Mechanism study on pressure fluctuation of pump-turbine runner with large blade lean angle

NASA Astrophysics Data System (ADS)

Yulin, Fan; Xuhe, Wang; Baoshan, Zhu; Dongyue, Zhou; Xijun, Zhou

2016-11-01

Excessive pressure fluctuations in the vaneless space can cause mechanical vibration and even mechanical failures in pump-turbine operation. Mechanism studies on the pressure fluctuations and optimization design of blade geometry to reduce the pressure fluctuations have important significance in industrial production. In the present paper, two pump-turbine runners with big positive and negative blade lean angle were designed by using a multiobjective design strategy. Model test showed that the runner with negative blade lean angle not only had better power performance, but also had lower pressure fluctuation than the runner with positive blade lean angle. In order to figure out the mechanism of pressure fluctuation reduction in the vaneless;jik8space, full passage model for both runners were built and transient CFD computations were conducted to simulate the flow states inside the channel. Detailed flow field analyses indicated that the difference of low-pressure area in the trailing edge of blade pressure side were the main causes of pressure fluctuation reduction in the vaneless space.

Effect of Niagara power project on ground-water flow in the upper part of the Lockport Dolomite, Niagara Falls area, New York

USGS Publications Warehouse

Miller, Todd S.; Kappel, W.M.

1987-01-01

The Niagara River Power Project near Niagara Falls, N.Y., has created recharge and discharge areas that have modified the direction of groundwater flow east and northeast of the falls. Before construction of the power project in 1962, the configuration of the potentiometric surface in the upper part of the Silurian Lockport Dolomite generally paralleled the buried upper surface of the bedrock. Ground water in the central and east parts of the city of Niagara Falls flowed south and southwestward toward the upper Niagara River (above the falls), and ground water in the western part flowed westward into Niagara River gorge. The power project consists of two hydroelectric powerplants separated by a forebay canal that receives water from the upper Niagara River through two 4-mi-long, parallel, buried conduits. During periods of nonpeak power demand, some water in the forebay canal is pumped to a storage reservoir for later release to generate electricity during peak-demand periods. Since the power project began operation in 1962, groundwater within 0.5 mi of the buried conduits has seeped into the drain system that surrounds the conduits, then flows both south from the forebay canal and north from the Niagara River toward the Falls Street tunnel--a former sewer that crosses the conduits 0.65 mi north of the upper Niagara River. Approximately 6 million gallons of ground water a day leaks into the Falls Street tunnel, which carries it 2.3 mi westward to the Niagara River gorge below the falls. Daily water-level fluctuations in the forebay canal affect water levels in the drain system that surrounds the conduits, and this , in turn, affects the potentiometric surface in the Lockport Dolomite within 0.5 mi of the conduits. The drains transmit changes in pressure head near the forebay canal southward at least as far as the Falls Street tunnel area and possibly to the upper Niagara River. Some water in the pumped-storage reservoir recharges ground water in the Lockport Dolomite by seepage through bedding joints, which are exposed in the unlined reservoir bottom, and through the grout curtain beneath the reservoir 's dike. Water-level fluctuations in the reservoir cause slight ground-water fluctuations near the reservoir. (Author 's abstract)

USB environment measurements based on full-scale static engine ground tests

NASA Technical Reports Server (NTRS)

Sussman, M. B.; Harkonen, D. L.; Reed, J. B.

1976-01-01

Flow turning parameters, static pressures, surface temperatures, surface fluctuating pressures and acceleration levels were measured in the environment of a full-scale upper surface blowing (USB) propulsive lift test configuration. The test components included a flightworthy CF6-50D engine, nacelle, and USB flap assembly utilized in conjunction with ground verification testing of the USAF YC-14 Advanced Medium STOL Transport propulsion system. Results, based on a preliminary analysis of the data, generally show reasonable agreement with predicted levels based on model data. However, additional detailed analysis is required to confirm the preliminary evaluation, to help delineate certain discrepancies with model data, and to establish a basis for future flight test comparisons.

Roles of hot electrons in generating upper-hybrid waves in the earth's radiation belt

DOE PAGES

Hwang, J.; Shin, D. K.; Yoon, P. H.; ...

2017-05-01

Electrostatic fluctuations near upper-hybrid frequency, which are sometimes accompanied by multiple-harmonic electron cyclotron frequency bands above and below the upper-hybrid frequency, are common occurrences in the Earth's radiation belt, as revealed through the twin Van Allen Probe spacecrafts. It is customary to use the upper-hybrid emissions for estimating the background electron density, which in turn can be used to determine the plasmapause locations, but the role of hot electrons in generating such fluctuations has not been discussed in detail. The present paper carries out detailed analyses of data from the Waves instrument, which is part of the Electric and Magneticmore » Field Instrument Suite and Integrated Science suite onboard the Van Allen Probes. Combined with the theoretical calculation, it is shown that the peak intensity associated with the upper-hybrid fluctuations might be predominantly determined by tenuous but hot electrons and that denser cold background electrons do not seem to contribute much to the peak intensity. This finding shows that upper-hybrid fluctuations detected during quiet time are not only useful for the determination of the background cold electron density but also contain information on the ambient hot electrons population as well.« less

Roles of hot electrons in generating upper-hybrid waves in the earth's radiation belt

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hwang, J.; Shin, D. K.; Yoon, P. H.

Electrostatic fluctuations near upper-hybrid frequency, which are sometimes accompanied by multiple-harmonic electron cyclotron frequency bands above and below the upper-hybrid frequency, are common occurrences in the Earth's radiation belt, as revealed through the twin Van Allen Probe spacecrafts. It is customary to use the upper-hybrid emissions for estimating the background electron density, which in turn can be used to determine the plasmapause locations, but the role of hot electrons in generating such fluctuations has not been discussed in detail. The present paper carries out detailed analyses of data from the Waves instrument, which is part of the Electric and Magneticmore » Field Instrument Suite and Integrated Science suite onboard the Van Allen Probes. Combined with the theoretical calculation, it is shown that the peak intensity associated with the upper-hybrid fluctuations might be predominantly determined by tenuous but hot electrons and that denser cold background electrons do not seem to contribute much to the peak intensity. This finding shows that upper-hybrid fluctuations detected during quiet time are not only useful for the determination of the background cold electron density but also contain information on the ambient hot electrons population as well.« less

Dynamic Runner Forces and Pressure Fluctuations on the Draft Tube Wall of a Model Pump-Turbine

NASA Astrophysics Data System (ADS)

Kirschner, O.; Ruprecht, A.; Göde, E.; Riedelbauch, S.

2016-11-01

When Francis-turbines and pump-turbines operate at off-design conditions, typically a vortex rope develops. The vortex rope causes pressure oscillations leading to fluctuations of the forces affecting the runner. The presence of dynamic runner forces over a long period of time might damage the bearings and possibly the runner. In this experimental investigation, the fluctuating part of the runner forces and the pressure oscillations on the draft tube wall were measured on a model pump-turbine with a simplified straight cone draft tube in different operating conditions. The investigation focuses on the correlation of the pressure fluctuations frequency measured at the draft tube wall with the frequency of the fluctuating forces on the runner. The comparison between pressure fluctuations and dynamic forces shows a significant correlation in all operating points. For the comparison of different components in the spatial directions of the forces, the pressure fluctuations were separated in a synchronous part and a rotating part for operating points with higher amplitudes. The rotating pressure fluctuations correlate with the radial forces especially in the operating points with a rotating vortex rope. At frequencies with higher amplitudes in the pressure fluctuations caused by the vortex rope movement, there are also higher amplitudes in the radial forces at the same frequencies.

Elimination of fuel pressure fluctuation and multi-injection fuel mass deviation of high pressure common-rail fuel injection system

NASA Astrophysics Data System (ADS)

Li, Pimao; Zhang, Youtong; Li, Tieshuan; Xie, Lizhe

2015-03-01

The influence of fuel pressure fluctuation on multi-injection fuel mass deviation has been studied a lot, but the fuel pressure fluctuation at injector inlet is still not eliminated efficiently. In this paper, a new type of hydraulic filter consisting of a damping hole and a chamber is developed for elimination of fuel pressure fluctuation and multi-injection fuel mass deviation. Linear model of the improved high pressure common-rail system(HPCRS) including injector, the pipe connecting common-rail with injector and the hydraulic filter is built. Fuel pressure fluctuation at injector inlet, on which frequency domain analysis is conducted through fast Fourier transformation, is acquired at different target pressure and different damping hole diameter experimentally. The linear model is validated and can predict the natural frequencies of the system. Influence of damping hole diameter on fuel pressure fluctuation is analyzed qualitatively based on the linear model, and it can be inferred that an optimal diameter of the damping hole for elimination of fuel pressure fluctuation exists. Fuel pressure fluctuation and fuel mass deviation under different damping hole diameters are measured experimentally, and it is testified that the amplitude of both fuel pressure fluctuation and fuel mass deviation decreases first and then increases with the increasing of damping hole diameter. The amplitude of main injection fuel mass deviation can be reduced by 73% at most under pilot-main injection mode, and the amplitude of post injection fuel mass deviation can be reduced by 92% at most under main-post injection mode. Fuel mass of a single injection increases with the increasing of the damping hole diameter. The hydraulic filter proposed by this research can be potentially used to eliminate fuel pressure fluctuation at injector inlet and improve the stability of HPCRS fuel injection.

Investigation of the spatial variability and possible origins of wind-induced air pressure fluctuations responsible for pressure pumping

NASA Astrophysics Data System (ADS)

Mohr, Manuel; Laemmel, Thomas; Maier, Martin; Zeeman, Matthias; Longdoz, Bernard; Schindler, Dirk

2017-04-01

The exchange of greenhouse gases between the soil and the atmosphere is highly relevant for the climate of the Earth. Recent research suggests that wind-induced air pressure fluctuations can alter the soil gas transport and therefore soil gas efflux significantly. Using a newly developed method, we measured soil gas transport in situ in a well aerated forest soil. Results from these measurements showed that the commonly used soil gas diffusion coefficient is enhanced up to 30% during periods of strong wind-induced air pressure fluctuations. The air pressure fluctuations above the forest floor are only induced at high above-canopy wind speeds (> 5 m s-1) and lie in the frequency range 0.01-0.1 Hz. Moreover, the amplitudes of air pressure fluctuations in this frequency range show a clear quadratic dependence on mean above-canopy wind speed. However, the origin of these wind-induced pressure fluctuations is still unclear. Airflow measurements and high-precision air pressure measurements were conducted at three different vegetation-covered sites (conifer forest, deciduous forest, grassland) to investigate the spatial variability of dominant air pressure fluctuations, their origin and vegetation-dependent characteristics. At the conifer forest site, a vertical profile of air pressure fluctuations was measured and an array consisting of five pressure sensors were installed at the forest floor. At the grassland site, the air pressure measurements were compared with wind observations made by ground-based LIDAR and spatial temperature observations from a fibre-optic sensing network (ScaleX Campaign 2016). Preliminary results show that at all sites the amplitudes of relevant air pressure fluctuations increase with increasing wind speed. Data from the array measurements reveal that there are no time lags between the air pressure signals of different heights, but a time lag existed between the air pressure signals of the sensors distributed laterally on the forest floor, suggesting a horizontal propagation of the air pressure waves.

Correlation between non-Fermi-liquid behavior and superconductivity in (Ca, La)(Fe,Co)As2 iron arsenides: A high-pressure study

NASA Astrophysics Data System (ADS)

Zhou, W.; Ke, F.; Xu, Xiaofeng; Sankar, R.; Xing, X.; Xu, C. Q.; Jiang, X. F.; Qian, B.; Zhou, N.; Zhang, Y.; Xu, M.; Li, B.; Chen, B.; Shi, Z. X.

2017-11-01

Non-Fermi-liquid (NFL) phenomena associated with correlation effects have been widely observed in the phase diagrams of unconventional superconducting families. Exploration of the correlation between the normal state NFL, regardless of its microscopic origins, and the superconductivity has been argued as a key to unveiling the mystery of the high-Tc pairing mechanism. Here we systematically investigate the pressure-dependent in-plane resistivity (ρ ) and Hall coefficient (RH) of a high-quality 112-type Fe-based superconductor Ca1 -xLaxFe1 -yCoyAs2 (x =0.2 ,y =0.02 ). With increasing pressure, the normal-state resistivity of the studied sample exhibits a pronounced crossover from non-Fermi-liquid to Fermi-liquid behaviors. Accompanied with this crossover, Tc is gradually suppressed. In parallel, the extremum in the Hall coefficient RH(T ) curve, possibly due to anisotropic scattering induced by spin fluctuations, is also gradually suppressed. The symbiosis of NFL and superconductivity implies that these two phenomena are intimately related. Further study on the pressure-dependent upper critical field reveals that the two-band effects are also gradually weakened with increasing pressure and reduced to the one-band Werthamer-Helfand-Hohenberg limit in the low-Tc regime. Overall, our paper supports the picture that NFL, multigap, and extreme RH(T ) are all of the same magnetic origin, i.e., the spin fluctuations in the 112 iron arsenide superconductors.

Influence of high-frequency ambient pressure pumping on carbon dioxide efflux from soil

Treesearch

Eugene S. Takle; William J. Massman; James R. Brandle; R. A. Schmidt; Xinhua Zhou; Irina V. Litvina; Rick Garcia; Geoffrey Doyle; Charles W. Rice

2004-01-01

We report measurements at 2Hz of pressure fluctuations at and beneath the soil in an agricultural field with dry soil and no vegetation. The objective of our study was to examine the possible role of pressure fluctuations produced by fluctuations in ambient wind on the efflux of CO2 at the soil surface.We observed that pressure fluctuations penetrate to 50 cm in the...

Effect of pressure fluctuations on Richtmyer-Meshkov coherent structures

NASA Astrophysics Data System (ADS)

Bhowmick, Aklant K.; Abarzhi, Snezhana

2016-11-01

We investigate the formation and evolution of Richtmyer Meshkov bubbles after the passage of a shock wave across a two fluid interface in the presence of pressure fluctuations. The fluids are ideal and incompressible and the pressure fluctuations are scale invariant in space and time, and are modeled by a power law time dependent acceleration field with exponent -2. Solutions indicate sensitivity to pressure fluctuations. In the linear regime, the growth of curvature and bubble velocity is linear. The growth rate is dominated by the initial velocity for weak pressure fluctuations, and by the acceleration term for strong pressure fluctuations. In the non-linear regime, the bubble curvature is constant and the solutions form a one parameter family (parametrized by the bubble curvature). The solutions are shown to be convergent and asymptotically stable. The physical solution (stable fastest growing) is a flat bubble for small pressure fluctuations and a curved bubble for large pressure fluctuations. The velocity field (in the frame of references accounting for the background motion) involves intense motion of the fluids in a vicinity of the interface, effectively no motion of the fluids away from the interfaces, and formation of vortical structures at the interface. The work is supported by the US National Science Foundation.

Effect of pressure fluctuations on Richtmyer-Meshkov coherent structures

NASA Astrophysics Data System (ADS)

Bhowmick, Aklant K.; Abarzhi, Snezhana

2016-10-01

We investigate the formation and evolution of Richtmyer Meshkov bubbles after the passage of a shock wave across a two fluid interface in the presence of pressure fluctuations. The fluids are ideal and incompressible and the pressure fluctuations are scale invariant in space and time, and are modeled by a power law time dependent acceleration field with exponent -2. Solutions indicate sensitivity to pressure fluctuations. In the linear regime, the growth of curvature and bubble velocity is linear. The growth rate is dominated by the initial velocity for weak pressure fluctuations, and by the acceleration term for strong pressure fluctuations. In the non-linear regime, the bubble curvature is constant and the solutions form a one parameter family (parametrized by the bubble curvature). The solutions are shown to be convergent and asymptotically stable. The physical solution (stable fastest growing) is a flat bubble for small pressure fluctuations and a curved bubble for large pressure fluctuations. The velocity field (in the frame of references accounting for the background motion) involves intense motion of the fluids in a vicinity of the interface, effectively no motion of the fluids away from the interfaces, and formation of vortical structures at the interface. The work is supported by the US National Science Foundation.

Pressure fluctuation generated by the interaction of blade and tongue

NASA Astrophysics Data System (ADS)

Zheng, Lulu; Dou, Hua-Shu; Chen, Xiaoping; Zhu, Zuchao; Cui, Baoling

2018-02-01

Pressure fluctuation around the tongue has large effect on the stable operation of a centrifugal pump. In this paper, the Reynolds averaged Navier-Stokes equations (RANS) and the RNG k-epsilon turbulence model is employed to simulate the flow in a pump. The flow field in the centrifugal pump is computed for a range of flow rate. The simulation results have been compared with the experimental data and good agreement has been achieved. In order to study the interaction of the tongue with the impeller, fifteen monitor probes are evenly distributed circumferentially at three radii around the tongue. Pressure distribution is investigated at various blade positions while the blade approaches to and leaves the tongue region. Results show that pressure signal fluctuates largely around the tongue, and it is more intense near the tongue surface. At design condition, standard deviation of pressure fluctuation is the minimum. At large flow rate, the increased low pressure region at the blade trailing edge results in the increases of pressure fluctuation amplitude and pressure spectra at the monitor probes. Minimum pressure is obtained when the blade is facing to the tongue. It is found that the amplitude of pressure fluctuation strongly depends on the blade positions at large flow rate, and pressure fluctuation is caused by the relative movement between blades and tongue. At small flow rate, the rule of pressure fluctuation is mainly depending on the structure of vortex flow at blade passage exit besides the influence from the relative position between the blade and the tongue.

Poynting vector, energy densities, and pressure of collective transverse electromagnetic fluctuations in unmagnetized plasmas

NASA Astrophysics Data System (ADS)

Schlickeiser, R.

2012-01-01

A systematic calculation of the electromagnetic properties (Poynting vector, electromagnetic energy, and pressure) of the collective transverse fluctuations in unmagnetized plasmas with velocity-anisotropic plasma particle distributions functions is presented. Time-averaged electromagnetic properties for monochromatic weakly damped wave-like fluctuations and space-averaged electromagnetic properties for monochromatic weakly propagating and aperiodic fluctuations are calculated. For aperiodic fluctuations, the Poynting vector as well as the sum of the space-averaged electric and magnetic field energy densities vanish. However, aperiodic fluctuations possess a positive pressure given by its magnetic energy density. This finite pressure density pa of aperiodic fluctuations has important consequences for the dynamics of cosmic unmagnetized plasmas such as the intergalactic medium after reionization. Adopting the standard cosmological evolution model, we show that this additional pressure changes the expansion law of the universe leading to further deceleration. Negative vacuum pressure counterbalances this deceleration to an accelerating universe provided that the negative vacuum pressure is greater than 1.5pa, which we estimate to be of the order 2.1 . 10-16 dyn cm-2.

Numerical Study of Pressure Fluctuations due to High-Speed Turbulent Boundary Layers

NASA Technical Reports Server (NTRS)

Duan, Lian; Choudhari, Meelan M.; Wu, Minwei

2012-01-01

Direct numerical simulations (DNS) are used to examine the pressure fluctuations generated by fully developed turbulence in supersonic turbulent boundary layers with an emphasis on both pressure fluctuations at the wall and the acoustic fluctuations radiated into the freestream. The wall and freestream pressure fields are first analyzed for a zero pressure gradient boundary layer with Mach 2.5 and Reynolds number based on momentum thickness of approximately 2835. The single and multi-point statistics reported include the wall pressure fluctuation intensities, frequency spectra, space-time correlations, and convection velocities. Single and multi-point statistics of surface pressure fluctuations show good agreement with measured data and previously published simulations of turbulent boundary layers under similar flow conditions. Spectral analysis shows that the acoustic fluctuations outside the boundary layer region have much lower energy content within the high-frequency region. The space-time correlations reflect the convective nature of the pressure field both at the wall and in the freestream, which is characterized by the downstream propagation of pressure-carrying eddies. Relative to those at the wall, the pressure-carrying eddies associated with the freestream signal are larger and convect at a significantly lower speed. The preliminary DNS results of a Mach 6 boundary layer show that the pressure rms in the freestream region is significantly higher than that of the lower Mach number case.

Relationship of Early Spontaneous Type V Blood Pressure Fluctuation after Thrombolysis in Acute Cerebral Infarction Patients and the Prognosis

PubMed Central

Zuo, Lian; Wan, Ting; Xu, Xiahong; Liu, Feifeng; Li, Changsong; Li, Ying; Zhang, Yue; Zhang, Jing; Bao, Huan; Li, Gang

2016-01-01

We examined the relationship between an early spontaneous type V blood pressure fluctuation and the post-thrombolysis prognosis of patients with acute cerebral infarction. Patients were admitted consecutively. All patients were categorized into the type V blood pressure fluctuation group or non-type V blood pressure group. Their blood pressure was monitored before thrombolysis and until 6 h after thrombolysis. Baseline data and clinical outcomes were compared. Of 170 patients, 43 (25.2%) had an early type V blood pressure fluctuation. The National Institute of Health Stroke Scale (NIHSS) score before thrombolysis and 24 h after thrombolysis, and the modified Rankin scale score at 90 days differed significantly between the two groups (P < 0.05). Multiple logistic regression analysis showed that an unfavorable prognosis at 3 months was associated with the NIHSS score before thrombolysis (P = 0.000) but probably not with this blood pressure fluctuation (P = 0.058). An early spontaneous type V blood pressure fluctuation is common in patients with acute cerebral infarction who received venous thrombolysis, especially if they have a higher NIHSS score before thrombolysis. The type V blood pressure fluctuation may not influence patients’ prognosis; however, this needs to be confirmed in future trials. PMID:27278121

Effects of wrist tendon vibration on targeted upper-arm movements in poststroke hemiparesis.

PubMed

Conrad, Megan O; Scheidt, Robert A; Schmit, Brian D

2011-01-01

Impaired motor control of the upper extremity after stroke may be related to lost sensory, motor, and integrative functions of the brain. Artificial activation of sensory afferents might improve control of movement by adding excitatory drive to sensorimotor control structures. The authors evaluated the effect of wrist tendon vibration (TV) on paretic upper-arm stability during point-to-point planar movements. TV (70 Hz) was applied to the forearm wrist musculature of 10 hemiparetic stroke patients as they made center-out planar arm movements. End-point stability, muscle activity, and grip pressure were compared as patients stabilized at the target position for trials completed before, during, and after the application of the vibratory stimulus. Prior to vibration, hand position fluctuated as participants attempted to maintain the hand at the target after movement termination. TV improved arm stability, as evidenced by decreased magnitude of hand tangential velocity at the target. Improved stability was accompanied by a decrease in muscle activity throughout the arm as well as a mean decrease in grip pressure. These results suggest that vibratory stimulation of the distal wrist musculature enhances stability of the proximal arm and can be studied further as a mode for improving end-point stability during reaching in hemiparetic patients.

Wavenumber-frequency Spectra of Pressure Fluctuations Measured via Fast Response Pressure Sensitive Paint

NASA Technical Reports Server (NTRS)

Panda, J.; Roozeboom, N. H.; Ross, J. C.

2016-01-01

The recent advancement in fast-response Pressure-Sensitive Paint (PSP) allows time-resolved measurements of unsteady pressure fluctuations from a dense grid of spatial points on a wind tunnel model. This capability allows for direct calculations of the wavenumber-frequency (k-?) spectrum of pressure fluctuations. Such data, useful for the vibro-acoustics analysis of aerospace vehicles, are difficult to obtain otherwise. For the present work, time histories of pressure fluctuations on a flat plate subjected to vortex shedding from a rectangular bluff-body were measured using PSP. The light intensity levels in the photographic images were then converted to instantaneous pressure histories by applying calibration constants, which were calculated from a few dynamic pressure sensors placed at selective points on the plate. Fourier transform of the time-histories from a large number of spatial points provided k-? spectra for pressure fluctuations. The data provides first glimpse into the possibility of creating detailed forcing functions for vibro-acoustics analysis of aerospace vehicles, albeit for a limited frequency range.

Studies on unsteady pressure fields in the region of separating and reattaching flows

NASA Astrophysics Data System (ADS)

Govinda Ram, H. S.; Arakeri, V. H.

1990-12-01

Experimental studies on the measurement of pressure fields in the region of separating and reattaching flows behind several two-dimensional fore-bodies and one axisymmetric body are reported. In particular, extensive measurements of mean pressure, surface pressure fluctuation, and pressure fluctuation within the flow were made for a series of two-dimensional fore-body shapes consisting of triangular nose with varying included angle. The measurements from different bodies are compared and one of the important findings is that the maximum values of rms pressure fluctuation levels in the shear layer approaching reattachment are almost equal to the maximum value of the surface fluctuation levels.

Saltwater-freshwater mixing fluctuation in shallow beach aquifers

NASA Astrophysics Data System (ADS)

Han, Qiang; Chen, Daoyi; Guo, Yakun; Hu, Wulong

2018-07-01

Field measurements and numerical simulations demonstrate the existence of an upper saline plume in tidally dominated beaches. The effect of tides on the saltwater-freshwater mixing occurring at both the upper saline plume and lower salt wedge is well understood. However, it is poorly understood whether the tidal driven force acts equally on the mixing behaviours of above two regions and what factors control the mixing fluctuation features. In this study, variable-density, saturated-unsaturated, transient groundwater flow and solute transport numerical models are proposed and performed for saltwater-freshwater mixing subject to tidal forcing on a sloping beach. A range of tidal amplitude, fresh groundwater flux, hydraulic conductivity, beach slope and dispersivity anisotropy are simulated. Based on the time sequential salinity data, the gross mixing features are quantified by computing the spatial moments in three different aspects, namely, the centre point, length and width, and the volume (or area in a two-dimensional case). Simulated salinity distribution varies significantly at saltwater-freshwater interfaces. Mixing characteristics of the upper saline plume greatly differ from those in the salt wedge for both the transient and quasi-steady state. The mixing of the upper saline plume largely inherits the fluctuation characteristics of the sea tide in both the transverse and longitudinal directions when the quasi-steady state is reached. On the other hand, the mixing in the salt wedge is relatively steady and shows little fluctuation. The normalized mixing width and length, mixing volume and the fluctuation amplitude of the mass centre in the upper saline plume are, in general, one-magnitude-order larger than those in the salt wedge region. In the longitudinal direction, tidal amplitude, fresh groundwater flux, hydraulic conductivity and beach slope are significant control factors of fluctuation amplitude. In the transverse direction, tidal amplitude and beach slope are the main control parameters. Very small dispersivity anisotropy (e.g., αL /αT < 5) could greatly suppress mixing fluctuation in the longitudinal direction. This work underlines the close connection between the sea tides and the upper saline plume in the aspect of mixing, thereby enhancing understanding of the interplay between tidal oscillations and mixing mechanisms in tidally dominated sloping beach systems.

Inelastic Light Scattering Measurements of a Pressure-Induced Quantum Liquid in KCuF3

NASA Astrophysics Data System (ADS)

Yuan, S.; Kim, M.; Seeley, J. T.; Lee, J. C. T.; Lal, S.; Abbamonte, P.; Cooper, S. L.

2012-11-01

Pressure-dependent, low-temperature inelastic light (Raman) scattering measurements of KCuF3 show that applied pressure above P*˜7kbar suppresses a previously observed structural phase transition temperature to zero temperature in KCuF3, resulting in the development of a fluctuational (quasielastic) response near T˜0K. This pressure-induced fluctuational response—which we associate with slow fluctuations of the CuF6 octahedral orientation—is temperature independent and exhibits a characteristic fluctuation rate that is much larger than the temperature, consistent with quantum fluctuations of the CuF6 octahedra. A model of pseudospin-phonon coupling provides a qualitative description of both the temperature- and pressure-dependent evolution of the Raman spectra of KCuF3.

Pressure Fluctuation Characteristics of Narrow Gauge Train Running Through Tunnel

NASA Astrophysics Data System (ADS)

Suzuki, Masahiro; Sakuma, Yutaka

Pressure fluctuations on the sides of narrow (1067 mm) gauge trains running in tunnels are measured for the first time to investigate the aerodynamic force acting on the trains. The present measurements are compared with earlier measurements obtained with the Shinkansen trains. The results are as follows: (1) The aerodynamic force, which stems from pressure fluctuations on the sides of cars, puts the energy into the vibration of the car body running through a tunnel. (2) While the pressure fluctuations appear only on one of the two sides of the trains running in double-track tunnels, the fluctuations in opposite phase on both sides in single-track tunnels. (3) The on-track test data of the narrow gauge trains show the same tendency as those of the Shinkansen trains, although it is suggested that the pressure fluctuations develop faster along the narrow gauge trains than the Shinkansen trains.

Numerical simulations of a nonequilibrium argon plasma in a shock-tube experiment

NASA Technical Reports Server (NTRS)

Cambier, Jean-Luc

1991-01-01

A code developed for the numerical modeling of nonequilibrium radiative plasmas is applied to the simulation of the propagation of strong ionizing shock waves in argon gas. The simulations attempt to reproduce a series of shock-tube experiments which will be used to validate the numerical models and procedures. The ability to perform unsteady simulations makes it possible to observe some fluctuations in the shock propagation, coupled to the kinetic processes. A coupling mechanism by pressure waves, reminiscent of oscillation mechanisms observed in detonation waves, is described. The effect of upper atomic levels is also briefly discussed.

The dynamics and control of fluctuating pressure loads in the reattachment region of a supersonic free shear layer

NASA Technical Reports Server (NTRS)

Smits, A. J.

1990-01-01

The primary aim is to investigate the mechanisms which cause the unsteady wall-pressure fluctuations in shock wave turbulent shear layer interactions. The secondary aim is to find means to reduce the magnitude of the fluctuating pressure loads by controlling the unsteady shock motion. The particular flow proposed for study is the unsteady shock wave interaction formed in the reattachment zone of a separated supersonic flow. Similar flows are encountered in many practical situations, and they are associated with high levels of fluctuating wall pressure. Wall pressure fluctuations were measured in the reattachment region of the supersonic free shear layer. The free shear layer was formed by the separation of a Mach 2.9 turbulent boundary layer from a backward facing step. Reattachment occurred on a 20 deg ramp. By adjusting the position of the ramp, the base pressure was set equal to the freestream pressure, and the free shear layer formed in the absence of a separation shock. An array of flush-mounted, miniature, high-frequency pressure transducers was used to make multichannel measurements of the fluctuating wall pressure in the vicinity of the reattachment region. Contrary to previous observations of this flow, the reattachment region was found to be highly unsteady, and the pressure fluctuations were found to be significant. The overall behavior of the wall pressure loading is similar in scale and magnitude to the unsteadiness of the wall pressure field in compression ramp flows at the same Mach number. Rayleigh scattering was used to visualize the instantaneous shock structure in the streamwise and spanwise direction. Spanwise wrinkles on the order of half the boundary layer thickness were observed.

Fluctuation of a Piston in Vacuum Induced by Thermal Radiation Pressure

NASA Astrophysics Data System (ADS)

Inui, Norio

2017-10-01

We consider the displacement of a piston dividing a vacuum cavity at a finite temperature T induced by fluctuations in the thermal radiation pressure. The correlation function of the thermal radiation pressure is calculated using the theoretical framework developed by Barton, which was first applied to the fluctuation of the Casimir force at absolute zero. We show that the variance of the radiation pressure at a fixed point is proportional to T8 and evaluate the mean square displacement for a piston with a small cross section in a characteristic correlation timescale ħ/(kBT). At room temperature, the contribution of the thermal radiation to the fluctuation is larger than that of the vacuum fluctuation.

Stereo particle image velocimetry of nonequilibrium turbulence relaxation in a supersonic boundary layer

NASA Astrophysics Data System (ADS)

Lapsa, Andrew P.; Dahm, Werner J. A.

2011-01-01

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.

Pressure Fluctuations Induced by a Hypersonic Turbulent Boundary Layer

NASA Technical Reports Server (NTRS)

Duan, Lian; Choudhari, Meelan M.; Zhang, Chao

2016-01-01

Direct numerical simulations (DNS) are used to examine the pressure fluctuations generated by a spatially-developed Mach 5.86 turbulent boundary layer. The unsteady pressure field is analyzed at multiple wall-normal locations, including those at the wall, within the boundary layer (including inner layer, the log layer, and the outer layer), and in the free stream. The statistical and structural variations of pressure fluctuations as a function of wall-normal distance are highlighted. Computational predictions for mean velocity pro les and surface pressure spectrum are in good agreement with experimental measurements, providing a first ever comparison of this type at hypersonic Mach numbers. The simulation shows that the dominant frequency of boundary-layer-induced pressure fluctuations shifts to lower frequencies as the location of interest moves away from the wall. The pressure wave propagates with a speed nearly equal to the local mean velocity within the boundary layer (except in the immediate vicinity of the wall) while the propagation speed deviates from the Taylor's hypothesis in the free stream. Compared with the surface pressure fluctuations, which are primarily vortical, the acoustic pressure fluctuations in the free stream exhibit a significantly lower dominant frequency, a greater spatial extent, and a smaller bulk propagation speed. The freestream pressure structures are found to have similar Lagrangian time and spatial scales as the acoustic sources near the wall. As the Mach number increases, the freestream acoustic fluctuations exhibit increased radiation intensity, enhanced energy content at high frequencies, shallower orientation of wave fronts with respect to the flow direction, and larger propagation velocity.

Influence analysis of fluctuation parameters on flow stability based on uncertainty method

NASA Astrophysics Data System (ADS)

Meng, Tao; Fan, Shangchun; Wang, Chi; Shi, Huichao

2018-05-01

The relationship between flow fluctuation and pressure in a flow facility is studied theoretically and experimentally in this paper, and a method for measuring the flow fluctuation is proposed. According to the synchronicity of pressure and flow fluctuation, the amplitude of the flow fluctuation is calculated using the pressure measured in the flow facility and measurement of the flow fluctuation in a wide range of frequency is realized. Based on the method proposed, uncertainty analysis is used to evaluate the influences of different parameters on the flow fluctuation by the help of a sample-based stochastic model established and the parameters that have great influence are found, which can be a reference for the optimization design and the stability improvement of the flow facility.

A Experimental Study of Fluctuating Pressure Loads Beneath Swept Shock Wave/boundary Layer Interactions

NASA Astrophysics Data System (ADS)

Garg, Sanjay

An experimental research program providing basic knowledge and establishing a database on the fluctuating pressure loads produced on aerodynamic surfaces beneath three-dimensional shock wave/boundary layer interactions is described. Such loads constitute a fundamental problem of critical concern to future supersonic and hypersonic flight vehicles. A turbulent boundary layer on a flat plate is subjected to interactions with swept planar shock waves generated by sharp fins. Fin angles from 10 ^circ to 20^circ at freestream Mach numbers of 3 and 4 produce a variety of interaction strengths from weak to very strong. Miniature pressure transducers flush-mounted in the flat plate have been used to measure interaction-induced wall pressure fluctuations. The distributions of properties of the pressure fluctuations, such as their rms level, amplitude distribution and power spectra, are also determined. Measurements have been made for the first time in the aft regions of these interactions, revealing fluctuating pressure levels as high as 155 dB, which places them in the category of significant aeroacoustic load generators. The fluctuations near the foot of the fin are dominated by low frequency (0-5 kHz) components, and are caused by a previously unrecognized random motion of the primary attachment line. This phenomenon is probably intimately linked to the unsteadiness of the separation shock at the start of the interaction. The characteristics of the pressure fluctuations are explained in light of the features of the interaction flowfield. In particular, physical mechanisms responsible for the generation of high levels of surface pressure fluctuations are proposed based on the results of the study. The unsteadiness of the flowfield of the surface is also examined via a novel, non-intrusive optical technique. Results show that the entire shock structure generated by the interaction undergoes relatively low-frequency oscillations.

Scales of Heterogeneities in the Continental Crust and Upper Mantle

NASA Astrophysics Data System (ADS)

Tittgemeyer, M.; Wenzel, F.; Ryberg, T.; Fuchs, K.

1999-09-01

A seismological characterization of crust and upper mantle can refer to large-scale averages of seismic velocities or to fluctuations of elastic parameters. Large is understood here relative to the wavelength used to probe the earth.¶In this paper we try to characterize crust and upper mantle by the fluctuations in media properties rather than by their average velocities. As such it becomes evident that different scales of heterogeneities prevail in different layers of crust and mantle. Although we cannot provide final models and an explanation of why these different scales exist, we believe that scales of inhomogeneities carry significant information regarding the tectonic processes that have affected the lower crust, the lithospheric and the sublithospheric upper mantle.¶We focus on four different types of small-scale inhomogeneities (1) the characteristics of the lower crust, (2) velocity fluctuations in the uppermost mantle, (3) scattering in the lowermost lithosphere and on (4) heterogeneities in the mantle transition zone.

Psycho-Circulatory Responses Caused by Listening to Music, and Exposure to Fluctuating Noise or Steady Noise

NASA Astrophysics Data System (ADS)

SAKAMOTO, H.; HAYASHI, F.; SUGIURA, S.; TSUJIKAWA, M.

2002-02-01

This study investigated the effect of steady noise, fluctuating noise and music on circulatory function. Pulse-wave and blood pressure were continuously measured in 35 healthy young females who listened to three types of music or were exposed to steady noise or fluctuating noise, synchronized with each type of music with respect to intensity variations. The pulse-wave did not change during any exposure conditions. Regarding blood pressure, several modes were observed. The critical level for a blood pressure change was estimated to be 54 LAeqduring exposure to steady noise. The frequency of high-intensity peaks in the mode of sound fluctuation was associated with elevation in blood pressure. The blood pressure change was analyzed by distinguishing the intensity variation in sound fluctuation from other attributes of music. The effects of music on blood pressure were modified not only by the melody and timbre of the music but also by emotional responses during listing.

Measured wavenumber: frequency spectrum associated with acoustic and aerodynamic wall pressure fluctuations.

PubMed

Arguillat, Blandine; Ricot, Denis; Bailly, Christophe; Robert, Gilles

2010-10-01

Direct measurements of the wavenumber-frequency spectrum of wall pressure fluctuations beneath a turbulent plane channel flow have been performed in an anechoic wind tunnel. A rotative array has been designed that allows the measurement of a complete map, 63×63 measuring points, of cross-power spectral densities over a large area. An original post-processing has been developed to separate the acoustic and the aerodynamic exciting loadings by transforming space-frequency data into wavenumber-frequency spectra. The acoustic part has also been estimated from a simple Corcos-like model including the contribution of a diffuse sound field. The measured acoustic contribution to the surface pressure fluctuations is 5% of the measured aerodynamic surface pressure fluctuations for a velocity and boundary layer thickness relevant for automotive interior noise applications. This shows that for aerodynamically induced car interior noise, both contributions to the surface pressure fluctuations on car windows have to be taken into account.

Passive control of base pressure on an axisymmetric blunt body using a perimetric slit

NASA Astrophysics Data System (ADS)

García de la Cruz, Juan Marcos; Oxlade, Anthony R.; Morrison, Jonathan F.

2017-04-01

The effect on the base pressure of a thin slit located at the base edge of a blunt axisymmetric body, communicating an internal cavity with the external flow, is investigated. A parametric study is performed of the effect on base pressure of changes in slit size and cavity depth. The base pressure increases initially with increasing cavity depth, but saturates at a depth which depends on the slit size. The base pressure increases monotonically up to 5 % with increasing slit size for the geometries tested. An upper limit of base pressure recovery of 20 % is extrapolated from the data. It is observed that the main effect of the slit is to reduce the instantaneous pressure asymmetry, which is linked to the total base pressure in a similar fashion for all the slit sizes. As a second-order effect, for highly asymmetric pressure distributions, the slit produces a base pressure increase not associated with the base pressure asymmetry. The results suggest a global effect of the slit on the wake due to a diametrical flow within the cavity driven by the pressure differences across the slit and regulated by the largest of the pressure drops between the slit and cavity. The slit also reduces the periodic base pressure fluctuations, corresponding mainly to the vortex shedding, and increases the rotational speed of the wake.

Non-Gaussian PDF Modeling of Turbulent Boundary Layer Fluctuating Pressure Excitation

NASA Technical Reports Server (NTRS)

Steinwolf, Alexander; Rizzi, Stephen A.

2003-01-01

The purpose of the study is to investigate properties of the probability density function (PDF) of turbulent boundary layer fluctuating pressures measured on the exterior of a supersonic transport aircraft. It is shown that fluctuating pressure PDFs differ from the Gaussian distribution even for surface conditions having no significant discontinuities. The PDF tails are wider and longer than those of the Gaussian model. For pressure fluctuations upstream of forward-facing step discontinuities and downstream of aft-facing step discontinuities, deviations from the Gaussian model are more significant and the PDFs become asymmetrical. Various analytical PDF distributions are used and further developed to model this behavior.

Evidence for pressure-tuned quantum structural fluctuations in KCuF3

NASA Astrophysics Data System (ADS)

Yuan, S.; Kim, M.; Seeley, J.; Lal, S.; Abbamonte, P.; Cooper, S. L.

2012-02-01

Frustrated magnetic systems are currently of great interest because of the possibility that these materials exhibit novel ground states such as orbital and spin liquids. We provide evidence in the orbital-ordering material KCuF3 for pressure-tuned quantum melting of a static structural phase to a phase that dynamically fluctuates even near T ˜ 0K.[1] Pressure-dependent Raman scattering measurements show that applied pressure above P* ˜ 7kbar reverses a low temperature structural distortion in KCuF3, resulting in the development of a φ ˜ 0 fluctuational (quasielastic) response near T ˜ 0K. This pressure-induced fluctuational response is temperature independent and exhibits a characteristic fluctuation rate that is much larger than the temperature, γ >> KBT, consistent with quantum fluctuations of the CuF6 octahedra. We show that a previous developed model of pseudospin-phonon coupling qualitatively describes both the temperature- and pressure-dependent evolution of the Raman spectra of KCuF3. Work supported by the U.S. Department of Energy under Award No. DE-FG02-07ER46453 and by the National Science Foundation under Grant NSF DMR 08-56321. [4pt] [1] S. Yuan et al., arXiv:1107.1433 (2011).

Upper bound on the Abelian gauge coupling from asymptotic safety

NASA Astrophysics Data System (ADS)

Eichhorn, Astrid; Versteegen, Fleur

2018-01-01

We explore the impact of asymptotically safe quantum gravity on the Abelian gauge coupling in a model including a charged scalar, confirming indications that asymptotically safe quantum fluctuations of gravity could trigger a power-law running towards a free fixed point for the gauge coupling above the Planck scale. Simultaneously, quantum gravity fluctuations balance against matter fluctuations to generate an interacting fixed point, which acts as a boundary of the basin of attraction of the free fixed point. This enforces an upper bound on the infrared value of the Abelian gauge coupling. In the regime of gravity couplings which in our approximation also allows for a prediction of the top quark and Higgs mass close to the experimental value [1], we obtain an upper bound approximately 35% above the infrared value of the hypercharge coupling in the Standard Model.

Limits of Gaussian fluctuations in the cosmic microwave background at 19.2 GHz

NASA Technical Reports Server (NTRS)

Boughn, S. P.; Cheng, E. S.; Cottingham, D. A.; Fixsen, D. J.

1992-01-01

The Northern Hemisphere data from the 19.2 GHz full sky survey are analyzed to place limits on the magnitude of Gaussian fluctuations in the cosmic microwave background implied by a variety of correlation functions. Included among the models tested are the monochromatic and Gaussian-shaped families, and those with power-law spectra for n values between -2 and 1. An upper bound is placed on the quadrupole anisotropy of Delta T/T less than 3.2 x 10 exp -5 rms, and an upper bound on scale-invariant (n = 1) fluctuations of a2 less than 4.5 x 10 exp -5 (95 percent confidence level). There is significant contamination of these data from Galactic emission, and improvement of the modeling of the Galaxy could yield a significant reduction of these upper bounds.

Limits on Gaussian fluctuations in the cosmic microwave background at 19.2 GHz

NASA Technical Reports Server (NTRS)

Boughn, S. P.; Cheng, E. S.; Cottingham, D. A.; Fixsen, D. J.

1991-01-01

The Northern Hemisphere data from the 19.2 GHz full sky survey are analyzed to place limits on the magnitude of Gaussian fluctuations in the cosmic microwave background implied by a variety of correlation functions. Included among the models tested are the monochromatic and Gaussian-shaped families, and those with power law spectra for n from -2 to 1. We place an upper bound on the quadrupole anisotropy of DeltaT/T less than 3.2 x 10 exp -5 rms, and an upper bound on scale-invariant (n = 1) fluctuations of a2 less than 4.5 x 10 exp -5 (95 percent confidence level). There is significant contamination of these data from Galactic emission, and improvement of our modeling of the Galaxy could yield a significant reduction of these upper bounds.

Analysis of Numerical Simulation Database for Pressure Fluctuations Induced by High-Speed Turbulent Boundary Layers

NASA Technical Reports Server (NTRS)

Duan, Lian; Choudhari, Meelan M.

2014-01-01

Direct numerical simulations (DNS) of Mach 6 turbulent boundary layer with nominal freestream Mach number of 6 and Reynolds number of Re(sub T) approximately 460 are conducted at two wall temperatures (Tw/Tr = 0.25, 0.76) to investigate the generated pressure fluctuations and their dependence on wall temperature. Simulations indicate that the influence of wall temperature on pressure fluctuations is largely limited to the near-wall region, with the characteristics of wall-pressure fluctuations showing a strong temperature dependence. Wall temperature has little influence on the propagation speed of the freestream pressure signal. The freestream radiation intensity compares well between wall-temperature cases when normalized by the local wall shear; the propagation speed of the freestream pressure signal and the orientation of the radiation wave front show little dependence on the wall temperature.

Pressure fluctuations on the surface of a cylinder in uniform flow

NASA Technical Reports Server (NTRS)

Ayoub, A.; Karamcheti, K.

1976-01-01

The problem of determining the pressure fluctuations induced on the surface of a cylinder by the fluctuating wake behind it is formulated. A formal solution relating the unsteady surface pressure field to the velocity field in the wake is derived and used to obtain general results independent of cylinder shape and Reynolds number. The case of the circular cylinder is then examined in detail.

Assessment of fluctuating pressure gradient using acceleration spectra in near wall flows

NASA Astrophysics Data System (ADS)

Cadel, Daniel; Lowe, K. Todd

2015-11-01

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.

A study of spin fluctuations and superconductivity in the iron pnictides

NASA Astrophysics Data System (ADS)

Gooch, Melissa J.

In early 2008, Hosono's group published results of their discovery of an iron-based layered superconductor, LaFeAsO1-- xFx (x = 0.11). Their discovery gave new life to condensed matter research, being that it was the first high Tc layered superconductor since the discovery of the cuprates. Within only- a few short months, three additional structures were added to the iron pnictide family. The pnictides share a similar layered structure to that of the cuprates, which sparked questions about what role charge doping plays in the superconductivity of the pnictides. An ideal candidate to investigate the physical properties as the doping varies is KxSr1--xFe 2As2, which forms a solid solution for 0 ≤ x ≤ 1. Upper critical fields, HC2, were investigated for select polycrystalline samples and revealed high HC 2 varies upwards to ˜ 100 T. Pressure measurements revealed similar doping dependent pressure coefficients to the cuprates; however, for the cuprates there is a well understood charge transfer that is induced with the application of pressure. This is not the case for the pnictides where a suppression of the magnetic fluctuations is seen. Resistivity and thermoelectric power measurements provide evidence for a possible hidden magnetic quantum critical point (MQCP). The effects of the MQCP extend up to ˜ 150K and were also seen for K xBa1--xFe 2As2, this suggests that magnetic spin fluctuations may play a crucial role in superconductivity for the pnictides. Superconductivity was seen for KFe2As2, as well as RbFe2As 2, CsFe2As2, and the metastable NaFe2As 2. LiFeAs is an undoped stoichiometric superconductor with a T c = 18 K, but it has been suggested that superconductivity arises from a Li deficiency. These conflicting statements prompted further investigation into the physical properties of LiFeAs. In conclusion, magnetic fluctuations may play a. key role in superconductivity of the pnictides and not charge doping.

Buckling of thermally fluctuating spherical shells: Parameter renormalization and thermally activated barrier crossing

NASA Astrophysics Data System (ADS)

Baumgarten, Lorenz; Kierfeld, Jan

2018-05-01

We study the influence of thermal fluctuations on the buckling behavior of thin elastic capsules with spherical rest shape. Above a critical uniform pressure, an elastic capsule becomes mechanically unstable and spontaneously buckles into a shape with an axisymmetric dimple. Thermal fluctuations affect the buckling instability by two mechanisms. On the one hand, thermal fluctuations can renormalize the capsule's elastic properties and its pressure because of anharmonic couplings between normal displacement modes of different wavelengths. This effectively lowers its critical buckling pressure [Košmrlj and Nelson, Phys. Rev. X 7, 011002 (2017), 10.1103/PhysRevX.7.011002]. On the other hand, buckled shapes are energetically favorable already at pressures below the classical buckling pressure. At these pressures, however, buckling requires to overcome an energy barrier, which only vanishes at the critical buckling pressure. In the presence of thermal fluctuations, the capsule can spontaneously overcome an energy barrier of the order of the thermal energy by thermal activation already at pressures below the critical buckling pressure. We revisit parameter renormalization by thermal fluctuations and formulate a buckling criterion based on scale-dependent renormalized parameters to obtain a temperature-dependent critical buckling pressure. Then we quantify the pressure-dependent energy barrier for buckling below the critical buckling pressure using numerical energy minimization and analytical arguments. This allows us to obtain the temperature-dependent critical pressure for buckling by thermal activation over this energy barrier. Remarkably, both parameter renormalization and thermal activation lead to the same parameter dependence of the critical buckling pressure on temperature, capsule radius and thickness, and Young's modulus. Finally, we study the combined effect of parameter renormalization and thermal activation by using renormalized parameters for the energy barrier in thermal activation to obtain our final result for the temperature-dependent critical pressure, which is significantly below the results if only parameter renormalization or only thermal activation is considered.

Effects of pressure fluctuations on the combustion process in turbulent premixed flames

NASA Astrophysics Data System (ADS)

Beardsell, Guillaume; Lapointe, Simon; Blanquart, Guillaume

2016-11-01

The need for a thorough understanding of turbulence-combustion interactions in compressible flows is driven by recent technological developments in propulsion as well as renewed interest in the development of next generation supersonic and hypersonic vehicles. In such flows, pressure fluctuations displaying a wide range of length and timescales are present. These fluctuations are expected to impact the combustion process to varying degrees, depending amongst other things on the amplitude of the pressure variations and the timescales of the chemical reactions taking place in the flame. In this context, numerical simulations of these flows can provide insight into the impact of pressure fluctuations on the combustion process. In the present work, we analyze data from simulations of statistically-flat premixed n-heptane/air flames at high Karlovitz numbers. The compressible Navier-Stokes equations are solved exactly (DNS) and results obtained with both detailed kinetic modeling and one-step chemistry are considered. The effects of pressure fluctuations on the fuel burning rate are investigated. The findings are compared with results obtained from simulations of one-dimensional premixed flames subjected to various pressure waves.

Spectra of turbulent static pressure fluctuations in jet mixing layers

NASA Technical Reports Server (NTRS)

Jones, B. G.; Adrian, R. J.; Nithianandan, C. K.; Planchon, H. P., Jr.

1977-01-01

Spectral similarity laws are derived for the power spectra of turbulent static pressure fluctuations by application of dimensional analysis in the limit of large turbulent Reynolds number. The theory predicts that pressure spectra are generated by three distinct types of interaction in the velocity fields: a fourth order interaction between fluctuating velocities, an interaction between the first order mean shear and the third order velocity fluctuations, and an interaction between the second order mean shear rate and the second order fluctuating velocity. Measurements of one-dimensional power spectra of the turbulent static pressure fluctuations in the driven mixing layer of a subsonic, circular jet are presented, and the spectra are examined for evidence of spectral similarity. Spectral similarity is found for the low wavenumber range when the large scale flow on the centerline of the mixing layer is self-preserving. The data are also consistent with the existence of universal inertial subranges for the spectra of each interaction mode.

On the thermodynamics of phase transitions in metal hydrides

NASA Astrophysics Data System (ADS)

di Vita, Andrea

2012-02-01

Metal hydrides are solutions of hydrogen in a metal, where phase transitions may occur depending on temperature, pressure etc. We apply Le Chatelier's principle of thermodynamics to a particular phase transition in TiH x , which can approximately be described as a second-order phase transition. We show that the fluctuations of the order parameter correspond to fluctuations both of the density of H+ ions and of the distance between adjacent H+ ions. Moreover, as the system approaches the transition and the correlation radius increases, we show -with the help of statistical mechanics-that the statistical weight of modes involving a large number of H+ ions (`collective modes') increases sharply, in spite of the fact that the Boltzmann factor of each collective mode is exponentially small. As a result, the interaction of the H+ ions with collective modes makes a tiny suprathermal fraction of the H+ population appear. Our results hold for similar transitions in metal deuterides, too. A violation of an -insofar undisputed-upper bound on hydrogen loading follows.

An experimental study of the sources of fluctuating pressure loads beneath swept shock/boundary-layer interactions

NASA Technical Reports Server (NTRS)

Settles, G. S.; Garg, S.

1993-01-01

An experimental research program providing basic knowledge and establishing a database on the fluctuating pressure loads produced on aerodynamic surfaces beneath three dimensional shock wave/boundary layer interactions is described. Such loads constitute a fundamental problem of critical concern to future supersonic and hypersonic flight vehicles. A turbulent boundary layer on a flat plate is subjected to interactions with swept planar shock waves generated by sharp fins at angle of attack. Fin angles from 10 to 20 deg at freestream Mach numbers of 3 and 4 produce a variety of interaction strengths from weak to very strong. Miniature Kulite pressure transducers flush-mounted in the flat plate are used to measure interaction-induced wall pressure fluctuations. The distributions of properties of the pressure fluctuations, such as their ring levels, amplitude distributions, and power spectra, are also determined. Measurements were made for the first time in the aft regions of these interactions, revealing fluctuating pressure levels as high as 160 dB. These fluctuations are dominated by low frequency (0-5 kHz) signals. The maximum ring levels in the interactions show an increasing trend with increasing interaction strength. On the other hand, the maximum ring levels in the forward portion of the interactions decrease linearly with increasing interaction sweep back. These ring pressure distributions and spectra are correlated with the features of the interaction flowfield. The unsteadiness of the off-surface flowfield is studied using a new, non-intrusive technique based on the shadow graph method. The results indicate that the entire lambda-shock structure generated by the interaction undergoes relatively low-frequency oscillations. Some regions where particularly strong fluctuations are generated were identified. Fluctuating pressure measurements are also made along the line of symmetry of an axisymmetric jet impinging upon a flat plate at an angle. This flow was chosen as a simple analog to the impinging jet region found in the rear portion of the shock wave/boundary layer interactions under study. It is found that a sharp peak in ring pressure level exists at or near the mean stagnation point. It is suggested that the phenomena responsible for this peak may be active in the swept interactions as well, and may cause the extremely high fluctuating pressures observed in the impinging jet region in the present experimental program.

Specific Features of Pressure-Fluctuation Fields in the Vicinity of a Forward-Facing Step-Backward-Facing Step Configuration

NASA Astrophysics Data System (ADS)

Golubev, A. Yu.

2018-01-01

A computational model of inhomogeneous pressure-fluctuation fields in the vicinity of a forward-facing step-backward-facing step configuration taking into account the high degree of their mutual correlation (global correlation) is generalized from experimental data. It is shown that when determining the characteristics of pressure fluctuations that act on an elastic structure, the global correlation is represented by an additional inhomogeneous field. It is demonstrated that a high degree of correlation may lead to a significant change in the main characteristics of the pressure-fluctuation field in the wake behind the configuration. This is taken into consideration in the model by correcting the local properties of this field.

Quasilinear quantum magnetoresistance in pressure-induced nonsymmorphic superconductor chromium arsenide

NASA Astrophysics Data System (ADS)

Niu, Q.; Yu, W. C.; Yip, K. Y.; Lim, Z. L.; Kotegawa, H.; Matsuoka, E.; Sugawara, H.; Tou, H.; Yanase, Y.; Goh, Swee K.

2017-06-01

In conventional metals, modification of electron trajectories under magnetic field gives rise to a magnetoresistance that varies quadratically at low field, followed by a saturation at high field for closed orbits on the Fermi surface. Deviations from the conventional behaviour, for example, the observation of a linear magnetoresistance, or a non-saturating magnetoresistance, have been attributed to exotic electron scattering mechanisms. Recently, linear magnetoresistance has been observed in many Dirac materials, in which the electron-electron correlation is relatively weak. The strongly correlated helimagnet CrAs undergoes a quantum phase transition to a nonmagnetic superconductor under pressure. Here we observe, near the magnetic instability, a large and non-saturating quasilinear magnetoresistance from the upper critical field to 14 T at low temperatures. We show that the quasilinear magnetoresistance may arise from an intricate interplay between a nontrivial band crossing protected by nonsymmorphic crystal symmetry and strong magnetic fluctuations.

Reproducibility of intraocular pressure peak and fluctuation of the water-drinking test.

PubMed

Hatanaka, Marcelo; Alencar, Luciana M; De Moraes, Carlos G; Susanna, Remo

2013-01-01

The water-drinking test has been used as a stress test to evaluate the drainage system of the eye. However, in order to be clinically applicable,a test must provide reproducible results with consistent measurements. This study was performed to verify the reproducibility of intraocular pressure peaks and fluctuation detected during the water-drinking test in patients with ocular hypertension and open-angle glaucoma. A prospective analysis of patients in a tertiary care unit for glaucoma treatment. Twenty-four ocular hypertension and 64 open-angle glaucoma patients not under treatment. The water-drinking test was performed in 2 consecutive days by the same examiners in patients not under treatment. Reproducibility was assessed using the intraclass correlation coefficient. Peak and fluctuation of intraocular pressure obtained with the water-drinking test were analysed for reproducibility. Eighty-eight eyes from 24 ocular hypertension and 64 open-angle glaucoma patients not under treatment were evaluated. Test and retest intraocular pressure peak values were 28.38 ± 4.64 and 28.38 ± 4.56 mmHg, respectively (P = 1.00). Test and retest intraocular pressure fluctuation values were 5.75 ± 3.9 and 4.99 ± 2.7 mmHg, respectively (P = 0.06). Based on intraclass coefficient, reproducibility was excellent for peak intraocular pressure (intraclass correlation coefficient = 0.79) and fair for intraocular pressure fluctuation (intraclass correlation coefficient = 0.37). Intraocular pressure peaks detected during the water-drinking test presented excellent reproducibility, whereas the reproducibility of fluctuation was considered fair. © 2012 The Authors. Clinical and Experimental Ophthalmology © 2012 Royal Australian and New Zealand College of Ophthalmologists.

Initial Assessment of the Ares I-X Launch Vehicle Upper Stage to Vibroacoustic Flight Environments

NASA Technical Reports Server (NTRS)

Larko, Jeffrey M.; Hughes, William O.

2008-01-01

The Ares I launch vehicle will be NASA s first new launch vehicle since 1981. Currently in design, it will replace the Space Shuttle in taking astronauts to the International Space Station, and will eventually play a major role in humankind s return to the Moon and eventually to Mars. Prior to any manned flight of this vehicle, unmanned test readiness flights will be flown. The first of these readiness flights, named Ares I-X, is scheduled to be launched in April 2009. The NASA Glenn Research Center is responsible for the design, manufacture, test and analysis of the Ares I-X upper stage simulator (USS) element. As part of the design effort, the structural dynamic response of the Ares I-X launch vehicle to its vibroacoustic flight environments must be analyzed. The launch vehicle will be exposed to extremely high acoustic pressures during its lift-off and aerodynamic stages of flight. This in turn will cause high levels of random vibration on the vehicle's outer surface that will be transmitted to its interior. Critical flight equipment, such as its avionics and flight guidance components are susceptible to damage from this excitation. This study addresses the modelling, analysis and predictions from examining the structural dynamic response of the Ares I-X upper stage to its vibroacoustic excitations. A statistical energy analysis (SEA) model was used to predict the high frequency response of the vehicle at locations of interest. Key to this study was the definition of the excitation fields corresponding to lift off acoustics and the unsteady aerodynamic pressure fluctuations during flight. The predicted results will be used by the Ares I-X Project to verify the flight qualification status of the Ares I-X upper stage components.

Shock wave oscillation driven by turbulent boundary layer fluctuations

NASA Technical Reports Server (NTRS)

Plotkin, K. J.

1972-01-01

Pressure fluctuations due to the interaction of a shock wave with a turbulent boundary layer were investigated. A simple model is proposed in which the shock wave is convected from its mean position by velocity fluctuations in the turbulent boundary layer. Displacement of the shock is assumed limited by a linear restoring mechanism. Predictions of peak root mean square pressure fluctuation and spectral density are in excellent agreement with available experimental data.

Fluctuation Pressure Assisted Ejection of DNA From Bacteriophage

NASA Astrophysics Data System (ADS)

Harrison, Michael J.

2011-03-01

The role of thermal pressure fluctuations excited within tightly packaged DNA while it is ejected from protein capsid shells is discussed in a model calculation. At equilibrium before ejection we assume the DNA is folded many times into a bundle of parallel segments that forms an equilibrium conformation at minimum free energy, which presses tightly against capsid walls. Using a canonical ensemble at temperature T we calculate internal pressure fluctuations against a slowly moving or static capsid mantle for an elastic continuum model of the folded DNA bundle. It is found that fluctuating pressures on the capsid from thermal excitation of longitudinal acoustic vibrations in the bundle whose wavelengths are exceeded by the bend persistence length may have root-mean-square values that are several tens of atmospheres for typically small phage dimensions. Comparisons are given with measured data on three mutants of lambda phage with different base pair lengths and total genome ejection pressures.

Dynamic characteristic investigation on the fuel pressure of diesel engines electronic in-line pump system

NASA Astrophysics Data System (ADS)

Liu, You; Yuan, Zhi-Guo; Fan, Li-Yun; Tian, Bin-Qi

2010-12-01

The electronic in-line pump (EIP) is a complex system consisting of mechanical, hydraulic, and electromagnetic parts. Experimental study showed that the fuel pressure of the plunger and the fuel drainage of the pressure system after fuel injection could result in fuel pressure fluctuation in the low pressure system. Such fluctuation exhibited pulsating cycle fluctuation as the amplitude rose with the increase of the injection pulse width. The time domain analysis found that the pressure time history curve and injection cylinders corresponded with a one-to-one relationship. By frequency domain analysis, the result was that with the increase of the working cylinder number, the high frequency amplitude gradually increased and the basic frequency amplitude gradually decreased. The conclusion was that through wavelet transformation, the low pressure signal simultaneously moved towards low frequency as the high frequency of the wavelet transformation signal with the working cylinder number increased. Lastly, by using the numerical model, the study investigated the simulation research concerning the relationship of the fluctuation dynamic characteristic in the low pressure system and the fuel injection characteristic of the high pressure system, completing the conclusions obtained by the experimental study.

An investigation of combustion and entropy noise

NASA Technical Reports Server (NTRS)

Strahle, W. C.

1977-01-01

The relative importance of entropy and direct combustion noise in turbopropulsion systems and the parameters upon which these noise sources depend were studied. Theory and experiment were employed to determine that at least with the apparatus used here, entropy noise can dominate combustion noise if there is a sufficient pressure gradient terminating the combustor. Measurements included combustor interior fluctuating pressure, near and far field fluctuating pressure, and combustor exit plane fluctuating temperatures, as well as mean pressures and temperatures. Analysis techniques included spectral, cross-correlation, cross power spectra, and ordinary and partial coherence analysis. Also conducted were combustor liner modification experiments to investigate the origin of the frequency content of combustion noise. Techniques were developed to extract nonpropagational pseudo-sound and the heat release fluctuation spectra from the data.

The pressure and entropy of a unitary Fermi gas with particle-hole fluctuation

NASA Astrophysics Data System (ADS)

Gong, Hao; Ruan, Xiao-Xia; Zong, Hong-Shi

2018-01-01

We calculate the pressure and entropy of a unitary Fermi gas based on universal relations combined with our previous prediction of energy which was calculated within the framework of the non-self-consistent T-matrix approximation with particle-hole fluctuation. The resulting entropy and pressure are compared with the experimental data and the theoretical results without induced interaction. For entropy, we find good agreement between our results with particle-hole fluctuation and the experimental measurements reported by ENS group and MIT experiment. For pressure, our results suffer from a systematic upshift compared to MIT data.

Wall-pressure fluctuations beneath a spatially evolving turbulent boundary layer

NASA Astrophysics Data System (ADS)

Mahesh, Krishnan; Kumar, Praveen

2016-11-01

Wall-pressure fluctuations beneath a turbulent boundary layer are important in applications dealing with structural deformation and acoustics. Simulations are performed for flat plate and axisymmetric, spatially evolving zero-pressure-gradient turbulent boundary layers at inflow Reynolds number of 1400 and 2200 based on momentum thickness. The simulations generate their own inflow using the recycle-rescale method. The results for mean velocity and second-order statistics show excellent agreement with the data available in literature. The spectral characteristics of wall-pressure fluctuations and their relation to flow structure will be discussed. This work is supported by ONR.

Effects of sound level fluctuations on annoyance caused by aircraft-flyover noise

NASA Technical Reports Server (NTRS)

Mccurdy, D. A.

1979-01-01

A laboratory experiment was conducted to determine the effects of variations in the rate and magnitude of sound level fluctuations on the annoyance caused by aircraft-flyover noise. The effects of tonal content, noise duration, and sound pressure level on annoyance were also studied. An aircraft-noise synthesis system was used to synthesize 32 aircraft-flyover noise stimuli representing the factorial combinations of 2 tone conditions, 2 noise durations, 2 sound pressure levels, 2 level fluctuation rates, and 2 level fluctuation magnitudes. Thirty-two test subjects made annoyance judgements on a total of 64 stimuli in a subjective listening test facility simulating an outdoor acoustic environment. Variations in the rate and magnitude of level fluctuations were found to have little, if any, effect on annoyance. Tonal content, noise duration, sound pressure level, and the interaction of tonal content with sound pressure level were found to affect the judged annoyance significantly. The addition of tone corrections and/or duration corrections significantly improved the annoyance prediction ability of noise rating scales.

Turbulent pressure fluctuations measured during CHATS

Treesearch

Steven P. Oncley; William J. Massman; Edward G. Patton

2008-01-01

Fast-response pressure fluctuations were included in the Canopy Horizontal Array of Turbulence Study (CHATS) at several heights within and just above the canopy in a walnut orchard. Two independent systems were intercompared and then separated. We present an evaluation of turbulence statistics - including the pressure transport term in the turbulence kinetic energy...

EXPERIMENTAL ATHEROSCLEROSIS AND BLOOD PRESSURE IN THE RABBIT

PubMed Central

Dominguez, R.

1927-01-01

1. Van Leersum's range for the normal blood pressure in the rabbit, as recorded by his method, is confirmed. 2. Van Leersum's conclusion concerning the influence of a liver diet on the blood pressure of the rabbit is not substantiated by his data, since the fluctuations of blood pressure he obtained do not surpass his own recorded figures for normal animals. 3. Fluctuations of systolic blood pressure beyond the "normal" range are not necessary for the production of experimental atherosclerosis of the aorta in rabbits. Inversely, egg yolk feeding experiments in rabbits in which atherosclerosis of varying degree, even extreme, is obtained, are not accompanied by an elevation of blood pressure outside the "normal" range. 4. The fluctuations of blood pressure observed during experimental atherosclerosis do not simulate the condition of essential hypertension in man. PMID:19869349

An experimental study of fluctuating pressure loads beneath swept shock/boundary-layer interactions

NASA Technical Reports Server (NTRS)

Settles, Gary S.

