electromagnetic phenomenon, but recent publications showing pressure transients, ROS production, temperature gradients, and pH waves suggest the stimulus may be physically and chemically multifactorial causing elicitation of diverse biological conditions and stressors. Our research group's goal is to quantify the breadth and participation of these stressors generated during nsPEF exposure and determine their relative importance to the observed cellular response. In this paper, we used advanced imaging techniques to identify a possible source of nsPEF-induced acoustic shock waves. nsPEFs were delivered in an aqueous media via a pair of 125 μm tungsten electrodes separated by 100 μm, mirroring our previously published cellular exposure experiments. To visualize any pressure transients emanating from the electrodes or surrounding medium, we used the Schlieren imaging technique. Resulting images and measurements confirmed that mechanical pressure waves and electrode-based stresses are formed during nsPEF, resulting in a clearer understanding of the whole exposure dosimetry. This information will be used to better quantify the impact of nsPEF-induced acoustic shock waves on cells, and has provided further evidence of non-electrical-field induced exposures for elicitation of bioieffects.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150003278','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150003278"><span>High Sensitivity Stress Sensor Based on Hybrid Materials</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Cao, Xian-An (Inventor)</p> <p>2014-01-01</p> <p>A sensing device is used to detect the spatial distributions of stresses applied by physical contact with the surface of the sensor or induced by pressure, temperature gradients, and surface absorption. The sensor comprises a hybrid active layer that includes luminophores doped in a polymeric or organic host, altogether embedded in a matrix. Under an electrical bias, the sensor simultaneously converts stresses into electrical and optical signals. Among many applications, the device may be used for tactile sensing and biometric imaging.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4241768','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4241768"><span>A novel microfluidic flow focusing method</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Jiang, Hai; Weng, Xuan; Li, Dongqing</p> <p>2014-01-01</p> <p>A new microfluidic method that allows hydrodynamic focusing in a microchannel with two sheath flows is demonstrated. The microchannel network consists of a T-shaped main channel and two T-shaped branch channels. The flows of the sample stream and the sheath streams in the microchannel are generated by electroosmotic flow-induced pressure gradients. In comparison with other flow focusing methods, this novel method does not expose the sample to electrical field, and does not need any external pumps, tubing, and valves. PMID:25538810</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li class="active"><span>11</span></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_11 --> <div id="page_12" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li class="active"><span>12</span></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="221"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017APS..DFDA24008M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017APS..DFDA24008M"><span>Evaluation of the accuracy of the Rotating Parallel Ray Omnidirectional Integration for instantaneous pressure reconstruction from the measured pressure gradient</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Moreto, Jose; Liu, Xiaofeng</p> <p>2017-11-01</p> <p>The accuracy of the Rotating Parallel Ray omnidirectional integration for pressure reconstruction from the measured pressure gradient (Liu et al., AIAA paper 2016-1049) is evaluated against both the Circular Virtual Boundary omnidirectional integration (Liu and Katz, 2006 and 2013) and the conventional Poisson equation approach. Dirichlet condition at one boundary point and Neumann condition at all other boundary points are applied to the Poisson solver. A direct numerical simulation database of isotropic turbulence flow (JHTDB), with a homogeneously distributed random noise added to the entire field of DNS pressure gradient, is used to assess the performance of the methods. The random noise, generated by the Matlab function Rand, has a magnitude varying randomly within the range of +/-40% of the maximum DNS pressure gradient. To account for the effect of the noise distribution pattern on the reconstructed pressure accuracy, a total of 1000 different noise distributions achieved by using different random number seeds are involved in the evaluation. Final results after averaging the 1000 realizations show that the error of the reconstructed pressure normalized by the DNS pressure variation range is 0.15 +/-0.07 for the Poisson equation approach, 0.028 +/-0.003 for the Circular Virtual Boundary method and 0.027 +/-0.003 for the Rotating Parallel Ray method, indicating the robustness of the Rotating Parallel Ray method in pressure reconstruction. Sponsor: The San Diego State University UGP program.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/8149707','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/8149707"><span>Assessment of coronary artery stenosis pressure gradient by quantitative coronary arteriography in patients with coronary artery disease.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Atar, D; Ramanujam, P S; Saunamäki, K; Haunsø, S</p> <p>1994-01-01</p> <p>The aim of the study described here was to correlate coronary artery (CA) stenosis pressure gradients calculated by quantitative coronary arteriography (QCA) to invasively measured transstenotic pressure drops in patients with anginal symptoms and with known or suspected coronary artery disease. Furthermore, the known mathematical models are improved by introducing (1) pressure catheter-corrected minimal stenosis area, (2) modification of flow assumptions, and (3) stenosis exit angle. Included in the study were 45 patients with 61 stenoses. The visually estimated CA lesion severity in these non-complex stenoses was in the equivocal range of 40-70%. All measurements were performed after intracoronary administration of nifedipine and nitroglycerin. Stenosis dimensions were assessed from magnified cinefilms, using hand-held calipers. Highly significant overall correlation was found between measured and calculated pressure gradients with correction for the impact of the intracoronary catheter (P < 0.00001, r = 0.84). In particular, a substantial number of stenoses with haemodynamically-insignificant pressure gradients were identified by hydrodynamic calculations. In conclusion, the great majority of the coronary artery stenoses could be classified reliably by QCA as being haemodynamically insignificant or significant, respectively.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018JMMM..446...54A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018JMMM..446...54A"><span>Impact of induced magnetic field on synovial fluid with peristaltic flow in an asymmetric channel</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Afsar Khan, Ambreen; Farooq, Arfa; Vafai, Kambiz</p> <p>2018-01-01</p> <p>In this paper, we have worked for the impact of induced magnetic field on peristaltic motion of a non-Newtonian, incompressible, synovial fluid in an asymmetric channel. We have solved the problem for two models, Model-1 which behaves as shear thinning fluid and Model-2 which behaves as shear thickening fluid. The problem is solved by using modified Adomian Decomposition method. It has seen that two models behave quite opposite to each other for some parameters. The impact of various parameters on u, dp/dx, Δp and induced magnetic field bx have been studied graphically. The significant findings of this study is that the size of the trapped bolus and the pressure gradient increases by increasing M for both models.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/16657786','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/16657786"><span>Water potential gradient in a tall sequoiadendron.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Tobiessen, P</p> <p>1971-09-01</p> <p>With an elevator installed in a 90-meter tall Sequoiadendron to collect the samples, xylem pressure potential measurements were made approximately every 15 meters along 60 meters of the tree's height. The measured gradient was about -0.8 bar per 10 meters of height, i.e., less than the hydrostatic gradient. Correction of the xylem pressure potential data by calibration against a thermocouple psychrometer confirmed this result. Similar gradients are described in the literature in tall conifers at times of low transpiration, although a different sampling technique was used. If the data in the present study and those supporting it are typical, they imply a re-evaluation of either the use of the pressure chamber to estimate water potential or the present theories describing water transport in tall trees.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=396854','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=396854"><span>Water Potential Gradient in a Tall Sequoiadendron</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Tobiessen, Peter; Rundel, Philip W.; Stecker, R. E.</p> <p>1971-01-01</p> <p>With an elevator installed in a 90-meter tall Sequoiadendron to collect the samples, xylem pressure potential measurements were made approximately every 15 meters along 60 meters of the tree's height. The measured gradient was about −0.8 bar per 10 meters of height, i.e., less than the hydrostatic gradient. Correction of the xylem pressure potential data by calibration against a thermocouple psychrometer confirmed this result. Similar gradients are described in the literature in tall conifers at times of low transpiration, although a different sampling technique was used. If the data in the present study and those supporting it are typical, they imply a re-evaluation of either the use of the pressure chamber to estimate water potential or the present theories describing water transport in tall trees. PMID:16657786</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015ITNS...62.2017S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015ITNS...62.2017S"><span>Simulated Design Strategies for SPECT Collimators to Reduce the Eddy Currents Induced by MRI Gradient Fields</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Samoudi, Amine M.; Van Audenhaege, Karen; Vermeeren, Günter; Verhoyen, Gregory; Martens, Luc; Van Holen, Roel; Joseph, Wout</p> <p>2015-10-01</p> <p>Combining single photon emission computed tomography (SPECT) with magnetic resonance imaging (MRI) requires the insertion of highly conductive SPECT collimators inside the MRI scanner, resulting in an induced eddy current disturbing the combined system. We reduced the eddy currents due to the insert of a novel tungsten collimator inside transverse and longitudinal gradient coils. The collimator was produced with metal additive manufacturing, that is part of a microSPECT insert for a preclinical SPECT/MRI scanner. We characterized the induced magnetic field due to the gradient field and adapted the collimators to reduce the induced eddy currents. We modeled the x-, y-, and z-gradient coil and the different collimator designs and simulated them with FEKO, a three-dimensional method of moments / finite element methods (MoM/FEM) full-wave simulation tool. We used a time analysis approach to generate the pulsed magnetic field gradient. Simulation results show that the maximum induced field can be reduced by 50.82% in the final design bringing the maximum induced magnetic field to less than 2% of the applied gradient for all the gradient coils. The numerical model was validated with measurements and was proposed as a tool for studying the effect of a SPECT collimator within the MRI gradient coils.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5402700','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5402700"><span>Elimination of Trans-coarctation Pressure Gradients Has No Impact on Left Ventricular Function or Aortic Shear Stress Post Intervention in Patients with Mild Coarctation</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Keshavarz-Motamed, Zahra; Nezami, Farhad Rikhtegar; Partida, Ramon A.; Nakamura, Kenta; Staziaki, Pedro Vinícius; Ben-Assa, Eyal; Ghoshhajra, Brian; Bhatt, Ami B.; Edelman, Elazer R.</p> <p>2017-01-01</p> <p>OBJECTIVES To investigate the impact of transcatheter intervention on left ventricular (LV) function and aortic hemodynamics in patients with mild coarctation of the aorta (COA). BACKGROUND The optimal method and timing of transcatheter intervention for COA remains unclear, especially when the severity of COA is mild (peak-to-peak trans-coarctation pressure gradient, PKdP < 20 mmHg). Debate rages regarding the risk/benefit ratio of intervention vs. long-term effects of persistent minimal gradient in this heterogeneous population with differing blood pressures, ventricular function and peripheral perfusion. METHODS We developed a unique computational fluid dynamics and lumped parameter modeling framework based on patient-specific hemodynamic input parameters and validated it against patient-specific clinical outcomes (pre- and post-intervention). We used clinically measured hemodynamic metrics and imaging of the aorta and the LV in thirty-four patients with mild COA to make these correlations. RESULTS Despite dramatic reduction in trans-coarctation pressure gradient (catheter and Doppler echocardiography pressure gradients reduced 75% and 47.3%,), there was only modest effect on aortic flow and no significant impact on aortic shear stress (maximum time-averaged wall shear stress in descending aorta was reduced 5.1%). In no patient did transcatheter intervention improve LV function (e.g., stroke work and normalized stroke work were reduced by only 4.48% and 3.9%). CONCLUSIONS Transcatheter intervention which successfully relieves mild COA pressure gradients does not translate to decrease myocardial strain. The effects of intervention were determined to the greatest degree by ventricular-vascular coupling hemodynamics, and provide a novel valuable mechanism to evaluate patients with COA which may influence clinical practice. PMID:27659574</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20040110902&hterms=Automata&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3DAutomata','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20040110902&hterms=Automata&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3DAutomata"><span>Minnowbrook IV: 2003 Workshop on Transition and Unsteady Aspects of Turbomachinery Flows</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>LaGraff, John E. (Editor); Ashpis, David E.</p> <p>2004-01-01</p> <p>This Minnowbrook IV 2003 workshop on Transition and Unsteady Aspects of Turbomachinery Flows includes the following topics: 1) Current Issues in Unsteady Turbomachinery Flows; 2) Global Instability and Control of Low-Pressure Turbine Flows; 3) Influence of End Wall Leakage on Secondary Flow Development in Axial Turbines; 4) Active and Passive Flow Control on Low Pressure Turbine Airfoils; 5) Experimental and Numerical Investigation of Transitional Flows as Affected by Passing Wakes; 6) Effects of Freestream Turbulence on Turbine Blade Heat Transfer; 7) Bypass Transition Via Continuous Modes and Unsteady Effects on Film Cooling; 8) High Frequency Surface Heat Flux Imaging of Bypass Transition; 9) Skin Friction and Heat Flux Oscillations in Upstream Moving Wave Packets; 10) Transition Mechanisms and Use of Surface Roughness to Enhance the Benefits of Wake Passing in LP Turbines; 11) Transient Growth Approach to Roughness-Induced Transition; 12) Roughness- and Freestream-Turbulence-Induced Transient Growth as a Bypass Transition Mechanism; 13) Receptivity Calculations as a Means to Predicting Transition; 14) On Streamwise Vortices in a Curved Wall Jet and Their Effect on the Mean Flow; 15) Plasma Actuators for Separation Control of Low Pressure Turbine Blades; 16) Boundary-Layer Separation Control Under Low-Pressure-Turbine Conditions Using Glow-Discharge Plasma Actuators; 17) Control of Separation for Low Pressure Turbine Blades: Numerical Simulation; 18) Effects of Elevated Free-Stream Turbulence on Active Control of a Separation Bubble; 19) Wakes, Calming and Transition Under Strong Adverse Pressure Gradients; 20) Transitional Bubble in Periodic Flow Phase Shift; 21) Modelling Spots: The Calmed Region, Pressure Gradient Effects and Background; 22) Modeling of Unsteady Transitional Flow on Axial Compressor Blades; 23) Challenges in Predicting Component Efficiencies in Turbomachines With Low Reynolds Number Blading; 24) Observations on the Causal Relationship Between Blade Count and Developing Rotating Stall in a Four Stage Axial Compressor; 25) Experimental and Numerical Study of Non-Linear Interactions in Transonic Nozzle Flow; 26) Clocking Effects on a Modern Stage and One-Half Transonic Turbine; 27) DNS and LES of Transition on Turbine Blades; 28) The Use of Cellular Automata in Modeling the Transition; 29) Predicting Unsteady Buffet Onset Using RANS Solutions; 30) Transition Modelling With the SST Turbulence Model and an Intermittency Transport; and 31) Equation Workshop Summary Transcript</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19830044446&hterms=blood+glucose+level&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dblood%2Bglucose%2Blevel','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19830044446&hterms=blood+glucose+level&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dblood%2Bglucose%2Blevel"><span>Evaluation of a Reverse Gradient Garment for prevention of bed-rest deconditioning</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sandler, H.; Dolkas, D.; Newsom, B.; Webb, P.; Annis, J.; Pace, N.; Grunbaum, B. W.</p> <p>1983-01-01</p> <p>A Reverse Gradient Garment (RGG) was used to intermittently induce venous pooling in the extremities of a magnitude similar to that seen in going from a lying to standing position during the course of a 15-d period of horizontal bed rest. Venous pooling failed to improve bed-rest-induced losses in +2.5 Gz and +3.0 Gz centrifugation tolerance or to prevent increased heart-rate responses to lower-body negative pressure (LBNP). Four subjects served as controls, four were treated. Tests during the 7-d recovery period showed fluid/electrolyte and body composition values to have returned to pre-bed-rest levels with continued depression of acceleration tolerance times (56% decreased at +2.5 Gz and 74% decreased at +3.0 Gz compared to pre-bed-rest levels) and exaggerated blood insulin response on glucose tolerance testing (blood insulin for treated group increased 95% at 1 h before bed rest and 465% during recovery). This study demonstrates that the physiologic changes after bed rest persist for significant periods of time. Acceleration tolerance time proved to be a sensitive test for the deconditioning process.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/18585377','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/18585377"><span>Vitamin D(2) supplementation induces the development of aortic stenosis in rabbits: interactions with endothelial function and thioredoxin-interacting protein.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ngo, Doan T M; Stafford, Irene; Kelly, Darren J; Sverdlov, Aaron L; Wuttke, Ronald D; Weedon, Helen; Nightingale, Angus K; Rosenkranz, Anke C; Smith, Malcolm D; Chirkov, Yuliy Y; Kennedy, Jennifer A; Horowitz, John D</p> <p>2008-08-20</p> <p>Understanding of the pathophysiology of aortic valve stenosis (AVS) and finding potentially effective treatments are impeded by the lack of suitable AVS animal models. A previous study demonstrated the development of AVS in rabbits with vitamin D(2) and cholesterol supplementation without any hemodynamic changes in the cholesterol supplemented group alone. The current study aimed to determine whether AVS develops in an animal model with vitamin D(2) supplementation alone, and to explore pathophysiological mechanisms underlying this process. The effects of 8 weeks' treatment with vitamin D(2) alone (n=8) at 25,000 IU/4 days weekly on aortic valve structure and function were examined in male New Zealand white rabbits. Echocardiographic aortic valve backscatter (AV(BS)), transvalvular velocity, and transvalvular pressure gradient were utilized to quantitate changes in valve structure and function. Valvular histology/immunochemistry and function were examined after 8 weeks. Changes in valves were compared with those in endothelial function and in valvular measurement of thioredoxin-interacting protein (TXNIP), a marker/mediator of reactive oxygen species-induced oxidative stress. Vitamin D(2) treated rabbits developed AVS with increased AV(BS) (17.6+/-1.4 dB vs 6.7+/-0.8 dB, P<0.0001), increased transvalvular velocity and transvalvular pressure gradient (both P<0.01 via 2-way ANOVA) compared to the control group. There was associated valve calcification, lipid deposition and macrophage infiltration. Endothelial function was markedly impaired, and intravalvular TXNIP concentration increased. In this model, vitamin D(2) induces the development of AVS with histological features similar to those of early AVS in humans and associated endothelial dysfunction/redox stress. AVS development may result from the loss of nitric oxide suppression of TXNIP expression.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1985PhDT.......127H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1985PhDT.......127H"><span>Heat release effects in a turbulent, reacting shear layer</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hermanson, James Carl</p> <p></p> <p>The effects of heat release were studied in a planar, gaseous reacting mixing layer formed between free streams containing hydrogen and fluorine in inert diluents. Sufficiently high concentrations of reactants were employed to produce adiabatic flame temperature rises of up to 940 K (1240 K absolute). The Reynolds number at the measuring station, based on velocity difference, 1% temperature thickness and cold kinematic viscosity was approximately 6x10^4. The temperature field was measured with cold wire resistance thermometers and thermocouples. Flow visualization was accomplished by schlieren spark and motion picture photography. Mean velocity information was extracted from mean pitot probe dynamic pressure measurements.Though the displacement thickness of the layer, for zero streamwise pressure gradient, increased with increasing heat release, the actual growth rate of the layer did not increase, but instead decreased slightly. The overall entrainment into the layer was seen to be substantially reduced as a consequence of heat release. Calculations showed that the decrease in layer growth rate can be accounted for by a corresponding reduction in turbulent shear stress.The mean temperature rise profiles, normalized by the adiabatic flame temperature rise, were not greatly changed in shape by heat release. A small decrease in normalized mean temperature rise with heat release was observed. Large scale coherent structures were observed to persist at all levels of heat release in this investigation. The mean structure spacing decreased with increasing temperature. This decrease exceeded the rate of layer growth rate reduction, and suggests that the mechanisms of vortex amalgamation were, to some extent, inhibited by heat release.Imposition of a favorable pressure gradient resulted in additional thinning of the layer, and caused a slight increase in the mixing and amount of chemical product formation. The change in layer growth rate can be shown to be related to a change in free stream velocity ratio induced by pressure gradient.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25426597','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25426597"><span>Analysis of eddy currents induced by transverse and longitudinal gradient coils in different tungsten collimators geometries for SPECT/MRI integration.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Samoudi, Amine M; Van Audenhaege, Karen; Vermeeren, Günter; Poole, Michael; Tanghe, Emmeric; Martens, Luc; Van Holen, Roel; Joseph, Wout</p> <p>2015-12-01</p> <p>We investigated the temporal variation of the induced magnetic field due to the transverse and the longitudinal gradient coils in tungsten collimators arranged in hexagonal and pentagonal geometries with and without gaps between the collimators. We modeled x-, y-, and z-gradient coils and different arrangements of single-photon emission computed tomography (SPECT) collimators using FEKO, a three-dimensional electromagnetic simulation tool. A time analysis approach was used to generate the pulsed magnetic field gradient. The approach was validated with measurements using a 7T MRI scanner. Simulations showed an induced magnetic field representing 4.66% and 0.87% of the applied gradient field (gradient strength = 500 mT/m) for longitudinal and transverse gradient coils, respectively. These values can be reduced by 75% by adding gaps between the collimators for the pentagonal arrangement, bringing the maximum induced magnetic field to less than 2% of the applied gradient for all of the gradient coils. Characterization of the maximum induced magnetic field shows that by adding gaps between the collimators for an integrated SPECT/MRI system, eddy currents can be corrected by the MRI system to avoid artifact. The numerical model was validated and was proposed as a tool for studying the effect of a SPECT collimator within the MRI gradient coils. © 2014 Wiley Periodicals, Inc.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26774257','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26774257"><span>Severity assessment of intracranial large artery stenosis by pressure gradient measurements: A feasibility study.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Han, Yun-Fei; Liu, Wen-Hua; Chen, Xiang-Liang; Xiong, Yun-Yun; Yin, Qin-; Xu, Ge-Lin; Zhu, Wu-Sheng; Zhang, Ren-Liang; Ma, Min-Min; Li, Min-; Dai, Qi-Liang; Sun, Wen-; Liu, De-Zhi; Duan, Li-Hui; Liu, Xin-Feng</p> <p>2016-08-01</p> <p>Fractional flow reserve (FFR)-guided revascularization strategy is popular in coronary intervention. However, the feasibility of assessing stenotic severity in intracranial large arteries using pressure gradient measurements still remains unclear. Between March 2013 and May 2014, 12 consecutive patients with intracranial large artery stenosis (including intracranial internal carotid artery, middle cerebral M1 segment, intracranial vertebral artery, and basilar artery) were enrolled in this study. The trans-stenotic pressure gradient was measured before and/or after percutaneous transluminal angioplasty and stenting (PTAS), and was then compared with percent diameter stenosis. A Pd /Pa cut-off of ≤0.70 was used to guide stenting of hemodynamically significant stenoses. The device-related and procedure-related serious adverse events and recurrent cerebral ischemic events were recorded. The target vessel could be reached in all cases. No technical complications occurred due to the specific study protocol. Excellent pressure signals were obtained in all patients. For seven patients who performed PTAS, the mean pre-procedural pressure gradient decreased from 59.0 ± 17.2 to 13.3 ± 13.6 mm Hg after the procedure (P < 0.01). Only one patient who refused stenting experienced a TIA event in the ipsilateral MCA territory. No recurrent ischemic event was observed in other patients. Mean trans-stenotic pressure gradients can be safely and easily measured with a 0.014-inch fluid-filled guide wire in intracranial large arteries. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19950038023&hterms=convection+currents&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Dconvection%2Bcurrents','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19950038023&hterms=convection+currents&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Dconvection%2Bcurrents"><span>Generation of region 1 current by magnetospheric pressure gradients</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Yang, Y. S.; Spiro, R. W.; Wolf, R. A.</p> <p>1994-01-01</p> <p>The Rice Convection Model (RCM) is used to illustrate theoretical possibilities for generating region 1 Birkeland currents by pressure gradients on closed field lines in the Earth's magnetosphere. Inertial effects and viscous forces are neglected. The RCM is applied to idealized cases, to emphasize the basic physical ideas rather than realistic representation of the actual magnetosphere. Ionospheric conductance is taken to be uniform, and the simplest possible representations of the magnetospheric plasma are used. Three basic cases are considered: (1) the case of pure northward Interplanetary Magnetic Field (IMF), with cusp merging assumed to create new closed field lines near the nose of the magnetosphere, following the suggestion by Song and Russell (1992); (2) the case where Dungey-type reconnection occurs at the nose, but magnetosheath plasma somehow enters closed field lines on the dawnside and duskside of the merging region, causing a pressure-driven low-latitude boundary layer; and (3) the case where Dungey-type reconnection occurs at the nose, but region 1 currents flow on sunward drifting plasma sheet field lines. In case 1, currents of region 1 sense are generated by pressure gradients, but those currents do not supply the power for ionospheric convection. Results for case 2 suggest that pressure gradients at the inner edge of the low-latitude boundary layer might generate a large fraction of the region 1 Birkeland currents that drive magnetospheric convection. Results for case 3 indicate that pressure gradients in the plasma sheet could provide part of the region 1 current.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..1713547P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..1713547P"><span>The Phase Rule in a System Subject to a Pressure Gradient</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Podladchikov, Yuri; Connolly, James; Powell, Roger; Aardvark, Alberto</p> <p>2015-04-01</p> <p>It can be shown by diligent application of Lagrange's method of undetermined multipliers that the phase rule in a system subject to a pressure gradient is: � + 赑 ≥ ρ. We explore the consequence of this important relationship for natural systems.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19930092247','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19930092247"><span>Analysis and calculation by integral methods of laminar compressible boundary-layer with heat transfer and with and without pressure gradient</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Morduchow, Morris</p> <p>1955-01-01</p> <p>A survey of integral methods in laminar-boundary-layer analysis is first given. A simple and sufficiently accurate method for practical purposes of calculating the properties (including stability) of the laminar compressible boundary layer in an axial pressure gradient with heat transfer at the wall is presented. For flow over a flat plate, the method is applicable for an arbitrarily prescribed distribution of temperature along the surface and for any given constant Prandtl number close to unity. For flow in a pressure gradient, the method is based on a Prandtl number of unity and a uniform wall temperature. A simple and accurate method of determining the separation point in a compressible flow with an adverse pressure gradient over a surface at a given uniform wall temperature is developed. The analysis is based on an extension of the Karman-Pohlhausen method to the momentum and the thermal energy equations in conjunction with fourth- and especially higher degree velocity and stagnation-enthalpy profiles.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014PhDT.......181P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014PhDT.......181P"><span>Fluid Production Induced Stress Analysis Surrounding an Elliptic Fracture</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pandit, Harshad Rajendra</p> <p></p> <p>Hydraulic fracturing is an effective technique used in well stimulation to increase petroleum well production. A combination of multi-stage hydraulic fracturing and horizontal drilling has led to the recent boom in shale gas production which has changed the energy landscape of North America. During the fracking process, highly pressurized mixture of water and proppants (sand and chemicals) is injected into to a crack, which fractures the surrounding rock structure and proppants help in keeping the fracture open. Over a longer period, however, these fractures tend to close due to the difference between the compressive stress exerted by the reservoir on the fracture and the fluid pressure inside the fracture. During production, fluid pressure inside the fracture is reduced further which can accelerate the closure of a fracture. In this thesis, we study the stress distribution around a hydraulic fracture caused by fluid production. It is shown that fluid flow can induce a very high hoop stress near the fracture tip. As the pressure gradient increases stress concentration increases. If a fracture is very thin, the flow induced stress along the fracture decreases, but the stress concentration at the fracture tip increases and become unbounded for an infinitely thin fracture. The result from the present study can be used for studying the fracture closure problem, and ultimately this in turn can lead to the development of better proppants so that prolific well production can be sustained for a long period of time.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018PhRvE..97c3204S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018PhRvE..97c3204S"><span>Fully kinetic Biermann battery and associated generation of pressure anisotropy</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schoeffler, K. M.; Loureiro, N. F.; Silva, L. O.</p> <p>2018-03-01</p> <p>The dynamical evolution of a fully kinetic, collisionless system with imposed background density and temperature gradients is investigated analytically. The temperature gradient leads to the generation of temperature anisotropy, with the temperature along the gradient becoming larger than that in the direction perpendicular to it. This causes the system to become unstable to pressure anisotropy driven instabilities, dominantly to the electron Weibel instability. When both density and temperature gradients are present and nonparallel to each other, we obtain a Biermann-like linear-in-time magnetic field growth. Accompanying particle-in-cell numerical simulations are shown to confirm our analytical results.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMSA31A2569C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMSA31A2569C"><span>Ionospheric Scintillation Induced by Solar Wind Dynamic Pressure Enhancements in the Southern Hemisphere</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Coppeans, T.; Zou, S.; Weatherwax, A. T.; Coster, A. J.</p> <p>2017-12-01</p> <p>Ionospheric scintillation is the random fluctuation in GPS signal radio waves passing through the ionosphere, a phenomenon that can result in the loss of GPS tracking, but can also reveal information about plasma structures in the ionosphere. Sudden compression of the Earth's magnetosphere by a solar wind dynamic pressure enhancement can cause dramatic changes in the E and F region ionospheric plasma. In this study, we investigate the possible ionospheric scintillation induced by solar wind pressure enhancements using ground-based scintillation receivers located at the McMurdo station and the South Pole station in Antarctica. Various studies of scintillation effects have been carried out, mainly in the northern hemisphere, while the southern hemisphere remains less studied. A pool of storm sudden commencements occurring between Jan. 2011 and Dec. 2014 were sorted based on solar wind dynamic pressure enhancement, background conditions, availability of data, and magnitude of scintillation response. Among the 89 events examined, 14 of them exhibited enhanced scintillation and were selected for detailed examination. Besides the scintillation receivers, other datasets have also been used to carry out the above study, including field-aligned currents from AMPERE, and global GPS TEC. Effects of FACs and TEC/TEC gradients on the generation of these scintillations are studied.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26940013','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26940013"><span>Cardiomyopathy in children: Can we rely on echocardiographic tricuspid regurgitation gradient estimates of right ventricular and pulmonary arterial pressure?</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Lee, Simon; Lytrivi, Irene D; Roytman, Zhanna; Ko, Hyun-Sook Helen; Vinograd, Cheryl; Srivastava, Shubhika</p> <p>2016-10-01</p> <p>Introduction Agreement between echocardiography and right heart catheterisation-derived right ventricular systolic pressure is modest in the adult heart failure population, but is unknown in the paediatric cardiomyopathy population. All patients at a single centre from 2001 to 2012 with a diagnosis of cardiomyopathy who underwent echocardiography and catheterisation within 30 days were included in this study. The correlation between tricuspid regurgitation gradient and catheterisation-derived right ventricular systolic pressure and mean pulmonary artery pressure was determined. Agreement between echocardiography and catheterisation-derived right ventricular systolic pressure was assessed using Bland-Altman plots. Analysis was repeated for patients who underwent both procedures within 7 days. Haemodynamic data from those with poor agreement and good agreement between echocardiography and catheterisation were compared. A total of 37 patients who underwent 48 catheterisation procedures were included in our study. The median age was 11.8 (0.1-20.6 years) with 22 males (58% total). There was a modest correlation (r=0.65) between echocardiography and catheterisation-derived right ventricular systolic pressure, but agreement was poor. Agreement between tricuspid regurgitation gradient and right ventricular systolic pressure showed wide 95% limits of agreement. There was a modest correlation between the tricuspid regurgitation gradient and mean pulmonary artery pressure (r=0.6). Shorter time interval between the two studies did not improve agreement. Those with poor agreement between echocardiography and catheterisation had higher right heart pressures, but this difference became insignificant after accounting for right atrial pressure. Transthoracic echocardiography estimation of right ventricular systolic pressure shows modest correlation with right heart pressures, but has limited agreement and may underestimate the degree of pulmonary hypertension in paediatric cardiomyopathy patients.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li class="active"><span>12</span></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_12 --> <div id="page_13" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li class="active"><span>13</span></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="241"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19810012482','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19810012482"><span>The influence of a high pressure gradient on unsteady velocity perturbations in the case of a turbulent supersonic flow</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Dussauge, J. P.; Debieve, J. F.</p> <p>1980-01-01</p> <p>The amplification or reduction of unsteady velocity perturbations under the influence of strong flow acceleration or deceleration was studied. Supersonic flows with large velocity, pressure gradients, and the conditions in which the velocity fluctuations depend on the action of the average gradients of pressure and velocity rather than turbulence, are described. Results are analyzed statistically and interpreted as a return to laminar process. It is shown that this return to laminar implies negative values in the turbulence production terms for kinetic energy. A simple geometrical representation of the Reynolds stress production is given.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19930017365','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19930017365"><span>Incompressible spectral-element method: Derivation of equations</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Deanna, Russell G.</p> <p>1993-01-01</p> <p>A fractional-step splitting scheme breaks the full Navier-Stokes equations into explicit and implicit portions amenable to the calculus of variations. Beginning with the functional forms of the Poisson and Helmholtz equations, we substitute finite expansion series for the dependent variables and derive the matrix equations for the unknown expansion coefficients. This method employs a new splitting scheme which differs from conventional three-step (nonlinear, pressure, viscous) schemes. The nonlinear step appears in the conventional, explicit manner, the difference occurs in the pressure step. Instead of solving for the pressure gradient using the nonlinear velocity, we add the viscous portion of the Navier-Stokes equation from the previous time step to the velocity before solving for the pressure gradient. By combining this 'predicted' pressure gradient with the nonlinear velocity in an explicit term, and the Crank-Nicholson method for the viscous terms, we develop a Helmholtz equation for the final velocity.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70179130','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70179130"><span>Barrier island breach evolution: Alongshore transport and bay-ocean pressure gradient interactions</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Safak, Ilgar; Warner, John C.; List, Jeffrey</p> <p>2016-01-01</p> <p>Physical processes controlling repeated openings and closures of a barrier island breach between a bay and the open ocean are studied using aerial photographs and atmospheric and hydrodynamic observations. The breach site is located on Pea Island along the Outer Banks, separating Pamlico Sound from the Atlantic Ocean. Wind direction was a major control on the pressure gradients between the bay and the ocean to drive flows that initiate or maintain the breach opening. Alongshore sediment flux was found to be a major contributor to breach closure. During the analysis period from 2011 to 2016, three hurricanes had major impacts on the breach. First, Hurricane Irene opened the breach with wind-driven flow from bay to ocean in August 2011. Hurricane Sandy in October 2012 quadrupled the channel width from pressure gradient flows due to water levels that were first higher on the ocean side and then higher on the bay side. The breach closed sometime in Spring 2013, most likely due to an event associated with strong alongshore sediment flux but minimal ocean-bay pressure gradients. Then, in July 2014, Hurricane Arthur briefly opened the breach again from the bay side, in a similar fashion to Irene. In summary, opening and closure of breaches are shown to follow a dynamic and episodic balance between along-channel pressure gradient driven flows and alongshore sediment fluxes.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/20060004797','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20060004797"><span>Pressure Gradient Effects on Hypersonic Cavity Flow Heating</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Everhart, Joel L.; Alter, Stephen J.; Merski, N. Ronald; Wood, William A.; Prabhu, Ramadas K.</p> <p>2006-01-01</p> <p>The effect of a pressure gradient on the local heating disturbance of rectangular cavities tested at hypersonic freestream conditions has been globally assessed using the two-color phosphor thermography method. These experiments were conducted in the Langley 31-Inch Mach 10 Tunnel and were initiated in support of the Space Shuttle Return-To-Flight Program. Two blunted-nose test surface geometries were developed, including an expansion plate test surface with nearly constant negative pressure gradient and a flat plate surface with nearly zero pressure gradient. The test surface designs and flow characterizations were performed using two-dimensional laminar computational methods, while the experimental boundary layer state conditions were inferred using the measured heating distributions. Three-dimensional computational predictions of the entire model geometry were used as a check on the design process. Both open-flow and closed-flow cavities were tested on each test surface. The cavity design parameters and the test condition matrix were established using the computational predictions. Preliminary conclusions based on an analysis of only the cavity centerline data indicate that the presence of the pressure gradient did not alter the open cavity heating for laminar-entry/laminar-exit flows, but did raise the average floor heating for closed cavities. The results of these risk-reduction studies will be used to formulate a heating assessment of potential damage scenarios occurring during future Space Shuttle flights.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/20080013583','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20080013583"><span>Pressure Gradient Effects on Hypersonic Cavity Flow Heating</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Everhart, Joel L.; Alter, Stephen J.; Merski, N. Ronald; Wood, William A.; Prabhu, Ramdas K.</p> <p>2007-01-01</p> <p>The effect of a pressure gradient on the local heating disturbance of rectangular cavities tested at hypersonic freestream conditions has been globally assessed using the two-color phosphor thermography method. These experiments were conducted in the Langley 31-Inch Mach 10 Tunnel and were initiated in support of the Space Shuttle Return-To-Flight Program. Two blunted-nose test surface geometries were developed, including an expansion plate test surface with nearly constant negative pressure gradient and a flat plate surface with nearly zero pressure gradient. The test surface designs and flow characterizations were performed using two-dimensional laminar computational methods, while the experimental boundary layer state conditions were inferred using the measured heating distributions. Three-dimensional computational predictions of the entire model geometry were used as a check on the design process. Both open-flow and closed-flow cavities were tested on each test surface. The cavity design parameters and the test condition matrix were established using the computational predictions. Preliminary conclusions based on an analysis of only the cavity centerline data indicate that the presence of the pressure gradient did not alter the open cavity heating for laminar-entry/laminar-exit flows, but did raise the average floor heating for closed cavities. The results of these risk-reduction studies will be used to formulate a heating assessment of potential damage scenarios occurring during future Space Shuttle flights.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/1985089','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/1985089"><span>Effect of sodium chloride gradients on water flux in rat descending vasa recta.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Pallone, T L</p> <p>1991-01-01</p> <p>In the hydropenic kidney, volume efflux from descending vasa recta (DVR) occurs despite an intracapillary oncotic pressure that exceeds hydraulic pressure. That finding has been attributed to small solute gradients which may provide an additional osmotic driving force favoring water transport from DVR plasma to the papillary interstitium. To test this hypothesis, axial gradients of NaCl and urea in the papilla were eliminated by administration of furosemide and saline. DVR were then blocked with paraffin and microperfused at 10 nl/min with a buffer containing albumin, fluorescein isothiocyanate labeled dextran (FITC-Dx), 22Na, and NaCl in a concentration of 0 (hypotonic to the interstitium), 161 (isotonic) or 322 mM (hypertonic). Collectate was obtained from the perfused DVR by micropuncture and the collectate-to-perfusate ratios of FITC-Dx and 22Na were measured. A mathematical model was employed to determine DVR permeability (Ps) and reflection coefficient to NaCl (sigma NaCl). The rate of transport of water from the DVR lumen to the papillary interstitium was 2.8 +/- 0.3 (Nv = 22), -0.19 +/- 0.4 (Nv = 15), and -2.3 +/- 0.3 nl/min (Nv = 21) (mean +/- SE) when perfusate NaCl was 0, 161, or 322 mM, respectively (Nv = number of DVR perfused). The collectate-to-perfusate 22Na concentration ratios were 0.34 +/- 0.04, 0.36 +/- 0.04 and 0.37 +/- 0.03 for those groups, respectively. Based on these data, Ps is calculated to be 60.4 x 10(-5) +/- 4.0 x 10(-5) cm/s and sigma NaCl less than 0.05. The results of this study confirm that transcapillary NaCl concentrations gradients induce water movement across the wall of the DVR.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018MS%26E..297a2028S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018MS%26E..297a2028S"><span>Large Eddy Simulation of turbulence induced secondary flows in stationary and rotating straight square ducts</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sudjai, W.; Juntasaro, V.; Juttijudata, V.</p> <p>2018-01-01</p> <p>The accuracy of predicting turbulence induced secondary flows is crucially important in many industrial applications such as turbine blade internal cooling passages in a gas turbine and fuel rod bundles in a nuclear reactor. A straight square duct is popularly used to reveal the characteristic of turbulence induced secondary flows which consists of two counter rotating vortices distributed in each corner of the duct. For a rotating duct, the flow can be divided into the pressure side and the suction side. The turbulence induced secondary flows are converted to the Coriolis force driven two large circulations with a pair of additional vortices on the pressure wall due to the rotational effect. In this paper, the Large Eddy Simulation (LES) of turbulence induced secondary flows in a straight square duct is performed using the ANSYS FLUENT CFD software. A dynamic kinetic energy subgrid-scale model is used to describe the three-dimensional incompressible turbulent flows in the stationary and the rotating straight square ducts. The Reynolds number based on the friction velocity and the hydraulic diameter is 300 with the various rotation numbers for the rotating cases. The flow is assumed fully developed by imposing the constant pressure gradient in the streamwise direction. For the rotating cases, the rotational axis is placed perpendicular to the streamwise direction. The simulation results on the secondary flows and the turbulent statistics are found to be in good agreement with the available Direct Numerical Simulation (DNS) data. Finally, the details of the Coriolis effects are discussed.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1985asme.confU....M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1985asme.confU....M"><span>The influence of the radial pressure gradient on the blade root loss in an annular subsonic nozzle cascade</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Meng, D.; Weng, Z.; Xiang, Y.</p> <p>1985-09-01</p> <p>This paper presents a method for predicting the blade root loss in an annular nozzle cascade in which consideration is given to the influence of the radial pressure gradient (RPG) on it. The variation of blade root losses under different RPG is obtained experimentally, and finite element method is used to calculate the pressure distribution in the blade passage.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JGRA..119.1827C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JGRA..119.1827C"><span>The quiet evening auroral arc and the structure of the growth phase near-Earth plasma sheet</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Coroniti, F. V.; Pritchett, P. L.</p> <p>2014-03-01</p> <p>The plasma pressure and current configuration of the near-Earth plasma sheet that creates and sustains the quiet evening auroral arc during the growth phase of magnetospheric substorms is investigated. We propose that the quiet evening arc (QEA) connects to the thin near-Earth current sheet, which forms during the development of the growth phase enhancement of convection. The current sheet's large polarization electric fields are shielded from the ionosphere by an Inverted-V parallel potential drop, thereby producing the electron precipitation responsible for the arc's luminosity. The QEA is located in the plasma sheet region of maximal radial pressure gradient and, in the east-west direction, follows the vanishing of the approximately dawn-dusk-directed gradient or fold in the plasma pressure. In the evening sector, the boundary between the Region1 and Region 2 current systems occurs where the pressure maximizes (approximately radial gradient of the pressure vanishes) and where the approximately radial gradient of the magnetic flux tube volume also vanishes in an inflection region. The proposed intricate balance of plasma sheet pressure and currents may well be very sensitive to disruption by the arrival of equatorward traveling auroral streamers and their associated earthward traveling dipolarization fronts.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20040141463&hterms=left&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dleft','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20040141463&hterms=left&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dleft"><span>Doppler echo evaluation of pulmonary venous-left atrial pressure gradients: human and numerical model studies</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Firstenberg, M. S.; Greenberg, N. L.; Smedira, N. G.; Prior, D. L.; Scalia, G. M.; Thomas, J. D.; Garcia, M. J.</p> <p>2000-01-01</p> <p>The simplified Bernoulli equation relates fluid convective energy derived from flow velocities to a pressure gradient and is commonly used in clinical echocardiography to determine pressure differences across stenotic orifices. Its application to pulmonary venous flow has not been described in humans. Twelve patients undergoing cardiac surgery had simultaneous high-fidelity pulmonary venous and left atrial pressure measurements and pulmonary venous pulsed Doppler echocardiography performed. Convective gradients for the systolic (S), diastolic (D), and atrial reversal (AR) phases of pulmonary venous flow were determined using the simplified Bernoulli equation and correlated with measured actual pressure differences. A linear relationship was observed between the convective (y) and actual (x) pressure differences for the S (y = 0.23x + 0.0074, r = 0.82) and D (y = 0.22x + 0.092, r = 0.81) waves, but not for the AR wave (y = 0. 030x + 0.13, r = 0.10). Numerical modeling resulted in similar slopes for the S (y = 0.200x - 0.127, r = 0.97), D (y = 0.247x - 0. 354, r = 0.99), and AR (y = 0.087x - 0.083, r = 0.96) waves. Consistent with numerical modeling, the convective term strongly correlates with but significantly underestimates actual gradient because of large inertial forces.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011APS..DFD.LA046H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011APS..DFD.LA046H"><span>Pore-scale Analysis of the effects of Contact Angle Hysteresis on Blob Mobilization in a Pore Doublet</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hsu, Shao-Yiu; Glantz, Roland; Hilpert, Markus</p> <p>2011-11-01</p> <p>The mobilization of residual oil blobs in porous media is of major interest to the petroleum industry. We studied the Jamin effect, which hampers the blob mobilization, experimentally in a pore doublet model and explain the Jamin effect through contact angle hysteresis. A liquid blob was trapped in one of the tubes of the pore doublet model and then subjected to different pressure gradients. We measured the contact angles (in 2D and 3D) as well as the mean curvatures of the blob. Due to gravity effects and hysteresis, the contact angles of the blob were initially (zero pressure gradient) non-uniform and exhibited a pronounced altitude dependence. As the pressure gradient was increased, the contact angles became more uniform and the altitude dependence of the contact angle decreased. At the same time, the mean curvature of the drainage interface increased, and the mean curvature of the imbibition interface decreased. The pressure drops across the pore model, which we inferred with our theory from the measured contact angles and mean curvatures, were in line with the directly measured pressure data. We not only show that a trapped blob can sustain a finite pressure gradient but also develop methods to measure the contact angles and mean curvatures in 3D.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/10924058','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/10924058"><span>Doppler echo evaluation of pulmonary venous-left atrial pressure gradients: human and numerical model studies.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Firstenberg, M S; Greenberg, N L; Smedira, N G; Prior, D L; Scalia, G M; Thomas, J D; Garcia, M J</p> <p>2000-08-01</p> <p>The simplified Bernoulli equation relates fluid convective energy derived from flow velocities to a pressure gradient and is commonly used in clinical echocardiography to determine pressure differences across stenotic orifices. Its application to pulmonary venous flow has not been described in humans. Twelve patients undergoing cardiac surgery had simultaneous high-fidelity pulmonary venous and left atrial pressure measurements and pulmonary venous pulsed Doppler echocardiography performed. Convective gradients for the systolic (S), diastolic (D), and atrial reversal (AR) phases of pulmonary venous flow were determined using the simplified Bernoulli equation and correlated with measured actual pressure differences. A linear relationship was observed between the convective (y) and actual (x) pressure differences for the S (y = 0.23x + 0.0074, r = 0.82) and D (y = 0.22x + 0.092, r = 0.81) waves, but not for the AR wave (y = 0. 030x + 0.13, r = 0.10). Numerical modeling resulted in similar slopes for the S (y = 0.200x - 0.127, r = 0.97), D (y = 0.247x - 0. 354, r = 0.99), and AR (y = 0.087x - 0.083, r = 0.96) waves. Consistent with numerical modeling, the convective term strongly correlates with but significantly underestimates actual gradient because of large inertial forces.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5362907','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5362907"><span>“Breakthrough” osmosis and unusually high power densities in Pressure-Retarded Osmosis in non-ideally semi-permeable supported membranes</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Yaroshchuk, Andriy</p> <p>2017-01-01</p> <p>Osmosis is the movement of solvent across a membrane induced by a solute-concentration gradient. It is very important for cell biology. Recently, it has started finding technological applications in the emerging processes of Forward Osmosis and Pressure-Retarded Osmosis. They use ultrathin and dense membranes supported mechanically by much thicker porous layers. Until now, these processes have been modelled by assuming the membrane to be ideally-semipermeable. We show theoretically that allowing for even minor deviations from ideal semipermeability to solvent can give rise to a previously overlooked mode of “breakthrough” osmosis. Here the rate of osmosis is very large (compared to the conventional mode) and practically unaffected by the so-called Internal Concentration Polarization. In Pressure-Retarded Osmosis, the power densities can easily exceed the conventional mode by one order of magnitude. Much more robust support layers can be used, which is an important technical advantage (reduced membrane damage) in Pressure-Retarded Osmosis. PMID:28332607</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20060041530&hterms=torque&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dtorque','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20060041530&hterms=torque&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dtorque"><span>A General Pressure Gradient Formulation for Ocean Models, Part 1: Scheme Design and Diagnostic Analysis, Part II: Energy, Momentum, and Bottom Torque Consistency</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Song, Y. T.