Shape evolution of a core-shell spherical particle under hydrostatic pressure.

PubMed

Colin, Jérôme

2012-03-01

The morphological evolution by surface diffusion of a core-shell spherical particle has been investigated theoretically under hydrostatic pressure when the shear modulii of the core and shell are different. A linear stability analysis has demonstrated that depending on the pressure, shear modulii, and radii of both phases, the free surface of the composite particle may be unstable with respect to a shape perturbation. A stability diagram finally emphasizes that the roughness development is favored in the case of a hard shell with a soft core.

Cold-air performance of a tip turbine designed to drive a lift fan. 1: Baseline performance

NASA Technical Reports Server (NTRS)

Haas, J. E.; Kofskey, M. G.; Hotz, G. M.; Futral, S. M., Jr.

1976-01-01

Full admission baseline performance was obtained for a 0.4 linear scale of the LF460 lift fan turbine over a range of speeds and pressure ratios without leakage air. These cold-air tests covered a range of speeds from 40 to 140 percent of design equivalent speed and a range of scroll inlet to diffuser exit static pressure ratios from 2.0 to 4.2. Results are presented in terms of specific work, torque, mass flow, efficiency, and total pressure drop.

Effect of clamping pressure on ohmic resistance and compression of gas diffusion layers for polymer electrolyte fuel cells

NASA Astrophysics Data System (ADS)

Mason, Thomas J.; Millichamp, Jason; Neville, Tobias P.; El-kharouf, Ahmad; Pollet, Bruno G.; Brett, Daniel J. L.

2012-12-01

This paper describes the use of an in situ analytical technique based on simultaneous displacement and resistance measurement of gas diffusion layers (GDLs) used in polymer electrolyte fuel cells (PEFCs), when exposed to varying compaction pressure. In terms of the losses within fuel cells, the ohmic loss makes up a significant portion. Of this loss, the contact resistance between the GDL and the bipolar plate (BPP) is an important constituent. By analysing the change in thickness and ohmic resistance of GDLs under compression, important mechanical and electrical properties are obtained. Derived parameters such as the 'displacement factor' are used to characterise a representative range of commercial GDLs. Increasing compaction pressure leads to a non-linear decrease in resistance for all GDLs. For Toray paper, compaction becomes more irreversible with pressure with no elastic region observed. Different GDLs have different intrinsic resistance; however, all GDLs of the same class share a common compaction profile (change in resistance with pressure). Cyclic compression of Toray GDL leads to progressive improvement in resistance and reduction in thickness that stabilises after ∼10 cycles.

Dynamic Stability of the Rate, State, Temperature, and Pore Pressure Friction Model at a Rock Interface

NASA Astrophysics Data System (ADS)

Sinha, Nitish; Singh, Arun K.; Singh, Trilok N.

2018-05-01

In this article, we study numerically the dynamic stability of the rate, state, temperature, and pore pressure friction (RSTPF) model at a rock interface using standard spring-mass sliding system. This particular friction model is a basically modified form of the previously studied friction model namely the rate, state, and temperature friction (RSTF). The RSTPF takes into account the role of thermal pressurization including dilatancy and permeability of the pore fluid due to shear heating at the slip interface. The linear stability analysis shows that the critical stiffness, at which the sliding becomes stable to unstable or vice versa, increases with the coefficient of thermal pressurization. Critical stiffness, on the other hand, remains constant for small values of either dilatancy factor or hydraulic diffusivity, but the same decreases as their values are increased further from dilatancy factor (˜ 10^{ - 4} ) and hydraulic diffusivity (˜ 10^{ - 9} {m}2 {s}^{ - 1} ) . Moreover, steady-state friction is independent of the coefficient of thermal pressurization, hydraulic diffusivity, and dilatancy factor. The proposed model is also used for predicting time of failure of a creeping interface of a rock slope under the constant gravitational force. It is observed that time of failure decreases with increase in coefficient of thermal pressurization and hydraulic diffusivity, but the dilatancy factor delays the failure of the rock fault under the condition of heat accumulation at the creeping interface. Moreover, stiffness of the rock-mass also stabilizes the failure process of the interface as the strain energy due to the gravitational force accumulates in the rock-mass before it transfers to the sliding interface. Practical implications of the present study are also discussed.

Diffusion in Jammed Particle Packs.

PubMed

Bolintineanu, Dan S; Grest, Gary S; Lechman, Jeremy B; Silbert, Leonardo E

2015-08-21

Using random walk simulations we explore diffusive transport through monodisperse sphere packings over a range of packing fractions ϕ in the vicinity of the jamming transition at ϕ(c). Various diffusion properties are computed over several orders of magnitude in both time and packing pressure. Two well-separated regimes of normal "Fickian" diffusion, where the mean squared displacement is linear in time, are observed. The first corresponds to diffusion inside individual spheres, while the latter is the long-time bulk diffusion. The intermediate anomalous diffusion regime and the long-time value of the diffusion coefficient are both shown to be controlled by particle contacts, which in turn depend on proximity to ϕ(c). The time required to recover normal diffusion t* scales as (ϕ-ϕ(c))(-0.5) and the long-time diffusivity D(∞)∼(ϕ-ϕ(c))0.5, or D(∞)∼1/t*. It is shown that the distribution of mean first passage times associated with the escape of random walkers between neighboring particles controls both t* and D(∞) in the limit ϕ→ϕ(c).

High fluid pressure and triggered earthquakes in the enhanced geothermal system in Basel, Switzerland

NASA Astrophysics Data System (ADS)

Terakawa, T.; Miller, S. A.; Deichmann, N.

2011-12-01

We estimate the pore fluid pressure field of the stimulated region during the fluid injection experiment in Basel, Switzerland by analyzing 118 well-constrained focal mechanisms. This technique, termed focal mechanism tomography (FMT), uses the orientations of the slip planes within the prevailing regional stress field as indicator of the fluid pressure along the plane at the time of slip. Elevated pore fluid pressures were concentrated within 500 m of the open hole section, and we find average earthquake triggering excess pressures of about 10MPa, with a peak value of 19.3 MPa, consistent with the known wellhead pressure applied at the borehole. Our results demonstrate that FMT is a robust approach, being validated at the macroscopic scale of the Basel stimulation experiment. Over-pressurized fluids induced many small events (M < 3) along faults unfavourably-oriented relative to the tectonic stress pattern, while larger events tended to occur along optimally-oriented faults. This suggests that small-scale hydraulic networks, developed from the high pressure stimulation, interact to load (hydraulically isolated) high strength bridges that produce the larger events. The triggering pore fluid pressures are substantially higher than that predicted from a linear pressure diffusion process from the source boundary, showing that the system is highly permeable along flow paths, allowing fast pressure diffusion to the boundaries of the stimulated region.

The Effect of Composition on Diffusion of Au in Fe and Fe-Ni Alloys

NASA Astrophysics Data System (ADS)

Johanesen, K. E.; Watson, H. C.; Fei, Y.

2005-12-01

Understanding siderophile element diffusion in Fe-Ni alloys will lead to tighter constraints on processes such as meteoritic body cooling rates, and inner core-outer core communication. Recent studies have determined the effect of temperature and pressure on diffusion in this system, but the effect of composition has not yet been explored adequately. The effect of Ni content on Au diffusion in an Fe-Ni system was explored for Fe-Ni alloys with concentrations of 0, 20, and 30 wt. % Ni. Diffusion couple experiments were conducted using a piston cylinder press at 1 GPa and temperatures ranging from 1150°C to 1400°C. Concentration profiles were measured by electron microprobe and were fitted to the linear diffusion solution for an semi-infinite diffusion couple to extract diffusion coefficients (D) using a non-linear least squares fit routine. As predicted, D increases with Ni content and also with temperature. The diffusivities ranged from 2.06×10-9 at 1150°C to 5.76×10-8 at 1350°C for 0 wt. % Ni; 5.17×10-9 at 1150° C to 1.93×10-7 at 1400°C for 20 wt. % Ni; and 2.41×10-8 at 1150°C to 2.13×10-7 at 1400°C for 30 wt. % Ni. As temperature increases, the effect of Ni on diffusion rates increases, implying a possible change in diffusion mechanism between 1250°C and 1300°C. Ni appears to have a negligible effect at lower temperatures, which would indicate that Ni may not need to be considered when modeling siderophile trace element diffusion rates in iron meteorites.

Pre-Darcy Flow in Porous Media

NASA Astrophysics Data System (ADS)

Dejam, Morteza; Hassanzadeh, Hassan; Chen, Zhangxin

2017-10-01

Fluid flow in porous media is very important in a wide range of science and engineering applications. The entire establishment of fluid flow application in porous media is based on the use of an experimental law proposed by Darcy (1856). There are evidences in the literature that the flow of a fluid in consolidated and unconsolidated porous media does not follow Darcy law at very low fluxes, which is called pre-Darcy flow. In this paper, the unsteady flow regimes of a slightly compressible fluid under the linear and radial pre-Darcy flow conditions are modeled and the corresponding highly nonlinear diffusivity equations are solved analytically by aid of a generalized Boltzmann transformation technique. The influence of pre-Darcy flow on the pressure diffusion for homogeneous porous media is studied in terms of the nonlinear exponent and the threshold pressure gradient. In addition, the pressure gradient, flux, and cumulative production per unit area are compared with the classical solution of the diffusivity equation based on Darcy flow. The presented results advance our understanding of fluid flow in low-permeability media such as shale and tight formations, where pre-Darcy is the dominant flow regime.

A comparison/validation of a fractional derivative model with an empirical model of non-linear shock waves in swelling shales

NASA Astrophysics Data System (ADS)

Droghei, Riccardo; Salusti, Ettore

2013-04-01

Control of drilling parameters, as fluid pressure, mud weight, salt concentration is essential to avoid instabilities when drilling through shale sections. To investigate shale deformation, fundamental for deep oil drilling and hydraulic fracturing for gas extraction ("fracking"), a non-linear model of mechanic and chemo-poroelastic interactions among fluid, solute and the solid matrix is here discussed. The two equations of this model describe the isothermal evolution of fluid pressure and solute density in a fluid saturated porous rock. Their solutions are quick non-linear Burger's solitary waves, potentially destructive for deep operations. In such analysis the effect of diffusion, that can play a particular role in fracking, is investigated. Then, following Civan (1998), both diffusive and shock waves are applied to fine particles filtration due to such quick transients , their effect on the adjacent rocks and the resulting time-delayed evolution. Notice how time delays in simple porous media dynamics have recently been analyzed using a fractional derivative approach. To make a tentative comparison of these two deeply different methods,in our model we insert fractional time derivatives, i.e. a kind of time-average of the fluid-rocks interactions. Then the delaying effects of fine particles filtration is compared with fractional model time delays. All this can be seen as an empirical check of these fractional models.

Modeling Disturbance Dynamics in Transitional and Turbulent Boundary Layers

NASA Technical Reports Server (NTRS)

Grosch, C. E.; Gatski, T. B. (Technical Monitor)

2002-01-01

The dynamics of an ensemble of linear disturbances in boundary-layer flows at various Reynolds numbers is studied through an analysis of the transport equations for the mean disturbance kinetic energy and energy dissipation rate. Effects of adverse and favorable pressure-gradients on the disturbance dynamics are also included in the analysis. Unlike the fully turbulent regime where nonlinear phase scrambling of the fluctuations affects the flow field even in proximity to the wall, the early stage transition regime fluctuations studied here are influenced across the boundary layer by the solid boundary. In addition, the dominating dynamics in the disturbance kinetic energy equation is governed by the energy production, pressure-transport and viscous diffusion - also in contrast to the fully turbulent regime. For the disturbance dissipation rate, a dynamic balance exists between the destruction and diffusion of dissipation.

Modelling and control of a diffusion/LPCVD furnace

NASA Astrophysics Data System (ADS)

Dewaard, H.; Dekoning, W. L.

1988-12-01

Heat transfer inside a cylindrical resistance diffusion/Low Pressure Chemical Vapor Deposition (LPCVD) furnace is studied with the aim of developing an improved temperature controller. A model of the thermal behavior is derived, which covers the important class of furnaces equipped with semitransparent quartz process tubes. The model takes into account the thermal behavior of the thermocouples. Currently used temperature controllers are shown to be highly inefficient for very large scale integration applications. Based on the model an alternative temperature controller of the LQG (linear quadratic Gaussian) type is proposed which features direct wafer temperature control. Some simulation results are given.

The role of surface oxides on hydrogen sorption kinetics in titanium thin films

NASA Astrophysics Data System (ADS)

Hadjixenophontos, Efi; Michalek, Lukas; Roussel, Manuel; Hirscher, Michael; Schmitz, Guido

2018-05-01

Titanium is presently discussed as a catalyst to accelerate the hydrogenation kinetics of hydrogen storage materials. It is however known that H absorption in Ti decisively depends on the surface conditions (presence or absence of the natural surface oxide). In this work, we use Ti thin films of controlled thickness (50-800 nm) as a convenient tool for quantifying the atomic transport. XRD and TEM investigations allow us to follow the hydrogenation progress inside the film. Hydrogenation of TiO2/Ti bi-layers is studied at 300 °C, for different durations (10 s to 600 min) and at varying pressures of pure H2 atmosphere. Under these conditions, the hydrogenation is found to be linear in time. By comparing films with and without TiO2, as well as by studying the pressure dependence of hydrogenation, it is demonstrated that hydrogen transport across the oxide represents the decisive kinetic barrier rather than the splitting of H2 molecules at the surface. Hydrogenation appears by a layer-like reaction initiated by heterogeneous nucleation at the backside interface to the substrate. The linear growth constant and the H diffusion coefficient inside the oxide are quantified, as well as a reliable lower bound to the hydrogen diffusion coefficient in Ti is derived. The pressure dependence of hydrogen absorption is quantitatively modelled.

Effect of Cross-Linking on Free Volume Properties of PEG Based Thiol-Ene Networks

NASA Astrophysics Data System (ADS)

Ramakrishnan, Ramesh; Vasagar, Vivek; Nazarenko, Sergei

According to the Fox and Loshaek theory, in elastomeric networks, free volume decreases linearly with the cross-link density increase. The aim of this study is to show whether the poly(ethylene glycol) (PEG) based multicomponent thiol-ene elastomeric networks demonstrate this model behavior? Networks with a broad cross-link density range were prepared by changing the ratio of the trithiol crosslinker to PEG dithiol and then UV cured with PEG diene while maintaining 1:1 thiol:ene stoichiometry. Pressure-volume-temperature (PVT) data of the networks was generated from the high pressure dilatometry experiments which was fit using the Simha-Somcynsky Equation-of-State analysis to obtain the fractional free volume of the networks. Using Positron Annihilation Lifetime Spectroscopy (PALS) analysis, the average free volume hole size of the networks was also quantified. The fractional free volume and the average free volume hole size showed a linear change with the cross-link density confirming that the Fox and Loshaek theory can be applied to this multicomponent system. Gas diffusivities of the networks showed a good correlation with free volume. A free volume based model was developed to describe the gas diffusivity trends as a function of cross-link density.

Kinetic-MHD simulations of gyroresonance instability driven by CR pressure anisotropy

NASA Astrophysics Data System (ADS)

Lebiga, O.; Santos-Lima, R.; Yan, H.

2018-05-01

The transport of cosmic rays (CRs) is crucial for the understanding of almost all high-energy phenomena. Both pre-existing large-scale magnetohydrodynamic (MHD) turbulence and locally generated turbulence through plasma instabilities are important for the CR propagation in astrophysical media. The potential role of the resonant instability triggered by CR pressure anisotropy to regulate the parallel spatial diffusion of low-energy CRs (≲100 GeV) in the interstellar and intracluster medium of galaxies has been shown in previous theoretical works. This work aims to study the gyroresonance instability via direct numerical simulations, in order to access quantitatively the wave-particle scattering rates. For this, we employ a 1D PIC-MHD code to follow the growth and saturation of the gyroresonance instability. We extract from the simulations the pitch-angle diffusion coefficient Dμμ produced by the instability during the linear and saturation phases, and a very good agreement (within a factor of 3) is found with the values predicted by the quasi-linear theory (QLT). Our results support the applicability of the QLT for modelling the scattering of low-energy CRs by the gyroresonance instability in the complex interplay between this instability and the large-scale MHD turbulence.

Time-resolved production and detection of reactive atoms

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

Grossman, L. W.; Hurst, G. S.

1977-09-01

Cesium iodide in the presence of a buffer gas was dissociated with a pulsed ultraviolet laser, which will be referred to as the source laser. This created a population of atoms at a well defined time and in a compact, well defined volume. A second pulsed laser, with a beam that completely surrounded that of the first, photoionized the cesium after a known time delay. This laser will be referred to as the detector laser. It was determined that for short time delays, all of the cesium atoms were easily ionized. When focused, the source laser generated an extremely intensemore » fluence. By accounting for the beam intensity profile it was shown that all of the molecules in the central portion of the beam can be dissociated and detected. Besides proving the feasibility of single-molecule detection, this enabled a determination of the absolute photodissociation cross section as a function of wavelength. Initial studies of the time decay of the cesium signal at low argon pressures indicated a non-exponential decay. This was consistent with a diffusion mechanism transporting cesium atoms out of the laser beam. Therefore, it was desired to conduct further experiments using a tightly focused source beam, passing along the axis of the detector beam. The theoretical behavior of this simple geometry accounting for diffusion and reaction is easily calculated. A diffusion coefficient can then be extracted by data fitting. If reactive decay is due to impurities constituting a fixed percentage of the buffer gas, then two-body reaction rates will scale linearly with pressure and three-body reaction rates will scale quadratically. Also, the diffusion coefficient will scale inversely with pressure. At low pressures it is conceivable that decay due to diffusion would be sufficiently rapid that all other processes can be neglected. Extraction of a diffusion coefficient would then be quite direct. Finally, study of the reaction of cesium and oxygen was undertaken.« less

Orthotropic and time-dependent moisture diffusion measurements in polymer matrix composites using nuclear reaction analysis

NASA Astrophysics Data System (ADS)

Pilli, Siva P.

Moisture plays a significant role in influencing the mechanical behavior and long-term durability of composites. The objective of this dissertation was to understand the basic concepts of moisture transport in polymeric composites. Humidity test chambers were used in combination with D2O water to characterize the diffusion of D2O using Nuclear Reaction Analysis (NRA). Moisture content was measured as a function of through-thickness depth using NRA. In this study a novel method to measure the orthotropic diffusivities of polymer matrix composites has been demonstrated. This was achieved by soaking the samples in D2O vapor and subsequently characterizing the diffusion of D2O at all edges of the coupon using NRA. The diffusivity through the surface was 3½ times higher than the diffusivity through the edges. A direct comparison of experimental data with models using orthotropic diffusivities was in relatively good agreement. Surface moisture content was also measured as a function of time using NRA. It was shown that the surface concentration reaches an intermediate value of 79% Mm very rapidly and is followed by a slow linear increase to the saturation level (Mm). This research also interrogates the effect of pressure on diffusion. Test chambers were built to maintain a constant relative humidity of 80% at 60°C at three different pressures (0.101 MPa, 0.517 MPa and 1.034 MPa) including a liquid water immersion test chamber at 60°C. In this study it was observed that the time to saturation increased with increasing chamber pressure. This was primarily due to the increased maximum moisture content at higher pressures. Liquid immersion of the test samples provided the upper bound for maximum moisture content and a lower bound for time to saturation. The effects of material systems and layups on humidity measurements were also studied using two different polymer composite material systems, Cycom and Toray. Diffusivity results were identical for different layups whereas differences were observed for different material systems. Finally three-dimensional numeric models were developed, using ANSYS, to compare with the measured moisture content. Models incorporating the time-dependent and 3-D diffusion have shown an improved correlation with experiments.

High fluid pressure and triggered earthquakes in the enhanced geothermal system in Basel, Switzerland

NASA Astrophysics Data System (ADS)

Terakawa, Toshiko; Miller, Stephen A.; Deichmann, Nicholas

2012-07-01

We analyzed 118 well-constrained focal mechanisms to estimate the pore fluid pressure field of the stimulated region during the fluid injection experiment in Basel, Switzerland. This technique, termed focal mechanism tomography (FMT), uses the orientations of slip planes within the prevailing regional stress field as an indicator of the fluid pressure along the plane at the time of slip. The maximum value and temporal change of excess pore fluid pressures are consistent with the known history of the wellhead pressure applied at the borehole. Elevated pore fluid pressures were concentrated within 500 m of the open hole section, which are consistent with the spatiotemporal evolution of the induced microseismicity. Our results demonstrate that FMT is a robust approach, being validated at the meso-scale of the Basel stimulation experiment. We found average earthquake triggering excess pore fluid pressures of about 10 MPa above hydrostatic. Overpressured fluids induced many small events (M < 3) along faults unfavorably oriented relative to the tectonic stress pattern, while the larger events tended to occur along optimally oriented faults. This suggests that small-scale hydraulic networks, developed from the high pressure stimulation, interact to load (hydraulically isolated) high strength bridges that produce the larger events. The triggering pore fluid pressures are substantially higher than that predicted from a linear pressure diffusion process from the source boundary, and shows that the system is highly permeable along flow paths that allow fast pressure diffusion to the boundaries of the stimulated region.

Fabrication of All-SiC Fiber-Optic Pressure Sensors for High-Temperature Applications

PubMed Central

Jiang, Yonggang; Li, Jian; Zhou, Zhiwen; Jiang, Xinggang; Zhang, Deyuan

2016-01-01

Single-crystal silicon carbide (SiC)-based pressure sensors can be used in harsh environments, as they exhibit stable mechanical and electrical properties at elevated temperatures. A fiber-optic pressure sensor with an all-SiC sensor head was fabricated and is herein proposed. SiC sensor diaphragms were fabricated via an ultrasonic vibration mill-grinding (UVMG) method, which resulted in a small grinding force and low surface roughness. The sensor head was formed by hermetically bonding two layers of SiC using a nickel diffusion bonding method. The pressure sensor illustrated a good linearity in the range of 0.1–0.9 MPa, with a resolution of 0.27% F.S. (full scale) at room temperature. PMID:27763494

Fabrication of All-SiC Fiber-Optic Pressure Sensors for High-Temperature Applications.

PubMed

Jiang, Yonggang; Li, Jian; Zhou, Zhiwen; Jiang, Xinggang; Zhang, Deyuan

2016-10-17

Single-crystal silicon carbide (SiC)-based pressure sensors can be used in harsh environments, as they exhibit stable mechanical and electrical properties at elevated temperatures. A fiber-optic pressure sensor with an all-SiC sensor head was fabricated and is herein proposed. SiC sensor diaphragms were fabricated via an ultrasonic vibration mill-grinding (UVMG) method, which resulted in a small grinding force and low surface roughness. The sensor head was formed by hermetically bonding two layers of SiC using a nickel diffusion bonding method. The pressure sensor illustrated a good linearity in the range of 0.1-0.9 MPa, with a resolution of 0.27% F.S. (full scale) at room temperature.

Aortic stiffness is associated with white matter integrity in patients with type 1 diabetes.

PubMed

Tjeerdema, Nathanja; Van Schinkel, Linda D; Westenberg, Jos J; Van Elderen, Saskia G; Van Buchem, Mark A; Smit, Johannes W; Van der Grond, Jeroen; De Roos, Albert

2014-09-01

To assess the association between aortic pulse wave velocity (PWV) as a marker of arterial stiffness and diffusion tensor imaging of brain white matter integrity in patients with type 1 diabetes using advanced magnetic resonance imaging (MRI) technology. Forty-one patients with type 1 diabetes (23 men, mean age 44 ± 12 years, mean diabetes duration 24 ± 13 years) were included. Aortic PWV was assessed using through-plane velocity-encoded MRI. Brain diffusion tensor imaging (DTI) measurements were performed on 3-T MRI. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were calculated for white and grey matter integrity. Pearson correlation and multivariable linear regression analyses including cardiovascular risk factors as covariates were assessed. Multivariable linear regression analyses revealed that aortic PWV is independently associated with white matter integrity FA (β = -0.777, p = 0.008) in patients with type 1 diabetes. This effect was independent of age, gender, mean arterial pressure, body mass index, smoking, duration of diabetes and glycated haemoglobin levels. Aortic PWV was not significantly related to grey matter integrity. Our data suggest that aortic stiffness is independently associated with reduced white matter integrity in patients with type 1 diabetes. Aortic stiffness is associated with brain injury. Aortic stiffness exposes small vessels to high pressure fluctuations and flow. Aortic stiffness is associated with microvascular brain injury in diabetes. This suggests a vascular contribution to early subtle microstructural deficits.

Nonlinear vibration and radiation from a panel with transition to chaos induced by acoustic waves

NASA Technical Reports Server (NTRS)

Maestrello, Lucio; Frendi, Abdelkader; Brown, Donald E.

1992-01-01

The dynamic response of an aircraft panel forced at resonance and off-resonance by plane acoustic waves at normal incidence is investigated experimentally and numerically. Linear, nonlinear (period doubling) and chaotic responses are obtained by increasing the sound pressure level of the excitation. The response time history is sensitive to the input level and to the frequency of excitation. The change in response behavior is due to a change in input conditions, triggered either naturally or by modulation of the bandwidth of the incident waves. Off-resonance, bifurcation is diffused and difficult to maintain, thus the panel response drifts into a linear behavior. The acoustic pressure emanated by the panel is either linear or nonlinear as is the vibration response. The nonlinear effects accumulate during the propagation with distance. Results are also obtained on the control of the panel response using damping tape on aluminum panel and using a graphite epoxy panel having the same size and weight. Good agreement is obtained between the experimental and numerical results.

Nonlinear vibration and radiation from a panel with transition to chaos

NASA Technical Reports Server (NTRS)

Maestrello, Lucio; Frendi, Abdelkader; Brown, Donald E.

1992-01-01

The dynamic response of an aircraft panel forced at resonance and off-resonance by plane acoustic waves at normal incidence is investigated experimentally and numerically. Linear, nonlinear (period doubling), and chaotic responses are obtained by increasing the sound pressure level of the excitation. The response time history is sensitive to the input level and to the frequency of excitation. The change in response behavior is due to a change in input conditions, triggered either naturally or by modulation of the bandwidth of the incident waves. Off-resonance bifurcation is diffused and difficult to maintain; thus the panel response drifts into a linear behavior. The acoustic pressure emanated by the panel is either linear or nonlinear as is the vibration response. The nonlinear effects accumulate during the propagation with distance. Results are also obtained on the control of the panel response using damping tape on an aluminum panel and a graphite epoxy panel having the same size and weight. Good agreement is obtained betwen the experimental and numerical results.

Creeping gaseous flows through elastic tube and annulus micro-configurations

NASA Astrophysics Data System (ADS)

Elbaz, Shai; Jacob, Hila; Gat, Amir

2016-11-01

Gaseous flows in elastic micro-configurations is relevant to biological systems (e.g. alveolar ducts in the lungs) as well as to applications such as gas actuated soft micro-robots. We here examine the effect of low-Mach-number compressibility on creeping gaseous axial flows through linearly elastic tube and annulus micro-configurations. For steady flows, the leading-order effects of elasticity on the pressure distribution and mass-flux are obtained. For transient flow in a tube with small deformations, elastic effects are shown to be negligible in leading order due to compressibility. We then examine transient flows in annular configurations where the deformation is significant compared with the gap between the inner and outer cylinders defining the annulus. Both compressibility and elasticity are obtained as dominant terms interacting with viscosity. For a sudden flux impulse, the governing non-linear leading order diffusion equation is initially approximated by a porous-medium-equation of order 2.5 for the pressure square. However, as the fluid expand and the pressure decreases, the governing equation degenerates to a porous-medium-equation of order 2 for the pressure.

Laser-Induced Fluorescence Measurements and Modeling of Nitric Oxide in Counterflow Diffusion Flames

NASA Technical Reports Server (NTRS)

Ravikrishna, Rayavarapu V.

2000-01-01

The feasibility of making quantitative nonintrusive NO concentration ([NO]) measurements in nonpremixed flames has been assessed by obtaining laser-induced fluorescence (LIF) measurements of [NO] in counterflow diffusion flames at atmospheric and higher pressures. Comparisons at atmospheric pressure between laser-saturated fluorescence (LSF) and linear LIF measurements in four diluted ethane-air counterflow diffusion flames with strain rates from 5 to 48/s yielded excellent agreement from fuel-lean to moderately fuel-rich conditions, thus indicating the utility of a model-based quenching correction technique, which was then extended to higher pressures. Quantitative LIF measurements of [NO] in three diluted methane-air counterflow diffusion flames with strain rates from 5 to 35/s were compared with OPPDIF model predictions using the GRI (version 2.11) chemical kinetic mechanism. The comparisons revealed that the GRI mechanism underpredicts prompt-NO by 30-50% at atmospheric pressure. Based on these measurements, a modified reaction rate coefficient for the prompt-NO initiation reaction was proposed which causes the predictions to match experimental data. Temperature measurements using thin filament pyrometry (TFP) in conjunction with a new calibration method utilizing a near-adiabatic H2-air Hencken burner gave very good comparisons with model predictions in these counterflow diffusion flames. Quantitative LIF measurements of [NO] were also obtained in four methane-air counterflow partially-premixed flames with fuel-side equivalence ratios (phi(sub B)) of 1.45, 1.6, 1.8 and 2.0. The measurements were in excellent agreement with model predictions when accounting for radiative heat loss. Spatial separation between regions dominated by the prompt and thermal NO mechanisms was observed in the phi(sub B) = 1.45 flame. The modified rate coefficient proposed earlier for the prompt-NO initiation reaction improved agreement between code predictions and measurements in the region where prompt-NO dominates. Finally, LIF measurements of NO were obtained in counterflow diffusion flames at 2 to 5 atm. Comparisons between [NO] measurements and predictions show that the GRI mechanism underpredicts prompt-NO by a factor of two to three at all pressures. In general, the results indicate a need for refinement of the CH chemistry, especially the pressure-dependent CH formation and destruction reactions.

Group invariant solution for a pre-existing fluid-driven fracture in impermeable rock

NASA Astrophysics Data System (ADS)

Fitt, A. D.; Mason, D. P.; Moss, E. A.

2007-11-01

The propagation of a two-dimensional fluid-driven fracture in impermeable rock is considered. The fluid flow in the fracture is laminar. By applying lubrication theory a partial differential equation relating the half-width of the fracture to the fluid pressure is derived. To close the model the PKN formulation is adopted in which the fluid pressure is proportional to the half-width of the fracture. By considering a linear combination of the Lie point symmetries of the resulting non-linear diffusion equation the boundary value problem is expressed in a form appropriate for a similarity solution. The boundary value problem is reformulated as two initial value problems which are readily solved numerically. The similarity solution describes a preexisting fracture since both the total volume and length of the fracture are initially finite and non-zero. Applications in which the rate of fluid injection into the fracture and the pressure at the fracture entry are independent of time are considered.

Study of parameter of nonlinearity in 2-chloroethanol with 2-dimethylethanolamine/2-diethylethanolamine at different temperatures

NASA Astrophysics Data System (ADS)

Awasthi, Anjali; Awasthi, Aashees

2017-06-01

The acoustic non-linearity parameter (B/A) for binary mixtures of 2-chloroethanol with 2-dimethylethanolamine (2-DMAE) and 2-diethylethanolamine (2-DEAE) are evaluated using Tong Dong, Beyer and Beyer-Tong Dong coefficients at varying concentrations and temperatures ranging from 293.15 to 313.15 K. The nonlinearity parameter is used to calculate various molecular properties such as internal pressure, cohesive energy density, Van der waals' constant, distance of closest approach, diffusion coefficient and rotational correlation time. Additionally, the intermediate quantities like temperature and pressure derivatives of sound velocity and phase shift parameter as a function of temperature are also deduced. The extent of intermolecular interactions, anharmonicity and structural configuration of the binaries under investigation are discussed in terms of excess non-linearity parameter (B/A)E.

Primal-mixed formulations for reaction-diffusion systems on deforming domains

NASA Astrophysics Data System (ADS)

Ruiz-Baier, Ricardo

2015-10-01

We propose a finite element formulation for a coupled elasticity-reaction-diffusion system written in a fully Lagrangian form and governing the spatio-temporal interaction of species inside an elastic, or hyper-elastic body. A primal weak formulation is the baseline model for the reaction-diffusion system written in the deformed domain, and a finite element method with piecewise linear approximations is employed for its spatial discretization. On the other hand, the strain is introduced as mixed variable in the equations of elastodynamics, which in turn acts as coupling field needed to update the diffusion tensor of the modified reaction-diffusion system written in a deformed domain. The discrete mechanical problem yields a mixed finite element scheme based on row-wise Raviart-Thomas elements for stresses, Brezzi-Douglas-Marini elements for displacements, and piecewise constant pressure approximations. The application of the present framework in the study of several coupled biological systems on deforming geometries in two and three spatial dimensions is discussed, and some illustrative examples are provided and extensively analyzed.

Scaling results for the magnetic field line trajectories in the stochastic layer near the separatrix in divertor tokamaks with high magnetic shear using the higher shear map

NASA Astrophysics Data System (ADS)

Punjabi, Alkesh; Ali, Halima; Farhat, Hamidullah

2009-07-01

Extra terms are added to the generating function of the simple map (Punjabi et al 1992 Phys. Rev. Lett. 69 3322) to adjust shear of magnetic field lines in divertor tokamaks. From this new generating function, a higher shear map is derived from a canonical transformation. A continuous analog of the higher shear map is also derived. The method of maps (Punjabi et al 1994 J. Plasma Phys. 52 91) is used to calculate the average shear, stochastic broadening of the ideal separatrix near the X-point in the principal plane of the tokamak, loss of poloidal magnetic flux from inside the ideal separatrix, magnetic footprint on the collector plate, and its area, and the radial diffusion coefficient of magnetic field lines near the X-point. It is found that the width of the stochastic layer near the X-point and the loss of poloidal flux from inside the ideal separatrix scale linearly with average shear. The area of magnetic footprints scales roughly linearly with average shear. Linear scaling of the area is quite good when the average shear is greater than or equal to 1.25. When the average shear is in the range 1.1-1.25, the area of the footprint fluctuates (as a function of average shear) and scales faster than linear scaling. Radial diffusion of field lines near the X-point increases very rapidly by about four orders of magnitude as average shear increases from about 1.15 to 1.5. For higher values of average shear, diffusion increases linearly, and comparatively very slowly. The very slow scaling of the radial diffusion of the field can flatten the plasma pressure gradient near the separatrix, and lead to the elimination of type-I edge localized modes.

COMPARISON OF IMPLICIT SCHEMES TO SOLVE EQUATIONS OF RADIATION HYDRODYNAMICS WITH A FLUX-LIMITED DIFFUSION APPROXIMATION: NEWTON–RAPHSON, OPERATOR SPLITTING, AND LINEARIZATION

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

Tetsu, Hiroyuki; Nakamoto, Taishi, E-mail: h.tetsu@geo.titech.ac.jp

Radiation is an important process of energy transport, a force, and a basis for synthetic observations, so radiation hydrodynamics (RHD) calculations have occupied an important place in astrophysics. However, although the progress in computational technology is remarkable, their high numerical cost is still a persistent problem. In this work, we compare the following schemes used to solve the nonlinear simultaneous equations of an RHD algorithm with the flux-limited diffusion approximation: the Newton–Raphson (NR) method, operator splitting, and linearization (LIN), from the perspective of the computational cost involved. For operator splitting, in addition to the traditional simple operator splitting (SOS) scheme,more » we examined the scheme developed by Douglas and Rachford (DROS). We solve three test problems (the thermal relaxation mode, the relaxation and the propagation of linear waves, and radiating shock) using these schemes and then compare their dependence on the time step size. As a result, we find the conditions of the time step size necessary for adopting each scheme. The LIN scheme is superior to other schemes if the ratio of radiation pressure to gas pressure is sufficiently low. On the other hand, DROS can be the most efficient scheme if the ratio is high. Although the NR scheme can be adopted independently of the regime, especially in a problem that involves optically thin regions, the convergence tends to be worse. In all cases, SOS is not practical.« less

A robust and accurate numerical method for transcritical turbulent flows at supercritical pressure with an arbitrary equation of state

NASA Astrophysics Data System (ADS)

Kawai, Soshi; Terashima, Hiroshi; Negishi, Hideyo

2015-11-01

This paper addresses issues in high-fidelity numerical simulations of transcritical turbulent flows at supercritical pressure. The proposed strategy builds on a tabulated look-up table method based on REFPROP database for an accurate estimation of non-linear behaviors of thermodynamic and fluid transport properties at the transcritical conditions. Based on the look-up table method we propose a numerical method that satisfies high-order spatial accuracy, spurious-oscillation-free property, and capability of capturing the abrupt variation in thermodynamic properties across the transcritical contact surface. The method introduces artificial mass diffusivity to the continuity and momentum equations in a physically-consistent manner in order to capture the steep transcritical thermodynamic variations robustly while maintaining spurious-oscillation-free property in the velocity field. The pressure evolution equation is derived from the full compressible Navier-Stokes equations and solved instead of solving the total energy equation to achieve the spurious pressure oscillation free property with an arbitrary equation of state including the present look-up table method. Flow problems with and without physical diffusion are employed for the numerical tests to validate the robustness, accuracy, and consistency of the proposed approach.

A robust and accurate numerical method for transcritical turbulent flows at supercritical pressure with an arbitrary equation of state

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

Kawai, Soshi, E-mail: kawai@cfd.mech.tohoku.ac.jp; Terashima, Hiroshi; Negishi, Hideyo

2015-11-01

This paper addresses issues in high-fidelity numerical simulations of transcritical turbulent flows at supercritical pressure. The proposed strategy builds on a tabulated look-up table method based on REFPROP database for an accurate estimation of non-linear behaviors of thermodynamic and fluid transport properties at the transcritical conditions. Based on the look-up table method we propose a numerical method that satisfies high-order spatial accuracy, spurious-oscillation-free property, and capability of capturing the abrupt variation in thermodynamic properties across the transcritical contact surface. The method introduces artificial mass diffusivity to the continuity and momentum equations in a physically-consistent manner in order to capture themore » steep transcritical thermodynamic variations robustly while maintaining spurious-oscillation-free property in the velocity field. The pressure evolution equation is derived from the full compressible Navier–Stokes equations and solved instead of solving the total energy equation to achieve the spurious pressure oscillation free property with an arbitrary equation of state including the present look-up table method. Flow problems with and without physical diffusion are employed for the numerical tests to validate the robustness, accuracy, and consistency of the proposed approach.« less

Cold-air performance of a tip turbine designed to drive a lift fan

NASA Technical Reports Server (NTRS)

Haas, J. E.; Kofskey, M. G.; Hotz, G. M.

1978-01-01

Performance was obtained over a range of speeds and pressure ratios for a 0.4 linear scale version of the LF460 lift fan turbine with the rotor radial tip clearance reduced to about 2.5 percent of the rotor blade height. These tests covered a range of speeds from 60 to 140 percent of design equivalent speed and a range of scroll inlet total to diffuser exit static pressure ratios from 2.6 to 4.2. Results are presented in terms of equivalent mass flow, equivalent torque, equivalent specific work, and efficiency.

Energy transfers in internal tide generation, propagation and dissipation in the deep ocean

NASA Astrophysics Data System (ADS)

Floor, J. W.; Auclair, F.; Marsaleix, P.

The energy transfers associated with internal tide (IT) generation by a semi-diurnal surface tidal wave impinging on a supercritical meridionally uniform deep ocean ridge on the f-plane, and subsequent IT-propagation are analysed using the Boussinesq, free-surface, terrain-following ocean model Symphonie. The energy diagnostics are explicitly based on the numerical formulation of the governing equations, permitting a globally conservative, high-precision analysis of all physical and numerical/artificial energy transfers in a sub-domain with open lateral boundaries. The net primary energy balances are quantified using a moving average of length two tidal periods in a simplified control simulation using a single time-step, minimal diffusion, and a no-slip sea floor. This provides the basis for analysis of enhanced vertical and horizontal diffusion and a free-slip bottom boundary condition. After a four tidal period spin-up, the tidally averaged (net) primary energy balance in the generation region, extending ±20 km from the ridge crest, shows that the surface tidal wave loses approximately C = 720 W/m or 0.3% of the mean surface tidal energy flux (2.506 × 10 5 W/m) in traversing the ridge. This corresponds mainly to the barotropic-to-baroclinic energy conversion due to stratified flow interaction with sloping topography. Combined with a normalised net advective flux of baroclinic potential energy of 0.9 × C this causes a net local baroclinic potential energy gain of 0.72 × C and a conversion into baroclinic kinetic energy through the baroclinic buoyancy term of 1.18 × C. Tidally averaged, about 1.14 × C is radiated into the abyssal ocean through the total baroclinic flux of internal pressure associated with the IT- and background density field. This total baroclinic pressure flux is therefore not only determined by the classic linear surface-to-internal tide conversion, but also by the net advection of baroclinic (background) potential energy, indicating the importance of local processes other than linear IT-motion. In the propagation region (PR), integrated over the areas between 20 and 40 km from the ridge crest, the barotropic and baroclinic tide are decoupled. The net incoming total baroclinic pressure flux is balanced by local potential energy gain and outward baroclinic flux of potential energy associated with the total baroclinic density. The primary net energy balances are robust to changes in the vertical diffusion coefficient, whereas relatively weak horizontal diffusion significantly reduces the outward IT energy flux. Diapycnal mixing due to vertical diffusion causes an available potential energy loss of about 1% of the total domain-averaged potential energy gain, which matches {km-1}/{km}ρ0KVN2 to within 0.5%, for km linearly distributed grid-levels and constant background density ρ0, vertical diffusivity ( KV) and buoyancy frequency ( N).

Diffusion of major and trace elements in natural silicate melts as a tool to investigate timescales in magma mixing

NASA Astrophysics Data System (ADS)

González-García, Diego; Zezza, Angela; Behrens, Harald; Vetere, Francesco; Petrelli, Maurizio; Morgavi, Daniele; Perugini, Diego

2016-04-01

New melt injection into a shallow magma chamber is regarded as one of the potential triggers for explosive volcanic eruptions. Chemical diffusion occurring between the two mixing melts is a time-dependent process, and thus has the potential to shed light on the timescales involved in magma mixing events leading to an eruption. In order to achieve this, a complete database of diffusion coefficients in natural melts is a necessary prerequisite. We have carried out a set of 12 diffusion couple experiments in order to determine diffusion coefficients (D) of major and trace elements in two natural silicate melts. Two end-members from the Vulcano island (Aeolian archipelago, Italy) have been chosen for the experiments: a shoshonite (Vulcanello lava platform) and a rhyolitic obsidian (Pietre Cotte lava flow, La Fossa cone). Glasses from each end-member with added water contents of 0 wt%, 1 wt% and 2 wt% were produced in an Internally Heated Pressure Vessel (IHPV). Two glass cylinders with similar water content but different base composition are inserted in Au-Pd capsules and experiments are run in the IHPV at 1200° C with pressure from 0.5 to 3 kbar. Experiment capsules are rapidly quenched and analyzed by FTIR, EPMA and LA-ICP-MS for H2O, major and trace elements, respectively, along 2 mm linear profiles extending across the interface. A Boltzmann-Matano approach is used to obtain concentration-dependent diffusivities. The obtained concentration-distance profiles are asymmetric and extend deeper into the shoshonite relative to the rhyolite, indicating that diffusion is slower in the latter. Results show that diffusivities are notably accelerated by the presence of H2O in the melt. Experiments performed by using water-free glass show diffusivities one order of magnitude lower compared to glasses containing up to 2 wt% H2O. The effect of pressure, in the investigated range, is negligible and falls within measurement error. Among major elements, Si and Ti are the slowest diffusing components, while Na is the fastest. Uphill diffusion minima are observed in Al, Na and some trace elements (Y, Nb, Pb). In contrast to other trace elements, light REE show prominent minima next to the interface between the two melts, with the minimum depth diminishing towards HREE.

Instrument modifications that produced reduced plate heights <2 with sub-2 μm particles and 95% of theoretical efficiency at k=2 in supercritical fluid chromatography.

PubMed

Berger, Terry A

2016-04-29

The concept of peak fidelity was shown to be helpful in modeling tubing and detector cell dimensions. Connection tubing and flow cell variances were modeled to determine appropriate internal ID's, lengths, and volumes. A low dispersion plumbing configuration, based on these calculations, was assembled to replace the standard plumbing and produced the reported results. The modifications made were straightforward using commercially available parts. The full theoretical efficiency of a 3×100 mm column packed with 1.8 μm totally porous particles was achieved for the first time in supercritical fluid chromatography (SFC). Peak fidelity of >0.95 was maintained to below k=2. A reduced plate height as low as 1.87 was measured. Thus, true "ultra high performance" SFC was achieved, with the results a major improvement from all previous SFC reports. Since there were no efficiency losses, none could be attributed to thermal gradients caused by the expansion of the fluid over large pressure drops, under the conditions used. Similarly, changes in diffusion coefficients caused by significant decreases in density during expansion are apparently balanced by the increase in linear velocity, keeping the ratio between the diffusion coefficient and the linear velocity a constant. Changing modifier concentration to change retention was shown to not be a significant problem. All these issues have been a concern in the past. Diffusion coefficients, and viscosity data needs to be collected at high pressures before the actual limits of SFC can be discovered. Copyright © 2016 Elsevier B.V. All rights reserved.

Vibration characteristics of the HPOTP (High-Pressure Oxygen Turbopump) of the SSME (Space Shuttle Main Engine)

NASA Technical Reports Server (NTRS)

Childs, D. W.; Moyer, D. S.

1984-01-01

Attention is given to rotor dynamic problems that have been encountered and eliminated in the course of Space Shuttle Main Engine (SSME) development, as well as continuing, subsynchronous problems which are being encountered in the development of a 109-percent power level engine. The basic model for the SSME's High Pressure Oxygen Turbopump (HPOTP) encompasses a structural dynamic model for the rotor and housing, and component models for the liquid and gas seals, turbine clearance excitation forces, and impeller diffuser forces. Linear model results are used to examine the synchronous response and stability characteristics of the HPOTP, with attention to bearing load and stability problems associated with the second critical speed. Differences between linear and nonlinear model results are discussed and explained in terms of simple models. Simulation results indicate that while synchronous bearing loads can be reduced, subsynchronous motion is not eliminated by seal modifications.

Effect of Geometric Parameters on the Performance of Second Throat Annular Steam Ejectors

DTIC Science & Technology

1991-07-01

Cell Pressure versus Rake Average Exit Pitot Pressure . . . . . . . . . . . 42 15. Baseline Wall Pressure Profiles...diffuser exit plane pitot pressure rake . 2.5.2 Alternate Configurations Six alternate ejector diffuser configurations were tested. A summary of...along the walls of the diffusers to help characterize the flow. The ejector diffuser exit pitot pressure was measured with a 6-probe pitot pressure rake

Effects of inlet flow field conditions on the performance of centrifugal compressor diffusers: Part 1 -- Discrete-passage diffuser

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

Filipenco, V.G.; Deniz, S.; Johnston, J.M.

2000-01-01

This is Part 1 of a two-part paper considering the performance of radial diffusers for use in a high-performance centrifugal compressor. Part 1 reports on discrete-passage diffusers, while Part 2 describes a test of a straight-channel diffuser designed for equivalent duty. Two builds of discrete-passage diffuser were tested, with 30 and 38 separate passages. Both the 30 and 38 passage diffusers investigated showed comparable range of unstalled operation and similar level of overall diffuser pressure recovery. The paper concentrates on the influence of inlet flow conditions on the pressure recovery and operating range of radial diffusers for centrifugal compressor stages.more » The flow conditions examined include diffuser inlet Mach number, flow angle, blockage, and axial flow nonuniformity. The investigation was carried out in a specially built test facility, designed to provide a controlled inlet flow field to the test diffusers. The facility can provide a wide range of diffuser inlet velocity profile distortion and skew with Mach numbers up to unity and flow angles of 63 to 75 deg from the radical direction. The consequences of different averaging methods for the inlet total pressure distributions, which are needed in the definition of diffuser pressure recovery coefficient for nonuniform diffuser inlet conditions, were also assessed. The overall diffuser pressure recovery coefficient, based on suitably averaged inlet total pressure, was found to correlate well with the momentum-averaged flow angle into the diffuser. It is shown that the generally accepted sensitivity of diffuser pressure recovery performance to inlet flow distortion and boundary layer blockage can be largely attributed to inappropriate quantification of the average dynamic pressure at diffuser inlet. Use of an inlet dynamic pressure based on availability or mass-averaging in combination with definition of inlet flow angle based on mass average of the radial and tangential velocity at diffuser inlet removes this sensitivity.« less

Pressure modulation algorithm to separate cerebral hemodynamic signals from extracerebral artifacts.

PubMed

Baker, Wesley B; Parthasarathy, Ashwin B; Ko, Tiffany S; Busch, David R; Abramson, Kenneth; Tzeng, Shih-Yu; Mesquita, Rickson C; Durduran, Turgut; Greenberg, Joel H; Kung, David K; Yodh, Arjun G

2015-07-01

We introduce and validate a pressure measurement paradigm that reduces extracerebral contamination from superficial tissues in optical monitoring of cerebral blood flow with diffuse correlation spectroscopy (DCS). The scheme determines subject-specific contributions of extracerebral and cerebral tissues to the DCS signal by utilizing probe pressure modulation to induce variations in extracerebral blood flow. For analysis, the head is modeled as a two-layer medium and is probed with long and short source-detector separations. Then a combination of pressure modulation and a modified Beer-Lambert law for flow enables experimenters to linearly relate differential DCS signals to cerebral and extracerebral blood flow variation without a priori anatomical information. We demonstrate the algorithm's ability to isolate cerebral blood flow during a finger-tapping task and during graded scalp ischemia in healthy adults. Finally, we adapt the pressure modulation algorithm to ameliorate extracerebral contamination in monitoring of cerebral blood oxygenation and blood volume by near-infrared spectroscopy.

Turbulent shear layers in confining channels

NASA Astrophysics Data System (ADS)

Benham, Graham P.; Castrejon-Pita, Alfonso A.; Hewitt, Ian J.; Please, Colin P.; Style, Rob W.; Bird, Paul A. D.

2018-06-01

We present a simple model for the development of shear layers between parallel flows in confining channels. Such flows are important across a wide range of topics from diffusers, nozzles and ducts to urban air flow and geophysical fluid dynamics. The model approximates the flow in the shear layer as a linear profile separating uniform-velocity streams. Both the channel geometry and wall drag affect the development of the flow. The model shows good agreement with both particle image velocimetry experiments and computational turbulence modelling. The simplicity and low computational cost of the model allows it to be used for benchmark predictions and design purposes, which we demonstrate by investigating optimal pressure recovery in diffusers with non-uniform inflow.

The experimental study of matching between centrifugal compressor impeller and diffuser

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

Tamaki, H.; Nakao, H.; Saito, M.

1999-01-01

the centrifugal compressor for a marine use turbocharger with its design pressure ratio of 3.2 was tested with a vaneless diffuser and various vaned diffusers. Vaned diffusers were chosen to cover impeller operating range as broad as possible. The analysis of the static pressure ratio in the impeller and the diffusing system, consisting of the diffuser and scroll, showed that there were four possible combinations of characteristics of impeller pressure ratio and diffusing system pressure ratio. The flow rate, Q{sub P}, where the impeller achieved maximum static pressure ratio, was surge flow rate of the centrifugal compressor determined by themore » critical flow rate. In order to operate the compressor at a rate lower than Q{sub P}, the diffusing system, whose pressure recovery factor was steep negative slope near Q{sub P}, was needed. When the diffuser throat area was less than a certain value, the compressor efficiency deteriorated; however, the compressor stage pressure ratio was almost constant. In this study, by reducing the diffuser throat area, the compressor could be operated at a flow rate less than 40% of its design flow rate. Analysis of the pressure ratio in the impeller and diffusing systems at design and off-design speeds showed that the irregularities in surge line occurred when the component that controlled the negative slope on the compressor stage pressure ratio changed.« less

Imaging hydraulic fractures using temperature transients in the Belridge Diatomite

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

Shahin, G.T.; Johnston, R.M.

1995-12-31

Results of a temperature transient analysis of Shell`s Phase 1 and Phase 2 Diatomite Steamdrive Pilots are used to image hydraulic injection fracture lengths, angles, and heat injectivities into the low-permeability formation. The Phase 1 Pilot is a limited-interval injection test. In Phase 2, steam is injected into two 350 ft upper and lower zones through separate hydraulic fractures. Temperature response of both pilots is monitored with sixteen logging observation wells. A perturbation analysis of the non-linear pressure diffusion and heat transport equations indicates that at a permeability of about 0.1 md or less, heat transport in the Diatomite tendsmore » to be dominated by thermal diffusivity, and pressure diffusion is dominated by the ratio of thermal expansion to fluid compressibility. Under these conditions, the temperature observed at a logging observation well is governed by a dimensionless quantity that depends on the perpendicular distance between the observation well and the hydraulic fracture, divided by the square root of time. Using this dependence, a novel method is developed for imaging hydraulic fracture geometry and relative heat injectivity from the temperature history of the pilot.« less

Effect of confining pressure on diffusion coefficients in clay-rich, low-permeability sedimentary rocks.

PubMed

Xiang, Y; Al, T; Mazurek, M

2016-12-01

The effect of confining pressure (CP) on the diffusion of tritiated-water (HTO) and iodide (I - ) tracers through Ordovician rocks from the Michigan Basin, southwestern Ontario, Canada, and Opalinus Clay from Schlattingen, Switzerland was investigated in laboratory experiments. Four samples representing different formations and lithologies in the Michigan Basin were studied: Queenston Formation shale, Georgian Bay Formation shale, Cobourg Formation limestone and Cobourg Formation argillaceous limestone. Estimated in situ vertical stresses at the depths from which the samples were retrieved range from 12.0 to 17.4MPa (Michigan Basin) and from 21 to 23MPa (Opalinus Clay). Effective diffusion coefficients (D e ) were determined in through-diffusion experiments. With HTO tracer, applying CP resulted in decreases in D e of 12.5% for the Queenston Formation shale (CP max =12MPa), 30% for the Georgian Bay Formation shale (15MPa), 34% for the Cobourg Formation limestone (17.4MPa), 31% for the Cobourg Formation argillaceous limestone (17.4MPa) and 43-46% for the Opalinus Clay (15MPa). Decreases in D e were larger for the I - tracer: 13.8% for the Queenston shale, 42% for the Georgian Bay shale, 50% for the Cobourg Formation limestone, 55% for the Cobourg Formation argillaceous limestone and 63-68% for the Opalinus Clay. The tracer-specific nature of the response is attributed to an increasing influence of anion exclusion as the pore size decreases at higher CP. Results from the shales (including Opalinus Clay) indicate that the pressure effect on D e can be represented by a linear relationship between D e and ln(CP), which provides valuable predictive capability. The nonlinearity results in a relatively small change in D e at high CP, suggesting that it is not necessary to apply the exact in situ pressure conditions in order to obtain a good estimate of the in situ diffusion coefficient. Most importantly, the CP effect on shale is reversible (±12%) suggesting that, for argillaceous rocks, it is possible to obtain D e values that are representative of the in-situ condition by conducting measurements on re-pressurized samples that were obtained with standard drilling practices. This may not be the case for brittle rock samples as the results from limestone suggest that irreversible damage occurred during the pressure cycling. Copyright © 2016 Elsevier B.V. All rights reserved.

Passive phloem loading and long-distance transport in a synthetic tree-on-a-chip.

PubMed

Comtet, Jean; Jensen, Kaare H; Turgeon, Robert; Stroock, Abraham D; Hosoi, A E

2017-03-20

Vascular plants rely on differences in osmotic pressure to export sugars from regions of synthesis (mature leaves) to sugar sinks (roots, fruits). In this process, known as Münch pressure flow, the loading of sugars from photosynthetic cells to the export conduit (the phloem) is crucial, as it sets the pressure head necessary to power long-distance transport. Whereas most herbaceous plants use active mechanisms to increase phloem sugar concentration above that of the photosynthetic cells, in most tree species, for which transport distances are largest, loading seems, counterintuitively, to occur by means of passive symplastic diffusion from the mesophyll to the phloem. Here, we use a synthetic microfluidic model of a passive loader to explore the non-linear dynamics that arise during export and determine the ability of passive loading to drive long-distance transport. We first demonstrate that in our device, the phloem concentration is set by the balance between the resistances to diffusive loading from the source and convective export through the phloem. Convection-limited export corresponds to classical models of Münch transport, where the phloem concentration is close to that of the source; in contrast, diffusion-limited export leads to small phloem concentrations and weak scaling of flow rates with hydraulic resistance. We then show that the effective regime of convection-limited export is predominant in plants with large transport resistances and low xylem pressures. Moreover, hydrostatic pressures developed in our synthetic passive loader can reach botanically relevant values as high as 10 bars. We conclude that passive loading is sufficient to drive long-distance transport in large plants, and that trees are well suited to take full advantage of passive phloem loading strategies.

Ion radial diffusion in an electrostatic impulse model for stormtime ring current formation

NASA Technical Reports Server (NTRS)

Chen, Margaret W.; Schulz, Michael; Lyons, Larry R.; Gorney, David J.

1992-01-01

Two refinements to the quasi-linear theory of ion radial diffusion are proposed and examined analytically with simulations of particle trajectories. The resonance-broadening correction by Dungey (1965) is applied to the quasi-linear diffusion theory by Faelthammar (1965) for an individual model storm. Quasi-linear theory is then applied to the mean diffusion coefficients resulting from simulations of particle trajectories in 20 model storms. The correction for drift-resonance broadening results in quasi-linear diffusion coefficients with discrepancies from the corresponding simulated values that are reduced by a factor of about 3. Further reductions in the discrepancies are noted following the averaging of the quasi-linear diffusion coefficients, the simulated coefficients, and the resonance-broadened coefficients for the 20 storms. Quasi-linear theory provides good descriptions of particle transport for a single storm but performs even better in conjunction with the present ensemble-averaging.

New Models for Velocity/Pressure-Gradient Correlations in Turbulent Boundary Layers

NASA Astrophysics Data System (ADS)

Poroseva, Svetlana; Murman, Scott

2014-11-01

To improve the performance of Reynolds-Averaged Navier-Stokes (RANS) turbulence models, one has to improve the accuracy of models for three physical processes: turbulent diffusion, interaction of turbulent pressure and velocity fluctuation fields, and dissipative processes. The accuracy of modeling the turbulent diffusion depends on the order of a statistical closure chosen as a basis for a RANS model. When the Gram-Charlier series expansions for the velocity correlations are used to close the set of RANS equations, no assumption on Gaussian turbulence is invoked and no unknown model coefficients are introduced into the modeled equations. In such a way, this closure procedure reduces the modeling uncertainty of fourth-order RANS (FORANS) closures. Experimental and direct numerical simulation data confirmed the validity of using the Gram-Charlier series expansions in various flows including boundary layers. We will address modeling the velocity/pressure-gradient correlations. New linear models will be introduced for the second- and higher-order correlations applicable to two-dimensional incompressible wall-bounded flows. Results of models' validation with DNS data in a channel flow and in a zero-pressure gradient boundary layer over a flat plate will be demonstrated. A part of the material is based upon work supported by NASA under award NNX12AJ61A.

Effects of High Hydrostatic Pressure on Water Absorption of Adzuki Beans

PubMed Central

Ueno, Shigeaki; Shigematsu, Toru; Karo, Mineko; Hayashi, Mayumi; Fujii, Tomoyuki

2015-01-01

The effect of high hydrostatic pressure (HHP) treatment on dried soybean, adzuki bean, and kintoki kidney bean, which are low-moisture-content cellular biological materials, was investigated from the viewpoint of water absorption. The samples were vacuum-packed with distilled water and pressurized at 200 MPa and 25 °C for 10 min. After the HHP treatment, time courses of the moisture contents of the samples were measured, and the dimensionless moisture contents were estimated. Water absorption in the case of soybean could be fitted well by a simple water diffusion model. High pressures were found to have negligible effects on water absorption into the cotyledon of soybean and kintoki kidney bean. A non-linear least square method based on the Weibull equation was applied for the adzuki beans, and the effective water diffusion coefficient was found to increase significantly from 8.6 × 10−13 to 6.7 × 10−10 m2/s after HHP treatment. Approximately 30% of the testa of the adzuki bean was damaged upon HHP treatment, which was comparable to the surface area of the testa in the partially peeled adzuki bean sample. Thus, HHP was confirmed to promote mass transfer to the cotyledon of legumes with a tight testa. PMID:28231195

Load Diffusion in Composite and Smart Structures

NASA Technical Reports Server (NTRS)

Horgan, Cornelius O.; Ambur, D. (Technical Monitor); Nemeth, M. P. (Technical Monitor)

2003-01-01

The research carried out here builds on our previous NASA supported research on the general topic of edge effects and load diffusion in composite structures. Further fundamental solid mechanics studies were carried out to provide a basis for assessing the complicated modeling necessary for the multi-functional large scale structures used by NASA. An understanding of the fundamental mechanisms of load diffusion in composite subcomponents is essential in developing primary composite structures. Some specific problems recently considered were those of end effects in smart materials and structures, study of the stress response of pressurized linear piezoelectric cylinders for both static and steady rotating configurations, an analysis of the effect of pre-stressing and pre-polarization on the decay of end effects in piezoelectric solids and investigation of constitutive models for hardening rubber-like materials. Our goal in the study of load diffusion is the development of readily applicable results for the decay lengths in terms of non-dimensional material and geometric parameters. Analytical models of load diffusion behavior are extremely valuable in building an intuitive base for developing refined modeling strategies and assessing results from finite element analyses.

Liquid Hydrogen Propellant Tank Sub-Surface Pressurization with Gaseous Helium

NASA Technical Reports Server (NTRS)

Stephens, J. R.; Cartagena, W.

2015-01-01

A series of tests were conducted to evaluate the performance of a propellant tank pressurization system with the pressurant diffuser intentionally submerged beneath the surface of the liquid. Propellant tanks and pressurization systems are typically designed with the diffuser positioned to apply pressurant gas directly into the tank ullage space when the liquid propellant is settled. Space vehicles, and potentially propellant depots, may need to conduct tank pressurization operations in micro-gravity environments where the exact location of the liquid relative to the diffuser is not well understood. If the diffuser is positioned to supply pressurant gas directly to the tank ullage space when the propellant is settled, then it may become partially or completely submerged when the liquid becomes unsettled in a microgravity environment. In such case, the pressurization system performance will be adversely affected requiring additional pressurant mass and longer pressurization times. This series of tests compares and evaluates pressurization system performance using the conventional method of supplying pressurant gas directly to the propellant tank ullage, and then supplying pressurant gas beneath the liquid surface. The pressurization tests were conducted on the Engineering Development Unit (EDU) located at Test Stand 300 at NASA Marshall Space Flight Center (MSFC). EDU is a ground based Cryogenic Fluid Management (CFM) test article supported by Glenn Research Center (GRC) and MSFC. A 150 ft3 propellant tank was filled with liquid hydrogen (LH2). The pressurization system used regulated ambient helium (GHe) as a pressurant, a variable position valve to maintain flow rate, and two identical independent pressurant diffusers. The ullage diffuser was located in the forward end of the tank and was completely exposed to the tank ullage. The submerged diffuser was located in the aft end of the tank and was completely submerged when the tank liquid level was 10% or greater. The ullage diffuser tests were conducted as a baseline to evaluate the performance of the pressurization system, and the submerged diffuser tests showed how the performance of the pressurization system was compromised when the diffuser was submerged in LH2. The test results are evaluated and compared, and included in this report for various propellant tank fill levels.

A projection hybrid high order finite volume/finite element method for incompressible turbulent flows

NASA Astrophysics Data System (ADS)

Busto, S.; Ferrín, J. L.; Toro, E. F.; Vázquez-Cendón, M. E.

2018-01-01

In this paper the projection hybrid FV/FE method presented in [1] is extended to account for species transport equations. Furthermore, turbulent regimes are also considered thanks to the k-ε model. Regarding the transport diffusion stage new schemes of high order of accuracy are developed. The CVC Kolgan-type scheme and ADER methodology are extended to 3D. The latter is modified in order to profit from the dual mesh employed by the projection algorithm and the derivatives involved in the diffusion term are discretized using a Galerkin approach. The accuracy and stability analysis of the new method are carried out for the advection-diffusion-reaction equation. Within the projection stage the pressure correction is computed by a piecewise linear finite element method. Numerical results are presented, aimed at verifying the formal order of accuracy of the scheme and to assess the performance of the method on several realistic test problems.

A cosmic ray driven instability

NASA Technical Reports Server (NTRS)

Dorfi, E. A.; Drury, L. O.

1985-01-01

The interaction between energetic charged particles and thermal plasma which forms the basis of diffusive shock acceleration leads also to interesting dynamical phenomena. For a compressional mode propagating in a system with homogeneous energetic particle pressure it is well known that friction with the energetic particles leads to damping. The linear theory of this effect has been analyzed in detail by Ptuskin. Not so obvious is that a non-uniform energetic particle pressure can addition amplify compressional disturbances. If the pressure gradient is sufficiently steep this growth can dominate the frictional damping and lead to an instability. It is important to not that this effect results from the collective nature of the interaction between the energetic particles and the gas and is not connected with the Parker instability, nor with the resonant amplification of Alfven waves.

Effect of Soret diffusion on lean hydrogen/air flames at normal and elevated pressure and temperature

NASA Astrophysics Data System (ADS)

Zhou, Zhen; Hernández-Pérez, Francisco E.; Shoshin, Yuriy; van Oijen, Jeroen A.; de Goey, Laurentius P. H.

2017-09-01

The influence of Soret diffusion on lean premixed flames propagating in hydrogen/air mixtures is numerically investigated with a detailed chemical and transport models at normal and elevated pressure and temperature. The Soret diffusion influence on the one-dimensional (1D) flame mass burning rate and two-dimensional (2D) flame propagating characteristics is analysed, revealing a strong dependency on flame stretch rate, pressure and temperature. For 1D flames, at normal pressure and temperature, with an increase of Karlovitz number from 0 to 0.4, the mass burning rate is first reduced and then enhanced by Soret diffusion of H2 while it is reduced by Soret diffusion of H. The influence of Soret diffusion of H2 is enhanced by pressure and reduced by temperature. On the contrary, the influence of Soret diffusion of H is reduced by pressure and enhanced by temperature. For 2D flames, at normal pressure and temperature, during the early phase of flame evolution, flames with Soret diffusion display more curved flame cells. Pressure enhances this effect, while temperature reduces it. The influence of Soret diffusion of H2 on the global consumption speed is enhanced at elevated pressure. The influence of Soret diffusion of H on the global consumption speed is enhanced at elevated temperature. The flame evolution is more affected by Soret diffusion in the early phase of propagation than in the long run due to the local enrichment of H2 caused by flame curvature effects. The present study provides new insights into the Soret diffusion effect on the characteristics of lean hydrogen/air flames at conditions that are relevant to practical applications, e.g. gas engines and turbines.

Anomalous diffusion with linear reaction dynamics: from continuous time random walks to fractional reaction-diffusion equations.

PubMed

Henry, B I; Langlands, T A M; Wearne, S L

2006-09-01

We have revisited the problem of anomalously diffusing species, modeled at the mesoscopic level using continuous time random walks, to include linear reaction dynamics. If a constant proportion of walkers are added or removed instantaneously at the start of each step then the long time asymptotic limit yields a fractional reaction-diffusion equation with a fractional order temporal derivative operating on both the standard diffusion term and a linear reaction kinetics term. If the walkers are added or removed at a constant per capita rate during the waiting time between steps then the long time asymptotic limit has a standard linear reaction kinetics term but a fractional order temporal derivative operating on a nonstandard diffusion term. Results from the above two models are compared with a phenomenological model with standard linear reaction kinetics and a fractional order temporal derivative operating on a standard diffusion term. We have also developed further extensions of the CTRW model to include more general reaction dynamics.

Stage design

DOEpatents

Shacter, J.

1975-12-01

A method is described of cycling gases through a plurality of diffusion stages comprising the steps of admitting the diffused gases from a first diffusion stage into an axial compressor, simultaneously admitting the undiffused gases from a second diffusion stage into an intermediate pressure zone of said compressor corresponding in pressure to the pressure of said undiffused gases, and then admitting the resulting compressed mixture of diffused and undiffused gases into a third diffusion stage.

Calculating Mass Diffusion in High-Pressure Binary Fluids

NASA Technical Reports Server (NTRS)

Bellan, Josette; Harstad, Kenneth

2004-01-01

A comprehensive mathematical model of mass diffusion has been developed for binary fluids at high pressures, including critical and supercritical pressures. Heretofore, diverse expressions, valid for limited parameter ranges, have been used to correlate high-pressure binary mass-diffusion-coefficient data. This model will likely be especially useful in the computational simulation and analysis of combustion phenomena in diesel engines, gas turbines, and liquid rocket engines, wherein mass diffusion at high pressure plays a major role.

Spin-labeled small unilamellar vesicles with the T1-sensitive saturation-recovery EPR display as an oxygen sensitive analyte for measurement of cellular respiration

PubMed Central

Mainali, Laxman; Vasquez-Vivar, Jeannette; Hyde, James S.; Subczynski, Witold K.

2015-01-01

This study validated the use of small unilamellar vesicles (SUVs) made of 1-palmitoyl-2-oleoylphosphatidylcholine with 1 mol% spin label of 1-palmitoyl-2-(16-doxylstearoyl)phosphatidylcholine (16-PC) as an oxygen sensitive analyte to study cellular respiration. In the analyte the hydrocarbon environment surrounds the nitroxide moiety of 16-PC. This ensures high oxygen concentration and oxygen diffusion at the location of the nitroxide as well as isolation of the nitroxide moiety from cellular reductants and paramagnetic ions that might interfere with spin-label oximetry measurements. The saturation-recovery EPR approach was applied in the analysis since this approach is the most direct method to carry out oximetric studies. It was shown that this display (spin-lattice relaxation rate) is linear in oxygen partial pressure up to 100% air (159 mmHg). Experiments using a neuronal cell line in suspension were carried out at X-band for closed chamber geometry. Oxygen consumption rates showed a linear dependence on the number of cells. Other significant benefits of the analyte are: the fast effective rotational diffusion and slow translational diffusion of the spin-probe is favorable for the measurements, and there is no cross reactivity between oxygen and paramagnetic ions in the lipid bilayer. PMID:26441482

Spin-labeled small unilamellar vesicles with the T1-sensitive saturation-recovery EPR display as an oxygen sensitive analyte for measurement of cellular respiration.

PubMed

Mainali, Laxman; Vasquez-Vivar, Jeannette; Hyde, James S; Subczynski, Witold K

2015-08-01

This study validated the use of small unilamellar vesicles (SUVs) made of 1-palmitoyl-2-oleoylphosphatidylcholine with 1 mol% spin label of 1-palmitoyl-2-(16-doxylstearoyl)phosphatidylcholine (16-PC) as an oxygen sensitive analyte to study cellular respiration. In the analyte the hydrocarbon environment surrounds the nitroxide moiety of 16-PC. This ensures high oxygen concentration and oxygen diffusion at the location of the nitroxide as well as isolation of the nitroxide moiety from cellular reductants and paramagnetic ions that might interfere with spin-label oximetry measurements. The saturation-recovery EPR approach was applied in the analysis since this approach is the most direct method to carry out oximetric studies. It was shown that this display (spin-lattice relaxation rate) is linear in oxygen partial pressure up to 100% air (159 mmHg). Experiments using a neuronal cell line in suspension were carried out at X-band for closed chamber geometry. Oxygen consumption rates showed a linear dependence on the number of cells. Other significant benefits of the analyte are: the fast effective rotational diffusion and slow translational diffusion of the spin-probe is favorable for the measurements, and there is no cross reactivity between oxygen and paramagnetic ions in the lipid bilayer.

Prediction of pulmonary hypertension in idiopathic pulmonary fibrosis☆

PubMed Central

Zisman, David A.; Ross, David J.; Belperio, John A.; Saggar, Rajan; Lynch, Joseph P.; Ardehali, Abbas; Karlamangla, Arun S.