1991-01-01

A database is established on the fluctuating pressure loads produced on aerodynamic surfaces beneath 3-D shock wave/boundary layer interactions. Such loads constitute a fundamental problem of critical concern to future supersonic and hypersonic flight vehicles. A turbulent boundary layer on a flat plate is subjected to interactions with swept planar shock waves generated by sharp fins. Fin angles from 5 to 25 deg at freestream Mach numbers between 2.5 and 4 produce a variety of interaction strengths from weak to very strong. Miniature Kulite pressure transducers mounted in the flat plate were used to measure interaction-induced wall pressure fluctuations. These data will be correlated with proposed new optical data on the fluctuations of the interaction structure, especially that of the lambda-shock system and its associated high-speed jet impingement.

High-Reynolds-number turbulent-boundary-layer wall pressure fluctuations with skin-friction reduction by air injection.

PubMed

Winkel, Eric S; Elbing, Brian R; Ceccio, Steven L; Perlin, Marc; Dowling, David R

2008-05-01

The hydrodynamic pressure fluctuations that occur on the solid surface beneath a turbulent boundary layer are a common source of flow noise. This paper reports multipoint surface pressure fluctuation measurements in water beneath a high-Reynolds-number turbulent boundary layer with wall injection of air to reduce skin-friction drag. The experiments were conducted in the U.S. Navy's Large Cavitation Channel on a 12.9-m-long, 3.05-m-wide hydrodynamically smooth flat plate at freestream speeds up to 20 ms and downstream-distance-based Reynolds numbers exceeding 200 x 10(6). Air was injected from one of two spanwise slots through flush-mounted porous stainless steel frits (approximately 40 microm mean pore diameter) at volume flow rates from 17.8 to 142.5 l/s per meter span. The two injectors were located 1.32 and 9.78 m from the model's leading edge and spanned the center 87% of the test model. Surface pressure measurements were made with 16 flush-mounted transducers in an "L-shaped" array located 10.7 m from the plate's leading edge. When compared to no-injection conditions, the observed wall-pressure variance was reduced by as much as 87% with air injection. In addition, air injection altered the inferred convection speed of pressure fluctuation sources and the streamwise coherence of pressure fluctuations.

Fluctuations of wormlike micelle fluids in capillary flow

NASA Astrophysics Data System (ADS)

Salipante, Paul; Meek, Stephen; Hudson, Steven; Polymers; Complex Fluids Group Team

2017-11-01

We investigate the effect of entrance geometry on the flow stability of wormlike micelles solutions in capillary flow. These solutions exhibit strong shear thinning behavior resulting from micelle breakage and have been observed to undergo large flow rate fluctuations. We investigate these fluctuations using simultaneous measurements of flow rate and pressure drop across a capillary, and we adjust entrance geometry. With a tapered constriction, we observe large persistent fluctuations above a critical flow rate, characterized by rapid decreases in the pressure drop with corresponding increase in flow rate followed by a period of recovery where pressure increases and flow rate decreases. Flow field observations in the tapered entrance show large flow circulations. An abrupt contraction produces smaller transient fluidized jets forming upstream of the constriction and the magnitude of the fluctuations are significantly diminished. The effect of fluid properties is studied by comparing the magnitude and timescales of the fluctuations for surfactant systems with different relaxation times. The onset of fluctuations is compared to a criterion for the onset of elastic instabilities and the magnitude is compared to estimates for changes in channel resistance. NIST on a Chip.

Identification and measurement of combustion noise from a turbofan engine using correlation and coherence techniques. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Karchmer, A. M.

1977-01-01

Fluctuating pressure measurements within the combustor and tailpipe of a turbofan engine are made simultaneously with far field acoustic measurements. The pressure measurements within the engine are accomplished with cooled semi-infinite waveguide probes utilizing conventional condenser microphones as the transducers. The measurements are taken over a broad range of engine operating conditions and for 16 far field microphone positions between 10 deg and 160 deg relative to the engine inlet axis. Correlation and coherence techniques are used to determine the relative phase and amplitude relationships between the internal pressures and far field acoustic pressures. The results indicate that the combustor is a low frequency source region for acoustic propagation through the tailpipe and out to the far field. Specifically, it is found that the relation between source pressure and the resulting sound pressure involves a 180 deg phase shift. The latter result is obtained by Fourier transforming the cross correlation function between the source pressure and acoustic pressure after removing the propagation delay time. Further, it is found that the transfer function between the source pressure and acoustic pressure has a magnitude approximately proportional to frequency squared. These results are shown to be consistent with a model using a modified source term in Lighthill's turbulence stress tensor, wherein the fluctuating Reynolds stresses are replaced with the pressure fluctuations due to fluctuating entropy.

Effects of experimentally measured pressure oscillations on the vibration of a solid rocket motor

NASA Technical Reports Server (NTRS)

Schoenster, J. A.; Pierce, H. B.

1972-01-01

Results are presented of firing a Nike rocket against a backstop for the purpose of obtaining pressure fluctuations in the rocket case and determining their relationship to structural vibrations of the case. Special care was required to obtain these pressure fluctuations because of the much higher static pressure generated in the rocket. Very small pressure fluctuations within the rocket case can cause significant vibration levels. A previously observed high frequency was shown to decrease with time before completely disappearing at about 1 second of burning time. The vibration of the case itself is probably related to the longitudinal structural modes at frequencies below 500 Hz and is dependent on local structural conditions at frequencies above this value.

High-frequency pressure variations in the vicinity of a surface CO2 flux chamber

Treesearch

Eugene S. Takle; James R. Brandle; R. A. Schmidt; Rick Garcia; Irina V. Litvina; William J. Massman; Xinhua Zhou; Geoffrey Doyle; Charles W. Rice

2003-01-01

We report measurements of 2Hz pressure fluctuations at and below the soil surface in the vicinity of a surface-based CO2 flux chamber. These measurements were part of a field experiment to examine the possible role of pressure pumping due to atmospheric pressure fluctuations on measurements of surface fluxes of CO2. Under the moderate wind speeds, warm temperatures,...

Vortex dynamics and surface pressure fluctuations on a normal flat plate

NASA Astrophysics Data System (ADS)

Hemmati, Arman; Wood, David H.; Martinuzzi, Robert J.; Ferrari, Simon W.; Hu, Yaoping

2016-11-01

The effect of vortex formation and interactions on surface pressure fluctuations is examined in the wake of a normal flat plate by analyzing Direct Numerical Simulations at Re =1200. A novel local maximum score-based 3D method is used to track vortex development in the region close to the plate where the major contributions to the surface pressure are generated. Three distinct vortex shedding regimes are identified by changes in the lift and drag fluctuations. The instances of maximum drag coincide with impingement of newly formed vortices on the plate. This results in large and concentrated areas of rotational and strain contributions to generation of pressure fluctuations. Streamwise vortex straining and chordwise stretching are correlated with the large ratios of streamwise to chordwise normal stresses and regions of significant rotational contribution to the pressure. In contrast at the minimum drag, the vorticity field close to the plate is disorganized, and vortex roll-up occurs farther downstream. This leads to a uniform distribution of pressure. This study was supported by Alberta Innovates Technology Futures (AITF) and Natural Sciences and Engineering Research Council of Canada (NSERC).

A root-mean-square pressure fluctuations model for internal flow applications

NASA Technical Reports Server (NTRS)

Chen, Y. S.

1985-01-01

A transport equation for the root-mean-square pressure fluctuations of turbulent flow is derived from the time-dependent momentum equation for incompressible flow. Approximate modeling of this transport equation is included to relate terms with higher order correlations to the mean quantities of turbulent flow. Three empirical constants are introduced in the model. Two of the empirical constants are estimated from homogeneous turbulence data and wall pressure fluctuations measurements. The third constant is determined by comparing the results of large eddy simulations for a plane channel flow and an annulus flow.

Numerical Study of Pressure Fluctuations due to a Mach 6 Turbulent Boundary Layer

NASA Technical Reports Server (NTRS)

Duan, Lian; Choudhari, Meelan M.

2013-01-01

Direct numerical simulations (DNS) are used to examine the pressure fluctuations generated by a Mach 6 turbulent boundary layer with nominal freestream Mach number of 6 and Reynolds number of Re(sub t) approx. =. 464. The emphasis is on comparing the primarily vortical pressure signal at the wall with the acoustic freestream signal under higher Mach number conditions. Moreover, the Mach-number dependence of pressure signals is demonstrated by comparing the current results with those of a supersonic boundary layer at Mach 2.5 and Re(sub t) approx. = 510. It is found that the freestream pressure intensity exhibits a strong Mach number dependence, irrespective of whether it is normalized by the mean wall shear stress or by the mean pressure, with the normalized fluctuation amplitude being significantly larger for the Mach 6 case. Spectral analysis shows that both the wall and freestream pressure fluctuations of the Mach 6 boundary layer have enhanced energy content at high frequencies, with the peak of the premultiplied frequency spectrum of freestream pressure fluctuations being at a frequency of omega(delta)/U(sub infinity) approx. = 3.1, which is more than twice the corresponding frequency in the Mach 2.5 case. The space-time correlations indicate that the pressure-carrying eddies for the higher Mach number case are of smaller size, less elongated in the spanwise direction, and convect with higher convection speeds relative to the Mach 2.5 case. The demonstrated Mach-number dependence of the pressure field, including radiation intensity, directionality, and convection speed, is consistent with the trend exhibited in experimental data and can be qualitatively explained by the notion of "eddy Mach wave" radiation.

Fiber-optic interferometric sensors for measurements of pressure fluctuations: Experimental evaluation

NASA Technical Reports Server (NTRS)

Cho, Y. C.; Soderman, P. T.

1993-01-01

This paper addresses an anechoic chamber evaluation of a fiber-optic interferometric sensor (fiber-optic microphone), which is being developed at NASA Ames Research Center for measurements of pressure fluctuations in wind tunnels.

Prediction of fluctuating pressure environments associated with plume-induced separated flow fields

NASA Technical Reports Server (NTRS)

Plotkin, K. J.

1973-01-01

The separated flow environment induced by underexpanded rocket plumes during boost phase of rocket vehicles has been investigated. A simple semi-empirical model for predicting the extent of separation was developed. This model offers considerable computational economy as compared to other schemes reported in the literature, and has been shown to be in good agreement with limited flight data. The unsteady pressure field in plume-induced separated regions was investigated. It was found that fluctuations differed from those for a rigid flare only at low frequencies. The major difference between plume-induced separation and flare-induced separation was shown to be an increase in shock oscillation distance for the plume case. The prediction schemes were applied to PRR shuttle launch configuration. It was found that fluctuating pressures from plume-induced separation are not as severe as for other fluctuating environments at the critical flight condition of maximum dynamic pressure.

Acoustic gravity microseismic pressure signal at shallow stations

NASA Astrophysics Data System (ADS)

Peureux, Charles; Ardhuin, Fabrice; Royer, Jean-Yves

2017-04-01

It has been known for decades that the background permanent seismic noise, the so-called microseimic signal, is generated by the nonlinear interaction of oppositely travelling ocean surface waves [Longuet-Higgins 1951]. It can especially be used to infer the time variability of short ocean waves statistics [Peureux and Ardhuin 2016]. However, better quantitative estimates of the latter are made difficult due to a poor knowledge of the Earth's crust characteristics, whose coupling with acoustic modes can affect large uncertainties to the frequency response at the bottom of the ocean. The pressure field at depths less than an acoustic wave length to the surface is made of evanescent acoustic-gravity modes [Cox and Jacobs 1989]. For this reason, they are less affected by the ocean bottom composition. This near field is recorded and analyzed in the frequency range 0.1 to 0.5 Hz approximately, at two locations : at a shallow site in the North-East Atlantic continental shelf and a deep water site in the Southern Indian ocean, at the ocean bottom and 100 m below sea-surface and in the upper part of the water column respectively. Evanescent and propagating Rayleigh modes are compared against theoretical predictions. Comparisons against surface waves hindcast based on WAVEWATCH(R) III modelling framework help assessing its performances and can be used to help future model improvements. References Longuet-Higgins, M. S., A Theory of the Origin of Microseisms, Philos. Trans. Royal Soc. A, The Royal Society, 1950, 243, 1-3. Peureux, C. and Ardhuin, F., Ocean bottom pressure records from the Cascadia array and short surface gravity waves, J. Geophys. Res. Oceans, 2016, 121, 2862-2873. Cox, C. S. & Jacobs, D. C., Cartesian diver observations of double frequency pressure fluctuations in the upper levels of the ocean, Geophys. Res. Lett., 1989, 16, 807-810.

Cold hands, warm feet: sleep deprivation disrupts thermoregulation and its association with vigilance.

PubMed

Romeijn, Nico; Verweij, Ilse M; Koeleman, Anne; Mooij, Anne; Steimke, Rosa; Virkkala, Jussi; van der Werf, Ysbrand; Van Someren, Eus J W

2012-12-01

Vigilance is affected by induced and spontaneous skin temperature fluctuations. Whereas sleep deprivation strongly affects vigilance, no previous study examined in detail its effect on human skin temperature fluctuations and their association with vigilance. In a repeated-measures constant routine design, skin temperatures were assessed continuously from 14 locations while performance was assessed using a reaction time task, including eyes-open video monitoring, performed five times a day for 2 days, after a normal sleep or sleep deprivation night. Participants were seated in a dimly lit, temperature-controlled laboratory. Eight healthy young adults (five males, age 22.0 ± 1.8 yr (mean ± standard deviation)). One night of sleep deprivation. Mixed-effect regression models were used to evaluate the effect of sleep deprivation on skin temperature gradients of the upper (ear-mastoid), middle (hand-arm), and lower (foot-leg) body, and on the association between fluctuations in performance and in temperature gradients. Sleep deprivation induced a marked dissociation of thermoregulatory skin temperature gradients, indicative of attenuated heat loss from the hands co-occurring with enhanced heat loss from the feet. Sleep deprivation moreover attenuated the association between fluctuations in performance and temperature gradients; the association was best preserved for the upper body gradient. Sleep deprivation disrupts coordination of fluctuations in thermoregulatory skin temperature gradients. The dissociation of middle and lower body temperature gradients may therefore be evaluated as a marker for sleep debt, and the upper body gradient as a possible aid in vigilance assessment when sleep debt is unknown. Importantly, our findings suggest that sleep deprivation affects the coordination between skin blood flow fluctuations and the baroreceptor-mediated cardiovascular regulation that prevents venous pooling of blood in the lower limbs when there is the orthostatic challenge of an upright posture.

Development and Assessment of Altitude Adjustable Convergent Divergent Nozzles Using Passive Flow Control

NASA Astrophysics Data System (ADS)

Mandour Eldeeb, Mohamed

The backward facing steps nozzle (BFSN) is a new developed flow adjustable exit area nozzle. It consists of two parts, the first is a base nozzle with small area ratio and the second part is a nozzle extension with surface consists of backward facing steps. The steps number and heights are carefully chosen to produce controlled flow separation at steps edges that adjust the nozzle exit area at all altitudes (pressure ratios). The BFSN performance parameters are assessed numerically in terms of thrust and side loads against the dual-bell nozzle with the same pressure ratios and cross sectional areas. Cold flow inside the planar BFSN and planar DBN are simulated using three-dimensional turbulent Navier-Stoke equations solver at different pressure ratios. The pressure distribution over the upper and the lower nozzles walls show symmetrical flow separation location inside the BFSN and an asymmetrical flow separation location inside the DBN at same vertical plane. The side loads are calculated by integrate the pressure over the nozzles walls at different pressure ratios for both nozzles. Time dependent solution for the DBN and the BFSN are obtained by solving two-dimensional turbulent flow. The side loads over the upper and lower nozzles walls are plotted against the flow time. The BFSN side loads history shows a small values of fluctuated side loads compared with the DBN which shows a high values with high fluctuations. Hot flow 3-D numerical solutions inside the axi-symmetric BFSN and DBN are obtained at different pressure ratios and compared to assess the BFSN performance against the DBN. Pressure distributions over the nozzles walls at different circumferential angels are plotted for both nozzles. The results show that the flow separation location is axi-symmetric inside the BFSN with symmetrical pressure distributions over the nozzle circumference at different pressure ratios. While the DBN results show an asymmetrical flow separation locations over the nozzle circumference at all pressure ratios.The results show that the side loads in the BFSN is 0.01%-0.6% of its value in the DBN for same pressure ratio. For further confirmation of the axi-symmetric nature of the flow in the BFSN, 2-D axi-symmetric solutions are obtained at same pressure ratios and boundary conditions. The flow parameters at the nozzle exit are calculated the 3-D and the 2-D solutions and compared to each other. The maximum difference between the 3-D and the 2-D solutions is less than 1%. Parametric studies are carried out with number of the backward facing steps varied from two to forty. The results show that as the number of backward facing steps increase, the nozzle performance in terms of thrust approach the DBN performance. The BFSN with two and six steps are simulated for pressure ratios range from 148 to 1500 and compared with the DBN and a conventional bell nozzle. Expandable BFSN study is carried out on the BFSN with two steps where the nozzle operation is divided into three modes related to the operating altitude (PR). Backward facing steps concept is applied to a full scale conventional bell nozzle by adding two backward facing steps at the end of the nozzle increasing its expansion area results in 1.8% increasing in its performance in terms of thrust coefficient at high altitudes.

Study of stator-vane fluctuating pressures in a turbofan engine for static and flight tests

NASA Technical Reports Server (NTRS)

Mueller, A. W.

1984-01-01

As part of a program to study the fan noise generated from turbofan engines, fluctuating surface pressures induced by fan-rotor wakes were measured on core- and bypass-stator outlet guide vanes of a modified JT15D-1 engine. Tests were conducted with the engine operating on an outdoor test stand and in flight. The amplitudes of pressures measured at fan-rotor blade-passage fundamental frequencies were generally higher and appeared less stable for the static tests than for the flight tests. Fluctuating pressures measured at the blade-passage frequency of the high-speed core compressor were interpreted to be acoustic; however, disturbance trace velocities for either the convected rotor wakes or acoustic pressures were difficult to interpret because of the complex environment.

[Effect of maximum blood pressure fluctuation on prognosis of patients with acute ischemic stroke within 24 hours after hospital admission].

PubMed

Wang, H; Tang, Y; Zhang, Y; Xu, K; Zhao, J B

2018-05-10

Objective: To investigate the relationship between the maximum blood pressure fluctuation within 24 hours after admission and the prognosis at discharge. Methods: The patients with ischemic stroke admitted in Department of Neurology of the First Affiliated Hospital of Harbin Medical University within 24 hours after onset were consecutively selected from April 2016 to March 2017. The patients were grouped according to the diagnostic criteria of hypertension. Ambulatory blood pressure of the patients within 24 hours after admission were measured with bedside monitors and baseline data were collected. The patients were scored by NIHSS at discharge. The relationships between the maximum values of systolic blood pressure (SBP) or diastolic blood pressure (DBP) and the prognosis at discharge were analyzed. Results: A total of 521 patients with acute ischemic stroke were enrolled. They were divided into normal blood pressure group (82 cases) and hypertension group(439 cases). In normal blood pressure group, the maximum values of SBP and DBP were all in normal distribution ( P >0.05). The maximum value of SBP fluctuation was set at 146.6 mmHg. After adjustment for potential confounders, the OR for poor prognosis at discharge in patients with SBP fluctuation ≥146.6 mmHg was 2.669 (95 %CI : 0.594-11.992) compared with those with SBP fluctuation <146.6 mmHg. The maximum value of DBP fluctuation was set at 90.0 mmHg, and the adjusted OR for poor prognosis at discharge in patients with DBP fluctuation ≥90.0 mmHg was 0.416 (95 %CI : 0.087-1.992) compared with those with DBP fluctuation <90.0 mmHg. In hypertension group, the maximum values of SBP and DBP were not in normal distribution ( P <0.05). The maximum value of SBP fluctuation was set at median 171.0 mmHg. After adjustment for the confounders, the greater the maximum of SBP, the greater the risk of poor prognosis at discharge was, the OR was 1.636 (95 %CI : 1.014-2.641). The maximum value of DBP fluctuation was set at median 98.0 mmHg. After adjustment for the confounders, the greater the maximum of DBP, the greater the risk of poor prognosis at discharge was, the OR was 1.645 (95 %CI : 1.003-2.697). Conclusion: In acute ischemic stroke patients with normal blood pressure at admission, the maximum values of SBP and DBP within 24 hours after admission had no relationship with prognosis at discharge. In acute ischemic stroke patients with hypertension at admission, the maximum values of SBP and DBP within 24 hours after admission were associated with poor prognosis at discharge.

Fundamental relations between short-term RR interval and arterial pressure oscillations in humans

NASA Technical Reports Server (NTRS)

Taylor, J. A.; Eckberg, D. L.

1996-01-01

BACKGROUND: One of the principal explanations for respiratory sinus arrhythmia is that it reflects arterial baroreflex buffering of respiration-induced arterial pressure fluctuations. If this explanation is correct, then elimination of RR interval fluctuations should increase respiratory arterial pressure fluctuations. METHODS AND RESULTS: We measured RR interval and arterial pressure fluctuations during normal sinus rhythm and fixed-rate atrial pacing at 17.2+/-1.8 (SEM) beats per minute greater than the sinus rate in 16 healthy men and 4 healthy women, 20 to 34 years of age. Measurements were made during controlled-frequency breathing (15 breaths per minute or 0.25 Hz) with subjects in the supine and 40 degree head-up tilt positions. We characterized RR interval and arterial pressure variabilities in low-frequency (0.05 to 0.15 Hz) and respiratory-frequency (0.20 to 0.30 Hz) ranges with fast Fourier transform power spectra and used cross-spectral analysis to determine the phase relation between the two signals. As expected, cardiac pacing eliminated beat-to-beat RR interval variability. Against expectations, however, cardiac pacing in the supine position significantly reduced arterial pressure oscillations in the respiratory frequency (systolic, 6.8+/-1.8 to 2.9 +/-0.6 mm Hg2/Hz, P=.017). In contrast, cardiac pacing in the 40 degree tilt position increased arterial pressure variability (systolic, 8.0+/-1.8 to 10.8 +/-2.6, P=.027). Cross-spectral analysis showed that 40 degree tilt shifted the phase relation between systolic pressure and RR interval at the respiratory frequency from positive to negative (9 +/-7 degrees versus -17+/-11 degrees, P=.04); that is, in the supine position, RR interval changes appeared to lead arterial pressure changes, and in the upright position, RR interval changes appeared to follow arterial pressure changes. CONCLUSIONS: These results demonstrate that respiratory sinus arrhythmia can actually contribute to respiratory arterial pressure fluctuations. Therefore, respiratory sinus arrhythmia does not represent simple baroreflex buffering of arterial pressure.

Barometric fluctuations in wells tapping deep unconfined aquifers

USGS Publications Warehouse

Weeks, Edwin P.

1979-01-01

Water levels in wells screened only below the water table in unconfined aquifers fluctuate in response to atmospheric pressure changes. These fluctuations occur because the materials composing the unsaturated zone resist air movement and have capacity to store air with a change in pressure. Consequently, the translation of any pressure change at land surface is slowed as it moves through the unsaturated zone to the water table, but it reaches the water surface in the well instantaneously. Thus a pressure imbalance is created that results in a water level fluctuation. Barometric effects on water levels in unconfined aquifers can be computed by solution of the differential equation governing the flow of gas in the unsaturated zone subject to the appropriate boundary conditions. Solutions to this equation for two sets of boundary conditions were applied to compute water level response in a well tapping the Ogallala Formation near Lubbock, Texas from simultaneous microbarograph records. One set of computations, based on the step function unit response solution and convolution, resulted in a very good match between computed and measured water levels. A second set of computations, based on analysis of the amplitude ratios of simultaneous cyclic microbarograph and water level fluctuations, gave inconsistent results in terms of the unsaturated zone pneumatic properties but provided useful insights on the nature of unconfined-aquifer water level fluctuations.

Clinical comparison of automatic, noninvasive measurements of blood pressure in the forearm and upper arm.

PubMed

Schell, Kathleen; Bradley, Elisabeth; Bucher, Linda; Seckel, Maureen; Lyons, Denise; Wakai, Sandra; Bartell, Deborah; Carson, Elizabeth; Chichester, Melanie; Foraker, Teresa; Simpson, Kathleen

2005-05-01

When the upper arm (area from shoulder to elbow) is inaccessible and/or a standard-sized blood pressure cuff does not fit, some healthcare workers use the forearm to measure blood pressure. To compare automatic noninvasive measurements of blood pressure in the upper arm and forearm. A descriptive, correlational comparison study was conducted in the emergency department of a 1071-bed teaching hospital. Subjects were 204 English-speaking patients 6 to 91 years old in medically stable condition who had entered the department on foot or by wheelchair and who had no exclusions to using their left upper extremity. A Welch Allyn Vital Signs 420 series monitor was used to measure blood pressure in the left upper arm and forearm with the subject seated and the upper arm or forearm at heart level. Pearson r correlation coefficients between measurements in the upper arm and forearm were 0.88 for systolic blood pressure and 0.76 for diastolic blood pressure (P < .001 for both). Mean systolic pressures, but not mean diastolic pressures, in the upper arm and forearm differed significantly (t = 2.07, P = .04). A Bland-Altman analysis indicated that the distances between the mean values and the limits of agreement for the 2 sites ranged from 15 mm Hg (mean arterial pressure) to 18.4 mm Hg (systolic pressure). Despite strict attention to correct cuff size and placement of the upper arm or forearm at heart level, measurements of blood pressure obtained noninvasively in the arm and forearm of seated patients in stable condition are not interchangeable.

Respiratory sinus arrhythmia: opposite effects on systolic and mean arterial pressure in supine humans

NASA Technical Reports Server (NTRS)

Elstad, M.; Toska, K.; Chon, K. H.; Raeder, E. A.; Cohen, R. J.

2001-01-01

1. Are arterial blood pressure fluctuations buffered or reinforced by respiratory sinus arrhythmia (RSA)? There is still considerable debate about this simple question. Different results have been obtained, triggering a discussion as to whether or not the baroreflexes are responsible for RSA. We suspected that the measurements of different aspects of arterial pressure (mean arterial pressure (MAP) and systolic pressure (SP)) can explain the conflicting results. 2. Simultaneous recordings of beat-to-beat MAP, SP, left cardiac stroke volume (SV, pulsed ultrasound Doppler), heart rate (HR) and respiration (RE) were obtained in 10 healthy young adults during spontaneous respiration. In order to eliminate HR variations at respiratory frequency we used propranolol and atropine administration in the supine and tilted positions. Respiration-synchronous variation in the recorded variables was quantified by spectral analysis of the recordings of each of these variables, and the phase relations between them were determined by cross-spectral analysis. 3. MAP fluctuations increased after removing heart rate variations in both supine and tilted position, whereas SP fluctuations decreased in the supine position and increased in the head-up tilted position. 4. RSA buffers respiration-synchronous fluctuations in MAP in both positions. However, fluctuations in SP were reinforced by RSA in the supine and buffered in the tilted position.

Effects of the lateral amplitude and regularity of upper body fluctuation on step time variability evaluated using return map analysis

PubMed Central

2017-01-01

The aim of this study was to evaluate the effects of the lateral amplitude and regularity of upper body fluctuation on step time variability. Return map analysis was used to clarify the relationship between step time variability and a history of falling. Eleven healthy, community-dwelling older adults and twelve younger adults participated in the study. All of the subjects walked 25 m at a comfortable speed. Trunk acceleration was measured using triaxial accelerometers attached to the third lumbar vertebrae (L3) and the seventh cervical vertebrae (C7). The normalized average magnitude of acceleration, the coefficient of determination ($R^2$) of the return map, and the step time variabilities, were calculated. Cluster analysis using the average fluctuation and the regularity of C7 fluctuation identified four walking patterns in the mediolateral (ML) direction. The participants with higher fluctuation and lower regularity showed significantly greater step time variability compared with the others. Additionally, elderly participants who had fallen in the past year had higher amplitude and a lower regularity of fluctuation during walking. In conclusion, by focusing on the time evolution of each step, it is possible to understand the cause of stride and/or step time variability that is associated with a risk of falls. PMID:28700633

Effects of the lateral amplitude and regularity of upper body fluctuation on step time variability evaluated using return map analysis.

PubMed

Chidori, Kazuhiro; Yamamoto, Yuji

2017-01-01

The aim of this study was to evaluate the effects of the lateral amplitude and regularity of upper body fluctuation on step time variability. Return map analysis was used to clarify the relationship between step time variability and a history of falling. Eleven healthy, community-dwelling older adults and twelve younger adults participated in the study. All of the subjects walked 25 m at a comfortable speed. Trunk acceleration was measured using triaxial accelerometers attached to the third lumbar vertebrae (L3) and the seventh cervical vertebrae (C7). The normalized average magnitude of acceleration, the coefficient of determination ($R^2$) of the return map, and the step time variabilities, were calculated. Cluster analysis using the average fluctuation and the regularity of C7 fluctuation identified four walking patterns in the mediolateral (ML) direction. The participants with higher fluctuation and lower regularity showed significantly greater step time variability compared with the others. Additionally, elderly participants who had fallen in the past year had higher amplitude and a lower regularity of fluctuation during walking. In conclusion, by focusing on the time evolution of each step, it is possible to understand the cause of stride and/or step time variability that is associated with a risk of falls.

Numerical simulation of pressure fluctuation in 1000MW Francis turbine under small opening condition

NASA Astrophysics Data System (ADS)

Gong, R. Z.; Wang, H. G.; Yao, Y.; Shu, L. F.; Huang, Y. J.

2012-11-01

In order to study the cause of abnormal vibration in large Francis turbine under small opening condition, CFD method was adopted to analyze the flow filed and pressure fluctuation. Numerical simulation was performed on the commercial CFD code Ansys FLUENT 12, using DES method. After an effective validation of the computation result, the flow behaviour of internal flow field under small opening condition is analyzed. Pressure fluctuation in different working mode is obtained by unsteady CFD simulation, and results is compared to study its change. Radial force fluctuation is also analyzed. The result shows that the unstable flow under small opening condition leads to an increase of turbine instability in reverse pump mode, and is one possible reason of the abnormal oscillation.

Fluctuation of blood pressure and pulse rate during colostomy irrigation.

PubMed

Sadahiro, S; Noto, T; Tajima, T; Mitomi, T; Miyazaki, T; Numata, M

1995-06-01

The aim of this study was to determine the effects of colostomy irrigation on the vital signs of patients with left colostomy. Twenty-two consecutive patients who underwent abdominoperineal resection for cancer of the lower rectum and had left lower quadrant end colostomy were included in this study. Subjective symptoms, blood pressure, and pulse rate during the first irrigation were investigated. Fluctuation of blood pressure during instillation was 8.0/8.5 mmHg (average) and 25.0/17.9 mmHg during evacuation. Fluctuation of pulse rate was 5.5 per minute (average) during instillation and 11.5 per minute during evacuation. The number of subjects who showed more than 20% fluctuation of systolic pressure was 12 (54.5 percent) and that of diastolic pressure was 14 (63.6 percent). One of 22 patients complained of illness during irrigation. Although colostomy irrigation showed no significant effects on vital signs in the majority of patients, it caused a significant reduction in both blood pressure and pulse rate in a small number of patients. Careful attention should be paid to vital signs considering the possibility of such effects, especially on the initial irrigation.

Reducing the pressure drag of a D-shaped bluff body using linear feedback control

NASA Astrophysics Data System (ADS)

Dalla Longa, L.; Morgans, A. S.; Dahan, J. A.

2017-12-01

The pressure drag of blunt bluff bodies is highly relevant in many practical applications, including to the aerodynamic drag of road vehicles. This paper presents theory revealing that a mean drag reduction can be achieved by manipulating wake flow fluctuations. A linear feedback control strategy then exploits this idea, targeting attenuation of the spatially integrated base (back face) pressure fluctuations. Large-eddy simulations of the flow over a D-shaped blunt bluff body are used as a test-bed for this control strategy. The flow response to synthetic jet actuation is characterised using system identification, and controller design is via shaping of the frequency response to achieve fluctuation attenuation. The designed controller successfully attenuates integrated base pressure fluctuations, increasing the time-averaged pressure on the body base by 38%. The effect on the flow field is to push the roll-up of vortices further downstream and increase the extent of the recirculation bubble. This control approach uses only body-mounted sensing/actuation and input-output model identification, meaning that it could be applied experimentally.

Pressure fluctuations and time scales in turbulent channel flow

NASA Astrophysics Data System (ADS)

Septham, Kamthon; Morrison, Jonathan; Diwan, Sourabh

2015-11-01

Pressure fluctuations in turbulent channel flow subjected to globally stabilising linear feedback control are investigated at Reτ = 400 . The passivity-based control is adopted and explained by the conservative characteristics of the nonlinear terms contributing to the Reynolds-Orr equation (Sharma et al. Phys. Fluids 2011). The linear control operates via vU' ; the maximum forcing is located at y+ ~ 20 , corresponding to the location of the maximum in the mean-square pressure gradient. The responses of the rapid (linear) and slow (nonlinear) pressure fluctuations to the linear control are investigated using the Green's function representations. It demonstrates that the linear control operates via the linear source terms of the Poisson equation for pressure fluctuations. Landahl's timescales of the minimal flow unit (MFU) in turbulent channel flow are examined at y+ = 20 . It shows that the timescales of MFU agree well with the theoretical values proposed by Landahl (1993). Therefore, the effectiveness of the linear control to attenuate wall turbulence is explained by Landahl's theory for timescales, in that the control proceeds via the shear interaction timescale which is significantly shorter than both the nonlinear and viscous timescales.

Fluctuating pressures in pump diffuser and collector scrolls, part 1

NASA Technical Reports Server (NTRS)

Sloteman, Donald P.

1989-01-01

The cracking of scroll liners on the SSME High Pressure Fuel Turbo Pump (HPFTP) on hot gas engine test firings has prompted a study into the nature of pressure fluctuations in centrifugal pump states. The amplitudes of these fluctuations and where they originate in the pump stage are quantified. To accomplish this, a test program was conducted to map the pressure pulsation activity in a centrifugal pump stage. This stage is based on typical commercial (or generic) pump design practice and not the specialized design of the HPFTP. Measurements made in the various elements comprising the stage indicate that pulsation activity is dominated by synchronous related phenomena. Pulsation amplitudes measured in the scroll are low, on the order of 2 to 7 percent of the impeller exit tip speed velocity head. Significant non-sychronous pressure fluctuations occur at low flow, and while of interest to commercial pump designers, have little meaning to the HPFTP experience. Results obtained with the generic components do provide insights into possible pulsation related scroll failures on the HPFTP, and provide a basis for further study.

Pressure fluctuation caused by moderate acceleration

NASA Astrophysics Data System (ADS)

Tagawa, Yoshiyuki; Kurihara, Chihiro; Kiyama, Akihito

2017-11-01

Pressure fluctuation caused by acceleration of a liquid column is observed in various important technologies, e.g. water-hammer in a pipeline. The magnitude of fluctuation can be estimated by two different approaches: When the duration time of acceleration is much shorter than the propagation time for a pressure wave to travel the length of the liquid column, e.g. sudden valve closure for a long pipe, Joukowsky equation is applied. In contrast, if the acceleration duration is much longer, the liquid is modeled as a rigid column, ignoring compressibility of the fluid. However, many of practical cases exist between these two extremes. In this study we propose a model describing pressure fluctuation when the duration of acceleration is in the same order of the propagation time for a pressure wave, i.e. under moderate acceleration. The novel model considers both temporal and spatial evolutions of pressure propagation as well as gradual pressure rise during the acceleration. We conduct experiments in which we impose acceleration to a liquid with varying the length of the liquid column, acceleration duration, and properties of liquids. The ratio between the acceleration duration and the propagation time is in the range of 0.02 - 2. The model agrees well with measurement results. JSPS KAKENHI Grant Numbers 26709007 and 17H01246.

Plasma radiofrequency preceded by pressure recording enhances success for treating sleep-related breathing disorders.

PubMed

Tvinnereim, Magne; Mitic, Svetislav; Hansen, Rolf K

2007-04-01

Sleep-related breathing disorders (SRBD) that cannot be treated conservatively are commonly treated using uvulopalatopharyngoplasty, although success rates are generally less than 70%. The purpose of this study was to assess a plasma-mediated radiofrequency (RF)-based coblation assisted upper airway procedure (CAUP) to treat SRBD patients determined to have obstruction localized to the upper (mid)-pharyngeal region. Prospective case series (n = 40). Six patients had socially bothersome snoring, and 34 patients had mild to moderate sleep apnea (apnea/hypopnea index [AHI] <20), with the primary level of obstruction (>50%) within the upper pharyngeal region as determined using whole night recordings, including airway pressure fluctuation monitoring (ApneaGraph, MRA-Medical Ltd, Gloucestershire, UK). CAUP consisted of making a lateral palatal incision, ablating three upward channels on each side of the midline (fan-shaped) into the soft palate using a plasma mediated RF-based device (ArthroCare Corporation, Austin, TX), and performing a partial uvulectomy. Clinical outcomes included the Epworth Sleepiness Scale (ESS), partner rating of snoring using a visual analogue scale (VAS), and night-time apnea and hypopnea events (AHI, hypopnea index [HI], apnea index [AI]). Patients were 28 to 68 (46 +/- 12) years old; 28 (70%) were male. Preoperatively, clinical assessment scores (median +/- interquartile range) were as follows: ESS (11.0 +/- 3.0), VAS (8.15 +/- 1.00), AHI (9.58 +/- 5.58), HI (9.00 +/- 5.29), AI (0.333 +/- 0.625). After CAUP, no postoperative scarring, fibrosis, or any other clinically significant side effects were observed. Postoperatively (9.1 +/- 1.5; 7-15 mo), ESS (4.0 +/- 1.0), VAS (2.70 +/- 1.38), AHI (3.75 +/- 2.92), HI (3.58 +/- 2.50), and AI (0.167 +/- 0.167) were significantly improved (P < .001). CAUP preceded by site-specific obstruction diagnosis using pressure recording is a well-tolerated outpatient treatment that is well suited for treating SRBD.

Adiabatic electron thermal pressure fluctuations in tokamak plasmas.

PubMed

Meier, M A; Bengtson, R D; Hallock, G A; Wootton, A J

2001-08-20

Electron thermal pressure fluctuations measured in the edge plasma of the Texas Experimental Tokamak Upgrade are a fundamental component of plasma turbulence on both sides of the velocity shear layer. The ratio of specific heats, estimated from fluctuations in electron temperature and electron number density measured simultaneously at the same electrode, indicates that observed fluctuations are adiabatic. The observations are made by means of a novel Langmuir probe technique, the time domain triple-probe method, which concurrently measures multiple plasma properties at each of two electrodes with the temporal and the spatial resolution required to estimate thermodynamic properties in a turbulent plasma.

A measurement of the large-scale cosmic microwave background anisotropy at 1.8 millimeter wavelength

NASA Technical Reports Server (NTRS)

Meyer, Stephan S.; Cheng, Edward S.; Page, Lyman A.

1991-01-01

This measurement of the large-scale cosmic microwave background radiation (CMBR) anisotropy places the most stringent constraints to date on fluctuations in the CMBR on angular scales greater than about 4 deg. Using a four-channel bolometric radiometer operating at 1.8, 1.1, 0.63, and 0.44 mm, the diffuse sky brightness over half of the northern hemisphere has been mapped with an angular resolution of 3.8 deg. Analysis of the sky map at the longest wavelength for Galactic latitudes of 15 deg or more yields a 95-percent confidence level upper limit on fluctuations of the CMBR at Delta T/T of 1.6 x 10 to the -5th with a statistical power of 92 percent for Gaussian fluctuations at a correlation angle of 13 deg. Between 3 deg and 22 deg, the upper limit of fluctuations is 4.0 x 10 to the -5th . An anisotropy is detected in the map, but it cannot yet be attributed to primordial sources. The ultimate sensitivity for this experiment is 7 x 10 to the -6th over this angular range for Gaussian fluctuations.

Propagations of fluctuations and flow separation on an unsteadily loaded airfoil

NASA Astrophysics Data System (ADS)

Tenney, Andrew; Lewalle, Jacques

2014-11-01

We analyze pressure data from 18 taps located along the surface of a DU-96-W180 airfoil in bothand steady flow conditions. The conditions were set to mimic the flow conditions experienced by a wind turbine blade under unsteady loading to test and to quantify the effects of several flow control schemes. Here we are interested in the propagation of fluctuations along the pressure and suction sides, particularly in relation to the fluctuating separation point. An unsteady phase of the incoming fluctuations is defined using Morlet wavelets, and phase-conditioned cross-correlations are calculated. Using wavelet-based pattern recognition, individual events in the pressure data are identified with several different algorithms utilizing both the original time series pressure signals and their corresponding scalograms. The data analyzed in this study was collected by G. Wang in the Skytop anechoic chamber at Syracuse University in the spring of 2013; the work of Zhe Bai on this data is also acknowledged.

Cascading of Fluctuations in Interdependent Energy Infrastructures. Gas-Grid Coupling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chertkov, Michael; Lebedev, Vladimir; Backhaus, Scott N.

2014-09-05

The revolution of hydraulic fracturing has dramatically increased the supply and lowered the cost of natural gas in the United States driving an expansion of natural gas-fired generation capacity in many electrical grids. Unrelated to the natural gas expansion, lower capital costs and renewable portfolio standards are driving an expansion of intermittent renewable generation capacity such as wind and photovoltaic generation. These two changes may potentially combine to create new threats to the reliability of these interdependent energy infrastructures. Natural gas-fired generators are often used to balance the fluctuating output of wind generation. However, the time-varying output of these generatorsmore » results in time-varying natural gas burn rates that impact the pressure in interstate transmission pipelines. Fluctuating pressure impacts the reliability of natural gas deliveries to those same generators and the safety of pipeline operations. We adopt a partial differential equation model of natural gas pipelines and use this model to explore the effect of intermittent wind generation on the fluctuations of pressure in natural gas pipelines. The mean square pressure fluctuations are found to grow linearly in time with points of maximum deviation occurring at the locations of flow reversals.« less

Estimation of velocity fluctuation in internal combustion engine exhaust systems through beamforming techniques

NASA Astrophysics Data System (ADS)

Piñero, G.; Vergara, L.; Desantes, J. M.; Broatch, A.

2000-11-01

The knowledge of the particle velocity fluctuations associated with acoustic pressure oscillation in the exhaust system of internal combustion engines may represent a powerful aid in the design of such systems, from the point of view of both engine performance improvement and exhaust noise abatement. However, usual velocity measurement techniques, even if applicable, are not well suited to the aggressive environment existing in exhaust systems. In this paper, a method to obtain a suitable estimate of velocity fluctuations is proposed, which is based on the application of spatial filtering (beamforming) techniques to instantaneous pressure measurements. Making use of simulated pressure-time histories, several algorithms have been checked by comparison between the simulated and the estimated velocity fluctuations. Then, problems related to the experimental procedure and associated with the proposed methodology are addressed, making application to measurements made in a real exhaust system. The results indicate that, if proper care is taken when performing the measurements, the application of beamforming techniques gives a reasonable estimate of the velocity fluctuations.

Energetic Interrelationship between Spontaneous Low-Frequency Fluctuations in Regional Cerebral Blood Volume, Arterial Blood Pressure, Heart Rate, and Respiratory Rhythm

NASA Astrophysics Data System (ADS)

Katura, Takusige; Yagyu, Akihiko; Obata, Akiko; Yamazaki, Kyoko; Maki, Atsushi; Abe, Masanori; Tanaka, Naoki

2007-07-01

Strong spontaneous fluctuations around 0.1 and 0.3 Hz have been observed in blood-related brain-function measurements such as functional magnetic resonance imaging and optical topography (or functional near-infrared spectroscopy). These fluctuations seem to reflect the interaction between the cerebral circulation system and the systemic circulation system. We took an energetic viewpoint in our analysis of the interrelationships between fluctuations in cerebral blood volume (CBV), mean arterial blood pressure (MAP), heart rate (HR), and respiratory rhythm based on multivariate autoregressive modeling. This approach involves evaluating the contribution of each fluctuation or rhythm to specific ones by performing multivariate spectral analysis. The results we obtained show MAP and HR can account slightly for the fluctuation around 0.1 Hz in CBV, while the fluctuation around 0.3 Hz is derived mainly from the respiratory rhythm. During our presentation, we will report on the effects of posture on the interrelationship between the fluctuations and the respiratory rhythm.

Experimental Verification of Buffet Calculation Procedure Using Unsteady PSP

NASA Technical Reports Server (NTRS)

Panda, Jayanta

2016-01-01

Typically a limited number of dynamic pressure sensors are employed to determine the unsteady aerodynamic forces on large, slender aerospace structures. The estimated forces are known to be very sensitive to the number of the dynamic pressure sensors and the details of the integration scheme. This report describes a robust calculation procedure, based on frequency-specific correlation lengths, that is found to produce good estimation of fluctuating forces from a few dynamic pressure sensors. The validation test was conducted on a flat panel, placed on the floor of a wind tunnel, and was subjected to vortex shedding from a rectangular bluff-body. The panel was coated with fast response Pressure Sensitive Paint (PSP), which allowed time-resolved measurements of unsteady pressure fluctuations on a dense grid of spatial points. The first part of the report describes the detail procedure used to analyze the high-speed, PSP camera images. The procedure includes steps to reduce contamination by electronic shot noise, correction for spatial non-uniformities, and lamp brightness variation, and finally conversion of fluctuating light intensity to fluctuating pressure. The latter involved applying calibration constants from a few dynamic pressure sensors placed at selective points on the plate. Excellent comparison in the spectra, coherence and phase, calculated via PSP and dynamic pressure sensors validated the PSP processing steps. The second part of the report describes the buffet validation process, for which the first step was to use pressure histories from all PSP points to determine the "true" force fluctuations. In the next step only a selected number of pixels were chosen as "virtual sensors" and a correlation-length based buffet calculation procedure was applied to determine "modeled" force fluctuations. By progressively decreasing the number of virtual sensors it was observed that the present calculation procedure was able to make a close estimate of the "true" unsteady forces only from four sensors. It is believed that the present work provides the first validation of the buffet calculation procedure which has been used for the development of many space vehicles.

Measurements of surface-pressure fluctuations on the XB-70 airplane at local Mach numbers up to 2.45

NASA Technical Reports Server (NTRS)

Lewis, T. L.; Dods, J. B., Jr.; Hanly, R. D.

1973-01-01

Measurements of surface-pressure fluctuations were made at two locations on the XB-70 airplane for nine flight-test conditions encompassing a local Mach number range from 0.35 to 2.45. These measurements are presented in the form of estimated power spectral densities, coherence functions, and narrow-band-convection velocities. The estimated power spectral densities compared favorably with wind-tunnel data obtained by other experimenters. The coherence function and convection velocity data supported conclusions by other experimenters that low-frequency surface-pressure fluctuations consist of small-scale turbulence components with low convection velocity.

Embedded Acoustic Sensor Array for Engine Fan Noise Source Diagnostic Test: Feasibility of Noise Telemetry via Wireless Smart Sensors

NASA Technical Reports Server (NTRS)

Zaman, Afroz; Bauch, Matthew; Raible, Daniel

2011-01-01

Aircraft engines have evolved into a highly complex system to meet ever-increasing demands. The evolution of engine technologies has primarily been driven by fuel efficiency, reliability, as well as engine noise concerns. One of the sources of engine noise is pressure fluctuations that are induced on the stator vanes. These local pressure fluctuations, once produced, propagate and coalesce with the pressure waves originating elsewhere on the stator to form a spinning pressure pattern. Depending on the duct geometry, air flow, and frequency of fluctuations, these spinning pressure patterns are self-sustaining and result in noise which eventually radiate to the far-field from engine. To investigate the nature of vane pressure fluctuations and the resulting engine noise, unsteady pressure signatures from an array of embedded acoustic sensors are recorded as a part of vane noise source diagnostics. Output time signatures from these sensors are routed to a control and data processing station adding complexity to the system and cable loss to the measured signal. "Smart" wireless sensors have data processing capability at the sensor locations which further increases the potential of wireless sensors. Smart sensors can process measured data locally and transmit only the important information through wireless communication. The aim of this wireless noise telemetry task was to demonstrate a single acoustic sensor wireless link for unsteady pressure measurement, and thus, establish the feasibility of distributed smart sensors scheme for aircraft engine vane surface unsteady pressure data transmission and characterization.

Temperature and density anti-correlations in solar wind fluctuations

NASA Technical Reports Server (NTRS)

Zank, G. P.; Matthaeus, W. H.; Klein, L. W.

1990-01-01

Recent theoretical investigations of low Mach number flows, that describe two distinct approaches by fluids to the incompressible regime are summarized. The first includes the effects of relatively strong density and temperature fluctuations (Type I), while the second places fluctuations in mechanical pressure, density, and temperature on an equal footing (Type II). In the latter case, the relations between density and pressure are recovered, whereas the former case yields departures from incompressible behavior in that density and temperature fluctuations are predicted to be anti-correlated. It is suggested that nearly incompressible fluids can be classified as either Type I or II, and it is shown that the well-known pressure-balanced structures represent a subclass of static solutions within this classification. Two examples from Voyager data illustrate the potential for observing these distinct nearly incompressible dynamical ordering in the solar wind.

Measurements of Ion and Neutral Fluctuation Changes with Pressure in a Large-Scale Helicon Plasma

NASA Astrophysics Data System (ADS)

Dwyer, R. H.; Fisher, D. M.; Kelly, R. F.; Hatch, M. W.; Gilmore, M.

2017-10-01

Neutral particle dynamics may play an important role both in laboratory plasmas and in the edge of magnetic fusion devices. However, studies of neutral dynamics in these plasmas have been limited to date. Here we report on a basic study of ion and neutral fluctuations as a function of background neutral gas pressure. These experiments have been conducted in helicon discharges in the HelCat (Helicon-Cathode) dual-source plasma device at the University of New Mexico. The goal is to measure changes in ion and neutral density fluctuations with pressure and to gain an improved understanding of plasma-neutral interactions. Langmuir probe, Ar-I LIF, and high-speed imaging measurements of the fluctuations will be presented. Supported by U.S. National Science Foundation Award 1500423 and The University of New Mexico School of Engineering.

Energy harvesting from cerebrospinal fluid pressure fluctuations for self-powered neural implants.

PubMed

Beker, Levent; Benet, Arnau; Meybodi, Ali Tayebi; Eovino, Ben; Pisano, Albert P; Lin, Liwei

2017-06-01

In this paper, a novel method to generate electrical energy by converting available mechanical energy from pressure fluctuations of the cerebrospinal fluid within lateral ventricles of the brain is presented. The generated electrical power can be supplied to the neural implants and either eliminate their battery need or extend the battery lifespan. A diaphragm type harvester comprised of piezoelectric material is utilized to convert the pressure fluctuations to electrical energy. The pressure fluctuations cause the diaphragm to bend, and the strained piezoelectric materials generate electricity. In the framework of this study, an energy harvesting structure having a diameter of 2.5 mm was designed and fabricated using microfabrication techniques. A 1:1 model of lateral ventricles was 3D-printed from raw MRI images to characterize the harvester. Experimental results show that a maximum power of 0.62 nW can be generated from the harvester under similar physical conditions in lateral ventricles which corresponds to energy density of 12.6 nW/cm 2 . Considering the available area within the lateral ventricles and the size of harvesters that can be built using microfabrication techniques it is possible to amplify to power up to 26 nW. As such, the idea of generating electrical energy by making use of pressure fluctuations within brain is demonstrated in this work via the 3D-printed model system.

Leg raise increases pressure in lower and upper esophageal sphincter among patients with gastroesophageal reflux disease.

PubMed

Bitnar, P; Stovicek, J; Andel, R; Arlt, J; Arltova, M; Smejkal, M; Kolar, P; Kobesova, A

2016-07-01

The purpose of this study was to determine the relation between posturally increased intra-abdominal pressure and lower/upper esophageal sphincter pressure changes in patients with gastroesophageal reflux disease. We used high resolution manometry to measure pressure changes in lower and upper esophageal sphincter during bilateral leg rise. We also examined whether the rate of lower and upper esophageal sphincter pressure would increase during leg raise differentially in individuals with versus without normal resting pressure. Fifty eight patients with gastroesophageal reflux disease participated in the study. High resolution manometry was performed in relaxed supine position, then lower and upper esophageal sphincter pressure was measured. Finally, the subjects were instructed to keep their legs lifted while performing 90-degree flexion at the hips and knees and the pressure was measured again. Paired t-test and independent samples t-test were used. There was a significant increase in both lower (P < 0.001) and upper esophageal sphincter pressure (P = 0.034) during leg raise compared to the initial resting position. Individuals with initially higher pressure in lower esophageal sphincter (>10 mmHg) exhibited a greater pressure increase during leg raise than those with initially lower pressure (pressure ≤10 mmHg; P = 0.002). Similarly individuals with higher resting upper esophageal sphincter pressure (>44 mmHg) showed a greater pressure increase during leg raise than those with lower resting pressure (≤44 mmHg; P < 0.001). The results illustrate the influence of postural leg activities on intraesophageal pressure in patients with gastroesophageal reflux disease, indicating by means of high resolution manometry that diaphragmatic postural and sphincter function are likely interrelated in this population. Copyright © 2015 Elsevier Ltd. All rights reserved.

Simultaneous optimization of spin fluctuations and superconductivity under pressure in an iron-based superconductor.

PubMed

Ji, G F; Zhang, J S; Ma, Long; Fan, P; Wang, P S; Dai, J; Tan, G T; Song, Y; Zhang, C L; Dai, Pengcheng; Normand, B; Yu, Weiqiang

2013-09-06

We present a high-pressure NMR study of the overdoped iron pnictide superconductor NaFe0.94Co0.06As. The low-energy antiferromagnetic spin fluctuations in the normal state, manifest as the Curie-Weiss upturn in the spin-lattice relaxation rate 1/(75)T1T, first increase strongly with pressure but fall again at P>Popt=2.2  GPa. Neither long-ranged magnetic order nor a structural phase transition is encountered up to 2.5 GPa. The superconducting transition temperature Tc shows a pressure dependence identical to the spin fluctuations. Our observations demonstrate that magnetic correlations and superconductivity are optimized simultaneously as a function of the electronic structure, thereby supporting very strongly a magnetic origin of superconductivity.

A theoretical prediction of the acoustic pressure generated by turbulence-flame front interactions

NASA Technical Reports Server (NTRS)

Huff, R. G.

1984-01-01

The equations of momentum annd continuity are combined and linearized yielding the one dimensional nonhomogeneous acoustic wave equation. Three terms in the non-homogeneous equation act as acoustic sources and are taken to be forcing functions acting on the homogeneous wave equation. The three source terms are: fluctuating entropy, turbulence gradients, and turbulence-flame interactions. Each source term is discussed. The turbulence-flame interaction source is used as the basis for computing the source acoustic pressure from the Fourier transformed wave equation. Pressure fluctuations created in turbopump gas generators and turbines may act as a forcing function for turbine and propellant tube vibrations in Earth to orbit space propulsion systems and could reduce their life expectancy. A preliminary assessment of the acoustic pressure fluctuations in such systems is presented.

A theoretical prediction of the acoustic pressure generated by turbulence-flame front interactions

NASA Technical Reports Server (NTRS)

Huff, R. G.

1984-01-01

The equations of momentum and continuity are combined and linearized yielding the one dimensional nonhomogeneous acoustic wave equation. Three terms in the non-homogeneous equation act as acoustic sources and are taken to be forcing functions acting on the homogeneous wave equation. The three source terms are: fluctuating entropy, turbulence gradients, and turbulence-flame interactions. Each source term is discussed. The turbulence-flame interaction source is used as the basis for computing the source acoustic pressure from the Fourier transformed wave equation. Pressure fluctuations created in turbopump gas generators and turbines may act as a forcing function for turbine and propellant tube vibrations in earth to orbit space propulsion systems and could reduce their life expectancy. A preliminary assessment of the acoustic pressure fluctuations in such systems is presented.

Near Field Pressure Fluctuations in the Exit Plane of a Choked Axisymmetric Nozzle

NASA Technical Reports Server (NTRS)

Ponton, Michael K.; Seiner, John M.; Brown, Martha C.

1997-01-01

Nearfield pressure data are presented for an unheated jet issuing from an underexpanded sonic nozzle for two exit lip thicknesses of 0.200 and 0.625 nozzle diameters. Fluctuating measurements were obtained on the nozzle exit surface as well as in the acoustic nearfield. Narrowband spectra are presented for numerous operating conditions expressed in terms of the fully expanded Mach number based on nozzle pressure ratio.

Numerical study of dynamic glottis and tidal breathing on respiratory sounds in a human upper airway model

PubMed Central

Wang, Zhaoxuan; Talaat, Khaled; Glide-Hurst, Carri; Dong, Haibo

2018-01-01

Background Human snores are caused by vibrating anatomical structures in the upper airway. The glottis is a highly variable structure and a critical organ regulating inhaled flows. However, the effects of the glottis motion on airflow and breathing sound are not well understood, while static glottises have been implemented in most previous in silico studies. The objective of this study is to develop a computational acoustic model of human airways with a dynamic glottis and quantify the effects of glottis motion and tidal breathing on airflow and sound generation. Methods Large eddy simulation and FW-H models were adopted to compute airflows and respiratory sounds in an image-based mouth-lung model. User-defined functions were developed that governed the glottis kinematics. Varying breathing scenarios (static vs. dynamic glottis; constant vs. sinusoidal inhalations) were simulated to understand the effects of glottis motion and inhalation pattern on sound generation. Pressure distributions were measured in airway casts with different glottal openings for model validation purpose. Results Significant flow fluctuations were predicted in the upper airways at peak inhalation rates or during glottal constriction. The inhalation speed through the glottis was the predominating factor in the sound generation while the transient effects were less important. For all frequencies considered (20–2500 Hz), the static glottis substantially underestimated the intensity of the generated sounds, which was most pronounced in the range of 100–500 Hz. Adopting an equivalent steady flow rather than a tidal breathing further underestimated the sound intensity. An increase of 25 dB in average was observed for the life condition (sine-dynamic) compared to the idealized condition (constant-rigid) for the broadband frequencies, with the largest increase of approximately 40 dB at the frequency around 250 Hz. Conclusion Results show that a severely narrowing glottis during inhalation, as well as flow fluctuations in the downstream trachea, can generate audible sound levels. PMID:29101633

Numerical study of dynamic glottis and tidal breathing on respiratory sounds in a human upper airway model.

PubMed

Xi, Jinxiang; Wang, Zhaoxuan; Talaat, Khaled; Glide-Hurst, Carri; Dong, Haibo

2018-05-01

Human snores are caused by vibrating anatomical structures in the upper airway. The glottis is a highly variable structure and a critical organ regulating inhaled flows. However, the effects of the glottis motion on airflow and breathing sound are not well understood, while static glottises have been implemented in most previous in silico studies. The objective of this study is to develop a computational acoustic model of human airways with a dynamic glottis and quantify the effects of glottis motion and tidal breathing on airflow and sound generation. Large eddy simulation and FW-H models were adopted to compute airflows and respiratory sounds in an image-based mouth-lung model. User-defined functions were developed that governed the glottis kinematics. Varying breathing scenarios (static vs. dynamic glottis; constant vs. sinusoidal inhalations) were simulated to understand the effects of glottis motion and inhalation pattern on sound generation. Pressure distributions were measured in airway casts with different glottal openings for model validation purpose. Significant flow fluctuations were predicted in the upper airways at peak inhalation rates or during glottal constriction. The inhalation speed through the glottis was the predominating factor in the sound generation while the transient effects were less important. For all frequencies considered (20-2500 Hz), the static glottis substantially underestimated the intensity of the generated sounds, which was most pronounced in the range of 100-500 Hz. Adopting an equivalent steady flow rather than a tidal breathing further underestimated the sound intensity. An increase of 25 dB in average was observed for the life condition (sine-dynamic) compared to the idealized condition (constant-rigid) for the broadband frequencies, with the largest increase of approximately 40 dB at the frequency around 250 Hz. Results show that a severely narrowing glottis during inhalation, as well as flow fluctuations in the downstream trachea, can generate audible sound levels.

Flight Measurement of Wall-Pressure Fluctuations and Boundary-Layer Turbulence

NASA Technical Reports Server (NTRS)

Mull, Harold R.; Algranti, Joseph S.

1960-01-01

The results are presented for a flight test program using a fighter type jet aircraft flying at pressure altitudes of 10,000, 20,000, and 30,000 feet at Mach numbers from 0.3 to 0.8. Specially designed apparatus was used to measure and record the output of microphones and hot-wire anemometers mounted on the forward-fuselage section and wing of the airplane. Mean-velocity profiles in the boundary layers were obtained from total-pressure measurements. The ratio of the root-mean-square fluctuating wall pressure to the free-stream dynamic pressure is presented as a function of Reynolds number and Mach number. The longitudinal component of the turbulent-velocity fluctuations was measured, and the turbulence-intensity profiles are presented for the wing and forward-fuselage section. In general, the results are in agreement with wind-tunnel measurements which have been-reported in the literature. For example, the variation the square root of p(sup 2)/q times the square root of p(sup 2) is the root mean square of the wall-pressure fluctuation, and q is the free-stream dynamic pressure) with Reynolds number was found to be essentially constant for the forward-fuselage-section boundary layer, while variations at the wing station were probably unduly affected by the microphone diameter (5/8 in.), which was large compared with the boundary-layer thickness.

Fourier and wavelet analyses of intermittent and resonant pressure components in a slot burner

NASA Astrophysics Data System (ADS)

Pagliaroli, Tiziano; Mancinelli, Matteo; Troiani, Guido; Iemma, Umberto; Camussi, Roberto

2018-01-01

In laboratory-scale burner it has been observed that the acoustic excitations change the flame topology inducing asymmetry and oscillations. Hence, an acoustic and aeroacoustic study in non reactive condition is of primary importance during the design stage of a new burner in order to avoid the development of standing waves which can force the flame. So wall pressure fluctuations inside and outside of a novel slot burner have been studied experimentally and numerically for a broad range of geometrical parameters and mass flow rates. Wall pressure fluctuations have been measured through cavity-mounted microphones, providing uni- and multi-variate pressure statistics in both the time and frequency domains. Furthermore, since the onset of combustion-driven oscillations is always presaged by intermittent bursts of high amplitude, a wavelet-based conditional sampling procedure was applied to the database in order to detect coherent signatures embedded in the pressure time signals. Since for a particular case the coherent structures identified have a multi-scale signature, a wavelet-based decomposition technique was proposed as well to separate the contribution of the large- and small-scale flow structures to the pressure fluctuation field. As a main outcome of the activity no coupling between standing waves and velocity fluctuations was observed, but only well localized pressure signatures with shape strongly affected by the neighbouring flow physics.

Spectral Behavior of Weakly Compressible Aero-Optical Distortions

NASA Astrophysics Data System (ADS)

Mathews, Edwin; Wang, Kan; Wang, Meng; Jumper, Eric

2016-11-01

In classical theories of optical distortions by atmospheric turbulence, an appropriate and key assumption is that index-of-refraction variations are dominated by fluctuations in temperature and the effects of turbulent pressure fluctuations are negligible. This assumption is, however, not generally valid for aero-optical distortions caused by turbulent flow over an optical aperture, where both temperature and pressures fluctuations may contribute significantly to the index-of-refraction fluctuations. A general expression for weak fluctuations in refractive index is derived using the ideal gas law and Gladstone-Dale relation and applied to describe the spectral behavior of aero-optical distortions. Large-eddy simulations of weakly compressible, temporally evolving shear layers are then used to verify the theoretical results. Computational results support theoretical findings and confirm that if the log slope of the 1-D density spectrum in the inertial range is -mρ , the optical phase distortion spectral slope is given by - (mρ + 1) . The value of mρ is then shown to be dependent on the ratio of shear-layer free-stream densities and bounded by the spectral slopes of temperature and pressure fluctuations. Supported by HEL-JTO through AFOSR Grant FA9550-13-1-0001 and Blue Waters Graduate Fellowship Program.

Measurements of surface-pressure and wake-flow fluctuations in the flow field of a whitcomb supercritical airfoil

NASA Technical Reports Server (NTRS)

Roos, F. W.; Riddle, D. W.

1977-01-01

Measurements of surface pressure and wake flow fluctuations were made as part of a transonic wind tunnel investigation into the nature of a supercritical airfoil flow field. Emphasis was on a range of high subsonic Mach numbers and moderate lift coefficients corresponding to the development of drag divergence and buffeting. Fluctuation data were analyzed statistically for intensity, frequency content, and spatial coherence. Variations in these parameters were correlated with changes in the mean airfoil flow field.

Measurements of temperature and pressure fluctuations in the T prime 2 cryogenic wind tunnel

NASA Technical Reports Server (NTRS)

Blanchard, A.; Dor, J. B.; Breil, J. F.

1980-01-01

Cold wire measurement of temperature fluctuations were made in a DERAT T'2 induction powered cryogenic wind tunnel for 2 types of liquid nitrogen injectors. Thermal turbulence measured in the tranquilization chamber depends to a great extent on the injector used; for fine spray of nitrogen drops, this level of turbulence seemed completely acceptable. Fluctuations in static pressure taken from the walls of the vein by Kulite sensors showed that there was no increase in aerodynamic noise during cryogenic gusts.

Investigations on the self-excited oscillations in a kerosene spray flame

DOE Office of Scientific and Technical Information (OSTI.GOV)

de la Cruz Garcia, M.; Mastorakos, E.; Dowling, A.P.

2009-02-15

A laboratory scale gas turbine type burner at atmospheric pressure and with air preheat was operated with aviation kerosene Jet-A1 injected from a pressure atomiser. Self-excited oscillations were observed and analysed to understand better the relationship between the spray and thermo-acoustic oscillations. The fluctuations of CH{sup *} chemiluminescence measured simultaneously with the pressure were used to determine the flame transfer function. The Mie scattering technique was used to record spray fluctuations in reacting conditions with a high speed camera. Integrating the Mie intensity over the imaged region gave a temporal signal acquired simultaneously with pressure fluctuations and the transfer functionmore » between the light scattered from the spray and the velocity fluctuations in the plenum was evaluated. Phase Doppler anemometry was used for axial velocity and drop size measurements at different positions downstream the injection plane and for various operating conditions. Pressure spectra showed peaks at a frequency that changed with air mass flow rate. The peak for low air mass flow rate operation was at 220 Hz and was associated with a resonance of the supply plenum. At the same global equivalence ratio but at high air mass flow rates, the pressure spectrum peak was at 323 Hz, a combustion chamber resonant frequency. At low air flow rates, the spray fluctuation motion was pronounced and followed the frequency of the pressure oscillation. At high air flow rates, more effective evaporation resulted in a complete disappearance of droplets at an axial distance of about 1/3 burner diameters from the injection plane, leading to a different flame transfer function and frequency of the self-excited oscillation. The results highlight the sensitivity of the self-excited oscillation to the degree of mixing achieved before the main recirculation zone. (author)« less

Early results from the MIT millimeter and sub-millimeter balloon-borne anisotropy measurement. [of cosmic microwave background radiation

NASA Technical Reports Server (NTRS)

Meyer, Stephan S.; Cheng, Edward S.; Page, Lyman A.

1991-01-01

The MIT balloon-borne bolometric search for Cosmic Microwave Background Radiation (CMBR) anisotropies places the most stringent constraints to date on fluctuations in the CMBR. Four maps of half of the Northern Hemisphere at 1.8, 1.1, 0.63 and 0.44 mm wavelength, have a beam size of 3.8 deg with a 1 sigma sensitivity of less than 0.1 mK (thermodynamic) per FOV in each of the first two channels. Analysis of the sky map at 1.8 mm wavelength using a likelihood ratio test for galactic latitudes of 15 deg and greater yields a 95 percent confidence level (CL) upper limit on fluctuations of the CMBR at DeltaT/T less than or equal to 1.6 x 10 exp -5 with a statistical power of 92 percent for Gaussian fluctuations at a correlation angle of 13 deg. Between 3 deg and 22 deg, the upper limit for fluctuations is DeltaT/T less than or equal to 4.0 x 10 exp -5 (95 percent CL).