</p> <p>1998-01-01</p> <p>A Jacobian formulation of the pressure gradient force for use in models with topography following coordinates is proposed. It can be used in conjunction with any vertical coordinate system and is easily implemented.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26771916','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26771916"><span>Patient-specific interface pressure case study at transradial prosthetic socket: comparison trials between ICRC polypropylene socket and air splint socket.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Abd Razak, Nasrul A; Abu Osman, Noor A; Ali, Sadeeq A; Gholizadeh, Hossein</p> <p>2016-01-15</p> <p>While considering how important the interface between the amputees with the prostheses socket, we have carried out research to compare the gradient pressure occur at the interface socket that may lead to the discomforting effects to the user using common ICRC polypropylene socket and air splint socket. Not Applicable SETTING: Not Applicable POPULATION: The subject was a 23 year old who suffered a traumatic defect on the right arm caused by higher electrical volt. F-Socket sensors have been used to measure dynamic socket interface pressure for the transradial amputee wearer during static and dynamic movements. The printed circuit with a thickness of 0.18 mm is equipped between the socket and the surface of the residual limb. Two F-Socket sensor is required to cover the entire socket surface attached to the residual limb. The average of 10 trials made on prosthetic user using both type of sockets for static and dynamic movements was recorded. The pressure gradient shows that the circumference of the socket interface for the ICRC polypropylene socket gives the most pressure distributions to the amputees compared to the pressure gradient for the air splint socket. The pressure gradient for ICRC socket increased consistently when the user makes movements while for the air splint socket remain constantly. The specific interface pressure occur at the socket interface help in determine the comfort and pain of the socket design and improve the correlation between the user and the prosthesis.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017OcMod.116....1E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017OcMod.116....1E"><span>High-order accurate finite-volume formulations for the pressure gradient force in layered ocean models</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Engwirda, Darren; Kelley, Maxwell; Marshall, John</p> <p>2017-08-01</p> <p>Discretisation of the horizontal pressure gradient force in layered ocean models is a challenging task, with non-trivial interactions between the thermodynamics of the fluid and the geometry of the layers often leading to numerical difficulties. We present two new finite-volume schemes for the pressure gradient operator designed to address these issues. In each case, the horizontal acceleration is computed as an integration of the contact pressure force that acts along the perimeter of an associated momentum control-volume. A pair of new schemes are developed by exploring different control-volume geometries. Non-linearities in the underlying equation-of-state definitions and thermodynamic profiles are treated using a high-order accurate numerical integration framework, designed to preserve hydrostatic balance in a non-linear manner. Numerical experiments show that the new methods achieve high levels of consistency, maintaining hydrostatic and thermobaric equilibrium in the presence of strongly-sloping layer geometries, non-linear equations-of-state and non-uniform vertical stratification profiles. These results suggest that the new pressure gradient formulations may be appropriate for general circulation models that employ hybrid vertical coordinates and/or terrain-following representations.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003SPIE.5031...22Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003SPIE.5031...22Y"><span>Estimation of pressure gradients at renal artery stenoses</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yim, Peter J.; Cebral, Juan R.; Weaver, Ashley; Lutz, Robert J.; Vasbinder, G. Boudewijn C.</p> <p>2003-05-01</p> <p>Atherosclerotic disease of the renal artery can reduce the blood flow leading to renovascular hypertension and ischemic nephopathy. The kidney responds to a decrease in blood flow by activation of the renin-angiotensin system that increases blood pressure and can result in severe hypertension. Percutaneous translumenal angioplasty (PTA) may be indicated for treatment of renovascular hypertension (RVH). However, direct measurement of renal artery caliber and degree of stenosis has only moderate specificity for detection of RVH. A confounding factor in assessment of the proximal renal artery is that diffuse atherosclerotic disease of the distal branches of the renal artery can produce the same effect on blood-flow as atherosclerotic disease of the proximal renal artery. A methodology is proposed for estimation of pressure gradients at renal artery stenoses from magnetic resonance imaging that could improve the evaluation of renal artery disease. In the proposed methodology, pressure gradients are estimated using computational fluid dynamics (CFD) modeling. Realistic CFD models are constructed from images of vessel shape and measurements of blood-flow rates which are available from magnetic resonance angiography (MRA) and phase-contrast magnetic resonance (MR) imaging respectively. CFD measurement of renal artery pressure gradients has been validated in a physical flow-through model.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70025703','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70025703"><span>Temperature-pressure conditions in coalbed methane reservoirs of the Black Warrior basin: Implications for carbon sequestration and enhanced coalbed methane recovery</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Pashin, J.C.; McIntyre, M.R.</p> <p>2003-01-01</p> <p>Sorption of gas onto coal is sensitive to pressure and temperature, and carbon dioxide can be a potentially volatile supercritical fluid in coalbed methane reservoirs. More than 5000 wells have been drilled in the coalbed methane fields of the Black Warrior basin in west-central Alabama, and the hydrologic and geothermic information from geophysical well logs provides a robust database that can be used to assess the potential for carbon sequestration in coal-bearing strata.Reservoir temperature within the coalbed methane target zone generally ranges from 80 to 125 ??F (27-52 ??C), and geothermal gradient ranges from 6.0 to 19.9 ??F/1000 ft (10.9-36.2 ??C/km). Geothermal gradient data have a strong central tendency about a mean of 9.0 ??F/1000 ft (16.4 ??C/km). Hydrostatic pressure gradients in the coalbed methane fields range from normal (0.43 psi/ft) to extremely underpressured (<0.05 psi/ft). Pressure-depth plots establish a bimodal regime in which 70% of the wells have pressure gradients greater than 0.30 psi/ft, and 20% have pressure gradients lower than 0.10 psi/ft. Pockets of underpressure are developed around deep longwall coal mines and in areas distal to the main hydrologic recharge zone, which is developed in structurally upturned strata along the southeastern margin of the basin.Geothermal gradients within the coalbed methane fields are high enough that reservoirs never cross the gas-liquid condensation line for carbon dioxide. However, reservoirs have potential for supercritical fluid conditions beyond a depth of 2480 ft (756 m) under normally pressured conditions. All target coal beds are subcritically pressured in the northeastern half of the coalbed methane exploration fairway, whereas those same beds were in the supercritical phase window prior to gas production in the southwestern half of the fairway. Although mature reservoirs are dewatered and thus are in the carbon dioxide gas window, supercritical conditions may develop as reservoirs equilibrate toward a normal hydrostatic pressure gradient after abandonment. Coal can hold large quantities of carbon dioxide under supercritical conditions, and supercritical isotherms indicate non-Langmiur conditions under which some carbon dioxide may remain mobile in coal or may react with formation fluids or minerals. Hence, carbon sequestration and enhanced coalbed methane recovery show great promise in subcritical reservoirs, and additional research is required to assess the behavior of carbon dioxide in coal under supercritical conditions where additional sequestration capacity may exist. ?? 2003 Elsevier Science B.V. All rights reserved.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AIPC.1786s0002P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AIPC.1786s0002P"><span>Thermal lift generation and drag reduction in rarefied aerodynamics</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pekardan, Cem; Alexeenko, Alina</p> <p>2016-11-01</p> <p>With the advent of the new technologies in low pressure environments such as Hyperloop and helicopters designed for Martian applications, understanding the aerodynamic behavior of airfoils in rarefied environments are becoming more crucial. In this paper, verification of rarefied ES-BGK solver and ideas such as prediction of the thermally induced lift and drag reduction in rarefied aerodynamics are investigated. Validation of the rarefied ES-BGK solver with Runge-Kutta discontinous Galerkin method with experiments in transonic regime with a Reynolds number of 73 showed that ES-BGK solver is the most suitable solver in near slip transonic regime. For the quantification of lift generation, A NACA 0012 airfoil is studied with a high temperature surface on the bottom for the lift creation for different Knudsen numbers. It was seen that for lower velocities, continuum solver under predicts the lift generation when the Knudsen number is 0.00129 due to local velocity gradients reaching slip regime although lift coefficient is higher with the Boltzmann ES-BGK solutions. In the second part, the feasibility of using thermal transpiration for drag reduction is studied. Initial study in drag reduction includes an application of a thermal gradient at the upper surface of a NACA 0012 airfoil near trailing edge at a 12-degree angle of attack and 5 Pa pressure. It was seen that drag is reduced by 4 percent and vortex shedding frequency is reduced due to asymmetry introduced in the flow due to temperature gradient causing reverse flow due to thermal transpiration phenomena.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23446417','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23446417"><span>Giant osmotic energy conversion measured in a single transmembrane boron nitride nanotube.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Siria, Alessandro; Poncharal, Philippe; Biance, Anne-Laure; Fulcrand, Rémy; Blase, Xavier; Purcell, Stephen T; Bocquet, Lydéric</p> <p>2013-02-28</p> <p>New models of fluid transport are expected to emerge from the confinement of liquids at the nanoscale, with potential applications in ultrafiltration, desalination and energy conversion. Nevertheless, advancing our fundamental understanding of fluid transport on the smallest scales requires mass and ion dynamics to be ultimately characterized across an individual channel to avoid averaging over many pores. A major challenge for nanofluidics thus lies in building distinct and well-controlled nanochannels, amenable to the systematic exploration of their properties. Here we describe the fabrication and use of a hierarchical nanofluidic device made of a boron nitride nanotube that pierces an ultrathin membrane and connects two fluid reservoirs. Such a transmembrane geometry allows the detailed study of fluidic transport through a single nanotube under diverse forces, including electric fields, pressure drops and chemical gradients. Using this device, we discover very large, osmotically induced electric currents generated by salinity gradients, exceeding by two orders of magnitude their pressure-driven counterpart. We show that this result originates in the anomalously high surface charge carried by the nanotube's internal surface in water at large pH, which we independently quantify in conductance measurements. The nano-assembly route using nanostructures as building blocks opens the way to studying fluid, ionic and molecule transport on the nanoscale, and may lead to biomimetic functionalities. Our results furthermore suggest that boron nitride nanotubes could be used as membranes for osmotic power harvesting under salinity gradients.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li class="active"><span>13</span></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_13 --> <div id="page_14" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li class="active"><span>14</span></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="261"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/20040083982','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20040083982"><span>Numerical Modeling, Thermomechanical Testing, and NDE Procedures for Prediction of Microcracking Induced Permeability of Cryogenic Composites</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Noh, Jae; Whitcomb, John; Oh, Bongtaek; Lagoudas, Dimitris; Maslov, Konstatin; Ganpatyre, Atul; Kinra, Vikram</p> <p>2003-01-01</p> <p>Reusable Space Vehicles will include light cryogenic composite fuel tanks that must not leak excessively even after multiple launches. Damage in cryogenic composite fuel tanks induced during manufacturing and advanced by thermomechanical cycling can accelerate leakage of the propellant. Whether the leakage exceeds tolerable levels depends on many factors, including pressure gradients, microcrack density, other damage such as delamination, connectivity of the cracks, residual stresses from manufacture, service-induced stresses from thermal and mechanical loads, and composite lay-up. Although it is critical to experimentally characterize permeability during various thermal and mechanical load histories, optimal design depends on having analytical models that can predict the effect of various parameters on performance. Our broad goal is to develop such models that are experimentally validated by destructive and non-destructive evaluation means.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28292038','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28292038"><span>[Discordance between mitral valve area (MVA) and pressure gradient in patients with mitral valve stenosis: mean transmitral valve gradient is a severity index or a tolerance index of severity of mitralss valve stenosis?</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Najih, Hayat; Arous, Salim; Laarje, Aziza; Baghdadi, Dalila; Benouna, Mohamed Ghali; Azzouzi, Leila; Habbal, Rachida</p> <p>2016-01-01</p> <p>Rheumatic mitral valve stenosis (MVS) is a frequent valvulopathy in developing countries. However, industrialized countries have seen the emergence of new etiologies of MVS in recent years, in particular drug-induced and/or toxic valvular regurgitation and stenosis. For this reason, the echocardiographic assessment of MVS and especially the definition of objective diagnostic criteria for severe MVS remains relevant. The objectives are: to determine whether there is a direct causal link between mean transmitral gradient (MTG) and severity of MVS in patients with severe MVS or true severe MVS (primary criterion); to analyze different parameters determining mean transmitral gradient (MTG) (secondary criterion). We conducted a single-center cross-sectional study including all patients with severe or true severe MVS admitted to the Department of Cardiology, University Hospital Ibn Rushd, Casablanca over a period of one year (January 2014-December 2014). We analyzed data from two groups of patients separately: those with a mean transmitral gradient<10 mmHg (group 1) and those with a gradient>10mmHg (group 2). 50 patients with severe or true severe MVS have been included in the study. The average age of our patients was 41.7 years with a female predominance (sex ratio 0,25). 64% of patients had severe MVS and 36% of patients had true severe MVS. 52% (26 patients) had MTG < 10mmHg and 48% (24 patients) had mean gradient> 10mmHg, suggesting no direct correlation between the severity of MVS and MTG (Pearson's correlation coefficient R: -0,137). With regards to dyspnea, 80% of patients of group 1 had stage II NYHA dyspnea (classification system) and 70% of patients of group 2 had stage III NYHA dyspnea (41%) or IV NYHA dyspnea (29%), which means that there was a significant correlation between MTG and the severity of dyspnea (R: 0,586 and p: 0,001). The analytical study of heart rate and the presence of cardiac decompensation compared with mean gradient transmitral showed a significant correlation. Indeed, among patients in group 1, 96% had HR between 60 and 100 bpm and no patient had decompensated heart failure. In group 2, 54% (13 patients) had a HR> 100 bpm and 7 of them (53%) had left decompensated heart failure. The analysis of systolic pulmonary artery pressure conducted in both groups of the study revealed the existence of a statistically significant correlation (R: 0,518 and P: 0,001) between systolic pulmonary artery pressure (SPAP) and MTG. Ventricular rhythm regularity and right ventricular function were not correlated with MTG (R: 0,038 and R: - 0,002 respectively). Mean transmitral gradient is a good indicator of mitral stenosis tolerance but it imperfectly reflects mitral stenosis severity as this depends on several hemodynamic parameters. True severe mitral stenosis may have mean transmitral gradient < 10mmHg, that is why the value of MTG should never be interpreted as single value.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19970000448','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19970000448"><span>A Theoretical Study of Remobilizing Surfactant Retarded Fluid Particle Interfaces</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Wang, Yanping; Papageorgiou, Dimitri; Maldarelli, Charles</p> <p>1996-01-01</p> <p>Microgravity processes must rely on mechanisms other than bouyancy to move bubbles or droplets from one region to another in a continuous liquid phase. One suggested method is thermocapillary migration in which a temperature gradient is applied to the continuous phase. When a fluid particle contacts this gradient, one pole of the particle becomes warmer than the opposing pole. The interfacial tension between the drop or bubble phase and the continuous phase usually decreases with temperature. Thus the cooler pole is of higher interfacial tension than the warmer pole, and the interface is tugged in the direction of the cooler end. This thermocapillary or thermally induced Marangoni surface stress causes a fluid streaming in the continuous phase from which develops a viscous shear traction and pressure gradient which together propel the particle in the direction of the warmer fluid. In this paper, we provide a theoretical basis for remobilizing surfactant retarded fluid particle interfaces in an effort to make viable the use of thermocapillary migrations for the management of bubbles and drops in microgravity,</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19920030325&hterms=geothermal+gradient&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dgeothermal%2Bgradient','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19920030325&hterms=geothermal+gradient&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dgeothermal%2Bgradient"><span>The role of thermal vapor diffusion in the subsurface hydrologic evolution of Mars</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Clifford, Stephen M.</p> <p>1991-01-01</p> <p>The hydrologic response of groundwater to the thermal evolution of the early martian crust is considered. When a temperature gradient is present in a moist porous medium, it gives rise to a vapor-pressure gradient that drives the diffusion of water vapor from regions of high to low temperature. By this process, a geothermal gradient as small as 15 K/km could drive the vertical transport of 1 km of water to the freezing front at the base of the martian crysophere every 10 exp 6-10 exp 7 years, or the equivalent of about 100-1000 km of water over the course of martian geologic history. Models of the thermal history of Mars suggest that this thermally-driven vapor flux may have been as much as 3-5 times greater in the past. The magnitude of this transport suggests that the process of geothermally-induced vapor diffusion may have played a critical role in the initial emplacement of ground ice and the subsequent geomorphic and geochemical evolution of the martian crust.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.H23D1727R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.H23D1727R"><span>Variability in benthic exchange rate, depth, and residence time beneath a shallow coastal estuary</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Russoniello, C. J.; Michael, H. A.; Heiss, J.</p> <p>2017-12-01</p> <p>Hydrodynamically-driven exchange of water between the water column and shallow seabed aquifer, benthic exchange, is a significant and dynamic component of coastal and estuarine fluid budgets, but wave-induced benthic exchange has not been measured in the field. Mixing between surface water and groundwater solutes promotes ecologically important chemical reactions, so quantifying benthic exchange rates, depths, and residence times, constrains estimates of coastal chemical cycling. In this study, we present the first field-based direct measurements of wave-induced exchange and compare it to exchange induced by the other primary drivers of exchange - tides, and currents. We deployed instruments in a shallow estuary to measure benthic exchange and temporal variability over an 11-day period. Differential pressure sensors recorded pressure gradients across the seabed, and up-and down-looking ADCPs recorded currents and pressures from which wave parameters, surface-water currents, and water depth were determined. Wave-induced exchange was calculated directly from 1) differential pressure measurements, and indirectly with an analytical solution based on wave parameters from 2) ADCP and 3) weather station data. Groundwater flow models were used to assess the effects of aquifer properties on benthic exchange depth and residence time. Benthic exchange driven by tidal pumping or current-bedform interaction was calculated from tidal stage variation and from ADCP-measured currents at the bed, respectively. Waves were the primary benthic exchange driver (average = 20.0 cm/d, maximum = 92.3 cm/d) during the measurement period. Benthic exchange due to tides (average = 3.7 cm/d) and current-bedform interaction (average = 6.5x10-2 cm/d) was much lower. Wave-induced exchange calculated from pressure measurements and ADCP-measured wave parameters matched well, but wind-based rates underestimated wave energy and exchange. Groundwater models showed that residence time and depth increased in high-permeability, incompressible aquifers, and exchange rates increased in low-permeability, compressible aquifers. These findings support and extend the utility of existing wave-induced exchange solutions and will help managers assess the importance of benthic exchange on coastal chemical cycling.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010EGUGA..1215286L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010EGUGA..1215286L"><span>Effects Of Bedrock Shape And Hillslope Gradient On The Pore-Water Pressure Development: Implication For Slope Stability</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lanni, Cristiano; McDonnell, Jeff</p> <p>2010-05-01</p> <p>Shallow Landslides are one of the most important causes of loss of human life and socio-economic damage related to the hydro-geological risk issues. The danger of these phenomena is related to their speed of development, the diffculty of foreseeing their location, and the high density of individual phenomena, whose downhill trajectories have a relevant probability of interfering with urbanized areas. Research activity on precipitation-induced landslides has focused mainly on developing predictive understanding of where and when landslides are likely to occur. Nevertheless, some major aspects that may be related to activation of landslides have been poorly investigated. For instance, landslide susceptibility zones are generally predicted assuming constant thickness of soil over an impervious bedrock layer. Nevertheless, recent studies showed subsurface topography could be a first order control for subsurface water-flow dynamics, because of the effects of its own irregular shape. Tromp-van Meerveld and McDonnell (2006) argued that connectivity of patches of transient saturation were a necessary prerequisite for exceeding the rainfall threshold necessary to drive lateral flow. Connectivity - "how the hillslope architecture controls the filling and spilling of isolated patches of saturation" (Hopp and McDonnell, 2009) - appears to be a possible unifying concept and theoretical platform for moving hillslope and watershed hydrology forward. Connectivity could also have important implications on triggering of shallow landslides, because the particular shape of bedrock may limit the water-flow downhill. Here we present a number of virtual numerical experiments performed to investigate the role of bedrock shape and hillslope gradient on pore-water pressure development. On this purpose, our test is represented by the subsurface topography of the Panola Experiment Hillslope (PEH). That is because scientific literature on PEH provides substantial documentation about the role of bedrock layer on subsurface water-flow dynamics. We also exploit the concept of Downslope Index (DWI) (Hjerdt et al., 2004) and Upslope Contributing Area (UCA) as indicators of the areas more susceptible to landslide. The results indicate that bedrock shape influences the max pore-water pressure, even with different hillslope gradients; meanwhile, hillslope gradient affects the persistence-time of the max pore-water pressure. Moreover, results suggest DWI as an useful index to improve the capability of the very-used SHALSTAB model to assess for landslide susceptibility areas.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19790011874','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19790011874"><span>Wake curvature and trailing edge interaction effects in viscous flow over airfoils</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Melnik, R. E.</p> <p>1979-01-01</p> <p>A theory developed for analyzing viscous flows over airfoils at high Reynolds numbers is described. The theory includes a complete treatment of viscous interaction effects induced by the curved wake behind the airfoil and accounts for normal pressure gradients across the boundary layer in the trailing edge region. A brief description of a computer code that was developed to solve the extended viscous interaction equations is given. Comparisons of the theoretical results with wind tunnel data for two rear loaded airfoils at supercritical conditions are presented.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA191294','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA191294"><span>Oakland Harbor. Deep-Draft Navigation Improvements. Design Memorandum Number 1, General Design and Final Supplement 1 to the Environmental Impact Statement, Alameda County, California.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.dtic.mil/">DTIC Science & Technology</a></p> <p></p> <p>1988-03-01</p> <p>presentations to the Panal , the Department of the Navy’s restrictions on submarine operating areas were mentioned, iniating that the Nxwy opposed...impacts of dredged material disposal and/or till gaps in data. Panal .fUtrugtgra and Oranh~AtaoAin The panel is comprised of five representatives from 2A...riverine inflow is the low and prevailing winds from the west or northwest are augmented by daily pressure gradient induced movement of air due to solar</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018NucFu..58d6006S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018NucFu..58d6006S"><span>On the physics of the pressure and temperature gradients in the edge of tokamak plasmas</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stacey, Weston M.</p> <p>2018-04-01</p> <p>An extended plasma fluid theory including atomic physics, radiation, electromagnetic and themodynamic forces, external sources of particles, momentum and energy, and kinetic ion orbit loss is employed to derive theoretical expressions that display the role of the various factors involved in the determination of the pressure and temperature gradients in the edge of tokamak plasmas. Calculations for current experiments are presented to illustrate the magnitudes of various effects including strong radiative and atomic physics edge cooling effects and strong reduction in ion particle and energy fluxes due to ion orbit loss in the plasma edge. An important new insight is the strong relation between rotation and the edge pressure gradient.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19720007523','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19720007523"><span>Calculation of turbulent boundary layers with heat transfer and pressure gradient utilizing a compressibility transformation. Part 3: Computer program manual</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Schneider, J.; Boccio, J.</p> <p>1972-01-01</p> <p>A computer program is described capable of determining the properties of a compressible turbulent boundary layer with pressure gradient and heat transfer. The program treats the two-dimensional problem assuming perfect gas and Crocco integral energy solution. A compressibility transformation is applied to the equation for the conservation of mass and momentum, which relates this flow to a low speed constant property flow with simultaneous mass transfer and pressure gradient. The resulting system of describing equations consists of eight ordinary differential equations which are solved numerically. For Part 1, see N72-12226; for Part 2, see N72-15264.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/20040086862','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20040086862"><span>Computation of Turbulent Wake Flows in Variable Pressure Gradient</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Duquesne, N.; Carlson, J. R.; Rumsey, C. L.; Gatski, T. B.</p> <p>1999-01-01</p> <p>Transport aircraft performance is strongly influenced by the effectiveness of high-lift systems. Developing wakes generated by the airfoil elements are subjected to strong pressure gradients and can thicken very rapidly, limiting maximum lift. This paper focuses on the effects of various pressure gradients on developing symmetric wakes and on the ability of a linear eddy viscosity model and a non-linear explicit algebraic stress model to accurately predict their downstream evolution. In order to reduce the uncertainties arising from numerical issues when assessing the performance of turbulence models, three different numerical codes with the same turbulence models are used. Results are compared to available experimental data to assess the accuracy of the computational results.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19930092289','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19930092289"><span>Similar solutions for the compressible laminar boundary layer with heat transfer and pressure gradient</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Cohen, Clarence B; Reshotko, Eli</p> <p>1956-01-01</p> <p>Stewartson's transformation is applied to the laminar compressible boundary-layer equations and the requirement of similarity is introduced, resulting in a set of ordinary nonlinear differential equations previously quoted by Stewartson, but unsolved. The requirements of the system are Prandtl number of 1.0, linear viscosity-temperature relation across the boundary layer, an isothermal surface, and the particular distributions of free-stream velocity consistent with similar solutions. This system admits axial pressure gradients of arbitrary magnitude, heat flux normal to the surface, and arbitrary Mach numbers. The system of differential equations is transformed to integral system, with the velocity ratio as the independent variable. For this system, solutions are found by digital computation for pressure gradients varying from that causing separation to the infinitely favorable gradient and for wall temperatures from absolute zero to twice the free-stream stagnation temperature. Some solutions for separated flows are also presented.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/20040027041','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20040027041"><span>Computational Study of Axisymmetric Off-Design Nozzle Flows</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>DalBello, Teryn; Georgiadis, Nicholas; Yoder, Dennis; Keith, Theo</p> <p>2003-01-01</p> <p>Computational Fluid Dynamics (CFD) analyses of axisymmetric circular-arc boattail nozzles operating off-design at transonic Mach numbers have been completed. These computations span the very difficult transonic flight regime with shock-induced separations and strong adverse pressure gradients. External afterbody and internal nozzle pressure distributions computed with the Wind code are compared with experimental data. A range of turbulence models were examined, including the Explicit Algebraic Stress model. Computations have been completed at freestream Mach numbers of 0.9 and 1.2, and nozzle pressure ratios (NPR) of 4 and 6. Calculations completed with variable time-stepping (steady-state) did not converge to a true steady-state solution. Calculations obtained using constant timestepping (timeaccurate) indicate less variations in flow properties compared with steady-state solutions. This failure to converge to a steady-state solution was the result of using variable time-stepping with large-scale separations present in the flow. Nevertheless, time-averaged boattail surface pressure coefficient and internal nozzle pressures show reasonable agreement with experimental data. The SST turbulence model demonstrates the best overall agreement with experimental data.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29167331','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29167331"><span>Spaceflight-Induced Intracranial Hypertension and Visual Impairment: Pathophysiology and Countermeasures.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Zhang, Li-Fan; Hargens, Alan R</p> <p>2018-01-01</p> <p>Visual impairment intracranial pressure (VIIP) syndrome is considered an unexplained major risk for future long-duration spaceflight. NASA recently redefined this syndrome as Spaceflight-Associated Neuro-ocular Syndrome (SANS). Evidence thus reviewed supports that chronic, mildly elevated intracranial pressure (ICP) in space (as opposed to more variable ICP with posture and activity on Earth) is largely accounted for by loss of hydrostatic pressures and altered hemodynamics in the intracranial circulation and the cerebrospinal fluid system. In space, an elevated pressure gradient across the lamina cribrosa, caused by a chronic but mildly elevated ICP, likely elicits adaptations of multiple structures and fluid systems in the eye which manifest themselves as the VIIP syndrome. A chronic mismatch between ICP and intraocular pressure (IOP) in space may acclimate the optic nerve head, lamina cribrosa, and optic nerve subarachnoid space to a condition that is maladaptive to Earth, all contributing to the pathogenesis of space VIIP syndrome. Relevant findings help to evaluate whether artificial gravity is an appropriate countermeasure to prevent this seemingly adverse effect of long-duration spaceflight. Copyright © 2018 the American Physiological Society.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/biblio/4137844','DOE-PATENT-XML'); return false;" href="https://www.osti.gov/biblio/4137844"><span>ARC DISCHARGE AND METHOD OF PRODUCING THE SAME</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/doepatents">DOEpatents</a></p> <p>Neidigh, R.V.</p> <p>1960-03-15</p> <p>A device for producing an energetic gas arc discharge between spaced electrodes in an evacuated chamber and within a magnetic field is described. Gas is fed into the arc in a direction normal to a refluxing stream of electrons and at a pressure higher than the pressure within the chamber to establish a pressure gradient along the arc discharge formed between the electrodes. This pressure gradient establishes rotating, time varying, radial electrical fields in the volume surroundimg the discharge, causing the discharge to rotate about the arc center line.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018PhPl...25f2102V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018PhPl...25f2102V"><span>Diffusion-driven fluid dynamics in ideal gases and plasmas</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vold, E. L.; Yin, L.; Taitano, W.; Molvig, K.; Albright, B. J.</p> <p>2018-06-01</p> <p>The classical transport theory based on Chapman-Enskog methods provides self-consistent approximations for the kinetic flux of mass, heat, and momentum in a fluid limit characterized with a small Knudsen number. The species mass fluxes relative to the center of mass, or "diffusive fluxes," are expressed as functions of known gradient quantities with kinetic coefficients evaluated using similar analyses for mixtures of gases or plasma components. The sum over species of the diffusive mass fluxes is constrained to be zero in the Lagrange frame, and thus results in a non-zero molar flux leading to a pressure perturbation. At an interface between two species initially in pressure equilibrium, the pressure perturbation driven by the diffusive molar flux induces a center of mass velocity directed from the species of greater atomic mass towards the lighter atomic mass species. As the ratio of the species particle masses increases, this center of mass velocity carries an increasingly greater portion of the mass across the interface and for a particle mass ratio greater than about two, the center of mass velocity carries more mass than the gradient driven diffusion flux. Early time transients across an interface between two species in a 1D plasma regime and initially in equilibrium are compared using three methods; a fluid code with closure in a classical transport approximation, a particle in cell simulation, and an implicit Fokker-Planck solver for the particle distribution functions. The early time transient phenomenology is shown to be similar in each of the computational simulation methods, including a pressure perturbation associated with the stationary "induced" component of the center of mass velocity which decays to pressure equilibrium during diffusion. At early times, the diffusive process generates pressure and velocity waves which propagate outward from the interface and are required to maintain momentum conservation. The energy in the outgoing waves dissipates as heat in viscous regions, and it is hypothesized that these diffusion driven waves may sustain fluctuations in less viscid finite domains after reflections from the boundaries. These fluid dynamic phenomena are similar in gases or plasmas and occur in flow transients with a moderate Knudsen number. The analysis and simulation results show how the kinetic flux, represented in the fluid transport closure, directly modifies the mass averaged flow described with the Euler equations.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/7614499','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/7614499"><span>Reappraisal of quantitative evaluation of pulmonary regurgitation and estimation of pulmonary artery pressure by continuous wave Doppler echocardiography.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Lei, M H; Chen, J J; Ko, Y L; Cheng, J J; Kuan, P; Lien, W P</p> <p>1995-01-01</p> <p>This study assessed the usefulness of continuous wave Doppler echocardiography and color flow mapping in evaluating pulmonary regurgitation (PR) and estimating pulmonary artery (PA) pressure. Forty-three patients were examined, and high quality Doppler spectral recordings of PR were obtained in 32. All patients underwent cardiac catheterization, and simultaneous PA and right ventricular (RV) pressures were recorded in 17. Four Doppler regurgitant flow velocity patterns were observed: pandiastolic plateau, biphasic, peak and plateau, and early diastolic triangular types. The peak diastolic and end-diastolic PA-to-RV pressure gradients derived from the Doppler flow profiles correlated well with the catheter measurements (r = 0.95 and r = 0.95, respectively). As PA pressure increased, the PR flow velocity became higher; a linear relationship between either systolic or mean PA pressure and Doppler-derived peak diastolic pressure gradient was noted (r = 0.90 and 0.94, respectively). Based on peak diastolic gradients of < 15, 15-30 or > 30 mm Hg, patients could be separated as those with mild, moderate or severe pulmonary hypertension, respectively (p < 0.05). A correlation was also observed between PA diastolic pressure and Doppler-derived end-diastolic pressure gradient (r = 0.91). Moreover, the Doppler velocity decay slope of PR closely correlated with that derived from the catheter method (r = 0.98). The decay slope tended to be steeper with the increment in regurgitant jet area and length obtained from color flow mapping. In conclusion, continuous wave Doppler evaluation of PR is a useful means for noninvasive estimation of PA pressure, and the Doppler velocity decay slope seems to reflect the severity of PR.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JThSc..24..334C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JThSc..24..334C"><span>Numerical investigation on the self-induced unsteadiness in tip leakage flow of a micro-axial fan rotor</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chen, Jinxin; Lai, Huanxin</p> <p>2015-06-01</p> <p>The self-induced unsteadiness in tip leakage flow (TLF) of a micro-axial fan rotor is numerically studied by solvingReynolds-averaged Navier-Stokes equations. The micro-axial fan, which is widely used in cooling systems of electronic devices, has a tip clearance of 6% of the axial chord length of the blade. At the design rotation speed, four cases near the peak efficiency point (PEP) with self-induced unsteadiness and four steady cases which have much weaker pressure fluctuations are investigated Using the "interface" separating the incoming main flow and the TLF defined by Du et al. [1], an explanation based on the propagation of the low energy spot and its multi-passing through the high gradient zone of the relativetotal pressure, is proposed to clarify the originating mechanism of the unsteadiness. At the operating points near the PEP, the main flow is weaker than the TLF and the interface moves upstream. The low energy spot which propagates along in the close behind of the interface has opportunity to circulate in the circumferential direction and passes through the sensitive interfaces several times, a slight perturbation therefore may be magnified significantlyand develops into the self-induced unsteadiness. The explanation is demonstrated by numerical results</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70024483','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70024483"><span>Effects of tidal current phase at the junction of two straits</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Warner, J.; Schoellhamer, D.; Burau, J.; Schladow, G.</p> <p>2002-01-01</p> <p>Estuaries typically have a monotonic increase in salinity from freshwater at the head of the estuary to ocean water at the mouth, creating a consistent direction for the longitudinal baroclinic pressure gradient. However, Mare Island Strait in San Francisco Bay has a local salinity minimum created by the phasing of the currents at the junction of Mare Island and Carquinez Straits. The salinity minimum creates converging baroclinic pressure gradients in Mare Island Strait. Equipment was deployed at four stations in the straits for 6 months from September 1997 to March 1998 to measure tidal variability of velocity, conductivity, temperature, depth, and suspended sediment concentration. Analysis of the measured time series shows that on a tidal time scale in Mare Island Strait, the landward and seaward baroclinic pressure gradients in the local salinity minimum interact with the barotropic gradient, creating regions of enhanced shear in the water column during the flood and reduced shear during the ebb. On a tidally averaged time scale, baroclinic pressure gradients converge on the tidally averaged salinity minimum and drive a converging near-bed and diverging surface current circulation pattern, forming a "baroclinic convergence zone" in Mare Island Strait. Historically large sedimentation rates in this area are attributed to the convergence zone. </p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19930015352','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19930015352"><span>Experimental Study of a Three-Dimensional Shear-Driven Turbulent Boundary Layer with Streamwise Adverse Pressure Gradient</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Driver, David M.; Johnston, James P.</p> <p>1990-01-01</p> <p>The effects of a strong adverse pressure gradient on a three-dimensional turbulent boundary layer are studied in an axisymmetric spinning cylinder geometry. Velocity measurements made with a three-component laser Doppler velocimeter include all three mean flow components, all six Reynolds stress components, and all ten triple-product correlations. Reynolds stress diminishes as the flow becomes three-dimensional. Lower levels of shear stress were seen to persist under adverse pressure gradient conditions. This low level of stress was seen to roughly correlate with the magnitude of cross-flow (relative to free stream flow) for this experiment as well as most of the other experiments in the literature. Variations in pressure gradient do not appear to alter this correlation. For this reason, it is hypothesized that a three-dimensional boundary layer is more prone to separate than a two-dimensional boundary layer, although it could not be directly shown here. None of the computations performed with either a Prandtl mixing length, k-epsilon, or a Launder-Reece-Rodi full Reynolds-stress model were able to predict the reduction in Reynolds stress.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li class="active"><span>14</span></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_14 --> <div id="page_15" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="281"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19740023646','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19740023646"><span>Turbulent transport of heat and momentum in a boundary layer subject to deceleration, suction and variable wall temperature</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Orlando, A. F.; Moffat, R. J.; Kays, W. M.</p> <p>1974-01-01</p> <p>The relationship between the turbulent transport of heat and momentum in an adverse pressure gradient boundary layer was studied. An experimental study was conducted of turbulent boundary layers subject to strong adverse pressure gradients with suction. Near-equilibrium flows were attained, evidenced by outer-region similarity in terms of defect temperature and defect velocity profiles. The relationship between Stanton number and enthalpy thickness was shown to be the same as for a flat plate flow both for constant wall temperature boundary conditions and for steps in wall temperature. The superposition principle used with the step-wall-temperature experimental result was shown to accurately predict the Stanton number variation for two cases of arbitrarily varying wall temperature. The Reynolds stress tensor components were measured for strong adverse pressure gradient conditions and different suction rates. Two peaks of turbulence intensity were found: one in the inner and one in the outer regions. The outer peak is shown to be displaced outward by an adverse pressure gradient and suppressed by suction.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018ClDy..tmp...41C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018ClDy..tmp...41C"><span>Mechanisms of the intensification of the upwelling-favorable winds during El Niño 1997-1998 in the Peruvian upwelling system</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chamorro, Adolfo; Echevin, Vincent; Colas, François; Oerder, Vera; Tam, Jorge; Quispe-Ccalluari, Carlos</p> <p>2018-01-01</p> <p>The physical processes driving the wind intensification in a coastal band of 100 km off Peru during the intense 1997-1998 El Niño (EN) event were studied using a regional atmospheric model. A simulation performed for the period 1994-2000 reproduced the coastal wind response to local sea surface temperature (SST) forcing and large scale atmospheric conditions. The model, evaluated with satellite data, represented well the intensity, seasonal and interannual variability of alongshore (i.e. NW-SE) winds. An alongshore momentum budget showed that the pressure gradient was the dominant force driving the surface wind acceleration. The pressure gradient tended to accelerate the coastal wind, while turbulent vertical mixing decelerated it. A quasi-linear relation between surface wind and pressure gradient anomalies was found. Alongshore pressure gradient anomalies were caused by a greater increase in near-surface air temperature off the northern coast than off the southern coast, associated with the inhomogeneous SST warming. Vertical profiles of wind, mixing coefficient, and momentum trends showed that the surface wind intensification was not caused by the increase of turbulence in the planetary boundary layer. Moreover, the temperature inversion in the vertical mitigated the development of pressure gradient due to air convection during part of the event. Sensitivity experiments allowed to isolate the respective impacts of the local SST forcing and large scale condition on the coastal wind intensification. It was primarily driven by the local SST forcing whereas large scale variability associated with the South Pacific Anticyclone modulated its effects. Examination of other EN events using reanalysis data confirmed that intensifications of alongshore wind off Peru were associated with SST alongshore gradient anomalies, as during the 1997-1998 event.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17257345','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17257345"><span>The effect of the earth's rotation on ground water motion.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Loáiciga, Hugo A</p> <p>2007-01-01</p> <p>The average pore velocity of ground water according to Darcy's law is a function of the fluid pressure gradient and the gravitational force (per unit volume of ground water) and of aquifer properties. There is also an acceleration exerted on ground water that arises from the Earth's rotation. The magnitude and direction of this rotation-induced force are determined in exact mathematical form in this article. It is calculated that the gravitational force is at least 300 times larger than the largest rotation-induced force anywhere on Earth, the latter force being maximal along the equator and approximately equal to 34 N/m(3) there. This compares with a gravitational force of approximately 10(4) N/m(3).</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/16105779','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/16105779"><span>On the ejection-induced instability in Navier-Stokes solutions of unsteady separation.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Obabko, Aleksandr V; Cassel, Kevin W</p> <p>2005-05-15</p> <p>Numerical solutions of the flow induced by a thick-core vortex have been obtained using the unsteady, two-dimensional Navier-Stokes equations. The presence of the vortex causes an adverse pressure gradient along the surface, which leads to unsteady separation. The calculations by Brinckman and Walker for a similar flow identify a possible instability, purported to be an inviscid Rayleigh instability, in the region where ejection of near-wall vorticity occurs during the unsteady separation process. In results for a range of Reynolds numbers in the present investigation, the oscillations are also found to occur. However, they can be eliminated with increased grid resolution. Despite this behaviour, the instability may be physical but requires a sufficient amplitude of disturbances to be realized.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/biblio/22599126-shock-formation-induced-poloidal-flow-its-effects-edge-stability-tokamaks','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/22599126-shock-formation-induced-poloidal-flow-its-effects-edge-stability-tokamaks"><span>Shock formation induced by poloidal flow and its effects on the edge stability in tokamaks</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Seol, J.; Aydemir, A. Y.; Shaing, K. C.</p> <p>2016-04-15</p> <p>In the high confinement mode of tokamaks, magnitude of the radial electric field increases at the edge. Thus, the poloidal flow inside the transport barrier can be sonic when the edge pressure gradient is not steep enough to make the poloidal flow subsonic. When the poloidal Mach number is close to unity, a shock appears in the low field side and causes a large density perturbation. In this study, we describe a shock induced by the sonic poloidal plasma flow. Then, an entropy production across the shock is calculated. Finally, we introduce a simple model for Type III edge localizedmore » modes using the poloidal density variation driven by the sonic poloidal flow.« less</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19920021728','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19920021728"><span>Navier-Stokes analysis and experimental data comparison of compressible flow within ducts</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Harloff, G. J.; Reichert, B. A.; Sirbaugh, J. R.; Wellborn, S. R.</p> <p>1992-01-01</p> <p>Many aircraft employ ducts with centerline curvature or changing cross-sectional shape to join the engine with inlet and exhaust components. S-ducts convey air to the engine compressor from the intake and often decelerate the flow to achieve an acceptable Mach number at the engine compressor by increasing the cross-sectional area downstream. Circular-to-rectangular transition ducts are used on aircraft with rectangular exhaust nozzles to connect the engine and nozzle. To achieve maximum engine performance, the ducts should minimize flow total pressure loss and total pressure distortion at the duct exit. Changes in the curvature of the duct centerline or the duct cross-sectional shape give rise to streamline curvature which causes cross stream pressure gradients. Secondary flows can be caused by deflection of the transverse vorticity component of the boundary layer. This vortex tilting results in counter-rotating vortices. Additionally, the adverse streamwise pressure gradient caused by increasing cross-sectional area can lead to flow separation. Vortex pairs have been observed in the exit planes of both duct types. These vortices are due to secondary flows induced by pressure gradients resulting from streamline curvature. Regions of low total pressure are produced when the vortices convect boundary layer fluid into the main flow. The purpose of the present study is to predict the measured flow field in a diffusing S-duct and a circular-to-rectangular transition duct with a full Navier-Stokes computer program, PARC3D, and to compare the numerical predictions with new detailed experimental measurements. The work was undertaken to extend previous studies and to provide additional CFD validation data needed to help model flows with strong secondary flow and boundary layer separation. The S-duct computation extends the study of Smith et al, and Harloff et al, which concluded that the computation might be improved by using a finer grid and more advanced turbulence models. The present study compares results for both the Baldwin-Lomas and k-epsilon turbulence models and is conducted with a refined grid. For the transition duct, two inlet conditions were considered, the first with straight flow and the second with swirling flow. The first case permits examination of the effects of the geometric transition on the flow field, while the second case includes the rotational flow effect characteristic of a gas turbine engine.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/1455646','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/1455646"><span>Closed transventricular dilation of discrete subvalvular aortic stenosis in dogs.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Linn, K; Orton, E C</p> <p>1992-01-01</p> <p>Discrete subvalvular aortic stenosis with peak systolic pressure gradients of more than 60 mm Hg was treated by closed transventricular dilation in six young dogs. Peak systolic pressure gradients were measured by direct catheterization before surgery, immediately after dilation, and 3 months after surgery. Maximum instantaneous pressure gradients were measured by continuous wave Doppler echocardiography before surgery and 6 weeks to 9 months after surgery. All dogs survived the procedure, and two dogs were clinically normal after 9 and 14 months. Two dogs died at week 6 and month 7. One dog was receiving medication for pulmonary edema 15 months after surgery. One dog underwent open resection of the subvalvular ring at month 3, and was clinically normal 6 months after the second procedure. Complications included intraoperative ventricular fibrillation in one dog, and mild postoperative aortic insufficiency in one dog. Closed transventricular dilation resulted in an immediate 83% decrease in the peak systolic pressure gradient from a preoperative mean of 97 +/- 22 mm Hg to a mean of 14 +/- 15 mm Hg. However, systolic pressure gradients measured by direct catheterization at month 3 (77 +/- 26 mm Hg), and by Doppler echocardiography at week 6 to month 9 (85 +/- 32 mm Hg) were not significantly different from preoperative values, which suggested recurrence of the aortic stenosis. Closed transventricular dilation should not be considered a definitive treatment for discrete subvalvular aortic stenosis in dogs, but may be useful in young dogs with critical aortic stenosis as a bridge to more definitive surgery.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4689682','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4689682"><span>Gradient-Induced Voltages on 12-Lead ECGs during High Duty-Cycle MRI Sequences and a Method for Their Removal considering Linear and Concomitant Gradient Terms</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Zhang, Shelley HuaLei; Ho Tse, Zion Tsz; Dumoulin, Charles L.; Kwong, Raymond Y.; Stevenson, William G.; Watkins, Ronald; Ward, Jay; Wang, Wei; Schmidt, Ehud J.