2007-01-01

Summary Background Reliable, noninvasive approaches to the diagnosis of pulmonary hypertension in idiopathic pulmonary fibrosis are needed. We tested the hypothesis that the forced vital capacity to diffusing capacity ratio and room air resting pulse oximetry may be combined to predict mean pulmonary artery pressure (MPAP) in idiopathic pulmonary fibrosis. Methods Sixty-one idiopathic pulmonary fibrosis patients with available right-heart catheterization were studied. We regressed measured MPAP as a continuous variable on pulse oximetry (SpO2) and percent predicted forced vital capacity (FVC) to percent-predicted diffusing capacity ratio (% FVC/% DLco) in a multivariable linear regression model. Results Linear regression generated the following equation: MPAP = −11.9+0.272 × SpO2+0.0659 × (100−SpO2)2+3.06 × (% FVC/% DLco); adjusted R2 = 0.55, p<0.0001. The sensitivity, specificity, positive predictive and negative predictive value of model-predicted pulmonary hypertension were 71% (95% confidence interval (CI): 50–89%), 81% (95% CI: 68–92%), 71% (95% CI: 51–87%) and 81% (95% CI: 68–94%). Conclusions A pulmonary hypertension predictor based on room air resting pulse oximetry and FVC to diffusing capacity ratio has a relatively high negative predictive value. However, this model will require external validation before it can be used in clinical practice. PMID:17604151

Transport Coefficients in weakly compressible turbulence

NASA Technical Reports Server (NTRS)

Rubinstein, Robert; Erlebacher, Gordon

1996-01-01

A theory of transport coefficients in weakly compressible turbulence is derived by applying Yoshizawa's two-scale direct interaction approximation to the compressible equations of motion linearized about a state of incompressible turbulence. The result is a generalization of the eddy viscosity representation of incompressible turbulence. In addition to the usual incompressible eddy viscosity, the calculation generates eddy diffusivities for entropy and pressure, and an effective bulk viscosity acting on the mean flow. The compressible fluctuations also generate an effective turbulent mean pressure and corrections to the speed of sound. Finally, a prediction unique to Yoshizawa's two-scale approximation is that terms containing gradients of incompressible turbulence quantities also appear in the mean flow equations. The form these terms take is described.

Assessment of diffuser pressure loss on WWTPs in Baden-Württemberg.

PubMed

Krampe, J

2011-01-01

Aeration of activated sludge is a critical treatment step for the operation of activated sludge plants. To achieve a cost effective treatment process, assessing and benchmarking of aeration system performance are important measures. A simple means of gauging the relative condition of a fine bubble diffused aeration system is to evaluate the pressure loss of the diffusers as oxygen transfer tests are rarely applied during the lifetime of an aeration system. This paper shows an assessment of fine bubble diffuser systems in Baden-Württemberg, Germany, based on the results of a questionnaire sent to 941 WWTPs. Apart from the results with regards to the diffuser pressure loss, this paper also presents information on the current state of diffuser technology such as types and materials as well as the diffuser cleaning methods used in Baden-Württemberg. The majority of the WWTPs were equipped with tube diffusers (71%) with 50% of all plants having EPDM membranes installed. Regular mechanical cleaning is the most common cleaning method followed by regular pressure release/air-bumping programs during operations. With regard to the diffuser pressure loss it was found that 50% of the evaluated plants had a diffuser pressure loss that was twice as high as measured for new diffusers.

Cylindrical diffuser performance using a truncated plug nozzle

NASA Technical Reports Server (NTRS)

Galanga, F. L.; Mueller, T. J.

1976-01-01

Cylindrical diffuser performance for a truncated plug nozzle without external flow was tested in a blowdown wind tunnel. The nozzle was designed for an exit Mach number of 1.9 and the plug was conical in shape from the throat and converged to the axis of symmetry at an angle of 10 degrees. The diffuser section was fashioned into two 13.97 cm lengths to facilitate boring of the duct diameter and to allow for testing of two different duct lengths. A slotted hypotube was installed in the base of the diffuser to measure pressure distribution down the centerline of the diffuser. The data obtained included: the typical centerline and sidewall pressure ratio variation along the diffuser, cell pressure ratio vs overall pressure ratio for long and short diffusers and a comparison of minimum experimental cell pressure ratio vs area ratio.

Rhenium/Oxygen Interactions at Elevated Temperatures

NASA Technical Reports Server (NTRS)

Jacobson, Nathan; Myers, Dwight; Zhu, Dong-Ming; Humphrey, Donald

2000-01-01

The oxidation of pure rhenium is examined from 600-1400 C in oxygen/argon mixtures. Linear weight loss kinetics are observed. Gas pressures, flow rates, and temperatures are methodically varied to determine the rate controlling steps. The reaction at 600 and 800 C appears to be controlled by a chemical reaction step at the surface; whereas the higher temperature reactions appear to be controlled by gas phase diffusion of oxygen to the rhenium surface. Attack of the rhenium appears to be along grain boundaries and crystallographic planes.

Pressure modulation algorithm to separate cerebral hemodynamic signals from extracerebral artifacts

PubMed Central

Baker, Wesley B.; Parthasarathy, Ashwin B.; Ko, Tiffany S.; Busch, David R.; Abramson, Kenneth; Tzeng, Shih-Yu; Mesquita, Rickson C.; Durduran, Turgut; Greenberg, Joel H.; Kung, David K.; Yodh, Arjun G.

2015-01-01

Abstract. We introduce and validate a pressure measurement paradigm that reduces extracerebral contamination from superficial tissues in optical monitoring of cerebral blood flow with diffuse correlation spectroscopy (DCS). The scheme determines subject-specific contributions of extracerebral and cerebral tissues to the DCS signal by utilizing probe pressure modulation to induce variations in extracerebral blood flow. For analysis, the head is modeled as a two-layer medium and is probed with long and short source-detector separations. Then a combination of pressure modulation and a modified Beer-Lambert law for flow enables experimenters to linearly relate differential DCS signals to cerebral and extracerebral blood flow variation without a priori anatomical information. We demonstrate the algorithm’s ability to isolate cerebral blood flow during a finger-tapping task and during graded scalp ischemia in healthy adults. Finally, we adapt the pressure modulation algorithm to ameliorate extracerebral contamination in monitoring of cerebral blood oxygenation and blood volume by near-infrared spectroscopy. PMID:26301255

The tracer diffusion coefficient of soft nanoparticles in a linear polymer matrix

DOE PAGES

Imel, Adam E.; Rostom, Sahar; Holley, Wade; ...

2017-03-09

The diffusion properties of nanoparticles in polymer nanocomposites are largely unknown and are often difficult to determine experimentally. To address this shortcoming, we have developed a novel method to determine the tracer diffusion coefficient of soft polystyrene nanoparticles in a linear polystyrene matrix. Monitoring the interdiffusion of soft nanoparticles into a linear polystyrene matrix provides the mutual diffusion coefficient of this system, from which the tracer diffusion coefficient of the soft nanoparticle can be determined using the slow mode theory. Utilizing this protocol, the role of nanoparticle molecular weight and rigidity on its tracer diffusion coefficient is provided. These resultsmore » demonstrate that the diffusive behavior of these soft nanoparticles differ from that of star polymers, which is surprising since our recent studies suggest that the nanoparticle interacts with a linear polymer similarly to that of a star polymer. It appears that these deformable nanoparticles mostly closely mimic the diffusive behavior of fractal macromolecular architectures or microgels, where the transport of the nanoparticle relies on the cooperative motion of neighboring linear chains. Finally, the less cross-linked, and thus more deformable, nanoparticles diffuse faster than the more highly crosslinked nanoparticles, presumably because the increased deformability allows the nanoparticle to distort and fit into available space.« less

Gaseous diffusion system

DOEpatents

Garrett, George A.; Shacter, John

1978-01-01

1. A gaseous diffusion system comprising a plurality of diffusers connected in cascade to form a series of stages, each of said diffusers having a porous partition dividing it into a high pressure chamber and a low pressure chamber, and means for combining a portion of the enriched gas from a succeeding stage with a portion of the enriched gas from the low pressure chamber of each stage and feeding it into one extremity of the high pressure chamber thereof.

Water boiling inside carbon nanotubes: toward efficient drug release.

PubMed

Chaban, Vitaly V; Prezhdo, Oleg V

2011-07-26

We show using molecular dynamics simulation that spatial confinement of water inside carbon nanotubes (CNTs) substantially increases its boiling temperature and that a small temperature growth above the boiling point dramatically raises the inside pressure. Capillary theory successfully predicts the boiling point elevation down to 2 nm, below which large deviations between the theory and atomistic simulation take place. Water behaves qualitatively different inside narrow CNTs, exhibiting transition into an unusual phase, where pressure is gas-like and grows linearly with temperature, while the diffusion constant is temperature-independent. Precise control over boiling by CNT diameter, together with the rapid growth of inside pressure above the boiling point, suggests a novel drug delivery protocol. Polar drug molecules are packaged inside CNTs; the latter are delivered into living tissues and heated by laser. Solvent boiling facilitates drug release.

Reservoir monitoring and characterization using satellite geodetic data: Interferometric Synthetic Aperture Radar observations from the Krechba field, Algeria

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

Vasco, D.W.; Ferretti, Alessandro; Novali, Fabrizio

2008-05-01

Deformation in the material overlying an active reservoir is used to monitor pressure change at depth. A sequence of pressure field estimates, eleven in all, allow us to construct a measure of diffusive travel time throughout the reservoir. The dense distribution of travel time values means that we can construct an exactly linear inverse problem for reservoir flow properties. Application to Interferometric Synthetic Aperture Radar (InSAR) data gathered over a CO{sub 2} injection in Algeria reveals pressure propagation along two northwest trending corridors. An inversion of the travel times indicates the existence of two northwest-trending high permeability zones. The highmore » permeability features trend in the same direction as the regional fault and fracture zones. Model parameter resolution estimates indicate that the features are well resolved.« less

Measurement of effective bulk and contact resistance of gas diffusion layer under inhomogeneous compression - Part II: Thermal conductivity

NASA Astrophysics Data System (ADS)

Roy Chowdhury, Prabudhya; Vikram, Ajit; Phillips, Ryan K.; Hoorfar, Mina

2016-07-01

The gas diffusion layer (GDL) is a thin porous layer sandwiched between a bipolar plate (BPP) and a catalyst coated membrane in a fuel cell. Besides providing passage for water and gas transport from and to the catalyst layer, it is responsible for electron and heat transfer from and to the BPP. In this paper, a method has been developed to measure the GDL bulk thermal conductivity and the contact resistance at the GDL/BPP interface under inhomogeneous compression occurring in an actual fuel cell assembly. Toray carbon paper GDL TGP-H-060 was tested under a range of compression pressure of 0.34 to 1.71 MPa. The results showed that the thermal contact resistance decreases non-linearly (from 3.8 × 10-4 to 1.17 × 10-4 Km2 W-1) with increasing pressure due to increase in microscopic contact area between the GDL and BPP; while the effective bulk thermal conductivity increases (from 0.56 to 1.42 Wm-1 K-1) with increasing the compression pressure. The thermal contact resistance was found to be greater (by a factor of 1.6-2.8) than the effective bulk thermal resistance for all compression pressure ranges applied here. This measurement technique can be used to identify optimum GDL based on minimum bulk and contact resistances measured under inhomogeneous compression.

A New Ghost Cell/Level Set Method for Moving Boundary Problems: Application to Tumor Growth

PubMed Central

Macklin, Paul

2011-01-01

In this paper, we present a ghost cell/level set method for the evolution of interfaces whose normal velocity depend upon the solutions of linear and nonlinear quasi-steady reaction-diffusion equations with curvature-dependent boundary conditions. Our technique includes a ghost cell method that accurately discretizes normal derivative jump boundary conditions without smearing jumps in the tangential derivative; a new iterative method for solving linear and nonlinear quasi-steady reaction-diffusion equations; an adaptive discretization to compute the curvature and normal vectors; and a new discrete approximation to the Heaviside function. We present numerical examples that demonstrate better than 1.5-order convergence for problems where traditional ghost cell methods either fail to converge or attain at best sub-linear accuracy. We apply our techniques to a model of tumor growth in complex, heterogeneous tissues that consists of a nonlinear nutrient equation and a pressure equation with geometry-dependent jump boundary conditions. We simulate the growth of glioblastoma (an aggressive brain tumor) into a large, 1 cm square of brain tissue that includes heterogeneous nutrient delivery and varied biomechanical characteristics (white matter, gray matter, cerebrospinal fluid, and bone), and we observe growth morphologies that are highly dependent upon the variations of the tissue characteristics—an effect observed in real tumor growth. PMID:21331304

Gas diffusion in and out of super-hydrophobic surface in transitional and turbulent boundary layers

NASA Astrophysics Data System (ADS)

Ling, Hangjian; Fu, Matthew; Hultmark, Marcus; Katz, Joseph

2017-11-01

The rate of gas diffusion in and out of a super-hydrophobic surface (SHS) located in boundary layers is investigated at varying Reynolds numbers and ambient pressures. The hierarchical SHS consists of nano-textured, 100 μm wide spanwise grooves. The boundary layers over the SHS under the Cassie-Baxter and Wenzel states as well as a smooth wall at same conditions are characterized by particle image velocimetry. The Reynolds number based on momentum thickness of the smooth wall, ReΘ0, ranges from 518 to 2088, covering transitional and turbulent boundary layer regimes. The mass diffusion rate is estimated by using microscopy to measure the time-evolution of plastron shape and volume. The data is used for calculating the Sherwood number based on smooth wall momentum thickness, ShΘ0. As expected, the diffusion rate increases linearly with the under- or super-saturation level, i.e., ShΘ0 is independent of ambient pressure. For the turbulent boundary layers, the data collapses onto ShΘ0 = 0.47ReΘ00.77 . For the transitional boundary layer, ShΘ0 is lower than the turbulent power law. When ShΘ0 is plotted against the friction Reynolds number (Reτ0) , both the transitional and turbulent boundary layer data collapse onto a single power law, ShΘ0 = 0.34Reτ00.913 . Results scaled based on Wenzel state momentum thickness show very similar trends. Sponsored by ONR.

Role of shell diffusion area in incubating eggs at simulated high altitude.

PubMed

Weiss, H S

1978-10-01

Embryonic development is inhibited when eggs are incubated at 9,100 m (0.3 atm) despite a normoxic environment. The problem apparently relates to respiratory gas exchange occurring by diffusion through gas-filled pores in the shell. Gaseous flux is therefore inversely proportional to ambient pressure and is affected by the physical characteristics of the ambient gas (Chapman-Enskog equation). Excess loss of H2O and CO2 occurs in eggs incubating at altitude and could be detrimental. Such increased loss should be correctable by decreasing diffusion area. This was tested by progressively increasing coverage of the shell with paraffin and incubating at simulated 0.3 ATA (225 Torr) in 100% O2. Uncoated eggs failed to hatch, but numbers of chicks increased with increased coverage. Maximum hatch was an extrapolated 90% of controls at 69% shell coverage. With further coverage, hatch size decreased. Egg weight loss, and estimate of H2O diffusion, was around three times controls in uncoated eggs but decreased linearly with paraffin coverage, reaching near normal at maximum hatch. Reduction of diffusion area to 0.3 normal at maximum hatch generally balanced the increased flux predicted for 0.3 ATA.

Thermophysical properties and oxygen transport in (Th x,Pu 1-x)O 2

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

Galvin, C. O. T.; Cooper, M. W. D.; Rushton, M. J. D.

Using Molecular Dynamics, this paper investigates the thermophysical properties and oxygen transport of (Th x,Pu 1–x)O 2 (0 ≤ x ≤ 1) between 300–3500 K. Specifically, the superionic transition is investigated and viewed via the thermal dependence of lattice parameter, linear thermal expansion coefficient, enthalpy and specific heat at constant pressure. Oxygen diffusivity and activation enthalpy are also investigated. Below the superionic temperature an increase of oxygen diffusivity for certain compositions of (Th x,Pu 1–x)O 2 compared to the pure end members is predicted. Oxygen defect formation enthalpies are also examined, as they underpin the superionic transition temperature and themore » increase in oxygen diffusivity. The increase in oxygen diffusivity for (Th x,Pu 1–x)O 2 is explained in terms of lower oxygen defect formation enthalpies for (Th x,Pu 1–x)O 2 than PuO 2 and ThO 2, while links are drawn between the superionic transition temperature and oxygen Frenkel disorder.« less

Thermophysical properties and oxygen transport in (Th x,Pu 1-x)O 2

DOE PAGES

Galvin, C. O. T.; Cooper, M. W. D.; Rushton, M. J. D.; ...

2016-10-31

Using Molecular Dynamics, this paper investigates the thermophysical properties and oxygen transport of (Th x,Pu 1–x)O 2 (0 ≤ x ≤ 1) between 300–3500 K. Specifically, the superionic transition is investigated and viewed via the thermal dependence of lattice parameter, linear thermal expansion coefficient, enthalpy and specific heat at constant pressure. Oxygen diffusivity and activation enthalpy are also investigated. Below the superionic temperature an increase of oxygen diffusivity for certain compositions of (Th x,Pu 1–x)O 2 compared to the pure end members is predicted. Oxygen defect formation enthalpies are also examined, as they underpin the superionic transition temperature and themore » increase in oxygen diffusivity. The increase in oxygen diffusivity for (Th x,Pu 1–x)O 2 is explained in terms of lower oxygen defect formation enthalpies for (Th x,Pu 1–x)O 2 than PuO 2 and ThO 2, while links are drawn between the superionic transition temperature and oxygen Frenkel disorder.« less

Multilevel Preconditioners for Reaction-Diffusion Problems with Discontinuous Coefficients

DOE PAGES

Kolev, Tzanio V.; Xu, Jinchao; Zhu, Yunrong

2015-08-23

In this study, we extend some of the multilevel convergence results obtained by Xu and Zhu, to the case of second order linear reaction-diffusion equations. Specifically, we consider the multilevel preconditioners for solving the linear systems arising from the linear finite element approximation of the problem, where both diffusion and reaction coefficients are piecewise-constant functions. We discuss in detail the influence of both the discontinuous reaction and diffusion coefficients to the performance of the classical BPX and multigrid V-cycle preconditioner.

The effect of a realistic thermal diffusivity on numerical model of a subducting slab

NASA Astrophysics Data System (ADS)

Maierova, P.; Steinle-Neumann, G.; Cadek, O.

2010-12-01

A number of numerical studies of subducting slab assume simplified (constant or only depth-dependent) models of thermal conductivity. The available mineral physics data indicate, however, that thermal diffusivity is strongly temperature- and pressure-dependent and may also vary among different mantle materials. In the present study, we examine the influence of realistic thermal properties of mantle materials on the thermal state of the upper mantle and the dynamics of subducting slabs. On the basis of the data published in mineral physics literature we compile analytical relationships that approximate the pressure and temperature dependence of thermal diffusivity for major mineral phases of the mantle (olivine, wadsleyite, ringwoodite, garnet, clinopyroxenes, stishovite and perovskite). We propose a simplified composition of mineral assemblages predominating in the subducting slab and the surrounding mantle (pyrolite, mid-ocean ridge basalt, harzburgite) and we estimate their thermal diffusivity using the Hashin-Shtrikman bounds. The resulting complex formula for the diffusivity of each aggregate is then approximated by a simpler analytical relationship that is used in our numerical model as an input parameter. For the numerical modeling we use the Elmer software (open source finite element software for multiphysical problems, see http://www.csc.fi/english/pages/elmer). We set up a 2D Cartesian thermo-mechanical steady-state model of a subducting slab. The model is partly kinematic as the flow is driven by a boundary condition on velocity that is prescribed on the top of the subducting lithospheric plate. Reology of the material is non-linear and is coupled with the thermal equation. Using the realistic relationship for thermal diffusivity of mantle materials, we compute the thermal and flow fields for different input velocity and age of the subducting plate and we compare the results against the models assuming a constant thermal diffusivity. The importance of the realistic description of thermal properties in models of subducted slabs is discussed.

Analysis of aldehydes in beer by gas-diffusion microextraction: characterization by high-performance liquid chromatography-diode-array detection-atmospheric pressure chemical ionization-mass spectrometry.

PubMed

Gonçalves, Luís Moreira; Magalhães, Paulo Jorge; Valente, Inês Maria; Pacheco, João Grosso; Dostálek, Pavel; Sýkora, David; Rodrigues, José António; Barros, Aquiles Araújo

2010-06-11

In this work, a recently developed extraction technique for sample preparation aiming the analysis of volatile and semi-volatile compounds named gas-diffusion microextraction (GDME) is applied in the chromatographic analysis of aldehydes in beer. Aldehydes-namely acetaldehyde (AA), methylpropanal (MA) and furfural (FA)-were simultaneously extracted and derivatized with 2,4-dinitrophenylhydrazine (DNPH), then the derivatives were separated and analyzed by high-performance liquid chromatography with spectrophotometric detection (HPLC-UV). The identity of the eluted compounds was confirmed by high-performance liquid chromatography-atmospheric pressure chemical ionization-mass-spectrometry detection in the negative ion mode (HPLC-APCI-MS). The developed methodology showed good repeatability (ca. 5%) and linearity as well as good limits of detection (AA-12.3, FA-1.5 and MA 5.4microgL(-1)) and quantification (AA-41, FA-4.9 and MA 18microgL(-1)); it also appears to be competitive in terms of speed and cost of analysis. Copyright 2010 Elsevier B.V. All rights reserved.

Diffusion by one wave and by many waves

NASA Astrophysics Data System (ADS)

Albert, J. M.

2010-03-01

Radiation belt electrons and chorus waves are an outstanding instance of the important role cyclotron resonant wave-particle interactions play in the magnetosphere. Chorus waves are particularly complex, often occurring with large amplitude, narrowband but drifting frequency and fine structure. Nevertheless, modeling their effect on radiation belt electrons with bounce-averaged broadband quasi-linear theory seems to yield reasonable results. It is known that coherent interactions with monochromatic waves can cause particle diffusion, as well as radically different phase bunching and phase trapping behavior. Here the two formulations of diffusion, while conceptually different, are shown to give identical diffusion coefficients, in the narrowband limit of quasi-linear theory. It is further shown that suitably averaging the monochromatic diffusion coefficients over frequency and wave normal angle parameters reproduces the full broadband quasi-linear results. This may account for the rather surprising success of quasi-linear theory in modeling radiation belt electrons undergoing diffusion by chorus waves.

Weighted linear least squares estimation of diffusion MRI parameters: strengths, limitations, and pitfalls.

PubMed

Veraart, Jelle; Sijbers, Jan; Sunaert, Stefan; Leemans, Alexander; Jeurissen, Ben

2013-11-01

Linear least squares estimators are widely used in diffusion MRI for the estimation of diffusion parameters. Although adding proper weights is necessary to increase the precision of these linear estimators, there is no consensus on how to practically define them. In this study, the impact of the commonly used weighting strategies on the accuracy and precision of linear diffusion parameter estimators is evaluated and compared with the nonlinear least squares estimation approach. Simulation and real data experiments were done to study the performance of the weighted linear least squares estimators with weights defined by (a) the squares of the respective noisy diffusion-weighted signals; and (b) the squares of the predicted signals, which are reconstructed from a previous estimate of the diffusion model parameters. The negative effect of weighting strategy (a) on the accuracy of the estimator was surprisingly high. Multi-step weighting strategies yield better performance and, in some cases, even outperformed the nonlinear least squares estimator. If proper weighting strategies are applied, the weighted linear least squares approach shows high performance characteristics in terms of accuracy/precision and may even be preferred over nonlinear estimation methods. Copyright © 2013 Elsevier Inc. All rights reserved.

Effects of radial diffuser hydraulic design on a double-suction centrifugal pump

NASA Astrophysics Data System (ADS)

Hou, H. C.; Zhang, Y. X.; Xu, C.; Zhang, J. Y.; Li, Z. L.

2016-05-01

In order to study effects of radial diffuser on hydraulic performance of crude oil pump, the steady CFD numerical method is applied and one large double-suction oil pump running in long-distance pipeline is considered. The research focuses on analysing the influence of its diffuser vane profile on hydraulic performance of oil pump. The four different types of cylindrical vane have been designed by in-house codes mainly including double arcs (DA), triple arcs (TA), equiangular spiral line (ES) and linear variable angle spiral line (LVS). During design process diffuser vane angles at inlet and outlet are tentatively given within a certain range and then the wrapping angle of the four types of diffuser vanes can be calculated automatically. Under the given inlet and outlet angles, the linear variable angle spiral line profile has the biggest wrapping angle and profile length which is good to delay channel diffusion but bring more friction hydraulic loss. Finally the vane camber line is thickened at the certain uniform thickness distribution and the 3D diffuser models are generated. The whole flow passage of oil pump with different types of diffusers under various flow rate conditions are numerically simulated based on RNG k-ɛ turbulent model and SIMPLEC algorithm. The numerical results show that different types of diffusers can bring about great difference on the hydraulic performance of oil pump, of which the ES profile diffuser with its proper setting angle shows the best hydraulic performance and its inner flow field is improved obviously. Compared with the head data from model sample, all designed diffusers can make a certain improvement on head characteristic. At the large flow rate conditions the hydraulic efficiency increases obviously and the best efficiency point shift to the large flow rate range. The ES profile diffuser embodies the better advantages on pump performance which can be explained theoretically that the diffuser actually acts as a diffusion device and is good to transform the dynamic energy to pressure energy. Then through the hydraulic loss analysis of each pump component for all diffusers, it shows that the impeller takes up the biggest part of the whole loss about 8.19% averagely, the radial diffuser about 3.70% and the volute about 1.65%. The hydraulic loss of impeller is dominant at the large flow rate while the radial diffuser is at the small flow rate. Among all diffusers, the ES profile diffuser generates the least loss and combined to the distribution of velocity vector and turbulent kinetic energy for two kinds of diffusers it also shows that ES profile is fit to apply in radial diffuser. This research can offer a significant reference for the radial diffuser hydraulic design of such centrifugal pumps.

Altered carnitine transport in pressure-overload hypertrophied rat hearts

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

O'Rourke, B.; Foster, K.; Reibel, D.K.

1986-03-01

The authors have previously observed reduced carnitine levels in hypertrophied hearts of rats subjected to aortic constriction. In an attempt to determine the mechanism for reduced myocardial carnitine content, carnitine transport was examined in isolated perfused hearts. Hearts were excised from sham-operated and aortic-constricted rats 3 weeks following surgery and perfused at 60 mm Hg aortic pressure with buffer containing various concentrations of L-/sup 14/C-carnitine. Carnitine uptake by control and hypertrophied hearts was linear throughout 30 minutes of perfusion with 40 ..mu..M carnitine. Total carnitine uptake was significantly reduced by 25% in hypertrophied hearts at each time point examined. Themore » reduction in uptake by hypertrophied hearts was also evident when hearts were perfused with 100 or 200 ..mu..M carnitine. When 0.05 mM mersalyl acid was included in the buffer to inhibit the carrier-mediated component of transport, no difference in carnitine uptake was observed indicating that the transport of carnitine by diffusion was unaltered in the hypertrophied myocardium. Carrier-mediated carnitine uptake (total uptake - uptake by diffusion) was significantly reduced by approximately 40% in hypertrophied hearts at all concentrations examined. Thus, the reduction in carnitine content in the pressure-overload hypertrophied rat heart appears to be due to a reduction in carrier-mediated carnitine uptake by the heart.« less

The interaction of intense, ultra-short microwave beams with the plasma generated by gas ionization

NASA Astrophysics Data System (ADS)

Shafir, G.; Cao, Y.; Bliokh, Y.; Leopold, J. G.; Levko, D.; Rostov, V.; Gad, R.; Fisher, A.; Bernshtam, V.; Krasik, Ya. E.

2018-03-01

Results of the non-linear interaction of an extremely short (0.6 ns) high power (˜500 MW) X-band focused microwave beam with the plasma generated by gas ionization are presented. Within certain gas pressure ranges, specific to the gas type, the plasma density is considerably lower around the microwave beam axis than at its periphery, thus forming guiding channel through which the beam self-focuses. Outside these pressure ranges, either diffuse or streamer-like plasma is observed. We also observe high energy electrons (˜15 keV), accelerated by the very high-power microwaves. A simplified analytical model of this complicated dynamical system and particle-in-cell numerical simulations confirm the experimental results.

High-pressure spectroscopic measurement on diffusion with a diamond-anvil cell

NASA Astrophysics Data System (ADS)

Aoki, K.; Katoh, Eriko; Yamawaki, H.; Fujihisa, H.; Sakashita, M.

2003-04-01

We report a diamond-anvil-cell (DAC) technique developed for spectroscopic measurement on the diffusion process in molecular solids at high pressure. The diffusion processes of atoms, molecules, or their ionic species are investigated for a bilayer specimen by measuring the variation of infrared vibrational spectra with time. The experimental procedures for the protonic and molecular diffusion measurements on ice at 400 K and 10.2 GPa are presented as an example study. The in situ spectroscopic technique with a DAC significantly extends the pressure range accessible for diffusion measurement. The diffusion process at a rate of 10-16-10-14 m2/s can currently be observed at temperatures of 300-600 K and pressures up to several tens of gigaPascals.

The operational stability of a centrifugal compressor and its dependence on the characteristics of the subcomponents

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

Hunziker, R.; Gyarmathy, G.

1994-04-01

A centrifugal compressor was tested with three different diffusers with circular-arc vanes. The vane inlet angle was varied from 15 to 30 deg. Detailed static wall pressure measurements show that the pressure field in the diffuser inlet is very sensitive to flow rate. The stability limit regularly occurred at the flow rate giving the maximum pressure rise for the overall stage. Mild surge arises as a dynamic instability of the compression system. The analysis of the pressure rise characteristic of each individual subcomponent (impeller, diffuser inlet, diffuser channel,...) reveals their contribution to the overall pressure rise. The diffuser channels playmore » an inherently destabilizing role while the impeller and the diffuser inlet are typically stabilizing. The stability limit was mainly determined by a change in the characteristic of the diffuser inlet. Further, the stability limit was found to be independent of the development of inducer-tip recirculation.« less

Modelling oxygen self-diffusion in UO 2 under pressure

DOE PAGES

Cooper, Michael William D.; Grimes, R. W.; Fitzpatrick, M. E.; ...

2015-10-22

Access to values for oxygen self-diffusion over a range of temperatures and pressures in UO 2 is important to nuclear fuel applications. Here, elastic and expansivity data are used in the framework of a thermodynamic model, the cBΩ model, to derive the oxygen self-diffusion coefficient in UO 2 over a range of pressures (0–10 GPa) and temperatures (300–1900 K). Furthermore, the significant reduction in oxygen self-diffusion as a function of increasing hydrostatic pressure, and the associated increase in activation energy, is identified.

Numerical Prediction of Combustion-induced Noise using a hybrid LES/CAA approach

NASA Astrophysics Data System (ADS)

Ihme, Matthias; Pitsch, Heinz; Kaltenbacher, Manfred

2006-11-01

Noise generation in technical devices is an increasingly important problem. Jet engines in particular produce sound levels that not only are a nuisance but may also impair hearing. The noise emitted by such engines is generated by different sources such as jet exhaust, fans or turbines, and combustion. Whereas the former acoustic mechanisms are reasonably well understood, combustion-generated noise is not. A methodology for the prediction of combustion-generated noise is developed. In this hybrid approach unsteady acoustic source terms are obtained from an LES and the propagation of pressure perturbations are obtained using acoustic analogies. Lighthill's acoustic analogy and a non-linear wave equation, accounting for variable speed of sound, have been employed. Both models are applied to an open diffusion flame. The effects on the far field pressure and directivity due to the variation of speed of sound are analyzed. Results for the sound pressure level will be compared with experimental data.

Fundamental Flux Equations for Fracture-Matrix Interactions with Linear Diffusion

NASA Astrophysics Data System (ADS)

Oldenburg, C. M.; Zhou, Q.; Rutqvist, J.; Birkholzer, J. T.

2017-12-01

The conventional dual-continuum models are only applicable for late-time behavior of pressure propagation in fractured rock, while discrete-fracture-network models may explicitly deal with matrix blocks at high computational expense. To address these issues, we developed a unified-form diffusive flux equation for 1D isotropic (spheres, cylinders, slabs) and 2D/3D rectangular matrix blocks (squares, cubes, rectangles, and rectangular parallelepipeds) by partitioning the entire dimensionless-time domain (Zhou et al., 2017a, b). For each matrix block, this flux equation consists of the early-time solution up until a switch-over time after which the late-time solution is applied to create continuity from early to late time. The early-time solutions are based on three-term polynomial functions in terms of square root of dimensionless time, with the coefficients dependent on dimensionless area-to-volume ratio and aspect ratios for rectangular blocks. For the late-time solutions, one exponential term is needed for isotropic blocks, while a few additional exponential terms are needed for highly anisotropic blocks. The time-partitioning method was also used for calculating pressure/concentration/temperature distribution within a matrix block. The approximate solution contains an error-function solution for early times and an exponential solution for late times, with relative errors less than 0.003. These solutions form the kernel of multirate and multidimensional hydraulic, solute and thermal diffusion in fractured reservoirs.

Characteristics of Perforated Diffusers at Free-stream Mach Number 1.90

NASA Technical Reports Server (NTRS)

Hunczak, Henry R; Kremzier, Emil J

1950-01-01

An investigation was conducted at Mach number 1.90 to determine pressure recovery and mass-flow characteristics of series of perforated convergent-divergent supersonic diffusers. Pressure recoveries as high as 96 percent were obtained, but at reduced mass flows through the diffuser. Theoretical considerations of effect of perforation distribution on shock stability in converging section of diffuser are presented and correlated with experimental data. A method of estimating relative importance of pressure recovery and mass flow on internal thrust coefficient basis is given and a comparison of various diffusers investigated is made.

Pressure Characteristics of a Diffuser in a Ram RDE Propulsive Device

DTIC Science & Technology

2017-07-21

Continuous detonation Rotating-detonation- engine Ethylene-air Diffuser Pressure feedback Modeling and simulation Office of Naval Research 875 N. Randolph...RDE PROPULSIVE DEVICE INTRODUCTION This report focuses on the diffuser of a ram Rotating Detonation Engine (RDE) device. A ram RDE is a ramjet with...the constant pressure combustion chamber replaced with a Rotating Detonation Engine combustor to accomplish pressure gain combustion. A ram engine

Compressor Performance Scaling in the Presence of Non-Uniform Flow

NASA Astrophysics Data System (ADS)

Hill, David Jarrod

Fuselage-embedded engines in future aircraft will see increased flow distortions due to the ingestion of airframe boundary layers. This reduces the required propulsive power compared to podded engines. Inlet flow distortions mean that localized regions of flow within the fan and first stage compressor are operating at off-design conditions. It is important to weigh the benefit of increased vehicle propulsive efficiency against the resultant reduction in engine efficiency. High computational cost has limited most past research to single distortion studies. The objective of this thesis is to extract scaling laws for transonic compressor performance in the presence of various distortion patterns and intensities. The machine studied is the NASA R67 transonic compressor. Volumetric source terms are used to model rotor and stator blade rows. The modelling approach is an innovative combination of existing flow turning and loss models, combined with a compressible flow correction. This approach allows for a steady calculation to capture distortion transfer; as a result, the computational cost is reduced by two orders of magnitude. At peak efficiency, the rotor work coefficient and isentropic efficiency are matched within 1.4% of previously published experimental results. A key finding of this thesis is that, in non-uniform flow, the state-of-the-art loss model employed is unable to capture the impact of variations in local flow coefficient, limiting the analysis of local entropy generation. New insight explains the mechanism governing the interaction between a total temperature distortion and a compressor rotor. A parametric study comprising 16 inlet distortions reveals that for total temperature distortions, upstream flow redistribution and rotor diffusion factor changes are shown to scale linearly with distortion severity. Linear diffusion factor scaling does not hold true for total pressure distortions. For combined total temperature and total pressure distortions, the changes in rotor diffusion factor are predicted by the summation of the individual distortions, within 3.65%.

Performance Characteristics of Plane-Wall Two-Dimensional Diffusers

NASA Technical Reports Server (NTRS)

Reid, Elliott G

1953-01-01

Experiments have been made at Stanford University to determine the performance characteristics of plane-wall, two-dimensional diffusers which were so proportioned as to insure reasonable approximation of two-dimensional flow. All of the diffusers had identical entrance cross sections and discharged directly into a large plenum chamber; the test program included wide variations of divergence angle and length. During all tests a dynamic pressure of 60 pounds per square foOt was maintained at the diffuser entrance and the boundary layer there was thin and fully turbulent. The most interesting flow characteristics observed were the occasional appearance of steady, unseparated, asymmetric flow - which was correlated with the boundary-layer coalescence - and the rapid deterioration of flow steadiness - which occurred as soon as the divergence angle for maximum static pressure recovery was exceeded. Pressure efficiency was found to be controlled almost exclusively by divergence angle, whereas static pressure recovery was markedly influenced by area ratio (or length) as well as divergence angle. Volumetric efficiency. diminished as area ratio increased, and at a greater rate with small lengths than with large ones. Large values of the static-pressure-recovery coefficient were attained only with long diffusers of large area ratio; under these conditions pressure efficiency was high and. volumetric efficiency low. Auxiliary tests with asymmetric diffusers demonstrated that longitudinal pressure gradient, rather than wall divergence angle, controlled flow separation. Others showed that the addition of even a short exit duct of uniform section augmented pressure recovery. Finally, it was found that the installation of a thin, central, longitudinal partition suppressed flow separation in short diffusers and thereby improved pressure recovery

Effects of High Pressure on Membrane Ion Binding and Transport.

DTIC Science & Technology

1980-12-31

diffusion in red cell membranes have appar- ent activation volumes of 40 ml/mol in agreement with data on liposomes, and ,6) perturbations in osmotic...Extrapolated to the Red Cell? (page 15) B. Pressure Dependence of Butanol Diffusion (page 17) C. Development of a High Pressure Stop-Flow (page 19...page 16 Figure 3 -- Pressure effect on the diffusion coefficient n-butanol in packed human red cells ................... page 18 Figure 9

Effects of inlet flow field conditions on the performance of centrifugal compressor diffusers: Part 2 -- Straight-channel diffuser

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

Deniz, S.; Greitzer, E.M.; Cumpsty, N.A.

2000-01-01

This is Part 2 of an examination of the influence of inlet flow conditions on the performance and operating range of centrifugal compressor vaned diffusers. The paper describes tests of a straight-channel type diffuser, sometimes called a wedge-vane diffuser, and compares the results with those from the discrete-passage diffusers described in Part 1. Effects of diffuser inlet Mach number, flow angle, blockage, and axial flow nonuniformity on diffuser pressure recovery and operating range are addressed. The straight-channel diffuser investigated has 30 vanes and was designed for the same aerodynamic duty as the discrete-passage diffuser described in Part 1. The rangesmore » of the overall pressure recovery coefficients were 0.50--0.78 for the straight-channel diffuser and 0.50--0.70 for the discrete-passage diffuser, except when the diffuser was choked. In other words, the maximum pressure recovery of the straight-channel diffuser was found to be roughly 10% higher than that of the discrete-passage diffuser investigated. The two types of diffuser showed similar behavior regarding the dependence of pressure recovery on diffuser inlet flow angle and the insensitivity of the performance to inlet flow field axial distortion and Mach number. The operating range of the straight-channel diffuser, as for the discrete-passage diffusers, was limited by the onset of rotating stall at a fixed momentum-averaged flow angle into the diffuser, which was for the straight-channel diffuser, {alpha}{sub crit} = 70 {+-} 0.5 deg. The background, nomenclature, and description of the facility and method are all given in Part 1.« less

An Update on the Non-Mass-Dependent Isotope Fractionation under Thermal Gradient

NASA Technical Reports Server (NTRS)

Sun, Tao; Niles, Paul; Bao, Huiming; Socki, Richard; Liu, Yun

2013-01-01

Mass flow and compositional gradient (elemental and isotope separation) occurs when flu-id(s) or gas(es) in an enclosure is subjected to a thermal gradient, and the phenomenon is named thermal diffusion. Gas phase thermal diffusion has been theoretically and experimentally studied for more than a century, although there has not been a satisfactory theory to date. Nevertheless, for isotopic system, the Chapman-Enskog theory predicts that the mass difference is the only term in the thermal diffusion separation factors that differs one isotope pair to another,with the assumptions that the molecules are spherical and systematic (monoatomic-like structure) and the particle collision is elastic. Our previous report indicates factors may be playing a role because the Non-Mass Dependent (NMD) effect is found for both symmetric and asymmetric, linear and spherical polyatomic molecules over a wide range of temperature (-196C to +237C). The observed NMD phenomenon in the simple thermal-diffusion experiments demands quantitative validation and theoretical explanation. Besides the pressure and temperature dependency illustrated in our previous reports, efforts are made in this study to address issues such as the role of convection or molecular structure and whether it is a transient, non-equilibrium effect only.

The Effect of Physician and Hospital Market Structure on Medical Technology Diffusion.

PubMed

Karaca-Mandic, Pinar; Town, Robert J; Wilcock, Andrew

2017-04-01

To examine the influence of physician and hospital market structures on medical technology diffusion, studying the diffusion of drug-eluting stents (DESs), which became available in April 2003. Medicare claims linked to physician demographic data from the American Medical Association and to hospital characteristics from the American Hospital Association Survey. Retrospective claims data analyses. All fee-for-service Medicare beneficiaries who received a percutaneous coronary intervention (PCI) with a cardiac stent in 2003 or 2004. Each PCI record was joined to characteristics on the patient, the procedure, the cardiologist, and the hospital where the PCI was delivered. We accounted for the endogeneity of physician and hospital market structure using exogenous variation in the distances between patient, physician, and hospital locations. We estimated multivariate linear probability models that related the use of a DES in the PCI on market structure while controlling for patient, physician, and hospital characteristics. DESs diffused faster in markets where cardiology practices faced more competition. Conversely, we found no evidence that the structure of the hospital market mattered. Competitive pressure to maintain or expand PCI volume shares compelled cardiologists to adopt DESs more quickly. © Health Research and Educational Trust.

A framework to analyze cerebral mean diffusivity using surface guided diffusion mapping in diffusion tensor imaging

PubMed Central

Kwon, Oh-Hun; Park, Hyunjin; Seo, Sang-Won; Na, Duk L.; Lee, Jong-Min

2015-01-01

The mean diffusivity (MD) value has been used to describe microstructural properties in Diffusion Tensor Imaging (DTI) in cortical gray matter (GM). Recently, researchers have applied a cortical surface generated from the T1-weighted volume. When the DTI data are analyzed using the cortical surface, it is important to assign an accurate MD value from the volume space to the vertex of the cortical surface, considering the anatomical correspondence between the DTI and the T1-weighted image. Previous studies usually sampled the MD value using the nearest-neighbor (NN) method or Linear method, even though there are geometric distortions in diffusion-weighted volumes. Here we introduce a Surface Guided Diffusion Mapping (SGDM) method to compensate for such geometric distortions. We compared our SGDM method with results using NN and Linear methods by investigating differences in the sampled MD value. We also projected the tissue classification results of non-diffusion-weighted volumes to the cortical midsurface. The CSF probability values provided by the SGDM method were lower than those produced by the NN and Linear methods. The MD values provided by the NN and Linear methods were significantly greater than those of the SGDM method in regions suffering from geometric distortion. These results indicate that the NN and Linear methods assigned the MD value in the CSF region to the cortical midsurface (GM region). Our results suggest that the SGDM method is an effective way to correct such mapping errors. PMID:26236180

Susceptibility of experimental faults to pore pressure increase: insights from load-controlled experiments on calcite-bearing rocks

NASA Astrophysics Data System (ADS)

Spagnuolo, Elena; Violay, Marie; Nielsen, Stefan; Cornelio, Chiara; Di Toro, Giulio

2017-04-01

Fluid pressure has been indicated as a major factor controlling natural (e.g., L'Aquila, Italy, 2009 Mw 6.3) and induced seismicity (e.g., Wilzetta, Oklahoma, 2011 Mw 5.7). Terzaghi's principle states that the effective normal stress is linearly reduced by a pore pressure (Pf) increase σeff=σn(1 - αPf), where the effective stress parameter α, may be related to the fraction of the fault area that is flooded. A value of α =1 is often used by default, with Pf shifting the Mohr circle towards lower normal effective stresses and anticipating failure on pre-existing faults. However, within a complex fault core of inhomogeneous permeability, α may vary in a yet poorly understood way. To shed light on this problem, we conducted experiments on calcite-bearing rock samples (Carrara marble) at room humidity conditions and in the presence of pore fluids (drained conditions) using a rotary apparatus (SHIVA). A pre-cut fault is loaded by constant shear stress τ under constant normal stress σn=15 MPa until a target value corresponding roughly to the 80 % of the frictional fault strength. The pore pressure Pf is then raised with regular pressure and time steps to induce fault instability. Assuming α=1 and a threshold for instability τp_eff=μp σeff, the experiments reveal that an increase of Pf does not necessarily induce an instability even when the effective strength threshold is largely surpassed (e.g., τp_eff=1.3 μpσeff). This result may indicate that the Pf increase did not instantly diffuse throughout the slip zone, but took a finite time to equilibrate with the external imposed pressure increase due to finite permeability. Under our experimental conditions, a significant departure from α=1 is observed provided that the Pf step is shorter than about < 20s. We interpret this delay as indicative of the diffusion time (td), which is related to fluid penetration length l by l = √ κtd-, where κ is the hydraulic diffusivity on the fault plane. We show that a simple cubic law relates td to hydraulic aperture, pore pressure gradient and injection rate. We redefine α as the ratio between the fluid penetration length and sample dimension L resulting in α = min(√ktd,L) L. Under several pore pressure loading rates this relation yields an approximate hydraulic diffusivity κ ˜10-8 m2 s-1 which is compatible, for example, with a low porosity shale. Our results highlight that a high injection flow rate in fault plane do not necessarily induce seismogenic fault slip: a critical pore penetration length or fluid patch size is necessary to trigger fault instability.

Generating a Simulated Fluid Flow Over an Aircraft Surface Using Anisotropic Diffusion

NASA Technical Reports Server (NTRS)

Rodriguez, David L. (Inventor); Sturdza, Peter (Inventor)

2013-01-01

A fluid-flow simulation over a computer-generated aircraft surface is generated using a diffusion technique. The surface is comprised of a surface mesh of polygons. A boundary-layer fluid property is obtained for a subset of the polygons of the surface mesh. A pressure-gradient vector is determined for a selected polygon, the selected polygon belonging to the surface mesh but not one of the subset of polygons. A maximum and minimum diffusion rate is determined along directions determined using a pressure gradient vector corresponding to the selected polygon. A diffusion-path vector is defined between a point in the selected polygon and a neighboring point in a neighboring polygon. An updated fluid property is determined for the selected polygon using a variable diffusion rate, the variable diffusion rate based on the minimum diffusion rate, maximum diffusion rate, and angular difference between the diffusion-path vector and the pressure-gradient vector.

Ion profiling in an ambient drift tube-ion mobility spectrometer using a high pixel density linear array detector IonCCD.

PubMed

Davila, Stephen J; Hadjar, Omar; Eiceman, Gary A

2013-07-16

A linear pixel-based detector array, the IonCCD, is characterized for use under ambient conditions with thermal (<1 eV) positive ions derived from purified air and a 10 mCi (63)Ni foil. The IonCCD combined with a drift tube-ion mobility spectrometer permitted the direct detection of gas phase ions at atmospheric pressure and confirmed a limit of detection of 3000 ions/pixel/frame established previously in both the keV (1-2 keV) and the hyper-thermal (10-40 eV) regimes. Results demonstrate the "broad-band" application of the IonCCD over 10(5) orders in ion energy and over 10(10) in operating pressure. The Faraday detector of a drift tube for an ion mobility spectrometer was replaced with the IonCCD providing images of ion profiles over the cross-section of the drift tube. Patterns in the ion profiles were developed in the drift tube cross-section by control of electric fields between wires of Bradbury Nielson and Tyndall Powell shutter designs at distances of 1-8 cm from the detector. Results showed that ion beams formed in wire sets, retained their shape with limited mixing by diffusion and Coulombic repulsion. Beam broadening determined as 95 μm/cm for hydrated protons in air with moisture of ~10 ppmv. These findings suggest a value of the IonCCD in further studies of ion motion and diffusion of thermalized ions, enhancing computational results from simulation programs, and in the design or operation of ion mobility spectrometers.

Oxygen self-diffusion in ThO 2 under pressure: Connecting point defect parameters with bulk properties

DOE PAGES

Cooper, Michael William D.; Fitzpatrick, M. E.; Tsoukalas, L. H.; ...

2016-06-06

ThO 2 is a candidate material for use in nuclear fuel applications and as such it is important to investigate its materials properties over a range of temperatures and pressures. In the present study molecular dynamics calculations are used to calculate elastic and expansivity data. These are used in the framework of a thermodynamic model, the cBΩ model, to calculate the oxygen self-diffusion coefficient in ThO 2 over a range of pressures (–10–10 GPa) and temperatures (300–1900 K). As a result, increasing the hydrostatic pressure leads to a significant reduction in oxygen self-diffusion. Conversely, negative hydrostatic pressure significantly enhances oxygenmore » self-diffusion.« less

Fourth order Douglas implicit scheme for solving three dimension reaction diffusion equation with non-linear source term

NASA Astrophysics Data System (ADS)

Hasnain, Shahid; Saqib, Muhammad; Mashat, Daoud Suleiman

2017-07-01

This research paper represents a numerical approximation to non-linear three dimension reaction diffusion equation with non-linear source term from population genetics. Since various initial and boundary value problems exist in three dimension reaction diffusion phenomena, which are studied numerically by different numerical methods, here we use finite difference schemes (Alternating Direction Implicit and Fourth Order Douglas Implicit) to approximate the solution. Accuracy is studied in term of L2, L∞ and relative error norms by random selected grids along time levels for comparison with analytical results. The test example demonstrates the accuracy, efficiency and versatility of the proposed schemes. Numerical results showed that Fourth Order Douglas Implicit scheme is very efficient and reliable for solving 3-D non-linear reaction diffusion equation.

Effect of stress on the diffusion kinetics of methane during gas desorption in coal matrix under different equilibrium pressures

NASA Astrophysics Data System (ADS)

Li, Chengwu; Xue, Honglai; Hu, Po; Guan, Cheng; Liu, Wenbiao

2018-06-01

Stress has a significant influence on gas diffusion, which is a key factor for methane recovery in coal mines. In this study, a series of experiments were performed to investigate effect of stress on the gas diffusivity during desorption in tectonic coal. Additionally, the desorbed data were modeled using the unipore and bidisperse models. The results show that the bidisperse model better describes the diffusion kinetics than the unipore model in this study. Additionally, the modeling results using the bidisperse approach suggest that the stress impact on the macropore diffusivity is greater than the stress on the micropore diffusivity. Under the same equilibrium pressure, the diffusivity varies with stress according to a four-stage function, which shows an ‘M-shape’. As the equilibrium gas pressure increased from 0.6 to 1.7 MPa, the critical point between stage 2 and stage 3 and between stage 3 and stage 4 transferred to a low stress. This difference is attributed to the gas pressure effects on the physical and mechanical properties of coal. These observations indicate that both the stress and gas pressure can significantly impact gas diffusion and may have significant implications on methane recovery in coal mines.

A Validated All-Pressure Fluid Drop Model and Lewis Number Effects for a Binary Mixture

NASA Technical Reports Server (NTRS)

Harstad, K.; Bellan, J.

1999-01-01

The differences between subcritical liquid drop and supercritical fluid drop behavior are discussed. Under subcritical, evaporative high emission rate conditions, a film layer is present in the inner part of the drop surface which contributes to the unique determination of the boundary conditions; it is this film layer which contributes to the solution's convective-diffusive character. In contrast, under supercritical condition as the boundary conditions contain a degree of arbitrariness due to the absence of a surface, and the solution has then a purely diffusive character. Results from simulations of a free fluid drop under no-gravity conditions are compared to microgravity experimental data from suspended, large drop experiments at high, low and intermediary temperatures and in a range of pressures encompassing the sub-and supercritical regime. Despite the difference between the conditions of the simulations and experiments (suspension vs. free floating), the time rate of variation of the drop diameter square is remarkably well predicted in the linear curve regime. The drop diameter is determined in the simulations from the location of the maximum density gradient, and agrees well with the data. It is also shown that the classical calculation of the Lewis number gives qualitatively erroneous results at supercritical conditions, but that an effective Lewis number previously defined gives qualitatively correct estimates of the length scales for heat and mass transfer at all pressures.

Wake orientation and its influence on the performance of diffusers with inlet distortion

NASA Astrophysics Data System (ADS)

Coffman, Jesse M.

Distortion at the inlet to diffusers is very common in internal flow applications. Inlet velocity distortion influences the pressure recovery and flow regimes of diffusers. This work introduced a centerline wake at the square inlet of a plane wall diffuser in two orthogonal orientations to investigate its influence on the diffuser performance. Two different wakes were generated. One was from a mesh strip which produced a velocity deficit with low turbulence intensity and two shear layers. The other wake generator was a D-shaped cylinder which produced a wake with high turbulence intensity and large length scales. These inlet conditions were generated for a diffuser with a diffusion angle of 3° and 6°. A pair of RANS simulations were used to investigate the influence of the orthogonal inlet orientations on the solution. The inlet conditions were taken from the inlet velocity field measured for the mesh strip. The flow development and exit conditions showed some similarities and some differences with the experimental results. The performance of a diffuser is typically measured through the static pressure recovery coefficient and the total pressure losses. The definition of these metrics commonly found in the literature were insufficient to discern differences between the wake orientations. New metrics were derived using the momentum flux profile parameter which related the static pressure recovery, the total pressure losses, and the velocity uniformity at the inlet and exit of the diffuser. These metrics revealed a trade-off between the total pressure losses and the uniformity of the velocity field.

The Linear Mixing Approximation for Planetary Ices

NASA Astrophysics Data System (ADS)

Bethkenhagen, M.; Meyer, E. R.; Hamel, S.; Nettelmann, N.; French, M.; Scheibe, L.; Ticknor, C.; Collins, L. A.; Kress, J. D.; Fortney, J. J.; Redmer, R.

2017-12-01

We investigate the validity of the widely used linear mixing approximation for the equations of state (EOS) of planetary ices, which are thought to dominate the interior of the ice giant planets Uranus and Neptune. For that purpose we perform density functional theory molecular dynamics simulations using the VASP code.[1] In particular, we compute 1:1 binary mixtures of water, ammonia, and methane, as well as their 2:1:4 ternary mixture at pressure-temperature conditions typical for the interior of Uranus and Neptune.[2,3] In addition, a new ab initio EOS for methane is presented. The linear mixing approximation is verified for the conditions present inside Uranus ranging up to 10 Mbar based on the comprehensive EOS data set. We also calculate the diffusion coefficients for the ternary mixture along different Uranus interior profiles and compare them to the values of the pure compounds. We find that deviations of the linear mixing approximation from the real mixture are generally small; for the EOS they fall within about 4% uncertainty while the diffusion coefficients deviate up to 20% . The EOS of planetary ices are applied to adiabatic models of Uranus. It turns out that a deep interior of almost pure ices is consistent with the gravity field data, in which case the planet becomes rather cold (T core ˜ 4000 K). [1] G. Kresse and J. Hafner, Physical Review B 47, 558 (1993). [2] R. Redmer, T.R. Mattsson, N. Nettelmann and M. French, Icarus 211, 798 (2011). [3] N. Nettelmann, K. Wang, J. J. Fortney, S. Hamel, S. Yellamilli, M. Bethkenhagen and R. Redmer, Icarus 275, 107 (2016).

Measurement of effective bulk and contact resistance of gas diffusion layer under inhomogeneous compression - Part I: Electrical conductivity

NASA Astrophysics Data System (ADS)

Vikram, Ajit; Chowdhury, Prabudhya Roy; Phillips, Ryan K.; Hoorfar, Mina

2016-07-01

This paper describes a measurement technique developed for the determination of the effective electrical bulk resistance of the gas diffusion layer (GDL) and the contact resistance distribution at the interface of the GDL and the bipolar plate (BPP). The novelty of this study is the measurement and separation of the bulk and contact resistance under inhomogeneous compression, occurring in an actual fuel cell assembly due to the presence of the channels and ribs on the bipolar plates. The measurement of the electrical contact resistance, contributing to nearly two-third of the ohmic losses in the fuel cell assembly, shows a non-linear distribution along the GDL/BPP interface. The effective bulk resistance of the GDL under inhomogeneous compression showed a decrease of nearly 40% compared to that estimated for homogeneous compression at different compression pressures. Such a decrease in the effective bulk resistance under inhomogeneous compression could be due to the non-uniform distribution of pressure under the ribs and the channels. This measurement technique can be used to identify optimum GDL, BPP and channel-rib structures based on minimum bulk and contact resistances measured under inhomogeneous compression.

Anisotropic diffusion at the field scale in a 4-year multi-tracer diffusion and retention experiment - I: Insights from the experimental data

NASA Astrophysics Data System (ADS)

Gimmi, Thomas; Leupin, Olivier X.; Eikenberg, Jost; Glaus, Martin A.; Van Loon, Luc R.; Waber, H. Niklaus; Wersin, Paul; Wang, Hao A. O.; Grolimund, Daniel; Borca, Camelia N.; Dewonck, Sarah; Wittebroodt, Charles

2014-01-01

Claystones are considered worldwide as barrier materials for nuclear waste repositories. In the Mont Terri underground research laboratory (URL), a nearly 4-year diffusion and retention (DR) experiment has been performed in Opalinus Clay. It aimed at (1) obtaining data at larger space and time scales than in laboratory experiments and (2) under relevant in situ conditions with respect to pore water chemistry and mechanical stress, (3) quantifying the anisotropy of in situ diffusion, and (4) exploring possible effects of a borehole-disturbed zone. The experiment included two tracer injection intervals in a borehole perpendicular to bedding, through which traced artificial pore water (APW) was circulated, and a pressure monitoring interval. The APW was spiked with neutral tracers (HTO, HDO, H2O-18), anions (Br, I, SeO4), and cations (Na-22, Ba-133, Sr-85, Cs-137, Co-60, Eu-152, stable Cs, and stable Eu). Most tracers were added at the beginning, some were added at a later stage. The hydraulic pressure in the injection intervals was adjusted according to the measured value in the pressure monitoring interval to ensure transport by diffusion only. Concentration time-series in the APW within the borehole intervals were obtained, as well as 2D concentration distributions in the rock at the end of the experiment after overcoring and subsampling which resulted in ∼250 samples and ∼1300 analyses. As expected, HTO diffused the furthest into the rock, followed by the anions (Br, I, SeO4) and by the cationic sorbing tracers (Na-22, Ba-133, Cs, Cs-137, Co-60, Eu-152). The diffusion of SeO4 was slower than that of Br or I, approximately proportional to the ratio of their diffusion coefficients in water. Ba-133 diffused only into ∼0.1 m during the ∼4 a. Stable Cs, added at a higher concentration than Cs-137, diffused further into the rock than Cs-137, consistent with a non-linear sorption behavior. The rock properties (e.g., water contents) were rather homogeneous at the centimeter scale, with no evidence of a borehole-disturbed zone. In situ anisotropy ratios for diffusion, derived for the first time directly from field data, are larger for HTO and Na-22 (∼5) than for anions (∼3-4 for Br and I). The lower ionic strength of the pore water at this location (∼0.22 M) as compared to locations of earlier experiments in the Mont Terri URL (∼0.39 M) had no notable effect on the anion accessible pore fraction for Cl, Br, and I: the value of 0.55 is within the range of earlier data. Detailed transport simulations involving different codes will be presented in a companion paper.

On Large Time Behavior and Selection Principle for a Diffusive Carr-Penrose Model

NASA Astrophysics Data System (ADS)

Conlon, Joseph G.; Dabkowski, Michael; Wu, Jingchen

2016-04-01

This paper is concerned with the study of a diffusive perturbation of the linear LSW model introduced by Carr and Penrose. A main subject of interest is to understand how the presence of diffusion acts as a selection principle, which singles out a particular self-similar solution of the linear LSW model as determining the large time behavior of the diffusive model. A selection principle is rigorously proven for a model which is a semiclassical approximation to the diffusive model. Upper bounds on the rate of coarsening are also obtained for the full diffusive model.

Analysis of pressure losses in the diffuser of a control valve

NASA Astrophysics Data System (ADS)

Turecký, Petr; Mrózek, Lukáš; Tajč, Ladislav; Kolovratník, Michal

The pressure loss in the diffuser of a control valve is evaluated by using CFD computations. Pressure ratios and lifts of a cone for the recommended flow characteristics of an experimental turbine are considered. The pressure loss in a valve is compared with the pressure loss in a nozzle, i.e. the embodiment of the valve without a cone. Computations are carried out for the same mass flow. Velocity profiles are evaluated in both versions of computations. Comparison of computed pressure losses, with the loss evaluated by using relations for diffusers with the ideal velocity conditions in the input cross-section, is carried out.

Modified chloride diffusion model for concrete under the coupling effect of mechanical load and chloride salt environment

NASA Astrophysics Data System (ADS)

Lei, Mingfeng; Lin, Dayong; Liu, Jianwen; Shi, Chenghua; Ma, Jianjun; Yang, Weichao; Yu, Xiaoniu

2018-03-01

For the purpose of investigating lining concrete durability, this study derives a modified chloride diffusion model for concrete based on the odd continuation of boundary conditions and Fourier transform. In order to achieve this, the linear stress distribution on a sectional structure is considered, detailed procedures and methods are presented for model verification and parametric analysis. Simulation results show that the chloride diffusion model can reflect the effects of linear stress distribution of the sectional structure on the chloride diffusivity with reliable accuracy. Along with the natural environmental characteristics of practical engineering structures, reference value ranges of model parameters are provided. Furthermore, a chloride diffusion model is extended for the consideration of multi-factor coupling of linear stress distribution, chloride concentration and diffusion time. Comparison between model simulation and typical current research results shows that the presented model can produce better considerations with a greater universality.

Determination of diffusion coefficients of carbon dioxide in water between 268 and 473 K in a high-pressure capillary optical cell with in situ Raman spectroscopic measurements

USGS Publications Warehouse

Lu, Wanjun; Guo, Huirong; Chou, I.-Ming; Burruss, R.C.; Li, Lanlan

2013-01-01

Accurate values of diffusion coefficients for carbon dioxide in water and brine at reservoir conditions are essential to our understanding of transport behavior of carbon dioxide in subsurface pore space. However, the experimental data are limited to conditions at low temperatures and pressures. In this study, diffusive transfer of carbon dioxide in water at pressures up to 45 MPa and temperatures from 268 to 473 K was observed within an optical capillary cell via time-dependent Raman spectroscopy. Diffusion coefficients were estimated by the least-squares method for the measured variations in carbon dioxide concentration in the cell at various sample positions and time. At the constant pressure of 20 MPa, the measured diffusion coefficients of carbon dioxide in water increase with increasing temperature from 268 to 473 K. The relationship between diffusion coefficient of carbon dioxide in water [D(CO2) in m2/s] and temperature (T in K) was derived with Speedy–Angell power-law approach as: D(CO2)=D0[T/Ts-1]m where D0 = 13.942 × 10−9 m2/s, Ts = 227.0 K, and m = 1.7094. At constant temperature, diffusion coefficients of carbon dioxide in water decrease with pressure increase. However, this pressure effect is rather small (within a few percent).

The Fisher-KPP problem with doubly nonlinear diffusion

NASA Astrophysics Data System (ADS)

Audrito, Alessandro; Vázquez, Juan Luis

2017-12-01

The famous Fisher-KPP reaction-diffusion model combines linear diffusion with the typical KPP reaction term, and appears in a number of relevant applications in biology and chemistry. It is remarkable as a mathematical model since it possesses a family of travelling waves that describe the asymptotic behaviour of a large class solutions 0 ≤ u (x , t) ≤ 1 of the problem posed in the real line. The existence of propagation waves with finite speed has been confirmed in some related models and disproved in others. We investigate here the corresponding theory when the linear diffusion is replaced by the "slow" doubly nonlinear diffusion and we find travelling waves that represent the wave propagation of more general solutions even when we extend the study to several space dimensions. A similar study is performed in the critical case that we call "pseudo-linear", i.e., when the operator is still nonlinear but has homogeneity one. With respect to the classical model and the "pseudo-linear" case, the "slow" travelling waves exhibit free boundaries.

High-Pressure Transport Properties Of Fluids: Theory And Data From Levitated Drops At Combustion-Relevant Temperatures

NASA Technical Reports Server (NTRS)

Bellan, Josette; Harstad, Kenneth; Ohsaka, Kenichi

2003-01-01

Although the high pressure multicomponent fluid conservation equations have already been derived and approximately validated for binary mixtures by this PI, the validation of the multicomponent theory is hampered by the lack of existing mixing rules for property calculations. Classical gas dynamics theory can provide property mixing-rules at low pressures exclusively. While thermal conductivity and viscosity high-pressure mixing rules have been documented in the literature, there is no such equivalent for the diffusion coefficients and the thermal diffusion factors. The primary goal of this investigation is to extend the low pressure mixing rule theory to high pressures and validate the new theory with experimental data from levitated single drops. The two properties that will be addressed are the diffusion coefficients and the thermal diffusion factors. To validate/determine the property calculations, ground-based experiments from levitated drops are being conducted.

Quantitative model of diffuse speckle contrast analysis for flow measurement.

PubMed

Liu, Jialin; Zhang, Hongchao; Lu, Jian; Ni, Xiaowu; Shen, Zhonghua

2017-07-01

Diffuse speckle contrast analysis (DSCA) is a noninvasive optical technique capable of monitoring deep tissue blood flow. However, a detailed study of the speckle contrast model for DSCA has yet to be presented. We deduced the theoretical relationship between speckle contrast and exposure time and further simplified it to a linear approximation model. The feasibility of this linear model was validated by the liquid phantoms which demonstrated that the slope of this linear approximation was able to rapidly determine the Brownian diffusion coefficient of the turbid media at multiple distances using multiexposure speckle imaging. Furthermore, we have theoretically quantified the influence of optical property on the measurements of the Brownian diffusion coefficient which was a consequence of the fact that the slope of this linear approximation was demonstrated to be equal to the inverse of correlation time of the speckle.

S{sub 2}SA preconditioning for the S{sub n} equations with strictly non negative spatial discretization

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

Bruss, D. E.; Morel, J. E.; Ragusa, J. C.

2013-07-01

Preconditioners based upon sweeps and diffusion-synthetic acceleration have been constructed and applied to the zeroth and first spatial moments of the 1-D S{sub n} transport equation using a strictly non negative nonlinear spatial closure. Linear and nonlinear preconditioners have been analyzed. The effectiveness of various combinations of these preconditioners are compared. In one dimension, nonlinear sweep preconditioning is shown to be superior to linear sweep preconditioning, and DSA preconditioning using nonlinear sweeps in conjunction with a linear diffusion equation is found to be essentially equivalent to nonlinear sweeps in conjunction with a nonlinear diffusion equation. The ability to use amore » linear diffusion equation has important implications for preconditioning the S{sub n} equations with a strictly non negative spatial discretization in multiple dimensions. (authors)« less

A fault constitutive relation accounting for thermal pressurization of pore fluid

USGS Publications Warehouse

Andrews, D.J.

2002-01-01

The heat generated in a slip zone during an earthquake can raise fluid pressure and thereby reduce frictional resistance to slip. The amount of fluid pressure rise depends on the associated fluid flow. The heat generated at a given time produces fluid pressure that decreases inversely with the square root of hydraulic diffusivity times the elapsed time. If the slip velocity function is crack-like, there is a prompt fluid pressure rise at the onset of slip, followed by a slower increase. The stress drop associated with the prompt fluid pressure rise increases with rupture propagation distance. The threshold propagation distance at which thermally induced stress drop starts to dominate over frictionally induced stress drop is proportional to hydraulic diffusivity. If hydraulic diffusivity is 0.02 m2/s, estimated from borehole samples of fault zone material, the threshold propagation distance is 300 m. The stress wave in an earthquake will induce an unknown amount of dilatancy and will increase hydraulic diffusivity, both of which will lessen the fluid pressure effect. Nevertheless, if hydraulic diffusivity is no more than two orders of magnitude larger than the laboratory value, then stress drop is complete in large earthquakes.

A network model of successive partitioning-limited solute diffusion through the stratum corneum.

PubMed

Schumm, Phillip; Scoglio, Caterina M; van der Merwe, Deon

2010-02-07

As the most exposed point of contact with the external environment, the skin is an important barrier to many chemical exposures, including medications, potentially toxic chemicals and cosmetics. Traditional dermal absorption models treat the stratum corneum lipids as a homogenous medium through which solutes diffuse according to Fick's first law of diffusion. This approach does not explain non-linear absorption and irregular distribution patterns within the stratum corneum lipids as observed in experimental data. A network model, based on successive partitioning-limited solute diffusion through the stratum corneum, where the lipid structure is represented by a large, sparse, and regular network where nodes have variable characteristics, offers an alternative, efficient, and flexible approach to dermal absorption modeling that simulates non-linear absorption data patterns. Four model versions are presented: two linear models, which have unlimited node capacities, and two non-linear models, which have limited node capacities. The non-linear model outputs produce absorption to dose relationships that can be best characterized quantitatively by using power equations, similar to the equations used to describe non-linear experimental data.

Numerical solutions of Navier-Stokes equations for compressible turbulent two/three dimensional flows in terminal shock region of an inlet/diffuser

NASA Technical Reports Server (NTRS)

Liu, N. S.; Shamroth, S. J.; Mcdonald, H.

1983-01-01

The multidimensional ensemble averaged compressible time dependent Navier Stokes equations in conjunction with mixing length turbulence model and shock capturing technique were used to study the terminal shock type of flows in various flight regimes occurring in a diffuser/inlet model. The numerical scheme for solving the governing equations is based on a linearized block implicit approach and the following high Reynolds number calculations were carried out: (1) 2 D, steady, subsonic; (2) 2 D, steady, transonic with normal shock; (3) 2 D, steady, supersonic with terminal shock; (4) 2 D, transient process of shock development and (5) 3 D, steady, transonic with normal shock. The numerical results obtained for the 2 D and 3 D transonic shocked flows were compared with corresponding experimental data; the calculated wall static pressure distributions agree well with the measured data.

B2.5-Eirene modeling of radial transport in the MAGPIE linear plasma device

NASA Astrophysics Data System (ADS)

Owen, L. W.; Caneses, J. F.; Canik, J.; Lore, J. D.; Corr, C.; Blackwell, B.; Bonnin, X.; Rapp, J.

2017-05-01

Radial transport in helicon heated hydrogen plasmas in the MAGnetized Plasma Interaction Experiment (MAGPIE) is studied with the B2.5-Eirene (SOLPS5.0) code. Radial distributions of plasma density, temperature and ambipolar potential are computed for several magnetic field configurations and compared to double Langmuir probe measurements. Evidence for an unmagnetized ion population is seen in the requirement for a convective pinch term in the continuity equation in order to fit the centrally peaked density profile data. The measured slightly hollow electron temperature profiles are reproduced with combinations of on-axis and edge heating which can be interpreted as helicon and Trivelpiece-Gould wave absorption, respectively. Pressure gradient driven radial charged particle diffusion is chosen to describe the diffusive particle flux since the hollowness of the temperature profiles assists the establishment of on-axis density peaking.

Self-diffusivity and interdiffusivity of molten aluminum-copper alloys under pressure, derived from molecular dynamics.

PubMed

Rudd, Robert E; Cabot, William H; Caspersen, Kyle J; Greenough, Jeffrey A; Richards, David F; Streitz, Frederick H; Miller, Paul L

2012-03-01

We use molecular dynamics (MD) to simulate diffusion in molten aluminum-copper (AlCu) alloys. The self-diffusivities and Maxwell-Stefan diffusivities are calculated for AlCu mixtures using the Green-Kubo formulas at temperatures from 1000 to 4000 K and pressures from 0 to 25 GPa, along with additional points at higher temperatures and pressures. The diffusivities are corrected for finite-size effects. The Maxwell-Stefan diffusivity is compared to the diffusivity calculated from the self-diffusivities using a generalization of the Darken equation. We find that the effects of cross-correlation are small. Using the calculated self-diffusivities, we have assessed whether dilute hard-sphere and dilute Lennard-Jones models apply to the molten mixture. Neither of the two dilute gas diffusivities describes the diffusivity in molten Al and Cu. We report generalized analytic models for the self-diffusivities and interdiffusivity (mutual diffusivity) that fit the MD results well. The MD-derived transport coefficients are in good agreement with the available experimental data. We also report MD calculations of the viscosity and an analytic fit to those results. The ionic thermal conductivity is discussed briefly.