Hydrostatic pressure-induced huge enhancement of critical current density and flux pinning in Fe1-x Co x Se0.5Te0.5 single crystals

NASA Astrophysics Data System (ADS)

Sang, Lina; Shabbir, Babar; Maheshwari, Pankaj; Qiu, Wenbin; Ma, Zongqing; Dou, Shixue; Cai, Chuanbing; Awana, V. P. S.; Wang, Xiaolin

2018-07-01

We performed a systematic study of the hydrostatic pressure (HP) effect on the supercon-ducting transition temperature (T c), critical current density (J c), irreversibility field (H irr), upper critical field (H c2), and flux pinning mechanism in un-doped and 3 at.% Co-doped FeSe0.5Te0.5 crystals. We found that T c is increased from 11.5 to 17 K as HP increases from 0 to 1.2 GPa. Remarkably, the J c is significantly enhanced by a factor of 3 to 100 for low and high temperature and field, and the H irr line is shifted to higher fields by HP up to 1.2 GPa. Based on the collective pinning model, the δl pinning associated with charge-carrier mean free path fluctuation is responsible for the pinning mechanism of Fe1-x Co x Se0.5Te0.5 samples with or without pressure. A comprehensive vortex phase diagram in the mixed state is constructed and analysed for the 3 at.% Co-doped sample.

Responses to negative pressure surrounding the neck in anesthetized animals.

PubMed

Wolin, A D; Strohl, K P; Acree, B N; Fouke, J M

1990-01-01

Continuous positive pressure applied at the nose has been shown to cause a decrease in upper airway resistance. The present study was designed to determine whether a similar positive transmural pressure gradient, generated by applying a negative pressure at the body surface around the neck, altered upper airway patency. Studies were performed in nine spontaneously breathing anesthetized supine dogs. Airflow was measured with a pneumotachograph mounted on an airtight muzzle placed over the nose and mouth of each animal. Upper airway pressure was measured as the differential pressure between the extrathoracic trachea and the inside of the muzzle. Upper airway resistance was monitored as an index of airway patency. Negative pressure (-2 to -20 cmH2O) was applied around the neck by using a cuirass extending from the jaw to the thorax. In each animal, increasingly negative pressures were transmitted to the airway wall in a progressive, although not linear, fashion. Decreasing the pressure produced a progressive fall in upper airway resistance, without causing a significant change in respiratory drive or respiratory timing. At -5 cmH2O pressure, there occurred a significant fall in upper airway resistance, comparable with the response of a single, intravenous injection of sodium cyanide (0.5-3.0 mg), a respiratory stimulant that produces substantial increases in respiratory drive. We conclude that upper airway resistance is influenced by the transmural pressure across the airway wall and that such a gradient can be accomplished by making the extraluminal pressure more negative.(ABSTRACT TRUNCATED AT 250 WORDS)

Normalized fluctuations, H2O vs n-hexane: Site-correlated percolation

NASA Astrophysics Data System (ADS)

Koga, Yoshikata; Westh, Peter; Sawamura, Seiji; Taniguchi, Yoshihiro

1996-08-01

Entropy, volume and the cross fluctuations were normalized to the average volume of a coarse grain with a fixed number of molecules, within which the local and instantaneous value of interest is evaluated. Comparisons were made between liquid H2O and n-hexane in the range from -10 °C to 120 °C and from 0.1 MPa to 500 MPa. The difference between H2O and n-hexane in temperature and pressure dependencies of these normalized fluctuations was explained in terms of the site-correlated percolation theory for H2O. In particular, the temperature increase was confirmed to reduce the hydrogen bond probability, while the pressure appeared to have little effect on the hydrogen bond probability. According to the Le Chatelier principle, however, the putative formation of ``ice-like'' patches at low temperatures due to the site-correlated percolation requirement is retarded by pressure increases. Thus, only in the limited region of low pressure (<300 MPa) and temperature (<60 °C), the fluctuating ice-like patches are considered to persist.

Non-Gaussian Analysis of Turbulent Boundary Layer Fluctuating Pressure on Aircraft Skin Panels

NASA Technical Reports Server (NTRS)

Rizzi, Stephen A.; Steinwolf, Alexander

2005-01-01

The purpose of the study is to investigate the probability density function (PDF) of turbulent boundary layer fluctuating pressures measured on the outer sidewall of a supersonic transport aircraft and to approximate these PDFs by analytical models. Experimental flight results show that the fluctuating pressure PDFs differ from the Gaussian distribution even for standard smooth surface conditions. The PDF tails are wider and longer than those of the Gaussian model. For pressure fluctuations in front of forward-facing step discontinuities, deviations from the Gaussian model are more significant and the PDFs become asymmetrical. There is a certain spatial pattern of the skewness and kurtosis behavior depending on the distance upstream from the step. All characteristics related to non-Gaussian behavior are highly dependent upon the distance from the step and the step height, less dependent on aircraft speed, and not dependent on the fuselage location. A Hermite polynomial transform model and a piecewise-Gaussian model fit the flight data well both for the smooth and stepped conditions. The piecewise-Gaussian approximation can be additionally regarded for convenience in usage after the model is constructed.

Use of Heated Helium to Simulate Surface Pressure Fluctuations on the Launch Abort Vehicle During Abort Motor Firing

NASA Technical Reports Server (NTRS)

Panda, Jayanta; James, George H.; Burnside, Nathan J.; Fong, Robert; Fogt, Vincent A.

2011-01-01

The solid-rocket plumes from the Abort motor of the Multi-Purpose Crew Vehicle (MPCV, also know as Orion) were simulated using hot, high pressure, Helium gas to determine the surface pressure fluctuations on the vehicle in the event of an abort. About 80 different abort situations over a wide Mach number range, (0.3< or =M< or =1.2) and vehicle attitudes (+/-15deg) were simulated inside the NASA Ames Unitary Plan, 11-Foot Transonic Wind Tunnel. For each abort case, typically two different Helium plume and wind tunnel conditions were used to bracket different flow matching critera. This unique, yet cost-effective test used a custom-built hot Helium delivery system, and a 6% scale model of a part of the MPCV, known as the Launch Abort Vehicle. The test confirmed the very high level of pressure fluctuations on the surface of the vehicle expected during an abort. In general, the fluctuations were found to be dominated by the very near-field hydrodynamic fluctuations present in the plume shear-layer. The plumes were found to grow in size for aborts occurring at higher flight Mach number and altitude conditions. This led to an increase in the extent of impingement on the vehicle surfaces; however, unlike some initial expectations, the general trend was a decrease in the level of pressure fluctuations with increasing impingement. In general, the highest levels of fluctuations were found when the outer edges of the plume shear layers grazed the vehicle surface. At non-zero vehicle attitudes the surface pressure distributions were found to become very asymmetric. The data from these wind-tunnel simulations were compared against data collected from the recent Pad Abort 1 flight test. In spite of various differences between the transient flight situation and the steady-state wind tunnel simulations, the hot-Helium data were found to replicate the PA1 data fairly reasonably. The data gathered from this one-of-a-kind wind-tunnel test fills a gap in the manned-space programs, and will be used to establish the acoustic environment for vibro-acoustic qualification testing of the MPCV.

Event-by-Event Fluctuations of Azimuthal Particle Anisotropy in Au+Au Collisions at sNN=200GeV

NASA Astrophysics Data System (ADS)

Alver, B.; Back, B. B.; Baker, M. D.; Ballintijn, M.; Barton, D. S.; Betts, R. R.; Bickley, A. A.; Bindel, R.; Busza, W.; Carroll, A.; Chai, Z.; Decowski, M. P.; García, E.; Gburek, T.; George, N.; Gulbrandsen, K.; Halliwell, C.; Hamblen, J.; Hauer, M.; Henderson, C.; Hofman, D. J.; Hollis, R. S.; Hołyński, R.; Holzman, B.; Iordanova, A.; Johnson, E.; Kane, J. L.; Khan, N.; Kulinich, P.; Kuo, C. M.; Li, W.; Lin, W. T.; Loizides, C.; Manly, S.; Mignerey, A. C.; Nouicer, R.; Olszewski, A.; Pak, R.; Reed, C.; Roland, C.; Roland, G.; Sagerer, J.; Seals, H.; Sedykh, I.; Smith, C. E.; Stankiewicz, M. A.; Steinberg, P.; Stephans, G. S. F.; Sukhanov, A.; Tonjes, M. B.; Trzupek, A.; Vale, C.; van Nieuwenhuizen, G. J.; Vaurynovich, S. S.; Verdier, R.; Veres, G. I.; Walters, P.; Wenger, E.; Wolfs, F. L. H.; Wosiek, B.; Woźniak, K.; Wysłouch, B.

2010-04-01

This Letter presents the first measurement of event-by-event fluctuations of the elliptic flow parameter v2 in Au+Au collisions at sNN=200GeV as a function of collision centrality. The relative nonstatistical fluctuations of the v2 parameter are found to be approximately 40%. The results, including contributions from event-by-event elliptic flow fluctuations and from azimuthal correlations that are unrelated to the reaction plane (nonflow correlations), establish an upper limit on the magnitude of underlying elliptic flow fluctuations. This limit is consistent with predictions based on spatial fluctuations of the participating nucleons in the initial nuclear overlap region. These results provide important constraints on models of the initial state and hydrodynamic evolution of relativistic heavy ion collisions.

Fan Noise Source Diagnostic Test: Vane Unsteady Pressure Results

NASA Technical Reports Server (NTRS)

Envia, Edmane

2002-01-01

To investigate the nature of fan outlet guide vane pressure fluctuations and their link to rotor-stator interaction noise, time histories of vane fluctuating pressures were digitally acquired as part of the Fan Noise Source Diagnostic Test. Vane unsteady pressures were measured at seven fan tip speeds for both a radial and a swept vane configuration. Using time-domain averaging and spectral analysis, the blade passing frequency (BPF) harmonic and broadband contents of the vane pressures were individually analyzed. Significant Sound Pressure Level (SPL) reductions were observed for the swept vane relative to the radial vane for the BPF harmonics of vane pressure, but vane broadband reductions due to sweep turned out to be much smaller especially on an average basis. Cross-correlation analysis was used to establish the level of spatial coherence of broadband pressures between different locations on the vane and integral length scales of pressure fluctuations were estimated from these correlations. Two main results of this work are: (1) the average broadband level on the vane (in dB) increases linearly with the fan tip speed for both the radial and swept vanes, and (2) the broadband pressure distribution on the vane is nearly homogeneous and its integral length scale is a monotonically decreasing function of fan tip speed.

Detection of small-amplitude periodic surface pressure fluctuation by pressure-sensitive paint measurements using frequency-domain methods

NASA Astrophysics Data System (ADS)

Noda, Takahiro; Nakakita, Kazuyki; Wakahara, Masaki; Kameda, Masaharu

2018-06-01

Image measurement using pressure-sensitive paint (PSP) is an effective tool for analyzing the unsteady pressure field on the surface of a body in a low-speed air flow, which is associated with wind noise. In this study, the surface pressure fluctuation due to the tonal trailing edge (TE) noise for a two-dimensional NACA 0012 airfoil was quantitatively detected using a porous anodized aluminum PSP (AA-PSP). The emission from the PSP upon illumination by a blue laser diode was captured using a 12-bit high-speed complementary metal-oxide-semiconductor (CMOS) camera. The intensities of the captured images were converted to pressures using a standard intensity-based method. Three image-processing methods based on the fast Fourier transform (FFT) were tested to determine their efficiency in improving the signal-to-noise ratio (SNR) of the unsteady PSP data. In addition to two fundamental FFT techniques (the full data and ensemble averaging FFTs), a technique using the coherent output power (COP), which involves the cross correlation between the PSP data and the signal measured using a pointwise sound-level meter, was tested. Preliminary tests indicated that random photon shot noise dominates the intensity fluctuations in the captured PSP emissions above 200 Hz. Pressure fluctuations associated with the TE noise, whose dominant frequency is approximately 940 Hz, were successfully measured by analyzing 40,960 sequential PSP images recorded at 10 kfps. Quantitative validation using the power spectrum indicates that the COP technique is the most effective method of identification of the pressure fluctuation directly related to TE noise. It is possible to distinguish power differences with a resolution of 10 Pa^2 (4 Pa in amplitude) when the COP was employed without use of another wind-off data. This resolution cannot be achieved by the ensemble averaging FFT because of an insufficient elimination of the background noise.

[Comparison of invasive blood pressure measurement in the aorta with indirect oscillometric blood pressure measurement at the wrist and forearm].

PubMed

Saul, F; Aristidou, Y; Klaus, D; Wiemeyer, A; Lösse, B

1995-09-01

Indirectly measured blood pressure at the wrist or upper arm was compared with directly measured values in the aortic arch during routinely performed diagnostic cardiac catheterization in 100 patients (31-80 years, mean 59.3 years, 60% males). The noninvasive measurements were carried out by oscillometric devices, NAiS Blood Pressure Watch for measurements at the wrist, and Hestia OZ80 at the upper arm. Systolic blood pressure measured at the wrist was 4.3 +/- 14.1 mm Hg, and the diastolic value 6.0 +/- 8.9 mm Hg higher than when measured at the aortic arch; the difference was significant in both cases. Correlation coefficients were 0.85 for systolic and 0.71 for diastolic blood pressure. In 16% of the patients the systolic blood pressure at the wrist differed more than +/- 20 mm Hg. The diastolic blood pressure at the wrist measured more than +/- 20 mm Hg higher than in the aorta in 5% of the patients. At the upper arm mean systolic values were not different to the aorta. The diastolic pressure was 9.3 +/- 9.8 mm Hg higher in the aorta than at the upper arm. To verify the accuracy of values measured with the NAiS Blood Pressure Watch compared with the standard technique at the upper arm, sequential measurements were made at wrist and ipsilateral upper arm in the same group of 100 patients. The systolic blood pressure at the left wrist was 3.4 +/- 13.3 mm Hg higher and the diastolic pressure 3.8 +/- 9.5 mm Hg lower than at the upper arm. Only 53% of systolic values lay within a range of +/- 10 mm Hg. The correspondence between wrist and upper arm values was better for diastolic blood pressure, the values differing by less than +/- 10 mm Hg in two-thirds of patients. Self-measurement of arterial blood pressure with an oscillometric device at the wrist can be recommended only in individual cases with a difference of simultaneously measured values at the upper arm of less than +/- 10 mm Hg for systolic and diastolic blood pressures. The standard method for indirectly measuring arterial blood pressure remains the measurement at the upper arm site, which nevertheless showed a systolic pseudohypertension (deviation of more than 10 mm Hg) in comparison to the invasively measured values in 15% of our selected patients and a diastolic pseudohypertension (deviation of more than 15 mm Hg) in 23% of the patients.

Separated-flow unsteady pressures and forces on elastically responding structures

NASA Technical Reports Server (NTRS)

Coke, C. F.; Riddle, D. W.; Hwang, C.

1977-01-01

Broadband rms, spectral density, and spatial correlation information that characterizes the fluctuating pressures and forces that cause aircraft buffet is presented. The main theme is to show the effects of elasticity. In order to do so, data are presented that were obtained in regions of separated flow on wings of wind-tunnel models of varying stiffness and on the wing of a full-scale aircraft. Reynolds number effects on the pressure fluctuations are also discussed.

Correlation of combustor acoustic power levels inferred from internal fluctuating pressure measurements

NASA Technical Reports Server (NTRS)

Vonglahn, U. H.

1978-01-01

Combustion chamber acoustic power levels inferred from internal fluctuating pressure measurements are correlated with operating conditions and chamber geometries over a wide range. The variables include considerations of chamber design (can, annular, and reverse-flow annular) and size, number of fuel nozzles, burner staging and fuel split, airflow and heat release rates, and chamber inlet pressure and temperature levels. The correlated data include those obtained with combustion component development rigs as well as engines.

Attenuation of centre-of-pressure trajectory fluctuations under the prosthetic foot when using an articulating hydraulic ankle attachment compared to fixed attachment.

PubMed

De Asha, Alan R; Johnson, Louise; Munjal, Ramesh; Kulkarni, Jai; Buckley, John G

2013-02-01

Disruptions to the progress of the centre-of-pressure trajectory beneath prosthetic feet have been reported previously. These disruptions reflect how body weight is transferred over the prosthetic limb and are governed by the compliance of the prosthetic foot device and its ability to simulate ankle function. This study investigated whether using an articulating hydraulic ankle attachment attenuates centre-of-pressure trajectory fluctuations under the prosthetic foot compared to a fixed attachment. Twenty active unilateral trans-tibial amputees completed walking trials at their freely-selected, comfortable walking speed using both their habitual foot with either a rigid or elastic articulating attachment and a foot with a hydraulic ankle attachment. Centre-of-pressure displacement and velocity fluctuations beneath the prosthetic foot, prosthetic shank angular velocity during stance, and walking speed were compared between foot conditions. Use of the hydraulic device eliminated or reduced the magnitude of posteriorly directed centre-of-pressure displacements, reduced centre-of-pressure velocity variability across single-support, increased mean forward angular velocity of the shank during early stance, and increased freely chosen comfortable walking speed (P ≤ 0.002). The attenuation of centre-of-pressure trajectory fluctuations when using the hydraulic device indicated bodyweight was transferred onto the prosthetic limb in a smoother, less faltering manner which allowed the centre of mass to translate more quickly over the foot. Copyright © 2012 Elsevier Ltd. All rights reserved.

Pressure Fluctuations in a Common-Rail Fuel Injection System

NASA Technical Reports Server (NTRS)

Rothrock, A M

1931-01-01

This report presents the results of an investigation to determine experimentally the instantaneous pressures at the discharge orifice of a common-rail fuel injection system in which the timing valve and cut-off valve were at some distance from the automatic fuel injection valve, and also to determine the methods by which the pressure fluctuations could be controlled. The results show that pressure wave phenomena occur between the high-pressure reservoir and the discharge orifice, but that these pressure waves can be controlled so as to be advantageous to the injection of the fuel. The results also give data applicable to the design of such an injection system for a high-speed compression-ignition engine.

Processes controlling dissolved oxygen and pH in the upper Willamette River basin, Oregon, 1994

USGS Publications Warehouse

Pogue, Ted R.; Anderson, Chauncey W.

1995-01-01

In July and August of 1994, the U. S. Geological Survey in cooperation with the Oregon Department of Environmental Quality (ODEQ) collected data to document the spatial extent and diel variability of dissolved oxygen (DO) concentrations and pH levels in selected reaches of streams in the upper Willamette River Basin. These data were also collected to identify primary factors that control DO concentrations downstream from major point sources as well as to provide ODEQ with data to refine calibration of their steady-state DO and nutrient models for the upper Willamette River Basin. All of the reaches studied had diel variations in DO and pH. The magnitude of the diel variations in DO ranged from 0.2 to 3.9 milligrams per liter (7 to 50 percent-saturation units based on ambient water temperature and barometric pressure) and in pH from 0.3 to 1.4 units. However, of the reaches studied, only the Coast Fork Willamette River from river mile (RM) 21.7 to 12.5 and the Willamette River from RM 151 to 141.6 had field measured violations of State standards for DO and pH. DO concentration and pH in water depend on many factors. Data were collected to examine several major factors, including BOD (biochemical oxygen demand), carbonaceous BOD, nitrogenous BOD, and measures of photosynthetic activity. Of the four study reaches, only a short stretch of the Coast Fork Willamette River has potential for important levels of oxygen consumption from BOD or nitrification. Additionally, water-column primary-productivity measurements indicated that respiration and photosynthesis by free-floating algae did not explain the observed diel variations in DO in the study reaches. Results from a simple mathematical model incorporating measures of community respiration and net primary productivities indicated that periphyton are capable of producing a diel variation of the order of magnitude observed during the August study period. In the Willamette River near Peoria, the combined periphyton DO consumption and production estimate at RM 151 (2.4 mg/L) and RM 144.6 (1.7 mg/L) would account for 90 and 63 percent, respectively, of the observed diel fluctuation. The estimates for the Corvallis reach at RM 132.6 (0.4 mg/L) and RM 130.7 (2.9 mg/L) had a considerably larger range of 36 to 264 percent of DO saturation, respectively. Therefore, because BOD and phytoplankton do not appear to be important contributors to diel DO fluctuations, periphyton are likely the primary contributor to diel fluctuations in the upper Willamette River Basin during July and August.

Computational Analysis of an effect of aerodynamic pressure on the side view mirror geometry

NASA Astrophysics Data System (ADS)

Murukesavan, P.; Mu'tasim, M. A. N.; Sahat, I. M.

2013-12-01

This paper describes the evaluation of aerodynamic flow effects on side mirror geometry for a passenger car using ANSYS Fluent CFD simulation software. Results from analysis of pressure coefficient on side view mirror designs is evaluated to analyse the unsteady forces that cause fluctuations to mirror surface and image blurring. The fluctuation also causes drag forces that increase the overall drag coefficient, with an assumption resulting in higher fuel consumption and emission. Three features of side view mirror design were investigated with two input velocity parameters of 17 m/s and 33 m/s. Results indicate that the half-sphere design shows the most effective design with less pressure coefficient fluctuation and drag coefficient.

Transonic buffet behavior of Northrop F-5A aircraft

NASA Technical Reports Server (NTRS)

Hwang, C.; Pi, W. S.

1974-01-01

Flight tests were performed on an F-5A aircraft to investigate the dynamic buffet pressure distribution on the wing surfaces and the responses during a series of transonic maneuvers called wind-up turns. The conditions under which the tests were conducted are defined. The fluctuating buffet pressure data on the right wing of the aircraft were acquired by miniaturized semiconductor-type pressure transducers flush mounted on the wing. Processing of the fluctuating pressures and responses included the generation of the auto- and cross-power spectra, and of the spatial correlation functions. An analytical correlation procedure was introduced to compute the aircraft response spectra based on the measured buffet pressures.

Water-chemistry and chloride fluctuations in the Upper Floridan Aquifer in the Port Royal Sound area, South Carolina, 1917-93

USGS Publications Warehouse

Landmeyer, J.E.; Belval, D.L.

1996-01-01

Withdrawal of water from the Upper Floridan aquifer south of Port Royal Sound in Beaufort and Jasper Counties, South Carolina, has lowered water levels and reversed the hydraulic gradient beneath Hilton Head Island, South Carolina. Ground water that had previously discharged at the Sound is now being deflected southwest, toward withdrawals located near the city of Savannah, Georgia, and the island of Hilton Head. The reversal of this hydraulic gradient and the decline of water levels have caused saltwater in the Upper Floridan aquifer north of Port Royal Sound to begin moving southwest, toward water-supply wells for the town of Hilton Head and toward industries pumping ground water near Savannah. Analytical results from ground-water samples collected from wells in the Upper Floridan aquifer beneath and adjacent to Port Royal Sound show two plumes in the aquifer with chloride concentrations above the drinking- water standard. One plume of high chloride concentration extends slightly south of the theoretical predevelopment location of the steady- state freshwater-saltwater interface as indicated by numerical modeling. The other plume is present beneath the town of Port Royal, where the upper confining unit above the Upper Floridan aquifer is thin or absent. In these areas, the decline in water levels caused by ground-water withdrawals may have made it possible for water from tidal creeks to enter the Upper Floridan aquifer. Many wells completed in the upper permeable zone of the Upper Floridan aquifer show a distinct specific- conductance profile. One non-producing, monitoring well on Hilton Head Island (BFT-1810) was selected to depict a worst-case scenario to examine the short- and long-term water-chemistry and chloride fluctuations in the aquifer. Specific conductance was monitored at depths of 170, 190, and 200 feet below the top of the well casing. The specific conductance measured in 1987 ranged from approximately 450 microsiemens per centimeter near the top of the Upper Floridan aquifer to 1,500 microsiemens per centimeter near the lower, less permeable zone. Short-term fluctuations in conductance were measured at each probe and were found to be related to water-level fluctuations in the well caused by tidal cycles. The conductance varied regularly up to 100 microsiemens per centimeter, with an increasing time lag between high and low tides and low and high specific conductance for progressively shallower depths. Well BFT-1810 was monitored for specific conductance and water levels from October 1987 through September 1993. Specific conductance at the 170-foot probe showed little long-term change, while the 190- and the 200-foot probes showed long-term increases to approximately 4,000 and 10,000 microsiemens per centimeter, respectively. This well is located closest to one of the two plumes of saltwater delineated in the Upper Floridan aquifer, and the long-term chloride increases are a result of the movement of saltwater in the Upper Floridan aquifer toward Hilton Head Island under the influence of regional ground-water withdrawals.

Water hammer reduces fouling during natural water ultrafiltration.

PubMed

Broens, F; Menne, D; Pothof, I; Blankert, B; Roesink, H D W; Futselaar, H; Lammertink, R G H; Wessling, M

2012-03-15

Today's ultrafiltration processes use permeate flow reversal to remove fouling deposits on the feed side of ultrafiltration membranes. We report an as effective method: the opening and rapid closing of a valve on the permeate side of an ultrafiltration module. The sudden valve closure generates pressure fluctuations due to fluid inertia and is commonly known as "water hammer". Surface water was filtrated in hollow fiber ultrafiltration membranes with a small (5%) crossflow. Filtration experiments above sustainable flux levels (>125 l (m2h)(-1)) show that a periodic closure of a valve on the permeate side improves filtration performance as a consequence of reduced fouling. It was shown that this effect depends on flux and actuation frequency of the valve. The time period that the valve was closed proved to have no effect on filtration performance. The pressure fluctuations generated by the sudden stop in fluid motion due to the valve closure are responsible for the effect of fouling reduction. High frequency recording of the dynamic pressure evolution shows water hammer related pressure fluctuations to occur in the order of 0.1 bar. The pressure fluctuations were higher at higher fluxes (higher velocities) which is in agreement with the theory. They were also more effective at higher fluxes with respect to fouling mitigation. Copyright © 2011 Elsevier Ltd. All rights reserved.

Structure and interactions of fully hydrated dioleoylphosphatidylcholine bilayers.

PubMed Central

Tristram-Nagle, S; Petrache, H I; Nagle, J F

1998-01-01

This study focuses on dioleoylphosphatidylcholine (DOPC) bilayers near full hydration. Volumetric data and high-resolution synchrotron x-ray data are used in a method that compares DOPC with well determined gel phase dipalmitoylphosphatidylcholine (DPPC). The key structural quantity obtained is fully hydrated area/lipid A0 = 72.2 +/- 1.1 A2 at 30 degrees C, from which other quantities such as thickness of the bilayer are obtained. Data for samples over osmotic pressures from 0 to 56 atmospheres give an estimate for the area compressibility of KA = 188 dyn/cm. Obtaining the continuous scattering transform and electron density profiles requires correction for liquid crystal fluctuations. Quantitation of these fluctuations opens an experimental window on the fluctuation pressure, the primary repulsive interaction near full hydration. The fluctuation pressure decays exponentially with water spacing, in agreement with analytical results for soft confinement. However, the ratio of decay length lambda(fl) = 5.8 A to hydration pressure decay length lambda = 2.2 A is significantly larger than the value of 2 predicted by analytical theory and close to the ratio obtained in recent simulations. We also obtain the traditional osmotic pressure versus water spacing data. Our analysis of these data shows that estimates of the Hamaker parameter H and the bending modulus Kc are strongly coupled. PMID:9675192

Numerical investigation on pressure fluctuations in centrifugal compressor with different inlet guide vanes pre-whirl angles

NASA Astrophysics Data System (ADS)

Wang, Y. C.; Shi, M.; Cao, S. L.; Li, Z. H.

2013-12-01

The pressure fluctuations in a centrifugal compressor with different inlet guide vanes (IGV) pre-whirl angles were investigated numerically, as well as the pre-stress model and static structural of blade. The natural frequency was evaluated by pre-stress model analysis. The results show that, the aero-dynamic pressure acting on blade surface is smaller than rotation pre-stress, which wouldn't result in large deformation of blade. The natural frequencies with rotation pre-stress are slightly higher than without rotation pre-stress. The leading mechanism of pressure fluctuations for normal conditions is the rotor-stator (IGVs) interaction, while is serious flow separations for conditions that are close to surge line. A few frequency components in spectra are close to natural frequency, which possibly result in resonant vibration if amplitude is large enough, which is dangerous for compressor working, and should be avoided.

Acoustic Radiation from a Mach 14 Turbulent Boundary layer

NASA Astrophysics Data System (ADS)

Duan, Lian; Choudhari, Meelan

2014-11-01

Direct numerical simulations (DNS) are used to examine the pressure fluctuations generated by a high-speed turbulent boundary layer with a nominal freestream Mach number of 14 and wall temperature of 0.15 times the recovery temperature. The emphasis is on characterizing the acoustic radiation from the turbulent boundary layer and comparing it with previous simulations at Mach 2.5 and Mach 6 to assess the Mach-number dependence of the freestream pressure fluctuations. In particular, the numerical database is used to provide insights into the pressure disturbance spectrum and amplitude scaling with respect to the freestream Mach number as well as to understand the acoustic source mechanisms at very high Mach numbers. Such information is important for characterizing the freestream disturbance environment in conventional (i.e., noisy) hypersonic wind tunnels. Spectral characteristics of pressure fluctuations at the surface are also investigated. Supported by AFOSR and NASA Langley Research Center.

Copernicus observations of C I: pressures and carbon abundances in diffuse interstellar clouds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jenkins, E.B.; Jura, M.; Loewenstein, M.

1983-07-01

Using the Copernicus satellite, we observed ultraviolet absorption lines of interstellar neutral carbon atoms toward 27 stars. In addition to deriving column densities of C I (both in its ground state and the two excited fine-structure levels), we used our equivalent widths to revise the f-values of some of the C I transitions measured by other investigators. We also observed H/sub 2/ from the J = 4 level so that we could compare the rotational excitation of H/sub 2/ with the fine-structure excitation of C I. From the amount of fine-structure excitation of C I in each case, we havemore » derived information on the thermal gas pressures within the diffuse clouds. Most clouds have p/k between 10/sup 3/ cm/sup -3/ K and 10/sup 4/ cm/sup -3/ K, but we found that at least 6% of the C I-bearing material is at p/k>10/sup 4/ cm/sup -3/ K, and one-third of the gas has upper limits for pressure below 10/sup 3/ cm/sup -3/ K, assuming temperatures are not appreciably below 20 K. An analysis of radial velocities for the absorption lines showed no distinctive trends for the kinematics of high- or low-pressure gas components. From the apparent lack of acceleration of high-pressure clouds, we conclude that it is unlikely that streaming intercloud material is causing significant ram pressurization. We have compared our results with the predictions for pressure fluctuations caused by supernova explosions in the theory of McKee and Ostriker.« less

Numerical assessment of pulsating water jet in the conical diffusers

NASA Astrophysics Data System (ADS)

Tanasa, Constantin; Ciocan, Tiberiu; Muntean, Sebastian

2017-11-01

The hydraulic fluctuations associated with partial load operating conditions of Francis turbines are often periodic and characterized by the presence of a vortex rope. Two types of pressure fluctuations associated with the draft tube surge are identified in the literature. The first is an asynchronous (rotating) pressure fluctuation due to the precession of the helical vortex around the axis of the draft tube. The second type of fluctuation is a synchronous (plunging) fluctuation. The plunging fluctuations correspond to the flow field oscillations in the whole hydraulic passage, and are generally propagated overall in the hydraulic system. The paper introduced a new control method, which consists in injecting a pulsating axial water jet along to the draft tube axis. Nevertheless, the great calling of this control method is to mitigate the vortex rope effects targeting the vortex sheet and corresponding plunging component. In this paper, is presented our 3D numerical investigations with and without pulsating axial water jet control method in order to evaluate the concept.

Parallel electron force balance and the L-H transition

DOE PAGES

Stoltzfus-Dueck, T.

2016-05-23

In one popular paradigm for the L-H transition, energy transfer to the mean flows directly depletes turbulence fluctuation energy, resulting in suppression of the turbulence and a corresponding transport bifurcation. To quantitatively evaluate this mechanism, one must remember that electron parallel force balance couples nonzonal velocity fluctuations with electron pressure fluctuations on rapid timescales, comparable with the electron transit time. For this reason, energy in the nonzonal velocity stays in a fairly fixed ratio to the free energy in electron density fluctuations, at least for frequency scales much slower than electron transit. Furthermore, in order for direct depletion of themore » energy in turbulent fluctuations to cause the L-H transition, energy transfer via Reynolds stress must therefore drain enough energy to significantly reduce the sum of the free energy in nonzonal velocities and electron pressure fluctuations. At low k⊥, the electron thermal free energy is much larger than the energy in nonzonal velocities, posing a stark challenge for this model of the L-H transition.« less

Fluctuating pressures on fan blades of a turbofan engine: Static and wind-tunnel investigations

NASA Technical Reports Server (NTRS)

Schoenster, J. A.

1982-01-01

To investigate the fan noise generated from turbofan engines, miniature pressure transducers were used to measure the fluctuating pressure on the fan blades of a JT15D engine. Tests were conducted with the engine operating on an outdoor test stand and in a wind tunnel. It was found that a potential flow interaction between the fan blades and six, large support struts in the bypass duct is a dominant noise source in the JT15D engine. Effects of varying fan speed and the forward speed on the blade pressure are also presented.

Pressure effects on collective density fluctuations in water and protein solutions

PubMed Central

Russo, Daniela; Laloni, Alessio; Filabozzi, Alessandra; Heyden, Matthias

2017-01-01

Neutron Brillouin scattering and molecular dynamics simulations have been used to investigate protein hydration water density fluctuations as a function of pressure. Our results show significant differences between the pressure and density dependence of collective dynamics in bulk water and in concentrated protein solutions. Pressure-induced changes in the tetrahedral order of the water HB network have direct consequences for the high-frequency sound velocity and damping coefficients, which we find to be a sensitive probe for changes in the HB network structure as well as the wetting of biomolecular surfaces. PMID:29073065

Clinical comparison of automatic, noninvasive measurements of blood pressure in the forearm and upper arm with the patient supine or with the head of the bed raised 45 degrees: a follow-up study.

PubMed

Schell, Kathleen; Lyons, Denise; Bradley, Elisabeth; Bucher, Linda; Seckel, Maureen; Wakai, Sandra; Carson, Elizabeth; Waterhouse, Julie; Chichester, Melanie; Bartell, Deborah; Foraker, Theresa; Simpson, E Kathleen

2006-03-01

Noninvasive measurement of blood pressure in the forearm is used when the upper arm is inaccessible and/or when available blood pressure cuffs do not fit a patient's arm. Evidence supporting this practice is limited. To compare noninvasive measurements of blood pressure in the forearm and upper arm of medical-surgical inpatients positioned supine and with the head of the bed raised 45 degrees . Cuff size was selected on the basis of forearm and upper arm circumference and manufacturers' recommendations. With a Welch Allyn Vital Signs 420 Series monitor, blood pressures were measured in the forearm and then in the upper arm of 221 supine patients with their arms resting at their sides. Patients were repositioned with the head of the bed elevated 45 degrees and after 2 minutes, blood pressures were measured in the upper arm and then the forearm. Starting position was alternated on subsequent subjects. Paired t tests revealed significant differences between systolic and diastolic blood pressures measured in the upper arm and forearm with patients supine and with the head of the bed elevated 45 degrees . The Bland-Altman procedure revealed that the distances between the mean values and the limits of agreement were from 15 to 33 mm Hg for individual subjects. Noninvasive measurements of blood pressure in the forearm and upper arm cannot be interchanged in medical-surgical patients who are supine or in patients with the head of the bed elevated 45 degrees .

Prediction of space shuttle fluctuating pressure environments, including rocket plume effects

NASA Technical Reports Server (NTRS)

Plotkin, K. J.; Robertson, J. E.

1973-01-01

Preliminary estimates of space shuttle fluctuating pressure environments have been made based on prediction techniques developed by Wyle Laboratories. Particular emphasis has been given to the transonic speed regime during launch of a parallel-burn space shuttle configuration. A baseline configuration consisting of a lightweight orbiter and monolithic SRB, together with a typical flight trajectory, have been used as models for the predictions. Critical fluctuating pressure environments are predicted at transonic Mach numbers. Comparisons between predicted environments and wind tunnel test results, in general, showed good agreement. Predicted one-third octave band spectra for the above environments were generally one of three types: (1) attached turbulent boundary layer spectra (typically high frequencies); (2) homogeneous separated flow and shock-free interference flow spectra (typically intermediate frequencies); and (3) shock-oscillation and shock-induced interference flow spectra (typically low frequencies). Predictions of plume induced separated flow environments were made. Only the SRB plumes are important, with fluctuating levels comparable to compression-corner induced separated flow shock oscillation.

Arctic Contribution to Upper-Ocean Variability in the North Atlantic.

NASA Astrophysics Data System (ADS)

Walsh, John E.; Chapman, William L.

1990-12-01

Because much of the deep water of the world's oceans forms in the high-latitude North Atlantic, the potential climatic leverage of salinity and temperature anomalies in this region is large. Substantial variations of sea ice have accompanied North Atlantic salinity and temperature anomalies, especially the extreme and long-lived `Great Salinity Anomaly' of the late 1960s and early 1970s. Atmospheric pressure data are used hem to show that the local forcing of high-latitude North Atlantic Ocean fluctuations is augmented by antecedent atmospheric circulation anomalies over the central Arctic. These circulation anomalies are consistent with enhanced wind-forcing of thicker, older ice into the Transpolar Drift Stream and an enhanced export of sea ice (fresh water) from the Arctic into the Greenland Sea prior to major episodes of ice severity in the Greenland and Iceland seas. An index of the pressure difference between southern Greenland and the Arctic-Asian coast reached its highest value of the twentieth century during the middle-to-late 1960s, the approximate time of the earliest observation documentation of the Great Salinity Anomaly.

An interaction algorithm for prediction of mean and fluctuating velocities in two-dimensional aerodynamic wake flows

NASA Technical Reports Server (NTRS)

Baker, A. J.; Orzechowski, J. A.

1980-01-01

A theoretical analysis is presented yielding sets of partial differential equations for determination of turbulent aerodynamic flowfields in the vicinity of an airfoil trailing edge. A four phase interaction algorithm is derived to complete the analysis. Following input, the first computational phase is an elementary viscous corrected two dimensional potential flow solution yielding an estimate of the inviscid-flow induced pressure distribution. Phase C involves solution of the turbulent two dimensional boundary layer equations over the trailing edge, with transition to a two dimensional parabolic Navier-Stokes equation system describing the near-wake merging of the upper and lower surface boundary layers. An iteration provides refinement of the potential flow induced pressure coupling to the viscous flow solutions. The final phase is a complete two dimensional Navier-Stokes analysis of the wake flow in the vicinity of a blunt-bases airfoil. A finite element numerical algorithm is presented which is applicable to solution of all partial differential equation sets of inviscid-viscous aerodynamic interaction algorithm. Numerical results are discussed.

Improved Statistical Model Of 10.7-cm Solar Radiation

NASA Technical Reports Server (NTRS)

Vedder, John D.; Tabor, Jill L.

1993-01-01

Improved mathematical model simulates short-term fluctuations of flux of 10.7-cm-wavelength solar radiation during 91-day averaging period. Called "F10.7 flux", important as measure of solar activity and because it is highly correlated with ultraviolet radiation causing fluctuations in heating and density of upper atmosphere. F10.7 flux easily measureable at surface of Earth.

Neurologic decompression sickness following cabin pressure fluctuations at high altitude.

PubMed

Auten, Jonathan D; Kuhne, Michael A; Walker, Harlan M; Porter, Henry O

2010-04-01

Decompression sickness (DCS) occurs in diving, altitude chamber exposures, and unpressurized or depressurized high-altitude flights. Because DCS takes many forms, in-flight cases may be misinterpreted as hypoxia, hyperventilation, or viral illness, with resulting failure to respond appropriately. In this case, a 28-yr-old male pilot of a single-seat, tactical aircraft experienced 12 rapid pressure fluctuations while flying at 43,000 ft above sea level. He had no symptoms and decided to complete the flight, which required an additional 2 h in the air. Approximately 1 h later he began to experience fatigue, lightheadedness, and confusion, which he interpreted as onset of a viral illness. However, symptoms progressed to visual, cognitive, motor, and sensory degradations and it was with some difficulty that he landed safely at his destination. Neurologic DCS was suspected on initial evaluation by flight line medical personnel because of the delayed onset and symptom progression. He was transferred to a local Emergency Department and noted to have altered mental status, asymmetric motor deficits, and non-dermatomal paresthesias of the upper and lower extremities. Approximately 3.5 h after the incident and 2.5 h after the onset of symptoms he began hyperbaric oxygen therapy. He received partial relief at 30 min of the Navy DiveTable 6 and full resolution at 90 min; there were no recurrent symptoms at a 1-yr follow-up. This case highlights the importance of early recognition of in-flight DCS symptoms and landing as soon as possible rather than as soon as practical in all likely scenarios.

Fiber-optic interferometric sensors for measurements of pressure fluctuations - Experimental evaluation

NASA Technical Reports Server (NTRS)

Cho, Y. C.; Soderman, P. T.

1993-01-01

A fiber optic interferometric sensor that is being developed at NASA Ames Research Center for pressure fluctuation measurements in wind tunnels is considered. Preliminary evaluation indicates that the fiber optic interferometric sensor can be successfully used as an aeroacoustic sensor and is capable of providing a powerful instrument to solve complex acoustic measurement problems in wind tunnels.

Systemic changes and adverse effects induced by retinopathy of prematurity screening.

PubMed

Jiang, Jing-Bo; Zhang, Zhi-Wei; Zhang, Jia-Wen; Wang, Yan-Li; Nie, Chuan; Luo, Xian-Qiong

2016-01-01

To estimate the potential systemic events during and after retinopathy of prematurity (ROP) screening. A prospective and descriptive designed study was conducted to detect the physiologic and pathological changes 24h before, during, and 72h after ROP screening. Control blood pressure (BP), saturation, pulse rate, and body temperature were routinely taken at various time internals before and after screening. Adverse effects pertain to cardiovascular system, respiratory system, gastric system, urinary system and nervous system were retrospect 0-72h after ROP screening at a 24-hour interval. Totally 1254 prematurity babies receiving ROP screening during Jan. 1(st) 2013 to Dec. 31(th) 2013 were enrolled in our survey. Compared to control vital sign data taken before the examination, there was a fluctuation in the diastolic BP with the increased 3.03 mm Hg (P=0.04) after 3 doses of mydriatic drops. Immediately after the examination, there was a further 12.64 mm Hg (P<0.01) increase in systolic BP and a 7.24 mm Hg (P<0.01) in diastolic BP. The mean pulse rate during examination was 22.4 bpm (P<0.01) higher than the 133.3±9.0 bpm control level. The oxygen saturation shared an average drop of 5% (P<0.01) during screening. In prematurity with postconceptional age less than 31wk, the incidence of apnea (23.5%), necrotizing enterocolitis (NEC) (8.7%), gastric residual (25.4%) and upper digestive tract hemorrhage (6.4%) also demonstrated a significant rise (P<0.01). In our study sample, ROP screening was associated with NEC, gastric residual and upper digestive tract hemorrhage. These gastrointestinal side effects, along with breath activity pattern change and vital signs indicators fluctuation, may be results of additional stress responses.

A 'Quad-Disc' static pressure probe for measurement in adverse atmospheres - With a comparative review of static pressure probe designs

NASA Astrophysics Data System (ADS)

Nishiyama, Randall T.; Bedard, Alfred J., Jr.

1991-09-01

There are many areas of need for accurate measurements of atmospheric static pressure. These include observations of surface meteorology, airport altimeter settings, pressure distributions around buildings, moving measurement platforms, as well as basic measurements of fluctuating pressures in turbulence. Most of these observations require long-term observations in adverse environments (e.g., rain, dust, or snow). Currently, many pressure measurements are made, of necessity, within buildings, thus involving potential errors of several millibars in mean pressure during moderate winds, accompanied by large fluctuating pressures induced by the structure. In response to these needs, a 'Quad-Disk' pressure probe for continuous, outdoor monitoring purposes was designed which is inherently weather-protected. This Quad-Disk probe has the desirable features of omnidirectional response and small error in pitch. A review of past static pressure probes contrasts design approaches and capabilities.

Simulation of Surface Pressure Induced by Vortex/Body Interaction

NASA Astrophysics Data System (ADS)

He, M.; Islam, M.; Veitch, B.; Bose, N.; Colbourne, M. B.; Liu, P.

When a strong vortical wake impacts a structure, the pressure on the impacted surface sees large variations in its amplitude. This pressure fluctuation is one of the main sources causing severe structural vibration and hydrodynamic noise. Economical and effective prediction methods of the fluctuating pressure are required by engineers in many fields. This paper presents a wake impingement model (WIM) that has been incorporated into a panel method code, Propella, and its applications in simulations of a podded propeller wake impacting on a strut. Simulated strut surface pressure distributions and variations are compared with experimental data in terms of time-averaged components and phase-averaged components. The pressure comparisons show that the calculated results are in a good agreement with experimental data.

Sampling rare fluctuations of discrete-time Markov chains

NASA Astrophysics Data System (ADS)

Whitelam, Stephen

2018-03-01

We describe a simple method that can be used to sample the rare fluctuations of discrete-time Markov chains. We focus on the case of Markov chains with well-defined steady-state measures, and derive expressions for the large-deviation rate functions (and upper bounds on such functions) for dynamical quantities extensive in the length of the Markov chain. We illustrate the method using a series of simple examples, and use it to study the fluctuations of a lattice-based model of active matter that can undergo motility-induced phase separation.

Sampling rare fluctuations of discrete-time Markov chains.

PubMed

Whitelam, Stephen

2018-03-01

We describe a simple method that can be used to sample the rare fluctuations of discrete-time Markov chains. We focus on the case of Markov chains with well-defined steady-state measures, and derive expressions for the large-deviation rate functions (and upper bounds on such functions) for dynamical quantities extensive in the length of the Markov chain. We illustrate the method using a series of simple examples, and use it to study the fluctuations of a lattice-based model of active matter that can undergo motility-induced phase separation.

Influence of wind-induced air pressure fluctuations on topsoil gas concentrations within a Scots pine forest

NASA Astrophysics Data System (ADS)

Mohr, Manuel; Laemmel, Thomas; Maier, Martin; Schindler, Dirk

2017-04-01

Commonly it is assumed that soil gas transport is dominated by molecular diffusion. Few recent studies indicate that the atmosphere above the soil triggers non-diffusive gas transport processes in the soil, which can enhance soil gas transport and therefore soil gas efflux significantly. During high wind speed conditions, the so called pressure pumping effect has been observed: the enhancement of soil gas transport through dynamic changes in the air pressure field above the soil. However, the amplitudes and frequencies of the air pressure fluctuations responsible for pressure pumping are still uncertain. Moreover, an in situ observation of the pressure pumping effect is still missing. To investigate the pressure pumping effect, airflow measurements above and below the canopy of a Scots pine forest and high-precision relative air pressure measurements were conducted in the below-canopy space and in the soil over a measurement period of 16 weeks. To monitor the soil gas transport, a newly developed gas measurement system was used. The gas measurement system continuously injects helium as a tracer gas into the soil until a diffusive steady state is reached. With the steady state concentration profile of the tracer gas, it is possible to inversely model the gas diffusion coefficient profile of the soil. If the gas diffusion coefficient profile differed from steady state, we deduced that the soil gas transport is not only diffusive, but also influenced by non-diffusive processes. Results show that the occurrence of small air pressure fluctuations is strongly dependent on the mean above-canopy wind speed. The wind-induced air pressure fluctuations have mean amplitudes up to 10 Pa and lie in the frequency range 0.01-0.1 Hz. To describe the pumping motion of the air pressure field, the pressure pumping coefficient (PPC) was defined as the mean change in pressure per second. The PPC shows a clear quadratic dependence on mean above-canopy wind speed. Empirical modelling of the measured topsoil helium concentration demonstrated that the PPC is the most important predictor for changes in the topsoil helium concentration. Comparison of time periods with high PPC and periods of low PPC showed that the soil gas diffusion coefficient in depths between 5-10 cm increased up to 30% during periods of high PPC compared to steady state. Thus, the air pressure fluctuations observed in the atmosphere and described by the PPC penetrate into the soil and influence the topsoil gas transport.

Proposal and verification numerical simulation for a microwave forward scattering technique at upper hybrid resonance for the measurement of electron gyroscale density fluctuations in the electron cyclotron frequency range in magnetized plasmas

NASA Astrophysics Data System (ADS)

Kawamori, E.; Igami, H.

2017-11-01

A diagnostic technique for detecting the wave numbers of electron density fluctuations at electron gyro-scales in an electron cyclotron frequency range is proposed, and the validity of the idea is checked by means of a particle-in-cell (PIC) numerical simulation. The technique is a modified version of the scattering technique invented by Novik et al. [Plasma Phys. Controlled Fusion 36, 357-381 (1994)] and Gusakov et al., [Plasma Phys. Controlled Fusion 41, 899-912 (1999)]. The novel method adopts forward scattering of injected extraordinary probe waves at the upper hybrid resonance layer instead of the backward-scattering adopted by the original method, enabling the measurement of the wave-numbers of the fine scale density fluctuations in the electron-cyclotron frequency band by means of phase measurement of the scattered waves. The verification numerical simulation with the PIC method shows that the technique has a potential to be applicable to the detection of electron gyro-scale fluctuations in laboratory plasmas if the upper-hybrid resonance layer is accessible to the probe wave. The technique is a suitable means to detect electron Bernstein waves excited via linear mode conversion from electromagnetic waves in torus plasma experiments. Through the numerical simulations, some problems that remain to be resolved are revealed, which include the influence of nonlinear processes such as the parametric decay instability of the probe wave in the scattering process, and so on.

Role of transient water pressure in quarrying: A subglacial experiment using acoustic emissions

USGS Publications Warehouse

Cohen, D.; Hooyer, T.S.; Iverson, N.R.; Thomason, J.F.; Jackson, M.

2006-01-01

Probably the most important mechanism of glacial erosion is quarrying: the growth and coalescence of cracks in subglacial bedrock and dislodgement of resultant rock fragments. Although evidence indicates that erosion rates depend on sliding speed, rates of crack growth in bedrock may be enhanced by changing stresses on the bed caused by fluctuating basal water pressure in zones of ice-bed separation. To study quarrying in real time, a granite step, 12 cm high with a crack in its stoss surface, was installed at the bed of Engabreen, Norway. Acoustic emission sensors monitored crack growth events in the step as ice slid over it. Vertical stresses, water pressure, and cavity height in the lee of the step were also measured. Water was pumped to the lee of the step several times over 8 days. Pumping initially caused opening of a leeward cavity, which then closed after pumping was stopped and water pressure decreased. During cavity closure, acoustic emissions emanating mostly from the vicinity of the base of the crack in the step increased dramatically. With repeated pump tests this crack grew with time until the step's lee surface was quarried. Our experiments indicate that fluctuating water pressure caused stress thresholds required for crack growth to be exceeded. Natural basal water pressure fluctuations should also concentrate stresses on rock steps, increasing rates of crack growth. Stress changes on the bed due to water pressure fluctuations will increase in magnitude and duration with cavity size, which may help explain the effect of sliding speed on erosion rates. Copyright 2006 by the American Geophysical Union.

Laser velocimetry applied to transonic and supersonic aerodynamics

NASA Technical Reports Server (NTRS)

Johnson, D. A.; Bachalo, W. D.; Moddaress, D.

1976-01-01

As a further demonstration of the capabilities of laser velocity in compressible aerodynamics, measurements obtained in a Mach 2.9 separated turbulent boundary layer and in the transonic flow past a two-dimensional airfoil section are presented and compared to data realized by conventional techniques. In the separated-flow study, the comparisons were made against pitot-static pressure data. Agreement in mean velocities was realized where the pressure measurements could be considered reliable; however, in regions of instantaneous reverse velocities, the laser results were found to be consistent with the physics of the flow whereas the pressure data were not. The laser data obtained in regions of extremely high turbulence suggest that velocity biasing does not occur if the particle occurrence rate is low relative to the turbulent fluctuation rate. Streamwise turbulence intensities are also presented. In the transonic airfoil study, velocity measurements obtained immediately outside the upper surface boundary layer of a 6-inch chord MACA 64A010 airfoil are compared to edge velocities inferred from surface pressure measurements. For free-stream Mach numbers of 0.6 and 0.8, the agreement in results was very good. Dual scatter optical arrangements in conjunction with a single particle, counter-type signal processor were employed in these investigations. Half-micron-diameter polystyrene spheres and naturally occurring condensed oil vapor acted as light scatterers in the two respective flows. Bragg-cell frequency shifting was utilized in the separated flow study.

Category 3: Sound Generation by Interacting With a Gust

NASA Technical Reports Server (NTRS)

Envia, Edmane

2004-01-01

Solve the time-dependent inviscid flow equations for this geometry subject to the specified inflow/outflow mean conditions and the fluctuating inflow velocity distortion. (1) Compute the unsteady solution until periodicity in pressure is achieved by showing that at least two successive periods are identical. Periodicity must be achieved on both the airfoil surface and the inflow/outflow boundaries. (2) Once periodicity is achieved, compute the pressure frequency spectra on the reference airfoil on both the upper and lower surfaces at x=(-0.25c,0.00, +0.25c), on the inflow boundary at (x,y)={1.5c,-0.3c), (-1.5c,0.0),(-1.5c,0.3c)} and on the outflow boundary at (x,y)= {(1.5c,-0.3c),(1.5c,0.0), (1.5c,0.3c)}. Express the spectral results in dB using the standard definition 20 log(P(sub(r.m.s)/P(sub ref), where p(sub ref) == 20 microPa. (3) Extract the harmonic pressure distributions on the inflow and outflow boundaries (i.e., on x= -/+ 1.5c lines) at the fundamental frequency omega and apply a Fourier transform in y direction to identify the spatial (i.e., mode order) structure of the pressure perturbations. Express the result in dB for each mode order. Repeat the process for the frequencies 2omega and 3omega.

On the estimation of wall pressure coherence using time-resolved tomographic PIV

NASA Astrophysics Data System (ADS)

Pröbsting, Stefan; Scarano, Fulvio; Bernardini, Matteo; Pirozzoli, Sergio

2013-07-01

Three-dimensional time-resolved velocity field measurements are obtained using a high-speed tomographic Particle Image Velocimetry (PIV) system on a fully developed flat plate turbulent boundary layer for the estimation of wall pressure fluctuations. The work focuses on the applicability of tomographic PIV to compute the coherence of pressure fluctuations, with attention to the estimation of the stream and spanwise coherence length. The latter is required for estimations of aeroacoustic noise radiation by boundary layers and trailing edge flows, but is also of interest for vibro-structural problems. The pressure field is obtained by solving the Poisson equation for incompressible flows, where the source terms are provided by time-resolved velocity field measurements. Measured 3D velocity data is compared to results obtained from planar PIV, and a Direct Numerical Simulation (DNS) at similar Reynolds number. An improved method for the estimation of the material based on a least squares estimator of the velocity derivative along a particle trajectory is proposed and applied. Computed surface pressure fluctuations are further verified by means of simultaneous measurements by a pinhole microphone and compared to the DNS results and a semi-empirical model available from literature. The correlation coefficient for the reconstructed pressure time series with respect to pinhole microphone measurements attains approximately 0.5 for the band-pass filtered signal over the range of frequencies resolved by the velocity field measurements. Scaled power spectra of the pressure at a single point compare favorably to the DNS results and those available from literature. Finally, the coherence of surface pressure fluctuations and the resulting span- and streamwise coherence lengths are estimated and compared to semi-empirical models and DNS results.

Compression force on the upper jaw during neonatal intubation: mannequin study.

PubMed

Doreswamy, Srinivasa Murthy; Almannaei, Khaled; Fusch, Chris; Shivananda, Sandesh

2015-03-01

Neonatal intubation is a technically challenging procedure, and pressure-related injuries to surrounding structures have been reported. The primary objective of this study was to determine the pressure exerted on the upper jaw during tracheal intubation using a neonatal mannequin. Multidisciplinary care providers working at a neonatal intensive care unit were requested to intubate a neonatal mannequin using the standard laryngoscope and 3.0-mm (internal diameter) endotracheal tube. Compression force exerted was measured by using pressure-sensitive film taped on the upper jaw before every intubation attempt. Pressure, area under pressure and time taken to intubate were compared between the different types of health-care professionals. Thirty care providers intubated the mannequin three times each. Pressure impressions were observed on the developer film after every intubation attempt (n = 90). The mean pressure exerted during intubation across all health-care providers was 568 kPa (SD 78). The mean area placed under pressure was 142 mm(2) (SD 45), and the mean time taken for intubation was 14.7 s (SD 4.3). There was no difference in pressure exerted on the upper jaw between frequent and less frequent intubators. It was found that pressure greater than 400 kPa was inadvertently applied on the upper jaw during neonatal intubation, far exceeding the 250 kPa shown to cause tissue injury in animal models. The upper jaw is exposed to a significant compression force during intubation. Although such exposure is brief, it has the potential to cause tissue injury. Contact of the laryngoscope blade with the upper jaw occurred in all intubation attempts with the currently used design of laryngoscope. © 2014 The Authors. Journal of Paediatrics and Child Health © 2014 Paediatrics and Child Health Division (Royal Australasian College of Physicians).

Fluctuations in Cerebral Hemodynamics

DTIC Science & Technology

2003-12-01

Determination of scaling properties Detrended Fluctuations Analysis (see (28) and references therein) is commonly used to determine scaling...pressure (averaged over a cardiac beat) of a healthy subject. First 1000 values of the time series are shown. (b) Detrended fluctuation analysis (DFA...1000 values of the time series are shown. (b) Detrended fluctuation analysis of the time series shown in (a). Fig . 3 Side-by-side boxplot for the

[Special artificial respiration procedures and intracranial pressure. Animal experiment studies, development and use of a new pressure measuring technic, clinical aspects].

PubMed

Schedl, R

1985-01-01

We investigated the influence of Forced Diffusion Ventilation (FDV), a special form of High Frequency Ventilation (HFV), on elevated intracranial pressure (ICP) in 5 dogs. Elevation of ICP was standardized by inflation of an epidural balloon. A typical finding with FDV is a reduced intrapleural pressure and therefore one could expect a better cerebrovenous drainage influencing ICP. Nevertheless, we found no changes in mean ICP under conditions of FDV compared with IPPV. Respirator-synchronous fluctuations of ICP, cisternal cerebrospinal fluid pressure and intrapleural pressure were drastically reduced with FDV. This phenomenon has been already reported by other groups as a typical effect of HFV with rates of 100/min. One can speculate, that this immediate impact of HFV on ICP-curves might be of some advantage in patients with critically reduced intracranial compliance requiring long-term artificial ventilation, because peaks and amplitudes of ICP are reduced. Our clinical experience with High Frequency Pulsation (HFP) includes 11 patients with severe brain trauma. In clinical routine this method of HFV is more facile to applicate than FDV, because there is no need of a special endotracheal tube and sufficient CO2-elimination is not strongly dependent on precise position of the tube. But HFP, as FDV, includes all advantages of respiratory systems, that are open against atmosphere (coughing and simultaneous breathing, without drastically increasing airway pressure, suction during respiration, etc.). However, we could find no special advantages or disadvantages in ICP-course during long-term application of HFP (up to 10 days). Because application of HFV is dependent on special technical equipment, we investigated in 6 patients the influence of respiratory frequency, tidal volume and inspiratory flow on ICP-fluctuations using conventional ventilators. ICP was recorded by a new, self constructed pneumatic epidural pressure sensor. Ventilator-related ICP-fluctuations were found to be markedly reduced at frequencies of 20/min and usually eliminated at 30/min. We found an exponential correlation between ICP-fluctuations and respiratory frequency and there was no correlation between tidal volume and ICP. Central venous pressure amplitudes were found to be in linear correlation with respiratory frequency and tidal volumes as well. The amplitude of respiratory ICP-fluctuations seems to be more dependent on duration of expiratory time. As our findings demonstrate, artificial ventilation without entilator-related fluctuations in ICP ("brain-protective" ventilation) may be performed by conventional volume-constant, time-cycled ventilators.(ABSTRACT TRUNCATED AT 400 WORDS)

Morphing Wing: Experimental Boundary Layer Transition Determination and Wing Vibrations Measurements and Analysis =

NASA Astrophysics Data System (ADS)

Tondji Chendjou, Yvan Wilfried

This Master's thesis is written within the framework of the multidisciplinary international research project CRIAQ MDO-505. This global project consists of the design, manufacture and testing of a morphing wing box capable of changing the shape of the flexible upper skin of a wing using an actuator system installed inside the wing. This changing of the shape generates a delay in the occurrence of the laminar to turbulent transition area, which results in an improvement of the aerodynamic performances of the morphed wing. This thesis is focused on the technologies used to gather the pressure data during the wind tunnel tests, as well as on the post processing methodologies used to characterize the wing airflow. The vibration measurements of the wing and their real-time graphical representation are also presented. The vibration data acquisition system is detailed, and the vibration data analysis confirms the predictions of the flutter analysis performed on the wing prior to wind tunnel testing at the IAR-NRC. The pressure data was collected using 32 highly-sensitive piezoelectric sensors for sensing the pressure fluctuations up to 10 KHz. These sensors were installed along two wing chords, and were further connected to a National Instrument PXI real-time acquisition system. The acquired pressure data was high-pass filtered, analyzed and visualized using Fast Fourier Transform (FFT) and Standard Deviation (SD) approaches to quantify the pressure fluctuations in the wing airflow, as these allow the detection of the laminar to turbulent transition area. Around 30% of the cases tested in the IAR-NRC wind tunnel were optimized for drag reduction by the morphing wing procedure. The obtained pressure measurements results were compared with results obtained by infrared thermography visualization, and were used to validate the numerical simulations. Two analog accelerometers able to sense dynamic accelerations up to +/-16g were installed in both the wing and the aileron boxes to obtain the vibration sensing measurements. The measured accelerations were acquired by an NI real-time acquisition system using LABVIEW software for a real-time graphical visualization. The recorded data were then analyzed and the analysis indicated that no aeroelastic phenomenon occurred on the model during the wind tunnel tests, at speeds of 50 m/s and 80m/s.

Pressure-volume behavior of the upper airway.

PubMed

Fouke, J M; Teeter, J P; Strohl, K P

1986-09-01

The study was performed to investigate the relationship between force generation and upper airway expansion during respiratory efforts by upper airway muscles. In 11 anesthetized dogs we isolated the upper airway (nasal, oral, pharyngeal, and laryngeal regions) by transecting the cervical trachea and sealing the nasal and oral openings. During spontaneous respiratory efforts the pressure within the sealed upper airway, used as an index of dilating force, decreased during inspiration. On alternate breaths the upper airway was opened to a pneumotachograph, and an increase in volume occurred, also during inspiration. Progressive hyperoxic hypercapnia produced by rebreathing increased the magnitude of change in pressure and volume. At any level of drive, peak pressure or volume occurred at the same point during inspiration. At any level of drive, volume and pressure changes increased with end-expiratory occlusion of the trachea. The force-volume relationship determined from measurements during rebreathing was compared with pressure-volume curves performed by passive inflation of the airway while the animal was apneic. The relationship during apnea was 1.06 +/- 0.55 (SD) ml/cmH2O, while the force-volume relationship from rebreathing trials was -1.09 +/- 0.45 ml/cmH2O. We conclude that there is a correspondence between force production and volume expansion in the upper airway during active respiratory efforts.

Quantification of the transient mass flow rate in a simplex swirl injector

NASA Astrophysics Data System (ADS)

Khil, Taeock; Kim, Sunghyuk; Cho, Seongho; Yoon, Youngbin

2009-07-01

When a heat release and acoustic pressure fluctuations are generated in a combustor by irregular and local combustions, these fluctuations affect the mass flow rate of the propellants injected through the injectors. In addition, variations of the mass flow rate caused by these fluctuations bring about irregular combustion, which is associated with combustion instability, so it is very important to identify a mass variation through the pressure fluctuation on the injector and to investigate its transfer function. Therefore, quantification of the variation of the mass flow rate generated in a simplex swirl injector via the injection pressure fluctuation was the subject of an initial study. To acquire the transient mass flow rate in the orifice with time, the axial velocity of flows and the liquid film thickness in the orifice were measured. The axial velocity was acquired through a theoretical approach after measuring the pressure in the orifice. In an effort to understand the flow area in the orifice, the liquid film thickness was measured by an electric conductance method. In the results, the mass flow rate calculated from the axial velocity and the liquid film thickness measured by the electric conductance method in the orifice was in good agreement with the mass flow rate acquired by the direct measuring method in a small error range within 1% in the steady state and within 4% for the average mass flow rate in a pulsated state. Also, the amplitude (gain) of the mass flow rate acquired by the proposed direct measuring method was confirmed using the PLLIF technique in the low pressure fluctuation frequency ranges with an error under 6%. This study shows that our proposed method can be used to measure the mass flow rate not only in the steady state but also in the unsteady state (or the pulsated state). Moreover, this method shows very high accuracy based on the experimental results.

Interaction of the electron density fluctuations with electron cyclotron waves from the equatorial launcher in ITER

NASA Astrophysics Data System (ADS)

Snicker, A.; Poli, E.; Maj, O.; Guidi, L.; Köhn, A.; Weber, H.; Conway, G. D.; Henderson, M.; Saibene, G.

2018-01-01

We present a numerical investigation of electron cyclotron beams interacting with electron density fluctuations in the ITER 15 MA H-mode scenario. In particular, here we study how the beam from the equatorial launcher, which shall be utilized to influence the sawtooth instability, is affected by the fluctuations. Moreover, we present the theory and first estimates of the power that is scattered from the injected O-mode to a secondary X-mode in the presence of the fluctuations. It is shown that for ITER parameters the scattered power stays within acceptable limits and broadening of the equatorial beams is less than those from the upper launcher.

Direct numerical simulation of a turbulent boundary layer with separation and reattachment at Reθ = 1500

NASA Astrophysics Data System (ADS)

Abe, Hiroyuki

2017-11-01

Direct numerical simulation (DNS) has been performed in a flat-plate turbulent boundary layer with large adverse and favorable pressure gradients, thus involving separation and reattachment. This work extends a series of our DNSs at lower Reynolds numbers (Abe et al. 2012; 2015), where suction and blowing are imposed at the upper boundary for providing pressure gradients. Particular attention is given to the Re dependence. The present inlet Reynolds number is equal to Reθ = 1500 , which is by a factor of five larger than that for seminal DNSs (Spalart & Coleman 1997; Na & Moin 1998). Number of grid points used are 13 billion (Nx ×Ny ×Nz = 4096 × 1536 × 2048 in the streamwise (x), wall-normal (y) and spanwise (z) directions, respectively) to resolve the essential motions. At the inlet, spatial resolution normalized by wall units is set to Δx+ = 8 , Δy+ = 0.1 10 , Δz+ = 5 . Significant Re effect is observed for skin friction outside the bubble, while it is small for mean quantities inside the bubble. In the separated region, large-scale structures of streamwise velocity fluctuations and pressure rollers become more prominent with increasing Reθ , which impinge significantly on the wall at reattachment.

An experimental study of the turbulent boundary layer on a transport wing in subsonic and transonic flow

NASA Technical Reports Server (NTRS)

Spaid, Frank W.; Roos, Frederick W.; Hicks, Raymond M.