</p> <p>2015-01-01</p> <p>Purpose To restore 12-lead ECG signal fidelity inside MRI by removing magnetic-field gradient induced-voltages during high gradient-duty-cycle sequences. Theory and Methods A theoretical equation was derived, providing first- and second-order electrical fields induced at individual ECG electrode as a function of gradient fields. Experiments were performed at 3T on healthy volunteers, using a customized acquisition system which captured full amplitude and frequency response of ECGs, or a commercial recording system. The 19 equation coefficients were derived by linear regression of data from accelerated sequences, and used to compute induced-voltages in real-time during full-resolution sequences to remove ECG artifacts. Restored traces were evaluated relative to ones acquired without imaging. Results Measured induced-voltages were 0.7V peak-to-peak during balanced Steady-State Free Precession (bSSFP) with heart at the isocenter. Applying the equation during gradient echo sequencing, three-dimensional fast spin echo and multi-slice bSSFP imaging restored nonsaturated traces and second-order concomitant terms showed larger contributions in electrodes farther from the magnet isocenter. Equation coefficients are evaluated with high repeatability (ρ = 0.996) and are subject, sequence, and slice-orientation dependent. Conclusion Close agreement between theoretical and measured gradient-induced voltages allowed for real-time removal. Prospective estimation of sequence-periods where large induced-voltages occur may allow hardware removal of these signals. PMID:26101951</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/servlets/purl/1169240','SCIGOV-STC'); return false;" href="https://www.osti.gov/servlets/purl/1169240"><span>3D J-Integral Capability in Grizzly</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Spencer, Benjamin; Backman, Marie; Chakraborty, Pritam</p> <p>2014-09-01</p> <p>This report summarizes work done to develop a capability to evaluate fracture contour J-Integrals in 3D in the Grizzly code. In the current fiscal year, a previously-developed 2D implementation of a J-Integral evaluation capability has been extended to work in 3D, and to include terms due both to mechanically-induced strains and due to gradients in thermal strains. This capability has been verified against a benchmark solution on a model of a curved crack front in 3D. The thermal term in this integral has been verified against a benchmark problem with a thermal gradient. These developments are part of a largermore » effort to develop Grizzly as a tool that can be used to predict the evolution of aging processes in nuclear power plant systems, structures, and components, and assess their capacity after being subjected to those aging processes. The capabilities described here have been developed to enable evaluations of Mode- stress intensity factors on axis-aligned flaws in reactor pressure vessels. These can be compared with the fracture toughness of the material to determine whether a pre-existing flaw would begin to propagate during a pos- tulated pressurized thermal shock accident. This report includes a demonstration calculation to show how Grizzly is used to perform a deterministic assessment of such a flaw propagation in a degraded reactor pressure vessel under pressurized thermal shock conditions. The stress intensity is calculated from J, and the toughness is computed using the fracture master curve and the degraded ductile to brittle transition temperature.« less</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PhPl...24i2519K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PhPl...24i2519K"><span>Theory and discretization of ideal magnetohydrodynamic equilibria with fractal pressure profiles</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kraus, B. F.; Hudson, S. R.</p> <p>2017-09-01</p> <p>In three-dimensional ideal magnetohydrodynamics, closed flux surfaces cannot maintain both rational rotational-transform and pressure gradients, as these features together produce unphysical, infinite currents. A proposed set of equilibria nullifies these currents by flattening the pressure on sufficiently wide intervals around each rational surface. Such rational surfaces exist at every scale, which characterizes the pressure profile as self-similar and thus fractal. The pressure profile is approximated numerically by considering a finite number of rational regions and analyzed mathematically by classifying the irrational numbers that support gradients into subsets. Applying these results to a given rotational-transform profile in cylindrical geometry, we find magnetic field and current density profiles compatible with the fractal pressure.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28009240','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28009240"><span>Venous sinus stenting for reduction of intracranial pressure in IIH: a prospective pilot study.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Liu, Kenneth C; Starke, Robert M; Durst, Christopher R; Wang, Tony R; Ding, Dale; Crowley, R Webster; Newman, Steven A</p> <p>2017-11-01</p> <p>OBJECTIVE Idiopathic intracranial hypertension (IIH) may cause blindness due to elevated intracranial pressure (ICP). Venous sinus stenosis has been identified in select patients, leading to stenting as a potential treatment, but its effects on global ICP have not been completely defined. The purpose of this pilot study was to assess the effects of venous sinus stenting on ICP in a small group of patients with IIH. METHODS Ten patients for whom medical therapy had failed were prospectively followed. Ophthalmological examinations were assessed, and patients with venous sinus stenosis on MR angiography proceeded to catheter angiography, venography with assessment of pressure gradient, and ICP monitoring. Patients with elevated ICP measurements and an elevated pressure gradient across the stenosis were treated with stent placement. RESULTS All patients had elevated venous pressure (mean 39.5 ± 14.9 mm Hg), an elevated gradient across the venous sinus stenosis (30.0 ± 13.2 mm Hg), and elevated ICP (42.2 ± 15.9 mm Hg). Following stent placement, all patients had resolution of the stenosis and gradient (1 ± 1 mm Hg). The ICP values showed an immediate decrease (to a mean of 17.0 ± 8.3 mm Hg), and further decreased overnight (to a mean of 8 ± 4.2 mm Hg). All patients had subjective and objective improvement, and all but one improved during follow-up (median 23.4 months; range 15.7-31.6 months). Two patients developed stent-adjacent stenosis; retreatment abolished the stenosis and gradient in both cases. Patients presenting with papilledema had resolution on follow-up funduscopic imaging and optical coherence tomography (OCT) and improvement on visual field testing. Patients presenting with optic atrophy had optic nerve thinning on follow-up OCT, but improved visual fields. CONCLUSIONS For selected patients with IIH and venous sinus stenosis with an elevated pressure gradient and elevated ICP, venous sinus stenting results in resolution of the venous pressure gradient, reduction in ICP, and functional, neurological, and ophthalmological improvement. As patients are at risk for stent-adjacent stenosis, further follow-up is necessary to determine long-term outcomes and gain an understanding of venous sinus stenosis as a primary or secondary pathological process behind elevated ICP.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29620871','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29620871"><span>Skin-Inspired Hierarchical Polymer Architectures with Gradient Stiffness for Spacer-Free, Ultrathin, and Highly Sensitive Triboelectric Sensors.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ha, Minjeong; Lim, Seongdong; Cho, Soowon; Lee, Youngoh; Na, Sangyun; Baig, Chunggi; Ko, Hyunhyub</p> <p>2018-04-24</p> <p>The gradient stiffness between stiff epidermis and soft dermis with interlocked microridge structures in human skin induces effective stress transmission to underlying mechanoreceptors for enhanced tactile sensing. Inspired by skin structure and function, we fabricate hierarchical nanoporous and interlocked microridge structured polymers with gradient stiffness for spacer-free, ultrathin, and highly sensitive triboelectric sensors (TESs). The skin-inspired hierarchical polymers with gradient elastic modulus enhance the compressibility and contact areal differences due to effective transmission of the external stress from stiff to soft layers, resulting in highly sensitive TESs capable of detecting human vital signs and voice. In addition, the microridges in the interlocked polymers provide an effective variation of gap distance between interlocked layers without using the bulk spacer and thus facilitate the ultrathin and flexible design of TESs that could be worn on the body and detect a variety of pressing, bending, and twisting motions even in humid and underwater environments. Our TESs exhibit the highest power density (46.7 μW/cm 2 ), pressure (0.55 V/kPa), and bending (∼0.1 V/°) sensitivities ever reported on flexible TESs. The proposed design of hierarchical polymer architectures for the flexible and wearable TESs can find numerous applications in next-generation wearable electronics.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70025500','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70025500"><span>Magma supply dynamics at Westdahl volcano, Alaska, modeled from satellite radar interferometry</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Lu, Z.; Masterlark, Timothy; Dzurisin, D.; Rykhus, Russ; Wicks, C.</p> <p>2003-01-01</p> <p>A group of satellite radar interferograms that span the time period from 1991 to 2000 shows that Westdahl volcano, Alaska, deflated during its 1991-1992 eruption and is reinflating at a rate that could produce another eruption within the next several years. The rates of inflation and deflation are approximated by exponential decay functions having time constants of about 6 years and a few days, respectively. This behavior is consistent with a deep, constant-pressure magma source connected to a shallow reservoir by a magma-filled conduit. An elastic deformation model indicates that the reservoir is located about 6 km below sea level and beneath Westdahl Peak. We propose that the magma flow rate through the conduit is governed by the pressure gradient between the deep source and the reservoir. The pressure gradient, and hence the flow rate, are greatest immediately after eruptions. Pressurization of the reservoir decreases both the pressure gradient and the flow rate, but eventually the reservoir ruptures and an eruption or intrusion ensues. The eruption rate is controlled partly by the pressure gradient between the reservoir and surface, and therefore it, too, decreases with time. When the supply of eruptible magma is exhausted, the eruption stops, the reservoir begins to repressurize at a high rate, and the cycle repeats. This model might also be appropriate for other frequently active volcanoes with stable magma sources and relatively simple magma storage systems.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1983BoLMe..27...69G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1983BoLMe..27...69G"><span>Low-level wind response to mesoscale pressure systems</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Garratt, J. R.; Physick, W. L.</p> <p>1983-09-01</p> <p>Observations are presented which show a strong correlation between low-level wind behaviour (e.g., rotation near the surface) and the passage of mesoscale pressure systems. The latter are associated with frontal transition zones, are dominated by a pressure-jump line and a mesoscale high pressure area, and produce locally large horizontal pressure gradients. The wind observations are simulated by specifying a time sequence of perturbation pressure gradient and subsequently solving the vertically-integrated momentum equations with appropriate initial conditions. Very good agreement is found between observed and calculated winds; in particular, (i) a 360 ° rotation in wind on passage of the mesoscale high; (ii) wind-shift lines produced dynamically by the pressure-jump line; (iii) rapid linear increase in wind speed on passage of the pressure jump.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19840015581','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19840015581"><span>Investigation of the effects of pressure gradient, temperature and wall temperature ratio on the stagnation point heat transfer for circular cylinders and gas turbine vanes</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Nagamatsu, H. T.; Duffy, R. E.</p> <p>1984-01-01</p> <p>Low and high pressure shock tubes were designed and constructed for the purpose of obtaining heat transfer data over a temperature range of 390 to 2500 K, pressures of 0.3 to 42 atm, and Mach numbers of 0.15 to 1.5 with and without pressure gradient. A square test section with adjustable top and bottom walls was constructed to produce the favorable and adverse pressure gradient over the flat plate with heat gages. A water cooled gas turbine nozzle cascade which is attached to the high pressure shock tube was obtained to measuse the heat flux over pressure and suction surfaces. Thin-film platinum heat gages with a response time of a few microseconds were developed and used to measure the heat flux for laminar, transition, and turbulent boundary layers. The laminar boundary heat flux on the shock tube wall agreed with Mirel's flat plate theory. Stagnation point heat transfer for circular cylinders at low temperature compared with the theoretical prediction, but for a gas temperature of 922 K the heat fluxes were higher than the predicted values. Preliminary flat plate heat transfer data were measured for laminar, transition, and turbulent boundary layers with and without pressure gradients for free-stream temperatures of 350 to 2575 K and flow Mach numbers of 0.11 to 1.9. The experimental heat flux data were correlated with the laminar and turbulent theories and the agreement was good at low temperatures which was not the case for higher temperatures.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28085320','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28085320"><span>Mass-flow-rate-controlled fluid flow in nanochannels by particle insertion and deletion.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Barclay, Paul L; Lukes, Jennifer R</p> <p>2016-12-01</p> <p>A nonequilibrium molecular dynamics method to induce fluid flow in nanochannels, the insertion-deletion method (IDM), is introduced. IDM inserts and deletes particles within distinct regions in the domain, creating locally high and low pressures. The benefits of IDM are that it directly controls a physically meaningful quantity, the mass flow rate, allows for pressure and density gradients to develop in the direction of flow, and permits treatment of complex aperiodic geometries. Validation of IDM is performed, yielding good agreement with the analytical solution of Poiseuille flow in a planar channel. Comparison of IDM to existing methods indicates that it is best suited for gases, both because it intrinsically accounts for compressibility effects on the flow and because the computational cost of particle insertion is lowest for low-density fluids.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3781324','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3781324"><span>Functional analysis of embolism induced by air injection in Acer rubrum and Salix nigra</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Melcher, Peter J.; Zwieniecki, Maciej A.</p> <p>2013-01-01</p> <p>The goal of this study was to assess the effect of induced embolism with air injection treatments on the function of xylem in Acer rubrum L. and Salix nigra Marsh. Measurements made on mature trees of A. rubrum showed that pneumatic pressurization treatments that created a pressure gradient of 5.5 MPa across pit membranes (ΔPpit) had no effect on stomatal conductance or on branch-level sap flow. The same air injection treatments made on 3-year-old potted A. rubrum plants also had no effect on whole plant transpiration. A separate study made on mature A. rubrum trees showed that 3.0 and 5.5 MPa of ΔPpit values resulted in an immediate 100% loss in hydraulic conductance (PLC) in petioles. However, the observed change in PLC was short lived, and significant hydraulic recovery occurred within 5–10 min post air-pressurization treatments. Similar experiments conducted on S. nigra plants exposed to ΔPpit of 3 MPa resulted in a rapid decline in whole plant transpiration followed by leaf wilting and eventual plant death, showing that this species lacks the ability to recover from induced embolism. A survey that measured the effect of air-pressurization treatments on seven other species showed that some species are very sensitive to induction of embolism resulting in leaf wilting and branch death while others show minimal to no effect despite that in each case, the applied ΔPpit of 5.5 MPa significantly exceeded any native stress that these plants would experience naturally. PMID:24069025</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24069025','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24069025"><span>Functional analysis of embolism induced by air injection in Acer rubrum and Salix nigra.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Melcher, Peter J; Zwieniecki, Maciej A</p> <p>2013-01-01</p> <p>The goal of this study was to assess the effect of induced embolism with air injection treatments on the function of xylem in Acer rubrum L. and Salix nigra Marsh. Measurements made on mature trees of A. rubrum showed that pneumatic pressurization treatments that created a pressure gradient of 5.5 MPa across pit membranes (ΔP pit) had no effect on stomatal conductance or on branch-level sap flow. The same air injection treatments made on 3-year-old potted A. rubrum plants also had no effect on whole plant transpiration. A separate study made on mature A. rubrum trees showed that 3.0 and 5.5 MPa of ΔP pit values resulted in an immediate 100% loss in hydraulic conductance (PLC) in petioles. However, the observed change in PLC was short lived, and significant hydraulic recovery occurred within 5-10 min post air-pressurization treatments. Similar experiments conducted on S. nigra plants exposed to ΔP pit of 3 MPa resulted in a rapid decline in whole plant transpiration followed by leaf wilting and eventual plant death, showing that this species lacks the ability to recover from induced embolism. A survey that measured the effect of air-pressurization treatments on seven other species showed that some species are very sensitive to induction of embolism resulting in leaf wilting and branch death while others show minimal to no effect despite that in each case, the applied ΔP pit of 5.5 MPa significantly exceeded any native stress that these plants would experience naturally.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=433198','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=433198"><span>Thermal Motion and Forced Migration of Colloidal Particles Generate Hydrostatic Pressure in Solvent</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Hammel, H. T.; Scholander, P. F.</p> <p>1973-01-01</p> <p>A colloidal solution of ferrite particles in an osmometer has been used to demonstrate that the property that propels water across the semipermeable membrane is the decrease in hydrostatic pressure in the water of the solution. A magnetic field gradient directed so as to force the ferrite particles away from the semipermeable membrane of the osmometer and toward the free surface of the solution enhanced the colloidal osmotic pressure. The enhancement of this pressure was always exactly equal to the augmentation of the pressure as measured by the outward force of the particles, against the area of the free surface. Contrariwise, directing the magnetic field gradient so as to force the ferrite particles away from the free surface and toward the semipermeable membrane diminished the colloidal osmotic pressure of the solution. For a sufficiently forceful field gradient, the initial colloidal osmotic pressure could be negative, followed by an equilibrium pressure approaching zero regardless of the force of the particles against the membrane. Thus, the osmotic pressure of a solution is to be attributed to the pressure in the solvent generated in opposition to the pressure of the solute particles caused by their interaction with the free surface (Brownian motion and/or an external field force), or by their viscous shear when they migrate through the solvent, or both. PMID:16592046</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25536861','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25536861"><span>Resistance to forced airflow through layers of composting organic material.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Teixeira, Denis Leocádio; de Matos, Antonio Teixeira; Melo, Evandro de Castro</p> <p>2015-02-01</p> <p>The objective of this study was to adjust equations to estimate the static pressure gradient of airflow through layers of organic residues submitted to two stages of biochemical degradation, and to evaluate the static pressure drop of airflow thought the material layer. Measurements of static pressure drop in the layers of sugarcane bagasse and coffee husks mixed with poultry litter on day 0 and after 30 days of composting were performed using a prototype with specific airflow rates ranging from 0.02 to 0.13 m(3) s(-1) m(-2). Static pressure gradient and specific airflow rate data were properly fit to the Shedd, Hukill & Ives and Ergun models, which may be used to predict the static pressure gradient of air to be blown through the organic residue layers. However, the Shedd model was that which best represented the phenomenon studied. The static pressure drop of airflow increased as a power of the material layer thickness and showed tendency for decreasing with the biochemical degradation time of the organic material. Copyright © 2014 Elsevier Ltd. All rights reserved.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_15 --> <div id="page_16" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="301"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018E3SWC..3801038B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018E3SWC..3801038B"><span>The Researches on Reasonable Well Spacing of Gas Wells in Deep and low Permeability Gas Reservoirs</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bei, Yu Bei; Hui, Li; Lin, Li Dong</p> <p>2018-06-01</p> <p>This Gs64 gas reservoir is a condensate gas reservoir which is relatively integrated with low porosity and low permeability found in Dagang Oilfield in recent years. The condensate content is as high as 610g/m3. At present, there are few reports about the well spacing of similar gas reservoirs at home and abroad. Therefore, determining the reasonable well spacing of the gas reservoir is important for ensuring the optimal development effect and economic benefit of the gas field development. This paper discusses the reasonable well spacing of the deep and low permeability gas reservoir from the aspects of percolation mechanics, gas reservoir engineering and numerical simulation. considering there exist the start-up pressure gradient in percolation process of low permeability gas reservoir, this paper combined with productivity equation under starting pressure gradient, established the formula of gas well spacing with the formation pressure and start-up pressure gradient. The calculation formula of starting pressure gradient and well spacing of gas wells. Adopting various methods to calculate values of gas reservoir spacing are close to well testing' radius, so the calculation method is reliable, which is very important for the determination of reasonable well spacing in low permeability gas reservoirs.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/20120011823','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20120011823"><span>Transition Within Leeward Plane of Axisymmetric Bodies at Incidence in Supersonic Flow</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Tokugawa, Naoko; Choudhari, Meelan; Ishikawa, Hiroaki; Ueda, Yoshine; Fujii, Keisuke; Atobe, Takashi; Li, Fei; Chang, Chau-Lyan; White, Jeffery</p> <p>2012-01-01</p> <p>Boundary layer transition along the leeward symmetry plane of axisymmetric bodies at nonzero angle of attack in supersonic flow was investigated experimentally and numerically as part of joint research between the Japan Aerospace Exploration Agency (JAXA) and National Aeronautics and Space Administration (NASA). Transition over four axisymmetric bodies (namely, Sears-Haack body, semi-Sears-Haack body, straight cone and flared cone) with different axial pressure gradients was measured in two different facilities with different unit Reynolds numbers. The semi-Sears-Haack body and flared cone were designed at JAXA to broaden the range of axial pressure distributions. For a body shape with an adverse pressure gradient (i.e., flared cone), the experimentally measured transition patterns show an earlier transition location along the leeward symmetry plane in comparison with the neighboring azimuthal locations. For nearly zero pressure gradient (i.e.,straight cone), this feature is only observed at the larger unit Reynolds number. Later transition along the leeward plane was observed for the remaining two body shapes with a favorable pressure gradient. The observed transition patterns are only partially consistent with the numerical predictions based on linear stability analysis. Additional measurements are used in conjunction with the stability computations to explore the phenomenon of leeward line transition and the underlying transition mechanism in further detail.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/pages/biblio/1345540-models-sol-transport-relation-scaling-divertor-heat-flux-width-diii','SCIGOV-DOEP'); return false;" href="https://www.osti.gov/pages/biblio/1345540-models-sol-transport-relation-scaling-divertor-heat-flux-width-diii"><span>Models of SOL transport and their relation to scaling of the divertor heat flux width in DIII-D</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/pages">DOE PAGES</a></p> <p>Makowski, M. A.; Lasnier, C. J.; Leonard, A. W.; ...</p> <p>2014-10-06</p> <p>Strong support for the critical pressure gradient model for the heat flux width has been obtained, in that the measured separatrix pressure gradient lies below and scales similarly to the pressure gradient limit obtained from the ideal, infinite-n stability codes, BALOO and 2DX, in all cases that have been examined. Predictions of a heuristic drift model for the heat flux width are also in qualitative agreement with the measurements. We obtained these results by using an improved high rep-rate and higher edge spatial resolution Thomson scattering system on DIII-D to measure the upstream electron temperature and density profiles. In ordermore » to compare theory and experiment, profiles of density, temperature, and pressure for both electrons and ions are needed as well values of these quantitities at the separatrix. We also developed a simple method to identify a proxy for the separatrix.« less</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/20080008346','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20080008346"><span>Supersonic/Hypersonic Laminar Heating Correlations for Rectangular and Impact-Induced Open and Closed Cavities</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Everhart, Joel L.</p> <p>2008-01-01</p> <p>Impact and debris damage to the Space Shuttle Orbiter Thermal Protection System tiles is a random phenomenon, occurring at random locations on the vehicle surface, resulting in random geometrical shapes that are exposed to a definable range of surface flow conditions. In response to the 2003 Final Report of the Columbia Accident Investigation Board, wind tunnel aeroheating experiments approximating a wide range of possible damage scenarios covering both open and closed cavity flow conditions were systematically tested in hypersonic ground based facilities. These data were analyzed and engineering assessment tools for damage-induced fully-laminar heating were developed and exercised on orbit. These tools provide bounding approximations for the damaged-surface heating environment. This paper presents a further analysis of the baseline, zero-pressure-gradient, idealized, rectangular-geometry cavity heating data, yielding new laminar correlations for the floor-averaged heating, peak cavity endwall heating, and the downstream decay rate. Correlation parameters are derived in terms of cavity geometry and local flow conditions. Prediction Limit Uncertainty values are provided at the 95%, 99% and 99.9% levels of significance. Non-baseline conditions, including non-rectangular geometries and flows with known pressure gradients, are used to assess the range of applicability of the new correlations. All data variations fall within the 99% Prediction Limit Uncertainty bounds. Importantly, both open-flow and closed-flow cavity heating are combined into a single-curve parameterization of the heating predictions, and provide a concise mathematical model of the laminar cavity heating flow field with known uncertainty.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24748150','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24748150"><span>The influence of body position on cerebrospinal fluid pressure gradient and movement in cats with normal and impaired craniospinal communication.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Klarica, Marijan; Radoš, Milan; Erceg, Gorislav; Petošić, Antonio; Jurjević, Ivana; Orešković, Darko</p> <p>2014-01-01</p> <p>Intracranial hypertension is a severe therapeutic problem, as there is insufficient knowledge about the physiology of cerebrospinal fluid (CSF) pressure. In this paper a new CSF pressure regulation hypothesis is proposed. According to this hypothesis, the CSF pressure depends on the laws of fluid mechanics and on the anatomical characteristics inside the cranial and spinal space, and not, as is today generally believed, on CSF secretion, circulation and absorption. The volume and pressure changes in the newly developed CSF model, which by its anatomical dimensions and basic biophysical features imitates the craniospinal system in cats, are compared to those obtained on cats with and without the blockade of craniospinal communication in different body positions. During verticalization, a long-lasting occurrence of negative CSF pressure inside the cranium in animals with normal cranio-spinal communication was observed. CSF pressure gradients change depending on the body position, but those gradients do not enable unidirectional CSF circulation from the hypothetical site of secretion to the site of absorption in any of them. Thus, our results indicate the existence of new physiological/pathophysiological correlations between intracranial fluids, which opens up the possibility of new therapeutic approaches to intracranial hypertension.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27165918','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27165918"><span>Automatic Calculation of Hydrostatic Pressure Gradient in Patients with Head Injury: A Pilot Study.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Moss, Laura; Shaw, Martin; Piper, Ian; Arvind, D K; Hawthorne, Christopher</p> <p>2016-01-01</p> <p>The non-surgical management of patients with traumatic brain injury is the treatment and prevention of secondary insults, such as low cerebral perfusion pressure (CPP). Most clinical pressure monitoring systems measure pressure relative to atmospheric pressure. If a patient is managed with their head tilted up, relative to their arterial pressure transducer, then a hydrostatic pressure gradient (HPG) can act against arterial pressure and cause significant errors in calculated CPP.To correct for HPG, the arterial pressure transducer should be placed level with the intracranial pressure transducer. However, this is not always achieved. In this chapter, we describe a pilot study investigating the application of speckled computing (or "specks") for the automatic monitoring of the patient's head tilt and subsequent automatic calculation of HPG. In future applications this will allow us to automatically correct CPP to take into account any HPG.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28429723','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28429723"><span>Pressure Self-focusing Effect and Novel Methods for Increasing the Maximum Pressure in Traditional and Rotational Diamond Anvil Cells.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Feng, Biao; Levitas, Valery I</p> <p>2017-04-21</p> <p>The main principles of producing a region near the center of a sample, compressed in a diamond anvil cell (DAC), with a very high pressure gradient and, consequently, with high pressure are predicted theoretically. The revealed phenomenon of generating extremely high pressure gradient is called the pressure self-focusing effect. Initial analytical predictions utilized generalization of a simplified equilibrium equation. Then, the results are refined using our recent advanced model for elastoplastic material under high pressures in finite element method (FEM) simulations. The main points in producing the pressure self-focusing effect are to use beveled anvils and reach a very thin sample thickness at the center. We find that the superposition of torsion in a rotational DAC (RDAC) offers drastic enhancement of the pressure self-focusing effect and allows one to reach the same pressure under a much lower force and deformation of anvils.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/pages/biblio/1395556-theory-discretization-ideal-magnetohydrodynamic-equilibria-fractal-pressure-profiles','SCIGOV-DOEP'); return false;" href="https://www.osti.gov/pages/biblio/1395556-theory-discretization-ideal-magnetohydrodynamic-equilibria-fractal-pressure-profiles"><span>Theory and discretization of ideal magnetohydrodynamic equilibria with fractal pressure profiles</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/pages">DOE PAGES</a></p> <p>Kraus, B. F.; Hudson, S. R.</p> <p>2017-09-29</p> <p>In three-dimensional ideal magnetohydrodynamics, closed flux surfaces cannot maintain both rational rotational-transform and pressure gradients, as these features together produce unphysical, infinite currents. A proposed set of equilibria nullifies these currents by flattening the pressure on sufficiently wide intervals around each rational surface. Such rational surfaces exist at every scale, which characterizes the pressure profile as self-similar and thus fractal. The pressure profile is approximated numerically by considering a finite number of rational regions and analyzed mathematically by classifying the irrational numbers that support gradients into subsets. As a result, applying these results to a given rotational-transform profile in cylindricalmore » geometry, we find magnetic field and current density profiles compatible with the fractal pressure.« less</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/biblio/1395556-theory-discretization-ideal-magnetohydrodynamic-equilibria-fractal-pressure-profiles','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/1395556-theory-discretization-ideal-magnetohydrodynamic-equilibria-fractal-pressure-profiles"><span>Theory and discretization of ideal magnetohydrodynamic equilibria with fractal pressure profiles</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Kraus, B. F.; Hudson, S. R.</p> <p></p> <p>In three-dimensional ideal magnetohydrodynamics, closed flux surfaces cannot maintain both rational rotational-transform and pressure gradients, as these features together produce unphysical, infinite currents. A proposed set of equilibria nullifies these currents by flattening the pressure on sufficiently wide intervals around each rational surface. Such rational surfaces exist at every scale, which characterizes the pressure profile as self-similar and thus fractal. The pressure profile is approximated numerically by considering a finite number of rational regions and analyzed mathematically by classifying the irrational numbers that support gradients into subsets. As a result, applying these results to a given rotational-transform profile in cylindricalmore » geometry, we find magnetic field and current density profiles compatible with the fractal pressure.« less</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29439881','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29439881"><span>Prospective assessment of the frequency of low gradient severe aortic stenosis with preserved left ventricular ejection fraction: Critical impact of aortic flow misalignment and pressure recovery phenomenon.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ringle, Anne; Castel, Anne-Laure; Le Goffic, Caroline; Delelis, François; Binda, Camille; Bohbot, Yohan; Ennezat, Pierre Vladimir; Guerbaai, Raphaëlle A; Levy, Franck; Vincentelli, André; Graux, Pierre; Tribouilloy, Christophe; Maréchaux, Sylvestre</p> <p>2018-02-10</p> <p>The frequency of paradoxical low-gradient severe aortic stenosis (AS) varies widely across studies. The impact of misalignment of aortic flow and pressure recovery phenomenon on the frequency of low-gradient severe AS with preserved left ventricular ejection fraction (LVEF) has not been evaluated in prospective studies. To investigate prospectively the impact of aortic flow misalignment by Doppler and lack of pressure recovery phenomenon correction on the frequency of low-gradient (LG) severe aortic stenosis (AS) with preserved LVEF. Aortic jet velocities and mean pressure gradient (MPG) were obtained by interrogating all windows in 68 consecutive patients with normal LVEF and severe AS (aortic valve area [AVA] ≤1cm 2 ) on the basis of the apical imaging window alone (two-dimensional [2D] apical approach). Patients were classified as having LG or high-gradient (HG) AS according to MPG <40mmHg or ≥40mmHg, and normal flow (NF) or low flow (LF) according to stroke volume index >35mL/m 2 or ≤35mL/m 2 , on the basis of the 2D apical approach, the multiview approach (multiple windows evaluation) and AVA corrected for pressure recovery. The proportion of LG severe AS was 57% using the 2D apical approach alone. After the multiview approach and correction for pressure recovery, the proportion of LG severe AS decreased from 57% to 13% (LF-LG severe AS decreased from 23% to 3%; NF-LG severe AS decreased from 34% to 10%). As a result, 25% of patients were reclassified as having HG severe AS (AVA ≤1cm 2 and MPG ≥40mmHg) and 19% as having moderate AS. Hence, 77% of patients initially diagnosed with LG severe AS did not have "true" LG severe AS when the multiview approach and the pressure recovery phenomenon correction were used. Aortic flow misevaluation, resulting from lack of use of multiple windows evaluation and pressure recovery phenomenon correction, accounts for a large proportion of incorrectly graded AS and considerable overestimation of the frequency of LG severe AS with preserved LVEF. Copyright © 2018 Elsevier Masson SAS. All rights reserved.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006ApPhL..89v1909X','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006ApPhL..89v1909X"><span>Effect of electromigration-induced back stress gradient on nanoindentation marker movement in SnAgCu solder joints</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Xu, Luhua; Pang, John H. L.; Tu, K. N.</p> <p>2006-11-01</p> <p>The electromigration-induced back stress in Pb-free SnAgCu solder was studied by an area array of nanoindentation markers on the cross section of a solder joint. The marker movements driven by combined electron wind force and electromigration-induced back stress gradient were measured at different locations. The back stress gradient was determined from the observation of marker motion using the proposed model. With the applied current density of 104A/cm2 at 125°C, the stress gradient near the anode is 97kPa/μm.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AIPC.1233..662W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AIPC.1233..662W"><span>Efficient Meshfree Large Deformation Simulation of Rainfall Induced Soil Slope Failure</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Dongdong; Li, Ling</p> <p>2010-05-01</p> <p>An efficient Lagrangian Galerkin meshfree framework is presented for large deformation simulation of rainfall-induced soil slope failure. Detailed coupled soil-rainfall seepage equations are given for the proposed formulation. This nonlinear meshfree formulation is featured by the Lagrangian stabilized conforming nodal integration method where the low cost nature of nodal integration approach is kept and at the same time the numerical stability is maintained. The initiation and evolution of progressive failure in the soil slope is modeled by the coupled constitutive equations of isotropic damage and Drucker-Prager pressure-dependent plasticity. The gradient smoothing in the stabilized conforming integration also serves as a non-local regularization of material instability and consequently the present method is capable of effectively capture the shear band failure. The efficacy of the present method is demonstrated by simulating the rainfall-induced failure of two typical soil slopes.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EPSC...10...63T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EPSC...10...63T"><span>Sun-stirred Kraken Mare: Circulation in Titan's seas induced by solar heating and methane precipitation</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tokano, T.; Lorenz, R. D.</p> <p>2015-10-01</p> <p>Density-driven circulation in Titan's seas forced by solar heating and methane evaporation/precipitation is simulated by an ocean circulation model. If the sea is transparent to sunlight, solar heating can induce anti-clockwise gyres near the sea surface and clockwise gyres near the sea bottom. The gyres are in geostrophic balance between the radially symmetric pressure gradient force and Coriolis force. If instead the sea is turbid and most sunlight is absorbed near the sea surface, the sea gets stratified in warm seasons and the circulation remains weak. Strong summer precipitation at high latitudes causes compositional stratification and increase of the nearsurface methane mole fraction towards the north pole. The resultant latitudinal density contrast drives a meridional overturning with equatorward currents near the sea surface and poleward currents near the sea bottom. Weak precipitation induces gyres rather than meridional overturning.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27986288','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27986288"><span>A practical approach for predicting retention time shifts due to pressure and temperature gradients in ultra-high-pressure liquid chromatography.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Åsberg, Dennis; Chutkowski, Marcin; Leśko, Marek; Samuelsson, Jörgen; Kaczmarski, Krzysztof; Fornstedt, Torgny</p> <p>2017-01-06</p> <p>Large pressure gradients are generated in ultra-high-pressure liquid chromatography (UHPLC) using sub-2μm particles causing significant temperature gradients over the column due to viscous heating. These pressure and temperature gradients affect retention and ultimately result in important selectivity shifts. In this study, we developed an approach for predicting the retention time shifts due to these gradients. The approach is presented as a step-by-step procedure and it is based on empirical linear relationships describing how retention varies as a function of temperature and pressure and how the average column temperature increases with the flow rate. It requires only four experiments on standard equipment, is based on straightforward calculations, and is therefore easy to use in method development. The approach was rigorously validated against experimental data obtained with a quality control method for the active pharmaceutical ingredient omeprazole. The accuracy of retention time predictions was very good with relative errors always less than 1% and in many cases around 0.5% (n=32). Selectivity shifts observed between omeprazole and the related impurities when changing the flow rate could also be accurately predicted resulting in good estimates of the resolution between critical peak pairs. The approximations which the presented approach are based on were all justified. The retention factor as a function of pressure and temperature was studied in an experimental design while the temperature distribution in the column was obtained by solving the fundamental heat and mass balance equations for the different experimental conditions. We strongly believe that this approach is sufficiently accurate and experimentally feasible for this separation to be a valuable tool when developing a UHPLC method. After further validation with other separation systems, it could become a useful approach in UHPLC method development, especially in the pharmaceutical industry where demands are high for robustness and regulatory oversight. Copyright © 2016 Elsevier B.V. All rights reserved.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26290109','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26290109"><span>Body height and arterial pressure in seated and supine young males during +2 G centrifugation.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Arvedsen, Sine K; Eiken, Ola; Kölegård, Roger; Petersen, Lonnie G; Norsk, Peter; Damgaard, Morten</p> <p>2015-11-01</p> <p>It is known that arterial pressure correlates positively with body height in males, and it has been suggested that this is due to the increasing vertical hydrostatic gradient from the heart to the carotid baroreceptors. Therefore, we tested the hypothesis that a higher gravito-inertial stress induced by the use of a human centrifuge would increase mean arterial pressure (MAP) more in tall than in short males in the seated position. In short (162-171 cm; n = 8) and tall (194-203 cm; n = 10) healthy males (18-41 yr), brachial arterial pressure, heart rate (HR), and cardiac output were measured during +2G centrifugation, while they were seated upright with the legs kept horizontal (+2Gz). In a separate experiment, the same measurements were done with the subjects supine (+2Gx). During +2Gz MAP increased in the short (22 ± 2 mmHg, P < 0.0001) and tall (23 ± 2 mmHg, P < 0.0001) males, with no significant difference between the groups. HR increased more (P < 0.05) in the tall than in the short group (14 ± 2 vs. 7 ± 2 bpm). Stroke volume (SV) decreased in the short group (26 ± 4 ml, P = 0.001) and more so in the tall group (39 ± 5 ml, P < 0.0001; short vs. tall, P = 0.047). During +2Gx, systolic arterial pressure increased (P < 0.001) and SV (P = 0.012) decreased in the tall group only. In conclusion, during +2Gz, MAP increased in both short and tall males, with no difference between the groups. However, in the tall group, HR increased more during +2Gz, which could be caused by a larger hydrostatic pressure gradient from heart to head, leading to greater inhibition of the carotid baroreceptors. Copyright © 2015 the American Physiological Society.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19950004440','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19950004440"><span>Nonlinear stability of oscillatory core-annular flow: A generalized Kuramoto-Sivashinsky equation with time periodic coefficients</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Coward, Adrian V.; Papageorgiou, Demetrios T.; Smyrlis, Yiorgos S.</p> <p>1994-01-01</p> <p>In this paper the nonlinear stability of two-phase core-annular flow in a pipe is examined when the acting pressure gradient is modulated by time harmonic oscillations and viscosity stratification and interfacial tension is present. An exact solution of the Navier-Stokes equations is used as the background state to develop an asymptotic theory valid for thin annular layers, which leads to a novel nonlinear evolution describing the spatio-temporal evolution of the interface. The evolution equation is an extension of the equation found for constant pressure gradients and generalizes the Kuramoto-Sivashinsky equation with dispersive effects found by Papageorgiou, Maldarelli & Rumschitzki, Phys. Fluids A 2(3), 1990, pp. 340-352, to a similar system with time periodic coefficients. The distinct regimes of slow and moderate flow are considered and the corresponding evolution is derived. Certain solutions are described analytically in the neighborhood of the first bifurcation point by use of multiple scales asymptotics. Extensive numerical experiments, using dynamical systems ideas, are carried out in order to evaluate the effect of the oscillatory pressure gradient on the solutions in the presence of a constant pressure gradient.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017APS..MAR.T1383K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017APS..MAR.T1383K"><span>Study of the Pressure and Velocity Across the Aortic Valve</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kyung, Seo Young; Chung, Erica Soyun; Lee, Joo Hee; Kyung, Hayoung; Choi, Si Young</p> <p></p> <p>Biomechanics of the heart, requiring an extensive understanding of the complexity of the heart, have become the interests of many biomedical engineers in cardiology today. In order to study aortic valve disease, engineers have focused on the data obtained through bio-fluid flow analysis. To further this study, physical and computational analysis on the biomechanical determinants of blood flow in the stenosed aortic valve have been examined. These observations, along with the principles of cardiovascular physiology, confirm that when blood flows through the valve opening, pressure gradient across the valve is produced as a result of stenosis of the aortic valve. The aortic valve gradient is used to interpret the increase and decrease on each side of the defective valve. To compute different pressure gradients across the aortic valve, this paper analyzes Aortic Valve Areas (AVA) using simulations based on the continuity equation and Gorlin equation. The data obtained from such analysis consist of patients in the AS category that display mild Aortic Valve Velocity (AVV) and pressure gradient. Such correlation results in the construction of a dependent relationship between severe AS causing LV systolic dysfunction and the transaortic velocity.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19940006720','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19940006720"><span>A Galilean and tensorial invariant k-epsilon model for near wall turbulence</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Yang, Z.; Shih, T. H.</p> <p>1993-01-01</p> <p>A k-epsilon model is proposed for wall bounded turbulent flows. In this model, the eddy viscosity is characterized by a turbulent velocity scale and a turbulent time scale. The time scale is bounded from below by the Kolmogorov time scale. The dissipation rate equation is reformulated using this time scale and no singularity exists at the wall. A new parameter R = k/S(nu) is introduced to characterize the damping function in the eddy viscosity. This parameter is determined by local properties of both the mean and the turbulent flow fields and is free from any geometry parameter. The proposed model is then Galilean and tensorial invariant. The model constants used are the same as in the high Reynolds number Standard k-epsilon Model. Thus, the proposed model will also be suitable for flows far from the wall. Turbulent channel flows and turbulent boundary layer flows with and without pressure gradients are calculated. Comparisons with the data from direct numerical simulations and experiments show that the model predictions are excellent for turbulent channel flows and turbulent boundary layers with favorable pressure gradients, good for turbulent boundary layers with zero pressure gradients, and fair for turbulent boundary layer with adverse pressure gradients.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017APS..DFD.Q6008A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017APS..DFD.Q6008A"><span>Compressibility Effects on Particle-Fluid Interaction Force for Eulerian-Eulerian Simulations</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Akiki, Georges; Francois, Marianne; Zhang, Duan</p> <p>2017-11-01</p> <p>Particle-fluid interaction forces are essential in modeling multiphase flows. Several models can be found in the literature based on empirical, numerical, and experimental results from various simplified flow conditions. Some of these models also account for finite Mach number effects. Using these models is relatively straightforward with Eulerian-Lagrangian calculations if the model for the total force on particles is used. In Eulerian-Eulerian simulations, however, there is the pressure gradient terms in the momentum equation for particles. For low Mach number flows, the pressure gradient force is negligible if the particle density is much greater than that of the fluid. For supersonic flows where a standing shock is present, even for a steady and uniform flow, it is unclear whether the significant pressure-gradient force should to be separated out from the particle force model. To answer this conceptual question, we perform single-sphere fully-resolved DNS simulations for a wide range of Mach numbers. We then examine whether the total force obtained from the DNS can be categorized into well-established models, such as the quasi-steady, added-mass, pressure-gradient, and history forces. Work sponsored by Advanced Simulation and Computing (ASC) program of NNSA and LDRD-CNLS of LANL.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5457225','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5457225"><span>Separation of Hydrogen from Carbon Dioxide through Porous Ceramics</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Shimonosono, Taro; Imada, Hikari; Maeda, Hikaru; Hirata, Yoshihiro</p> <p>2016-01-01</p> <p>The gas permeability of α-alumina, yttria-stabilized zirconia (YSZ), and silicon carbide porous ceramics toward H2, CO2, and H2–CO2 mixtures were investigated at room temperature. The permeation of H2 and CO2 single gases occurred above a critical pressure gradient, which was smaller for H2 gas than for CO2 gas. When the Knudsen number (λ/r ratio, λ: molecular mean free path, r: pore radius) of a single gas was larger than unity, Knudsen flow became the dominant gas transportation process. The H2 fraction for the mixed gas of (20%–80%) H2–(80%–20%) CO2 through porous Al2O3, YSZ, and SiC approached unity with decreasing pressure gradient. The high fraction of H2 gas was closely related to the difference in the critical pressure gradient values of H2 and CO2 single gas, the inlet mixed gas composition, and the gas flow mechanism of the mixed gas. Moisture in the atmosphere adsorbed easily on the porous ceramics and affected the critical pressure gradient, leading to the increased selectivity of H2 gas. PMID:28774051</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_16 --> <div id="page_17" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="321"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/18959664','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/18959664"><span>Physiological control of a rotary blood pump with selectable therapeutic options: control of pulsatility gradient.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Arndt, Andreas; Nüsser, Peter; Graichen, Kurt; Müller, Johannes; Lampe, Bernhard</p> <p>2008-10-01</p> <p>A control strategy for rotary blood pumps meeting different user-selectable control objectives is proposed: maximum support with the highest feasible flow rate versus medium support with maximum ventricular washout and controlled opening of the aortic valve (AoV). A pulsatility index (PI) is calculated from the pressure difference, which is deduced from the axial thrust measured by the magnetic bearing of the pump. The gradient of PI with respect to pump speed (GPI) is estimated via online system identification. The outer loop of a cascaded controller regulates GPI to a reference value satisfying the selected control objective. The inner loop controls the PI to a reference value set by the outer loop. Adverse pumping states such as suction and regurgitation can be detected on the basis of the GPI estimates and corrected by the controller. A lumped-parameter computer model of the assisted circulation was used to simulate variations of ventricular contractility, pulmonary venous pressure, and aortic pressure. The performance of the outer control loop was demonstrated by transitions between the two control modes. Fast reaction of the inner loop was tested by stepwise reduction of venous return. For maximum support, a low PI was maintained without inducing ventricular collapse. For maximum washout, the pump worked at a high PI in the transition region between the opening and the permanently closed AoV. The cascaded control of GPI and PI is able to meet different control objectives and is worth testing in vitro and in vivo.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JGRD..122.1387D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JGRD..122.1387D"><span>Lagrangian dynamics of the mistral during the HyMeX SOP2</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Drobinski, P.; Alonzo, B.; Basdevant, C.; Cocquerez, P.; Doerenbecher, A.; Fourrié, N.; Nuret, M.</p> <p>2017-02-01</p> <p>The mistral refers to a severe wind blowing over the Gulf of Lions after being channeled in the Rhone valley. It influences the western Mediterranean climate as it brings cold and dry continental air over the warm western Mediterranean, generating intense air-sea heat exchanges and sea surface cooling, inducing the formation of the western Mediterranean deep water that moves into the Atlantic Ocean. The mistral is frequently observed to extend as far as a few hundred kilometers from the coast, and its fine-scale dynamics over the sea is still only partially understood as finely resolved observations in time and space are lacking. The boundary layer pressurized balloons (BLPB) developed by the Centre National d'Etudes Spatiales and deployed during HyMeX SOP2 allowed the Lagrangian documentation of the mistral events that occurred between beginning of February to mid-March 2013. Analyzed in synergy with the AROME-WMED weather forecast model, all the terms of the Lagrangian formulation of the momentum conservation equation could be quantified showing three different regions: (1) an injection zone where the mistral flow is directed toward the center of the Genoa cyclone due to a strong zonal pressure gradient, enhanced friction, and entrainment in the mountain wake; (2) an ejection zone where the flow is deflected outward of the cyclone due to either the nonnegligible inertia pseudoforce or an inertial oscillation caused by a sudden friction decrease; and (3) a region of geostrophic deceleration due to the weakening of the pressure gradient.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.7726D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.7726D"><span>Lagrangian dynamics of the mistral during the HyMeX SOP2</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Drobinski, Philippe; Alonzo, Bastien; Basdevant, Claude; Cocquerez, Philippe; Fourrié, Nadia; Nuret, Mathieu</p> <p>2017-04-01</p> <p>The mistral refers to a severe wind blowing over the Gulf of Lions after being channeled in the Rhone valley. It influences the western Mediterranean climate as it brings cold and dry continental air over the warm western Mediterranean, generating intense air-sea heat exchanges and sea surface cooling, inducing the formation of the western Mediterranean deep water that moves into the Atlantic Ocean. The mistral is frequently observed to extend as far as a few hundred kilometers from the coast, and its fine-scale dynamics over the sea is still only partially understood as finely resolved observations in time and space are lacking. The boundary layer pressurized balloons (BLPB) developed by the Centre National d'Etudes Spatiales and deployed during HyMeX SOP2 allowed the Lagrangian documentation of the mistral events that occurred between beginning of February to mid-March 2013. Analyzed in synergy with the AROME-WMED weather forecast model, all the terms of the Lagrangian formulation of the momentum conservation equation could be quantified showing three different regions: (1) an injection zone where the mistral flow is directed toward the center of the Genoa cyclone due to a strong zonal pressure gradient, enhanced friction, and entrainment in the mountain wake; (2) an ejection zone where the flow is deflected outward of the cyclone due to either the nonnegligible inertia pseudoforce or an inertial oscillation caused by a sudden friction decrease; and (3) a region of geostrophic deceleration due to the weakening of the pressure gradient.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.usgs.gov/of/2013/1058/','USGSPUBS'); return false;" href="https://pubs.usgs.gov/of/2013/1058/"><span>Regional maps of subsurface geopressure gradients of the onshore and offshore Gulf of Mexico basin</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Burke, Lauri A.; Kinney, Scott A.; Dubiel, Russell F.; Pitman, Janet K.