Self-diffusivity and interdiffusivity of molten aluminum-copper alloys under pressure, derived from molecular dynamics

NASA Astrophysics Data System (ADS)

Rudd, Robert E.; Cabot, William H.; Caspersen, Kyle J.; Greenough, Jeffrey A.; Richards, David F.; Streitz, Frederick H.; Miller, Paul L.

2012-03-01

We use molecular dynamics (MD) to simulate diffusion in molten aluminum-copper (AlCu) alloys. The self-diffusivities and Maxwell-Stefan diffusivities are calculated for AlCu mixtures using the Green-Kubo formulas at temperatures from 1000 to 4000 K and pressures from 0 to 25 GPa, along with additional points at higher temperatures and pressures. The diffusivities are corrected for finite-size effects. The Maxwell-Stefan diffusivity is compared to the diffusivity calculated from the self-diffusivities using a generalization of the Darken equation. We find that the effects of cross-correlation are small. Using the calculated self-diffusivities, we have assessed whether dilute hard-sphere and dilute Lennard-Jones models apply to the molten mixture. Neither of the two dilute gas diffusivities describes the diffusivity in molten Al and Cu. We report generalized analytic models for the self-diffusivities and interdiffusivity (mutual diffusivity) that fit the MD results well. The MD-derived transport coefficients are in good agreement with the available experimental data. We also report MD calculations of the viscosity and an analytic fit to those results. The ionic thermal conductivity is discussed briefly.

Molecular dynamics simulations of propane in slit shaped silica nano-pores: direct comparison with quasielastic neutron scattering experiments.

PubMed

Gautam, Siddharth; Le, Thu; Striolo, Alberto; Cole, David

2017-12-13

Molecular motion under confinement has important implications for a variety of applications including gas recovery and catalysis. Propane confined in mesoporous silica aerogel as studied using quasielastic neutron scattering (QENS) showed anomalous pressure dependence in its diffusion coefficient (J. Phys. Chem. C, 2015, 119, 18188). Molecular dynamics (MD) simulations are often employed to complement the information obtained from QENS experiments. Here, we report an MD simulation study to probe the anomalous pressure dependence of propane diffusion in silica aerogel. Comparison is attempted based on the self-diffusion coefficients and on the time scales of the decay of the simulated intermediate scattering functions. While the self-diffusion coefficients obtained from the simulated mean squared displacement profiles do not exhibit the anomalous pressure dependence observed in the experiments, the time scales of the decay of the intermediate scattering functions calculated from the simulation data match the corresponding quantities obtained in the QENS experiment and thus confirm the anomalous pressure dependence of the diffusion coefficient. The origin of the anomaly in pressure dependence lies in the presence of an adsorbed layer of propane molecules that seems to dominate the confined propane dynamics at low pressure, thereby lowering the diffusion coefficient. Further, time scales for rotational motion obtained from the simulations explain the absence of rotational contribution to the QENS spectra in the experiments. In particular, the rotational motion of the simulated propane molecules is found to exhibit large angular jumps at lower pressure. The present MD simulation work thus reveals important new insights into the origin of anomalous pressure dependence of propane diffusivity in silica mesopores and supplements the information obtained experimentally by QENS data.

Lack of anomalous diffusion in linear translationally-invariant systems determined by only one initial condition

NASA Astrophysics Data System (ADS)

Khorrami, Mohammad; Shariati, Ahmad; Aghamohammadi, Amir; Fatollahi, Amir H.

2012-01-01

It is shown that as far as the linear diffusion equation meets both time- and space-translational invariance, the time dependence of a moment of degree α is a polynomial of degree at most equal to α, while all connected moments are at most linear functions of time. As a special case, the variance is an at most linear function of time.

On the meaning of the diffusion layer thickness for slow electrode reactions.

PubMed

Molina, A; González, J; Laborda, E; Compton, R G

2013-02-21

A key concept underpinning electrochemical science is that of the diffusion layer - the zone of depletion around an electrode accompanying electrolysis. The size of this zone can be found either from the simulated or measured concentration profiles (yielding the 'true' diffusion layer thickness) or, in the case of the Nernst ('linear') diffusion layer by extrapolating the concentration gradient at the electrode surface to the distance at which the concentration takes its bulk value. The latter concept is very well developed in the case of fast (so-called reversible) electrode processes, however the study of the linear diffusion layer has received scant attention in the case of slow charge transfer processes, despite its study being of great interest in the analysis of the influence of different experimental variables which determine the electrochemical response. Analytical explicit solutions for the concentration profiles, surface concentrations and real and linear diffusion layers corresponding to the application of a potential step to a slow charge transfer process are presented. From these expressions the dependence of the diffusion layer thickness on the potential, pulse time, heterogeneous rate constant and ratio of bulk concentrations of electroactive species and of diffusion coefficients is quantified. A profound influence of the reversibility degree of the charge transfer on the diffusion layer thickness is clear, showing that for non-reversible processes the real and linear diffusion layers reveal a minimum thickness which coincides with the equilibrium potential of the redox couple in the former case and with the reversible half-wave potential in the latter one.

Lateral Diffusion in a DMPC:DMPE-EO Binary Monolayer at the Air/Water Interface

NASA Astrophysics Data System (ADS)

Adalsteinsson, Thorsteinn; Porter, Ryan; Yu, Hyuk

2002-03-01

Polyethylene glycol tethered phospholipids (lipo-polymers) have recently attracted attention for improving the stability of liposomes and other bilayer delivery systems. Here, we report a study of surface pressure measurement and diffusion measurements of a probe lipid (NBD-DMPC) in a binary monolayer of DMPC and DMPE-EO at the Air/Water interface. Our findings are that the DMPE-EO lipo-polymer desorbs from the interface at intermediate surface pressures if the EO tail is sufficiently large (i.e. EO_45) and does not interfere with the diffusion of the probe thereafter. In the case where the EO tail is short (i.e. EO_17) the lipo-polymer retards the diffusion of the probe, but as the surface pressure increases, the diffusion behavior approaches that of pure DMPC monolayer independent of lipo-polymer. Thus, we conclude that the surface pressure and EO molar mass dependent desorption of the lipo-polymer modulates the probe diffusion retardation.

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.

Experimental investigation on pressurization performance of cryogenic tank during high-temperature helium pressurization process

NASA Astrophysics Data System (ADS)

Lei, Wang; Yanzhong, Li; Yonghua, Jin; Yuan, Ma

2015-03-01

Sufficient knowledge of thermal performance and pressurization behaviors in cryogenic tanks during rocket launching period is of importance to the design and optimization of a pressurization system. In this paper, ground experiments with liquid oxygen (LO2) as the cryogenic propellant, high-temperature helium exceeding 600 K as the pressurant gas, and radial diffuser and anti-cone diffuser respectively at the tank inlet were performed. The pressurant gas requirements, axial and radial temperature distributions, and energy distributions inside the propellant tank were obtained and analyzed to evaluate the comprehensive performance of the pressurization system. It was found that the pressurization system with high-temperature helium as the pressurant gas could work well that the tank pressure was controlled within a specified range and a stable discharging liquid rate was achieved. For the radial diffuser case, the injected gas had a direct impact on the tank inner wall. The severe gas-wall heat transfer resulted in about 59% of the total input energy absorbed by the tank wall. For the pressurization case with anti-cone diffuser, the direct impact of high-temperature gas flowing toward the liquid surface resulted in a greater deal of energy transferred to the liquid propellant, and the percentage even reached up to 38%. Moreover, both of the two cases showed that the proportion of energy left in ullage to the total input energy was quite small, and the percentage was only about 22-24%. This may indicate that a more efficient diffuser should be developed to improve the pressurization effect. Generally, the present experimental results are beneficial to the design and optimization of the pressurization system with high-temperature gas supplying the pressurization effect.

Diffusion and Monod kinetics model to determine in vivo human corneal oxygen-consumption rate during soft contact lens wear

PubMed Central

Del Castillo, Luis F.; da Silva, Ana R. Ferreira; Hernández, Saul I.; Aguilella, M.; Andrio, Andreu; Mollá, Sergio; Compañ, Vicente

2014-01-01

Purpose We present an analysis of the corneal oxygen consumption Qc from non-linear models, using data of oxygen partial pressure or tension (pO2) obtained from in vivo estimation previously reported by other authors.1 Methods Assuming that the cornea is a single homogeneous layer, the oxygen permeability through the cornea will be the same regardless of the type of lens that is available on it. The obtention of the real value of the maximum oxygen consumption rate Qc,max is very important because this parameter is directly related with the gradient pressure profile into the cornea and moreover, the real corneal oxygen consumption is influenced by both anterior and posterior oxygen fluxes. Results Our calculations give different values for the maximum oxygen consumption rate Qc,max, when different oxygen pressure values (high and low pO2) are considered at the interface cornea-tears film. Conclusion Present results are relevant for the calculation on the partial pressure of oxygen, available at different depths into the corneal tissue behind contact lenses of different oxygen transmissibility. PMID:25649636

Conserved linear dynamics of single-molecule Brownian motion.

PubMed

Serag, Maged F; Habuchi, Satoshi

2017-06-06

Macromolecular diffusion in homogeneous fluid at length scales greater than the size of the molecule is regarded as a random process. The mean-squared displacement (MSD) of molecules in this regime increases linearly with time. Here we show that non-random motion of DNA molecules in this regime that is undetectable by the MSD analysis can be quantified by characterizing the molecular motion relative to a latticed frame of reference. Our lattice occupancy analysis reveals unexpected sub-modes of motion of DNA that deviate from expected random motion in the linear, diffusive regime. We demonstrate that a subtle interplay between these sub-modes causes the overall diffusive motion of DNA to appear to conform to the linear regime. Our results show that apparently random motion of macromolecules could be governed by non-random dynamics that are detectable only by their relative motion. Our analytical approach should advance broad understanding of diffusion processes of fundamental relevance.

Conserved linear dynamics of single-molecule Brownian motion

PubMed Central

Serag, Maged F.; Habuchi, Satoshi

2017-01-01

Macromolecular diffusion in homogeneous fluid at length scales greater than the size of the molecule is regarded as a random process. The mean-squared displacement (MSD) of molecules in this regime increases linearly with time. Here we show that non-random motion of DNA molecules in this regime that is undetectable by the MSD analysis can be quantified by characterizing the molecular motion relative to a latticed frame of reference. Our lattice occupancy analysis reveals unexpected sub-modes of motion of DNA that deviate from expected random motion in the linear, diffusive regime. We demonstrate that a subtle interplay between these sub-modes causes the overall diffusive motion of DNA to appear to conform to the linear regime. Our results show that apparently random motion of macromolecules could be governed by non-random dynamics that are detectable only by their relative motion. Our analytical approach should advance broad understanding of diffusion processes of fundamental relevance. PMID:28585925

Conserved linear dynamics of single-molecule Brownian motion

NASA Astrophysics Data System (ADS)

Serag, Maged F.; Habuchi, Satoshi

2017-06-01

Macromolecular diffusion in homogeneous fluid at length scales greater than the size of the molecule is regarded as a random process. The mean-squared displacement (MSD) of molecules in this regime increases linearly with time. Here we show that non-random motion of DNA molecules in this regime that is undetectable by the MSD analysis can be quantified by characterizing the molecular motion relative to a latticed frame of reference. Our lattice occupancy analysis reveals unexpected sub-modes of motion of DNA that deviate from expected random motion in the linear, diffusive regime. We demonstrate that a subtle interplay between these sub-modes causes the overall diffusive motion of DNA to appear to conform to the linear regime. Our results show that apparently random motion of macromolecules could be governed by non-random dynamics that are detectable only by their relative motion. Our analytical approach should advance broad understanding of diffusion processes of fundamental relevance.

Serpentine Diffuser Performance with Emphasis on Future Introduction to a Transonic Fan (Postprint)

DTIC Science & Technology

2013-01-01

conditioning barrel . The velocity distribution across the flow conditioning barrel was measured at the same axial location of inlet temperature and...rakes at the same axial plane (AIP) of the total pressure probe tips. The probes were constructed from stainless steel tubing with 0.027 inch inside...numbers with 195 axial and circumferential static pressure measurements within the diffuser flow path. Pressure distortion at the diffuser discharge

Diffusion in porous layers with memory

NASA Astrophysics Data System (ADS)

Caputo, Michele; Plastino, Wolfango

2004-07-01

The process of diffusion of fluid in porous media and biological membranes has usually been modelled with Darcy's constitutive equation, which states that the flux is proportional to the pressure gradient. However, when the permeability of the matrix changes during the process, solution of the equations governing the diffusion presents severe analytical difficulties because the variation of permeability is not known a priori. A diverse formulation of the constitutive law of diffusion is therefore needed and many authors have studied this problem using various methods and solutions. In this paper Darcy's constitutive equation is modified with the introduction of a memory formalism. We have also modified the second constitutive equation of diffusion which relates the density variations in the fluid to the pressure, introducing rheology in the fluid represented by memory formalisms operating on pressure variations as well as on density variations. The memory formalisms are then specified as derivatives of fractional order, solving the problem in the case of a porous layer when constant pressures are applied to its sides. For technical reasons many studies of diffusion are devoted to the flux rather than to the pressure; in this work we shall devote our attention to studying the pressure and compute the Green's function of the pressure in the layer when a constant pressure is applied to the boundary (Case A) for which we have found closed-form formulae. The described problem has already been considered for a half space (Caputo 2000); however, the results for a half space are mostly qualitative since in most practical problems the diffusion occurs in layers. The solution is also readily extended to the case when a periodic pressure is applied to one of the boundary planes while on the other the pressure is constant (Case B) which mimics the effect of the tides on sea coasts. In this case we have found a skin effect for the flux which limits the flux to a surface layer whose thickness decreases with increasing frequency. Regarding the effect of pressure due to tidal waters on the coast, it has been observed that when the medium is sand and the fluid is water, for a sinusoidal pressure of 2 × 104 Pa and a period of 24 hr at one of the boundaries and zero pressure at the other boundary, the flux is sinusoidal with the same period and amplitude decaying exponentially with distance to become negligible at a distance of a few hundred metres. A brief discussion is given concerning the mode of determination of the parameters of memory formalisms governing the diffusion using the observed pressure at several frequencies. We shall also see that, as in the classic case of pure Darcy's law behaviour, the equation governing the flux resulting in the diffusion through porous media with memory is the same as that governing the pressure.

Numerical investigation of rotating stall in centrifugal compressor with vaned and vaneless diffuser

NASA Astrophysics Data System (ADS)

Halawa, Taher; Alqaradawi, Mohamed; Gadala, Mohamed S.; Shahin, Ibrahim; Badr, Osama

2015-06-01

This study presents a numerical simulation of the stall and surge in a centrifugal compressor and presents a descriptionof the stall development in two different cases. The first case is for a compressor with vaneless diffuser and the second is for a compressor with vaned diffuser of the vane island shape. The main aim of this study is to compare the flow characteristics and behavior for the two compressors near the surge operating condition and provide further understanding of the diffuser role when back flow occurs at surge. Results showed that for a locationnear the diffuser entrance, the amplitude of the static pressure fluctuations for the vaneless diffuser case is higher than that for the vaned diffuser case near surge condition. These pressure fluctuations in the case of the vaneless diffuser appear with a gradual decrease of the mean pressure value as a part of the surge cycle. While for the case of the vaned diffuser, the pressure drop during surge occurs faster than the case of the vaneless diffuser. Also, results indicated that during surge in the case of vaneless diffuser, there is a region with low velocity and back flow that appears as a layer connecting all impeller passages near shroud surface and this layer develops in size with time. On the other hand, for the case of vaned diffuser during surge, the low velocity regions appear in random locations in some passages and these regions expand with time towards the shroud surface. Results showed that during stall, the impeller passages are exposed to identical impact from stall cells in the case of vaneless diffuser while the stall effect varies from passage to another in the case of the vaned diffuser.

Quantitative body DW-MRI biomarkers uncertainty estimation using unscented wild-bootstrap.

PubMed

Freiman, M; Voss, S D; Mulkern, R V; Perez-Rossello, J M; Warfield, S K

2011-01-01

We present a new method for the uncertainty estimation of diffusion parameters for quantitative body DW-MRI assessment. Diffusion parameters uncertainty estimation from DW-MRI is necessary for clinical applications that use these parameters to assess pathology. However, uncertainty estimation using traditional techniques requires repeated acquisitions, which is undesirable in routine clinical use. Model-based bootstrap techniques, for example, assume an underlying linear model for residuals rescaling and cannot be utilized directly for body diffusion parameters uncertainty estimation due to the non-linearity of the body diffusion model. To offset this limitation, our method uses the Unscented transform to compute the residuals rescaling parameters from the non-linear body diffusion model, and then applies the wild-bootstrap method to infer the body diffusion parameters uncertainty. Validation through phantom and human subject experiments shows that our method identify the regions with higher uncertainty in body DWI-MRI model parameters correctly with realtive error of -36% in the uncertainty values.

Diffusion phenomenon for linear dissipative wave equations in an exterior domain

NASA Astrophysics Data System (ADS)

Ikehata, Ryo

Under the general condition of the initial data, we will derive the crucial estimates which imply the diffusion phenomenon for the dissipative linear wave equations in an exterior domain. In order to derive the diffusion phenomenon for dissipative wave equations, the time integral method which was developed by Ikehata and Matsuyama (Sci. Math. Japon. 55 (2002) 33) plays an effective role.

A simulation model of the oxygen alveolo-capillary exchange in normal and pathological conditions.

PubMed

Brighenti, Chiara; Gnudi, Gianni; Avanzolini, Guido

2003-05-01

This paper presents a mathematical model of the oxygen alveolo-capillary exchange to provide the capillary oxygen partial pressure profile in normal and pathological conditions. In fact, a thickening of the blood-gas barrier, heavy exercise or a low oxygen partial pressure (PO2) in the alveolar space can reduce the O2 alveolo-capillary exchange. Since the reversible binding between haemoglobin and oxygen makes it impossible to determine the closed form for the mathematical description of the PO2 profile along the pulmonary capillaries, an approximate analytical solution of the capillary PO2 profile is proposed. Simulation results are compared with the capillary PO2 profile obtained by numerical integration and by a piecewise linear interpolation of the oxyhaemoglobin dissociation curve. Finally, the proposed model is evaluated in a large range of physiopathological diffusive conditions. The good fit to numerical solutions in all experimental conditions seems to represent a substantial improvement with respect to the approach based on a linear approximation of the oxyhaemoglobin dissociation curve, and makes this model a candidate to be incorporated into the integrated descriptions of the entire respiratory system, where the datum of primary interest is the value of end capillary PO2.

Fractional calculus phenomenology in two-dimensional plasma models

NASA Astrophysics Data System (ADS)

Gustafson, Kyle; Del Castillo Negrete, Diego; Dorland, Bill

2006-10-01

Transport processes in confined plasmas for fusion experiments, such as ITER, are not well-understood at the basic level of fully nonlinear, three-dimensional kinetic physics. Turbulent transport is invoked to describe the observed levels in tokamaks, which are orders of magnitude greater than the theoretical predictions. Recent results show the ability of a non-diffusive transport model to describe numerical observations of turbulent transport. For example, resistive MHD modeling of tracer particle transport in pressure-gradient driven turbulence for a three-dimensional plasma reveals that the superdiffusive (2̂˜t^α where α> 1) radial transport in this system is described quantitatively by a fractional diffusion equation Fractional calculus is a generalization involving integro-differential operators, which naturally describe non-local behaviors. Our previous work showed the quantitative agreement of special fractional diffusion equation solutions with numerical tracer particle flows in time-dependent linearized dynamics of the Hasegawa-Mima equation (for poloidal transport in a two-dimensional cold-ion plasma). In pursuit of a fractional diffusion model for transport in a gyrokinetic plasma, we now present numerical results from tracer particle transport in the nonlinear Hasegawa-Mima equation and a planar gyrokinetic model. Finite Larmor radius effects will be discussed. D. del Castillo Negrete, et al, Phys. Rev. Lett. 94, 065003 (2005).

A theoretical signal processing framework for linear diffusion MRI: Implications for parameter estimation and experiment design.

PubMed

Varadarajan, Divya; Haldar, Justin P

2017-11-01

The data measured in diffusion MRI can be modeled as the Fourier transform of the Ensemble Average Propagator (EAP), a probability distribution that summarizes the molecular diffusion behavior of the spins within each voxel. This Fourier relationship is potentially advantageous because of the extensive theory that has been developed to characterize the sampling requirements, accuracy, and stability of linear Fourier reconstruction methods. However, existing diffusion MRI data sampling and signal estimation methods have largely been developed and tuned without the benefit of such theory, instead relying on approximations, intuition, and extensive empirical evaluation. This paper aims to address this discrepancy by introducing a novel theoretical signal processing framework for diffusion MRI. The new framework can be used to characterize arbitrary linear diffusion estimation methods with arbitrary q-space sampling, and can be used to theoretically evaluate and compare the accuracy, resolution, and noise-resilience of different data acquisition and parameter estimation techniques. The framework is based on the EAP, and makes very limited modeling assumptions. As a result, the approach can even provide new insight into the behavior of model-based linear diffusion estimation methods in contexts where the modeling assumptions are inaccurate. The practical usefulness of the proposed framework is illustrated using both simulated and real diffusion MRI data in applications such as choosing between different parameter estimation methods and choosing between different q-space sampling schemes. Copyright © 2017 Elsevier Inc. All rights reserved.

Stem Hydraulic Conductivity depends on the Pressure at Which It Is Measured and How This Dependence Can Be Used to Assess the Tempo of Bubble Pressurization in Recently Cavitated Vessels1[OPEN

PubMed Central

Liu, Jinyu; Tyree, Melvin T.

2015-01-01

Cavitation of water in xylem vessels followed by embolism formation has been authenticated for more than 40 years. Embolism formation involves the gradual buildup of bubble pressure (air) to atmospheric pressure as demanded by Henry’s law of equilibrium between gaseous and liquid phases. However, the tempo of pressure increase has not been quantified. In this report, we show that the rate of pressurization of embolized vessels is controlled by both fast and slow kinetics, where both tempos are controlled by diffusion but over different spatial scales. The fast tempo involves a localized diffusion from endogenous sources: over a distance of about 0.05 mm from water-filled wood to the nearest embolized vessels; this process, in theory, should take <2 min. The slow tempo involves diffusion of air from exogenous sources (outside the stem). The latter diffusion process is slower because of the increased distance of diffusion of up to 4 mm. Radial diffusion models and experimental measurements both confirm that the average time constant is >17 h, with complete equilibrium requiring 1 to 2 d. The implications of these timescales for the standard methods of measuring percentage loss of hydraulic conductivity are discussed in theory and deserve more research in future. PMID:26468516

Stem Hydraulic Conductivity depends on the Pressure at Which It Is Measured and How This Dependence Can Be Used to Assess the Tempo of Bubble Pressurization in Recently Cavitated Vessels.

PubMed

Wang, Yujie; Liu, Jinyu; Tyree, Melvin T

2015-12-01

Cavitation of water in xylem vessels followed by embolism formation has been authenticated for more than 40 years. Embolism formation involves the gradual buildup of bubble pressure (air) to atmospheric pressure as demanded by Henry's law of equilibrium between gaseous and liquid phases. However, the tempo of pressure increase has not been quantified. In this report, we show that the rate of pressurization of embolized vessels is controlled by both fast and slow kinetics, where both tempos are controlled by diffusion but over different spatial scales. The fast tempo involves a localized diffusion from endogenous sources: over a distance of about 0.05 mm from water-filled wood to the nearest embolized vessels; this process, in theory, should take <2 min. The slow tempo involves diffusion of air from exogenous sources (outside the stem). The latter diffusion process is slower because of the increased distance of diffusion of up to 4 mm. Radial diffusion models and experimental measurements both confirm that the average time constant is >17 h, with complete equilibrium requiring 1 to 2 d. The implications of these timescales for the standard methods of measuring percentage loss of hydraulic conductivity are discussed in theory and deserve more research in future. © 2015 American Society of Plant Biologists. All Rights Reserved.

Observation and interpretation of energy efficient, diffuse direct current glow discharge at atmospheric pressure

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

Tang, Jie, E-mail: tangjie1979@opt.ac.cn; Jiang, Weiman; Wang, Yishan

2015-08-24

A diffuse direct-current glow discharge was realized with low energy consumption and high energy utilization efficiency at atmospheric pressure. The formation of diffuse discharge was demonstrated by examining and comparing the electrical properties and optical emissions of plasmas. In combination with theoretical derivation and calculation, we draw guidelines that appearance of nitrogen ions at low electron density is crucial to enhance the ambipolar diffusion for the expansion of discharge channel and the increasing ambipolar diffusion near the cathode plays a key role in the onset of diffuse discharge. An individual-discharge-channel expansion model is proposed to explain the diffuse discharge formation.

Three mechanisms model of shale gas in real state transport through a single nanopore

NASA Astrophysics Data System (ADS)

Li, Dongdong; Zhang, Yanyu; Sun, Xiaofei; Li, Peng; Zhao, Fengkai

2018-02-01

At present, the apparent permeability models of shale gas consider only the viscous flow and Knudsen diffusion of free gas, but do not take into account the influence of surface diffusion. Moreover, it is assumed that shale gas is in ideal state. In this paper, shale gas is assumed in real state, a new apparent permeability model for shale gas transport through a single nanopore is developed that captures many important migration mechanisms, such as viscous flow and Knudsen diffusion of free gas, surface diffusion of adsorbed gas. According to experimental data, the accuracy of apparent permeability model was verified. What’s more, the effects of pressure and pore radius on apparent permeability, and the effects on the permeability fraction of viscous flow, Knudsen diffusion and surface diffusion were analysed, separately. Finally, the results indicate that the error of the developed model in this paper was 3.02%, which is less than the existing models. Pressure and pore radius seriously affect the apparent permeability of shale gas. When the pore radius is small or pressure is low, the surface diffusion cannot be ignored. When the pressure and the pore radius is big, the viscous flow occupies the main position.

Nonequilibrium transition and pattern formation in a linear reaction-diffusion system with self-regulated kinetics

NASA Astrophysics Data System (ADS)

Paul, Shibashis; Ghosh, Shyamolina; Ray, Deb Shankar

2018-02-01

We consider a reaction-diffusion system with linear, stochastic activator-inhibitor kinetics where the time evolution of concentration of a species at any spatial location depends on the relative average concentration of its neighbors. This self-regulating nature of kinetics brings in spatial correlation between the activator and the inhibitor. An interplay of this correlation in kinetics and disparity of diffusivities of the two species leads to symmetry breaking non-equilibrium transition resulting in stationary pattern formation. The role of initial noise strength and the linear reaction terms has been analyzed for pattern selection.

The role of nanoparticle rigidity on the diffusion of linear polystyrene in a polymer nanocomposite

DOE PAGES

Miller, Brad; Imel, Adam E.; Holley, Wade; ...

2015-11-12

The impact of the inclusion of a nanoparticle in a polymer matrix on the dynamics of the polymer chains is an area of recent interest. In this article, we describe the role of nanoparticle rigidity or softness on the impact of the presence of that nanoparticle on the diffusive behavior of linear polymer chains. The neutron reflectivity results clearly show that the inclusion of 10 nm soft nanoparticles in a polymer matrix (R g ~ 20 nm) increases the diffusion coefficient of the linear polymer chain. Surprisingly, thermal analysis shows that these nanocomposites exhibit an increase in their glass transitionmore » temperature, which is incommensurate with an increase in free volume. Therefore, it appears that this effect is more complex than a simple plasticizing effect. Results from small-angle neutron scattering of the nanoparticles in solution show a structure that consists of a gel like core with a corona of free chain ends and loops. Furthermore, the increase in linear polymer diffusion may be related to an increase in constraint release mechanisms in the reptation of the polymer chain, in a similar manner to that which has been reported for the diffusion of linear polymer chains in the presence of star polymers.« less

The role of nanoparticle rigidity on the diffusion of linear polystyrene in a polymer nanocomposite

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

Miller, Brad; Imel, Adam E.; Holley, Wade

The impact of the inclusion of a nanoparticle in a polymer matrix on the dynamics of the polymer chains is an area of recent interest. In this article, we describe the role of nanoparticle rigidity or softness on the impact of the presence of that nanoparticle on the diffusive behavior of linear polymer chains. The neutron reflectivity results clearly show that the inclusion of 10 nm soft nanoparticles in a polymer matrix (R g ~ 20 nm) increases the diffusion coefficient of the linear polymer chain. Surprisingly, thermal analysis shows that these nanocomposites exhibit an increase in their glass transitionmore » temperature, which is incommensurate with an increase in free volume. Therefore, it appears that this effect is more complex than a simple plasticizing effect. Results from small-angle neutron scattering of the nanoparticles in solution show a structure that consists of a gel like core with a corona of free chain ends and loops. Furthermore, the increase in linear polymer diffusion may be related to an increase in constraint release mechanisms in the reptation of the polymer chain, in a similar manner to that which has been reported for the diffusion of linear polymer chains in the presence of star polymers.« less

Understanding Coupling of Global and Diffuse Solar Radiation with Climatic Variability

NASA Astrophysics Data System (ADS)

Hamdan, Lubna

Global solar radiation data is very important for wide variety of applications and scientific studies. However, this data is not readily available because of the cost of measuring equipment and the tedious maintenance and calibration requirements. Wide variety of models have been introduced by researchers to estimate and/or predict the global solar radiations and its components (direct and diffuse radiation) using other readily obtainable atmospheric parameters. The goal of this research is to understand the coupling of global and diffuse solar radiation with climatic variability, by investigating the relationships between these radiations and atmospheric parameters. For this purpose, we applied multilinear regression analysis on the data of National Solar Radiation Database 1991--2010 Update. The analysis showed that the main atmospheric parameters that affect the amount of global radiation received on earth's surface are cloud cover and relative humidity. Global radiation correlates negatively with both variables. Linear models are excellent approximations for the relationship between atmospheric parameters and global radiation. A linear model with the predictors total cloud cover, relative humidity, and extraterrestrial radiation is able to explain around 98% of the variability in global radiation. For diffuse radiation, the analysis showed that the main atmospheric parameters that affect the amount received on earth's surface are cloud cover and aerosol optical depth. Diffuse radiation correlates positively with both variables. Linear models are very good approximations for the relationship between atmospheric parameters and diffuse radiation. A linear model with the predictors total cloud cover, aerosol optical depth, and extraterrestrial radiation is able to explain around 91% of the variability in diffuse radiation. Prediction analysis showed that the linear models we fitted were able to predict diffuse radiation with efficiency of test adjusted R2 values equal to 0.93, using the data of total cloud cover, aerosol optical depth, relative humidity and extraterrestrial radiation. However, for prediction purposes, using nonlinear terms or nonlinear models might enhance the prediction of diffuse radiation.

Nanoparticle Motion in Entangled Melts of Linear and Nonconcatenated Ring Polymers

PubMed Central

2017-01-01

The motion of nanoparticles (NPs) in entangled melts of linear polymers and nonconcatenated ring polymers are compared by large-scale molecular dynamics simulations. The comparison provides a paradigm for the effects of polymer architecture on the dynamical coupling between NPs and polymers in nanocomposites. Strongly suppressed motion of NPs with diameter d larger than the entanglement spacing a is observed in a melt of linear polymers before the onset of Fickian NP diffusion. This strong suppression of NP motion occurs progressively as d exceeds a and is related to the hopping diffusion of NPs in the entanglement network. In contrast to the NP motion in linear polymers, the motion of NPs with d > a in ring polymers is not as strongly suppressed prior to Fickian diffusion. The diffusion coefficient D decreases with increasing d much slower in entangled rings than in entangled linear chains. NP motion in entangled nonconcatenated ring polymers is understood through a scaling analysis of the coupling between NP motion and the self-similar entangled dynamics of ring polymers. PMID:28392603

The latent fingerprint in mass transport of polycrystalline materials

NASA Astrophysics Data System (ADS)

Thirunavukarasu, Gopinath; Kundu, Sukumar; Chatterjee, Subrata

2016-02-01

Herein, a systematic investigation was carried out to reach a rational understanding and to provide information concerning the possible causes for a significant influence of pressure variation in the underlying processes of mass transport in polycrystalline materials. The authors focused their research in solid-state diffusion, a part of the subject "Mass Transport in Solids". Theories on diffusion are the subject by itself which exists as a latent fingerprint in every text of higher learning in interdisciplinary science. In this research, authors prepared sandwich samples of titanium alloy and stainless steel using nickel as an intermediate metal. The samples were processed at three different levels of bonding pressure (3, 4 and 5 MPa) while bonding temperature and bonding time was maintained at 750 °C and 1 h, respectively, throughout the experiments. It was observed that the net flux of atomic diffusion of nickel atoms into Ti-alloy at TiA/Ni interface increased by ~63 % with the rise in the bonding pressure from 3 to 4 MPa, but decreased by ~40 % with the rise in the bonding pressure from 4 to 5 MPa. At the same time, the net flux of atomic diffusion of nickel atoms into stainless steel at Ni/SS interface increased by ~19 % with the rise in the bonding pressure from 3 to 4 MPa, but increased by ~17 % with the rise in the bonding pressure from 4 to 5 MPa. Here authors showed that the pressure variations have different effects at the TiA/Ni interface and Ni/SS interface, and tried to explain the explicit mechanisms operating behind them. In general for sandwich samples processed irrespective of bonding pressure chosen, the net flux of Ni-atoms diffused into SS is greater than that of the net flux of Ni-atoms diffused in Ti-alloy matrix by four orders of magnitude. The calculated diffusivity of Ni-atoms into Ti-alloy reaches its highest value of ~5.083 × 10-19 m2/s for the sandwich sample processed using 4-MPa bonding-pressure, whereas the diffusivity of Ni-atoms into SS reaches its peak value of ~1.615 × 10-14 m2/s for the sample bonded using 5-MPa bonding-pressure.

Numerical Study of Pressure Influence on Methane-Oxygen Laminar Counterflow Diffusion Flames

NASA Astrophysics Data System (ADS)

Iino, Kimio; Akamatsu, Fumiteru; Katsuki, Masashi

We carried out numerical studies on methane/oxygen diffusion flames of counter-flow configuration to elucidate the influence of pressure on flame structure, heat release rate and reaction mechanisms. The chemistry in gas-phase was based on GRI-Mech 3.0 database. The thickness of diffusion flame became thinner with increasing strain rate a , with its characteristic flame thickness varying inversely with √a, especially its relation became significant with increasing pressure. Flame temperature increased with increasing pressure. Enhanced H2O production reactions, especially chain terminal reactions for H2O production, were found to be important in determining the flame temperature at high pressures. The small reduction in the flame temperature with increasing strain rate at high pressures, compared to the atmospheric pressure, is caused by the capacitor effect of product dissociation. From QRPDs, the third body dependent reactions were enhanced in high pressure conditions, hence C2 pathway was enhanced.

Experimental and computational data from a small rocket exhaust diffuser

NASA Astrophysics Data System (ADS)

Stephens, Samuel E.

1993-06-01

The Diagnostics Testbed Facility (DTF) at the NASA Stennis Space Center in Mississippi is a versatile facility that is used primarily to aid in the development of nonintrusive diagnostics for liquid rocket engine testing. The DTF consists of a fixed, 1200 lbf thrust, pressure fed, liquid oxygen/gaseous hydrogen rocket engine, and associated support systems. An exhaust diffuser has been fabricated and installed to provide subatmospheric pressures at the exit of the engine. The diffuser aerodynamic design was calculated prior to fabrication using the PARC Navier-Stokes computational fluid dynamics code. The diffuser was then fabricated and tested at the DTF. Experimental data from these tests were acquired to determine the operational characteristics of the system and to correlate the actual and predicted flow fields. The results show that a good engineering approximation of overall diffuser performance can be made using the PARC Navier-Stokes code and a simplified geometry. Correlations between actual and predicted cell pressure and initial plume expansion in the diffuser are good; however, the wall pressure profiles do not correlate as well with the experimental data.

Network diffusion accurately models the relationship between structural and functional brain connectivity networks

PubMed Central

Abdelnour, Farras; Voss, Henning U.; Raj, Ashish

2014-01-01

The relationship between anatomic connectivity of large-scale brain networks and their functional connectivity is of immense importance and an area of active research. Previous attempts have required complex simulations which model the dynamics of each cortical region, and explore the coupling between regions as derived by anatomic connections. While much insight is gained from these non-linear simulations, they can be computationally taxing tools for predicting functional from anatomic connectivities. Little attention has been paid to linear models. Here we show that a properly designed linear model appears to be superior to previous non-linear approaches in capturing the brain’s long-range second order correlation structure that governs the relationship between anatomic and functional connectivities. We derive a linear network of brain dynamics based on graph diffusion, whereby the diffusing quantity undergoes a random walk on a graph. We test our model using subjects who underwent diffusion MRI and resting state fMRI. The network diffusion model applied to the structural networks largely predicts the correlation structures derived from their fMRI data, to a greater extent than other approaches. The utility of the proposed approach is that it can routinely be used to infer functional correlation from anatomic connectivity. And since it is linear, anatomic connectivity can also be inferred from functional data. The success of our model confirms the linearity of ensemble average signals in the brain, and implies that their long-range correlation structure may percolate within the brain via purely mechanistic processes enacted on its structural connectivity pathways. PMID:24384152

Solution of the nonlinear Poisson-Boltzmann equation: Application to ionic diffusion in cementitious materials

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

Arnold, J.; Kosson, D.S., E-mail: david.s.kosson@vanderbilt.edu; Garrabrants, A.

2013-02-15

A robust numerical solution of the nonlinear Poisson-Boltzmann equation for asymmetric polyelectrolyte solutions in discrete pore geometries is presented. Comparisons to the linearized approximation of the Poisson-Boltzmann equation reveal that the assumptions leading to linearization may not be appropriate for the electrochemical regime in many cementitious materials. Implications of the electric double layer on both partitioning of species and on diffusive release are discussed. The influence of the electric double layer on anion diffusion relative to cation diffusion is examined.

Experimental investigation on flow in diffuser of 1090 MW steam turbine

NASA Astrophysics Data System (ADS)

Hoznedl, Michal; Sedlák, Kamil; Mrózek, Lukáš; Bednář, Lukáš; Kalista, Robert

2016-06-01

The paper deals with flow of wet water steam in diffuser of turbine engine 1090 MW on saturated water steam. Experimental measurements were done while the turbine was in operation for a wide range of outputs. Defining the outlet velocity from the last stage and with knowledge of static pressures on the diffuser outlet, it is possible to define the contribution of the diffuser to the whole low pressure part efficiency.

Dynamic physiological modeling for functional diffuse optical tomography

PubMed Central

Diamond, Solomon Gilbert; Huppert, Theodore J.; Kolehmainen, Ville; Franceschini, Maria Angela; Kaipio, Jari P.; Arridge, Simon R.; Boas, David A.

2009-01-01

Diffuse optical tomography (DOT) is a noninvasive imaging technology that is sensitive to local concentration changes in oxy- and deoxyhemoglobin. When applied to functional neuroimaging, DOT measures hemodynamics in the scalp and brain that reflect competing metabolic demands and cardiovascular dynamics. The diffuse nature of near-infrared photon migration in tissue and the multitude of physiological systems that affect hemodynamics motivate the use of anatomical and physiological models to improve estimates of the functional hemodynamic response. In this paper, we present a linear state-space model for DOT analysis that models the physiological fluctuations present in the data with either static or dynamic estimation. We demonstrate the approach by using auxiliary measurements of blood pressure variability and heart rate variability as inputs to model the background physiology in DOT data. We evaluate the improvements accorded by modeling this physiology on ten human subjects with simulated functional hemodynamic responses added to the baseline physiology. Adding physiological modeling with a static estimator significantly improved estimates of the simulated functional response, and further significant improvements were achieved with a dynamic Kalman filter estimator (paired t tests, n = 10, P < 0.05). These results suggest that physiological modeling can improve DOT analysis. The further improvement with the Kalman filter encourages continued research into dynamic linear modeling of the physiology present in DOT. Cardiovascular dynamics also affect the blood-oxygen-dependent (BOLD) signal in functional magnetic resonance imaging (fMRI). This state-space approach to DOT analysis could be extended to BOLD fMRI analysis, multimodal studies and real-time analysis. PMID:16242967

Probe pressure effects on human skin diffuse reflectance and fluorescence spectroscopy measurements

PubMed Central

Lim, Liang; Nichols, Brandon; Rajaram, Narasimhan; Tunnell, James W.

2011-01-01

Diffuse reflectance and fluorescence spectroscopy are popular research techniques for noninvasive disease diagnostics. Most systems include an optical fiber probe that transmits and collects optical spectra in contact with the suspected lesion. The purpose of this study is to investigate probe pressure effects on human skin spectroscopic measurements. We conduct an in-vivo experiment on human skin tissue to study the short-term (<2 s) and long-term (>30 s) effects of probe pressure on diffuse reflectance and fluorescence measurements. Short-term light probe pressure (P0 < 9 mN∕mm2) effects are within 0 ± 10% on all physiological properties extracted from diffuse reflectance and fluorescence measurements, and less than 0 ± 5% for diagnostically significant physiological properties. Absorption decreases with site-specific variations due to blood being compressed out of the sampled volume. Reduced scattering coefficient variation is site specific. Intrinsic fluorescence shows a large standard error, although no specific pressure-related trend is observed. Differences in tissue structure and morphology contribute to site-specific probe pressure effects. Therefore, the effects of pressure can be minimized when the pressure is small and applied for a short amount of time; however, long-term and large pressures induce significant distortions in measured spectra. PMID:21280899

Multigrid approaches to non-linear diffusion problems on unstructured meshes

NASA Technical Reports Server (NTRS)

Mavriplis, Dimitri J.; Bushnell, Dennis M. (Technical Monitor)

2001-01-01

The efficiency of three multigrid methods for solving highly non-linear diffusion problems on two-dimensional unstructured meshes is examined. The three multigrid methods differ mainly in the manner in which the nonlinearities of the governing equations are handled. These comprise a non-linear full approximation storage (FAS) multigrid method which is used to solve the non-linear equations directly, a linear multigrid method which is used to solve the linear system arising from a Newton linearization of the non-linear system, and a hybrid scheme which is based on a non-linear FAS multigrid scheme, but employs a linear solver on each level as a smoother. Results indicate that all methods are equally effective at converging the non-linear residual in a given number of grid sweeps, but that the linear solver is more efficient in cpu time due to the lower cost of linear versus non-linear grid sweeps.

The X-ray-emitting trail of the nearby pulsar PSR1929 + 10

NASA Technical Reports Server (NTRS)

Wang, Q. D.; Li, Zhi-Yun; Begelman, Mitchell C.

1993-01-01

The paper reports the detection by the Rosat satellite of a nebula associated with the nearby pulsar PSR1929 + 10, which is of a type different from the pulsar-wind nebulae produced by direct interaction of the relativistic wind from older pulsars with the interstellar medium (ISM) (Blandorf et al., 1973). The PSR1929 + 10 nebula appears as a linear diffuse X-ray feature in the direction opposite to the pulsar's proper motion, with the pulsar wind confined by the ram-pressure arising from the high velocity of the pulsar through the ISM. This results in a trail of relativistic electrons with enhanced emissions of synchrotron radiation.

Cold air performance of a tip turbine designed to drive a lift fan. 2: Partial admission

NASA Technical Reports Server (NTRS)

Haas, J. E.; Kofskey, M. G.; Hotz, G. M.; Futral, S. M., Jr.

1977-01-01

Partial admission performance was obtained for a 0.4 linear scale version of the LF460 lift fan turbine over a range of speed from 40 to 140 percent of design equivalent speed and a range of scroll inlet total to diffuser exit static pressure ratio from 2.2 to 5.0. The investigation was conducted in two parts, with each part using a different side of the turbine scroll to simulate loss of a gas generator. Each side had an arc of admission of 180. Results are presented in terms of specific work, torque, mass flow, and efficiency.

Cold-air performance of a tip turbine designed to drive a lift fan. 3: Effect of simulated fan leakage on turbine performance

NASA Technical Reports Server (NTRS)

Haas, J. E.; Kofskey, M. G.; Hotz, G. M.; Futral, S. M., Jr.

1978-01-01

Performance data were obtained experimentally for a 0.4 linear scale version of the LF460 lift fan turbine for a range of scroll inlet total to diffuser exit static pressure ratios at design equivalent speed with simulated fan leakage air. Tests were conducted for full and partial admission operation with three separate combinations of rotor inlet and rotor exit leakage air. Data were compared to the results obtained from previous investigations in which no leakage air was present. Results are presented in terms of mass flow, torque, and efficiency.

A Micromechanics-Based Elastoplastic Damage Model for Rocks with a Brittle-Ductile Transition in Mechanical Response

NASA Astrophysics Data System (ADS)

Hu, Kun; Zhu, Qi-zhi; Chen, Liang; Shao, Jian-fu; Liu, Jian

2018-06-01

As confining pressure increases, crystalline rocks of moderate porosity usually undergo a transition in failure mode from localized brittle fracture to diffused damage and ductile failure. This transition has been widely reported experimentally for several decades; however, satisfactory modeling is still lacking. The present paper aims at modeling the brittle-ductile transition process of rocks under conventional triaxial compression. Based on quantitative analyses of experimental results, it is found that there is a quite satisfactory linearity between the axial inelastic strain at failure and the confining pressure prescribed. A micromechanics-based frictional damage model is then formulated using an associated plastic flow rule and a strain energy release rate-based damage criterion. The analytical solution to the strong plasticity-damage coupling problem is provided and applied to simulate the nonlinear mechanical behaviors of Tennessee marble, Indiana limestone and Jinping marble, each presenting a brittle-ductile transition in stress-strain curves.

Physicochemical properties of macrogol ointment and emulsion ointment blend developed for regulation of water absorption.

PubMed

Noda, Yasuhiro; Watanabe, Kazuya; Sanagawa, Akimasa; Sobajima, Yu; Fujii, Satoshi

2011-10-31

Pressure ulcers can form with excess pressure and shearing stress on skin tissue. Because pressure ulcer is often accompanies by exudates, selection of appropriate topical emulsion ointment is difficult. Blended ointments consisting of emulsion base and water-soluble base are clinically used for adjustment of wound moist environment. Because regulating the amount of wound exudates can enhance treatment efficacy, two new blended ointments were developed. LY-SL blended ointment consisted of lysozyme hydrochloride water-in-oil (w/o) emulsion (LY-cream) and sulfadiazine macrogol (polyethylene glycol) ointment (SL-pasta). TR-SL blended ointment consisted of tretinoin tocoferil oil-in-water (o/w) emulsion (TR-cream) and SL-pasta (TR-SL). LY-SL and TR-SL were applied to Franz diffusion cell with cellulose membranes for the evaluation of water absorption characteristics at 32 °C. Water absorption rate constants (mg/cm(2)/min(0.5)) were 12.5, 16.3 and 34.6 for LY-cream, TR-cream and SL-pasta, respectively. Water absorption rate constants for LY-SL and TR-SL (SL-pasta 70%) exhibited intermediate values of 21.2 and 27.2, as compared to each ointment alone, respectively. Because amount of water absorbed was linearly related to square root of time, it was suggested that water-absorbable macrogol was surrounded by oily ingredients forming matrix structure. This diffusion-limited structure may regulate water absorption capacity. This is the first report of physicochemical properties of macrogol ointment and emulsion ointment blend developed for regulation of water absorption. The blended ointment can properly regulate amount of exudates in wounds and may be useful for treatment of pressure ulcers. Copyright © 2011 Elsevier B.V. All rights reserved.

The Turbulent Flow in Diffusers of Small Divergence Angle

NASA Technical Reports Server (NTRS)

Gourzhienko, G. A.

1947-01-01

The turbulent flow in a conical diffuser represents the type of turbulent boundary layer with positive longitudinal pressure gradient. In contrast to the boundary layer problem, however, it is not necessary that the pressure distribution along the limits of the boundary layer(along the axis of the diffuser) be given, since this distribution can be obtained from the computation. This circumstance, together with the greater simplicity of the problem as a whole, provides a useful basis for the study of the extension of the results of semiempirical theories to the case of motion with a positive pressure gradient. In the first part of the paper,formulas are derived for the computation of the velocity and.pressure distributions in the turbulent flow along, and at right angles to, the axis of a diffuser of small cone angle. The problem is solved.

A computationally efficient scheme for the non-linear diffusion equation

NASA Astrophysics Data System (ADS)

Termonia, P.; Van de Vyver, H.

2009-04-01

This Letter proposes a new numerical scheme for integrating the non-linear diffusion equation. It is shown that it is linearly stable. Some tests are presented comparing this scheme to a popular decentered version of the linearized Crank-Nicholson scheme, showing that, although this scheme is slightly less accurate in treating the highly resolved waves, (i) the new scheme better treats highly non-linear systems, (ii) better handles the short waves, (iii) for a given test bed turns out to be three to four times more computationally cheap, and (iv) is easier in implementation.

On solutions of the fifth-order dispersive equations with porous medium type non-linearity

NASA Astrophysics Data System (ADS)

Kocak, Huseyin; Pinar, Zehra

2018-07-01

In this work, we focus on obtaining the exact solutions of the fifth-order semi-linear and non-linear dispersive partial differential equations, which have the second-order diffusion-like (porous-type) non-linearity. The proposed equations were not studied in the literature in the sense of the exact solutions. We reveal solutions of the proposed equations using the classical Riccati equations method. The obtained exact solutions, which can play a key role to simulate non-linear waves in the medium with dispersion and diffusion, are illustrated and discussed in details.

Linear diffusion model dating of cinder cones in Central Anatolia, Turkey

NASA Astrophysics Data System (ADS)

O'Sadnick, L. G.; Reid, M. R.; Cline, M. L.; Cosca, M. A.; Kuscu, G.

2013-12-01

The progressive decrease in slope angle, cone height and cone height/width ratio over time provides the basis for geomorphic dating of cinder cones using linear diffusion models. Previous research using diffusion models to date cinder cones has focused on the cone height/width ratio as the basis for dating cones of unknown age [1,2]. Here we apply linear diffusion models to dating cinder cones. A suite of 16 cinder cones from the Hasandağ volcano area of the Neogene-Quaternary Central Anatolian Volcanic Zone, for which samples are available, were selected for morphologic dating analysis. New 40Ar/39Ar dates for five of these cones range from 62 × 4 to 517 × 9 ka. Linear diffusion models were used to model the erosional degradation of each cone. Diffusion coefficients (κ) for the 5 cinder cones with known ages were constrained by comparing various modeled slope profiles to the current slope profile. The resulting κ is 7.5×0.5 m2kyr-1. Using this κ value, eruption ages were modeled for the remaining 11 cinder cones and range from 53×3 to 455×30 ka. These ages are within the range of ages previously reported for cinder cones in the Hasandağ region. The linear diffusion model-derived ages are being compared to additional new 40Ar/39Ar dates in order to further assess the applicability of morphological dating to constrain the ages of cinder cones. The relatively well-constrained κ value we obtained by applying the linear diffusion model to cinder cones that range in age by nearly 500 ka suggests that this model can be used to date cinder cones. This κ value is higher than the well-established value of κ =3.9 for a cinder cone in a similar climate [3]. Therefore our work confirms the importance of determining appropriate κ values from nearby cones with known ages. References 1. C.A. Wood, J. Volcanol. Geotherm. Res. 8, 137 (1980) 2. D.M. Wood, M.F. Sheridan, J. Volcanol. Geotherm. Res. 83, 241 (1998) 3. J.D. Pelletier, M.L. Cline, Geology 35, 1067 (2007)

Thermal and ultrasonic evaluation of porosity in composite laminates

NASA Technical Reports Server (NTRS)

Johnston, Patrick H.; Winfree, William P.; Long, Edward R., Jr.; Kullerd, Susan M.; Nathan, N.; Partos, Richard D.

1992-01-01

The effects of porosity on damage incurred by low-velocity impact are investigated. Specimens of graphite/epoxy composite were fabricated with various volume fractions of voids. The void fraction was independently determined using optical examination and acid resin digestion methods. Thermal diffusivity and ultrasonic attenuation were measured, and these results were related to the void volume fraction. The relationship between diffusivity and fiber volume fraction was also considered. The slope of the ultrasonic attenuation coefficient was found to increase linearly with void content, and the diffusivity decreased linearly with void volume fraction, after compensation for an approximately linear dependence on the fiber volume fraction.

Reduced xenon diffusion for quantitative lung study--the role of SF(6)

NASA Technical Reports Server (NTRS)

Mair, R. W.; Hoffmann, D.; Sheth, S. A.; Wong, G. P.; Butler, J. P.; Patz, S.; Topulos, G. P.; Walsworth, R. L.

2000-01-01

The large diffusion coefficients of gases result in significant spin motion during the application of gradient pulses that typically last a few milliseconds in most NMR experiments. In restricted environments, such as the lung, this rapid gas diffusion can lead to violations of the narrow pulse approximation, a basic assumption of the standard Stejskal-Tanner NMR method of diffusion measurement. We therefore investigated the effect of a common, biologically inert buffer gas, sulfur hexafluoride (SF(6)), on (129)Xe NMR and diffusion. We found that the contribution of SF(6) to (129)Xe T(1) relaxation in a 1:1 xenon/oxygen mixture is negligible up to 2 bar of SF(6) at standard temperature. We also measured the contribution of SF(6) gas to (129)Xe T(2) relaxation, and found it to scale inversely with pressure, with this contribution approximately equal to 1 s for 1 bar SF(6) pressure and standard temperature. Finally, we found the coefficient of (129)Xe diffusion through SF(6) to be approximately 4.6 x 10(-6) m(2)s(-1) for 1 bar pressure of SF(6) and standard temperature, which is only 1.2 times smaller than the (129)Xe self diffusion coefficient for 1 bar (129)Xe pressure and standard temperature. From these measurements we conclude that SF(6) will not sufficiently reduce (129)Xe diffusion to allow accurate surface-area/volume ratio measurements in human alveoli using time-dependent gas diffusion NMR.

Pressure recovery performance of conical diffusers at high subsonic Mach numbers

NASA Technical Reports Server (NTRS)

Dolan, F. X.; Runstadler, P. W., Jr.

1973-01-01

The pressure recovery performance of conical diffusers has been measured for a wide range of geometries and inlet flow conditions. The approximate level and location (in terms of diffuser geometry of optimum performance were determined. Throat Mach numbers from low subsonic (m sub t equals 0.2) through choking (m sub t equals 1.0) were investigated in combination with throat blockage from 0.03 to 0.12. For fixed Mach number, performance was measured over a fourfold range of inlet Reynolds number. Maps of pressure recovery are presented as a function of diffuser geometry for fixed sets of inlet conditions. The influence of inlet blockage, throat Mach number, and inlet Reynolds number is discussed.

Do TFSA anions slither? Pressure exposes the role of TFSA conformational exchange in self-diffusion

DOE PAGES

Suarez, Sophia N.; Wishart, James F.; Rua, Armando; ...

2015-10-28

Multi-nuclear ( 1H, 2H, and 19F) magnetic resonance spectroscopy techniques as functions of temperature and pressure were applied to the study of selectively deuterated 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (EMIM TFSA) ionic liquid isotopologues and related ionic liquids. For EMIM TFSA, temperature-dependent 2H T 1 data indicate stronger electric field gradients in the alkyl chain region compared to the imidazolium ring. Most significantly, the pressure dependences of the EMIM and TFSA self-diffusion coefficients revealed that the displacements of the cations and anions are independent, with diffusion of the TFSA anions being slowed much more by increasing pressure than for the EMIM cations, asmore » shown by their respective activation volumes (28.8 ± 2.5 cm³/mol for TFSA vs. 14.6 ± 1.3 cm³/mol for EMIM). Increasing pressure may lower the mobility of the TFSA anion by hindering its interconversion between trans and cis conformers, a process that is coupled to diffusion according to published molecular dynamics simulations. Measured activation volumes (ΔV ‡) for ion self-diffusion in EMIM bis(fluoromethylsulfonyl)amide and EMIM tetrafluoroborate support this hypothesis.« less

Do TFSA anions slither? Pressure exposes the role of TFSA conformational exchange in self-diffusion

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

Suarez, Sophia N.; Wishart, James F.; Rua, Armando

Multi-nuclear ( 1H, 2H, and 19F) magnetic resonance spectroscopy techniques as functions of temperature and pressure were applied to the study of selectively deuterated 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (EMIM TFSA) ionic liquid isotopologues and related ionic liquids. For EMIM TFSA, temperature-dependent 2H T 1 data indicate stronger electric field gradients in the alkyl chain region compared to the imidazolium ring. Most significantly, the pressure dependences of the EMIM and TFSA self-diffusion coefficients revealed that the displacements of the cations and anions are independent, with diffusion of the TFSA anions being slowed much more by increasing pressure than for the EMIM cations, asmore » shown by their respective activation volumes (28.8 ± 2.5 cm³/mol for TFSA vs. 14.6 ± 1.3 cm³/mol for EMIM). Increasing pressure may lower the mobility of the TFSA anion by hindering its interconversion between trans and cis conformers, a process that is coupled to diffusion according to published molecular dynamics simulations. Measured activation volumes (ΔV ‡) for ion self-diffusion in EMIM bis(fluoromethylsulfonyl)amide and EMIM tetrafluoroborate support this hypothesis.« less

Translational and Rotational Diffusion in Water in the Gigapascal Range

NASA Astrophysics Data System (ADS)

Bove, L. E.; Klotz, S.; Strässle, Th.; Koza, M.; Teixeira, J.; Saitta, A. M.

2013-11-01

First measurements of the self-dynamics of liquid water in the GPa range are reported. The GPa range has here become accessible through a new setup for the Paris-Edinburgh press specially conceived for quasielastic neutron scattering studies. A direct measurement of both the translational and rotational diffusion coefficients of water along the 400 K isotherm up to 3 GPa, corresponding to the melting point of ice VII, is provided and compared with molecular dynamics simulations. The translational diffusion is observed to strongly decrease with pressure, though its variation slows down for pressures higher than 1 GPa and decouples from that of the shear viscosity. The rotational diffusion turns out to be insensitive to pressure. Through comparison with structural data and molecular dynamics simulations, we show that this is a consequence of the rigidity of the first neighbors shell and of the invariance of the number of hydrogen bonds of a water molecule under high pressure. These results show the inadequacy of the Stokes-Einstein-Debye equations to predict the self-diffusive behavior of water at high temperature and high pressure, and challenge the usual description of hot dense water behaving as a simple liquid.

Effect of Structure on Transport Properties (Viscosity, Ionic Conductivity, and Self-Diffusion Coefficient) of Aprotic Heterocyclic Anion (AHA) Room-Temperature Ionic Liquids. 1. Variation of Anionic Species.

PubMed

Sun, Liyuan; Morales-Collazo, Oscar; Xia, Han; Brennecke, Joan F

2015-12-03

A series of room temperature ionic liquids (RTILs) based on 1-ethyl-3-methylimidazolium ([emim](+)) with different aprotic heterocyclic anions (AHAs) were synthesized and characterized as potential electrolyte candidates for lithium ion batteries. The density and transport properties of these ILs were measured over the temperature range between 283.15 and 343.15 K at ambient pressure. The temperature dependence of the transport properties (viscosity, ionic conductivity, self-diffusion coefficient, and molar conductivity) is fit well by the Vogel-Fulcher-Tamman (VFT) equation. The best-fit VFT parameters, as well as linear fits to the density, are reported. The ionicity of these ILs was quantified by the ratio of the molar conductivity obtained from the ionic conductivity and molar concentration to that calculated from the self-diffusion coefficients using the Nernst-Einstein equation. The results of this study, which is based on ILs composed of both a planar cation and planar anions, show that many of the [emim][AHA] ILs exhibit very good conductivity for their viscosities and provide insight into the design of ILs with enhanced dynamics that may be suitable for electrolyte applications.

The Pawnee Sequence: Poroelastic Effects from Injection in Osage County, Oklahoma

NASA Astrophysics Data System (ADS)

Barbour, A. J.; Rubinstein, J. L.

2016-12-01

Aggregate multi-year records of wastewater injection in Oklahoma show that the strongest change in injection within 20 km of the 2016 M5.8 Pawnee strike-slip earthquake was in Osage County, where injection rates increased rapidly in late-2012 by nearly a factor of three above previous levels. After this increase, rates there declined steadily over two years to an average rate characteristic of all other injection wells in Pawnee and Noble Counties, remaining relatively constant until the beginning of the earthquake sequence. Here we test if poroelastic effects associated with this injection-rate transient can help explain the relative timing between peak injection rates and the beginning of the Pawnee sequence. Although the alternative hypothesis that regional-scale faults and fractures in critically stressed rock serve as fast-pathways for fluid diffusion cannot be ruled out, it appears to be difficult to reconcile based solely on injection data and space-time patterns for this seismic sequence. We simulate the cylindrically symmetric, transient strain and pore pressure fields for an injection-source time function emulating the injection history in a layered half-space in accordance with linear poroelasticity. In the simulation domain, injection occurs at depths of 1300 - 1900 m, into a homogeneous basal sedimentary reservoir representing the Arbuckle Group, overlying a semi-infinite layer representing granitic basement; we determined the hydraulic, elastic, and poroelastic properties of these layers from published literature. At the mainshock hypocenter, this numerical model predicts a delay between peak injection rates and pore pressure increase that is strongly dependent on hydraulic diffusivity; however, the duration is also controlled by the bulk elastic properties and the undrained Skempton's coefficient of the rock. Furthermore, because of fluid-strain coupling, pore pressures in the basement rock decrease during this delay period, which would tend to stabilize temporarily a critically stressed fault. Even though pore pressure diffusion is the dominant mechanism at play, poroelastic effects do affect the relative timing assuming a reasonable set of material parameters, even though strain rates in the basement are relatively low compared to rates in the Arbuckle layer (and above).

The three-zone composite productivity model for a multi-fractured horizontal shale gas well

NASA Astrophysics Data System (ADS)

Qi, Qian; Zhu, Weiyao

2018-02-01

Due to the nano-micro pore structures and the massive multi-stage multi-cluster hydraulic fracturing in shale gas reservoirs, the multi-scale seepage flows are much more complicated than in most other conventional reservoirs, and are crucial for the economic development of shale gas. In this study, a new multi-scale non-linear flow model was established and simplified, based on different diffusion and slip correction coefficients. Due to the fact that different flow laws existed between the fracture network and matrix zone, a three-zone composite model was proposed. Then, according to the conformal transformation combined with the law of equivalent percolation resistance, the productivity equation of a horizontal fractured well, with consideration given to diffusion, slip, desorption, and absorption, was built. Also, an analytic solution was derived, and the interference of the multi-cluster fractures was analyzed. The results indicated that the diffusion of the shale gas was mainly in the transition and Fick diffusion regions. The matrix permeability was found to be influenced by slippage and diffusion, which was determined by the pore pressure and diameter according to the Knudsen number. It was determined that, with the increased half-lengths of the fracture clusters, flow conductivity of the fractures, and permeability of the fracture network, the productivity of the fractured well also increased. Meanwhile, with the increased number of fractures, the distance between the fractures decreased, and the productivity slowly increased due to the mutual interfere of the fractures.

Stochastic field-line wandering in magnetic turbulence with shear. I. Quasi-linear theory

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

Shalchi, A.; Negrea, M.; Petrisor, I.

2016-07-15

We investigate the random walk of magnetic field lines in magnetic turbulence with shear. In the first part of the series, we develop a quasi-linear theory in order to compute the diffusion coefficient of magnetic field lines. We derive general formulas for the diffusion coefficients in the different directions of space. We like to emphasize that we expect that quasi-linear theory is only valid if the so-called Kubo number is small. We consider two turbulence models as examples, namely, a noisy slab model as well as a Gaussian decorrelation model. For both models we compute the field line diffusion coefficientsmore » and we show how they depend on the aforementioned Kubo number as well as a shear parameter. It is demonstrated that the shear effect reduces all field line diffusion coefficients.« less

Reaction-diffusion systems coupled at the boundary and the Morse-Smale property

NASA Astrophysics Data System (ADS)

Broche, Rita de Cássia D. S.; de Oliveira, Luiz Augusto F.

We study an one-dimensional nonlinear reaction-diffusion system coupled on the boundary. Such system comes from modeling problems of temperature distribution on two bars of same length, jointed together, with different diffusion coefficients. We prove the transversality property of unstable and stable manifolds assuming all equilibrium points are hyperbolic. To this end, we write the system as an equation with noncontinuous diffusion coefficient. We then study the nonincreasing property of the number of zeros of a linearized nonautonomous equation as well as the Sturm-Liouville properties of the solutions of a linear elliptic problem.

Apparent diffusion coefficient measurement in a moving phantom simulating linear respiratory motion.

PubMed

Kwee, Thomas C; Takahara, Taro; Muro, Isao; Van Cauteren, Marc; Imai, Yutaka; Nievelstein, Rutger A J; Mali, Willem P T M; Luijten, Peter R

2010-10-01

The aim of this study was to examine the effect of simulated linear respiratory motion on apparent diffusion coefficient (ADC) measurements. Six rectangular test tubes (14 × 92 mm) filled with either water, tomato ketchup, or mayonnaise were positioned in a box containing agarose gel. This box was connected to a double-acting pneumatic cylinder, capable of inducing periodic linear motion in the long-axis direction of the magnetic bore (23-mm stroke). Diffusion-weighted magnetic resonance imaging was performed for both the static and moving phantoms, and ADC measurements were made in the six test tubes in both situations. In the three test tubes whose long axes were parallel to the direction of motion, ADCs agreed well between the moving and static phantom situations. However, in two test tubes that were filled with fluids that had a considerably lower diffusion coefficient than the surrounding agarose gel, and whose long axes were perpendicular to the direction of motion, the ADCs agreed poorly between the moving and static phantom situations. ADC measurements of large homogeneous structures are not affected by linear respiratory motion. However, ADC measurements of inhomogeneous or small structures are affected by linear respiratory motion due to partial volume effects.

Nanoparticle Motion in Entangled Melts of Linear and Nonconcatenated Ring Polymers [Nanoparticle Motion in Entangled Melts of Non-Concatenated Ring Polymers].

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

Ge, Ting; Kalathi, Jagannathan T.; Halverson, Jonathan D.

The motion of nanoparticles (NPs) in entangled melts of linear polymers and non-concatenated ring polymers are compared by large-scale molecular dynamics simulations. The comparison provides a paradigm for the effects of polymer architecture on the dynamical coupling between NPs and polymers in nanocomposites. Strongly suppressed motion of NPs with diameter d larger than the entanglement spacing a is observed in a melt of linear polymers before the onset of Fickian NP diffusion. This strong suppression of NP motion occurs progressively as d exceeds a, and is related to the hopping diffusion of NPs in the entanglement network. In contrast tomore » the NP motion in linear polymers, the motion of NPs with d > a in ring polymers is not as strongly suppressed prior to Fickian diffusion. The diffusion coefficient D decreases with increasing d much slower in entangled rings than in entangled linear chains. NP motion in entangled non-concatenated ring polymers is understood through a scaling analysis of the coupling between NP motion and the self-similar entangled dynamics of ring polymers.« less

Nanoparticle Motion in Entangled Melts of Linear and Nonconcatenated Ring Polymers [Nanoparticle Motion in Entangled Melts of Non-Concatenated Ring Polymers].

DOE PAGES

Ge, Ting; Kalathi, Jagannathan T.; Halverson, Jonathan D.; ...

2017-02-13

The motion of nanoparticles (NPs) in entangled melts of linear polymers and non-concatenated ring polymers are compared by large-scale molecular dynamics simulations. The comparison provides a paradigm for the effects of polymer architecture on the dynamical coupling between NPs and polymers in nanocomposites. Strongly suppressed motion of NPs with diameter d larger than the entanglement spacing a is observed in a melt of linear polymers before the onset of Fickian NP diffusion. This strong suppression of NP motion occurs progressively as d exceeds a, and is related to the hopping diffusion of NPs in the entanglement network. In contrast tomore » the NP motion in linear polymers, the motion of NPs with d > a in ring polymers is not as strongly suppressed prior to Fickian diffusion. The diffusion coefficient D decreases with increasing d much slower in entangled rings than in entangled linear chains. NP motion in entangled non-concatenated ring polymers is understood through a scaling analysis of the coupling between NP motion and the self-similar entangled dynamics of ring polymers.« less

The influence of wedge diffuser blade number and divergence angle on the performance of a high pressure ratio centrifugal compressor

NASA Astrophysics Data System (ADS)

Wang, Yi; Han, Ge; Lu, Xingen; Zhu, Junqiang

2018-02-01

Wedge diffuser is widely used in centrifugal compressors due to its high performance and compact size. This paper is aimed to research the influence of wedge diffuser blade number and divergence angle on centrifugal compressor performance. The impact of wedge diffuser blade number on compressor stage performance is investigated, and then the wedge diffusers with different divergence angle are studied by varying diffuser wedge angle and blade number simultaneously. It is found that wedge diffuser with 27 blades could have about 0.8% higher adiabatic efficiency and 0.14 higher total pressure ratio than the wedge diffuser with 19 blades and the best compressor performance is achieved when diffuser divergence angle is 8.3°.These results could give some advices on centrifugal compressor design.

Extension of Pressure Measurement to 6× 10-11 Torr Using the Dynamics of the m=1 Diocotron Mode*

NASA Astrophysics Data System (ADS)

Paul, Stephen F.; Morrison, Kyle; Davidson, Ronald C.; Jenkins, Thomas

2001-10-01

Damping of the m=1 diocotron mode is used to measure neutral pressure in the Electron Diffusion Gauge (EDG). The drag exerted on the rotating plasma by collisions with neutrals is expected to excite the mode. However, previous studies in the EDG showed that the diocotron mode is more strongly damped at higher neutral pressures. The damping scaled as P-1/2 in the range from 5× 10-10 to 2× 10-7 Torr. This range has been extended from 6× 10-11 to 5× 10-7 Torr. Above 10-7 Torr, the damping increases linearly with P. Below 5× 10-9 Torr, the scaling is less sensitive, ≈ P-1/4, exhibiting a smooth transition. Sensitivity to pressure increments of less than ΔP = 1× 10-10 Torr are observed. Mode damping is correlated with the rate of expansion of the plasma, which occurs simultaneously. At high pressure, collisions with neutrals dominate the expansion, resulting in a similarly sensitive dependence on pressure. At low pressure, device asymmetries dominate the plasma expansion. Whereas plasma expansion is virtually insensitive to pressures below 5× 10-8 Torr, diocotron mode measurements have shown sensitivity over two orders of magnitude lower in pressure. Both diocotron mode damping and plasma expansion also depend similarly on electron density and magnetic field. Conditions that favor expansion (low field, high collisionality) also favor mode damping. *Research supported by the Office of Naval Research

Gauge calibration by diffusion

NASA Technical Reports Server (NTRS)

Brock, F. J.; Feakes, F. (Inventor)

1968-01-01

Vacuum gage calibration by diffusing a known quantity of gas through a heated barrier into a gauge is examined. The gas flow raises the pressure in the gauge to known level and is then compared with the gauge's pressure reading.

Carbon diffusion in solid iron as function of pressure and temperature

NASA Astrophysics Data System (ADS)

Stagno, V.; Crispin, K. L.; Fei, Y.

2012-12-01

The knowledge of carbon diffusion in metallic iron is of importance for both industrial and geological applications. In industry the diffusion properties of carbon apply to the massive production of steel through carburizing and galvanization processes at high temperature with the aim to improve the hardness and rust resistance of such materials. In geoscience the diffusion of carbon in metallic phases at high pressure and temperature is important for determining the rate of reactions and crystal growth of carbide phases likely coexisting with mantle silicates. Due to a small atomic radius, carbon is expected to dissolve by interstitial diffusion in solid metals. However, to date there are no experimental data available to understand the role that pressure plays on the mobilization of carbon through solid iron. Further, for light elements such as carbon or sulfur the activation energy is assumed to be lower than in case of lattice diffusion. However, with increasing pressure the activation volume must be taken into account to better understand diffusion processes at the atomic scale. We performed experiments using multianvil and piston cylinder devices at pressures between 1.5 and 6 GPa and temperature of 700-1200°C. Experiments were carried out using cylindrical glassy carbon sandwiched between layers of pure iron rods of known thickness enclosed in MgO capsule. Analytical techniques included FE-SEM for textural observation and accurate analyses of the interface between layers, while concentration profiles were measured using the electron microprobe with an optimized standardization procedure. Concentration profiles of carbon in iron were computed to determine the diffusion coefficients based on Fick's second law formulation assuming isotropic one dimension diffusion. Preliminary results confirm the positive temperature dependence of the diffusion coefficient for carbon widely discussed in literature. However, our results also show that a significant increase in pressure is required to affect the mobility of carbon through metallic iron by almost the same order of magnitude as cooling. The variation of the diffusion coefficient as function of temperature and pressure will be used to determine the activation energy and volume. It is known that the stability of carbide phases in the Earth's interior is mainly governed by the local Fe/C ratios. In the case of enriched mantle model, for instance, carbon in form of diamond will coexist with Fe7C3 for small amounts of metallic iron. In contrast, this would imply that at low carbon contents (<50 ppm) typical of a depleted mantle source, and at oxygen fugacity conditions lower than EMOD buffer, the transport of carbon will likely occur by diffusion through the coexisting metal phase. Results from this study will improve our understanding on the transport of carbon by diffusion at conditions of the Earth's interior and will provide new thermodynamic data to explain the fractionation of carbon by diffusion in other planetary bodies.

