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Sample records for gas diffusion media

  1. a Diffusivity Model for Gas Diffusion in Dry Porous Media Composed of Converging-Diverging Capillaries

    NASA Astrophysics Data System (ADS)

    Wang, Shifang; Wu, Tao; Deng, Yongju; Zheng, Qiusha; Zheng, Qian

    2016-08-01

    Gas diffusion in dry porous media has been a hot topic in several areas of technology for many years. In this paper, a diffusivity model for gas diffusion in dry porous media is developed based on fractal theory and Fick’s law, which incorporates the effects of converging-diverging pores and tortuous characteristics of capillaries as well as Knudsen diffusion. The effective gas diffusivity model is expressed as a function of the fluctuation amplitude of the capillary cross-section size variations, the porosity, the pore area fractal dimension and the tortuosity fractal dimension. The results show that the relative diffusivity decreases with the increase of the fluctuation amplitude and increases with the increase of pore area fractal dimension. To verify the validity of the present model, the relative diffusivity from the proposed fractal model is compared with the existing experimental data as well as two available models of Bruggeman and Shou. Our proposed diffusivity model with pore converging-diverging effect included is in good agreement with reported experimental data.

  2. Unifying diffusion and seepage for nonlinear gas transport in multiscale porous media

    NASA Astrophysics Data System (ADS)

    Song, Hongqing; Wang, Yuhe; Wang, Jiulong; Li, Zhengyi

    2016-09-01

    We unify the diffusion and seepage process for nonlinear gas transport in multiscale porous media via a proposed new general transport equation. A coherent theoretical derivation indicates the wall-molecule and molecule-molecule collisions drive the Knudsen and collective diffusive fluxes, and constitute the system pressure across the porous media. A new terminology, nominal diffusion coefficient can summarize Knudsen and collective diffusion coefficients. Physical and numerical experiments show the support of the new formulation and provide approaches to obtain the diffusion coefficient and permeability simultaneously. This work has important implication for natural gas extraction and greenhouse gases sequestration in geological formations.

  3. Gas and solute diffusion in partially saturated porous media: Percolation theory and Effective Medium Approximation compared with lattice Boltzmann simulations

    NASA Astrophysics Data System (ADS)

    Ghanbarian, Behzad; Daigle, Hugh; Hunt, Allen G.; Ewing, Robert P.; Sahimi, Muhammad

    2015-01-01

    Understanding and accurate prediction of gas or liquid phase (solute) diffusion are essential to accurate prediction of contaminant transport in partially saturated porous media. In this study, we propose analytical equations, using concepts from percolation theory and the Effective Medium Approximation (EMA) to model the saturation dependence of both gas and solute diffusion in porous media. The predictions of our theoretical approach agree well with the results of nine lattice Boltzmann simulations. We find that the universal quadratic scaling predicted by percolation theory, combined with the universal linear scaling predicted by the EMA, describes diffusion in porous media with both relatively broad and extremely narrow pore size distributions.

  4. Dynamic characterization of partially saturated engineered porous media and gas diffusion layers using hydraulic admittance

    NASA Astrophysics Data System (ADS)

    Cheung, Perry; Fairweather, Joseph D.; Schwartz, Daniel T.

    2012-09-01

    Simple laboratory methods for determining liquid water distribution in polymer electrolyte membrane fuel cell gas diffusion layers (GDLs) are needed to engineer better GDL materials. Capillary pressure vs. liquid saturation measurements are attractive, but lack the ability to probe the hydraulic interconnectivity and distribution within the pore structure. Hydraulic admittance measurements of simple capillary bundles have recently been shown to nicely measure characteristics of the free-interfaces and hydraulic path. Here we examine the use of hydraulic admittance with a succession of increasingly complex porous media, starting with a laser-drilled sample with 154 asymmetric pores and progress to the behavior of Toray TGP-H090 carbon papers. The asymmetric laser-drilled sample clearly shows hydraulic admittance measurements are sensitive to sample orientation, especially when examined as a function of saturation state. Finite element modeling of the hydraulic admittance is consistent with experimental measurements. The hydraulic admittance spectra from GDL samples are complex, so we examine trends in the spectra as a function of wet proofing (0% and 40% Teflon loadings) as well as saturation state of the GDL. The presence of clear peaks in the admittance spectra for both GDL samples suggests a few pore types are largely responsible for transporting liquid water.