1990-01-01

The upper surface boundary layer on a transport wing model was extensively surveyed with miniature yaw probes at a subsonic and a transonic cruise condition. Additional data were obtained at a second transonic test condition, for which a separated region was present at mid-semispan, aft of mid-chord. Significant variation in flow direction with distance from the surface was observed near the trailing edge except at the wing root and tip. The data collected at the transonic cruise condition show boundary layer growth associated with shock wave/boundary layer interaction, followed by recovery of the boundary layer downstream of the shock. Measurements of fluctuating surface pressure and wingtip acceleration were also obtained. The influence of flow field unsteadiness on the boundary layer data is discussed. Comparisons among the data and predictions from a variety of computational methods are presented. The computed predictions are in reasonable agreement with the experimental data in the outboard regions where 3-D effects are moderate and adverse pressure gradients are mild. In the more highly loaded mid-span region near the trailing edge, displacement thickness growth was significantly underpredicted, except when unrealistically severe adverse pressure gradients associated with inviscid calculations were used to perform boundary layer calculations.

Study of tip clearance flow in a turbomachinery cascade using large eddy simulation

NASA Astrophysics Data System (ADS)

You, Donghyun

In liquid handling systems like pumps and ducted propulsors, low pressure events in the vicinity and downstream of the rotor tip gap can induce tip-leakage cavitation which leads to noise, vibration, performance loss, and erosions of blade and casing wall. In order to analyze the dynamics of the tip-clearance flow and determine the underlying mechanism for the low pressure events, a newly developed large-eddy simulation (LES) solver which combines an immersed-boundary method with a generalized curvilinear structured grid has been employed. An analysis of the LES results has been performed to understand the mean flow field, turbulence characteristics, vortex dynamics, and pressure fluctuations in the turbomachinery cascade with tip gap. In the cascade passage, the tip-leakage jet, which is generated by the pressure difference between the pressure and suction sides of the blade tip, is found to produce highly enhanced vorticity magnitude and significant levels of turbulent kinetic energy. Based on the understanding of the flow field, a guideline for reducing viscous loss in the cascade is provided. Analyses of the energy spectra and space-time correlations of the velocity fluctuations suggest that the tip-leakage vortex is subject to pitchwise wandering motion. The largest pressure drop and most intense pressure fluctuations due to the formation of the tip-leakage vortex are found at the location where the strongest portion of the tip-leakage vortex is found. Present study suggests that the tip-leakage vortex needs to be controlled in its origin to reduce cavitation in the present configuration. The effects of tip-gap size on the end-wall vortical structures and on the velocity and pressure fields have been investigated. The present analysis indicates that the mechanism for the generation of the vorticity and turbulent kinetic energy is mostly unchanged by the tip-gap size variation. However, larger tip-gap sizes are found to be more inductive to tip-leakage cavitation judged by the levels of negative mean pressure and pressure fluctuations.

High-pressure electronic phase diagrams in FeSe1-xSx superconductors

NASA Astrophysics Data System (ADS)

Matsuura, Kohei; Arai, Yuki; Hosoi, Suguru; Ishida, Kousuke; Mizukami, Yuta; Watashige, Tatsuya; Kasahara, Shigeru; Matsuda, Yuji; Maejima, Naoyuki; Machida, Akihiko; Watanuki, Tetsu; Fukuda, Tatsuo; Uwatoko, Yoshiya; Shibauchi, Takasada

The spin fluctuations are believed to be related to the mechanism of the unconventional superconductors. On the other hand, many recent studies suggest that the nematic order that spontaneously breaks rotational symmetry of the system exists in the Fe-based superconductors and its quantum fluctuations may play an essential role for the superconductivity. However, this remains unclear because the nematic order usually coexists with the magnetic order. To solve this issue, FeSe exhibiting a nonmagnetic nematic order is a key system. Under pressure, this order is suppressed and concurrently magnetic order appears, which competes with high-Tc superconducting phase. In isovalent substitution system FeSe1-xSx, we found a nonmagnetic nematic quantum critical point. Here we report our recent high-pressure studies in high-quality single-crystalline FeSe1-xSx up to 8 GPa. We find a systematic change of the pressure phase diagram in FeSe by the S-substitution. Our results imply that the respective role of nematic and magnetic fluctuations can be elucidated from the precise control of pressure and substitution in this system.

THERMAL CONDUCTIVITY ANALYSIS OF GASES

DOEpatents

Clark, W.J.

1949-06-01

This patent describes apparatus for the quantitative analysis of a gaseous mixture at subatmospheric pressure by measurement of its thermal conductivity. A heated wire forms one leg of a bridge circuit, while the gas under test is passed about the wire at a constant rate. The bridge unbalance will be a measure of the change in composition of the gas, if compensation is made for the effect due to gas pressure change. The apparatus provides a voltage varying with fluctuations of pressure in series with the indicating device placed across the bridge, to counterbalance the voltage change caused by fluctuations in the pressure of the gaseous mixture.

Flowfield dynamics in blunt fin-induced shock wave/turbulent boundary layer interactions

NASA Technical Reports Server (NTRS)

Dolling, David S.; Brusniak, Leon

1994-01-01

Fluctuating wall pressure measurements have been made on centerline upstream of a blunt fin in a Mach 5 turbulent boundary layer. By examining the ensemble averaged wall pressure distributions for different separation shock foot positions, it has been shown that local fluctuating wall pressure measurements are due to a distinct pressure distribution, Rho(sub i), which undergoes a stretching and flattening effect as its upstream boundary translates aperiodically between the upstream influence and separation lines. The locations of the maxima and minima in the wall pressure standard deviation can be accurately predicted using this distribution, providing quantitative confirmation of the model. This model also explains the observed cross-correlations and ensemble average measurements within the interaction. Using the Rho(sub i) model, wall pressure signals from under the separated flow region were used to reproduce the position-time history of the separation shock foot. Further, the negative time delay peak in the cross-correlation between the predicted and actual shock foot histories suggests that the separated region fluctuations precede shock foot motion. The unsteady behavior of the primary horseshoe vortex and its relation to the unsteady separation shock are described.

Reactor pressure vessel head vents and methods of using the same

DOEpatents

Gels, John L; Keck, David J; Deaver, Gerald A

2014-10-28

Internal head vents are usable in nuclear reactors and include piping inside of the reactor pressure vessel with a vent in the reactor upper head. Piping extends downward from the upper head and passes outside of the reactor to permit the gas to escape or be forcibly vented outside of the reactor without external piping on the upper head. The piping may include upper and lowers section that removably mate where the upper head joins to the reactor pressure vessel. The removable mating may include a compressible bellows and corresponding funnel. The piping is fabricated of nuclear-reactor-safe materials, including carbon steel, stainless steel, and/or a Ni--Cr--Fe alloy. Methods install an internal head vent in a nuclear reactor by securing piping to an internal surface of an upper head of the nuclear reactor and/or securing piping to an internal surface of a reactor pressure vessel.

Experimental and numerical investigation of the turbulent wake flow of a generic space launcher configuration

NASA Astrophysics Data System (ADS)

Statnikov, V.; Saile, D.; Meiß, J.-H.; Henckels, A.; Meinke, M.; Gülhan, A.; Schröder, W.

2015-06-01

The turbulent wake of a generic space launcher at cold hypersonic freestream conditions is investigated experimentally and numerically to gain detailed insight into the intricate base flow phenomena of space vehicles at upper stages of the flight trajectory. The experiments are done at Ma∞ = 6 and ReD = 1.7 · 106 m-1 by the German Aerospace Center (DLR) and the corresponding computations are performed by the Institute of Aerodynamics Aachen using a zonal Reynolds-averaged Navier-Stokes / Large-Eddy Simulation (RANS/LES) approach. Two different aft-body geometries consisting of a blunt base and an attached cylindrical nozzle dummy are considered. It is found that the wind tunnel model support attached to the upper side of the main body has a nonnegligible impact on the wake along the whole circumference, albeit on the opposite side, the effects are minimal compared to an axisymmetric configuration. In the blunt-base case, the turbulent supersonic boundary layer undergoes a strong aftexpansion on the model shoulder leading to the formation of a confined low-pressure (p/p∞ ≈ 0.2) recirculation region. Adding a nozzle dummy causes the shear layer to reattach on the its wall at x/D ˜ 0.6 and the base pressure level to increase (p/p∞ ≈ 0.25) compared to the blunt-base case. For both configurations, the pressure fluctuations on the base wall feature dominant frequencies at SrD ≈ 0.05 and SrD ≈ 0.2-0.27, but are of small amplitudes (prms/p∞ = 0.02-0.025) compared to the main body boundary layer. For the nozzle dummy configuration, when moving downstream along the nozzle extension, the wall pressure is increasingly influenced by the reattaching shear layer and the periodic low-frequency behavior becomes less pronounced. Directly behind the reattachment point, the wall pressure reaches maximum mean and root-mean-square (rms) values of about p/p∞ = 1 and p'rms/p∞ = 0.1 and features a broadband specrms trum without distinct frequencies determined by the incoming turbulent supersonic boundary layer.

Periodic Heat Transfer at Small Pressure Fluctuations

NASA Technical Reports Server (NTRS)

Pfriem, H.

1943-01-01

The effect of cyclic gas pressure variations on the periodic heat transfer at a flat wall is theoretically analyzed and the differential equation describing the process and its solution for relatively. Small pressure fluctuations developed, thus explaining the periodic heat cycle between gas and wall surface. The processes for pure harmonic pressure and temperature oscillations, respectively, in the gas space are described by means of a constant heat transfer coefficient and the equally constant phase angle between the appearance of the maximum values of the pressure and heat flow most conveniently expressed mathematically in the form of a complex heat transfer coefficient. Any cyclic pressure oscillations, can be reduced by Fourier analysis to harmonic oscillations, which result in specific, mutual relationships of heat-transfer coefficients and phase angles for the different harmonics.

The Effects of Aspiration Status, Liquid Type, and Bolus Volume on Pharyngeal Peak Pressure in Healthy Older Adults

PubMed Central

Stuart, Andrew; Wilhelm, Erika; Rees, Catherine; Williamson, Jeff; Kritchevsky, Stephen

2015-01-01

The reasons for aspiration in healthy adults remain unknown. Given that the pharyngeal phase of swallowing is a key component of the safe swallow, it was hypothesized that healthy older adults who aspirate are likely to generate less pharyngeal peak pressures when swallowing. Accordingly, pharyngeal and upper esophageal sphincter pressures were examined as a function of aspiration status (i.e., nonaspirator vs. aspirator), sensor location (upper vs. lower pharynx), liquid type (i.e., water vs. milk), and volume (i.e., 5 vs. 10 ml) in healthy older adults. Manometric measurements were acquired with a 2.1-mm catheter during flexible endoscopic evaluation. Participants (N = 19, mean age = 79.2 years) contributed 28 swallows; during 8 swallows, simultaneous manometric measurements of upper and lower pharyngeal and upper esophageal pressures were obtained. Pharyngeal manometric peak pressure was significantly less for aspirators (mean = 82, SD = 31 mmHg) than for nonaspirators (mean = 112, SD = 20 mmHg), and upper pharyngeal pressures (mean = 85, SD = 32 mmHg) generated less pressure than lower pharyngeal pressures (mean = 116, SD = 38 mmHg). Manometric measurements vary with respect to aspiration status and sensor location. Lower pharyngeal pressures in healthy older adults may predispose them to aspiration. PMID:20623303

Dynamics of phenotypic switching of bacterial cells with temporal fluctuations in pressure

NASA Astrophysics Data System (ADS)

Nepal, Sudip; Kumar, Pradeep

2018-05-01

Phenotypic switching is one of the mechanisms by which bacteria thrive in ever changing environmental conditions around them. Earlier studies have shown that the application of steady high hydrostatic pressure leads to stochastic switching of mesophilic bacteria from a cellular phenotype having a normal cell cycle to another phenotype lacking cell division. Here, we have studied the dynamics of this phenotypic switching with fluctuating periodic pressure using a set of experiments and a theoretical model. Our results suggest that the phenotypic switching rate from high-pressure phenotype to low-pressure phenotype in the reversible regime is larger as compared to the switching rate from low-pressure phenotype to high-pressure phenotype. Furthermore, we find that even though the cell division and elongation are presumably regulated by a large number of genes the underlying physics of the dynamics of stochastic switching at high pressure is captured reasonably well by a simple two-state model.

Comparison of vibrations of a combination of solid-rocket launch vehicle and payload during a ground firing and launching

NASA Technical Reports Server (NTRS)

Schoenster, J. A.; Pierce, H. B.

1975-01-01

The results of a study into the environmental vibrations of a payload mounted on the Nike rocket launch vehicle were presented. Data were obtained during the flight acceptance test of the payload, the firing of the total vehicle in a special test stand, and the powered and unpowered flights of the vehicle. The vibrational response of the structure was measured. Data were also obtained on the fluctuating pressure on the outside surface of the vehicle and inside the forward and after ends of the rocket chamber. A comparison of the data from the three test conditions indicated that external pressure fluctuations were the major source of vibrations in the payload area, and pressure fluctuations within the rocket motor were the major source of vibrations contiguous to the payload area.

Limits on the fluctuating part of y-type distortion monopole from Planck and SPT results

NASA Astrophysics Data System (ADS)

Khatri, Rishi; Sunyaev, Rashid

2015-08-01

We use the published Planck and SPT cluster catalogs [1,2] and recently published y-distortion maps [3] to put strong observational limits on the contribution of the fluctuating part of the y-type distortions to the y-distortion monopole. Our bounds are 5.4× 10-8 < langle yrangle < 2.2× 10-6. Our upper bound is a factor of 6.8 stronger than the currently best upper 95% confidence limit from COBE-FIRAS of langle yrangle <15× 10-6. In the standard cosmology, large scale structure is the only source of such distortions and our limits therefore constrain the baryonic physics involved in the formation of the large scale structure. Our lower limit, from the detected clusters in the Planck and SPT catalogs, also implies that a Pixie-like experiment should detect the y-distortion monopole at >27-σ. The biggest sources of uncertainty in our upper limit are the monopole offsets between different HFI channel maps that we estimate to be <10-6.

Supplemental Carbon Dioxide Stabilizes the Upper Airway in Volunteers Anesthetized with Propofol.

PubMed

Ruscic, Katarina Jennifer; Bøgh Stokholm, Janne; Patlak, Johann; Deng, Hao; Simons, Jeroen Cedric Peter; Houle, Timothy; Peters, Jürgen; Eikermann, Matthias

2018-05-10

Propofol impairs upper airway dilator muscle tone and increases upper airway collapsibility. Preclinical studies show that carbon dioxide decreases propofol-mediated respiratory depression. We studied whether elevation of end-tidal carbon dioxide (PETCO2) via carbon dioxide insufflation reverses the airway collapsibility (primary hypothesis) and impaired genioglossus muscle electromyogram that accompany propofol anesthesia. We present a prespecified, secondary analysis of previously published experiments in 12 volunteers breathing via a high-flow respiratory circuit used to control upper airway pressure under propofol anesthesia at two levels, with the deep level titrated to suppression of motor response. Ventilation, mask pressure, negative pharyngeal pressure, upper airway closing pressure, genioglossus electromyogram, bispectral index, and change in end-expiratory lung volume were measured as a function of elevation of PETCO2 above baseline and depth of propofol anesthesia. PETCO2 augmentation dose-dependently lowered upper airway closing pressure with a decrease of 3.1 cm H2O (95% CI, 2.2 to 3.9; P < 0.001) under deep anesthesia, indicating improved upper airway stability. In parallel, the phasic genioglossus electromyogram increased by 28% (23 to 34; P < 0.001). We found that genioglossus electromyogram activity was a significant modifier of the effect of PETCO2 elevation on closing pressure (P = 0.005 for interaction term). Upper airway collapsibility induced by propofol anesthesia can be reversed in a dose-dependent manner by insufflation of supplemental carbon dioxide. This effect is at least partly mediated by increased genioglossus muscle activity.

Prediction of HR/BP response to the spontaneous breathing trial by fluctuation dissipation theory

NASA Astrophysics Data System (ADS)

Chen, Man

2014-03-01

We applied the non-equilibrium fluctuation dissipation theorem to predict how critically-ill patients respond to treatment, based on both heart rate data and blood pressure data collected by standard hospital monitoring devices. The non-equilibrium fluctuation dissipation theorem relates the response of a system to a perturbation to the fluctuations in the stationary state of the system. It is shown that the response of patients to a standard procedure performed on patients, the spontaneous breathing trial (SBT), can be predicted by the non-equilibrium fluctuation dissipation approach. We classify patients into different groups according to the patients' characteristics. For each patient group, we extend the fluctuation dissipation theorem to predict interactions between blood pressure and beat-to-beat dynamics of heart rate in response to a perturbation (SBT), We also extract the form of the perturbation function directly from the physiological data, which may help to reduce the prediction error. We note this method is not limited to the analysis of the heart rate dynamics, but also can be applied to analyze the response of other physiological signals to other clinical interventions.

Fluctuation spectra in the NASA Lewis bumpy-torus plasma

NASA Technical Reports Server (NTRS)

Singh, C. M.; Krawczonek, W. M.; Roth, J. R.; Hong, J. Y.; Powers, E. J.

1978-01-01

The electrostatic potential fluctuation spectrum in the NASA Lewis bumpy-torus plasma was studied with capacitive probes in the low pressure (high impedance) mode and in the high pressure (low impedance) mode. Under different operating conditions, the plasma exhibited electrostatic potential fluctuations (1) at a set of discrete frequencies, (2) at a continuum of frequencies, and (3) as incoherent high-frequency turbulence. The frequencies and azimuthal wave numbers were determined from digitally implemented autopower and cross-power spectra. The azimuthal dispersion characteristics of the unstable waves were examined by varying the electrode voltage, the polarity of the voltage, and the neutral background density at a constant magnetic field strength.

Numerical analysis of flow induced noise propagation in supercavitating vehicles at subsonic speeds.

PubMed

Ramesh, Sai Sudha; Lim, Kian Meng; Zheng, Jianguo; Khoo, Boo Cheong

2014-04-01

Flow supercavitation begins when fluid is accelerated over a sharp edge, usually at the nose of an underwater vehicle, where phase change occurs and causes low density gaseous cavity to gradually envelop the whole object (supercavity) and thereby enabling higher speeds of underwater vehicles. The process of supercavity inception/development by means of "natural cavitation" and its sustainment through ventilated cavitation result in turbulence and fluctuations at the water-vapor interface that manifest themselves as major sources of hydrodynamic noise. Therefore in the present context, three main sources are investigated, namely, (1) flow generated noise due to turbulent pressure fluctuations around the supercavity, (2) small scale pressure fluctuations at the vapor-water interface, and (3) pressure fluctuations due to direct impingement of ventilated gas-jets on the supercavity wall. An understanding of their relative contributions toward self-noise is very crucial for the efficient operation of high frequency acoustic sensors that facilitate the vehicle's guidance system. Qualitative comparisons of acoustic pressure distribution resulting from aforementioned sound sources are presented by employing a recently developed boundary integral method. By using flow data from a specially developed unsteady computational fluid dynamics solver for simulating supercavitating flows, the boundary-element method based acoustic solver was developed for computing flow generated sound.

Examination of fluctuations in atmospheric pressure related to migraine.

PubMed

Okuma, Hirohisa; Okuma, Yumiko; Kitagawa, Yasuhisa

2015-01-01

Japan has four seasons and many chances of low atmospheric pressure or approaches of typhoon, therefore it has been empirically known that the fluctuation of weather induces migraine in people. Generally, its mechanism has been interpreted as follows: physical loading, attributed by atmospheric pressure to human bodies, compresses or dilates human blood vessels, which leads to abnormality in blood flow and induces migraine. We report our examination of the stage in which migraine tends to be induced focusing on the variation of atmospheric pressure. Subjects were 34 patients with migraine, who were treated in our hospital. The patients included 31 females and three males, whose mean age was 32 ± 6.7. 22 patients had migraine with aura and 12 patients had migraine without aura. All of patients with migraine maintained a headache diary to record atmospheric pressures when they developed a migraine. The standard atmospheric pressure was defined as 1013 hPa, and with this value as the criterion, we investigated slight fluctuations in the atmospheric pressure when they developed a migraine. It was found that the atmospheric pressure when the patients developed a migraine was within 1003-1007 hPa in the approach of low atmospheric pressure and that the patients developed a migraine when the atmospheric pressure decreased by 6-10 hPa, slightly less than the standard atmospheric pressure. Small decreases of 6-10 hPa relative to the standard atmospheric pressure of 1013 hPa induced migraine attacks most frequently in patients with migraine.

Ginzburg-Landau theory, strong coupling corrections and exchange enhancements: Can spin fluctuations give high T c's?

NASA Astrophysics Data System (ADS)

Quader, Khandker F.; Salamon, M. B.

1988-06-01

Ginzburg-Landau theory is used to explore the thermodynamic and electrodynamic properties of YBa 2Cu 3O 7-δ, and to determine γ, m ∗/m and the exchange enhancement. This material is found to be in a moderately strong coupling regime, intermediate between dirty and clean limits; strong coupling corrections are estimated. It is shown that, irrespective of the choice of the carrier density, spin fluctuations are unable to give a sufficiently large T c. An upper bound is given for the T c due spin-fluctuation-mediated pairing.

A physics link between venous stenosis and multiple sclerosis.

PubMed

Tucker, Trevor W

2011-12-01

This paper hypothesizes that a stenosis or obstruction at a lower extremity of an internal jugular vein (IJV) would, in accordance with the physics of fluid dynamics, cause a standing pressure wave within the vein. This pressure wave would possess regions of large pressure fluctuations and other regions of relatively little fluctuation which also have substantially lower peak pressure values. If the wavelength of the hypothesized pressure wave is comparable to the distance from the obstruction to the venule end of the capillary bed, then a region of high pressure fluctuation would exist at the venules. Depending on the degree of obstruction, the pressure fluctuations at the venules of the capillary bed would be substantially greater than those that would exist in a healthy unobstructed vein. This increase in blood pressure fluctuation located at the venule end of the capillary bed, which would be equivalent to local hypertension, is predicted to reduce the pressure drop across the bed which, in turn, would reduce blood flow through the bed in accordance with Darcy's Law. Such a reduction in blood flow through the bed would be accompanied by a reduction in the transfer of oxygen, glucose and other nutrients into the brain tissue in accordance with Fick's Principle. The reduction in oxygen levels in the brain tissue (i.e. hypoxia), would, in turn, be associated with increased fatigue and decreased mental acuity in the subject patient. Also the deprivation of oxygen in the brain tissue may result in the death of oligodendrocyte cells, which, in turn would result in the deterioration of the myelin surrounding the brain's neural axons. In addition, the paper also predicts that, in cases of extreme obstruction, the predicted localized hypertension at the venule end of the capillary bed may be sufficiently high to cause a localized disruption in the blood-brain barrier. Such a disruption of the blood-brain barrier could then allow the migration of leukocytes (auto-immune attack cells), from the blood into the brain tissue, enabling them to attack myelin, which has degenerated or deteriorated from the reduction in repair function normally provided by oligodendrocyte cells. Such leukocyte attack on myelin has long been associated with multiple sclerosis. Copyright © 2011 Elsevier Ltd. All rights reserved.

Mathematical modelling of cyclic pressure swing adsorption processes

NASA Astrophysics Data System (ADS)

Skvortsov, S. A.; Akulinin, E. I.; Golubyatnikov, O. O.; Dvoretsky, D. S.; Dvoretsky, S. I.

2018-05-01

The paper discusses the results of a numerical analysis of the properties and regimes of the adsorption air separation and oxygen concentration process with a purity of ∼ 40-60%, carried out in a 2-adsorption vacuum-pressure plant with a granular zeolite adsorbent 13X with a productivity of 1.6 · 10-5 m3/s. Computational experiments were carried out using the developed mathematical model and the influence of temperature, pressure, reflux ratio, the duration of the adsorption and desorption stages, the harmonic fluctuations of the inlet pressure during the adsorption stage and the outlet pressure during the desorption stage on the kinetics, and the efficiency of the air separation process by the PSA method were investigated. It is established that the specially organized harmonic fluctuations of the inlet pressure at the stage of adsorption and outlet pressure during the desorption stage lead to an increase in the purity of product oxygen by 4% (vol.).

Two-statge sorption type cryogenic refrigerator including heat regeneration system

NASA Technical Reports Server (NTRS)

Jones, Jack A. (Inventor); Wen, Liang-Chi (Inventor); Bard, Steven (Inventor)

1989-01-01

A lower stage chemisorption refrigeration system physically and functionally coupled to an upper stage physical adsorption refrigeration system. Waste heat generated by the lower stage cycle is regenerated to fuel the upper stage cycle thereby greatly improving the energy efficiency of a two-stage sorption refrigerator. The two stages are joined by disposing a first pressurization chamber providing a high pressure flow of a first refrigerant for the lower stage refrigeration cycle within a second pressurization chamber providing a high pressure flow of a second refrigerant for the upper stage refrigeration cycle. The first pressurization chamber is separated from the second pressurization chamber by a gas-gap thermal switch which at times is filled with a thermoconductive fluid to allow conduction of heat from the first pressurization chamber to the second pressurization chamber.

Dynamic Characteristics of The DSI-Type Constant-Flow Valves

NASA Astrophysics Data System (ADS)

Kang, Yuan; Hu, Sheng-Yan; Chou, Hsien-Chin; Lee, Hsing-Han

Constant flow valves have been presented in industrial applications or academic studies, which compensate recess pressures of a hydrostatic bearing to resist load fluctuating. The flow rate of constant-flow valves can be constant in spite of the pressure changes in recesses, however the design parameters must be specified. This paper analyzes the dynamic responses of DSI-type constant-flow valves that is designed as double pistons on both ends of a spool with single feedback of working pressure and regulating restriction at inlet. In this study the static analysis presents the specific relationships among design parameters for constant flow rate and the dynamic analyses give the variations around the constant flow rate as the working pressure fluctuates.

Apparatus for testing high pressure injector elements

NASA Technical Reports Server (NTRS)

Myers, William Neill (Inventor); Scott, Ewell M. (Inventor); Forbes, John C. (Inventor); Shadoan, Michael D. (Inventor)

1995-01-01

An apparatus for testing and evaluating the spray pattern of high pressure fuel injector elements for use in supplying fuel to combustion engines is presented. Prior art fuel injector elements were normally tested by use of low pressure apparatuses which did not provide a purge to prevent mist from obscuring the injector element or to prevent frosting of the view windows; could utilize only one fluid during each test; and had their viewing ports positioned one hundred eighty (180 deg) apart, thus preventing optimum use of laser diagnostics. The high pressure fluid injector test apparatus includes an upper hub, an upper weldment or housing, a first clamp and stud/nut assembly for securing the upper hub to the upper weldment, a standoff assembly within the upper weldment, a pair of window housings having view glasses within the upper weldment, an injector block assembly and purge plate within the upper weldment for holding an injector element to be tested and evaluated, a lower weldment or housing, a second clamp and stud/nut assembly for securing the lower weldment to the upper hub, a third clamp and stud/nut assembly for securing the lower hub to the lower weldment, mechanisms for introducing fluid under high pressure for testing an injector element, and mechanisms for purging the apparatus to prevent frosting of view glasses within the window housings and to permit unobstructed viewing of the injector element.

Apparatus for testing high pressure injector elements

NASA Technical Reports Server (NTRS)

Myers, William Neill (Inventor); Scott, Ewell M. (Inventor); Forbes, John C. (Inventor); Shadoan, Michael D. (Inventor)

1993-01-01

An apparatus for testing and evaluating the spray pattern of high pressure fuel injector elements for use in supplying fuel to combustion engines is presented. Prior art fuel injector elements were normally tested by use of low pressure apparatuses which did not provide a purge to prevent mist from obscuring the injector element or to prevent frosting of the view windows; could utilize only one fluid during each test; and had their viewing ports positioned one hundred eighty (180 deg) apart, thus preventing optimum use of laser diagnostics. The high pressure fluid injector test apparatus includes an upper hub, an upper weldment or housing, a first clamp and stud/nut assembly for securing the upper hub to the upper weldment, a standoff assembly within the upper weldment, a pair of window housings having view glasses within the upper weldment, an injector block assembly and purge plate within the upper weldment for holding an injector element to be tested and evaluated, a lower weldment or housing, a second clamp and stud/nut assembly for securing the lower weldment to the upper weldment, a lower hub, a third clamp and stud/nut assembly for securing the lower hub to the lower weldment, mechanisms for introducing fluid under high pressure for testing an injector element, and mechanisms for purging the apparatus to prevent frosting of view glasses within the window housings and to permit unobstructed viewing of the injector element.

Study on Combustion Oscillation of Premixed Flame with Pilot Fuel at Elevated Pressures

NASA Astrophysics Data System (ADS)

Ohtsuka, Masaya; Yoshida, Shohei; Hirata, Yoshitaka; Kobayashi, Nariyoshi

Acoustically-coupled combustion oscillation is studied for premixed flame with pilot fuel to be used in gas turbine combustors. Premixed gas is passed through swirl vanes and burnt with the centrally injected pilot fuel. The dependencies of pressure, fuel to air ratio, premixed fuel rate, inlet velocity and air temperature on the combustion oscillation are investigated. Two kinds of oscillation modes of ˜100Hz and ˜350Hz are activated according to inlet velocities. Fluctuating pressures are amplified when the premixed fuel rate is over ˜80% at elevated pressures. The fluctuating pressure peak moves to a higher premixed fuel ratio region with increased pressure or fuel to air ratio for the Helmholz type mode. Combustion oscillation occurs when the pilot fuel velocity is changed proportionally with the flame length.

Combustion Instability in an Acid-Heptane Rocket with a Pressurized-Gas Propellant Pumping System

NASA Technical Reports Server (NTRS)

Tischler, Adelbert O.; Bellman, Donald R.

1951-01-01

Results of experimental measurements of low-frequency combustion instability of a 300-pound thrust acid-heptane rocket engine were compared to the trends predicted by an analysis of combustion instability in a rocket engine with a pressurized-gas propellant pumping system. The simplified analysis, which assumes a monopropellant model, was based on the concept of a combustion the delay occurring from the moment of propellant injection to the moment of propellant combustion. This combustion time delay was experimentally measured; the experimental values were of approximately half the magnitude predicted by the analysis. The pressure-fluctuation frequency for a rocket engine with a characteristic length of 100 inches and operated at a combustion-chamber pressure of 280 pounds per square inch absolute was 38 cycles per second; the analysis indicated. a frequency of 37 cycles per second. Increasing combustion-chamber characteristic length decreased the pressure-fluctuation frequency, in conformity to the analysis. Increasing the chamber operating pressure or increasing the injector pressure drop increased the frequency. These latter two effects are contrary to the analysis; the discrepancies are attributed to the conflict between the assumptions made to simplify the analysis and the experimental conditions. Oxidant-fuel ratio had no apparent effect on the experimentally measured pressure-fluctuation frequency for acid-heptane ratios from 3.0 to 7.0. The frequencies decreased with increased amplitude of the combustion-chamber pressure variations. The analysis indicated that if the combustion time delay were sufficiently short, low-frequency combustion instability would be eliminated.

Boundary layer transition detection on the X-15 vertical fin using surface-pressure-fluctuation measurements

NASA Technical Reports Server (NTRS)

Lewis, T. L.; Banner, R. D.

1971-01-01

A flush-mounted microphone on the vertical fin of an X-15 airplane was used to investigate boundary layer transition phenomenon during flights to peak altitudes of approximately 70,000 meters. The flight results were compared with those from wind tunnel studies, skin temperature measurements, and empirical prediction data. The Reynolds numbers determined for the end of transition were consistent with those obtained from wind tunnel studies. Maximum surface-pressure-fluctuation coefficients in the transition region were about an order of magnitude greater than those for fully developed turbulent flow. This was also consistent with wind tunnel data. It was also noted that the power-spectral-density estimates of the surface-pressure fluctuations were characterized by a shift in power from high frequencies to low frequencies as the boundary layer changed from turbulent to laminar flow. Large changes in power at the lowest frequencies appeared to mark the beginning of transition.

RANS simulation of cavitation and hull pressure fluctuation for marine propeller operating behind-hull condition

NASA Astrophysics Data System (ADS)

Paik, Kwang-Jun; Park, Hyung-Gil; Seo, Jongsoo

2013-12-01

Simulations of cavitation flow and hull pressure fluctuation for a marine propeller operating behind a hull using the unsteady Reynolds-Averaged Navier-Stokes equations (RANS) are presented. A full hull body submerged under the free surface is modeled in the computational domain to simulate directly the wake field of the ship at the propeller plane. Simulations are performed in design and ballast draught conditions to study the effect of cavitation number. And two propellers with slightly different geometry are simulated to validate the detectability of the numerical simulation. All simulations are performed using a commercial CFD software FLUENT. Cavitation patterns of the simulations show good agreement with the experimental results carried out in Samsung CAvitation Tunnel (SCAT). The simulation results for the hull pressure fluctuation induced by a propeller are also compared with the experimental results showing good agreement in the tendency and amplitude, especially, for the first blade frequency.

Observation of acoustic-gravity waves in the upper atmosphere during severe storm activity

NASA Technical Reports Server (NTRS)

Hung, R. J.

1975-01-01

A nine-element continuum wave spectrum, high-frequency, Doppler sounder array has been used to detect upper atmospheric wave-like disturbances during periods with severe weather activity, particularly severe thunderstorms and tornadoes. Five events of severe weather activity, including extreme tornado outbreak of April 3, 1974, were chosen for the present study. The analysis of Doppler records shows that both infrasonic waves and gravity waves were excited when severe storms appeared in the north Alabama area. Primarily, in the case of tornado activity, S-shaped Doppler fluctuations or Doppler fold-backs are observed, while quasi-sinusoidal fluctuations are more common in the case of thunderstorm activity. A criterion for the production of Doppler fold-backs is derived and compared with possible tornado conditions.

Pressure at the ground in a large tornado

NASA Astrophysics Data System (ADS)

Winn, W. P.; Hunyady, S. J.; Aulich, G. D.

1999-09-01

A number of instruments were placed on the ground across the path of a large tornado that passed west of the town of Allison, Texas, on June 8, 1995. The center of the tornado came within 660 m of the closest instrument, which recorded a pressure drop of 55 mbar and a subsequent pressure rise of 60 mbar. During the lowest recorded pressures (near r = 660 m), there were large and rapid pressure fluctuations; the largest fluctuation was a 10-mbar spike lasting 2 s. A second instrument on the opposite side of the tornado recorded a pressure drop of 26 mbar. From the pressure variations with time P(t) at the two instruments, the variation of pressure with distance p(r) from the center of the tornado has been deduced for r>660 m. As r decreases, the measured pressure function p(r) drops more abruptly than would be expected from conservation of angular momentum of air spiraling inward near the ground level.

Forearm and upper-arm oscillometric blood pressure comparison in acutely ill adults.

PubMed

Schell, Kathleen; Morse, Kate; Waterhouse, Julie K

2010-04-01

When patients' upper arms are not accessible and/or when cuffs do not fit large upper arms, the forearm site is often used for blood pressure (BP) measurement. The purpose of this study is to compare forearm and upper-arm BPs in 70 acutely ill adults, admitted to a community hospital's 14-bed ICU. Using Philips oscillometric monitors, three repeated measures of forearm and upper-arm BPs are obtained with head of bed flat and with head of bed elevated at 30 degrees. Arms are resting on the bed. Paired t tests show statistically significant differences in systolic BPs, diastolic BPs, and mean arterial pressures in the supine and head-elevated positions. Bland-Altman analyses indicate that forearm and upper-arm oscillometric BPs are not interchangeable in acutely ill adults.

Effects of multi-pulsed coaxial helicity injection on dynamics of spherical torus

NASA Astrophysics Data System (ADS)

Kanki, T.; Nagata, M.; Kagei, Y.

2012-10-01

The mechanism to rebuild the magnetic fields and to amplify the currents in the high-q spherical torus (ST) by the multi-pulsed coaxial helicity injection is investigated using the resistive nonlinear 3D-MHD simulations. During the driven phase, the dynamics is almost axisymmetric because the magnetic fluctuation level of n=0 mode compared with other higher modes is much larger. The toroidal current It is effectively amplified due to the merging of plasmoid ejected from the gun region with the pre-existing ST in the confinement region. The poloidal flux is not significantly amplified because the current sheet generated by the merging process does not rapidly decay. The negative toroidal flow vt is then induced in the direction of It around the central open flux column (OFC) region by inductive toroidal electric field Et (=-vzBr) because of the plasmoid ejection. The strong poloidal flow vz (=ErBt) is also driven from the gun to confinement region due to the Lorentz force. As the result of vz, the flow vortices associated with the dynamo effect are caused around the upper confinement region. During the decay phase, the closed field lines are regenerated due to the dissipation of magnetic fluctuations. The helical distortion of the OFC becomes small, and then ordered magnetic field structures without flows are built. Just after turning off the external electric field, the poloidal flow from the confinement to gun region is caused by the pressure gradients. The parallel current density λ concentrated in the OFC diffuses to the core region, but does not relax in the direction of the Taylor state due to the pressure gradients.

Tidal and atmospheric forcing of the upper ocean in the Gulf of California. I - Sea surface temperature variability

NASA Technical Reports Server (NTRS)

Paden, Cynthia A.; Winant, Clinton D.; Abbott, Mark R.

1991-01-01

SST variability in the northern Gulf of California is examined on the basis of findings of two years of satellite infrared imagery (1984-1986). Empirical orthogonal functions of the temporal and spatial SST variance for 20 monthly mean images show that the dominant SST patterns are generated by spatially varying tidal mixing in the presence of seasonal heating and cooling. Atmospheric forcing of the northern gulf appears to occur over large spatial scales. Area-averaged SSTs for the Guaymas Basin, island region, and northern basin exhibit significant fluctuations which are highly correlated. These fluctuations in SST correspond to similar fluctuations in the air temperature which are related to synoptic weather events over the gulf. A regression analysis of the SST relative to the fortnightly tidal range shows that tidal mixing occurs over the sills in the island region as well as on the shallow northern shelf. Mixing over the sills occurs as a result of large breaking internal waves of internal hydraulic jumps which mix over water in the upper 300-500 m.

Statistics of pressure fluctuations in decaying isotropic turbulence.

PubMed

Kalelkar, Chirag

2006-04-01

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.

Spherical shells buckling to the sound of music

NASA Astrophysics Data System (ADS)

Lee, Anna; Marthelot, Joel; Reis, Pedro

We study how the critical buckling load of spherical elastic shells can be modified by a fluctuating external pressure field. In our experiments, we employ thin elastomeric shells of nearly uniform thickness fabricated by the coating of a hemispherical mold with a polymer solution, which upon curing yields elastic structures. A shell is submerged in a water bath and loaded quasi-statically until buckling occurs by reducing its inner volume with a syringe pump. Simultaneously, a plunger connected to an electromagnetic shaker is placed above the shell and driven sinusoidally to create a fluctuating external pressure field that can excite dynamic vibration modes of the shell. These dynamic modes induce effective compressive stresses, in addition to those from the inner pressure loading, which can modify the critical conditions for the onset of buckling. We systematically quantify how the frequency and amplitude of the external driving affects the buckling strength of our shells. In specific regions of the parameter space, we find that pressure fluctuations can result in large reductions of the critical buckling pressure. This is analogous to the classic knock-down effect in shells due to intrinsic geometric imperfections, albeit now in a way that can be controlled externally.

Linear Mechanisms and Pressure Fluctuations in Wall Turbulence

NASA Astrophysics Data System (ADS)

Septham, Kamthon; Morrison, Jonathan

2014-11-01

Full-domain, linear feedback control of turbulent channel flow at Reτ <= 400 via vU' at low wavenumbers is an effective method to attenuate turbulent channel flow such that it is relaminarised. The passivity-based control approach is adopted and explained by the conservative characteristics of the nonlinear terms contributing to the Reynolds-Orr equation (Sharma et al .Phys .Fluids 2011). The linear forcing acts on the wall-normal velocity field and thus the pressure field via the linear (rapid) source term of the Poisson equation for pressure fluctuations, 2U'∂v/∂x . The minimum required spanwise wavelength resolution without losing control is constant at λz+ = 125, based on the wall friction velocity at t = 0 . The result shows that the maximum forcing is located at y+ ~ 20 , corresponding to the location of the maximum in the mean-square pressure gradient. The effectiveness of linear control is qualitatively explained by Landahl's theory for timescales, in that the control proceeds via the shear interaction timescale which is much shorter than both the nonlinear and viscous timescales. The response of the rapid (linear) and slow (nonlinear) pressure fluctuations to the linear control is examined and discussed.

Upper internals arrangement for a pressurized water reactor

DOEpatents

Singleton, Norman R; Altman, David A; Yu, Ching; Rex, James A; Forsyth, David R

2013-07-09

In a pressurized water reactor with all of the in-core instrumentation gaining access to the core through the reactor head, each fuel assembly in which the instrumentation is introduced is aligned with an upper internals instrumentation guide-way. In the elevations above the upper internals upper support assembly, the instrumentation is protected and aligned by upper mounted instrumentation columns that are part of the instrumentation guide-way and extend from the upper support assembly towards the reactor head in hue with a corresponding head penetration. The upper mounted instrumentation columns are supported laterally at one end by an upper guide tube and at the other end by the upper support plate.

Comparison study of upper arm and forearm non-invasive blood pressures in adult Emergency Department patients.

PubMed

Schimanski, Karen; Jull, Andrew; Mitchell, Nancy; McLay, Jessica

2014-12-01

Forearm blood pressures have been suggested as an alternative site to measure blood pressures when the upper arm is unavailable. However there is little evidence utilising clinical populations to support this substitution. To determine agreement between blood pressures measured in the left upper arm and forearm using a singular oscillometric non-invasive device in adult Emergency Department patients. The secondary objective was to explore the relationship of blood pressure differences with age, sex, ethnicity, smoking history and obesity. Single centre comparison study. Adult Emergency Department, Tertiary Trauma Centre. Forty-four participants who met inclusion/exclusion criteria selected sequentially from the Emergency Department arrival board. A random assignment of order of measurement for left upper arm and forearm blood pressures was utilised. Participants were eligible if they were aged 18 years or older, had been assigned an Australasian Triage Scale code of 2, 3, 4, or 5, were able to consent, and able to have blood pressures measured on their left arm whilst lying at a 45° angle. The Bland-Altman method of statistical analysis was used, with the level of agreement for clinical acceptability for the systolic, diastolic and mean arterial pressure defined as ±10 mmHg. The forearm measure overestimated systolic (mean difference 2.2 mmHg, 95% limits of agreement ±19 mmHg), diastolic (mean difference 3.4 mmHg, 95% limits of agreement ±14.4 mmHg), and mean arterial pressures (mean difference 4.1 mmHg, 95% limits of agreement ±13.7 mmHg). The systolic measure was not significantly different from zero. Evidence of better agreement was found with upper arm/forearm systolic measures below 140 mmHg compared to systolic measures above 140 mmHg using the Levene's test (p=0.002, F-statistic=11.09). Blood pressure disparity was not associated with participant characteristics. Forearm measures cannot routinely replace upper arm measures for blood pressure measurement. If the clinical picture requires use of forearm blood pressure, the potential variance from an upper arm measure is ±19 mmHg for systolic pressure, although the variability may be close to ±10 mmHg if the systolic blood pressure is below 140 mmHg. Copyright © 2014 Elsevier Ltd. All rights reserved.

Two stage sorption type cryogenic refrigerator including heat regeneration system

NASA Technical Reports Server (NTRS)

Jones, Jack A. (Inventor); Wen, Liang-Chi (Inventor); Bard, Steven (Inventor)

1989-01-01

A lower stage chemisorption refrigeration system physically and functionally coupled to an upper stage physical adsorption refrigeration system is disclosed. Waste heat generated by the lower stage cycle is regenerated to fuel the upper stage cycle thereby greatly improving the energy efficiency of a two-stage sorption refrigerator. The two stages are joined by disposing a first pressurization chamber providing a high pressure flow of a first refrigerant for the lower stage refrigeration cycle within a second pressurization chamber providing a high pressure flow of a second refrigerant for the upper stage refrigeration cycle. The first pressurization chamber is separated from the second pressurization chamber by a gas-gap thermal switch which at times is filled with a thermoconductive fluid to allow conduction of heat from the first pressurization chamber to the second pressurization chamber.

High redshift signatures in the 21 cm forest due to cosmic string wakes

NASA Astrophysics Data System (ADS)

Tashiro, Hiroyuki; Sekiguchi, Toyokazu; Silk, Joseph

2014-01-01

Cosmic strings induce minihalo formation in the early universe. The resultant minihalos cluster in string wakes and create a ``21 cm forest'' against the cosmic microwave background (CMB) spectrum. Such a 21 cm forest can contribute to angular fluctuations of redshifted 21 cm signals integrated along the line of sight. We calculate the root-mean-square amplitude of the 21 cm fluctuations due to strings and show that these fluctuations can dominate signals from minihalos due to primordial density fluctuations at high redshift (zgtrsim10), even if the string tension is below the current upper bound, Gμ < 1.5 × 10-7. Our results also predict that the Square Kilometre Array (SKA) can potentially detect the 21 cm fluctuations due to strings with Gμ ≈ 7.5 × 10-8 for the single frequency band case and 4.0 × 10-8 for the multi-frequency band case.

Effects of age, gender, bolus condition, viscosity, and volume on pharyngeal and upper esophageal sphincter pressure and temporal measurements during swallowing.

PubMed

Butler, Susan G; Stuart, Andrew; Castell, Donald; Russell, Gregory B; Koch, Kenneth; Kemp, Shannon

2009-02-01

The purpose of this study was to determine the effects of trial (i.e., Trial 1 vs. Trial 2); viscosity (i.e., saliva, thin, nectar-thick, honey-thick, and pudding-thick water); volume (i.e., 5 mL vs. 10 mL); age (i.e., young vs. older adults); and gender on pharyngeal (i.e., upper and lower) and upper esophageal sphincter (UES) pressures, durations, and onsets (i.e., onset of upper pharyngeal pressures relative to onsets of UES relaxations and onset of lower relative to upper pharyngeal pressures). Twenty-three young adults (M=30 years) and 21 older healthy adults (M=75 years) participated. Measurements were acquired with a 2.1-mm catheter during simultaneous manometric and endoscopic swallowing assessment. Participants contributed 18 swallows, affording a study total of 792 swallows for analyses. There was no significant effect of trial on any measurement of pressure, duration, and onset (ps=.63, .39, and .71, respectively). It was found that viscosity, volume, age, and gender affected pressure, duration, and onset measurements (e.g., onset of upper pharyngeal pressures relative to onsets of UES relaxations) but in varying degrees relative to the location in the pharynx or UES and the type of measurement (e.g., pressure, onset). Manometric measurements vary with respect to age, gender, and bolus variables and interactions of each. Consideration of these variables is paramount in understanding normal and pathological swallowing if manometry is to develop as a quantitative adjunct to videofluoroscopic and endoscopic swallowing tools.

Magnetohydrodynamic simulations of noninductive helicity injection in the reversed-field pinch and tokamak

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sovinec, Carl R.

1995-11-01

Numerical computation is used to investigate resistive magnetohydrodynamic (MHD) fluctuations in the reversed-field pinch (RFP) and in tokamak-like configurations driven solely by direct current (DC) helicity injection. A Lundquist number (S) scan of RFP turbulence without plasma pressure produces the weak scaling of S -0.18 for the root-mean-square magnetic fluctuation level for 2.5x10 3≤S≤4x10 4. The temporal behavior of fluctuations and the reversal parameter becomes more regular as S is increased, acquiring a "sawtooth" shape at the largest value of S. Simulations with plasma pressure and anisotropic thermal conduction demonstrate energy transport resulting from parallel heat fluctuations. To investigate meansmore » of improving RFP energy confinement, three forms of current profile modification are tested. Radio frequency (RF) current drive is modeled with an auxiliary electron force, and linear stability calculations are used.« less

Measurements and Computations of Second-Mode Instability Waves in Three Hypersonic Wind Tunnels

NASA Technical Reports Server (NTRS)

Berridge, Dennis C.; Casper, Katya M.; Rufer, Shann J.; Alba, Christopher R.; Lewis, Daniel R.; Beresh, Steven J.; Schneider, Steven P.

2010-01-01

High-frequency pressure-fluctuation measurements were made in AEDC Tunnel 9 at Mach 10 and the NASA Langley 15-Inch Mach 6 and 31-Inch Mach 10 tunnels. Measurements were made on a 7deg-half-angle cone model. Pitot measurements of freestream pressure fluctuations were also made in Tunnel 9 and the Langley Mach-6 tunnel. For the first time, second-mode waves were measured in all of these tunnels, using 1-MHz-response pressure sensors. In Tunnel 9, second-mode waves could be seen in power spectra computed from records as short as 80 micro-s. The second-mode wave amplitudes were observed to saturate and then begin to decrease in the Langley tunnels, indicating wave breakdown. Breakdown was estimated to occur near N approx. equals 5 in the Langley Mach-10 tunnel. The unit-Reynolds-number variations in the data from Tunnel 9 were too large to see the same processes. In Tunnel 9, the measured transition locations were found to be at N = 4.5 using thermocouples, and N = 5.3 using 50-kHz-response pressure sensors. What appears to be a very long transitional region was observed at a unit Reynolds number of 13.5 million per meter in Tunnel 9. These results were consistent with the high-frequency pressure fluctuation measurements. High-frequency pressure fluctuation measurements indicated that transition did occur in the Langley Mach-6 tunnel, but the location of transition was not precisely determined. Unit Reynolds numbers in the Langley Mach-10 tunnel were too low to observe transition. More analysis of this data set is expected in the future.

Determining the mean hydraulic gradient of ground water affected by tidal fluctuations

USGS Publications Warehouse

Serfes, Michael E.

1991-01-01

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.

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

The top bow deck of the Woods Hole Oceanographic Institution's research vessel Knorr is seen on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. Knorr is scheduled to depart on Sept. 6 to take part in the Salinity Processes in the Upper Ocean Regional Study (SPURS). The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

Woods Hole Oceanographic Institution workers load scientific instruments onboard the Institution's research vessel Knorr on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. Knorr is scheduled to depart on Sept. 6 to take part in the Salinity Processes in the Upper Ocean Regional Study (SPURS). The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

The Woods Hole Oceanographic Institution's research vessel Knorr is seen docked on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. Knorr is scheduled to depart on Sept. 6 to take part in the Salinity Processes in the Upper Ocean Regional Study (SPURS). The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

Scientific instruments are loaded onboard the Woods Hole Oceanographic Institution's research vessel Knorr on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. Knorr is scheduled to depart on Sept. 6 to take part in the Salinity Processes in the Upper Ocean Regional Study (SPURS). The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

The Bridge of the Woods Hole Oceanographic Institution's research vessel Knorr is seen on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. Knorr is scheduled to depart on Sept. 6 to take part in the Salinity Processes in the Upper Ocean Regional Study (SPURS). The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

Food and supplies are loaded onboard the Woods Hole Oceanographic Institution's research vessel Knorr on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. Knorr is scheduled to depart on Sept. 6 to take part in the Salinity Processes in the Upper Ocean Regional Study (SPURS). The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

NASA Physical Oceanography Program Scientist Eric Lindstrom boards the Woods Hole Oceanographic Institution's research vessel Knorr on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. Lindstrom will depart on Knorr Sept. 6 to take part in the Salinity Processes in the Upper Ocean Regional Study (SPURS). The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

The Upper Mississippi River System—Topobathy

USGS Publications Warehouse

Stone, Jayme M.; Hanson, Jenny L.; Sattler, Stephanie R.

2017-03-23

The Upper Mississippi River System (UMRS), the navigable part of the Upper Mississippi and Illinois Rivers, is a diverse ecosystem that contains river channels, tributaries, shallow-water wetlands, backwater lakes, and flood-plain forests. Approximately 10,000 years of geologic and hydrographic history exist within the UMRS. Because it maintains crucial wildlife and fish habitats, the dynamic ecosystems of the Upper Mississippi River Basin and its tributaries are contingent on the adjacent flood plains and water-level fluctuations of the Mississippi River. Separate data for flood-plain elevation (lidar) and riverbed elevation (bathymetry) were collected on the UMRS by the U.S. Army Corps of Engineers’ (USACE) Upper Mississippi River Restoration (UMRR) Program. Using the two elevation datasets, the U.S. Geological Survey (USGS) Upper Midwest Environmental Sciences Center (UMESC) developed a systemic topobathy dataset.

Fast PSP measurements of wall-pressure fluctuation in low-speed flows: improvements using proper orthogonal decomposition

NASA Astrophysics Data System (ADS)

Peng, Di; Wang, Shaofei; Liu, Yingzheng

2016-04-01

Fast pressure-sensitive paint (PSP) is very useful in flow diagnostics due to its fast response and high spatial resolution, but its applications in low-speed flows are usually challenging due to limitations of paint's pressure sensitivity and the capability of high-speed imagers. The poor signal-to-noise ratio in low-speed cases makes it very difficult to extract useful information from the PSP data. In this study, unsteady PSP measurements were made on a flat plate behind a cylinder in a low-speed wind tunnel (flow speed from 10 to 17 m/s). Pressure fluctuations (Δ P) on the plate caused by vortex-plate interaction were recorded continuously by fast PSP (using a high-speed camera) and a microphone array. Power spectrum of pressure fluctuations and phase-averaged Δ P obtained from PSP and microphone were compared, showing good agreement in general. Proper orthogonal decomposition (POD) was used to reduce noise in PSP data and extract the dominant pressure features. The PSP results reconstructed from selected POD modes were then compared to the pressure data obtained simultaneously with microphone sensors. Based on the comparison of both instantaneous Δ P and root-mean-square of Δ P, it was confirmed that POD analysis could effectively remove noise while preserving the instantaneous pressure information with good fidelity, especially for flows with strong periodicity. This technique extends the application range of fast PSP and can be a powerful tool for fundamental fluid mechanics research at low speed.

Flight and wind-tunnel correlation of boundary-layer transition on the AEDC transition cone

NASA Technical Reports Server (NTRS)

Fisher, D. L.; Dougherty, N. S., Jr.

1982-01-01

Transition and fluctuating surface pressure data were acquired on a 10 deg included angle cone, using the same instrumentation and technique over a wide range of Mach and Reynolds numbers in 23 wind tunnels and in flight. Transition was detected with a traversing pitot-pressure probe in contact with the surface. The surface pressure fluctuations were measured with microphones set flush in the cone surface. Good correlation of end of transition Reynolds number RE(T) was obtained between data from the lower disturbance wind tunnels and flight up to a boundary layer edge Mach number, M(e) = 1.2. Above M(e) = 1.2, however, this correlation deteriorates, with the flight Re(T) being 25 to 30% higher than the wind tunnel Re(T) at M(e) = 1.6. The end of transition Reynolds number correlated within + or - 20% with the surface pressure fluctuations, according to the equation used. Broad peaks in the power spectral density distributions indicated that Tollmien-Schlichting waves were the probable cause of transition in flight and in some of the wind tunnels.

Gas centrifuge purge method

DOEpatents

Theurich, Gordon R.

1976-01-01

1. In a method of separating isotopes in a high speed gas centrifuge wherein a vertically oriented cylindrical rotor bowl is adapted to rotate about its axis within an evacuated chamber, and wherein an annular molecular pump having an intake end and a discharge end encircles the uppermost portion of said rotor bowl, said molecular pump being attached along its periphery in a leak-tight manner to said evacuated chamber, and wherein end cap closure means are affixed to the upper end of said rotor bowl, and a process gas withdrawal and insertion system enters said bowl through said end cap closure means, said evacuated chamber, molecular pump and end cap defining an upper zone at the discharge end of said molecular pump, said evacuated chamber, molecular pump and rotor bowl defining a lower annular zone at the intake end of said molecular pump, a method for removing gases from said upper and lower zones during centrifuge operation with a minimum loss of process gas from said rotor bowl, comprising, in combination: continuously measuring the pressure in said upper zone, pumping gas from said lower zone from the time the pressure in said upper zone equals a first preselected value until the pressure in said upper zone is equal to a second preselected value, said first preselected value being greater than said second preselected value, and continuously pumping gas from said upper zone from the time the pressure in said upper zone equals a third preselected value until the pressure in said upper zone is equal to a fourth preselected value, said third preselected value being greater than said first, second and fourth preselected values.

Regulation of pressure anisotropy in the solar wind: processes within inertial range of turbulence

NASA Astrophysics Data System (ADS)

Strumik, M.; Schekochihin, A. A.; Squire, J.; Bale, S. D.

2016-12-01

Dynamics of weakly collisional plasmas may lead to thermal pressure anisotropies that are driven by velocity shear, plasma expansion/compression or temperature gradients. The pressure anisotropies can provide free energy for the growth of micro-scale instabilities, like the mirror of firehose instabilities, that are commonly believed to constrain the pressure anisotropy in the solar wind if appropriate thresholds are exceeded. We discuss possible alternative mechanisms of regulation of the pressure anisotropy in the inertial range of solar wind turbulence that provide β-dependent constraints on the amplitude of fluctuations of pressure components and other quantities. In particular it is shown that double-adiabatic (CGL) closure for magnetohydrodynamic regime leads to 1/β scaling of the amplitude of the pressure component fluctuations and the pressure anisotropy. Both freely decaying and forced turbulence are discussed based on results of 3D numerical simulations and analytical theoretical predictions. The theoretical results are contrasted with WIND spacecraft measurements.

Fast gradient separation by very high pressure liquid chromatography: reproducibility of analytical data and influence of delay between successive runs.

PubMed

Stankovicha, Joseph J; Gritti, Fabrice; Beaver, Lois Ann; Stevensona, Paul G; Guiochon, Georges

2013-11-29

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.

Acute Positive Effects of Exercise on Center-of-Pressure Fluctuations During Quiet Standing in Middle-Aged and Elderly Women.

PubMed

Fukusaki, Chiho; Masani, Kei; Miyasaka, Maya; Nakazawa, Kimitaka

2016-01-01

Acute effects of exercise on postural stability have been studied with a focus on fatigue. This study investigated the acute effects of moderate-intensity exercise on center-of-pressure (COP) fluctuation measures in middle-aged and elderly women. Thirty-five healthy women volunteered: 18 women performed a moderate aquatic exercise session for 80 minutes and 17 remained calm in a sitting position for the same duration. Center-of-pressure fluctuations during quiet standing were recorded for 60 seconds with eyes open and closed before and after the exercise and sitting tasks. The time- and frequency-domain measures of the COP time series were calculated. The frequency-domain measures were also calculated for the COP velocity time series. According to 2-way analysis of variance and paired t-tests with a Bonferroni's correction, mean velocity of COP fluctuations, mean velocity of COP fluctuations in the medial-lateral (ML) direction, and total power of the COP velocity time series in the ML direction exhibited significant reductions after 1 session of exercise. These results indicated that a moderate-intensity aquatic exercise decreased COP velocity, counteracting age-related and fatigue-inducing postural deterioration. Therefore, we concluded that a single session of moderate-intensity aquatic exercise has acute positive effects on postural stability in middle-aged and elderly women.

Estimating Transmissivity from the Water Level Fluctuations of a Sinusoidally Forced Well

USGS Publications Warehouse

Mehnert, E.; Valocchi, A.J.; Heidari, M.; Kapoor, S.G.; Kumar, P.

1999-01-01

The water levels in wells are known to fluctuate in response to earth tides and changes in atmospheric pressure. These water level fluctuations can be analyzed to estimate transmissivity (T). A new method to estimate transmissivity, which assumes that the atmospheric pressure varies in a sinusoidal fashion, is presented. Data analysis for this simplified method involves using a set of type curves and estimating the ratio of the amplitudes of the well response over the atmospheric pressure. Type curves for this new method were generated based on a model for ground water flow between the well and aquifer developed by Cooper et al. (1965). Data analysis with this method confirmed these published results: (1) the amplitude ratio is a function of transmissivity, the well radius, and the frequency of the sinusoidal oscillation; and (2) the amplitude ratio is a weak function of storativity. Compared to other methods, the developed method involves simpler, more intuitive data analysis and allows shorter data sets to be analyzed. The effect of noise on estimating the amplitude ratio was evaluated and found to be more significant at lower T. For aquifers with low T, noise was shown to mask the water level fluctuations induced by atmospheric pressure changes. In addition, reducing the length of the data series did not affect the estimate of T, but the variance of the estimate was higher for the shorter series of noisy data.

Stabilization of composition fluctuations in mixed membranes by hybrid lipids

NASA Astrophysics Data System (ADS)

Safran, Samuel; Palmieri, Benoit

2013-03-01

A ternary mixture model is proposed to describe composition fluctuations in mixed membranes composed of saturated, unsaturated and hybrid lipids. The asymmetric hybrid lipid has one saturated and one unsaturated hydrocarbon chain and it can reduce the packing incompatibility between saturated and unsaturated lipids. A methodology to recast the free-energy of the lattice in terms of a continuous isotropic field theory is proposed and used to analyze composition fluctuations above the critical temperature. The effect of hybrid lipids on fluctuations domains rich in saturated/unsaturated lipids is predicted. The correlation length of such fluctuations decreases significantly with increasing amounts of hybrids even if the temperature is maintained close to the critical temperature. This provides an upper bound for the domain sizes expected in rafts stabilized by hybrids, above the critical temperature. When the hybrid composition of the membrane is increased further, a crossover value is found above which ``stripe-like'' fluctuations are observed. The wavelength of these fluctuations decreases with increasing hybrid fraction and tends toward a molecular size in a membrane that contains only hybrids.

Trophic interactions and direct physical effects control phytoplankton biomass and production in an estuary

USGS Publications Warehouse

Alpine, A.E.; Cloern, J.E.

1992-01-01

San Francisco Bay has recently been invaded by the suspension-feeding clam Potamocorbula amurensis. Previous work has shown that phytoplankton biomass in the upper estuary is low (2-3 mg Chl a m-3) during seasonal periods of high river flow and short residence time and it is usually high (peak >30 mg Chl a m-3) during the summer-autumn seasons of low river flow and long residence time. However since P. amurensis became widespread and abundant in 1987, the summer phytoplankton biomass maximum has disappeared, presumably because of increased grazing pressure by this newly introduced species. For 1977-1990, mean estimated primary production was only 39 g C m-2 yr-1 during years when bivalve suspension feeders were abundant (>2000 m-2), compared to 106 g C m-2 yr-1 when bivalves were absent or present in low numbers. These observations support the hypothesis that seasonal and interannual fluctuations in estuarine phytoplankton biomass and primary production can be regulated jointly by direct physical effects (eg river-driven transport) and trophic interactions (episodes of enhanced grazing pressure by immigrant populations of benthic suspension feeders). -from Authors

Discovery of Short-Timescale Oscillations in the Transition Region by CLASP

NASA Technical Reports Server (NTRS)

Kubo, M.; Katsukawa, Y.; Kano, R.; Winebarger, A.; Kobayashi, K.; Ishikawa, R.; Narukage, N.; Bando, T.; Suematsu, Y.; Giono, G.;

Inferring Pre-shock Acoustic Field From Post-shock Pitot Pressure Measurement

NASA Astrophysics Data System (ADS)

Wang, Jian-Xun; Zhang, Chao; Duan, Lian; Xiao, Heng; Virginia Tech Team; Missouri Univ of Sci; Tech Team

2017-11-01

Linear interaction analysis (LIA) and iterative ensemble Kalman method are used to convert post-shock Pitot pressure fluctuations to static pressure fluctuations in front of the shock. The LIA is used as the forward model for the transfer function associated with a homogeneous field of acoustic waves passing through a nominally normal shock wave. The iterative ensemble Kalman method is then employed to infer the spectrum of upstream acoustic waves based on the post-shock Pitot pressure measured at a single point. Several test cases with synthetic and real measurement data are used to demonstrate the merits of the proposed inference scheme. The study provides the basis for measuring tunnel freestream noise with intrusive probes in noisy supersonic wind tunnels.

Evolution of pressures and correlations in the glasma produced in high energy nuclear collisions

NASA Astrophysics Data System (ADS)

Ruggieri, M.; Liu, J. H.; Oliva, L.; Peng, G. X.; Greco, V.

2018-04-01

We consider the SU(2) glasma with Gaussian fluctuations and study its evolution by means of classical Yang-Mills equations solved numerically on a lattice. Neglecting in this first study the longitudinal expansion, we follow the evolution of the pressures of the system and compute the effect of the fluctuations in the early stage up to t ≈2 fm /c , that is the time range in which the glasma is relevant for high energy collisions. We measure the ratio of the longitudinal over the transverse pressure, PL/PT, and we find that unless the fluctuations carry a substantial amount of the energy density at the initial time, they do not change significantly the evolution of PL/PT in the early stage and that the system remains quite anisotropic. We also measure the longitudinal fields correlators both in the transverse plane and along the longitudinal direction: while at initial time fields appear to be anticorrelated in the transverse plane, this anticorrelation disappears in the very early stage, and the correlation length in the transverse plane increases. On the other hand, we find a dependence of the gauge invariant correlator on the longitudinal coordinate, which we interpret as a partial loss of correlation induced by the dynamics that we dub the gauge invariant string breaking. We finally study the effect of fluctuations on the longitudinal correlations: we find that string breaking is accelerated by the fluctuations and waiting for a sufficiently long time fluctuations lead to the complete breaking of the color strings.

Fate of a mutation in a fluctuating environment

PubMed Central

Cvijović, Ivana; Good, Benjamin H.; Jerison, Elizabeth R.; Desai, Michael M.

2015-01-01

Natural environments are never truly constant, but the evolutionary implications of temporally varying selection pressures remain poorly understood. Here we investigate how the fate of a new mutation in a fluctuating environment depends on the dynamics of environmental variation and on the selective pressures in each condition. We find that even when a mutation experiences many environmental epochs before fixing or going extinct, its fate is not necessarily determined by its time-averaged selective effect. Instead, environmental variability reduces the efficiency of selection across a broad parameter regime, rendering selection unable to distinguish between mutations that are substantially beneficial and substantially deleterious on average. Temporal fluctuations can also dramatically increase fixation probabilities, often making the details of these fluctuations more important than the average selection pressures acting on each new mutation. For example, mutations that result in a trade-off between conditions but are strongly deleterious on average can nevertheless be more likely to fix than mutations that are always neutral or beneficial. These effects can have important implications for patterns of molecular evolution in variable environments, and they suggest that it may often be difficult for populations to maintain specialist traits, even when their loss leads to a decline in time-averaged fitness. PMID:26305937

Thermodynamic Behavior in Decaying Compressible Turbulence with Initially Dominant Temperature Fluctuations

NASA Astrophysics Data System (ADS)

Cai, X. D.; O'Brien, Edward E.; Ladeinde, Foluso

1996-11-01

Direct numerical simulation of decaying, isotropic, compressible turbulence in three dimensions is used to examine the behavior of fluctuations in density, temperature, and pressure when the initial conditions include temperature fluctuations larger than pressure fluctuations. The numerical procedure is described elsewhere (Ladeinde, F. et al.,) Phys. Fluids 7(11), pp. 2848 (1995), the initial turbulence Mach number range is subsonic, 0.3 to 0.7, and, following Ghosh and Matthaeus(Ghosh, S. and Matthaeus, W. H. Phys. Fluids A, pp. 148 (1991)), the initial compressible turbulence is characterized as a: mostly solenoidal, b: random, or c: longitudinal. These cases represent, respectively, ratios of initial kinetic energy in the compressible modes to total initial kinetic energy, say \\chi_0, which are either a: very small, b: about 0.6, or c: near unity. Thermodynamic scalings at the lowest values of initial Mach number and \\chi0 follow the predictions of Zank and Matthaeus (Zank, G. P. and Matthaeus, W. H. Phys. Fluids A(3), pp. 69 (1991)), but not otherwise. The relationship between \\chi, Mach number, and compressible pressure predicted by Sarkar et al.(Sarkar, S. et al.,) J. Fluid Mech. 227, pp. 473 (1991) applies, on average, to all cases computed.

Surface pressure fluctuations in hypersonic turbulent boundary layers

NASA Technical Reports Server (NTRS)

Raman, K. R.