Heat of transport of air in clay.

PubMed

Minkin, Leonid; Shapovalov, Alexander S

2007-01-01

By measuring the thermomolecular pressure difference and using principles of irreversible thermodynamics, heat of transport of air in clay and its coefficient of diffusion are found. A comparison of thermotranspiration and pressure driven gas fluxes through concrete slab in homes is examined. It is shown that thermotranspiration air/radon flow may greatly exceed diffusion (pressure driven) flow in homes.

Diffusion and Monod kinetics model to determine in vivo human corneal oxygen-consumption rate during soft contact lens wear.

PubMed

Del Castillo, Luis F; da Silva, Ana R Ferreira; Hernández, Saul I; Aguilella, M; Andrio, Andreu; Mollá, Sergio; Compañ, Vicente

2015-01-01

We present an analysis of the corneal oxygen consumption Qc from non-linear models, using data of oxygen partial pressure or tension (P(O2) ) obtained from in vivo estimation previously reported by other authors. (1) METHODS: Assuming that the cornea is a single homogeneous layer, the oxygen permeability through the cornea will be the same regardless of the type of lens that is available on it. The obtention of the real value of the maximum oxygen consumption rate Qc,max is very important because this parameter is directly related with the gradient pressure profile into the cornea and moreover, the real corneal oxygen consumption is influenced by both anterior and posterior oxygen fluxes. Our calculations give different values for the maximum oxygen consumption rate Qc,max, when different oxygen pressure values (high and low P(O2)) are considered at the interface cornea-tears film. Present results are relevant for the calculation on the partial pressure of oxygen, available at different depths into the corneal tissue behind contact lenses of different oxygen transmissibility. Copyright © 2014. Published by Elsevier Espana.

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

Kapustin, Eugene A.; Lee, Seungkyu; Alshammari, Ahmad S.

Despite numerous studies on chemical and thermal stability of metal-organic frameworks (MOFs), mechanical stability remains largely undeveloped. No strategy exists to control the mechanical deformation of MOFs under ultrahigh pressure, to date. We show that the mechanically unstable MOF-520 can be retrofitted by precise placement of a rigid 4,4'-biphenyldicarboxylate (BPDC) linker as a "girder" to afford a mechanically robust framework: MOF-520-BPDC. This retrofitting alters how the structure deforms under ultrahigh pressure and thus leads to a drastic enhancement of its mechanical robustness. While in the parent MOF-520 the pressure transmitting medium molecules diffuse into the pore and expand the structuremore » from the inside upon compression, the girder in the new retrofitted MOF-520-BPDC prevents the framework from expansion by linking two adjacent secondary building units together. As a result, the modified MOF is stable under hydrostatic compression in a diamond-anvil cell up to 5.5 gigapascal. The increased mechanical stability of MOF-520-BPDC prohibits the typical amorphization observed for MOFs in this pressure range. Direct correlation between the orientation of these girders within the framework and its linear strain was estimated, providing new insights for the design of MOFs with optimized mechanical properties.« less

A multi-commuted flow injection system with a multi-channel propulsion unit placed before detection: Spectrophotometric determination of ammonium.

PubMed

Oliveira, Sara M; Lopes, Teresa I M S; Tóth, Ildikó V; Rangel, António O S S

2007-09-26

A flow system with a multi-channel peristaltic pump placed before the solenoid valves is proposed to overcome some limitations attributed to multi-commuted flow injection systems: the negative pressure can lead to the formation of unwanted air bubbles and limits the use of devices for separation processes (gas diffusion, dialysis or ion-exchange). The proposed approach was applied to the colorimetric determination of ammonium nitrogen. In alkaline medium, ammonium is converted into ammonia, which diffuses over the membrane, causing a pH change and subsequently a colour change in the acceptor stream (bromothymol blue solution). The system allowed the re-circulation of the acceptor solution and was applied to ammonium determination in surface and tap water, providing relative standard deviations lower than 1.5%. A stopped flow approach in the acceptor stream was adopted to attain a low quantification limit (42 microgL(-1)) and a linear dynamic range of 50-1000 microgL(-1) with a determination rate of 20 h(-1).

The carrier gas pressure effect in a laminar flow diffusion chamber, homogeneous nucleation of n-butanol in helium.

PubMed

Hyvärinen, Antti-Pekka; Brus, David; Zdímal, Vladimír; Smolík, Jiri; Kulmala, Markku; Viisanen, Yrjö; Lihavainen, Heikki

2006-06-14

Homogeneous nucleation rate isotherms of n-butanol+helium were measured in a laminar flow diffusion chamber at total pressures ranging from 50 to 210 kPa to investigate the effect of carrier gas pressure on nucleation. Nucleation temperatures ranged from 265 to 280 K and the measured nucleation rates were between 10(2) and 10(6) cm(-3) s(-1). The measured nucleation rates decreased as a function of increasing pressure. The pressure effect was strongest at pressures below 100 kPa. This negative carrier gas effect was also temperature dependent. At nucleation temperature of 280 K and at the same saturation ratio, the maximum deviation between nucleation rates measured at 50 and 210 kPa was about three orders of magnitude. At nucleation temperature of 265 K, the effect was negligible. Qualitatively the results resemble those measured in a thermal diffusion cloud chamber. Also the slopes of the isothermal nucleation rates as a function of saturation ratio were different as a function of total pressure, 50 kPa isotherms yielded the steepest slopes, and 210 kPa isotherms the shallowest slopes. Several sources of inaccuracies were considered in the interpretation of the results: uncertainties in the transport properties, nonideal behavior of the vapor-carrier gas mixture, and shortcomings of the used mathematical model. Operation characteristics of the laminar flow diffusion chamber at both under-and over-pressure were determined to verify a correct and stable operation of the device. We conclude that a negative carrier gas pressure effect is seen in the laminar flow diffusion chamber and it cannot be totally explained with the aforementioned reasons.

Flow measurements in two cambered vane diffusers with different passage widths

NASA Astrophysics Data System (ADS)

Stein, W.; Rautenberg, M.

1985-03-01

To investigate the influence of the vaneless space between impeller exit and the diffuser vanes, detailed flow measurements in two diffusers with the same vane geometry but different passage width are compared. The three-dimensional character of the flow changes between impeller exit and the entry to the two dimensional vanes depending on the shape of the shroud. After initial measurements with a constant area vaneless space, the width of the vaned diffuser was later on reduced by 10 percent. The compressor maps show increases in overall pressure rise and efficiency with the width reduction. To get further details of the flow field, measurements of the static pressure distribution at hub and shroud have been performed at several operation points for both diffusers. At the same points, the flow angle and total pressure distribution between hub and shroud upstream and downstream of the vanes have been measured with probes. The maximum efficiency of the narrow diffuser is nearly 2 percent higher than for the wide diffuser. The measurements give further details to explain this improvement.

Measurement of gas diffusion coefficient in liquid-saturated porous media using magnetic resonance imaging

NASA Astrophysics Data System (ADS)

Song, Yongchen; Hao, Min; Zhao, Yuechao; Zhang, Liang

2014-12-01

In this study, the dual-chamber pressure decay method and magnetic resonance imaging (MRI) were used to dynamically visualize the gas diffusion process in liquid-saturated porous media, and the relationship of concentration-distance for gas diffusing into liquid-saturated porous media at different times were obtained by MR images quantitative analysis. A non-iterative finite volume method was successfully applied to calculate the local gas diffusion coefficient in liquid-saturated porous media. The results agreed very well with the conventional pressure decay method, thus it demonstrates that the method was feasible of determining the local diffusion coefficient of gas in liquid-saturated porous media at different times during diffusion process.

Molecular Retrofitting Adapts a Metal–Organic Framework to Extreme Pressure

DOE PAGES

Kapustin, Eugene A.; Lee, Seungkyu; Alshammari, Ahmad S.; ...

2017-06-07

Despite numerous studies on chemical and thermal stability of metal-organic frameworks (MOFs), mechanical stability remains largely undeveloped. No strategy exists to control the mechanical deformation of MOFs under ultrahigh pressure, to date. We show that the mechanically unstable MOF-520 can be retrofitted by precise placement of a rigid 4,4'-biphenyldicarboxylate (BPDC) linker as a "girder" to afford a mechanically robust framework: MOF-520-BPDC. This retrofitting alters how the structure deforms under ultrahigh pressure and thus leads to a drastic enhancement of its mechanical robustness. While in the parent MOF-520 the pressure transmitting medium molecules diffuse into the pore and expand the structuremore » from the inside upon compression, the girder in the new retrofitted MOF-520-BPDC prevents the framework from expansion by linking two adjacent secondary building units together. As a result, the modified MOF is stable under hydrostatic compression in a diamond-anvil cell up to 5.5 gigapascal. The increased mechanical stability of MOF-520-BPDC prohibits the typical amorphization observed for MOFs in this pressure range. Direct correlation between the orientation of these girders within the framework and its linear strain was estimated, providing new insights for the design of MOFs with optimized mechanical properties.« less

A first-principles and experimental study of helium diffusion in periclase MgO

NASA Astrophysics Data System (ADS)

Song, Zhewen; Wu, Henry; Shu, Shipeng; Krawczynski, Mike; Van Orman, James; Cherniak, Daniele J.; Bruce Watson, E.; Mukhopadhyay, Sujoy; Morgan, Dane

2018-02-01

The distribution of He isotopes is used to trace heterogeneities in the Earth's mantle, and is particularly useful for constraining the length scale of heterogeneity due to the generally rapid diffusivity of helium. However, such an analysis is challenging because He diffusivities are largely unknown in lower mantle phases, which can influence the He profiles in regions that cycle through the lower mantle. With this motivation, we have used first-principles simulations based on density functional theory to study He diffusion in MgO, an important lower mantle phase. We first studied the case of interstitial helium diffusion in perfect MgO and found a migration barrier of 0.73 eV at zero pressure. Then we used the kinetic Monte Carlo method to study the case of substitutional He diffusion in MgO, where we assumed that He diffuses on the cation sublattice through cation vacancies. We also performed experiments on He diffusion at atmospheric pressure using ion implantation and nuclear reaction analysis in both as-received and Ga-doped samples. A comparison between the experimental and simulation results are shown. This work provides a foundation for further studies at high-pressure.

Design of an efficient space constrained diffuser for supercritical CO2 turbines

NASA Astrophysics Data System (ADS)

Keep, Joshua A.; Head, Adam J.; Jahn, Ingo H.

2017-03-01

Radial inflow turbines are an arguably relevant architecture for energy extraction from ORC and supercritical CO 2 power cycles. At small scale, design constraints can prescribe high exit velocities for such turbines, which lead to high kinetic energy in the turbine exhaust stream. The inclusion of a suitable diffuser in a radial turbine system allows some exhaust kinetic energy to be recovered as static pressure, thereby ensuring efficient operation of the overall turbine system. In supercritical CO 2 Brayton cycles, the high turbine inlet pressure can lead to a sealing challenge if the rotor is supported from the rotor rear side, due to the seal operating at rotor inlet pressure. An alternative to this is a cantilevered layout with the rotor exit facing the bearing system. While such a layout is attractive for the sealing system, it limits the axial space claim of any diffuser. Previous studies into conical diffuser geometries for supercritical CO 2 have shown that in order to achieve optimal static pressure recovery, longer geometries of a shallower cone angle are necessitated when compared to air. A diffuser with a combined annular-radial arrangement is investigated as a means to package the aforementioned geometric characteristics into a limited space claim for a 100kW radial inflow turbine. Simulation results show that a diffuser of this design can attain static pressure rise coefficients greater than 0.88. This confirms that annular-radial diffusers are a viable design solution for supercritical CO2 radial inflow turbines, thus enabling an alternative cantilevered rotor layout.

Impact of functional focal versus diffuse coronary artery disease on bypass graft patency.

PubMed

Shiono, Yasutsugu; Kubo, Takashi; Honda, Kentaro; Katayama, Yosuke; Aoki, Hiroshi; Satogami, Keisuke; Kashiyama, Kuninobu; Taruya, Akira; Nishiguchi, Tsuyoshi; Kuroi, Akio; Orii, Makoto; Kameyama, Takeyoshi; Yamano, Takashi; Yamaguchi, Tomoyuki; Matsuo, Yoshiki; Ino, Yasushi; Tanaka, Atsushi; Hozumi, Takeshi; Nishimura, Yoshiharu; Okamura, Yoshitaka; Akasaka, Takashi

2016-11-01

Pressure guidewire pullback recording can differentiate between functional focal and diffuse disease types in coronary artery disease. The aim of this study was to compare the outcome of coronary artery bypass graft (CABG) patency between patients with functional focal versus diffuse disease types in recipient coronary arteries. We investigated 89 patients who underwent pressure guidewire pullback in the left anterior descending (LAD) artery before CABG using internal mammary artery (IMA). Based on the pressure guidewire pullback data, the LAD lesions were classified into functional focal disease (abrupt pressure step-up; n=58) or functional diffuse disease (gradual pressure increase; n=31). Follow-up computed tomography (CT) angiography was conducted within 1year after CABG to assess the bypass graft patency. Pre CABG, LAD angiographic percent diameter stenosis (57±10% vs. 54±12%, p=0.228) and fractional flow reserve (FFR) (0.68±0.07 vs. 0.69±0.07, p=0.244) were not different between the functional focal and diffuse disease groups. The CABG procedure characteristics were similarly comparable between the two groups. In the follow-up CT angiography after CABG, occlusion or string sign of the IMA graft to LAD was more frequently observed in the functional diffuse disease group than in the functional focal disease group (26% vs. 7%, p=0.021). In CABG, functional diffuse disease in the recipient coronary artery was associated with an increased risk of the graft failure in comparison with functional focal disease. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

Thermal conductivity and thermal diffusivity of methane hydrate formed from compacted granular ice

NASA Astrophysics Data System (ADS)

Zhao, Jie; Sun, Shicai; Liu, Changling; Meng, Qingguo

2018-05-01

Thermal conductivity and thermal diffusivity of pure methane hydrate samples, formed from compacted granular ice (0-75 μm), and were measured simultaneously by the transient plane source (TPS) technique. The temperature dependence was measured between 263.15 and 283.05 K, and the gas-phase pressure dependence was measured between 2 and 10 MPa. It is revealed that the thermal conductivity of pure methane hydrate exhibits a positive trend with temperature and increases from 0.4877 to 0.5467 W·m-1·K-1. The thermal diffusivity of methane hydrate has inverse dependence on temperature and the values in the temperature range from 0.2940 to 0.3754 mm2·s-1, which is more than twice that of water. The experimental results show that the effects of gas-phase pressure on the thermal conductivity and thermal diffusivity are very small. Thermal conductivity of methane hydrate is found to have weakly positive gas-phase pressure dependence, whereas the thermal diffusivity has slightly negative trend with gas-phase pressure.

Direct monitoring of wind-induced pressure-pumping on gas transport in soil

NASA Astrophysics Data System (ADS)

Laemmel, Thomas; Mohr, Manuel; Schindler, Dirk; Schack-Kirchner, Helmer; Maier, Martin

2017-04-01

Gas exchange between soil and atmosphere is important for the biogeochemistry of soils and is commonly assumed to be governed by molecular diffusion. Yet a few previous field studies identified other gas transport processes such as wind-induced pressure-pumping to enhance soil-atmosphere fluxes significantly. However, since these wind-induced non-diffusive gas transport processes in soil often occur intermittently, the quantification of their contribution to soil gas emissions is challenging. To quantify the effects of wind-induced pressure-pumping on soil gas transport, we developed a method for in situ monitoring of soil gas transport. The method includes the use of Helium (He) as a tracer gas which was continuously injected into the soil. The resulting He steady-state concentration profile was monitored. Gas transport parameters of the soil were inversely modelled. We used our method during a field campaign in a well-aerated forest soil over three months. During periods of low wind speed, soil gas transport was modelled assuming diffusion as transport process. During periods of high wind speed, the previously steady diffusive He concentration profile showed temporary concentration decreases in the topsoil, indicating an increase of the effective gas transport rate in the topsoil up to 30%. The enhancement of effective topsoil soil gas diffusivity resulted from wind-induced air pressure fluctuations which are referred to as pressure-pumping. These air pressure fluctuations had frequencies between 0.1 and 0.01 Hz and amplitudes up to 10 Pa and occurred at above-canopy wind speeds greater than 5 m s-1. We could show the importance of the enhancement of the gas transport rate in relation with the wind intensity and corresponding air pressure fluctuations characteristics. We directly detected and quantified the pressure-pumping effect on gas transport in soil in a field study for the first time, and could thus validate and underpin the importance of this non-diffusive gas transport process. Our method can also be used to study other non-diffusive gas transport processes occurring in soil and snow, and their possible feedbacks or interactions with biogeochemical processes.

Breakdown and Limit of Continuum Diffusion Velocity for Binary Gas Mixtures from Direct Simulation

NASA Astrophysics Data System (ADS)

Martin, Robert Scott; Najmabadi, Farrokh

2011-05-01

This work investigates the breakdown of the continuum relations for diffusion velocity in inert binary gas mixtures. Values of the relative diffusion velocities for components of a gas mixture may be calculated using of Chapman-Enskog theory and occur not only due to concentration gradients, but also pressure and temperature gradients in the flow as described by Hirschfelder. Because Chapman-Enskog theory employs a linear perturbation around equilibrium, it is expected to break down when the velocity distribution deviates significantly from equilibrium. This breakdown of the overall flow has long been an area of interest in rarefied gas dynamics. By comparing the continuum values to results from Bird's DS2V Monte Carlo code, we propose a new limit on the continuum approach specific to binary gases. To remove the confounding influence of an inconsistent molecular model, we also present the application of the variable hard sphere (VSS) model used in DS2V to the continuum diffusion velocity calculation. Fitting sample asymptotic curves to the breakdown, a limit, Vmax, that is a fraction of an analytically derived limit resulting from the kinetic temperature of the mixture is proposed. With an expected deviation of only 2% between the physical values and continuum calculations within ±Vmax/4, we suggest this as a conservative estimate on the range of applicability for the continuum theory.

The investigation of die-pressing and sintering behavior of ITP CP-Ti and Ti-6Al-4V powders

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

Chen, Wei; Yamamoto, Yukinori; Peter, William H

This paper investigated the die-pressing and sintering behavior of the low-cost CP-Ti and Ti-6Al- 4V powders made by the Armstrong Process . The Armstrong powders have an irregular coral like, dendritic morphology, with a dendrite size of approximately 2-5 m. As-received as well as milled powders were uniaxially pressed at designated pressures up to 690 MPa to form disk samples with different aspect ratios. In the studied pressure range, an empirical powder compaction equation was applied to linearize the green density pressure relationship, and powder compaction parameters were obtained. The Armstrong Ti-64 powder exhibited a significantly higher sinterability than themore » CP-Ti powder. This was explained to be due to the higher diffusivity of V at the sintering temperature. The Ti-64 samples with a green density of 71.0% increased to 99.6% after sintering at 1300oC for 1 hour. An ex-situ technique was used to track the powder morphology change before and after sintering.« less

Linear response theory and transient fluctuation relations for diffusion processes: a backward point of view

NASA Astrophysics Data System (ADS)

Liu, Fei; Tong, Huan; Ma, Rui; Ou-Yang, Zhong-can

2010-12-01

A formal apparatus is developed to unify derivations of the linear response theory and a variety of transient fluctuation relations for continuous diffusion processes from a backward point of view. The basis is a perturbed Kolmogorov backward equation and the path integral representation of its solution. We find that these exact transient relations could be interpreted as a consequence of a generalized Chapman-Kolmogorov equation, which intrinsically arises from the Markovian characteristic of diffusion processes.

Passive Rocket Diffuser Testing: Reacting Flow Performance of Four Second-Throat Geometries

NASA Technical Reports Server (NTRS)

Jones, Daniel R.; Allgood, Daniel C.; Saunders, Grady P.

2016-01-01

Second-throat diffusers serve to isolate rocket engines from the effects of ambient back pressure. As one of the nation's largest rocket testing facilities, the performance and design limitations of diffusers are of great interest to NASA's Stennis Space Center. This paper describes a series of tests conducted on four diffuser configurations to better understand the effects of inlet geometry and throat area on starting behavior and boundary layer separation. The diffusers were tested for a duration of five seconds with a 1455-pound thrust, LO2/GH2 thruster to ensure they each reached aerodynamic steady state. The effects of a water spray ring at the diffuser exits and a water-cooled deflector plate were also evaluated. Static pressure and temperature measurements were taken at multiple axial locations along the diffusers, and Computational Fluid Dynamics (CFD) simulations were used as a tool to aid in the interpretation of data. The hot combustion products were confirmed to enable the diffuser start condition with tighter second throats than predicted by historical cold-flow data or the theoretical normal shock method. Both aerodynamic performance and heat transfer were found to increase with smaller diffuser throats. Spray ring and deflector cooling water had negligible impacts on diffuser boundary layer separation. CFD was found to accurately capture diffuser shock structures and full-flowing diffuser wall pressures, and the qualitative behavior of heat transfer. However, the ability to predict boundary layer separated flows was not consistent.

Formulation, Implementation and Validation of a Two-Fluid model in a Fuel Cell CFD Code

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

Jain, Kunal; Cole, J. Vernon; Kumar, Sanjiv

2008-12-01

Water management is one of the main challenges in PEM Fuel Cells. While water is essential for membrane electrical conductivity, excess liquid water leads to flooding of catalyst layers. Despite the fact that accurate prediction of two-phase transport is key for optimal water management, understanding of the two-phase transport in fuel cells is relatively poor. Wang et. al. have studied the two-phase transport in the channel and diffusion layer separately using a multiphase mixture model. The model fails to accurately predict saturation values for high humidity inlet streams. Nguyen et. al. developed a two-dimensional, two-phase, isothermal, isobaric, steady state modelmore » of the catalyst and gas diffusion layers. The model neglects any liquid in the channel. Djilali et. al. developed a three-dimensional two-phase multicomponent model. The model is an improvement over previous models, but neglects drag between the liquid and the gas phases in the channel. In this work, we present a comprehensive two-fluid model relevant to fuel cells. Models for two-phase transport through Channel, Gas Diffusion Layer (GDL) and Channel-GDL interface, are discussed. In the channel, the gas and liquid pressures are assumed to be same. The surface tension effects in the channel are incorporated using the continuum surface force (CSF) model. The force at the surface is expressed as a volumetric body force and added as a source to the momentum equation. In the GDL, the gas and liquid are assumed to be at different pressures. The difference in the pressures (capillary pressure) is calculated using an empirical correlations. At the Channel-GDL interface, the wall adhesion affects need to be taken into account. SIMPLE-type methods recast the continuity equation into a pressure-correction equation, the solution of which then provides corrections for velocities and pressures. However, in the two-fluid model, the presence of two phasic continuity equations gives more freedom and more complications. A general approach would be to form a mixture continuity equation by linearly combining the phasic continuity equations using appropriate weighting factors. Analogous to mixture equation for pressure correction, a difference equation is used for the volume/phase fraction by taking the difference between the phasic continuity equations. The relative advantages of the above mentioned algorithmic variants for computing pressure correction and volume fractions are discussed and quantitatively assessed. Preliminary model validation is done for each component of the fuel cell. The two-phase transport in the channel is validated using empirical correlations. Transport in the GDL is validated against results obtained from LBM and VOF simulation techniques. The Channel-GDL interface transport will be validated against experiment and empirical correlation of droplet detachment at the interface.« less

In-Situ Ultra Low Frequency Poroelastic Response of a Natural Macro-Fracture

NASA Astrophysics Data System (ADS)

Guglielmi, Y.; Cappa, F.; Rutqvist, J.; Tsang, C.; Gaffet, S.

2008-12-01

The seismic visibility of macro-fractures filled with fluids is a central problem in the exploration of thermo- hydro-mechanical and chemical processes that occur in Earth' s subsurface. Most studies have been concerned (1) with cracks of a small size relative to the seismic wavelength (2) with "core-sized" samples of single macro-fractures. In comparison, in-situ studies of macro-fractures are very rare and no real estimate is made of the relevance of this convenient "core-sized" data to in-situ reservoirs in general. In this study, we present a new experimental approach to in-situ characterize mechanical and hydraulic properties of fractures using the innovative HPPP protocol. This protocol allows simultaneous high-frequency (120.2 Hz) sampling of normal displacement and fluid pressure in a borehole intersecting the fracture. We show preliminary results conducted in a single fracture vertically embedded in a carbonate reservoir that contains 3 sets of macro-fractures with an average 2m spacing. Two HPPP probes were set, spaced one meter vertically in the fracture. Two types of ULF seismic sources are applied: a fluid pressure pulse injected in the fracture and a hammer hit at a point located 5m far from the fracture plane. There is a highly non-linear variation of fracture normal displacement-versus- fluid pressure as a function of frequency, the higher the frequency, the lower the displacement spectral amplitude is. The pressure pulse and the hammer hit allow exploring the fracture poroelastic response in the [0 - 3Hz] frequency range. The fracture plays the role of a "low-pass" filter for fluid pressure waves; only a quasi-static pressure signal being registered at the receiver. The displacement wave propagation is more complex resulting in uncoupled quasi-static-pressure-2Hz-deformation signals at the receiver. For low magnitude seismic sources (low amplitude pulse and seismic wave), the fracture natural resonance is amplified resulting in separate signals power spectral peaks. When fluid pressure is enough increased, hydraulic diffusion takes place at frequencies lower than 1.2 Hz. Poroelastic effects related to static hydraulic diffusion and to wave propagation were described separately using a linear elastic model where the fracture was treated as a displacement discontinuity across which stresses are continuous but displacement are discontinuous. It appears that the dynamic fracture normal stiffness at 2 to 3 Hz is a factor of 2.8 higher than the static stiffness although the fracture displays a high hydraulic aperture of 10-4 m. This surprising result is related to a high heterogeneity of the fracture channel network with a large porosity/permeability contrast that does not allow fluid displacement under dynamic loading. The HPPP approach appears as a possibility to in-situ characterize such fractures static to seismic poroelastic heterogeneous properties.

Cosmic ray diffusion: Report of the Workshop in Cosmic Ray Diffusion Theory

NASA Technical Reports Server (NTRS)

Birmingham, T. J.; Jones, F. C.

1975-01-01

A workshop in cosmic ray diffusion theory was held at Goddard Space Flight Center on May 16-17, 1974. Topics discussed and summarized are: (1) cosmic ray measurements as related to diffusion theory; (2) quasi-linear theory, nonlinear theory, and computer simulation of cosmic ray pitch-angle diffusion; and (3) magnetic field fluctuation measurements as related to diffusion theory.

Diffusive sensitivity to muscle architecture: a magnetic resonance diffusion tensor imaging study of the human calf.

PubMed

Galbán, Craig J; Maderwald, Stefan; Uffmann, Kai; de Greiff, Armin; Ladd, Mark E

2004-12-01

The aim of this study was to examine the diffusive properties of adjacent muscles at rest, and to determine the relationship between diffusive and architectural properties, which are task-specific to muscles. The principle, second, and third eigenvalues, trace of the diffusion tensor, and two anisotropic parameters, ellipsoid eccentricity (e) and fractional anisotropy (FA), of various muscles in the human calf were calculated by diffusion tensor imaging (DTI). Linear correlations of the calculated parameters to the muscle physiological cross-sectional area (PCSA), which is proportional to maximum muscle force, were performed to ascertain any linear relation between muscle architecture and diffusivity. Images of the left calf were acquired from six healthy male volunteers. Seven muscles were investigated in this study. These comprised the soleus, lateral gastrocnemius, medial gastrocnemius, posterior tibialis, anterior tibialis, extensor digitorum longus, and peroneus longus. All data were presented as the mean and standard error of the mean (SEM). In general, differences in diffusive parameter values occurred primarily between functionally different muscles. A strong correlation was also found between PCSA and the third eigenvalue, e, and FA. A mathematical derivation revealed a linear relationship between PCSA and the third eigenvalue as a result of their dependence on the average radius of all fibers within a single muscle. These findings demonstrated the ability of DTI to differentiate between functionally different muscles in the same region of the body on the basis of their diffusive properties.

Air Circulation and Heat Exchange under Reduced Pressures

NASA Astrophysics Data System (ADS)

Rygalov, Vadim; Wheeler, Raymond; Dixon, Mike; Hillhouse, Len; Fowler, Philip

Low pressure atmospheres were suggested for Space Greenhouses (SG) design to minimize sys-tem construction and re-supply materials, as well as system manufacturing and deployment costs. But rarified atmospheres modify heat exchange mechanisms what finally leads to alter-ations in thermal control for low pressure closed environments. Under low atmospheric pressures (e.g., lower than 25 kPa compare to 101.3 kPa for normal Earth atmosphere), convection is becoming replaced by diffusion and rate of heat exchange reduces significantly. During a period from 2001 to 2009, a series of hypobaric experiments were conducted at Space Life Sciences Lab (SLSLab) NASA's Kennedy Space Center and the Department of Space Studies, University of North Dakota. Findings from these experiments showed: -air circulation rate decreases non-linearly with lowering of total atmospheric pressure; -heat exchange slows down with pressure decrease creating risk of thermal stress (elevated leaf tem-peratures) for plants in closed environments; -low pressure-induced thermal stress could be reduced by either lowering system temperature set point or increasing forced convection rates (circulation fan power) within certain limits; Air circulation is an important constituent of controlled environments and plays crucial role in material and heat exchange. Theoretical schematics and mathematical models are developed from a series of observations. These models can be used to establish optimal control algorithms for low pressure environments, such as a space greenhouse, as well as assist in fundamental design concept developments for these or similar habitable structures.

Self-diffusion in a stochastically heated two-dimensional dusty plasma

NASA Astrophysics Data System (ADS)

Sheridan, T. E.

2016-09-01

Diffusion in a two-dimensional dusty plasma liquid (i.e., a Yukawa liquid) is studied experimentally. The dusty plasma liquid is heated stochastically by a surrounding three-dimensional toroidal dusty plasma gas which acts as a thermal reservoir. The measured dust velocity distribution functions are isotropic Maxwellians, giving a well-defined kinetic temperature. The mean-square displacement for dust particles is found to increase linearly with time, indicating normal diffusion. The measured diffusion coefficients increase approximately linearly with temperature. The effective collision rate is dominated by collective dust-dust interactions rather than neutral gas drag, and is comparable to the dusty-plasma frequency.

Effects of superparamagnetic iron oxide nanoparticles on the longitudinal and transverse relaxation of hyperpolarized xenon gas

NASA Astrophysics Data System (ADS)

Burant, Alex; Antonacci, Michael; McCallister, Drew; Zhang, Le; Branca, Rosa Tamara

2018-06-01

SuperParamagnetic Iron Oxide Nanoparticles (SPIONs) are often used in magnetic resonance imaging experiments to enhance Magnetic Resonance (MR) sensitivity and specificity. While the effect of SPIONs on the longitudinal and transverse relaxation time of 1H spins has been well characterized, their effect on highly diffusive spins, like those of hyperpolarized gases, has not. For spins diffusing in linear magnetic field gradients, the behavior of the magnetization is characterized by the relative size of three length scales: the diffusion length, the structural length, and the dephasing length. However, for spins diffusing in non-linear gradients, such as those generated by iron oxide nanoparticles, that is no longer the case, particularly if the diffusing spins experience the non-linearity of the gradient. To this end, 3D Monte Carlo simulations are used to simulate the signal decay and the resulting image contrast of hyperpolarized xenon gas near SPIONs. These simulations reveal that signal loss near SPIONs is dominated by transverse relaxation, with little contribution from T1 relaxation, while simulated image contrast and experiments show that diffusion provides no appreciable sensitivity enhancement to SPIONs.

Characterization of Ultrasound Energy Diffusion Due to Small-Size Damage on an Aluminum Plate Using Piezoceramic Transducers

PubMed Central

Lu, Guangtao; Feng, Qian; Li, Yourong; Wang, Hao; Song, Gangbing

2017-01-01

During the propagation of ultrasonic waves in structures, there is usually energy loss due to ultrasound energy diffusion and dissipation. The aim of this research is to characterize the ultrasound energy diffusion that occurs due to small-size damage on an aluminum plate using piezoceramic transducers, for the future purpose of developing a damage detection algorithm. The ultrasonic energy diffusion coefficient is related to the damage distributed in the medium. Meanwhile, the ultrasonic energy dissipation coefficient is related to the inhomogeneity of the medium. Both are usually employed to describe the characteristics of ultrasound energy diffusion. The existence of multimodes of Lamb waves in metallic plate structures results in the asynchronous energy transport of different modes. The mode of Lamb waves has a great influence on ultrasound energy diffusion as a result, and thus has to be chosen appropriately. In order to study the characteristics of ultrasound energy diffusion in metallic plate structures, an experimental setup of an aluminum plate with a through-hole, whose diameter varies from 0.6 mm to 1.2 mm, is used as the test specimen with the help of piezoceramic transducers. The experimental results of two categories of damages at different locations reveal that the existence of damage changes the energy transport between the actuator and the sensor. Also, when there is only one dominate mode of Lamb wave excited in the structure, the ultrasound energy diffusion coefficient decreases approximately linearly with the diameter of the simulated damage. Meanwhile, the ultrasonic energy dissipation coefficient increases approximately linearly with the diameter of the simulated damage. However, when two or more modes of Lamb waves are excited, due to the existence of different group velocities between the different modes, the energy transport of the different modes is asynchronous, and the ultrasonic energy diffusion is not strictly linear with the size of the damage. Therefore, it is recommended that only one dominant mode of Lamb wave should be excited during the characterization process, in order to ensure that the linear relationship between the damage size and the characteristic parameters is maintained. In addition, the findings from this paper demonstrate the potential of developing future damage detection algorithms using the linear relationships between damage size and the ultrasound energy diffusion coefficient or ultrasonic energy dissipation coefficient when a single dominant mode is excited. PMID:29207530

Surge dynamics coupled to pore-pressure evolution in debris flows

USGS Publications Warehouse

Savage, S.B.; Iverson, R.M.; ,

2003-01-01

Temporally and spatially varying pore-fluid pressures exert strong controls on debris-flow motion by mediating internal and basal friction at grain contacts. We analyze these effects by deriving a one-dimensional model of pore-pressure diffusion explicitly coupled to changes in debris-flow thickness. The new pore-pressure equation is combined with Iverson's (1997) extension of the depth-averaged Savage-Hutter (1989, 1991) granular avalanche equations to predict motion of unsteady debris-flow surges with evolving pore-pressure distributions. Computational results illustrate the profound effects of pore-pressure diffusivities on debris-flow surge depths and velocities. ?? 2003 Millpress,.

Test of the diffusing-diffusivity mechanism using near-wall colloidal dynamics

NASA Astrophysics Data System (ADS)

Matse, Mpumelelo; Chubynsky, Mykyta V.; Bechhoefer, John

2017-10-01

The mechanism of diffusing diffusivity predicts that, in environments where the diffusivity changes gradually, the displacement distribution becomes non-Gaussian, even though the mean-square displacement grows linearly with time. Here, we report single-particle tracking measurements of the diffusion of colloidal spheres near a planar substrate. Because the local effective diffusivity is known, we have been able to carry out a direct test of this mechanism for diffusion in inhomogeneous media.

Linear Temporal Stability Analysis of a Low-Density Round Gas Jet Injected into a High-Density Gas

NASA Technical Reports Server (NTRS)

Lawson, Anthony L.; Parthasarathy, Ramkumar N.

2002-01-01

It has been observed in previous experimental studies that round helium jets injected into air display a repetitive structure for a long distance, somewhat similar to the buoyancy-induced flickering observed in diffusion flames. In order to investigate the influence of gravity on the near-injector development of the flow, a linear temporal stability analysis of a round helium jet injected into air was performed. The flow was assumed to be isothermal and locally parallel; viscous and diffusive effects were ignored. The variables were represented as the sum of the mean value and a normal-mode small disturbance. An ordinary differential equation governing the amplitude of the pressure disturbance was derived. The velocity and density profiles in the shear layer, and the Froude number (signifying the effects of gravity) were the three important parameters in this equation. Together with the boundary conditions, an eigenvalue problem was formulated. Assuming that the velocity and density profiles in the shear layer to be represented by hyperbolic tangent functions, the eigenvalue problem was solved for various values of Froude number. The temporal growth rates and the phase velocity of the disturbances were obtained. The temporal growth rates of the disturbances increased as the Froude number was reduced (i.e. gravitational effects increased), indicating the destabilizing role played by gravity.

Diffusion in plasma: The Hall effect, compositional waves, and chemical spots

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

Urpin, V., E-mail: Vadim.urpin@uv.es

2017-03-15

Diffusion caused by a combined influence of the electric current and Hall effect is considered, and it is argued that such diffusion can form inhomogeneities of a chemical composition in plasma. The considered mechanism can be responsible for the formation of element spots in laboratory and astrophysical plasmas. This current-driven diffusion can be accompanied by propagation of a particular type of waves in which the impurity number density oscillates alone. These compositional waves exist if the magnetic pressure in plasma is much greater than the gas pressure.

Long-time behavior and Turing instability induced by cross-diffusion in a three species food chain model with a Holling type-II functional response.

PubMed

Haile, Dawit; Xie, Zhifu

2015-09-01

In this paper, we study a strongly coupled reaction-diffusion system describing three interacting species in a food chain model, where the third species preys on the second one and simultaneously the second species preys on the first one. An intra-species competition b2 among the second predator is introduced to the food chain model. This parameter produces some very interesting result in linear stability and Turing instability. We first show that the unique positive equilibrium solution is locally asymptotically stable for the corresponding ODE system when the intra-species competition exists among the second predator. The positive equilibrium solution remains linearly stable for the reaction diffusion system without cross diffusion, hence it does not belong to the classical Turing instability scheme. But it becomes linearly unstable only when cross-diffusion also plays a role in the reaction-diffusion system, hence the instability is driven solely from the effect of cross diffusion. Our results also exhibit some interesting combining effects of cross-diffusion, intra-species competitions and inter-species interactions. Numerically, we conduct a one parameter analysis which illustrate how the interactions change the existence of stable equilibrium, limit cycle, and chaos. Some interesting dynamical phenomena occur when we perform analysis of interactions in terms of self-production of prey and intra-species competition of the middle predator. By numerical simulations, it illustrates the existence of nonuniform steady solutions and new patterns such as spot patterns, strip patterns and fluctuations due to the diffusion and cross diffusion in two-dimension. Published by Elsevier Inc.

Negative Ion Drift Velocity and Longitudinal Diffusion in Mixtures of Carbon Disulfide and Methane

NASA Technical Reports Server (NTRS)

Dion, Michael P.; Son, S.; Hunter, S. D.; deNolfo, G. A.

2011-01-01

Negative ion drift velocity and longitudinal diffusion has been measured for gas mixtures of carbon disulfide (CS2) and methane (CH4)' Measurements were made as a function of total pressure, CS2 partial pressure and electric field. Constant mobility and thermal-limit longitudinal diffusion is observed for all gas mixtures tested. Gas gain for some of the mixtures is also included.

Numerical analysis of flows of rarefied gases in long channels with octagonal cross section shapes

NASA Astrophysics Data System (ADS)

Szalmas, L.

2014-12-01

Isothermal, pressure driven rarefied gas flows through long channels with octagonal cross section shapes are analyzed computationally. The capillary is between inlet and outlet reservoirs. The cross section is constant along the axial direction. The boundary condition at the solid-gas interface is assumed to be diffuse reflection. Since the channel is long, the gaseous velocity is small compared to the average molecular speed. Consequently, a linearized description can be used. The flow is described by the linearized Bhatnagar-Gross-Krook kinetic model. The solution of the problem is divided into two stages. First, the local flow field is determined by assuming the local pressure gradient. Secondly, the global flow behavior is deduced by the consideration of the conservation of the mass along the axis of the capillary. The kinetic equation is solved by the discrete velocity method on the cross section. Both spatial and velocity spaces are discretized. A body fitted rectangular grid is used for the spatial space. Near the boundary, first-order, while in the interior part of the flow domain, second-order finite-differences are applied to approximate the spatial derivatives. This combination results into an efficient and straightforward numerical treatment. The velocity space is represented by a Gauss-Legendre quadrature. The kinetic equation is solved in an iterative manner. The local dimensionless flow rate is calculated and tabulated for a wide range of the gaseous rarefaction for octagonal cross sections with various geometrical parameters. It exhibits the Knudsen minimum phenomenon. The flow rates in the octagonal channel are compared to those through capillaries with circular and square cross sections. Typical velocity profiles are also shown. The mass flow rate and the distribution of the pressure are determined and presented for global pressure driven flows.

Anomalous dielectric relaxation with linear reaction dynamics in space-dependent force fields.

PubMed

Hong, Tao; Tang, Zhengming; Zhu, Huacheng

2016-12-28

The anomalous dielectric relaxation of disordered reaction with linear reaction dynamics is studied via the continuous time random walk model in the presence of space-dependent electric field. Two kinds of modified reaction-subdiffusion equations are derived for different linear reaction processes by the master equation, including the instantaneous annihilation reaction and the noninstantaneous annihilation reaction. If a constant proportion of walkers is added or removed instantaneously at the end of each step, there will be a modified reaction-subdiffusion equation with a fractional order temporal derivative operating on both the standard diffusion term and a linear reaction kinetics term. If the walkers are added or removed at a constant per capita rate during the waiting time between steps, there will be a standard linear reaction kinetics term but a fractional order temporal derivative operating on an anomalous diffusion term. The dielectric polarization is analyzed based on the Legendre polynomials and the dielectric properties of both reactions can be expressed by the effective rotational diffusion function and component concentration function, which is similar to the standard reaction-diffusion process. The results show that the effective permittivity can be used to describe the dielectric properties in these reactions if the chemical reaction time is much longer than the relaxation time.

Helium Diffusion in Olivine

NASA Astrophysics Data System (ADS)

Cherniak, D. J.; Watson, E. B.

2011-12-01

Diffusion of helium has been characterized in natural Fe-bearing olivine (~Fo90) and synthetic forsterite. Polished, oriented slabs of olivine were implanted with 3He, at 100 keV at a dose of 5x1015/cm2 or at 3.0 MeV at a dose of 1x1016/cm2. A set of experiments on the implanted olivine were run in 1-atm furnaces. In addition to the one-atm experiments, experiments on implanted samples were also run at higher pressures (2.6 and 2.7 GPa) to assess the potential effects of pressure on He diffusion and the applicability of the measured diffusivities in describing He transport in the mantle. The high-pressure experiments were conducted in a piston-cylinder apparatus using an "ultra-soft" pressure cell, with the diffusion sample directly surrounded by AgCl. 3He distributions following experiments were measured with Nuclear Reaction Analysis using the reaction 3He(d,p)4He. This direct profiling method permits us to evaluate anisotropy of diffusion, which cannot be easily assessed using bulk-release methods. For diffusion in forsterite parallel to c we obtain the following Arrhenius relation over the temperatures 250-950°C: D = 3.91x10-6exp(-159 ± 4 kJ mol-1/RT) m2/sec. The data define a single Arrhenius line spanning more than 7 orders of magnitude in D and 700°C in temperature. Diffusion parallel to a appears slightly slower, yielding an activation energy for diffusion of 135 kJ/mol and a pre-exponential factor of 3.73x10-8 m2/sec. Diffusion parallel to b is slower than diffusion parallel to a (by about two-thirds of a log unit); for this orientation an activation energy of 138 kJ/mol and a pre-exponential factor of 1.34x10-8 m2/sec are obtained. This anisotropy is broadly consistent with observations for diffusion of Ni and Fe-Mg in olivine. Diffusion in Fe-bearing olivine (transport parallel to b) agrees within uncertainty with findings for He diffusion in forsterite. The higher-pressure experiments yield diffusivities in agreement with those from the 1-atm experiments, indicating that the results reported here can be reasonably applied to modeling He transport in the upper mantle. The insensitivity of He diffusion to pressure over the investigated range of conditions suggests that compression of the mineral lattice is not sufficient to significantly influence migration of the relatively small helium atoms, which likely diffuse via crystal interstices. The He diffusivities in this work are generally consistent with results from the study of Futagami et al. (1993), who measured He diffusion in natural olivine by outgassing 4He implanted samples, and with the diffusivities measured by bulk-release of 4He and 3He by Shuster et al. (2003), but are about 2 orders of magnitude slower than the recent findings of Tolstikhin et al. (2010) and Blard et al. (2008) . An up-temperature extrapolation of our data also show reasonable agreement with the higher-temperature measurements of Hart (1984). Blard et al. (2008) GCA 72, 3788-3803; Futagami et al. (1993) GCA 57, 3177-3194; Hart (1984) EPSL 70, 297-302; Shuster et al.( 2003) EPSL 217, 19-32; Tolstikhin et al. (2010) GCA 74, 1436-1447

Monotonic non-linear transformations as a tool to investigate age-related effects on brain white matter integrity: A Box-Cox investigation.

PubMed

Morozova, Maria; Koschutnig, Karl; Klein, Elise; Wood, Guilherme

2016-01-15

Non-linear effects of age on white matter integrity are ubiquitous in the brain and indicate that these effects are more pronounced in certain brain regions at specific ages. Box-Cox analysis is a technique to increase the log-likelihood of linear relationships between variables by means of monotonic non-linear transformations. Here we employ Box-Cox transformations to flexibly and parsimoniously determine the degree of non-linearity of age-related effects on white matter integrity by means of model comparisons using a voxel-wise approach. Analysis of white matter integrity in a sample of adults between 20 and 89years of age (n=88) revealed that considerable portions of the white matter in the corpus callosum, cerebellum, pallidum, brainstem, superior occipito-frontal fascicle and optic radiation show non-linear effects of age. Global analyses revealed an increase in the average non-linearity from fractional anisotropy to radial diffusivity, axial diffusivity, and mean diffusivity. These results suggest that Box-Cox transformations are a useful and flexible tool to investigate more complex non-linear effects of age on white matter integrity and extend the functionality of the Box-Cox analysis in neuroimaging. Copyright © 2015 Elsevier Inc. All rights reserved.

Validation of a Computational Model for the SLS Core Stage Oxygen Tank Diffuser Concept and the Low Profile Diffuser - An Advanced Development Design for the SLS

NASA Technical Reports Server (NTRS)

Brodnick, Jacob; Richardson, Brian; Ramachandran, Narayanan

2015-01-01

The Low Profile Diffuser (LPD) project originated as an award from the Marshall Space Flight Center (MSFC) Advanced Development (ADO) office to the Main Propulsion Systems Branch (ER22). The task was created to develop and test an LPD concept that could produce comparable performance to a larger, traditionally designed, ullage gas diffuser while occupying a smaller volume envelope. Historically, ullage gas diffusers have been large, bulky devices that occupy a significant portion of the propellant tank, decreasing the tank volume available for propellant. Ullage pressurization of spacecraft propellant tanks is required to prevent boil-off of cryogenic propellants and to provide a positive pressure for propellant extraction. To achieve this, ullage gas diffusers must slow hot, high-pressure gas entering a propellant tank from supersonic speeds to only a few meters per second. Decreasing the incoming gas velocity is typically accomplished through expansion to larger areas within the diffuser which has traditionally led to large diffuser lengths. The Fluid Dynamics Branch (ER42) developed and applied advanced Computational Fluid Dynamics (CFD) analysis methods in order to mature the LPD design from and initial concept to an optimized test prototype and to provide extremely accurate pre-test predictions of diffuser performance. Additionally, the diffuser concept for the Core Stage of the Space Launch System (SLS) was analyzed in a short amount of time to guide test data collection efforts of the qualification of the device. CFD analysis of the SLS diffuser design provided new insights into the functioning of the device and was qualitatively validated against hot wire anemometry of the exterior flow field. Rigorous data analysis of the measurements was performed on static and dynamic pressure data, data from two microphones, accelerometers and hot wire anemometry with automated traverse. Feasibility of the LPD concept and validation of the computational model were demonstrated by the test data.

Three distinct modes in a surface micro-discharge in atmospheric pressure He + N{sub 2} mixtures

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

Li, Dong; Liu, Dingxin, E-mail: liudingxin@mail.xjtu.edu.cn; He, Tongtong

2015-12-15

A surface micro-discharge in atmospheric pressure He + N{sub 2} mixtures is studied in this paper with an emphasis on the discharge modes. With the N{sub 2} admixture increasing from 0.1% to 20%, the discharge evolves from a spatially diffuse mode to a filamentary mode during positive half-cycles of the applied voltage. However during the negative half-cycles, an additional patterned mode emerges between the diffuse and the filamentary modes, which has not been reported before to exist in surface micro-discharges. In the diffuse and patterned modes, the plasmas cover almost the entirety of the mesh area during one cycle after plasma ignitionmore » in all mesh elements, and the discharge power increases linearly with the applied voltage. In contrast, plasma coverage of the mesh area is only partial in the filamentary mode and the plasma is more unstable with the discharge power increasing exponentially with the applied voltage. As the surface micro-discharge evolves through the three modes, the density of excited species changes significantly, for instance, the density of N{sub 2}{sup +}(B) drops by ∼20-fold from [N{sub 2}] = 0.2% to 20%. The N{sub 2}{sup +}(B) is predicted to be generated mainly through successive processes of Penning ionization by helium metastables and electron-impact excitation of N{sub 2}{sup +}(X), the latter is most responsible for the density decrease of N{sub 2}{sup +}(B) because much more N{sub 2}{sup +}(X) is converted to N{sub 4}{sup +}(X) as the increase of N{sub 2} fraction. Also, the electron density and electron temperature decrease with the discharge mode transition.« less

Diffusion, Viscosity and Crystal Growth in Microgravity

NASA Technical Reports Server (NTRS)

Myerson, Allan S.

1996-01-01

The diffusivity of TriGlycine Sulfate (TGS), Potassium Dihydrogen Phosphate (KDP), Ammonium Dihydrogen Phosphate (ADF) and other compounds of interest to microgravity crystal growth, in supersaturated solutions as a function of solution concentration, 'age' and 'history was studied experimentally. The factors that affect the growth of crystals from water solutions in microgravity have been examined. Three non-linear optical materials have been studied, potassium dihydrogen phosphate (KDP), ammonium dihydrogen phosphate (ADP) and triglycine sulfate (TGC). The diffusion coefficient and viscosity of supersaturated water solutions were measured. Also theoretical model of diffusivity and viscosity in a metastable state, model of crystal growth from solution including non-linear time dependent diffusivity and viscosity effect and computer simulation of the crystal growth process which allows simulation of the microgravity crystal growth were developed.

An experimental investigation of two large annular diffusers with swirling and distorted inflow

NASA Technical Reports Server (NTRS)

Eckert, W. T.; Johnston, J. P.; Simons, T. D.; Mort, K. W.; Page, V. R.

1980-01-01

Two annular diffusers downstream of a nacelle-mounted fan were tested for aerodynamic performance, measured in terms of two static pressure recovery parameters (one near the diffuser exit plane and one about three diameters downstream in the settling duct) in the presence of several inflow conditions. The two diffusers each had an inlet diameter of 1.84 m, an area ratio of 2.3, and an equivalent cone angle of 11.5, but were distinguished by centerbodies of different lengths. The dependence of diffuser performance on various combinations of swirling, radially distorted, and/or azimuthally distorted inflow was examined. Swirling flow and distortions in the axial velocity profile in the annulus upstream of the diffuser inlet were caused by the intrinsic flow patterns downstream of a fan in a duct and by artificial intensification of the distortions. Azimuthal distortions or defects were generated by the addition of four artificial devices (screens and fences). Pressure recovery data indicated beneficial effects of both radial distortion (for a limited range of distortion levels) and inflow swirl. Small amounts of azimuthal distortion created by the artificial devices produced only small effects on diffuser performance. A large artificial distortion device was required to produce enough azimuthal flow distortion to significantly degrade the diffuser static pressure recovery.

Measurement of CO2 diffusivity for carbon sequestration: a microfluidic approach for reservoir-specific analysis.

PubMed

Sell, Andrew; Fadaei, Hossein; Kim, Myeongsub; Sinton, David

2013-01-02

Predicting carbon dioxide (CO(2)) security and capacity in sequestration requires knowledge of CO(2) diffusion into reservoir fluids. In this paper we demonstrate a microfluidic based approach to measuring the mutual diffusion coefficient of carbon dioxide in water and brine. The approach enables formation of fresh CO(2)-liquid interfaces; the resulting diffusion is quantified by imaging fluorescence quenching of a pH-dependent dye, and subsequent analyses. This method was applied to study the effects of site-specific variables--CO(2) pressure and salinity levels--on the diffusion coefficient. In contrast to established, macro-scale pressure-volume-temperature cell methods that require large sample volumes and testing periods of hours/days, this approach requires only microliters of sample, provides results within minutes, and isolates diffusive mass transport from convective effects. The measured diffusion coefficient of CO(2) in water was constant (1.86 [± 0.26] × 10(-9) m(2)/s) over the range of pressures (5-50 bar) tested at 26 °C, in agreement with existing models. The effects of salinity were measured with solutions of 0-5 M NaCl, where the diffusion coefficient varied up to 3 times. These experimental data support existing theory and demonstrate the applicability of this method for reservoir-specific testing.

Experimental Study on Properties of Methane Diffusion of Coal Block under Triaxial Compressive Stress

PubMed Central

Zhao, Hong-Bao

2014-01-01

Taking the standard size coal block samples defined by ISRM as research objects, both properties of methane diffusion of coal block under triaxial compressive stress and characteristic influences caused by methane pressure were systematically studied with thermo-fluid-solid coupling with triaxial servocontrolled seepage equipment of methane-containing coal. The result shows the methane diffusion property of coal block under triaxial compressive stress was shown in four-stage as follow, first is sharply reduce stage, second is hyperbolic reduce stage, third is close to a fixed value stage, fourth stage is 0. There is a special point making the reduced rate of characteristic curve of methane diffusion speed become sharply small; the influences of shape of methane diffusion speed characteristic curve caused by methane pressure are not obvious, which only is shown in numerical size of methane diffusion speed. Test time was extended required by appear of the special point makes the reduce rate of methane diffusion speed become sharply small. The fitting four-phase relation of methane diffusion of coal block under triaxial compressive stress was obtained, and the idea is proposed that influences of the fitting four-phase relation caused by methane pressure were only shown in value of fitting parameters. PMID:25531000

Polymeric hydrogen diffusion barrier, high-pressure storage tank so equipped, method of fabricating a storage tank and method of preventing hydrogen diffusion

DOEpatents

Lessing, Paul A [Idaho Falls, ID

2008-07-22

An electrochemically active hydrogen diffusion barrier which comprises an anode layer, a cathode layer, and an intermediate electrolyte layer, which is conductive to protons and substantially impermeable to hydrogen. A catalytic metal present in or adjacent to the anode layer catalyzes an electrochemical reaction that converts any hydrogen that diffuses through the electrolyte layer to protons and electrons. The protons and electrons are transported to the cathode layer and reacted to form hydrogen. The hydrogen diffusion barrier is applied to a polymeric substrate used in a storage tank to store hydrogen under high pressure. A storage tank equipped with the electrochemically active hydrogen diffusion barrier, a method of fabricating the storage tank, and a method of preventing hydrogen from diffusing out of a storage tank are also disclosed.

Polymeric hydrogen diffusion barrier, high-pressure storage tank so equipped, method of fabricating a storage tank and method of preventing hydrogen diffusion

DOEpatents

Lessing, Paul A.

2004-09-07

An electrochemically active hydrogen diffusion barrier which comprises an anode layer, a cathode layer, and an intermediate electrolyte layer, which is conductive to protons and substantially impermeable to hydrogen. A catalytic metal present in or adjacent to the anode layer catalyzes an electrochemical reaction that converts any hydrogen that diffuses through the electrolyte layer to protons and electrons. The protons and electrons are transported to the cathode layer and reacted to form hydrogen. The hydrogen diffusion barrier is applied to a polymeric substrate used in a storage tank to store hydrogen under high pressure. A storage tank equipped with the electrochemically active hydrogen diffusion barrier, a method of fabricating the storage tank, and a method of preventing hydrogen from diffusing out of a storage tank are also disclosed.

Coupled nonequilibrium flow, energy and radiation transport for hypersonic planetary entry

NASA Astrophysics Data System (ADS)

Frederick, Donald Jerome

An ever increasing demand for energy coupled with a need to mitigate climate change necessitates technology (and lifestyle) changes globally. An aspect of the needed change is a decrease in the amount of anthropogenically generated CO2 emitted to the atmosphere. The decrease needed cannot be expected to be achieved through only one source of change or technology, but rather a portfolio of solutions are needed. One possible technology is Carbon Capture and Storage (CCS), which is likely to play some role due to its combination of mature and promising emerging technologies, such as the burning of hydrogen in gas turbines created by pre-combustion CCS separation processes. Thus research on effective methods of burning turbulent hydrogen jet flames (mimicking gas turbine environments) are needed, both in terms of experimental investigation and model development. The challenge in burning (and modeling the burning of) hydrogen lies in its wide range of flammable conditions, its high diffusivity (often requiring a diluent such as nitrogen to produce a lifted turbulent jet flame), and its behavior under a wide range of pressures. In this work, numerical models are used to simulate the environment of a gas turbine combustion chamber. Concurrent experimental investigations are separately conducted using a vitiated coflow burner (which mimics the gas turbine environment) to guide the numerical work in this dissertation. A variety of models are used to simulate, and occasionally guide, the experiment. On the fundamental side, mixing and chemistry interactions motivated by a H2/N2 jet flame in a vitiated coflow are investigated using a 1-D numerical model for laminar flows and the Linear Eddy Model for turbulent flows. A radial profile of the jet in coflow can be modeled as fuel and oxidizer separated by an initial mixing width. The effects of species diffusion model, pressure, coflow composition, and turbulent mixing on the predicted autoignition delay times and mixture composition at ignition are considered. We find that in laminar simulations the differential diffusion model allows the mixture to autoignite sooner and at a fuel-richer mixture than the equal diffusion model. The effect of turbulence on autoignition is classified in two regimes, which are dependent on a reference laminar autoignition delay and turbulence time scale. For a turbulence timescale larger than the reference laminar autoignition time, turbulence has little influence on autoignition or the mixture at ignition. However, for a turbulence timescale smaller than the reference laminar timescale, the influence of turbulence on autoignition depends on the diffusion model. Differential diffusion simulations show an increase in autoignition delay time and a subsequent change in mixture composition at ignition with increasing turbulence. Equal diffusion simulations suggest the effect of increasing turbulence on autoignition delay time and the mixture fraction at ignition is minimal. More practically, the stabilizing mechanism of a lifted jet flame is thought to be controlled by either autoignition, flame propagation, or a combination of the two. Experimental data for a turbulent hydrogen diluted with nitrogen jet flame in a vitiated coflow at atmospheric pressure, demonstrates distinct stability regimes where the jet flame is either attached, lifted, lifted-unsteady, or blown out. A 1-D parabolic RANS model is used, where turbulence-chemistry interactions are modeled with the joint scalar-PDF approach, and mixing is modeled with the Linear Eddy Model. The model only accounts for autoignition as a flame stabilization mechanism. However, by comparing the local turbulent flame speed to the local turbulent mean velocity, maps of regions where the flame speed is greater than the flow speed are created, which allow an estimate of lift-off heights based on flame propagation. Model results for the attached, lifted, and lifted-unsteady regimes show that the correct trend is captured. Additionally, at lower coflow equivalence ratios flame propagation appears dominant, while at higher coflow equivalence ratios autoignition appears dominant.

Expanding the calculation of activation volumes: Self-diffusion in liquid water

NASA Astrophysics Data System (ADS)

Piskulich, Zeke A.; Mesele, Oluwaseun O.; Thompson, Ward H.

2018-04-01

A general method for calculating the dependence of dynamical time scales on macroscopic thermodynamic variables from a single set of simulations is presented. The approach is applied to the pressure dependence of the self-diffusion coefficient of liquid water as a particularly useful illustration. It is shown how the activation volume associated with diffusion can be obtained directly from simulations at a single pressure, avoiding approximations that are typically invoked.

Diffusive Gas Loss from Silica Glass Ampoules at Elevated Temperatures

NASA Technical Reports Server (NTRS)

Palosz, W.

1998-01-01

Changes in the pressure of hydrogen, helium and neon due to diffusion through the wall of silica crystal growth ampoules at elevated temperatures were determined experimentally. We show that, while both He- and Ne-losses closely follow conventional model of diffusive gas permeation through the wall, hydrogen losses, in particular at low fill pressures, can be much larger. This is interpreted in terms of the high solubility of hydrogen in silica glasses.

High-pressure nuclear magnetic resonance studies of fuel cell membranes

NASA Astrophysics Data System (ADS)

Mananga, Eugene Stephane

This thesis focuses on the use of high pressure NMR to study transport properties in electrolyte membranes used for fuel cells. The main concern is in studying the self-diffusion coefficients of ions and molecules in membranes and solutions, which can be used to characterize electrolytes in fuel cells. For this purpose, a high-pressure fringe field NMR method to study transport properties in material systems useful for fuel cell and battery electrolytes, was designed, developed, and implemented. In this investigation, pressure is the thermodynamic variable to obtain additional information about the ionic transport process, which could yield the crucial parameter, activation volume. Most of the work involves proton NMR, with additional investigations of others nuclei, such as fluorine, phosphorus and lithium. Using the FFG method, two fuel cell membrane types (NAFION-117, SPTES), and different dilutions of phosphoric acid were investigated, as was LiTf salt in Diglyme solution, which is used as a lithium battery electrolyte. In addition to high-pressure NMR diffusion measurements carried out in the fringe field gradient for the investigation of SPTES, pulse field gradient spin echo NMR was also used to characterize the water diffusion, in addition to measuring diffusion rates as a function of temperature. This second method allows us to measure distinct diffusion coefficients in cases where the different nuclear (proton) environments can be resolved in the NMR spectrum. Polymer electrolyte systems, in which the mobility of both cations and anions is probed by NMR self-diffusion measurements using standard pulsed field gradient methods and static gradient measurements as a function of applied hydrostatic pressure, were also investigated. The material investigated is the low molecular weight liquid diglyme/LiCF3SO3 (LiTf) complexes which can be used as electrolytes in lithium batteries. Finally, high-pressure diffusion coefficient measurements of phosphoric acid in water at different concentrations: proton (1H) and phosphorus (31P) nuclei have been performed using the static field gradient spin-echo nuclear magnetic resonance. This study is expected to be helpful in improving the understanding of phosphoric acid fuel cell technology.

Vacancies in MgO at ultrahigh pressure: About mantle rheology of super-Earths

NASA Astrophysics Data System (ADS)

Ritterbex, Sebastian; Harada, Takafumi; Tsuchiya, Taku

2018-05-01

First-principles calculations are performed to investigate vacancy formation and migration in the B2 phase of MgO. Defect energetics suggest the importance of intrinsic non-interacting vacancy pairs, even though the extrinsic vacancy concentration might govern atomic diffusion in the B2 phase of MgO. The enthalpies of ionic vacancy migration are generally found to decrease across the B1-B2 phase transition around a pressure of 500 GPa. It is shown that this enthalpy change induces a substantial increase in the rate of vacancy diffusion in MgO of almost four orders of magnitude (∼104) when the B1 phase transforms into the B2 phase with increasing pressure. If plastic deformation is controlled by vacancy diffusion, mantle viscosity is expected to decrease in relation to this enhanced diffusion rate in MgO across the B1-B2 transition in the interior of Earth-like large exoplanets. Our results of atomic relaxations near the defects suggest that diffusion controlled creep viscosity may generally decrease across high-pressure phase transitions with increasing coordination number. Plastic flow and resulting mantle convection in the interior of these super-Earths may be therefore less sluggish than previously thought.

Scaling Law for Cross-stream Diffusion in Microchannels under Combined Electroosmotic and Pressure Driven Flow.

PubMed

Song, Hongjun; Wang, Yi; Pant, Kapil

2013-01-01

This paper presents an analytical study of the cross-stream diffusion of an analyte in a rectangular microchannel under combined electroosmotic flow (EOF) and pressure driven flow to investigate the heterogeneous transport behavior and spatially-dependent diffusion scaling law. An analytical model capable of accurately describing 3D steady-state convection-diffusion in microchannels with arbitrary aspect ratios is developed based on the assumption of the thin Electric Double Layer (EDL). The model is verified against high-fidelity numerical simulation in terms of flow velocity and analyte concentration profiles with excellent agreement (<0.5% relative error). An extensive parametric analysis is then undertaken to interrogate the effect of the combined flow velocity field on the transport behavior in both the positive pressure gradient (PPG) and negative pressure gradient (NPG) cases. For the first time, the evolution from the spindle-shaped concentration profile in the PPG case, via the stripe-shaped profile (pure EOF), and finally to the butterfly-shaped profile in the PPG case is obtained using the analytical model along with a quantitative depiction of the spatially-dependent diffusion layer thickness and scaling law across a wide range of the parameter space.

Scaling Law for Cross-stream Diffusion in Microchannels under Combined Electroosmotic and Pressure Driven Flow

PubMed Central

Song, Hongjun; Wang, Yi; Pant, Kapil

2012-01-01

This paper presents an analytical study of the cross-stream diffusion of an analyte in a rectangular microchannel under combined electroosmotic flow (EOF) and pressure driven flow to investigate the heterogeneous transport behavior and spatially-dependent diffusion scaling law. An analytical model capable of accurately describing 3D steady-state convection-diffusion in microchannels with arbitrary aspect ratios is developed based on the assumption of the thin Electric Double Layer (EDL). The model is verified against high-fidelity numerical simulation in terms of flow velocity and analyte concentration profiles with excellent agreement (<0.5% relative error). An extensive parametric analysis is then undertaken to interrogate the effect of the combined flow velocity field on the transport behavior in both the positive pressure gradient (PPG) and negative pressure gradient (NPG) cases. For the first time, the evolution from the spindle-shaped concentration profile in the PPG case, via the stripe-shaped profile (pure EOF), and finally to the butterfly-shaped profile in the PPG case is obtained using the analytical model along with a quantitative depiction of the spatially-dependent diffusion layer thickness and scaling law across a wide range of the parameter space. PMID:23554584

Effect of inducer inlet and diffuser throat areas on performance of a low pressure ratio sweptback centrifugal compressor

NASA Technical Reports Server (NTRS)

Klassen, H. A.

1975-01-01

A low-pressure-ratio centrifugal compressor was tested with nine combinations of three diffuser throat areas and three impeller inducer inlet areas which were 75, 100, and 125 percent of design values. For a given inducer inlet area, increases in diffuser area within the range investigated resulted in increased mass flow and higher peak efficiency. Changes in both diffuser and inducer areas indicated that efficiencies within one point of the maximum efficiency were obtained over a compressor specific speed range of 27 percent. The performance was analyzed of an assumed two-spool open-cycle engine using the 75 percent area inducer with a variable area diffuser.

Dynamic Distortion in a Short S-Shaped Subsonic Diffuser with Flow Separation. [Lewis 8 by 6 foot Supersonic Wind Tunnel

NASA Technical Reports Server (NTRS)

Stumpf, R.; Neumann, H. E.; Giamati, C. C.

1983-01-01

An experimental investigation of the time varying distortion at the diffuser exit of a subscale HiMAT forebody and inlet was conducted at Mach 0.9 in the Lewis 8 by 6 foot Supersonic Wind Tunnel. A transitory separation was detected within the subsonic diffuser. Vortex generators were installed to eliminate the flow separation. Results from a study of the instantaneous pressure variations at the diffuser exit are presented. The time unsteady total pressures at the diffuser exit are computer interpolated and presented in the form of a movie showing the transitory separation. Limited data showing the instantaneous distortion levels is also presented.

Influence of Wind Pressure on the Carbonation of Concrete

PubMed Central

Zou, Dujian; Liu, Tiejun; Du, Chengcheng; Teng, Jun

2015-01-01

Carbonation is one of the major deteriorations that accelerate steel corrosion in reinforced concrete structures. Many mathematical/numerical models of the carbonation process, primarily diffusion-reaction models, have been established to predict the carbonation depth. However, the mass transfer of carbon dioxide in porous concrete includes molecular diffusion and convection mass transfer. In particular, the convection mass transfer induced by pressure difference is called penetration mass transfer. This paper presents the influence of penetration mass transfer on the carbonation. A penetration-reaction carbonation model was constructed and validated by accelerated test results under high pressure. Then the characteristics of wind pressure on the carbonation were investigated through finite element analysis considering steady and fluctuating wind flows. The results indicate that the wind pressure on the surface of concrete buildings results in deeper carbonation depth than that just considering the diffusion of carbon dioxide. In addition, the influence of wind pressure on carbonation tends to increase significantly with carbonation depth. PMID:28793462

Influence of Wind Pressure on the Carbonation of Concrete.

PubMed

Zou, Dujian; Liu, Tiejun; Du, Chengcheng; Teng, Jun

2015-07-24

Carbonation is one of the major deteriorations that accelerate steel corrosion in reinforced concrete structures. Many mathematical/numerical models of the carbonation process, primarily diffusion-reaction models, have been established to predict the carbonation depth. However, the mass transfer of carbon dioxide in porous concrete includes molecular diffusion and convection mass transfer. In particular, the convection mass transfer induced by pressure difference is called penetration mass transfer. This paper presents the influence of penetration mass transfer on the carbonation. A penetration-reaction carbonation model was constructed and validated by accelerated test results under high pressure. Then the characteristics of wind pressure on the carbonation were investigated through finite element analysis considering steady and fluctuating wind flows. The results indicate that the wind pressure on the surface of concrete buildings results in deeper carbonation depth than that just considering the diffusion of carbon dioxide. In addition, the influence of wind pressure on carbonation tends to increase significantly with carbonation depth.

Effect of temperature and pressure on the dynamics of nanoconfined propane

NASA Astrophysics Data System (ADS)

Gautam, Siddharth; Liu, Tingting; Rother, Gernot; Jalarvo, Niina; Mamontov, Eugene; Welch, Susan; Cole, David

2014-04-01

We report the effect of temperature and pressure on the dynamical properties of propane confined in nanoporous silica aerogel studied using quasielastic neutron scattering (QENS). Our results demonstrate that the effect of a change in the pressure dominates over the effect of temperature variation on the dynamics of propane nano-confined in silica aerogel. At low pressures, most of the propane molecules are strongly bound to the pore walls, only a small fraction is mobile. As the pressure is increased, the fraction of mobile molecules increases. A change in the mechanism of motion, from continuous diffusion at low pressures to jump diffusion at higher pressures has also been observed.

Interpreting the sub-linear Kennicutt-Schmidt relationship: the case for diffuse molecular gas

NASA Astrophysics Data System (ADS)

Shetty, Rahul; Clark, Paul C.; Klessen, Ralf S.

2014-08-01

Recent statistical analysis of two extragalactic observational surveys strongly indicate a sub-linear Kennicutt-Schmidt (KS) relationship between the star formation rate (ΣSFR) and molecular gas surface density (Σmol). Here, we consider the consequences of these results in the context of common assumptions, as well as observational support for a linear relationship between ΣSFR and the surface density of dense gas. If the CO traced gas depletion time (τ_dep^CO) is constant, and if CO only traces star-forming giant molecular clouds (GMCs), then the physical properties of each GMC must vary, such as the volume densities or star formation rates. Another possibility is that the conversion between CO luminosity and Σmol, the XCO factor, differs from cloud-to-cloud. A more straightforward explanation is that CO permeates the hierarchical interstellar medium, including the filaments and lower density regions within which GMCs are embedded. A number of independent observational results support this description, with the diffuse gas comprising at least 30 per cent of the total molecular content. The CO bright diffuse gas can explain the sub-linear KS relationship, and consequently leads to an increasing τ_dep^CO with Σmol. If ΣSFR linearly correlates with the dense gas surface density, a sub-linear KS relationship indicates that the fraction of diffuse gas fdiff grows with Σmol. In galaxies where Σmol falls towards the outer disc, this description suggests that fdiff also decreases radially.