  5. Review of enhanced vapor diffusion in porous media

    SciTech Connect

    Webb, S.W.; Ho, C.K.

    1998-08-01

    Vapor diffusion in porous media in the presence of its own liquid has often been treated similar to gas diffusion. The gas diffusion rate in porous media is much lower than in free space due to the presence of the porous medium and any liquid present. However, enhanced vapor diffusion has also been postulated such that the diffusion rate may approach free-space values. Existing data and models for enhanced vapor diffusion, including those in TOUGH2, are reviewed in this paper.

  6. Gas fluidized-bed stirred media mill

    DOEpatents

    Sadler, III, Leon Y.

    1997-01-01

    A gas fluidized-bed stirred media mill is provided for comminuting solid ticles. The mill includes a housing enclosing a porous fluidizing gas diffuser plate, a baffled rotor and stator, a hollow drive shaft with lateral vents, and baffled gas exhaust exit ports. In operation, fluidizing gas is forced through the mill, fluidizing the raw material and milling media. The rotating rotor, stator and milling media comminute the raw material to be ground. Small entrained particles may be carried from the mill by the gas through the exit ports when the particles reach a very fine size.

  7. Marmot-Fission-Gas-Diffusion

    SciTech Connect

    Andersson, Anders; Matthews, Christopher

    2016-10-22

    The MARMOT-FISSION-GAS-DIFFUSION software solves a coupled set of partial differential equations describing fission gas evolution in UO2 nuclear fuel. It is part of the MARMOT code, which builds on the MOOSE framework. Both the MARMOT code and the MOOSE framework are developed and maintained by Idaho National Laboratory. The model in MARMOT-FISSION-GAS-DIFFUSION consists of a set of continuum reaction-diffusion equations capturing formation and annihilation of defects, reactions between defects, diffusion of defects and segregation of defects to grain boundaries. Defects refer to vacancies and interstitials as well fission gas atoms (Xe) occupying various trap sites such as uranium and oxygen vacancies and interstitials sites. The code can treat a large number of defect types. The model is formulated within the phase field framework to be compatible with other MARMOT kernels. The driving forces for all reactions, diffusion and segregation events are consistently formulated as a variational derivatives of the free energy of the system. The rates of the reactions are controlled by the corresponding kinetic coefficients. The free energy and the kinetic coefficients for UO2 have been parameterized by lower length scale simulations. The code can be used to simulate defect evolution in a prescribed UO2 microstructure as well as to solve defect clustering problems that control effective diffusivities under both thermal and irradiation conditions. It I possible to extend the current UO2 model to other fuel types such as accident tolerant fuels based on the U3Si2 compound. This would obviously require a new set of material properties describing the behavior of defects in U3Si2 rather than UO2. The framework is however designed to be generic.

  8. Ternary gas mixture for diffuse discharge switch

    DOEpatents

    Christophorou, Loucas G.; Hunter, Scott R.

    1988-01-01

    A new diffuse discharge gas switch wherein a mixture of gases is used to take advantage of desirable properties of the respective gases. There is a conducting gas, an insulating gas, and a third gas that has low ionization energy resulting in a net increase in the number of electrons available to produce a current.

  9. Water Transport Characteristics of Gas Diffusion Layer in a PEM Fuel Cell

    SciTech Connect

    Damle, Ashok S; Cole, J Vernon

    2008-12-01

    A presentation addressing the following: Water transport in PEM Fuel Cells - a DoE Project 1. Gas Diffusion Layer--Role and Characteristics 2. Capillary Pressure Determinations of GDL Media 3. Gas Permeability Measurements of GDL Media 4. Conclusions and Future Activities