1974-01-01

The surface pressure fluctuations on a flat plate model at hypersonic Mach numbers of 5.2, 7.4 and 10.4 with an attached turbulent boundary layer were measured using flush mounted small piezoelectric sensors. A high frequency resolution of the pressure field was achieved using specially designed small piezoelectric sensors that had a good frequency response well above 300 KHz. The RMS pressures and non-dimensional energy spectra for all above Mach numbers are presented. The convective velocities, obtained from space time correlation considerations are equal to 0.7 U sub infinity. The results indicate the RMS pressures vary from 5 to 25 percent of the mean static pressures. The ratios of RMS pressure to dynamic pressure are less than the universally accepted subsonic value of 6 x 10/3. The ratio decreases in value as the Mach number or the dynamic pressure is increased. The ratio of RMS pressure to wall shear for Mach number 7.4 satisfies one smaller than or equal to p/tau sub w smaller than or equal to three.

Analysis of Meniscus Fluctuation in a Continuous Casting Slab Mold

NASA Astrophysics Data System (ADS)

Zhang, Kaitian; Liu, Jianhua; Cui, Heng; Xiao, Chao

2018-06-01

A water model of slab mold was established to analyze the microscopic and macroscopic fluctuation of meniscus. The fast Fourier transform and wavelet entropy were adopted to analyze the wave amplitude, frequency, and components of fluctuation. The flow patterns under the meniscus were measured by using particle image velocimetry measurement and then the mechanisms of meniscus fluctuation were discussed. The results reflected that wavelet entropy had multi-scale and statistical properties, and it was suitable for the study of meniscus fluctuation details both in time and frequency domain. The basic wave, frequency of which exceeding 1 Hz in the condition of no mold oscillation, was demonstrated in this work. In fact, three basic waves were found: long-wave with low frequency, middle-wave with middle frequency, and short-wave with high frequency. In addition, the upper roll flow in mold had significant effect on meniscus fluctuation. When the position of flow impinged was far from the meniscus, long-wave dominated the fluctuation and the stability of meniscus was enhanced. However, when the velocity of flow was increased, the short-wave dominated the meniscus fluctuation and the meniscus stability was decreased.

Deformation analysis and prediction of bank protection structure with river level fluctuations

NASA Astrophysics Data System (ADS)

Hu, Rui; Xing, Yixuan

2017-04-01

Bank structure is an important barrier to maintain the safety of the embankment. The deformation of bank protection structure is not only affected by soil pressure caused by the excavation of the riverway, but also by the water pressure caused river water level fluctuations. Thus, it is necessary to establish a coupled soil-water model to analyze the deformation of bank structure. Based on Druck-Prager failure criteria and groundwater seepage theory, a numerical model of bank protection structure with consideration of the pore water pressure of soil mass is established. According to the measured river level data with seasonal fluctuating, numerical analysis of the deformation of bank protection structure is implemented. The simulation results show that the river water level fluctuation has clear influence on the maximum lateral displacement of the pile. Meanwhile, the distribution of plastic zone is related to the depth of groundwater level. Finally, according to the river water level data of the recent ten years, we analyze the deformation of the bank structure under extreme river level. The result shows that, compared with the scenario of extreme high river level, the horizontal displacement of bank protection structure is larger (up to 65mm) under extreme low river level, which is a potential risk to the embankment. Reference Schweiger H F. On the use of drucker-prager failure criteria for earth pressure problems[J]. Computers and Geotechnics, 1994, 16(3): 223-246. DING Yong-chun，CHENG Ze-kun. Numerical study on performance of waterfront excavation[J]. Chinese Journal of Geotechnical Engineering，2013，35(2):515-521. Wu L M, Wang Z Q. Three gorges reservoir water level fluctuation influents on the stability of the slope[J]. Advanced Materials Research. Trans Tech Publications, 2013, 739: 283-286.

Pheochromocytoma Crisis With Severe Cyclic Blood Pressure Fluctuations in a Cardiac Pheochromocytoma Patient Successfully Resuscitated by Extracorporeal Membrane Oxygenation

PubMed Central

Zhou, Xiang; Liu, Dawei; Su, Longxiang; Long, Yun; Du, Wei; Miao, Qi; Li, Fang; Jin, Zhengyu; Zeng, Zhengpei; Luo, Ailun; Huang, Yuguang

2015-01-01

Abstract Cardiac pheochromocytoma is relatively rare. Few reports describe the intraoperative and postoperative progression of patients experiencing a life-threatening pheochromocytoma crisis treated with extracorporeal membrane oxygenation (ECMO). A 35-year-old man was referred to our facility for paroxysmal hypertension with a 10-year history of sweating, headaches, cardiac palpitations, and postexercise dyspnea. The patient initially underwent urine catecholamine measurement and an isotope scan, somatostatin receptor scintigraphy, and 18F-fluorodeoxyglucose positron emission tomography/computer tomography (CT), which indicated a multiple, cardiac pheochromocytoma. Echocardiography, cardiac magnetic resonance imaging (MRI), CT reconstruction, and a coronary CT angiography revealed several lesions at the aortic root and along the cardiac vasculature. Multifocal cardiac pheochromocytoma was diagnosed and pheochromocytoma crisis with severe cyclic blood pressure fluctuation occurred during surgery. Surgical resection of multiple pheochromocytomas in the right medial carotid sheath, mediastinum between the main and pulmonary arteries, and between the abdominal aorta and inferior vena artery was performed. To ensure cardiac perfusion and avoid severe circulatory fluctuation, the cardiac paraganglioma resection was prioritized. After resecting the cardiac pheochromocytoma, a severe pheochromocytoma crisis with rapid cyclic blood pressure fluctuation developed. ECMO and intraaortic balloon pump (IABP) were initiated to stabilize circulation and perfusion. Phenoxybenzamine, norepinephrine, epinephrine, and fluid resuscitation were administered to support cardiovascular function. The magnitude of blood pressure fluctuation steadily decreased with treatment. IABP was discontinued after 3 days, and ECMO was discontinued after 16 days. The patient was discharged 3 months postoperatively. This case indicates that mechanical life support with ECMO is a valuable option for pheochromocytoma-induced cardiac shock and should be considered as an effective therapeutic choice in patients with highly unstable hemodynamic function. PMID:25929929

Acoustic Database for Turbofan Engine Core-Noise Sources. I; Volume

NASA Technical Reports Server (NTRS)

Gordon, Grant

2015-01-01

In this program, a database of dynamic temperature and dynamic pressure measurements were acquired inside the core of a TECH977 turbofan engine to support investigations of indirect combustion noise. Dynamic temperature and pressure measurements were recorded for engine gas dynamics up to temperatures of 3100 degrees Fahrenheit and transient responses as high as 1000 hertz. These measurements were made at the entrance of the high pressure turbine (HPT) and at the entrance and exit of the low pressure turbine (LPT). Measurements were made at two circumferential clocking positions. In the combustor and inter-turbine duct (ITD), measurements were made at two axial locations to enable the exploration of time delays. The dynamic temperature measurements were made using dual thin-wire thermocouple probes. The dynamic pressure measurements were made using semi-infinite probes. Prior to the engine test, a series of bench, oven, and combustor rig tests were conducted to characterize the performance of the dual wire temperature probes and to define and characterize the data acquisition systems. A measurement solution for acquiring dynamic temperature and pressure data on the engine was defined. A suite of hardware modifications were designed to incorporate the dynamic temperature and pressure instrumentation into the TECH977 engine. In particular, a probe actuation system was developed to protect the delicate temperature probes during engine startup and transients in order to maximize sensor life. A set of temperature probes was procured and the TECH977 engine was assembled with the suite of new and modified hardware. The engine was tested at four steady state operating speeds, with repeats. Dynamic pressure and temperature data were acquired at each condition for at least one minute. At the two highest power settings, temperature data could not be obtained at the forward probe locations since the mean temperatures exceeded the capability of the probes. The temperature data were processed using software that accounts for the effects of convective and conductive heat transfer. The software was developed under previous NASA sponsored programs. Compensated temperature spectra and compensated time histories corresponding to the dynamic temperature of the gas stream were generated. Auto-spectral and cross-spectral analyses of the data were performed to investigate spectral features, acoustic circumferential mode content, signal coherence, and time delays. The dynamic temperature data exhibit a wideband and fairly flat spectral content. The temperature spectra do not change substantially with operating speed. The pressure spectra in the combustor and ITD exhibit generally similar shapes and amplitudes, making it difficult to identify any features that suggest the presence of indirect combustion noise. Cross-spectral analysis reveal a strong correlation between pressure and temperature fluctuations in the ITD, but little correlation between temperature fluctuations at the entrance of the HPT and pressure fluctuations downstream of it. Temperature fluctuations at the entrance of the low pressure turbine were an order of magnitude smaller than those at the entrance to the high pressure turbine. Time delay analysis of the temperature fluctuations in the combustor was inconclusive, perhaps due to the substantial mixing that occurs between the upstream and downstream locations. Time delay analysis of the temperature fluctuations in the ITD indicate that they convect at the mean flow speed. Analysis of the data did not reveal any convincing indications of the presence of indirect combustion noise. However, this analysis has been preliminary and additional exploration of the data is recommended including the use of more sophisticated signal processing to explore subtle issues that have been revealed but which are not yet fully understood or explained.

Low Mach number fluctuating hydrodynamics of multispecies liquid mixtures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Donev, Aleksandar, E-mail: donev@courant.nyu.edu; Bhattacharjee, Amit Kumar; Nonaka, Andy

We develop a low Mach number formulation of the hydrodynamic equations describing transport of mass and momentum in a multispecies mixture of incompressible miscible liquids at specified temperature and pressure, which generalizes our prior work on ideal mixtures of ideal gases [Balakrishnan et al., “Fluctuating hydrodynamics of multispecies nonreactive mixtures,” Phys. Rev. E 89 013017 (2014)] and binary liquid mixtures [Donev et al., “Low mach number fluctuating hydrodynamics of diffusively mixing fluids,” Commun. Appl. Math. Comput. Sci. 9(1), 47-105 (2014)]. In this formulation, we combine and extend a number of existing descriptions of multispecies transport available in the literature. Themore » formulation applies to non-ideal mixtures of arbitrary number of species, without the need to single out a “solvent” species, and includes contributions to the diffusive mass flux due to gradients of composition, temperature, and pressure. Momentum transport and advective mass transport are handled using a low Mach number approach that eliminates fast sound waves (pressure fluctuations) from the full compressible system of equations and leads to a quasi-incompressible formulation. Thermal fluctuations are included in our fluctuating hydrodynamics description following the principles of nonequilibrium thermodynamics. We extend the semi-implicit staggered-grid finite-volume numerical method developed in our prior work on binary liquid mixtures [Nonaka et al., “Low mach number fluctuating hydrodynamics of binary liquid mixtures,” http://arxiv.org/abs/1410.2300 (2015)] and use it to study the development of giant nonequilibrium concentration fluctuations in a ternary mixture subjected to a steady concentration gradient. We also numerically study the development of diffusion-driven gravitational instabilities in a ternary mixture and compare our numerical results to recent experimental measurements [Carballido-Landeira et al., “Mixed-mode instability of a miscible interface due to coupling between Rayleigh–Taylor and double-diffusive convective modes,” Phys. Fluids 25, 024107 (2013)] in a Hele-Shaw cell. We find that giant nonequilibrium fluctuations can trigger the instability but are eventually dominated by the deterministic growth of the unstable mode, in both quasi-two-dimensional (Hele-Shaw) and fully three-dimensional geometries used in typical shadowgraph experiments.« less

Modeling deformation processes of salt caverns for gas storage due to fluctuating operation pressures

NASA Astrophysics Data System (ADS)

Böttcher, N.; Nagel, T.; Goerke, U.; Khaledi, K.; Lins, Y.; König, D.; Schanz, T.; Köhn, D.; Attia, S.; Rabbel, W.; Bauer, S.; Kolditz, O.

2013-12-01

In the course of the Energy Transition in Germany, the focus of the country's energy sources is shifting from fossil to renewable and sustainable energy carriers. Since renewable energy sources, such as wind and solar power, are subjected to annual, seasonal, and diurnal fluctuations, the development and extension of energy storage capacities is a priority in German R&D programs. Common methods of energy storage are the utilization of subsurface caverns as a reservoir for natural or artificial fuel gases, such as hydrogen, methane, or the storage of compressed air. The construction of caverns in salt rock is inexpensive in comparison to solid rock formations due to the possibility of solution mining. Another advantage of evaporite as a host material is the self-healing capacity of salt rock. Gas caverns are capable of short-term energy storage (hours to days), so the operating pressures inside the caverns are fluctuating periodically with a high number of cycles. This work investigates the influence of fluctuating operation pressures on the stability of the host rock of gas storage caverns utilizing numerical models. Therefore, we developed a coupled Thermo-Hydro-Mechanical (THM) model based on the finite element method utilizing the open-source software platform OpenGeoSys. Our simulations include the thermodynamic behaviour of the gas during the loading/ unloading of the cavern. This provides information on the transient pressure and temperature distribution on the cavern boundary to calculate the deformation of its geometry. Non-linear material models are used for the mechanical analysis, which describe the creep and self-healing behavior of the salt rock under fluctuating loading pressures. In order to identify the necessary material parameters, we perform experimental studies on the mechanical behaviour of salt rock under varying pressure and temperature conditions. Based on the numerical results, we further derive concepts for monitoring THM quantities in the vicinity of the cavern. These programs will allow detecting changes of the host rock properties during the construction and operation of the storage facility. The developed model will be used by public authorities for land use planning issues.

Receptivity of a Cryogenic Coaxial Liquid Jet to Acoustic Disturbances

DTIC Science & Technology

2014-01-01

PAGES 19a. NAME OF RESPONSIBLE PERSON D. Talley a. REPORT Unclassified b. ABSTRACT Unclassified c . THIS PAGE Unclassified SAR 13 19b... c pu c    (1) where u’ is the magnitude of the velocity fluctuation in the velocity antinode region, p’ is the magnitude of the pressure...fluctuation in the pressure antinode region,  c is the density of the ambient gas in the chamber, which is nominal room temperature nitrogen, and c

78 FR 64417 - Airworthiness Directives; Twin Commander Aircraft LLC Airplanes; Initial Regulatory Flexibility...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-10-29

... window channels, aft cabin pressure web, external wing to fuselage fillets, and fasteners; repair or..., the vertical channels, the upper picture window channels, aft cabin pressure web, external wing to... lower wing main spar, the vertical channels, the upper picture window channels, aft cabin pressure web...

The trade-off between heat tolerance and metabolic cost drives the bimodal life strategy at the air-water interface

PubMed Central

Fusi, Marco; Cannicci, Stefano; Daffonchio, Daniele; Mostert, Bruce; Pörtner, Hans-Otto; Giomi, Folco

2016-01-01

The principle of oxygen and capacity limitation of thermal tolerance in ectotherms suggests that the long-term upper limits of an organism's thermal niche are equivalent to the upper limits of the organism's functional capacity for oxygen provision to tissues. Air-breathing ectotherms show wider thermal tolerances, since they can take advantage of the higher availability of oxygen in air than in water. Bimodal species move from aquatic to aerial media and switch between habitats in response to environmental variations such as cyclical or anomalous temperature fluctuations. Here we tested the prediction that bimodal species cope better with thermal stress than truly aquatic species using the crab Pachygrapsus marmoratus as a model species. When in water, oxygen consumption rates of P. marmoratus acutely rise during warming. Beyond a temperature threshold of 23 °C the crab's aerobic metabolism in air remains lower than in water. In parallel, the haemolymph oxygen partial pressure of submerged animals progressive decreases during warming, while it remains low but constant during emersion. Our results demonstrate the ability of a bimodal breathing ectotherm to extend its thermal tolerance during air-breathing, suggesting that there are temperature-related physiological benefits during the evolution of the bimodal life style. PMID:26758742

The trade-off between heat tolerance and metabolic cost drives the bimodal life strategy at the air-water interface.

PubMed

Fusi, Marco; Cannicci, Stefano; Daffonchio, Daniele; Mostert, Bruce; Pörtner, Hans-Otto; Giomi, Folco

2016-01-13

The principle of oxygen and capacity limitation of thermal tolerance in ectotherms suggests that the long-term upper limits of an organism's thermal niche are equivalent to the upper limits of the organism's functional capacity for oxygen provision to tissues. Air-breathing ectotherms show wider thermal tolerances, since they can take advantage of the higher availability of oxygen in air than in water. Bimodal species move from aquatic to aerial media and switch between habitats in response to environmental variations such as cyclical or anomalous temperature fluctuations. Here we tested the prediction that bimodal species cope better with thermal stress than truly aquatic species using the crab Pachygrapsus marmoratus as a model species. When in water, oxygen consumption rates of P. marmoratus acutely rise during warming. Beyond a temperature threshold of 23 °C the crab's aerobic metabolism in air remains lower than in water. In parallel, the haemolymph oxygen partial pressure of submerged animals progressive decreases during warming, while it remains low but constant during emersion. Our results demonstrate the ability of a bimodal breathing ectotherm to extend its thermal tolerance during air-breathing, suggesting that there are temperature-related physiological benefits during the evolution of the bimodal life style.

Stringent limits on the amplitude of Alfvénic perturbations at high-beta

NASA Astrophysics Data System (ADS)

Squire, J.; Quataert, E.; Schekochihin, A. A.; Bale, S. D.; Chen, C. H. K.; Strumik, M.

2016-12-01

It is shown that low-collisionality plasmas cannot support linearly polarized shear-Alfvén fluctuations above a critical amplitude δB⊥/B0 ˜ β-1/2, where β is the ratio of thermal to magnetic pressure. Above this cutoff, a developing fluctuation will generate a pressure anisotropy that is sufficient to destabilize itself through the parallel firehose instability. This causes the wave frequency to approach zero, interrupting the fluctuation before any oscillation. The magnetic field lines rapidly relax into a sequence of angular zig-zag structures. Such a restrictive bound on shear-Alfvén-wave amplitudes has interesting implications for magnetized turbulence in weakly collisional plasmas, in particular for the solar wind at 1AU where β 1.

Aeroacoustic Measurements of a Wing-Flap Configuration

NASA Technical Reports Server (NTRS)

Meadows, Kristine R.; Brooks, Thomas F.; Humphreys, William M.; Hunter, William H.; Gerhold, Carl H.

1997-01-01

Aeroacoustic measurements are being conducted to investigate the mechanisms of sound generation in high-lift wing configurations, and initial results are presented. The model is approximately 6 percent of a full scale configuration, and consists of a main element NACA 63(sub 2) - 215 wing section and a 30 percent chord half-span flap. Flow speeds up to Mach 0.17 are tested at Reynolds number up to approximately 1.7 million. Results are presented for a main element at a 16 degree angle of attack, and flap deflection angles of 29 and 39 degrees. The measurement systems developed for this test include two directional arrays used to localize and characterize the noise sources, and an array of unsteady surface pressure transducers used to characterize wave number spectra and correlate with acoustic measurements. Sound source localization maps show that locally dominant noise sources exist on the flap-side edge. The spectral distribution of the noise sources along the flap-side edge shows a decrease in frequency of the locally dominant noise source with increasing distance downstream of the flap leading edge. Spectra are presented which show general spectral characteristics of Strouhal dependent flow-surface interaction noise. However, the appearance of multiple broadband tonal features at high frequency indicates the presence of aeroacoustic phenomenon following different scaling characteristics. The scaling of the high frequency aeroacoustic phenomenon is found to be different for the two flap deflection angles tested. Unsteady surface pressure measurements in the vicinity of the flap edge show high coherence levels between adjacent sensors on the flap-side edge and on the flap edge upper surface in a region which corresponds closely to where the flap-side edge vortex begins to spill over to the flap upper surface. The frequency ranges where these high levels of coherence occur on the flap surface are consistent with the frequency ranges in which dominant features appear in far field acoustic spectra. The consistency of strongly correlated unsteady surface pressures and far field pressure fluctuations suggests the importance of regions on the flap edge in generating sound.

Fluctuating pressures measured beneath a high-temperature, turbulent boundary layer on a flat plate at Mach number of 5

NASA Technical Reports Server (NTRS)

Parrott, Tony L.; Jones, Michael G.; Albertson, Cindy W.

1989-01-01

Fluctuating pressures were measured beneath a Mach 5, turbulent boundary layer on a flat plate with an array of piezoresistive sensors. The data were obtained with a digital signal acquisition system during a test run of 4 seconds. Data sampling rate was such that frequency analysis up to 62.5 kHz could be performed. To assess in situ frequency response of the sensors, a specially designed waveguide calibration system was employed to measure transfer functions of all sensors and related instrumentation. Pressure time histories were approximated well by a Gaussian prohibiting distribution. Pressure spectra were very repeatable over the array span of 76 mm. Total rms pressures ranged from 0.0017 to 0.0046 of the freestream dynamic pressure. Streamwise, space-time correlations exhibited expected decaying behavior of a turbulence generated pressure field. Average convection speed was 0.87 of freestream velocity. The trendless behavior with sensor separation indicated possible systematic errors.

Magnetic evaluation of hydrogen pressures changes on MHD fluctuations in IR-T1 tokamak plasma

NASA Astrophysics Data System (ADS)

Alipour, Ramin; Ghanbari, Mohamad R.

2018-04-01

Identification of tokamak plasma parameters and investigation on the effects of each parameter on the plasma characteristics is important for the better understanding of magnetohydrodynamic (MHD) activities in the tokamak plasma. The effect of different hydrogen pressures of 1.9, 2.5 and 2.9 Torr on MHD fluctuations of the IR-T1 tokamak plasma was investigated by using of 12 Mirnov coils, singular value decomposition and wavelet analysis. The parameters such as plasma current, loop voltage, power spectrum density, energy percent of poloidal modes, dominant spatial structures and temporal structures of poloidal modes at different plasma pressures are plotted. The results indicate that the MHD activities at the pressure of 2.5 Torr are less than them at other pressures. It also has been shown that in the stable area of plasma and at the pressure of 2.5 Torr, the magnetic force and the force of plasma pressure are in balance with each other and the MHD activities are at their lowest level.

Pressure estimation from single-snapshot tomographic PIV in a turbulent boundary layer

NASA Astrophysics Data System (ADS)

Schneiders, Jan F. G.; Pröbsting, Stefan; Dwight, Richard P.; van Oudheusden, Bas W.; Scarano, Fulvio

2016-04-01

A method is proposed to determine the instantaneous pressure field from a single tomographic PIV velocity snapshot and is applied to a flat-plate turbulent boundary layer. The main concept behind the single-snapshot pressure evaluation method is to approximate the flow acceleration using the vorticity transport equation. The vorticity field calculated from the measured instantaneous velocity is advanced over a single integration time step using the vortex-in-cell (VIC) technique to update the vorticity field, after which the temporal derivative and material derivative of velocity are evaluated. The pressure in the measurement volume is subsequently evaluated by solving a Poisson equation. The procedure is validated considering data from a turbulent boundary layer experiment, obtained with time-resolved tomographic PIV at 10 kHz, where an independent surface pressure fluctuation measurement is made by a microphone. The cross-correlation coefficient of the surface pressure fluctuations calculated by the single-snapshot pressure method with respect to the microphone measurements is calculated and compared to that obtained using time-resolved pressure-from-PIV, which is regarded as benchmark. The single-snapshot procedure returns a cross-correlation comparable to the best result obtained by time-resolved PIV, which uses a nine-point time kernel. When the kernel of the time-resolved approach is reduced to three measurements, the single-snapshot method yields approximately 30 % higher correlation. Use of the method should be cautioned when the contributions to fluctuating pressure from outside the measurement volume are significant. The study illustrates the potential for simplifying the hardware configurations (e.g. high-speed PIV or dual PIV) required to determine instantaneous pressure from tomographic PIV.

Enhanced H-mode pedestals with lithium injection in DIII-D

DOE PAGES

Osborne, Thomas H.; Jackson, Gary L.; Yan, Zheng; ...

2015-05-08

Periods of edge localized mode (ELM)-free H-mode with increased pedestal pressure and width were observed in the DIII-D tokamak when density fluctuations localized to the region near the separatrix were present. Injection of a powder of 45 μm diameter lithium particles increased the duration of the enhanced pedestal phases to up to 350 ms, and also increased the likelihood of a transition to the enhanced phase. Lithium injection at a level sufficient for triggering the extended enhanced phases resulted in significant lithium in the plasma core, but carbon and other higher Z impurities as well as radiated power levels weremore » reduced. Recycling of the working deuterium gas appeared unaffected by this level of lithium injection. The ion scale, k θ ρ s ~ 0.1–0.2, density fluctuations propagated in the electron drift direction with f ~ 80 kHz and occurred in bursts every ~1 ms. The fluctuation bursts correlated with plasma loss resulting in a flattening of the pressure profile in a region near the separatrix. This localized flattening 2 allowed higher overall pedestal pressure at the peeling-ballooning stability limit and higher pressure than expected under the EPED model due to reduction of the pressure gradient below the “ballooning critical profile”. Furthermore, reduction of the ion pressure by lithium dilution may contribute to the long ELM-free periods.« less

Assessment of upper airway mechanics during sleep.

PubMed

Farré, Ramon; Montserrat, Josep M; Navajas, Daniel

2008-11-30

Obstructive sleep apnea, which is the most prevalent sleep breathing disorder, is characterized by recurrent episodes of upper airway collapse and reopening. However, the mechanical properties of the upper airway are not directly measured in routine polysomnography because only qualitative sensors (thermistors for flow and thoraco-abdominal bands for pressure) are used. This review focuses on two techniques that quantify upper airway obstruction during sleep. A Starling model of collapsible conduit allows us to interpret the mechanics of the upper airway by means of two parameters: the critical pressure (Pcrit) and the upstream resistance (Rup). A simple technique to measure Pcrit and Rup involves the application of different levels of continuous positive airway pressure (CPAP) during sleep. The forced oscillation technique is another non-invasive procedure for quantifying upper airway impedance during the breathing cycle in sleep studies. The latest developments in these two methods allow them to be easily applied on a routine basis in order to more fully characterize upper airway mechanics in patients with sleep breathing disorders.

Effect of Sweep on Cavity Flow Fields at Subsonic and Transonic Speeds

NASA Technical Reports Server (NTRS)

Tracy, Maureen B.; Plentovich, Elizabeth B.; Hemsch, Michael J.; Wilcox, Floyd J.

2012-01-01

An experimental investigation was conducted in the NASA Langley 7 x 10-Foot High Speed Tunnel (HST) to study the effect of leading- and trailing-edge sweep on cavity flow fields for a range of cavity length-to-height (l/h) ratios. The free-stream Mach number was varied from 0.2 to 0.8. The cavity had a depth of 0.5 inches, a width of 2.5 inches, and a maximum length of 12.0 inches. The leading- and trailing-edge sweep was adjusted using block inserts to achieve leading edge sweep angles of 65 deg, 55 deg, 45 deg, 35 deg, and 0 deg. The fore and aft cavity walls were always parallel. The aft wall of the cavity was remotely positioned to achieve a range of length-to-depth ratios. Fluctuating- and static-pressure data were obtained on the floor of the cavity. The fluctuating pressure data were used to determine whether or not resonance occurred in the cavity rather than to provide a characterization of the fluctuating pressure field. Qualitative surface flow visualization was obtained using a technique in which colored water was introduced into the model through static-pressure orifices. A complete tabulation of the mean static-pressure data for the swept leading edge cavities is included.

Waves in the middle and upper atmosphere of Mars as seen by the Radio Science Experiment MaRS on Mars Express

NASA Astrophysics Data System (ADS)

Tellmann, S.; Paetzold, M.; Häusler, B.; Hinson, D. P.; Peter, K.; Tyler, G. L.

2017-12-01

Atmospheric waves play a crucial role in the Martian atmosphere. They are responsible for the redistribution of momentum, energy and dust and for the coupling of the different atmospheric regions on Mars. Almost all kinds of waves have been observed in the lower atmosphere (e.g. stationary and transient waves, baroclinic waves as well as migrating and non-migrating thermal tides, gravity waves, etc...). Atmospheric waves are also known to exist in the middle atmosphere of Mars ( 70-120 km, e.g. by the SPICAM instrument on Mars Express). In the thermosphere, thermal tides have been observed e.g. by radio occultation or accelerometer measurements on MGS. Recently, the NGIMS instrument on MAVEN reported gravity waves in the thermosphere of Mars. Radio Science profiles from the Mars Express Radio Science experiment MaRS on Mars Express can analyse the temperature, pressure and neutral number density profiles in the lower atmosphere (from a few hundred metres above the surface up to 40-50 km) and electron density profiles in the ionosphere of Mars. Wavelike structures have been detected below the main ionospheric layers (M1 & M2) and in the topside of the ionosphere. The two coherent frequencies of the MaRS experiment allow to discriminate between plasma density fluctuations in the ionosphere and Doppler related frequency shifts caused by spacecraft movement. A careful analysis of the observed electron density fluctuations in combination with sensitivity studies of the radio occultation technique will be used to classify the observed fluctuations. The MaRS experiment is funded by DLR under grant 50QM1401.

Waves in the middle and upper atmosphere of Mars as seen by the Radio Science Experiment MaRS on Mars Express

NASA Astrophysics Data System (ADS)

Tellmann, Silvia Anna; Paetzold, Martin; Häusler, Bernd; Hinson, David P.; Peter, Kerstin; Tyler, G. Leonard

2017-10-01

Atmospheric waves play a crucial role for the dynamics in the Martian atmosphere. They are responsible for the redistribution of momentum, energy and dust and the coupling of the different atmospheric regions on Mars.Almost all kinds of waves have been observed in the lower atmosphere (e.g. stationary and transient waves, baroclinic waves as well as migrating and non-migrating thermal tides, and gravity waves). Atmospheric waves are also known to exist in the middle atmosphere of Mars (~70-120 km, e.g. by the SPICAM instrument on Mars Express). In the thermosphere, thermal tides have been observed e.g. by radio occultation or accelerometer measurements on MGS. Recently, the NGIMS instrument on MAVEN reported gravity waves in the thermosphere of Mars.Radio Science profiles from the Mars Express Radio Science experiment MaRS on Mars Express can analyse the temperature, pressure and neutral number density profiles in the lower atmosphere (from a few hundred metres above the surface up to ~ 40-50 km) and electron density profiles in the ionosphere of Mars.Wavelike structures have been detected below the main ionospheric layers (M1 & M2) and in the topside of the ionosphere. The two coherent frequencies of the MaRS experiment allow to discriminate between plasma density fluctuations in the ionosphere and Doppler related frequency shifts caused by spacecraft movement.A careful analysis of the observed electron density fluctuations in combination with sensitivity studies of the radio occultation technique will be used to classify the observed fluctuations.The MaRS experiment is funded by DLR under grant 50QM1401.

Analysis of Fluctuating Static Pressure Measurements in the National Transonic Facility

NASA Technical Reports Server (NTRS)

Igoe, William B.

1996-01-01

Dynamic measurements of fluctuating static pressure levels were taken with flush-mounted, high-frequency response pressure transducers at 11 locations in the circuit of the National Transonic Facility (NTF) across the complete operating range of this wind tunnel. Measurements were taken at test-section Mach numbers from 0.1 to 1.2, at pressures from 1 to 8.6 atm, and at temperatures from ambient to -250 F, which resulted in dynamic flow disturbance measurements at the highest Reynolds numbers available in a transonic ground test facility. Tests were also made by independent variation of the Mach number, the Reynolds number, or the fan drive power while the other two parameters were held constant, which for the first time resulted in a distinct separation of the effects of these three important parameters.

Upflow bioreactor with septum and pressure release mechanism

DOEpatents

Hansen, Conly L.; Hansen, Carl S.; Pack, Kevin; Milligan, John; Benefiel, Bradley C.; Tolman, C. Wayne; Tolman, Kenneth W.

2010-04-20

An upflow bioreactor includes a vessel having an inlet and an outlet configured for upflow operation. A septum is positioned within the vessel and defines a lower chamber and an upper chamber. The septum includes an aperture that provides fluid communication between the upper chamber and lower chamber. The bioreactor also includes means for releasing pressure buildup in the lower chamber. In one configuration, the septum includes a releasable portion having an open position and a closed position. The releasable portion is configured to move to the open position in response to pressure buildup in the lower chamber. In the open position fluid communication between the lower chamber and the upper chamber is increased. Alternatively the lower chamber can include a pressure release line that is selectively actuated by pressure buildup. The pressure release mechanism can prevent the bioreactor from plugging and/or prevent catastrophic damage to the bioreactor caused by high pressures.

Coherent entropy induced and acoustic noise separation in compact nozzles

NASA Astrophysics Data System (ADS)

Tao, Wenjie; Schuller, Thierry; Huet, Maxime; Richecoeur, Franck

2017-04-01

A method to separate entropy induced noise from an acoustic pressure wave in an harmonically perturbed flow through a nozzle is presented. It is tested on an original experimental setup generating simultaneously acoustic and temperature fluctuations in an air flow that is accelerated by a convergent nozzle. The setup mimics the direct and indirect noise contributions to the acoustic pressure field in a confined combustion chamber by producing synchronized acoustic and temperature fluctuations, without dealing with the complexity of the combustion process. It allows generating temperature fluctuations with amplitude up to 10 K in the frequency range from 10 to 100 Hz. The noise separation technique uses experiments with and without temperature fluctuations to determine the relative level of acoustic and entropy fluctuations in the system and to identify the nozzle response to these forcing waves. It requires multi-point measurements of acoustic pressure and temperature. The separation method is first validated with direct numerical simulations of the nonlinear Euler equations. These simulations are used to investigate the conditions for which the separation technique is valid and yield similar trends as the experiments for the investigated flow operating conditions. The separation method then gives successfully the acoustic reflection coefficient but does not recover the same entropy reflection coefficient as predicted by the compact nozzle theory due to the sensitivity of the method to signal noises in the explored experimental conditions. This methodology provides a framework for experimental investigation of direct and indirect combustion noises originating from synchronized perturbations.

Electron Thermal Transport due to Magnetic Diffusion in the MST RFP

NASA Astrophysics Data System (ADS)

Reusch, J. A.; Anderson, J. K.; den Hartog, D. J.; Forest, C. B.; Kasten, C. P.; Schnack, D. D.; Stephens, H. D.

2011-10-01

Comparison of measurements made in the MST RFP to the results from extensive nonlinear resistive MHD simulations has provided two key observations. First, trapped particles reduce electron thermal diffusion; inclusion of this effect is required for quantitative agreement of simulation to measurement. Second, the structure and evolution of long-wavelength temperature fluctuations measured in MST shows remarkable qualitative similarity to fluctuations appearing in a finite-pressure simulation. These simulations were run at parameters matching those of 400 kA discharges in MST (S ~ 4 ×106). In a zero β simulation, the measured χe is compared to the thermal diffusion due to parallel losses along diffusing magnetic field lines, χst =v∥Dmag . Agreement is only found if the reduction in χst due to trapped particles is taken into account. In a second simulation, the pressure field was evolved self consistently assuming Ohmic heating and anisotropic thermal conduction. Fluctuations in the simulated temperature are very similar in character and time evolution to temperature fluctuations measured in MST. This includes m = 1 , n = 6 fluctuations that flatten the temperature profile as well as m = 1 , n = 5 fluctuations that generate hot island structures near the core shortly after sawtooth crashes. This work supported by the US DOE and NSF.

Compressible turbulence measurements in a supersonic boundary layer including favorable pressure gradient effects

NASA Astrophysics Data System (ADS)

Miller, Raymond S.

1994-12-01

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.

Dynamic Temperature and Pressure Measurements in the Core of a Propulsion Engine

NASA Technical Reports Server (NTRS)

Schuster, Bill; Gordon, Grant; Hultgren, Lennart S.

2015-01-01

Dynamic temperature and pressure measurements were made in the core of a TECH977 propulsion engine as part of a NASA funded investigation into indirect combustion noise. Dynamic temperature measurements were made in the combustor, the inter-turbine duct, and the mixer using ten two-wire thermocouple probes. Internal dynamic pressure measurements were made at the same locations using piezoresistive transducers installed in semi-infinite coils. Measurements were acquired at four steady state operating conditions covering the range of aircraft approach power settings. Fluctuating gas temperature spectra were computed from the thermocouple probe voltage measurements using a compensation procedure that was developed under previous NASA test programs. A database of simultaneously acquired dynamic temperature and dynamic pressure measurements was produced. Spectral and cross-spectral analyses were conducted to explore the characteristics of the temperature and pressure fluctuations inside the engine, with a particular focus on attempting to identify the presence of indirect combustion noise.

Recent Topics of Organic Superconductors

NASA Astrophysics Data System (ADS)

Ardavan, Arzhang; Brown, Stuart; Kagoshima, Seiichi; Kanoda, Kazushi; Kuroki, Kazuhiko; Mori, Hatsumi; Ogata, Masao; Uji, Shinya; Wosnitza, Jochen

2012-01-01

Recent developments in research into superconductivity in organic materials are reviewed. In the epoch-defining quasi-one-dimensional TMTSF superconductors with Tc ˜ 1 K, Tc decreases monotonically with increasing pressure, as do signatures of spin fluctuations in the normal state, providing good evidence for magnetically-mediated pairing. Upper critical fields exceed the Zeeman-limiting field by several times, suggesting triplet pairing or a transition to an inhomogeneous superconducting state at high magnetic fields, while triplet pairing is ruled out at low fields by NMR Knight-shift measurements. Evidence for a spatially inhomogeneous superconducting state, Fulde--Ferrel--Larkin--Ovchinnikov state, which has long been sought in various superconducting systems, is now captured by thermodynamic and transport measurements for clean and highly two-dimensional BEDT-TTF and BETS superconductors. Some of the layered superconductors also serve as model systems for Mott physics on anisotropic triangular lattice. For example, the Nernst effect and the pseudo-gap behavior in NMR relaxation are enhanced near to the Mott transition. In the case of increasing spin frustration, the superconducting transition temperature is depressed, and antiferromagnetic ordering is eliminated altogether in the adjacent Mott insulating phase. There is an increasing number of materials exhibiting superconductivity in competition or cooperation with charge order. Theoretical studies shed light on the role of spin and/or charge fluctuations for superconductivity appearing under conditions close to those of correlation-induced insulating phases in the diversity of organic materials.

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

Crates containing scientific instruments are seen on the stern of the Woods Hole Oceanographic Institution's research vessel Knorr on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. Knorr is scheduled to depart on Sept. 6 to take part in the Salinity Processes in the Upper Ocean Regional Study (SPURS). The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-05

A sensor-laden buoy is lifted onboard the Woods Hole Oceanographic Institution's research vessel Knorr on wednesday, Sept. 5, 2012, in Woods Hole, Mass. The buoy will be deployed in the Atlantic Ocean as part of the Salinity Processes in the Upper Ocean Regional Study (SPURS) which is set to sail on Sept. 6. The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

The bow of the Woods Hole Oceanographic Institution's research vessel Knorr is seen from the bridge on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. Knorr is scheduled to depart on Sept. 6 to take part in the Salinity Processes in the Upper Ocean Regional Study (SPURS). The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

Scientific instruments are seen on the stern of the Woods Hole Oceanographic Institution's research vessel Knorr on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. Knorr is scheduled to depart on Sept. 6 to take part in the Salinity Processes in the Upper Ocean Regional Study (SPURS). The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

Two NOAA Pacific Marine Environmental Laboratory (PMEL) buoys are seen on the stern of the Woods Hole Oceanographic Institution's research vessel Knorr on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. Knorr is scheduled to depart on Sept. 6 to take part in the Salinity Processes in the Upper Ocean Regional Study (SPURS). The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

An engineer is raised by crane to work on the Woods Hole Oceanographic Institution's research vessel Knorr on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. Knorr is scheduled to depart on Sept. 6 to take part in the Salinity Processes in the Upper Ocean Regional Study (SPURS). The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

A Rosette water sampler system that will be used during the Salinity Processes in the Upper Ocean Regional Study (SPURS) is seen onboard the Woods Hole Oceanographic Institution's research vessel Knorr on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. Knorr is scheduled to depart for the NASA-sponsored expedition on Sept. 6 and will head into the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

Scientific instruments, buoys, and shipping crates are seen on the stern of the Woods Hole Oceanographic Institution's research vessel Knorr on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. Knorr is scheduled to depart on Sept. 6 to take part in the Salinity Processes in the Upper Ocean Regional Study (SPURS). The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

International maritime signal flags are seen on the bridge of the Woods Hole Oceanographic Institution's research vessel Knorr on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. Knorr is scheduled to depart on Sept. 6 to take part in the Salinity Processes in the Upper Ocean Regional Study (SPURS). The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

A sculpture resembling the Roman god Neptune is seen dockside of the Woods Hole Oceanographic Institution research vessel Knorr on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. Knorr is scheduled to depart on Sept. 6 to take part in the Salinity Processes in the Upper Ocean Regional Study (SPURS). The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

NASA Physical Oceanography Program Scientist Eric Lindstrom poses for a photograph next to the Woods Hole Oceanographic Institution research vessel Knorr on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. Lindstrom will depart on Knorr Sept. 6 to take part in the Salinity Processes in the Upper Ocean Regional Study (SPURS). The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Resonance oscillations of the Soufrière Hills Volcano (Montserrat, W.I.) magmatic system induced by forced magma flow from the reservoir into the upper plumbing dike

NASA Astrophysics Data System (ADS)

Chen, Chin-Wu; Huang, Hsin-Fu; Hautmann, Stefanie; Sacks, I. Selwyn; Linde, Alan T.; Taira, Taka'aki

2018-01-01

Short-period deformation cycles are a common phenomenon at active volcanoes and are often attributed to the instability of magma flow in the upper plumbing system caused by fluctuations in magma viscosity related to cooling, degassing, and crystallization. Here we present 20-min periodic oscillations in ground deformation based on high-precision continuous borehole strain data that were associated with the 2003 massive dome-collapse at the Soufrière Hills Volcano, Montserrat (West Indies). These high-frequency oscillations lasted 80 min and were preceded by a 4-hour episode of rapid expansion of the shallow magma reservoir. Strain amplitude ratios indicate that the deformational changes were generated by pressure variations in the shallow magma reservoir and - with reversed polarity - the adjacent plumbing dike. The unusually short period of the oscillations cannot be explained with thermally induced variations in magma properties. We investigate the underlying mechanism of the oscillations via a numerical model of forced magma flow through a reservoir-dike system accounting for time-dependent dilation/contraction of the dike due to a viscous response in the surrounding host rock. Our results suggest that the cyclic pressure variations are modulated by the dynamical interplay between rapid expansion of the magma chamber and the incapacity of the narrow dike to take up fast enough the magma volumes supplied by the reservoir. Our results allow us to place first order constraints on the viscosity of crustal host rocks and consequently its fractional melt content. Hence, we present for the first time crustal-scale in situ measurements of rheological properties of mush zones surrounding magmatic systems.

Basin-Wide Temperature Constraints On Gas Hydrate Stability In The Gulf Of Mexico

NASA Astrophysics Data System (ADS)

MacDonald, I. R.; Reagan, M. T.; Guinasso, N. L.; Garcia-Pineda, O. G.

2012-12-01

Gas hydrate deposits commonly occur at the seafloor-water interface on marine margins. They are especially prevalent in the Gulf of Mexico where they are associated with natural oil seeps. The stability of these deposits is potentially challenged by fluctuations in bottom water temperature, on an annual time-scale, and under the long-term influence of climate change. We mapped the locations of natural oil seeps where shallow gas hydrate deposits are known to occur across the entire Gulf of Mexico basin based on a comprehensive review of synthetic aperture radar (SAR) data (~200 images). We prepared a bottom water temperature map based on the archive of CTD casts from the Gulf (~6000 records). Comparing the distribution of gas hydrate deposits with predicted bottom water temperature, we find that a broad area of the upper slope lies above the theoretical stability horizon for structure 1 gas hydrate, while all sites where gas hydrate deposits occur are within the stability horizon for structure 2 gas hydrate. This is consistent with analytical results that structure 2 gas hydrates predominate on the upper slope (Klapp et al., 2010), where bottom water temperatures fluctuate over a 7 to 10 C range (approx. 600 m depth), while pure structure 1 hydrates are found at greater depths (approx. 3000 m). Where higher hydrocarbon gases are available, formation of structure 2 gas hydrate should significantly increase the resistance of shallow gas hydrate deposits to destabilizing effects variable or increasing bottom water temperature. Klapp, S.A., Bohrmann, G., Kuhs, W.F., Murshed, M.M., Pape, T., Klein, H., Techmer, K.S., Heeschen, K.U., and Abegg, F., 2010, Microstructures of structure I and II gas hydrates from the Gulf of Mexico: Marine and Petroleum Geology, v. 27, p. 116-125.Bottom temperature and pressure for Gulf of Mexico gas hydrate outcrops and stability horizons for sI and sII hydrate.

NMR evidence for static local nematicity and its cooperative interplay with low-energy magnetic fluctuations in FeSe under pressure

DOE PAGES

Wiecki, P.; Nandi, M.; Bohmer, Anna; ...

2017-11-13

Here, we present 77Se -NMR measurements on single-crystalline FeSe under pressures up to 2 GPa. Based on the observation of the splitting and broadening of the NMR spectrum due to structural twin domains, we discovered that static, local nematic ordering exists well above the bulk nematic ordering temperature, T s. The static, local nematic order and the low-energy stripe-type antiferromagnetic spin fluctuations, as revealed by NMR spin-lattice relaxation rate measurements, are both insensitive to pressure application. Our NMR results provide clear evidence for the microscopic cooperation between magnetism and local nematicity in FeSe.

NMR evidence for static local nematicity and its cooperative interplay with low-energy magnetic fluctuations in FeSe under pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wiecki, P.; Nandi, M.; Bohmer, Anna

Here, we present 77Se -NMR measurements on single-crystalline FeSe under pressures up to 2 GPa. Based on the observation of the splitting and broadening of the NMR spectrum due to structural twin domains, we discovered that static, local nematic ordering exists well above the bulk nematic ordering temperature, T s. The static, local nematic order and the low-energy stripe-type antiferromagnetic spin fluctuations, as revealed by NMR spin-lattice relaxation rate measurements, are both insensitive to pressure application. Our NMR results provide clear evidence for the microscopic cooperation between magnetism and local nematicity in FeSe.

An experimental study of the wall-pressure fluctuations beneath low Reynolds number turbulent boundary layers.

PubMed

Van Blitterswyk, Jared; Rocha, Joana

2017-02-01

A more complete understanding of the physical relationships, between wall-pressure and turbulence, is required for modeling flow-induced noise and developing noise reduction strategies. In this study, the wall-pressure fluctuations, induced by low Reynolds number turbulent boundary layers, are experimentally studied using a high-resolution microphone array. Statistical characteristics obtained using traditional cross-correlation and cross-spectra analyses are complimented with wall-pressure-velocity cross-spectra and wavelet cross-correlations. Wall-pressure-velocity correlations revealed that turbulent activity in the buffer layer contributes at least 40% of the energy to the wall-pressure spectrum at all measured frequencies. As Reynolds number increases, the low-frequency energy shifts from the buffer layer to the logarithmic layer, as expected for regions of uniform streamwise momentum formed by hairpin packets. Conditional cross-spectra suggests that the majority of broadband wall-pressure energy is concentrated within the packets, with the pressure signatures of individual hairpin vortices estimated to decay on average within traveling ten displacement thicknesses, and the packet signature is retained for up to seven boundary layer thicknesses on average.

The dynamics of subtidal poleward flows over a narrow continental shelf, Palos Verdes, CA

USGS Publications Warehouse

Noble, M.A.; Ryan, H.F.; Wiberg, P.L.

2002-01-01

The Palos Verdes peninsula is a short, very narrow (< 3 km) shelf in southern California that is bracketed by two large embayments. In May 1992, arrays of up to 4 moorings and 2 benthic tripods were deployed in a yearlong study of the circulation processes over this shelf and the adjacent slope. Wind stress, coastal sea level, atmospheric pressure and wave records were obtained from offshore sites and from coastal stations surrounding Palos Verdes. Bottom stress calculated for the mid-shelf sites using a boundary-layer model and data from the above instruments indicated the bottom drag coefficient over this shelf is about 0.003 Currents flow toward the northwest along the shelf and upper slope. Speeds are generally around 20-30 cm/s. There was no obvious seasonal structure in the flow. The first EOF for subtidal alongshelf current accounted for nearly 70% of the variance at sites on the shelf and upper slope. The dominant fluctuations had periods between 5 and 20 days, periods longer than seen in the regional wind stress field. Coastal sea level and the alongshore gradient in sea level had a similar concentration of energy in the 5-20 day frequency band. About 30% of the alongshelf flow was coherent with the alongshelf pressure gradient; currents flowed down the pressure gradient with minimal phase lag. Winds accounted for only 15-20% of the variance in subtidal currents, but the measured effect of wind stress was large. A 1 dyne/cm2 wind stress was associated with a 20-30 cm/s alongshore current. Both the regional wind stress and the alongshelf pressure gradients had spatial scales much larger than found on this small shelf. Subtidal flows forced by these regional fields were set up in the adjacent, much broader basins. The currents amplified as they moved onto the narrow shelf between the basins. Hence, local wind-driven currents had anomalously large amplitudes. The momentum equations for alongshelf wind or pressure gradients did not balance because some of the measured terms were associated with regional fields, others with local process. Our observations suggest that it is more difficult to determine which measured fields reflect the local processes in regions with rapidly changing topography. ?? 2002 Elsevier Science Ltd. All rights reserved.

LDV survey of cavitation and resonance effect on the precessing vortex rope dynamics in the draft tube of Francis turbines

NASA Astrophysics Data System (ADS)

Favrel, A.; Müller, A.; Landry, C.; Yamamoto, K.; Avellan, F.

2016-11-01

The large-scale penetration of the electrical grid by intermittent renewable energy sources requires a continuous operating range extension of hydropower plants. This causes the formation of unfavourable flow patterns in the draft tube of turbines and pump-turbines. At partial load operation, a precessing cavitation vortex rope is formed at the Francis turbine runner outlet, acting as an excitation source for the hydraulic system. In case of resonance, the resulting high-amplitude pressure pulsations can put at risk the stability of the machine and of the electrical grid to which it is connected. It is therefore crucial to understand and accurately simulate the underlying physical mechanisms in such conditions. However, the exact impact of cavitation and hydro-acoustic resonance on the flow velocity fluctuations in the draft tube remains to be established. The flow discharge pulsations expected to occur in the draft tube in resonance conditions have for instance never been verified experimentally. In this study, two-component Laser Doppler Velocimetry is used to investigate the axial and tangential velocity fluctuations at the runner outlet of a reduced scale physical model of a Francis turbine. The investigation is performed for a discharge equal to 64 % of the nominal value and three different pressure levels in the draft tube, including resonance and cavitation-free conditions. Based on the convective pressure fluctuations induced by the vortex precession, the periodical velocity fluctuations over one typical precession period are recovered by phase averaging. The impact of cavitation and hydro-acoustic resonance on both axial and tangential velocity fluctuations in terms of amplitude and phase shift is highlighted for the first time. It is shown that the occurrence of resonance does not have significant effects on the draft tube velocity fields, suggesting that the synchronous axial velocity fluctuations are surprisingly negligible compared to the velocity fluctuations induced by the vortex precession.

Evidence for the presence of quasi-two-dimensional nearly incompressible fluctuations in the solar wind

NASA Technical Reports Server (NTRS)

Matthaeus, William H.; Goldstein, Melvyn L.; Roberts, D. Aaron

1990-01-01

Assuming that the slab and isotropic models of solar wind turbulence need modification (largely due to the observed anisotropy of the interplanetary fluctuations and the results of laboratory plasma experiments), this paper proposes a model of the solar wind. The solar wind is seen as a fluid which contains both classical transverse Alfvenic fluctuations and a population of quasi-transverse fluctuations. In quasi-two-dimensional turbulence, the pitch angle scattering by resonant wave-particle interactions is suppressed, and the direction of minimum variance of interplanetary fluctuations is parallel to the mean magnetic field. The assumed incompressibility is consistent with the fact that the density fluctuations are small and anticorrelated, and that the total pressure at small scales is nearly constant.

Quasi-Lagrangian measurements of density surface fluctuations and power spectra in the stratosphere

NASA Technical Reports Server (NTRS)

Quinn, Elizabeth P.; Holzworth, Robert H.

1987-01-01

Pressure and temperature data from eight superpressure balloon flights at 26 km in the southern hemisphere stratosphere are analyzed. The balloons, which float on a constant density surface, travel steadily westward during summer and eastward during winter, as expected from local climatology. Two types of fluctuations are observed: neutral buoyancy oscillations (NBO) of around 4 min, and 0.1- to 1-hour oscillations that are characterized as small-amplitude density surface fluctuations. Lapse rates and densities are calculated and found to agree well with the expected values. Examples of wave damping and simultaneous fluctuation at two nearby balloons are presented. Spectral analysis is performed clearly showing the NBO and that the majority of the power is in the mesoscale range. Spectral slopes of power versus frequency are measured to be on the average -2.18 + or - 0.24 for pressure and -1.72 + or - 0.24 for temperature. These slopes are compared to the predictions of turbulence theories and the theory of a universal gravity wave spectrum.

A numerical investigation of choked flow dynamics and its application to the triggering mechanism of long-period events at Redoubt Volcano, Alaska

USGS Publications Warehouse

Morrissey, M.M.; Chouet, B.A.

1997-01-01

We use numerical simulations of transonic flow through a crack to study the dynamics of the formation of shock waves downstream from a nozzle-like constriction inside the crack. The model solves the full set of Navier-Stokes equations in two dimensions via an explicit multifield finite difference representation. The crack walls are assumed to be perfectly rigid, and elastic coupling to the solid is not considered. The simulations demonstrate how the behavior of unsteady shock waves near the walls can produce recurring step-like pressure transients in the flow, which in turn induce resonance of the fluid-filled crack. The motion of the shock waves is governed primarily by smooth, low-amplitude pressure fluctuations at the outlet of the crack. The force induced on the walls scales with the amplitude of the shock, which is a function of the magnitude of the inlet pressure, aperture of the constriction, and thickness of the boundary layer. The applied force also scales in proportion to the spatial extent of the shock excursion, which depends on the fluctuation rate of outlet pressure. Using the source parameters of long-period (LP) events at Redoubt Volcano, Alaska, as a guide for our simulations, we infer that coupling of the shock to the walls occurs for crack inlet to outlet pressure ratios pipo > 2.31 and that the position of the shock front becomes most sensitive to outlet pressure fluctuations for flow regimes with pipo > 2.48. For such regimes, fluctuations of outlet pressure of up to ??0.5 MPa at rates up to 3 MPa/s are sufficient to induce pressure transients with magnitudes up to 12.5 MPa over 0.1-2.5 m of the walls within ???0.5 s. These flow parameters may be adequate for triggering the LP events in the precursory swarm to the December 14, 1989, eruption of Redoubt. According to the flow model the recurrence rate and amplitudes of LP events are inferred to be a manifestation of the response of a shallow hydrothermal reservoir to the sustained injection of superheated steam from a magma column roofing below this reservoir.

Review on airflow in unsaturated zones induced by natural forcings

NASA Astrophysics Data System (ADS)

Kuang, Xingxing; Jiao, Jiu Jimmy; Li, Hailong

2013-10-01

Subsurface airflow in unsaturated zones induced by natural forcings is of importance in many environmental and engineering fields, such as environmental remediation, water infiltration and groundwater recharge, coastal soil aeration, mine and tunnel ventilation, and gas exchange between soil and atmosphere. This review synthesizes the published literature on subsurface airflow driven by natural forcings such as atmospheric pressure fluctuations, topographic effect, water table fluctuations, and water infiltration. The present state of knowledge concerning the mechanisms, analytical and numerical models, and environmental and engineering applications related to the naturally occurring airflow is discussed. Airflow induced by atmospheric pressure fluctuations is studied the most because of the applications to environmental remediation and transport of trace gases from soil to atmosphere, which are very important in understanding biogeochemical cycling and global change. Airflow induced by infiltration is also an extensively investigated topic because of its implications in rainfall infiltration and groundwater recharge. Airflow induced by water table fluctuations is important in coastal areas because it plays an important role in coastal environmental remediation and ecological systems. Airflow induced by topographic effect is studied the least. However, it has important applications in unsaturated zone gas transport and natural ventilation of mines and tunnels. Finally, the similarities and differences in the characteristics of the air pressure and airflow are compared and future research efforts are recommended.

Part 1 - Experimental study of the pressure fluctuations on propeller turbine runner blades during steady-state operation

NASA Astrophysics Data System (ADS)

Houde, S.; Fraser, R.; Ciocan, G. D.; Deschênes, C.

2012-11-01

A good evaluation of the unsteady pressure field on hydraulic turbine blades is critical in evaluating the turbine lifespan and its maintenance schedule. Low-head turbines such as Kaplan and Propeller, using a relatively low number of blades supported only at the hub, may also undergo significant deflections at the blade tips which will lead to higher amplitude vibration compared to Francis turbines. Furthermore, the precise evaluation of the unsteady pressure distribution on low-head turbines is still a challenge for computational fluid dynamics (CFD). Within the framework of an international research consortium on low-head turbines, a research project was instigated at the Hydraulic Machines Laboratory in Laval University (LAMH) to perform experimental measurements of the unsteady pressure field on propeller turbine model runner blades. The main objective of the project was to measure the pressure fluctuations on a wide band of frequencies, both in a blade-to-blade channel and on the pressure and suction side of the same blade, to provide validation data for CFD computations. To do so, a 32 channels telemetric data transmission system was used to extract the signal of 31 pressure transducers and two strain gages from the rotating part at an acquisition frequency of 5 KHz. The miniature piezoelectric pressure transducers were placed on two adjacent runner blades according to an estimated pressure distribution coming from flow simulations. Two suction sides and one pressure side were instrumented. The strain gages were mounted in full-bridge on both pressure and suction sides to measure the blade span wise deflection. In order to provide boundary conditions for flow simulations, the test bench conditions during the measurements were acquired. The measurements were made in different operating conditions ranging from part load, where a cavitating vortex occurs, to full load under different heads. The results enabled the identification and the quantification of the major known sources of pressure fluctuation as well as some unexpected ones. The paper first presents the experimental methodology discussing relevant topics such as telemetric system setup, transducers calibration and errors analysis. The main results are then presented to illustrate the relative amplitude of the main source of pressure fluctuations under different operating conditions. The discussion and conclusion addresses the important observations stemming from the data analysis and illustrates that most of the results can be correlated with the known behavior of hydraulic turbines while some require further investigation.

Upper temperature tolerance of loach minnow under acute, chronic, and fluctuating thermal regimes

USGS Publications Warehouse

Widmer, A.M.; Carveth, C.J.; Bonar, Scott A.; Simms, J.R.

2006-01-01

We used four methods to estimate the upper lethal temperature of loach minnow Rhinichthys cobitis: the lethal thermal method (LTM), chronic lethal method (CLM), acclimated chronic exposure (ACE) method with static temperatures, and ACE method with diel temperature fluctuations. The upper lethal temperature of this species ranged between 32??C and 38??C, depending on the method and exposure time; however, temperatures as low as 28??C resulted in slowed growth compared with the control groups. In LTM trials, we increased temperatures 0.3??C/min and death occurred at 36.8 ?? 0.2??C (mean ?? SE) for fish (37-19 mm total length) acclimated to 30??C and at 36.4 ?? 0.07??C for fish acclimated to 25??C. In CLM trials, temperatures were increased more slowly (1??C/d), allowing fish to acclimate. Mean temperature at death was 33.4 ?? 0.1??C for fish 25-35 mm and 32.9 ?? 0.4??C for fish 45-50 mm. In the ACE experiment with static temperatures, we exposed fish for 30 d to four constant temperatures. No fish (20-40 mm) survived beyond 30 d at 32??C and the 30-d temperature lethal to 50% of the test animals was 30.6??C. Growth at static 28??C and 30??C was slower than growth at 25??C, suggesting that fish were stressed at sublethal temperatures. In ACE trials with diel temperature fluctuations of 4,6, and 10??C and a 32??C peak temperature, over 80% of fish (20-40 mm) survived 30 d. Although brief exposures to 32??C were not lethal, the growth of fish in the three fluctuating-temperature treatments was significantly less than the growth at the ambient temperature (25-29??C). To minimize thermal stress and buffer against temperature spikes, we recommend that loach minnow habitat be managed to avoid water temperatures above 28??C. ?? Copyright by the American Fisheries Society 2006.

Ocean acidification alters the photosynthetic responses of a coccolithophorid to fluctuating ultraviolet and visible radiation.

PubMed

Jin, Peng; Gao, Kunshan; Villafañe, Virginia E; Campbell, Douglas A; Helbling, E Walter

2013-08-01

Mixing of seawater subjects phytoplankton to fluctuations in photosynthetically active radiation (400-700 nm) and ultraviolet radiation (UVR; 280-400 nm). These irradiance fluctuations are now superimposed upon ocean acidification and thinning of the upper mixing layer through stratification, which alters mixing regimes. Therefore, we examined the photosynthetic carbon fixation and photochemical performance of a coccolithophore, Gephyrocapsa oceanica, grown under high, future (1,000 μatm) and low, current (390 μatm) CO₂ levels, under regimes of fluctuating irradiances with or without UVR. Under both CO₂ levels, fluctuating irradiances, as compared with constant irradiance, led to lower nonphotochemical quenching and less UVR-induced inhibition of carbon fixation and photosystem II electron transport. The cells grown under high CO₂ showed a lower photosynthetic carbon fixation rate but lower nonphotochemical quenching and less ultraviolet B (280-315 nm)-induced inhibition. Ultraviolet A (315-400 nm) led to less enhancement of the photosynthetic carbon fixation in the high-CO₂-grown cells under fluctuating irradiance. Our data suggest that ocean acidification and fast mixing or fluctuation of solar radiation will act synergistically to lower carbon fixation by G. oceanica, although ocean acidification may decrease ultraviolet B-related photochemical inhibition.

Fluctuations of radio occultation signals in sounding the Earth's atmosphere

NASA Astrophysics Data System (ADS)

Kan, Valery; Gorbunov, Michael E.; Sofieva, Viktoria F.

2018-02-01

We discuss the relationships that link the observed fluctuation spectra of the amplitude and phase of signals used for the radio occultation sounding of the Earth's atmosphere, with the spectra of atmospheric inhomogeneities. Our analysis employs the approximation of the phase screen and of weak fluctuations. We make our estimates for the following characteristic inhomogeneity types: (1) the isotropic Kolmogorov turbulence and (2) the anisotropic saturated internal gravity waves. We obtain the expressions for the variances of the amplitude and phase fluctuations of radio occultation signals as well as their estimates for the typical parameters of inhomogeneity models. From the GPS/MET observations, we evaluate the spectra of the amplitude and phase fluctuations in the altitude interval from 4 to 25 km in the middle and polar latitudes. As indicated by theoretical and experimental estimates, the main contribution into the radio signal fluctuations comes from the internal gravity waves. The influence of the Kolmogorov turbulence is negligible. We derive simple relationships that link the parameters of internal gravity waves and the statistical characteristics of the radio signal fluctuations. These results may serve as the basis for the global monitoring of the wave activity in the stratosphere and upper troposphere.

Effect of blade outlet angle on radial thrust of single-blade centrifugal pump

NASA Astrophysics Data System (ADS)

Nishi, Y.; Fukutomi, J.; Fujiwara, R.

2012-11-01

Single-blade centrifugal pumps are widely used as sewage pumps. However, a large radial thrust acts on a single blade during pump operation because of the geometrical axial asymmetry of the impeller. This radial thrust causes vibrations of the pump shaft, reducing the service life of bearings and shaft seal devices. Therefore, to ensure pump reliability, it is necessary to quantitatively understand the radial thrust and clarify the behavior and generation mechanism. This study investigated the radial thrust acting on two kinds of single-blade centrifugal impellers having different blade outlet angles by experiments and computational fluid dynamics (CFD) analysis. Furthermore, the radial thrust was modeled by a combination of three components, inertia, momentum, and pressure, by applying an unsteady conservation of momentum to this impeller. As a result, the effects of the blade outlet angle on both the radial thrust and the modeled components were clarified. The total head of the impeller with a blade outlet angle of 16 degrees increases more than the impeller with a blade outlet angle of 8 degrees at a large flow rate. In this case, since the static pressure of the circumference of the impeller increases uniformly, the time-averaged value of the radial thrust of both impellers does not change at every flow rate. On the other hand, since the impeller blade loading becomes large, the fluctuation component of the radial thrust of the impeller with the blade outlet angle of 16 degrees increases. If the blade outlet angle increases, the fluctuation component of the inertia component will increase, but the time-averaged value of the inertia component is located near the origin despite changes in the flow rate. The fluctuation component of the momentum component becomes large at all flow rates. Furthermore, although the time-averaged value of the pressure component is almost constant, the fluctuation component of the pressure component becomes large at a large flow rate. In addition to the increase of the fluctuation component of this pressure component, because the fluctuation component of the inertia and momentum components becomes large (as mentioned above), the radial thrust increases at a large flow rate, as is the case for the impeller with a large blade outlet angle.

Controls on Thermal Discharge in Yellowstone NAtional Park, Wyoming

NASA Astrophysics Data System (ADS)

Mohrmann, Jacob Steven

2007-10-01

Significant fluctuations in discharge occur in hot springs in Yellowstone National Park on a seasonal to decadal scale (Ingebritsen et al., 2001) and an hourly scale (Vitale, 2002). The purpose of this study was to determine the interval of the fluctuations in discharge and to explain what causes those discharge patterns in three thermally influenced streams in Yellowstone National Park. By monitoring flow in these streams, whose primary source of input is thermal discharge, we were able to find several significant patterns of discharge fluctuations. Patterns were found by using two techniques of spectral analysis. The spectral analyses completed involved using the program "R" as well as Microsoft Excel, both of which use Fourier transforms. The Fourier transform is a linear operator that identifies frequencies in the original function. Stream flow data were collected using a FloDar open channel flow monitor. The flow meter collected data at15-minute intervals at White Creek and Rabbit Creek for a period of approximately two weeks each during the Fall. Flow data were also used from 15-minute data interval from a USGS gaging station at Tantalus Creek. Patterns of discharge fluctuation were found in each stream. By comparing spectral analysis results of flow data with spectral analysis of published tide data and barometric pressure data, connections were drawn between fluctuations in tidal and barometric-pressure patterns and flow patterns. Also, visual comparisons used to identify potential correspondence with earthquakes and precipitation events. At Tantalus Creek, patterns were affected only by barometric pressure changes. At White Creek, one pattern was attributed to barometric pressure fluctuations, and another pattern was found that could be associated with earth-tide forces. At Rabbit Creek, these patterns were absent. A pattern at 8.55 hours, which could not be attributed to barometric pressure or earth tide forces, was found at Rabbit and White Creeks. The 8.55 hour pattern in discharge found at both Rabbit and White Creeks may suggest a physical link between the sites, which are close (2.5 km). The time pattern could be a result of a shared hydrothermal aquifer, convectively heating and discharging at both streams. However, the common time pattern could also be the result of independent factors, which coincidentally caused a similar time pattern.

Investigation of Three-Dimensional Unsteady Flow Characteristics in Transonic Diffusers

NASA Astrophysics Data System (ADS)

Proshchanka, Dzianis; Yonezawa, Koichi; Tsujimoto, Yoshinobu

Three-dimensional characteristics of unsteady flow in supercritical transonic diffuser are investigated. For various pressure ratios three-dimensional flow containing a normal shock/turbulent boundary layer interaction regions with shockwave and pseudo-shockwaves fluctuating in longitudinal and spanwise directions is observed. Experimental and numerical investigations show details of the flowfield in the vicinity of terminal shock, interaction regions and downstream turbulent unsteady flow. Spectral analysis of pressure fluctuations reveals existence of two characteristic frequencies attributed to the shockwave fluctuation in longitudinal direction for the lower frequency case and acoustic resonance in spanwise direction for the higher one. Vortices appear at each corner in transversal sections modifying the core flow. As a result, size and depth of longitudinal and vertical penetration of separation regions impelled by the terminal shock is either increased or decreased.