Comparison of Rocket Performance using Exhaust Diffuser and Conventional Techniques for Altitude Simulation

NASA Technical Reports Server (NTRS)

Sivo, Joseph N.; Peters, Daniel J.

1959-01-01

A rocket engine with an exhaust-nozzle area ratio of 25 was operated at a constant chamber pressure of 600 pounds per square inch absolute over a range of oxidant-fuel ratios at an altitude pressure corresponding to approximately 47,000 feet. At this condition, the nozzle flow is slightly underexpanded as it leaves the nozzle. The altitude simulation was obtained first through the use of an exhaust diffuser coupled with the rocket engine and secondly, in an altitude test chamber where separate exhauster equipment provided the altitude pressure. A comparison of performance data from these two tests has established that a diffuser used with a rocket engine operating at near-design nozzle pressure ratio can be a valid means of obtaining altitude performance data for rocket engines.

Effects of Diffusion Time on Short-Range Hyperpolarized 3He Diffusivity Measurements in Emphysema

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

Gierada, David S.; Woods, Jason C.; Bierhals, Andrew J.

2009-09-28

Purpose: To characterize the effect of diffusion time on short-range hyperpolarized 3He MR diffusion measurements across a wide range of emphysema severity. Materials and Methods: 3He diffusion MR imaging was performed on 19 lungs or lobes resected from 18 subjects with varying degrees of emphysema using 3 diffusion times (1.6 msec, 5 msec, and 10 msec) at constant b value. Emphysema severity was quantified as the mean apparent diffusion coefficient (ADC) and as the percentage of pixels with ADC higher than multiple thresholds from 0.30-0.55 cm2/sec (ADC index). Quantitative histology (mean linear intercept) was obtained in 10 of the lungmore » specimens from 10 of the subjects. Results: The mean ADCs with diffusion times of 1.6, 5.0, and 10.0 msec were 0.46, 0.40, and 0.37 cm2/sec, respectively (P <0.0001, ANOVA). There was no relationship between the ADC magnitude and the effect of diffusion time on ADC values. Mean linear intercept correlated with ADC (r=0.91-0.94, P<0.001) and ADC index (r=0.78-0.92, P<0.01) at all diffusion times.« less

Correction of Altitude-Induced Changes in Performance of the Volumetric Diffusive Respirator

DTIC Science & Technology

2017-04-05

to a plateau pressure. The positive pressure delivery of each percussive pulse is followed by a passive fall in pressure as the spring moves the ...AFRL-SA-WP-SR-2017-0007 Correction of Altitude- Induced Changes in Performance of the Volumetric Diffusive Respirator Thomas...Blakeman, MSc RRT April 2017 Air Force Research Laboratory 711th Human Performance Wing U.S. Air Force School of Aerospace

A novel formulation for unsteady counterflow flames using a thermal-conductivity-weighted coordinate

NASA Astrophysics Data System (ADS)

Weiss, Adam D.; Vera, Marcos; Liñán, Amable; Sánchez, Antonio L.; Williams, Forman A.

2018-01-01

A general formulation is given for the description of reacting mixing layers in stagnation-type flows subject to both time-varying strain and pressure. The salient feature of the formulation is the introduction of a thermal-conductivity-weighted transverse coordinate that leads to a compact transport operator that facilitates numerical integration and theoretical analysis. For steady counterflow mixing layers, the associated transverse mass flux is shown to be effectively linear in terms of the new coordinate, so that the conservation equations for energy and chemical species uncouple from the mass and momentum conservation equations, thereby greatly simplifying the solution. Comparisons are shown with computations of diffusion flames with infinitely fast reaction using both the classic Howarth-Dorodnitzyn density-weighted coordinate and the new thermal-conductivity-weighted coordinate, illustrating the advantages of the latter. Also, as an illustrative application of the formulation to the computation of unsteady counterflows, the flame response to harmonically varying strain is examined in the linear limit.

Quantum State Diffusion

NASA Astrophysics Data System (ADS)

Percival, Ian

2005-10-01

1. Introduction; 2. Brownian motion and Itô calculus; 3. Open quantum systems; 4. Quantum state diffusion; 5. Localisation; 6. Numerical methods and examples; 7. Quantum foundations; 8. Primary state diffusion; 9. Classical dynamics of quantum localisation; 10. Semiclassical theory and linear dynamics.

Self-diffusion of polycrystalline ice Ih under confining pressure: Hydrogen isotope analysis using 2-D Raman imaging

NASA Astrophysics Data System (ADS)

Noguchi, Naoki; Kubo, Tomoaki; Durham, William B.; Kagi, Hiroyuki; Shimizu, Ichiko

2016-08-01

We have developed a high-resolution technique based on micro Raman spectroscopy to measure hydrogen isotope diffusion profiles in ice Ih. The calibration curve for quantitative analysis of deuterium in ice Ih was constructed using micro Raman spectroscopy. Diffusion experiments using diffusion couples composed of dense polycrystalline H2O and D2O ice were carried out under a gas confining pressure of 100 MPa (to suppress micro-fracturing and pore formation) at temperatures from 235 K to 245 K and diffusion times from 0.2 to 94 hours. Two-dimensional deuterium profiles across the diffusion couples were determined by Raman imaging. The location of small spots of frost from room air could be detected from the shapes of the Raman bands of OH and OD stretching modes, which change because of the effect of the molar ratio of deuterium on the molecular coupling interaction. We emphasize the validity for screening the impurities utilizing the coupling interaction. Some recrystallization and grain boundary migration occurred in recovered diffusion couples, but analysis of two-dimensional diffusion profiles of regions not affected by grain boundary migration allowed us to measure a volume diffusivity for ice at 100 MPa of (2.8 ± 0.4) ×10-3exp[ -57.0 ± 15.4kJ /mol RT ] m2 /s (R is the gas constant, T is temperature). Based on ambient pressure diffusivity measurements by others, this value indicates a high (negative) activation volume for volume diffusivity of -29.5 cm3/mol or more. We can also constrain the value of grain boundary diffusivity in ice at 100 MPa to be <104 that of volume diffusivity.

Rotating diffuser for pressure recovery in a steam cooling circuit of a gas turbine

DOEpatents

Eldrid, Sacheverel Q.; Salamah, Samir A.; DeStefano, Thomas Daniel

2002-01-01

The buckets of a gas turbine are steam-cooled via a bore tube assembly having concentric supply and spent cooling steam return passages rotating with the rotor. A diffuser is provided in the return passage to reduce the pressure drop. In a combined cycle system, the spent return cooling steam with reduced pressure drop is combined with reheat steam from a heat recovery steam generator for flow to the intermediate pressure turbine. The exhaust steam from the high pressure turbine of the combined cycle unit supplies cooling steam to the supply conduit of the gas turbine.

Axial diffusivity of the corona radiata correlated with ventricular size in adult hydrocephalus.

PubMed

Cauley, Keith A; Cataltepe, Oguz

2014-07-01

Hydrocephalus causes changes in the diffusion-tensor properties of periventricular white matter. Understanding the nature of these changes may aid in the diagnosis and treatment planning of this relatively common neurologic condition. Because ventricular size is a common measure of the severity of hydrocephalus, we hypothesized that a quantitative correlation could be made between the ventricular size and diffusion-tensor changes in the periventricular corona radiata. In this article, we investigated this relationship in adult patients with hydrocephalus and in healthy adult subjects. Diffusion-tensor imaging metrics of the corona radiata were correlated with ventricular size in 14 adult patients with acute hydrocephalus, 16 patients with long-standing hydrocephalus, and 48 consecutive healthy adult subjects. Regression analysis was performed to investigate the relationship between ventricular size and the diffusion-tensor metrics of the corona radiata. Subject age was analyzed as a covariable. There is a linear correlation between fractional anisotropy of the corona radiata and ventricular size in acute hydrocephalus (r = 0.784, p < 0.001), with positive correlation with axial diffusivity (r = 0.636, p = 0.014) and negative correlation with radial diffusivity (r = 0.668, p = 0.009). In healthy subjects, axial diffusion in the periventricular corona radiata is more strongly correlated with ventricular size than with patient age (r = 0.466, p < 0.001, compared with r = 0.058, p = 0.269). Axial diffusivity of the corona radiata is linearly correlated with ventricular size in healthy adults and in patients with hydrocephalus. Radial diffusivity of the corona radiata decreases linearly with ventricular size in acute hydrocephalus but is not significantly correlated with ventricular size in healthy subjects or in patients with long-standing hydrocephalus.

Effects of convergent diffusion and charge transfer kinetics on the diffusion layer thickness of spherical micro- and nanoelectrodes.

PubMed

Molina, A; Laborda, E; González, J; Compton, R G

2013-05-21

Nuances of the linear diffusion layer approximation are examined for slow charge transfer reactions at (hemi)spherical micro- and nanoelectrodes. This approximation is widely employed in Electrochemistry to evaluate the extent of electrolyte solution perturbed by the electrode process, which is essential to the understanding of the effects arising from thin-layer diffusion, convergent diffusion, convection, coupled chemical reactions and the double layer. The concept was well established for fast charge transfer processes at macroelectrodes, but remains unclear under other conditions such that a thorough assessment of its meaning was necessary. In a previous publication [A. Molina, J. González, E. Laborda and R. G. Compton, Phys. Chem. Chem. Phys., 2013, 15, 2381-2388] we shed some light on the influence of the reversibility degree. In the present work, the meaning of the diffusion layer thickness is investigated when very small electrodes are employed and so the contribution of convergent diffusion to the mass transport is very important. An analytical expression is given to calculate the linear diffusion layer thickness at (hemi)spherical electrodes and its behaviour is studied for a wide range of conditions of reversibility (from reversible to fully-irreversible processes) and electrode size (from macro- to nano-electrodes). Rigorous analytical solutions are deduced for true concentration profiles, surface concentrations, linear diffusion layer thickness and current densities when a potential pulse is applied at (hemi)spherical electrodes. The expressions for the magnitudes mentioned above are valid for electrodes of any size (including (hemi)spherical nanoelectrodes) and for any degree of reversibility, provided that mass transport occurs exclusively via diffusion. The variation of the above with the electrode size, applied potential and charge transfer kinetics is studied.

A probabilistic assessment of waste water injection induced seismicity in central California

NASA Astrophysics Data System (ADS)

Goebel, T.; Hauksson, E.; Ampuero, J. P.; Aminzadeh, F.; Cappa, F.; Saleeby, J.

2014-12-01

The recent, large increase in seismic activity within the central and eastern U.S. may be connected to an increase in fluid injection activity since ~2001. Anomalous seismic sequences can easily be identified in regions with low background seismicity rates. Here, we analyze seismicity in plate boundary regions where tectonically-driven earthquake sequences are common, potentially masking injection-induced events. We show results from a comprehensive analysis of waste water disposal wells in Kern county, the largest oil-producing county in California. We focus on spatial-temporal correlations between seismic and injection activity and seismicity-density changes due to injection. We perform a probabilistic assessment of induced vs. tectonic earthquakes, which can be applied to different regions independent of background rates and may provide insights into the probability of inducing earthquakes as a function of injection parameters and local geological conditions. Our results show that most earthquakes are caused by tectonic forcing, however, waste water injection contributes to seismic activity in four different regions with several events above M4. The seismicity shows different migration characteristics relative to the injection sites, including linear and non-linear trends. The latter is indicative of diffusive processes which take advantage of reservoir properties and fault structures and can induce earthquakes at distances of up to 10 km. Our results suggest that injection-related triggering processes are complex, possibly involving creep, and delayed triggering. Pore-pressure diffusion may be more extensive in the presence of active faults and high-permeability damage zones thus altering the local seismic hazard in a non-linear fashion. As a consequence, generic "best-practices" for fluid injections like a maximum distance from the nearest active fault may not be sufficient to mitigate a potential seismic hazard increase.

Validation of drift and diffusion coefficients from experimental data

NASA Astrophysics Data System (ADS)

Riera, R.; Anteneodo, C.

2010-04-01

Many fluctuation phenomena, in physics and other fields, can be modeled by Fokker-Planck or stochastic differential equations whose coefficients, associated with drift and diffusion components, may be estimated directly from the observed time series. Its correct characterization is crucial to determine the system quantifiers. However, due to the finite sampling rates of real data, the empirical estimates may significantly differ from their true functional forms. In the literature, low-order corrections, or even no corrections, have been applied to the finite-time estimates. A frequent outcome consists of linear drift and quadratic diffusion coefficients. For this case, exact corrections have been recently found, from Itô-Taylor expansions. Nevertheless, model validation constitutes a necessary step before determining and applying the appropriate corrections. Here, we exploit the consequences of the exact theoretical results obtained for the linear-quadratic model. In particular, we discuss whether the observed finite-time estimates are actually a manifestation of that model. The relevance of this analysis is put into evidence by its application to two contrasting real data examples in which finite-time linear drift and quadratic diffusion coefficients are observed. In one case the linear-quadratic model is readily rejected while in the other, although the model constitutes a very good approximation, low-order corrections are inappropriate. These examples give warning signs about the proper interpretation of finite-time analysis even in more general diffusion processes.

A coupled model between mechanical deformation and chemical diffusion: An explanation for the preservation of chemical zonation in plagioclase at high temperatures

NASA Astrophysics Data System (ADS)

Zhong, Xin; Vrijmoed, Johannes; Moulas, Evangelos; Tajcmanová, Lucie

2016-04-01

Compositional zoning in metamorphic minerals have been generally recognized as an important geological feature to decipher the metamorphic history of rocks. The observed chemical zoning of, e.g. garnet, is commonly interpreted as disequilibrium between the fractionated inner core and the surrounding matrix. However, chemically zoned minerals were also observed in high grade rocks (T>800 degree C) where the duration of metamorphic processes was independently dated to take several Ma. This implies that temperature may not be the only factor that controls diffusion timescales, and grain scale pressure variation was proposed to be a complementary factor that may significantly contribute to the formation and preservation of chemical zoning in high temperature metamorphic minerals [Tajcmanová 2013, 2015]. Here, a coupled model is developed to simulate viscous deformation and chemical diffusion. The numerical approach considers the conservation of mass, momentum, and a constitutive relation developed from equilibrium thermodynamics. A compressible viscoelastic rheology is applied, which associates the volumetric change triggered by deformation and diffusion to a change of pressure. The numerical model is applied to the chemically zoned plagioclase rim described by [Tajcmanová 2014]. The diffusion process operating during the plagioclase rim formation can lead to a development of a pressure gradient. Such a pressure gradient, if maintained during ongoing viscous relaxation, can lead to the preservation of the observed chemical zonation in minerals. An important dimensionless number, the Deborah number, is defined as the ratio between the Maxwell viscoelastic relaxation time and the characteristic diffusion time. It characterizes the relative influence between the maintenance of grain scale pressure variation and chemical diffusion. Two extreme regimes are shown: the mechanically-controlled regime (high Deborah number) and diffusion-controlled regime (low Deborah number). In the mechanically-controlled regime, the grain scale pressure variation and thus the chemical zonation can be maintained due to slow viscous relaxation. Furthermore, by utilizing experimental flow laws and diffusion coefficients, the Deborah number is estimated in a variety of physical conditions. References Tajcmanová, L., Y. Podladchikov, R. Powell, E. Moulas, J.C. Vrijmoed, and J.A.D. Connolly, 2014. Journal of Metamorphic Geology, 32(2):195-207. Tajcmanová, L., J.C. Vrijmoed, and E. Moulas, 2015. Lithos, 216-217:338-351.

Mass transfer equation for proteins in very high-pressure liquid chromatography.

PubMed

Gritti, Fabrice; Guiochon, Georges

2009-04-01

The mass transfer kinetics of human insulin was investigated on a 50 mm x 2.1 mm column packed with 1.7 microm BEH-C(18) particles, eluted with a water/acetonitrile/trifluoroacetic acid (TFA) (68/32/0.1, v/v/v) solution. The different contributions to the mass transfer kinetics, e.g., those of longitudinal diffusion, eddy dispersion, the film mass transfer resistance, cross-particle diffusivity, adsorption-desorption kinetics, and transcolumn differential sorption, were incorporated into a general mass transfer equation designed to account for the mass transfer kinetics of proteins under high pressure. More specifically, this equation includes the effects of pore size exclusion, pressure, and temperature on the band broadening of a protein. The flow rate was first increased from 0.001 to 0.250 mL/min, the pressure drop increasing from 2 to 298 bar, and the column being placed in stagnant air at 296.5 K, in order to determine the effective diffusivity of insulin through the porous particles, the mass transfer rate constants, and the adsorption equilibrium constant in the low-pressure range. Then, the column inlet pressure was increased by using capillary flow restrictors downstream the column, at the constant flow rate of 0.03 mL/min. The column temperature was kept uniform by immersing the column in a circulating water bath thermostatted at 298.7 and 323.15 K, successively. The results showed that the surface diffusion coefficient of insulin decreases faster than its bulk diffusion coefficient with increasing average column pressure. This is consistent with the adsorption energy of insulin onto the BEH-C(18) surface increasing strongly with increasing pressure. In contrast, given the precision of the height equivalent to a theoretical plate (HETP) measurement (+/-12%), the adsorption kinetics of insulin appears to be rather independent of the pressure. On average, the adsorption rate constant of insulin is doubled from about 40 to 80 s(-1) when the temperature increases from 298.7 to 323.15 K.

Ensemble Grouping Strategies for Embedded Stochastic Collocation Methods Applied to Anisotropic Diffusion Problems

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

D'Elia, M.; Edwards, H. C.; Hu, J.

Previous work has demonstrated that propagating groups of samples, called ensembles, together through forward simulations can dramatically reduce the aggregate cost of sampling-based uncertainty propagation methods [E. Phipps, M. D'Elia, H. C. Edwards, M. Hoemmen, J. Hu, and S. Rajamanickam, SIAM J. Sci. Comput., 39 (2017), pp. C162--C193]. However, critical to the success of this approach when applied to challenging problems of scientific interest is the grouping of samples into ensembles to minimize the total computational work. For example, the total number of linear solver iterations for ensemble systems may be strongly influenced by which samples form the ensemble whenmore » applying iterative linear solvers to parameterized and stochastic linear systems. In this paper we explore sample grouping strategies for local adaptive stochastic collocation methods applied to PDEs with uncertain input data, in particular canonical anisotropic diffusion problems where the diffusion coefficient is modeled by truncated Karhunen--Loève expansions. Finally, we demonstrate that a measure of the total anisotropy of the diffusion coefficient is a good surrogate for the number of linear solver iterations for each sample and therefore provides a simple and effective metric for grouping samples.« less

Ensemble Grouping Strategies for Embedded Stochastic Collocation Methods Applied to Anisotropic Diffusion Problems

DOE PAGES

D'Elia, M.; Edwards, H. C.; Hu, J.; ...

2018-01-18

Previous work has demonstrated that propagating groups of samples, called ensembles, together through forward simulations can dramatically reduce the aggregate cost of sampling-based uncertainty propagation methods [E. Phipps, M. D'Elia, H. C. Edwards, M. Hoemmen, J. Hu, and S. Rajamanickam, SIAM J. Sci. Comput., 39 (2017), pp. C162--C193]. However, critical to the success of this approach when applied to challenging problems of scientific interest is the grouping of samples into ensembles to minimize the total computational work. For example, the total number of linear solver iterations for ensemble systems may be strongly influenced by which samples form the ensemble whenmore » applying iterative linear solvers to parameterized and stochastic linear systems. In this paper we explore sample grouping strategies for local adaptive stochastic collocation methods applied to PDEs with uncertain input data, in particular canonical anisotropic diffusion problems where the diffusion coefficient is modeled by truncated Karhunen--Loève expansions. Finally, we demonstrate that a measure of the total anisotropy of the diffusion coefficient is a good surrogate for the number of linear solver iterations for each sample and therefore provides a simple and effective metric for grouping samples.« less

Effects of spin transition on diffusion of Fe2+ in ferropericlase in Earth's lower mantle

NASA Astrophysics Data System (ADS)

Saha, Saumitra; Bengtson, Amelia; Crispin, Katherine L.; van Orman, James A.; Morgan, Dane

2011-11-01

Knowledge of Fe composition in lower-mantle minerals (primarily perovskite and ferropericlase) is essential to a complete understanding of the Earth's interior. Fe cation diffusion potentially controls many aspects of the distribution of Fe in the Earth's lower mantle, including mixing of chemical heterogeneities, element partitioning, and the extent of core-mantle communications. Fe in ferropericlase has been shown to undergo a spin transition starting at about 40 GPa and exists in a mixture of high-spin and low-spin states over a wide range of pressures. Present experimental data on Fe transport in ferropericlase is limited to pressures below 35 GPa and provides little information on the pressure dependence of the activation volume and none on the impact of the spin transition on diffusion. Therefore, known experimental data on Fe diffusion cannot be reliably extrapolated to predict diffusion throughout the lower mantle. Here, first-principles and statistical modeling are combined to predict diffusion of Fe in ferropericlase over the entire lower mantle, including the effects of the Fe spin transition. A thorough statistical thermodynamic treatment is given to fully incorporate the coexistence of high- and low-spin Fe in the model of overall Fe diffusion in the lower mantle. Pure low-spin Fe diffuses approximately 104 times slower than high-spin Fe in ferropericlase but Fe diffusion of the mixed-spin state is only about 10 times slower than that of high-spin Fe. The predicted Fe diffusivities demonstrate that ferropericlase is unlikely to be rate limiting in transporting Fe in deep earth since much slower Fe diffusion in perovskite is predicted.

Uncertainty for calculating transport on Titan: A probabilistic description of bimolecular diffusion parameters

NASA Astrophysics Data System (ADS)

Plessis, S.; McDougall, D.; Mandt, K.; Greathouse, T.; Luspay-Kuti, A.

2015-11-01

Bimolecular diffusion coefficients are important parameters used by atmospheric models to calculate altitude profiles of minor constituents in an atmosphere. Unfortunately, laboratory measurements of these coefficients were never conducted at temperature conditions relevant to the atmosphere of Titan. Here we conduct a detailed uncertainty analysis of the bimolecular diffusion coefficient parameters as applied to Titan's upper atmosphere to provide a better understanding of the impact of uncertainty for this parameter on models. Because temperature and pressure conditions are much lower than the laboratory conditions in which bimolecular diffusion parameters were measured, we apply a Bayesian framework, a problem-agnostic framework, to determine parameter estimates and associated uncertainties. We solve the Bayesian calibration problem using the open-source QUESO library which also performs a propagation of uncertainties in the calibrated parameters to temperature and pressure conditions observed in Titan's upper atmosphere. Our results show that, after propagating uncertainty through the Massman model, the uncertainty in molecular diffusion is highly correlated to temperature and we observe no noticeable correlation with pressure. We propagate the calibrated molecular diffusion estimate and associated uncertainty to obtain an estimate with uncertainty due to bimolecular diffusion for the methane molar fraction as a function of altitude. Results show that the uncertainty in methane abundance due to molecular diffusion is in general small compared to eddy diffusion and the chemical kinetics description. However, methane abundance is most sensitive to uncertainty in molecular diffusion above 1200 km where the errors are nontrivial and could have important implications for scientific research based on diffusion models in this altitude range.

78 FR 64419 - Airworthiness Directives; Pratt & Whitney Turbofan Engines

Federal Register 2010, 2011, 2012, 2013, 2014

2013-10-29

... Turbofan Engines AGENCY: Federal Aviation Administration (FAA), DOT. ACTION: Notice of proposed rulemaking... turbofan engines. This proposed AD was prompted by a rupture of the diffuser-to-high-pressure turbine (HPT... turbofan engines. (d) Unsafe Condition This AD was prompted by a rupture of the diffuser-to-high- pressure...

FORMATION OF POLYCYCLIC AROMATIC HYDROCARBONS IN AN ATMOSPHERIC PRESSURE ETHYLENE DIFFUSION FLAME. (R825412)

EPA Science Inventory

Abstract

The microstructure of an atmospheric pressure, counterflow, sooting, flat, laminar ethylene diffusion flame has been studied experimentally by withdrawing samples from within the flame using a heated quartz microprobe coupled to an online gas chromatograph/mas...

Bayesian inference of radiation belt loss timescales.

NASA Astrophysics Data System (ADS)

Camporeale, E.; Chandorkar, M.

2017-12-01

Electron fluxes in the Earth's radiation belts are routinely studied using the classical quasi-linear radial diffusion model. Although this simplified linear equation has proven to be an indispensable tool in understanding the dynamics of the radiation belt, it requires specification of quantities such as the diffusion coefficient and electron loss timescales that are never directly measured. Researchers have so far assumed a-priori parameterisations for radiation belt quantities and derived the best fit using satellite data. The state of the art in this domain lacks a coherent formulation of this problem in a probabilistic framework. We present some recent progress that we have made in performing Bayesian inference of radial diffusion parameters. We achieve this by making extensive use of the theory connecting Gaussian Processes and linear partial differential equations, and performing Markov Chain Monte Carlo sampling of radial diffusion parameters. These results are important for understanding the role and the propagation of uncertainties in radiation belt simulations and, eventually, for providing a probabilistic forecast of energetic electron fluxes in a Space Weather context.

Deformations of a pre-stretched and lubricated finite elastic membrane driven by non-uniform external forcing

NASA Astrophysics Data System (ADS)

Boyko, Evgeniy; Gat, Amir; Bercovici, Moran

2017-11-01

We study viscous-elastic dynamics of a fluid confined between a rigid plate and a finite pre-stretched circular elastic membrane, pinned at its boundaries. The membrane is subjected to forces acting either directly on the membrane or through a pressure distribution in the fluid. Under the assumptions of strong pre-stretching and small deformations of the elastic sheet, and by applying the lubrication approximation for the flow, we derive the Green's function for the resulting linearized 4th order diffusion equation governing the deformation field in cylindrical coordinates. In addition, defining an asymptotic expansion with the ratio of the induced to prescribed tension serving as the small parameter, we reduce the coupled Reynolds and non-linear von-Karman equations to a set of three one-way coupled linear equations. The solutions to these equations provide insight onto the effects of induced tension, and enable simplified prediction of the correction for the deformation field. Funded by the European Research Council (ERC) under the European Union'sHorizon 2020 Research and Innovation Programme, Grant Agreement No. 678734 (MetamorphChip). E.B. is supported by the Adams Fellowship Program.

A locally conservative stabilized continuous Galerkin finite element method for two-phase flow in poroelastic subsurfaces

NASA Astrophysics Data System (ADS)

Deng, Q.; Ginting, V.; McCaskill, B.; Torsu, P.

2017-10-01

We study the application of a stabilized continuous Galerkin finite element method (CGFEM) in the simulation of multiphase flow in poroelastic subsurfaces. The system involves a nonlinear coupling between the fluid pressure, subsurface's deformation, and the fluid phase saturation, and as such, we represent this coupling through an iterative procedure. Spatial discretization of the poroelastic system employs the standard linear finite element in combination with a numerical diffusion term to maintain stability of the algebraic system. Furthermore, direct calculation of the normal velocities from pressure and deformation does not entail a locally conservative field. To alleviate this drawback, we propose an element based post-processing technique through which local conservation can be established. The performance of the method is validated through several examples illustrating the convergence of the method, the effectivity of the stabilization term, and the ability to achieve locally conservative normal velocities. Finally, the efficacy of the method is demonstrated through simulations of realistic multiphase flow in poroelastic subsurfaces.

Simulations of anti-parallel reconnection using a nonlocal heat flux closure

DOE PAGES

Ng, Jonathan; Hakim, Ammar; Bhattacharjee, A.; ...

2017-08-08

The integration of kinetic effects in fluid models is important for global simulations of the Earth's magnetosphere. In particular, it has been shown that ion kinetics play a crucial role in the dynamics of large reconnecting systems, and that higher-order fluid moment models can account for some of these effects. Here, we use a ten-moment model for electrons and ions, which includes the off diagonal elements of the pressure tensor that are important for magnetic reconnection. Kinetic effects are recovered by using a nonlocal heat flux closure, which approximates linear Landau damping in the fluid framework. Moreover, the closure ismore » tested using the island coalescence problem, which is sensitive to ion dynamics. We also demonstrate that the nonlocal closure is able to self-consistently reproduce the structure of the ion diffusion region, pressure tensor, and ion velocity without the need for fine-tuning of relaxation coefficients present in earlier models.« less

Diffusivity of hydrogen in iron-bearing olivine at 3 GPa

NASA Astrophysics Data System (ADS)

Demouchy, Sylvie; Thoraval, Catherine; Bolfan-Casanova, Nathalie; Manthilake, Geeth

2016-11-01

The kinetics of hydrogenation of dry iron-bearing olivine single crystals was determined by performing hydration experiments under hydrothermal conditions at high pressure. The experiments were performed in a multi-anvil press at 3 GPa, for a temperature range between 900 and 1200 °C and for various durations. The oxygen fugacity was buffered along Ni-NiO joint. Polarized Fourier transform infrared spectroscopy and recent empirical calibration were used to quantify the hydroxyl distributions in the samples along crystallographic axes after the experiments. The chemical diffusion coefficients are similar (barely slower) than in olivine hydrated at lower pressure (0.2 and 0.3 GPa) for the same diffusion mechanism. Under the given experimental conditions, the anisotropy of diffusion is the same as for proton-vacancy mechanism, with diffusion along the [0 0 1] axis faster than along the [1 0 0]. However, the anisotropy at 3 GPa is weaker compared to measurements at lower pressures and the analysis of concentration profiles using 3D models shows that an isotropic solution could also be relevant. Fits of the diffusion data to an Arrhenius law yield activation energies for the slightly faster [0 0 1] axis of the crystallographic axes around 198 ± 5 kJ mol-1, a value only slightly lower than the results from previous experimental studies for natural iron-bearing olivine hydrogenated at lower confining pressure. At 3 GPa, hydrogenation can be well approximated by a single mechanism controlled by coupled diffusion of protons and octahedral vacancies (di- and tri-valent ions). The diffusion rates are fast enough to alter hydrogen concentration within olivine in xenoliths ascending from the mantle or experiencing hydrogen-rich metasomatism events, but too slow to permit complete homogenization of hydrogen in olivine-rich rocks at kilometer scale in less than one My.

Self-diffusion of protons in H{sub 2}O ice VII at high pressures: Anomaly around 10 GPa

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

Noguchi, Naoki, E-mail: noguchi-n@okayama-u.ac.jp; Okuchi, Takuo

2016-06-21

The self-diffusion of ice VII in the pressure range of 5.5–17 GPa and temperature range of 400–425 K was studied using micro Raman spectroscopy and a diamond anvil cell. The diffusion was monitored by observing the distribution of isotope tracers: D{sub 2}O and H{sub 2}{sup 18}O. The diffusion coefficient of hydrogen reached a maximum value around 10 GPa. It was two orders of magnitude greater at 10 GPa than at 6 GPa. Hydrogen diffusion was much faster than oxygen diffusion, which indicates that protonic diffusion is the dominant mechanism for the diffusion of hydrogen in ice VII. This mechanism ismore » in remarkable contrast to the self-diffusion in ice I{sub h} that is dominated by an interstitial mechanism for the whole water molecule. An anomaly around 10 GPa in ice VII indicates that the rate-determining process for the proton diffusion changes from the diffusion of ionic defects to the diffusion of rotational defects, which was suggested by proton conductivity measurements and molecular dynamics simulations.« less

Deflation opening pressure of the eustachian tube.

PubMed

Cohen, D

1989-03-01

Measurements derived from tests of the performance of the eustachian tube (ET) under a variety of normal and pathologic conditions are widely diffuse and overlap considerably. In this survey, the deflation opening pressure (DOP) of the ET was tested in 31 patients suffering either from recurrent otitis (these patients had ventilating tubes inserted) or from chronic otitis media. Oxygen was deflated from the external ear canal, through the middle ear to the pharyngeal end of the ET. The DOP was the pressure needed for the passing of the oxygen. This pressure was usually between 100 to 200 mm H2O. No difference was found in the DOP between infants and adults or between discharging ears and dry ones. A second measurement was obtained through measuring the deflation flow pressure (DFP) required for the continuous passage of oxygen through the ET. The DFP was less than the DOP by approximately 20 to 60 mm H2O, and again no difference was noted between age groups or between infected and noninfected ears. It was concluded that DOP and DFP measurements of the ET are similar in a variety of conditions and therefore cannot indicate whether the ET is normally or abnormally functioning. The existence of a linear connection between the health of the ET and its performance is not proven; hence the role of the ET in predicting the likely outcome of tympanoplasty should be assessed within a different context.

Comments on the Diffusive Behavior of Two Upwind Schemes

NASA Technical Reports Server (NTRS)

Wood, William A.; Kleb, William L.

1998-01-01

The diffusive characteristics of two upwind schemes, multi-dimensional fluctuation splitting and locally one-dimensional finite volume, are compared for scalar advection-diffusion problems. Algorithms for the two schemes are developed for node-based data representation on median-dual meshes associated with unstructured triangulations in two spatial dimensions. Four model equations are considered: linear advection, non-linear advection, diffusion, and advection-diffusion. Modular coding is employed to isolate the effects of the two approaches for upwind flux evaluation, allowing for head-to-head accuracy and efficiency comparisons. Both the stability of compressive limiters and the amount of artificial diffusion generated by the schemes is found to be grid-orientation dependent, with the fluctuation splitting scheme producing less artificial diffusion than the finite volume scheme. Convergence rates are compared for the combined advection-diffusion problem, with a speedup of 2.5 seen for fluctuation splitting versus finite volume when solved on the same mesh. However, accurate solutions to problems with small diffusion coefficients can be achieved on coarser meshes using fluctuation splitting rather than finite volume, so that when comparing convergence rates to reach a given accuracy, fluctuation splitting shows a speedup of 29 over finite volume.

Diffusion Characteristics of Upwind Schemes on Unstructured Triangulations

NASA Technical Reports Server (NTRS)

Wood, William A.; Kleb, William L.

1998-01-01

The diffusive characteristics of two upwind schemes, multi-dimensional fluctuation splitting and dimensionally-split finite volume, are compared for scalar advection-diffusion problems. Algorithms for the two schemes are developed for node-based data representation on median-dual meshes associated with unstructured triangulations in two spatial dimensions. Four model equations are considered: linear advection, non-linear advection, diffusion, and advection-diffusion. Modular coding is employed to isolate the effects of the two approaches for upwind flux evaluation, allowing for head-to-head accuracy and efficiency comparisons. Both the stability of compressive limiters and the amount of artificial diffusion generated by the schemes is found to be grid-orientation dependent, with the fluctuation splitting scheme producing less artificial diffusion than the dimensionally-split finite volume scheme. Convergence rates are compared for the combined advection-diffusion problem, with a speedup of 2-3 seen for fluctuation splitting versus finite volume when solved on the same mesh. However, accurate solutions to problems with small diffusion coefficients can be achieved on coarser meshes using fluctuation splitting rather than finite volume, so that when comparing convergence rates to reach a given accuracy, fluctuation splitting shows a 20-25 speedup over finite volume.

Flexible Ferroelectric Sensors with Ultrahigh Pressure Sensitivity and Linear Response over Exceptionally Broad Pressure Range.

PubMed

Lee, Youngoh; Park, Jonghwa; Cho, Soowon; Shin, Young-Eun; Lee, Hochan; Kim, Jinyoung; Myoung, Jinyoung; Cho, Seungse; Kang, Saewon; Baig, Chunggi; Ko, Hyunhyub

2018-04-24

Flexible pressure sensors with a high sensitivity over a broad linear range can simplify wearable sensing systems without additional signal processing for the linear output, enabling device miniaturization and low power consumption. Here, we demonstrate a flexible ferroelectric sensor with ultrahigh pressure sensitivity and linear response over an exceptionally broad pressure range based on the material and structural design of ferroelectric composites with a multilayer interlocked microdome geometry. Due to the stress concentration between interlocked microdome arrays and increased contact area in the multilayer design, the flexible ferroelectric sensors could perceive static/dynamic pressure with high sensitivity (47.7 kPa -1 , 1.3 Pa minimum detection). In addition, efficient stress distribution between stacked multilayers enables linear sensing over exceptionally broad pressure range (0.0013-353 kPa) with fast response time (20 ms) and high reliability over 5000 repetitive cycles even at an extremely high pressure of 272 kPa. Our sensor can be used to monitor diverse stimuli from a low to a high pressure range including weak gas flow, acoustic sound, wrist pulse pressure, respiration, and foot pressure with a single device.

Antifungal susceptibility testing of Malassezia yeast: comparison of two different methodologies.

PubMed

Rojas, Florencia D; Córdoba, Susana B; de Los Ángeles Sosa, María; Zalazar, Laura C; Fernández, Mariana S; Cattana, María E; Alegre, Liliana R; Carrillo-Muñoz, Alfonso J; Giusiano, Gustavo E

2017-02-01

All Malassezia species are lipophilic; thus, modifications are required in susceptibility testing methods to ensure their growth. Antifungal susceptibility of Malassezia species using agar and broth dilution methods has been studied. Currently, few tests using disc diffusion methods are being performed. The aim was to evaluate the in vitro susceptibility of Malassezia yeast against antifungal agents using broth microdilution and disc diffusion methods, then to compare both methodologies. Fifty Malassezia isolates were studied. Microdilution method was performed as described in reference document and agar diffusion test was performed using antifungal tablets and discs. To support growth, culture media were supplemented. To correlate methods, linear regression analysis and categorical agreement was determined. The strongest linear association was observed for fluconazole and miconazole. The highest agreement between both methods was observed for itraconazole and voriconazole and the lowest for amphotericin B and fluconazole. Although modifications made to disc diffusion method allowed to obtain susceptibility data for Malassezia yeast, variables cannot be associated through a linear correlation model, indicating that inhibition zone values cannot predict MIC value. According to the results, disc diffusion assay may not represent an alternative to determine antifungal susceptibility of Malassezia yeast. © 2016 Blackwell Verlag GmbH.

Exact Solutions of Linear Reaction-Diffusion Processes on a Uniformly Growing Domain: Criteria for Successful Colonization

PubMed Central

Simpson, Matthew J

2015-01-01

Many processes during embryonic development involve transport and reaction of molecules, or transport and proliferation of cells, within growing tissues. Mathematical models of such processes usually take the form of a reaction-diffusion partial differential equation (PDE) on a growing domain. Previous analyses of such models have mainly involved solving the PDEs numerically. Here, we present a framework for calculating the exact solution of a linear reaction-diffusion PDE on a growing domain. We derive an exact solution for a general class of one-dimensional linear reaction—diffusion process on 0

Exact solutions of linear reaction-diffusion processes on a uniformly growing domain: criteria for successful colonization.

PubMed

Simpson, Matthew J

2015-01-01

Many processes during embryonic development involve transport and reaction of molecules, or transport and proliferation of cells, within growing tissues. Mathematical models of such processes usually take the form of a reaction-diffusion partial differential equation (PDE) on a growing domain. Previous analyses of such models have mainly involved solving the PDEs numerically. Here, we present a framework for calculating the exact solution of a linear reaction-diffusion PDE on a growing domain. We derive an exact solution for a general class of one-dimensional linear reaction-diffusion process on 0

Desorption of oxygen from YBa2Cu3O6+x films studied by Raman spectroscopy

NASA Astrophysics Data System (ADS)

Bock, A.; Kürsten, R.; Brühl, M.; Dieckmann, N.; Merkt, U.

1996-08-01

Phonons of laser-deposited YBa2Cu3O6+x films on MgO(100) substrates are investigated in a Raman setup as a function of laser power density. Investigations of YBa2Cu3O7 films allow us to study oxygen out-diffusion, where the onset of out-diffusion is indicated by the appearance of disorder-induced modes in the Raman spectra. At a pressure of 5×10-6 mbar the temperature threshold of the out-diffusion is (490+/-15) K. With increasing oxygen pressure the observed temperature thresholds rise only moderately in contrast to the behavior expected from the pox-T phase diagram of YBa2Cu3O6+x. Even at 1 bar oxygen partial pressure out-diffusion is observed and tetragonal sites with x=0 develop. These observations can be explained by photon-stimulated desorption of oxygen. Investigations of YBa2Cu3O6 films allow us to study oxygen in-diffusion. In 1 bar oxygen we observe competing oxygen fluxes due to thermally activated diffusion and photon-stimulated desorption. From these measurements we determine an upper bound of the thermal activation energy of the oxygen in-diffusion into YBa2Cu3O6 films of (0.19+/-0.01) eV.

Coupled low-energy - ring current plasma diffusion in the Jovian magnetosphere

NASA Technical Reports Server (NTRS)

Summers, D.; Siscoe, G. L.

1985-01-01

The outwardly diffusing Iogenic plasma and the simultaneously inwardly diffusing ring current plasma in the Jovian magnetosphere are described using a coupled diffusion model which incorporates the effects of the pressure gradient of the ring current into the cross-L diffusion coefficient. The coupled diffusion coefficient is derived by calculating the total energy available to drive the diffusion process. The condition is imposed that the diffusion coefficient takes on a local minimum value at some point in the region L = 7-8, at which point the gradient of the Io plasma density is specified as ramp value given by Siscoe et al. (1981). The hypothesis that the pressure gradient of the ring current causes the diminution of radial plasma transport is tested, and solution profiles for the Iogenic and ring current plasma densities are obtained which imply that the Io plasma ramp is caused by a high-density, low-energy component of the ring current hitherto unobserved directly.

On modeling pressure diffusion in non-homogeneous shear flows

NASA Technical Reports Server (NTRS)

Demuren, A. O.; Rogers, M. M.; Durbin, P.; Lele, S. K.

1996-01-01

New models are proposed for the 'slow and 'rapid' parts of the pressure diffusive transport based on the examination of DNS databases for plane mixing layers and wakes. The model for the 'slow' part is non-local, but requires the distribution of the triple-velocity correlation as a local source. The latter can be computed accurately for the normal component from standard gradient diffusion models, but such models are inadequate for the cross component. More work is required to remedy this situation.

Effect of membranes on oxygen transfer rate and consumption within a newly developed three-compartment bioartificial liver device: Advanced experimental and theoretical studies.

PubMed

Hilal-Alnaqbi, Ali; Mourad, Abdel-Hamid I; Yousef, Basem F

2014-01-01

A mathematical model is developed to predict oxygen transfer in the fiber-in-fiber (FIF) bioartificial liver device. The model parameters are taken from the constructed and tested FIF modules. We extended the Krogh cylinder model by including one more zone for oxygen transfer. Cellular oxygen uptake was based on Michaelis-Menten kinetics. The effect of varying a number of important model parameters is investigated, including (1) oxygen partial pressure at the inlet, (2) the hydraulic permeability of compartment B (cell region), (3) the hydraulic permeability of the inner membrane, and (4) the oxygen diffusivity of the outer membrane. The mathematical model is validated by comparing its output against the experimentally acquired values of an oxygen transfer rate and the hydrostatic pressure drop. Three governing simultaneous linear differential equations are derived to predict and validate the experimental measurements, e.g., the flow rate and the hydrostatic pressure drop. The model output simulated the experimental measurements to a high degree of accuracy. The model predictions show that the cells in the annulus can be oxygenated well even at high cell density or at a low level of gas phase PG if the value of the oxygen diffusion coefficient Dm is 16 × 10(-5) . The mathematical model also shows that the performance of the FIF improves by increasing the permeability of polypropylene membrane (inner fiber). Moreover, the model predicted that 60% of plasma has access to the cells in the annulus within the first 10% of the FIF bioreactor axial length for a specific polypropylene membrane permeability and can reach 95% within the first 30% of its axial length. © 2013 International Union of Biochemistry and Molecular Biology, Inc.

Nanoprobe diffusion in entangled polymer solutions: Linear vs. unconcatenated ring chains

NASA Astrophysics Data System (ADS)

Nahali, Negar; Rosa, Angelo

2018-05-01

We employ large-scale molecular dynamics computer simulations to study the problem of nanoprobe diffusion in entangled solutions of linear polymers and unknotted and unconcatenated circular (ring) polymers. By tuning both the diameter of the nanoprobe and the density of the solution, we show that nanoprobes of diameter smaller than the entanglement distance (tube diameter) of the solution display the same (Rouse-like) behavior in solutions of both polymer architectures. Instead, nanoprobes with larger diameters appear to diffuse markedly faster in solutions of rings than in solutions of linear chains. Finally, by analysing the distribution functions of spatial displacements, we find that nanoprobe motion in rings' solutions shows both Gaussian and ergodic behaviors, in all regimes considered, while, in solutions of linear chains, nanoprobes exceeding the size of the tube diameter show a transition to non-Gaussian and non-ergodic motion. Our results emphasize the role of chain architecture in the motion of nanoprobes dispersed in polymer solutions.

Size effects in non-linear heat conduction with flux-limited behaviors

NASA Astrophysics Data System (ADS)

Li, Shu-Nan; Cao, Bing-Yang

2017-11-01

Size effects are discussed for several non-linear heat conduction models with flux-limited behaviors, including the phonon hydrodynamic, Lagrange multiplier, hierarchy moment, nonlinear phonon hydrodynamic, tempered diffusion, thermon gas and generalized nonlinear models. For the phonon hydrodynamic, Lagrange multiplier and tempered diffusion models, heat flux will not exist in problems with sufficiently small scale. The existence of heat flux needs the sizes of heat conduction larger than their corresponding critical sizes, which are determined by the physical properties and boundary temperatures. The critical sizes can be regarded as the theoretical limits of the applicable ranges for these non-linear heat conduction models with flux-limited behaviors. For sufficiently small scale heat conduction, the phonon hydrodynamic and Lagrange multiplier models can also predict the theoretical possibility of violating the second law and multiplicity. Comparisons are also made between these non-Fourier models and non-linear Fourier heat conduction in the type of fast diffusion, which can also predict flux-limited behaviors.

Communication: Relationship between solute localization and diffusion in a dynamically constrained polymer system

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

Saylor, David M.; Jawahery, Sudi; Silverstein, Joshua S.

2016-07-21

We investigate the link between dynamic localization, characterized by the Debye–Waller factor, 〈u{sup 2}〉, and solute self-diffusivity, D, in a polymer system using atomistic molecular dynamics simulations and vapor sorption experiments. We find a linear relationship between lnD and 1/〈u{sup 2}〉 over more than four decades of D, encompassing most of the glass formation regime. The observed linearity is consistent with the Langevin dynamics in a periodically varying potential field and may offer a means to rapidly assess diffusion based on the characterization of dynamic localization.

Improvement of gray-scale representation of horizontally scanning holographic display using error diffusion.

PubMed

Matsumoto, Yuji; Takaki, Yasuhiro

2014-06-15

Horizontally scanning holography can enlarge both screen size and viewing zone angle. A microelectromechanical-system spatial light modulator, which can generate only binary images, is used to generate hologram patterns. Thus, techniques to improve gray-scale representation in reconstructed images should be developed. In this study, the error diffusion technique was used for the binarization of holograms. When the Floyd-Steinberg error diffusion coefficients were used, gray-scale representation was improved. However, the linearity in the gray-scale representation was not satisfactory. We proposed the use of a correction table and showed that the linearity was greatly improved.

Scarp degraded by linear diffusion: inverse solution for age.

USGS Publications Warehouse

Andrews, D.J.; Hanks, T.C.

1985-01-01

Under the assumption that landforms unaffected by drainage channels are degraded according to the linear diffusion equation, a procedure is developed to invert a scarp profile to find its 'diffusion age'. The inverse procedure applied to synthetic data yields the following rules of thumb. Evidence of initial scarp shape has been lost when apparent age reaches twice its initial value. A scarp that appears to have been formed by one event may have been formed by two with an interval between them as large as apparent age. The simplicity of scarp profile measurement and this inversion makes profile analysis attractive. -from Authors

Space simulation ultimate pressure lowered two decades by removal of diffusion pump oil contaminants during operation

NASA Technical Reports Server (NTRS)

Buggele, A. E.

1973-01-01

The complex problem why large space simulation chambers do not realize the true ultimate vacuum was investigated. Some contaminating factors affecting diffusion pump performance have been identified and some advances in vacuum/distillation/fractionation technology have been achieved which resulted in a two decade or more lower ultimate pressure. Data are presented to show the overall or individual contaminating effect of commonly used phthalate ester plasticizers of 390 to 530 molecular weight on diffusion pump performance. Methods for removing contaminants from diffusion pump silicone oil during operation and reclaiming contaminated oil by high vacuum molecular distillation are described.

The diffuse interstellar medium

NASA Technical Reports Server (NTRS)

Cox, Donald P.

1990-01-01

The last 20 years of the efforts to understand the diffuse ISM are reviewed, with recent changes of fundamental aspects being highlighted. Attention is given to the interstellar pressure and its components, the weight of the ISM, the midplane pressure contributions, and pressure contributions at 1 kpc. What velocity dispersions, cosmic ray pressure, and magnetic field pressure that can be expected for a gas in a high magnetic field environment is addressed. The intercloud medium is described, with reference to the work of Cox and Slavin (1989). Various caveats are discussed and a number of areas for future investigation are identified. Steps that could be taken toward a successful phase segregation model are discussed.

LABORATORY ASSESSMENT OF THE PERMEABILITY AND DIFFUSION CHARACTERISTICS OF FLORIDA CONCRETES - PHASE I - METHODS DEVELOPMENT AND TESTING

EPA Science Inventory

The report gives results of Phase I of a laboratory assessment of the permeability and diffusion characteristics of Florida concretes. (NOTE: The ability of concrete to permit air flow under pressure (permeability) and the passage of radon gas without any pressure difference (dif...

Scaling of seismicity induced by nonlinear fluid-rock interaction after an injection stop

NASA Astrophysics Data System (ADS)

Johann, L.; Dinske, C.; Shapiro, S. A.

2016-11-01

Fluid injections into unconventional reservoirs, performed for fluid-mobility enhancement, are accompanied by microseismic activity also after the injection. Previous studies revealed that the triggering of seismic events can be effectively described by nonlinear diffusion of pore fluid pressure perturbations where the hydraulic diffusivity becomes pressure dependent. The spatiotemporal distribution of postinjection-induced microseismicity has two important features: the triggering front, corresponding to early and distant events, and the back front, representing the time-dependent spatial envelope of the growing seismic quiescence zone. Here for the first time, we describe analytically the temporal behavior of these two fronts after the injection stop in the case of nonlinear pore fluid pressure diffusion. We propose a scaling law for the fronts and show that they are sensitive to the degree of nonlinearity and to the Euclidean dimension of the dominant growth of seismicity clouds. To validate the theoretical finding, we numerically model nonlinear pore fluid pressure diffusion and generate synthetic catalogs of seismicity. Additionally, we apply the new scaling relation to several case studies of injection-induced seismicity. The derived scaling laws describe well synthetic and real data.

In situ study of mass transfer in aqueous solutions under high pressures via Raman spectroscopy: A new method for the determination of diffusion coefficients of methane in water near hydrate formation conditions

USGS Publications Warehouse

Lu, W.J.; Chou, I.-Ming; Burruss, R.C.; Yang, M.Z.

2006-01-01

A new method was developed for in situ study of the diffusive transfer of methane in aqueous solution under high pressures near hydrate formation conditions within an optical capillary cell. Time-dependent Raman spectra of the solution at several different spots along the one-dimensional diffusion path were collected and thus the varying composition profile of the solution was monitored. Diffusion coefficients were estimated by the least squares method based on the variations in methane concentration data in space and time in the cell. The measured diffusion coefficients of methane in water at the liquid (L)-vapor (V) stable region and L-V metastable region are close to previously reported values determined at lower pressure and similar temperature. This in situ monitoring method was demonstrated to be suitable for the study of mass transfer in aqueous solution under high pressure and at various temperature conditions and will be applied to the study of nucleation and dissolution kinetics of methane hydrate in a hydrate-water system where the interaction of methane and water would be more complicated than that presented here for the L-V metastable condition. ?? 2006 Society for Applied Spectroscopy.

Discovery of the linear region of Near Infrared Diffuse Reflectance spectra using the Kubelka-Munk theory

NASA Astrophysics Data System (ADS)

Dai, Shengyun; Pan, Xiaoning; Ma, Lijuan; Huang, Xingguo; Du, Chenzhao; Qiao, Yanjiang; Wu, Zhisheng

2018-05-01

Particle size is of great importance for the quantitative model of the NIR diffuse reflectance. In this paper, the effect of sample particle size on the measurement of harpagoside in Radix Scrophulariae powder by near infrared diffuse (NIR) reflectance spectroscopy was explored. High-performance liquid chromatography (HPLC) was employed as a reference method to construct the quantitative particle size model. Several spectral preprocessing methods were compared, and particle size models obtained by different preprocessing methods for establishing the partial least-squares (PLS) models of harpagoside. Data showed that the particle size distribution of 125-150 μm for Radix Scrophulariae exhibited the best prediction ability with R2pre=0.9513, RMSEP=0.1029 mg·g-1, and RPD = 4.78. For the hybrid granularity calibration model, the particle size distribution of 90-180 μm exhibited the best prediction ability with R2pre=0.8919, RMSEP=0.1632 mg·g-1, and RPD = 3.09. Furthermore, the Kubelka-Munk theory was used to relate the absorption coefficient k (concentration-dependent) and scatter coefficient s (particle size-dependent). The scatter coefficient s was calculated based on the Kubelka-Munk theory to study the changes of s after being mathematically preprocessed. A linear relationship was observed between k/s and absorption A within a certain range and the value for k/s was greater than 4. According to this relationship, the model was more accurately constructed with the particle size distribution of 90-180 μm when s was kept constant or in a small linear region. This region provided a good reference for the linear modeling of diffuse reflectance spectroscopy. To establish a diffuse reflectance NIR model, further accurate assessment should be obtained in advance for a precise linear model.

Product diffusion through on-demand information-seeking behaviour.

PubMed

Riedl, Christoph; Bjelland, Johannes; Canright, Geoffrey; Iqbal, Asif; Engø-Monsen, Kenth; Qureshi, Taimur; Sundsøy, Pål Roe; Lazer, David

2018-02-01

Most models of product adoption predict S-shaped adoption curves. Here we report results from two country-scale experiments in which we find linear adoption curves. We show evidence that the observed linear pattern is the result of active information-seeking behaviour: individuals actively pulling information from several central sources facilitated by modern Internet searches. Thus, a constant baseline rate of interest sustains product diffusion, resulting in a linear diffusion process instead of the S-shaped curve of adoption predicted by many diffusion models. The main experiment seeded 70 000 (48 000 in Experiment 2) unique voucher codes for the same product with randomly sampled nodes in a social network of approximately 43 million individuals with about 567 million ties. We find that the experiment reached over 800 000 individuals with 80% of adopters adopting the same product-a winner-take-all dynamic consistent with search engine driven rankings that would not have emerged had the products spread only through a network of social contacts. We provide evidence for (and characterization of) this diffusion process driven by active information-seeking behaviour through analyses investigating (a) patterns of geographical spreading; (b) the branching process; and (c) diffusion heterogeneity. Using data on adopters' geolocation we show that social spreading is highly localized, while on-demand diffusion is geographically independent. We also show that cascades started by individuals who actively pull information from central sources are more effective at spreading the product among their peers. © 2018 The Authors.

Product diffusion through on-demand information-seeking behaviour

PubMed Central

Bjelland, Johannes; Canright, Geoffrey; Iqbal, Asif; Qureshi, Taimur; Sundsøy, Pål Roe

2018-01-01

Most models of product adoption predict S-shaped adoption curves. Here we report results from two country-scale experiments in which we find linear adoption curves. We show evidence that the observed linear pattern is the result of active information-seeking behaviour: individuals actively pulling information from several central sources facilitated by modern Internet searches. Thus, a constant baseline rate of interest sustains product diffusion, resulting in a linear diffusion process instead of the S-shaped curve of adoption predicted by many diffusion models. The main experiment seeded 70 000 (48 000 in Experiment 2) unique voucher codes for the same product with randomly sampled nodes in a social network of approximately 43 million individuals with about 567 million ties. We find that the experiment reached over 800 000 individuals with 80% of adopters adopting the same product—a winner-take-all dynamic consistent with search engine driven rankings that would not have emerged had the products spread only through a network of social contacts. We provide evidence for (and characterization of) this diffusion process driven by active information-seeking behaviour through analyses investigating (a) patterns of geographical spreading; (b) the branching process; and (c) diffusion heterogeneity. Using data on adopters' geolocation we show that social spreading is highly localized, while on-demand diffusion is geographically independent. We also show that cascades started by individuals who actively pull information from central sources are more effective at spreading the product among their peers. PMID:29467257

Magnetic resonance imaging study on near miscible supercritical CO2 flooding in porous media

NASA Astrophysics Data System (ADS)

Song, Yongchen; Zhu, Ningjun; Zhao, Yuechao; Liu, Yu; Jiang, Lanlan; Wang, Tonglei

2013-05-01

CO2 flooding is one of the most popular secondary or tertiary recoveries for oil production. It is also significant for studying the mechanisms of the two-phase and multiphase flow in porous media. In this study, an experimental study was carried out by using magnetic resonance imaging technique to examine the detailed effects of pressure and rates on CO2/decane flow in a bead-pack porous media. The displacing processes were conducted under various pressures in a region near the minimum miscibility pressure (the system tuned from immiscible to miscible as pressure is increasing in this region) and the temperature of 37.8 °C at several CO2 injection volumetric rates of 0.05, 0.10, and 0.15 ml/min (or linear rates of 3.77, 7.54, and 11.3 ft/day). The evolution of the distribution of decane and the characteristics of the two phase flow were investigated and analyzed by considering the pressure and rate. The area and velocity of the transition zone between the two phases were calculated and analyzed to quantify mixing. The area of transition zone decreased with pressure at near miscible region and a certain injection rate and the velocity of the transition zone was always less than the "volumetric velocity" due to mutual solution and diffusion of the two phases. Therefore, these experimental results give the fundamental understanding of tertiary recovery processes at near miscible condition.

On the transition between two-phase and single-phase interface dynamics in multicomponent fluids at supercritical pressures

NASA Astrophysics Data System (ADS)

Dahms, Rainer N.; Oefelein, Joseph C.

2013-09-01

A theory that explains the operating pressures where liquid injection processes transition from exhibiting classical two-phase spray atomization phenomena to single-phase diffusion-dominated mixing is presented. Imaging from a variety of experiments have long shown that under certain conditions, typically when the pressure of the working fluid exceeds the thermodynamic critical pressure of the liquid phase, the presence of discrete two-phase flow processes become diminished. Instead, the classical gas-liquid interface is replaced by diffusion-dominated mixing. When and how this transition occurs, however, is not well understood. Modern theory still lacks a physically based model to quantify this transition and the precise mechanisms that lead to it. In this paper, we derive a new model that explains how the transition occurs in multicomponent fluids and present a detailed analysis to quantify it. The model applies a detailed property evaluation scheme based on a modified 32-term Benedict-Webb-Rubin equation of state that accounts for the relevant real-fluid thermodynamic and transport properties of the multicomponent system. This framework is combined with Linear Gradient Theory, which describes the detailed molecular structure of the vapor-liquid interface region. Our analysis reveals that the two-phase interface breaks down not necessarily due to vanishing surface tension forces, but due to thickened interfaces at high subcritical temperatures coupled with an inherent reduction of the mean free molecular path. At a certain point, the combination of reduced surface tension, the thicker interface, and reduced mean free molecular path enter the continuum length scale regime. When this occurs, inter-molecular forces approach that of the multicomponent continuum where transport processes dominate across the interfacial region. This leads to a continuous phase transition from compressed liquid to supercritical mixture states. Based on this theory, a regime diagram for liquid injection is developed that quantifies the conditions under which classical sprays transition to dense-fluid jets. It is shown that the chamber pressure required to support diffusion-dominated mixing dynamics depends on the composition and temperature of the injected liquid and ambient gas. To illustrate the method and analysis, we use conditions typical of diesel engine injection. We also present a companion set of high-speed images to provide experimental validation of the presented theory. The basic theory is quite general and applies to a wide range of modern propulsion and power systems such as liquid rockets, gas turbines, and reciprocating engines. Interestingly, the regime diagram associated with diesel engine injection suggests that classical spray phenomena at typical injection conditions do not occur.

An experimental description of the flow in a centrifugal compressor from alternate stall to surge

NASA Astrophysics Data System (ADS)

Moënne-Loccoz, V.; Trébinjac, I.; Benichou, E.; Goguey, S.; Paoletti, B.; Laucher, P.

2017-08-01

The present paper gives the experimental results obtained in a centrifugal compressor stage designed and built by SAFRAN Helicopter Engines. The compressor is composed of inlet guide vanes, a backswept splittered unshrouded impeller, a splittered vaned radial diffuser and axial outlet guide vanes. Previous numerical simulations revealed a particular S-shape pressure rise characteristic at partial rotation speed and predicted an alternate flow pattern in the vaned radial diffuser at low mass flow rate. This alternate flow pattern involves two adjacent vane passages. One passage exhibits very low momentum and a low pressure recovery, whereas the adjacent passage has very high momentum in the passage inlet and diffuses efficiently. Experimental measurements confirm the S-shape of the pressure rise characteristic even if the stability limit experimentally occurs at higher mass flow than numerically predicted. At low mass flow the alternate stall pattern is confirmed thanks to the data obtained by high-frequency pressure sensors. As the compressor is throttled the path to instability has been registered and a first scenario of the surge inception is given. The compressor first experiences a steady alternate stall in the diffuser. As the mass flow decreases, the alternate stall amplifies and triggers the mild surge in the vaned diffuser. An unsteady behavior results from the interaction of the alternate stall and the mild surge. Finally, when the pressure gradient becomes too strong, the alternate stall blows away and the compressor enters into deep surge.

Optimal Network Modularity for Information Diffusion

NASA Astrophysics Data System (ADS)

Nematzadeh, Azadeh; Ferrara, Emilio; Flammini, Alessandro; Ahn, Yong-Yeol

2014-08-01

We investigate the impact of community structure on information diffusion with the linear threshold model. Our results demonstrate that modular structure may have counterintuitive effects on information diffusion when social reinforcement is present. We show that strong communities can facilitate global diffusion by enhancing local, intracommunity spreading. Using both analytic approaches and numerical simulations, we demonstrate the existence of an optimal network modularity, where global diffusion requires the minimal number of early adopters.

Transition regime analytical solution to gas mass flow rate in a rectangular micro channel

NASA Astrophysics Data System (ADS)

Dadzie, S. Kokou; Dongari, Nishanth

2012-11-01

We present an analytical model predicting the experimentally observed gas mass flow rate in rectangular micro channels over slip and transition regimes without the use of any fitting parameter. Previously, Sone reported a class of pure continuum regime flows that requires terms of Burnett order in constitutive equations of shear stress to be predicted appropriately. The corrective terms to the conventional Navier-Stokes equation were named the ghost effect. We demonstrate in this paper similarity between Sone ghost effect model and newly so-called 'volume diffusion hydrodynamic model'. A generic analytical solution to gas mass flow rate in a rectangular micro channel is then obtained. It is shown that the volume diffusion hydrodynamics allows to accurately predict the gas mass flow rate up to Knudsen number of 5. This can be achieved without necessitating the use of adjustable parameters in boundary conditions or parametric scaling laws for constitutive relations. The present model predicts the non-linear variation of pressure profile along the axial direction and also captures the change in curvature with increase in rarefaction.

[Correlation of molecular weight and nanofiltration mass transfer coefficient of phenolic acid composition from Salvia miltiorrhiza].

PubMed

Li, Cun-Yu; Wu, Xin; Gu, Jia-Mei; Li, Hong-Yang; Peng, Guo-Ping

2018-04-01

Based on the molecular sieving and solution-diffusion effect in nanofiltration separation, the correlation between initial concentration and mass transfer coefficient of three typical phenolic acids from Salvia miltiorrhiza was fitted to analyze the relationship among mass transfer coefficient, molecular weight and concentration. The experiment showed a linear relationship between operation pressure and membrane flux. Meanwhile, the membrane flux was gradually decayed with the increase of solute concentration. On the basis of the molecular sieving and solution-diffusion effect, the mass transfer coefficient and initial concentration of three phenolic acids showed a power function relationship, and the regression coefficients were all greater than 0.9. The mass transfer coefficient and molecular weight of three phenolic acids were negatively correlated with each other, and the order from high to low is protocatechualdehyde >rosmarinic acid> salvianolic acid B. The separation mechanism of nanofiltration for phenolic acids was further clarified through the analysis of the correlation of molecular weight and nanofiltration mass transfer coefficient. The findings provide references for nanofiltration separation, especially for traditional Chinese medicine with phenolic acids. Copyright© by the Chinese Pharmaceutical Association.

Effect of migration in a diffusion model for template coexistence in protocells.

PubMed

Fontanari, José F; Serva, Maurizio

2014-03-01

The compartmentalization of distinct templates in protocells and the exchange of templates between them (migration) are key elements of a modern scenario for prebiotic evolution. Here we use the diffusion approximation of population genetics to study analytically the steady-state properties of such a prebiotic scenario. The coexistence of distinct template types inside a protocell is achieved by a selective pressure at the protocell level (group selection) favoring protocells with a mixed template composition. In the degenerate case, where the templates have the same replication rate, we find that a vanishingly small migration rate suffices to eliminate the segregation effect of random drift and so to promote coexistence. In the nondegenerate case, a small migration rate greatly boosts coexistence as compared with the situation where there is no migration. However, increase of the migration rate beyond a critical value leads to the complete dominance of the more efficient template type (homogeneous regime). In this case, we find a continuous phase transition separating the homogeneous and the coexistence regimes, with the order parameter vanishing linearly with the distance to the transition point.

The speed of sound in a gas–vapour bubbly liquid

PubMed Central

Prosperetti, Andrea

2015-01-01

In addition to the vapour of the liquid, bubbles in cavitating flows usually contain also a certain amount of permanent gas that diffuses out of the liquid as they grow. This paper presents a simplified linear model for the propagation of monochromatic pressure waves in a bubbly liquid with these characteristics. Phase change effects are included in detail, while the gas is assumed to follow a polytropic law. It is shown that even a small amount of permanent gas can have a major effect on the behaviour of the system. Particular attention is paid to the low-frequency range, which is of special concern in flow cavitation. Numerical results for water and liquid oxygen illustrate the implications of the model. PMID:26442146

The speed of sound in a gas-vapour bubbly liquid.

PubMed

Prosperetti, Andrea

2015-10-06

In addition to the vapour of the liquid, bubbles in cavitating flows usually contain also a certain amount of permanent gas that diffuses out of the liquid as they grow. This paper presents a simplified linear model for the propagation of monochromatic pressure waves in a bubbly liquid with these characteristics. Phase change effects are included in detail, while the gas is assumed to follow a polytropic law. It is shown that even a small amount of permanent gas can have a major effect on the behaviour of the system. Particular attention is paid to the low-frequency range, which is of special concern in flow cavitation. Numerical results for water and liquid oxygen illustrate the implications of the model.

Direct simulation Monte Carlo investigation of the Richtmyer-Meshkov instability

DOE PAGES

Gallis, Michail A.; Koehler, Timothy P.; Torczynski, John R.; ...

2015-08-14

The Rayleigh-Taylor instability (RTI) is investigated using the Direct Simulation Monte Carlo (DSMC) method of molecular gas dynamics. Here, fully resolved two-dimensional DSMC RTI simulations are performed to quantify the growth of flat and single-mode perturbed interfaces between two atmospheric-pressure monatomic gases as a function of the Atwood number and the gravitational acceleration. The DSMC simulations reproduce all qualitative features of the RTI and are in reasonable quantitative agreement with existing theoretical and empirical models in the linear, nonlinear, and self-similar regimes. At late times, the instability is seen to exhibit a self-similar behavior, in agreement with experimental observations. Formore » the conditions simulated, diffusion can influence the initial instability growth significantly.« less

Energetics of multicomponent diffusion in molten CaO-Al 2O 3-SiO 2

NASA Astrophysics Data System (ADS)

Liang, Yan; Davis, Andrew M.

2002-02-01

The energetics of multicomponent diffusion in molten CaO-Al2O3-SiO2 (CAS) were examined experimentally at 1440 to 1650°C and 0.5 to 2 GPa. Two melt compositions were investigated: a haplodacitic melt (25 wt.% CaO, 15% Al2O3, and 60% SiO2) and a haplobasaltic melt (35% CaO, 20% Al2O3, and 45% SiO2). Diffusion matrices were measured in a mass-fixed frame of reference with simple oxides as end-member components and Al2O3 as a dependent variable. Chemical diffusion in molten CAS shows clear evidence of diffusive coupling among the components. The diffusive flux of SiO2 is significantly enhanced whenever there is a large CaO gradient that is oriented in a direction opposite to the SiO2 gradient. This coupling effect is more pronounced in the haplodacitic melt and is likely to be significant in natural magmas of rhyolitic to andesitic compositions. The relative magnitude of coupled chemical diffusion is not very sensitive to changes in temperature and pressure. To a good approximation, the measured diffusion matrices follow well-defined Arrhenius relationships with pressure and reciprocal temperature. Typically, a change in temperature of 100°C results in a relative change in the elements of diffusion matrix of 50 to 100%, whereas a change in pressure of 1 GPa introduces a relative change in elements of diffusion matrix of 4 to 6% for the haplobasalt, and less than 5% for the haplodacite. At a pressure of 1 GPa, the ratios between the major and minor eigenvalues of the diffusion matrix λ1/λ2 are not very sensitive to temperature variations, with an average of 5.5 ± 0.2 for the haplobasalt and 3.7 ± 0.6 for the haplodacite. The activation energies for the major and minor eigenvalues of the diffusion matrix are 215 ± 12 and 240 ± 21 kJ mol-1, respectively, for the haplodacite and 192 ± 8 and 217 ± 14 kJ mol-1 for the haplobasalt. These values are comparable to the activation energies for self-diffusion of calcium and silicon at the same melt compositions and pressure. At a fixed temperature of 1500°C, the ratios λ1/λ2 increase with the increase of pressure, with λ1/λ2 varying from 2.5 to 4.1 (0.5 to 1.3 GPa) for the haplodacite and 4 to 6.5 (0.5 to 2.0 GPa) for the haplobasalt. The activation volumes for the major and minor eigenvalues of the diffusion matrix are 0.31 ± 0.44 and 2.3 ± 0.8 cm3 mol-1, respectively, for the haplodacite and -1.48 ± 0.18 and -0.42 ± 0.24 cm3 mol-1 for the haplobasalt. These values are quite different from the activation volumes for self-diffusion of calcium and silicon at the same melt compositions and temperature. These differences in activation volumes between the two melts likely result from a difference in the structure and thermodynamic properties of the melt between the two compositions (e.g., partial molar volume). Applications of the measured diffusion matrices to quartz crystal dissolution in molten CAS reveal that the activation energy and activation volume for quartz dissolution are almost identical to the activation energy and activation volume for diffusion of the minor or slower eigencomponent of the diffusion matrix. This suggests that the diffusion rate of slow eigencomponent is the rate-limiting factor in isothermal crystal dissolution, a conclusion that is likely to be valid for crystal growth and dissolution in natural magmas when diffusion in liquid is the rate-limiting factor.

SiC and Si3N4 Recession Due to SiO2 Scale Volatility Under Combustor Conditions

NASA Technical Reports Server (NTRS)

Smialek, James L.; Robinson, R. Craig; Opila, Elizabeth J.; Fox, Dennis S.; Jacobson, Nathan S.

1999-01-01

SiC and Si3N4 materials were tested under various turbine engine combustion environments, chosen to represent either conventional fuel-lean or fuel-rich mixtures proposed for high speed aircraft. Representative CVD, sintered, and composite materials were evaluated in both furnace and high pressure burner rig exposure. While protective SiO2 scales form in all cases, evidence is presented to support paralinear growth kinetics, i.e. parabolic growth moderated simultaneously by linear volatilization. The volatility rate is dependent on temperature, moisture content, system pressure, and gas velocity. The burner tests were used to map SiO2 volatility (and SiC recession) over a range of temperature, pressure, and velocity. The functional dependency of material recession (volatility) that emerged followed the form: exp(-QIRT) * P(exp x) * v(exp y). These empirical relations were compared to rates predicted from the thermodynamics of volatile SiO and SiO(sub x)H(sub Y) reaction products and a kinetic model of diffusion through a moving, boundary layer. For typical combustion conditions, recession of 0.2 to 2 micron/h is predicted at 1200- 1400C, far in excess of acceptable long term limits.