</p> <p>2013-01-01</p> <p>The U.S. Geological Survey created a comprehensive geopressure-gradient model of the regional pressure system spanning the onshore and offshore Gulf of Mexico basin, USA. This model was used to generate ten maps that included (1) five contour maps characterizing the depth to the surface defined by the first occurrence of isopressure gradients ranging from 0.60 psi/ft to 1.00 psi/ft, in 0.10-psi/ft increments; and (2) five supporting maps illustrating the spatial density of the data used to construct the contour maps. These contour maps of isopressure-gradients at various increments enable the identification and quantification of the occurrence, magnitude, location, and depth of the subsurface pressure system, which allows for the broad characterization of regions exhibiting overpressured, underpressured, and normally pressured strata. Identification of overpressured regions is critical for exploration and evaluation of potential undiscovered hydrocarbon accumulations based on petroleum-generation pressure signatures and pressure-retention properties of reservoir seals. Characterization of normally pressured regions is essential for field development decisions such as determining the dominant production drive mechanisms, evaluating well placement and drainage patterns, and deciding on well stimulation methods such as hydraulic fracturing. Identification of underpressured regions is essential for evaluating the feasibility of geological sequestration and long-term containment of fluids such as supercritical carbon dioxide for alternative disposal methods of greenhouse gases. This study is the first, quantitative investigation of the regional pressure systems of one of the most important petroleum provinces in the United States. Although this methodology was developed for pressure studies in the Gulf of Mexico basin, it is applicable to any basin worldwide.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1999SPIE.3874..412G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1999SPIE.3874..412G"><span>Doping and structural properties for the phosphorous-doped polysilicon layers used for micromechanical applications</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gaiseanu, Florin; Esteve, Jaume; Cane, Carles; Perez-Rodriguez, Alejandro; Morante, Juan R.; Serre, Christoph</p> <p>1999-08-01</p> <p>Our researches were devoted to the micromechanical elements fabricated by the surface micromachining technology, in order to reduce or to eliminate the internal stress or the stress gradients. We used an analysis based on secondary ion mass spectroscopy and the spreading resistance profiling determinations, correlated with cross-section electron transmission spectroscopy. The stress induced in the polysilicon layers by the technological processes depends on: (i) the conditions of the low pressure chemical vapor deposition process; (ii) the phosphorus doping technique; (iii) the subsequent multi-step annealing processes. In our experiments the LP-CVD conditions were maintained the same, but the condition specified previously as items (ii) was varied by using two different doping techniques: thermal- chemical doping consisting in prediffusion from a POCl3 source in an open furnace tube; ionic implantation with an energy E equals 65KeV and a dose N equals 4.5 X 1015 cm-2. The implantation process was followed by an annealing at 900 degrees C in an oxygen ambient for 30 minutes. The thermal budget was varied after the doping in order to reduce the stress gradient in the polysilicon layers. The results of our analysis allow us to show that: (1) the doping gradients are correlated with the slower phosphorus grains forme by an excess of the oxygen atoms; a concurrent process induced by the silicon self-interstitial injection during the diffusion and oxidation, determines the enhancement of the grain growth and therefore the enhancement of the electrical activation especially near the internal polysilicon interface; (2) the post-doping annealing conditions could be varied in a convenient manner, so that the doping induced stress gradients into the polysilicon layers to be reduced or completely eliminated for suitable micromechanical induced stress gradients into the polysilicon layers to be reduced or completely eliminated for suitable micromechanical applications. The results were used for the process optimization of micromechanical elements. The internal stress was determined by using anew, pull-in voltage method, allowing the comparison of the theory with the experimental data. It was deduced a new form of the equations set useful to extract the mechanical parameters like the internal stress and the Young's module. It was also deduced a simplified approximate formula useful to apply the least square fitting method for the extraction of the mechanical parameters. The results confirms the conclusions of the doping and the structural analysis.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JSV...332.5322L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JSV...332.5322L"><span>Frequency-domain prediction of broadband trailing edge noise from a blunt flat plate</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lee, Gwang-Se; Cheong, Cheolung</p> <p>2013-10-01</p> <p>The aim of this study is to develop an efficient methodology for frequency-domain prediction of broadband trailing edge noise from a blunt flat plate where non-zero pressure gradient may exist in its boundary layer. This is achieved in two ways: (i) by developing new models for point pressure spectra within the boundary layer over a flat plate, and (ii) by deriving a simple formula to approximate the effect of convective velocity on the radiated noise spectrum. Firstly, two types of point pressure spectra-required as input data to predict the trailing edge noise in the frequency domain-are used. One is determined using the semi-analytic (S-A) models based on the boundary-layer theory combined with existing empirical models. It is shown that the prediction using these models show good agreements with the measurements where zero-pressure gradient assumption is valid. However, the prediction show poor agreement with that obtained from large eddy simulation results where negative (favorable) pressure gradient is observed with the boundary layer. Based on boundary layer characteristics predicted using the large eddy simulations, new model for point wall pressure spectra is proposed to account for the effect of favorable pressure gradient over the blunt flat plate on the wall pressure spectra. Sound spectra that were predicted using these models are compared with measurements to validate the proposed prediction scheme. The advantage of the semi-analytic model is that it can be applied to problems at Reynolds numbers for which the empirical model is not available. In addition, it is expected that the current models can be applied to the cases where favorable pressure gradient exists in the boundary layer over a blunt flat plate. Secondly, in order to quantitatively analyze contributions of the pressure field within the turbulent boundary layer on the flat plate to trailing edge noise, total pressure over the surface of airfoil is decomposed into its two constituents: incident pressure generated in the boundary layer without a trailing edge and the pressure formed by the scattering of the incident pressure at the trailing edge. The predictions made using each of the incident and scattered pressures reveal that the convective velocity of turbulence in the boundary layer dominantly affects the radiated sound pressure spectrum, both in terms of the gross behavior of the overall acoustic pressure spectrum through the scattered pressure and in terms of the narrow band small fluctuations of the spectrum through the incident pressure. The interaction term between the incident and the scattered is defined and the incident is shown to contribute to the radiated acoustic pressure through the interaction term. Based on this finding, a simple model to effectively compute the effects of convection velocities of the turbulence on the radiated sound pressure spectrum is proposed. It is shown that the proposed method can effectively and accurately predict the broadband trailing edge noise from the plate with considering both the incident and the scattered contributions.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JAMES...7..938T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JAMES...7..938T"><span>A strategy for representing the effects of convective momentum transport in multiscale models: Evaluation using a new superparameterized version of the Weather Research and Forecast model (SP-WRF)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tulich, S. N.</p> <p>2015-06-01</p> <p>This paper describes a general method for the treatment of convective momentum transport (CMT) in large-scale dynamical solvers that use a cyclic, two-dimensional (2-D) cloud-resolving model (CRM) as a "superparameterization" of convective-system-scale processes. The approach is similar in concept to traditional parameterizations of CMT, but with the distinction that both the scalar transport and diagnostic pressure gradient force are calculated using information provided by the 2-D CRM. No assumptions are therefore made concerning the role of convection-induced pressure gradient forces in producing up or down-gradient CMT. The proposed method is evaluated using a new superparameterized version of the Weather Research and Forecast model (SP-WRF) that is described herein for the first time. Results show that the net effect of the formulation is to modestly reduce the overall strength of the large-scale circulation, via "cumulus friction." This statement holds true for idealized simulations of two types of mesoscale convective systems, a squall line, and a tropical cyclone, in addition to real-world global simulations of seasonal (1 June to 31 August) climate. In the case of the latter, inclusion of the formulation is found to improve the depiction of key synoptic modes of tropical wave variability, in addition to some aspects of the simulated time-mean climate. The choice of CRM orientation is also found to importantly affect the simulated time-mean climate, apparently due to changes in the explicit representation of wide-spread shallow convective regions.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2000JChPh.11310820R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2000JChPh.11310820R"><span>Young-Laplace equation for liquid crystal interfaces</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rey, Alejandro D.</p> <p>2000-12-01</p> <p>This letter uses the classical theories of liquid crystal physics to derive the Young-Laplace equation of capillary hydrostatics for interfaces between viscous isotropic (I) fluids and nematic liquid crystals (NLC's), and establishes the existence of four energy contributions to pressure jumps across these unusual anisotropic interfaces. It is shown that in addition to the usual curvature contribution, bulk and surface gradient elasticity, elastic stress, and anchoring energy contribute to pressure differentials across the interface. The magnitude of the effect is proportional to the elastic moduli of the NLC, and to the bulk and surface orientation gradients that may be present in the nematic phase. In contrast to the planar interface between isotropic fluids, flat liquid crystal interfaces support pressure jumps if elastic stresses, bulk and surface gradient energy, and/or anchoring energies are finite.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016APS..DFDG32008A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016APS..DFDG32008A"><span>Experimental Measurements of a High Reynolds Num- ber Adverse Pressure Gradient Turbulent Boundary Layer</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Atkinson, Callum; Amili, Omid; Stanislas, Michel; Cuvier, Christophe; Foucaut, Jean-Marc; Srinath, Sricharan; Laval, Jean-Philippe; Kaehler, Christian; Hain, Rainer; Scharnowski, Sven; Schroeder, Andreas; Geisler, Reinhard; Agocs, Janos; Roese, Anni; Willert, Christian; Klinner, Joachim; Soria, Julio</p> <p>2016-11-01</p> <p>The study of adverse pressure gradient turbulent boundary layers is complicated by the need to characterise both the local pressure gradient and it's upstream flow history. It is therefore necessary to measure a significant streamwise domain at a resolution sufficient to resolve the small scales features. To achieve this collaborative particle image velocimetry (PIV) measurements were performed in the large boundary layer wind-tunnel at the Laboratoire de Mecanique de Lille, including: planar measurements spanning a streamwise domain of 3.5m using 16 cameras covering 15 δ spanwise wall-normal stereo-PIV measurements, high-speed micro-PIV of the near wall region and wall shear stress; and streamwise wall-normal PIV in the viscous sub layer. Details of the measurements and preliminary results will be presented.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013APS..DFDA25002K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013APS..DFDA25002K"><span>Plasma Streamwise Vortex Generators in an Adverse Pressure Gradient</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kelley, Christopher; Corke, Thomas; Thomas, Flint</p> <p>2013-11-01</p> <p>A wind tunnel experiment was conducted to compare plasma streamwise vortex generators (PSVGs) and passive vortex generators (VGs). These devices were installed on a wing section by which the angle of attack could be used to vary the streamwise pressure gradient. The experiment was performed for freestream Mach numbers 0.1-0.2. Three-dimensional velocity components were measured using a 5-hole Pitot probe in the boundary layer. These measurements were used to quantify the production of streamwise vorticity and the magnitude of the reorientation term from the vorticity transport equation. The effect of Mach number, pressure gradient, operating voltage, and electrode length was then investigated for the PSVGs. The results indicate that the PSVGs could easily outperform the passive VGs and provide a suitable alternative for flow control.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70103862','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70103862"><span>Seasonal circulation over the Catalan inner-shelf (northwest Mediterranean Sea)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Grifoll, Manel; Aretxabaleta, Alfredo L.; Pelegrí, Josep L.; Espino, Manuel; Warner, John C.; Sánchez-Arcilla, Agustín</p> <p>2013-01-01</p> <p>This study characterizes the seasonal cycle of the Catalan inner-shelf circulation using observations and complementary numerical results. The relation between seasonal circulation and forcing mechanisms is explored through the depth-averaged momentum balance, for the period between May 2010 and April 2011, when velocity observations were partially available. The monthly-mean along-shelf flow is mainly controlled by the along-shelf pressure gradient and by surface and bottom stresses. During summer, fall, and winter, the along-shelf momentum balance is dominated by the barotropic pressure gradient and local winds. During spring, both wind stress and pressure gradient act in the same direction and are compensated by bottom stress. In the cross-shelf direction the dominant forces are in geostrophic balance, consistent with dynamic altimetry data.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JGRC..118.5844G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JGRC..118.5844G"><span>Seasonal circulation over the Catalan inner-shelf (northwest Mediterranean Sea)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Grifoll, Manel; Aretxabaleta, Alfredo L.; Pelegrí, Josep L.; Espino, Manuel; Warner, John C.; Sánchez-Arcilla, Agustín.</p> <p>2013-10-01</p> <p>This study characterizes the seasonal cycle of the Catalan inner-shelf circulation using observations and complementary numerical results. The relation between seasonal circulation and forcing mechanisms is explored through the depth-averaged momentum balance, for the period between May 2010 and April 2011, when velocity observations were partially available. The monthly-mean along-shelf flow is mainly controlled by the along-shelf pressure gradient and by surface and bottom stresses. During summer, fall, and winter, the along-shelf momentum balance is dominated by the barotropic pressure gradient and local winds. During spring, both wind stress and pressure gradient act in the same direction and are compensated by bottom stress. In the cross-shelf direction the dominant forces are in geostrophic balance, consistent with dynamic altimetry data.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19970021679','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19970021679"><span>Latitudinal Dependence of the Radial IMF Component - Interplanetary Imprint</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Suess, S. T.; Smith, E. J.; Phillips, J.; Goldstein, B. E.; Nerney, S.</p> <p>1996-01-01</p> <p>Ulysses measurements have confirmed that there is no significant gradient with respect to heliomagnetic latitude in the radial component, B(sub r,), of the interplanetary magnetic field. There are two processes responsible for this observation. In the corona, the plasma beta is much less than 1, except directly above streamers, so both longitudinal and latitudinal (meridional) gradients in field strength will relax, due to the transverse magnetic pressure gradient force, as the solar wind carries magnetic flux away from the Sun. This happens so quickly that the field is essentially uniform by 5 solar radius. Beyond 10 solar radius, beta is greater than 1 and it is possible for a meridional thermal pressure gradient to redistribute magnetic flux - an effect apparently absent in Ulysses and earlier ICE and Interplanetary Magnetic Physics (IMP) data. We discuss this second effect here, showing that its absence is mainly due to the perpendicular part of the anisotropic thermal pressure gradient in the interplanetary medium being too small to drive significant meridional transport between the Sun and approx. 4 AU. This is done using a linear analytic estimate of meridional transport. The first effect was discussed in an earlier paper.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017APJAS..53..445H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017APJAS..53..445H"><span>Marginal sea surface temperature variation as a pre-cursor of heat waves over the Korean Peninsula</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ham, Yoo-Geun; Na, Hye-Yun</p> <p>2017-11-01</p> <p>This study examines the role of the marginal sea surface temperature (SST) on heat waves over Korea. It is found that sea surface warming in the south sea of Korea/Japan (122-138°E, 24- 33°N) causes heat waves after about a week. Due to the frictional force, the positive geopotential height anomalies associated with the south sea warming induce divergent flows over the boundary layer. This divergent flow induces the southerly in Korea, which leads to a positive temperature advection. On the other hand, over the freeatmosphere, the geostrophic wind around high-pressure anomalies flows in a westerly direction over Korea during the south sea warming, which is not effective in temperature advection. Therefore, the positive temperature advection in Korea due to the south sea warming decreases with height. This reduces the vertical potential temperature gradient, which indicates a negative potential vorticity (PV) tendency over Korea. Therefore, the high-pressure anomaly over the south sea of Korea is propagated northward, which results in heat waves due to more incoming solar radiation.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/8061869','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/8061869"><span>An experimental-computational analysis of MHV cavitation: effects of leaflet squeezing and rebound.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Makhijani, V B; Yang, H Q; Singhal, A K; Hwang, N H</p> <p>1994-04-01</p> <p>A combined experimental-computational study was performed to investigate the flow mechanics which could cause cavitation during the squeezing and rebounding phases of valve closure in the 29 mm mitral bileaflet Edwards-Duromedics (ED) mechanical heart valve (MHV). Leaflet closing motion was measured in vitro, and input into a computational fluid mechanics software package, CFD-ACE, to compute flow velocities and pressures in the small gap space between the occluder tip and valve housing. The possibility of cavitation inception was predicted when fluid pressures dropped below the saturated vapor pressure for blood plasma. The computational analysis indicated that cavitation is more likely to be induced during valve rebound rather than the squeezing phase of valve closure in the 29 mm ED-MHV. Also, there is a higher probability of cavitation at lower values of the gap width at the point of impact between the leaflet tip and housing. These predictions of cavitation inception are not likely to be significantly influenced by the water-hammer pressure gradient that develops during valve closure.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/servlets/purl/865383','DOE-PATENT-XML'); return false;" href="https://www.osti.gov/servlets/purl/865383"><span>High pressure liquid chromatographic gradient mixer</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/doepatents">DOEpatents</a></p> <p>Daughton, Christian G.; Sakaji, Richard H.</p> <p>1985-01-01</p> <p>A gradient mixer which effects the continuous mixing of any two miscible solvents without excessive decay or dispersion of the resultant isocratic effluent or of a linear or exponential gradient. The two solvents are fed under low or high pressure by means of two high performance liquid chromatographic pumps. The mixer comprises a series of ultra-low dead volume stainless steel tubes and low dead volume chambers. The two solvent streams impinge head-on at high fluxes. This initial nonhomogeneous mixture is then passed through a chamber packed with spirally-wound wires which cause turbulent mixing thereby homogenizing the mixture with minimum "band-broadening".</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/biblio/5708006','DOE-PATENT-XML'); return false;" href="https://www.osti.gov/biblio/5708006"><span>High-pressure liquid chromatographic gradient mixer</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/doepatents">DOEpatents</a></p> <p>Daughton, C.G.; Sakaji, R.H.</p> <p>1982-09-08</p> <p>A gradient mixer effects the continuous mixing of any two miscible solvents without excessive decay or dispersion of the resultant isocratic effluent or of a linear or exponential gradient. The two solvents are fed under low or high pressure by means of two high performance liquid chromatographic pumps. The mixer comprises a series of ultra-low dead volume stainless steel tubes and low dead volume chambers. The two solvent streams impinge head-on at high fluxes. This initial nonhomogeneous mixture is then passed through a chamber packed with spirally-wound wires which cause turbulent mixing thereby homogenizing the mixture with minimum band-broadening.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/biblio/21175582-situ-stress-evolution-during-magnetron-sputtering-transition-metal-nitride-thin-films','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/21175582-situ-stress-evolution-during-magnetron-sputtering-transition-metal-nitride-thin-films"><span>In situ stress evolution during magnetron sputtering of transition metal nitride thin films</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Abadias, G.; Guerin, Ph.</p> <p>2008-09-15</p> <p>Stress evolution during reactive magnetron sputtering of TiN, ZrN, and TiZrN layers was studied using real-time wafer curvature measurements. The presence of stress gradients is revealed, as the result of two kinetically competing stress generation mechanisms: atomic peening effect, inducing compressive stress, and void formation, leading to a tensile stress regime predominant at higher film thickness. No stress relaxation is detected during growth interrupt in both regimes. A change from compressive to tensile stress is evidenced with increasing film thickness, Ti content, sputtering pressure, and decreasing bias voltage.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012ApPhL.100e4101B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012ApPhL.100e4101B"><span>Thermally induced secondary atomization of droplet in an acoustic field</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Basu, Saptarshi; Saha, Abhishek; Kumar, Ranganathan</p> <p>2012-01-01</p> <p>We study the thermal effects that lead to instability and break up in acoustically levitated vaporizing fuel droplets. For selective liquids, atomization occurs at the droplet equator under external heating. Short wavelength [Kelvin-Helmholtz (KH)] instability for diesel and bio-diesel droplets triggers this secondary atomization. Vapor pressure, latent heat, and specific heat govern the vaporization rate and temperature history, which affect the surface tension gradient and gas phase density, ultimately dictating the onset of KH instability. We develop a criterion based on Weber number to define a condition for the inception of secondary atomization.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1983AcAau..10..453W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1983AcAau..10..453W"><span>Shock-induced flow separation and the orbiter thermal protection system</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Waiter, S.-A.</p> <p></p> <p>The Space Shuttle orbiter's thermal protection system (TPS) is composed of reusable tiles separated by narrow gaps that accommodate the contraction and expansion of the aluminum structure that the tiles protect. When local pressure gradients exist, air flows through the tile gaps and releases heat energy by convection. The gaps represent a heat short to the structure, strain isolator pad (SIP), and filler bar. A typical problem is the pressure gradient created during entry by body flap deflection. After a brief description of how this problem affects the Space Shuttle orbiter, a theoretical and experimental review of the major parameters involved in gap heating are analyzed. Then, a review of well-known classical methods to resolve the gap aeroheating problem in the presence of a pressure gradient is presented, and a few solutions are illustrated to assess the sensitivity of each one. The following section starts with a basic relationship (called "eyeball" because of its simplicity) and follows the results up through the most modern engineering approach available in the literature. It shows that in all cases calculated significant areas of overtemperature were predicted. However, none of these methods could be correlated by experimental data. Lastly, the paper presents the solution obtained by using the most sophisticated method, based upon the Navier-Stokes equations. This approach shows excellent correlation with wind tunnel data. The application to four trajectory time points shows less severe results than the other methods. This can be explained by the introduction of a certain amount of conservatism to account for uncertainties inherent in the previous analyses. No correlation of this "exact solution" with the simple preestablished relationships has been found, indicating that more parameters than expected could be involved. However, an after-the-fact, semi-empirical engineering solution that fits the Navier-Stokes solution with good agreement was established.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_17 --> <div id="page_18" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="341"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27501815','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27501815"><span>Latitudinal Gradients in Induced and Constitutive Resistance against Herbivores.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Anstett, Daniel N; Chen, Wen; Johnson, Marc T J</p> <p>2016-08-01</p> <p>Plants are hypothesized to evolve increased defense against herbivores at lower latitudes, but an increasing number of studies report evidence that contradicts this hypothesis. Few studies have examined the evolution of constitutive and induced resistance along latitudinal gradients. When induction is not considered, underlying patterns of latitudinal clines in resistance can be obscured because plant resistance represents a combination of induced and constitutive resistance, which may show contrasting patterns with latitude. Here, we asked if there are latitudinal gradients in constitutive versus induced resistance by using genotypes of Oenothera biennis (Onagraceae) sampled along an 18° latitudinal gradient. We conducted two bioassay experiments to compare the resistance of plant genotypes against one generalist (Spodoptera exigua) and one specialist (Acanthoscelidius acephalus) herbivore. These insects were assayed on: i) undamaged control plants, ii) plants that had been induced with jasmonic acid, and iii) plants induced with herbivore damage. Additionally, we examined latitudinal gradients of constitutive and induced chemical resistance by measuring the concentrations of total phenolics, the concentration of oxidized phenolics, and the percentage of phenolics that were oxidized. Spodoptera exigua showed lower performance on plants from lower latitudes, whereas A. acephalus showed no latitudinal pattern. Constitutive total phenolics were greater in plants from lower latitudes, but induced plants showed higher total phenolics at higher latitudes. Oxidative activity was greatest at higher latitudes regardless of induction. Overall, both latitude and induction have an impact on different metrics of plant resistance to herbivory. Further studies should consider the effect of induction and herbivore specialization more explicitly, which may help to resolve the controversy in latitudinal gradients in herbivory and defense.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25502599','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25502599"><span>Characterization of the startup transient electrokinetic flow in rectangular channels of arbitrary dimensions, zeta potential distribution, and time-varying pressure gradient.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Miller, Andrew; Villegas, Arturo; Diez, F Javier</p> <p>2015-03-01</p> <p>The solution to the startup transient EOF in an arbitrary rectangular microchannel is derived analytically and validated experimentally. This full 2D transient solution describes the evolution of the flow through five distinct periods until reaching a final steady state. The derived analytical velocity solution is validated experimentally for different channel sizes and aspect ratios under time-varying pressure gradients. The experiments used a time resolved micro particle image velocimetry technique to calculate the startup transient velocity profiles. The measurements captured the effect of time-varying pressure gradient fields derived in the analytical solutions. This is tested by using small reservoirs at both ends of the channel which allowed a time-varying pressure gradient to develop with a time scale on the order of the transient EOF. Results showed that under these common conditions, the effect of the pressure build up in the reservoirs on the temporal development of the transient startup EOF in the channels cannot be neglected. The measurements also captured the analytical predictions for channel walls made of different materials (i.e., zeta potentials). This was tested in channels that had three PDMS and one quartz wall, resulting in a flow with an asymmetric velocity profile due to variations in the zeta potential between the walls. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70029246','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70029246"><span>The controlling effect of viscous dissipation on magma flow in silicic conduits</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Mastin, L.G.</p> <p>2005-01-01</p> <p>Nearly all volcanic conduit models assume that flow is Newtonian and isothermal. Such models predict that, during high-flux silicic eruptions, gradients in pressure with depth increase upward as magma accelerates and becomes more viscous, leading to extremely low pressure and fragmentation at a depth of kilometers below the surface. In this paper I show that shear heating, also known as viscous dissipation, dramatically reduces the pressure gradient required for flow and concentrates shear in narrow zones along the conduit margin. The reduction in friction may eliminate the zone of low pressure predicted by isothermal models and move the fragmentation level up to the surface.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/servlets/purl/867668','DOE-PATENT-XML'); return false;" href="https://www.osti.gov/servlets/purl/867668"><span>Methods and apparatus for moving and separating materials exhibiting different physical properties</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/doepatents">DOEpatents</a></p> <p>Peterson, Stephen C.; Brimhall, Owen D.; McLaughlin, Thomas J.; Baker, Charles D.; Sparks, Sam L.</p> <p>1991-01-01</p> <p>Methods and apparatus for controlling the movement of materials having different physical properties when one of the materials is a fluid. The invention does not rely on flocculation, sedimentation, centrifugation, the buoyancy of the materials, or any other gravity dependent characteristic, in order to achieve its desired results. The methods of the present invention provide that a first acoustic wave is propagated through a vessel containing the materials. A second acoustic wave, at a frequency different than the first acoustic wave, is also propagated through the vessel so that the two acoustic waves are superimposed upon each other. The superimposition of the two waves creates a beat frequency wave. The beat frequency wave comprises pressure gradients dividing regions of maximum and minimum pressure. The pressure gradients and the regions of maximum and minimum pressure move through space and time at a group velocity. The moving pressure gradients and regions of maximum and minimum pressure act upon the materials so as to move one of the materials towards a predetermined location in the vessel. The present invention provides that the materials may be controllably moved toward a location, aggregated at a particular location, or physically separated from each other.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/servlets/purl/866654','DOE-PATENT-XML'); return false;" href="https://www.osti.gov/servlets/purl/866654"><span>Methods and apparatus for moving and separating materials exhibiting different physical properties</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/doepatents">DOEpatents</a></p> <p>Peterson, Stephen C.; Brimhall, Owen D.; McLaughlin, Thomas J.; Baker, Charles D.; Sparks, Sam L.</p> <p>1988-01-01</p> <p>Methods and apparatus for controlling the movement of materials having different physical properties when one of the materials is a fluid. The invention does not rely on flocculation, sedimentation, centrifugation, the buoyancy of the materials, or any other gravity dependent characteristic, in order to achieve its desired results. The methods of the present invention provide that a first acoustic wave is progpagated through a vessel containing the materials. A second acoustic wave, at a frequency different than the first acoustic wave, is also propagated through the vessel so that the two acoustic waves are superimposed upon each other. The superimposition of the two waves creates a beat frequency wave. The beat frequency wave comprises pressure gradients dividing regions of maximum and minimum pressure. The pressure gradients and the regions of maximum and minimum pressure move through space and time at a group velocity. The moving pressure gradients and regions of maximum and minimum pressure act upon the marterials so as to move one of the materials towards a predetermined location in the vessel. The present invention provides that the materials may be controllably moved toward a location, aggreated at a particular location, or physically separated from each other.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFMOS43B1402M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFMOS43B1402M"><span>A Model based Examination of Conditions for Ignition of Turbidity Currents on Slopes</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mehta, A. J.; Krishna, G.</p> <p>2009-12-01</p> <p>Turbidity currents form a major mechanism for the movement of sediment in the natural environment. Self-accelerating turbidity currents over continental slopes are of considerable scientific and engineering interest due to their role as agents for submarine sediment transportation from the shelf to the seabed. Such currents are called ignitive provided they eventually reach a catastrophic state as acceleration results in high sediment loads due to erosion of the sloping bed. A numerical model, which treats the fluid and the particles as two separate phases, is applied to investigate the effects of particle size, initial flow friction velocity and mild bed slope on the ignitive condition. Laboratory experimental data have been included as part of the analysis for qualitative comparison purposes. Ignition for the smallest of the three selected sizes (0.21mm) of medium sand typical of Florida beaches was found to depend on the initial conditions at the head of the slope as determined by the pressure gradient. Bed slope seemed to be of secondary importance. For the two sands with larger grain sizes (0.28mm and 0.35mm) the slope was found to play a more important role when compared to the initial pressure gradient. For a given pressure gradient, increasing the slope increased the likelihood of self-acceleration. It is concluded that in general ignition cannot be defined merely in terms of positive values of the velocity gradient and the sediment flux gradient along the slope. Depending on particle size the initial pressure gradient can also play a role. For the selected initial conditions (grain size, pressure gradient and bed slope), out of the 54 combinations tested, all except three satisfied the Knapp-Bagnold criterion for auto-suspension irrespective of whether the turbid current was ignitive or non-ignitive. In all 54 cases the current was found to erode the bed. Further use of the model will require accommodation of wider ranges of sediment size and bed density, and a thorough verification against experimental data.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015APS..DPPC12042C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015APS..DPPC12042C"><span>Fast ion beta limit measurements by collimated neutron detection in MST plasmas</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Capecchi, William; Anderson, Jay; Bonofiglo, Phillip; Kim, Jungha; Sears, Stephanie</p> <p>2015-11-01</p> <p>Fast ion orbits in the reversed field pinch (RFP) are well ordered and classically confined despite magnetic field stochasticity generated by multiple tearing modes. Classical TRANSP modeling of a 1MW tangentially injected hydrogen neutral beam in MST deuterium plasmas predicts a core-localized fast ion density that can be up to 25% of the electron density and a fast ion beta of many times the local thermal beta. However, neutral particle analysis of an NBI-driven mode (presumably driven by a fast ion pressure gradient) shows mode-induced transport of core-localized fast ions and a saturated fast ion density. The TRANSP modeling is presumed valid until the onset of the beam-driven mode and gives an initial estimate of the volume-averaged fast ion beta of 1-2% (local core value up to 10%). A collimated neutron detector for fusion product profile measurements will be used to determine the spatial distribution of fast ions, allowing for a first measurement of the critical fast-ion pressure gradient required for mode destabilization. Testing/calibration data and initial fast-ion profiles will be presented. Characterization of both the local and global fast ion beta will be done for deuterium beam injection into deuterium plasmas for comparison to TRANSP predictions. Work supported by US DOE.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUOSEC21A..02R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUOSEC21A..02R"><span>Observations of Inner Shelf Flows Influenced by a Small-Scale River Plume in the Northern Gulf of Mexico</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Roth, M.; MacMahan, J.; Reniers, A.; Ozgokmen, T. M.</p> <p>2016-02-01</p> <p>Recent work has demonstrated that wind and waves are important forcing mechanisms for the inner shelf vertical current structure. Here, the inner shelf flows are evaluated away from an adjacent inlet where a small-scale buoyant plume emerges. The plume's nearshore extent, speed, vertical thickness, and density are controlled by the passage of low-pressure extratropical cyclones that are common in the northern Gulf of Mexico. The colder, brackish plume water provides vertical stratification and a cross-shore density gradient with the warmer, saline oceanic water. An Acoustic Doppler Current Profiler (ADCP) was deployed in 10m water depth as part of an intensive 2-week experiment (SCOPE), which also obtained wind and cross-shelf temperature, salinity, and velocity. The 10m ADCP remained collecting an additional year of velocity observations. The plume was not always present, but episodically influenced the experiment site. When the plume reached the site, the alongshore surface and subsurface typically flowed in opposite directions, likely caused by plume-induced pressure gradients. Plumes that extended into the subsurface appear to have caused depth-averaged onshore flow above that expected from wind and wave-driven forcing. Observations from SCOPE and the 1-year ADCP are used to describe seasonal full-depth flow patterns influenced by wind, waves, and plume presence.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1990JAtS...47.2969X','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1990JAtS...47.2969X"><span>A Theoretical Study of Cold Air Damming.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Xu, Qin</p> <p>1990-12-01</p> <p>The dynamics of cold air damming are examined analytically with a two-layer steady state model. The upper layer is a warm and saturated cross-mountain (easterly or southeasterly onshore) flow. The lower layer is a cold mountain-parallel (northerly) jet trapped on the windward (eastern) side of the mountain. The interface between the two layers represents a coastal front-a sloping inversion layer coupling the trapped cold dome with the warm onshore flow above through pressure continuity.An analytical expression is obtained for the inviscid upper-layer flow with hydrostatic and moist adiabatic approximations. Blackadar's PBL parameterization of eddy viscosity is used in the lower-layer equations. Solutions for the mountain-parallel jet and its associated secondary transverse circulation are obtained by expanding asymptotically upon a small parameter proportional to the square root of the inertial aspect ratio-the ratio between the mountain height and the radius of inertial oscillation. The geometric shape of the sloping interface is solved numerically from a differential-integral equation derived from the pressure continuity condition imposed at the interface.The observed flow structures and force balances of cold air damming events are produced qualitatively by the model. In the cold dome the mountain-parallel jet is controlled by the competition between the mountain-parallel pressure gradient and friction: the jet is stronger with smoother surfaces, higher mountains, and faster mountain-normal geostrophic winds. In the mountain-normal direction the vertically averaged force balance in the cold dome is nearly geostrophic and controls the geometric shape of the cold dome. The basic mountain-normal pressure gradient generated in the cold dome by the negative buoyancy distribution tends to flatten the sloping interface and expand the cold dome upstream against the mountain-normal pressure gradient (produced by the upper-layer onshore wind) and Coriolis force (induced by the lower-layer mountain-parallel jet). It is found that the interface slope increases and the cold dome shrinks as the Froude number and/or upstream mountain-parallel geostrophic wind increase, or as the Rossby number, upper-layer depth, and/or surface roughness length decrease, and vice versa. The cold dome will either vanish or not be in a steady state if the Froude number is large enough or the roughness length gets too small. The theoretical findings are explained physically based on detailed analyses of the force balance along the inversion interface.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017NJPh...19j3005S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017NJPh...19j3005S"><span>Isochoric heating and strong blast wave formation driven by fast electrons in solid-density targets</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Santos, J. J.; Vauzour, B.; Touati, M.; Gremillet, L.; Feugeas, J.-L.; Ceccotti, T.; Bouillaud, R.; Deneuville, F.; Floquet, V.; Fourment, C.; Hadj-Bachir, M.; Hulin, S.; Morace, A.; Nicolaï, Ph; d'Oliveira, P.; Reau, F.; Samaké, A.; Tcherbakoff, O.; Tikhonchuk, V. T.; Veltcheva, M.; Batani, D.</p> <p>2017-10-01</p> <p>We experimentally investigate the fast (< 1 {ps}) isochoric heating of multi-layer metallic foils and subsequent high-pressure hydrodynamics induced by energetic electrons driven by high-intensity, high-contrast laser pulses. The early-time temperature profile inside the target is measured from the streaked optical pyrometry of the target rear side. This is further characterized from benchmarked simulations of the laser-target interaction and the fast electron transport. Despite a modest laser energy (< 1 {{J}}), the early-time high pressures and associated gradients launch inwards a strong compression wave developing over ≳ 10 ps into a ≈ 140 {Mbar} blast wave, according to hydrodynamic simulations, consistent with our measurements. These experimental and numerical findings pave the way to a short-pulse-laser-based platform dedicated to high-energy-density physics studies.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/2139552','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/2139552"><span>[Left auricular hypertrophy in aortic stenosis in adults].</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Boschat, J; Le Mehaute, H; Le Potier, J; Roriz, R; Gilard, M; Bergez, C; Etienne, Y; Blanc, J J; Penther, P</p> <p>1990-02-01</p> <p>Left atrial hypertrophy (LAH) was noted from the electrocardiograms of 72 of 98 adult patients (81%) who underwent hemodynamic evaluation of calcified aortostenosis (CAS). The relations between LAH and clinical, echographic and hemodynamic findings are specified. The frequency of LAH was not higher in cases of a history of hypertension, angina pectoris, lipothymia or exercise-induced syncope. In contrast, dyspnea was more frequently associated with LAH (84%) than not (17%). An approximately linear relation was seen between LAH and the mean pulmonary capillary pressure, the mean rate of circumferential decrease (RCF), the coefficient of muscle rigidity (ks of Mirsky), the left ventricular mass (LVM) and the left ventricle-aorta gradient. LAH is, therefore, a frequent sign in patients presenting CAS. Its origin is multifactorial, with a predominance of increased mean capillary pressure in cases of clinical signs of poor safety.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19860037687&hterms=electrotechnique&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Delectrotechnique','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19860037687&hterms=electrotechnique&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Delectrotechnique"><span>Numerical study of Reynolds stress in compressible flows</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Vandromme, D.; Hamin, H.</p> <p>1985-01-01</p> <p>A second order closure has been implemented in an implicit Navier-Stokes solver to study the behavior of the Reynolds stresses under the influence of severe pressure gradients. In the boundary layer zone, the strongly sheared character of the mean flow dominates the turbulence generation mechanisms. However, the pressure gradients also play a very important role for these processes, but at different locations within the boundary layer.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20040090128&hterms=ZEA+MAYS&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DZEA%2BMAYS','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20040090128&hterms=ZEA+MAYS&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DZEA%2BMAYS"><span>A gradient of endogenous calcium forms in mucilage of graviresponding roots of Zea mays</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Moore, R.; Fondren, W. M.</p> <p>1988-01-01</p> <p>Agar blocks that contacted the upper sides of tips of horizontally-oriented roots of Zea mays contain significantly less calcium (Ca) than blocks that contacted the lower sides of such roots. This gravity-induced gradient of Ca forms prior to the onset of gravicurvature, and does not form across tips of vertically-oriented roots or roots of agravitropic mutants. These results indicate that (1) Ca can be collected from mucilage of graviresponding roots, (2) gravity induces a downward movement of endogenous Ca in mucilage overlying the root tip, (3) this gravity-induced gradient of Ca does not form across tips of agravitropic roots, and (4) formation of a Ca gradient is not a consequence of gravicurvature. These results are consistent with gravity-induced movement of Ca being a trigger for subsequent redistribution of growth effectors (e.g. auxin) that induce differential growth and gravicurvature.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005AGUFMNG23A0093L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005AGUFMNG23A0093L"><span>Toward the Application of the Maximum Entropy Production Principle to a Broader Range of Far From Equilibrium Dissipative Systems</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lineweaver, C. H.</p> <p>2005-12-01</p> <p>The principle of Maximum Entropy Production (MEP) is being usefully applied to a wide range of non-equilibrium processes including flows in planetary atmospheres and the bioenergetics of photosynthesis. Our goal of applying the principle of maximum entropy production to an even wider range of Far From Equilibrium Dissipative Systems (FFEDS) depends on the reproducibility of the evolution of the system from macro-state A to macro-state B. In an attempt to apply the principle of MEP to astronomical and cosmological structures, we investigate the problematic relationship between gravity and entropy. In the context of open and non-equilibrium systems, we use a generalization of the Gibbs free energy to include the sources of free energy extracted by non-living FFEDS such as hurricanes and convection cells. Redox potential gradients and thermal and pressure gradients provide the free energy for a broad range of FFEDS, both living and non-living. However, these gradients have to be within certain ranges. If the gradients are too weak, FFEDS do not appear. If the gradients are too strong FFEDS disappear. Living and non-living FFEDS often have different source gradients (redox potential gradients vs thermal and pressure gradients) and when they share the same gradient, they exploit different ranges of the gradient. In a preliminary attempt to distinguish living from non-living FFEDS, we investigate the parameter space of: type of gradient and steepness of gradient.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EPJP..132..315B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EPJP..132..315B"><span>Effect of Knudsen thermal force on the performance of low-pressure micro gas sensor</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Barzegar Gerdroodbary, M.; Ganji, D. D.; Taeibi-Rahni, M.; Vakilipour, Shidvash</p> <p>2017-07-01</p> <p>In this paper, Direct Simulation Monte Carlo (DSMC) simulations were applied to investigate the mechanism of the force generation inside a low-pressure gas sensor. The flow feature and force generation mechanism inside a rectangular enclosure with heat and cold arms as the non-isothermal walls are comprehensively explained. In addition, extensive parametric studies are done to study the effects of physical parameters on the performance and characteristics of this device in different operating conditions. In this research, the Knudsen number is varied from 0.1 to 4.5 (0.5 to 11torr) to reveal all the characteristics of the thermally driven force inside the MEMS sensor. In order to simulate a rarefied gas inside the micro gas detector, Boltzmann equations are applied to obtain high-precision results. The effects of ambient pressure and temperature difference of arms are comprehensively investigated. Our findings show that maximum force increases more than 7 times when the temperature difference of the cold and hot arms is increased from 10 to 100K. In addition, the results demonstrate that the thermal gradient at rarefied pressure induces complex structure, and the mechanism of force generation highly varies at different pressure conditions.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20020067682&hterms=bubble+sort&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dbubble%2Bsort','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20020067682&hterms=bubble+sort&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dbubble%2Bsort"><span>Experimental Investigation of Separated and Transitional Boundary Layers Under Low-Pressure Turbine Airfoil Conditions</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hultgren, Lennart S.; Volino, Ralph J.</p> <p>2002-01-01</p> <p>Modern low-pressure turbine airfoils are subject to increasingly stronger pressure gradients as designers impose higher loading in an effort to improve efficiency and to reduce part count. The adverse pressure gradients on the suction side of these airfoils can lead to boundary-layer separation, particularly under cruise conditions. Separation bubbles, notably those which fail to reattach, can result in a significant degradation of engine efficiency. Accurate prediction of separation and reattachment is hence crucial to improved turbine design. This requires an improved understanding of the transition flow physics. Transition may begin before or after separation, depending on the Reynolds number and other flow conditions, has a strong influence on subsequent reattachment, and may even eliminate separation. Further complicating the problem are the high free-stream turbulence levels in a real engine environment, the strong pressure gradients along the airfoils, the curvature of the airfoils, and the unsteadiness associated with wake passing from upstream stages. Because of the complicated flow situation, transition in these devices can take many paths that can coexist, vary in importance, and possibly also interact, at different locations and instances in time. The present work was carried out in an attempt to systematically sort out some of these issues. Detailed velocity measurements were made along a flat plate subject to the same nominal dimensionless pressure gradient as the suction side of a modern low-pressure turbine airfoil ('Pak-B'). The Reynolds number based on wetted plate length and nominal exit velocity, Re, was varied from 50;000 to 300; 000, covering cruise to takeoff conditions. Low, 0.2%, and high, 7%, inlet free-stream turbulence intensities were set using passive grids. These turbulence levels correspond to about 0.2% and 2.5% turbulence intensity in the test section when normalized with the exit velocity. The Reynolds number and free-stream turbulence level do not have a significant effect on the location of boundary-layer separation unless they are high enough to induce transition upstream of separation. The location and extent of the transition zone, in contrast, depend strongly on Re and TI. The beginning of reattachment closely follows the onset of transition. Under low free-stream turbulence conditions the boundary layer is laminar at separation and then begins to exhibit fluctuations in a finite frequency band in the shear layer over the separation bubble. These fluctuations are due to instability waves. The fluctuations grow in magnitude, higher harmonics are generated, and finally lead to a breakdown to turbulence. Transition begins in the shear layer, but quickly spreads to the near wall region and causes the boundary layer to reattach. The transition is rapid and the resulting turbulence contains a full range of high and low frequencies. Under high free-stream turbulence conditions, slowly growing low-frequency fluctuations are induced in the pretransitional boundary layer by the free-stream. The separation bubbles are considerably thinner than in the low TI cases, resulting in thinner boundary layers at the end of the test wall. At Re=50,000 and 100,000, the pre-transitional boundary layer separates at about the same location as in the low TI cases. Transition occurs through a bypass mode, begins upstream of the corresponding low-TI location, and proceeds in a manner similar to that of an attached boundary layer. Under high TI at Re=200,000 and 300,000, transition begins before separation. The boundary layer may separate, but if it does the separation bubble is very short and does not significantly affect the downstream development of the boundary layer. A comparison is made to previous work in a simulated cascade.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3991613','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3991613"><span>The Influence of Body Position on Cerebrospinal Fluid Pressure Gradient and Movement in Cats with Normal and Impaired Craniospinal Communication</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Radoš, Milan; Erceg, Gorislav; Petošić, Antonio; Jurjević, Ivana</p> <p>2014-01-01</p> <p>Intracranial hypertension is a severe therapeutic problem, as there is insufficient knowledge about the physiology of cerebrospinal fluid (CSF) pressure. In this paper a new CSF pressure regulation hypothesis is proposed. According to this hypothesis, the CSF pressure depends on the laws of fluid mechanics and on the anatomical characteristics inside the cranial and spinal space, and not, as is today generally believed, on CSF secretion, circulation and absorption. The volume and pressure changes in the newly developed CSF model, which by its anatomical dimensions and basic biophysical features imitates the craniospinal system in cats, are compared to those obtained on cats with and without the blockade of craniospinal communication in different body positions. During verticalization, a long-lasting occurrence of negative CSF pressure inside the cranium in animals with normal cranio-spinal communication was observed. CSF pressure gradients change depending on the body position, but those gradients do not enable unidirectional CSF circulation from the hypothetical site of secretion to the site of absorption in any of them. Thus, our results indicate the existence of new physiological/pathophysiological correlations between intracranial fluids, which opens up the possibility of new therapeutic approaches to intracranial hypertension. PMID:24748150</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011ExFl...50...89L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011ExFl...50...89L"><span>Stereo particle image velocimetry of nonequilibrium turbulence relaxation in a supersonic boundary layer</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lapsa, Andrew P.; Dahm, Werner J. A.</p> <p>2011-01-01</p> <p>Measurements using stereo particle image velocimetry are presented for a developing turbulent boundary layer in a wind tunnel with a Mach 2.75 free stream. As the boundary layer exits from the tunnel nozzle and moves through the wave-free test section, small initial departures from equilibrium turbulence relax, and the boundary layer develops toward the equilibrium zero-pressure-gradient form. This relaxation process is quantified by comparison of first and second order mean, fluctuation, and gradient statistics to classical inner and outer layer scalings. Simultaneous measurement of all three instantaneous velocity components enables direct assessment of the complete turbulence anisotropy tensor. Profiles of the turbulence Mach number show that, despite the M = 2.75 free stream, the incompressibility relation among spatial gradients in the velocity fluctuations applies. This result is used in constructing various estimates of the measured-dissipation rate, comparisons among which show only remarkably small differences over most of the boundary layer. The resulting measured-dissipation profiles, together with measured profiles of the turbulence kinetic energy and mean-flow gradients, enable an assessment of how the turbulence anisotropy relaxes toward its equilibrium zero-pressure-gradient state. The results suggest that the relaxation of the initially disturbed turbulence anisotropy profile toward its equilibrium zero-pressure-gradient form begins near the upper edge of the boundary layer and propagates downward through the defect layer.