Electrical conductivity anomaly beneath Mare Serenitatis detected by Lunokhod 2 and Apollo 16 magnetometers

NASA Technical Reports Server (NTRS)

Vanian, L. L.; Vnuchkova, T. A.; Egorov, I. V.; Basilevskii, A. T.; Eroshenko, E. G.; Fainberg, E. B.; Dyal, P.; Daily, W. D.

1979-01-01

Magnetic fluctuations measured by the Lunokhod 2 magnetometer in the Bay Le Monnier are distinctly anisotropic when compared to simultaneous Apollo 16 magnetometer data measured 1100 km away in the Descartes highlands. This anisotropy can be explained by an anomalous electrical conductivity of the upper mantle beneath Mare Serenitatis. A model is presented of anomalously lower electrical conductivity beneath Serenitatis and the simultaneous magnetic data from the Lunokhod 2 site at the mare edge and the Apollo 16 site are compared to the numerically calculated model solutions. This comparison indicates that the anisotropic fluctuations can be modeled by a nonconducting layer in the lunar lithosphere which is 150 km thick beneath the highlands and 300 km thick beneath Mare Serenitatis. A decreased electrical conductivity in the upper mantle beneath the mare may be due to a lower temperature resulting from heat carried out the magma source regions to the surface during mare flooding.

Probing entropic repulsion through mesoscopic simulations

NASA Astrophysics Data System (ADS)

Vaiwala, Rakesh; Thaokar, Rochish

2017-11-01

Following the publication of Freund's work on entropic pressure (Freund L., Proc. Natl. Acad. Sci. U.S.A., 110 (2013) 2047), which states that the undulation pressure for a biomembrane confined between two parallel rigid walls decays linearly with wall separation (d), different contradictory views on the pressure law evolved; some supporting Helfrich's prediction that the entropic pressure scales as 1/d3 . Attempts were made to resolve this stark contradiction by distinct groups of researchers. In this work, using dissipative particle dynamics simulations it has been shown for the first time that the height fluctuations are suppressed by wall confinement. An analysis of the fluctuation spectrum reveals that the entropic loss manifests as a membrane tension for a membrane that conserves its local area, and this fact is confirmed by the rise in stresses with an increase in wall confinement. Furthermore, we theorize a pressure law, which interestingly is congruous with Freund's prediction that the entropic pressure scales as 1/d .

Pressure-strain-rate events in homogeneous turbulent shear flow

NASA Technical Reports Server (NTRS)

Brasseur, James G.; Lee, Moon J.

1988-01-01

A detailed study of the intercomponent energy transfer processes by the pressure-strain-rate in homogeneous turbulent shear flow is presented. Probability density functions (pdf's) and contour plots of the rapid and slow pressure-strain-rate show that the energy transfer processes are extremely peaky, with high-magnitude events dominating low-magnitude fluctuations, as reflected by very high flatness factors of the pressure-strain-rate. A concept of the energy transfer class was applied to investigate details of the direction as well as magnitude of the energy transfer processes. In incompressible flow, six disjoint energy transfer classes exist. Examination of contours in instantaneous fields, pdf's and weighted pdf's of the pressure-strain-rate indicates that in the low magnitude regions all six classes play an important role, but in the high magnitude regions four classes of transfer processes, dominate. The contribution to the average slow pressure-strain-rate from the high magnitude fluctuations is only 50 percent or less. The relative significance of high and low magnitude transfer events is discussed.

Determination of Pressure Fluctuations in Rotor Bundle of Centrifugal Compressor at Critical Conditions of Operation

NASA Astrophysics Data System (ADS)

Levashov, V. A.; Lyubchenko, K. Yu

2017-08-01

This article describes the physical processes that occur in the stage flow part of the compressor while it is operating and can create conditions for the occurrence of forced vibrations, which in turn can lead to the destruction of the impellers. Critical conditions of compressor operation are determined. To understand that critical condition of operation is cause of the destruction of the impellers, transient CFD analysis was carried for test stage of compressor. The obtained pressure fluctuation amplitudes allow to evaluate the critical conditions of compressor operation.

Effect of standing transverse acoustic oscillations on fuel-oxidant mixing in cylindrical combustion chambers

NASA Technical Reports Server (NTRS)

Mickelsen, William R

1957-01-01

Vapor fuel-oxidant mixing is analyzed for standing transverse acoustic fields simulating those existing in screeching or screaming combustors. The additional mixing due to the acoustic field is shown to be a function of sound pressure and frequency, stream velocity, and turbulence. The effects of these parameters are shown graphically for a realistic range of combustor conditions. The fuel-oxidant ratio at various combustor stations is shown to have a cyclic fluctuation which is in phase with the pressure fluctuations. Possible mechanisms contributing to screech and scream are discussed.

Effect of particle velocity fluctuations on the inertia coupling in two-phase flow

NASA Technical Reports Server (NTRS)

Drew, Donald A.

1989-01-01

Consistent forms for the interfacial force, the interfacial pressure, the Reynolds stresses and the particle stress have been derived for the inviscid, irrotational incompressible flow of fluid in a dilute suspension of spheres. The particles are assumed to have a velocity distribution, giving rise to an effective pressure and stress in the particle phase. The velocity fluctuations also contribute in the fluid Reynolds stress and in the (elastic) stress field inside the spheres. The relation of these constitutive equations to the force on an individual sphere is discussed.

[Clinical application of modified upper gluteal rhomboid fasciocutaneous flap in repairing sacrococcygeal pressure sores].

PubMed

Jiang, Maohua; Yang, Xiaoliang; Wei, Bangmin; Li, Yinghao

2012-03-01

To investigate the method and effectiveness of repairing sacrococcygeal pressure sores with modified upper gluteal rhomboid fasciocutaneous flap. Between January 2004 and March 2011, 43 patients with sacrococcygeal pressure sores were treated. There were 25 males and 18 females with an average age of 63 years (range, 38-95 years). The disease duration was 3 months to 2 years and 6 months (mean, 8.5 months). The size of pressure sores ranged from 6 cm x 5 cm to 18 cm x 13 cm. According to the extent and lesion degree of pressure scores, 23 pressure sores were rated as degree III and 20 pressure sores as degree IV. The modified upper gluteal rhomboid flap was designed, one-side upper gluteal fasciocutaneous flaps were transplanted to repair sacrococcygeal pressure sores in 19 cases and two-side flaps in 24 cases. The size of one side flap ranged from 6.5 cm x 4.5 cm to 18.0 cm x 11.5 cm. Fluid under flap occurred in 1 case and edge necrosis of the flaps in 3 cases at 7 days after operation, which were cured after drainage and dressing change; the other flaps survived, and incisions healed by first intention. All patients were followed up 6 months to 3 years with an average of 11 months. Two patients relapsed at 5 months and 8 months, respectively; the other patients had no recurrence. The color of the flaps was normal, and the appearance and elasticity of the flaps were good. The modified upper gluteal rhomboid fasciocutaneous flap has the advantages of simple design and operation, less injury, and reliable effect in repairing sacrococcygeal pressure sores.

Experiment 2033. Injection Test of Upper EE-3 Fracture Zone

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grigsby, Charles O.

1983-09-12

This experiment is designed to investigate the apparent lithologic boundary between the low-opening-pressure fracture system (upper EE-3 fracture and Phase I system) and the high-opening-pressure fracture system (lower fracture in EE-3 and in EE-2). The experiment will test for resistence to breakthrough into the lower EE-2 fracture system at relatively low pressure and will define the veting behavior of the low pressure system.

Combustion characteristics of paper and sewage sludge in a pilot-scale fluidized bed.

PubMed

Yu, Yong-Ho; Chung, Jinwook

2015-01-01

This study characterizes the combustion of paper and sewage sludge in a pilot-scale fluidized bed. The highest temperature during combustion within the system was found at the surface of the fluidized bed. Paper sludge containing roughly 59.8% water was burned without auxiliary fuel, but auxiliary fuel was required to incinerate the sewage sludge, which contained about 79.3% water. The stability of operation was monitored based on the average pressure and the standard deviation of pressure fluctuations. The average pressure at the surface of the fluidized bed decreased as the sludge feed rate increased. However, the standard deviation of pressure fluctuations increased as the sludge feed rate increased. Finally, carbon monoxide (CO) emissions decreased as oxygen content increased in the flue gas, and nitrogen oxide (NOx) emissions were also tied with oxygen content.

Numerical calculation and analysis of radial force on the single-action vane pump

NASA Astrophysics Data System (ADS)

Y He, Y.; Y Kong, F.

2013-12-01

Unbalanced radial force is a serious adversity that restricts the working pressure and reduces service life of the single-action vane pump. For revealing and predicting the distribution of radial force on the rotor, a numerical simulation about its transient flow field was performed by using dynamic mesh method with RNG κ ε-turbulent model. The details of transient flow characteristic and pressure fluctuation were obtained, and the radial force and periodic variation can be calculated based on the details. The results show: the radial force has a close relationship with the pressure pulsation; the radial force can be reduced drastically by optimizing the angle of port plate and installing the V-shaped cavity; if the odd number vanes are chosen, it will help reduce the radial force of rotor and optimize the pressure fluctuation effectively.

Characterization of swallow modulation in response to bolus volume in healthy subjects accounting for catheter diameter.

PubMed

Ferris, Lara; Schar, Mistyka; McCall, Lisa; Doeltgen, Sebastian; Scholten, Ingrid; Rommel, Nathalie; Cock, Charles; Omari, Taher

2018-06-01

Characterization of the pharyngeal swallow response to volume challenges is important for swallowing function assessment. The diameter of the pressure-impedance recording catheter may influence these results. In this study, we captured key physiological swallow measures in response to bolus volume utilizing recordings acquired by two catheters of different diameter. Ten healthy adults underwent repeat investigations with 8- and 10-Fr catheters. Liquid bolus swallows of volumes 2.5, 5, 10, 20, and 30 mL were recorded. Measures indicative of distension, contractility, and flow timing were assessed. Pressure-impedance recordings with pressure-flow analysis were used to capture key distension, contractility, and pressure-flow timing parameters. Larger bolus volumes increased upper esophageal sphincter distension diameter (P < .001) and distension pressures within the hypopharynx and upper esophageal sphincter (P < .05). Bolus flow timing measures were longer, particularly latency of bolus propulsion ahead of the pharyngeal stripping wave (P < .001). Use of a larger-diameter catheter produced higher occlusive pressures, namely upper esophageal sphincter basal pressure (P < .005) and upper esophageal sphincter postdeglutitive pressure peak (P < .001). The bolus volume swallowed changed measurements indicative of distension pressure, luminal diameter, and pressure-flow timing; this is physiologically consistent with swallow modulation to accommodate larger, faster-flowing boluses. Additionally, catheter diameter predominantly affects lumen occlusive pressures. Appropriate physiological interpretation of the pressure-impedance recordings of pharyngeal swallowing requires consideration of the effects of volume and catheter diameter. NA. Laryngoscope, 128:1328-1334, 2018. © 2017 The American Laryngological, Rhinological and Otological Society, Inc.

Elasticity of Orthoenstatite at High Pressure and Temperature: Implications for the Origin of Low VP/VS Zones in the Mantle Wedge

NASA Astrophysics Data System (ADS)

Qian, Wangsheng; Wang, Wenzhong; Zou, Fan; Wu, Zhongqing

2018-01-01

Orthopyroxene (opx) is an important mineral in petrologic models for the upper mantle. Its elastic properties are fundamental for understanding the chemical composition and geodynamics of the upper mantle. Here we calculate the elastic properties of orthoenstatite (MgSiO3), the Mg end-member orthopyroxene under upper mantle pressure and temperature conditions using first principle calculations with local density approximation. Bulk and shear moduli increase nonlinearly with pressure at mantle temperatures, but the shear modulus and VS show very weak pressure dependence in comparison with VP. Compared to other major minerals in the upper mantle, orthoenstatite has the lowest compressional velocities (VP), shear velocities (VS), and VP/VS ratio down to the depth of approximately 300 km. The enrichment of opx in the upper mantle can cause the unusually low VP/VS observed in the mantle wedge.

High-Pressure Transvenous Perfusion of the Upper Extremity in Human Muscular Dystrophy: A Safety Study with 0.9% Saline.

PubMed

Fan, Zheng; Kocis, Keith; Valley, Robert; Howard, James F; Chopra, Manisha; Chen, Yasheng; An, Hongyu; Lin, Weili; Muenzer, Joseph; Powers, William

2015-09-01

We evaluated safety and feasibility of high-pressure transvenous limb perfusion in an upper extremity of adult patients with muscular dystrophy, after completing a similar study in a lower extremity. A dose escalation study of single-limb perfusion with 0.9% saline was carried out in nine adults with muscular dystrophies under intravenous analgesia. Our study demonstrates that it is feasible and definitely safe to perform high-pressure transvenous perfusion with 0.9% saline up to 35% of limb volume in the upper extremities of young adults with muscular dystrophy. Perfusion at 40% limb volume is associated with short-lived physiological changes in peripheral nerves without clinical correlates in one subject. This study provides the basis for a phase 1/2 clinical trial using pressurized transvenous delivery into upper limbs of nonambulatory patients with Duchenne muscular dystrophy. Furthermore, our results are applicable to other conditions such as limb girdle muscular dystrophy as a method for delivering regional macromolecular therapeutics in high dose to skeletal muscles of the upper extremity.

Ground-water and water-chemistry data for the upper Deschutes Basin, Oregon

USGS Publications Warehouse

Caldwell, Rodney R.; Truini, Margot

1997-01-01

This report presents ground-water data collected and compiled as part of a study of the ground-water resources of the upper Deschutes Basin, Oregon. Data in this report include tabulated information and a location map for more than 1,500 field-located water wells, hydrographs showing water-level fluctuations over various time periods for 102 of the wells, and water-chemistry analyses from 26 wells, 7 springs, and 5 surface-water sites.

Fiber-Optic Pressure Sensor With Dynamic Demodulation Developed

NASA Technical Reports Server (NTRS)

Lekki, John D.

2002-01-01

Researchers at the NASA Glenn Research Center developed in-house a method to detect pressure fluctuations using a fiber-optic sensor and dynamic signal processing. This work was in support of the Intelligent Systems Controls and Operations project under NASA's Information Technology Base Research Program. We constructed an optical pressure sensor by attaching a fiber-optic Bragg grating to a flexible membrane and then adhering the membrane to one end of a small cylinder. The other end of the cylinder was left open and exposed to pressure variations from a pulsed air jet. These pressure variations flexed the membrane, inducing a strain in the fiber-optic grating. This strain was read out optically with a dynamic spectrometer to record changes in the wavelength of light reflected from the grating. The dynamic spectrometer was built in-house to detect very small wavelength shifts induced by the pressure fluctuations. The spectrometer is an unbalanced interferometer specifically designed for maximum sensitivity to wavelength shifts. An optimum pathlength difference, which was determined empirically, resulted in a 14-percent sensitivity improvement over theoretically predicted path-length differences. This difference is suspected to be from uncertainty about the spectral power difference of the signal reflected from the Bragg grating. The figure shows the output of the dynamic spectrometer as the sensor was exposed to a nominally 2-kPa peak-to-peak square-wave pressure fluctuation. Good tracking, sensitivity, and signal-to-noise ratios are evident even though the sensor was constructed as a proof-of-concept and was not optimized in any way. Therefore the fiber-optic Bragg grating, which is normally considered a good candidate as a strain or temperature sensor, also has been shown to be a good candidate for a dynamic pressure sensor.

High-Beta Electromagnetic Turbulence in LAPD Plasmas

NASA Astrophysics Data System (ADS)

Rossi, G.; Carter, T. A.; Pueschel, M. J.; Jenko, F.; Told, D.; Terry, P. W.

2015-11-01

The introduction of a new LaB6 cathode plasma source in the Large Plasma Device has enabled the study of pressure-gradient-driven turbulence and transport variations at significantly higher plasma β. Density fluctuations are observed to decrease with increasing β while magnetic fluctuations increase. Furthermore, the perpendicular magnetic fluctuations are seen to saturate while parallel (compressional) magnetic fluctuations increase continuously with β. These observations are compared to linear and nonlinear simulations with the GENE code. The results are consistent with the linear excitation of a Gradient-driven Drift Coupling mode (GDC) which relies on grad-B drift due to parallel magnetic fluctuations and can be driven by density or temperature gradients.

Sensitivity Analysis and Accuracy of a CFD-TFM Approach to Bubbling Bed Using Pressure Drop Fluctuations

PubMed Central

Tricomi, Leonardo; Melchiori, Tommaso; Chiaramonti, David; Boulet, Micaël; Lavoie, Jean Michel

2017-01-01

Based upon the two fluid model (TFM) theory, a CFD model was implemented to investigate a cold multiphase-fluidized bubbling bed reactor. The key variable used to characterize the fluid dynamic of the experimental system, and compare it to model predictions, was the time-pressure drop induced by the bubble motion across the bed. This time signal was then processed to obtain the power spectral density (PSD) distribution of pressure fluctuations. As an important aspect of this work, the effect of the sampling time scale on the empirical power spectral density (PSD) was investigated. A time scale of 40 s was found to be a good compromise ensuring both simulation performance and numerical validation consistency. The CFD model was first numerically verified by mesh refinement process, after what it was used to investigate the sensitivity with regards to minimum fluidization velocity (as a calibration point for drag law), restitution coefficient, and solid pressure term while assessing his accuracy in matching the empirical PSD. The 2D model provided a fair match with the empirical time-averaged pressure drop, the relating fluctuations amplitude, and the signal’s energy computed as integral of the PSD. A 3D version of the TFM was also used and it improved the match with the empirical PSD in the very first part of the frequency spectrum. PMID:28695119

Sensitivity Analysis and Accuracy of a CFD-TFM Approach to Bubbling Bed Using Pressure Drop Fluctuations.

PubMed

Tricomi, Leonardo; Melchiori, Tommaso; Chiaramonti, David; Boulet, Micaël; Lavoie, Jean Michel

2017-01-01

Based upon the two fluid model (TFM) theory, a CFD model was implemented to investigate a cold multiphase-fluidized bubbling bed reactor. The key variable used to characterize the fluid dynamic of the experimental system, and compare it to model predictions, was the time-pressure drop induced by the bubble motion across the bed. This time signal was then processed to obtain the power spectral density (PSD) distribution of pressure fluctuations. As an important aspect of this work, the effect of the sampling time scale on the empirical power spectral density (PSD) was investigated. A time scale of 40 s was found to be a good compromise ensuring both simulation performance and numerical validation consistency. The CFD model was first numerically verified by mesh refinement process, after what it was used to investigate the sensitivity with regards to minimum fluidization velocity (as a calibration point for drag law), restitution coefficient, and solid pressure term while assessing his accuracy in matching the empirical PSD. The 2D model provided a fair match with the empirical time-averaged pressure drop, the relating fluctuations amplitude, and the signal's energy computed as integral of the PSD. A 3D version of the TFM was also used and it improved the match with the empirical PSD in the very first part of the frequency spectrum.

Pressure fluctuations beneath instability wavepackets and turbulent spots in a hypersonic boundary layer

DOE PAGES

Casper, Katya M.; Beresh, Steven J.; Schneider, Steven P.

2014-09-09

To investigate the pressure-fluctuation field beneath turbulent spots in a hypersonic boundary layer, a study was conducted on the nozzle wall of the Boeing/AFOSR Mach-6 Quiet Tunnel. Controlled disturbances were created by pulsed-glow perturbations based on the electrical breakdown of air. Under quiet-flow conditions, the nozzle-wall boundary layer remains laminar and grows very thick over the long nozzle length. This allows the development of large disturbances that can be well-resolved with high-frequency pressure transducers. A disturbance first grows into a second-mode instability wavepacket that is concentrated near its own centreline. Weaker disturbances are seen spreading from the centre. The wavesmore » grow and become nonlinear before breaking down to turbulence. The breakdown begins in the core of the packets where the wave amplitudes are largest. Second-mode waves are still evident in front of and behind the breakdown point and can be seen propagating in the spanwise direction. The turbulent core grows downstream, resulting in a spot with a classical arrowhead shape. Behind the spot, a low-pressure calmed region develops. However, the spot is not merely a localized patch of turbulence; instability waves remain an integral part. Limited measurements of naturally occurring disturbances show many similar characteristics. From the controlled disturbance measurements, the convection velocity, spanwise spreading angle, and typical pressure-fluctuation field were obtained.« less

Characterization of cavity flow fields using pressure data obtained in the Langley 0.3-Meter Transonic Cryogenic Tunnel

NASA Technical Reports Server (NTRS)

Tracy, M. B.; Plentovich, E. B.

1993-01-01

Static and fluctuating pressure distributions were obtained along the floor of a rectangular-box cavity in an experiment performed in the LaRC 0.3-Meter Transonic Cryogenic Tunnel. The cavity studied was 11.25 in. long and 2.50 in. wide with a variable height to obtain length-to-height ratios of 4.4, 6.7, 12.67, and 20.0. The data presented herein were obtained for yaw angles of 0 deg and 15 deg over a Mach number range from 0.2 to 0.9 at a Reynolds number of 30 x 10(exp 6) per ft with a boundary-layer thickness of approximately 0.5 in. The results indicated that open and transitional-open cavity flow supports tone generation at subsonic and transonic speeds at Mach numbers of 0.6 and above. Further, pressure fluctuations associated with acoustic tone generation can be sustained when static pressure distributions indicate that transitional-closed and closed flow fields exist in the cavity. Cavities that support tone generation at 0 deg yaw also supported tone generation at 15 deg yaw when the flow became transitional-closed. For the latter cases, a reduction in tone amplitude was observed. Both static and fluctuating pressure data must be considered when defining cavity flow fields, and the flow models need to be refined to accommodate steady and unsteady flows.

Fluctuation Theorem for Many-Body Pure Quantum States.

PubMed

Iyoda, Eiki; Kaneko, Kazuya; Sagawa, Takahiro

2017-09-08

We prove the second law of thermodynamics and the nonequilibrium fluctuation theorem for pure quantum states. The entire system obeys reversible unitary dynamics, where the initial state of the heat bath is not the canonical distribution but is a single energy eigenstate that satisfies the eigenstate-thermalization hypothesis. Our result is mathematically rigorous and based on the Lieb-Robinson bound, which gives the upper bound of the velocity of information propagation in many-body quantum systems. The entanglement entropy of a subsystem is shown connected to thermodynamic heat, highlighting the foundation of the information-thermodynamics link. We confirmed our theory by numerical simulation of hard-core bosons, and observed dynamical crossover from thermal fluctuations to bare quantum fluctuations. Our result reveals a universal scenario that the second law emerges from quantum mechanics, and can be experimentally tested by artificial isolated quantum systems such as ultracold atoms.

Fluctuation Theorem for Many-Body Pure Quantum States

NASA Astrophysics Data System (ADS)

Iyoda, Eiki; Kaneko, Kazuya; Sagawa, Takahiro

2017-09-01

We prove the second law of thermodynamics and the nonequilibrium fluctuation theorem for pure quantum states. The entire system obeys reversible unitary dynamics, where the initial state of the heat bath is not the canonical distribution but is a single energy eigenstate that satisfies the eigenstate-thermalization hypothesis. Our result is mathematically rigorous and based on the Lieb-Robinson bound, which gives the upper bound of the velocity of information propagation in many-body quantum systems. The entanglement entropy of a subsystem is shown connected to thermodynamic heat, highlighting the foundation of the information-thermodynamics link. We confirmed our theory by numerical simulation of hard-core bosons, and observed dynamical crossover from thermal fluctuations to bare quantum fluctuations. Our result reveals a universal scenario that the second law emerges from quantum mechanics, and can be experimentally tested by artificial isolated quantum systems such as ultracold atoms.

Limits on the fluctuating part of y-type distortion monopole from Planck and SPT results

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khatri, Rishi; Sunyaev, Rashid, E-mail: khatri@mpa-garching.mpg.de, E-mail: sunyaev@mpa-garching.mpg.de

2015-08-01

We use the published Planck and SPT cluster catalogs [1,2] and recently published y-distortion maps [3] to put strong observational limits on the contribution of the fluctuating part of the y-type distortions to the y-distortion monopole. Our bounds are 5.4× 10{sup −8} < ( y) < 2.2× 10{sup −6}. Our upper bound is a factor of 6.8 stronger than the currently best upper 95% confidence limit from COBE-FIRAS of ( y) <15× 10{sup −6}. In the standard cosmology, large scale structure is the only source of such distortions and our limits therefore constrain the baryonic physics involved in the formation of the large scale structure. Our lower limit, from themore » detected clusters in the Planck and SPT catalogs, also implies that a Pixie-like experiment should detect the y-distortion monopole at >27-σ. The biggest sources of uncertainty in our upper limit are the monopole offsets between different HFI channel maps that we estimate to be <10{sup −6}.« less

Spray outputs from a variable-rate sprayer manipulated with PWM solenoid valves

USDA-ARS?s Scientific Manuscript database

Pressure fluctuations during variable-rate spray applications can affect nozzle flow rate fluctuations, resulting in spray outputs that do not coincide with the prescribed canopy structure volume. Variations in total flow rate discharged from 40 nozzles, each coupled with a pulse-width-modulated (PW...

The Effects of Turbulence on Tthe Measurements of Five-Hole Probes

NASA Astrophysics Data System (ADS)

Diebold, Jeffrey Michael

The primary goals of this research were to quantify the effects of turbulence on the measurements of five-hole pressure probes (5HP) and to develop a model capable of predicting the response of a 5HP to turbulence. The five-hole pressure probe is a commonly used device in experimental fluid dynamics and aerodynamics. By measuring the pressure at the five pressure ports located on the tip of the probe it is possible to determine the total pressure, static pressure and the three components of velocity at a point in the flow. Previous research has demonstrated that the measurements of simple pressure probes such as Pitot probes are significantly influenced by the presence of turbulence. Turbulent velocity fluctuations contaminate the measurement of pressure due to the nonlinear relationship between pressure and velocity as well as the angular response characteristics of the probe. Despite our understanding of the effects of turbulence on Pitot and static pressure probes, relatively little is known about the influence of turbulence on five-hole probes. This study attempts to fill this gap in our knowledge by using advanced experimental techniques to quantify these turbulence-induced errors and by developing a novel method of predicting the response of a five-hole probe to turbulence. A few studies have attempted to quantify turbulence-induced errors in five-hole probe measurements but they were limited by their inability to accurately measure the total and static pressure in the turbulent flow. The current research utilizes a fast-response five-hole probe (FR5HP) in order to accurately quantify the effects of turbulence on different standard five-hole probes (Std5HP). The FR5HP is capable of measuring the instantaneous flowfield and unlike the Std5HP the FR5HP measurements are not contaminated by the turbulent velocity fluctuations. Measurements with the FR5HP and two different Std5HPs were acquired in the highly turbulent wakes of 2D and 3D cylinders in order to quantify the turbulence-induced errors in Std5HP measurements. The primary contribution of this work is the development and validation of a simulation method to predict the measurements of a Std5HP in an arbitrary turbulent flow. This simulation utilizes a statistical approach to estimating the pressure at each port on the tip of the probe. The angular response of the probe is modeled using experimental calibration data for each five-hole probe. The simulation method is validated against the experimental measurements of the Std5HPs, and then used to study the how the characteristics of the turbulent flowfield influence the measurements of the Std5HPs. It is shown that total pressure measured by a Std5HP is increased by axial velocity fluctuations but decreased by the transverse fluctuations. The static pressure was shown to be very sensitive to the transverse fluctuations while the axial fluctuations had a negligible effect. As with Pitot probes, the turbulence-induced errors in the Std5HPs measurements were dependent on both the properties of the turbulent flow and the geometry of the probe tip. It is then demonstrated that this simulation method can be used to correct the measurements of a Std5HP in a turbulent flow if the characteristics of the turbulence are known. Finally, it is demonstrated that turbulence-induced errors in Std5HP measurements can have a substantial effect on the determination of the profile and vortex-induced drag from measurements in the wake of a 3D body. The results showed that while the calculation of both drag components was influenced by turbulence-induced errors the largest effect was on the determination of vortex-induced drag.

Observation of magnetic fluctuations and rapid density decay of magnetospheric plasma in Ring Trap 1

NASA Astrophysics Data System (ADS)

Saitoh, H.; Yoshida, Z.; Morikawa, J.; Yano, Y.; Mikami, H.; Kasaoka, N.; Sakamoto, W.

2012-06-01

The Ring Trap 1 device, a magnetospheric configuration generated by a levitated dipole field magnet, has created high-β (local β ˜ 70%) plasma by using electron cyclotron resonance heating (ECH). When a large population of energetic electrons is generated at low neutral gas pressure operation, high frequency magnetic fluctuations are observed. When the fluctuations are strongly excited, rapid loss of plasma was simultaneously observed especially in a quiet decay phase after the ECH microwave power is turned off. Although the plasma is confined in a strongly inhomogeneous dipole field configuration, the frequency spectra of the fluctuations have sharp frequency peaks, implying spatially localized sources of the fluctuations. The fluctuations are stabilized by decreasing the hot electron component below approximately 40%, realizing stable high-β confinement.

Experimental and numerical analysis on noise reduction in a multi-blade centrifugal fan

NASA Astrophysics Data System (ADS)

Chen, X. J.; Y Cao, T.; Su, J.; Qin, G. L.

2013-12-01

In this work, analysis on noise source and reduction in a multi-blade centrifugal fan used for air-conditioners was carried out by experimental and numerical methods. Firstly, an experimental system using microphone mounted on volute surface for measuring surface pressure fluctuations of volute was designed and introduced, then surface pressure fluctuations of the whole volute for a multi-blade centrifugal fan were measured by this system, and the inlet noise for this fan was also obtained. And then, based on the experimental results, the aerodynamic noise source of the studied fan was analysed. The surface pressure fluctuations of the volute showed that there were largest surface pressure fluctuations near the volute tongue, and peaks appeared at the Blade Passing Frequency (BPF). The spectra of fan inlet noise showed that the peaks also appeared at BPF, and noise levels in a wide range of frequency were also larger. Secondly, the internal flow of the fan was simulated by commercial software under the same conditions with the experiment, and then the fluid flow and acoustic power field were obtained and discussed. The contours of acoustic power level showed that the larger noise was generated at the impeller area close to the outlet of scroll and at the volute tongue, which is same as that from experiment. Based on all of the results, we can find that the vortex noise is an important part of fan noise for the studied fan, and the rotation noise also cannot be neglected. Finally, several reduction methods that are thought to be effective based on experimental and numerical results were suggested.

Investigation of steady and fluctuating pressures associated with the transonic buffeting and wing rock of a one-seventh scale model of the F-5A aircraft

NASA Technical Reports Server (NTRS)

Hwang, C.; Pi, W. S.

1978-01-01

A wind tunnel test of a 1/7 scale F-5A model is described. The pressure, force, and dynamic response measurements during buffet and wing rock are evaluated. Effects of Mach number, angle of attack, sideslip angle, and control surface settings were investigated. The mean and fluctuating static pressure data are presented and correlated with some corresponding flight test data of a F-5A aircraft. Details of the instrumentation and the specially designed support system which allowed the model to oscillate in roll to simulate wing rock are also described. A limit cycle mechanism causing wing rock was identified from this study, and this mechanism is presented.

Interferometric tests of Planckian quantum geometry models

DOE PAGES

Kwon, Ohkyung; Hogan, Craig J.

2016-04-19

The effect of Planck scale quantum geometrical effects on measurements with interferometers is estimated with standard physics, and with a variety of proposed extensions. It is shown that effects are negligible in standard field theory with canonically quantized gravity. Statistical noise levels are estimated in a variety of proposals for nonstandard metric fluctuations, and these alternatives are constrained using upper bounds on stochastic metric fluctuations from LIGO. Idealized models of several interferometer system architectures are used to predict signal noise spectra in a quantum geometry that cannot be described by a fluctuating metric, in which position noise arises from holographicmore » bounds on directional information. Lastly, predictions in this case are shown to be close to current and projected experimental bounds.« less

Modeling and stability analysis for the upper atmosphere research satellite auxiliary array switch component

NASA Technical Reports Server (NTRS)

Wolfgang, R.; Natarajan, T.; Day, J.

1987-01-01

A feedback control system, called an auxiliary array switch, was designed to connect or disconnect auxiliary solar panel segments from a spacecraft electrical bus to meet fluctuating demand for power. A simulation of the control system was used to carry out a number of design and analysis tasks that could not economically be performed with a breadboard of the hardware. These tasks included: (1) the diagnosis of a stability problem, (2) identification of parameters to which the performance of the control system was particularly sensitive, (3) verification that the response of the control system to anticipated fluctuations in the electrical load of the spacecraft was satisfactory, and (4) specification of limitations on the frequency and amplitude of the load fluctuations.

Superposed epoch analysis of physiological fluctuations: possible space weather connections

NASA Astrophysics Data System (ADS)

Wanliss, James; Cornélissen, Germaine; Halberg, Franz; Brown, Denzel; Washington, Brien

2018-03-01

There is a strong connection between space weather and fluctuations in technological systems. Some studies also suggest a statistical connection between space weather and subsequent fluctuations in the physiology of living creatures. This connection, however, has remained controversial and difficult to demonstrate. Here we present support for a response of human physiology to forcing from the explosive onset of the largest of space weather events—space storms. We consider a case study with over 16 years of high temporal resolution measurements of human blood pressure (systolic, diastolic) and heart rate variability to search for associations with space weather. We find no statistically significant change in human blood pressure but a statistically significant drop in heart rate during the main phase of space storms. Our empirical findings shed light on how human physiology may respond to exogenous space weather forcing.

Superposed epoch analysis of physiological fluctuations: possible space weather connections.

PubMed

Wanliss, James; Cornélissen, Germaine; Halberg, Franz; Brown, Denzel; Washington, Brien

2018-03-01

There is a strong connection between space weather and fluctuations in technological systems. Some studies also suggest a statistical connection between space weather and subsequent fluctuations in the physiology of living creatures. This connection, however, has remained controversial and difficult to demonstrate. Here we present support for a response of human physiology to forcing from the explosive onset of the largest of space weather events-space storms. We consider a case study with over 16 years of high temporal resolution measurements of human blood pressure (systolic, diastolic) and heart rate variability to search for associations with space weather. We find no statistically significant change in human blood pressure but a statistically significant drop in heart rate during the main phase of space storms. Our empirical findings shed light on how human physiology may respond to exogenous space weather forcing.

Dislocation-accommodated grain boundary sliding as the major deformation mechanism of olivine in the Earth’s upper mantle

PubMed Central

Ohuchi, Tomohiro; Kawazoe, Takaaki; Higo, Yuji; Funakoshi, Ken-ichi; Suzuki, Akio; Kikegawa, Takumi; Irifune, Tetsuo

2015-01-01

Understanding the deformation mechanisms of olivine is important for addressing the dynamic processes in Earth’s upper mantle. It has been thought that dislocation creep is the dominant mechanism because of extrapolated laboratory data on the plasticity of olivine at pressures below 0.5 GPa. However, we found that dislocation-accommodated grain boundary sliding (DisGBS), rather than dislocation creep, dominates the deformation of olivine under middle and deep upper mantle conditions. We used a deformation-DIA apparatus combined with synchrotron in situ x-ray observations to study the plasticity of olivine aggregates at pressures up to 6.7 GPa (that is, ~200-km depth) and at temperatures between 1273 and 1473 K, which is equivalent to the conditions in the middle region of the upper mantle. The creep strength of olivine deforming by DisGBS is apparently less sensitive to pressure because of the competing pressure-hardening effect of the activation volume and pressure-softening effect of water fugacity. The estimated viscosity of olivine controlled by DisGBS is independent of depth and ranges from 1019.6 to 1020.7 Pa·s throughout the asthenospheric upper mantle with a representative water content (50 to 1000 parts per million H/Si), which is consistent with geophysical viscosity profiles. Because DisGBS is a grain size–sensitive creep mechanism, the evolution of the grain size of olivine is an important process controlling the dynamics of the upper mantle. PMID:26601281

Dislocation-accommodated grain boundary sliding as the major deformation mechanism of olivine in the Earth's upper mantle.

PubMed

Ohuchi, Tomohiro; Kawazoe, Takaaki; Higo, Yuji; Funakoshi, Ken-Ichi; Suzuki, Akio; Kikegawa, Takumi; Irifune, Tetsuo

2015-10-01

Understanding the deformation mechanisms of olivine is important for addressing the dynamic processes in Earth's upper mantle. It has been thought that dislocation creep is the dominant mechanism because of extrapolated laboratory data on the plasticity of olivine at pressures below 0.5 GPa. However, we found that dislocation-accommodated grain boundary sliding (DisGBS), rather than dislocation creep, dominates the deformation of olivine under middle and deep upper mantle conditions. We used a deformation-DIA apparatus combined with synchrotron in situ x-ray observations to study the plasticity of olivine aggregates at pressures up to 6.7 GPa (that is, ~200-km depth) and at temperatures between 1273 and 1473 K, which is equivalent to the conditions in the middle region of the upper mantle. The creep strength of olivine deforming by DisGBS is apparently less sensitive to pressure because of the competing pressure-hardening effect of the activation volume and pressure-softening effect of water fugacity. The estimated viscosity of olivine controlled by DisGBS is independent of depth and ranges from 10(19.6) to 10(20.7) Pa·s throughout the asthenospheric upper mantle with a representative water content (50 to 1000 parts per million H/Si), which is consistent with geophysical viscosity profiles. Because DisGBS is a grain size-sensitive creep mechanism, the evolution of the grain size of olivine is an important process controlling the dynamics of the upper mantle.

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

A full suite of instruments are seen onboard the the Woods Hole Oceanographic Institution research vessel Knorr on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. The various instruments will be deployed in the Atlantic Ocean as part of the Salinity Processes in the Upper Ocean Regional Study (SPURS) which is set to sail on Sept. 6. The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

Autonomous wave gliders are seen onboard the the Woods Hole Oceanographic Institution research vessel Knorr on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. The autonomous gliders will be deployed in the Atlantic Ocean as part of the Salinity Processes in the Upper Ocean Regional Study (SPURS) which is set to sail on Sept. 6. The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

University of Washington Graduate Student Jesse Anderson settles into her cabin onboard the Woods Hole Oceanographic Institution research vessel Knorr on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. Anderson will work with the Argo Floats instruments in the Atlantic Ocean as part of the Salinity Processes in the Upper Ocean Regional Study (SPURS) which is set to sail on Sept. 6. The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

CTD instruments used to measure Conductivity, Temperature, and Depth, are seen onboard the Woods Hole Oceanographic Institution's research vessel Knorr on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. The CTDs will be deployed in the Atlantic Ocean as part of the Salinity Processes in the Upper Ocean Regional Study (SPURS) which is set to sail on Sept. 6. The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

Autonomous wave gliders, right, are seen onboard the the Woods Hole Oceanographic Institution research vessel Knorr on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. The autonomous gliders will be deployed in the Atlantic Ocean as part of the Salinity Processes in the Upper Ocean Regional Study (SPURS) which is set to sail on Sept. 6. The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

A sensor-laden buoy is seen prior to being loaded onboard the Woods Hole Oceanographic Institution's vessel Knorr on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. The buoy will be deployed in the Atlantic Ocean as part of the Salinity Processes in the Upper Ocean Regional Study (SPURS) which is set to sail on Sept. 6. The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

Buoys used to support scientific instruments at sea are seen in the foreground prior to being loaded onboard the Woods Hole Oceanographic Institution's research vessel Knorr, seen in the background, on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. Knorr is scheduled to depart on Sept. 6 to take part in the Salinity Processes in the Upper Ocean Regional Study (SPURS). The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

Ken Decoteau, left, and Chip Beniot, both of the Woods Hole Oceanographic Institution, move scientific instruments to the research vessel Knorr on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. The instruments will be deployed in the Atlantic Ocean as part of the Salinity Processes in the Upper Ocean Regional Study (SPURS) which is set to sail on Sept. 6. The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

Chip Beniot, left, and Ken Decoteau, both of the Woods Hole Oceanographic Institution, move scientific instruments to the research vessel Knorr on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. The instruments will be deployed in the Atlantic Ocean as part of the Salinity Processes in the Upper Ocean Regional Study (SPURS) which is set to sail on Sept. 6. The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

NASA Physical Oceanography Program Scientist Eric Lindstrom talks about the instruments onboard the Woods Hole Oceanographic Institution research vessel Knorr on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. Various scientific instruments will be deployed in the Atlantic Ocean as part of the Salinity Processes in the Upper Ocean Regional Study (SPURS) which is set to sail on Sept. 6. The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

NASA Physical Oceanography Program Scientist Eric Lindstrom inspects an autonomous wave glider onboard the Woods Hole Oceanographic Institution research vessel Knorr on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. The autonomous gliders will be deployed in the Atlantic Ocean as part of the Salinity Processes in the Upper Ocean Regional Study (SPURS) which is set to sail on Sept. 6. The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

Woods Hole Oceanographic Institution Senior Scientist Ray Schmitt, left, and NASA Physical Oceanography Program Scientist Eric Lindstrom pose for a photograph in front of the Institution's research vessel Knorr on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. Knorr is scheduled to depart on Sept. 6 to take part in the Salinity Processes in the Upper Ocean Regional Study (SPURS). The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

Woods Hole Oceanographic Institution Scientist Dave Fratantoni works on the EcoMapper AUVs (autonomous underwater vehicles) onboard the Institute's research vessel Knorr, Tuesday, Sept. 4, 2012, in Woods Hole, Mass. The EcoMappers will be deployed in the Atlantic Ocean as part of the Salinity Processes in the Upper Ocean Regional Study (SPURS) which is set to sail on Sept. 6. The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

Two EcoMapper AUVs (autonomous underwater vehicles) are seen onboard the the Woods Hole Oceanographic Institution research vessel Knorr on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. The EcoMappers will be deployed in the Atlantic Ocean as part of the Salinity Processes in the Upper Ocean Regional Study (SPURS) which is set to sail on Sept. 6. The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

High-Reynolds-number turbulent-boundary-layer wall-pressure fluctuations with dilute polymer solutions

NASA Astrophysics Data System (ADS)

Elbing, Brian R.; Winkel, Eric S.; Ceccio, Steven L.; Perlin, Marc; Dowling, David R.

2010-08-01

Wall-pressure fluctuations were investigated within a high-Reynolds-number turbulent boundary layer (TBL) modified by the addition of dilute friction-drag-reducing polymer solutions. The experiment was conducted at the U.S. Navy's Large Cavitation Channel on a 12.9 m long flat-plate test model with the surface hydraulically smooth (k+<0.2) and achieving downstream-distance-based Reynolds numbers to 220×106. The polymer (polyethylene oxide) solution was injected into the TBL through a slot in the surface. The primary flow diagnostics were skin-friction drag balances and an array of flush-mounted dynamic pressure transducers 9.8 m from the model leading edge. Parameters varied included the free-stream speed (6.7, 13.4, and 20.2 m s-1) and the injection condition (polymer molecular weight, injection concentration, and volumetric injection flux). The behavior of the pressure spectra, convection velocity, and coherence, regardless of the injection condition, were determined primarily based on the level of drag reduction. Results were divided into two regimes dependent on the level of polymer drag reduction (PDR), nominally separated at a PDR of 40%. The low-PDR regime is characterized by decreasing mean-square pressure fluctuations and increasing convection velocity with increasing drag reduction. This shows that the decrease in the pressure spectra with increasing drag reduction is due in part to the moving of the turbulent structures from the wall. Conversely, with further increases in drag reduction, the high-PDR regime has negligible variation in the mean-squared pressure fluctuations and convection velocity. The convection velocity remains constant at approximately 10% above the baseline-flow convection velocity, which suggests that the turbulent structures no longer move farther from the wall with increasing drag reduction. In light of recent numerical work, the coherence results indicate that in the low-PDR regime, the turbulent structures are being elongated in the streamwise direction and occurring at decreasing frequency. In the high-PDR regime, the rate of occurrence continues to decrease until large-scale coherent turbulent structures are potentially no longer present.

Prediction of Francis Turbine Prototype Part Load Pressure and Output Power Fluctuations with Hydroelectric Model

NASA Astrophysics Data System (ADS)

Alligné, S.; Nicolet, C.; Béguin, A.; Landry, C.; Gomes, J.; Avellan, F.

2017-04-01

The prediction of pressure and output power fluctuations amplitudes on Francis turbine prototype is a challenge for hydro-equipment industry since it is subjected to guarantees to ensure smooth and reliable operation of the hydro units. The European FP7 research project Hyperbole aims to setup a methodology to transpose the pressure fluctuations induced by the cavitation vortex rope from the reduced scale model to the prototype generating units. A Francis turbine unit of 444MW with a specific speed value of ν = 0.29, is considered as case study. A SIMSEN model of the power station including electrical system, controllers, rotating train and hydraulic system with transposed draft tube excitation sources is setup. Based on this model, a frequency analysis of the hydroelectric system is performed for all technologies to analyse potential interactions between hydraulic excitation sources and electrical components. Three technologies have been compared: the classical fixed speed configuration with Synchronous Machine (SM) and the two variable speed technologies which are Doubly Fed Induction Machine (DFIM) and Full Size Frequency Converter (FSFC).

Modeling of Turbulent Boundary Layer Surface Pressure Fluctuation Auto and Cross Spectra - Verification and Adjustments Based on TU-144LL Data

NASA Technical Reports Server (NTRS)

Rackl, Robert; Weston, Adam

2005-01-01

The literature on turbulent boundary layer pressure fluctuations provides several empirical models which were compared to the measured TU-144 data. The Efimtsov model showed the best agreement. Adjustments were made to improve its agreement further, consisting of the addition of a broad band peak in the mid frequencies, and a minor modification to the high frequency rolloff. The adjusted Efimtsov predicted and measured results are compared for both subsonic and supersonic flight conditions. Measurements in the forward and middle portions of the fuselage have better agreement with the model than those from the aft portion. For High Speed Civil Transport supersonic cruise, interior levels predicted by use of this model are expected to increase by 1-3 dB due to the adjustments to the Efimtsov model. The space-time cross-correlations and cross-spectra of the fluctuating surface pressure were also investigated. This analysis is an important ingredient in structural acoustic models of aircraft interior noise. Once again the measured data were compared to the predicted levels from the Efimtsov model.

On the generation of side-edge flap noise. [part span trailing edge flaps

NASA Technical Reports Server (NTRS)

Howe, M. S.

1981-01-01

A theory is proposed for estimating the noise generated at the side edges of part span trailing edge flaps in terms of pressure fluctuations measured just in-board of the side edge of the upper surface of the flap. Asymptotic formulae are developed in the opposite extremes of Lorentz contracted acoustic wavelength large/small compared with the chord of the flap. Interpolation between these limiting results enables the field shape and its dependence on subsonic forward flight speed to be predicted over the whole frequency range. It is shown that the mean width of the side edge gap between the flap and the undeflected portion of the airfoil has a significant influence on the intensity of the radiated sound. It is estimated that the noise generated at a single side edge of a full scale part span flap can exceed that produced along the whole of the trailing edge of the flap by 3 dB or more.

Cirrus Cloud Retrieval Using Infrared Sounding Data: Multilevel Cloud Errors.

NASA Astrophysics Data System (ADS)

Baum, Bryan A.; Wielicki, Bruce A.

1994-01-01

In this study we perform an error analysis for cloud-top pressure retrieval using the High-Resolution Infrared Radiometric Sounder (HIRS/2) 15-µm CO2 channels for the two-layer case of transmissive cirrus overlying an overcast, opaque stratiform cloud. This analysis includes standard deviation and bias error due to instrument noise and the presence of two cloud layers, the lower of which is opaque. Instantaneous cloud pressure retrieval errors are determined for a range of cloud amounts (0.1 1.0) and cloud-top pressures (850250 mb). Large cloud-top pressure retrieval errors are found to occur when a lower opaque layer is present underneath an upper transmissive cloud layer in the satellite field of view (FOV). Errors tend to increase with decreasing upper-cloud elective cloud amount and with decreasing cloud height (increasing pressure). Errors in retrieved upper-cloud pressure result in corresponding errors in derived effective cloud amount. For the case in which a HIRS FOV has two distinct cloud layers, the difference between the retrieved and actual cloud-top pressure is positive in all casts, meaning that the retrieved upper-cloud height is lower than the actual upper-cloud height. In addition, errors in retrieved cloud pressure are found to depend upon the lapse rate between the low-level cloud top and the surface. We examined which sounder channel combinations would minimize the total errors in derived cirrus cloud height caused by instrument noise and by the presence of a lower-level cloud. We find that while the sounding channels that peak between 700 and 1000 mb minimize random errors, the sounding channels that peak at 300—500 mb minimize bias errors. For a cloud climatology, the bias errors are most critical.

High-pressure injection injuries to the upper extremity: a review of the literature.

PubMed

Hogan, Christopher J; Ruland, Robert T

2006-07-01

The purpose of this review was to identify the relative impact of injected material, location of injury, time to debridement, injection pressure, infection, and the use of adjuvant steroid medication upon the need for amputation after high-pressure injection injuries to the upper extremity. A Medline literature search extending from 1966 to December 2003 was performed, referencing the key words "high-pressure injection injury," "grease gun injury," "paint gun injury," "pressure gun injury," and "high-pressure injection." The results were limited to the English language and to reports involving human subjects. Each abstract was reviewed to confirm that the described injury had occurred in the upper extremity and that it had truly been a high-pressure injection. The reference pages from each of the papers were reviewed to identify additional reports of high-pressure injection injury. Manuscripts describing injuries resulting from hand held syringes or other low-pressure mechanisms were excluded. All of the manuscripts were analyzed to identify the clinical outcome, age, hand dominance, site of injection, substance injected, injection pressure, elapsed time to wide debridement, use of steroids, and incidence of infection. These variables were subjected to a Pearson chi test to determine their impact upon the need for amputation. Four hundred thirty-five cases of high-pressure injection injury to the upper extremity were identified. The amputation rate after these injuries was 30%. The location of the injury and the material injected contributed significantly to the need for amputation. For injections of paint, paint thinner, gasoline, oil, or jet fuel (organic solvents), the amputation risk was lower if wide surgical debridement occurred within 6 hours of injury. Steroids did not impact the amputation rate or incidence of infection. The presence of infection did not affect the incidence of amputation. The risk of amputation after high-pressure injection injury to the upper extremity is highest with organic solvent injection into the fingers. Injections into the thumb or palm result in a much lower frequency of tissue loss. Emergent surgical debridement reduces the amputation risk after injections of organic solvents. From the available data, no conclusions could be reached regarding functional outcomes, other than amputation, after high-pressure injection injury.

Estimating Fluctuating Pressures From Distorted Measurements

NASA Technical Reports Server (NTRS)

Whitmore, Stephen A.; Leondes, Cornelius T.

1994-01-01

Two algorithms extract estimates of time-dependent input (upstream) pressures from outputs of pressure sensors located at downstream ends of pneumatic tubes. Effect deconvolutions that account for distoring effects of tube upon pressure signal. Distortion of pressure measurements by pneumatic tubes also discussed in "Distortion of Pressure Signals in Pneumatic Tubes," (ARC-12868). Varying input pressure estimated from measured time-varying output pressure by one of two deconvolution algorithms that take account of measurement noise. Algorithms based on minimum-covariance (Kalman filtering) theory.

70. DETAIL OF OXYGEN TRANSFER PRESSURE GAUGE IN UPPER LEFT ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

70. DETAIL OF OXYGEN TRANSFER PRESSURE GAUGE IN UPPER LEFT CORNER OF SKID ON RIGHT IN CA-133-1-C-69 - Vandenberg Air Force Base, Space Launch Complex 3, Launch Pad 3 West, Napa & Alden Roads, Lompoc, Santa Barbara County, CA

The Shoreline Vegetation of Lake Oahe a Man Made Fluctuating Water Level Reservoir of the Upper Missouri River Basin.

DTIC Science & Technology

1973-06-01

VANDERVEEN ET AL . UNCLASSIFIED 01 JUN 73 DACW45-73-C-0002 F/G 6/6. NL mmmmmmmmIIIIIIIIIIIIIu IIEIIIEEIIIIEE EEIIIIIIIIIEEE IIIIIIIIIIIIIIfl L 2. i~iIi...fluctuation to be the most impor- tant factor affecting vegetation along reservoir shorelines. Hall et al . (1946) studied reservoirs in the Tennessee Valley...Hall, T. F. et al . 1946. Water level relationships of plants in the Tennessee valley. Tenn. Acad. Sci. 10: 18-60. Houston, W. R. 1960. Effects of water

Effects of precision demands and mental pressure on muscle activation and hand forces in computer mouse tasks.

PubMed

Visser, Bart; De Looze, Michiel; De Graaff, Matthijs; Van Dieën, Jaap

2004-02-05

The objective of the present study was to gain insight into the effects of precision demands and mental pressure on the load of the upper extremity. Two computer mouse tasks were used: an aiming and a tracking task. Upper extremity loading was operationalized as the myo-electric activity of the wrist flexor and extensor and of the trapezius descendens muscles and the applied grip- and click-forces on the computer mouse. Performance measures, reflecting the accuracy in both tasks and the clicking rate in the aiming task, indicated that the levels of the independent variables resulted in distinguishable levels of accuracy and work pace. Precision demands had a small effect on upper extremity loading with a significant increase in the EMG-amplitudes (21%) of the wrist flexors during the aiming tasks. Precision had large effects on performance. Mental pressure had substantial effects on EMG-amplitudes with an increase of 22% in the trapezius when tracking and increases of 41% in the trapezius and 45% and 140% in the wrist extensors and flexors, respectively, when aiming. During aiming, grip- and click-forces increased by 51% and 40% respectively. Mental pressure had small effects on accuracy but large effects on tempo during aiming. Precision demands and mental pressure in aiming and tracking tasks with a computer mouse were found to coincide with increased muscle activity in some upper extremity muscles and increased force exertion on the computer mouse. Mental pressure caused significant effects on these parameters more often than precision demands. Precision and mental pressure were found to have effects on performance, with precision effects being significant for all performance measures studied and mental pressure effects for some of them. The results of this study suggest that precision demands and mental pressure increase upper extremity load, with mental pressure effects being larger than precision effects. The possible role of precision demands as an indirect mental stressor in working conditions is discussed.

Triple bar, high efficiency mechanical sealer

DOEpatents

Pak, Donald J.; Hawkins, Samantha A.; Young, John E.

2013-03-19

A clamp with a bottom clamp bar that has a planar upper surface is provided. The clamp may also include a top clamp bar connected to the bottom clamp bar, and a pressure distribution bar between the top clamp bar and the bottom clamp bar. The pressure distribution bar may have a planar lower surface in facing relation to the upper surface of the bottom clamp bar. An object is capable of being disposed in a clamping region between the upper surface and the lower surface. The width of the planar lower surface may be less than the width of the upper surface within the clamping region. Also, the pressure distribution bar may be capable of being urged away from the top clamp bar and towards the bottom clamp bar.

Unsteady pressure measurement instrumentation using anodized-aluminium PSP applied in a transonic wind tunnel

NASA Astrophysics Data System (ADS)

Mérienne, Marie-Claire; LeSant, Yves; Ancelle, Jacques; Soulevant, Didier

2004-12-01

The objective of this work is to demonstrate the feasibility of pressure measurement instrumentation using anodized-aluminium pressure-sensitive paint (or AA-PSP) for application in unsteady flows. An anodized procedure was applied to an aluminium tape that can be easily placed on a model even when it is mounted in a wind tunnel. The response time of the PSP coating is assessed using a calibration rig that generates fast pressure steps or sinusoidal pressure fluctuations up to 1 kHz. A pointwise measurement system made with a Cassegrain telescope and a photomultiplier tube was designed to collect the PSP luminescence. The spot displacement on the model surface was carried out by using a 3D moving bench. A camera is used to identify the spot position according to the model geometry. An application in a wind tunnel was performed on a forced shock wave oscillation test, generating amplitude variations up to 25 kPa. The calibration problem due to non-uniformity of the anodized properties did not allow quantitative data processing of pressure levels. Nevertheless frequency analysis demonstrates that the coating is able to follow the pressure fluctuations, as shown by comparison with standard pressure transducers.

Kinetic evolution and correlation of fluctuations in an expanding quark gluon plasma

NASA Astrophysics Data System (ADS)

Sarwar, Golam; Alam, Jan-E.

2018-03-01

Evolution of spatially anisotropic perturbation created in the system formed after Relativistic Heavy Ion Collisions has been studied. The microscopic evolution of the fluctuations has been examined within the ambit of Boltzmann Transport Equation (BTE) in a hydrodynamically expanding background. The expansion of the background composed of quark gluon plasma (QGP) is treated within the framework of relativistic hydrodynamics. Spatial anisotropic fluctuations with different geometries have been evolved through Boltzmann equation. It is observed that the trace of such fluctuation survives the evolution. Within the relaxation time approximation, analytical results have been obtained for the evolution of these anisotropies. Explicit relations between fluctuations and transport coefficients have been derived. The mixing of various Fourier (or k) modes of the perturbations during the evolution of the system has been explicitly demonstrated. This study is very useful in understanding the presumption that the measured anisotropies in the data from heavy ion collisions at relativistic energies imitate the initial state effects. The evolution of correlation function for the perturbation in pressure has been studied and shows that the initial correlation between two neighbouring points in real space evolves to a constant value at later time which gives rise to Dirac delta function for the correlation function in Fourier space. The power spectrum of the fluctuation in thermodynamic quantities (like temperature estimated in this work) can be connected to the fluctuation in transverse momentum of the thermal hadrons measured experimentally. The bulk viscous coefficient of the QGP has been estimated by using correlations of pressure fluctuation with the help of Green-Kubo relation. Angular power spectrum of the anisotropies has been estimated in the appendix.

Measurement of Correlation Between Flow Density, Velocity, and Density*velocity(sup 2) with Far Field Noise in High Speed Jets

NASA Technical Reports Server (NTRS)

Panda, Jayanta; Seasholtz, Richard G.; Elam, Kristie A.

2002-01-01

To locate noise sources in high-speed jets, the sound pressure fluctuations p', measured at far field locations, were correlated with each of radial velocity v, density rho, and phov(exp 2) fluctuations measured from various points in jet plumes. The experiments follow the cause-and-effect method of sound source identification, where correlation is related to the first, and correlation to the second source terms of Lighthill's equation. Three fully expanded, unheated plumes of Mach number 0.95, 1.4 and 1.8 were studied for this purpose. The velocity and density fluctuations were measured simultaneously using a recently developed, non-intrusive, point measurement technique based on molecular Rayleigh scattering. It was observed that along the jet centerline the density fluctuation spectra S(sub rho) have different shapes than the radial velocity spectra S(sub v), while data obtained from the peripheral shear layer show similarity between the two spectra. Density fluctuations in the jet showed significantly higher correlation, than either rhov(sub 2) or v fluctuations. It is found that a single point correlation from the peak sound emitting region at the end of the potential core can account for nearly 10% of all noise at 30 to the jet axis. The correlation, representing the effectiveness of a longitudinal quadrupole in generating noise 90 to the jet axis, is found to be zero within experimental uncertainty. In contrast rhov(exp 2) fluctuations were better correlated with sound pressure fluctuation at the 30 location. The strongest source of sound is found to lie at the centerline and beyond the end of potential core.

Method and apparatus for reducing cleaning blade wear

DOEpatents

Grannes, Steven G.; Rhoades, Charles A.; Hebbie, Terry L.

1992-01-01

An improved cleaning blade construction (10) for eliminating erosion troughs (6) in the upper surface (15) of a cleaning blade member (14) by introducing pressurized fluid through a pressure manifold chamber (16) formed in the upper surface (15) of the cleaning blade member (14). The pressurized fluid will prevent carryback material (7) from passing through a wear groove (6) formed in the cleaning blade member.

Pressure and temperature fluctuation simulation of J-PARC cryogenic hydrogen system

NASA Astrophysics Data System (ADS)

Tatsumoto, H.; Ohtsu, K.; Aso, T.; Kawakami, Y.

2015-12-01

The J-PARC cryogenic hydrogen system provides supercritical cryogenic hydrogen to the moderators at a pressure of 1.5 MPa and temperature of 18 K and removes 3.8 kW of nuclear heat from the 1 MW proton beam operation. We prepared a heater for thermal compensation and an accumulator, with a bellows structure for volume control, to mitigate the pressure fluctuation caused by switching the proton beam on and off. In this study, a 1-D simulation code named DiSC-SH2 was developed to understand the propagation of pressure and temperature propagations through the hydrogen loop due to on and off switching of the proton beam. We confirmed that the simulated dynamic behaviors in the hydrogen loop for 300-kW and 500-kW proton beam operations agree well with the experimental data under the same conditions.

Fatigue life analysis of cracked gas receiver of emergency cut-off system in gas gathering station

NASA Astrophysics Data System (ADS)

Hu, Junzhi; Zhou, Jiyong; Li, Siyuan

2017-06-01

Small-scale air compressor and gas receiver are used as the driving gas of the emergency cut-off system in gas gathering station. Operation of block valve is ensured by starting and stopping compressor automatically. The frequent start-stop of compressor and the pressure fluctuation pose a threat to the service life of gas receiver, and then affect normal operation of the emergency cut-off system and security of gas gathering station. In this paper, the fatigue life of a pressure vessel with axial semi-elliptical surface crack in the inner wall is analyzed under the varying pressure by means of the theory of fracture mechanics. The influences of the amplitude of pressure fluctuation and the initial crack size on the residual life of gas receiver are discussed. It provides a basis for setting the working parameters of gas receiver of emergency cut-off system and determining the maintenance cycle.

Influence of the Proton Pressure Tensor on the Turbulent Velocity Spectrum at Ion Kinetic Scales

NASA Astrophysics Data System (ADS)

Vasquez, B. J.; Markovskii, S.

2011-12-01

Numerical hybrid simulations with particle protons and fluid electrons are presented for turbulent fluctuations with spatial variations in a plane perpendicular to the background magnetic field. The steepened portion of the proton bulk velocity spectrum is found at smaller wavenumbers for larger background proton temperature. The velocity spectrum is determined, in part, by the proton pressure tensor. The proton pressure tensor is shown to possess non-gyrotropic and finite off-diagonal components in the places where the turbulent fluctuations have developed strong gradients. Proton demagnetization at these places is a factor in the departure from a Maxwellian velocity distribution function. How demagnetization could connect with both reversible and effectively irreversible aspects of the pressure tensor is considered. The effectively irreversible aspect corresponds to the net heating of the protons and to the dissipation of the turbulent energy cascade.

Transient simulation of hydropower station with consideration of three-dimensional unsteady flow in turbine

NASA Astrophysics Data System (ADS)

Huang, W. D.; Fan, H. G.; Chen, N. X.

2012-11-01

To study the interaction between the transient flow in pipe and the unsteady turbulent flow in turbine, a coupled model of the transient flow in the pipe and three-dimensional unsteady flow in the turbine is developed based on the method of characteristics and the fluid governing equation in the accelerated rotational relative coordinate. The load-rejection process under the closing of guide vanes of the hydraulic power plant is simulated by the coupled method, the traditional transient simulation method and traditional three-dimensional unsteady flow calculation method respectively and the results are compared. The pressure, unit flux and rotation speed calculated by three methods show a similar change trend. However, because the elastic water hammer in the pipe and the pressure fluctuation in the turbine have been considered in the coupled method, the increase of pressure at spiral inlet is higher and the pressure fluctuation in turbine is stronger.

Pressure dependence of critical temperature of bulk FeSe from spin fluctuation theory

NASA Astrophysics Data System (ADS)

Hirschfeld, Peter; Kreisel, Andreas; Wang, Yan; Tomic, Milan; Jeschke, Harald; Jacko, Anthony; Valenti, Roser; Maier, Thomas; Scalapino, Douglas

2013-03-01

The critical temperature of the 8K superconductor FeSe is extremely sensitive to pressure, rising to a maximum of 40K at about 10GPa. We test the ability of the current generation of fluctuation exchange pairing theories to account for this effect, by downfolding the density functional theory electronic structure for each pressure to a tight binding model. The Fermi surface found in such a procedure is then used with fixed Hubbard parameters to determine the pairing strength using the random phase approximation for the spin singlet pairing vertex. We find that the evolution of the Fermi surface captured by such an approach is alone not sufficient to explain the observed pressure dependence, and discuss alternative approaches. PJH, YW, AK were supported by DOE DE-FG02-05ER46236, the financial support of MT, HJ, and RV from the DFG Schwerpunktprogramm 1458 is kindly acknowledged.

Measurements of Flow Turbulence in the NASA Langley Transonic Dynamics Tunnel

NASA Technical Reports Server (NTRS)

Wiesman, Carol D.; Sleeper, Robert K.

2005-01-01

An assessment of the flow turbulence in the NASA Langley Transonic Dynamics Tunnel (TDT) was conducted during calibration activities following the facility conversion from a Freon-12 heavy-gas test medium to an R134a heavy-gas test medium. Total pressure, static pressure, and acoustic pressure levels were measured at several locations on a stingmounted rake. The test measured wall static pressures at several locations although this paper presents only those from one location. The test used two data acquisition systems, one sampling at 1000 Hz and the second sampling at 125 000 Hz, for acquiring time-domain data. This paper presents standard deviations and power spectral densities of the turbulence points throughout the wind tunnel envelope in air and R134a. The objective of this paper is to present the turbulence characteristics for the test section. No attempt is made to assess the causes of the turbulence. The present paper looks at turbulence in terms of pressure fluctuations. Reference 1 looked at tunnel turbulence in terms of velocity fluctuations.

Experimental investigation into vortex structure and pressure drop across microcavities in 3D integrated electronics

NASA Astrophysics Data System (ADS)

Renfer, Adrian; Tiwari, Manish K.; Brunschwiler, Thomas; Michel, Bruno; Poulikakos, Dimos

2011-09-01

Hydrodynamics in microcavities with cylindrical micropin fin arrays simulating a single layer of a water-cooled electronic chip stack is investigated experimentally. Both inline and staggered pin arrangements are investigated using pressure drop and microparticle image velocimetry (μPIV) measurements. The pressure drop across the cavity shows a flow transition at pin diameter-based Reynolds numbers ( Re d ) ~200. Instantaneous μPIV, performed using a pH-controlled high seeding density of tracer microspheres, helps visualize vortex structure unreported till date in microscale geometries. The post-transition flow field shows vortex shedding and flow impingement onto the pins explaining the pressure drop increase. The flow fluctuations start at the chip outlet and shift upstream with increasing Re d . No fluctuations are observed for a cavity with pin height-to-diameter ratio h/ d = 1 up to Re d ~330; however, its pressure drop was higher than for a cavity with h/d = 2 due to pronounced influence of cavity walls.

Ocean Acidification Alters the Photosynthetic Responses of a Coccolithophorid to Fluctuating Ultraviolet and Visible Radiation1[OPEN

PubMed Central

Jin, Peng; Gao, Kunshan; Villafañe, Virginia E.; Campbell, Douglas A.; Helbling, E. Walter

2013-01-01

Mixing of seawater subjects phytoplankton to fluctuations in photosynthetically active radiation (400–700 nm) and ultraviolet radiation (UVR; 280–400 nm). These irradiance fluctuations are now superimposed upon ocean acidification and thinning of the upper mixing layer through stratification, which alters mixing regimes. Therefore, we examined the photosynthetic carbon fixation and photochemical performance of a coccolithophore, Gephyrocapsa oceanica, grown under high, future (1,000 μatm) and low, current (390 μatm) CO2 levels, under regimes of fluctuating irradiances with or without UVR. Under both CO2 levels, fluctuating irradiances, as compared with constant irradiance, led to lower nonphotochemical quenching and less UVR-induced inhibition of carbon fixation and photosystem II electron transport. The cells grown under high CO2 showed a lower photosynthetic carbon fixation rate but lower nonphotochemical quenching and less ultraviolet B (280–315 nm)-induced inhibition. Ultraviolet A (315–400 nm) led to less enhancement of the photosynthetic carbon fixation in the high-CO2-grown cells under fluctuating irradiance. Our data suggest that ocean acidification and fast mixing or fluctuation of solar radiation will act synergistically to lower carbon fixation by G. oceanica, although ocean acidification may decrease ultraviolet B-related photochemical inhibition. PMID:23749851

Simulations of Instabilities in Complex Valve and Feed Systems

NASA Technical Reports Server (NTRS)

Ahuja, Vineet; Hosangadi, Ashvin; Shipman, Jeremy; Cavallo, Peter A.