Numerical investigation on an array of Helmholtz resonators for the reduction of micro-pressure waves in modern and future high-speed rail tunnel systems

NASA Astrophysics Data System (ADS)

Tebbutt, J. A.; Vahdati, M.; Carolan, D.; Dear, J. P.

2017-07-01

Previous research has proposed that an array of Helmholtz resonators may be an effective method for suppressing the propagation of pressure and sound waves, generated by a high-speed train entering and moving in a tunnel. The array can be used to counteract environmental noise from tunnel portals and also the emergence of a shock wave in the tunnel. The implementation of an array of Helmholtz resonators in current and future high-speed train-tunnel systems is studied. Wave propagation in the tunnel is modelled using a quasi-one-dimensional formulation, accounting for non-linear effects, wall friction and the diffusivity of sound. A multi-objective genetic algorithm is then used to optimise the design of the array, subject to the geometric constraints of a demonstrative tunnel system and the incident wavefront in order to attenuate the propagation of pressure waves. It is shown that an array of Helmholtz resonators can be an effective countermeasure for various tunnel lengths. In addition, the array can be designed to function effectively over a wide operating envelope, ensuring it will still function effectively as train speeds increase into the future.

Elastic stress transfer as a diffusive process due to aseismic fault slip in response to fluid injection

NASA Astrophysics Data System (ADS)

Viesca, R. C.

2015-12-01

Subsurface fluid injection is often followed by observations of an enlarging cloud of microseismicity. The cloud's diffusive growth is thought to be a direct response to the diffusion of elevated pore fluid pressure reaching pre-stressed faults, triggering small instabilities; the observed high rates of this growth are interpreted to reflect a relatively high permeability of a fractured subsurface [e.g., Shapiro, GJI 1997]. We investigate an alternative mechanism for growing a microseismic cloud: the elastic transfer of stress due to slow, aseismic slip on a subset of the pre-existing faults in this damaged subsurface. We show that the growth of the slipping region of the fault may be self-similar in a diffusive manner. While this slip is driven by fluid injection, we show that, for critically stressed faults, the apparent diffusion of this slow slip may quickly exceed the poroelastically driven diffusion of the elevated pore fluid pressure. Under these conditions, microseismicity can be first triggered by the off-fault stress perturbation due to the expanding region of slip on principal faults. This provides an alternative interpretation of diffusive growth rates in terms of the subsurface stress state rather than an enhanced hydraulic diffusivity. That such aseismic slip may occur, outpace fluid diffusion, and in turn trigger microseismic events, is also suggested by on- and near-fault observations in past and recently reported fluid injection experiments [e.g., Cornet et al., PAGEOPH 1997; Guglielmi et al., Science 2015]. The model of injection-induced slip assumes elastic off-fault behavior and a fault strength determined by the product of a constant friction coefficient and the local effective normal stress. The sliding region is enlarged by the pore pressure increase resolved on the fault plane. Remarkably, the rate of self-similar expansion may be determined by a single parameter reflecting both the initial stress state and the magnitude of the pore pressure increase.

A diffusion-free and linear-energy-transfer-independent nanocomposite Fricke gel dosimeter

NASA Astrophysics Data System (ADS)

Maeyama, T.; Fukunishi, N.; Ishikawa, K. L.; Furuta, T.; Fukasaku, K.; Takagi, S.; Noda, S.; Himeno, R.; Fukuda, S.

2014-03-01

We report a new magnetic-resonance-imaging (MRI) based nanocomposite Fricke gel (NC-FG) dosimeter system, which is free from two main drawbacks of conventional Fricke gel dosimeters, namely, the diffusion of the radiation products and the linear-energy-transfer (LET) dependence of the radiation sensitivity when used for ion beams. The NC-FG dosimeter was prepared by incorporating 1% (w/w) clay nanoparticles into deaerated Fricke gel. We have dosimetrically characterized the NC-FG by using MRI measurements after irradiation with a monoenergetic 290 MeV/nucleon carbon beam. No diffusion of the radiation products was observed during nine days after the irradiation. Moreover, its response faithfully reproduced the depth-dose distribution measured by an ionization chamber, which indicates the absence of the LET dependence. Also, the NC-FG dosimeter exhibited a good linearity up to 800 Gy.

The effects of the Asselin time filter on numerical solutions to the linearized shallow-water wave equations

NASA Technical Reports Server (NTRS)

Schlesinger, R. E.; Johnson, D. R.; Uccellini, L. W.

1983-01-01

In the present investigation, a one-dimensional linearized analysis is used to determine the effect of Asselin's (1972) time filter on both the computational stability and phase error of numerical solutions for the shallow water wave equations, in cases with diffusion but without rotation. An attempt has been made to establish the approximate optimal values of the filtering parameter nu for each of the 'lagged', Dufort-Frankel, and Crank-Nicholson diffusion schemes, suppressing the computational wave mode without materially altering the physical wave mode. It is determined that in the presence of diffusion, the optimum filter length depends on whether waves are undergoing significant propagation. When moderate propagation is present, with or without diffusion, the Asselin filter has little effect on the spatial phase lag of the physical mode for the leapfrog advection scheme of the three diffusion schemes considered.

Levitation effect: Distinguishing anomalous from linear regime of guests sorbed in zeolites through the decay of intermediate scattering function and wavevector dependence of self-diffusivity.

PubMed

Ghorai, Pradip Kr; Yashonath, S

2005-03-10

Previous work investigating the dependence of self-diffusivity, D, on the size of the guest diffusing within the porous solid such as zeolite has reported the existence of an anomalous maximum in the diffusion coefficient (J. Phys. Chem. 1994, 98, 6368). Two distinct regimes of dependence of D on sigma(gg), diameter of the guest were reported. D proportional to 1/sigma(gg)2, often referred to as linear regime (LR), is found when sigma(gg) is smaller than sigma(v), the diameter of the void. A maximum in D has been observed when sigma(gg) is comparable to sigma(v) and this regime is referred to as anomalous regime (AR). Here we report the intermediate scattering function for a particle from LR and AR in zeolite faujasite. A particle from LR exhibits a biexponential decay while a particle from AR exhibits a single-exponential decay at small k. Variation with k of the full width at half-maximum of the self-part of the dynamic structure factor is nonmonotonic for a particle in the linear regime. In contrast, this variation is monotonic for a particle in the anomalous regime. These results can be understood in terms of the existence of energetic barrier at the bottleneck, the 12-ring window, in the path of diffusion. They provide additional signatures for the linear regime and anomalous regimes and therefore for levitation effect (LE).

Anger response styles and blood pressure: at least don't ruminate about it!

PubMed

Hogan, Brenda E; Linden, Wolfgang

2004-02-01

Research on anger suggests a link with blood pressure (BP), but the findings are complex and highly variable; this is at least partly attributable to measurement issues. In this study we used a new model of anger responding that comprises 6 independent anger response styles in 2 dimensions: Aggression, Assertion, Social Support Seeking, Diffusion, Avoidance, and Rumination. Linear and interactive relations between the anger response styles and resting and ambulatory BP were tested, controlling for traditional risk factors and level of hostility. Data from 2 samples of different cardiovascular health status were examined. In Study 1, 109 healthy participants (45 men and 64 women) were recruited. Study 2 involved a sample of 159 hypertensive patients (90 men and 69 women). All participants provided demographic and health information; completed the Behavioral Anger Response Questionnaire, a hostility measure; and underwent resting BP measurement. Study 2 participants also provided 24-hr ambulatory BPs. Examination of linear effects revealed inconsistent associations between anger response styles and BP. The moderating effect of Rumination on the relationship between the other anger response styles and BP was examined next. Rumination had a deleterious influence on the relation between Avoidance and Assertion and resting and ambulatory BP levels. The moderating influence of Rumination on Social Support Seeking varied between the genders. Overall, the results suggest that rumination is a critical moderating variable in the relation of anger and BP.

Mapping diffuse photosynthetically active radiation from satellite data in Thailand

NASA Astrophysics Data System (ADS)

Choosri, P.; Janjai, S.; Nunez, M.; Buntoung, S.; Charuchittipan, D.

2017-12-01

In this paper, calculation of monthly average hourly diffuse photosynthetically active radiation (PAR) using satellite data is proposed. Diffuse PAR was analyzed at four stations in Thailand. A radiative transfer model was used for calculating the diffuse PAR for cloudless sky conditions. Differences between the diffuse PAR under all sky conditions obtained from the ground-based measurements and those from the model are representative of cloud effects. Two models are developed, one describing diffuse PAR only as a function of solar zenith angle, and the second one as a multiple linear regression with solar zenith angle and satellite reflectivity acting linearly and aerosol optical depth acting in logarithmic functions. When tested with an independent data set, the multiple regression model performed best with a higher coefficient of variance R2 (0.78 vs. 0.70), lower root mean square difference (RMSD) (12.92% vs. 13.05%) and the same mean bias difference (MBD) of -2.20%. Results from the multiple regression model are used to map diffuse PAR throughout the country as monthly averages of hourly data.

Diffusion-driven fluid dynamics in ideal gases and plasmas

NASA Astrophysics Data System (ADS)

Vold, E. L.; Yin, L.; Taitano, W.; Molvig, K.; Albright, B. J.

2018-06-01

The classical transport theory based on Chapman-Enskog methods provides self-consistent approximations for the kinetic flux of mass, heat, and momentum in a fluid limit characterized with a small Knudsen number. The species mass fluxes relative to the center of mass, or "diffusive fluxes," are expressed as functions of known gradient quantities with kinetic coefficients evaluated using similar analyses for mixtures of gases or plasma components. The sum over species of the diffusive mass fluxes is constrained to be zero in the Lagrange frame, and thus results in a non-zero molar flux leading to a pressure perturbation. At an interface between two species initially in pressure equilibrium, the pressure perturbation driven by the diffusive molar flux induces a center of mass velocity directed from the species of greater atomic mass towards the lighter atomic mass species. As the ratio of the species particle masses increases, this center of mass velocity carries an increasingly greater portion of the mass across the interface and for a particle mass ratio greater than about two, the center of mass velocity carries more mass than the gradient driven diffusion flux. Early time transients across an interface between two species in a 1D plasma regime and initially in equilibrium are compared using three methods; a fluid code with closure in a classical transport approximation, a particle in cell simulation, and an implicit Fokker-Planck solver for the particle distribution functions. The early time transient phenomenology is shown to be similar in each of the computational simulation methods, including a pressure perturbation associated with the stationary "induced" component of the center of mass velocity which decays to pressure equilibrium during diffusion. At early times, the diffusive process generates pressure and velocity waves which propagate outward from the interface and are required to maintain momentum conservation. The energy in the outgoing waves dissipates as heat in viscous regions, and it is hypothesized that these diffusion driven waves may sustain fluctuations in less viscid finite domains after reflections from the boundaries. These fluid dynamic phenomena are similar in gases or plasmas and occur in flow transients with a moderate Knudsen number. The analysis and simulation results show how the kinetic flux, represented in the fluid transport closure, directly modifies the mass averaged flow described with the Euler equations.

Stochastic Estimation and Non-Linear Wall-Pressure Sources in a Separating/Reattaching Flow

NASA Technical Reports Server (NTRS)

Naguib, A.; Hudy, L.; Humphreys, W. M., Jr.

2002-01-01

Simultaneous wall-pressure and PIV measurements are used to study the conditional flow field associated with surface-pressure generation in a separating/reattaching flow established over a fence-with-splitter-plate geometry. The conditional flow field is captured using linear and quadratic stochastic estimation based on the occurrence of positive and negative pressure events in the vicinity of the mean reattachment location. The results shed light on the dominant flow structures associated with significant wall-pressure generation. Furthermore, analysis based on the individual terms in the stochastic estimation expansion shows that both the linear and non-linear flow sources of the coherent (conditional) velocity field are equally important contributors to the generation of the conditional surface pressure.

Non-Linear Dynamics and Emergence in Laboratory Fusion Plasmas

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

Hnat, B.

2011-09-22

Turbulent behaviour of laboratory fusion plasma system is modelled using extended Hasegawa-Wakatani equations. The model is solved numerically using finite difference techniques. We discuss non-linear effects in such a system in the presence of the micro-instabilities, specifically a drift wave instability. We explore particle dynamics in different range of parameters and show that the transport changes from diffusive to non-diffusive when large directional flows are developed.

Time of flight dependent linearity in diffuse imaging: how effective is it to evaluate the spatial resolution by measuring the edge response function?

PubMed

Ortiz-Rascón, E; Bruce, N C; Rodríguez-Rosales, A A; Garduño-Mejía, J

2016-03-01

We describe the behavior of linearity in diffuse imaging by evaluating the differences between time-resolved images produced by photons arriving at the detector at different times. Two approaches are considered: Monte Carlo simulations and experimental results. The images of two complete opaque bars embedded in a transparent or in a turbid medium with a slab geometry are analyzed; the optical properties of the turbid medium sample are close to those of breast tissue. A simple linearity test was designed involving a direct comparison between the intensity profile produced by two bars scanned at the same time and the intensity profile obtained by adding two profiles of each bar scanned one at a time. It is shown that the linearity improves substantially when short time of flight photons are used in the imaging process, but even then the nonlinear behavior prevails. As the edge response function (ERF) has been used widely for testing the spatial resolution in imaging systems, the main implication of a time dependent linearity is the weakness of the linearity assumption when evaluating the spatial resolution through the ERF in diffuse imaging systems, and the need to evaluate the spatial resolution by other methods.

Apparatus and method for excluding gas from a liquid

DOEpatents

Murphy, Jr., Robert J.

1985-01-01

The present invention is directed to an apparatus and method for preventing diffusion of a gas under high pressure into the bulk of a liquid filling a substantially closed chamber. This apparatus and method is particularly useful in connection with test devices for testing fluid characteristics under harsh conditions of extremely high pressure and high temperature. These devices typically pressurize the liquid by placing the liquid in pressure and fluid communication with a high pressure inert gas. The apparatus and method of the present invention prevent diffusion of the pressurizing gas into the bulk of the test liquid by decreasing the chamber volume at a rate sufficient to maintain the bulk of the liquid free of absorbed or dissolved gas by expelling that portion of the liquid which is contaminated by the pressurizing gas.

Synthesis of Fullerenes in Low Pressure Benzene/Oxygen Diffusion Flames

NASA Technical Reports Server (NTRS)

Hebgen, Peter; Howard, Jack B.

1999-01-01

The interest in fullerenes is strongly increasing since their discovery by Kroto et al. in 1985 as products of the evaporation of carbon into inert gas at low pressure. Due to their all carbon closed-shell structure, fullerenes have many exceptional physical and chemical properties and a large potential for applications such as superconductors, sensors, catalysts, optical and electronic devices, polymers, high energy fuels, and biological and medical materials. This list is still growing, because the research on fullerenes is still at an early stage. Fullerenes can be formed not only in a system containing only carbon and an inert gas, but also in premixed hydrocarbon flames under reduced pressure and fuel rich conditions. The highest yields of fullerenes in flames are obtained under conditions of substantial soot formation. There is a need for more information on the yields of fullerenes under different conditions in order to understand the mechanisms of their formation and to enable the design of practical combustion systems for large-scale fullerene production. Little work has been reported on the formation of fullerenes in diffusion flames. In order to explore the yields of fullerenes and the effect of low pressure in diffusion flames, therefore we constructed and used a low pressure diffusion flame burner in this study.

Annealing of gallium nitride under high-N 2 pressure

NASA Astrophysics Data System (ADS)

Porowski, S.; Jun, J.; Krukowski, S.; Grzegory, I.; Leszczynski, M.; Suski, T.; Teisseyre, H.; Foxon, C. T.; Korakakis, D.

1999-04-01

GaN is the key material for blue and ultraviolet optoelectronics. It is a strongly bonded wurztite structure semiconductor with the direct energy gap 3.5 eV. Due to strong bonding, the diffusion processes require high temperatures, above 1300 K. However at this temperature range at ambient pressure, GaN becomes unstable and dissociates into Ga and N 2. Therefore high pressure of N 2 is required to study the diffusion and other annealing related processes. We studied annealing of bulk GaN nitride single crystals grown under high pressure and also annealing of homo- and heteroepitaxial GaN layers grown by MOCVD technique. Annealing at temperatures above 1300 K influences strongly the structural and optical properties of GaN crystals and layers. At this temperature diffusion of the Mg and Zn acceptors have been observed. In spite of very interesting experimental observations the understanding of microscopic mechanisms of these processes is limited.

Correlations, soliton modes, and non-Hermitian linear mode transmutation in the one-dimensional noisy Burgers equation.

PubMed

Fogedby, Hans C

2003-08-01

Using the previously developed canonical phase space approach applied to the noisy Burgers equation in one dimension, we discuss in detail the growth morphology in terms of nonlinear soliton modes and superimposed linear modes. We moreover analyze the non-Hermitian character of the linear mode spectrum and the associated dynamical pinning, and mode transmutation from diffusive to propagating behavior induced by the solitons. We discuss the anomalous diffusion of growth modes, switching and pathways, correlations in the multisoliton sector, and in detail the correlations and scaling properties in the two-soliton sector.

Influence of the light propagation models on a linearized photoacoustic image reconstruction of the light absorption coefficient

NASA Astrophysics Data System (ADS)

Okawa, Shinpei; Hirasawa, Takeshi; Kushibiki, Toshihiro; Ishihara, Miya

2015-03-01

Quantification of the optical properties of the tissues and blood by noninvasive photoacoustic (PA) imaging may provide useful information for screening and early diagnosis of diseases. Linearized 2D image reconstruction algorithm based on PA wave equation and the photon diffusion equation (PDE) can reconstruct the image with computational cost smaller than a method based on 3D radiative transfer equation. However, the reconstructed image is affected by the differences between the actual and assumed light propagations. A quantitative capability of a linearized 2D image reconstruction was investigated and discussed by the numerical simulations and the phantom experiment in this study. The numerical simulations with the 3D Monte Carlo (MC) simulation and the 2D finite element calculation of the PDE were carried out. The phantom experiment was also conducted. In the phantom experiment, the PA pressures were acquired by a probe which had an optical fiber for illumination and the ring shaped P(VDF-TrFE) ultrasound transducer. The measured object was made of Intralipid and Indocyanine green. In the numerical simulations, it was shown that the linearized image reconstruction method recovered the absorption coefficients with alleviating the dependency of the PA amplitude on the depth of the photon absorber. The linearized image reconstruction method worked effectively under the light propagation calculated by 3D MC simulation, although some errors occurred. The phantom experiments validated the result of the numerical simulations.

Tomographic Imaging of Water Injection and Withdrawal in PEMFC Gas Diffusion Layers

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

McGill U; Gostick, J. T.; Gunterman, H. P.

2010-06-25

X-ray computed tomography was used to visualize the water configurations inside gas diffusion layers for various applied capillary pressures, corresponding to both water invasion and withdrawal. A specialized sample holder was developed to allow capillary pressure control on the small-scale samples required. Tests were performed on GDL specimens with and without hydrophobic treatments.

Flow Through a Rectangular-to-Semiannular Diffusing Transition Duct

NASA Technical Reports Server (NTRS)

Foster, Jeff; Wendt, Bruce J.; Reichert, Bruce A.; Okiishi, Theodore H.

1997-01-01

Rectangular-to-semiannular diffusing transition ducts are critical inlet components on supersonic airplanes having bifucated engine inlets. This paper documents measured details of the flow through a rectangular-to-semiannular transition duct having an expansion area ratio of 1.53. Three-dimensional velocity vectors and total pressures at the exit plane of the diffuser are presented. Surface oil-flow visualization and surface static pressure data are shown. The tests were conducted with an inlet Mach number of 0.786 and a Reynolds number based on the inlet centerline velocity and exit diameter of 3.2 x 10(exp 6). The measured data are compared with previously published computational results. The ability of vortex generators to reduce circumferential total pressure distortion is demonstrated.

Combined hydraulic and regenerative braking system

DOEpatents

Venkataperumal, R.R.; Mericle, G.E.

1979-08-09

A combined hydraulic and regenerative braking system and method for an electric vehicle is disclosed. The braking system is responsive to the applied hydraulic pressure in a brake line to control the braking of the vehicle to be completely hydraulic up to a first level of brake line pressure, to be partially hydraulic at a constant braking force and partially regenerative at a linearly increasing braking force from the first level of applied brake line pressure to a higher second level of brake line pressure, to be partially hydraulic at a linearly increasing braking force and partially regenerative at a linearly decreasing braking force from the second level of applied line pressure to a third and higher level of applied line pressure, and to be completely hydraulic at a linearly increasing braking force from the third level to all higher applied levels of line pressure.

Combined hydraulic and regenerative braking system

DOEpatents

Venkataperumal, Rama R.; Mericle, Gerald E.

1981-06-02

A combined hydraulic and regenerative braking system and method for an electric vehicle, with the braking system being responsive to the applied hydraulic pressure in a brake line to control the braking of the vehicle to be completely hydraulic up to a first level of brake line pressure, to be partially hydraulic at a constant braking force and partially regenerative at a linearly increasing braking force from the first level of applied brake line pressure to a higher second level of brake line pressure, to be partially hydraulic at a linearly increasing braking force and partially regenerative at a linearly decreasing braking force from the second level of applied line pressure to a third and higher level of applied line pressure, and to be completely hydraulic at a linearly increasing braking force from the third level to all higher applied levels of line pressure.

Investigation of the expansion rate scaling of plasmas in the Electron Diffusion Gauge experiment

NASA Astrophysics Data System (ADS)

Morrison, Kyle A.; Davidson, Ronald C.; Paul, Stephen F.; Jenkins, Thomas G.

2002-01-01

The expansion of the Electron Diffusion Gauge (EDG) pure electron plasma due to collisions with background neutral gas atoms is characterized by the pressure and magnetic field scaling of the profile expansion rate (d/dt). Data obtained at higher background gas pressures [1] than previously studied [2] is presented. The measured expansion rate in the higher pressure regime is found to be in good agreement with the classical estimate of the expansion rate [3].

Implications of pressure diffusion for shock waves

NASA Technical Reports Server (NTRS)

Ram, Ram Bachan

1989-01-01

The report deals with the possible implications of pressure diffusion for shocks in one dimensional traveling waves in an ideal gas. From this new hypothesis all aspects of such shocks can be calculated except shock thickness. Unlike conventional shock theory, the concept of entropy is not needed or used. Our analysis shows that temperature rises near a shock, which is of course an experimental fact; however, it also predicts that very close to a shock, density increases faster than pressure. In other words, a shock itself is cold.

Finite-time robust passive control for a class of switched reaction-diffusion stochastic complex dynamical networks with coupling delays and impulsive control

NASA Astrophysics Data System (ADS)

Syed Ali, M.; Yogambigai, J.; Kwon, O. M.

2018-03-01

Finite-time boundedness and finite-time passivity for a class of switched stochastic complex dynamical networks (CDNs) with coupling delays, parameter uncertainties, reaction-diffusion term and impulsive control are studied. Novel finite-time synchronisation criteria are derived based on passivity theory. This paper proposes a CDN consisting of N linearly and diffusively coupled identical reaction- diffusion neural networks. By constructing of a suitable Lyapunov-Krasovskii's functional and utilisation of Jensen's inequality and Wirtinger's inequality, new finite-time passivity criteria for the networks are established in terms of linear matrix inequalities (LMIs), which can be checked numerically using the effective LMI toolbox in MATLAB. Finally, two interesting numerical examples are given to show the effectiveness of the theoretical results.

Stimulated echo diffusion tensor imaging (STEAM-DTI) with varying diffusion times as a probe of breast tissue.

PubMed

Teruel, Jose R; Cho, Gene Y; Moccaldi Rt, Melanie; Goa, Pål E; Bathen, Tone F; Feiweier, Thorsten; Kim, Sungheon G; Moy, Linda; Sigmund, Eric E

2017-01-01

To explore the application of diffusion tensor imaging (DTI) for breast tissue and breast pathologies using a stimulated-echo acquisition mode (STEAM) with variable diffusion times. In this Health Insurance Portability and Accountability Act-compliant study, approved by the local institutional review board, eight patients and six healthy volunteers underwent an MRI examination at 3 Tesla including STEAM-DTI with several diffusion times ranging from 68.5 to 902.5 ms. A DTI model was fitted to the data for each diffusion time, and parametric maps of mean diffusivity, fractional anisotropy, axial diffusivity, and radial diffusivity were computed for healthy fibroglandular tissue (FGT) and lesions. The median value of radial diffusivity for FGT was fitted to a linear decay to obtain an estimation of the surface-to-volume ratio, from which the radial diameter was calculated. For healthy FGT, radial diffusivity presented a linear decay with the square root of the diffusion time resulting in a range of estimated radial diameters from 202 to 496 µm, while axial diffusivity presented a nearly time-independent diffusion. Residual fat signal was reduced at longer diffusion times due to the shorter T1 of fat. Residual fat signal to the overall signal in the healthy volunteers' FGT was found to range from 2.39% to 2.55% (shortest mixing time), and from 0.40% to 0.51% (longest mixing time) for the b500 images. The use of variable diffusion times may provide an in vivo noninvasive tool to probe diffusion lengths in breast tissue and breast pathology, and might aid by improving fat suppression at longer diffusion times. 2 J. Magn. Reson. Imaging 2017;45:84-93. © 2016 International Society for Magnetic Resonance in Medicine.

Melting properties of Pt and its transport coefficients in liquid states under high pressures

NASA Astrophysics Data System (ADS)

Wang, Pan-Pan; Shao, Ju-Xiang; Cao, Qi-Long

2016-11-01

Molecular dynamics (MD) simulations of the melting and transport properties in liquid states of platinum for the pressure range (50-200 GPa) are reported. The melting curve of platinum is consistent with previous ab initio MD simulation results and the first-principles melting curve. Calculated results for the pressure dependence of fusion entropy and fusion volume show that the fusion entropy and the fusion volume decrease with increasing pressure, and the ratio of the fusion volume to fusion entropy roughly reproduces the melting slope, which has a moderate decrease along the melting line. The Arrhenius law well describes the temperature dependence of self-diffusion coefficients and viscosity under high pressure, and the diffusion activation energy decreases with increasing pressure, while the viscosity activation energy increases with increasing pressure. In addition, the entropy-scaling law, proposed by Rosenfeld under ambient pressure, still holds well for liquid Pt under high pressure conditions.

Linear and nonlinear 2D finite element analysis of sloshing modes and pressures in rectangular tanks subject to horizontal harmonic motions

NASA Astrophysics Data System (ADS)

Virella, Juan C.; Prato, Carlos A.; Godoy, Luis A.

2008-05-01

The influence of nonlinear wave theory on the sloshing natural periods and their modal pressure distributions are investigated for rectangular tanks under the assumption of two-dimensional behavior. Natural periods and mode shapes are computed and compared for both linear wave theory (LWT) and nonlinear wave theory (NLWT) models, using the finite element package ABAQUS. Linear wave theory is implemented in an acoustic model, whereas a plane strain problem with large displacements is used in NLWT. Pressure distributions acting on the tank walls are obtained for the first three sloshing modes using both linear and nonlinear wave theory. It is found that the nonlinearity does not have significant effects on the natural sloshing periods. For the sloshing pressures on the tank walls, different distributions were found using linear and nonlinear wave theory models. However, in all cases studied, the linear wave theory conservatively estimated the magnitude of the pressure distribution, whereas larger pressures resultant heights were obtained when using the nonlinear theory. It is concluded that the nonlinearity of the surface wave does not have major effects in the pressure distribution on the walls for rectangular tanks.

Passive Rocket Diffuser Theory: A Re-Examination of Minimum Second Throat Size

NASA Technical Reports Server (NTRS)

Jones, Daniel R.

2016-01-01

Second-throat diffusers serve to isolate rocket engines from the effects of ambient back pressure during testing without using active control systems. Among the most critical design parameters is the relative area of the diffuser throat to that of the nozzle throat. A smaller second throat is generally desirable because it decreases the stagnation-to-ambient pressure ratio the diffuser requires for nominal operation. There is a limit, however. Below a certain size, the second throat can cause pressure buildup within the diffuser and prevent it from reaching the start condition that protects the nozzle from side-load damage. This paper presents a method for improved estimation of the minimum second throat area which enables diffuser start. The new 3-zone model uses traditional quasi-one-dimensional compressible flow theory to approximate the structure of two distinct diffuser flow fields observed in Computational Fluid Dynamics (CFD) simulations and combines them to provide a less-conservative estimate of the second throat size limit. It is unique among second throat sizing methods in that it accounts for all major conical nozzle and second throat diffuser design parameters within its limits of application. The performance of the 3-zone method is compared to the historical normal shock and force balance methods, and verified against a large number of CFD simulations at specific heat ratios of 1.4 and 1.25. Validation is left as future work, and the model is currently intended to function only as a first-order design tool.

Flash crystallization kinetics of methane (sI) hydrate in a thermoelectrically-cooled microreactor.

PubMed

Chen, Weiqi; Pinho, Bruno; Hartman, Ryan L

2017-09-12

The crystallization kinetics of methane (sI) hydrate were investigated in a thermoelectrically-cooled microreactor with in situ Raman spectroscopy. Step-wise and precise control of the temperature allowed acquisition of reproducible data within minutes, while the nucleation of methane hydrates can take up to 24 h in traditional batch reactors. The propagation rates of methane hydrate (from 3.1-196.3 μm s -1 ) at the gas-liquid interface were measured for different Reynolds' numbers (0.7-68.9), pressures (30.0-80.9 bar), and sub-cooling temperatures (1.0-4.0 K). The precise measurement of the propagation rates and their subsequent analyses revealed a transition from mixed heat-transfer-crystallization-rate-limited to mixed heat-transfer-mass-transfer-crystallization-rate-limited kinetics. A theoretical model, based on heat transfer, mass transfer, and intrinsic crystallization kinetics, was derived for the first time to understand the non-linear relationship between the propagation rate and sub-cooling temperature. The molecular diffusivity of methane within a stagnant film (ahead of the propagation front) was discovered to follow Stokes-Einstein, while calculated Hatta (0.50-0.68), Lewis (128-207), and beta (0.79-116) numbers also confirmed that the diffusive flux influences crystal growth. Understanding methane hydrate crystal growth is important to the atmospheric, oceanic, and planetary sciences and to energy production, storage, and transportation. Our discoveries could someday advance the science of other multiphase, high-pressure, and sub-cooled crystallizations.

A novel method for calculating the energy barriers for carbon diffusion in ferrite under heterogeneous stress

NASA Astrophysics Data System (ADS)

Tchitchekova, Deyana S.; Morthomas, Julien; Ribeiro, Fabienne; Ducher, Roland; Perez, Michel

2014-07-01

A novel method for accurate and efficient evaluation of the change in energy barriers for carbon diffusion in ferrite under heterogeneous stress is introduced. This method, called Linear Combination of Stress States, is based on the knowledge of the effects of simple stresses (uniaxial or shear) on these diffusion barriers. Then, it is assumed that the change in energy barriers under a complex stress can be expressed as a linear combination of these already known simple stress effects. The modifications of energy barriers by either uniaxial traction/compression and shear stress are determined by means of atomistic simulations with the Climbing Image-Nudge Elastic Band method and are stored as a set of functions. The results of this method are compared to the predictions of anisotropic elasticity theory. It is shown that, linear anisotropic elasticity fails to predict the correct energy barrier variation with stress (especially with shear stress) whereas the proposed method provides correct energy barrier variation for stresses up to ˜3 GPa. This study provides a basis for the development of multiscale models of diffusion under non-uniform stress.

A novel method for calculating the energy barriers for carbon diffusion in ferrite under heterogeneous stress.

PubMed

Tchitchekova, Deyana S; Morthomas, Julien; Ribeiro, Fabienne; Ducher, Roland; Perez, Michel

2014-07-21

A novel method for accurate and efficient evaluation of the change in energy barriers for carbon diffusion in ferrite under heterogeneous stress is introduced. This method, called Linear Combination of Stress States, is based on the knowledge of the effects of simple stresses (uniaxial or shear) on these diffusion barriers. Then, it is assumed that the change in energy barriers under a complex stress can be expressed as a linear combination of these already known simple stress effects. The modifications of energy barriers by either uniaxial traction/compression and shear stress are determined by means of atomistic simulations with the Climbing Image-Nudge Elastic Band method and are stored as a set of functions. The results of this method are compared to the predictions of anisotropic elasticity theory. It is shown that, linear anisotropic elasticity fails to predict the correct energy barrier variation with stress (especially with shear stress) whereas the proposed method provides correct energy barrier variation for stresses up to ∼3 GPa. This study provides a basis for the development of multiscale models of diffusion under non-uniform stress.

Laminar Soot Processes (Lsp) Experiment: Findings From Ground-Based Measurements

NASA Technical Reports Server (NTRS)

Kim, C. H.; El-Leathy, A. M.; Faeth, G. M.; Xu, F.

2003-01-01

Processes of soot formation and oxidation must be understood in order to achieve reliable computational combustion calculations for nonpremixed (diffusion) flames involving hydrocarbon fuels. Motivated by this observation, the present investigation extended earlier work on soot formation and oxidation in laminar jet ethylene/air and methane/oxygen premixed and acetylene-nitrogen/air diffusion flames at atmospheric pressure in this laboratory, emphasizing soot surface growth and early soot surface oxidation in laminar diffusion flames fueled with a variety of hydrocarbons at pressures in the range 0.1 - 1.0 atm.

High pressure flame system for pollution studies with results for methane-air diffusion flames

NASA Technical Reports Server (NTRS)

Miller, I. M.; Maahs, H. G.

1977-01-01

A high pressure flame system was designed and constructed for studying nitrogen oxide formation in fuel air combustion. Its advantages and limitations were demonstrated by tests with a confined laminar methane air diffusion flame over the pressure range from 1 to 50 atm. The methane issued from a 3.06 mm diameter port concentrically into a stream of air contained within a 20.5 mm diameter chimney. As the combustion pressure is increased, the flame changes in shape from wide and convex to slender and concave, and there is a marked increase in the amount of luminous carbon. The height of the flame changes only moderately with pressure.

Influence of rotating wakes on separation in turbine exhaust diffusers

NASA Astrophysics Data System (ADS)

Sieker, Olaf; Seume, Joerg R.

2008-03-01

Highly efficient turbine exhaust diffuser cannot be designed without taking into account the unsteady interactions with the last rotating row of the turbine. Former investigations described in the literature show a very high potential compared to that of other parts of turbomachines for improving the diffuser. A scale model of a typical gas turbine exhaust diffuser is investigated experimentally. To investigate the influence of rotating wakes, measurements without a spoke wheel as well as measurements with a variable-speed rotating cylindrical spoke wheel with 2 mm-or 10 mm-spokes simulating turbine rotor wakes were made. Miniaturized 3-hole pneumatic probes as well as a 2D-Laser-Doppler-Velocimeter (LDV) were used to investigate velocity profiles. 122 static pressure tapings were used to measure several axial and circumferential static pressure distributions. Without a spoke-wheel the annular diffuser separates at the shroud for all swirl configurations. For the measurements with the 2 mm spoke wheel, the separating diffuser was unstable while keeping the test rig operating parameters constant. For a non-rotating 10 mm spoke wheel and at rotational speeds less than 1,000 rpm, the annular diffuser separated at the shroud. In-creasing the rotational speed of the 10mm spoke wheel, flow did not separate at the shroud and much higher pressure recovery than without spoke wheel has achieved.

Mass Transport of Macromolecules within an In Vitro Model of Supragingival Plaque

PubMed Central

Thurnheer, Thomas; Gmür, Rudolf; Shapiro, Stuart; Guggenheim, Bernhard

2003-01-01

The aim of this study was to examine the diffusion of macromolecules through an in vitro biofilm model of supragingival plaque. Polyspecies biofilms containing Actinomyces naeslundii, Fusobacterium nucleatum, Streptococcus oralis, Streptococcus sobrinus, Veillonella dispar, and Candida albicans were formed on sintered hydroxyapatite disks and then incubated at room temperature for defined periods with fluorescent markers with molecular weights ranging from 3,000 to 900,000. Subsequent examination by confocal laser scanning microscopy revealed that the mean square penetration depths for all tested macromolecules except immunoglobulin M increased linearly with time, diffusion coefficients being linearly proportional to the cube roots of the molecular weights of the probes (range, 10,000 to 240,000). Compared to diffusion in bulk water, diffusion in the biofilms was markedly slower. The rate of diffusion for each probe appeared to be constant and not a function of biofilm depth. Analysis of diffusion phenomena through the biofilms suggested tortuosity as the most probable explanation for retarded diffusion. Selective binding of probes to receptors present in the biofilms could not explain the observed extent of retardation of diffusion. These results are relevant to oral health, as selective attenuated diffusion of fermentable carbohydrates and acids produced within dental plaque is thought to be essential for the development of carious lesions. PMID:12620862

Initiation and propagation of a PKN hydraulic fracture in permeable rock: Toughness dominated regime

NASA Astrophysics Data System (ADS)

Sarvaramini, E.; Garagash, D.

2011-12-01

The present work investigates the injection of a low-viscosity fluid into a pre-existing fracture with constrained height (PKN), as in waterflooding or supercritical CO2 injection. Contrary to conventional hydraulic fracturing, where 'cake build up' limits diffusion to a small zone, the low viscosity fluid allows for diffusion over a wider range of scales. Over large injection times the pattern becomes 2 or 3-D, necessitating a full-space diffusion modeling. In addition, the dissipation of energy associated with fracturing of rock dominates the energy needed for the low-viscosity fluid flow into the propagating crack. As a result, the fracture toughness is important in evaluating both the initiation and the ensuing propagation of these fractures. Classical PKN hydraulic fracturing model, amended to account for full-space leak-off and the toughness [Garagash, unpublished 2009], is used to evaluate the pressure history and fluid leak-off volume during the injection of low viscosity fluid into a pre-existing and initially stationary. In order to find the pressure history, the stationary crack is first subject to a step pressure increase. The response of the porous medium to the step pressure increase in terms of fluid leak-off volume provides the fundamental solution, which then can be used to find the transient pressurization using Duhamel theorem [Detournay & Cheng, IJSS 1991]. For the step pressure increase an integral equation technique is used to find the leak-off rate history. For small time the solution must converge to short time asymptote, which corresponds to 1-D diffusion pattern. However, as the diffusion length in the zone around the fracture increases the assumption of a 1-D pattern is no longer valid and the diffusion follows a 2-D pattern. The solution to the corresponding integral equation gives the leak-off rate history, which is used to find the cumulative leak-off volume. The transient pressurization solution is obtained using global conservation of fluid injected into the fracture. With increasing pressure in the fracture due to the fluid injection, the energy release rate eventually becomes equal to the toughness and fracture propagates. The evolution of the fracture length is established using the method similar to the one employed for the stationary crack.

A Framework for Linear and Non-Linear Registration of Diffusion-Weighted MRIs Using Angular Interpolation

PubMed Central

Duarte-Carvajalino, Julio M.; Sapiro, Guillermo; Harel, Noam; Lenglet, Christophe

2013-01-01

Registration of diffusion-weighted magnetic resonance images (DW-MRIs) is a key step for population studies, or construction of brain atlases, among other important tasks. Given the high dimensionality of the data, registration is usually performed by relying on scalar representative images, such as the fractional anisotropy (FA) and non-diffusion-weighted (b0) images, thereby ignoring much of the directional information conveyed by DW-MR datasets itself. Alternatively, model-based registration algorithms have been proposed to exploit information on the preferred fiber orientation(s) at each voxel. Models such as the diffusion tensor or orientation distribution function (ODF) have been used for this purpose. Tensor-based registration methods rely on a model that does not completely capture the information contained in DW-MRIs, and largely depends on the accurate estimation of tensors. ODF-based approaches are more recent and computationally challenging, but also better describe complex fiber configurations thereby potentially improving the accuracy of DW-MRI registration. A new algorithm based on angular interpolation of the diffusion-weighted volumes was proposed for affine registration, and does not rely on any specific local diffusion model. In this work, we first extensively compare the performance of registration algorithms based on (i) angular interpolation, (ii) non-diffusion-weighted scalar volume (b0), and (iii) diffusion tensor image (DTI). Moreover, we generalize the concept of angular interpolation (AI) to non-linear image registration, and implement it in the FMRIB Software Library (FSL). We demonstrate that AI registration of DW-MRIs is a powerful alternative to volume and tensor-based approaches. In particular, we show that AI improves the registration accuracy in many cases over existing state-of-the-art algorithms, while providing registered raw DW-MRI data, which can be used for any subsequent analysis. PMID:23596381

A Framework for Linear and Non-Linear Registration of Diffusion-Weighted MRIs Using Angular Interpolation.

PubMed

Duarte-Carvajalino, Julio M; Sapiro, Guillermo; Harel, Noam; Lenglet, Christophe

2013-01-01

Registration of diffusion-weighted magnetic resonance images (DW-MRIs) is a key step for population studies, or construction of brain atlases, among other important tasks. Given the high dimensionality of the data, registration is usually performed by relying on scalar representative images, such as the fractional anisotropy (FA) and non-diffusion-weighted (b0) images, thereby ignoring much of the directional information conveyed by DW-MR datasets itself. Alternatively, model-based registration algorithms have been proposed to exploit information on the preferred fiber orientation(s) at each voxel. Models such as the diffusion tensor or orientation distribution function (ODF) have been used for this purpose. Tensor-based registration methods rely on a model that does not completely capture the information contained in DW-MRIs, and largely depends on the accurate estimation of tensors. ODF-based approaches are more recent and computationally challenging, but also better describe complex fiber configurations thereby potentially improving the accuracy of DW-MRI registration. A new algorithm based on angular interpolation of the diffusion-weighted volumes was proposed for affine registration, and does not rely on any specific local diffusion model. In this work, we first extensively compare the performance of registration algorithms based on (i) angular interpolation, (ii) non-diffusion-weighted scalar volume (b0), and (iii) diffusion tensor image (DTI). Moreover, we generalize the concept of angular interpolation (AI) to non-linear image registration, and implement it in the FMRIB Software Library (FSL). We demonstrate that AI registration of DW-MRIs is a powerful alternative to volume and tensor-based approaches. In particular, we show that AI improves the registration accuracy in many cases over existing state-of-the-art algorithms, while providing registered raw DW-MRI data, which can be used for any subsequent analysis.

Metallic diffusion measured by a modified Knudsen technique

NASA Technical Reports Server (NTRS)

Fray, D. J.

1969-01-01

Diffusion coefficient of a metal in high temperature system is determined. From the measurement of the weight loss from a Knudsen cell, the vapor pressure of the escaping species can be calculated. If the only way this species can enter the Knudsen cell is by diffusion through a foil, the weight loss is diffusion flux.

Pickup protons and water ions at Comet Halley - Comparisons with Giotto observations

NASA Astrophysics Data System (ADS)

Ye, G.; Cravens, T. E.; Gombosi, T. I.

1993-02-01

The cometary ion pickup process along the sun-comet line at Comet Halley is investigated using a quasi-linear diffusion model including both pitch angle and energy diffusion, adiabatic compression, and convective motion with the solar wind flow. The model results are compared with energetic ion distributions observed by instruments on board the Giotto spacecraft. The observed power spectrum index of magnetic turbulence (gamma) is 2-2.5. The present simulation shows that when gamma was 2, the calculated proton distributions were much more isotropic than the observed ones. The numerical solutions of the quasi-linear diffusion equations show that the isotropization of the pickup ion distribution, particularly at the pickup velocity, is not complete even close to the bow shock. Given the observed turbulence level, quasi-linear theory yields pickup ion energy distributions that agree with the observed ones quite well and easily produces energetic ions with energies up to hundreds of keV.

The Dynamics of Entangled DNA Networks using Single-Molecule Methods

NASA Astrophysics Data System (ADS)

Chapman, Cole David

Single molecule experiments were performed on DNA, a model polymer, and entangled DNA networks to explore diffusion within complex polymeric fluids and their linear and non-linear viscoelasticity. DNA molecules of varying length and topology were prepared using biological methods. An ensemble of individual molecules were then fluorescently labeled and tracked in blends of entangled linear and circular DNA to examine the dependence of diffusion on polymer length, topology, and blend ratio. Diffusion was revealed to possess a non-monotonic dependence on the blend ratio, which we believe to be due to a second-order effect where the threading of circular polymers by their linear counterparts greatly slows the mobility of the system. Similar methods were used to examine the diffusive and conformational behavior of DNA within highly crowded environments, comparable to that experienced within the cell. A previously unseen gamma distributed elongation of the DNA in the presence of crowders, proposed to be due to entropic effects and crowder mobility, was observed. Additionally, linear viscoelastic properties of entangled DNA networks were explored using active microrheology. Plateau moduli values verified for the first time the predicted independence from polymer length. However, a clear bead-size dependence was observed for bead radii less than ~3x the tube radius, a newly discovered limit, above which microrheology results are within the continuum limit and may access the bulk properties of the fluid. Furthermore, the viscoelastic properties of entangled DNA in the non-linear regime, where the driven beads actively deform the network, were also examined. By rapidly driving a bead through the network utilizing optical tweezers, then removing the trap and tracking the bead's subsequent motion we are able to model the system as an over-damped harmonic oscillator and find the elasticity to be dominated by stress-dependent entanglements.

Models of collective cell spreading with variable cell aspect ratio: a motivation for degenerate diffusion models.

PubMed

Simpson, Matthew J; Baker, Ruth E; McCue, Scott W

2011-02-01

Continuum diffusion models are often used to represent the collective motion of cell populations. Most previous studies have simply used linear diffusion to represent collective cell spreading, while others found that degenerate nonlinear diffusion provides a better match to experimental cell density profiles. In the cell modeling literature there is no guidance available with regard to which approach is more appropriate for representing the spreading of cell populations. Furthermore, there is no knowledge of particular experimental measurements that can be made to distinguish between situations where these two models are appropriate. Here we provide a link between individual-based and continuum models using a multiscale approach in which we analyze the collective motion of a population of interacting agents in a generalized lattice-based exclusion process. For round agents that occupy a single lattice site, we find that the relevant continuum description of the system is a linear diffusion equation, whereas for elongated rod-shaped agents that occupy L adjacent lattice sites we find that the relevant continuum description is connected to the porous media equation (PME). The exponent in the nonlinear diffusivity function is related to the aspect ratio of the agents. Our work provides a physical connection between modeling collective cell spreading and the use of either the linear diffusion equation or the PME to represent cell density profiles. Results suggest that when using continuum models to represent cell population spreading, we should take care to account for variations in the cell aspect ratio because different aspect ratios lead to different continuum models.

Gyrokinetic modelling of the quasilinear particle flux for plasmas with neutral-beam fuelling

NASA Astrophysics Data System (ADS)

Narita, E.; Honda, M.; Nakata, M.; Yoshida, M.; Takenaga, H.; Hayashi, N.

2018-02-01

A quasilinear particle flux is modelled based on gyrokinetic calculations. The particle flux is estimated by determining factors, namely, coefficients of off-diagonal terms and a particle diffusivity. In this paper, the methodology to estimate the factors is presented using a subset of JT-60U plasmas. First, the coefficients of off-diagonal terms are estimated by linear gyrokinetic calculations. Next, to obtain the particle diffusivity, a semi-empirical approach is taken. Most experimental analyses for particle transport have assumed that turbulent particle fluxes are zero in the core region. On the other hand, even in the stationary state, the plasmas in question have a finite turbulent particle flux due to neutral-beam fuelling. By combining estimates of the experimental turbulent particle flux and the coefficients of off-diagonal terms calculated earlier, the particle diffusivity is obtained. The particle diffusivity should reflect a saturation amplitude of instabilities. The particle diffusivity is investigated in terms of the effects of the linear instability and linear zonal flow response, and it is found that a formula including these effects roughly reproduces the particle diffusivity. The developed framework for prediction of the particle flux is flexible to add terms neglected in the current model. The methodology to estimate the quasilinear particle flux requires so low computational cost that a database consisting of the resultant coefficients of off-diagonal terms and particle diffusivity can be constructed to train a neural network. The development of the methodology is the first step towards a neural-network-based particle transport model for fast prediction of the particle flux.

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

Wolfram, Phillip J.; Ringler, Todd D.

Meridional diffusivity is assessed in this paper for a baroclinically unstable jet in a high-latitudeIdealized Circumpolar Current (ICC) using the Model for Prediction Across Scales-Ocean (MPAS-O) and the online Lagrangian In-situ Global High-performance particle Tracking (LIGHT) diagnostic via space-time dispersion of particle clusters over 120 monthly realizations of O(10 6) particles on 11 potential density surfaces. Diffusivity in the jet reaches values of O(6000 m 2 s -1) and is largest near the critical layer supporting mixing suppression and critical layer theory. Values in the vicinity of the shelf break are suppressed to O(100 m 2 s -1) due tomore » the presence of westward slope front currents. Diffusivity attenuates less rapidly with depth in the jet than both eddy velocity and kinetic energy scalings would suggest. Removal of the mean flow via high-pass filtering shifts the nonlinear parameter (ratio of the eddy velocity to eddy phase speed) into the linear wave regime by increasing the eddy phase speed via the depth-mean flow. Low-pass filtering, in contrast, quantifies the effect of mean shear. Diffusivity is decomposed into mean flow shear, linear waves, and the residual nonhomogeneous turbulence components, where turbulence dominates and eddy-produced filamentation strained by background mean shear enhances mixing, accounting for ≥ 80% of the total diffusivity relative to mean shear [O(100 m 2 s -1)], linear waves [O(1000 m 2 s -1)], and undecomposed full diffusivity [O(6000 m 2 s -1)]. Finally, diffusivity parameterizations accounting for both the nonhomogeneous turbulence residual and depth variability are needed.« less

Sb lattice diffusion in Si1-xGex/Si(001) heterostructures: Chemical and stress effects

NASA Astrophysics Data System (ADS)

Portavoce, A.; Gas, P.; Berbezier, I.; Ronda, A.; Christensen, J. S.; Kuznetsov, A. Yu.; Svensson, B. G.

2004-04-01

The Sb diffusion coefficient in Si1-xGex/Si1-yGey(001) heterostructures grown by molecular beam epitaxy (MBE) was measured for temperatures ranging from 700 to 850 °C, Ge composition from 0 to 20 % and biaxial pressure from -0.8 (tension) to 1.4 GPa (compression). A quantitative separation of composition and biaxial stress effects is made. We show that the Sb lattice diffusion coefficient: (i) increases with Ge concentration in relaxed layers or at constant biaxial pressure and (ii) increases with compressive biaxial stress and decreases with tensile biaxial stress at constant Ge composition. The enhancement of Sb lattice diffusion in Si1-xGex layers in epitaxy on Si(001) is thus due to the cooperative effect of Ge composition and induced compressive biaxial stress. However, the first effect (composition) is predominant. The activation volume of Sb diffusion in Si1-xGex layers is deduced from the variation of the Sb diffusion coefficients with biaxial pressure. This volume is negative. The sign of the activation volume, its absolute value and its variation with temperature confirm the prediction of the thermodynamic model proposed by Aziz, namely, that under a biaxial stress the activation volume is reduced to the relaxation volume.

Permeability Variations Associated With Fault Reactivation in a Claystone Formation Investigated by Field Experiments and Numerical Simulations

NASA Astrophysics Data System (ADS)

Jeanne, Pierre; Guglielmi, Yves; Rutqvist, Jonny; Nussbaum, Christophe; Birkholzer, Jens

2018-02-01

We studied the relation between rupture and changes in permeability within a fault zone intersecting the Opalinus Clay formation at 300 m depth in the Mont Terri Underground Research Laboratory (Switzerland). A series of water injection experiments were performed in a borehole straddle interval set within the damage zone of the main fault. A three-component displacement sensor allowed an estimation of the displacement of a minor fault plane reactivated during a succession of step rate pressure tests. The experiment reveals that the fault hydromechanical (HM) behavior is different from one test to the other with varying pressure levels needed to trigger rupture and different slip behavior under similar pressure conditions. Numerical simulations were performed to better understand the reason for such different behavior and to investigate the relation between rupture nucleation, permeability change, pressure diffusion, and rupture propagation. Our main findings are as follows: (i) a rate frictional law and a rate-and-state permeability law can reproduce the first test, but it appears that the rate constitutive parameters must be pressure dependent to reproduce the complex HM behavior observed during the successive injection tests; (ii) almost similar ruptures can create or destroy the fluid diffusion pathways; (iii) a too high or too low diffusivity created by the main rupture prevents secondary rupture events from occurring whereas "intermediate" diffusivity favors the nucleation of a secondary rupture associated with the fluid diffusion. However, because rupture may in certain cases destroy permeability, this succession of ruptures may not necessarily create a continuous hydraulic pathway.

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.

Analysis of baseline, average, and longitudinally measured blood pressure data using linear mixed models.

PubMed

Hossain, Ahmed; Beyene, Joseph

2014-01-01

This article compares baseline, average, and longitudinal data analysis methods for identifying genetic variants in genome-wide association study using the Genetic Analysis Workshop 18 data. We apply methods that include (a) linear mixed models with baseline measures, (b) random intercept linear mixed models with mean measures outcome, and (c) random intercept linear mixed models with longitudinal measurements. In the linear mixed models, covariates are included as fixed effects, whereas relatedness among individuals is incorporated as the variance-covariance structure of the random effect for the individuals. The overall strategy of applying linear mixed models decorrelate the data is based on Aulchenko et al.'s GRAMMAR. By analyzing systolic and diastolic blood pressure, which are used separately as outcomes, we compare the 3 methods in identifying a known genetic variant that is associated with blood pressure from chromosome 3 and simulated phenotype data. We also analyze the real phenotype data to illustrate the methods. We conclude that the linear mixed model with longitudinal measurements of diastolic blood pressure is the most accurate at identifying the known single-nucleotide polymorphism among the methods, but linear mixed models with baseline measures perform best with systolic blood pressure as the outcome.

Persistent wind-induced enhancement of diffusive CO2 transport in a mountain forest snowpack

Treesearch

D. R. Bowling; W. J. Massman

2011-01-01

Diffusion dominates the transport of trace gases between soil and the atmosphere. Pressure gradients induced by atmospheric flow and wind interacting with topographical features cause a small but persistent bulk flow of air within soil or snow. This forcing, called pressure pumping or wind pumping, leads to a poorly quantified enhancement of gas transport beyond the...

Force and Pressure Recovery Characteristics at Supersonic Speeds of a Conical Spike Inlet with a Bypass Discharging from the Top or Bottom of the Diffuser in an Axial Direction

NASA Technical Reports Server (NTRS)

Allen, J L; Beke, Andrew

1953-01-01

Force and pressure-recovery characteristics of a nacelle-type conical-spike inlet with a fixed-area bypass located in the top or bottom of the diffuser are presented for flight Mach numbers of 1.6, 1.8, and 2.0 for angles of attack from 0 degrees to 9 degrees. Top or bottom location of the bypass did not have significant effects on diffuser pressure-recovery, bypass mass-flow ratio, or drag coefficient over the range of angles of attack, flight Mach numbers, and stable engine mass-flow ratios investigated. A larger stable subcritical operating range was obtained with the bypass on the bottom at angles of attack from 3 degrees to 9 degrees at a flight Mach number of 2.0. At a flight Mach number of 2.0, the discharge of 14 percent of the critical mass flow of the inlet by means of a bypass increased the drag only one-fifth of the additive drag that would result for equivalent spillage behind an inlet normal shock without significant reductions in diffuser pressure recovery.

Activation volume for phosphorus diffusion in silicon and Si0.93Ge0.07

NASA Astrophysics Data System (ADS)

Zhao, Yuechao; Aziz, Michael J.; Zangenberg, Nikolaj R.; Larsen, Arne Nylandsted

2005-04-01

The hydrostatic pressure dependence of the diffusivity of P in compressively strained Si0.93Ge0.07 and unalloyed Si has been measured. In both cases the diffusivity is almost independent of pressure, characterized by an activation volume V* of (+0.09±0.11) times the atomic volume Ω for the unalloyed Si, and (+0.01±0.06) Ω for Si0.93Ge0.07. The results are used in conjunction with the reported effect of biaxial strain on diffusion normal to the surface to test the prediction for an interstitialcy-based mechanism of Aziz's phenomenological thermodynamic treatment of diffusion under uniform nonhydrostatic stress states. The prediction agrees well with measured behavior, lending additional credence to the interstitial-based mechanism and supporting the nonhydrostatic thermodynamic treatment.

Analysis and design of numerical schemes for gas dynamics. 2: Artificial diffusion and discrete shock structure

NASA Technical Reports Server (NTRS)

Jameson, Antony

1994-01-01

The effect of artificial diffusion on discrete shock structures is examined for a family of schemes which includes scalar diffusion, convective upwind and split pressure (CUSP) schemes, and upwind schemes with characteristics splitting. The analysis leads to conditions on the diffusive flux such that stationary discrete shocks can contain a single interior point. The simplest formulation which meets these conditions is a CUSP scheme in which the coefficients of the pressure differences is fully determined by the coefficient of convective diffusion. It is also shown how both the characteristic and CUSP schemes can be modified to preserve constant stagnation enthalpy in steady flow, leading to four variants, the E and H-characteristic schemes, and the E and H-CUSP schemes. Numerical results are presented which confirm the properties of these schemes.

Pressure transfer function and absorption cross section from the diffuse field to the human infant ear canal.

PubMed

Keefe, D H; Bulen, J C; Campbell, S L; Burns, E M

1994-01-01

The diffuse-field pressure transfer function from a reverberant field to the ear canal of human infants, ages 1, 3, 6, 12, and 24 months, has been measured from 125-10700 Hz. The source was a loudspeaker using pink noise, and the diffuse-field pressure and the ear-canal pressure were simultaneously measured using a spatial averaging technique in a reverberant room. The results in most subjects show a two-peak structure in the 2-6-kHz range, corresponding to the ear-canal and concha resonances. The ear-canal resonance frequency decreases from 4.4 kHz at age 1 month to 2.9 kHz at age 24 months. The concha resonance frequency decreases from 5.5 kHz at age 1 month to 4.5 kHz at age 24 months. Below 2 kHz, the diffuse-field transfer function shows effects due to the torsos of the infant and parent, and varies with how the infant is held. Comparisons are reported of the diffuse-field absorption cross section for infants relative to adults. This quantity is a measure of power absorbed by the middle ear from a diffuse sound field, and large differences are observed in infants relative to adults. The radiation efficiencies of the infant and the adult ear are small at low frequencies, near unity at midfrequencies, and decrease at higher frequencies. The process of ear-canal development is not yet complete at age 24 months. The results have implications for experiments on hearing in infants.

Global Search of a Three-dimensional Low Solidity Circular Cascade Diffuser for Centrifugal Blowers by Meta-model Assisted Optimization

NASA Astrophysics Data System (ADS)

Sakaguchi, Daisaku; Sakue, Daiki; Tun, Min Thaw

2018-04-01

A three-dimensional blade of a low solidity circular cascade diffuser in centrifugal blowers is designed by means of a multi-point optimization technique. The optimization aims at improving static pressure coefficient at a design point and at a small flow rate condition. Moreover, a clear definition of secondary flow expressed by positive radial velocity at hub side is taken into consideration in constraints. The number of design parameters for three-dimensional blade reaches to 10 in this study, such as a radial gap, a radial chord length and mean camber angle distribution of the LSD blade with five control points, control point between hub and shroud with two design freedom. Optimization results show clear Pareto front and selected optimum design shows good improvement of pressure rise in diffuser at small flow rate conditions. It is found that three-dimensional blade has advantage to stabilize the secondary flow effect with improving pressure recovery of the low solidity circular cascade diffuser.

Repetitively pulsed UV radiation source based on a run-away electron preionised diffuse discharge in nitrogen

NASA Astrophysics Data System (ADS)

Baksht, E. Kh; Burachenko, A. G.; Lomaev, M. I.; Panchenko, A. N.; Tarasenko, V. F.

2015-04-01

An extended repetitively pulsed source of spontaneous UV radiation is fabricated, which may also be used for producing laser radiation. Voltage pulses with an incident wave amplitude of up to 30 kV, a half-amplitude duration of ~4 ns and a rise time of ~2.5 ns are applied to a gap with a nonuniform electric field. For an excitation region length of 35 cm and a nitrogen pressure of 30 - 760 Torr, a diffusive discharge up to a pulse repetition rate of 2 kHz is produced without using an additional system for gap preionisation. An investigation is made of the plasma of the run-away electron preionised diffuse discharge. Using a CCD camera it is found that the dense diffused plasma fills the gap in a time shorter than 1 ns. X-ray radiation is recorded from behind the foil anode throughout the pressure range under study; a supershort avalanche electron beam is recorded by the collector electrode at pressures below 100 Torr.

Laser excited atomic fluorescence spectrometry as a powerful tool for analytical applications and spectroscopic studies

NASA Astrophysics Data System (ADS)

Gornushkin, Igor B.

1997-12-01

Laser-excited atomic fluorescence spectrometry (LEAFS) with a novel diffusive tube electrothermal atomizer (ETA) has been used for the study of atomization and diffusion processes and for the direct trace analysis of complex matrices. A novel ETA was a graphite tube sealed by two graphite electrodes. A sample was introduced into the tube and the furnace assembly was heated. The vaporized sample diffused through the hot graphite and the atomic fraction of the vapor was excited by a tunable dye laser above the tube. Temporal behavior of atomic fluorescence of Cu, Ag, and Ni atoms, diffused through the furnace tube, was studied at different temperatures; the values for activation energies and diffusion coefficients were derived on the basis of the diffusion/vaporization kinetic model. The femtogram/nanogram concentrations of silver were determined in coastal Atlantic water and soil samples. Use of the new ETA resulted in significant reduction of matrix interferences, ultra-low limits of detection, good accuracy and precision. LEAFS coupled with laser ablation (LA) was studied in terms of its analytical and spectroscopic potential. Low concentrations of lead (0.15 ppm-750 ppm) in metallic matrices (copper, brass, steel, and zinc) were measured in a low pressure argon atmosphere. No matrix effect was observed, providing a universal calibration curve for all samples. A limit of detection of 22 ppb (0.5 fg) was achieved. Also, the lifetime of the metastable 6p21D level of lead was measured and found to be in good agreement with the literature data. A simple open-air LA-LEAFS system was used for the determination of cobalt in solid matrices (graphite, soil, and steel). The fluorescence of cobalt was excited from a level which was already populated in the ablation plasma and was monitored at the Stokes-shifted wavelength. Detection limits in the ppb to ppm range and linearity over four orders of magnitude were achieved. The resonance shadowgraph technique has been developed for time-resolved imaging of laser-produced plasmas. The shadowgraphs were obtained by igniting the plasma on the lead or tin surface and by illuminating the plasma by a laser tuned in resonance with a strong atomic transition. UV-photodecomposition of lead and tin clusters was visualized. The evolution of the plasmas was studied at different pressures of argon. A shock wave produced by the laser ablation was monitored and its speed was measured.

On the Occurrence of Liquation During Linear Friction Welding of Ni-Based Superalloys

NASA Astrophysics Data System (ADS)

Masoumi, F.; Shahriari, D.; Jahazi, M.; Cormier, J.; Flipo, B. C. D.

2017-06-01

A combination of experimental and analytical methods was used to study the possible occurrence of liquation during LFW of the newly developed AD730TM Ni-based superalloy. LFWed joints were produced using a semi-industrial size facility and the interfaces of the joints as well as the ejected flash were examined using optical and Field Emission Gun Scanning Electron Microscopy (FEG-SEM). Physical simulation of the LFW thermal cycle, using thermomechanical simulator Gleeble™ 3800, showed that incipient melting started from 1473 K (1200 °C). The analytical model, calibrated by experiments, predicted that the highest temperature of the interface was about 1523 K (1250 °C). The constitutive equations based on lattice and pipe diffusion models were developed to quantify the self-diffusivity of the elements and control the extent of liquation by considering the effect of LFW process parameters. Analytical results show that the application of compressive stresses during LFW results in 25 times increase in the diffusion of Ni atoms at the weld interface. Therefore, no presence of re-solidified phases, i.e., occurrence of liquation, was observed in the microstructure of the weld zone or the flash in the present study. Based on the obtained results, a methodology was developed for designing the optimum pressure above which no liquation, and hence cracking, will be observable.

A rate-based transcutaneous CO2 sensor for noninvasive respiration monitoring.

PubMed

Chatterjee, M; Ge, X; Kostov, Y; Luu, P; Tolosa, L; Woo, H; Viscardi, R; Falk, S; Potts, R; Rao, G

2015-05-01

The pain and risk of infection associated with invasive blood sampling for blood gas measurements necessitate the search for reliable noninvasive techniques. In this work we developed a novel rate-based noninvasive method for a safe and fast assessment of respiratory status. A small sampler was built to collect the gases diffusing out of the skin. It was connected to a CO2 sensor through gas-impermeable tubing. During a measurement, the CO2 initially present in the sampler was first removed by purging it with nitrogen. The gases in the system were then recirculated between the sampler and the CO2 sensor, and the CO2 diffusion rate into the sampler was measured. Because the measurement is based on the initial transcutaneous diffusion rate, reaching mass transfer equilibrium and heating the skin is no longer required, thus, making it much faster and safer than traditional method. A series of designed experiments were performed to analyze the effect of the measurement parameters such as sampler size, measurement location, subject positions, and movement. After the factor analysis tests, the prototype was sent to a level IV NICU for clinical trial. The results show that the measured initial rate of increase in CO2 partial pressure is linearly correlated with the corresponding arterial blood gas measurements. The new approach can be used as a trending tool, making frequent blood sampling unnecessary for respiratory status monitoring.

The kinetics of dolomite reaction rim growth under isostatic and non-isostatic pressure conditions

NASA Astrophysics Data System (ADS)

Helpa, V.; Rybacki, E.; Morales, L. G.; Abart, R.; Dresen, G. H.

2013-12-01

During burial and exhumation, rocks are simultaneously exposed to metamorphic reactions and tectonic stresses. Therefore, the reaction rate of newly formed minerals may depend on chemical and mechanical driving forces. Here, we investigate the reaction kinetics of dolomite (CaMg[CO3]2) rim growth by solid-state reactions experiments on oriented calcite (CaCO3) and magnesite (MgCO3) single crystals under isostatic and non-isostatic pressure conditions. Cylindrical samples of 3-5 mm length and 7 mm diameter were drilled and polished perpendicular to the rhombohedral cleavage planes of natural clear crystals. The tests were performed using a Paterson-type deformation apparatus at P = 400 MPa confining pressure, temperatures, T, between 750 and 850°C, and reaction durations, t, of 2 - 146 h to calculate the kinetic parameters of dolomite rim growth under isostatic stress conditions. For non-isostatic reaction experiments we applied in addition differential stresses, σ, up to 40 MPa perpendicular to the contact interface at T = 750°C for 4 - 171 h duration, initiating minor inelastic deformation of calcite. The thickness of the resulting dolomite reaction rims increases linearly with the square root of time, indicating a diffusion-controlled reaction. The rims consist of two different textural domains. Granular dolomite grains (≈ 2 -5 μm grain size) form next to calcite and elongated palisade-shaped grains (1-6 μm diameter) grow perpendicular to the magnesite interface. Texture measurements with the electron backscatter diffraction technique indicate that the orientations of dolomite grains are mainly influenced by the orientation of the calcite educt crystal, in particular in the granular rim. To some extent, the texture of dolomite palisades is also influenced by the orientation of magnesite. The thickness of the two individual layers increases with temperature. At 400 MPa isostatic pressure, T = 750°C and t = 29 hours, a 5 μm thick granular dolomite layer and a 7 μm thick palisade-shaped layer evolve. At similar conditions and a differential stress of 30 MPa, the rim thickness remains similar; consequently the effect of non-isostatic stress on dolomite rim growth is negligible. Platinum markers show that the initial calcite-magnesite interface is located between granular and palisade-forming dolomite, indicating that rim growth occurs by counter diffusion of MgO and CaO. Diffusion of MgO across the dolomite reaction rim into calcite forms additionally magnesio-calcite grains with diameters of ≈ 13 - 46 μm, depending on the experimental conditions and increasing with increasing distance to the dolomite boundary. At T = 750°C, t = 29 hours, the thickness of the magnesio-calcite layer is 32 μm (isostatic) - 35 μm (σ = 30 MPa). The experiments indicate that solid-state reaction rim growth of dolomite between calcite and magnesite is primarily controlled by diffusion of MgO and CaO, forming layers with different microstructures during growth into the educt phases. The kinetics of the reaction in the carbonate system are not significantly changed by differential stresses up to 40 MPa. We suggest that volume diffusion is the dominant transport mechanism, which is presumably less affected by non-isostatic stresses than grain boundary diffusion.

Superplastic Forming of Duplex Stainless Steel for Aerospace Part

NASA Astrophysics Data System (ADS)

Lee, Ho-Sung; Yoon, Jong-Hoon; Yoo, Joon-Tae; Yi, Young-Moo

2011-08-01

In this study, the high temperature forming behavior of duplex stainless steel has been characterized and the outer shell of a combustion chamber was fabricated with pressure difference of hot gas. It consists of two parts which are the outer skin made of stainless steel to sustain the internal pressure and the inner shell made of copper alloy for regenerative cooling channels. Two outer skins partitioned to half with respect to the symmetric axis was prepared by hot gas forming process with a maximum pressure of 7 MPa following to FEM analysis. For inner layer, copper alloy was machined for cooling channels and then placed in the gas pressure welding fixture. It is shown that the optimum condition of gas pressure welding is 7 MPa at 890 °C, for one hour. EDX analysis and scanning electron microscope micrograph confirm the atomic diffusion process is observed at the interface and copper atoms diffuse into steel, while iron and chrome atoms diffuse into copper. The result shows that the manufacturing method with superplastic forming and gas pressure welding of steel and copper alloy has been successful for near net shape manufacturing of scaled combustion chamber of launch vehicle.

Forward Osmosis Membranes under Null-Pressure Condition: Do Hydraulic and Osmotic Pressures Have Identical Nature?

PubMed

Kook, Seungho; Swetha, Chivukula D; Lee, Jangho; Lee, Chulmin; Fane, Tony; Kim, In S

2018-03-20

Forward osmosis (FO) membranes fall into the category of nonporous membranes, based on the assumption that water and solute transport occur solely based on diffusion. The solution-diffusion (S-D) model has been widely used in predicting their performances in the coexistence of hydraulic and osmotic driving forces, a model that postulates the hydraulic and osmotic driving forces have identical nature. It was suggested, however, such membranes may have pores and mass transport could occur both by convection (i.e., volumetric flow) as well as by diffusion assuming that the dense active layer of the membranes is composed of a nonporous structure with defects which induce volumetric flow through the membranes. In addition, the positron annihilation technique has revealed that the active layers can involve relatively uniform porous structures. As such, the assumption of a nonporous active layer in association with hydraulic pressure is questionable. To validate this assumption, we have tested FO membranes under the conditions where hydraulic and osmotic pressures are equivalent yet in opposite directions for water transport, namely the null-pressure condition. We have also established a practically valid characterization method which quantifies the vulnerability of the FO membranes to hydraulic pressure.

Developing ultrasensitive pressure sensor based on graphene nanoribbon: Molecular dynamics simulation

NASA Astrophysics Data System (ADS)

Kwon, Oh Kuen; Lee, Jun Ha; Kim, Ki-Sub; Kang, Jeong Won

2013-01-01

We propose schematics for an ultra-sensitive pressure sensor based on graphene-nanoribbon (GNR) and investigate its electromechanical properties using classical molecular dynamics simulations and piezo-electricity theory. Since the top plate applied to the actual pressure is large whereas the contact area on the GNR is very small, both the sensitivity and the sensing range can be adjusted by controlling the aspect ratio between the top plate and the contact point areas. Our calculation shows that the electrical conductivity of GNRs can be tuned by the applied pressure and the electric conductance of the deflected GNR linearly increases with increasing applied pressure for the linear elastic region in low pressure below the cut-off point. In the curves for both the deflection and potential energy, the linear elastic regime in low pressure was explicitly separated with the non-linear elastic regime in high pressure. The proposed GNR-based nanoelectromechanical devices have great potential for application as electromechanical memory, relay or switching devices.

Effect of rock rheology on fluid leak- off during hydraulic fracturing

NASA Astrophysics Data System (ADS)

Yarushina, V. M.; Bercovici, D.; Oristaglio, M. L.