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70022741','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70022741"><span>Secondary currents in a curved, stratified, estuarine channel</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Lacy, J.R.; Monismith, Stephen G.</p> <p>2001-01-01</p> <p>This paper presents a study of secondary circulation in a curved stratified channel in northern San Francisco Bay over a 12.5-hour tidal cycle. Secondary currents were strong at times (varying by up to 35 cm/s from top to bottom) but relatively transient, as the balance between centrifugal and lateral baroclinic forcing changed over time. The short travel time around the bend did not allow a steady state balance to develop between centrifugal and lateral baroclinic forcing. During the flood tide the confluence of two streams with different velocities produced a strong lateral gradient in streamwise velocity. As a result, lateral advection was a significant term in the streamwise momentum balance, having the same order of magnitude as the barotropic and baroclinic pressure gradients, and the frictional terms. During the first part of the ebb, secondary currents were induced by lateral baroclinic forcing. The direction of the secondary circulation reversed later in the ebb, as the baroclinic forcing became weaker than the centrifugal acceleration. The gradient Richardson number showed that stratification was stable over most of the tidal cycle, decreasing the importance of friction and allowing secondary currents to persist. Copyright 2001 by the American Geophysical Union.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28380260','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28380260"><span>A numerical study of the acoustic radiation due to eddy current-cryostat interactions.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wang, Yaohui; Liu, Feng; Zhou, Xiaorong; Li, Yu; Crozier, Stuart</p> <p>2017-06-01</p> <p>To investigate the acoustic radiation due to eddy current-cryostat interactions and perform a qualitative analysis on noise reduction methods. In order to evaluate the sound pressure level (SPL) of the eddy current induced warm bore wall vibration, a Finite Element (FE) model was created to simulate the noises from both the warm bore wall vibration and the gradient coil assembly. For the SPL reduction of the warm bore wall vibration, we first improved the active shielding of the gradient coil, thus reducing the eddy current on the warm bore wall. A damping treatment was then applied to the warm bore wall to control the acoustic radiation. Initial simulations show that the SPL of the warm bore wall is higher than that of the gradient assembly with typical design shielding ratios at many frequencies. Subsequent simulation results of eddy current control and damping treatment application show that the average SPL reduction of the warm bore wall can be as high as 9.6 dB, and even higher in some frequency bands. Combining eddy current control and suggested damping scheme, the noise level in a MRI system can be effectively reduced. © 2017 American Association of Physicists in Medicine.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_18 --> <div id="page_19" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="361"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21961402','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21961402"><span>G-protection mechanisms afforded by the anti-G suit abdominal bladder with and without pressure breathing.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Eiken, Ola; Bergsten, Eddie; Grönkvist, Mikael</p> <p>2011-10-01</p> <p>G protection afforded by the abdominal bladder of a pneumatic anti-G suit is usually attributed to counteraction of G-induced caudad displacement of the heart and pooling of blood in the abdominal veins. The study examined whether the abdominal bladder might provide G protection also via other mechanisms. Each subject was exposed to +Gz loads while sitting relaxed, wearing a full-coverage anti-G suit modified to permit separate pressurization of the abdominal and leg bladders. In two experimental series (N = 8, N = 14), subjects were breathing at positive airway pressure (PPB); in a third series, five subjects were breathing at atmospheric airway pressure. Intrathoracic pressures were estimated by use of esophageal catheters. During PPB at high G loads, intrathoracic pressure was higher with than without the pressurized abdominal bladder. In 7 of the 14 subjects, basilar intrathoracic pressure exceeded airway pressure during PPB when the abdominal bladder was pressurized. The mean arterial pressure response at high G loads was higher in this subset of subjects (55 +/- 23 mmHg) than in the subjects in whom airway pressure exceeded intrathoracic pressure (41 +/- 27 mmHg). Without PPB at increased G load, the intrathoracic pressure gradient was higher with than without the pressurized abdominal bladder. During PPB, the abdominal bladder acts as an airway counterpressure, thereby facilitating pressure transmission from the airways to the thorax and hence improving G protection. It also appears that in several individuals, pressure may be transmitted from the abdominal bladder to the thorax and heart.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://www.searchanddiscovery.com/documents/2012/41000nelson/ndx_nelson.pdf','USGSPUBS'); return false;" href="http://www.searchanddiscovery.com/documents/2012/41000nelson/ndx_nelson.pdf"><span>Overpressure and hydrocarbon accumulations in Tertiary strata, Gulf Coast of Louisiana</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Nelson, Philip H.</p> <p>2012-01-01</p> <p>Many oil and gas reservoirs in Tertiary strata of southern Louisiana are located close to the interface between a sand-rich, normally pressured sequence and an underlying sand-poor, overpressured sequence. This association, recognized for many years by Gulf Coast explorationists, is revisited here because of its relevance to an assessment of undiscovered oil and gas potential in the Gulf Coast of Louisiana. The transition from normally pressured to highly overpressured sediments is documented by converting mud weights to pressure, plotting all pressure data from an individual field as a function of depth, and selecting a top and base of the pressure transition zone. Vertical extents of pressure transition zones in 34 fields across southern onshore Louisiana range from 300 to 9000 ft and are greatest in younger strata and in the larger fields. Display of pressure transition zones on geologic cross sections illustrates the relative independence of the depth of the pressure transition zone and geologic age. Comparison of the depth distribution of pressure transition zones with production intervals confirms previous findings that production intervals generally overlap the pressure transition zone in depth and that the median production depth lies above the base of the pressure transition zone in most fields. However, in 11 of 55 fields with deep drilling, substantial amounts of oil and gas have been produced from depths deeper than 2000 ft below the base of the pressure transition zone. Mud-weight data in 7 fields show that "local" pressure gradients range from 0.91 to 1.26 psi/ft below the base of the pressure transition zone. Pressure gradients are higher and computed effective stress gradients are negative in younger strata in coastal areas, indicating that a greater potential for fluid and sediment movement exists there than in older Tertiary strata.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19920052415&hterms=weather+map+humidity&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dweather%2Bmap%2Bhumidity','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19920052415&hterms=weather+map+humidity&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dweather%2Bmap%2Bhumidity"><span>Surface pressure maps from scatterometer data</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Brown, R. A.; Levy, Gad</p> <p>1991-01-01</p> <p>The ability to determine surface pressure fields from satellite scatterometer data was shown by Brown and Levy (1986). The surface winds are used to calculate the gradient winds above the planetary boundary layer, and these are directly related to the pressure gradients. There are corrections for variable stratification, variable surface roughness, horizontal inhomogeneity, humidity and baroclinity. The Seasat-A Satellite Scatterometer (SASS) data have been used in a systematic study of 50 synoptic weather events (regions of approximately 1000 X 1000 km). The preliminary statistics of agreement with national weather service surface pressure maps are calculated. The resulting surface pressure maps can be used together with SASS winds and Scanning Multichannel Microwave Radiometer (SMMR) water vapor and liquid water analyses to provide good front and storm system analyses.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018JPhCS1001a2020S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018JPhCS1001a2020S"><span>Characterisation of minimal-span plane Couette turbulence with pressure gradients</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sekimoto, Atsushi; Atkinson, Callum; Soria, Julio</p> <p>2018-04-01</p> <p>The turbulence statistics and dynamics in the spanwise-minimal plane Couette flow with pressure gradients, so-called, Couette-Poiseuille (C-P) flow, are investigated using direct numerical simulation. The large-scale motion is limited in the spanwise box dimension as in the minimal-span channel turbulence of Flores & Jiménez (Phys. Fluids, vol. 22, 2010, 071704). The effect of the top wall, where normal pressure-driven Poiseuille flow is realised, is distinguished from the events on the bottom wall, where the pressure gradient results in mild or almost-zero wall-shear stress. A proper scaling of turbulence statistics in minimal-span C-P flows is presented. Also the ‘shear-less’ wall-bounded turbulence, where the Corrsin shear parameter is very weak compared to normal wall-bounded turbulence, represents local separation, which is also observed as spanwise streaks of reversed flow in full-size plane C-P turbulence. The local separation is a multi-scale event, which grows up to the order of the channel height even in the minimal-span geometry.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19870002652','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19870002652"><span>Modification of a variational objective analysis model for new equations for pressure gradient and vertical velocity in the lower troposphere and for spatial resolution and accuracy of satellite data</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Achtemeier, G. L.</p> <p>1986-01-01</p> <p>Since late 1982 NASA has supported research to develop a numerical variational model for the diagnostic assimilation of conventional and space-based meteorological data. In order to analyze the model components, four variational models are defined dividing the problem naturally according to increasing complexity. The first of these variational models (MODEL I), the subject of this report, contains the two nonlinear horizontal momentum equations, the integrated continuity equation, and the hydrostatic equation. This report summarizes the results of research (1) to improve the way the large nonmeteorological parts of the pressure gradient force are partitioned between the two terms of the pressure gradient force terms of the horizontal momentum equations, (2) to generalize the integrated continuity equation to account for variable pressure thickness over elevated terrain, and (3) to introduce horizontal variation in the precision modulus weights for the observations.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22225461','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22225461"><span>Surgical treatment of severe pulmonic stenosis under cardiopulmonary bypass in small dogs.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Fujiwara, M; Harada, K; Mizuno, T; Nishida, M; Mizukoshi, T; Mizuno, M; Uechi, M</p> <p>2012-02-01</p> <p>The aim of this study was to report the long-term outcome of the surgical palliation of pulmonic stenosis in dogs. The subjects comprised three female and six male dogs, mean (±sd) age: 23 (±25) months, mean (±sd) weight: 3·4 (±2·1) kg, diagnosed with severe pulmonic stenosis and right ventricular hypertrophy, with an average preoperative pressure gradient of 153 (±43) mmHg on echocardiography. The pressure overload with severe pulmonic stenosis was reduced by valvotomy, i.e., open pulmonary valve commissurotomy, with/without biomembrane patch grafting, under cardiopulmonary bypass. The postoperative pressure gradient at 1 to 7 days was significantly decreased to 65 (±39) mmHg (P<0·05). The reduced pressure gradient was maintained at 58 (±38) mmHg at final follow-up. Open valvotomy, pulmonary valve commissurotomy and biomembrane patch grafting were effective in reducing obstruction in severe pulmonic stenosis in dogs. © 2012 British Small Animal Veterinary Association.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19970022794&hterms=heinemann&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dheinemann','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19970022794&hterms=heinemann&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dheinemann"><span>Inertial Currents in Isotropic Plasma</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Heinemann, M.; Erickson, G. M.; Pontius, D. H., Jr.</p> <p>1993-01-01</p> <p>The magnetospheric convection electric field contributes to Birkeland currents. The effects of the field are to polarize the plasma by displacing the bounce paths of the ions from those of electrons, to redistribute the pressure so that it is not constant along magnetic field lines, and to enhance the pressure gradient by the gradient of the bulk speed. Changes in the polarization charge during the convection of the plasma are neutralized by electrons in the form of field-aligned currents that close through the ionosphere. The pressure drives field-aligned currents through its gradient in the same manner as in quasi-static plasma, but with modifications that are important if the bulk speed is of the order of the ion thermal speed; the variations in the pressure along field lines are maintained by a weak parallel potential drop. These effects are described in terms of the field-aligned currents in steady state, isotropic, MED plasma. Solutions are developed by taking the MHD limit of two-fluid solutions and illustrated in the special case of Maxwellian plasma for which the temperature is constant along magnetic field lines. The expression for the Birkeland current density is a generalization of Vasyliunas' expression for the field-aligned current density in quasi-static plasma and provides a unifying expression when both pressure gradients and ion inertia operate simultaneously as sources of field-aligned currents. It contains a full account of different aspects of the ion flow (parallel and perpendicular velocity and vorticity) that contribute to the currents. Contributions of ion inertia to field-aligned currents will occur in regions of strong velocity shear, electric field reversal, or large gradients in the parallel velocity or number density, and may be important in the low-latitude boundary layer, plasma sheet boundary layer, and the inner edge region of the plasma sheet.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19950033422&hterms=heinemann&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dheinemann','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19950033422&hterms=heinemann&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dheinemann"><span>Inertial currents in isotropic plasma</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Heinemann, M.; Erickson, G. M.; Pontius, D. H. JR.</p> <p>1994-01-01</p> <p>The magnetospheric convection electric field contributes to Birkeland currents. The effects of the field are to polarize the plasma by displacing the bounce paths of the ions from those of electrons, to redistribute the pressure so that it is not constant along magnetic field lines, and to enhance the pressure gradient by the gradient of the bulk speed. Changes in the polarization charge during the convection of the plasma are neutralized by electrons in the form of field-aligned currents that close through the ionosphere. The pressure drives field-aligned currents through its gradient in the same manner as in quasi-static plasma, but with modifications that are important if the bulk speed is of the order of the ion thermal speed; the variations in the pressure along field lines are maintained by a weak parallel potential drop. These effects are described in terms of the field-aligned currents in steady state, isotropic, magnetohyrodynamic (MHD) plasma. Solutions are developed by taking the MHD limit of two-fluid solutions and illustrated in the special case of Maxwellian plasma for which the temperature is constant along magnetic field lines. The expression for the Birkeland current density is a generalization of Vasyliunas' expression for the field-aligned current density in quasi-static plasma and provides a unifying expression when both pressure gradients and ion inertia operate simultaneously as sources of field-aligned currents. It contains a full account of different aspects of the ion flow (parallel and perpendicular velocity and vorticity) that contribute to the currents. Contributions of ion inertia to field-aligned currents will occur in regions of strong velocity shear, electric field reversal, or large gradients in the parallel velocity or number density, and may be important in the low-latitude boundary layer, plasma sheet boundary layer, and the inner edge region of the plasma sheet.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19960011455','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19960011455"><span>Inertial currents in isotropic plasma</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Heinemann, M.; Erickson, G. M.; Pontius, D. H., Jr.</p> <p>1994-01-01</p> <p>The magnetospheric convection electric field contributes to Birkeland currents. The effects of the field are to polarize the plasma by displacing the bounce paths of the ions from those of electrons, to redistribute the pressure so that it is not constant along magnetic field lines, and to enhance the pressure gradient by the gradient of the bulk speed. Changes in the polarization charge during the convection of the plasma are neutralized by electrons in the form of field-aligned currents that close through the ionosphere. The pressure drives field-aligned currents through its gradient in the same manner as in quasi-static plasmas, but with modifications that are important if the bulk speed is of the order of the ion thermal speed; the variations in the pressure along field lines are maintained by a weak parallel potential drop. These effects are described in terms of the field-aligned currents in steady state, isotropic, MHD plasma. Solutions are developed by taking the MHD limit ot two-fluid solutions and illustrated in the special case of Maxwellian plasma for which the temperature is constant along magnetic field lines. The expression for the Birkeland current density is a generalization of Vasyliunas' expression for the field-aligned current density in quasi-static plasma and provides a unifying expression when both pressure gradients and ion inertia operate simultaneously as sources of field-aligned currents. It contains a full account of different aspects of the ion flow (parallel and perpendicular velocity and vorticity) that contribute to the currents. Contributions of ion inertia to field-aligned currents will occur in regions of strong velocity shear, electric field reversal, or large gradients in the parallel velocity or number density, and may be important in the low-latitude boundary layer, plasma sheet boundary layer, and the inner edge region of the plasma sheet.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/servlets/purl/1204087','SCIGOV-STC'); return false;" href="https://www.osti.gov/servlets/purl/1204087"><span></span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>DeChant, Lawrence Justin; Smith, Justin A.</p> <p></p> <p>Here we discuss an improved Corcos (Corcos (1963), (1963)) style cross spectral density utilizing zero pressure gradient, supersonic (Beresh et. al. (2013)) data sets. Using the connection between narrow band measurements with broadband cross-spectral density, i.e. Γ(ξ ,η ,ω )= Φ (ω) A(ωη/U )exp (-i ωξ/U) we focus on estimating coherence expressions of the form: A (ξω nb/U) and B (ηω nb/ U) where ω nb denotes the narrow band frequency, i.e. the band center frequency value and ξ and η are sensors spacing in streamwise/longitudinal and cross-stream/lateral directions, respectively. A methodology to estimate the parameters which retains the Corcosmore » exponential functional form, A(ξω/U)=exp(-k lat ηω/U) but identifies new parameters (constants) consistent with the Beresh et. al. data sets is discussed. The Corcos result requires that the data be properly explained by self-similar variable: ξω/U and ηω/U. The longitudinal (streamwise) variable ξω/U tends to provide a better data collapse, while, consistent with the literature the lateral ηω/U is only successful for higher band center frequencies. Assuming the similarity variables provide a useful description of the data, the longitudinal coherence decay constant result using the Beresh et. al. data sets yields a value for the longitudinal constant k long≈0.36-0.28 that is approximately 3x larger than the “traditional” (low speed, large Reynolds number and zero pressure gradient) of k long≈0.11. We suggest that the most likely reason that the Beresh et. al. data sets incur increased longitudinal decay which results in reduced coherence lengths is due to wall shear induced compression causing an adverse pressure gradient. Focusing on the higher band center frequency measurements where the frequency dependent similarity variables are applicable, the lateral or transverse coherence decay constant k lat≈0.7 is consistent with the “traditional” (low speed, large Reynolds number and zero pressure gradient). It should be noted, that the longitudinal/streamwise coherence decay deviates from the value observed by other researchers while the lateral/ cross-stream value is consistent has been observed by other researchers. We believe that while the measurements used to obtain new decay constant estimates are from internal wind tunnel tests, they likely provide a useful estimate expected reentry flow behavior and are therefore recommended for use. These data could also be useful in determining the uncertainty of correlation length for a uncertainty quantification (UQ) analysis.« less</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28590028','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28590028"><span>Phenotypic plasticity drives a depth gradient in male conspicuousness in threespine stickleback, Gasterosteus aculeatus.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Brock, Chad D; Cummings, Molly E; Bolnick, Daniel I</p> <p>2017-08-01</p> <p>Signal evolution is thought to depend on both a signal's detectability or conspicuousness (signal design) as well as any extractable information it may convey to a potential receiver (signal content). While theoretical and empirical work in sexual selection has largely focused on signal content, there has been a steady accrual of evidence that signal design is also important for trait evolution. Despite this, relatively little attention has been paid to spatial variation in the conspicuousness of a given signal, especially over small spatial scales (relative to an organism's dispersal distance). Here, we show that visual signals of male threespine stickleback vary in conspicuousness, depending on a male's nest depth within a given lake. Deeper nesting males were typically more chromatically conspicuous than shallow nesting males. This trend is partly because all male stickleback are more conspicuous in deep optical environments. However, deep males are even more conspicuous than environmentally driven null expectations, while shallow males tend to be disproportionally cryptic. Experimental manipulation of male nesting depth induced plastic changes in nuptial color that replicated the natural gradients in conspicuousness. We discuss a number of potential mechanisms that could produce depth gradients in conspicuousness in male stickleback, including concomitant depth gradients in diet, predation pressure, male/female density, female preference, and opportunity for sexual selection. © 2017 The Author(s). Evolution © 2017 The Society for the Study of Evolution.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/20000063378','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20000063378"><span>Generalized Wall Function for Complex Turbulent Flows</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Shih, Tsan-Hsing; Povinelli, Louis A.; Liu, Nan-Suey; Chen, Kuo-Huey</p> <p>2000-01-01</p> <p>A generalized wall function was proposed by Shih et al., (1999). It accounts the effect of pressure gradients on the flow near the wall. Theory shows that the effect of pressure gradients on the flow in the inertial sublayer is very significant and the standard wall function should be replaced by a generalized wall function. Since the theory is also valid for boundary layer flows toward separation, the generalized wall function may be applied to complex turbulent flows with acceleration, deceleration, separation and recirculation. This paper is to verify the generalized wall function with numerical simulations for boundary layer flows with various adverse and favorable pressure gradients, including flows about to separate. Furthermore, a general procedure of implementation of the generalized wall function for National Combustion Code (NCC) is described, it can be applied to both structured and unstructured CFD codes.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..1913128L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..1913128L"><span>Bedforms induced by solitary waves: laboratory studies on generation and migration rate</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>la Forgia, Giovanni; Adduce, Claudia; Falcini, Federico; Paola, Chris</p> <p>2017-04-01</p> <p>This study presents experiments on the formation of sandy bedforms, produced by surface solitary waves (SSWs) in shallow water conditions. The experiments were carried out in a 12.0 m long, 0.15 m wide and 0.5 m high flume, at Saint Anthony Falls Laboratory in Minneapolis. The tank is filled by fresh water and a removable gate, placed at the left hand-side of the tank, divides the flume in two regions: the lock region and the ambient fluid region. The standard lock-release method generates SSWs by producing a displacement between the free surfaces that are divided by the gate. Wave amplitude, wavelength, and celerity depend on the lock length and on the water level difference between the two regions. Natural sand particles (D50=0.64) are arranged on the bottom in order to form a horizontal flat layer with a thickness of 2 cm. A digital pressure gauge and a high-resolution acoustic velocimeter allowed us to measure, locally, both pressure and 3D water velocity induced on the bottom by each wave. Image analysis technique is then used to obtain the main wave features: amplitude, wavelength, and celerity. Dye is finally used as vertical tracer to mark the horizontal speed induced by the wave. For each experiment we generated 400 waves, having the same features and we analyzed their action on sand particles placed on the bottom. The stroke, induced by each wave, entails a shear stress on the sand particles, causing sediment transport in the direction of wave propagation. Immediately after the wave passage, a back flow occurs near the bottom. The horizontal pressure gradient and the velocity field induced by the wave cause the boundary layer separation and the consequent reverse flow. Depending on the wave features and on the water depth, the boundary shear stress induced by the reverse flow can exceed the critical value inducing the back motion of the sand particles. The experiments show that the particle back motion is localized at particular cross sections along the tank, where the wave steepening occur. For this reason, the pressure and velocity measures were collected in several cross sections along the tank. The propagation of consecutive waves with the same features induces the generation of erosion and accumulation zones, which slowly evolve in isometric bedforms.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5116292','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5116292"><span>Computational modeling of venous sinus stenosis in idiopathic intracranial hypertension</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Levitt, Michael R; McGah, Patrick M; Moon, Karam; Albuquerque, Felipe C; McDougall, Cameron G; Kalani, M Yashar S; Kim, Louis J; Aliseda, Alberto</p> <p>2016-01-01</p> <p>Background and Purpose Idiopathic intracranial hypertension has been associated with dural venous sinus stenosis in some patients, but the hemodynamic environment of the dural venous sinuses has not been quantitatively described. Here, we present the first such computational fluid dynamics model using patient-specific blood pressure measurements. Materials and Methods Six patients with idiopathic intracranial hypertension and at least one stenosis or atresia at the transverse-sigmoid sinus junction underwent MRV followed by cerebral venography and manometry throughout the dural venous sinuses. Patient-specific computational fluid dynamics models were created using MRV anatomy, with venous pressure measurements as boundary conditions. Blood flow and wall shear stress were calculated for each patient. Results Computational models of dural venous sinuses were successfully reconstructed in all six patients with patient-specific boundary conditions. Three patients demonstrated a pathologic pressure gradient (≥ 8 mm Hg) across four dural venous sinus stenoses. Small sample size precludes statistical comparisons, but average overall flow throughout the dural venous sinuses of patients with pathologic pressure gradients was higher than in those without (1041.00 ± 506.52 vs. 358.00 ± 190.95 mL/min). Wall shear stress was also higher across stenoses in patients with pathologic pressure gradients (37.66 ± 48.39 vs 7.02 ± 13.60 Pa). Conclusion The hemodynamic environment of the dural venous sinuses can be computationally modeled using patient-specific anatomy and physiological measurements in patients with idiopathic intracranial hypertension. There was substantially higher blood flow and wall shear stress in patients with pathological pressure gradients. PMID:27197986</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003JGRA..108.1331G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003JGRA..108.1331G"><span>Pressure balance inconsistency exhibited in a statistical model of magnetospheric plasma</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Garner, T. W.; Wolf, R. A.; Spiro, R. W.; Thomsen, M. F.; Korth, H.</p> <p>2003-08-01</p> <p>While quantitative theories of plasma flow from the magnetotail to the inner magnetosphere typically assume adiabatic convection, it has long been understood that these convection models tend to overestimate the plasma pressure in the inner magnetosphere. This phenomenon is called the pressure crisis or the pressure balance inconsistency. In order to analyze it in a new and more detailed manner we utilize an empirical model of the proton and electron distribution functions in the near-Earth plasma sheet (-50 RE < X < -10 RE), which uses the [1989] magnetic field model and a plasma sheet representation based upon several previously published statistical studies. We compare our results to a statistically derived particle distribution function at geosynchronous orbit. In this analysis the particle distribution function is characterized by the isotropic energy invariant λ = EV2/3, where E is the particle's kinetic energy and V is the magnetic flux tube volume. The energy invariant is conserved in guiding center drift under the assumption of strong, elastic pitch angle scattering. If, in addition, loss is negligible, the phase space density f(λ) is also conserved along the same path. The statistical model indicates that f(λ, ?) is approximately independent of X for X ≤ -35 RE but decreases with increasing X for X ≥ -35 RE. The tailward gradient of f(λ, ?) might be attributed to gradient/curvature drift for large isotropic energy invariants but not for small invariants. The tailward gradient of the distribution function indicates a violation of the adiabatic drift condition in the plasma sheet. It also confirms the existence of a "number crisis" in addition to the pressure crisis. In addition, plasma sheet pressure gradients, when crossed with the gradient of flux tube volume computed from the [1989] magnetic field model, indicate Region 1 currents on the dawn and dusk sides of the outer plasma sheet.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017APS..DFDL26012K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017APS..DFDL26012K"><span>Characterization of Rare Reverse Flow Events in Adverse Pressure Gradient Turbulent Boundary Layers</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kaehler, Christian J.; Bross, Matthew; Fuchs, Thomas</p> <p>2017-11-01</p> <p>Time-resolved tomographic flow fields measured in the viscous sublayer region of a turbulent boundary layer subjected to an adverse pressure gradient (APG) are examined with the aim to resolve and characterize reverse flow events at Reτ = 5000. The fields were measured using a novel high resolution tomographic particle tracking technique. It is shown that this technique is able to fully resolve mean and time dependent features of the complex three-dimensional flow with high accuracy down to very near-wall distances ( 10 μm). From time resolved Lagrangian particle trajectories, statistical information as well as instantaneous topological features of near-wall flow events are deduced. Similar to the zero pressure gradient case (ZPG), it was found that individual events with reverse flow components still occur relatively rarely under the action of the pressure gradient investigated here. However, reverse flow events comprised of many individual events, are shown to appear in relatively organized groupings in both spanwise and streamise directions. Furthermore, instantaneous measurements of reverse flow events show that these events are associated with the motion of low-momentum streaks in the near-wall region. This work is supported by the Priority Programme SPP 1881 Turbulent Superstructures and the individual project Grant KA1808/8-2 of the Deutsche Forschungsgemeinschaft.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19920042432&hterms=amazon+rainforest&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Damazon%2Brainforest','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19920042432&hterms=amazon+rainforest&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Damazon%2Brainforest"><span>Low-level nocturnal wind maximum over the Central Amazon Basin</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Greco, Steven; Ulanski, Stanley; Garstang, Michael; Houston, Samuel</p> <p>1992-01-01</p> <p>A low-level nocturnal wind maximum is shown to exist over extensive and nearly undisturbed rainforest near the central Amazon city of Manaus. Meteorological data indicate the presence of this nocturnal wind maximum during both the wet and dry seasons of the Central Amazon Basin. Daytime wind speeds which are characteristically 3-7 m/s between 300 and 1000 m increase to 10-15 m/s shortly after sunset. The wind-speed maximum is reached in the early evening, with wind speeds remaining high until several hours after sunrise. The nocturnal wind maximum is closely linked to a strong low-level inversion formed by radiational cooling of the rainforest canopy. Surface and low-level pressure gradients between the undisturbed forest and the large Amazon river system and the city of Manaus are shown to be responsible for much of the nocturnal wind increase. The pressure gradients are interpreted as a function of the thermal differences between undisturbed forest and the river/city. The importance of both the frictional decoupling and the horizontal pressure gradient suggest that the nocturnal wind maximum does not occur uniformly over all Amazonia. Low-level winds are thought to be pervasive under clear skies and strong surface cooling and that, in many places (i.e., near rivers), local pressure gradients enhance the low-level nocturnal winds.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19980227970','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19980227970"><span>Charts and Tables for Estimating the Stability of the Compressible Laminar Boundary Layer with Heat Transfer and Arbitrary Pressure Gradient</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Tetervin, Neal</p> <p>1959-01-01</p> <p>The minimum critical Reynolds numbers for the similar solutions of the compressible laminar boundary layer computed by Cohen and Reshotko and also for the Falkner and Skan solutions as recomputed by Smith have been calculated by Lin's rapid approximate method for two-dimensional disturbances. These results enable the stability of the compressible laminar boundary layer with heat transfer and pressure gradient to be easily estimated after the behavior of the boundary layer has been computed by the approximate method of Cohen and Reshotko. The previously reported unusual result (NACA Technical Note 4037) that a highly cooled stagnation point flow is more unstable than a highly cooled flat-plate flow is again encountered. Moreover, this result is found to be part of the more general result that a favorable pressure gradient is destabilizing for very cool walls when the Mach number is less than that for complete stability. The minimum critical Reynolds numbers for these wall temperature ratios are, however, all larger than any value of the laminar-boundary-layer Reynolds number likely to be encountered. For Mach numbers greater than those for which complete stability occurs a favorable pressure gradient is stabilizing, even for very cool walls.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004AGUFM.T43B1327H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004AGUFM.T43B1327H"><span>Relationships between heat flow, thermal and pressure fields in the Gulf of Mexico</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Husson, L.; Henry, P.; Le Pichon, X.</p> <p>2004-12-01</p> <p>The thermal field of the Gulf of Mexico (GoM) is restored from a comprehensive temperature-depth database. A striking feature is the systematic sharp gradient increase between 2500 and 4000 m. The analysis of the pressure (fracturation tests and mud weights) indicates a systematic correlation between the pressure and temperature fields, as well as with the thickness of Plio-Pleistocene sedimentary layer, and is interpreted as the fact of cooling from fluid flow in the upper, almost hydrostatically pressured layer. The Nusselt number, that we characterize by the ratio between the near high-P gradient over low-P gradient varies spatially and is correlated to the structural pattern of the GoM; this observation outlines the complex relationships between heat and fluid flows, structure and sedimentation. The deep thermal signal is restored in terms of gradient and heat flow density from a statistical analysis of the thermal data combined to the thermal modelling of about 175 wells. At a regional scale, although the sedimentary cover is warmer in Texas than in Louisiana in terms of temperature, the steady state basal heat flow is higher in Louisiana. In addition, beneath the Corsair Fault, which lay offshore parallel to the Texan coast, the high heat flow suggests a zone of Tertiary lithospheric thinning.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19940023136','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19940023136"><span>Thermocapillary flow with evaporation and condensation and its effect on liquid retention in low-G fluid acquisition devices</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Schmidt, George R.</p> <p>1994-01-01</p> <p>The steady motion, thermal and free surface behavior of a volatile, wetting liquid in microgravity are studied using scaling and numerical techniques. The objective is to determine whether the thermocapillary and two-phase convection arising from thermodynamic nonequilibrium along the porous surfaces of spacecraft liquid acquisition devices could cause the retention failures observed with liquid hydrogen and heated vapor pressurant. Why these devices seem immune to retention loss when pressurized with heated helium or heated directly through the porous structure was also examined. Results show that highly wetting fluids exhibit large negative and positive dynamic pressure gradients towards the meniscus interline when superheated and subcooled, respectively. With superheating, the pressure variation and recoil force arising from liquid/vapor phase change exert the same influence on surface morphology and promote retention. With subcooling, however, the pressure distribution produces a suction that degrades mechanical equilibrium of the surface. This result indicates that thermocapillary-induced deformation arising from subcooling and condensation is the likely cause for retention loss. In addition, increasing the level of nonequilibrium by reducing accommodation coefficient suppresses deformation and explains why this failure mode does not occur in instances of direct screen heating or pressurization with a heated inert gas.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_19 --> <div id="page_20" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="381"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/biblio/7017613-thermal-pressure-histories-malay-basin-offshore-malaysia','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/7017613-thermal-pressure-histories-malay-basin-offshore-malaysia"><span>Thermal and pressure histories of the Malay Basin, offshore Malaysia</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Yusoff, W.I.; Swarbrick, R.E.</p> <p>1994-07-01</p> <p>The Malay Basin is a Neogene intracratonic basin characterized by high heat flow and rapid sedimentation; moderate to high overpressure is common in deeper reservoirs. Thermal conductivity and temperature data from 55 wells have been used to reassess the areal and vertical heat-flow distribution within the basin. Anomalously high temperatures have been observed in some sandstone intervals above the overpressured reservoir section. A narrow to rather abrupt pressure transition zone could be recognized. All hydrocarbon-filled reservoirs seemed to be associated with high heat flow (i.e., about 90 mW/m[sup 2]). Overpressure in some wells is approaching critical fracture pressure (i.e., 0.85more » psi/ft. pressure gradient) in the region. In the central part of the basin, the overpressured sections are found within the shallower (<2000 m) hydrocarbon-bearing units. Selective studies of the temporal development of the pore pressure indicated that overpressure development is associated with episodes of rapid sedimentation. A preliminary fluid flow model supported by pressure modeling is proposed whereby hot fluids are currently being expelled from deeper overpressured sandstone and mudrocks through a fractured seal induced by overpressure. The latter is caused by relatively rapid burial since late Tertiary times. Hydrocarbon migration may have been aided by this fluid movement.« less</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004PhDT........68C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004PhDT........68C"><span>Microscale electrokinetic transport and stability</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chen, Chuan-Hua</p> <p></p> <p>Electrokinetics is a leading mechanism for transport and separation of biochemical samples in microdevices due to its favorable scaling at small scales. However, electrokinetic systems can become highly unstable, and this instability adversely affects key processes such as sample stacking and electrophoretic separation. This dissertation deals with two major topics: a novel planar micropump exploiting the favorable scaling of electroosmosis at the microscale, and a fundamental study of electrokinetic flow instabilities induced by electrical conductivity gradients. Electroosmotic micropumps use field-induced ion drag to drive liquids and achieve high pressures in a compact design with no moving parts. An analytical model applicable to planar, etched-structure micropumps was developed to guide the geometrical design and working fluid selection. Standard microlithography and wet etching techniques were used to fabricate a pump 1 mm long along the flow direction and 0.9 mum by 38 mm in cross section. The pump produced a maximum pressure of 0.33 atm and a maximum flow rate of 15 mul/min at 1 kV applied potential with deionized water as working fluid. The pump performance agreed well with the theoretical model. Electrokinetic flow instabilities occur under high electric field in the presence of electrical conductivity gradients. In a microfluidic T-junction 11 mum by 155 mum in cross section, aqueous electrolytes of 10:1 conductivity ratio were electrokinetically driven into a common mixing channel. Convectively unstable waves were observed at 0.5 kV/cm, and upstream propagating waves at 1.5 kV/cm. A physical model for this instability has been developed. A linear stability analysis of the governing equations in the thin-layer limit predicts both qualitative trends and quantitative features that agree well with experimental data. Briggs-Bers criteria were applied to select physically unstable modes and determine the nature of instability. Conductivity gradients and bulk charge accumulation are a crucial factor in the instability. The role of electroosmotic flow is mainly as a convecting medium. The instability is governed by two key controlling parameters: the ratio of dynamic to dissipative forces which determines the onset of instability, and the ratio of electroviscous to electroosmotic velocities which governs the convective versus absolute nature of instability.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018PPCF...60a4037R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018PPCF...60a4037R"><span>Features of self-organized plasma physics in tokamaks</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Razumova, K. A.</p> <p>2018-01-01</p> <p>The history of investigations the role of self-organization processes in tokamak plasma confinement is presented. It was experimentally shown that the normalized pressure profile is the same for different tokamaks. Instead of the conventional Fick equation, where the thermal flux is proportional to a pressure gradient, processes in the plasma are well described by the Dyabilanin’s energy balance equation, in which the heat flux is proportional to the difference of normalized gradients for self-consistent and real pressure profiles. The transport coefficient depends on the values of heat flux, which compensates distortion of the pressure profile with external impacts. Radiative cooling of the plasma edge decreases the heat flux and improves the confinement.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/977679','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/977679"><span>A low-cost gradient system for high-performance liquid chromatography. Quantitation of complex pharmaceutical raw materials.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Erni, F; Frei, R W</p> <p>1976-09-29</p> <p>A device is described that makes use of an eight-port motor valve to generate step gradients on the low-pressure side of a piston pump with a low dead volume. Such a gradient device with an automatic control unit, which also permits repetition of previous steps, can be built for about half the cost of a gradient system with two pumps. Applications of this gradient unit to the separation of complex mixtures of glycosides and alkaloids are discussed and compared with separations systems using two high-pressure pumps. The gradients that are used on reversed-phase material with solvent mixtures of water and completely miscible organic solvents are suitable for quantitative routine control of pharmaceutical products. The reproducibility of retention data is excellent over several months and, with the use of loop injectors, major components can be determined quantitatively with a reproducibility of better than 2% (relative standard deviation). The step gradient selector valve can also be used as an introduction system for very large sample volumes. Up to 11 can be injected and samples with concentrations of less than 1 ppb can be determined with good reproducibilities.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27435687','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27435687"><span>Monitoring gradient profile on-line in micro- and nano-high performance liquid chromatography using conductivity detection.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Zhang, Min; Chen, Apeng; Lu, Joann J; Cao, Chengxi; Liu, Shaorong</p> <p>2016-08-19</p> <p>In micro- or nano-flow high performance liquid chromatography (HPLC), flow-splitters and gradient elutions are commonly used for reverse phase HPLC separations. When a flow splitter was used at a high split-ratio (e.g., 1000:1 or higher), the actual gradient may deviate away from the programmed gradient. Sometimes, mobile phase concentrations can deviate by as much as 5%. In this work, we noticed that the conductivity (σ) of a gradient decreased with the increasing organic-solvent fraction (φ). Based on the relationship between σ and φ, a method was developed for monitoring gradient profile on-line to record any deviations in these HPLC systems. The conductivity could be measured by a traditional conductivity detector or a capacitively coupled contactless conductivity detector (C(4)D). The method was applied for assessing the performance of an electroosmotic pump (EOP) based nano-HPLC. We also observed that σ value of the gradient changed with system pressure; a=0.0175ΔP (R(2)=0.964), where a is the percentage of the conductivity increase and ΔP is the system pressure in bar. This effect was also investigated. Copyright © 2016. Published by Elsevier B.V.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28024321','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28024321"><span>Strain-Gradient Modulated Exciton Emission in Bent ZnO Wires Probed by Cathodoluminescence.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Fu, Xue-Wen; Li, Cai-Zhen; Fang, Liang; Liu, Da-Meng; Xu, Jun; Yu, Da-Peng; Liao, Zhi-Min</p> <p>2016-12-27</p> <p>Photoelectrical properties of semiconductor nanostructures are expected to be improved significantly by strain engineering. Besides the local strain, the strain gradient is promising to tune the luminescence properties by modifying the crystal symmetry. Here, we report the investigation of strain-gradient induced symmetry-breaking effect on excitonic states in pure bending ZnO microwires by high spatial-resolved cathodoluminescence at low temperature of 80 K. In addition to the local-strain induced light emission peak shift, the bound exciton emission photon energy shows an extraordinary jump of ∼16.6 meV at a high strain-gradient of 1.22% μm -1 , which is ascribed to the strain gradient induced symmetry-breaking. Such a symmetry-breaking lifts the energy degeneracy of the electronic band structures, which significantly modifies the electron-hole interactions and the fine structures of the bound exciton states. These results provide a further understanding of the strain gradient effect on the excitonic states and possess a potential for the applications in optoelectronic devices.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/biblio/5384790-transformations-fluxes-forces-describing-simultaneous-transport-water-heat-unsaturated-porous-media','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/5384790-transformations-fluxes-forces-describing-simultaneous-transport-water-heat-unsaturated-porous-media"><span>Transformations of fluxes and forces describing the simultaneous transport of water and heat in unsaturated porous media</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Raats, P.A.C.</p> <p>1975-12-01</p> <p>Balances of mass for the water in N distinct phases and a balance of heat for the medium as a whole were formulated. Following Philip and de Vries, it was assumed that the flux of water in each phase is proportional to the gradient of the pressure in that phase and that the diffusive component of the flux of heat is proportional to the gradient of the temperature. Clapeyron equations were used to express the gradient of the pressure in any phase in terms of the gradient of the pressure in a reference state and of the temperature. The referencemore » state may be the water in one of the phases or the water in some measuring device such as a tensiometer or a psychrometer. Expressions for the total flux of water and for the diffusive flux of heat plus the convective flux of heat associated with the conversion from any phase to the reference state were shown to satisfy the onsager reciprocal relations. A theorem due to Meixner was used to delineate the class of fluxes and forces that preserves these relations. In particular, it was shown that if the gradients of water content and temperature are used as the driving forces, the onsager relations are no longer satisfied.« less</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/servlets/purl/1062557','SCIGOV-STC'); return false;" href="https://www.osti.gov/servlets/purl/1062557"><span>The Relationships Between ELM Suppression, Pedestal Profiles, and Lithium Wall Coatings in NSTX</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>D.P. Boyle, R. Maingi, P.B. Snyder, J. Manickam, T.H. Osborne, R.E. Bell, B.P. LeBlanc, and the NSTX Team</p> <p>2012-08-17</p> <p>Recently in the National Spherical Torus Experiment (NSTX), increasing lithium wall coatings suppressed edge localized modes (ELMs), gradually but not quite monotonically. This work details profile and stability analysis as ELMs disappeared throughout the lithium scan. While the quantity of lithium deposited between discharges did not uniquely determine the presence of ELMs, profile analysis demonstrated that lithium was correlated to wider density and pressure pedestals with peak gradients farther from the separatrix. Moreover, the ELMy and ELM-free discharges were cleanly separated by their density and pedestal widths and peak gradient locations. Ultimately, ELMs were only suppressed when lithium caused themore » density pedestal to widen and shift inward. These changes in the density gradient were directly reflected in the pressure gradient and calculated bootstrap current. This supports the theory that ELMs in NSTX are caused by peeling and/or ballooning modes, as kink/peeling modes are stabilized when the edge current and pressure gradient shift away from the separatrix. Edge stability analysis using ELITE corroborated this picture, as reconstructed equilibria from ELM-free discharges were generally farther from their kink/peeling stability boundaries than ELMy discharges. We conclude that density profile control provided by lithium is the key first step to ELM suppression in NSTX« less</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/biblio/1037129-relationships-between-edge-localized-modes-suppression-pedestal-profiles-lithium-wall-coatings-nstx','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/1037129-relationships-between-edge-localized-modes-suppression-pedestal-profiles-lithium-wall-coatings-nstx"><span>The relationships between edge localized modes suppression, pedestal profiles and lithium wall coatings in NSTX</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Boyle, D. P.; Maingi, R.; Snyder, P. B.</p> <p>2011-01-01</p> <p>Recently in the National Spherical Torus Experiment (NSTX), increasing lithium wall coatings suppressed edge localized modes (ELMs), gradually but not quite monotonically. This work details profile and stability analysis as ELMs disappeared throughout the lithium scan. While the quantity of lithium deposited between discharges did not uniquely determine the presence of ELMs, profile analysis demonstrated that lithium was correlated with wider density and pressure pedestals with peak gradients farther from the separatrix. Moreover, the ELMy and ELM-free discharges were cleanly separated by their density and pedestal widths and peak gradient locations. Ultimately, ELMs were only suppressed when lithium caused themore » density pedestal to widen and shift inward. These changes in the density gradient were directly reflected in the pressure gradient and calculated bootstrap current. This supports the theory that ELMs in NSTX are caused by peeling and/or ballooning modes, as kink/peeling modes are stabilized when the edge current and pressure gradient shift away from the separatrix. Edge stability analysis using ELITE corroborated this picture, as reconstructed equilibria from ELM-free discharges were generally farther from their kink/peeling stability boundaries than ELMy discharges. We conclude that density profile control provided by lithium is the key first step to ELM suppression in NSTX.« less</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JMagR.265...52T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JMagR.265...52T"><span>Intra-coil interactions in split gradient coils in a hybrid MRI-LINAC system</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tang, Fangfang; Freschi, Fabio; Sanchez Lopez, Hector; Repetto, Maurizio; Liu, Feng; Crozier, Stuart</p> <p>2016-04-01</p> <p>An MRI-LINAC system combines a magnetic resonance imaging (MRI) system with a medical linear accelerator (LINAC) to provide image-guided radiotherapy for targeting tumors in real-time. In an MRI-LINAC system, a set of split gradient coils is employed to produce orthogonal gradient fields for spatial signal encoding. Owing to this unconventional gradient configuration, eddy currents induced by switching gradient coils on and off may be of particular concern. It is expected that strong intra-coil interactions in the set will be present due to the constrained return paths, leading to potential degradation of the gradient field linearity and image distortion. In this study, a series of gradient coils with different track widths have been designed and analyzed to investigate the electromagnetic interactions between coils in a split gradient set. A driving current, with frequencies from 100 Hz to 10 kHz, was applied to study the inductive coupling effects with respect to conductor geometry and operating frequency. It was found that the eddy currents induced in the un-energized coils (hereby-referred to as passive coils) positively correlated with track width and frequency. The magnetic field induced by the eddy currents in the passive coils with wide tracks was several times larger than that induced by eddy currents in the cold shield of cryostat. The power loss in the passive coils increased with the track width. Therefore, intra-coil interactions should be included in the coil design and analysis process.