2006-01-01

CFD analyses are playing an increasingly important role in identifying and characterizing flow induced instabilities in rocket engine test facilities and flight systems. In this paper, we analyze instability mechanisms that range from turbulent pressure fluctuations due to vortex shedding in structurally complex valve systems to flow resonance in plug cavities to large scale pressure fluctuations due to collapse of cavitation induced vapor clouds. Furthermore, we discuss simulations of transient behavior related to valve motion that can serve as guidelines for valve scheduling. Such predictions of valve response to varying flow conditions is of crucial importance to engine operation and testing.

Numerical simulation of soft palate movement and airflow in human upper airway by fluid-structure interaction method

NASA Astrophysics Data System (ADS)

Sun, Xiuzhen; Yu, Chi; Wang, Yuefang; Liu, Yingxi

2007-08-01

In this paper, the authors present airflow field characteristics of human upper airway and soft palate movement attitude during breathing. On the basis of the data taken from the spiral computerized tomography images of a healthy person and a patient with Obstructive Sleep Apnea-Hypopnea Syndrome (OSAHS), three-dimensional models of upper airway cavity and soft palate are reconstructed by the method of surface rendering. Numerical simulation is performed for airflow in the upper airway and displacement of soft palate by fluid-structure interaction analysis. The reconstructed three-dimensional models precisely preserve the original configuration of upper airways and soft palate. The results of the pressure and velocity distributions in the airflow field are quantitatively determined, and the displacement of soft palate is presented. Pressure gradients of airway are lower for the healthy person and the airflow distribution is quite uniform in the case of free breathing. However, the OSAHS patient remarkably escalates both the pressure and velocity in the upper airway, and causes higher displacement of the soft palate. The present study is useful in revealing pathogenesis and quantitative mutual relationship between configuration and function of the upper airway as well as in diagnosing diseases related to anatomical structure and function of the upper airway.

Fitness consequences of avian personalities in a fluctuating environment.

PubMed Central

Dingemanse, Niels J.; Both, Christiaan; Drent, Piet J.; Tinbergen, Joost M.

2004-01-01

Individual animals differ in the way they cope with challenges in their environment, comparable with variation in human personalities. The proximate basis of variation in personality traits has received considerable attention, and one general finding is that personality traits have a substantial genetic basis. This poses the question of how variation in personality is maintained in natural populations. We show that selection on a personality trait with high heritability fluctuates across years within a natural bird population. Annual adult survival was related to this personality trait (behaviour in novel environments) but the effects were always opposite for males and females, and reversed between years. The number of offspring surviving to breeding was also related to their parents' personalities, and again selection changed between years. The observed annual changes in selection pressures coincided with changes in environmental conditions (masting of beeches) that affect the competitive regimes of the birds. We expect that the observed fluctuations in environmental factors lead to fluctuations in competition for space and food, and these, in association with variations in population density, lead to a variation in selection pressure, which maintains genetic variation in personalities. PMID:15255104

Range-dependence of acoustic channel with traveling sinusoidal surface wave.

PubMed

Choo, Youngmin; Seong, Woojae; Lee, Keunhwa

2014-04-01

Range-dependence of time-varying acoustic channels caused by a traveling surface wave is investigated through water tank experiments and acoustic propagation analysis schemes. As the surface wave travels, surface reflected signals fluctuate and the fluctuation varies with source-receiver horizontal range. Amplitude fluctuations of surface reflected signals increase with increasing horizontal range whereas the opposite occurs in delay fluctuations. The scattered pressure field at a fixed time shows strong dependence on the receiver position because of caustics and shadow zones formed by the surface. The Doppler shifts of surface reflected signals also depend on the horizontal range. Comparison between measurement data and model results indicates the Doppler shift relies on the delay fluctuation under current experimental conditions.

Prediction model of velocity field around circular cylinder over various Reynolds numbers by fusion convolutional neural networks based on pressure on the cylinder

NASA Astrophysics Data System (ADS)

Jin, Xiaowei; Cheng, Peng; Chen, Wen-Li; Li, Hui

2018-04-01

A data-driven model is proposed for the prediction of the velocity field around a cylinder by fusion convolutional neural networks (CNNs) using measurements of the pressure field on the cylinder. The model is based on the close relationship between the Reynolds stresses in the wake, the wake formation length, and the base pressure. Numerical simulations of flow around a cylinder at various Reynolds numbers are carried out to establish a dataset capturing the effect of the Reynolds number on various flow properties. The time series of pressure fluctuations on the cylinder is converted into a grid-like spatial-temporal topology to be handled as the input of a CNN. A CNN architecture composed of a fusion of paths with and without a pooling layer is designed. This architecture can capture both accurate spatial-temporal information and the features that are invariant of small translations in the temporal dimension of pressure fluctuations on the cylinder. The CNN is trained using the computational fluid dynamics (CFD) dataset to establish the mapping relationship between the pressure fluctuations on the cylinder and the velocity field around the cylinder. Adam (adaptive moment estimation), an efficient method for processing large-scale and high-dimensional machine learning problems, is employed to implement the optimization algorithm. The trained model is then tested over various Reynolds numbers. The predictions of this model are found to agree well with the CFD results, and the data-driven model successfully learns the underlying flow regimes, i.e., the relationship between wake structure and pressure experienced on the surface of a cylinder is well established.

Space-Time Correlations and Spectra of Wall Pressure in a Turbulent Boundary Layer

NASA Technical Reports Server (NTRS)

Willmarth, W. W.

1959-01-01

Measurements of the statistical properties of the fluctuating wall pressure produced by a subsonic turbulent boundary layer are described. The measurements provide additional information about the structure of the turbulent boundary layer; they are applicable to the problems of boundary-layer induced noise inside an airplane fuselage and to the generation of waves-on water. The spectrum of the wall pressure is presented in dimensionless form. The ratio of the root-mean-square wall pressure to the free-stream dynamic pressure is found to be a constant square root of bar P(sup 2)/q(sub infinity) = 0.006 independent of Mach number and Reynolds number. In addition, space- time correlation measurements in the stream direction show that pressure fluctuations whose scale is greater than or equal to 0.3 times the boundary-layer thickness are convected with the convection speed U(sub c) = 0.82U(sub infinity) where U(infinity) is the free-stream velocity and have lost their identity in a distance approximately equal to 10 boundary-layer thicknesses.

An Assessment of Combustion Dynamics in a Low-Nox, Second-Generation Swirl-Venturi Lean Direct Injection Combustion Concept

NASA Technical Reports Server (NTRS)

Tacina, K. M.; Chang, C. T.; Lee, P.; Mongia, H.; Podboy, D. P.; Dam, B.

2015-01-01

Dynamic pressure measurements were taken during flame-tube emissions testing of three second-generation swirl-venturi lean direct injection (SV-LDI) combustor configurations. These measurements show that combustion dynamics were typically small. However, a small number of points showed high combustion dynamics, with peak-to-peak dynamic pressure fluctuations above 0.5 psi. High combustion dynamics occurred at low inlet temperatures in all three SV-LDI configurations, so combustion dynamics were explored further at low temperature conditions. A point with greater than 1.5 psi peak-to-peak dynamic pressure fluctuations was identified at an inlet temperature of 450!F, a pressure of 100 psia, an air pressure drop of 3%, and an overall equivalence ratio of 0.35. This is an off design condition: the temperature and pressure are typical of 7% power conditions, but the equivalence ratio is high. At this condition, the combustion dynamics depended strongly on the fuel staging. Combustion dynamics could be reduced significantly without changing the overall equivalence ratio by shifting the fuel distribution between stages. Shifting the fuel distribution also decreased NOx emissions.

Unsteady loads due to propulsive lift configurations. Part C: Development of experimental techniques for investigation of unsteady pressures behind a cold model jet

NASA Technical Reports Server (NTRS)

Haviland, J. K.; Schroeder, J. C.

1978-01-01

As part of an overall study of the scaling laws for the fluctuating pressures induced on the wings and flaps of STOL aircraft by jet engine impingement, an experimental investigation was made of the near field fluctuating pressures behind a cold circular jet, both when it was free and when it was impinging on a flat plate. Miniature static pressure probes were developed for measurements in the free jet and on the flat plate which were connected by plastic tubing to 1/8 inch microphones and acted as pressure transducers. Using a digital correlator together with an FFT program on the CDC 6400 computer, spectral densities, relative amplitudes, phase lags, and coherences were also obtained for the signals from pairs of these probes, and were used to calibrate these probes directly against microphones. This system of instrumentation was employed to obtain single point rms and third octave surveys of the static pressures in the free jet and on the surface of the plate.

Upper Tropospheric Ozone Between Latitudes 60S and 60N Derived from Nimbus 7 TOMS/THIR Cloud Slicing

NASA Technical Reports Server (NTRS)

Ziemke, Jerald R.; Chandra, Sushil; Bhartia, P. K.

2002-01-01

This study evaluates the spatial distributions and seasonal cycles in upper tropospheric ozone (pressure range 200-500 hPa) from low to high latitudes (60S to 60N) derived from the satellite retrieval method called "Cloud Slicing." Cloud Slicing is a unique technique for determining ozone profile information in the troposphere by combining co-located measurements of cloud-top, pressure and above-cloud column ozone. For upper tropospheric ozone, co-located measurements of Nimbus 7 Total Ozone Mapping Spectrometer (TOMS) above-cloud column ozone, and Nimbus 7 Temperature Humidity Infrared Radiometer (THIR) cloud-top pressure during 1979-1984 were incorporated. In the tropics, upper tropospheric ozone shows year-round enhancement in the Atlantic region and evidence of a possible semiannual variability. Upper tropospheric ozone outside the tropics shows greatest abundance in winter and spring seasons in both hemispheres with largest seasonal and largest amounts in the NH. These characteristics are similar to lower stratospheric ozone. Comparisons of upper tropospheric column ozone with both stratospheric ozone and a proxy of lower stratospheric air mass (i.e., tropopause pressure) from National Centers for Environmental Prediction (NCEP) suggest that stratosphere-troposphere exchange (STE) may be a significant source for the seasonal variability of upper tropospheric ozone almost everywhere between 60S and 60N except in low latitudes around 10S to 25N where other sources (e.g., tropospheric transport, biomass burning, aerosol effects, lightning, etc.) may have a greater role.

Significance of the antireflux valve for upper urinary tract pressure. An experimental study in patients with urinary diversion via a continent ileal reservoir.

PubMed

Berglund, B; Brevinge, H; Akerlund, S; Kock, N G

1992-01-01

When bladder substitution is required, a low pressure receptacle and an antireflux valve with low resistance to flow is essential for preservation of the upper urinary tract. The aim of this study was to evaluate whether these criteria are attained in the continent ileal reservoir used for urinary diversion. The investigations were performed in six patients more than one year after supravesical urinary diversion via a continent ileal reservoir. The pressure was recorded simultaneously both in the afferent loop and in the reservoir during filling of the reservoir. There was a slow parallel increase in the basal pressure in the reservoir and the afferent loop. Pressure waves appeared sometimes simultaneously and sometimes in only one compartment at a time. Only during short periods of time did the pressure exceed 25 cm of water. The frequency of pressure waves increased with increased filling of the reservoir. The "total pressure" was larger in the reservoir than in the afferent loop. It is the antireflux valve which prevents pressure rises in the reservoir from being conveyed to the upper urinary tract. The resistance to urinary flow was moderate.

73. DETAIL OF LIQUID OXYGEN STORAGE PRESSURE GAUGE IN UPPER ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

73. DETAIL OF LIQUID OXYGEN STORAGE PRESSURE GAUGE IN UPPER LEFT CORNER OF WEST SIDE OF CENTER SKID IN CA-133-1-C-69 - Vandenberg Air Force Base, Space Launch Complex 3, Launch Pad 3 West, Napa & Alden Roads, Lompoc, Santa Barbara County, CA

Support of selected X-ray studies to be performed using data from the Uhuru (SAS-A) satellite

NASA Technical Reports Server (NTRS)

Garmire, G. P.

1976-01-01

A new measurement of the diffuse X-ray emission sets more stringent upper limits on the fluctuations of the background and on the number counts of X-ray sources with absolute value of b 20 deg than previous measurements. A random sample of background data from the Uhuru satellite gives a relative fluctuation in excess of statistics of 2.0% between 2.4 and 6.9 keV. The hypothesis that the relative fluctuation exceeds 2.9% can be rejected at the 90% confidence level. No discernable energy dependence is evident in the fluctuations in the pulse height data, when separated into three energy channels of nearly equal width from 1.8 to 10.0 keV. The probability distribution of fluctuations was convolved with the photon noise and cosmic ray background deviation (obtained from the earth-viewing data) to yield the differential source count distribution for high latitude sources. Results imply that a maximum of 160 sources could be between 1.7 and 5.1 x 10 to the -11 power ergs/sq cm/sec (1-3 Uhuru counts).

Observations of rapid changes in N:P ratio associated with non-Redfield nutrient utilization in mesoscale eddies in the upper ocean

NASA Astrophysics Data System (ADS)

Dai, M.; Xu, Y.; Kao, S. J.; Huang, B.; Sun, J.; Sun, Z.

2016-02-01

The concept of Redfield Ratio,or the ocean's nutrient stoichiometry has been fundamental to understanding the ocean biogeochemistry, reflecting the balance of elements between the organisms and the chemical environment and thereby modulating to a large extent the metabolic status of an ecosystem as well as the ecosystem structure. Nutrient stoichiometry of the deep ocean as a consequence of the organic matter regeneration therein is very much homogeneous worldwide while at the upper ocean, changes in nutrient stoichiometryas being frequently observed are to be better understood in terms of their mechanism. Here we report direct observations of fast on a weekly time scale and large fluctuations of nitrate+nitrite (N+N) to soluble reactive phosphorus (SRP) ratios in the ambient seawater in responding to development of meso-scale eddies in an oligotrophic sea, the South China Sea. At the spin up and/or matured stages of eddies, the N:P ratio fluctuated up to 44 in the upper 100 m water column. Along the decay of theeddy, N:P ratio declined back to 3- 20; similar to a "no eddy" condition of 4-22. Along with the fluctuations of N:P ratio was the diatom dominance with the eddy development, while the community structure of the region in typical or non-eddy conditions was predominated by the pico-/nano-plankton as revealed by both the taxa identification and biogenic silicate measurements. This fast growing diatom group apparently had lower nutrient utilization of nitrogenrelative to silicate and/or phosphorus, augmenting the ambient seawater N:P and N:Si. Such preferential P utilization therefore by the fast growing diatomsresulted in significant variations during the different stages of the eddy development.

Spontaneous fluctuations in cerebral blood flow: insights from extended-duration recordings in humans

NASA Technical Reports Server (NTRS)

Zhang, R.; Zuckerman, J. H.; Levine, B. D.; Blomqvist, C. G. (Principal Investigator)

2000-01-01

To determine the dependence of cerebral blood flow (CBF) on arterial pressure over prolonged time periods, we measured beat-to-beat changes in mean CBF velocity in the middle cerebral artery (transcranial Doppler) and mean arterial pressure (Finapres) continuously for 2 h in six healthy subjects (5 men and 1 woman, 18-40 yr old) during supine rest. Fluctuations in velocity and pressure were quantified by the range [(peak - trough)/mean] and coefficients of variation (SD/mean) in the time domain and by spectral analysis in the frequency domain. Mean velocity and pressure over the 2-h recordings were 60 +/- 7 cm/s and 83 +/- 8 mmHg, associated with ranges of 77 +/- 8 and 89 +/- 10% and coefficients of variation of 9.3 +/- 2.2 and 7.9 +/- 2.3%, respectively. Spectral power of the velocity and pressure was predominantly distributed in the frequency range of 0.00014-0.1 Hz and increased inversely with frequency, indicating characteristics of an inverse power law (1/f(alpha)). However, linear regression on a log-log scale revealed that the slope of spectral power of pressure and velocity was steeper in the high-frequency (0.02-0.5 Hz) than in the low-frequency range (0.002-0.02 Hz), suggesting different regulatory mechanisms in these two frequency ranges. Furthermore, the spectral slope of pressure was significantly steeper than that of velocity in the low-frequency range, consistent with the low transfer function gain and low coherence estimated at these frequencies. We conclude that 1) long-term fluctuations in CBF velocity are prominent and similar to those observed in arterial pressure, 2) spectral power of CBF velocity reveals characteristics of 1/f(alpha), and 3) cerebral attenuation of oscillations in CBF velocity in response to changes in pressure may be more effective at low than that at high frequencies, emphasizing the frequency dependence of cerebral autoregulation.

Effects of Rotor Blade Scaling on High-Pressure Turbine Unsteady Loading

NASA Astrophysics Data System (ADS)

Lastiwka, Derek; Chang, Dongil; Tavoularis, Stavros

2013-03-01

The present work is a study of the effects of rotor blade scaling of a single-stage high pressure turbine on the time-averaged turbine performance and on parameters that influence vibratory stresses on the rotor blades and stator vanes. Three configurations have been considered: a reference case with 36 rotor blades and 24 stator vanes, a case with blades upscaled by 12.5%, and a case with blades downscaled by 10%. The present results demonstrate that blade scaling effects were essentially negligible on the time-averaged turbine performance, but measurable on the unsteady surface pressure fluctuations, which were intensified as blade size was increased. In contrast, blade torque fluctuations increased significantly as blade size decreased. Blade scaling effects were also measurable on the vanes.

Shape and Displacement Fluctuations in Soft Vesicles Filled by Active Particles

PubMed Central

Paoluzzi, Matteo; Di Leonardo, Roberto; Marchetti, M. Cristina; Angelani, Luca

2016-01-01

We investigate numerically the dynamics of shape and displacement fluctuations of two-dimensional flexible vesicles filled with active particles. At low concentration most of the active particles accumulate at the boundary of the vesicle where positive particle number fluctuations are amplified by trapping, leading to the formation of pinched spots of high density, curvature and pressure. At high concentration the active particles cover the vesicle boundary almost uniformly, resulting in fairly homogeneous pressure and curvature, and nearly circular vesicle shape. The change between polarized and spherical shapes is driven by the number of active particles. The center-of-mass of the vesicle performs a persistent random walk with a long time diffusivity that is strongly enhanced for elongated active particles due to orientational correlations in their direction of propulsive motion. In our model shape-shifting induces directional sensing and the cell spontaneously migrate along the polarization direction. PMID:27678166

Stochastic heating of a single Brownian particle by charge fluctuations in a radio-frequency produced plasma sheath

NASA Astrophysics Data System (ADS)

Schmidt, Christian; Piel, Alexander

2015-10-01

The Brownian motion of a single particle in the plasma sheath is studied to separate the effect of stochastic heating by charge fluctuations from heating by collective effects. By measuring the particle velocities in the ballistic regime and by carefully determining the particle mass from the Epstein drag it is shown that for a pressure of 10 Pa, which is typical of many experiments, the proper kinetic temperature of the Brownian particle remains close to the gas temperature and rises only slightly with particle size. This weak effect is confirmed by a detailed model for charging and charge fluctuations in the sheath. A substantial temperature rise is found for decreasing pressure, which approximately shows the expected scaling with p-2. The system under study is an example for non-equilibrium Brownian motion under the influence of white noise without corresponding dissipation.

Widespread cardiovascular autonomic dysfunction in primary amyloidosis: does spontaneous hyperventilation have a compensatory role against postural hypotension?

PubMed Central

Bernardi, L; Passino, C; Porta, C; Anesi, E; Palladini, G; Merlini, G

2002-01-01

Objective: To investigate the possible causes of abnormal blood pressure control in light chain related (primary, AL) amyloidosis. Design: Cardiovascular, autonomic, and respiratory response to passive tilting were investigated in 51 patients with primary amyloidosis (mean (SEM) age 56 (2) years) and in 20 age matched controls. Spontaneous fluctuations in RR interval, respiration, end tidal carbon dioxide, blood pressure, and skin microcirculation were recorded during supine rest and with tilting. The values were subjected to spectral analysis to assess baroreflex sensitivity and the autonomic modulation of cardiac and vascular responses. Setting: Tertiary referral centre. Results: Autonomic modulation of the heart and blood pressure was nearly absent in the patients with amyloidosis: thus baroreflex sensitivity and the low frequency (0.1 Hz) fluctuations in all cardiovascular signals were severely reduced (p < 0.01 or more), as were respiratory fluctuations in the RR interval, and no change was observed upon tilting. Despite reduced autonomic modulation, blood pressure remained relatively stable in the amyloid group from supine to tilting. End tidal carbon dioxide was reduced in the amyloid patients (p < 0.001) indicating persistent hyperventilation; the breathing rate correlated inversely with the fall in blood pressure on tilting (p < 0.05). Conclusions: In primary amyloidosis, pronounced abnormalities in arterial baroreflexes and cardiovascular autonomic modulation to the heart and the vessels may be partly compensated for by hyperventilation at a slow breathing rate. PMID:12433892

A model investigation of turbulence-driven pressure-pumping effects on the rate of diffusion of CO2, N2O, and CH4 through layered snowpacks

Treesearch

W. J. Massman; R. A. Sommerfeld; A. R. Mosier; K. F. Zeller; T.J . Hehn; S. G. Rochelle

1997-01-01

Pressure pumping at the Earth's surface is caused by short-period atmospheric turbulence, longer-period barometric changes, and quasi-static pressure fields induced by wind blowing across irregular topography. These naturally occurring atmospheric pressure variations induce periodic fluctuations in airflow through snowpacks, soils, and any other porous media at...

Studies of Halogen Bonding Using High-Pressure Diffractometry

DTIC Science & Technology

2007-11-08

mixed at room temperature. The 1:1 cocrystal was melted by heating it to and in the liquid form loaded to a DAC. Single-crystal of each compound or...upper edge. Figure 6. Isochoric growth of the 1,2-diiodoperfluoroethane:1,4-dioxane 1:1 cocrystal : (a) the melting process of the polycrystal...impurities in the mixture, which condensed at high pressure and grouped between the cocrystal upper face (001) and the upper culet. Figure 7. Isochoric

Effects of Age, Gender, Bolus Condition, Viscosity, and Volume on Pharyngeal and Upper Esophageal Sphincter Pressure and Temporal Measurements during Swallowing

ERIC Educational Resources Information Center

Butler, Susan G.; Stuart, Andrew; Castell, Donald; Russell, Gregory B.; Koch, Kenneth; Kemp, Shannon

2009-01-01

Purpose: The purpose of this study was to determine the effects of trial (i.e., Trial 1 vs. Trial 2); viscosity (i.e., saliva, thin, nectar-thick, honey-thick, and pudding-thick water); volume (i.e., 5 mL vs. 10 mL); age (i.e., young vs. older adults); and gender on pharyngeal (i.e., upper and lower) and upper esophageal sphincter (UES) pressures,…

Positive pressure ventilation in a patient with a right upper lobar bronchocutaneous fistula: right upper bronchus occlusion using the cuff of a left-sided double lumen endobronchial tube.

PubMed

Omori, Chieko; Toyama, Hiroaki; Takei, Yusuke; Ejima, Yutaka; Yamauchi, Masanori

2017-08-01

In patients with a bronchocutaneous fistula, positive pressure ventilation leads to air leakage and potential hypoxemia. A male patient with a right upper bronchocutaneous fistula was scheduled for esophageal reconstruction. His preoperative chest computed tomography image revealed aeration in the right middle and lower lobe, a large bulla in the left upper lobe, and pleural effusion and pneumonia in the left lower lobe. Therefore, left one-lung ventilation was considered to result in hypoxemia. Before anesthesia induction, the bronchocutaneous fistula was covered with gauze and film to prevent air leakage. After anesthesia induction, mask ventilation was performed with a peak positive pressure of 10 cmH 2 O. A left-sided double lumen endobronchial tube (DLT) was then inserted into the right main bronchus for occluding only the right superior bronchus, and two-lung ventilation was performed to minimize airway pressure and maintain oxygenation, which did not cause air leakage through the fistula. During anesthesia, no ventilation-related difficulty was faced. The method of inserting a left-sided DLT into the right main bronchus and occluding the right upper bronchus selectively by bronchial cuff is considered to be an option for mechanical ventilation in patients with a right upper bronchial fistula, as demonstrated in the present case.

Carbon Dioxide Fluctuations in Comet Hartley 2

NASA Image and Video Library

2010-11-04

The upper panel of this figure shows small images of comet Hartley 2 taken by NASA EPOXI mission over time. The lower panel is a graph showing the variation of total brightness, and the variation of the total amount of carbon dioxide, during the time.

Optimal scheduling and its Lyapunov stability for advanced load-following energy plants with CO 2 capture

DOE PAGES

Bankole, Temitayo; Jones, Dustin; Bhattacharyya, Debangsu; ...

2017-11-03

In this study, a two-level control methodology consisting of an upper-level scheduler and a lower-level supervisory controller is proposed for an advanced load-following energy plant with CO 2 capture. With the use of an economic objective function that considers fluctuation in electricity demand and price at the upper level, optimal scheduling of energy plant electricity production and carbon capture with respect to several carbon tax scenarios is implemented. The optimal operational profiles are then passed down to corresponding lower-level supervisory controllers designed using a methodological approach that balances control complexity with performance. Finally, it is shown how optimal carbon capturemore » and electricity production rate profiles for an energy plant such as the integrated gasification combined cycle (IGCC) plant are affected by electricity demand and price fluctuations under different carbon tax scenarios. As a result, the paper also presents a Lyapunov stability analysis of the proposed scheme.« less

Optimal scheduling and its Lyapunov stability for advanced load-following energy plants with CO 2 capture

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bankole, Temitayo; Jones, Dustin; Bhattacharyya, Debangsu

In this study, a two-level control methodology consisting of an upper-level scheduler and a lower-level supervisory controller is proposed for an advanced load-following energy plant with CO 2 capture. With the use of an economic objective function that considers fluctuation in electricity demand and price at the upper level, optimal scheduling of energy plant electricity production and carbon capture with respect to several carbon tax scenarios is implemented. The optimal operational profiles are then passed down to corresponding lower-level supervisory controllers designed using a methodological approach that balances control complexity with performance. Finally, it is shown how optimal carbon capturemore » and electricity production rate profiles for an energy plant such as the integrated gasification combined cycle (IGCC) plant are affected by electricity demand and price fluctuations under different carbon tax scenarios. As a result, the paper also presents a Lyapunov stability analysis of the proposed scheme.« less

Gas-dynamic modeling of gas flow in semi-closed space including channel surface fluctuation

NASA Astrophysics Data System (ADS)

Petrova, E. N.; Salnikov, A. F.

2016-10-01

In this article frequency interaction conditions, that affect on acoustic stability of solid-propellant rocket engine (SPRE) action, and its influence on level change of pressure fluctuations with longitudinal gas oscillations in the combustion chamber (CC) are considered. Studies of CC in the assessment of the operating rocket engine stability are reported.

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

University of Washington Graduate Student Jesse Anderson tries to find her cabin onboard the Woods Hole Oceanographic Institution research vessel Knorr on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. Anderson will work with the Argo Floats instruments in the Atlantic Ocean as part of the Salinity Processes in the Upper Ocean Regional Study (SPURS) which is set to sail on Sept. 6. The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

Woods Hole Oceanographic Institution Senior Engineer Steve Faluotico works on the SPURS buoy prior to it being loaded onto the Institute's research vessel Knorr, Tuesday, Sept. 4, 2012, in Woods Hole, Mass. The SPURS buoy will be deployed in the Atlantic Ocean as part of the Salinity Processes in the Upper Ocean Regional Study (SPURS) which is set to sail on Sept. 6. The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-05

An worker prepares to attached a crane hook onto a sensor-laden buoy so that it may be loaded onboard the Woods Hole Oceanographic Institution's research vessel Knorr on wednesday, Sept. 5, 2012, in Woods Hole, Mass. The buoy will be deployed in the Atlantic Ocean as part of the Salinity Processes in the Upper Ocean Regional Study (SPURS) which is set to sail on Sept. 6. The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

Sean Whelan, a Marine Technician for the Woods Hole Oceanographic Institution, prepares CTD instruments used to measure Conductivity, Temperature, and Depth, onboard the Institute's research vessel Knorr on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. The CTDs will be deployed in the Atlantic Ocean as part of the Salinity Processes in the Upper Ocean Regional Study (SPURS) which is set to sail on Sept. 6. The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

NASA Physical Oceanography Program Scientist Eric Lindstrom inspects a sensor-laden buoy prior to it being loaded onboard the Woods Hole Oceanographic Institution's vessel Knorr on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. The buoy will be deployed in the Atlantic Ocean as part of the Salinity Processes in the Upper Ocean Regional Study (SPURS) which is set to sail on Sept. 6. The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

University of Washington Applied Physics Laboratory Senior Oceanographer Andrey Shcherbina, left, and University of Washington Applied Physics Laboratory Senior Principal Oceanographer Jason Gobat work one of their instruments onboard the Woods Hole Oceanographic Institution's research vessel Knorr on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. Knorr is scheduled to depart on Sept. 6 to take part in the Salinity Processes in the Upper Ocean Regional Study (SPURS). The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

Salinity Processes in the Upper Ocean Regional Study (SPURS)

NASA Image and Video Library

2012-09-04

University of Washington Applied Physics Laboratory Senior Oceanographer Andrey Shcherbina, left, and University of Washington Applied Physics Laboratory Senior Principal Oceanographer Jason Gobat carry one of their instruments onboard the Woods Hole Oceanographic Institution's research vessel Knorr on Tuesday, Sept. 4, 2012, in Woods Hole, Mass. Knorr is scheduled to depart on Sept. 6 to take part in the Salinity Processes in the Upper Ocean Regional Study (SPURS). The NASA-sponsored expedition will sail to the North Atlantic's saltiest spot to get a detailed, 3-D picture of how salt content fluctuates in the ocean's upper layers and how these variations are related to shifts in rainfall patterns around the planet. Photo Credit: (NASA/Bill Ingalls)

AN INVESTIGATION OF SITE CHARACTERISTICS CONTROLLING AIRFLOW INTO AND OUT OF THE SHALLOW UNSATURATED ZONE IN RESPONSE TO ATMOSPHERIC PRESSURE CHANGES

EPA Science Inventory

Atmospheric pressure near the land surface is constantly changing, due both to short-term diurnal temperature fluctuations as well as longer-term cycles due to the passage of high-and-low-pressure weather systems. Depending upon soil properties, such as air-filled porosity and a...

Decadal variability of precipitation over Western North America

USGS Publications Warehouse

Cayan, D.R.; Dettinger, M.D.; Diaz, Henry F.; Graham, N.E.

1998-01-01

Decadal (>7- yr period) variations of precipitation over western North America account for 20%-50% of the variance of annual precipitation. Spatially, the decadal variability is broken into several regional [O(1000 km)] components. These decadal variations are contributed by fluctuations in precipitation from seasons of the year that vary from region to region and that are not necessarily concentrated in the wettest season(s) alone. The precipitation variations are linked to various decadal atmospheric circulation and SST anomaly patterns where scales range from regional to global scales and that emphasize tropical or extratropical connections, depending upon which precipitation region is considered. Further, wet or dry decades are associated with changes in frequency of at least a few short-period circulation 'modes' such as the Pacific-North American pattern. Precipitation fluctuations over the southwestern United States and the Saskatchewan region of western Canada are associated with extensive shifts of sea level pressure and SST anomalies, suggesting that they are components of low-frequency precipitation variability from global-scale climate proceses. Consistent with the global scale of its pressure and SST connection, the Southwest decadal precipitation is aligned with opposing precipitation fluctuations in northern Africa.Decadal (>7-yr period) variations of precipitation over western North America account for 20%-50% of the variance of annual precipitation. Spatially, the decadal variability is broken into several regional [O(1000 km)] components. These decadal variations are contributed by fluctuations in precipitation from seasons of the year that vary from region to region and that are not necessarily concentrated in the wettest season(s) alone. The precipitation variations are linked to various decadal atmospheric circulation and SST anomaly patterns where scales range from regional to global scales and that emphasize tropical or extratropical connections, depending upon which precipitation region is considered. Further, wet or dry decades are associated with changes in frequency of at least a few short-period circulation `modes' such as the Pacific-North American pattern. Precipitation fluctuations over the southwestern United States and the Saskatchewan region of western Canada are associated with extensive shifts of sea level pressure and SST anomalies, suggesting that they are components of low-frequency precipitation variability from global-scale climate processes. Consistent with the global scale of its pressure and SST connection, the Southwest decadal precipitation is aligned with opposing precipitation fluctuations in northern Africa.

REACTOR CONTROL

DOEpatents

Fortescue, P.; Nicoll, D.

1962-04-24

A control system employed with a high pressure gas cooled reactor in which a control rod is positioned for upward and downward movement into the neutron field from a position beneath the reactor is described. The control rod is positioned by a coupled piston cylinder releasably coupled to a power drive means and the pressurized coolant is directed against the lower side of the piston. The coolant pressure is offset by a higher fiuid pressure applied to the upper surface of the piston and means are provided for releasing the higher pressure on the upper side of the piston so that the pressure of the coolant drives the piston upwardly, forcing the coupled control rod into the ncutron field of the reactor. (AEC)

Results of coalbed-methane drilling, Mylan Park, Monongalia County, West Virginia: Chapter G.3 in Coal and petroleum resources in the Appalachian basin: distribution, geologic framework, and geochemical character

USGS Publications Warehouse

Ruppert, Leslie F.; Fedorko, Nick; Warwick, Peter D.; Grady, William C.; Britton, James Q.; Schuller, William A.; Crangle, Robert D.; Ruppert, Leslie F.; Ryder, Robert T.

2014-01-01

High-pressure carbon-dioxide adsorption isotherms were measured on composite coal samples of the Upper Kittanning coal bed and the Middle Kittanning and Clarion coal zones. Assuming that the reservoir pressure in the Mylan Park coals is equivalent to the normal hydrostatic pressure, the estimated maximum carbon-dioxide adsorption pressures range from a low of about 300 pounds per square inch (lb/in2 ) in coals from the Clarion coal zone to 500 lb/in2 for coals from the Upper Kittanning coal bed. The estimated maximum methane adsorption isotherms show that the coals from the Upper Kittanning coal bed and the Middle Kittanning coal zone are undersaturated in methane, but coals from the Clarion coal zone are close to saturation.

Does "hidden undercuffing" occur among obese patients? Effect of arm sizes and other predictors of the difference between wrist and upper arm blood pressures.

PubMed

Doshi, Hardik; Weder, Alan B; Bard, Robert L; Brook, Robert D

2010-02-01

Arm size can affect the accuracy of blood pressure (BP) measurement, and "undercuffing" of large upper arms is likely to be a growing problem. Therefore, the authors investigated the relationship between upper arm and wrist readings. Upper arm and wrist circumferences and BP were measured in 261 consecutive patients. Upper arm auscultation and wrist BP was measured in triplicate, rotating measurements every 30 seconds between sites. Upper arm BP was 131.9+/-20.6/71.6+/-12.6 mm Hg in an obese population (body mass index, 30.6+/-6.6 kg/m(2)) with mean upper arm size of 30.7+/-5.1 cm. Wrist BP was higher (2.6+/-9.2 mm Hg and 4.9+/-6.6 mm Hg, respectively, P<.001); however, there was moderate concordance for the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC 7) strata (kappa value=0.27-0.71), and the difference was >or=5 mm Hg in 72% of the patients. The authors conclude that there was poor concordance between arm and wrist BP measurement and found no evidence that "hidden undercuffing" was associated with obesity; therefore, they do not support routine use of wrist BP measurements.

Experimental triplet and quadruplet fluctuation densities and spatial distribution function integrals for pure liquids.

PubMed

Ploetz, Elizabeth A; Karunaweera, Sadish; Smith, Paul E

2015-01-28

Fluctuation solution theory has provided an alternative view of many liquid mixture properties in terms of particle number fluctuations. The particle number fluctuations can also be related to integrals of the corresponding two body distribution functions between molecular pairs in order to provide a more physical picture of solution behavior and molecule affinities. Here, we extend this type of approach to provide expressions for higher order triplet and quadruplet fluctuations, and thereby integrals over the corresponding distribution functions, all of which can be obtained from available experimental thermodynamic data. The fluctuations and integrals are then determined using the International Association for the Properties of Water and Steam Formulation 1995 (IAPWS-95) equation of state for the liquid phase of pure water. The results indicate small, but significant, deviations from a Gaussian distribution for the molecules in this system. The pressure and temperature dependence of the fluctuations and integrals, as well as the limiting behavior as one approaches both the triple point and the critical point, are also examined.

Experimental triplet and quadruplet fluctuation densities and spatial distribution function integrals for pure liquids

NASA Astrophysics Data System (ADS)

Ploetz, Elizabeth A.; Karunaweera, Sadish; Smith, Paul E.

2015-01-01

Fluctuation solution theory has provided an alternative view of many liquid mixture properties in terms of particle number fluctuations. The particle number fluctuations can also be related to integrals of the corresponding two body distribution functions between molecular pairs in order to provide a more physical picture of solution behavior and molecule affinities. Here, we extend this type of approach to provide expressions for higher order triplet and quadruplet fluctuations, and thereby integrals over the corresponding distribution functions, all of which can be obtained from available experimental thermodynamic data. The fluctuations and integrals are then determined using the International Association for the Properties of Water and Steam Formulation 1995 (IAPWS-95) equation of state for the liquid phase of pure water. The results indicate small, but significant, deviations from a Gaussian distribution for the molecules in this system. The pressure and temperature dependence of the fluctuations and integrals, as well as the limiting behavior as one approaches both the triple point and the critical point, are also examined.

Density Fluctuation in Asymmetric Nozzle Plumes and Correlation with Far Field Noise

NASA Technical Reports Server (NTRS)

Panda, J.; Zaman, K. B. M. Q.

2001-01-01

A comparative experimental study of air density fluctuations in the unheated plumes of a circular, 4-tabbed-circular, chevron-circular and 10-lobed rectangular nozzles was performed at a fixed Mach number of 0.95 using a recently developed Rayleigh scattering based technique. Subsequently, the flow density fluctuations are cross-correlated with the far field sound pressure fluctuations to determine sources for acoustics emission. The nearly identical noise spectra from the baseline circular and the chevron nozzles are found to be in agreement with the similarity in spreading, turbulence fluctuations, and flow-sound correlations measured in the plumes. The lobed nozzle produced the least low frequency noise, in agreement with the weakest overall density fluctuations and flow-sound correlation. The tabbed nozzle took an intermediate position in the hierarchy of noise generation, intensity of turbulent fluctuation and flow-sound correlation. Some of the features in the 4-tabbed nozzle are found to be explainable in terms of splitting of the jet in a central large core and 4 side jetlets.

Prediction of heat release effects on a mixing layer

NASA Technical Reports Server (NTRS)

Farshchi, M.

1986-01-01

A fully second-order closure model for turbulent reacting flows is suggested based on Favre statistics. For diffusion flames the local thermodynamic state is related to single conserved scalar. The properties of pressure fluctuations are analyzed for turbulent flows with fluctuating density. Closure models for pressure correlations are discussed and modeled transport equations for Reynolds stresses, turbulent kinetic energy dissipation, density-velocity correlations, scalar moments and dissipation are presented and solved, together with the mean equations for momentum and mixture fraction. Solutions of these equations are compared with the experimental data for high heat release free mixing layers of fluorine and hydrogen in a nitrogen diluent.

Characteristics of turbulence in boundary layer with zero pressure gradient

NASA Technical Reports Server (NTRS)

Klebanoff, P S

1955-01-01

The results of an experimental investigation of a turbulent boundary layer with zero pressure gradient are presented. Measurements with the hot-wire anemometer were made of turbulent energy and turbulent shear stress, probability density and flattening factor of u-fluctuation (fluctuation in x-direction), spectra of turbulent energy and shear stress, and turbulent dissipation. The importance of the region near the wall and the inadequacy of the concept of local isotropy are demonstrated. Attention is given to the energy balance and the intermittent character of the outer region of the boundary layer. Also several interesting features of the spectral distribution of the turbulent motions are discussed.

Core noise measurements on a YF-102 turbofan engine

NASA Technical Reports Server (NTRS)

Reshotko, M.; Karchmer, A. M.; Penko, P. F.; Mcardle, J. G.

1977-01-01

Core noise from a YF-102 high bypass ratio turbofan engine was investigated through the use of simultaneous measurements of internal fluctuating pressures and far field noise. Acoustic waveguide probes, located in the engine at the compressor exit, in the combustor, at the turbine exit, and in the core nozzle, were employed to measure internal fluctuating pressures. Spectra showed that the internal signals were free of tones, except at high frequency where machinery noise was present. Data obtained over a wide range of engine conditions suggest that below 60% of maximum fan speed the low frequency core noise contributes significantly to the far field noise.

Fluctuating Pressure Analysis of a 2-D SSME Nozzle Air Flow Test

NASA Technical Reports Server (NTRS)

Reed, Darren; Hidalgo, Homero

1996-01-01

To better understand the Space Shuttle Main Engine (SSME) startup/shutdown tansients, an airflow test of a two dimensional nozzle was conducted at Marshall Space Flight Center's trisonic wind tunnel. Photographic and other instrumentation show during an SSME start large nozzle shell distortions occur as the Mach disk is passing through the nozzle. During earlier develop of the SSME, this startup transient resulted in low cycle fatigue failure of one of the LH2 feedlines. The two dimensional SSME nozzle test was designed to measure the static and fluctuating pressure environment and color Schlieren video during the startup and shutdown phases of the run profile.

Nanolaser Spectroscopy of Genetically Engineered Yeast: New Tool for a Better Brew?

NASA Astrophysics Data System (ADS)

Gourley, Paul L.; Hendricks, Judy K.; Naviaux, Robert K.; Yaffe, Michael P.

2006-03-01

A basic function of the cell membrane is to selectively uptake ions or molecules from its environment to concentrate them into the interior. This concentration difference results in an osmostic pressure difference across the membrane. Ultimately, this pressure and its fluctuation from cell to cell will be limited by the availability and fluctuations of the solute concentrations in solution, the extent of inter-cell communication, and the state of respiring intracellular mitochondria that fuel the process. To measure these fluctuations, we have employed a high-speed nanolaser technique that samples the osmotic pressure in individual yeast cells and isolated mitochondria. We analyzed 2 yeast cell strains, normal baker’s yeast and a genetically-altered version, that differ only by the presence of mitochondrial DNA. The absence of mitochondrial DNA results in the complete loss of all the mtDNA-encoded proteins and RNAs, and loss of the pigmented, heme-containing cytochromes. These cells have mitochondria, but the mitochondria lack most normal respiratory chain complexes. The frequency distributions in the nanolaser spectra produced by wild-type and modified cells and mitochondria show a striking shift from Gaussian to Poissonian distributions, revealing a powerful novel method for studying statistical physics of yeast.

Gyrokinetic GDC turbulence simulations: confirming a new instability regime in LAPD plasmas

NASA Astrophysics Data System (ADS)

Pueschel, M. J.; Rossi, G.; Told, D.; Terry, P. W.; Jenko, F.; Carter, T. A.

2016-10-01

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.

Extraction of crustal deformations and oceanic fluctuations from ocean bottom pressures

NASA Astrophysics Data System (ADS)

Ariyoshi, Keisuke; Nagano, Akira; Hasegawa, Takuya; Matsumoto, Hiroyuki; Kido, Motoyuki; Igarashi, Toshihiro; Uchida, Naoki; Iinuma, Takeshi; Yamashita, Yusuke

2017-04-01

It has been well known that megathrust earthquakes such as the 2004 Sumatra-Andaman Earthquake (Mw 9.1) and the 2011 the Pacific Coast of Tohoku Earthquake (Mw 9.0) had devastated the coastal areas in the western of Indonesia and in the north-eastern of Japan, respectively. To mitigate the disaster of those forthcoming megathrust earthquakes along Nankai Trough, the Japanese government has established seafloor networks of cable-linked observatories around Japan: DONET (Dense Oceanfloor Network system for Earthquakes and Tsunamis along the Nankai Trough) and S-net (Seafloor Observation Network for Earthquakes and Tsunamis along the Japan Trench). The advantage of the cable-linked network is to monitor the propagation process of tsunami and seismic waves as well as seismic activity in real time. DONET contains pressure gauges as well as seismometers, which are expected to detect crustal deformations driven by peeling off subduction plate coupling process. From our simulation results, leveling changes are different sense among the DONET points even in the same science node. On the other hand, oceanic fluctuations such as melting ice masses through the global warming have so large scale as to cause ocean bottom pressure change coherently for all of DONET points especially in the same node. This difference suggests the possibility of extracting crustal deformations component from ocean bottom pressure data by differential of stacking data. However, this operation cannot be applied to local-scale fluctuations related to ocean mesoscale eddies and current fluctuations, which affect ocean bottom pressure through water density changes in the water column (from the sea surface to the bottom). Therefore, we need integral analysis by combining seismology, ocean physics and tsunami engineering so as to decompose into crustal deformation, oceanic fluctuations and instrumental drift, which will bring about high precision data enough to find geophysical phenomena. In this study, we propose a new interpretation of seismic plate coupling around the Tonankai region along the Nankai Trough, and discuss how to detect it by using the DONET data effectively. In the future, we have to extract the crustal deformation component by separating other components such as instrumental drift and oceanic changes as an integral study collaborated by seismology, geodesy, physical oceanography, and mechanical engineering.

Reed Valve Regulates Welding Back-Purge Pressure

NASA Technical Reports Server (NTRS)

Coby, J. Ben, Jr.; Weeks, Jack L.

1991-01-01

Simple modification yields welds of better quality. Reed valve halves fluctuations in pressure in back-purge chamber attached to workpiece undergoing keyhole plasma arc welding. Identical to one used in fuel system of two-cycle gasoline engine. Backbead smoother, and weld penetrates more uniformly.

Comparison of intraocular pressure fluctuations before and after ab interno trabeculectomy in pseudoexfoliation glaucoma patients

PubMed Central

Tojo, Naoki; Abe, Shinya; Miyakoshi, Mari; Hayashi, Atsushi

2017-01-01

Purpose Ab interno trabeculectomy (AIT) with the Trabectome has been shown to reduce intraocular pressure (IOP) in eyes with pseudoexfoliation (PEX) glaucoma. Here, we examined the change of IOP fluctuations before and after only AIT or AIT with cataract surgery in PEX patients using the contact lens sensor Triggerfish®. Methods This was a prospective open-label study. Twenty-four consecutive patients with PEX glaucoma were included. Twelve patients underwent cataract surgery and AIT (triple-surgery group), and 12 patients underwent only AIT (single-surgery group). In each eye, IOP fluctuations over 24 h were measured with the contact lens sensor before and at 3 months after the surgery. We compared the change of IOP fluctuation before and after operation. We also evaluated the difference in IOP changes between the triple- and single-surgery groups. Results At 3 months after the surgeries, the mean IOP was significantly reduced from 23.5±6.5 mmHg to 14.6±2.8 mmHg in the single-surgery group and from 22.5±3.0 mmHg to 11.5±2.9 mmHg in the triple-surgery group. The mean IOP reduction rate was significantly higher in the triple-surgery group compared to the single-surgery group (p=0.0358). In both groups, the mean range of IOP fluctuations was significantly decreased during nocturnal periods. The mean range of 24 h IOP fluctuations was decreased in the triple-surgery group (p=0.00425), not in the single-surgery group (p=0.970). Conclusion Triple surgery could decrease IOP value and the IOP fluctuations to a greater extent than single surgery in PEX glaucoma patients. PMID:28979095

Tight Budgets and Changing Educational Needs.

ERIC Educational Resources Information Center

OECD Observer, 1984

1984-01-01

Indicates that with fluctuating and falling school populations combined with public expenditure cuts, educational authorities must be more flexible in their allocation of funds. Data on enrollment trends and birth rates, and recommendations related to pre-primary, compulsory, upper secondary, and higher education (and training outside the formal…

Intrinsically-generated fluctuating activity in excitatory-inhibitory networks.

PubMed

Mastrogiuseppe, Francesca; Ostojic, Srdjan

2017-04-01

Recurrent networks of non-linear units display a variety of dynamical regimes depending on the structure of their synaptic connectivity. A particularly remarkable phenomenon is the appearance of strongly fluctuating, chaotic activity in networks of deterministic, but randomly connected rate units. How this type of intrinsically generated fluctuations appears in more realistic networks of spiking neurons has been a long standing question. To ease the comparison between rate and spiking networks, recent works investigated the dynamical regimes of randomly-connected rate networks with segregated excitatory and inhibitory populations, and firing rates constrained to be positive. These works derived general dynamical mean field (DMF) equations describing the fluctuating dynamics, but solved these equations only in the case of purely inhibitory networks. Using a simplified excitatory-inhibitory architecture in which DMF equations are more easily tractable, here we show that the presence of excitation qualitatively modifies the fluctuating activity compared to purely inhibitory networks. In presence of excitation, intrinsically generated fluctuations induce a strong increase in mean firing rates, a phenomenon that is much weaker in purely inhibitory networks. Excitation moreover induces two different fluctuating regimes: for moderate overall coupling, recurrent inhibition is sufficient to stabilize fluctuations; for strong coupling, firing rates are stabilized solely by the upper bound imposed on activity, even if inhibition is stronger than excitation. These results extend to more general network architectures, and to rate networks receiving noisy inputs mimicking spiking activity. Finally, we show that signatures of the second dynamical regime appear in networks of integrate-and-fire neurons.

BRIGHTNESS AND FLUCTUATION OF THE MID-INFRARED SKY FROM AKARI OBSERVATIONS TOWARD THE NORTH ECLIPTIC POLE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pyo, Jeonghyun; Jeong, Woong-Seob; Matsumoto, Toshio

2012-12-01

We present the smoothness of the mid-infrared sky from observations by the Japanese infrared astronomical satellite AKARI. AKARI monitored the north ecliptic pole (NEP) during its cold phase with nine wave bands covering from 2.4 to 24 {mu}m, out of which six mid-infrared bands were used in this study. We applied power-spectrum analysis to the images in order to search for the fluctuation of the sky brightness. Observed fluctuation is explained by fluctuation of photon noise, shot noise of faint sources, and Galactic cirrus. The fluctuations at a few arcminutes scales at short mid-infrared wavelengths (7, 9, and 11 {mu}m)more » are largely caused by the diffuse Galactic light of the interstellar dust cirrus. At long mid-infrared wavelengths (15, 18, and 24 {mu}m), photon noise is the dominant source of fluctuation over the scale from arcseconds to a few arcminutes. The residual fluctuation amplitude at 200'' after removing these contributions is at most 1.04 {+-} 0.23 nW m{sup -2} sr{sup -1} or 0.05% of the brightness at 24 {mu}m and at least 0.47 {+-} 0.14 nW m{sup -2} sr{sup -1} or 0.02% at 18 {mu}m. We conclude that the upper limit of the fluctuation in the zodiacal light toward the NEP is 0.03% of the sky brightness, taking 2{sigma} error into account.« less

Intrinsically-generated fluctuating activity in excitatory-inhibitory networks

PubMed Central

Mastrogiuseppe, Francesca; Ostojic, Srdjan

2017-01-01

Recurrent networks of non-linear units display a variety of dynamical regimes depending on the structure of their synaptic connectivity. A particularly remarkable phenomenon is the appearance of strongly fluctuating, chaotic activity in networks of deterministic, but randomly connected rate units. How this type of intrinsically generated fluctuations appears in more realistic networks of spiking neurons has been a long standing question. To ease the comparison between rate and spiking networks, recent works investigated the dynamical regimes of randomly-connected rate networks with segregated excitatory and inhibitory populations, and firing rates constrained to be positive. These works derived general dynamical mean field (DMF) equations describing the fluctuating dynamics, but solved these equations only in the case of purely inhibitory networks. Using a simplified excitatory-inhibitory architecture in which DMF equations are more easily tractable, here we show that the presence of excitation qualitatively modifies the fluctuating activity compared to purely inhibitory networks. In presence of excitation, intrinsically generated fluctuations induce a strong increase in mean firing rates, a phenomenon that is much weaker in purely inhibitory networks. Excitation moreover induces two different fluctuating regimes: for moderate overall coupling, recurrent inhibition is sufficient to stabilize fluctuations; for strong coupling, firing rates are stabilized solely by the upper bound imposed on activity, even if inhibition is stronger than excitation. These results extend to more general network architectures, and to rate networks receiving noisy inputs mimicking spiking activity. Finally, we show that signatures of the second dynamical regime appear in networks of integrate-and-fire neurons. PMID:28437436

Collisionless Isotropization of the Solar-Wind Protons by Compressive Fluctuations and Plasma Instabilities

NASA Astrophysics Data System (ADS)

Verscharen, D.; Chandran, B. D. G.; Klein, K. G.; Quataert, E.

2016-12-01

Compressive fluctuations are a minor yet significant component of astrophysical plasma turbulence. In the solar wind, long-wavelength compressive slow-mode fluctuations lead to changes in β∥p ≡ 8πnpkBT∥p/B2 and in Rp ≡ T⊥p/T∥p, where T⊥p and T∥p are the perpendicular and parallel temperatures of the protons, B is the magnetic field strength, and np is the proton density. If the amplitude of the compressive fluctuations is large enough, Rp crosses one or more instability thresholds for anisotropy-driven micro-instabilities. The enhanced field fluctuations from these micro-instabilities scatter the protons so as to reduce the anisotropy of the pressure tensor, driving the average value of Rp away from the marginal stability boundary until the fluctuating value of Rp stops crossing the boundary. We model this "fluctuating-anisotropy effect" using linear Vlasov-Maxwell theory to describe the large-scale compressive fluctuations. We show that this effect can explain why, in the nearly collisionless solar wind, the average value of Rp is close to unity.

The relation between skin friction fluctuations and turbulent fluctuating velocities in turbulent boundary layers

NASA Astrophysics Data System (ADS)

Diaz Daniel, Carlos; Laizet, Sylvain; Vassilicos, John Christos

2015-11-01

The Townsend-Perry hypothesis of wall-attached eddies relates the friction velocity uτ at the wall to velocity fluctuations at a position y from the wall, resulting in a wavenumber range where the streamwise fluctuating velocity spectrum scales as E (k) ~k-1 and the corresponding structure function scales as uτ2 in the corresponding length-scale range. However, this model does not take in account the fluctuations of the skin friction velocity, which are in fact strongly intermittent. A DNS of zero-pressure gradient turbulent boundary layer suggests a 10 to 15 degree angle from the lag of the peak in the cross-correlations between the fluctuations of the shear stress and streamwise fluctuating velocities at different heights in the boundary layer. Using this result, it is possible to refine the definition of the attached eddy range of scales, and our DNS suggests that, in this range, the second order structure function depends on filtered skin friction fluctuations in a way which is about the same at different distances from the wall and different local Reynolds numbers.

Excitation, response, and fatigue life estimation methods for the structural design of externally blown flaps

NASA Technical Reports Server (NTRS)

Ungar, E. E.; Chandiramani, K. L.; Barger, J. E.

1972-01-01

Means for predicting the fluctuating pressures acting on externally blown flap surfaces are developed on the basis of generalizations derived from non-dimensionalized empirical data. Approaches for estimation of the fatigue lives of skin-stringer and honeycomb-core sandwich flap structures are derived from vibration response analyses and panel fatigue data. Approximate expressions for fluctuating pressures, structural response, and fatigue life are combined to reveal the important parametric dependences. The two-dimensional equations of motion of multi-element flap systems are derived in general form, so that they can be specialized readily for any particular system. An introduction is presented of an approach to characterizing the excitation pressures and structural responses which makes use of space-time spectral concepts and promises to provide useful insights, as well as experimental and analytical savings.

Aeroacoustic Data for a High Reynolds Number Axisymmetric Subsonic Jet

NASA Technical Reports Server (NTRS)

Ponton, Michael K.; Ukeiley, Lawrence S.; Lee, Sang W.

1999-01-01

The near field fluctuating pressure and aerodynamic mean flow characteristics of a cold subsonic jet issuing from a contoured convergent nozzle are presented. The data are presented for nozzle exit Mach numbers of 0.30, 0.60, and 0.85 at a constant jet stagnation temperature of 104 F. The fluctuating pressure measurements were acquired via linear and semi-circular microphone arrays and the presented results include plots of narrowband spectra, contour maps, streamwise/azimuthal spatial correlations for zero time delay, and cross-spectra of the azimuthal correlations. A pitot probe was used to characterize the mean flow velocity by assuming the subsonic flow to be pressure-balanced with the ambient field into which it exhausts. Presented are mean flow profiles and the momentum thickness of the free shear layer as a function of streamwise position.

Geohydrology of the lower Apalachicola-Chattahoochee-Flint River basin, southwestern Georgia, northwestern Florida, and southeastern Alabama

USGS Publications Warehouse

Torak, Lynn J.; Painter, Jaime A.

2006-01-01

The lower Apalachicola-Chattahoochee-Flint (ACF) River Basin contains about 4,600 square miles of karstic and fluvial plains and nearly 100,000 cubic miles of predominantly karst limestone connected hydraulically to the principal rivers and lakes in the Coastal Plain of southwestern Georgia, northwestern Florida, and southwestern Alabama. Sediments of late-middle Eocene to Holocene in hydraulic connection with lakes, streams, and land surface comprise the surficial aquifer system, upper semiconfining unit, Upper Floridan aquifer, and lower semiconfining unit and contribute to the exchange of ground water and surface water in the stream-lake-aquifer flow system. Karst processes, hydraulic properties, and stratigraphic relations limit ground-water and surface-water interaction to the following hydrologic units of the stream-lake-aquifer flow system: the surficial aquifer system, upper semiconfining unit, Upper Floridan aquifer, and lower confining unit. Geologic units corresponding to these hydrologic units are, in ascending order: Lisbon Formation; Clinchfield Sand; Ocala, Marianna, Suwannee, and Tampa Limestones; Hawthorn Group; undifferentiated overburden (residuum); and terrace and undifferentiated (surficial) deposits. Similarities in hydraulic properties and direct or indirect interaction with surface water allow grouping sediments within these geologic units into the aforementioned hydrologic units, which transcend time-stratigraphic classifications and define the geohydrologic framework for the lower ACF River Basin. The low water-transmitting properties of the lower confining unit, principally the Lisbon Formation, allow it to act as a nearly impermeable base to the stream-lake-aquifer flow system. Hydraulic connection of the surficial aquifer system with surface water and the Upper Floridan aquifer is direct where sandy deposits overlie the limestone, or indirect where fluvial deposits overlie clayey limestone residuum. The water level in perched zones within the surficial aquifer system fluctuates independently of water-level changes in the underlying aquifer, adjacent streams, or lakes. Where the surficial aquifer system is connected with surface water and the Upper Floridan aquifer, water-table fluctuations parallel those in adjacent streams or the underlying aquifer. More...

Some Results Relevant to Statistical Closures for Compressible Turbulence

NASA Technical Reports Server (NTRS)

Ristorcelli, J. R.

1998-01-01

For weakly compressible turbulent fluctuations there exists a small parameter, the square of the fluctuating Mach number, that allows an investigation using a perturbative treatment. The consequences of such a perturbative analysis in three different subject areas are described: 1) initial conditions in direct numerical simulations, 2) an explanation for the oscillations seen in the compressible pressure in the direct numerical simulations of homogeneous shear, and 3) for turbulence closures accounting for the compressibility of velocity fluctuations. Initial conditions consistent with small turbulent Mach number asymptotics are constructed. The importance of consistent initial conditions in the direct numerical simulation of compressible turbulence is dramatically illustrated: spurious oscillations associated with inconsistent initial conditions are avoided, and the fluctuating dilatational field is some two orders of magnitude smaller for a compressible isotropic turbulence. For the isotropic decay it is shown that the choice of initial conditions can change the scaling law for the compressible dissipation. A two-time expansion of the Navier-Stokes equations is used to distinguish compressible acoustic and compressible advective modes. A simple conceptual model for weakly compressible turbulence - a forced linear oscillator is described. It is shown that the evolution equations for the compressible portions of turbulence can be understood as a forced wave equation with refraction. Acoustic modes of the flow can be amplified by refraction and are able to manifest themselves in large fluctuations of the compressible pressure.

Analysis of water levels in the Frenchman Flat area, Nevada Test Site

USGS Publications Warehouse

Bright, D.J.; Watkins, S.A.; Lisle, B.A.

2001-01-01

Analysis of water levels in 21 wells in the Frenchman Flat area, Nevada Test Site, provides information on the accuracy of hydraulic-head calculations, temporal water-level trends, and potential causes of water-level fluctuations. Accurate hydraulic heads are particularly important in Frenchman Flat where the hydraulic gradients are relatively flat (less than 1 foot per mile) in the alluvial aquifer. Temporal water-level trends with magnitudes near or exceeding the regional hydraulic gradient may have a substantial effect on ground-water flow directions. Water-level measurements can be adjusted for the effects of barometric pressure, formation water density (from water-temperature measurements), borehole deviation, and land-surface altitude in selected wells in the Frenchman Flat area. Water levels in one well were adjusted for the effect of density; this adjustment was significantly greater (about 17 feet) than the adjustment of water levels for barometric pressure, borehole deviation, or land-surface altitude (less than about 4 feet). Water-level measurements from five wells exhibited trends that were statistically and hydrologically significant. Statistically significant water-level trends were observed for three wells completed in the alluvial aquifer (WW-5a, UE-5n, and PW-3), for one well completed in the carbonate aquifer (SM-23), and for one well completed in the quartzite confining unit (Army-6a). Potential causes of water-level fluctuations in wells in the Frenchman Flat area include changes in atmospheric conditions (precipitation and barometric pressure), Earth tides, seismic activity, past underground nuclear testing, and nearby pumping. Periodic water-level measurements in some wells completed in the carbonate aquifer indicate cyclic-type water-level fluctuations that generally correlate with longer term changes (more than 5 years) in precipitation. Ground-water pumping fromthe alluvial aquifer at well WW-5c and pumping and discharge from well RNM-2s appear to cause water-level fluctuations in nearby observation wells. The remaining known sources of water-level fluctuations do not appear to substantially affect water-level changes (seismic activity and underground nuclear testing) or do not affect changes over a period of more than 1 year (barometric pressure and Earth tides) in wells in the Frenchman Flat area.

Estimation of Atlantic-Mediterranean netflow variability

NASA Astrophysics Data System (ADS)

Guerreiro, Catarina; Peliz, Alvaro; Miranda, Pedro

2016-04-01

The exchanges at the Strait of Gibraltar are extremely difficult to measure due to the strong temporal and across-strait variabilities; yet the Atlantic inflow into the Mediterranean is extremely important both for climate and to ecosystems. Most of the published numerical modeling studies do not resolve the Strait of Gibraltar realistically. Models that represent the strait at high resolution focus primarily in high frequency dynamics, whereas long-term dynamics are studied in low resolution model studies, and for that reason the Strait dynamics are poorly resolved. Estimating the variability of the exchanges requires long term and high-resolutions studies, thus an improved simulation with explicit and realistic representation of the Strait is necessary. On seasonal to inter-annual timescales the flow is essentially driven by the net evaporation contribution and consequently realistic fields of precipitation and evaporation are necessary for model setup. A comparison between observations, reanalysis and combined products shows ERA-Interim Reanalysis has the most suitable product for Mediterranean Sea. Its time and space variability are in close agreement with NOC 1.1 for the common period (1980 - 1993) and also with evaporation from OAFLUX (1989 - 2014). Subinertial fluctuations, periods from days to a few months, are the second most energetic, after tides, and are the response to atmospheric pressure fluctuations and local winds. Atmospheric pressure fluctuations in the Mediterranean cause sea level oscillations that induce a barotropic flow through the Strait. Candela's analytical model has been used to quantify this response in later studies, though comparison with observations points to an underestimation of the flow at strait. An improved representation of this term contribution to the Atlantic - Mediterranean exchange must be achieved on longer time-scales. We propose a new simulation for the last 36 years (1979 - 2014) for the Mediterranean - Atlantic domain with explicit representation of the Strait. The simulations are performed using the Regional Ocean Modeling System (ROMS) and forced with the different contributions of the freshwater budget, sea level pressure fluctuations and winds from ERA-Interim Reanalysis. The model of sea level pressure induced barotropic fluctuations simulates the barotropic variability at the Strait of Gibraltar for the last decades.

Some observations on the mechanism of aircraft wing rock

NASA Technical Reports Server (NTRS)

Hwang, C.; Pi, W. S.

1978-01-01

A pressure scale model of Northrop F-5A was tested in NASA Ames Research Center Eleven-Foot Transonic Tunnel to simulate the wing rock oscillations in a transonic maneuver. For this purpose, a flexible model support device was designed and fabricated which allowed the model to oscillate in roll at the scaled wing rock frequency. Two tunnel entries were performed to acquire the pressure (steady state and fluctuating) and response data when the model was held fixed and when it was excited by flow to oscillate in roll. Based on these data, a limit cycle mechanism was identified which supplied energy to the aircraft model and caused the Dutch roll type oscillations, commonly called wing rock. The major origin of the fluctuating pressures which contributed to the limit cycle was traced to the wing surface leading edge stall and the subsequent lift recovery. For typical wing rock oscillations, the energy balance between the pressure work input and the energy consumed by the model aerodynamic and mechanical damping was formulated and numerical data presented.

Autonomic control of ultradian and circadian rhythms of blood pressure, heart rate, and baroreflex sensitivity in spontaneously hypertensive rats.

PubMed

Oosting, J; Struijker-Boudier, H A; Janssen, B J

1997-04-01

To examine the influence of the autonomic nervous system on ultradian and circadian rhythms of blood pressure, heart rate and baroreflex sensitivity of heart rate (BRS) in spontaneously hypertensive rats (SHR). Spontaneous fluctuations in blood pressure, heart rate and BRS in SHR were recorded continuously for 24 h using a computerized system and compared with those in Wistar-Kyoto (WKY) rats. Furthermore, 24 h recordings were performed in SHR during cardiac autonomic blockade by metoprolol and methyl-atropine, vascular autonomic blockade by prazosin, ganglionic blockade by hexamethonium and vagal stimulation by a low dose of scopolamine. The magnitudes of the ultradian fluctuations in blood pressure, heart rate and BRS were assessed by wide-band spectral analysis techniques. The BRS was lower in SHR than it was in WKY rats throughout the 24 h cycle. In both strains high values were found during the light, resting period, whereas low values were found during the first hours of the dark, active period. The circadian rhythmicity of the blood pressure in SHR was abolished completely during the infusions of prazosin and hexamethonium. In contrast, the circadian rhythmicities of the blood pressure and heart rate were not altered by infusions of metoprolol, methyl-atropine and the low dose of scopolamine. Power spectra of the blood pressure and heart rate lacked predominant peaks at ultradian frequencies and showed 1/f characteristics. In the absence of autonomic tone, the ultradian fluctuations in heart rate, but not in blood pressure, were decreased. The ultradian BRS spectra had no 1/f shape, but showed a major peak at approximately equal to 20 min for 71% of the WKY rats and 42% of the SHR. The influence of the autonomic nervous system on the blood pressure and heart rats in SHR is frequency-dependent. The circadian, but not ultradian, blood pressure rhythmicity is controlled by vascular autonomic activity. Conversely, the circadian, but not ultradian, heart rate rhythmicity is independent of autonomic tone. In rats, just as in humans, the trough in baroreflex sensitivity occurred after the sleeping period, when locomotor activity is resumed.