2012-04-01

In this communication, we evaluate the effect of rock rheology on fluid leak­off during hydraulic fracturing of reservoirs. Fluid leak-off in hydraulic fracturing is often nonlinear. The simple linear model developed by Carter (1957) for flow of fracturing fluid into a reservoir has three different regions in the fractured zone: a filter cake on the fracture face, formed by solid additives from the fracturing fluid; a filtrate zone affected by invasion of the fracturing fluid; and a reservoir zone with the original formation fluid. The width of each zone, as well as its permeability and pressure drop, is assumed to remain constant. Physical intuition suggests some straightforward corrections to this classical theory to take into account the pressure dependence of permeability, the compressibility or non-Newtonian rheology of fracturing fluid, and the radial (versus linear) geometry of fluid leak­off from the borehole. All of these refinements, however, still assume that the reservoir rock adjacent to the fracture face is non­deformable. Although the effect of poroelastic stress changes on leak-off is usually thought to be negligible, at the very high fluid pressures used in hydraulic fracturing, where the stresses exceed the rock strength, elastic rheology may not be the best choice. For example, calculations show that perfectly elastic rock formations do not undergo the degree of compaction typically seen in sedimentary basins. Therefore, pseudo-elastic or elastoplastic models are used to fit observed porosity profiles with depth. Starting from balance equations for mass and momentum for fluid and rock, we derive a hydraulic flow equation coupled with a porosity equation describing rock compaction. The result resembles a pressure diffusion equation with the total compressibility being a sum of fluid, rock and pore-space compressibilities. With linear elastic rheology, the bulk formation compressibility is dominated by fluid compressibility. But the possibility of permanent, time-independent (plastic) rock deformation significantly increases the pore space compressibility (compaction), which becomes a leading term in the total compressibility. Inclusion of rock and fluid compressibilities in the model can explain both linear and nonlinear leak­off. In particular, inclusion of rock compaction and decompaction may be important for description of naturally fractured and tight gas reservoirs for which very strong dependence of permeability on porosity has been reported. Carter R.D. Derivation of the general equation for estimating the extent of the fractured area. Appendix I of "Optimum fluid characteristics for fracture extension", Drilling and Production Practice, G.C. Howard and C.R.Fast, New York, New York, USA, American Petroleum Institute (1957), 261-269.

Modeling Thermal Pressurization Around Shallow Dikes Using Temperature-Dependent Hydraulic Properties: Implications for Deformation Around Intrusions

NASA Astrophysics Data System (ADS)

Townsend, Meredith R.

2018-01-01

Pressurization and flow of groundwater around igneous intrusions depend in part on the hydraulic diffusivity of the host rocks and processes that enhance diffusivity, such as fracturing, or decrease diffusivity, such as mineral precipitation during chemical alteration. Characterizing and quantifying the coupled effects of alteration, pore pressurization, and deformation have significant implications for deformation around intrusions, geothermal energy, contact metamorphism, and heat transfer at mid-ocean ridges. Fractures around dikes at Ship Rock, New Mexico, indicate that pore pressures in the host rocks exceeded hydrostatic conditions by at least 15 MPa following dike emplacement. Hydraulic measurements and petrographic analysis indicate that mineral precipitation clogged the pores of the host rock, reducing porosity from 0.25 to <0.10 and reducing permeability by 5 orders of magnitude. Field data from Ship Rock are used to motivate and constrain numerical models for thermal pore fluid pressurization adjacent to a meter-scale dike, using temperature-dependent hydraulic properties in the host rock as a proxy for porosity loss by mineral precipitation during chemical alteration. Reduction in permeability by chemical alteration has a negligible effect on pressurization. However, reduction in porosity by mineral precipitation increases fluid pressure by constricting pore volume and is identified as a potentially significant source of pressure. A scaling relationship is derived to determine when porosity loss becomes important; if permeability is low enough, pressurization by porosity loss outweighs pressurization by thermal expansion of fluids.

Role of Rayleigh numbers on characteristics of double diffusive salt fingers

NASA Astrophysics Data System (ADS)

Rehman, F.; Singh, O. P.

2018-05-01

Double diffusion convection, driven by two constituents of the fluid with different molecular diffusivity, is widely applied in oceanography and large number of other fields like astrophysics, geology, chemistry and metallurgy. In case of ocean, heat (T) and salinity (S) are the two components with varying diffusivity, where heat diffuses hundred times faster than salt. Component (T) stabilizes the system whereas components (S) destabilizes the system with overall density remains stable and forms the rising and sinking fingers known as salt fingers. Recent observations suggest that salt finger characteristics such as growth rates, wavenumber, and fluxes are strongly depending on the Rayleigh numbers as major driving force. In this paper, we corroborate this observation with the help of experiments, numerical simulations and linear theory. An eigenvalue expression for growth rate is derived from the linearized governing equations with explicit dependence on Rayleigh numbers, density stability ratio, Prandtl number and diffusivity ratio. Expressions for fastest growing fingers are also derived as a function various non-dimensional parameter. The predicted results corroborate well with the data reported from the field measurements, experiments and numerical simulations.

Viscosity-dependent diffusion of fluorescent particles using fluorescence correlation spectroscopy.

PubMed

Jung, Chanbae; Lee, Jaeran; Kang, Manil; Kim, Sok Won

2014-11-01

Fluorescent particles show the variety characteristics by the interaction with other particles and solvent. In order to investigate the relationship between the dynamic properties of fluorescent particles and solvent viscosity, particle diffusion in various solvents was evaluated using a fluorescence correlation spectroscopy. Upon analyzing the correlation functions of AF-647, Q-dot, and beads with different viscosity values, the diffusion time of all particles was observed to increase with increasing solvent viscosity, and the ratio of diffusion time to solvent viscosity, τ D /η, showed a linear dependence on particle size. The particle diffusion coefficients calculated from the diffusion time decreased with increasing solvent viscosity. Further, the hydrodynamic radii of AF-647, Q-dot, and beads were 0.98 ± 0.1 nm, 64.8 ± 3.23 nm, and 89.8 ± 4.91 nm, respectively, revealing a linear dependence on τ D /η, which suggests that the hydrodynamic radius of a particle strongly depends on both the physical size of the particle and solvent viscosity.

Catalytic conversion reactions mediated by single-file diffusion in linear nanopores: hydrodynamic versus stochastic behavior.

PubMed

Ackerman, David M; Wang, Jing; Wendel, Joseph H; Liu, Da-Jiang; Pruski, Marek; Evans, James W

2011-03-21

We analyze the spatiotemporal behavior of species concentrations in a diffusion-mediated conversion reaction which occurs at catalytic sites within linear pores of nanometer diameter. Diffusion within the pores is subject to a strict single-file (no passing) constraint. Both transient and steady-state behavior is precisely characterized by kinetic Monte Carlo simulations of a spatially discrete lattice-gas model for this reaction-diffusion process considering various distributions of catalytic sites. Exact hierarchical master equations can also be developed for this model. Their analysis, after application of mean-field type truncation approximations, produces discrete reaction-diffusion type equations (mf-RDE). For slowly varying concentrations, we further develop coarse-grained continuum hydrodynamic reaction-diffusion equations (h-RDE) incorporating a precise treatment of single-file diffusion in this multispecies system. The h-RDE successfully describe nontrivial aspects of transient behavior, in contrast to the mf-RDE, and also correctly capture unreactive steady-state behavior in the pore interior. However, steady-state reactivity, which is localized near the pore ends when those regions are catalytic, is controlled by fluctuations not incorporated into the hydrodynamic treatment. The mf-RDE partly capture these fluctuation effects, but cannot describe scaling behavior of the reactivity.

Breaking The Ion Frozen-in Condition Via The Non-gyrotropic Pressure Effect In Magnetic Reconnection

NASA Astrophysics Data System (ADS)

Dai, L.; Wang, C.; Angelopoulos, V.; Glassmeier, K. H.

2016-12-01

For magnetic reconnection to proceed, the frozen-in condition for both ion fluid and electron fluid in a localized diffusion region must be violated. In the framework of fluid, the frozen-in can be broken by inertial effects, thermal pressure effects, or inter-species collisions. An essential question in reconnection physics is what effect breaks the ion/electron frozen-in in the diffusion region. We present clear in-situ evidence that the off-diagonal pressure tensor, which corresponds to a non-gyrotropic pressure effect, is mainly responsible for breaking the ion frozen-in condition in reconnection. The non-gyrotropic pressure tensor is a fluid manifestation of ion demagnetization in reconnection. As our experiences indicate, we feel the need to clarify several conceptual points regarding the approach to studying diffusion region. 1) Conceptually, the ion/electron momentum equations ("ion/electron Ohm's law"), rather than the generalized Ohm's law (Rossi and Olbert,1970, equation [12.25] ), are appropriate for investigating the fronzen-in or decoupling of individual fluid species. 2) The reconnection electric field is equally explainable in terms of ion momentum or electron momentum equation.

Pressure relaxation and diffusion of vacancies in rapidly grown helium crystals

NASA Astrophysics Data System (ADS)

Birchenko, A. P.; Mikhin, N. P.; Rudavskii, E. Ya.; Smirnov, S. N.; Fysun, Ya. Yu.

2018-04-01

An experimental study of the features of pressure relaxation in rapidly grown crystals of a diluted solid solution 3He-4He, at temperatures above 1.3 K, was performed. A cylindrical cell with capacitive pressure sensors at the ends was used for measurements. It was found that, when the helium crystals were grown at cooling rates ≳4 mK/s, the difference in pressure ΔP registered by the sensors at 1.3 K reached 2.4 bars. The ΔP value decreased with subsequent stepwise increase in temperature, but reached zero only after thorough annealing at the premelting temperatures. The kinetics of pressure changes at the sample ends at different temperatures was recorded. The results obtained were interpreted within the framework of the structural relaxation model based on the monovacancy diffusion mechanism. The proposed model made it possible to explain the dependence of ΔP on the time and temperature recorded in the experiment, as well as to determine the activation energy of the structural relaxation process and the diffusion coefficient of vacancies. The details of the vacancy model are described in the Appendix.

Pressure injury prediction using diffusely scattered light

NASA Astrophysics Data System (ADS)

Diaz, David; Lafontant, Alec; Neidrauer, Michael; Weingarten, Michael S.; DiMaria-Ghalili, Rose Ann; Scruggs, Ericka; Rece, Julianne; Fried, Guy W.; Kuzmin, Vladimir L.; Zubkov, Leonid

2017-02-01

Pressure injuries (PIs) originate beneath the surface of the skin at the interface between bone and soft tissue. We used diffuse correlation spectroscopy (DCS) and diffuse near-infrared spectroscopy (DNIRS) to predict the development of PIs by measuring dermal and subcutaneous red cell motion and optical absorption and scattering properties in 11 spinal cord injury subjects with only nonbleachable redness in the sacrococcygeal area in a rehabilitation hospital and 20 healthy volunteers. A custom optical probe was developed to obtain continuous DCS and DNIRS data from sacrococcygeal tissue while the subjects were placed in supine and lateral positions to apply pressure from body weight and to release pressure, respectively. Rehabilitation patients were measured up to four times over a two-week period. Three rehabilitation patients developed open PIs (POs) within four weeks and eight patients did not (PNOs). Temporal correlation functions in the area of redness were significantly different (p<0.01) during both baseline and applied pressure stages for POs and PNOs. The results show that our optical method may be used for the early prediction of ulcer progression.

The Organization as a Filter of Institutional Diffusion

ERIC Educational Resources Information Center

Penuel, William R.; Frank, Kenneth A.; Sun, Min; Kim, Chong Min; Singleton, Corrine

2013-01-01

Background/Context: Institutional theories sometimes characterize the normative influence of institutions as diffusing like waves and as exerting uniform pressures on individuals. This article contributes to a growing literature on the microfoundations of institutions, investigating how intraorganizational networks mediate the diffusion of…

The investigation of argon diffusion in phlogopite under high pressure conditions

NASA Astrophysics Data System (ADS)

Yudin, Denis; Korzhova, Sophia; Travin, Alexey; Zhimulev, Egor; Murzintsev, Nikolay; Moroz, Tatiana

2014-05-01

The present study deals with assessment of pressure effect on the mechanism of bleeding an argon from mica at high temperatures and pressures. The influence of pressure on the diffusion of argon in crustal conditions is not significant (Harrison et al., 2009), while in the mantle conditions, should be significant. The authors suggest that the findings will help to better understand the behavior of K/Ar isotopic system in mica under the lower crust and mantle, including xenoliths transport by kimberlite melt. The experiment was made by using high-pressure spacer "split-sphere" (BARS - 300). Phlogopite from veins cutting metamorphic rocks from the Sludyanka number 2 quarry was used as a testing material. Inclusions of other minerals were not found in the original phlogopite crystal. Chemical composition of phlogopite is homogeneous. 8 experiments was made at a constant pressure of 30 kbar and different temperature and duration: 20 degrees Celsius, 20 minutes; 700 degrees Celsius, 20 minutes; 800 degrees Celsius, 10 minutes; 800 degrees Celsius, 20 minutes; 800 degrees Celsius, 30 minutes; 900 degrees Celsius, 20 minutes; 1000 degrees Celsius, 20 minutes; 1100 degrees Celsius, 20 minutes. According the results of SEM-observation, there is no signs of recrystallization and solid state transformations and melting of phlogopite. It's chemical composition is identical to that of the original phlogopite. Diffractograms of phlogopites after the experiments are similar to the diffractograms of the original phlogopites. Research results of IR spectroscopy, together with the results of SEM and microprobe analysis suggest that phlogopite dehydroxylation in the temperature range T = 700-900 degrees Celsius was negligible. Numerical simulation of the behavior of radiogenic argon in phlogopite at high temperatures and pressure was performed using «Diffarg» software finite differences algorithm, based on the mechanism of bulk thermally activated diffusion (Wheeler, 1996). The size of the effective diffusion domain of mica was considered to be 100-150 microns, when modeling (Baxter, 2010). Comparison of results of simulations and experiments suggests that the mobility of argon isotopes in phlogopite at high temperatures and pressure is well described by the mechanism of thermally activated volume diffusion. Stepwise release of argon in a vacuum experiment was also conducted. The activation energy of 207,714 J/mol was calculated from the slope of the line on the Arrhenius chart. This value is consistent with data obtained by other authors in hydrothermal experiments (Baxter, 2010). The work was supported by the grant of the President of Russia MK-3240.2014.5. Baxter E.F. Diffusion of Noble Gases in Minerals // Reviews in Mineralogy & Geochemistry. 2010. V.72. P.509-557. Harrison T.M., Celerier J., Aikman A.B., Hermann J., Heizler M.T. Diffusion of 40Ar in muscovite // Geochim Cosmochim Acta. 2009. V.73. P.1039-1051. Wheeler J. Diffarg: A program for simulating argon diffusion profiles in minerals // Computers & Geosciences. 1996. V. 22(8). P. 919-929.

Deep-tissue temperature mapping by multi-illumination photoacoustic tomography aided by a diffusion optical model: a numerical study

NASA Astrophysics Data System (ADS)

Zhou, Yuan; Tang, Eric; Luo, Jianwen; Yao, Junjie

2018-01-01

Temperature mapping during thermotherapy can help precisely control the heating process, both temporally and spatially, to efficiently kill the tumor cells and prevent the healthy tissues from heating damage. Photoacoustic tomography (PAT) has been used for noninvasive temperature mapping with high sensitivity, based on the linear correlation between the tissue's Grüneisen parameter and temperature. However, limited by the tissue's unknown optical properties and thus the optical fluence at depths beyond the optical diffusion limit, the reported PAT thermometry usually takes a ratiometric measurement at different temperatures and thus cannot provide absolute measurements. Moreover, ratiometric measurement over time at different temperatures has to assume that the tissue's optical properties do not change with temperatures, which is usually not valid due to the temperature-induced hemodynamic changes. We propose an optical-diffusion-model-enhanced PAT temperature mapping that can obtain the absolute temperature distribution in deep tissue, without the need of multiple measurements at different temperatures. Based on the initial acoustic pressure reconstructed from multi-illumination photoacoustic signals, both the local optical fluence and the optical parameters including absorption and scattering coefficients are first estimated by the optical-diffusion model, then the temperature distribution is obtained from the reconstructed Grüneisen parameters. We have developed a mathematic model for the multi-illumination PAT of absolute temperatures, and our two-dimensional numerical simulations have shown the feasibility of this new method. The proposed absolute temperature mapping method may set the technical foundation for better temperature control in deep tissue in thermotherapy.

Influence of water on clumped-isotope bond reordering kinetics in calcite

NASA Astrophysics Data System (ADS)

Brenner, Dana C.; Passey, Benjamin H.; Stolper, Daniel A.

2018-03-01

Oxygen self-diffusion in calcite and many other minerals is considerably faster under wet conditions relative to dry conditions. Here we investigate whether this "water effect" also holds true for solid-state isotope exchange reactions that alter the abundance of carbonate groups with multiple rare isotopes ('clumped' isotope groups) via the process of solid-state bond reordering. We present clumped-isotope reordering rates for optical calcite heated under wet, high-pressure (100 MPa) conditions. We observe only modest increases in reordering rates under such conditions compared with rates for the same material reacted in dry CO2 under low-pressure conditions. Activation energies under wet, high-pressure conditions are indistinguishable from those for dry, low-pressure conditions, while rate constants are resolvably higher (up to ∼3 times) for wet, high-pressure relative to dry, low-pressure conditions in most of our interpretations of experimental results. This contrasts with the water effect for oxygen self-diffusion in calcite, which is associated with lower activation energies, and diffusion coefficients that are ≥103 times higher compared with dry (pure CO2) conditions in the temperature range of this study (385-450 °C). The water effect for clumped-isotopes leads to calculated apparent equilibrium temperatures ("blocking temperatures") for typical geological cooling rates that are only a few degrees higher than those for dry conditions, while O self-diffusion blocking temperatures in calcite grains are ∼150-200 °C lower in wet conditions compared with dry conditions. Since clumped-isotope reordering is a distributed process that occurs throughout the mineral volume, our clumped-isotope results support the suggestion of Labotka et al. (2011) that the water effect in calcite does not involve major changes in bulk (volume) diffusivity, but rather is primarily a surface phenomenon that facilitates oxygen exchange between the calcite surface and external fluids. We explore the mechanism(s) by which clumped isotope reordering rates may be modestly increased under wet, high-pressure conditions, including changes in defect concentrations in the near surface environment due to reactions at the water-mineral interface, and lattice deformation resulting from pressurization of samples.

Mechanism of Facilitated Diffusion during a DNA Search in Crowded Environments.

PubMed

Krepel, Dana; Gomez, David; Klumpp, Stefan; Levy, Yaakov

2016-11-03

The key feature explaining the rapid recognition of a DNA target site by its protein lies in the combination of one- and three-dimensional (1D and 3D) diffusion, which allows efficient scanning of the many alternative sites. This facilitated diffusion mechanism is expected to be affected by cellular conditions, particularly crowding, given that up to 40% of the total cellular volume may by occupied by macromolecules. Using coarse-grained molecular dynamics and Monte Carlo simulations, we show that the crowding particles can enhance facilitated diffusion and accelerate search kinetics. This effect originates from a trade-off between 3D and 1D diffusion. The 3D diffusion coefficient is lower under crowded conditions, but it has little influence because the excluded volume effect of molecular crowding restricts its use. Largely prevented from using 3D diffusion, the searching protein dramatically increases its use of the hopping search mode, which results in a higher linear diffusion coefficient. The coefficient of linear diffusion also increases under crowded conditions as a result of increased collisions between the crowding particles and the searching protein. Overall, less 3D diffusion coupled with an increase in the use of the hopping and speed of 1D diffusion results in faster search kinetics under crowded conditions. Our study shows that the search kinetics and mechanism are modulated not only by the crowding occupancy but also by the properties of the crowding particles and the salt concentration.

Diffusion in Ordered Alloys, Symposium Held in Chicago, Illinois on November 3 - 4, 1992

DTIC Science & Technology

1992-11-04

calculation of transport proneres The essence of an atomistic theory of diffusion within the linear approximation of the Onsager formalism is to derive...the pair model may be extended to the low temperature range and that this linear behavior exists nearly over the whole temperature range where SRO...being the concentration of the component X. The successive jumps of vacancies are considered to be the elementary process of orde- ring. The jump

Spectral analysis and multigrid preconditioners for two-dimensional space-fractional diffusion equations

NASA Astrophysics Data System (ADS)

Moghaderi, Hamid; Dehghan, Mehdi; Donatelli, Marco; Mazza, Mariarosa

2017-12-01

Fractional diffusion equations (FDEs) are a mathematical tool used for describing some special diffusion phenomena arising in many different applications like porous media and computational finance. In this paper, we focus on a two-dimensional space-FDE problem discretized by means of a second order finite difference scheme obtained as combination of the Crank-Nicolson scheme and the so-called weighted and shifted Grünwald formula. By fully exploiting the Toeplitz-like structure of the resulting linear system, we provide a detailed spectral analysis of the coefficient matrix at each time step, both in the case of constant and variable diffusion coefficients. Such a spectral analysis has a very crucial role, since it can be used for designing fast and robust iterative solvers. In particular, we employ the obtained spectral information to define a Galerkin multigrid method based on the classical linear interpolation as grid transfer operator and damped-Jacobi as smoother, and to prove the linear convergence rate of the corresponding two-grid method. The theoretical analysis suggests that the proposed grid transfer operator is strong enough for working also with the V-cycle method and the geometric multigrid. On this basis, we introduce two computationally favourable variants of the proposed multigrid method and we use them as preconditioners for Krylov methods. Several numerical results confirm that the resulting preconditioning strategies still keep a linear convergence rate.

Managing multiple diffuse pressures on water quality and ecological habitat: Spatially targeting effective mitigation actions at the landscape scale.

NASA Astrophysics Data System (ADS)

Joyce, Hannah; Reaney, Sim

2015-04-01

Catchment systems provide multiple benefits for society, including: land for agriculture, climate regulation and recreational space. Yet, these systems also have undesirable externalities, such as flooding, and the benefits they create can be compromised through societal use. For example, agriculture, forestry and urban land use practices can increase the export of fine sediment and faecal indicator organisms (FIO) delivered to river systems. These diffuse landscape pressures are coupled with pressures on the in stream temperature environment from projected climate change. Such pressures can have detrimental impacts on water quality and ecological habitat and consequently the benefits they provide for society. These diffuse and in-stream pressures can be reduced through actions at the landscape scale but are commonly tackled individually. Any intervention may have benefits for other pressures and hence the challenge is to consider all of the different pressures simultaneously to find solutions with high levels of cross-pressure benefits. This research presents (1) a simple but spatially distributed model to predict the pattern of multiple pressures at the landscape scale, and (2) a method for spatially targeting the optimum location for riparian woodland planting as mitigation action against these pressures. The model follows a minimal information requirement approach along the lines of SCIMAP (www.scimap.org.uk). This approach defines the critical source areas of fine sediment diffuse pollution, rapid overland flow and FIOs, based on the analysis of the pattern of the pressure in the landscape and the connectivity from source areas to rivers. River temperature was modeled using a simple energy balance equation; focusing on temperature of inflowing and outflowing water across a catchment. The model has been calibrated using a long term observed temperature record. The modelling outcomes enabled the identification of the severity of each pressure in relative rather than absolute sense at the landscape scale. Riparian woodland planting is proposed as one mitigation action to address these pressures. This planting disconnects the transfer of material from the landscape to the river channel by promoting increased infiltration and also provides river shading and hence decreases the rate of water heating. To identify the optimal locations for riparian woodland planting, a Monte Carlo based approach was used to identify multiple mitigation options and their influence on the pressures identified. These results were integrated into a decision support tool, which allows the user to explore the implications of individual and a set of pressures. This is achieved by allowing the user to change the importance of different pressures to identify the optimal locations for a custom combination of pressures. For example, reductions in flood risk can be prioritized over reductions in fine sediment. This approach provides an innovative way of identifying and targeting multiple diffuse pressures at the catchment scale simultaneously, which has presented a challenge in previous management efforts. The approach has been tested in the River Ribble Catchment, North West England.

Preliminary study on pressure brazing and diffusion welding of Nb-1Zr to Inconel 718

NASA Technical Reports Server (NTRS)

Moore, T. J.

1990-01-01

Future space power systems may include Nb-1Zr/Inconel 718 dissimilar metal joints for operation at 1000 K for 60,000 h. The serviceability of pressure-brazed and diffusion-welded joints was investigated. Ni-based metallic glass foil filler metals were used for brazing. Ni and Fe foils were used as diffusion welding inter-layers. Joint soundness was determined by metallographic examination in the as-brazed and as-welded condition, after aging at 1000 K, and after thermal cycling. Brazed joints thermally cycled in the as-brazed condition and diffusion-welded joints were unsatisfactory because of cracking problems. Brazed joints may meet the service requirements if the joints are aged at 1000 K prior to thermal cycling.

Possibility of increasing the fire-suppression efficiency of the foam in automatic extinguishing installations

NASA Astrophysics Data System (ADS)

Kachanov, I. V.; Veremenyuk, V. V.; Karpenchuk, I. V.; Pavlyukov, S. Yu.

2013-05-01

The mechanics of movement of a liquid in the diffuser of the injector of an automatic extinguishing installation with preaeration of the fire-fighting substance was theoretically investigated. An integral solution of the equation for movement of the preaerated fire-fighting gas-liquid mixture in the indicated diffuser has been obtained. A mathematical model of two-phase liquid flow in this diffuser, which allows one to calculate the distribution of the average pressure in the diffuser along its length and to determine the loss in this pressure, has been developed. This model can be used for designing the output region of a hydraulic system with a hydrodynamic drag providing the operation of its injector in a definite regime.

Microfluidic diffusion diluter: bulging of PDMS microchannels under pressure-driven flow

NASA Astrophysics Data System (ADS)

Holden, Matthew A.; Kumar, Saurabh; Beskok, Ali; Cremer, Paul S.

2003-05-01

The bulging of microfluidic systems during pressure-driven flow is potentially a major consideration for polydimethylsiloxane (PDMS)-based devices. Microchannel cross-sectional areas can change drastically as a function of flow rate and downstream microchannel position. Such geometrical flexibility leads to difficulties in predicting convective/diffusive transport for these systems. We have previously introduced a non-dimensional parameter, kappa, for characterizing convection and diffusion behavior for pressure-driven flow in rigid all-glass systems. This paper describes a modification of that concept for application to non-rigid systems, which is accomplished by incorporating an experimental step to account for the bulging in PDMS/glass microsystems. Specifically, an experimental measurement of channel height by fluorescence microscopy is combined with the aforementioned theory to characterize convective/diffusive behavior at a single location in the device. This allowed the parameter kappa to be determined at that point and applied to predict fluid flow in the subsequent portion of the PDMS microsystem. This procedure was applied to a PDMS/glass microfluidic diffusion dilution (muDD) device designed for generating concentration gradients. Theoretically predicted and experimentally measured distributions of concentrations within the microsystem matched well.

General anesthesia with methoxyflurane given intravenously to the dog.

PubMed

Hilwig, R W

1976-03-01

Dogs were anesthetized with liquid methoxyflurane administered intravenously by gaseous diffusion through sealed medical grade silicone rubber tubing placed in the femoral vein. A similar catheter placed in the other femoral vein and connected to a pressure transducer measured the increase in intraluminal pressure due to methoxyflurane diffusion into the 2nd catheter from the bloodstream 20 seconds after the catheter was flushed with room air. These pressures were plotted against venous blood methoxyflurane concentration, as determined by gas chromatography, for increasing lengths of anesthetic-administering catheter exposed to the bloodstream.

Recalibration of the sphalerite cosmobarometer: Experimental and theoretical treatment

NASA Astrophysics Data System (ADS)

Balabin, Alexey I.; Urusov, Vadim S.

1995-04-01

Temperature dependence of the composition of sphalerite in equilibrium with troilite + metallic iron has been determined experimentally from 400 to 840°C at 1 bar. The high-temperature runs (660-840°C) were conducted in evacuated silica tubes; a new version of the recrystallization in anhydrous halide flux technique was used for attaining equilibrium at 600-400°C. The zero-pressure solvus of sphalerite proved to be at higher FeS contents than was located by Barton and Toulmin (1966). Detailed calculations, based on updated thermochemical appraisal of the sphalerite (Zn,Fe)S solution, have shown the new solvus to be in apparent consistency with the high-pressure experimental data of Hutchison and Scott (1983 ). An improved calibration of the cosmobarometer is presented, based on our experimental results and those of Hutchison and Scott (1983) ; the calibration takes into account some inferences regarding thermodynamic properties of sphalerite solution and low-temperature polymorphism in FeS. Recently published metallographic cooling rates of iron meteorites (Saikumar and Goldstein, 1988) provide estimates of blocking temperatures for Fe diffusion in sphalerite, which fall in the range 205-217°C. Pressures of formation of these meteorites calculated from available sphalerite compositions range from 0 for Landes to 1.8 kbar for Toluca. The most reliable of the pressure estimates exhibit a linear relationship with wt% Ni of the meteorite.

Decay and Spatial Diffusion of Turbulent Kinetic Energy In The Presence of a Linear Kinetic Energy Gradient

NASA Astrophysics Data System (ADS)

Meneveau, Charles

2015-11-01

A topic that elicited the interest of John Lumley is pressure transport in turbulence. In 1978 (JL, in Advances in Applied Mechanics, pages 123-176) he showed that pressure transport likely acts in the opposite direction to the spatial flux of kinetic energy due to triple velocity correlations. Here we examine a flow in which the interplay of turbulent decay and spatial transport is particularly relevant. Specifically, using a specially designed active grid and screens placed in the Corrsin wind tunnel, such a flow is realized. Data are acquired using X-wire thermal anemometry at different spanwise and downstream locations. In order to resolve the dissipation rate accurately, measurements are also acquired using the NSTAP probe developed and manufactured by Princeton researchers and kindly provided to us (M. Hultmark, Y. Fan, L. Smits). The results show power-law decay with downstream distance, with a decay exponent that becomes larger in the high kinetic energy side of the flow. Measurements of the dissipation enable us to obtain the spanwise gradient of the spatial flux. One possible explanation for the observations is upgrading transport of kinetic energy due to pressure-velocity correlations, although its magnitude required to close the budget appears very large. Absence of simultaneous pressure velocity measurement preclude us to fully elucidate the observed trends. In collaboration with Adrien Thormann, Johns Hopkins University. Financial support: National Science Foundation.

The complex fluid dynamics of simple diffusion

NASA Astrophysics Data System (ADS)

Vold, Erik

2017-11-01

Diffusion as the mass transport process responsible for mixing fluids at the atomic level is often underestimated in its complexity. An initial discontinuity between two species of different atomic masses exhibits a mass density discontinuity under isothermal pressure equilibrium implying equal species molar densities. The self-consistent kinetic transport processes across such an interface leads to a zero sum of mass flux relative to the center of mass and so diffusion alone cannot relax an initially stationary mass discontinuity nor broaden the density profile at the interface. The diffusive mixing leads to a molar imbalance which drives a center of mass velocity which moves the heavier species toward the lighter species leading to the interfacial density relaxation. Simultaneously, the species non-zero molar flux modifies the pressure profile in a transient wave and in a local perturbation. The resulting center of mass velocity has two components; one, associated with the divergence of the flow, persists in the diffusive mixing region throughout the diffusive mixing process, and two, travelling waves at the front of the pressure perturbations propagate away from the mixing region. The momentum in these waves is necessary to maintain momentum conservation in the center of mass frame. Thus, in a number of ways, the diffusive mixing provides feedback into the small scale advective motions. Numerical methods which diffuse all species assuming P-T equilibrium may not recover the subtle dynamics of mass transport at an interface. Work performed by the LANS, LLC, under USDOE Contract No. DE-AC52-06NA25396, funded by the (ASC) Program.

Load Diffusion in Composite and Smart Structures

NASA Technical Reports Server (NTRS)

Horgan, C. O.

2003-01-01

The research carried out here builds on our previous NASA supported research on the general topic of edge effects and load diffusion in composite structures. Further fundamental solid mechanics studies were carried out to provide a basis for assessing the complicated modeling necessary for the multi-functional large scale structures used by NASA. An understanding of the fundamental mechanisms of load diffusion in composite subcomponents is essential in developing primary composite structures. Some specific problems recently considered were those of end effects in smart materials and structures, study of the stress response of pressurized linear piezoelectric cylinders for both static and steady rotating configurations, an analysis of the effect of pre-stressing and pre-polarization on the decay of end effects in piezoelectric solids and investigation of constitutive models for hardening rubber-like materials. Our goal in the study of load diffusion is the development of readily applicable results for the decay lengths in terms of non-dimensional material and geometric parameters. Analytical models of load diffusion behavior are extremely valuable in building an intuitive base for developing refined modeling strategies and assessing results from finite element analyses. The decay behavior of stresses and other field quantities provides a significant aid towards this process. The analysis is also amenable to parameter study with a large parameter space and should be useful in structural tailoring studies. Special purpose analytical models of load diffusion behavior are extremely valuable in building an intuitive base for developing refined modeling strategies and in assessing results from general purpose finite element analyses. For example, a rational basis is needed in choosing where to use three-dimensional to two-dimensional transition finite elements in analyzing stiffened plates and shells. The decay behavior of stresses and other field quantities furnished by this research provides a significant aid towards this element transition issue. A priori knowledge of the extent of boundary-layers induced by edge effects is also useful in determination of the instrumentation location in structural verification tests or in material characterization tests.

NMR Water Self–Diffusion and Relaxation Studies on Sodium Polyacrylate Solutions and Gels in Physiologic Ionic Solutions

PubMed Central

Bai, Ruiliang; Basser, Peter J.; Briber, Robert M.; Horkay, Ferenc

2013-01-01

Water self-diffusion coefficients and longitudinal relaxation rates in sodium polyacrylate solutions and gels were measured by NMR, as a function of polymer content and structure in a physiological concentration range of monovalent and divalent cations, Ca2+ and Na+. Several physical models describing the self-diffusion of the solvent were applied and compared. A free-volume model was found to be in good agreement with the experimental results over a wide range of polymer concentrations. The longitudinal relaxation rate exhibited linear dependence on polymer concentration below a critical concentration and showed non-linear behavior at higher concentrations. Both the water self-diffusion and relaxation were less influenced by the polymer in the gel state than in the uncrosslinked polymer solutions. The effect of Na+ on the mobility of water molecules was practically undetectable. By contrast, addition of Ca2+ strongly increased the longitudinal relaxation rate while its effect on the self-diffusion coefficient was much less pronounced. PMID:24409001

NMR Water Self-Diffusion and Relaxation Studies on Sodium Polyacrylate Solutions and Gels in Physiologic Ionic Solutions.

PubMed

Bai, Ruiliang; Basser, Peter J; Briber, Robert M; Horkay, Ferenc

2014-03-15

Water self-diffusion coefficients and longitudinal relaxation rates in sodium polyacrylate solutions and gels were measured by NMR, as a function of polymer content and structure in a physiological concentration range of monovalent and divalent cations, Ca 2+ and Na + . Several physical models describing the self-diffusion of the solvent were applied and compared. A free-volume model was found to be in good agreement with the experimental results over a wide range of polymer concentrations. The longitudinal relaxation rate exhibited linear dependence on polymer concentration below a critical concentration and showed non-linear behavior at higher concentrations. Both the water self-diffusion and relaxation were less influenced by the polymer in the gel state than in the uncrosslinked polymer solutions. The effect of Na + on the mobility of water molecules was practically undetectable. By contrast, addition of Ca 2+ strongly increased the longitudinal relaxation rate while its effect on the self-diffusion coefficient was much less pronounced.

The effects of nutrient chemotaxis on bacterial aggregation patterns with non-linear degenerate cross diffusion

NASA Astrophysics Data System (ADS)

Leyva, J. Francisco; Málaga, Carlos; Plaza, Ramón G.

2013-11-01

This paper studies a reaction-diffusion-chemotaxis model for bacterial aggregation patterns on the surface of thin agar plates. It is based on the non-linear degenerate cross diffusion model proposed by Kawasaki et al. (1997) [5] and it includes a suitable nutrient chemotactic term compatible with such type of diffusion, as suggested by Ben-Jacob et al. (2000) [20]. An asymptotic estimation predicts the growth velocity of the colony envelope as a function of both the nutrient concentration and the chemotactic sensitivity. It is shown that the growth velocity is an increasing function of the chemotactic sensitivity. High resolution numerical simulations using Graphic Processing Units (GPUs), which include noise in the diffusion coefficient for the bacteria, are presented. The numerical results verify that the chemotactic term enhances the velocity of propagation of the colony envelope. In addition, the chemotaxis seems to stabilize the formation of branches in the soft-agar, low-nutrient regime.

Cross-Diffusion Driven Instability for a Lotka-Volterra Competitive Reaction-Diffusion System

NASA Astrophysics Data System (ADS)

Gambino, G.; Lombardo, M. C.; Sammartino, M.

2008-04-01

In this work we investigate the possibility of the pattern formation for a reaction-diffusion system with nonlinear diffusion terms. Through a linear stability analysis we find the conditions which allow a homogeneous steady state (stable for the kinetics) to become unstable through a Turing mechanism. In particular, we show how cross-diffusion effects are responsible for the initiation of spatial patterns. Finally, we find a Fisher amplitude equation which describes the weakly nonlinear dynamics of the system near the marginal stability.

Hybrid finite element and Brownian dynamics method for diffusion-controlled reactions.

PubMed

Bauler, Patricia; Huber, Gary A; McCammon, J Andrew

2012-04-28

Diffusion is often the rate determining step in many biological processes. Currently, the two main computational methods for studying diffusion are stochastic methods, such as Brownian dynamics, and continuum methods, such as the finite element method. This paper proposes a new hybrid diffusion method that couples the strengths of each of these two methods. The method is derived for a general multidimensional system, and is presented using a basic test case for 1D linear and radially symmetric diffusion systems.

Air cycle machine for an aircraft environmental control system

NASA Technical Reports Server (NTRS)

Decrisantis, Angelo A. (Inventor); O'Coin, James R. (Inventor); Taddey, Edmund P. (Inventor)

2010-01-01

An ECS system includes an ACM mounted adjacent an air-liquid heat exchanger through a diffuser that contains a diffuser plate. The diffuser plate receives airflow from the ACM which strikes the diffuser plate and flows radially outward and around the diffuser plate and into the air-liquid heat exchanger to provide minimal pressure loss and proper flow distribution into the air-liquid heat exchanger with significantly less packaging space.

One-dimensional Numerical Model of Transient Discharges in Air of a Spatial Plasma Ignition Device

NASA Astrophysics Data System (ADS)

Saceleanu, Florin N.

This thesis examines the modes of discharge of a plasma ignition device. Oscilloscope data of the discharge voltage and current are analyzed for various pressures in air at ambient temperature. It is determined that the discharge operates in 2 modes: a glow discharge and a postulated streamer discharge. Subsequently, a 1-dimensional fluid simulation of plasma using the finite volume method (FVM) is developed to gain insight into the particle kinetics. Transient results of the simulation agree with theories of electric discharges; however, quasi-steady state results were not reached due to high diffusion time of ions in air. Next, an ordinary differential equation (ODE) is derived to understand the discharge transition. Simulated results were used to estimate the voltage waveform, which describes the ODE's forcing function; additional simulated results were used to estimate the discharge current and the ODE's non-linearity. It is found that the ODE's non-linearity increases exponentially for capacitive discharges. It is postulated that the non-linearity defines the mode transition observed experimentally. The research is motivated by Spatial Plasma Discharge Ignition (SPDI), an innovative ignition system postulated to increase combustion efficiency in automobile engines for up to 9%. The research thus far can only hypothesize SPDI's benefits on combustion, based on the literature review and the modes of discharge.

Iron diffusion from first principles calculations

NASA Astrophysics Data System (ADS)

Wann, E.; Ammann, M. W.; Vocadlo, L.; Wood, I. G.; Lord, O. T.; Brodholt, J. P.; Dobson, D. P.

2013-12-01

The cores of Earth and other terrestrial planets are made up largely of iron1 and it is therefore very important to understand iron's physical properties. Chemical diffusion is one such property and is central to many processes, such as crystal growth, and viscosity. Debate still surrounds the explanation for the seismologically observed anisotropy of the inner core2, and hypotheses include convection3, anisotropic growth4 and dendritic growth5, all of which depend on diffusion. In addition to this, the main deformation mechanism at the inner-outer core boundary is believed to be diffusion creep6. It is clear, therefore, that to gain a comprehensive understanding of the core, a thorough understanding of diffusion is necessary. The extremely high pressures and temperatures of the Earth's core make experiments at these conditions a challenge. Low-temperature and low-pressure experimental data must be extrapolated across a very wide gap to reach the relevant conditions, resulting in very poorly constrained values for diffusivity and viscosity. In addition to these dangers of extrapolation, preliminary results show that magnetisation plays a major role in the activation energies for diffusion at low pressures therefore creating a break down in homologous scaling to high pressures. First principles calculations provide a means of investigating diffusivity at core conditions, have already been shown to be in very good agreement with experiments7, and will certainly provide a better estimate for diffusivity than extrapolation. Here, we present first principles simulations of self-diffusion in solid iron for the FCC, BCC and HCP structures at core conditions in addition to low-temperature and low-pressure calculations relevant to experimental data. 1. Birch, F. Density and composition of mantle and core. Journal of Geophysical Research 69, 4377-4388 (1964). 2. Irving, J. C. E. & Deuss, A. Hemispherical structure in inner core velocity anisotropy. Journal of Geophysical Research 116, B04307 (2011). 3. Buffett, B. A. Onset and orientation of convection in the inner core. Geophysical Journal International 179, 711-719 (2009). 4. Bergman, M. Measurements of electric anisotropy due to solidification texturing and the implications for the Earth's inner core. Nature 389, 60-63 (1997). 5. Deguen, R. & Cardin, P. Thermochemical convection in Earth's inner core. Geophysical Journal International 187, 1101-1118 (2011). 6. Reaman, D. M., Daehn, G. S. & Panero, W. R. Predictive mechanism for anisotropy development in the Earth's inner core. Earth and Planetary Science Letters 312, 437-442 (2011). 7. Ammann, M. W., Brodholt, J. P., Wookey, J. & Dobson, D. P. First-principles constraints on diffusion in lower-mantle minerals and a weak D'' layer. Nature 465, 462-5 (2010).

An improved diffusion welding technique for TD-NiCr

NASA Technical Reports Server (NTRS)

Holko, K. H.

1973-01-01

An improved diffusion welding technique has been developed for TD-NiCr sheet. In the most preferred form, the improved technique consists of diffusion welding 320-grit sanded plus chemically polished surfaces of unrecrystallized TD-NiCr at 760 C under 140 MN/m2 pressure for 1hr followed by postheating at 1180 C for 2hr. Compared to previous work, this improved technique has the advantages of shorter welding time, lower welding temperature, lower welding pressure, and a simpler and more reproducible surface preparation procedure. Weldments were made that had parent-metal creep-rupture shear strength at 1100 C.

Reactive Orthotropic Lattice Diffuser for Noise Reduction

NASA Technical Reports Server (NTRS)

Khorrami, Mehdi R. (Inventor)

2016-01-01

An orthotropic lattice structure interconnects porous surfaces of the flap with internal lattice-structured perforations to equalize the steady pressure field on the flap surfaces adjacent to the end and to reduce the amplitude of the fluctuations in the flow field near the flap end. The global communication that exists within all of the perforations provides the mechanism to lessen the pressure gradients experienced by the end portion of the flap. In addition to having diffusive effects (diffusing the incoming flow), the three-dimensional orthogonal lattice structure is also reactive (acoustic wave phase distortion) due to the interconnection of the perforations.

A Nth-order linear algorithm for extracting diffuse correlation spectroscopy blood flow indices in heterogeneous tissues.

PubMed

Shang, Yu; Yu, Guoqiang

2014-09-29

Conventional semi-infinite analytical solutions of correlation diffusion equation may lead to errors when calculating blood flow index (BFI) from diffuse correlation spectroscopy (DCS) measurements in tissues with irregular geometries. Very recently, we created an algorithm integrating a N th-order linear model of autocorrelation function with the Monte Carlo simulation of photon migrations in homogenous tissues with arbitrary geometries for extraction of BFI (i.e., αD B ). The purpose of this study is to extend the capability of the N th-order linear algorithm for extracting BFI in heterogeneous tissues with arbitrary geometries. The previous linear algorithm was modified to extract BFIs in different types of tissues simultaneously through utilizing DCS data at multiple source-detector separations. We compared the proposed linear algorithm with the semi-infinite homogenous solution in a computer model of adult head with heterogeneous tissue layers of scalp, skull, cerebrospinal fluid, and brain. To test the capability of the linear algorithm for extracting relative changes of cerebral blood flow (rCBF) in deep brain, we assigned ten levels of αD B in the brain layer with a step decrement of 10% while maintaining αD B values constant in other layers. Simulation results demonstrate the accuracy (errors < 3%) of high-order ( N  ≥ 5) linear algorithm in extracting BFIs in different tissue layers and rCBF in deep brain. By contrast, the semi-infinite homogenous solution resulted in substantial errors in rCBF (34.5% ≤ errors ≤ 60.2%) and BFIs in different layers. The N th-order linear model simplifies data analysis, thus allowing for online data processing and displaying. Future study will test this linear algorithm in heterogeneous tissues with different levels of blood flow variations and noises.

Very Efficient High-order Hyperbolic Schemes for Time-dependent Advection Diffusion Problems: Third-, Fourth-, and Sixth-order

DTIC Science & Technology

2014-07-07

boundary condition (x ¼ 7p =2; j ¼ 2p; U ¼ 1; m ¼ 1) on N ¼ 10 uniform nodes (Dt ¼ 0:01.) Table 10 Unsteady linear advection–diffusion problem with periodic...500 3rd 55 2 4th 55 2 6th 55 2 1000 3rd 116 2 4th 116 2 6th 116 2 Table 11 Unsteady linear advection–diffusion problem with oscillatory BC (x ¼ 7p =2; a...dependent problem with oscillatory BC (x ¼ 7p =2; a ¼ 1.) using the third-order RD-GT scheme with the BDF3 time discretization. Number of nodes Dt (BDF3

Scalar rate correlation at a turbulent liquid free surface - A two-regime correlation for high Schmidt numbers

NASA Technical Reports Server (NTRS)

Khoo, Boo-Cheong; Sonin, Ain A.

1992-01-01

An experimental correlation is derived for gas absorption at a turbulent, shear-free liquid interface. The correlation is expressed in terms of the liquid-side turbulence intensity, liquid-side macroscale, and the properties of the diffusing gas and solvent. The transfer coefficient increases linearly with rms velocity up to a point where the eddy Reynolds number reaches a critical (Schmidt number dependent) value. At higher velocities, there is a more rapid linear rise. The slope of the lower Reynolds number region is proportional to the square root of the diffusivity; at Reynolds numbers much higher than that of the break point, the slope becomes independent of diffusivity.

Finite linear diffusion model for design of overcharge protection for rechargeable lithium batteries

NASA Technical Reports Server (NTRS)

Narayanan, S. R.; Surampudi, S.; Attia, A. I.

1991-01-01

The overcharge condition in secondary lithium batteries employing redox additives for overcharge protection has been theoretically analyzed in terms of a finite linear diffusion model. The analysis leads to expressions relating the steady-state overcharge current density and cell voltage to the concentration, diffusion coefficient, standard reduction potential of the redox couple, and interelectrode distance. The model permits the estimation of the maximum permissible overcharge rate for any chosen set of system conditions. The model has been experimentally verified using 1,1-prime-dimethylferrocene as a redox additive. The theoretical results may be exploited in the design and optimization of overcharge protection by the redox additive approach.

An upwind multigrid method for solving viscous flows on unstructured triangular meshes. M.S. Thesis

NASA Technical Reports Server (NTRS)

Bonhaus, Daryl Lawrence

1993-01-01

A multigrid algorithm is combined with an upwind scheme for solving the two dimensional Reynolds averaged Navier-Stokes equations on triangular meshes resulting in an efficient, accurate code for solving complex flows around multiple bodies. The relaxation scheme uses a backward-Euler time difference and relaxes the resulting linear system using a red-black procedure. Roe's flux-splitting scheme is used to discretize convective and pressure terms, while a central difference is used for the diffusive terms. The multigrid scheme is demonstrated for several flows around single and multi-element airfoils, including inviscid, laminar, and turbulent flows. The results show an appreciable speed up of the scheme for inviscid and laminar flows, and dramatic increases in efficiency for turbulent cases, especially those on increasingly refined grids.

Direct simulation Monte Carlo investigation of the Rayleigh-Taylor instability

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

Gallis, M. A.; Koehler, T. P.; Torczynski, J. R.

In this paper, the Rayleigh-Taylor instability (RTI) is investigated using the direct simulation Monte Carlo (DSMC) method of molecular gas dynamics. Here, fully resolved two-dimensional DSMC RTI simulations are performed to quantify the growth of flat and single-mode perturbed interfaces between two atmospheric-pressure monatomic gases as a function of the Atwood number and the gravitational acceleration. The DSMC simulations reproduce many qualitative features of the growth of the mixing layer and are in reasonable quantitative agreement with theoretical and empirical models in the linear, nonlinear, and self-similar regimes. In some of the simulations at late times, the instability enters themore » self-similar regime, in agreement with experimental observations. Finally, for the conditions simulated, diffusion can influence the initial instability growth significantly.« less

Direct simulation Monte Carlo investigation of the Rayleigh-Taylor instability

DOE PAGES

Gallis, M. A.; Koehler, T. P.; Torczynski, J. R.; ...

2016-08-31

In this paper, the Rayleigh-Taylor instability (RTI) is investigated using the direct simulation Monte Carlo (DSMC) method of molecular gas dynamics. Here, fully resolved two-dimensional DSMC RTI simulations are performed to quantify the growth of flat and single-mode perturbed interfaces between two atmospheric-pressure monatomic gases as a function of the Atwood number and the gravitational acceleration. The DSMC simulations reproduce many qualitative features of the growth of the mixing layer and are in reasonable quantitative agreement with theoretical and empirical models in the linear, nonlinear, and self-similar regimes. In some of the simulations at late times, the instability enters themore » self-similar regime, in agreement with experimental observations. Finally, for the conditions simulated, diffusion can influence the initial instability growth significantly.« less

Layer Structure of a Refractory Multilayer Ti/Al Composite After Pressure Diffusion Welding

NASA Astrophysics Data System (ADS)

Karpov, M. I.; Korzhov, V. P.; Zheltyakova, I. S.

2016-05-01

A composite refractory material with layer structure obtained by the method of pressure diffusion welding of multilayer Ti/Al packets composed of Ti- and Al-foils is studied. The welding temperature of the packets does not exceed 1200 - 1250°C. A layer structure forms in the process of interdiffusion of titanium and aluminum during welding of the packets.

Modeling of inhomogeneous mixing of plasma species in argon-steam arc discharge

NASA Astrophysics Data System (ADS)

Jeništa, J.; Takana, H.; Uehara, S.; Nishiyama, H.; Bartlová, M.; Aubrecht, V.; Murphy, A. B.

2018-01-01

This paper presents numerical simulation of mixing of argon- and water-plasma species in an argon-steam arc discharge generated in a thermal plasma generator with the combined stabilization of arc by axial gas flow (argon) and water vortex. The diffusion of plasma species itself is described by the combined diffusion coefficients method in which the coefficients describe the diffusion of argon ‘gas,’ with respect to water vapor ‘gas.’ Diffusion processes due to the gradients of mass density, temperature, pressure, and an electric field have been considered in the model. Calculations for currents 150-400 A with 15-22.5 standard liters per minute (slm) of argon reveal inhomogeneous mixing of argon and oxygen-hydrogen species with the argon species prevailing near the arc axis. All the combined diffusion coefficients exhibit highly nonlinear distribution of their values within the discharge, depending on the temperature, pressure, and argon mass fraction of the plasma. The argon diffusion mass flux is driven mainly by the concentration and temperature space gradients. Diffusions due to pressure gradients and due to the electric field are of about 1 order lower. Comparison with our former calculations based on the homogeneous mixing assumption shows differences in temperature, enthalpy, radiation losses, arc efficiency, and velocity at 400 A. Comparison with available experiments exhibits very good qualitative and quantitative agreement for the radial temperature and velocity profiles 2 mm downstream of the exit nozzle.

Influence of magnetic flutter on tearing growth in linear and nonlinear theory

NASA Astrophysics Data System (ADS)

Kreifels, L.; Hornsby, W. A.; Weikl, A.; Peeters, A. G.

2018-06-01

Recent simulations of tearing modes in turbulent regimes show an unexpected enhancement in the growth rate. In this paper the effect is investigated analytically. The enhancement is linked to the influence of turbulent magnetic flutter, which is modelled by diffusion terms in magnetohydrodynamics (MHD) momentum balance and Ohm’s law. Expressions for the linear growth rate as well as the island width in nonlinear theory for small amplitudes are derived. The results indicate an enhanced linear growth rate and a larger linear layer width compared with resistive MHD. Also the island width in the nonlinear regime grows faster in the diffusive model. These observations correspond well to simulations in which the effect of turbulence on the magnetic island width and tearing mode growth is analyzed.

Measurement of effective air diffusion coefficients for trichloroethene in undisturbed soil cores.

PubMed

Bartelt-Hunt, Shannon L; Smith, James A

2002-06-01

In this study, we measure effective diffusion coefficients for trichloroethene in undisturbed soil samples taken from Picatinny Arsenal, New Jersey. The measured effective diffusion coefficients ranged from 0.0053 to 0.0609 cm2/s over a range of air-filled porosity of 0.23-0.49. The experimental data were compared to several previously published relations that predict diffusion coefficients as a function of air-filled porosity and porosity. A multiple linear regression analysis was developed to determine if a modification of the exponents in Millington's [Science 130 (1959) 100] relation would better fit the experimental data. The literature relations appeared to generally underpredict the effective diffusion coefficient for the soil cores studied in this work. Inclusion of a particle-size distribution parameter, d10, did not significantly improve the fit of the linear regression equation. The effective diffusion coefficient and porosity data were used to recalculate estimates of diffusive flux through the subsurface made in a previous study performed at the field site. It was determined that the method of calculation used in the previous study resulted in an underprediction of diffusive flux from the subsurface. We conclude that although Millington's [Science 130 (1959) 100] relation works well to predict effective diffusion coefficients in homogeneous soils with relatively uniform particle-size distributions, it may be inaccurate for many natural soils with heterogeneous structure and/or non-uniform particle-size distributions.

Duration of bubble rearrangements in a coarsening foam probed by time-resolved diffusing-wave spectroscopy: Impact of interfacial rigidity

NASA Astrophysics Data System (ADS)

Le Merrer, Marie; Cohen-Addad, Sylvie; Höhler, Reinhard

2013-08-01

In aqueous foams, the diffusive gas transfer among neighboring bubbles drives a coarsening process which is accompanied by intermittent rearrangements of the structure. Using time-resolved diffusing-wave spectroscopy, we probe the dynamics of these events as a function of the rigidity of the gas-liquid interfaces, liquid viscosity, bubble size, and confinement pressure. We present in detail two independent techniques for analyzing the light scattering data, from which we extract the rearrangement duration. Our results show that interfacial rheology has a major impact on this duration. In the case of low interfacial rigidity, the rearrangements strongly slow down as the pressure is decreased close to the value zero where the bubble packing unjams. In contrast, if the interfaces are rigid, rearrangement durations are independent of the confinement pressure in the same investigated range. Using scaling arguments, we discuss dissipation mechanisms that may explain the observed dependency of the rearrangement dynamics on foam structure, pressure, and physicochemical solution properties.

A Full Navier-Stokes Analysis of Subsonic Diffuser of a Bifurcated 70/30 Supersonic Inlet for High Speed Civil Transport Application

NASA Technical Reports Server (NTRS)

Kapoor, Kamlesh; Anderson, Bernhard H.; Shaw, Robert J.

1994-01-01

A full Navier-Stokes analysis was performed to evaluate the performance of the subsonic diffuser of a NASA Lewis Research Center 70/30 mixed-compression bifurcated supersonic inlet for high speed civil transport application. The PARC3D code was used in the present study. The computations were also performed when approximately 2.5 percent of the engine mass flow was allowed to bypass through the engine bypass doors. The computational results were compared with the available experimental data which consisted of detailed Mach number and total pressure distribution along the entire length of the subsonic diffuser. The total pressure recovery, flow distortion, and crossflow velocity at the engine face were also calculated. The computed surface ramp and cowl pressure distributions were compared with experiments. Overall, the computational results compared well with experimental data. The present CFD analysis demonstrated that the bypass flow improves the total pressure recovery and lessens flow distortions at the engine face.

A diffusive atmospheric pressure glow discharge in a coaxial pin-to-ring gap with a transverse magnetic field

NASA Astrophysics Data System (ADS)

Wang, YongSheng; Ding, WeiDong; Yan, JiaQi; Wang, YaNan

2017-09-01

Atmospheric pressure glow discharge (APGD) has been widely used in the industrial field. The industrial applications are based on achieving stable and diffusive APGD in a relatively large space. The existing sources only achieved stable and diffusive APGD between a short inter-electrode distance within 5 millimeters. In this paper, the effect of a transverse stationary magnetic field on the diffusion of filamentary APGD was studied in a pin-to-ring coaxial gap. The APGD was driven by a high-voltage resonant power supply, and the stationary magnetic field was supplied by a permanent magnet. The stable and diffusive APGD was achieved in the circular area, which diameter was 20 millimeters. The experimental results revealed that more collision ionization occurred and the plasma was distributed diffusively in the discharge gap by applying the external transverse magnetic field. Besides, it is likely to obtain more stable and diffusive APGD in the coaxial pin-to-ring discharge gap when adjusting the input voltage, transverse magnetic flux density and resonant frequency of the power supply.

Diffusive and martensitic nucleation kinetics in solid-solid transitions of colloidal crystals

NASA Astrophysics Data System (ADS)

Peng, Yi; Li, Wei; Wang, Feng; Still, Tim; Yodh, Arjun G.; Han, Yilong

2017-05-01

Solid-solid transitions between crystals follow diffusive nucleation, or various diffusionless transitions, but these kinetics are difficult to predict and observe. Here we observed the rich kinetics of transitions from square lattices to triangular lattices in tunable colloidal thin films with single-particle dynamics by video microscopy. Applying a small pressure gradient in defect-free regions or near dislocations markedly transform the diffusive nucleation with an intermediate-stage liquid into a martensitic generation and oscillation of dislocation pairs followed by a diffusive nucleus growth. This transformation is neither purely diffusive nor purely martensitic as conventionally assumed but a combination thereof, and thus presents new challenges to both theory and the empirical criterion of martensitic transformations. We studied how pressure, density, grain boundary, triple junction and interface coherency affect the nucleus growth, shape and kinetic pathways. These novel microscopic kinetics cast new light on control solid-solid transitions and microstructural evolutions in polycrystals.

Evolution of Edge Pedestal Profiles Over the L-H Transition

NASA Astrophysics Data System (ADS)

Sayer, M. S.; Stacey, W. M.; Floyd, J. P.; Groebner, R. J.

2012-10-01

The detailed time evolution of thermal diffusivities, electromagnetic forces, pressure gradients, particle pinch and momentum transport frequencies (which determine the diffusion coefficient) have been analyzed during the L-H transition in a DIII-D discharge. Density, temperature, rotation velocity and electric field profiles at times just before and after the L-H transition are analyzed in terms of these quantities. The analysis is based on the fluid particle balance, energy balance, force balance and heat conduction equations, as in Ref. [1], but with much greater time resolution and with account for thermal ion orbit loss. The variation of diffusive and non-diffusive transport over the L-H transition is determined from the variation in the radial force balance (radial electric field, VxB force, and pressure gradient) and the variation in the interpreted diffusive transport coefficients. 6pt [1] W.M. Stacey and R.J. Groebner, Phys. Plasmas 17, 112512 (2010).

Diffusive and martensitic nucleation kinetics in solid-solid transitions of colloidal crystals

PubMed Central

Peng, Yi; Li, Wei; Wang, Feng; Still, Tim; Yodh, Arjun G.; Han, Yilong

2017-01-01

Solid–solid transitions between crystals follow diffusive nucleation, or various diffusionless transitions, but these kinetics are difficult to predict and observe. Here we observed the rich kinetics of transitions from square lattices to triangular lattices in tunable colloidal thin films with single-particle dynamics by video microscopy. Applying a small pressure gradient in defect-free regions or near dislocations markedly transform the diffusive nucleation with an intermediate-stage liquid into a martensitic generation and oscillation of dislocation pairs followed by a diffusive nucleus growth. This transformation is neither purely diffusive nor purely martensitic as conventionally assumed but a combination thereof, and thus presents new challenges to both theory and the empirical criterion of martensitic transformations. We studied how pressure, density, grain boundary, triple junction and interface coherency affect the nucleus growth, shape and kinetic pathways. These novel microscopic kinetics cast new light on control solid–solid transitions and microstructural evolutions in polycrystals. PMID:28504246

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.

Quantifying residual, eddy, and mean flow effects on mixing in an idealized circumpolar current

DOE PAGES

Wolfram, Phillip J.; Ringler, Todd D.

2017-07-13

Meridional diffusivity is assessed in this paper for a baroclinically unstable jet in a high-latitudeIdealized Circumpolar Current (ICC) using the Model for Prediction Across Scales-Ocean (MPAS-O) and the online Lagrangian In-situ Global High-performance particle Tracking (LIGHT) diagnostic via space-time dispersion of particle clusters over 120 monthly realizations of O(10 6) particles on 11 potential density surfaces. Diffusivity in the jet reaches values of O(6000 m 2 s -1) and is largest near the critical layer supporting mixing suppression and critical layer theory. Values in the vicinity of the shelf break are suppressed to O(100 m 2 s -1) due tomore » the presence of westward slope front currents. Diffusivity attenuates less rapidly with depth in the jet than both eddy velocity and kinetic energy scalings would suggest. Removal of the mean flow via high-pass filtering shifts the nonlinear parameter (ratio of the eddy velocity to eddy phase speed) into the linear wave regime by increasing the eddy phase speed via the depth-mean flow. Low-pass filtering, in contrast, quantifies the effect of mean shear. Diffusivity is decomposed into mean flow shear, linear waves, and the residual nonhomogeneous turbulence components, where turbulence dominates and eddy-produced filamentation strained by background mean shear enhances mixing, accounting for ≥ 80% of the total diffusivity relative to mean shear [O(100 m 2 s -1)], linear waves [O(1000 m 2 s -1)], and undecomposed full diffusivity [O(6000 m 2 s -1)]. Finally, diffusivity parameterizations accounting for both the nonhomogeneous turbulence residual and depth variability are needed.« less

Energy diffusion controlled reaction rate of reacting particle driven by broad-band noise

NASA Astrophysics Data System (ADS)

Deng, M. L.; Zhu, W. Q.

2007-10-01

The energy diffusion controlled reaction rate of a reacting particle with linear weak damping and broad-band noise excitation is studied by using the stochastic averaging method. First, the stochastic averaging method for strongly nonlinear oscillators under broad-band noise excitation using generalized harmonic functions is briefly introduced. Then, the reaction rate of the classical Kramers' reacting model with linear weak damping and broad-band noise excitation is investigated by using the stochastic averaging method. The averaged Itô stochastic differential equation describing the energy diffusion and the Pontryagin equation governing the mean first-passage time (MFPT) are established. The energy diffusion controlled reaction rate is obtained as the inverse of the MFPT by solving the Pontryagin equation. The results of two special cases of broad-band noises, i.e. the harmonic noise and the exponentially corrected noise, are discussed in details. It is demonstrated that the general expression of reaction rate derived by the authors can be reduced to the classical ones via linear approximation and high potential barrier approximation. The good agreement with the results of the Monte Carlo simulation verifies that the reaction rate can be well predicted using the stochastic averaging method.

Choice of crystal surface finishing for a dual-ended readout depth-of-interaction (DOI) detector.

PubMed

Fan, Peng; Ma, Tianyu; Wei, Qingyang; Yao, Rutao; Liu, Yaqiang; Wang, Shi

2016-02-07

The objective of this study was to choose the crystal surface finishing for a dual-ended readout (DER) DOI detector. Through Monte Carlo simulations and experimental studies, we evaluated 4 crystal surface finishing options as combinations of crystal surface polishing (diffuse or specular) and reflector (diffuse or specular) options on a DER detector. We also tested one linear and one logarithm DOI calculation algorithm. The figures of merit used were DOI resolution, DOI positioning error, and energy resolution. Both the simulation and experimental results show that (1) choosing a diffuse type in either surface polishing or reflector would improve DOI resolution but degrade energy resolution; (2) crystal surface finishing with a diffuse polishing combined with a specular reflector appears a favorable candidate with a good balance of DOI and energy resolution; and (3) the linear and logarithm DOI calculation algorithms show overall comparable DOI error, and the linear algorithm was better for photon interactions near the ends of the crystal while the logarithm algorithm was better near the center. These results provide useful guidance in DER DOI detector design in choosing the crystal surface finishing and DOI calculation methods.

Integrating Models of Diffusion and Behavior to Predict Innovation Adoption, Maintenance, and Social Diffusion.

PubMed

Smith, Rachel A; Kim, Youllee; Zhu, Xun; Doudou, Dimi Théodore; Sternberg, Eleanore D; Thomas, Matthew B

2018-01-01

This study documents an investigation into the adoption and diffusion of eave tubes, a novel mosquito vector control, during a large-scale scientific field trial in West Africa. The diffusion of innovations (DOI) and the integrated model of behavior (IMB) were integrated (i.e., innovation attributes with attitudes and social pressures with norms) to predict participants' (N = 329) diffusion intentions. The findings showed that positive attitudes about the innovation's attributes were a consistent positive predictor of diffusion intentions: adopting it, maintaining it, and talking with others about it. As expected by the DOI and the IMB, the social pressure created by a descriptive norm positively predicted intentions to adopt and maintain the innovation. Drawing upon sharing research, we argued that the descriptive norm may dampen future talk about the innovation, because it may no longer be seen as a novel, useful topic to discuss. As predicted, the results showed that as the descriptive norm increased, the intention to talk about the innovation decreased. These results provide broad support for integrating the DOI and the IMB to predict diffusion and for efforts to draw on other research to understand motivations for social diffusion.

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

Takahashi, Masayuki, E-mail: m.takahashi@al.t.u-tokyo.ac.jp; Ohnishi, Naofumi

A filamentary plasma is reproduced based on a fully kinetic model of electron and ion transports coupled with electromagnetic wave propagation. The discharge plasma transits from discrete to diffusive patterns at a 110-GHz breakdown, with decrease in the ambient pressure, because of the rapid electron diffusion that occurs during an increase in the propagation speed of the ionization front. A discrete plasma is obtained at low pressures when a low-frequency microwave is irradiated because the ionization process becomes more dominant than the electron diffusion, when the electrons are effectively heated by the low-frequency microwave. The propagation speed of the plasmamore » increases with decrease in the incident microwave frequency because of the higher ionization frequency and faster plasma diffusion resulting from the increase in the energy-absorption rate. An external magnetic field is applied to the breakdown volume, which induces plasma filamentation at lower pressures because the electron diffusion is suppressed by the magnetic field. The thrust performance of a microwave rocket is improved by the magnetic fields corresponding to the electron cyclotron resonance (ECR) and its higher-harmonic heating, because slower propagation of the ionization front and larger energy-absorption rates are obtained at lower pressures. It would be advantageous if the fundamental mode of ECR heating is coupled with a lower frequency microwave instead of combining the higher-harmonic ECR heating with the higher frequency microwave. This can improve the thrust performance with smaller magnetic fields even if the propagation speed increases because of the decrease in the incident microwave frequency.« less

Numerical Procedures for Inlet/Diffuser/Nozzle Flows

NASA Technical Reports Server (NTRS)

Rubin, Stanley G.

1998-01-01

Two primitive variable, pressure based, flux-split, RNS/NS solution procedures for viscous flows are presented. Both methods are uniformly valid across the full Mach number range, Le., from the incompressible limit to high supersonic speeds. The first method is an 'optimized' version of a previously developed global pressure relaxation RNS procedure. Considerable reduction in the number of relatively expensive matrix inversion, and thereby in the computational time, has been achieved with this procedure. CPU times are reduced by a factor of 15 for predominantly elliptic flows (incompressible and low subsonic). The second method is a time-marching, 'linearized' convection RNS/NS procedure. The key to the efficiency of this procedure is the reduction to a single LU inversion at the inflow cross-plane. The remainder of the algorithm simply requires back-substitution with this LU and the corresponding residual vector at any cross-plane location. This method is not time-consistent, but has a convective-type CFL stability limitation. Both formulations are robust and provide accurate solutions for a variety of internal viscous flows to be provided herein.

Passivity analysis for uncertain BAM neural networks with time delays and reaction-diffusions

NASA Astrophysics Data System (ADS)

Zhou, Jianping; Xu, Shengyuan; Shen, Hao; Zhang, Baoyong

2013-08-01

This article deals with the problem of passivity analysis for delayed reaction-diffusion bidirectional associative memory (BAM) neural networks with weight uncertainties. By using a new integral inequality, we first present a passivity condition for the nominal networks, and then extend the result to the case with linear fractional weight uncertainties. The proposed conditions are expressed in terms of linear matrix inequalities, and thus can be checked easily. Examples are provided to demonstrate the effectiveness of the proposed results.

Concentration-dependent changes in apparent diffusion coefficients as indicator for colloidal stability of protein solutions.

PubMed

Bauer, Katharina Christin; Göbel, Mathias; Schwab, Marie-Luise; Schermeyer, Marie-Therese; Hubbuch, Jürgen

2016-09-10

The colloidal stability of a protein solution during downstream processing, formulation, and storage is a key issue for the biopharmaceutical production process. Thus, knowledge about colloidal solution characteristics, such as the tendency to form aggregates or high viscosity, at various processing conditions is of interest. This work correlates changes in the apparent diffusion coefficient as a parameter of protein interactions with observed protein aggregation and dynamic viscosity of the respective protein samples. For this purpose, the diffusion coefficient, the protein phase behavior, and the dynamic viscosity in various systems containing the model proteins α-lactalbumin, lysozyme, and glucose oxidase were studied. Each of these experiments revealed a wide range of variations in protein interactions depending on protein type, protein concentration, pH, and the NaCl concentration. All these variations showed to be mirrored by changes in the apparent diffusion coefficient in the respective samples. Whereas stable samples with relatively low viscosity showed an almost linear dependence, the deviation from the concentration-dependent linearity indicated both an increase in the sample viscosity and probability of protein aggregation. This deviation of the apparent diffusion coefficient from concentration-dependent linearity was independent of protein type and solution properties for this study. Thus, this single parameter shows the potential to act as a prognostic tool for colloidal stability of protein solutions. Copyright © 2016 Elsevier B.V. All rights reserved.

Design and optimization of a single stage centrifugal compressor for a solar dish-Brayton system

NASA Astrophysics Data System (ADS)

Wang, Yongsheng; Wang, Kai; Tong, Zhiting; Lin, Feng; Nie, Chaoqun; Engeda, Abraham

2013-10-01

According to the requirements of a solar dish-Brayton system, a centrifugal compressor stage with a minimum total pressure ratio of 5, an adiabatic efficiency above 75% and a surge margin more than 12% needs to be designed. A single stage, which consists of impeller, radial vaned diffuser, 90° crossover and two rows of axial stators, was chosen to satisfy this system. To achieve the stage performance, an impeller with a 6:1 total pressure ratio and an adiabatic efficiency of 90% was designed and its preliminary geometry came from an in-house one-dimensional program. Radial vaned diffuser was applied downstream of the impeller. Two rows of axial stators after 90° crossover were added to guide the flow into axial direction. Since jet-wake flow, shockwave and boundary layer separation coexisted in the impeller-diffuser region, optimization on the radius ratio of radial diffuser vane inlet to impeller exit, diffuser vane inlet blade angle and number of diffuser vanes was carried out at design point. Finally, an optimized centrifugal compressor stage fulfilled the high expectations and presented proper performance. Numerical simulation showed that at design point the stage adiabatic efficiency was 79.93% and the total pressure ratio was 5.6. The surge margin was 15%. The performance map including 80%, 90% and 100% design speed was also presented.

Comparison of fluid neutral models for one-dimensional plasma edge modeling with a finite volume solution of the Boltzmann equation

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

Horsten, N., E-mail: niels.horsten@kuleuven.be; Baelmans, M.; Dekeyser, W.