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017APS..SHK.O3003H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017APS..SHK.O3003H"><span>Influence of Flow Gradients on Mach Stem Initiation of PBX-9502</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hull, Lawrence; Miller, Phillip; Mas, Eric; Focused Experiments Team</p> <p>2017-06-01</p> <p>Recent experiments and theory explore the effect of flow gradients on reaction acceleration and stability in the pressure-enhanced region between colliding sub-detonative shock waves in PBX-9502. The experiments are designed to produce divergent curved incident shock waves that interact in a convergent irregular reflection, or ``Mach stem'', configuration. Although this flow is fundamentally unsteady, such a configuration does feature particle paths having a single shock wave that increases the pressure from zero to the wave-reflected enhanced pressure. Thus, the possibility of pre-shock desensitization is precluded in this interaction region. Diagnostics record arrival wave velocity, shape, and material velocity along the angled free surface face of a large wedge. The wedge is large enough to allow observation of the wave structure for distances much larger than the run-to-detonation derived from classical ``Pop plot'' data. The explosive driver system produces the incident shocks and allows some control of the flow gradients in the collision region. Further, the incident shocks are very weak and do not transition to detonation. The experiments discussed feature incident shock waves that would be expected to cause initiation in the Mach stem, based on the Pop plot. Results show that the introduction of pressure/velocity gradients in the reaction zone strongly influences the ability of the flow to build to a steady ``CJ'' detonation. As expected, the ability of the Mach stem to stabilize or accelerate is strongly influenced by the incident shock pressure.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005BoLMe.114..413Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005BoLMe.114..413Y"><span>Numerical simulations of katabatic jumps in coats land, Antartica</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yu, Ye; Cai, Xiaoming; King, John C.; Renfrew, Ian A.</p> <p></p> <p>A non-hydrostatic numerical model, the Regional Atmospheric Modeling System (RAMS), has been used to investigate the development of katabatic jumps in Coats Land, Antarctica. In the control run with a 5 m s-1downslope directed initial wind, a katabatic jump develops near the foot of the idealized slope. The jump is manifested as a rapid deceleration of the downslope flow and a change from supercritical to subcritical flow, in a hydraulic sense, i.e., the Froude number (Fr) of the flow changes from Fr > 1 to Fr> 1. Results from sensitivity experiments show that an increase in the upstream flow rate strengthens the jump, while an increase in the downstream inversion-layer depth results in a retreat of the jump. Hydraulic theory and Bernoulli''s theorem have been used to explain the surface pressure change across the jump. It is found that hydraulic theory always underestimates the surface pressure change, while Bernoulli''s theorem provides a satisfactory estimation. An analysis of the downs balance for the katabatic jump indicates that the important forces are those related to the pressure gradient, advection and, to a lesser extent, the turbulent momentum divergence. The development of katabatic jumps can be divided into two phases. In phase I, the t gradient force is nearly balanced by advection, while in phase II, the pressure gradient force is counterbalanced by turbulent momentum divergence. The upslope pressure gradient force associated with a pool of cold air over the ice shelf facilitates the formation of the katabatic jump.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27743249','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27743249"><span>The association between the pulse pressure gradient at the cranio-cervical junction derived from phase-contrast magnetic resonance imaging and invasively measured pulsatile intracranial pressure in symptomatic patients with Chiari malformation type 1.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Frič, Radek; Lindstrøm, Erika Kristina; Ringstad, Geir Andre; Mardal, Kent-André; Eide, Per Kristian</p> <p>2016-12-01</p> <p>In symptomatic Chiari malformation type 1 (CMI), impaired intracranial compliance (ICC) is associated with an increased cranio-spinal pulsatile pressure gradient. Phase-contrast magnetic resonance imaging (MRI) represents a non-invasive modality for the assessment of the pulse pressure gradient at the cranio-cervical junction (CCJ). We wished to explore how the MRI-derived pulse pressure gradient (MRI-dP) compares with invasively measured pulsatile intracranial pressure (ICP) in CMI, and with healthy controls. From phase-contrast MRI of CMI patients and healthy controls, we computed cerebrospinal fluid (CSF) flow velocities and MRI-dP at the CCJ. We assessed bidirectional flow and compared the flow between the anterior and the posterior subarachnoid space at the CCJ. We computed total intracranial volume (ICV), ventricular CSF volume (VV), and posterior cranial fossa volume (PCFV). We analyzed the static and pulsatile ICP scores from overnight monitoring in CMI patients. Five CMI patients and four healthy subjects were included. The CMI group had a significantly larger extent of tonsillar ectopia, smaller PCFV, and a smaller area of CSF in the FM. The pulsatile ICP (mean ICP wave amplitude, MWA) was abnormally increased in 4/5 CMI patients and correlated positively with MRI-dP. However, the MRI-dP as well as the CSF flow velocities did not differ significantly between CMI and healthy subjects. Moreover, bidirectional flow was observed in both CMI as well as healthy subjects, with no significant difference. In symptomatic CMI patients, we found a significant association between the pulse pressure gradient at the CCJ derived from phase-contrast MRI and the pulsatile ICP (MWA) measured invasively. However, the MRI-dP was close to identical in CMI patients and healthy subjects. Moreover, the CSF flow velocities at the CCJ and the occurrence of bidirectional flow were not different in CMI patients and healthy individuals. Further studies are required to determine the diagnostic role of phase-contrast MRI in CMI patients.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005PhDT.......141M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005PhDT.......141M"><span>High-pressure nuclear magnetic resonance studies of fuel cell membranes</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mananga, Eugene Stephane</p> <p></p> <p>This thesis focuses on the use of high pressure NMR to study transport properties in electrolyte membranes used for fuel cells. The main concern is in studying the self-diffusion coefficients of ions and molecules in membranes and solutions, which can be used to characterize electrolytes in fuel cells. For this purpose, a high-pressure fringe field NMR method to study transport properties in material systems useful for fuel cell and battery electrolytes, was designed, developed, and implemented. In this investigation, pressure is the thermodynamic variable to obtain additional information about the ionic transport process, which could yield the crucial parameter, activation volume. Most of the work involves proton NMR, with additional investigations of others nuclei, such as fluorine, phosphorus and lithium. Using the FFG method, two fuel cell membrane types (NAFION-117, SPTES), and different dilutions of phosphoric acid were investigated, as was LiTf salt in Diglyme solution, which is used as a lithium battery electrolyte. In addition to high-pressure NMR diffusion measurements carried out in the fringe field gradient for the investigation of SPTES, pulse field gradient spin echo NMR was also used to characterize the water diffusion, in addition to measuring diffusion rates as a function of temperature. This second method allows us to measure distinct diffusion coefficients in cases where the different nuclear (proton) environments can be resolved in the NMR spectrum. Polymer electrolyte systems, in which the mobility of both cations and anions is probed by NMR self-diffusion measurements using standard pulsed field gradient methods and static gradient measurements as a function of applied hydrostatic pressure, were also investigated. The material investigated is the low molecular weight liquid diglyme/LiCF3SO3 (LiTf) complexes which can be used as electrolytes in lithium batteries. Finally, high-pressure diffusion coefficient measurements of phosphoric acid in water at different concentrations: proton (1H) and phosphorus (31P) nuclei have been performed using the static field gradient spin-echo nuclear magnetic resonance. This study is expected to be helpful in improving the understanding of phosphoric acid fuel cell technology.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4103668','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4103668"><span>The accuracy of the compressible Reynolds equation for predicting the local pressure in gas-lubricated textured parallel slider bearings</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Qiu, Mingfeng; Bailey, Brian N.; Stoll, Rob</p> <p>2014-01-01</p> <p>The validity of the compressible Reynolds equation to predict the local pressure in a gas-lubricated, textured parallel slider bearing is investigated. The local bearing pressure is numerically simulated using the Reynolds equation and the Navier-Stokes equations for different texture geometries and operating conditions. The respective results are compared and the simplifying assumptions inherent in the application of the Reynolds equation are quantitatively evaluated. The deviation between the local bearing pressure obtained with the Reynolds equation and the Navier-Stokes equations increases with increasing texture aspect ratio, because a significant cross-film pressure gradient and a large velocity gradient in the sliding direction develop in the lubricant film. Inertia is found to be negligible throughout this study. PMID:25049440</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26378495','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26378495"><span>Hand-Portable Gradient Capillary Liquid Chromatography Pumping System.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Sharma, Sonika; Plistil, Alex; Barnett, Hal E; Tolley, H Dennis; Farnsworth, Paul B; Stearns, Stanley D; Lee, Milton L</p> <p>2015-10-20</p> <p>In this work, a novel splitless nanoflow gradient generator integrated with a stop-flow injector was developed and evaluated using an on-column UV-absorption detector. The gradient pumping system consisted of two nanoflow pumps controlled by micro stepper motors, a mixer connected to a serpentine tube, and a high-pressure valve. The gradient system weighed only 4 kg (9 lbs) and could generate up to 55 MPa (8000 psi) pressure. The system could operate using a 24 V DC battery and required 1.2 A for operation. The total volume capacity of the pump was 74 μL, and a sample volume of 60 nL could be injected. The system provided accurate nanoflow rates as low as 10 nL/min without employing a splitter, making it ideal for capillary column use. The gradient dwell volume was calculated to be 1.3 μL, which created a delay of approximately 4 min with a typical flow rate of 350 nL/min. Gradient performance was evaluated for gradient step accuracy, and excellent reproducibility was obtained in day-to-day experiments (RSD < 1.2%, n = 4). Linear gradient reproducibility was tested by separating a three-component pesticide mixture on a poly(ethylene glycol) diacrylate (PEGDA) monolithic column. The retention time reproducibility was very good in run-to-run experiments (RSD < 1.42%, n = 4). Finally, excellent separation of five phenols was demonstrated using the nanoflow gradient system.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25454130','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25454130"><span>Using contemporary liquid chromatography theory and technology to improve capillary gradient ion-exchange separations.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wouters, Bert; Broeckhoven, Ken; Wouters, Sam; Bruggink, Cees; Agroskin, Yury; Pohl, Christopher A; Eeltink, Sebastiaan</p> <p>2014-11-28</p> <p>The gradient-performance limits of capillary ion chromatography have been assessed at maximum system pressure (34.5 MPa) using capillary columns packed with 4.1 μm macroporous anion-exchange particles coated with 65 nm positively-charged nanobeads. In analogy to the van-Deemter curve, the gradient performance was assessed applying different flow rates, while decreasing the gradient time inversely proportional to the increase in flow rate in order to maintain the same retention properties. The gradient kinetic-performance limits were determined at maximum system pressure, applying tG/t0=5, 10, and 20. In addition, the effect of retention on peak width was assessed in gradient mode for mono-, di-, and trivalent inorganic anions. The peak width of late-eluting ions can be significantly reduced by using concave gradient, resulting in better detection sensitivity. A signal enhancement factor of 8 was measured for a late-eluting ion when applying a concave instead of a linear gradient. For the analysis of a complex anion mixture, a coupled column with a total length of 1.05 m was operated at the kinetic-performance limit applying a linear 250 min gradient (tG/t0=10). The peak capacity varied between 200 and 380 depending on analyte retention, and hence on charge and size of the ion. Copyright © 2014 Elsevier B.V. All rights reserved.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19730055838&hterms=Aorta&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3DAorta','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19730055838&hterms=Aorta&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3DAorta"><span>Nonlinear analysis of aortic flow in living dogs.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Ling, S. C.; Atabek, H. B.; Letzing, W. G.; Patel, D. J.</p> <p>1973-01-01</p> <p>A nonlinear theory which considered the convective accelerations of blood and the nonlinear elastic behavior and taper angle of the vascular wall was used to study the nature of blood flow in the descending thoracic aorta of living dogs under a wide range of pressures and flows. Velocity profiles, wall friction, and discharge waves were predicted from locally measured input data about the pressure-gradient wave and arterial distention. The results indicated that a major part of the mean pressure gradient was balanced by convective accelerations; the theory, which took this factor into account, predicted the correct velocity distributions and flow waves.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JPhCS.894a2106A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JPhCS.894a2106A"><span>The unidirectional motion of two heat-conducting liquids in a flat channel</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Andreev, V. K.; Cheremnykh, E. N.</p> <p>2017-10-01</p> <p>The unidirectional motion of two viscous incompressible liquids in a flat channel is studied. Liquids contact on a flat interface. External boundaries are fixed solid walls, on which the non-stationary temperature gradients are given. The motion is induced by a joint action of thermogravitational and thermocapillary forces and given total non - stationary fluid flow rate in layers. The corresponding initial boundary value problem is conjugate and inverse because the pressure gradients along axes channel have to be determined together with the velocity and temperature field. For this problem the exact stationary solution is found and a priori estimates of non - stationary solutions are obtained. In Laplace images the solution of the non - stationary problem is found in quadratures. It is proved, that the solution converges to a steady regime with time, if the temperature on the walls and the fluid flow rate are stabilized. The numerical calculations for specific liquid media good agree with the theoretical results.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017SPIE10240E..0HW','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017SPIE10240E..0HW"><span>Accelerating gradient improvement using shape-tailor laser front in radiation pressure acceleration progress</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, W. P.; Shen, B. F.; Xu, Z. Z.</p> <p>2017-05-01</p> <p>The accelerating gradient of a proton beam is crucial for stable radiation pressure acceleration (RPA) because the multi-dimensional instabilities increase γ times slower in the relativistic region. In this paper, a shape-tailored laser is proposed to significantly accelerate the ions in a controllable high accelerating gradient. In this method, the fastest ions initially rest in the middle of the foil are controlled to catch the compressed electron layer at the end of the hole-boring stage, thus the light-sail stage can start as soon as possible. Then the compressed electron layer is accelerated tightly together with the fastest ions by the shaped laser intensity, which further increases the accelerating gradient in the light-sail stage. Such tailored pulse may be beneficial for the RPA driven by the 10-fs 10 petawatt laser in the future.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_20 --> <div id="page_21" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="401"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017APS..DFDA11005B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017APS..DFDA11005B"><span>Investigation of Flow Structures Downstream of SAPIEN 3, CoreValve, and PERIMOUNT Magna Using Particle Image Velocimetry</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Barakat, Mohammed; Lengsfeld, Corinne; Dvir, Danny; Azadani, Ali</p> <p>2017-11-01</p> <p>Transcatheter aortic valves provide superior systolic hemodynamic performance in terms of valvular pressure gradient and effective orifice area compared with equivalent size surgical bioprostheses. However, in depth investigation of the flow field structures is of interest to examine the flow field characteristics and provide experimental evidence necessary for validation of computational models. The goal of this study was to compare flow field characteristics of the three most commonly used transcatheter and surgical valves using phase-locked particle image velocimetry (PIV). 26mm SAPIEN 3, 26mm CoreValve, and 25mm PERIMOUNT Magna were examined in a pulse duplicator with input parameters matching ISO-5840. A 2D PIV system was used to obtain the velocity fields. Flow velocity and shear stress were obtained during the entire cardiac cycle. In-vitro testing showed that mean gradient was lowest for SAPIEN 3, followed by CoreValve and PERIMOUNT Magna. In all the valves, the peak jet velocity and maximum viscous shear stress were 2 m/s and 2 MPa, respectively. In conclusion, PIV was used to investigate flow field downstream of the three bioprostheses. Viscous shear stress was low and consequently shear-induced thrombotic trauma or shear-induced damage to red blood cells is unlikely.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4139393','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4139393"><span>Impact of Hypokalemia on Electromechanical Window, Excitation Wavelength and Repolarization Gradients in Guinea-Pig and Rabbit Hearts</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Osadchii, Oleg E.</p> <p>2014-01-01</p> <p>Normal hearts exhibit a positive time difference between the end of ventricular contraction and the end of QT interval, which is referred to as the electromechanical (EM) window. Drug-induced prolongation of repolarization may lead to the negative EM window, which was proposed to be a novel proarrhythmic marker. This study examined whether abnormal changes in the EM window may account for arrhythmogenic effects produced by hypokalemia. Left ventricular pressure, electrocardiogram, and epicardial monophasic action potentials were recorded in perfused hearts from guinea-pig and rabbit. Hypokalemia (2.5 mM K+) was found to prolong repolarization, reduce the EM window, and promote tachyarrhythmia. Nevertheless, during both regular pacing and extrasystolic excitation, the increased QT interval invariably remained shorter than the duration of mechanical systole, thus yielding positive EM window values. Hypokalemia-induced arrhythmogenicity was associated with slowed ventricular conduction, and shortened effective refractory periods, which translated to a reduced excitation wavelength index. Hypokalemia also evoked non-uniform prolongation of action potential duration in distinct epicardial regions, which resulted in increased spatial variability in the repolarization time. These findings suggest that arrhythmogenic effects of hypokalemia are not accounted for by the negative EM window, and are rather attributed to abnormal changes in ventricular conduction times, refractoriness, excitation wavelength, and spatial repolarization gradients. PMID:25141124</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/biblio/944909-gas-liquid-processing-microchannels','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/944909-gas-liquid-processing-microchannels"><span>Gas-Liquid Processing in Microchannels</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>TeGrotenhuis, Ward E.; Stenkamp, Victoria S.; Twitchell, Alvin</p> <p></p> <p>Processing gases and liquids together in microchannels having at least one dimension <1 mm has unique advantages for rapid heat and mass transfer. One approach for managing the two phases is to use porous structures as wicks within microchannels to segregate the liquid phase from the gas phase. Gas-liquid processing is accomplished by providing a gas flow path and inducing flow of the liquid phase through or along the wick under an induced pressure gradient. A variety of unit operations are enabled, including phase separation, partial condensation, absorption, desorption, and distillation. Results are reported of an investigation of microchannel phasemore » separation in a transparent, single-channel device. Next, heat exchange is integrated with the microchannel wick approach to create a partial condenser that also separates the condensate. Finally, the scale-up to a multi-channel phase separator is described.« less</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017ZNatA..72..763P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017ZNatA..72..763P"><span>Exploration of Characteristics Governing Dynamics of Whirlwinds: Application to Dust Devils</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pandey, Sanjay Kumar; Maurya, Jagdish Prasad</p> <p>2017-08-01</p> <p>It is intended to model mathematically an ideal whirlwind which characterises this geo-physical phenomenon and eventually helps us decode the inherent dynamics. A dense cylindrical aerial mass is taken into consideration surrounding a rarer aerial region in order to keep a radial favourable gradient of pressure to sustain a rotational motion. It has been concluded that the whirlwind will survive as long as the low pressure region exists. The vertical pressure gradient also plays an equally important role. Since it is not connected to any cloud and the axial velocity is in the vertically upward direction, the momentary vertical gradient of pressure is required for its growth and survival. Horizontal ambient winds that rush towards low pressure zone, crush the air in the buffer zone, and turn vertically upward may also take the dust carried with them visibly to some height. It is considered that the angular azimuthal velocity varies within the annulus. An inference is that no whirlwind without a low pressure region within it can survive. This may be termed as the fundamental characteristic of whirlwind. It is further concluded that if the radial pressure difference between the outermost and innermost layers is larger, the whirlwind is thicker and consequently, it will last longer. Moreover, another conclusion arrived at is that the angular velocity will vanish if the inner radius is zero.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19800004749','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19800004749"><span>Investigation of blown boundary layers with an improved wall jet system. Ph.D. Thesis. Final Technical Report, 1 Jul. 1978 - Dec. 1979; [to prevent turbulent boundary layer separation</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Saripalli, K. R.; Simpson, R. L.</p> <p>1979-01-01</p> <p>The behavior of two dimensional incompressible turbulent wall jets submerged in a boundary layer when they are used to prevent boundary layer separation on plane surfaces is investigated. The experimental set-up and instrumentation are described. Experimental results of zero pressure gradient flow and adverse pressure gradient flow are presented. Conclusions are given and discussed.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19790025267','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19790025267"><span>Survey and bibliography on attainment of laminar flow control in air using pressure gradient and suction, volume 1</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bushnell, D. M.; Tuttle, M. H.</p> <p>1979-01-01</p> <p>A survey was conducted and a bibliography compiled on attainment of laminar flow in air through the use of favorable pressure gradient and suction. This report contains the survey, summaries of data for both ground and flight experiments, and abstracts of referenced reports. Much early information is also included which may be of some immediate use as background material for LFC applications.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19840063318&hterms=blunt+tool&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dblunt%2Btool','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19840063318&hterms=blunt+tool&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dblunt%2Btool"><span>An experimental study of a supercritical trailing-edge flow</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Brown, J. L.; Viswanath, P. R.</p> <p>1984-01-01</p> <p>An experimental study has been conducted of a transonic, turbulent, high-Reynolds-number blunt trailing-edge flow. The model shape and the surface pressure distribution are characteristics of a modern supercritical airfoil under shock-free conditions. Reynolds number and pressure gradient scaling of the boundary layer are relevant to airfoil applications. The data set is exceptionally accurate and consistent, with the momentum balance accounting for the flux of momentum to within 1 percent, except in the immediate vicinity of the blunt trailing edge. The experimental flow exhibits strong viscous-inviscid interaction and higher-order boundary-layer effects including strong adverse streamwise pressure gradient, significant normal pressure gradients associated with surface and streamline curvature, and significant wake curvature. Navier-Stokes calculations with a two-equation K-epsilon turbulence model predict the correct pressure distribution which demonstrates the utility of these engineering tools. The experiment approaches separation at the strailing edge. However, in comparison to the experiment, the calculations predict too high skin friction and insufficient displacement thickness growth. An analysis of the turbulent and mean flow fields reveals the turbulence model defects are likely in modeling the dissipation source and sink terms, and in the eddy viscosity relation.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140016450','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140016450"><span>Generating a Simulated Fluid Flow Over an Aircraft Surface Using Anisotropic Diffusion</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Rodriguez, David L. (Inventor); Sturdza, Peter (Inventor)</p> <p>2013-01-01</p> <p>A fluid-flow simulation over a computer-generated aircraft surface is generated using a diffusion technique. The surface is comprised of a surface mesh of polygons. A boundary-layer fluid property is obtained for a subset of the polygons of the surface mesh. A pressure-gradient vector is determined for a selected polygon, the selected polygon belonging to the surface mesh but not one of the subset of polygons. A maximum and minimum diffusion rate is determined along directions determined using a pressure gradient vector corresponding to the selected polygon. A diffusion-path vector is defined between a point in the selected polygon and a neighboring point in a neighboring polygon. An updated fluid property is determined for the selected polygon using a variable diffusion rate, the variable diffusion rate based on the minimum diffusion rate, maximum diffusion rate, and angular difference between the diffusion-path vector and the pressure-gradient vector.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70015275','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70015275"><span>Flow separation of currents in shallow water</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Signell, Richard P.</p> <p>1989-01-01</p> <p>Flow separation of currents in shallow coastal areas is investigated using a boundary layer model for two-dimensional (depth-averaged) tidal flow past an elliptic headland. If the shoaling region near the coast is narrow compared to the scale of the headland, bottom friction causes the flow to separate just downstream of the point where the pressure gradient switches from favoring to adverse. As long as the shoaling region at the coast is well resolved, the inclusion of eddy viscosity and a no-slip boundary condition have no effect on this result. An approximate analytic solution for the pressure gradient along the boundary is obtained by assuming the flow away from the immediate vicinity of the boundary is irrotational. On the basis of the pressure gradient obtained from the irrotational flow solution, flow separation is a strong function of the headland aspect ratio, an equivalent Reynolds number, and a Keulegan-Carpenter number.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/18584093','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/18584093"><span>Effect of viscoelasticity on the flow pattern and the volumetric flow rate in electroosmotic flows through a microchannel.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Park, H M; Lee, W M</p> <p>2008-07-01</p> <p>Many lab-on-a-chip based microsystems process biofluids such as blood and DNA solutions. These fluids are viscoelastic and show extraordinary flow behaviors, not existing in Newtonian fluids. Adopting appropriate constitutive equations these exotic flow behaviors can be modeled and predicted reasonably using various numerical methods. In the present paper, we investigate viscoelastic electroosmotic flows through a rectangular straight microchannel with and without pressure gradient. It is shown that the volumetric flow rates of viscoelastic fluids are significantly different from those of Newtonian fluids under the same external electric field and pressure gradient. Moreover, when pressure gradient is imposed on the microchannel there appear appreciable secondary flows in the viscoelastic fluids, which is never possible for Newtonian laminar flows through straight microchannels. The retarded or enhanced volumetric flow rates and secondary flows affect dispersion of solutes in the microchannel nontrivially.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19750007146','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19750007146"><span>Neutral winds and electric fields from model studies using reduced ionograms</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Baran, D. E.</p> <p>1974-01-01</p> <p>A relationship between the vertical component of the ion velocity and electron density profiles derived from reduced ionograms is developed. Methods for determining the horizontal components of the neutral winds and electric fields by using this relationship and making use of the variations of the inclinations and declinations of the earth's magnetic field are presented. The effects that electric fields have on the neutral wind calculations are estimated to be small but not second order. Seasonal and latitudinal variations of the calculated neutral winds are presented. From the calculated neutral winds a new set of neutral pressure gradients is determined. The new pressure gradients are compared with those generated from several static neutral atmospheric models. Sensitivity factors relating the pressure gradients and neutral winds are calculated and these indicate that mode coupling and harmonic generation are important to studies which assume linearized theories.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017APS..DFDM28006G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017APS..DFDM28006G"><span>DNS of a non-equilibrium adverse pressure gradient turbulent boundary layer</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gungor, Taygun R.; Gungor, Ayse G.; Maciel, Yvan; Simens, Mark P.</p> <p>2017-11-01</p> <p>A new direct numerical simulation (DNS) dataset of a non-equilibrium adverse pressure gradient (APG) turbulent boundary layer (TBL) that evolves from a zero-pressure-gradient (ZPG) TBL to a TBL which is very close to separation at Reθ is around 8200 is presented. There are two simulations running together in the DNS computational setup. The APG TBL spans Reθ = 1476 - 8276 . Mean velocity results do not satisfy the log law as the defect in the velocity increases. The production and the Reynolds stress peak are observed around y /δ* = 1 after the flow is evolved up to a certain point. The new dataset is compared with other datasets in terms of mean values, Reynolds stresses and turbulent kinetic energy budgets and using this comparison scaling study is performed. Funded by in part by ITU-AYP and NSERC of Canada.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19840009072','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19840009072"><span>Trailing edge flow conditions as a factor in airfoil design</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Ormsbee, A. I.; Maughmer, M. D.</p> <p>1984-01-01</p> <p>Some new developments relevant to the design of single-element airfoils using potential flow methods are presented. In particular, the role played by the non-dimensional trailing edge velocity in design is considered and the relationship between the specified value and the resulting airfoil geometry is explored. In addition, the ramifications of the unbounded trailing edge pressure gradients generally present in the potential flow solution of the flow over an airfoil are examined, and the conditions necessary to obtain a class of airfoils having finite trailing edge pressure gradients developed. The incorporation of these conditions into the inverse method of Eppler is presented and the modified scheme employed to generate a number of airfoils for consideration. The detailed viscous analysis of airfoils having finite trailing edge pressure gradients demonstrates a reduction in the strong inviscid-viscid interactions generally present near the trailing edge of an airfoil.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24671111','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24671111"><span>The values of wall shear stress, turbulence kinetic energy and blood pressure gradient are associated with atherosclerotic plaque erosion in rabbits.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Sameshima, Naoki; Yamashita, Atsushi; Sato, Shinya; Matsuda, Shuntaro; Matsuura, Yunosuke; Asada, Yujiro</p> <p>2014-01-01</p> <p>To clarify the contribution of hemodynamic factors to the onset of plaque erosion in smooth muscle cell (SMC)-rich atherosclerotic plaque. We developed a rabbit model of SMC-rich atherosclerotic plaque with various degree of stenosis induced by incomplete ligation and generated three-dimensional models of five rabbit femoral arteries based on 130-162 serial histological cross-sections at 100-μm intervals per artery. We performed a computational blood flow simulation using the Reynolds-averaged Navier-Stokes model and calculated the wall shear stress (WSS), turbulence kinetic energy (TKE), blood pressure (BP) and blood pressure gradients (BPG) in eight sections (the inlet, the stenotic portion and areas 1, 2 and 5mm from the stenotic portion) in each rabbit. We also investigated whether the magnitude of WSS or TKE was related to the presence or absence of erosive injury by evaluating six points (the locally highest, median and lowest of WSS or TKE) in each section. The magnitudes of WSS, TKE and BPG, but not BP, correlated significantly with the extent of histologically-defined plaque erosion (WSS, r=0.55, p＜0.001; TKE, r=0.53, p＜0.001; BPG, r=0.61, p＜0.0001, n=40). The values for WSS and TKE were significantly larger at sites with, compared to without, erosive injury (n=107 and n=119 points, respectively; both p＜0.0001). These results suggest that increased values of WSS, TKE and BPG considerably contribute to the onset of plaque erosion.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27043243','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27043243"><span>Numerically simulated exposure of children and adults to pulsed gradient fields in MRI.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Samoudi, Amine M; Vermeeren, Gunter; Tanghe, Emmeric; Van Holen, Roel; Martens, Luc; Josephs, Wout</p> <p>2016-11-01</p> <p>To determine exposure to gradient switching fields of adults and children in a magnetic resonance imaging (MRI) scanner by evaluating internal electric fields within realistic models of adult male, adult female, and child inside transverse and longitudinal gradient coils, and to compare these results with compliance guidelines. Patients inside x-, y-, and z-gradient coils were simulated using anatomically realistic models of adult male, adult female, and child. The induced electric fields were computed for 1 kHz sinusoidal current with a magnitude of 1 A in the gradient coils. Rheobase electric fields were then calculated and compared to the International Commission on Non-Ionizing Radiation Protection (ICNIRP) 2004 and International Electrotechnical Commission (IEC) 2010 guidelines. The effect of the human body, coil type, and skin conductivity on the induced electric field was also investigated. The internal electric fields are within the first level controlled operating mode of the guidelines and range from 2.7V m -1 to 4.5V m -1 , except for the adult male inside the y-gradient coil (induced field reaches 5.4V m -1 ).The induced electric field is sensitive to the coil type (electric field in the skin of adult male: 4V m -1 , 4.6V m -1 , and 3.8V m -1 for x-, y-, and z-gradient coils, respectively), the human body model (electric field in the skin inside y-gradient coil: 4.6V m -1 , 4.2V m -1 , and 3V m -1 for adult male, adult female, and child, respectively), and the skin conductivity (electric field 2.35-4.29% higher for 0.1S m -1 skin conductivity compared to 0.2S m -1 ). The y-gradient coil induced the largest fields in the patients. The highest levels of internal electric fields occurred for the adult male model. J. Magn. Reson. Imaging 2016;44:1360-1367. © 2016 International Society for Magnetic Resonance in Medicine.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016MsT.........72S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016MsT.........72S"><span>June 9-10, 2015: A case study of the Great Plains Low-Level Jet during PECAN (Plains Elevated Convection at Night)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sullivan, Sharon M.</p> <p></p> <p>Observations as part of the Plains Elevated Convection at Night (PECAN) campaign have allowed for an examination of the thermodynamic and dynamic structure of the LLJ using ground-based and airborne measurements in central Kansas. A shallow jet with wind speeds near 20 m s-1 formed during the nighttime hours on 10 June 2015. The University of Wyoming King Air research aircraft conducted two research flights beginning at sunset and ending near dawn, capturing the full evolution of the LLJ. Each flight included a series of vertical sawtooth maneuvers and isobaric legs along a fixed track at 38.7°N between 98.89°W and 100.3°W. This case featured classic signatures of the LLJ, including but not limited to the inertial oscillation of the ageostrophic wind. Forcing of the LLJ was analyzed using cross sections of D-values that allowed the vertical structure of the horizontal pressure gradient and hence thermal wind to be examined. A series of numerical simulations of the 10 June 2015 case study were made using the Weather Research and Forecasting (WRF) model to compare with observations. Output grids indicated that a temperature gradient of 6°C over 500 km was present between the surface and 850 hPa. Warmer temperatures were found to the west from the surface up to 600 hPa. The 600 hPa geostrophic winds were from the north. As a result, only weak southerly geostrophic winds were able to develop at the surface. The terrain-induced thermal wind was sufficiently large to overcome the adverse pressure gradient in the free atmosphere, but could only produce weak southerly geostrophic winds at the surface of about 11.4 m s-1.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/7238275','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/7238275"><span>Nonoperative measurement of pancreatic and common bile duct pressures with a microtransducer catheter and effects of duodenoscopic sphincterotomy.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Tanaka, M; Ikeda, S; Nakayama, F</p> <p>1981-06-01</p> <p>Duodenoscopic manometry of the pancreatic duct (PD) and common bile duct (CBD) using a microtransducer catheter was distinct advantages over infusion manometry, giving absolute values of in situ intraluminal pressure. Microtransducer manometry was performed without medication in 49 patients with gallbladder stones (10), common bile duct stones (24), hepatic duct stones (6) and common bile duct dilatation (9), and was successful in 42 (86%) for PD and 36 (73%) for CBD. Ductal pressures showed respiration-synchronized biphasic variations superimposed by the arterial pulsation effect. Considerable postural change of the pressure values suggested that the recording posture should be predetermined. The PD-to-duodenum pressure gradient was higher than the CBD-to-duodenum gradient in most cases. Both were lower than those obtained previously by infusion methods. No significant differences were found in pressure profiles of the four disease groups. Endoscopic sphincterotomy significantly reduced not only CBD pressure but also PD pressure.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25817944','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25817944"><span>Directed transport by surface chemical potential gradients for enhancing analyte collection in nanoscale sensors.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Sitt, Amit; Hess, Henry</p> <p>2015-05-13</p> <p>Nanoscale detectors hold great promise for single molecule detection and the analysis of small volumes of dilute samples. However, the probability of an analyte reaching the nanosensor in a dilute solution is extremely low due to the sensor's small size. Here, we examine the use of a chemical potential gradient along a surface to accelerate analyte capture by nanoscale sensors. Utilizing a simple model for transport induced by surface binding energy gradients, we study the effect of the gradient on the efficiency of collecting nanoparticles and single and double stranded DNA. The results indicate that chemical potential gradients along a surface can lead to an acceleration of analyte capture by several orders of magnitude compared to direct collection from the solution. The improvement in collection is limited to a relatively narrow window of gradient slopes, and its extent strongly depends on the size of the gradient patch. Our model allows the optimization of gradient layouts and sheds light on the fundamental characteristics of chemical potential gradient induced transport.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19930038628&hterms=UNSTEADY+LIFT+AIRFOIL&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DUNSTEADY%2BLIFT%2BAIRFOIL','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19930038628&hterms=UNSTEADY+LIFT+AIRFOIL&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DUNSTEADY%2BLIFT%2BAIRFOIL"><span>The computation of the post-stall behavior of a circulation controlled airfoil</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Linton, Samuel W.</p> <p>1993-01-01</p> <p>The physics of the circulation controlled airfoil is complex and poorly understood, particularly with regards to jet stall, which is the eventual breakdown of lift augmentation by the jet at some sufficiently high blowing rate. The present paper describes the numerical simulation of stalled and unstalled flows over a two-dimensional circulation controlled airfoil using a fully implicit Navier-Stokes code, and the comparison with experimental results. Mach numbers of 0.3 and 0.5 and jet total to freestream pressure ratios of 1.4 and 1.8 are investigated. The Baldwin-Lomax and k-epsilon turbulence models are used, each modified to include the effect of strong streamline curvature. The numerical solutions of the post-stall circulation controlled airfoil show a highly regular unsteady periodic flowfield. This is the result of an alternation between adverse pressure gradient and shock induced separation of the boundary layer on the airfoil trailing edge.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/18654410','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/18654410"><span>A charge-driven molecular water pump.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Gong, Xiaojing; Li, Jingyuan; Lu, Hangjun; Wan, Rongzheng; Li, Jichen; Hu, Jun; Fang, Haiping</p> <p>2007-11-01</p> <p>Understanding and controlling the transport of water across nanochannels is of great importance for designing novel molecular devices, machines and sensors and has wide applications, including the desalination of seawater. Nanopumps driven by electric or magnetic fields can transport ions and magnetic quanta, but water is charge-neutral and has no magnetic moment. On the basis of molecular dynamics simulations, we propose a design for a molecular water pump. The design uses a combination of charges positioned adjacent to a nanopore and is inspired by the structure of channels in the cellular membrane that conduct water in and out of the cell (aquaporins). The remarkable pumping ability is attributed to the charge dipole-induced ordering of water confined in the nanochannels, where water can be easily driven by external fields in a concerted fashion. These findings may provide possibilities for developing water transport devices that function without osmotic pressure or a hydrostatic pressure gradient.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_21 --> <div id="page_22" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="421"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140012984','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140012984"><span>Mass Dependency of Isotope Fractionation of Gases Under Thermal Gradient and Its Possible Implications for Planetary Atmosphere Escaping Process</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sun, Tao; Niles, Paul; Bao, Huiming; Socki, Richard</p> <p>2014-01-01</p> <p>Physical processes that unmix elements/isotopes of gas molecules involve phase changes, diffusion (chemical or thermal), effusion and gravitational settling. Some of those play significant roles for the evolution of chemical and isotopic compositions of gases in planetary bodies which lead to better understanding of surface paleoclimatic conditions, e.g. gas bubbles in Antarctic ice, and planetary evolution, e.g. the solar-wind erosion induced gas escaping from exosphere on terrestrial planets.. A mass dependent relationship is always expected for the kinetic isotope fractionations during these simple physical processes, according to the kinetic theory of gases by Chapman, Enskog and others [3-5]. For O-bearing (O16, -O17, -O18) molecules the alpha O-17/ alpha O-18 is expected at 0.5 to 0.515, and for S-bearing (S32,-S33. -S34, -S36) molecules, the alpha S-33/ alpha S-34 is expected at 0.5 to 0.508, where alpha is the isotope fractionation factor associated with unmixing processes. Thus, one isotope pair is generally proxied to yield all the information for the physical history of the gases. However, we recently] reported the violation of mass law for isotope fractionation among isotope pairs of multiple isotope system during gas diffusion or convection under thermal gradient (Thermal Gradient Induced Non-Mass Dependent effect, TGI-NMD). The mechanism(s) that is responsible to such striking observation remains unanswered. In our past studies, we investigated polyatomic molecules, O2 and SF6, and we suggested that nuclear spin effect could be responsible to the observed NMD effect in a way of changing diffusion coefficients of certain molecules, owing to the fact of negligible delta S-36 anomaly for SF6.. On the other hand, our results also showed that for both diffusion and convection under thermal gradient, this NMD effect is increased by lower gas pressure, bigger temperature gradient and lower average temperature, which indicate that the nuclear spin effect may not be the significant contributor as the energies involved in the hyperfine effect are much smaller than those with molecular collisions, especially under convective conditions.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28516255','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28516255"><span>Water Quality Interaction with Alkaline Phosphatase in the Ganga River: Implications for River Health.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Yadav, Amita; Pandey, Jitendra</p> <p>2017-07-01</p> <p>Carbon, nitrogen and phosphorus inputs through atmospheric deposition, surface runoff and point sources were measured in the Ganga River along a gradient of increasing human pressure. Productivity variables (chlorophyll a, gross primary productivity, biogenic silica and autotrophic index) and heterotrophy (respiration, substrate induced respiration, biological oxygen demand and fluorescein diacetate hydrolysis) showed positive relationships with these inputs. Alkaline phosphatase (AP), however, showed an opposite trend. Because AP is negatively influenced by available P, and eutrophy generates a feedback on P fertilization, the study implies that the alkaline phosphatase can be used as a high quality criterion for assessing river health.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/18026409','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/18026409"><span>Optical levitation of absorbing particles with a nominally Gaussian laser beam.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Huisken, Jan; Stelzer, Ernst H K</p> <p>2002-07-15</p> <p>We use a Gaussian laser beam to study the levitation of absorbing Mie particles. Several metal oxide particles are stably levitated, and their movement over time is recorded. Our studies show that the position of each particle is highly dependent on the other particles' locations. The observations are explained by the phenomenon of thermal creep. The increased local pressure that is due to a temperature gradient along the particle's surface induces levitation. The particles rest close to minima in the intensity distribution near the optical axis. An experiment is suggested that can be used to locate these minima in a laser beam.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26000567','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26000567"><span>Geometric pumping in autophoretic channels.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Michelin, Sébastien; Montenegro-Johnson, Thomas D; De Canio, Gabriele; Lobato-Dauzier, Nicolas; Lauga, Eric</p> <p>2015-08-07</p> <p>Many microfluidic devices use macroscopic pressure differentials to overcome viscous friction and generate flows in microchannels. In this work, we investigate how the chemical and geometric properties of the channel walls can drive a net flow by exploiting the autophoretic slip flows induced along active walls by local concentration gradients of a solute species. We show that chemical patterning of the wall is not required to generate and control a net flux within the channel, rather channel geometry alone is sufficient. Using numerical simulations, we determine how geometric characteristics of the wall influence channel flow rate, and confirm our results analytically in the asymptotic limit of lubrication theory.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29096981','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29096981"><span>Osmosis and viscoelasticity both contribute to time-dependent behaviour of the intervertebral disc under compressive load: A caprine in vitro study.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Emanuel, Kaj S; van der Veen, Albert J; Rustenburg, Christine M E; Smit, Theodoor H; Kingma, Idsart</p> <p>2018-03-21</p> <p>The mechanical behaviour of the intervertebral disc highly depends on the content and transport of interstitial fluid. It is unknown, however, to what extent the time-dependent behaviour can be attributed to osmosis. Here we investigate the effect of both mechanical and osmotic loading on water content, nucleus pressure and disc height. Eight goat intervertebral discs, immersed in physiological saline, were subjected to a compressive force with a pressure needle inserted in the nucleus. The loading protocol was: 10 N (6 h); 150 N (42 h); 10 N (24 h). Half-way the 150 N-phase (24 h), we eliminated the osmotic gradient by adding 26% poly-ethylene glycol to the surrounding fluid. For 62 additional discs, we determined the water content of both nucleus and annulus after 6, 24, 48, or 72 h. The compressive load was initially counterbalanced by the hydrostatic pressure in the nucleus. The load forced 4.3% of the water out of the nucleus, which reduced nucleus pressure by 44(±6)%. Reduction of the osmotic gradient disturbed the equilibrium disc height, and a significant loss of annulus water content was found. Remarkably, pressure and water content of the nucleus pulposus remained unchanged. This shows that annulus water content is important in the response to axial loading. After unloading, in the absence of an osmotic gradient, there was substantial viscoelastic recovery of 53(±11)% of the disc height, without a change in water content. However, for restoration of the nucleus pressure and for full restoration of disc height, restoration of the osmotic gradient was needed. Copyright © 2017 Elsevier Ltd. All rights reserved.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19760000255&hterms=craft&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Dcraft','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19760000255&hterms=craft&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Dcraft"><span>Conical diffuser for fuel cells</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Craft, D. W.</p> <p>1976-01-01</p> <p>Diffuser is inserted into inlet manifold, producing smooth transition of flow from pipe diameter to manifold diameter. Expected pressure gradient and resulting cell-to-cell temperature gradient are reduced. Outlet manifold has nozzle insert that reduces exit losses.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016APS..DFDD40004G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016APS..DFDD40004G"><span>Preferential paths in yield stress fluid flow through a porous medium</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Guasto, Jeffrey; Waisbord, Nicolas; Stoop, Norbert; Dunkel, Jörn</p> <p>2016-11-01</p> <p>A broad range of biological, geological, and industrial materials with complex rheological properties are subjected to flow through porous media in applications ranging from oil recovery to food manufacturing. In this experimental study, we examine the flow of a model yield stress fluid (Carbopol micro-gel) through a quasi-2D porous medium, fabricated in a microfluidic channel. The flow is driven by applying a precisely-controlled pressure gradient and measured by particle tracking velocimetry, and our observations are complemented by a pore-network model of the yield stress fluid flow. While remaining unyielded at small applied pressure, the micro-gel begins to yield at a critical pressure gradient, exhibiting a single preferential flow path that percolates through the porous medium. As the applied pressure gradient increases, we observe a subsequent coarsening and invasion of the yielded, fluidized network. An examination of both the yielded network topology and pore-scale flow reveal that two cooperative phenomena are involved in sculpting the preferential flow paths: (1) the geometry of the porous microstructure, and (2) the adhesive surface interactions between the micro-gel and substrate. NSF CBET-1511340.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/20000108735','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20000108735"><span>Closed-loop Separation Control Using Oscillatory Flow Excitation</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Allan, Brian G.; Juang, Jer-Nan; Raney, David L.; Seifert, Avi; Pack, latunia G.; Brown, Donald E.</p> <p>2000-01-01</p> <p>Design and implementation of a digital feedback controller for a flow control experiment was performed. The experiment was conducted in a cryogenic pressurized wind tunnel on a generic separated configuration at a chord Reynolds number of 16 million and a Mach number of 0.25. The model simulates the upper surface of a 20% thick airfoil at zero angle-of-attack. A moderate favorable pressure gradient, up to 55% of the chord, is followed by a severe adverse pressure gradient which is relaxed towards the trailing edge. The turbulent separation bubble, behind the adverse pressure gradient, is then reduced by introducing oscillatory flow excitation just upstream of the point of flow separation. The degree of reduction in the separation region can be controlled by the amplitude of the oscillatory excitation. A feedback controller was designed to track a given trajectory for the desired degree of flow reattachment and to improve the transient behavior of the flow system. Closed-loop experiments demonstrated that the feedback controller was able to track step input commands and improve the transient behavior of the open-loop response.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/15044678','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/15044678"><span>Pleural mechanics and fluid exchange.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Lai-Fook, Stephen J</p> <p>2004-04-01</p> <p>The pleural space separating the lung and chest wall of mammals contains a small amount of liquid that lubricates the pleural surfaces during breathing. Recent studies have pointed to a conceptual understanding of the pleural space that is different from the one advocated some 30 years ago in this journal. The fundamental concept is that pleural surface pressure, the result of the opposing recoils of the lung and chest wall, is the major determinant of the pressure in the pleural liquid. Pleural liquid is not in hydrostatic equilibrium because the vertical gradient in pleural liquid pressure, determined by the vertical gradient in pleural surface pressure, does not equal the hydrostatic gradient. As a result, a viscous flow of pleural liquid occurs in the pleural space. Ventilatory and cardiogenic motions serve to redistribute pleural liquid and minimize contact between the pleural surfaces. Pleural liquid is a microvascular filtrate from parietal pleural capillaries in the chest wall. Homeostasis in pleural liquid volume is achieved by an adjustment of the pleural liquid thickness to the filtration rate that is matched by an outflow via lymphatic stomata.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/pages/biblio/1371564-experimental-verification-role-electron-pressure-fast-magnetic-reconnection-guide-field','SCIGOV-DOEP'); return false;" href="https://www.osti.gov/pages/biblio/1371564-experimental-verification-role-electron-pressure-fast-magnetic-reconnection-guide-field"><span>Experimental verification of the role of electron pressure in fast magnetic reconnection with a guide field</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/pages">DOE PAGES</a></p> <p>Fox, W.; Sciortino, F.; v. Stechow, A.; ...