Heavy-fermion superconductivity in CeAg2Si2 - Interplay of spin and valence fluctuations

NASA Astrophysics Data System (ADS)

Scheerer, Gernot W.; Ren, Zhi; Lapertot, Gérard; Garbarino, Gaston; Jaccard, Didier

2018-05-01

We present the pressure-temperature phase diagram of the antiferromagnet CeAg2Si2 established via resistivity and calorimetry measurements under quasi-hydrostatic conditions up to 22.5 GPa. With increasing pressure, the Néel temperature [TN (p = 0) = 8.6 K] slowly increases up to TN = 13.4 K at 9.4 GPa and then vanishes abruptly at the magnetic critical pressure pc ∼ 13 GPa. For the first time, heavy fermion superconductivity is observed in CeAg2Si2. Superconductivity emerges at ∼ 11 GPa and persists over roughly 10 GPa. Partial- and bulk-transition temperatures are highest at p = 16 GPa, with a maximal Tcbulk = 1.25 K. In the pressure region of superconductivity, Kondo and crystal-field splitting energies become comparable and resistivity exhibits clear signatures of a Ce-ion valence crossover. The crossover line is located at a rapid collapse in resistivity as function of pressure and extrapolates to a valence transition critical endpoint at critical pressure and temperature of pcr ∼ 17 GPa and Tcr ∼ - 13 K , respectively. Both critical spin and valence fluctuations may build up superconductivity in CeAg2Si2.

The effectiveness of manual versus algometer pressure release techniques for treating active myofascial trigger points of the upper trapezius.

PubMed

Abu Taleb, Walaa; Rehan Youssef, Aliaa; Saleh, Amir

2016-10-01

Manual pressure release (MPR) is a popular treatment of trigger points. Yet, treatment response may be influenced by inconsistent application of pressure. Further, it may contribute to increased risk of work-related musculoskeletal disorders of the wrist and hand in therapists. Therefore, this study aimed at introducing a novel method to apply pressure using the algometer and to compare its effectiveness to MPR. Forty-five volunteers with active trigger points of the upper trapezius received algometer pressure release (APR), MPR, or sham ultrasound (US). Pain pressure threshold (PPT) and contralateral active and passive neck side-bending ranges were assessed at baseline and immediately after a single session. Results showed no significant differences in post-treatment PPT between the study groups (p > 0.05). The APR group showed a significant increase in passive side-bending range compared with the two other groups, whereas active range improved in the APR compared with the US group (p < 0.05). Our results show that using algometer to apply pressure release to upper trapezius trigger points is more effective compared with manual release and sham US. Copyright © 2016 Elsevier Ltd. All rights reserved.

Validation of the SEJOY BP-1307 upper-arm blood pressure monitor for home blood pressure monitoring according to the European Society of Hypertension International Protocol revision 2010.

PubMed

Lei, Lei; Chen, Yi; Chen, Qi; Li, Yan; Wang, Ji-Guang

2017-12-01

The present study aimed to evaluate the accuracy of the automated oscillometric upper-arm blood pressure monitor SEJOY BP-1307 (also called JOYTECH DBP-1307) for home blood pressure monitoring according to the International Protocol of the European Society of Hypertension revision 2010. Systolic and diastolic blood pressures were sequentially measured in 33 adult Chinese individuals (13 women, 45.1 years of mean age) using a mercury sphygmomanometer (two observers) and the SEJOY BP-1307 device (one supervisor). Ninety-nine pairs of comparisons were obtained from 33 participants for judgments in two parts with three grading phases. The average±SD of the device-observer differences was 0.2±4.1 and -1.7±4.7 mmHg for systolic and diastolic blood pressure, respectively. The SEJOY BP-1307 device achieved the criteria in both part 1 and part 2 of the validation study. The SEJOY upper-arm blood pressure monitor BP-1307 has passed the requirements of the International Protocol revision 2010, and hence can be recommended for home use in adults.

Experimental investigation into the coupling effects of magnetic field, temperature and pressure on electrical resistivity of non-oriented silicon steel sheet

NASA Astrophysics Data System (ADS)

Xiao, Lijun; Yu, Guodong; Zou, Jibin; Xu, Yongxiang

2018-05-01

In order to analyze the performance of magnetic device which operate at high temperature and high pressure, such as submersible motor, oil well transformer, the electrical resistivity of non-oriented silicon steel sheets is necessary for precise analysis. But the reports of the examination of the measuring method suitable for high temperature up to 180 °C and high pressure up to 140 MPa are few. In this paper, a measurement system based on four-probe method and Archimedes spiral shape measurement specimens is proposed. The measurement system is suitable for measuring the electrical resistivity of unconventional specimens under high temperature and high pressure and can simultaneously consider the influence of the magnetic field on the electrical resistivity. It can be seen that the electrical resistivity of the non-oriented silicon steel sheets will fluctuate instantaneously when the magnetic field perpendicular to the conductive path of the specimens is loaded or removed. The amplitude and direction of the fluctuation are not constant. Without considering the effects of fluctuations, the electrical resistivity of the non-oriented silicon steel sheets is the same when the magnetic field is loaded or removed. And the influence of temperature on the electrical resistivity of the non-oriented silicon steel sheet is still the greatest even though the temperature and the pressure are coupled together. The measurement results also show that the electrical resistivity varies linearly with temperature, so the temperature coefficient of resistivity is given in the paper.

Acoustic Radiation From a Mach 14 Turbulent Boundary Layer

NASA Technical Reports Server (NTRS)

Zhang, Chao; Duan, Lian; Choudhari, Meelan M.

2016-01-01

Direct numerical simulations (DNS) are used to examine the turbulence statistics and the radiation field generated by a high-speed turbulent boundary layer with a nominal freestream Mach number of 14 and wall temperature of 0:18 times the recovery temperature. The flow conditions fall within the range of nozzle exit conditions of the Arnold Engineering Development Center (AEDC) Hypervelocity Tunnel No. 9 facility. The streamwise domain size is approximately 200 times the boundary-layer thickness at the inlet, with a useful range of Reynolds number corresponding to Re 450 ?? 650. Consistent with previous studies of turbulent boundary layer at high Mach numbers, the weak compressibility hypothesis for turbulent boundary layers remains applicable under this flow condition and the computational results confirm the validity of both the van Driest transformation and Morkovin's scaling. The Reynolds analogy is valid at the surface; the RMS of fluctuations in the surface pressure, wall shear stress, and heat flux is 24%, 53%, and 67% of the surface mean, respectively. The magnitude and dominant frequency of pressure fluctuations are found to vary dramatically within the inner layer (z/delta 0.< or approx. 0.08 or z+ < or approx. 50). The peak of the pre-multiplied frequency spectrum of the pressure fluctuation is f(delta)/U(sub infinity) approx. 2.1 at the surface and shifts to a lower frequency of f(delta)/U(sub infinity) approx. 0.7 in the free stream where the pressure signal is predominantly acoustic. The dominant frequency of the pressure spectrum shows a significant dependence on the freestream Mach number both at the wall and in the free stream.

Isolating Gas Sensor From Pressure And Temperature Effects

NASA Technical Reports Server (NTRS)

Sprinkle, Danny R.; Chen, Tony T. D.; Chaturvedi, Sushi K.

1994-01-01

Two-stage flow system enables oxygen sensor in system to measure oxygen content of low-pressure, possibly-high-temperature atmosphere in test environment while protecting sensor against possibly high temperature and fluctuations in pressure of atmosphere. Sensor for which flow system designed is zirconium oxide oxygen sensor sampling atmospheres in high-temperature wind tunnels. Also adapted to other gas-analysis instruments that must be isolated from pressure and temperature effects of test environments.

High-frequency fluctuations in Denmark Strait transport

NASA Astrophysics Data System (ADS)

Haine, T. W. N.

2010-07-01

Denmark Strait ocean current transport exhibits quasi-regular fluctuations immediately south of the sill with periods of 2-4 days. The transport variability is similar to the mean transport itself. Using a circulation model we explore prospects to monitor the fluctuations. The model has realistic transport and shows water leaving Denmark Strait in equivalent-barotropic cyclones that are nearly geostrophic and correlate with sea-surface height (SSH). Existing satellite altimeter observations of SSH have adequate space/time sampling to reconstruct the transport fluctuations using a regression developed from the model results, but measurement error overwhelms the signal. From the model results, the pending Surface Water and Ocean Topography (SWOT) wide-swath altimeter appears accurate enough, and with good-enough coverage, to allow the transport fluctuations to be reconstructed. Bottom pressure recorders at the exit of the Denmark Strait can also reproduce the transport variability.

[A man with pain in his upper jaw].

PubMed

Jaspers, Gijs; van Gool, Lex

2011-01-01

A 66-year-old man came to the hospital with pain in the frontal left side of his upper jaw. Pressure along the left nostril could evoke a sharp pain, which radiated upwards. The patient had already consulted several specialists. After extended clinical and radiological investigation a mesiodens was found that gave pressure on the nasopalatine nerve.

Dome of magnetic order inside the nematic phase of sulfur-substituted FeSe under pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xiang, Li; Kaluarachchi, Udhara; Bohmer, Anna

2017-07-18

The pressure dependence of the structural, magnetic, and superconducting transitions and of the superconducting upper critical field were studied in sulfur-substituted Fe ( Se 1 - x S x ) . We performed resistance measurements on single crystals with three substitution levels ( x = 0.043 , 0.096, 0.12) under hydrostatic pressures up to 1.8 GPa and in magnetic fields up to 9 T and were compared to data on pure FeSe. Our results illustrate the effects of chemical and physical pressure on Fe ( Se 1 - x S x ). Furthermore, on increasing sulfur content, magnetic order inmore » the low-pressure range is strongly suppressed to a small domelike region in the phase diagrams. But, T s is much less suppressed by sulfur substitution, and T c of Fe ( Se 1 - x S x ) exhibits similar nonmonotonic pressure dependence with a local maximum and a local minimum present in the low-pressure range for all x . The local maximum in T c coincides with the emergence of the magnetic order above T c . At this pressure the slope of the upper critical field decreases abruptly, which may indicate a Fermi-surface reconstruction. The minimum of T c correlates with a broad maximum of the upper critical field slope normalized by T c .« less

Simulink Model of the Ares I Upper Stage Main Propulsion System

NASA Technical Reports Server (NTRS)

Burchett, Bradley T.

2008-01-01

A numerical model of the Ares I upper stage main propulsion system is formulated based on first principles. Equation's are written as non-linear ordinary differential equations. The GASP fortran code is used to compute thermophysical properties of the working fluids. Complicated algebraic constraints are numerically solved. The model is implemented in Simulink and provides a rudimentary simulation of the time history of important pressures and temperatures during re-pressurization, boost and upper stage firing. The model is validated against an existing reliable code, and typical results are shown.

Oscillatory Excitation of Unsteady Compressible Flows over Airfoils at Flight Reynolds Numbers

NASA Technical Reports Server (NTRS)

Seifert, Avi; Pack, LaTunia G.

1999-01-01

An experimental investigation, aimed at delaying flow separation due to the occurrence of a shock-wave-boundary-layer interaction, is reported. The experiment was performed using a NACA 0012 airfoil and a NACA 0015 airfoil at high Reynolds number incompressible and compressible flow conditions. The effects of Mach and Reynolds numbers were identified, using the capabilities of the cryogenic-pressurized facility to maintain one parameter fixed and change the other. Significant Reynolds number effects were identified in the baseline compressible flow conditions even at Reynolds number of 10 and 20 million. The main objectives of the experiment were to study the effects of periodic excitation on airfoil drag-divergence and to alleviate the severe unsteadiness associated with shock-induced separation (known as "buffeting"). Zero-mass-flux oscillatory blowing was introduced through a downstream directed slot located at 10% chord on the upper surface of the NACA 0015 airfoil. The effective frequencies generated 2-4 vortices over the separated region, regardless of the Mach number. Even though the excitation was introduced upstream of the shock-wave, due to experimental limitations, it had pronounced effects downstream of it. Wake deficit (associated with drag) and unsteadiness (associated with buffeting) were significantly reduced. The spectral content of the wake pressure fluctuations indicates of steadier flow throughout the frequency range when excitation was applied. This is especially important at low frequencies which are more likely to interact with the airframe.

Ambulatory blood pressure profiles in familial dysautonomia.

PubMed

Goldberg, Lior; Bar-Aluma, Bat-El; Krauthammer, Alex; Efrati, Ori; Sharabi, Yehonatan

2018-02-12

Familial dysautonomia (FD) is a rare genetic disease that involves extreme blood pressure fluctuations secondary to afferent baroreflex failure. The diurnal blood pressure profile, including the average, variability, and day-night difference, may have implications for long-term end organ damage. The purpose of this study was to describe the circadian pattern of blood pressure in the FD population and relationships with renal and pulmonary function, use of medications, and overall disability. We analyzed 24-h ambulatory blood pressure monitoring recordings in 22 patients with FD. Information about medications, disease severity, renal function (estimated glomerular filtration, eGFR), pulmonary function (forced expiratory volume in 1 s, FEV1) and an index of blood pressure variability (standard deviation of systolic pressure) were analyzed. The mean (± SEM) 24-h blood pressure was 115 ± 5.6/72 ± 2.0 mmHg. The diurnal blood pressure variability was high (daytime systolic pressure standard deviation 22.4 ± 1.5 mmHg, nighttime 17.2 ± 1.6), with a high frequency of a non-dipping pattern (16 patients, 73%). eGFR, use of medications, FEV1, and disability scores were unrelated to the degree of blood pressure variability or to dipping status. This FD cohort had normal average 24-h blood pressure, fluctuating blood pressure, and a high frequency of non-dippers. Although there was evidence of renal dysfunction based on eGFR and proteinuria, the ABPM profile was unrelated to the measures of end organ dysfunction or to reported disability.

[Summary of Research on Relationship Between Core Convective Structure and Intensity Change in Tropical Cyclones

NASA Technical Reports Server (NTRS)

2005-01-01

The downshear reformation of Tropical Storm Gabrielle (2001) was investigated using radar reflectivity and lightning data that were nearly continuous in time, as well as frequent aircraft reconnaissance flights. Initially the storm was a marginal tropical storm in an environment with strong 850-200 hPa vertical wind shear of 12-13 meters per second and an approaching upper tropospheric trough. Both the observed outflow and an adiabatic balance model calculation showed that the radial-vertical circulation increased with time as the trough approached. Convection was highly asymmetric, with almost all radar return located in one quadrant left of downshear in the storm. Reconnaissance data show that an intense mesovortex formed downshear of the original center. This vortex was located just south of, rather than within, a strong downshear left lightning outbreak, consistent with tilting of the horizontal vorticity associated with the vertical wind shear. The downshear mesovortex contained a 972 hPa minimum central pressure, 20 hPa lower than minimum pressure in the original vortex just three hours earlier. The mesovortex became the new center of the storm, but weakened somewhat prior to landfall. It is argued that dry air carried around the storm from the region of upshear subsidence, as well as the direct effects of the shear, prevented the reformed vortex from continuing to intensify. Despite the subsequent weakening of the reformed center, it reached land with greater intensity than the original center. It is argued that this intensification process was set into motion by the vertical wind shear in the presence of an environment with upward motion forced by the upper tropospheric trough. In addition, the new center formed much closer to the coast and made landfall much earlier than predicted. Such vertical shear-induced intensity and track fluctuations are important to understand, especially in storms approaching the coast. The structures of the highly sheared tropical storm Chantal During CAMEX-4 is also discussed.

Unique Pressure Dependence of the Order-Disorder Transition Temperature of a Series of PEP-PDMS Diblock Copolymers

NASA Astrophysics Data System (ADS)

Mortensen, K.; Almdal, K.; Schwahn, D.; Frielinghaus, H.

1997-03-01

Studies of the phase behavior of polymer systems has proven that the sensitivity to fluctuations is much more distinct than originally anticipated based on theoretical arguments. In blends of homo-polymers, studies have revealed that fluctuations give rise to significant re-normalized critical behavior. It has been argued that the free volume causes an entropic contribution to the Flory-Huggins interaction parameter, \\chi, and is thereby responsible for the re-normalized behavior. In block copolymers fluctuations have even more pronounced effects, as it changes the second order critical point at f=0.5 to first order and additional complex phases are stabilized. Measurements of the structure factor S(q) of PEP-PDMS diblock copolymers have revealed unique character in the phase-diagram with re-entrant ordered structure. Moreover, an unexpected singularity in the conformational compressibility, as identified from the peak-position, q, is observed. In contrary to binary polymer blends, pressure does not affect the Ginzburg number.

Estimation of Kubo number and correlation length of fluctuating magnetic fields and pressure in BOUT + + edge pedestal collapse simulation

NASA Astrophysics Data System (ADS)

Kim, Jaewook; Lee, W.-J.; Jhang, Hogun; Kaang, H. H.; Ghim, Y.-C.

2017-10-01

Stochastic magnetic fields are thought to be as one of the possible mechanisms for anomalous transport of density, momentum and heat across the magnetic field lines. Kubo number and Chirikov parameter are quantifications of the stochasticity, and previous studies show that perpendicular transport strongly depends on the magnetic Kubo number (MKN). If MKN is smaller than one, diffusion process will follow Rechester-Rosenbluth model; whereas if it is larger than one, percolation theory dominates the diffusion process. Thus, estimation of Kubo number plays an important role to understand diffusion process caused by stochastic magnetic fields. However, spatially localized experimental measurement of fluctuating magnetic fields in a tokamak is difficult, and we attempt to estimate MKNs using BOUT + + simulation data with pedestal collapse. In addition, we calculate correlation length of fluctuating pressures and Chirikov parameters to investigate variation correlation lengths in the simulation. We, then, discuss how one may experimentally estimate MKNs.

Fundamental and applied research on core engine/combustion noise of aircraft engines

NASA Technical Reports Server (NTRS)

Plett, E. G.; Leshner, M. D.; Summerfield, M.

1974-01-01

Some results of a study of the importance of geometrical features of the combustor to combustion roughness and resulting noise are presented. Comparison is made among a perforated can flame holder, a plane slotted flame holder and a plane slotted flame holder which introduces two counter swirling streams. The latter is found to permit the most stable, quiet combustion. Crosscorrelations between the time derivative of chamber pressure fluctuations and far field noise are found to be stronger than between the far field noise and the direct chamber pressure signal. Temperature fluctuations in the combustor nozzle are also found to have a reasonably strong crosscorrelation with far field sound.

Mean Flow Augmented Acoustics in Rocket Systems

NASA Technical Reports Server (NTRS)

Fischbach, Sean R.

2015-01-01

Combustion instability in solid rocket motors and liquid engines is a complication that continues to plague designers and engineers. Many rocket systems experience violent fluctuations in pressure, velocity, and temperature originating from the complex interactions between the combustion process and gas dynamics. During sever cases of combustion instability fluctuation amplitudes can reach values equal to or greater than the average chamber pressure. Large amplitude oscillations lead to damaged injectors, loss of rocket performance, damaged payloads, and in some cases breach of case/loss of mission. Historic difficulties in modeling and predicting combustion instability has reduced most rocket systems experiencing instability into a costly fix through testing paradigm or to scrap the system entirely.

Measurement of Turbulent Pressure and Temperature Fluctuations in a Gas Turbine Combustor

NASA Technical Reports Server (NTRS)

Povinelli, Louis (Technical Monitor); LaGraff, John E.; Bramanti, Cristina; Pldfield, Martin; Passaro, Andrea; Biagioni, Leonardo

2004-01-01

The report summarizes the results of the redesign efforts directed towards the gas-turbine combustor rapid-injector flow diagnostic probe developed under sponsorship of NASA-GRC and earlier reported in NASA-CR-2003-212540. Lessons learned during the theoretical development, developmental testing and field-testing in the previous phase of this research were applied to redesign of both the probe sensing elements and of the rapid injection device. This redesigned probe (referred to herein as Turboprobe) has been fabricated and is ready, along with the new rapid injector, for field-testing. The probe is now designed to capture both time-resolved and mean total temperatures, total pressures and, indirectly, one component of turbulent fluctuations.

Astrophysical gyrokinetics: turbulence in pressure-anisotropic plasmas at ion scales and beyond

NASA Astrophysics Data System (ADS)

Kunz, M. W.; Abel, I. G.; Klein, K. G.

2018-04-01

We present a theoretical framework for describing electromagnetic kinetic turbulence in a multi-species, magnetized, pressure-anisotropic plasma. The turbulent fluctuations are assumed to be small compared to the mean field, to be spatially anisotropic with respect to it and to have frequencies small compared to the ion cyclotron frequency. At scales above the ion-Larmor radius, the theory reduces to the pressure-anisotropic generalization of kinetic reduced magnetohydrodynamics (KRMHD) formulated by Kunz et al. (J. Plasma Phys., vol. 81, 2015, 325810501). At scales at and below the ion-Larmor radius, three main objectives are achieved. First, we analyse the linear response of the pressure-anisotropic gyrokinetic system, and show it to be a generalization of previously explored limits. The effects of pressure anisotropy on the stability and collisionless damping of Alfvénic and compressive fluctuations are highlighted, with attention paid to the spectral location and width of the frequency jump that occurs as Alfvén waves transition into kinetic Alfvén waves. Secondly, we derive and discuss a very general gyrokinetic free-energy conservation law, which captures both the KRMHD free-energy conservation at long wavelengths and dual cascades of kinetic Alfvén waves and ion entropy at sub-ion-Larmor scales. We show that non-Maxwellian features in the distribution function change the amount of phase mixing and the efficiency of magnetic stresses, and thus influence the partitioning of free energy amongst the cascade channels. Thirdly, a simple model is used to show that pressure anisotropy, even within the bounds imposed on it by firehose and mirror instabilities, can cause order-of-magnitude variations in the ion-to-electron heating ratio due to the dissipation of Alfvénic turbulence. Our theory provides a foundation for determining how pressure anisotropy affects turbulent fluctuation spectra, the differential heating of particle species and the ratio of parallel and perpendicular phase mixing in space and astrophysical plasmas.

Pressure response of protein backbone structure. Pressure-induced amide 15N chemical shifts in BPTI.

PubMed Central

Akasaka, K.; Li, H.; Yamada, H.; Li, R.; Thoresen, T.; Woodward, C. K.

1999-01-01

The effect of pressure on amide 15N chemical shifts was studied in uniformly 15N-labeled basic pancreatic trypsin inhibitor (BPTI) in 90%1H2O/10%2H2O, pH 4.6, by 1H-15N heteronuclear correlation spectroscopy between 1 and 2,000 bar. Most 15N signals were low field shifted linearly and reversibly with pressure (0.468 +/- 0.285 ppm/2 kbar), indicating that the entire polypeptide backbone structure is sensitive to pressure. A significant variation of shifts among different amide groups (0-1.5 ppm/2 kbar) indicates a heterogeneous response throughout within the three-dimensional structure of the protein. A tendency toward low field shifts is correlated with a decrease in hydrogen bond distance on the order of 0.03 A/2 kbar for the bond between the amide nitrogen atom and the oxygen atom of either carbonyl or water. The variation of 15N shifts is considered to reflect site-specific changes in phi, psi angles. For beta-sheet residues, a decrease in psi angles by 1-2 degrees/2 kbar is estimated. On average, shifts are larger for helical and loop regions (0.553 +/- 0.343 and 0.519 +/- 0.261 ppm/2 kbar, respectively) than for beta-sheet (0.295 +/- 0.195 ppm/2 kbar), suggesting that the pressure-induced structural changes (local compressibilities) are larger in helical and loop regions than in beta-sheet. Because compressibility is correlated with volume fluctuation, the result is taken to indicate that the volume fluctuation is larger in helical and loop regions than in beta-sheet. An important aspect of the volume fluctuation inferred from pressure shifts is that they include motions in slower time ranges (less than milliseconds) in which many biological processes may take place. PMID:10548039

Pressure production in oral vestibule during gum chewing.

PubMed

Nishiura, M; Ono, T; Yoshinaka, M; Fujiwara, S; Yoshinaka, M; Maeda, Y

2015-12-01

The aim of this study was to record oral vestibule pressure (OVP) by the lip and cheek contraction during gum chewing, to examine the characteristics of these pressures and coordination between the OVP and jaw movement. The subjects were eight healthy adult men (mean age of 29·3 ± 3·3 years). An experimental plate that incorporated four pressure sensors on the midline of the upper jaw (Ch. 1), upper right canine (Ch. 2), upper right first molar (Ch. 3) and upper left first molar (Ch. 4) was used for measuring OVP. The right masseter electromyogram (EMG) was recorded simultaneously. Subjects chewed gum on the right side 20 times, and eight consecutive strokes were used for the analysis of the sequential order, maximal magnitude and duration of each OVP. Onset of OVP was observed at the molar on the non-chewing side (Ch. 4) before chewing side (Ch. 3), and offset was largely simultaneous at each site. On the chewing side (Chs. 1-3), OVP onset during the interval of EMG activity reached to the peak around the end of interval and offset in the duration of EMG activity. The maximal pressure was significantly larger at Chs. 1-3 than at Ch. 4, but no significant differences were observed in duration of pressure among each site. These results suggest that OVP is coordinated with jaw movement during gum chewing, and larger pressure is produced on the chewing side than on the non-chewing side. Our findings are quantitative indices for the evaluation of lip and cheek function during mastication. © 2015 John Wiley & Sons Ltd.

A theoretical and flight test study of pressure fluctuations under a turbulent boundary layer. Part 2: Flight test study

NASA Technical Reports Server (NTRS)

Panton, R. L.; Lowery, R. L.; Reischman, M. M.

1967-01-01

The study of pressure fluctuations under a turbulent boundary layer was undertaken with the objective of extending previous work to lower frequencies. Wind tunnel and flight test measurements are invalid at low frequencies because of extraneous acoustic noises and free stream turbulence. A glider was instrumented and used as a test bed to carry microphones into a smooth flow free of acoustic noise. Hodgson had previously measured the spectrum of boundary layer noise on a glider wing. These tests showed a drop off at low frequencies that could not be reproduced in any other facility. The measurements were made on the forward fuselage of a glider where the boundary layer could develop naturally and have some length in a zero pressure gradient before the measurements were made. Two different sets of measurements were made.

Spiral magnetic order and pressure-induced superconductivity in transition metal compounds.

PubMed

Wang, Yishu; Feng, Yejun; Cheng, J-G; Wu, W; Luo, J L; Rosenbaum, T F

2016-10-06

Magnetic and superconducting ground states can compete, cooperate and coexist. MnP provides a compelling and potentially generalizable example of a material where superconductivity and magnetism may be intertwined. Using a synchrotron-based non-resonant X-ray magnetic diffraction technique, we reveal a spiral spin order in MnP and trace its pressure evolution towards superconducting order via measurements in a diamond anvil cell. Judging from the magnetostriction, ordered moments vanish at the quantum phase transition as pressure increases the electron kinetic energy. Spins remain local in the disordered phase, and the promotion of superconductivity is likely to emerge from an enhanced coupling to residual spiral spin fluctuations and their concomitant suppression of phonon-mediated superconductivity. As the pitch of the spiral order varies across the 3d transition metal compounds in the MnP family, the magnetic ground state switches between antiferromagnet and ferromagnet, providing an additional tuning parameter in probing spin-fluctuation-induced superconductivity.

Flutter of High-Speed Civil Transport Flexible Semispan Model: Time-Frequency Analysis

NASA Technical Reports Server (NTRS)

Chabalko, Christopher C.; Hajj, Muhammad R.; Silva, Walter A.

2006-01-01

Time/frequency analysis of fluctuations measured by pressure taps and strain gauges in the experimental studies of the flexible semispan model of a high-speed civil transport wing configuration is performed. The interest is in determining the coupling between the aerodynamic loads and structural motions that led to the hard flutter conditions and loss of the model. The results show that, away from the hard flutter point, the aerodynamic loads at all pressure taps near the wing tip and the structural motions contained the same frequency components. On the other hand, in the flow conditions leading to the hard flutter, the frequency content of the pressure fluctuations near the leading and trailing edges varied significantly. This led to contribution to the structural motions over two frequency ranges. The ratio of these ranges was near 2:1, which suggests the possibility of nonlinear structural coupling.

Cathode Stalk Cooling System for the MK 1 Quarterwave Gun

DTIC Science & Technology

2012-06-01

is estimated to average 1 hour per response, including the time for reviewing instruction, searching existing data sources, gathering and...pressure increases and drops over the duration of the applied power. Right: Plots the pressure change over time , better representing the pressure...when the variac was turned off at 2348. No fluctuations in temperature occurred after this time . ......................51 Figure 32. Cooling worked

Direct characterization of hydrophobic hydration during cold and pressure denaturation.

PubMed

Das, Payel; Matysiak, Silvina

2012-05-10

Cold and pressure denaturation are believed to have their molecular origin in hydrophobic interactions between nonpolar groups and water. However, the direct characterization of the temperature- and pressure-dependent variations of those interactions with atomistic simulations remains challenging. We investigated the role of solvent in the cold and pressure denaturation of a model hydrophobic 32-mer polymer by performing extensive coarse-grained molecular dynamics simulations including explicit solvation. Our simulations showed that the water-excluded folded state of this polymer is marginally stable and can be unfolded by heating or cooling, as well as by applying pressure, similar to globular proteins. We further detected essential population of a hairpin-like configuration prior to the collapse, which is consistently accompanied by a vapor bubble at the elbow of the kink. Increasing pressure suppresses formation of this vapor bubble by reducing water fluctuations in the hydration shell of the polymer, thus promoting unfolding. Further analysis revealed a slight reduction of water tetrahedrality in the polymer hydration shell compared to the bulk. Cold denaturation is driven by an enhanced tetrahedral ordering of hydration shell water than bulk water. At elevated pressures, the strikingly reduced fluctuations combined with the increase in interstitial water molecules in the polymer hydration shell contribute to weakening of hydrophobic interactions, thereby promoting pressure unfolding. These findings provide critical molecular insights into the changes in hydrophobic hydration during cold and pressure unfolding of a hydrophobic polymer, which is strongly related to the cold and pressure denaturation of globular proteins.

Soil and ecosystem respiration responses to grazing, watering and experimental warming chamber treatments across topographical gradients in northern Mongolia.

PubMed

Sharkhuu, Anarmaa; Plante, Alain F; Enkhmandal, Orsoo; Gonneau, Cédric; Casper, Brenda B; Boldgiv, Bazartseren; Petraitis, Peter S

2016-05-01

Globally, soil respiration is one of the largest fluxes of carbon to the atmosphere and is known to be sensitive to climate change, representing a potential positive feedback. We conducted a number of field experiments to study independent and combined impacts of topography, watering, grazing and climate manipulations on bare soil and vegetated soil (i.e., ecosystem) respiration in northern Mongolia, an area known to be highly vulnerable to climate change and overgrazing. Our results indicated that soil moisture is the most important driving factor for carbon fluxes in this semi-arid ecosystem, based on smaller carbon fluxes under drier conditions. Warmer conditions did not result in increased respiration. Although the system has local topographical gradients in terms of nutrient, moisture availability and plant species, soil respiration responses to OTC treatments were similar on the upper and lower slopes, implying that local heterogeneity may not be important for scaling up the results. In contrast, ecosystem respiration responses to OTCs differed between the upper and the lower slopes, implying that the response of vegetation to climate change may override microbial responses. Our results also showed that light grazing may actually enhance soil respiration while decreasing ecosystem respiration, and grazing impact may not depend on climate change. Overall, our results indicate that soil and ecosystem respiration in this semi-arid steppe are more sensitive to precipitation fluctuation and grazing pressure than to temperature change.

Soil and ecosystem respiration responses to grazing, watering and experimental warming chamber treatments across topographical gradients in northern Mongolia

PubMed Central

Sharkhuu, Anarmaa; Plante, Alain F.; Enkhmandal, Orsoo; Gonneau, Cédric; Casper, Brenda B.; Boldgiv, Bazartseren; Petraitis, Peter S.

2017-01-01

Globally, soil respiration is one of the largest fluxes of carbon to the atmosphere and is known to be sensitive to climate change, representing a potential positive feedback. We conducted a number of field experiments to study independent and combined impacts of topography, watering, grazing and climate manipulations on bare soil and vegetated soil (i.e., ecosystem) respiration in northern Mongolia, an area known to be highly vulnerable to climate change and overgrazing. Our results indicated that soil moisture is the most important driving factor for carbon fluxes in this semi-arid ecosystem, based on smaller carbon fluxes under drier conditions. Warmer conditions did not result in increased respiration. Although the system has local topographical gradients in terms of nutrient, moisture availability and plant species, soil respiration responses to OTC treatments were similar on the upper and lower slopes, implying that local heterogeneity may not be important for scaling up the results. In contrast, ecosystem respiration responses to OTCs differed between the upper and the lower slopes, implying that the response of vegetation to climate change may override microbial responses. Our results also showed that light grazing may actually enhance soil respiration while decreasing ecosystem respiration, and grazing impact may not depend on climate change. Overall, our results indicate that soil and ecosystem respiration in this semi-arid steppe are more sensitive to precipitation fluctuation and grazing pressure than to temperature change. PMID:28239190

Vacuum fluctuations of the supersymmetric field in curved background

NASA Astrophysics Data System (ADS)

Bilić, Neven; Domazet, Silvije; Guberina, Branko

2012-01-01

We study a supersymmetric model in curved background spacetime. We calculate the effective action and the vacuum expectation value of the energy momentum tensor using a covariant regularization procedure. A soft supersymmetry breaking induces a nonzero contribution to the vacuum energy density and pressure. Assuming the presence of a cosmic fluid in addition to the vacuum fluctuations of the supersymmetric field an effective equation of state is derived in a self-consistent approach at one loop order. The net effect of the vacuum fluctuations of the supersymmetric fields in the leading adiabatic order is a renormalization of the Newton and cosmological constants.

Measurements of the Free-Stream Fluctuations above a Turbulent Boundary Layer

NASA Technical Reports Server (NTRS)

Wood, D. H.; Westphal, R. V.

1988-01-01

In this paper an investigation of the velocity fluctuations in the free stream above an incompressible turbulent boundary layer developing at constant pressure is described. It is assumed that the fluctuations receive contributions from three statistically independent sources: (1) one-dimensional unsteadiness, (2) free-stream turbulence, and (3) the irrotational motion induced by the turbulent boundary layer. Measurements were made in a wind tunnel with a root-mean-square level of the axial velocity fluctuations of about 0.2%. All three velocity components were measured using an X-wire probe. The unsteadiness was determined from the spanwise covariance of the axial velocity fluctuations, measured using two single-wire probes. The results show that it is possible to separate the contributions to the rms level of the velocity fluctuations without resorting to the dubious technique of high-pass filtering. This separation could be extended to the spectral densities of the contributions if measurements of sufficient accuracy were available.

Measurements of the free stream fluctuations above a turbulent boundary layer

NASA Technical Reports Server (NTRS)

Wood, David H.; Westphal, Russell V.

1987-01-01

This paper investigates the velocity fluctuations in the free stream above an incompressible turbulent boundary layer developing at constant pressure. It is assumed that the fluctuations receive contributions from three statistically independent sources: (1) one-dimensional unsteadiness, (2) free stream turbulence, and (3) the potential motion induced by the turbulent boundary layer. Measurements were made in a wind tunnel with a root-mean-square level of the axial velocity fluctuations of about 0.2 percent. All three velocity components were measured using an X-wire probe. The unsteadiness was determined from the spanwise covariance of the axial velocity, measured using two single wire probes. The results show that it is possible to separate the contributions to the r.m.s. level of the velocity fluctuations, without resorting to the dubious technique of high-pass filtering. The separation could be extended to the spectral densities of the contributions, if measurements of sufficient accuracy were available. The Appendix provides a general guide for the measurement of small free stream fluctuation levels.

Density Fluctuations in the Solar Wind Driven by Alfvén Wave Parametric Decay

NASA Astrophysics Data System (ADS)

Bowen, Trevor A.; Badman, Samuel; Hellinger, Petr; Bale, Stuart D.

2018-02-01

Measurements and simulations of inertial compressive turbulence in the solar wind are characterized by anti-correlated magnetic fluctuations parallel to the mean field and density structures. This signature has been interpreted as observational evidence for non-propagating pressure balanced structures, kinetic ion-acoustic waves, as well as the MHD slow-mode. Given the high damping rates of parallel propagating compressive fluctuations, their ubiquity in satellite observations is surprising and suggestive of a local driving process. One possible candidate for the generation of compressive fluctuations in the solar wind is the Alfvén wave parametric instability. Here, we test the parametric decay process as a source of compressive waves in the solar wind by comparing the collisionless damping rates of compressive fluctuations with growth rates of the parametric decay instability daughter waves. Our results suggest that generation of compressive waves through parametric decay is overdamped at 1 au, but that the presence of slow-mode-like density fluctuations is correlated with the parametric decay of Alfvén waves.

Properties of density and magnetic fluctuations occurring in density striations in the new LAPD

NASA Astrophysics Data System (ADS)

Maggs, J. E.; Morales, G. J.

2001-10-01

Previous studies of density striations (long, narrow magnetic-field-aligned density depletions) in the LAPD plasma device at UCLA revealed an eigenmode structure to fluctuations driven by the pressure gradient in the striation wall (Maggs and Morales, Phys. Plasmas, 4, 1997). The nature of these fluctuations depended on the plasma beta external to the striation, with shear Alfvén wave turbulence developing at betas less than the mass ratio and drift-Alfvén waves at betas above the mass ratio. These fluctuations were found to have a direct connection to turbulence observed at the plasma edge. The new LAPD is 18 meters in length with a background field up to twice previously attainable values. We report on the properties of fluctuations associated with density striations in the new device over a wider range of beta, and compare them to previous results. The behavior of fluctuations in density striations created in flared-field and magnetic-mirror geometries will also be presented. Research sponsored by ONR and NSF

A Comparison of Combustion Dynamics for Multiple 7-Point Lean Direct Injection Combustor Configurations

NASA Technical Reports Server (NTRS)

Tacina, Kathleen M.; Hicks, Yolanda R.

2017-01-01

The combustion dynamics of two 7-point lean direct injection (LDI) combustor configurations are compared. This 7-point LDI configuration has a circular cross section, with a center ("pilot") fuel-air mixer surrounded by six outer ("main") fuel-air mixers. Each fuel-air mixer consists of an axial air swirler followed by a converging-diverging venturi. A simplex fuel injector is inserted through the center of the air swirler, with the fuel injector tip located near the venturi throat. All 7 fuel-air mixers are identical except for the swirler blade angle. In the 'all-60' configuration, the swirler blade angle was 60 deg for all fuel-air mixers. In the '45-60' configuration, the swirler blade angle was 60 deg on the center and 45 deg on the outer fuel-air mixers. Testing was done in a 5-atm flame tube with inlet air temperatures from 630 to 830 F and equivalence ratios from 0.2 to 0.7. Combustion dynamics were measured using a cooled PCB pressure transducer flush-mounted in the wall of the combustor test section. Both configurations had large pressure fluctuations (greater than 2 psi peak-peak) near 730 Hz, the quarter-wave frequency. The all-60 configuration also had large pressure fluctuations near 1170 Hz; the 45-60 configuration did not. The 45-60 configuration had large pressure fluctuations near 480 Hz; the all-60 configuration did not.

The Measurement of Unsteady Surface Pressure Using a Remote Microphone Probe.

PubMed

Guan, Yaoyi; Berntsen, Carl R; Bilka, Michael J; Morris, Scott C

2016-12-03

Microphones are widely applied to measure pressure fluctuations at the walls of solid bodies immersed in turbulent flows. Turbulent motions with various characteristic length scales can result in pressure fluctuations over a wide frequency range. This property of turbulence requires sensing devices to have sufficient sensitivity over a wide range of frequencies. Furthermore, the small characteristic length scales of turbulent structures require small sensing areas and the ability to place the sensors in very close proximity to each other. The complex geometries of the solid bodies, often including large surface curvatures or discontinuities, require the probe to have the ability to be set up in very limited spaces. The development of a remote microphone probe, which is inexpensive, consistent, and repeatable, is described in the present communication. It allows for the measurement of pressure fluctuations with high spatial resolution and dynamic response over a wide range of frequencies. The probe is small enough to be placed within the interior of typical wind tunnel models. The remote microphone probe includes a small, rigid, and hollow tube that penetrates the model surface to form the sensing area. This tube is connected to a standard microphone, at some distance away from the surface, using a "T" junction. An experimental method is introduced to determine the dynamic response of the remote microphone probe. In addition, an analytical method for determining the dynamic response is described. The analytical method can be applied in the design stage to determine the dimensions and properties of the RMP components.

Ares I-X Upper Stage Simulator Compartment Pressure Comparisons During Ascent

NASA Technical Reports Server (NTRS)

Downs. William J.; Kirchner, Robert D.; McLachlan, Blair G.; Hand, Lawrence A.; Nelson, Stuart L.

2011-01-01

Predictions of internal compartment pressures are necessary in the design of interstage regions, systems tunnels, and protuberance covers of launch vehicles to assess potential burst and crush loading of the structure. History has proven that unexpected differential pressure loads can lead to catastrophic failure. Pressures measured in the Upper Stage Simulator (USS) compartment of Ares I-X during flight were compared to post-flight analytical predictions using the CHCHVENT chamber-to-chamber venting analysis computer program. The measured pressures were enveloped by the analytical predictions for most of the first minute of flight but were outside of the predictions thereafter. This paper summarizes the venting system for the USS, discusses the probable reasons for the discrepancies between the measured and predicted pressures, and provides recommendations for future flight vehicles.

Waterhammer Modeling for the Ares I Upper Stage Reaction Control System Cold Flow Development Test Article

NASA Technical Reports Server (NTRS)

Williams, Jonathan H.

2010-01-01

The Upper Stage Reaction Control System provides three-axis attitude control for the Ares I launch vehicle during active Upper Stage flight. The system design must accommodate rapid thruster firing to maintain the proper launch trajectory and thus allow for the possibility to pulse multiple thrusters simultaneously. Rapid thruster valve closure creates an increase in static pressure, known as waterhammer, which propagates throughout the propellant system at pressures exceeding nominal design values. A series of development tests conducted in the fall of 2009 at Marshall Space Flight Center were performed using a water-flow test article to better understand fluid performance characteristics of the Upper Stage Reaction Control System. A subset of the tests examined waterhammer along with the subsequent pressure and frequency response in the flight-representative system and provided data to anchor numerical models. This thesis presents a comparison of waterhammer test results with numerical model and analytical results. An overview of the flight system, test article, modeling and analysis are also provided.

Waterhammer modeling for the Ares I Upper Stage Reaction Control System cold flow development test article

NASA Astrophysics Data System (ADS)

Williams, Jonathan Hunter

The Upper Stage Reaction Control System provides in-flight three-axis attitude control for the Ares I Upper Stage. The system design must accommodate rapid thruster firing to maintain proper launch trajectory and thus allow for the possibility to pulse multiple thrusters simultaneously. Rapid thruster valve closure creates an increase in static pressure, known as waterhammer, which propagates throughout the propellant system at pressures exceeding nominal design values. A series of development tests conducted at Marshall Space Flight Center in 2009 were performed using a water-flow test article to better understand fluid characteristics of the Upper Stage Reaction Control System. A subset of the tests examined the waterhammer pressure and frequency response in the flight-representative system and provided data to anchor numerical models. This thesis presents a comparison of waterhammer test results with numerical model and analytical results. An overview of the flight system, test article, modeling and analysis are also provided.

Multistage crack seal vein and hydrothermal Ni enrichment in serpentinized ultramafic rocks (Koniambo massif, New Caledonia)

NASA Astrophysics Data System (ADS)

Cathelineau, Michel; Myagkiy, Andrey; Quesnel, Benoit; Boiron, Marie-Christine; Gautier, Pierre; Boulvais, Philippe; Ulrich, Marc; Truche, Laurent; Golfier, Fabrice; Drouillet, Maxime

2017-10-01

Sets of fractures and breccia sealed by Ni-rich silicates and quartz occur within saprock of the New Caledonian regolith developed over ultramafic rocks. The crystallization sequence in fractures is as follows: (1) serpentine stage: lizardite > polygonal serpentine > white lizardite; (2) Ni stage: Ni-Mg kerolite followed by red-brown microcrystalline quartz; and (3) supergene stages. The red-brown microcrystalline quartz corresponds to the very last stage of the Ni sequence and is inferred to have precipitated within the 50-95 °C temperature range. It constitutes also the main cement of breccia that has all the typical features of hydraulic fracturing. The whole sequence is therefore interpreted as the result of hydrothermal fluid circulation under medium to low temperature and fluctuating fluid pressure. Although frequently described as the result of a single downward redistribution of Ni and Mg leached in the upper part of the regolith under ambient temperature, the Ni silicate veins thus appear as the result of recurrent crack and seal process, corresponding to upward medium temperature fluid convection, hydraulic fracturing and subsequent fluid mixing, and mineral deposition.

Numerical study on the effect of a lobed nozzle on the flow characteristics of submerged exhaust

NASA Astrophysics Data System (ADS)

Miao, T. C.; Du, T.; Wu, D. Z.; Wang, L. Q.

2016-05-01

In order to investigate the effecting mechanism of nozzle structure on the flow characteristics of submerged exhaust, the processes of air exhausted from a lobed nozzle and a round nozzle into water have been numerically simulated using realizable k - ɛ model under the framework of the volume of fluid (VOF) model. Both the flow structure and the upstream pressure fluctuations are taken into consideration. The calculated results are in good agreement with the experimental results, showing that gas exhausted from the lobed nozzle would flow along the axial direction easier. Flow structure of the gas exhausted from the lobed nozzle is more continuous and smoother. The pressure fluctuations in the upstream pipeline would also be reduced when gas exhausted from the lobed nozzle. The resulting analysis indicates that the lobed structure could deflect water flow into the gas jet. The induced water would be mixed into the gas jet in form of small droplets, making the jet more continuous. As a result, the mixed jet flow would be less obstructed by the surrounding water, and the upstream pressure fluctuation would be reduced. The work in this paper partly explained the effecting mechanism of nozzle structure on the flow characteristics of submerged exhaust. The results are useful in the designing of exhaust nozzles.

Multimodal Pressure-Flow Analysis: Application of Hilbert Huang Transform in Cerebral Blood Flow Regulation

NASA Astrophysics Data System (ADS)

Lo, Men-Tzung; Hu, Kun; Liu, Yanhui; Peng, C.-K.; Novak, Vera

2008-12-01

Quantification of nonlinear interactions between two nonstationary signals presents a computational challenge in different research fields, especially for assessments of physiological systems. Traditional approaches that are based on theories of stationary signals cannot resolve nonstationarity-related issues and, thus, cannot reliably assess nonlinear interactions in physiological systems. In this review we discuss a new technique called multimodal pressure flow (MMPF) method that utilizes Hilbert-Huang transformation to quantify interaction between nonstationary cerebral blood flow velocity (BFV) and blood pressure (BP) for the assessment of dynamic cerebral autoregulation (CA). CA is an important mechanism responsible for controlling cerebral blood flow in responses to fluctuations in systemic BP within a few heart-beats. The MMPF analysis decomposes BP and BFV signals into multiple empirical modes adaptively so that the fluctuations caused by a specific physiologic process can be represented in a corresponding empirical mode. Using this technique, we showed that dynamic CA can be characterized by specific phase delays between the decomposed BP and BFV oscillations, and that the phase shifts are significantly reduced in hypertensive, diabetics and stroke subjects with impaired CA. Additionally, the new technique can reliably assess CA using both induced BP/BFV oscillations during clinical tests and spontaneous BP/BFV fluctuations during resting conditions.

Sloshing motion dynamics of a free surface in the draft tube cone of a Francis turbine operating in synchronous condenser mode

NASA Astrophysics Data System (ADS)

Vagnoni, Elena; Andolfatto, Loïc; Favrel, Arthur; Avellan, François

2016-11-01

The penetration of the electrical grid by intermittent renewable energy sources induces grid fluctuations which must be compensated in order to guarantee the stability of the grid. Hydropower plants can supply reactive power to ensure the grid stabilization by operating in condenser mode. In this operating mode, the turbine operates with the tail water depressed to let the runner spin in air to reduce the power consumption. Pressurized air is injected in the draft tube cone to maintain the water level below the runner and this induces air-water interaction phenomena which cause important power losses. Flow visualization and pressure fluctuation measurements are performed in a reduced scale physical model of a Francis turbine operating in condenser mode to investigate the dynamics of the air-water interaction in the draft tube cone which causes the sloshing motion of the free surface. An image post-processing method is developed, enabling a quantitative description of the sloshing motion. The latter depends on the Froude number. By increasing the value of the Froude number, the amplitude of the sloshing motion decreases, as well as the amplitude of the pressure fluctuations. The frequency of the sloshing motion corresponds to the first natural frequency of the water volume.

Water-level fluctuations, water temperatures, and tilts in sandbars -6.5R, 43.1L, and 172.3L, Grand Canyon, Arizona, 1990-93

USGS Publications Warehouse

Carpenter, Michael C.; Crosswhite, Jason A.; Carruth, R.L.

1995-01-01

Rill erosion, slumping, and fissuring develop on seepage faces of many sandbars along the Colorado River in the Grand Canyon at low river stage. Three sandbars were instrumented with sensors for continual monitoring of stage, pore pressure, ground-water temperature, and tilt to determine the relation between ground-water flow and sandbar deformation. Data were collected from October 1990 to July 1993 at sandbar -6.5R, which had 17 pore- pressure sensors, 1 stage sensor, 19 temperature sensors, and 8 tilt sensors. Data were collected from April 1991 to March 1993 at sandbar 172.3L, which had 15 pore-pressure sensors, 1 stage sensor, 29 temperature sensors, and 10 tilt sensors. Atten- uation of water-level fluctuation from the zone of fluctuating river stage to the back of the sandbars ranged from 70 percent at sandbar -6.5R to 40 percent for sandbars 43.1L and 172.3L. Shallow tilt occurred at sandbar 43.1L from July 7 to August 10, 1991. Tilt occurred at sandbar 172.3L on May 7-8, June 18-19, and September 1-2, 1991; July 3 and 31, 1992; January 12, 14, 20-21, and 31, 1993; and February 21 and 24, 1993.

A review of acoustic dampers applied to combustion chambers in aerospace industry

NASA Astrophysics Data System (ADS)

Zhao, Dan; Li, X. Y.

2015-04-01

In engine combustion systems such as rockets, aero-engines and gas turbines, pressure fluctuations are always present, even during normal operation. One of design prerequisites for the engine combustors is stable operation, since large-amplitude self-sustained pressure fluctuations (also known as combustion instability) have the potential to cause serious structural damage and catastrophic engine failure. To dampen pressure fluctuations and to reduce noise, acoustic dampers are widely applied as a passive control means to stabilize combustion/engine systems. However, they cannot respond to the dynamic changes of operating conditions and tend to be effective over certain narrow range of frequencies. To maintain their optimum damping performance over a broad frequency range, extensive researches have been conducted during the past four decades. The present work is to summarize the status, challenges and progress of implementing such acoustic dampers on engine systems. The damping effect and mechanism of various acoustic dampers, such as Helmholtz resonators, perforated liners, baffles, half- and quarter-wave tube are introduced first. A summary of numerical, experimental and theoretical studies are then presented to review the progress made so far. Finally, as an alternative means, ';tunable acoustic dampers' are discussed. Potential, challenges and issues associated with the dampers practical implementation are highlighted.

Changes in migration mode of brine and supercritical CO2 in imbibition process under steady flow state of very slow fluid velocities

NASA Astrophysics Data System (ADS)

Kogure, Tetsuya; Zhang, Yi; Nishizawa, Osamu; Xue, Ziqiu

2018-05-01

Relative permeability curves and flow mechanisms of CO2 and brine in Berea sandstone were investigated during a two-phase flow imbibition process, where CO2 saturation in the rock decreased from 55 per cent to 9 per cent by stepwise decrease of CO2/brine injection ratios. Total fluid flow velocity was 4.25 × 10-6 m/s, corresponding to the capillary number of order ˜10-8 for CO2 flow. The relative permeability curves showed a slight hysteresis compared to those during the drainage process. Local CO2 saturation and the differential pressure showed temporal fluctuations when the average differential pressure showed constant values or very small trends. The fluctuations in local CO2 saturation correlate with local porosity distributions. The differential pressure between the inlet and outlet ends showed the largest fluctuation when the CO2/brine ratio equals to one. A final brine-only injection resulted in more CO2 trapped within low porosity zones. These results suggest important roles of ganglion dynamics in the low flow rate ranges, where fluid pathways undergo repetitive brine snap-off and coalescence of CO2 ganglia that causes morphological changes in distributions of CO2 pathways.

Damping insert materials for settling chambers of supersonic wind tunnels

NASA Astrophysics Data System (ADS)

Wu, Jie; Radespiel, Rolf

2017-03-01

This study describes the application of a novel damping insert material for reducing the flow fluctuations in a tandem nozzle supersonic wind tunnel. This new damping material is composed of multi-layer stainless steel wired meshes. The influences of the multi-layer mesh, such as the quantity of the mesh layer and the installed location in the settling chamber, to the freestream quality have been investigated. A Pitot probe instrumented with a Kulite pressure sensor and a hot-wire probe are employed to monitor the flow fluctuation in the test section of the wind tunnel. Thereafter, a combined modal analysis is applied for the disturbance qualification. Additionally, the transient Mach number in the test section is measured. The disturbance qualification indicates that the multi-layer mesh performs well in providing reduction of vorticity reduction and acoustic fluctuations. Comparable flow quality of the freestream was also obtained using a combination of flexible damping materials. However, the life-span of the new damping materials is much longer. The time transient of the Mach number measured in the test section indicates that the mean flow is rather constant over run time. Furthermore, the time-averaged pressure along the settling chamber is recorded and it shows the distribution of pressure drop by settling chamber inserts.

Collisionless Isotropization of the Solar-wind Protons by Compressive Fluctuations and Plasma Instabilities

NASA Astrophysics Data System (ADS)

Verscharen, Daniel; Chandran, Benjamin D. G.; Klein, Kristopher G.; Quataert, Eliot

2016-11-01

Compressive fluctuations are a minor yet significant component of astrophysical plasma turbulence. In the solar wind, long-wavelength compressive slow-mode fluctuations lead to changes in {β }\\parallel {{p}}\\equiv 8π {n}{{p}}{k}{{B}}{T}\\parallel {{p}}/{B}2 and in {R}{{p}}\\equiv {T}\\perp {{p}}/{T}\\parallel {{p}}, where {T}\\perp {{p}} and {T}\\parallel {{p}} are the perpendicular and parallel temperatures of the protons, B is the magnetic field strength, and {n}{{p}} is the proton density. If the amplitude of the compressive fluctuations is large enough, {R}{{p}} crosses one or more instability thresholds for anisotropy-driven microinstabilities. The enhanced field fluctuations from these microinstabilities scatter the protons so as to reduce the anisotropy of the pressure tensor. We propose that this scattering drives the average value of {R}{{p}} away from the marginal stability boundary until the fluctuating value of {R}{{p}} stops crossing the boundary. We model this “fluctuating-anisotropy effect” using linear Vlasov-Maxwell theory to describe the large-scale compressive fluctuations. We argue that this effect can explain why, in the nearly collisionless solar wind, the average value of {R}{{p}} is close to unity.

Order parameter fluctuations at a buried quantum critical point

PubMed Central

Feng, Yejun; Wang, Jiyang; Jaramillo, R.; van Wezel, Jasper; Haravifard, S.; Srajer, G.; Liu, Y.; Xu, Z.-A.; Littlewood, P. B.; Rosenbaum, T. F.

2012-01-01

Quantum criticality is a central concept in condensed matter physics, but the direct observation of quantum critical fluctuations has remained elusive. Here we present an X-ray diffraction study of the charge density wave (CDW) in 2H-NbSe2 at high pressure and low temperature, where we observe a broad regime of order parameter fluctuations that are controlled by proximity to a quantum critical point. X-rays can track the CDW despite the fact that the quantum critical regime is shrouded inside a superconducting phase; and in contrast to transport probes, allow direct measurement of the critical fluctuations of the charge order. Concurrent measurements of the crystal lattice point to a critical transition that is continuous in nature. Our results confirm the long-standing expectations of enhanced quantum fluctuations in low-dimensional systems, and may help to constrain theories of the quantum critical Fermi surface. PMID:22529348

The Variability of Atmospheric Deuterium Brightness at Mars: Evidence for Seasonal Dependence

NASA Astrophysics Data System (ADS)

Mayyasi, Majd; Clarke, John; Bhattacharyya, Dolon; Deighan, Justin; Jain, Sonal; Chaffin, Michael; Thiemann, Edward; Schneider, Nick; Jakosky, Bruce

2017-10-01

The enhanced ratio of deuterium to hydrogen on Mars has been widely interpreted as indicating the loss of a large column of water into space, and the hydrogen content of the upper atmosphere is now known to be highly variable. The variation in the properties of both deuterium and hydrogen in the upper atmosphere of Mars is indicative of the dynamical processes that produce these species and propagate them to altitudes where they can escape the planet. Understanding the seasonal variability of D is key to understanding the variability of the escape rate of water from Mars. Data from a 15 month observing campaign, made by the Mars Atmosphere and Volatile Evolution Imaging Ultraviolet Spectrograph high-resolution echelle channel, are used to determine the brightness of deuterium as observed at the limb of Mars. The D emission is highly variable, with a peak in brightness just after southern summer solstice. The trends of D brightness are examined against extrinsic as well as intrinsic sources. It is found that the fluctuations in deuterium brightness in the upper atmosphere of Mars (up to 400 km), corrected for periodic solar variations, vary on timescales that are similar to those of water vapor fluctuations lower in the atmosphere (20-80 km). The observed variability in deuterium may be attributed to seasonal factors such as regional dust storm activity and subsequent circulation lower in the atmosphere.

Validation of the Andon KD-5851 upper arm blood pressure monitor, for self-measurement according to the European Society of Hypertension International Protocol revision 2010.

PubMed

Wu, Lili; Jiao, Yinghui; Wang, Chengdong; Chen, Lei; Di, Dalin; Zhang, Haiyan

2015-08-01

This study aimed to validate the Andon KD-5851 upper arm blood pressure (BP) monitor according to the European Society of Hypertension International Protocol (ESH-IP) revision 2010. A total of 33 eligible participants were included in the study. Sequential measurements of BPs were performed using a mercury sphygmomanometer and the device, and the data analysis was carried out following precisely the ESH-IP revision 2010. The device had 82, 98, and 99 measurements within 5, 10, and 15 mmHg for systolic blood pressure and 85, 95, and 99 measurements for diastolic blood pressure, respectively. The average device-observer difference was -0.53±4.00 mmHg for systolic blood pressure and -1.15±4.06 mmHg for diastolic blood pressure. The device passed all the criteria according to the ESH-IP revision 2010. According to the validation results on the basis of the ESH-IP revision 2010, the Andon KD-5851 upper arm BP monitor can be recommended for self/home measurement in adults. Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.

Thermal homogeneity of plastication processes in single-screw extruders

NASA Astrophysics Data System (ADS)

Bu, L. X.; Agbessi, Y.; Béreaux, Y.; Charmeau, J.-Y.

2018-05-01

Single-screw plastication, used in extrusion and in injection moulding, is a major way of processing commodity thermoplastics. During the plastication phase, the polymeric material is melted by the combined effects of shear-induced self-heating (viscous dissipation) and heat conduction coming from the barrel. In injection moulding, a high level of reliability is usually achieved that makes this process ideally suited to mass market production. Nonetheless, process fluctuations still appear that make moulded part quality control an everyday issue. In this work, we used a combined modelling of plastication, throughput calculation and laminar dispersion, to investigate if, and how, thermal fluctuations could propagate along the screw length and affect the melt homogeneity at the end of the metering section. To do this, we used plastication models to relate changes in processing parameters to changes in the plastication length. Moreover, a simple model of throughput calculation is used to relate the screw geometry, the polymer rheology and the processing parameters to get a good estimate of the mass flow rate. Hence, we found that the typical residence time in a single screw is around one tenth of the thermal diffusion time scale. This residence time is too short for the dispersion coefficient to reach a steady state, but too long to be able to neglect radial thermal diffusion and resort to a purely convective solution. Therefore, a full diffusion/convection problem has to be solved with a base flow described by the classic pressure and drag velocity field. Preliminary results already show the major importance of the processing parameters in the breakthrough curve of an arbitrary temperature fluctuation at the end of the metering section of injection moulding screw. When the flow back-pressure is high, the temperature fluctuation is spread more evenly with time, whereas a pressure drop in the flow will results in a breakthrough curve which presents a larger peak of fluctuation.

Physiological Mechanisms Mediating the Coupling between Heart Period and Arterial Pressure in Response to Postural Changes in Humans

PubMed Central

Silvani, Alessandro; Calandra-Buonaura, Giovanna; Johnson, Blair D.; van Helmond, Noud; Barletta, Giorgio; Cecere, Anna G.; Joyner, Michael J.; Cortelli, Pietro

2017-01-01

The upright posture strengthens the coupling between heart period (HP) and systolic arterial pressure (SAP) consistently with a greater contribution of the arterial baroreflex to cardiac control, while paradoxically decreasing cardiac baroreflex sensitivity (cBRS). To investigate the physiological mechanisms that mediate the coupling between HP and SAP in response to different postures, we analyzed the cross-correlation functions between low-frequency HP and SAP fluctuations and estimated cBRS with the sequence technique in healthy male subjects during passive head-up tilt test (HUTT, n = 58), during supine wakefulness, supine slow-wave sleep (SWS), and in the seated and active standing positions (n = 8), and during progressive loss of 1 L blood (n = 8) to decrease central venous pressure in the supine position. HUTT, SWS, the seated, and the standing positions, but not blood loss, entailed significant increases in the positive correlation between HP and the previous SAP values, which is the expected result of arterial baroreflex control, compared with baseline recordings in the supine position during wakefulness. These increases were mirrored by increases in the low-frequency variability of SAP in each condition but SWS. cBRS decreased significantly during HUTT, in the seated and standing positions, and after blood loss compared with baseline during wakefulness. These decreases were mirrored by decreases in the RMSSD index, which reflects cardiac vagal modulation. These results support the view that the cBRS decrease associated with the upright posture is a byproduct of decreased cardiac vagal modulation, triggered by the arterial baroreflex in response to central hypovolemia. Conversely, the greater baroreflex contribution to cardiac control associated with upright posture may be explained, at least in part, by enhanced fluctuations of SAP, which elicit a more effective entrainment of HP fluctuations by the arterial baroreflex. These SAP fluctuations may result from enhanced fluctuations of vascular resistance specific to the upright posture, and not be driven by the accompanying central hypovolemia. PMID:28396638

Physiological Mechanisms Mediating the Coupling between Heart Period and Arterial Pressure in Response to Postural Changes in Humans.

PubMed

Silvani, Alessandro; Calandra-Buonaura, Giovanna; Johnson, Blair D; van Helmond, Noud; Barletta, Giorgio; Cecere, Anna G; Joyner, Michael J; Cortelli, Pietro

2017-01-01

The upright posture strengthens the coupling between heart period (HP) and systolic arterial pressure (SAP) consistently with a greater contribution of the arterial baroreflex to cardiac control, while paradoxically decreasing cardiac baroreflex sensitivity (cBRS). To investigate the physiological mechanisms that mediate the coupling between HP and SAP in response to different postures, we analyzed the cross-correlation functions between low-frequency HP and SAP fluctuations and estimated cBRS with the sequence technique in healthy male subjects during passive head-up tilt test (HUTT, n = 58), during supine wakefulness, supine slow-wave sleep (SWS), and in the seated and active standing positions ( n = 8), and during progressive loss of 1 L blood ( n = 8) to decrease central venous pressure in the supine position. HUTT, SWS, the seated, and the standing positions, but not blood loss, entailed significant increases in the positive correlation between HP and the previous SAP values, which is the expected result of arterial baroreflex control, compared with baseline recordings in the supine position during wakefulness. These increases were mirrored by increases in the low-frequency variability of SAP in each condition but SWS. cBRS decreased significantly during HUTT, in the seated and standing positions, and after blood loss compared with baseline during wakefulness. These decreases were mirrored by decreases in the RMSSD index, which reflects cardiac vagal modulation. These results support the view that the cBRS decrease associated with the upright posture is a byproduct of decreased cardiac vagal modulation, triggered by the arterial baroreflex in response to central hypovolemia. Conversely, the greater baroreflex contribution to cardiac control associated with upright posture may be explained, at least in part, by enhanced fluctuations of SAP, which elicit a more effective entrainment of HP fluctuations by the arterial baroreflex. These SAP fluctuations may result from enhanced fluctuations of vascular resistance specific to the upright posture, and not be driven by the accompanying central hypovolemia.

Validation of the Rossmax CF175 upper-arm blood pressure monitor for home blood pressure monitoring according to the European Society of Hypertension International Protocol revision 2010.

PubMed

Zhang, Lu; Kang, Yuan-Yuan; Zeng, Wei-Fang; Li, Yan; Wang, Ji-Guang

2015-04-01

The present study aimed to evaluate the accuracy of the Rossmax CF175 upper-arm blood pressure monitor for home blood pressure monitoring according to the International Protocol of the European Society of Hypertension revision 2010. Systolic and diastolic blood pressures were sequentially measured in 33 adult Chinese (17 women, mean age 46 years) using a mercury sphygmomanometer (two observers) and the Rossmax CF175 device (one supervisor). A total of 99 pairs of comparisons were obtained from 33 participants for judgments in two parts with three grading phases. All the blood pressure requirements were fulfilled. The Rossmax CF175 device achieved the targets in part 1 of the validation study. The number of absolute differences between the device and observers within 5, 10, and 15 mmHg was 78/99, 94/99, and 98/99, respectively, for systolic blood pressure, and 81/99, 96/99, and 97/99, respectively, for diastolic blood pressure. The device also achieved the criteria in part 2 of the validation study. Twenty-nine participants, for both of systolic and diastolic blood pressure, had at least two of the three device-observers differences within 5 mmHg (required ≥24). Only one participant for diastolic blood pressure had all three device-observers comparisons greater than 5 mmHg. The Rossmax automated oscillometric upper-arm blood pressure monitor CF175 fulfilled the requirements of the International Protocol revision 2010, and hence can be recommended for blood pressure measurement in adults.

Validation of the Andon KD-5965 upper-arm blood pressure monitor for home blood pressure monitoring according to the European Society of Hypertension International Protocol revision 2010.

PubMed

Huang, Jinhua; Li, Zhijie; Li, Guimei; Liu, Zhaoying

2015-10-01

This study aimed to evaluate the accuracy of the Andon KD-5965 upper-arm blood pressure monitor according to the European Society of Hypertension International Protocol revision 2010. Systolic and diastolic blood pressures were sequentially measured in 33 adults, with 20 women using a mercury sphygmomanometer (two observers) and the Andon KD-5965 device (one supervisor). A total of 99 pairs of comparisons were obtained from 33 participants for judgments in two parts with three grading phases. The device achieved the targets in part 1 of the validation study. The number of absolute differences between the device and observers within 5, 10, and 15 mmHg was 70/99, 91/99, and 98/99, respectively, for systolic blood pressure and 81/99, 99/99, and 99/99, respectively, for diastolic blood pressure. The device also fulfilled the criteria in part 2 of the validation study. Twenty-five and 29 participants, for systolic and diastolic blood pressure, respectively, had at least two of the three device-observers differences within 5 mmHg (required≥24). Two and one participants for systolic and diastolic blood pressure, respectively, had all three device-observers comparisons greater than 5 mmHg. According to the validation results, with better performance for diastolic blood pressure than that for systolic blood pressure, the Andon automated oscillometric upper-arm blood pressure monitor KD-5965 fulfilled the requirements of the European Society of Hypertension International Protocol revision 2010, and hence can be recommended for blood pressure measurement in adults.