2016-01-15

We derive fluid neutral approximations for a simplified 1D edge plasma model, suitable to study the neutral behavior close to the target of a nuclear fusion divertor, and compare its solutions to the solution of the corresponding kinetic Boltzmann equation. The plasma is considered as a fixed background extracted from a detached 2D simulation. We show that the Maxwellian equilibrium distribution is already obtained very close to the target, justifying the use of a fluid approximation. We compare three fluid neutral models: (i) a diffusion model; (ii) a pressure-diffusion model (i.e., a combination of a continuity and momentum equation) assumingmore » equal neutral and ion temperatures; and (iii) the pressure-diffusion model coupled to a neutral energy equation taking into account temperature differences between neutrals and ions. Partial reflection of neutrals reaching the boundaries is included in both the kinetic and fluid models. We propose two methods to obtain an incident neutral flux boundary condition for the fluid models: one based on a diffusion approximation and the other assuming a truncated Chapman-Enskog distribution. The pressure-diffusion model predicts the plasma sources very well. The diffusion boundary condition gives slightly better results overall. Although including an energy equation still improves the results, the assumption of equal ion and neutral temperature already gives a very good approximation.« less

Plasma diffusion at the magnetopause - The case of lower hybrid drift waves

NASA Technical Reports Server (NTRS)

Treumann, R. A.; Labelle, J.; Pottelette, R.

1991-01-01

The diffusion expected from the quasi-linear theory of the lower hybrid drift instability at the earth's magnetopause is recalculated. The resulting diffusion coefficient is marginally large enough to explain the thickness of the boundary layer under quiet conditions, based on observational upper limits for the wave intensities. Thus, one possible model for the boundary layer could involve equilibrium between the diffusion arising from lower hybrid waves and various loss processes.

An asymptotic-preserving stochastic Galerkin method for the radiative heat transfer equations with random inputs and diffusive scalings

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

Jin, Shi, E-mail: sjin@wisc.edu; Institute of Natural Sciences, Department of Mathematics, MOE-LSEC and SHL-MAC, Shanghai Jiao Tong University, Shanghai 200240; Lu, Hanqing, E-mail: hanqing@math.wisc.edu

2017-04-01

In this paper, we develop an Asymptotic-Preserving (AP) stochastic Galerkin scheme for the radiative heat transfer equations with random inputs and diffusive scalings. In this problem the random inputs arise due to uncertainties in cross section, initial data or boundary data. We use the generalized polynomial chaos based stochastic Galerkin (gPC-SG) method, which is combined with the micro–macro decomposition based deterministic AP framework in order to handle efficiently the diffusive regime. For linearized problem we prove the regularity of the solution in the random space and consequently the spectral accuracy of the gPC-SG method. We also prove the uniform (inmore » the mean free path) linear stability for the space-time discretizations. Several numerical tests are presented to show the efficiency and accuracy of proposed scheme, especially in the diffusive regime.« less

LIF measurements and chemical kinetic analysis of methylidyne formation in high-pressure counter-flow partially premixed and non-premixed flames

NASA Astrophysics Data System (ADS)

Naik, S. V.; Laurendeau, N. M.

2004-11-01

We report quantitative, spatially resolved, linear laser-induced fluorescence (LIF) measurements of methylidyne concentration ([CH]) in laminar, methane air, counter-flow partially premixed and non-premixed flames using excitation near 431.5 nm in the A X (0,0) band. For partially premixed flames, fuel-side equivalence ratios (ϕB) of 1.45, 1.6 and 2.0 are studied at pressures of 1, 3, 6, 9 and 12 atm. For non-premixed flames, the fuel-side mixture consists of 25% CH4 and 75% N2; measurements are obtained at pressures of 1, 2, 3, 4, 5, 6, 9 and 12 atm. The quantitative CH measurements are compared with predictions from an opposed-flow flame code utilizing two GRI chemical kinetic mechanisms (versions 2.11 and 3.0). LIF measurements of [CH] are corrected for variations in the quenching rate coefficient by using major species concentrations and temperatures generated by the code along with suitable quenching cross sections for CH available from the literature. A pathway analysis provides relative contributions from important elementary reactions to the total amount of CH produced at various pressures. Key reactions controlling peak CH concentrations are also identified by using a sensitivity analysis. For the partially premixed flames, measured CH profiles are reproduced reasonably well by GRI 3.0, although some quantitative disagreement exists at all pressures. Two CH radical peaks are observed for ϕB=1.45 and ϕB=1.6 at pressures above 3 atm. Peak CH concentrations for the non-premixed flames are significantly underpredicted by GRI 3.0. The latter agrees with previously reported NO concentrations, which are also underpredicted in these same high-pressure counter-flow diffusion flames.

Linear air-fuel sensor development

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

Garzon, F.; Miller, C.

1996-12-14

The electrochemical zirconia solid electrolyte oxygen sensor, is extensively used for monitoring oxygen concentrations in various fields. They are currently utilized in automobiles to monitor the exhaust gas composition and control the air-to-fuel ratio, thus reducing harmful emission components and improving fuel economy. Zirconia oxygen sensors, are divided into two classes of devices: (1) potentiometric or logarithmic air/fuel sensors; and (2) amperometric or linear air/fuel sensors. The potentiometric sensors are ideally suited to monitor the air-to-fuel ratio close to the complete combustion stoichiometry; a value of about 14.8 to 1 parts by volume. This occurs because the oxygen concentration changesmore » by many orders of magnitude as the air/fuel ratio is varied through the stoichiometric value. However, the potentiometric sensor is not very sensitive to changes in oxygen partial pressure away from the stoichiometric point due to the logarithmic dependence of the output voltage signal on the oxygen partial pressure. It is often advantageous to operate gasoline power piston engines with excess combustion air; this improves fuel economy and reduces hydrocarbon emissions. To maintain stable combustion away from stoichiometry, and enable engines to operate in the excess oxygen (lean burn) region several limiting-current amperometric sensors have been reported. These sensors are based on the electrochemical oxygen ion pumping of a zirconia electrolyte. They typically show reproducible limiting current plateaus with an applied voltage caused by the gas diffusion overpotential at the cathode.« less

Associations of Infant Feeding and Timing of Weight Gain and Linear Growth during Early Life with Childhood Blood Pressure: Findings from a Prospective Population Based Cohort Study

PubMed Central

Vrijkotte, Tanja G. M.; van Eijsden, Manon; Gemke, Reinoud J. B. J.

2016-01-01

Objective Small birth size and rapid postnatal growth have been associated with higher future blood pressure. The timing of these effects, the relative importance of weight gain and linear growth and the role of infant feeding need to be clarified. Methods We assessed how blood pressure relates to birth weight, infant and childhood growth and infant feeding (duration of exclusive breastfeeding and timing of introduction of complementary feeding) in 2227 children aged 5 years from a prospective cohort study (Amsterdam Born Children and their Development). Postnatal growth was represented by statistically independent measures of relative weight gain (weight gain independent of height) and linear growth in four age periods during infancy (0–1 month; 1–3 months; 3–6 months; 6–12 months) and from 12 months to 5 years. Results Lower birth weight was associated with higher childhood diastolic blood pressure (-0.38 mm Hg.SD-1; P = 0.007). Faster relative weight gain and linear growth after 1 month were positively associated with systolic and diastolic blood pressure. Associations of linear growth with systolic blood pressure ranged from 0.47 to 1.49 mm Hg.SD-1; P<0.01 for all. Coefficients were similar for different periods of infancy and also for relative weight gain and linear growth. Compared to breastfeeding <1 month, breastfeeding >1 month was associated with lower blood pressure (e.g. >6 months -1.56 mm Hg systolic blood pressure; P<0.001). Compared to >6 months, introduction of complementary feeding <6 months was associated with higher blood pressure (e.g. 4–6 months 0.91 mm Hg systolic blood pressure; P = 0.004). Conclusions After the age of one month faster growth in either weight or height is associated with higher childhood blood pressure. It is unknown whether faster weight gain and linear growth carry the same risk for adult hypertension and cardiovascular morbidity. Longer breastfeeding and delayed introduction of complementary feeding may be associated with lower adult blood pressure. PMID:27832113

Associations of Infant Feeding and Timing of Weight Gain and Linear Growth during Early Life with Childhood Blood Pressure: Findings from a Prospective Population Based Cohort Study.

PubMed

de Beer, Marieke; Vrijkotte, Tanja G M; Fall, Caroline H D; van Eijsden, Manon; Osmond, Clive; Gemke, Reinoud J B J

2016-01-01

Small birth size and rapid postnatal growth have been associated with higher future blood pressure. The timing of these effects, the relative importance of weight gain and linear growth and the role of infant feeding need to be clarified. We assessed how blood pressure relates to birth weight, infant and childhood growth and infant feeding (duration of exclusive breastfeeding and timing of introduction of complementary feeding) in 2227 children aged 5 years from a prospective cohort study (Amsterdam Born Children and their Development). Postnatal growth was represented by statistically independent measures of relative weight gain (weight gain independent of height) and linear growth in four age periods during infancy (0-1 month; 1-3 months; 3-6 months; 6-12 months) and from 12 months to 5 years. Lower birth weight was associated with higher childhood diastolic blood pressure (-0.38 mm Hg.SD-1; P = 0.007). Faster relative weight gain and linear growth after 1 month were positively associated with systolic and diastolic blood pressure. Associations of linear growth with systolic blood pressure ranged from 0.47 to 1.49 mm Hg.SD-1; P<0.01 for all. Coefficients were similar for different periods of infancy and also for relative weight gain and linear growth. Compared to breastfeeding <1 month, breastfeeding >1 month was associated with lower blood pressure (e.g. >6 months -1.56 mm Hg systolic blood pressure; P<0.001). Compared to >6 months, introduction of complementary feeding <6 months was associated with higher blood pressure (e.g. 4-6 months 0.91 mm Hg systolic blood pressure; P = 0.004). After the age of one month faster growth in either weight or height is associated with higher childhood blood pressure. It is unknown whether faster weight gain and linear growth carry the same risk for adult hypertension and cardiovascular morbidity. Longer breastfeeding and delayed introduction of complementary feeding may be associated with lower adult blood pressure.

Reverse flexing as a physical/mechanical treatment to mitigate fouling of fine bubble diffusers.

PubMed

Odize, Victory O; Novak, John; De Clippeleir, Haydee; Al-Omari, Ahmed; Smeraldi, Joshua D; Murthy, Sudhir; Rosso, Diego

2017-10-01

Achieving energy neutrality has shifted focus towards aeration system optimization, due to the high energy consumption of aeration processes in modern advanced wastewater treatment plants. A study on fine bubble diffuser fouling and mitigation, quantified by dynamic wet pressure (DWP), oxygen transfer efficiency and alpha was carried out in Blue Plains, Washington, DC. Four polyurethane fine bubble diffusers were installed in a pilot reactor column fed with high rate activated sludge from a full scale system. A mechanical cleaning method, reverse flexing (RF), was used to treat two diffusers (RF1, RF2), while two diffusers were kept as a control (i.e., no reverse flexing). There was a 45% increase in DWP of the control diffuser after 17 months of operation, an indication of fouling. RF treated diffusers (RF1 and RF2) did not show significant increase in DWP, and in comparison to the control diffuser prevented about 35% increase in DWP. Hence, reverse flexing potentially saves blower energy, by reducing the pressure burden on the air blower which increases blower energy requirement. However, no significant impact of the RF treatment in preventing a decrease in alpha-fouling (αF) of the fine pore diffusers, over time in operation was observed.

SiC and Si3N4 Recession Due to SiO2 Scale Volatility Under Combustor Conditions

NASA Technical Reports Server (NTRS)

Smialek, James L.; Robinson, Raymond C.; Opila, Elizabeth J.; Fox, Dennis S.; Jacobson, Nathan S.

1999-01-01

Silicon carbide (SiC) and Si3N4 materials were tested in various turbine engine combustion environments chosen to represent either conventional fuel-lean or fuel-rich mixtures proposed for high-speed aircraft. Representative chemical vapor-deposited (CVD), sintered, and composite materials were evaluated by furnace and high-pressure burner rig exposures. Although protective SiO2 scales formed in all cases, the evidence presented supports a model based on paralinear growth kinetics (i.e., parabolic growth moderated simultaneously by linear volatilization). The volatility rate is dependent on temperature, moisture content, system pressure, and gas velocity. The burner tests were thus used to map SiO2 volatility (and SiC recession) over a range of temperatures, pressures, and velocities. The functional dependency of material recession (volatility) that emerged followed the form A[exp(-Q / RT)](P(sup x)v(sup y). These empirical relations were compared with rates predicted from the thermodynamics of volatile SiO and SiOxHy reaction products and a kinetic model of diffusion through a moving boundary layer. For typical combustion conditions, recession of 0.2 to 2 micrometers/hr is predicted at 1200 to 1400 C, far in excess of acceptable long-term limits.

On the Theory of Solitons of Fluid Pressure and Solute Density in Geologic Porous Media, with Applications to Shale, Clay and Sandstone

NASA Astrophysics Data System (ADS)

Caserta, A.; Kanivetsky, R.; Salusti, E.

2017-11-01

We here analyze a new model of transients of pore pressure p and solute density ρ in geologic porous media. This model is rooted in the nonlinear wave theory, its focus is on advection and effect of large pressure jumps on strain. It takes into account nonlinear and also time-dependent versions of the Hooke law about stress, rate and strain. The model solutions strictly relate p and ρ evolving under the effect of a strong external stress. As a result, the presence of quick and sharp transients in low permeability rocks is unveiled, i.e., the nonlinear "Burgers solitons". We, therefore, show that the actual transport process in porous rocks for large signals is not only the linear diffusion, but also a solitons presence could control the process. A test of a presence of solitons is applied to Pierre shale, Bearpaw shale, Boom clay and Oznam-Mugu silt and clay. An application about the presence of solitons for nuclear waste disposal and salt water intrusions is also discussed. Finally, in a kind of "theoretical experiment" we show that solitons could also be present in higher permeability rocks (Jordan and St. Peter sandstones), thus supporting the idea of a possible occurrence of osmosis also in sandstones.

The mysteries of the diffusion region in asymmetric systems

NASA Astrophysics Data System (ADS)

Hesse, M.; Aunai, N.; Zenitani, S.; Kuznetsova, M. M.; Birn, J.

2013-12-01

Unlike in symmetric systems, where symmetry dictates a comparatively simple structure of the reconnection region, asymmetric systems offer a surprising, much more complex, structure of the diffusion region. Beyond the well-known lack of colocation of flow stagnation and magnetic null, the physical mechanism underpinning the reconnection electric field also appears to be considerably more complex. In this presentation, we will perform a detailed analysis of the reconnection diffusion region in an asymmetric system. We will show that, unlike in symmetric systems, the immediate reconnection electric field is not given by electron pressure tensor nongyrotropies, but by electron inertial contributions. We will further discuss the role of pressure nongyrotropies, and we will study the origin of the complex structures of electron distributions in the central part of the diffusion region.

Production of atmospheric pressure diffuse nanosecond pulsed dielectric barrier discharge using the array needles-plate electrode in air

NASA Astrophysics Data System (ADS)

Yang, De-zheng; Wang, Wen-chun; Jia, Li; Nie, Dong-xia; Shi, Heng-chao

2011-04-01

In this paper, a bidirectional high pulse voltage with 20 ns rising time is employed to generate an atmospheric pressure diffuse dielectric barrier discharge using the array needles-plate electrode configuration. Both double needle and multiple needle electrode configurations nanosecond pulsed dielectric barrier discharges are investigated. It is found that a diffuse discharge plasma with low gas temperature can be obtained, and the plasma volume increases with the increase of the pulse peak voltage, but remains almost constant with the increase of the pulse repetition rate. In addition to showing the potential application on a topographically nonuniform surface treatment of the discharge, the multiple needle-plate electrode configuration with different needle-plate electrode gaps are also employed to generate diffuse discharge plasma.

Space, energy and anisotropy effects on effective cross sections and diffusion coefficients in the resonance region

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

Meftah, B.

1982-01-01

Present methods used in reactor analysis do not include adequately the effect of anisotropic scattering in the calculation of resonance effective cross sections. Also the assumption that the streaming term ..cap omega...del Phi is conserved when the total, absorption and transfer cross sections are conserved, is bad because the leakage from a heterogeneous cell will not be conserved and is strongly anisotropic. A third major consideration is the coupling between different regions in a multiregion reactor; currently this effect is being completely ignored. To assess the magnitude of these effects, a code based on integral transport formalism with linear anisotropicmore » scattering was developed. Also, a more adequate formulation of the diffusion coefficient in a heterogeneous cell was derived. Two reactors, one fast, ZPR-6/5, and one thermal, TRX-3, were selected for the study. The study showed that, in general, the inclusion of linear scattering anisotropy increases the cell effective capture cross section of U-238. The increase was up to 2% in TRX-3 and 0.5% in ZPR-6/5. The effect on the multiplication factor was -0.003% ..delta..k/k for ZPR-6/5 and -0.05% ..delta..k/k for TRX-3. For the case of the diffusion coefficient, the combined effect of heterogeneity and linear anisotropy gave an increase of up to 29% in the parallel diffusion coefficient of TRX-3 and 5% in the parallel diffusion coefficient of ZPR-6/5. In contrast, the change in the perpendicular diffusion coefficient did not exceed 2% in both systems.« less

Characterization of Mixed Polypeptide Colloidal Particles by Light Scattering

NASA Astrophysics Data System (ADS)

Shuman, Hannah E.; Gaeckle, Grace K.; Gavin, John; Holland, Nolan B.; Streletzky, Kiril A.

2014-03-01

Temperature-dependent polymer surfactants have been developed by connecting three elastin-like polypeptide (ELP) chains to a charged protein domain (foldon), forming a three-armed star polymer. At low temperatures the polymer is soluble, while at higher temperatures it forms micelles. The behavior of mixtures of the three-armed star ELP (E20-Foldon) and H40-Linear ELP chains was analyzed under different salt and protein concentrations and various foldon to linear ELP ratio using Depolarized Dynamic Light Scattering. It was expected that under certain conditions the pure E20-Foldon would form spherical micelles, which upon adding the linear ELP would change in size and possibly shape. The pure E20-Foldon indeed formed largely spherical micelles with Rh of 10-20nm in solutions with 15-100mM salt and protein concentration between 10 μM and 100 μM. For the mixtures of 50 μM E20-Foldon and varying concentrations of H40-Linear in 25mM of salt, it was discovered that low and high H40-Linear concentration (4 μM and 50 μM) had only one transition. For the mixtures with of 10 and 25 μM of H40-Linear the two distinct transition temperatures were observed by spectrophotometry. The first transition corresponded to significantly elongated diffusive particles of apparent Rh of 30-50nm, while the second transition corresponded to slightly anisotropic diffusive particles with apparent Rh of about 20nm. At all H40-Linear concentrations studied, diffusive particles were seen above the second transition. Their radius and ability to depolarize light increased with the increase of H40-Linear concentration.

Simulation of 2-dimensional viscous flow through cascades using a semi-elliptic analysis and hybrid C-H grids

NASA Technical Reports Server (NTRS)

Ramamurti, R.; Ghia, U.; Ghia, K. N.

1988-01-01

A semi-elliptic formulation, termed the interacting parabolized Navier-Stokes (IPNS) formulation, is developed for the analysis of a class of subsonic viscous flows for which streamwise diffusion is neglible but which are significantly influenced by upstream interactions. The IPNS equations are obtained from the Navier-Stokes equations by dropping the streamwise viscous-diffusion terms but retaining upstream influence via the streamwise pressure-gradient. A two-step alternating-direction-explicit numerical scheme is developed to solve these equations. The quasi-linearization and discretization of the equations are carefully examined so that no artificial viscosity is added externally to the scheme. Also, solutions to compressible as well as nearly compressible flows are obtained without any modification either in the analysis or in the solution process. The procedure is applied to constricted channels and cascade passages formed by airfoils of various shapes. These geometries are represented using numerically generated curilinear boundary-oriented coordinates forming an H-grid. A hybrid C-H grid, more appropriate for cascade of airfoils with rounded leading edges, was also developed. Satisfactory results are obtained for flows through cascades of Joukowski airfoils.

High Pressure, Transport Properties of Fluids: Theory and Data from Levitated Fluid-Drops at Combustion-Relevant Temperatures

NASA Technical Reports Server (NTRS)

Bellan, J.; Ohaska, K.

2001-01-01

The objective of this investigation is to derive a set of consistent mixing rules for calculating diffusivities and thermal diffusion factors over a thermodynamic regime encompassing the subcritical and supercritical ranges. These should serve for modeling purposes, and therefore for accurate simulations of high pressure phenomena such as fluid disintegration, turbulent flows and sprays. A particular consequence of this work will be the determination of effective Lewis numbers for supercritical conditions, thus enabling the examination of the relative importance of heat and mass transfer at supercritical pressures.

Compressible flow in a diffusing S-duct with flow separation

NASA Technical Reports Server (NTRS)

Vakili, A. D.; Wu, J. M.; Bhat, M. K.; Liver, P.

1987-01-01

Local flow velocity vectors, as well as static and total pressures along ten radial traverses, were obtained at six stations for secondary flows in a diffusing 30-30-deg S-duct with circular cross section. The strong secondary flow measured in the first bend continued into the second with new vorticity produced in the opposite direction. Contour plots representing the transverse velocity field, as well as total and static pressure contours, have been obtained. As a result of the secondary flow and subsequent separation, substantial total pressure distortion is noted to occur at the duct exit.

Repetitively pulsed UV radiation source based on a run-away electron preionised diffuse discharge in nitrogen

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

Baksht, E Kh; Burachenko, A G; Lomaev, M I

2015-04-30

An extended repetitively pulsed source of spontaneous UV radiation is fabricated, which may also be used for producing laser radiation. Voltage pulses with an incident wave amplitude of up to 30 kV, a half-amplitude duration of ∼4 ns and a rise time of ∼2.5 ns are applied to a gap with a nonuniform electric field. For an excitation region length of 35 cm and a nitrogen pressure of 30 – 760 Torr, a diffusive discharge up to a pulse repetition rate of 2 kHz is produced without using an additional system for gap preionisation. An investigation is made of themore » plasma of the run-away electron preionised diffuse discharge. Using a CCD camera it is found that the dense diffused plasma fills the gap in a time shorter than 1 ns. X-ray radiation is recorded from behind the foil anode throughout the pressure range under study; a supershort avalanche electron beam is recorded by the collector electrode at pressures below 100 Torr. (laser applications and other topics in quantum electronics)« less

Diffusion in Deterministic Interacting Lattice Systems

NASA Astrophysics Data System (ADS)

Medenjak, Marko; Klobas, Katja; Prosen, Tomaž

2017-09-01

We study reversible deterministic dynamics of classical charged particles on a lattice with hard-core interaction. It is rigorously shown that the system exhibits three types of transport phenomena, ranging from ballistic, through diffusive to insulating. By obtaining an exact expressions for the current time-autocorrelation function we are able to calculate the linear response transport coefficients, such as the diffusion constant and the Drude weight. Additionally, we calculate the long-time charge profile after an inhomogeneous quench and obtain diffusive profilewith the Green-Kubo diffusion constant. Exact analytical results are corroborated by Monte Carlo simulations.

Reactive diffusion in the presence of a diffusion barrier: Experiment and model

NASA Astrophysics Data System (ADS)

Mangelinck, D.; Luo, T.; Girardeaux, C.

2018-05-01

Reactions in thin films and diffusion barriers are important for applications such as protective coatings, electrical contact, and interconnections. In this work, the effect of a barrier on the kinetics of the formation for a single phase by reactive diffusion is investigated from both experimental and modeling point of views. Two types of diffusion barriers are studied: (i) a thin layer of W deposited between a Ni film and Si substrate and (ii) Ni alloy films, Ni(1%W) and Ni(5%Pt), that form a diffusion barrier during the reaction with the Si substrate. The effect of the barriers on the kinetics of δ-Ni2Si formation is determined by in situ X ray diffraction and compared to models that explain the kinetic slowdown induced by both types of barrier. A linear parabolic growth is found for the deposited barrier with an increasing linear contribution for increasing barrier thickness. On the contrary, the growth is mainly parabolic for the barrier formed by the reaction between an alloy film and the substrate. The permeability of the two types of barrier is determined and discussed. The developed models fit well with the dedicated model experiments, leading to a better understanding of the barrier effect on the reactive diffusion and allowing us to predict the barrier behaviour in various applications.

New Monte Carlo model of cylindrical diffusing fibers illustrates axially heterogeneous fluorescence detection: simulation and experimental validation

PubMed Central

Baran, Timothy M.; Foster, Thomas H.

2011-01-01

We present a new Monte Carlo model of cylindrical diffusing fibers that is implemented with a graphics processing unit. Unlike previously published models that approximate the diffuser as a linear array of point sources, this model is based on the construction of these fibers. This allows for accurate determination of fluence distributions and modeling of fluorescence generation and collection. We demonstrate that our model generates fluence profiles similar to a linear array of point sources, but reveals axially heterogeneous fluorescence detection. With axially homogeneous excitation fluence, approximately 90% of detected fluorescence is collected by the proximal third of the diffuser for μs'/μa = 8 in the tissue and 70 to 88% is collected in this region for μs'/μa = 80. Increased fluorescence detection by the distal end of the diffuser relative to the center section is also demonstrated. Validation of these results was performed by creating phantoms consisting of layered fluorescent regions. Diffusers were inserted into these layered phantoms and fluorescence spectra were collected. Fits to these spectra show quantitative agreement between simulated fluorescence collection sensitivities and experimental results. These results will be applicable to the use of diffusers as detectors for dosimetry in interstitial photodynamic therapy. PMID:21895311

a Cell Vertex Algorithm for the Incompressible Navier-Stokes Equations on Non-Orthogonal Grids

NASA Astrophysics Data System (ADS)

Jessee, J. P.; Fiveland, W. A.

1996-08-01

The steady, incompressible Navier-Stokes (N-S) equations are discretized using a cell vertex, finite volume method. Quadrilateral and hexahedral meshes are used to represent two- and three-dimensional geometries respectively. The dependent variables include the Cartesian components of velocity and pressure. Advective fluxes are calculated using bounded, high-resolution schemes with a deferred correction procedure to maintain a compact stencil. This treatment insures bounded, non-oscillatory solutions while maintaining low numerical diffusion. The mass and momentum equations are solved with the projection method on a non-staggered grid. The coupling of the pressure and velocity fields is achieved using the Rhie and Chow interpolation scheme modified to provide solutions independent of time steps or relaxation factors. An algebraic multigrid solver is used for the solution of the implicit, linearized equations.A number of test cases are anlaysed and presented. The standard benchmark cases include a lid-driven cavity, flow through a gradual expansion and laminar flow in a three-dimensional curved duct. Predictions are compared with data, results of other workers and with predictions from a structured, cell-centred, control volume algorithm whenever applicable. Sensitivity of results to the advection differencing scheme is investigated by applying a number of higher-order flux limiters: the MINMOD, MUSCL, OSHER, CLAM and SMART schemes. As expected, studies indicate that higher-order schemes largely mitigate the diffusion effects of first-order schemes but also shown no clear preference among the higher-order schemes themselves with respect to accuracy. The effect of the deferred correction procedure on global convergence is discussed.

Accurate measurement of dispersion data through short and narrow tubes used in very high-pressure liquid chromatography.

PubMed

Gritti, Fabrice; McDonald, Thomas; Gilar, Martin

2015-09-04

An original method is proposed for the accurate and reproducible measurement of the time-based dispersion properties of short L< 50cm and narrow rc< 50μm tubes at mobile phase flow rates typically used in very high-pressure liquid chromatography (vHPLC). Such tubes are used to minimize sample dispersion in vHPLC; however, their dispersion characteristics cannot be accurately measured at such flow rates due to system dispersion contribution of vHPLC injector and detector. It is shown that using longer and wider tubes (>10μL) enables a reliable measurement of the dispersion data. We confirmed that the dimensionless plot of the reduced dispersion coefficient versus the reduced linear velocity (Peclet number) depends on the aspect ratio, L/rc, of the tube, and unexpectedly also on the diffusion coefficient of the analyte. This dimensionless plot could be easily obtained for a large volume tube, which has the same aspect ratio as that of the short and narrow tube, and for the same diffusion coefficient. The dispersion data for the small volume tube are then directly extrapolated from this plot. For instance, it is found that the maximum volume variances of 75μm×30.5cm and 100μm×30.5cm prototype finger-tightened connecting tubes are 0.10 and 0.30μL(2), respectively, with an accuracy of a few percent and a precision smaller than seven percent. Copyright © 2015 Elsevier B.V. All rights reserved.

Hydrodynamic theory of diffusion in two-temperature multicomponent plasmas

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

Ramshaw, J.D.; Chang, C.H.

Detailed numerical simulations of multicomponent plasmas require tractable expressions for species diffusion fluxes, which must be consistent with the given plasma current density J{sub q} to preserve local charge neutrality. The common situation in which J{sub q} = 0 is referred to as ambipolar diffusion. The use of formal kinetic theory in this context leads to results of formidable complexity. We derive simple tractable approximations for the diffusion fluxes in two-temperature multicomponent plasmas by means of a generalization of the hydrodynamical approach used by Maxwell, Stefan, Furry, and Williams. The resulting diffusion fluxes obey generalized Stefan-Maxwell equations that contain drivingmore » forces corresponding to ordinary, forced, pressure, and thermal diffusion. The ordinary diffusion fluxes are driven by gradients in pressure fractions rather than mole fractions. Simplifications due to the small electron mass are systematically exploited and lead to a general expression for the ambipolar electric field in the limit of infinite electrical conductivity. We present a self-consistent effective binary diffusion approximation for the diffusion fluxes. This approximation is well suited to numerical implementation and is currently in use in our LAVA computer code for simulating multicomponent thermal plasmas. Applications to date include a successful simulation of demixing effects in an argon-helium plasma jet, for which selected computational results are presented. Generalizations of the diffusion theory to finite electrical conductivity and nonzero magnetic field are currently in progress.« less

Unstructured Polyhedral Mesh Thermal Radiation Diffusion

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

Palmer, T.S.; Zika, M.R.; Madsen, N.K.

2000-07-27

Unstructured mesh particle transport and diffusion methods are gaining wider acceptance as mesh generation, scientific visualization and linear solvers improve. This paper describes an algorithm that is currently being used in the KULL code at Lawrence Livermore National Laboratory to solve the radiative transfer equations. The algorithm employs a point-centered diffusion discretization on arbitrary polyhedral meshes in 3D. We present the results of a few test problems to illustrate the capabilities of the radiation diffusion module.

Molecular surface area based predictive models for the adsorption and diffusion of disperse dyes in polylactic acid matrix.

PubMed

Xu, Suxin; Chen, Jiangang; Wang, Bijia; Yang, Yiqi

2015-11-15

Two predictive models were presented for the adsorption affinities and diffusion coefficients of disperse dyes in polylactic acid matrix. Quantitative structure-sorption behavior relationship would not only provide insights into sorption process, but also enable rational engineering for desired properties. The thermodynamic and kinetic parameters for three disperse dyes were measured. The predictive model for adsorption affinity was based on two linear relationships derived by interpreting the experimental measurements with molecular structural parameters and compensation effect: ΔH° vs. dye size and ΔS° vs. ΔH°. Similarly, the predictive model for diffusion coefficient was based on two derived linear relationships: activation energy of diffusion vs. dye size and logarithm of pre-exponential factor vs. activation energy of diffusion. The only required parameters for both models are temperature and solvent accessible surface area of the dye molecule. These two predictive models were validated by testing the adsorption and diffusion properties of new disperse dyes. The models offer fairly good predictive ability. The linkage between structural parameter of disperse dyes and sorption behaviors might be generalized and extended to other similar polymer-penetrant systems. Copyright © 2015 Elsevier Inc. All rights reserved.

Morphological bubble evolution induced by air diffusion on submerged hydrophobic structures

NASA Astrophysics Data System (ADS)

Lv, Pengyu; Xiang, Yaolei; Xue, Yahui; Lin, Hao; Duan, Huiling

2017-03-01

Bubbles trapped in the cavities always play important roles in the underwater applications of structured hydrophobic surfaces. Air exchange between bubbles and surrounding water has a significant influence on the morphological bubble evolution, which in turn frequently affects the functionalities of the surfaces, such as superhydrophobicity and drag reduction. In this paper, air diffusion induced bubble evolution on submerged hydrophobic micropores under reduced pressures is investigated experimentally and theoretically. The morphological behaviors of collective and single bubbles are observed using confocal microscopy. Four representative evolution phases of bubbles are captured in situ. After depressurization, bubbles will not only grow and coalesce but also shrink and split although the applied pressure remains negative. A diffusion-based model is used to analyze the evolution behavior and the results are consistent with the experimental data. A criterion for bubble growth and shrinkage is also derived along with a phase diagram, revealing that the competition of effective gas partial pressures across the two sides of the diffusion layer dominates the bubble evolution process. Strategies for controlling the bubble evolution behavior are also proposed based on the phase diagram. The current work provides a further understanding of the general behavior of bubble evolution induced by air diffusion and can be employed to better designs of functional microstructured hydrophobic surfaces.

Construction of Fluid - solid Coupling Model with Improved Richards - BP & Its Engineering Application

NASA Astrophysics Data System (ADS)

Xie, Chengyu; Jia, Nan; Shi, Dongping; Lu, Hao

2017-10-01

In order to study the slurry diffusion law during grouting, Richards unsaturated-saturated model was introduced, the definition of the grouting model is clear, the Richards model control equation was established, And the BP neural network was introduced, the improved fluid-solid coupling model was constructed, Through the use of saturated - unsaturated seepage flow model, As well as the overflow boundary iterative solution of the mixed boundary conditions, the free surface is calculated. Engineering practice for an example, with the aid of multi - field coupling analysis software, the diffusion law of slurry was simulated numerically. The results show that the slurry diffusion rule is affected by grouting material, initial pressure and other factors. When the slurry starts, it flows in the cracks along the upper side of the grouting hole, when the pressure gradient is reduced to the critical pressure, that is, to the lower side of the flow, when the slurry diffusion stability, and ultimately its shape like an 8. The slurry is spread evenly from the overall point of view, from the grouting mouth toward the surrounding evenly spread, it gradually reaches saturation by non-saturation, and it is not a purely saturated flow, when the slurry spread and reach a saturated state, the diffusion time is the engineering grouting time.

A Systematic Procedure to Describe Shale Gas Permeability Evolution during the Production Process

NASA Astrophysics Data System (ADS)

Jia, B.; Tsau, J. S.; Barati, R.

2017-12-01

Gas flow behavior in shales is complex due to the multi-physics nature of the process. Pore size reduces as the in-situ stress increases during the production process, which will reduce intrinsic permeability of the porous media. Slip flow/pore diffusion enhances gas apparent permeability, especially under low reservoir pressures. Adsorption not only increases original gas in place but also influences gas flow behavior because of the adsorption layer. Surface diffusion between free gas and adsorption phase enhances gas permeability. Pore size reduction and the adsorption layer both have complex impacts on gas apparent permeability and non-Darcy flow might be a major component in nanopores. Previously published literature is generally incomplete in terms of coupling of all these four physics with fluid flow during gas production. This work proposes a methodology to simultaneously take them into account to describe a permeability evolution process. Our results show that to fully describe shale gas permeability evolution during gas production, three sets of experimental data are needed initially: 1) intrinsic permeability under different in-situ stress, 2) adsorption isotherm under reservoir conditions and 3) surface diffusivity measurement by the pulse-decay method. Geomechanical effects, slip flow/pore diffusion, adsorption layer and surface diffusion all play roles affecting gas permeability. Neglecting any of them might lead to misleading results. The increasing in-situ stress during shale gas production is unfavorable to shale gas flow process. Slip flow/pore diffusion is important for gas permeability under low pressures in the tight porous media. They might overwhelm the geomechanical effect and enhance gas permeability at low pressures. Adsorption layer reduces the gas permeability by reducing the effective pore size, but the effect is limited. Surface diffusion increases gas permeability more under lower pressures. The total gas apparent permeability might keep increasing during the gas production process when the surface diffusivity is larger than a critical value. We believe that our workflow proposed in this study will help describe shale gas permeability evolution considering all the underlying physics altogether.

Numerical simulations of unsteady transonic flow in diffusers

NASA Technical Reports Server (NTRS)

Liou, M.-S.; Coakley, T. J.

1982-01-01

Forced and naturally occurring, self-sustaining oscillations of transonic flows in two-dimensional diffusers were computed using MacCormack's hybrid method. Depending upon the shock strengths and the area ratios, the flow was fully attached or separated by either the shock or the adverse pressure gradient associated with the enlarging diffuser area. In the case of forced oscillations, a sinusoidal plane pressure wave at frequency 300 Hz was prescribed at the exit. A sufficiently large amount of data were acquired and Fourier analyzed. The distrbutions of time-mean pressures, the power spectral density, and the amplitude with phase angle along the top wall and in the core region were determined. Comparison with experimental results for the forced oscillation generally gave very good agreement; some success was achieved for the case of self-sustaining oscillation despite substantial three-dimensionality in the test. An observation of the sequence of self-sustaining oscillations was given.

Epidermis Microstructure Inspired Graphene Pressure Sensor with Random Distributed Spinosum for High Sensitivity and Large Linearity.

PubMed

Pang, Yu; Zhang, Kunning; Yang, Zhen; Jiang, Song; Ju, Zhenyi; Li, Yuxing; Wang, Xuefeng; Wang, Danyang; Jian, Muqiang; Zhang, Yingying; Liang, Renrong; Tian, He; Yang, Yi; Ren, Tian-Ling

2018-03-27

Recently, wearable pressure sensors have attracted tremendous attention because of their potential applications in monitoring physiological signals for human healthcare. Sensitivity and linearity are the two most essential parameters for pressure sensors. Although various designed micro/nanostructure morphologies have been introduced, the trade-off between sensitivity and linearity has not been well balanced. Human skin, which contains force receptors in a reticular layer, has a high sensitivity even for large external stimuli. Herein, inspired by the skin epidermis with high-performance force sensing, we have proposed a special surface morphology with spinosum microstructure of random distribution via the combination of an abrasive paper template and reduced graphene oxide. The sensitivity of the graphene pressure sensor with random distribution spinosum (RDS) microstructure is as high as 25.1 kPa -1 in a wide linearity range of 0-2.6 kPa. Our pressure sensor exhibits superior comprehensive properties compared with previous surface-modified pressure sensors. According to simulation and mechanism analyses, the spinosum microstructure and random distribution contribute to the high sensitivity and large linearity range, respectively. In addition, the pressure sensor shows promising potential in detecting human physiological signals, such as heartbeat, respiration, phonation, and human motions of a pushup, arm bending, and walking. The wearable pressure sensor array was further used to detect gait states of supination, neutral, and pronation. The RDS microstructure provides an alternative strategy to improve the performance of pressure sensors and extend their potential applications in monitoring human activities.

Slowing down of ring polymer diffusion caused by inter-ring threading.

PubMed

Lee, Eunsang; Kim, Soree; Jung, YounJoon

2015-06-01

Diffusion of long ring polymers in a melt is much slower than the reorganization of their internal structures. While direct evidence for entanglements has not been observed in the long ring polymers unlike linear polymer melts, threading between the rings is suspected to be the main reason for slowing down of ring polymer diffusion. It is, however, difficult to define the threading configuration between two rings because the rings have no chain end. In this work, evidence for threading dynamics of ring polymers is presented by using molecular dynamics simulation and applying a novel analysis method. The simulation results are analyzed in terms of the statistics of persistence and exchange times that have proved useful in studying heterogeneous dynamics of glassy systems. It is found that the threading time of ring polymer melts increases more rapidly with the degree of polymerization than that of linear polymer melts. This indicates that threaded ring polymers cannot diffuse until an unthreading event occurs, which results in the slowing down of ring polymer diffusion. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ion transport with charge-protected and non-charge-protected cations using the compensated Arrhenius formalism. Part 2. Relationship between ionic conductivity and diffusion.

PubMed

Petrowsky, Matt; Fleshman, Allison; Bopege, Dharshani N; Frech, Roger

2012-08-09

Temperature-dependent ionic conductivities and cation/anion self-diffusion coefficients are measured for four electrolyte families: TbaTf-linear primary alcohols, LiTf-linear primary alcohols, TbaTf-n-alkyl acetates, and LiTf-n-alkyl acetates. The Nernst-Einstein equation does not adequately describe the data. Instead, the compensated Arrhenius formalism is applied to both conductivity and diffusion data. General trends based on temperature and alkyl chain length are observed when conductivity is plotted against cation or anion diffusion coefficient, but there is no clear pattern to the data. However, plotting conductivity exponential prefactors against those for diffusion results in four distinct curves, one each for the alcohol and acetate families described above. Furthermore, the TbaTf-alcohol and TbaTf-acetate data are "in line" with each other. The conductivity prefactors for the LiTf-alcohol data are smaller than those for the TbaTf data. The LiTf-acetate data have the lowest conductivity prefactors. This trend in prefactors mirrors the observed trend in degree of ionic association for these electrolytes.

Diffusive Public Goods and Coexistence of Cooperators and Cheaters on a 1D Lattice

PubMed Central

Scheuring, István

2014-01-01

Many populations of cells cooperate through the production of extracellular materials. These materials (enzymes, siderophores) spread by diffusion and can be applied by both the cooperator and cheater (non-producer) cells. In this paper the problem of coexistence of cooperator and cheater cells is studied on a 1D lattice where cooperator cells produce a diffusive material which is beneficial to the individuals according to the local concentration of this public good. The reproduction success of a cell increases linearly with the benefit in the first model version and increases non-linearly (saturates) in the second version. Two types of update rules are considered; either the cooperative cell stops producing material before death (death-production-birth, DpB) or it produces the common material before it is selected to die (production-death-birth, pDB). The empty space is occupied by its neighbors according to their replication rates. By using analytical and numerical methods I have shown that coexistence of the cooperator and cheater cells is possible although atypical in the linear version of this 1D model if either DpB or pDB update rule is assumed. While coexistence is impossible in the non-linear model with pDB update rule, it is one of the typical behaviors in case of the non-linear model with DpB update rule. PMID:25025985

Occludin Independently Regulates Permeability under Hydrostatic Pressure and Cell Division in Retinal Pigment Epithelial Cells

PubMed Central

Phillips, Brett E.; Cancel, Limary; Tarbell, John M.; Antonetti, David A.

2008-01-01

Purpose The aim of this study was to determine the function of the tight junction protein occludin in the control of permeability, under diffusive and hydrostatic pressures, and its contribution to the control of cell division in retinal pigment epithelium. Methods Occludin expression was inhibited in the human retinal pigment epithelial cell line ARPE-19 by siRNA. Depletion of occludin was confirmed by Western blot, confocal microscopy, and RT-PCR. Paracellular permeability of cell monolayers to fluorescently labeled 70 kDa dextran, 10 kDa dextran, and 467 Da tetramethylrhodamine (TAMRA) was examined under diffusive conditions or after the application of 10 cm H2O transmural pressure. Cell division rates were determined by tritiated thymidine incorporation and Ki67 immunoreactivity. Cell cycle inhibitors were used to determine whether changes in cell division affected permeability. Results Occludin depletion increased diffusive paracellular permeability to 467 Da TAMRA by 15%, and permeability under hydrostatic pressure was increased 50% compared with control. Conversely, depletion of occludin protein with siRNA did not alter diffusive permeability to 70 kDa and 10 kDa RITC-dextran, and permeability to 70 kDa dextran was twofold lower in occludin-depleted cells under hydrostatic pressure conditions. Occludin depletion also increased thymidine incorporation by 90% and Ki67-positive cells by 50%. Finally, cell cycle inhibitors did not alter the effect of occludin siRNA on paracellular permeability. Conclusions The data suggest that occludin regulates tight junction permeability in response to changes in hydrostatic pressure. Furthermore, these data suggest that occludin also contributes to the control of cell division, demonstrating a novel function for this tight junction protein. PMID:18263810

The entrance of water into beef and dog red cells.

PubMed

VILLEGAS, R; BARTON, T C; SOLOMON, A K

1958-11-20

The rate constants for diffusion of THO across the red cell membrane of beef and dog, and the rate of entrance of water into the erythrocytes of these species under an osmotic pressure gradient have been measured. For water entrance into the erythrocyte by diffusion the rate constants are 0.10 +/- 0.02 msec.(-1) (beef) and 0.14 +/- 0.03 msec.(-1) (dog); the permeability coefficients for water entrance under a pressure gradient of 1 osmol./cm(3) are 0.28 See PDF for Equation These values permit the calculation of an equivalent pore radius for the erythrocyte membrane of 4.1 A for beef and 7.4 A for dog. In the beef red cell the change in THO diffusion due to osmotically produced cell volume shifts has been studied. The resistance to THO diffusion increases as the cell volume increases. At the maximum volume, (1.06 times normal), THO diffusion is decreased to 0.84 times the normal rate. This change in diffusion is attributed to swelling of the cellular membrane.

Diffuser Test

NASA Image and Video Library

2007-09-13

Tests begun at Stennis Space Center's E Complex Sept. 13 evaluated a liquid oxygen lead for engine start performance, part of the A-3 Test Facility Subscale Diffuser Risk Mitigation Project at SSC's E-3 Test Facility. Phase 1 of the subscale diffuser project, completed Sept. 24, was a series of 18 hot-fire tests using a 1,000-pound liquid oxygen and gaseous hydrogen thruster to verify maximum duration and repeatability for steam generation supporting the A-3 Test Stand project. The thruster is a stand-in for NASA's developing J-2X engine, to validate a 6 percent scale version of A-3's exhaust diffuser. Testing the J-2X at altitude conditions requires an enormous diffuser. Engineers will generate nearly 4,600 pounds per second of steam to reduce pressure inside A-3's test cell to simulate altitude conditions. A-3's exhaust diffuser has to be able to withstand regulated pressure, temperatures and the safe discharge of the steam produced during those tests. Before the real thing is built, engineers hope to work out any issues on the miniature version. Phase 2 testing is scheduled to begin this month.

Agent-based computational models to explore diffusion of medical innovations among cardiologists.

PubMed

Borracci, Raul A; Giorgi, Mariano A

2018-04-01

Diffusion of medical innovations among physicians rests on a set of theoretical assumptions, including learning and decision-making under uncertainty, social-normative pressures, medical expert knowledge, competitive concerns, network performance effects, professional autonomy or individualism and scientific evidence. The aim of this study was to develop and test four real data-based, agent-based computational models (ABM) to qualitatively and quantitatively explore the factors associated with diffusion and application of innovations among cardiologists. Four ABM were developed to study diffusion and application of medical innovations among cardiologists, considering physicians' network connections, leaders' opinions, "adopters' categories", physicians' autonomy, scientific evidence, patients' pressure, affordability for the end-user population, and promotion from companies. Simulations demonstrated that social imitation among local cardiologists was sufficient for innovation diffusion, as long as opinion leaders did not act as detractors of the innovation. Even in the absence of full scientific evidence to support innovation, up to one-fifth of cardiologists could accept it when local leaders acted as promoters. Patients' pressure showed a large effect size (Cohen's d > 1.2) on the proportion of cardiologists applying an innovation. Two qualitative patterns (speckled and granular) appeared associated to traditional Gompertz and sigmoid cumulative distributions. These computational models provided a semiquantitative insight on the emergent collective behavior of a physician population facing the acceptance or refusal of medical innovations. Inclusion in the models of factors related to patients' pressure and accesibility to medical coverage revealed the contrast between accepting and effectively adopting a new product or technology for population health care. Copyright © 2018 Elsevier B.V. All rights reserved.

A theoretical study of a laminar diffusion flame

NASA Technical Reports Server (NTRS)

Frair, K. L.

1978-01-01

Theoretical models of an axisymmetric laminar diffusion flame are discussed, with an emphasis on the behavior of such flames at increasing pressures. The flame-sheet or Burke-Schumann model (in terms of Bessel functions) and various boundary layer numerical solutions are presented and their results compared with experimental data. The most promising theoretical model combines the numerical flow field solution of the Patankar-Spalding computer code with the Pratt-Wormeck chemical reaction subroutine. The flame shapes for pressures of 1, 5, 10, 20, and 50 atmospheres were computed and agree remarkably well with experimental data. There is a noticeable shape change with pressure, believed to be a result of buoyancy effects. The chemical concentration profiles do not exhibit much dependence on pressure, a reflection of the fact that only one chemical mechanism was utilized at all pressures.

High-pressure hydrogen sulfide by diffusion quantum Monte Carlo.

PubMed

Azadi, Sam; Kühne, Thomas D

2017-02-28

We revisit the enthalpy-pressure phase diagram of the various products from the different proposed decompositions of H 2 S at pressures above 150 GPa by means of accurate diffusion Monte Carlo simulations. Our results entail a revision of the ground-state enthalpy-pressure phase diagram. Specifically, we find that the C2/c HS 2 structure is persistent up to 440 GPa before undergoing a phase transition into the C2/m phase. Contrary to density functional theory, our calculations suggest that the C2/m phase of HS is more stable than the I4 1 /amd HS structure over the whole pressure range from 150 to 400 GPa. More importantly, we predict that the Im-3m phase is the most likely candidate for H 3 S, which is consistent with recent experimental x-ray diffraction measurements.

Study of compressible flow through a rectangular-to-semiannular transition duct

NASA Technical Reports Server (NTRS)

Foster, Jeffry; Okiishi, Theodore H.; Wendt, Bruce J.; Reichert, Bruce A.

1995-01-01

Detailed flow field measurements are presented for compressible flow through a diffusing rectangular-to-semiannular transition duct. Comparisons are made with published computational results for flow through the duct. Three-dimensional velocity vectors and total pressures were measured at the exit plane of the diffuser model. The inlet flow was also measured. These measurements are made using calibrated five-hole probes. Surface oil flow visualization and surface static pressure data were also taken. The study was conducted with an inlet Mach number of 0.786. The diffuser Reynolds based on the inlet centerline velocity and the exit diameter of the diffuser was 3,200,000. Comparison of the measured data with previously published computational results are made. Data demonstrating the ability of vortex generators to reduce flow separation and circumferential distortion is also presented.

The Dynamics of Controlled Flow Separation within a Diverter Duct Diffuser

NASA Astrophysics Data System (ADS)

Peterson, C. J.; Vukasinovic, B.; Glezer, A.

2016-11-01

The evolution and receptivity to fluidic actuation of the flow separation within a rectangular, constant-width, diffuser that is branched off of a primary channel is investigated experimentally at speeds up to M = 0.4. The coupling between the diffuser's adverse pressure gradient and the internal separation that constricts nearly half of the flow passage through the duct is controlled using a spanwise array of fluidic actuators on the surface upstream of the diffuser's inlet plane. The dynamics of the separating surface vorticity layer in the absence and presence of actuation are investigated using high-speed particle image velocimetry combined with surface pressure measurements and total pressure distributions at the primary channel's exit plane. It is shown that the actuation significantly alters the incipient dynamics of the separating vorticity layer as the characteristic cross stream scales of the boundary layer upstream of separation and of the ensuing vorticity concentrations within the separated flow increase progressively with actuation level. It is argued that the dissipative (high frequency) actuation alters the balance between large- and small-scale motions near separation by intensifying the large-scale motions and limiting the small-scale dynamics. Controlling separation within the diffuser duct also has a profound effect on the global flow. In the presence of actuation, the mass flow rate in the primary duct increases 10% while the fraction of the diverted mass flow rate in the diffuser increases by more than 45% at 0.7% actuation mass fraction. Supported by the Boeing Company.

Nonlinear ELM simulations based on a nonideal peeling–ballooning model using the BOUT++ code

DOE PAGES

Xu, X. Q.; Dudson, B. D.; Snyder, P. B.; ...

2011-09-23

A minimum set of equations based on the peeling–ballooning (P–B) model with nonideal physics effects (diamagnetic drift, E × B drift, resistivity and anomalous electron viscosity) is found to simulate pedestal collapse when using the BOUT++ simulation code, developed in part from the original fluid edge code BOUT. Linear simulations of P–B modes find good agreement in growth rate and mode structure with ELITE calculations. The influence of the E × B drift, diamagnetic drift, resistivity, anomalous electron viscosity, ion viscosity and parallel thermal diffusivity on P–B modes is being studied; we find that (1) the diamagnetic drift and Emore » × B drift stabilize the P–B mode in a manner consistent with theoretical expectations; (2) resistivity destabilizes the P–B mode, leading to resistive P–B mode; (3) anomalous electron and parallel ion viscosities destabilize the P–B mode, leading to a viscous P–B mode; (4) perpendicular ion viscosity and parallel thermal diffusivity stabilize the P–B mode. With addition of the anomalous electron viscosity under the assumption that the anomalous kinematic electron viscosity is comparable to the anomalous electron perpendicular thermal diffusivity, or the Prandtl number is close to unity, it is found from nonlinear simulations using a realistic high Lundquist number that the pedestal collapse is limited to the edge region and the ELM size is about 5–10% of the pedestal stored energy. Furthermore, this is consistent with many observations of large ELMs. The estimated island size is consistent with the size of fast pedestal pressure collapse. In the stable α-zones of ideal P–B modes, nonlinear simulations of viscous ballooning modes or current-diffusive ballooning mode (CDBM) for ITER H-mode scenarios are presented.« less

The curved kinetic boundary layer of active matter.

PubMed

Yan, Wen; Brady, John F

2018-01-03

A body submerged in active matter feels the swim pressure through a kinetic accumulation boundary layer on its surface. The boundary layer results from a balance between translational diffusion and advective swimming and occurs on the microscopic length scale . Here , D T is the Brownian translational diffusivity, τ R is the reorientation time and l = U 0 τ R is the swimmer's run length, with U 0 the swim speed [Yan and Brady, J. Fluid. Mech., 2015, 785, R1]. In this work we analyze the swim pressure on arbitrary shaped bodies by including the effect of local shape curvature in the kinetic boundary layer. When δ ≪ L and l ≪ L, where L is the body size, the leading order effects of curvature on the swim pressure are found analytically to scale as J S λδ 2 /L, where J S is twice the (non-dimensional) mean curvature. Particle-tracking simulations and direct solutions to the Smoluchowski equation governing the probability distribution of the active particles show that λδ 2 /L is a universal scaling parameter not limited to the regime δ, l ≪ L. The net force exerted on the body by the swimmers is found to scale as F net /(n ∞ k s T s L 2 ) = f(λδ 2 /L), where f(x) is a dimensionless function that is quadratic when x ≪ 1 and linear when x ∼ 1. Here, k s T s = ζU 0 2 τ R /6 defines the 'activity' of the swimmers, with ζ the drag coefficient, and n ∞ is the uniform number density of swimmers far from the body. We discuss the connection of this boundary layer to continuum mechanical descriptions of active matter and briefly present how to include hydrodynamics into this purely kinetic study.

Fluid Induced Earthquakes: From KTB Experiments to Natural Seismicity Swarms.

NASA Astrophysics Data System (ADS)

Shapiro, S. A.

2006-12-01

Experiments with borehole fluid injections are typical for exploration and development of hydrocarbon or geothermal reservoirs (e.g., fluid-injection experiments at Soultz, France and at Fenton-Hill, USA). Microseismicity occurring during such operations has a large potential for understanding physics of the seismogenic process as well as for obtaining detailed information about reservoirs at locations as far as several kilometers from boreholes. The phenomenon of microseismicity triggering by borehole fluid injections is related to the process of the Frenkel-Biot slow wave propagation. In the low-frequency range (hours or days of fluid injection duration) this process reduces to the pore pressure diffusion. Fluid induced seismicity typically shows several diffusion indicating features, which are directly related to the rate of spatial grow, to the geometry of clouds of micro earthquake hypocentres and to their spatial density. Several fluid injection experiments were conducted at the German Continental Deep Drilling Site (KTB) in 1994, 2000 and 2003-2005. Microseismicity occurred at different depth intervals. We analyze this microseismicity in terms of its diffusion-related features. Its relation to the 3-D distribution of the seismic reflectivity has important rock physical and tectonic implications. Starting from such diffusion-typical signatures of man-made earthquakes, we seek analogous patterns for the earthquakes in Vogtland/Bohemia at the German/Czech border region in central Europe. There is strong geophysical evidence that there seismic events are correlated to fluid-related processes in the crust. We test the hypothesis that ascending magmatic fluids trigger earthquakes by the mechanism of pore pressure diffusion. This triggering process is mainly controlled by two physical fields, the hydraulic diffusivity and the seismic criticality (i.e., critical pore pressure value leading to failure; stable locations are characterized by higher critical pressures), both heterogeneously distributed in rocks. The results of the analysis of the most significant and best studied (year 2000) earthquake swarm support this concept. Using a numerical model, where spatially correlated diffusivity and criticalit y patches (where patches with higher diffusivity are assumed to be less stable) are considered, we successfully simulate a general seismicity pattern of the swarms, including the spatio-temporal clustering of events and the migration of seismic activity. Therefore, in some cases spontaneously triggered natural seismicity, like earthquake swarms, also shows diffusion-typical signatures mentioned above. However, it seems that there are also some principle differences. They are emphasized in this presentation.

Non-equilibrium dynamics in disordered materials: Ab initio molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Ohmura, Satoshi; Nagaya, Kiyonobu; Shimojo, Fuyuki; Yao, Makoto

2015-08-01

The dynamic properties of liquid B2O3 under pressure and highly-charged bromophenol molecule are studied by using molecular dynamics (MD) simulations based on density functional theory (DFT). Diffusion properties of covalent liquids under high pressure are very interesting in the sense that they show unexpected pressure dependence. It is found from our simulation that the magnitude relation of diffusion coefficients for boron and oxygen in liquid B2O3 shows the anomalous pressure dependence. The simulation clarified the microscopic origin of the anomalous diffusion properties. Our simulation also reveals the dissociation mechanism in the coulomb explosion of the highly-charged bromophenol molecule. When the charge state n is 6, hydrogen atom in the hydroxyl group dissociates at times shorter than 20 fs while all hydrogen atoms dissociate when n is 8. After the hydrogen dissociation, the carbon ring breaks at about 100 fs. There is also a difference on the mechanism of the ring breaking depending on charge states, in which the ring breaks with expanding (n = 6) or shrink (n = 8).

Numerical investigation of biogas diffusion flames characteristics under several operation conditions in counter-flow configuration with an emphasis on thermal and chemical effects of CO2 in the fuel mixture

NASA Astrophysics Data System (ADS)

Mameri, A.; Tabet, F.; Hadef, A.

2017-08-01

This study addresses the influence of several operating conditions (composition and ambient pressure) on biogas diffusion flame structure and NO emissions with particular attention on thermal and chemical effect of CO2. The biogas flame is modeled by a counter flow diffusion flame and analyzed in mixture fraction space using flamelet approach. The GRI Mech-3.0 mechanism that involves 53 species and 325 reactions is adopted for the oxidation chemistry. It has been observed that flame properties are very sensitive to biogas composition and pressure. CO2 addition decreases flame temperature by both thermal and chemical effects. Added CO2 may participate in chemical reaction due to thermal dissociation (chemical effect). Excessively supplied CO2 plays the role of pure diluent (thermal effect). The ambient pressure rise increases temperature and reduces flame thickness, radiation losses and dissociation amount. At high pressure, recombination reactions coupled with chain carrier radicals reduction, diminishes NO mass fraction.

Diffusion coalescence in НоBa2Cu3O7-x single crystals under the application of hydrostatic pressure

NASA Astrophysics Data System (ADS)

Boiko, Y. I.; Bogdanov, V. V.; Vovk, R. V.; Khadzhaj, G. Ya; Kamchatnaya, S. N.; Goulatis, I. L.; Chroneos, A.

2017-09-01

Experimental results on the effect of external hydrostatic pressure up to 5 kbar on the ρ(T) dependence in the ab plane of HoBa2Cu3O7-x single crystals (x  ≈  0.35) in the temperature range from 300 K to the superconducting transition temperature T c are presented and discussed. It was established that the application of external hydrostatic pressure P  =  5 kbar significantly intensified the process of diffusion coalescence of oxygen clusters, causing the growth of their average size. This leads to an increase in the number of negative U-centers, the presence of which results to the appearance of a phase capable of generating paired carriers of electric charge and, correspondingly, characterized by a higher transition temperature T c. Employing this hypothesis that concerns the mechanism of the diffusion coalescence of oxygen clusters, the change in the form of the temperature and time dependences of the electrical resistivity under the application of external hydrostatic pressure is discussed.

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

Ohmura, Satoshi; Nagaya, Kiyonobu; Yao, Makoto

The dynamic properties of liquid B{sub 2}O{sub 3} under pressure and highly-charged bromophenol molecule are studied by using molecular dynamics (MD) simulations based on density functional theory (DFT). Diffusion properties of covalent liquids under high pressure are very interesting in the sense that they show unexpected pressure dependence. It is found from our simulation that the magnitude relation of diffusion coefficients for boron and oxygen in liquid B{sub 2}O{sub 3} shows the anomalous pressure dependence. The simulation clarified the microscopic origin of the anomalous diffusion properties. Our simulation also reveals the dissociation mechanism in the coulomb explosion of the highly-chargedmore » bromophenol molecule. When the charge state n is 6, hydrogen atom in the hydroxyl group dissociates at times shorter than 20 fs while all hydrogen atoms dissociate when n is 8. After the hydrogen dissociation, the carbon ring breaks at about 100 fs. There is also a difference on the mechanism of the ring breaking depending on charge states, in which the ring breaks with expanding (n = 6) or shrink (n = 8)« less

A study on ?-dissipative synchronisation of coupled reaction-diffusion neural networks with time-varying delays

NASA Astrophysics Data System (ADS)

Ali, M. Syed; Zhu, Quanxin; Pavithra, S.; Gunasekaran, N.

2018-03-01

This study examines the problem of dissipative synchronisation of coupled reaction-diffusion neural networks with time-varying delays. This paper proposes a complex dynamical network consisting of N linearly and diffusively coupled identical reaction-diffusion neural networks. By constructing a suitable Lyapunov-Krasovskii functional (LKF), utilisation of Jensen's inequality and reciprocally convex combination (RCC) approach, strictly ?-dissipative conditions of the addressed systems are derived. Finally, a numerical example is given to show the effectiveness of the theoretical results.

Moist, Double-diffusive convection

NASA Astrophysics Data System (ADS)

Oishi, Jeffrey; Burns, Keaton; Brown, Ben; Lecoanet, Daniel; Vasil, Geoffrey

2017-11-01

Double-diffusive convection occurs when the competition between stabilizing and a destabilizing buoyancy source is mediated by a difference in the diffusivity of each source. Such convection is important in a wide variety of astrophysical and geophysical flows. However, in giant planets, double-diffusive convection occurs in regions where condensation of important components of the atmosphere occurs. Here, we present preliminary calculations of moist, double-diffusive convection using the Dedalus pseudospectral framework. Using a simple model for phase change, we verify growth rates for moist double diffusive convection from linear calculations and report on preliminary relationships between the ability to form liquid phase and the resulting Nusselt number in nonlinear simulations.

A prospective microstructure imaging study in mixed-martial artists using geometric measures and diffusion tensor imaging: methods and findings

PubMed Central

Mayer, Andrew R.; Ling, Josef M.; Dodd, Andrew B.; Meier, Timothy B.; Hanlon, Faith M.; Klimaj, Stefan D.

2018-01-01

Although diffusion magnetic resonance imaging (dMRI) has been widely used to characterize the effects of repetitive mild traumatic brain injury (rmTBI), to date no studies have investigated how novel geometric models of microstructure relate to more typical diffusion tensor imaging (DTI) sequences. Moreover, few studies have evaluated the sensitivity of different registration pipelines (non-linear, linear and tract-based spatial statistics) for detecting dMRI abnormalities in clinical populations. Results from single-subject analyses in healthy controls (HC) indicated a strong negative relationship between fractional anisotropy (FA) and orientation dispersion index (ODI) in both white and gray matter. Equally important, only moderate relationships existed between all other estimates of free/intracellular water volume fractions and more traditional DTI metrics (FA, mean, axial and radial diffusivity). These findings suggest that geometric measures provide differential information about the cellular microstructure relative to traditional DTI measures. Results also suggest greater sensitivity for non-linear registration pipelines that maximize the anatomical information available in T1-weighted images. Clinically, rmTBI resulted in a pattern of decreased FA and increased ODI, largely overlapping in space, in conjunction with increased intracellular and free water fractions, highlighting the potential role of edema following repeated head trauma. In summary, current results suggest that geometric models of diffusion can provide relatively unique information regarding potential mechanisms of pathology that contribute to long-term neurological damage. PMID:27071950

A prospective microstructure imaging study in mixed-martial artists using geometric measures and diffusion tensor imaging: methods and findings.

PubMed

Mayer, Andrew R; Ling, Josef M; Dodd, Andrew B; Meier, Timothy B; Hanlon, Faith M; Klimaj, Stefan D

2017-06-01

Although diffusion magnetic resonance imaging (dMRI) has been widely used to characterize the effects of repetitive mild traumatic brain injury (rmTBI), to date no studies have investigated how novel geometric models of microstructure relate to more typical diffusion tensor imaging (DTI) sequences. Moreover, few studies have evaluated the sensitivity of different registration pipelines (non-linear, linear and tract-based spatial statistics) for detecting dMRI abnormalities in clinical populations. Results from single-subject analyses in healthy controls (HC) indicated a strong negative relationship between fractional anisotropy (FA) and orientation dispersion index (ODI) in both white and gray matter. Equally important, only moderate relationships existed between all other estimates of free/intracellular water volume fractions and more traditional DTI metrics (FA, mean, axial and radial diffusivity). These findings suggest that geometric measures provide differential information about the cellular microstructure relative to traditional DTI measures. Results also suggest greater sensitivity for non-linear registration pipelines that maximize the anatomical information available in T 1 -weighted images. Clinically, rmTBI resulted in a pattern of decreased FA and increased ODI, largely overlapping in space, in conjunction with increased intracellular and free water fractions, highlighting the potential role of edema following repeated head trauma. In summary, current results suggest that geometric models of diffusion can provide relatively unique information regarding potential mechanisms of pathology that contribute to long-term neurological damage.

Hydro-mechanical pressure response to fluid injection into finite aquifers highlights the non-local behavior of storage

NASA Astrophysics Data System (ADS)

De Simone, Silvia; Carrera, Jesus

2017-04-01

Specific storage reflects the volumetric deformation capacity of permeable media. Classical groundwater hydrology equals elastic storage to medium compressibility, which is a constant-in-time and locally-defined parameter. This allows simplifying the flow equation into a linear diffusion equation that is relatively easy to solve. However, the hydraulic gradients, generated by fluid injection or pumping, act as forces that push the medium in the direction of flow causing it to deform, even in regions where pressure has not changed. Actual deformation depends on the elastic properties of the medium, but also on aquifer geometry and on surrounding strata, which act like constraints to displacements. Therefore the storage results to be non-local (i.e., the volume of water released at a point depends on the poroelastic response over the whole aquifer) and the proper evaluation of transient pressure requires acknowledging the hydro-mechanical (HM) coupling, which is generally disregarded by conventional hydrogeology. Here we discuss whether HM coupling effects are relevant, which is of special interest for the activities of enhanced geothermics, waste disposal, CO2 storage or shale gas extraction. We propose analytic solutions to the HM problem of fluid injection (or extraction) into finite aquifers with one-dimensional or cylindrical geometries. We find that the deviation respect to traditional purely hydraulic solutions is significant when the aquifer has limited capacity to deform. The most relevant implications are that the response time is faster and the pressure variation greater than expected, which may be relevant for aquifer characterization and for the evaluation of pressure build-up due to fluid injection.

Effective diffusion coefficients of gas mixture in heavy oil under constant-pressure conditions

NASA Astrophysics Data System (ADS)

Li, Huazhou Andy; Sun, Huijuan; Yang, Daoyong

2017-05-01

We develop a method to determine the effective diffusion coefficient for each individual component of a gas mixture in a non-volatile liquid (e.g., heavy oil) at high pressures with compositional analysis. Theoretically, a multi-component one-way diffusion model is coupled with the volume-translated Peng-Robinson equation of state to quantify the mass transfer between gas and liquid (e.g., heavy oil). Experimentally, the diffusion tests have been conducted with a PVT setup for one pure CO2-heavy oil system and one C3H8-CO2-heavy oil system under constant temperature and pressure, respectively. Both the gas-phase volume and liquid-phase swelling effect are simultaneously recorded during the measurement. As for the C3H8-CO2-heavy oil system, the gas chromatography method is employed to measure compositions of the gas phase at the beginning and end of the diffusion measurement, respectively. The effective diffusion coefficients are then determined by minimizing the discrepancy between the measured and calculated gas-phase composition at the end of diffusion measurement. The newly developed technique can quantify the contributions of each component of mixture to the bulk mass transfer from gas into liquid. The effective diffusion coefficient of C3H8 in the C3H8-CO2 mixture at 3945 ± 20 kPa and 293.85 K, i.e., 18.19 × 10^{ - 10} {{m}}^{ 2} / {{s}}, is found to be much higher than CO2 at 3950 ± 18 kPa and 293.85 K, i.e., 8.68 × 10^{ - 10} {{m}}^{ 2} / {{s}}. In comparison with pure CO2, the presence of C3H8 in the C3H8-CO2 mixture contributes to a faster diffusion of CO2 from the gas phase into heavy oil and consequently a larger swelling factor of heavy oil.

Strain effect on the adsorption, diffusion, and molecular dissociation of hydrogen on Mg (0001) surface

NASA Astrophysics Data System (ADS)

Lei, Huaping; Wang, Caizhuang; Yao, Yongxin; Wang, Yangang; Hupalo, Myron; McDougall, Dan; Tringides, Michael; Ho, Kaiming

2013-12-01

The adsorption, diffusion, and molecular dissociation of hydrogen on the biaxially strained Mg (0001) surface have been systematically investigated by the first principle calculations based on density functional theory. When the strain changes from the compressive to tensile state, the adsorption energy of H atom linearly increases while its diffusion barrier linearly decreases oppositely. The dissociation barrier of H2 molecule linearly reduces in the tensile strain region. Through the chemical bonding analysis including the charge density difference, the projected density of states and the Mulliken population, the mechanism of the strain effect on the adsorption of H atom and the dissociation of H2 molecule has been elucidated by an s-p charge transfer model. With the reduction of the orbital overlap between the surface Mg atoms upon the lattice expansion, the charge transfers from p to s states of Mg atoms, which enhances the hybridization of H s and Mg s orbitals. Therefore, the bonding interaction of H with Mg surface is strengthened and then the atomic diffusion and molecular dissociation barriers of hydrogen decrease accordingly. Our works will be helpful to understand and to estimate the influence of the lattice deformation on the performance of Mg-containing hydrogen storage materials.

Performance of high-area-ratio annular dump diffuser using suction-stabilized-vortex flow control

NASA Technical Reports Server (NTRS)

Juhasz, A. J.; Smith, J. M.

1977-01-01

A short annular dump diffuser having a geometry conductive to formation of suction stabilized toroidal vortices in the region of abrupt area change was tested. The overall diffuser area ratio was 4.0 and the length to inlet height ratio was 2.0. Performance data were obtained at near ambient temperature and pressure for inlet Mach numbers of 0.18 and 0.30 with suction rates ranging from 0 to 18 percent of total inlet mass flowrate. Results show that the exit velocity profile could be readily biased toward either wall by adjustment of inner and outer wall suction rates. Symmetric exit velocity profiles were inherently unstable with a tendency to revert to a hub or tip bias. Diffuser effectiveness was increased from about 38 percent without suction to over 85 percent at a total suction rate of 10 to 12 percent. At the same time diffuser total pressure loss was reduced from 3.1 percent to 1.1 percent at an inlet Mach number of 0.3.

Mixing of a passive scalar in isotropic and sheared homogeneous turbulence

NASA Technical Reports Server (NTRS)

Shirani, E.; Ferziger, J. H.; Reynolds, W. C.

1981-01-01

In order to calculate the velocity and scalar fields, the three dimensional, time-dependent equations of motion and the diffusion equation were solved numerically. The following cases were treated: isotropic, homogeneous turbulence with decay of a passive scalar; and homogeneous turbulent shear flow with a passive scalar whose mean varies linearly in the spanwise direction. The solutions were obtained at relatively low Reynolds numbers so that all of the turbulent scales could be resolved without modeling. Turbulent statistics such as integral length scales, Taylor microscales, Kolmogorov length scale, one- and two-point correlations of velocity-velocity and velocity-scalar, turbulent Prandtl/Schmidt number, r.m.s. values of velocities, the scalar quantity and pressure, skewness, decay rates, and decay exponents were calculated. The results are compared with the available expermental results, and good agreement is obtained.