</p> <p>2017-03-21</p> <p>We report detailed laboratory observations of the structure of a reconnection current sheet in a two-fluid plasma regime with a guide magnetic field. We observe and quantitatively analyze the quadrupolar electron pressure variation in the ion-diffusion region, as originally predicted by extended magnetohydrodynamics simulations. The projection of the electron pressure gradient parallel to the magnetic field contributes significantly to balancing the parallel electric field, and the resulting cross-field electron jets in the reconnection layer are diamagnetic in origin. Furthermore, these results demonstrate how parallel and perpendicular force balance are coupled in guide field reconnection and confirm basic theoretical models ofmore » the importance of electron pressure gradients for obtaining fast magnetic reconnection.« less</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/8538157','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/8538157"><span>The effect of partial portal decompression on portal blood flow and effective hepatic blood flow in man: a prospective study.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Rosemurgy, A S; McAllister, E W; Godellas, C V; Goode, S E; Albrink, M H; Fabri, P J</p> <p>1995-12-01</p> <p>With the advent of transjugular intrahepatic porta-systemic stent shunt and the wider application of the surgically placed small diameter prosthetic H-graft portacaval shunt (HGPCS), partial portal decompression in the treatment of portal hypertension has received increased attention. The clinical results supporting the use of partial portal decompression are its low incidence of variceal rehemorrhage due to decreased portal pressures and its low rate of hepatic failure, possibly due to maintenance of blood flow to the liver. Surprisingly, nothing is known about changes in portal hemodynamics and effective hepatic blood flow following partial portal decompression. To prospectively evaluate changes in portal hemodynamics and effective hepatic blood flow brought about by partial portal decompression, the following were determined in seven patients undergoing HGPCS: intraoperative pre- and postshunt portal vein pressures and portal vein-inferior vena cava pressure gradients, intraoperative pre- and postshunt portal vein flow, and pre- and postoperative effective hepatic blood flow. With HGPCS, portal vein pressures and portal vein-inferior vena cava pressure gradients decreased significantly, although portal pressures remained above normal. In contrast to the significant decreases in portal pressures, portal vein blood flow and effective hepatic blood flow do not decrease significantly. Changes in portal vein pressures and portal vein-inferior vena cava pressure gradients are great when compared to changes in portal vein flow and effective hepatic blood flow. Reduction of portal hypertension with concomitant maintenance of hepatic blood flow may explain why hepatic dysfunction is avoided following partial portal decompression.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17440238','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17440238"><span>Electric fields induced in the human body by time-varying magnetic field gradients in MRI: numerical calculations and correlation analysis.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Bencsik, Martin; Bowtell, Richard; Bowley, Roger</p> <p>2007-05-07</p> <p>The spatial distributions of the electric fields induced in the human body by switched magnetic field gradients in MRI have been calculated numerically using the commercial software package, MAFIA, and the three-dimensional, HUGO body model that comprises 31 different tissue types. The variation of |J|, |E| and |B| resulting from exposure of the body model to magnetic fields generated by typical whole-body x-, y- and z-gradient coils has been analysed for three different body positions (head-, heart- and hips-centred). The magnetic field varied at 1 kHz, so as to produce a rate of change of gradient of 100 T m(-1) s(-1) at the centre of each coil. A highly heterogeneous pattern of induced electric field and current density was found to result from the smoothly varying magnetic field in all cases, with the largest induced electric fields resulting from application of the y-gradient, in agreement with previous studies. By applying simple statistical analysis to electromagnetic quantities within axial planes of the body model, it is shown that the induced electric field is strongly correlated to the local value of resistivity, and the induced current density exhibits even stronger correlation with the local conductivity. The local values of the switched magnetic field are however shown to bear little relation to the local values of the induced electric field or current density.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17945575','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17945575"><span>Tailoring magnetic field gradient design to magnet cryostat geometry.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Trakic, A; Liu, F; Lopez, H S; Wang, H; Crozier, S</p> <p>2006-01-01</p> <p>Eddy currents induced within a magnetic resonance imaging (MRI) cryostat bore during pulsing of gradient coils can be applied constructively together with the gradient currents that generate them, to obtain good quality gradient uniformities within a specified imaging volume over time. This can be achieved by simultaneously optimizing the spatial distribution and temporal pre-emphasis of the gradient coil current, to account for the spatial and temporal variation of the secondary magnetic fields due to the induced eddy currents. This method allows the tailored design of gradient coil/magnet configurations and consequent engineering trade-offs. To compute the transient eddy currents within a realistic cryostat vessel, a low-frequency finite-difference time-domain (FDTD) method using total-field scattered-field (TFSF) scheme has been performed and validated.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19870007550','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19870007550"><span>Transitional Boundary Layers Under the Influence of High Free Stream Turbulence, Intensive Wall Cooling and High Pressure Gradients in Hot Gas Circulation. Ph.D. Thesis - Technische Hochschule, Karlsruhe, 1985</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Rued, Klaus</p> <p>1987-01-01</p> <p>The requirements for fundamental experimental studies of the influence of free stream turbulence, pressure gradients and wall cooling are discussed. Under turbine-like free stream conditions, comprehensive tests of transitional boundary layers with laminar, reversing and turbulent flow increments were performed to decouple the effects of the parameters and to determine the effects during mutual interaction.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26852418','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26852418"><span>Intra-coil interactions in split gradient coils in a hybrid MRI-LINAC system.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Tang, Fangfang; Freschi, Fabio; Sanchez Lopez, Hector; Repetto, Maurizio; Liu, Feng; Crozier, Stuart</p> <p>2016-04-01</p> <p>An MRI-LINAC system combines a magnetic resonance imaging (MRI) system with a medical linear accelerator (LINAC) to provide image-guided radiotherapy for targeting tumors in real-time. In an MRI-LINAC system, a set of split gradient coils is employed to produce orthogonal gradient fields for spatial signal encoding. Owing to this unconventional gradient configuration, eddy currents induced by switching gradient coils on and off may be of particular concern. It is expected that strong intra-coil interactions in the set will be present due to the constrained return paths, leading to potential degradation of the gradient field linearity and image distortion. In this study, a series of gradient coils with different track widths have been designed and analyzed to investigate the electromagnetic interactions between coils in a split gradient set. A driving current, with frequencies from 100 Hz to 10 kHz, was applied to study the inductive coupling effects with respect to conductor geometry and operating frequency. It was found that the eddy currents induced in the un-energized coils (hereby-referred to as passive coils) positively correlated with track width and frequency. The magnetic field induced by the eddy currents in the passive coils with wide tracks was several times larger than that induced by eddy currents in the cold shield of cryostat. The power loss in the passive coils increased with the track width. Therefore, intra-coil interactions should be included in the coil design and analysis process. Copyright © 2016 Elsevier Inc. All rights reserved.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21627655','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21627655"><span>Outcome in 55 dogs with pulmonic stenosis that did not undergo balloon valvuloplasty or surgery.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Francis, A J; Johnson, M J S; Culshaw, G C; Corcoran, B M; Martin, M W S; French, A T</p> <p>2011-06-01</p> <p>To determine the outcome, independent predictors of cardiac death, and the Doppler-derived pressure gradient cut-off for predicting cardiac death in dogs with pulmonic stenosis, with or without tricuspid regurgitation, that do not undergo balloon valvuloplasty or valve surgery. Review of medical records of two UK referral centres between July 1997 and October 2008 for all cases of pulmonic stenosis that had no balloon valvuloplasty or valve surgery. Inclusion criteria included a diagnosis of pulmonic stenosis; spectral Doppler pulmonic velocity greater than 1·6 m/s; characteristic valve leaflet morphological abnormalities. Exclusion criteria included concurrent significant cardiac defects, including tricuspid dysplasia. Dogs with tricuspid regurgitation were included. Dogs were classified according to Doppler-derived pressure gradients into mild, moderate or severe pulmonic stenosis categories. Presence of tricuspid regurgitation and severe stenosis were independent predictors of cardiac death. A pulmonic pressure gradient of more than 60 mmHg was associated with 86% sensitivity, and 71% specificity of predicting cardiac death. There is an increased probability of cardiac death in those cases which have a pulmonary pressure gradient greater than 60 mmHg and tricuspid regurgitation, though the effect of severity of tricuspid regurgitation on outcome was not measurable because of small sample sizes. These animals might benefit from intervention. © 2011 British Small Animal Veterinary Association.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25781166','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25781166"><span>Quantifying patterns of change in marine ecosystem response to multiple pressures.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Large, Scott I; Fay, Gavin; Friedland, Kevin D; Link, Jason S</p> <p>2015-01-01</p> <p>The ability to understand and ultimately predict ecosystem response to multiple pressures is paramount to successfully implement ecosystem-based management. Thresholds shifts and nonlinear patterns in ecosystem responses can be used to determine reference points that identify levels of a pressure that may drastically alter ecosystem status, which can inform management action. However, quantifying ecosystem reference points has proven elusive due in large part to the multi-dimensional nature of both ecosystem pressures and ecosystem responses. We used ecological indicators, synthetic measures of ecosystem status and functioning, to enumerate important ecosystem attributes and to reduce the complexity of the Northeast Shelf Large Marine Ecosystem (NES LME). Random forests were used to quantify the importance of four environmental and four anthropogenic pressure variables to the value of ecological indicators, and to quantify shifts in aggregate ecological indicator response along pressure gradients. Anthropogenic pressure variables were critical defining features and were able to predict an average of 8-13% (up to 25-66% for individual ecological indicators) of the variation in ecological indicator values, whereas environmental pressures were able to predict an average of 1-5 % (up to 9-26% for individual ecological indicators) of ecological indicator variation. Each pressure variable predicted a different suite of ecological indicator's variation and the shapes of ecological indicator responses along pressure gradients were generally nonlinear. Threshold shifts in ecosystem response to exploitation, the most important pressure variable, occurred when commercial landings were 20 and 60% of total surveyed biomass. Although present, threshold shifts in ecosystem response to environmental pressures were much less important, which suggests that anthropogenic pressures have significantly altered the ecosystem structure and functioning of the NES LME. Gradient response curves provide ecologically informed transformations of pressure variables to explain patterns of ecosystem structure and functioning. By concurrently identifying thresholds for a suite of ecological indicator responses to multiple pressures, we demonstrate that ecosystem reference points can be evaluated and used to support ecosystem-based management.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19740058005&hterms=Posture+measurement+blood+pressure&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DPosture%2Bmeasurement%2Bblood%2Bpressure','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19740058005&hterms=Posture+measurement+blood+pressure&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DPosture%2Bmeasurement%2Bblood%2Bpressure"><span>Intrathoracic and venous pressure relationships during responses to changes in body position</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Avasthey, P.; Wood, E. H.</p> <p>1974-01-01</p> <p>Simultaneous end-expiratory pressures, referred to midthoracic level, in the superior and abdominal venae cavae, pericardial space, and right and left heart, were recorded without thoracotomy in three anesthetized dogs during sudden changes from supine to vertical head-up or head-down body positions. Intrathoracic and dependent great vein pressures referred to midchest level (sixth thoracic vertebra) decreased and showed simple hydrostatic gradients in either vertical position. However, a discontinuity in the large vein hydrostatic gradient occurred just distal to the superior margin of the thorax in either body position and was resumed again above this level. It is concluded that, just as the cerebrospinal fluid and intraperitoneal pressures minimize the effects of gravitational and inertial forces on the cerebral and visceral circulations, the pericardial and pleural pressures have a similar role for the heart proper.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19980206236&hterms=cross+flow+turbine&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dcross%2Bflow%2Bturbine','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19980206236&hterms=cross+flow+turbine&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dcross%2Bflow%2Bturbine"><span>Prediction of Transitional Flows in the Low Pressure Turbine</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Huang, George; Xiong, Guohua</p> <p>1998-01-01</p> <p>Current turbulence models tend to give too early and too short a length of flow transition to turbulence, and hence fail to predict flow separation induced by the adverse pressure gradients and streamline flow curvatures. Our discussion will focus on the development and validation of transition models. The baseline data for model comparisons are the T3 series, which include a range of free-stream turbulence intensity and cover zero-pressure gradient to aft-loaded turbine pressure gradient flows. The method will be based on the conditioned N-S equations and a transport equation for the intermittency factor. First, several of the most popular 2-equation models in predicting flow transition are examined: k-e [Launder-Sharina], k-w [Wilcox], Lien-Leschiziner and SST [Menter] models. All models fail to predict the onset and the length of transition, even for the simplest flat plate with zero-pressure gradient(T3A). Although the predicted onset position of transition can be varied by providing different inlet turbulent energy dissipation rates, the appropriate inlet conditions for turbulence quantities should be adjusted to match the decay of the free-stream turbulence. Arguably, one may adjust the low-Reynolds-number part of the model to predict transition. This approach has so far not been very successful. However, we have found that the low-Reynolds-number model of Launder and Sharma [1974], which is an improved version of Jones and Launder [1972] gave the best overall performance. The Launder and Sharma model was designed to capture flow re-laminarization (a reverse of flow transition), but tends to give rise to a too early and too fast transition in comparison with the physical transition. The three test cases were for flows with zero pressure gradient but with different free-stream turbulent intensities. The same can be said about the model when considering flows subject to pressure gradient(T3C1). To capture the effects of transition using existing turbulence models, one approach is to make use of the concept of the intermittency to predict the flow transition. It was originally based on the intermittency distribution of Narasimha [1957], and then gradually evolved into a transport equation for the intermittency factor. Gostelow and associates [1994,1995] have made some improvements to Narasimha's method in an attempt to account for both favorable and adverse pressure gradients. Their approach is based on a linear, explicit combination of laminar and turbulent solutions. This approach fails to predict the overshoot of the skin friction on a flat plate near the end of transition zone, even though the length of transition is well predicted. The major flaw of Gostelow's approach is that it assumes the non-turbulent part being the laminar solution and the turbulent part being the turbulent solution and they do not interact across the transitional region. The technique in condition averaging the flow equations in intermittent flows was first introduced by Libby [1975] and Dopazo [1977] and further refined by Dick and associates [1988, 1996]. This approach employs two sets of transport equations for the non-turbulent part and the other for the turbulent part. The advantage of this approach is that it allows the interaction of non-turbulent and turbulent velocities through the introduction of additional source terms in the continuity and momentum equations for the non-turbulent and turbulent velocities. However, the strong coupling of the two sets of equations has caused some numerical difficulties, which requires special attention. The prediction of the skin friction can be improved by this approach via the implicit coupling of non-turbulent and turbulent velocity flelds. Another improvement of the interrmittency model can be further made by allowing the intermittency to vary in the cross-stream direction. This is one step prior to testing any proposal for the transport equation for the intermittency factor. Instead of solving the transport equation for the intermittency factor, the distribution for the intermittency factor is prescribed by Klebanoff's empirical formula [1955]. The skin friction is very well predicted by this new modification, including the overshoot of the profile near the end of the transition zone. The outcome of this study is very encouraging since it indicates that the proper description of the intermittency distribution is the key to the success of the model prediction. This study will be used to guide us on the modelling of the intermittency transport equation.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20040141421&hterms=Aorta&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DAorta','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20040141421&hterms=Aorta&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DAorta"><span>Microtubule depolymerization normalizes in vivo myocardial contractile function in dogs with pressure-overload left ventricular hypertrophy</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Koide, M.; Hamawaki, M.; Narishige, T.; Sato, H.; Nemoto, S.; DeFreyte, G.; Zile, M. R.; Cooper G, I. V.; Carabello, B. A.</p> <p>2000-01-01</p> <p>BACKGROUND: Because initially compensatory myocardial hypertrophy in response to pressure overloading may eventually decompensate to myocardial failure, mechanisms responsible for this transition have long been sought. One such mechanism established in vitro is densification of the cellular microtubule network, which imposes a viscous load that inhibits cardiocyte contraction. METHODS AND RESULTS: In the present study, we extended this in vitro finding to the in vivo level and tested the hypothesis that this cytoskeletal abnormality is important in the in vivo contractile dysfunction that occurs in experimental aortic stenosis in the adult dog. In 8 dogs in which gradual stenosis of the ascending aorta had caused severe left ventricular (LV) pressure overloading (gradient, 152+/-16 mm Hg) with contractile dysfunction, LV function was measured at baseline and 1 hour after the intravenous administration of colchicine. Cardiocytes obtained by biopsy before and after in vivo colchicine administration were examined in tandem. Microtubule depolymerization restored LV contractile function both in vivo and in vitro. CONCLUSIONS: These and additional corroborative data show that increased cardiocyte microtubule network density is an important mechanism for the ventricular contractile dysfunction that develops in large mammals with adult-onset pressure-overload-induced cardiac hypertrophy.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_22 --> <div id="page_23" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="441"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014APS..DFD.R5007S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014APS..DFD.R5007S"><span>The effect of gravity-induced pressure gradient on bubble luminescence</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Supponen, Outi; Obreschkow, Danail; Kobel, Philippe; Dorsaz, Nicolas; Tinguely, Marc; Farhat, Mohamed</p> <p>2014-11-01</p> <p>The violent collapse of a bubble can heat up its gaseous contents to temperatures exceeding those on the sun's surface, resulting in a short luminescence flash. Occurring at the very moment of the collapse, luminescence must be highly sensitive to the bubble geometry at the preceding final stage. This represents an important feature as any pressure anisotropy in the surrounding liquid will result in a deformation of an initially spherical bubble, inducing a micro-jet that pierces the bubble and makes it experience a toroidal collapse. We therefore present these as complementary phenomena by investigating the link between jets and luminescence of laser-generated single bubbles. Through ultra-high-speed imaging, the micro-jet formation and evolution of a single bubble are observed with unprecedented detail, whilst the bubble light emission is analyzed by means of a spectrometer. The bubble energy and the micro-jet size are controlled by adjusting the laser-pulse and by varying the gravity level aboard ESA parabolic flights, respectively. We here provide systematic evidence on how bubble-jets suppress luminescence in a considerable manner, even in normal gravity where the jet is barely observable. We conclude that gravity must be accounted for in accurate models of luminescence.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/20060023982','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20060023982"><span>Solar Sail Topology Variations Due to On-Orbit Thermal Effects</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Banik, Jeremy A.; Lively, Peter S.; Taleghani, Barmac K.; Jenkins, Chrostopher H.</p> <p>2006-01-01</p> <p>The objective of this research was to predict the influence of non-uniform temperature distribution on solar sail topology and the effect of such topology variations on sail performance (thrust, torque). Specifically considered were the thermal effects due to on orbit attitude control maneuvers. Such maneuvers are expected to advance the sail to a position off-normal to the sun by as much as 35 degrees; a solar sail initially deformed by typical pre-tension and solar pressure loads may suffer significant thermally induced strains due to the non-uniform heating caused by these maneuvers. This on-orbit scenario was investigated through development of an automated analytical shape model that iterates many times between sail shape and sail temperature distribution before converging on a final coupled thermal structural affected sail topology. This model utilizes a validated geometrically non-linear finite element model and a thermal radiation subroutine. It was discovered that temperature gradients were deterministic for the off-normal solar angle cases as were thermally induced strains. Performance effects were found to be moderately significant but not as large as initially suspected. A roll torque was detected, and the sail center of pressure shifted by a distance that may influence on-orbit sail control stability.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/pages/biblio/1356713-analysis-edge-stability-models-heat-flux-width','SCIGOV-DOEP'); return false;" href="https://www.osti.gov/pages/biblio/1356713-analysis-edge-stability-models-heat-flux-width"><span>Analysis of edge stability for models of heat flux width</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/pages">DOE PAGES</a></p> <p>Makowski, Michael A.; Lasnier, Charles J.; Leonard, Anthony W.; ...</p> <p>2017-05-12</p> <p>Detailed measurements of the n e, and T e, and T i profiles in the vicinity of the separatrix of ELMing H-mode discharges have been used to examine plasma stability at the extreme edge of the plasma and assess stability dependent models of the heat flux width. The results are strongly contrary to the critical gradient model, which posits that a ballooning instability determines a gradient scale length related to the heat flux width. The results of this analysis are not sensitive to the choice of location to evaluate stability. Significantly, it is also found that the results are completelymore » consistent with the heuristic drift model for the heat flux width. Here the edge pressure gradient scales with plasma density and is proportional to the pressure gradient inferred from the equilibrium in accordance with the predictions of that theory.« less</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017MS%26E..219a2047Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017MS%26E..219a2047Y"><span>Gradient microstructure and microhardness in a nitrided 18CrNiMo7-6 gear steel</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yang, R.; Wu, G. L.; Zhang, X.; Fu, W. T.; Huang, X.</p> <p>2017-07-01</p> <p>A commercial gear steel (18CrNiMo7-6) containing a tempered martensite structure was nitrided using a pressurized gas nitriding process under a pressure of 5 atm at 530 °C for 5 hours. The mechanical properties and microstructure of the nitrided sample were characterized by Vickers hardness measurements, X-ray diffraction, and backscatter electron imaging in a scanning electron microscope. A micro-hardness gradient was identified over a distance of 500 μm with hardness values of 900 HV at the top surface and 300 HV in the core. This micro-hardness gradient corresponds to a gradient in the microstructure that changes from a nitride compound layer at the top surface (∼ 20 μm thick) to a diffusion zone with a decreasing nitrogen concentration and precipitate density with distance from the surface, finally reaching the core matrix layer with a recovered martensite structure.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/20309904','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/20309904"><span>Comparison of various second-dimension gradient types in comprehensive two-dimensional liquid chromatography.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Jandera, Pavel; Hájek, Tomás; Cesla, Petr</p> <p>2010-06-01</p> <p>Gradient elution provides significant improvement in peak capacity with respect to isocratic conditions. In the second dimension, gradients are limited to a short-time period available for separation. Various types of second-dimension gradients in comprehensive LC x LC are compared: (i) "full in fraction", (ii) "segment in fraction" and (iii) "continuously shifting" gradients, applied in orthogonal LC x LC separations of phenolic acids and flavones on a polyethylene glycol column in the first dimension and two types of porous shell fused-core C18 columns in the second dimension (Ascentis Express and Kinetex). The porous shell columns provide narrow bandwidths and fast second-dimension separations at moderate operating pressure that allows important savings of the overall separation time in comprehensive LC x LC separations. The effects of the gradient type on the bandwidths, theoretical peak capacity, separation time and column pressure in the second dimension were investigated. The type of gradient program controls the range of lipophilicity of sample compounds that can be separated in the second-dimension reversed-phase time period. This range can be calibrated using alkylbenzene standards, to design the separation conditions for complete sample separation, avoiding harmful wrap around of non-eluted compounds to the subsequent second-dimension fractions.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018JPhD...51v4009C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018JPhD...51v4009C"><span>Investigating spin-transfer torques induced by thermal gradients in magnetic tunnel junctions by using micro-cavity ferromagnetic resonance</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cansever, H.; Narkowicz, R.; Lenz, K.; Fowley, C.; Ramasubramanian, L.; Yildirim, O.; Niesen, A.; Huebner, T.; Reiss, G.; Lindner, J.; Fassbender, J.; Deac, A. M.</p> <p>2018-06-01</p> <p>Similar to electrical currents flowing through magnetic multilayers, thermal gradients applied across the barrier of a magnetic tunnel junction may induce pure spin-currents and generate ‘thermal’ spin-transfer torques large enough to induce magnetization dynamics in the free layer. In this study, we describe a novel experimental approach to observe spin-transfer torques induced by thermal gradients in magnetic multilayers by studying their ferromagnetic resonance response in microwave cavities. Utilizing this approach allows for measuring the magnetization dynamics on micron/nano-sized samples in open-circuit conditions, i.e. without the need of electrical contacts. We performed first experiments on magnetic tunnel junctions patterned into 6 × 9 µm2 ellipses from Co2FeAl/MgO/CoFeB stacks. We conducted microresonator ferromagnetic resonance (FMR) under focused laser illumination to induce thermal gradients in the layer stack and compared them to measurements in which the sample was globally heated from the backside of the substrate. Moreover, we carried out broadband FMR measurements under global heating conditions on the same extended films the microstructures were later on prepared from. The results clearly demonstrate the effect of thermal spin-torque on the FMR response and thus show that the microresonator approach is well suited to investigate thermal spin-transfer-driven processes for small temperatures gradients, far below the gradients required for magnetic switching.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29745577','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29745577"><span>[Quantitative experiment and analysis of gradient-induced eddy currents on magnetic resonance imaging].</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>He, Wenjing; Zhu, Yuanzhong; Wang, Wenzhou; Zou, Kai; Zhang, Kai; He, Chao</p> <p>2017-04-01</p> <p>Pulsed magnetic field gradients generated by gradient coils are widely used in signal location in magnetic resonance imaging (MRI). However, gradient coils can also induce eddy currents in final magnetic field in the nearby conducting structures which lead to distortion and artifact in images, misguiding clinical diagnosis. We tried in our laboratory to measure the magnetic field of gradient-induced eddy current in 1.5 T superconducting magnetic resonance imaging device; and extracted key parameters including amplitude and time constant of exponential terms according to inductance-resistance series mathematical module. These parameters of both self-induced component and crossing component are useful to design digital filters to implement pulse pre-emphasize to reshape the waveform. A measure device that is a basement equipped with phantoms and receiving coils was designed and placed in the isocenter of the magnetic field. By applying testing sequence, contrast experiments were carried out in a superconducting magnet before and after eddy current compensation. Sets of one dimension signal were obtained as raw data to calculate gradient-induced eddy currents. Curve fitting by least squares method was also done to match inductance-resistance series module. The results also illustrated that pulse pre-emphasize measurement with digital filter was correct and effective in reducing eddy current effect. Pre-emphasize waveform was developed based on system function. The usefulness of pre-emphasize measurement in reducing eddy current was confirmed and the improvement was also presented. All these are valuable for reducing artifact in magnetic resonance imaging device.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AcAau.135..172S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AcAau.135..172S"><span>Incident shock strength evolution in overexpanded jet flow out of rocket nozzle</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Silnikov, Mikhail V.; Chernyshov, Mikhail V.</p> <p>2017-06-01</p> <p>The evolution of the incident shock in the plane overexpanded jet flow or in the axisymmetric one is analyzed theoretically and compared at the whole range of governing flow parameters. Analytical results can be applied to avoid jet flow instability and self-oscillation effects at rocket launch, to improve launch safety and to suppress shock-wave induced noise harmful to environment and personnel. The mathematical model of ;differential conditions of dynamic compatibility; was applied to the curved shock in non-uniform plane or axisymmetrical flow. It allowed us to study such features of the curved incident shock and flow downstream it as shock geometrical curvature, jet boundary curvature, local increase or decrease of the shock strength, flow vorticity rate (local pressure gradient) in the vicinity of the nozzle lip, static pressure gradient in the compressed layer downstream the shock, and many others. All these quantities sufficiently depend on the flow parameters (flow Mach number, jet overexpansion rate, nozzle throat angle, and ration of gas specific heats). These dependencies are sometimes unusual, especially at small Mach numbers. It was also surprising that there is no great difference among all these flowfield features in the plane jet and in the axisymmetrical jet flow out of a nozzle with large throat angle, but all these parameters behave in a quite different way in an axisymmetrical jet at small and moderate nozzle throat angles.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27457561','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27457561"><span>Repeatability of gradient ultrahigh pressure liquid chromatography-tandem mass spectrometry methods in instrument-controlled thermal environments.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Grinias, James P; Wong, Jenny-Marie T; Kennedy, Robert T</p> <p>2016-08-26</p> <p>The impact of viscous friction on eluent temperature and column efficiency in liquid chromatography is of renewed interest as the need for pressures exceeding 1000bar to use with columns packed with sub-2μm particles has grown. One way the development of axial and radial temperature gradients that arise due to viscous friction can be affected is by the thermal environment the column is placed in. In this study, a new column oven integrated into an ultrahigh pressure liquid chromatograph that enables both still-air and forced-air operating modes is investigated to find the magnitude of the effect of the axial thermal gradient that forms in 2.1×100mm columns packed with sub-2μm particles in these modes. Temperature increases of nearly 30K were observed when the generated power of the column exceeded 25W/m. The impact of the heating due to viscous friction on the repeatability of peak capacity, elution time, and peak area ratio to an internal standard for a gradient UHPLC-MS/MS method to analyze neurotransmitters was found to be limited. This result indicates that high speed UHPLC-MS/MS gradient methods under conditions of high viscous friction may be possible without the negative effects typically observed with isocratic separations under similar conditions. Copyright © 2016 Elsevier B.V. All rights reserved.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA536506','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA536506"><span>Gasdynamic Inlet Isolation in Rotating Detonation Engine</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.dtic.mil/">DTIC Science & Technology</a></p> <p></p> <p>2010-12-01</p> <p>2D Total Variation Diminishing (TVD): Continuous Riemann Solver Minimum Dissipation: LHS & RHS Activate pressure switch : Supersonic Activate...Total Variation Diminishing (TVD) limiter: Continuous Riemann Solver Minimum Dissipation: LHS & RHS Activate pressure switch : Supersonic Activate...Continuous 94 Riemann Solver Minimum Dissipation: LHS & RHS Activate pressure switch : Supersonic Activate pressure gradient switch: Normal</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010PhDT.......363B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010PhDT.......363B"><span>Micromachined diffraction based optical microphones and intensity probes with electrostatic force feedback</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bicen, Baris</p> <p></p> <p>Measuring acoustic pressure gradients is critical in many applications such as directional microphones for hearing aids and sound intensity probes. This measurement is especially challenging with decreasing microphone size, which reduces the sensitivity due to small spacing between the pressure ports. Novel, micromachined biomimetic microphone diaphragms are shown to provide high sensitivity to pressure gradients on one side of the diaphragm with low thermal mechanical noise. These structures have a dominant mode shape with see-saw like motion in the audio band, responding to pressure gradients as well as spurious higher order modes sensitive to pressure. In this dissertation, integration of a diffraction based optical detection method with these novel diaphragm structures to implement a low noise optical pressure gradient microphone is described and experimental characterization results are presented, showing 36 dBA noise level with 1mm port spacing, nearly an order of magnitude better than the current gradient microphones. The optical detection scheme also provides electrostatic actuation capability from both sides of the diaphragm separately which can be used for active force feedback. A 4-port electromechanical equivalent circuit model of this microphone with optical readout is developed to predict the overall response of the device to different acoustic and electrostatic excitations. The model includes the damping due to complex motion of air around the microphone diaphragm, and it calculates the detected optical signal on each side of the diaphragm as a combination of two separate dominant vibration modes. This equivalent circuit model is verified by experiments and used to predict the microphone response with different force feedback schemes. Single sided force feedback is used for active damping to improve the linearity and the frequency response of the microphone. Furthermore, it is shown that using two sided force feedback one can significantly suppress or enhance the desired vibration modes of the diaphragm. This approach provides an electronic means to tailor the directional response of the microphones, with significant implications in device performance for various applications. As an example, the use of this device as a particle velocity sensor for sound intensity and sound power measurements is investigated. Without force feedback, the gradient microphone provides accurate particle velocity measurement for frequencies below 2 kHz, after which the pressure response of the second order mode becomes significant. With two-sided force feedback, the calculations show that this upper frequency limit may be increased to 10 kHz. This improves the pressure residual intensity index by more than 15 dB in the 50 Hz--10 kHz range, matching the Class I requirements of IEC 1043 standards for intensity probes without any need for multiple spacers.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19930018239','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19930018239"><span>Turbulence: The chief outstanding difficulty of our subject</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bradshaw, Peter</p> <p>1992-01-01</p> <p>A review of interesting current topics in turbulence research is decorated with examples of popular fallacies about the behavior of turbulence. Topics include the status of the Law of the Wall, especially in compressible flow; analogies between the effects of Reynolds numbers, pressure gradient, unsteadiness and roughness change; the status of Kolmogorov's universal equilibrium theory and local isotropy of the small eddies; turbulence modelling, with reference to universality, pressure-strain modelling and the dissipation equation; and chaos. Fallacies include the mixing-length concept; the effect of pressure gradient on Reynolds shear stress; the separability of time and space derivatives; models of the dissipation equation; and chaos.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.H52A..07H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.H52A..07H"><span>On the development and benchmarking of an approach to model gas transport in fractured media with immobile water storage</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Harp, D. R.; Ortiz, J. P.; Pandey, S.; Karra, S.; Viswanathan, H. S.; Stauffer, P. H.; Anderson, D. N.; Bradley, C. R.</p> <p>2017-12-01</p> <p>In unsaturated fractured media, the rate of gas transport is much greater than liquid transport in many applications (e.g., soil vapor extraction operations, methane leaks from hydraulic fracking, shallow CO2 transport from geologic sequestration operations, and later-time radionuclide gas transport from underground nuclear explosions). However, the relatively immobile pore water can inhibit or promote gas transport for soluble constituents by providing storage. In scenarios with constant pressure gradients, the gas transport will be retarded. In scenarios with reversing pressure gradients (i.e. barometric pressure variations) pore water storage can enhance gas transport by providing a ratcheting mechanism. Recognizing the computational efficiency that can be gained using a single-phase model and the necessity of considering pore water storage, we develop a Richard's solution approach that includes kinetic dissolution/volatilization of constituents. Henry's Law governs the equilibrium gaseous/aqueous phase partitioning in the approach. The approach is implemented in a development branch of the PFLOTRAN simulator. We verify the approach with analytical solutions of: (1) 1D gas diffusion, (2) 1D gas advection, (3) sinusoidal barometric pumping of a fracture, and (4) gas transport along a fracture with uniform flow and diffusive walls. We demonstrate the retardation of gas transport in cases with constant pressure gradients and the enhancement of gas transport with reversing pressure gradients. The figure presents the verification of our approach to the analytical solution of barometric pumping of a fracture from Nilson et al (1991) where the x-axis "Horizontal axis" is the distance into the matrix block from the fracture.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.H52A..07H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.H52A..07H"><span>On the development and benchmarking of an approach to model gas transport in fractured media with immobile water storage</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Harp, D. R.; Ortiz, J. P.; Pandey, S.; Karra, S.; Viswanathan, H. S.; Stauffer, P. H.; Anderson, D. N.; Bradley, C. R.</p> <p>2016-12-01</p> <p>In unsaturated fractured media, the rate of gas transport is much greater than liquid transport in many applications (e.g., soil vapor extraction operations, methane leaks from hydraulic fracking, shallow CO2 transport from geologic sequestration operations, and later-time radionuclide gas transport from underground nuclear explosions). However, the relatively immobile pore water can inhibit or promote gas transport for soluble constituents by providing storage. In scenarios with constant pressure gradients, the gas transport will be retarded. In scenarios with reversing pressure gradients (i.e. barometric pressure variations) pore water storage can enhance gas transport by providing a ratcheting mechanism. Recognizing the computational efficiency that can be gained using a single-phase model and the necessity of considering pore water storage, we develop a Richard's solution approach that includes kinetic dissolution/volatilization of constituents. Henry's Law governs the equilibrium gaseous/aqueous phase partitioning in the approach. The approach is implemented in a development branch of the PFLOTRAN simulator. We verify the approach with analytical solutions of: (1) 1D gas diffusion, (2) 1D gas advection, (3) sinusoidal barometric pumping of a fracture, and (4) gas transport along a fracture with uniform flow and diffusive walls. We demonstrate the retardation of gas transport in cases with constant pressure gradients and the enhancement of gas transport with reversing pressure gradients. The figure presents the verification of our approach to the analytical solution of barometric pumping of a fracture from Nilson et al (1991) where the x-axis "Horizontal axis" is the distance into the matrix block from the fracture.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/6841947','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/6841947"><span>Pressures in the sphincter of Oddi in patients with gallstones, common duct stones, and recurrent pancreatitis.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Guelrud, M; Mendoza, S; Vicent, S; Gomez, M; Villalta, B</p> <p>1983-02-01</p> <p>To determine the significance of manometric pressure, measurements of the sphincter of Oddi in a control group and in patients with cholelithiasis with common duct stones with and without recurrent pancreatitis were studied. Sphincter of Oddi pressure was recorded continuously and by station pull-through by a triple lumen catheter. The basal sphincter of Oddi pressure, the mean pressure gradient between common duct and duodenum, and the sphincter of Oddi wave amplitude were measured. There was no significant difference between control subjects and patients with gallstones and common duct stones. In patients with common duct stones and recurrent pancreatitis the basal sphincter of Oddi pressure, the pressure gradient between common duct and duodenum, and the wave amplitude were significantly increased over control patients. These studies suggest that abnormalities in the sphincter of Oddi motor function are more common in patients with common duct stones with recurrent pancreatitis than in similar patients without pancreatitis.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19920034389&hterms=BALANCE+SHEET&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DBALANCE%2BSHEET','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19920034389&hterms=BALANCE+SHEET&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DBALANCE%2BSHEET"><span>Pressure anisotropy and radial stress balance in the Jovian neutral sheet</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Paranicas, C. P.; Mauk, B. H.; Krimigis, S. M.</p> <p>1991-01-01</p> <p>By examining particle and magnetic field data from the Voyager 1 and 2 spacecraft, signatures were found indicating that the (greater than about 28 keV) particle pressure parallel to the magnetic field is greater than the pressure perpendicular to the field within the nightside neutral sheet (three nightside neutral sheet crossings, with favorable experimental conditions, were used). By incorporating the pressure anisotropy into the calculation of radial forces within the hightside neutral sheet, it is found that (1) force balance is approximately achieved and (2) the anisotropy force term provides the largest contribution of the other particle forces considered (pressure gradients and the corotation centrifugal force). With regard to the problem of understanding the balance of radial forces within the dayside neutral sheet (McNutt, 1984; Mauk and Krimigis, 1987), the nightside pressure anisotropy force is larger than the dayside pressure gradient forces at equivalent radial distances; however, a full accounting of the dayside regions remains to be achieved.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26763649','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26763649"><span>Vasopressin-induced changes in splanchnic blood flow and hepatic and portal venous pressures in liver resection.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Bown, L Sand; Ricksten, S-E; Houltz, E; Einarsson, H; Söndergaard, S; Rizell, M; Lundin, S</p> <p>2016-05-01</p> <p>To minimize blood loss during hepatic surgery, various methods are used to reduce pressure and flow within the hepato-splanchnic circulation. In this study, the effect of low- to moderate doses of vasopressin, a potent splanchnic vasoconstrictor, on changes in portal and hepatic venous pressures and splanchnic and hepato-splanchnic blood flows were assessed in elective liver resection surgery. Twelve patients were studied. Cardiac output (CO), stroke volume (SV), mean arterial (MAP), central venous (CVP), portal venous (PVP) and hepatic venous pressures (HVP) were measured, intraoperatively, at baseline and during vasopressin infusion at two infusion rates (2.4 and 4.8 U/h). From arterial and venous blood gases, the portal (splanchnic) and hepato-splanchnic blood flow changes were calculated, using Fick's equation. CO, SV, MAP and CVP increased slightly, but significantly, while systemic vascular resistance and heart rate remained unchanged at the highest infusion rate of vasopressin. PVP was not affected by vasopressin, while HVP increased slightly. Vasopressin infusion at 2.4 and 4.8 U/h reduced portal blood flow (-26% and -37%, respectively) and to a lesser extent hepato-splanchnic blood flow (-9% and -14%, respectively). The arterial-portal vein lactate gradient was not significantly affected by vasopressin. Postoperative serum creatinine was not affected by vasopressin. Short-term low to moderate infusion rates of vasopressin induced a splanchnic vasoconstriction without metabolic signs of splanchnic hypoperfusion or subsequent renal impairment. Vasopressin caused a centralization of blood volume and increased cardiac output. Vasopressin does not lower portal or hepatic venous pressures in this clinical setting. © 2016 The Acta Anaesthesiologica Scandinavica Foundation. Published by John Wiley & Sons Ltd.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMMR13B0321M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMMR13B0321M"><span>Pore Pressure and Field stress variation from Salt Water Injection; A case Study from Beaver Lodge Field in Williston Basin</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mohammed, R. A.; Khatibi, S.</p> <p>2017-12-01</p> <p>One of the major concerns in producing from oil and gas reservoirs in North American Basins is the disposal of high salinity salt water. It is a misconception that Hydro frack triggers Earthquakes, but due to the high salinity and density of water being pumped to the formation that has pore space of the rock already filled, which is not the case in Hydro-frack or Enhanced Oil Recovery in which fracturing fluid is pumped into empty pore space of rocks in depleted reservoirs. A review on the Bakken history showed that the concerns related to induce seismicity has increased over time due to variations in Pore pressure and In-situ stress that have shown steep changes in the region over the time. In this study, we focused on Pore pressure and field Stress variations in lower Cretaceous Inyan Kara and Mississippian Devonian Bakken, Inyan Kara is the major source for class-II salt-water disposal in the basin. Salt-water disposal is the major cause for induced seismicity. A full field study was done on Beaver Lodge Field, which has many salt-water disposal wells Adjacent to Oil and Gas Wells. We analyzed formation properties, stresses, pore-pressure, and fracture gradient profile in the field and. The constructed Mechanical Earth Model (MEM) revealed changes in pore pressure and stresses over time due to saltwater injection. Well drilled in the past were compared to recently drilled wells, which showed much stress variations. Safe mud weight Window of wells near proximity of injection wells was examined which showed many cases of wellbore instabilities. Results of this study will have tremendous impact in studying environmental issues and the future drilling and Fracking operations.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018PSST...27c5008Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018PSST...27c5008Y"><span>Magnetical asymmetry effect in capacitively coupled plasmas: effects of the magnetic field gradient, pressure, and gap length</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yang, Shali; Chang, Lijie; Zhang, Ya; Jiang, Wei</p> <p>2018-03-01</p> <p>By applying the asymmetric magnetic field to a discharge, the dc self-bias and asymmetric plasma response can be generated even in a geometrically and electrically symmetric system. This is called magnetical asymmetric effect (MAE), which can be a new method to control the ion energy and flux independently (Yang et al 2017 Plasma Process. Polym. 14 1700087). In the present work, the effects of magnetic field gradient, gas pressure and gap length on MAE are investigated by using a one-dimensional implicit particle-in-cell/Monte Carlo collision simulation. It found that by appropriately increasing the magnetic field gradient and the gap length, the range of the self-bias voltage will be enlarged, which can be used as the effective approach to control the ion bombarding energy at the electrodes since the ion energy is determined by the voltage drop across the sheath. It also found that the ion flux asymmetry will disappear at high pressure when the magnetic field gradient is relative low, due to the frequent electron-neutral collisions can disrupt electron gyromotion and thus the MAE is greatly reduced.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016APS..DPPJO7004P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016APS..DPPJO7004P"><span>Gyrokinetic GDC turbulence simulations: confirming a new instability regime in LAPD plasmas</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pueschel, M. J.; Rossi, G.; Told, D.; Terry, P. W.; Jenko, F.; Carter, T. A.</p> <p>2016-10-01</p> <p>Recent high-beta experiments at the LArge Plasma Device have found significant parallel magnetic fluctuations in the region of large pressure gradients. Linear gyrokinetic simulations show the dominant instability at these radii to be the gradient-driven drift coupling (GDC) mode, a non-textbook mode driven by pressure gradients and destabilized by the coupling of ExB and grad-B∥ drifts. Unlike in previous studies, the large parallel extent of the device allows for finite-kz versions of this instability in addition to kz = 0 . The locations of maximum linear growth match very well with experimentally observed peaks of B∥ fluctuations. Local nonlinear simulations reproduce many features of the observations fairly well, with the exception of Bperp fluctuations, for which experimental profiles suggest a source unrelated to pressure gradients. In toto, the results presented here show that turbulence and transport in these experiments are driven by the GDC instability, that important characteristics of the linear instability carry over to nonlinear simulations, and - in the context of validation - that the gyrokinetic framework performs surprisingly well far outside its typical area of application, increasing confidence in its predictive abilities. Supported by U.S. DOE.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_23 --> <div id="page_24" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li class="active"><span>24</span></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="461"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24296292','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24296292"><span>Very high pressure liquid chromatography using fully porous particles: quantitative analysis of fast gradient separations without post-run times.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Stankovich, Joseph J; Gritti, Fabrice; Stevenson, Paul G; Beaver, Lois Ann; Guiochon, Georges</p> <p>2014-01-10</p> <p>Using a column packed with fully porous particles, four methods for controlling the flow rates at which gradient elution runs are conducted in very high pressure liquid chromatography (VHPLC) were tested to determine whether reproducible thermal conditions could be achieved, such that subsequent analyses would proceed at nearly the same initial temperature. In VHPLC high flow rates are achieved, producing fast analyses but requiring high inlet pressures. The combination of high flow rates and high inlet pressures generates local heat, leading to temperature changes in the column. Usually in this case a post-run time is input into the analytical method to allow the return of the column temperature to its initial state. An alternative strategy involves operating the column without a post-run equilibration period and maintaining constant temperature variations for subsequent analysis after conducting one or a few separations to bring the column to a reproducible starting temperature. A liquid chromatography instrument equipped with a pressure controller was used to perform constant pressure and constant flow rate VHPLC separations. Six replicate gradient separations of a nine component mixture consisting of acetophenone, propiophenone, butyrophenone, valerophenone, hexanophenone, heptanophenone, octanophenone, benzophenone, and acetanilide dissolved in water/acetonitrile (65:35, v/v) were performed under various experimental conditions: constant flow rate, two sets of constant pressure, and constant pressure operation with a programmed flow rate. The relative standard deviations of the response factors for all the analytes are lower than 5% across the methods. Programming the flow rate to maintain a fairly constant pressure instead of using instrument controlled constant pressure improves the reproducibility of the retention times by a factor of 5, when plotting the chromatograms in time. Copyright © 2013 Elsevier B.V. All rights reserved.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29084904','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29084904"><span>Gradients in Wall Mechanics and Polysaccharides along Growing Inflorescence Stems.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Phyo, Pyae; Wang, Tuo; Kiemle, Sarah N; O'Neill, Hugh; Pingali, Sai Venkatesh; Hong, Mei; Cosgrove, Daniel J</p> <p>2017-12-01</p> <p>At early stages of Arabidopsis ( Arabidopsis thaliana ) flowering, the inflorescence stem undergoes rapid growth, with elongation occurring predominantly in the apical ∼4 cm of the stem. We measured the spatial gradients for elongation rate, osmotic pressure, cell wall thickness, and wall mechanical compliances and coupled these macroscopic measurements with molecular-level characterization of the polysaccharide composition, mobility, hydration, and intermolecular interactions of the inflorescence cell wall using solid-state nuclear magnetic resonance spectroscopy and small-angle neutron scattering. Force-extension curves revealed a gradient, from high to low, in the plastic and elastic compliances of cell walls along the elongation zone, but plots of growth rate versus wall compliances were strikingly nonlinear. Neutron-scattering curves showed only subtle changes in wall structure, including a slight increase in cellulose microfibril alignment along the growing stem. In contrast, solid-state nuclear magnetic resonance spectra showed substantial decreases in pectin amount, esterification, branching, hydration, and mobility in an apical-to-basal pattern, while the cellulose content increased modestly. These results suggest that pectin structural changes are connected with increases in pectin-cellulose interaction and reductions in wall compliances along the apical-to-basal gradient in growth rate. These pectin structural changes may lessen the ability of the cell wall to undergo stress relaxation and irreversible expansion (e.g. induced by expansins), thus contributing to the growth kinematics of the growing stem. © 2017 American Society of Plant Biologists. All Rights Reserved.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2010-title14-vol1/pdf/CFR-2010-title14-vol1-sec23-67.pdf','CFR'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2010-title14-vol1/pdf/CFR-2010-title14-vol1-sec23-67.pdf"><span>14 CFR 23.67 - Climb: One engine inoperative.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2010&page.go=Go">Code of Federal Regulations, 2010 CFR</a></p> <p></p> <p>2010-01-01</p> <p>... knots must be able to maintain a steady climb gradient of at least 1.5 percent at a pressure altitude of... requirements prescribed in § 23.562(d), or that has a VSO of 61 knots or less, the steady gradient of climb or... acrobatic category— (1) The steady gradient of climb at an altitude of 400 feet above the takeoff must be...</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70016699','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70016699"><span>Determining the mean hydraulic gradient of ground water affected by tidal fluctuations</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Serfes, Michael E.</p> <p>1991-01-01</p> <p>Tidal fluctuations in surface-water bodies produce progressive pressure waves in adjacent aquifers. As these pressure waves propagate inland, ground-water levels and hydraulic gradients continuously fluctuate, creating a situation where a single set of water-level measurements cannot be used to accurately characterize ground-water flow. For example, a time series of water levels measured in a confined aquifer in Atlantic City, New Jersey, showed that the hydraulic gradient ranged from .01 to .001 with a 22-degree change in direction during a tidal day of approximately 25 hours. At any point where ground water tidally fluctuates, the magnitude and direction of the hydraulic gradient fluctuates about the mean or regional hydraulic gradient. The net effect of these fluctuations on ground-water flow can be determined using the mean hydraulic gradient, which can be calculated by comparing mean ground- and surface-water elevations. Filtering methods traditionally used to determine daily mean sea level can be similarly applied to ground water to determine mean levels. Method (1) uses 71 consecutive hourly water-level observations to accurately determine the mean level. Method (2) approximates the mean level using only 25 consecutive hourly observations; however, there is a small error associated with this method.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018JMPSo.116..370W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018JMPSo.116..370W"><span>A homogenized localizing gradient damage model with micro inertia effect</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Zhao; Poh, Leong Hien</p> <p>2018-07-01</p> <p>The conventional gradient enhancement regularizes structural responses during material failure. However, it induces a spurious damage growth phenomenon, which is shown here to persist in dynamics. Similar issues were reported with the integral averaging approach. Consequently, the conventional nonlocal enhancement cannot adequately describe the dynamic fracture of quasi-brittle materials, particularly in the high strain rate regime, where a diffused damage profile precludes the development of closely spaced macrocracks. To this end, a homogenization theory is proposed to translate the micro processes onto the macro scale. Starting with simple elementary models at the micro scale to describe the fracture mechanisms, an additional kinematic field is introduced to capture the variations in deformation and velocity within a unit cell. An energetic equivalence between micro and macro is next imposed to ensure consistency at the two scales. The ensuing homogenized microforce balance resembles closely the conventional gradient expression, albeit with an interaction domain that decreases with damage, complemented by a micro inertia effect. Considering a direct single pressure bar example, the homogenized model is shown to resolve the non-physical responses obtained with conventional nonlocal enhancement. The predictive capability of the homogenized model is furthermore demonstrated by considering the spall tests of concrete, with good predictions on failure characteristics such as fragmentation profiles and dynamic tensile strengths, at three different loading rates.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013PhDT........28V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013PhDT........28V"><span>Shock-induced nanobubble collapse and its applications</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vedadi, Mohammad Hossein</p> <p></p> <p>The shock-induced collapse of nanobubbles in water is investigated using molecular dynamics simulations based on a reactive force field. Monitoring the collapse of a cavitation nanobubble, we observe a focused nanojet at the onset of bubble shrinkage and a water hammer shock wave upon bubble collapse. The nanojet length scales linearly with the nanobubble radius, as observed in experiments on micron-to-millimeter size bubbles. The shock induces dramatic structural changes, including an ice-VII-like structural motif at a particle velocity of approximately 1 km/s. The incipient ice VII formation and the calculated Hugoniot curve are in good agreement with experimental results. Moreover, a substantial number of positive and negative ions appear when the nanojet hits the distal side of the nanobubble and the water hammer shock forms. Furthermore, two promising applications of shock-induced nanobubble collapse have been explored. Our simulations of poration in lipid bilayers due to shock-induced collapse of nanobubbles reveal penetration of nanojets into lipid bilayers. The nanojet impact generates shear flow of water on bilayer leaflets and pressure gradients across them, which transiently enhance the bilayer permeability by creating nanopores through which water molecules translocate across the bilayer. The effects of nanobubble size and temperature on the porosity of lipid bilayers are examined. Finally, the shock-induced collapse of CO2-filled nanobubbles in water is investigated. The energetic nanojet and high-pressure water hammer shock formed during and after collapse of the nanobubble trigger mechano-chemical H2O-CO2 reactions, some of which lead to splitting of water molecules. The dominant pathways through which splitting of water molecules occur are identified.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23057236','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23057236"><span>A study of unsteady physiological magneto-fluid flow and heat transfer through a finite length channel by peristaltic pumping.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Tripathi, Dharmendra; Bég, O Anwar</p> <p>2012-08-01</p> <p>Magnetohydrodynamic peristaltic flows arise in controlled magnetic drug targeting, hybrid haemodynamic pumps and biomagnetic phenomena interacting with the human digestive system. Motivated by the objective of improving an understanding of the complex fluid dynamics in such flows, we consider in the present article the transient magneto-fluid flow and heat transfer through a finite length channel by peristaltic pumping. Reynolds number is small enough and the wavelength to diameter ratio is large enough to negate inertial effects. Analytical solutions for temperature field, axial velocity, transverse velocity, pressure gradient, local wall shear stress, volume flowrate and averaged volume flowrate are obtained. The effects of the transverse magnetic field, Grashof number and thermal conductivity on the flow patterns induced by peristaltic waves (sinusoidal propagation along the length of channel) are studied using graphical plots. The present study identifies that greater pressure is required to propel the magneto-fluid by peristaltic pumping in comparison to a non-conducting Newtonian fluid, whereas, a lower pressure is required if heat transfer is effective. The analytical solutions further provide an important benchmark for future numerical simulations.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19860045471&hterms=stress+shock&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dstress%2Bshock','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19860045471&hterms=stress+shock&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dstress%2Bshock"><span>The behaviour of turbulence anisotropy through shock waves and expansions</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Minh, H. H.; Kollmann, W.; Vandromme, D.</p> <p>1985-01-01</p> <p>A second order closure has been implemented in an implicit Navier-Stokes solver to study the behavior of the Reynolds stresses under the influence of severe pressure gradients. In the boundary layer zone, the strongly sheared character of the mean flow dominates the turbulence generation mechanisms. However, the pressure gradients play also a very important role for these processes, but at different locations within the boundary layer. This aspect may be emphasized by the analysis of turbulence anisotropy through shock waves and expansions.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19720022609','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19720022609"><span>The turbulent boundary layer on a porous plate: An experimental study of the fluid mechanics for adverse free stream pressure gradients</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Anderson, P. S.; Kays, W. M.; Moffat, R. J.</p> <p>1972-01-01</p> <p>An experimental investigation of transpired turbulent boundary layers in zero and adverse pressure gradients has been carried out. Profiles of: (1) the mean velocity, (2) the three intensities of the turbulent fluctuations, and (3) the Reynolds stress were obtained by hot-wire anemometry. The friction coefficients were measured by using an integrated form of the boundary layer equation to extrapolate the measured shear stress profiles to the wall.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19860057407&hterms=drury&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAuthor-Name%26N%3D0%26No%3D20%26Ntt%3Ddrury','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19860057407&hterms=drury&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAuthor-Name%26N%3D0%26No%3D20%26Ntt%3Ddrury"><span>Cosmic-ray shock acceleration in oblique MHD shocks</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Webb, G. M.; Drury, L. OC.; Volk, H. J.</p> <p>1986-01-01</p> <p>A one-dimensional, steady-state hydrodynamical model of cosmic-ray acceleration at oblique MHD shocks is presented. Upstream of the shock the incoming thermal plasma is subject to the adverse pressure gradient of the accelerated particles, the J x B force, as well as the thermal gas pressure gradient. The efficiency of the acceleration of cosmic-rays at the shock as a function of the upstream magnetic field obliquity and upstream plasma beta is investigated. Astrophysical applications of the results are briefly discussed.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19980024672','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19980024672"><span>Numerical Study of Interaction of a Vortical Density Inhomogeneity with Shock and Expansion Waves</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Povitsky, A.; Ofengeim, D.</p> <p>1998-01-01</p> <p>We studied the interaction of a vortical density inhomogeneity (VDI) with shock and expansion waves. We call the VDI the region of concentrated vorticity (vortex) with a density different from that of ambiance. Non-parallel directions of the density gradient normal to the VDI surface and the pressure gradient across a shock wave results in an additional vorticity. The roll-up of the initial round VDI towards a non-symmetrical shape is studied numerically. Numerical modeling of this interaction is performed by a 2-D Euler code. The use of an adaptive unstructured numerical grid makes it possible to obtain high accuracy and capture regions of induced vorticity with a moderate overall number of mesh points. For the validation of the code, the computational results are compared with available experimental results and good agreement is obtained. The interaction of the VDI with a propagating shock wave is studied for a range of initial and induced circulations and obtained flow patterns are presented. The splitting of the VDI develops into the formation of a non-symmetrical vortex pair and not in a set of vortices. A method for the analytical computation of an overall induced circulation Gamma(sub 1) as a result of the interaction of a moving VDI with a number of waves is proposed. Simplified, approximated, expressions for Gamma(sub 1) are derived and their accuracy is discussed. The splitting of the VDI passing through the Prandtl-Meyer expansion wave is studied numerically. The obtained VDI patterns are compared to those for the interaction of the VDI with a propagating shock wave for the same values of initial and induced circulations. These patterns have similar shapes for corresponding time moments.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20030011387&hterms=blood&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dblood','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20030011387&hterms=blood&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dblood"><span>Understanding How Space Travel Affects Blood Vessels: Arterial Remodeling and Functional Adaptations Induced by Microgravity</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Delp, Michael; Vasques, Marilyn; Aquilina, Rudy (Technical Monitor)</p> <p>2002-01-01</p> <p>Ever rise quickly from the couch to get something from the kitchen and suddenly feel dizzy? With a low heart rate and relaxed muscles, the cardiovascular system does not immediately provide the resistance necessary to keep enough blood going to your head. Gravity wins, at least for a short time, before your heart and blood vessels can respond to the sudden change in position and correct the situation. Actually, the human cardiovascular system is quite well adapted to the constant gravitational force of the Earth. When standing, vessels in the legs constrict to prevent blood from collecting in the lower extremities. In the space environment, the usual head-to-foot blood pressure and tissue fluid gradients that exist during the upright posture on Earth are removed. The subsequent shift in fluids from the lower to the upper portions of the body triggers adaptations within the cardiovascular system to accommodate the new pressure and fluid gradients. In animal models that simulate microgravity, the vessels in the head become more robust while those in the lower limbs become thin and lax. Similar changes may also occur in humans during spaceflight and while these adaptations are appropriate for a microgravity environment, they can cause problems when the astronauts return to Earth or perhaps another planet. Astronauts often develop orthostatic intolerance which means they become dizzy or faint when standing upright. This dizziness can persist for a number of days making routine activities difficult. In an effort to understand the physiological details of these cardiovascular adaptations, Dr. Michael Delp at Texas A&M University, uses the rat as a model for his studies. For the experiment flown on STS-107, he will test the hypothesis that blood vessels in the rats' hindlimbs become thinner, weaker, and constrict less in response to pressure changes and to chemical signals when exposed to microgravity. In addition, he will test the hypothesis that arteries in the brain become thicker as a result of microgravity-induced fluid shifts toward the head.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24353194','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24353194"><span>Gradient structure-induced temperature responsiveness in styrene/methyl methacrylate gradient copolymers micelles.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Zheng, Chao; Huang, Haiying; He, Tianbai</p> <p>2014-02-01</p> <p>In this work, micelles are formed by gradient copolymer of styrene and methyl methacrylate in acetone-water mixture and their temperature responsiveness is investigated in a narrow range near room temperature. Three different kinds of structural transitions could be induced by temperature: unimers to micelle transition, shrinkage/stretching of micelles, and morphological transition from spherical micelles to vesicles. In addition, a model analysis on the interface of gradient copolymer micelle is made to better understand these phenomena. It is found that both position and composition of the interface could alter in response to the change in temperature. According to the experiments and model analysis, it is proposed that temperature responsiveness might be an intrinsic and universal property of gradient copolymer micelles, which only originates from the gradient structure. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/20040086553','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20040086553"><span>TIGER: Development of Thermal Gradient Compensation Algorithms and Techniques</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hereford, James; Parker, Peter A.; Rhew, Ray D.</p> <p>2004-01-01</p> <p>In a wind tunnel facility, the direct measurement of forces and moments induced on the model are performed by a force measurement balance. The measurement balance is a precision-machined device that has strain gages at strategic locations to measure the strain (i.e., deformations) due to applied forces and moments. The strain gages convert the strain (and hence the applied force) to an electrical voltage that is measured by external instruments. To address the problem of thermal gradients on the force measurement balance NASA-LaRC has initiated a research program called TIGER - Thermally-Induced Gradients Effects Research. The ultimate goals of the TIGER program are to: (a) understand the physics of the thermally-induced strain and its subsequent impact on load measurements and (b) develop a robust thermal gradient compensation technique. This paper will discuss the impact of thermal gradients on force measurement balances, specific aspects of the TIGER program (the design of a special-purpose balance, data acquisition and data analysis challenges), and give an overall summary.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21106418','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21106418"><span>Finite element analysis of gradient z-coil induced eddy currents in a permanent MRI magnet.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Li, Xia; Xia, Ling; Chen, Wufan; Liu, Feng; Crozier, Stuart; Xie, Dexin</p> <p>2011-01-01</p> <p>In permanent magnetic resonance imaging (MRI) systems, pulsed gradient fields induce strong eddy currents in the conducting structures of the magnet body. The gradient field for image encoding is perturbed by these eddy currents leading to MR image distortions. This paper presents a comprehensive finite element (FE) analysis of the eddy current generation in the magnet conductors. In the proposed FE model, the hysteretic characteristics of ferromagnetic materials are considered and a scalar Preisach hysteresis model is employed. The developed FE model was applied to study gradient z-coil induced eddy currents in a 0.5 T permanent MRI device. The simulation results demonstrate that the approach could be effectively used to investigate eddy current problems involving ferromagnetic materials. With the knowledge gained from this eddy current model, our next step is to design a passive magnet structure and active gradient coils to reduce the eddy current effects. Copyright © 2010 Elsevier Inc. All rights reserved.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19860021148','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19860021148"><span>Fugacity and concentration gradients in a gravity field</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>May, C. E.</p> <p>1986-01-01</p> <p>Equations are reviewed which show that at equilibrium fugacity and concentration gradients can exist in gravitational fields. At equilibrium, the logarithm of the ratio of the fugacities of a species at two different locations in a gravitational field is proportional to the difference in the heights of the two locations and the molecular weight of the species. An analogous relation holds for the concentration ratios in a multicomponent system. The ratio is calculated for a variety of examples. The kinetics for the general process are derived, and the time required to approach equilibrium is calculated for several systems. The following special topics are discussed: ionic solutions, polymers, multiphase systems, hydrostatic pressure, osmotic pressure, and solubility gradients in a gravity field.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007PhPl...14b2105P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007PhPl...14b2105P"><span>Electromagnetic eigenmodes of collisional and collisionless plasmas and their stability to stimulated Brillouin scattering</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pathak, Vishwa Bandhu; Tripathi, V. K.</p> <p>2007-02-01</p> <p>Nonlinear electromagnetic eigenmodes of collisional and collisionless plasmas, when the temporal extent of the modes is longer than the ambipolar diffusion time, have been investigated. The nonlinearity in a collisionless plasma arises through ponderomotive force, whereas in collisional plasmas Ohmic nonlinearity prevails. The mode structure in both cases, representing a balance between the nonlinearity-induced self-convergence and diffraction-induced divergence, closely resembles Gaussian form. The spot size of the mode decreases with the increasing axial amplitude of the laser, attains a minimum, and then rises very gradually. The modes are susceptible to stimulated Brillouin backscattering. The growth rate of the Brillouin process initially increases with mode amplitude, attains a maximum, and then decreases. The reduction in the growth rate is caused by strong electron evacuation from the axial region by the ponderomotive force and thermal pressure gradient force created by nonuniform Ohmic heating.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22864577','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22864577"><span>Photo-actuation of liquids for light-driven microfluidics: state of the art and perspectives.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Baigl, Damien</p> <p>2012-10-07</p> <p>Using light to control liquid motion is a new paradigm for the actuation of microfluidic systems. We review here the different principles and strategies to induce or control liquid motion using light, which includes the use of radiation pressure, optical tweezers, light-induced wettability gradients, the thermocapillary effect, photosensitive surfactants, the chromocapillary effect, optoelectrowetting, photocontrolled electroosmotic flows and optical dielectrophoresis. We analyze the performance of these approaches to control using light many kinds of microfluidic operations involving discrete pL- to μL-sized droplets (generation, driving, mixing, reaction, sorting) or fluid flows in microchannels (valve operation, injection, pumping, flow rate control). We show that a complete toolbox is now available to control microfluidic systems by light. We finally discuss the perspectives of digital optofluidics as well as microfluidics based on all optical fluidic chips and optically reconfigurable devices.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20020086971&hterms=Shrink&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3DShrink','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20020086971&hterms=Shrink&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3DShrink"><span>The Collapse of Vapor Bubbles in a Spatially Non-Uniform Flow</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hao, Y.; Prosperetti, A.</p> <p>2000-01-01</p> <p>Pressure gradients act differently on liquid particles and suspended bubbles and are, therefore, capable of inducing a relative motion between the phases even when no relative velocity initially exists. As a consequence of the enhanced heat transfer in the presence of convection, this fact may have a major impact on the evolution of a vapor bubble. The effect is particularly strong in the case of a collapsing bubble for which, due to the conservation of the system's impulse, the induced relative velocity tends to be magnified when the bubble volume shrinks. A practical application could be, for instance, the enhancement of the condensation rate of bubbles downstream of a heated region, thereby reducing the quality of a flowing liquid-vapor mixture. A simple model of the process, in which the bubble is assumed to be spherical and the flow potential, is developed in the paper.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GeoRL..44.6692U','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GeoRL..44.6692U"><span>Propagation and arrest of dikes under topography: Models applied to the 2014 Bardarbunga (Iceland) rifting event</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Urbani, S.; Acocella, V.; Rivalta, E.; Corbi, F.</p> <p>2017-07-01</p> <p>Dikes along rift zones propagate laterally downslope for tens of kilometers, often becoming arrested before topographic reliefs. We use analogue and numerical models to test the conditions controlling the lateral propagation and arrest of dikes, exploring the presence of a slope in connection with buoyancy and rigidity layering. A gentle downslope assists lateral propagation when combined with an effective barrier to magma ascent, e.g., gelatin stiffness contrasts, while antibuoyancy alone may be insufficient to prevent upward propagation. We also observe that experimental dikes become arrested when reaching a plain before opposite reliefs. Our numerical models show that below the plain the stress field induced by topography hinders further dike propagation. We suggest that lateral dike propagation requires an efficient barrier (rigidity) to upward propagation, assisting antibuoyancy, and a lateral pressure gradient perpendicular to the least compressive stress axis, while dike arrest may be induced by external reliefs.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li class="active"><span>24</span></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_24 --> <div id="page_25" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li class="active"><span>25</span></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="481"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21373963','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21373963"><span>Water flux through human aquaporin 1: inhibition by intracellular furosemide and maximal response with high osmotic gradients.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ozu, Marcelo; Dorr, Ricardo A; Teresa Politi, M; Parisi, Mario; Toriano, Roxana</p> <p>2011-06-01</p> <p>This work studies water permeability properties of human aquaporin 1 (hAQP1) expressed in Xenopus laevis oocyte membranes, applying a technique where cellular content is replaced with a known medium, with the possibility of measuring intracellular pressure. Consequences on water transport-produced by well-known anisotonic gradients and by the intracellular effect of probable aquaporin inhibitors-were tested. In this way, the specific intracellular inhibition of hAQP1 by the diuretic drug furosemide was demonstrated. In addition, experiments imposing anisotonic mannitol gradients with a constant ionic strength showed that the relationship between water flux and the applied mannitol gradient deflects from a perfect osmometer response when the gradient is higher than 150 mosmol kg (W) (-1) . These results would indicate that the passage of water molecules through hAQP1 may have a maximum rate. As a whole, this work demonstrates the technical advantage of controlling both intracellular pressure and medium composition in order to study biophysical properties of hAQP1, and contributes information on water channel behavior under osmotic challenges and the discovery of new inhibitors.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28659549','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28659549"><span>Predictors and Clinical Impact of Functional Mitral Stenosis Induced by Restrictive Annuloplasty for Ischemic and Functional Mitral Regurgitation.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kainuma, Satoshi; Taniguchi, Kazuhiro; Toda, Koichi; Funatsu, Toshihiro; Kondoh, Haruhiko; Miyagawa, Shigeru; Yoshikawa, Yasushi; Hata, Hiroki; Saito, Shunsuke; Ueno, Takayoshi; Kuratani, Toru; Daimon, Takashi; Masai, Takafumi; Sawa, Yoshiki</p> <p>2017-11-24</p> <p>There are few reports of the determinants of "functional" mitral stenosis in terms of a residual mitral valve (MV) pressure gradient >5 mmHg following restrictive mitral annuloplasty (RMA) or the effect on long-term outcome in patients with functional mitral regurgitation (MR).Methods and Results:Serial cardiac catheterization and echocardiographic studies were performed in 55 patients with functional MR who underwent RMA using a 24/26-mm semi-rigid complete ring. The mean postoperative (1 month) catheter-measured MV gradient was 3.4±1.6 mmHg, which was independently associated with corresponding cardiac output [standardized partial regression coefficient (SPRC)=0.59] and indexed effective orifice area (SPRC=-0.25). Body surface area (BSA) had the greatest contribution to MV gradient (SPRC=0.38), followed by use of a 24-mm ring (SPRC=0.33) and hemodialysis (SPRC=0.26). Receiver-operating characteristic curve analysis demonstrated an optimal BSA cutoff value of 1.86 m 2 to predict post-MV stenosis (21% for <1.86 m 2 vs. 86% for ≥1.86 m 2 , P=0.002). During follow-up (75±32 months), freedom from adverse events did not differ between patients with (n=16) and without (n=39) an MV gradient ≥5 mmHg (log-rank P=0.24). Post-RMA MV gradient was determined not only by the degree of annular reduction but also by patients' hemodynamic factors (e.g., cardiac output). Implantation of a 24/26-mm annuloplasty ring for patients with BSA ≥1.86 m 2 indicated a high likelihood of post-MV stenosis. However, mild MV stenosis did not adversely affect late outcome after RMA.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29490256','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29490256"><span>Theory of Epithelial Cell Shape Transitions Induced by Mechanoactive Chemical Gradients.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Dasbiswas, Kinjal; Hannezo, Edouard; Gov, Nir S</p> <p>2018-02-27</p> <p>Cell shape is determined by a balance of intrinsic properties of the cell as well as its mechanochemical environment. Inhomogeneous shape changes underlie many morphogenetic events and involve spatial gradients in active cellular forces induced by complex chemical signaling. Here, we introduce a mechanochemical model based on the notion that cell shape changes may be induced by external diffusible biomolecules that influence cellular contractility (or equivalently, adhesions) in a concentration-dependent manner-and whose spatial profile in turn is affected by cell shape. We map out theoretically the possible interplay between chemical concentration and cellular structure. Besides providing a direct route to spatial gradients in cell shape profiles in tissues, we show that the dependence on cell shape helps create robust mechanochemical gradients. Copyright © 2017 Biophysical Society. Published by Elsevier Inc. All rights reserved.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23970568','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23970568"><span>Mass flow and velocity profiles in Neurospora hyphae: partial plug flow dominates intra-hyphal transport.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Abadeh, Aryan; Lew, Roger R</p> <p>2013-11-01</p> <p>Movement of nuclei, mitochondria and vacuoles through hyphal trunks of Neurospora crassa were vector-mapped using fluorescent markers and green fluorescent protein tags. The vectorial movements of all three were strongly correlated, indicating the central role of mass (bulk) flow in cytoplasm movements in N. crassa. Profiles of velocity versus distance from the hyphal wall did not match the parabolic shape predicted by the ideal Hagen-Poiseuille model of flow at low Reynolds number. Instead, the profiles were flat, consistent with a model of partial plug flow due to the high concentration of organelles in the flowing cytosol. The intra-hyphal pressure gradients were manipulated by localized external osmotic treatments to demonstrate the dependence of velocity (and direction) on pressure gradients within the hyphae. The data support the concept that mass transport, driven by pressure gradients, dominates intra-hyphal transport. The transport occurs by partial plug flow due to the organelles in the cytosol.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/biblio/21269055-effects-internal-structure-equilibrium-field-reversed-configuration-plasma-sustained-rotating-magnetic-field','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/21269055-effects-internal-structure-equilibrium-field-reversed-configuration-plasma-sustained-rotating-magnetic-field"><span>Effects of internal structure on equilibrium of field-reversed configuration plasma sustained by rotating magnetic field</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Yambe, Kiyoyuki; Inomoto, Michiaki; Okada, Shigefumi</p> <p></p> <p>The effects of an internal structure on the equilibrium of a field-reversed configuration (FRC) plasma sustained by rotating magnetic field is investigated by using detailed electrostatic probe measurements in the FRC Injection Experiment apparatus [S. Okada, et al., Nucl. Fusion. 45, 1094 (2005)]. An internal structure installed axially on the geometrical axis, which simulates Ohmic transformer or external toroidal field coils on the FRC device, brings about substantial changes in plasma density profile. The internal structure generates steep density-gradients not only on the inner side but on the outer side of the torus. The radial electric field is observed tomore » sustain the ion thermal pressure-gradient in the FRC without the internal structure; however, the radial electric field is not sufficient to sustain the increased ion thermal pressure-gradient in the FRC with the internal structure. Spontaneously driven azimuthal ion flow will be accountable for the imbalance of the radial pressure which is modified by the internal structure.« less</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/20020062050','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20020062050"><span>A High-Lift Building Block Flow: Turbulent Boundary Layer Relaminarization</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bourassa, Corey; Thomas, Flint O.; Nelson, Robert C.</p> <p>2001-01-01</p> <p>A working wind tunnel test facility has been constructed at the University of Notre Dame's Hessert Center. The relaminarization test facility has been constructed in the 1.5m x 1.5m (5ft x 5 ft) atmospheric wind tunnel and generates a Re(theta)=4694 turbulent boundary layer in nominally zero-pressure gradient before it is exposed to the Case #1 pressure gradient (K approximately equal to 4.2 x 10(exp -6), which is believed to be sufficient to achieve relaminarization. Future work to be conducted will include measuring the response of the turbulent boundary layer to the favorable pressure gradients created in the test facility and documenting this response in order to understand the underlying flow physics responsible for relaminarization. It is the goal of this research to have a better understanding of accelerated turbulent boundary layers which will aid in the development of future flow diagnostic utilities to be implemented in applied aerodynamic research.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1999APS..DPP.FP190W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1999APS..DPP.FP190W"><span>How Artificial Should the Treatment of a Plasma's Viscosity Be?</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Whitney, K. G.; Velikovich, A. L.; Thornhill, J. W.; Davis, J.</p> <p>1999-11-01</p> <p>Electron viscosity dominates over ion viscosity and is important in describing the generation of shock fronts in highly ionizable plasmas. The sizes of shock front jumps in electron and ion temperature are determined from the magnitudes of the heat flow vector and pressure tensor, which, in turn, acquire non-negligible nonlinear contributions from the temperature and density gradients when these gradients are large. Thus, a consistent treatment of steep gradient formation in plasmas must come from investigations that include the effects of these nonlinear contributions to heat and momentum transport. Coefficients for each of five nonlinear contributions to the pressure tensor for an (r,z) Z-pinch geometry are presented and discussed in this talk. Hydrodynamic code calculations generally are not designed to provide a testbed for directly evaluating the kinetic energy dissipation that occurs at shock fronts; therefore, the strength of these nonlinear pressure tensor terms will be estimated by post-processing a Z-pinch hydrodynamics calculation and a steady-state planar shock wave calculation.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/12815648','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/12815648"><span>Echo planar imaging at 4 Tesla with minimum acoustic noise.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Tomasi, Dardo G; Ernst, Thomas</p> <p>2003-07-01</p> <p>To minimize the acoustic sound pressure levels of single-shot echo planar imaging (EPI) acquisitions on high magnetic field MRI scanners. The resonance frequencies of gradient coil vibrations, which depend on the coil length and the elastic properties of the materials in the coil assembly, were measured using piezoelectric transducers. The frequency of the EPI-readout train was adjusted to avoid the frequency ranges of mechanical resonances. Our MRI system exhibited two sharp mechanical resonances (at 720 and 1220 Hz) that can increase vibrational amplitudes up to six-fold. A small adjustment of the EPI-readout frequency made it possible to reduce the sound pressure level of EPI-based perfusion and functional MRI scans by 12 dB. Normal vibrational modes of MRI gradient coils can dramatically increase the sound pressure levels during echo planar imaging (EPI) scans. To minimize acoustic noise, the frequency of EPI-readout trains and the resonance frequencies of gradient coil vibrations need to be different. Copyright 2003 Wiley-Liss, Inc.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/biblio/20999347-vertical-two-phase-flow-regimes-pressure-gradients-under-influence-sds-surfactant','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/20999347-vertical-two-phase-flow-regimes-pressure-gradients-under-influence-sds-surfactant"><span>Vertical two-phase flow regimes and pressure gradients under the influence of SDS surfactant</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Duangprasert, Tanabordee; Sirivat, Anuvat; Siemanond, Kitipat</p> <p>2008-01-15</p> <p>Two-phase gas/liquid flows in vertical pipes have been systematically investigated. Water and SDS surfactant solutions at various concentrations were used as the working fluids. In particular, we focus our work on the influence of surfactant addition on the flow regimes, the corresponding pressure gradients, and the bubble sizes and velocity. Adding the surfactant lowers the air critical Reynolds numbers for the bubble-slug flow and the slug flow transitions. The pressure gradients of SDS solutions are lower than those of pure water especially in the slug flow and the slug-churn flow regimes, implying turbulent drag reduction. At low Re{sub air}, themore » bubble sizes of the surfactant solution are lower than those of pure water due to the increase in viscosity. With increasing and at high Re{sub air}, the bubble sizes of the SDS solution become greater than those of pure water which is attributed to the effect of surface tension. (author)« less</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1994MsT.........17M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1994MsT.........17M"><span>Compressible turbulence measurements in a supersonic boundary layer including favorable pressure gradient effects</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Miller, Raymond S.</p> <p>1994-12-01</p> <p>The effect of a favorable pressure gradient on the turbulent flow structure in a Mach 2.9 boundary layer (Re/m approximately equal to 1.5 x 10(exp 7)) is investigated experimentally. Conventional flow and hot film measurements of turbulent fluctuation properties have been made upstream of and along an expansion ramp. Upstream measurements were taken in a zero pressure gradient boundary layer 44 cm from the nozzle throat in a 6.35 cm square test section. Measurements are obtained in the boundary layer, above the expansion ramp, 71.5 cm from the nozzle throat. Mean flow and turbulent flow characteristics are measured in all three dimensions. Comparisons are made between data obtained using single and multiple-overheat cross-wire anemometry as well as conventional mean flow probes. Conventional flow measurements were taken using a Pitot probe and a 10 degree cone static probe. Flow visualization was conducted via imaging techniques (Schlieren and shadowgraph photographs). Results suggest that compressibility effects, as seen through the density fluctuations in the Reynolds shear stress, are roughly 10% relative to the mean velocity and are large relative to the velocity fluctuations. This is also observed in the total Reynolds shear stress; compressibility accounts for 50-75% of the total shear. This is particularly true in the favorable pressure gradient region, where though the peak fluctuation intensities are diminished, the streamwise component of the mean flow is larger, hence the contribution of the compressibility term is significant in the Reynolds shear.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29464985','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29464985"><span>Comparison of phase-contrast MR and flow simulations for the study of CSF dynamics in the cervical spine.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Lindstrøm, Erika Kristina; Schreiner, Jakob; Ringstad, Geir Andre; Haughton, Victor; Eide, Per Kristian; Mardal, Kent-Andre</p> <p>2018-06-01</p> <p>Background Investigators use phase-contrast magnetic resonance (PC-MR) and computational fluid dynamics (CFD) to assess cerebrospinal fluid dynamics. We compared qualitative and quantitative results from the two methods. Methods Four volunteers were imaged with a heavily T2-weighted volume gradient echo scan of the brain and cervical spine at 3T and with PC-MR. Velocities were calculated from PC-MR for each phase in the cardiac cycle. Mean pressure gradients in the PC-MR acquisition through the cardiac cycle were calculated with the Navier-Stokes equations. Volumetric MR images of the brain and upper spine were segmented and converted to meshes. Models of the subarachnoid space were created from volume images with the Vascular Modeling Toolkit. CFD simulations were performed with a previously verified flow solver. The flow patterns, velocities and pressures were compared in PC-MR and CFD flow images. Results PC-MR images consistently revealed more inhomogeneous flow patterns than CFD, especially in the anterolateral subarachnoid space where spinal nerve roots are located. On average, peak systolic and diastolic velocities in PC-MR exceeded those in CFD by 31% and 41%, respectively. On average, systolic and diastolic pressure gradients calculated from PC-MR exceeded those of CFD by 11% and 39%, respectively. Conclusions PC-MR shows local flow disturbances that are not evident in typical CFD. The velocities and pressure gradients calculated from PC-MR are systematically larger than those calculated from CFD.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19730009903','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19730009903"><span>Objective sea level pressure analysis for sparse data areas</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Druyan, L. M.</p> <p>1972-01-01</p> <p>A computer procedure was used to analyze the pressure distribution over the North Pacific Ocean for eleven synoptic times in February, 1967. Independent knowledge of the central pressures of lows is shown to reduce the analysis errors for very sparse data coverage. The application of planned remote sensing of sea-level wind speeds is shown to make a significant contribution to the quality of the analysis especially in the high gradient mid-latitudes and for sparse coverage of conventional observations (such as over Southern Hemisphere oceans). Uniform distribution of the available observations of sea-level pressure and wind velocity yields results far superior to those derived from a random distribution. A generalization of the results indicates that the average lower limit for analysis errors is between 2 and 2.5 mb based on the perfect specification of the magnitude of the sea-level pressure gradient from a known verification analysis. A less than perfect specification will derive from wind-pressure relationships applied to satellite observed wind speeds.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29337433','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29337433"><span>Numerical simulation of two consecutive nasal respiratory cycles: toward a better understanding of nasal physiology.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>de Gabory, Ludovic; Reville, Nicolas; Baux, Yannick; Boisson, Nicolas; Bordenave, Laurence</p> <p>2018-01-16</p> <p>Computational fluid dynamic (CFD) simulations have greatly improved the understanding of nasal physiology. We postulate that simulating the entire and repeated respiratory nasal cycles, within the whole sinonasal cavities, is mandatory to gather more accurate observations and better understand airflow patterns. A 3-dimensional (3D) sinonasal model was constructed from a healthy adult computed tomography (CT) scan which discretized in 6.6 million cells (mean volume, 0.008 mm 3 ). CFD simulations were performed with ANSYS©FluentTMv16.0.0 software with transient and turbulent airflow (k-ω model). Two respiratory cycles (8 seconds) were simulated to assess pressure, velocity, wall shear stress, and particle residence time. The pressure gradients within the sinus cavities varied according to their place of connection to the main passage. Alternations in pressure gradients induced a slight pumping phenomenon close to the ostia but no movement of air was observed within the sinus cavities. Strong movements were observed within the inferior meatus during expiration contrary to the inspiration, as in the olfactory cleft at the same time. Particle residence time was longer during expiration than inspiration due to nasal valve resistance, as if the expiratory phase was preparing the next inspiratory phase. Throughout expiration, some particles remained in contact with the lower turbinates. The posterior part of the olfactory cleft was gradually filled with particles that did not leave the nose at the next respiratory cycle. This pattern increased as the respiratory cycle was repeated. CFD is more efficient and reliable when the entire respiratory cycle is simulated and repeated to avoid losing information. © 2018 ARS-AAOA, LLC.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.A11J2010W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.A11J2010W"><span>Observations and predictability of gap winds in a steep, narrow, fire-prone canyon in central Idaho, USA</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wagenbrenner, N. S.; Forthofer, J.; Gibson, C.; Lamb, B. K.</p> <p>2017-12-01</p> <p>Frequent strong gap winds were measured in a deep, steep, wildfire-prone river canyon of central Idaho, USA during July-September 2013. Analysis of archived surface pressure data indicate that the gap wind events were driven by regional scale surface pressure gradients. The events always occurred between 0400 and 1200 LT and typically lasted 3-4 hours. The timing makes these events particularly hazardous for wildland firefighting applications since the morning is typically a period of reduced fire activity and unsuspecting firefighters could be easily endangered by the onset of strong downcanyon winds. The gap wind events were not explicitly forecast by operational numerical weather prediction (NWP) models due to the small spatial scale of the canyon ( 1-2 km wide) compared to the horizontal resolution of operational NWP models (3 km or greater). Custom WRF simulations initialized with NARR data were run at 1 km horizontal resolution to assess whether higher resolution NWP could accurately simulate the observed gap winds. Here, we show that the 1 km WRF simulations captured many of the observed gap wind events, although the strength of the events was underpredicted. We also present evidence from these WRF simulations which suggests that the Salmon River Canyon is near the threshold of WRF-resolvable terrain features when the standard WRF coordinate system and discretization schemes are used. Finally, we show that the strength of the gap wind events can be predicted reasonably well as a function of the surface pressure gradient across the gap, which could be useful in the absence of high-resolution NWP. These are important findings for wildland firefighting applications in narrow gaps where routine forecasts may not provide warning for wind effects induced by high-resolution terrain features.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28348630','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28348630"><span>Intracanalicular Optic Nerve Swelling and Signal Change in Fulminant Untreated Idiopathic Intracranial Hypertension.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Moodley, Anand A; Dlwati, Mahlubonke S; Durand, Miranda</p> <p>2017-04-01</p> <p>The role of the optic canal in the pathogenesis of papilloedema has been under scrutiny recently. Whether a larger canal precedes more severe papilloedema or is the result of bone remodelling from chronically raised pressure across a pressure gradient is not clear. The authors present the magnetic resonance imaging findings of a 29-year-old female with fulminant and untreated idiopathic intracranial hypertension. Imaging showed focal expansion and intrinsic signal changes of the intracanalicular optic nerve. The authors discuss the possibility of either fluid accumulation within the optic nerves from a water hammer effect across blocked optic canals resulting from the steep pressure gradient or opticomalacia (optic nerve softening) from chronic ischaemia.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/8000591','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/8000591"><span>Echocardiographic features of the normofunctional Labcor-Santiago pericardial bioprosthesis.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Gonzalez-Juanatey, J R; Garcia-Bengoechea, J B; Vega, M; Rubio, J; Sierra, J; Duran, D; Amaro, A; Gil, M</p> <p>1994-09-01</p> <p>Echocardiography was performed in 94 patients with a total of 99 normally functioning Labcor-Santiago bioprostheses, 62 in the aortic and 37 in the mitral position. The following variables were measured: peak and mean transvalvular velocities, peak and mean instantaneous pressure gradients as calculated from the modified Bernoulli equation, pressure half-time, cardiac index, stroke volume and effective orifice area (using continuity and Hatle equations). Regurgitation patterns were sought by transthoracic echocardiography (all valves) and, for selected mitral bioprostheses, by transesophageal echocardiography. Calculated mean aortic pressure gradient ranged from six to 10 mmHg and calculated effective aortic orifice area increased with ring diameter, with means of 1.27 cm2 for the 19 mm valve and 2.58 cm2 for the 27 mm valve. For mitral bioprostheses, mean pressure gradient ranged from 3.0 to 4.5 mmHg and calculated effective orifice area from 2.27 to 2.73 cm2. Only central regurgitation was observed. The Labcor-Santiago pericardial bioprostheses created little resistance to forward flow. In the small aortic root their hemodynamic performance was as good or better than that of other currently available devices. It is hoped that this new design will contribute increased in vivo mechanical durability.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017ResPh...7...57H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017ResPh...7...57H"><span>MHD pulsatile flow of engine oil based carbon nanotubes between two concentric cylinders</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Haq, Rizwan Ul; Shahzad, Faisal; Al-Mdallal, Qasem M.</p> <p></p> <p>In this article, thermal performance of engine oil in the presence of both single and multiple wall carbon nanotubes (SWCNTs and MWCNTs) between two concentric cylinders is presented. Flow is driven with oscillatory pressure gradient and magneto-hydrodynamics (MHDs) effects are also introduced to control the random motion of the nanoparticles. Arrived broad, it is perceived that the inclusion of nanoparticles increases the thermal conductivity of working fluid significantly for both turbulent and laminar regimes. Fundamental momentum and energy equations are based upon partial differential equations (PDEs) that contain thermos-physical properties of both SWCNTs and MWCNTs. The solution has been evaluated for each mixture, namely: SWCNT-engine oil and MWCNT-engine oil. Results are determined for each velocity, temperature, pressure and stress gradient. Graphical results for the numerical values of the emerging parameters, namely: Hartmann number (M), the solid volume fraction of the nanoparticles (ϕ), Reynolds number (Reω), and the pulsation parameter based on the periodic pressure gradient are analyzed for pressure difference, frictional forces, velocity profile, temperature profile, crux, streamlines and vorticity phenomena. In addition, the assets of various parameters on the flow quantities of observation are investigated.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014HMT....50..737Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014HMT....50..737Y"><span>Experimental investigation on circumferential and axial temperature gradient over fuel channel under LOCA</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yadav, Ashwini Kumar; kumar, Ravi; Gupta, Akhilesh; Chatterjee, Barun; Mukhopadhyay, Deb; Lele, H. G.</p> <p>2014-06-01</p> <p>In a nuclear reactor temperature rises drastically in fuel channels under loss of coolant accident due to failure of primary heat transportation system. Present investigation has been carried out to capture circumferential and axial temperature gradients during fully and partially voiding conditions in a fuel channel using 19 pin fuel element simulator. A series of experiments were carried out by supplying power to outer, middle and center rods of 19 pin fuel simulator in ratio of 1.4:1.1:1. The temperature at upper periphery of pressure tube (PT) was slightly higher than at bottom due to increase in local equivalent thermal conductivity from top to bottom of PT. To simulate fully voided conditions PT was pressurized at 2.0 MPa pressure with 17.5 kW power injection. Ballooning initiated from center and then propagates towards the ends and hence axial temperature difference has been observed along the length of PT. For asymmetric heating, upper eight rods of fuel simulator were activated and temperature difference up-to 250 °C has been observed from top to bottom periphery of PT. Such situation creates steep circumferential temperature gradient over PT and could lead to breaching of PT under high pressure.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/20110012977','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20110012977"><span>Implementation and Validation of an Impedance Eduction Technique</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Watson, Willie R.; Jones, Michael G.; Gerhold, Carl H.</p> <p>2011-01-01</p> <p>Implementation of a pressure gradient method of impedance eduction in two NASA Langley flow ducts is described. The Grazing Flow Impedance Tube only supports plane-wave sources, while the Curved Duct Test Rig supports sources that contain higher-order modes. Multiple exercises are used to validate this new impedance eduction method. First, synthesized data for a hard wall insert and a conventional liner mounted in the Grazing Flow Impedance Tube are used as input to the two impedance eduction methods, the pressure gradient method and a previously validated wall pressure method. Comparisons between the two results are excellent. Next, data measured in the Grazing Flow Impedance Tube are used as input to both methods. Results from the two methods compare quite favorably for sufficiently low Mach numbers but this comparison degrades at Mach 0.5, especially when the hard wall insert is used. Finally, data measured with a hard wall insert mounted in the Curved Duct Test Rig are used as input to the pressure gradient method. Significant deviation from the known solution is observed, which is believed to be largely due to 3-D effects in this flow duct. Potential solutions to this issue are currently being explored.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/20010018435','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20010018435"><span>Measurement of the Turbulence Kinetic Energy Budget of a Turbulent Planar Wake Flow in Pressure Gradients</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Liu, Xiao-Feng; Thomas, Flint O.; Nelson, Robert C.</p> <p>2001-01-01</p> <p>Turbulence kinetic energy (TKE) is a very important quantity for turbulence modeling and the budget of this quantity in its transport equation can provide insight into the flow physics. Turbulence kinetic energy budget measurements were conducted for a symmetric turbulent wake flow subjected to constant zero, favorable and adverse pressure gradients in year-three of research effort. The purpose of this study is to clarify the flow physics issues underlying the demonstrated influence of pressure gradient on wake development and provide experimental support for turbulence modeling. To ensure the reliability of these notoriously difficult measurements, the experimental procedure was carefully designed on the basis of an uncertainty analysis. Four different approaches, based on an isotropic turbulence assumption, a locally axisymmetric homogeneous turbulence assumption, a semi-isotropy assumption and a forced balance of the TKE equation, were applied for the estimate of the dissipation term. The pressure transport term is obtained from a forced balance of the turbulence kinetic energy equation. This report will present the results of the turbulence kinetic energy budget measurement and discuss their implication on the development of strained turbulent wakes.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li class="active"><span>25</span></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_25 --> <div class="footer-extlink text-muted" style="margin-bottom:1rem; text-align:center;">Some links on this page may take you to non-federal websites. 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