  10. Pathlength Determination for Gas in Scattering Media Absorption Spectroscopy

    PubMed Central

    Mei, Liang; Somesfalean, Gabriel; Svanberg, Sune

    2014-01-01

    Gas in scattering media absorption spectroscopy (GASMAS) has been extensively studied and applied during recent years in, e.g., food packaging, human sinus monitoring, gas diffusion studies, and pharmaceutical tablet characterization. The focus has been on the evaluation of the gas absorption pathlength in porous media, which a priori is unknown due to heavy light scattering. In this paper, three different approaches are summarized. One possibility is to simultaneously monitor another gas with known concentration (e.g., water vapor), the pathlength of which can then be obtained and used for the target gas (e.g., oxygen) to retrieve its concentration. The second approach is to measure the mean optical pathlength or physical pathlength with other methods, including time-of-flight spectroscopy, frequency-modulated light scattering interferometry and the frequency domain photon migration method. By utilizing these methods, an average concentration can be obtained and the porosities of the material are studied. The last method retrieves the gas concentration without knowing its pathlength by analyzing the gas absorption line shape, which depends upon the concentration of buffer gases due to intermolecular collisions. The pathlength enhancement effect due to multiple scattering enables also the use of porous media as multipass gas cells for trace gas monitoring. All these efforts open up a multitude of different applications for the GASMAS technique. PMID:24573311

  11. Simulation of gaseous diffusion in partially saturated porous media under variable gravity with lattice Boltzmann methods

    NASA Technical Reports Server (NTRS)

    Chau, Jessica Furrer; Or, Dani; Sukop, Michael C.; Steinberg, S. L. (Principal Investigator)

    2005-01-01

    Liquid distributions in unsaturated porous media under different gravitational accelerations and corresponding macroscopic gaseous diffusion coefficients were investigated to enhance understanding of plant growth conditions in microgravity. We used a single-component, multiphase lattice Boltzmann code to simulate liquid configurations in two-dimensional porous media at varying water contents for different gravity conditions and measured gas diffusion through the media using a multicomponent lattice Boltzmann code. The relative diffusion coefficients (D rel) for simulations with and without gravity as functions of air-filled porosity were in good agreement with measured data and established models. We found significant differences in liquid configuration in porous media, leading to reductions in D rel of up to 25% under zero gravity. The study highlights potential applications of the lattice Boltzmann method for rapid and cost-effective evaluation of alternative plant growth media designs under variable gravity.

  12. Simulation of gaseous diffusion in partially saturated porous media under variable gravity with lattice Boltzmann methods

    NASA Astrophysics Data System (ADS)

    Chau, Jessica Furrer; Or, Dani; Sukop, Michael C.

    2005-08-01

    Liquid distributions in unsaturated porous media under different gravitational accelerations and corresponding macroscopic gaseous diffusion coefficients were investigated to enhance understanding of plant growth conditions in microgravity. We used a single-component, multiphase lattice Boltzmann code to simulate liquid configurations in two-dimensional porous media at varying water contents for different gravity conditions and measured gas diffusion through the media using a multicomponent lattice Boltzmann code. The relative diffusion coefficients (Drel) for simulations with and without gravity as functions of air-filled porosity were in good agreement with measured data and established models. We found significant differences in liquid configuration in porous media, leading to reductions in Drel of up to 25% under zero gravity. The study highlights potential applications of the lattice Boltzmann method for rapid and cost-effective evaluation of alternative plant growth media designs under variable gravity.

  13. Purging of multilayer insulation by gas diffusion

    NASA Technical Reports Server (NTRS)

    Sumner, I. E.; Spuckler, C. M.

    1976-01-01

    An experimental investigation was conducted to determine the time required to purge a multilayer insulation (MLI) panel with gaseous helium by means of gas diffusion to obtain a condensable (nitrogen) gas concentration of less than 1 percent within the panel. Two flat, rectangular MLI panel configurations, one incorporating a butt joint, were tested. The insulation panels consisted of 15 double-aluminized Mylar radiation shields separated by double silk net spacers. The test results indicated that the rate which the condensable gas concentration at the edge or at the butt joint of an MLI panel was reduced was a significant factor in the total time required to reduce the condensable gas concentration within the panel to less than 1 percent. The experimental data agreed well with analytical predictions made by using a simple, one-dimensional gas diffusion model in which the boundary conditions at the edge of the MLI panel were time dependent.

  14. Diffusion NMR methods applied to xenon gas for materials study

    NASA Technical Reports Server (NTRS)

    Mair, R. W.; Rosen, M. S.; Wang, R.; Cory, D. G.; Walsworth, R. L.

    2002-01-01

    We report initial NMR studies of (i) xenon gas diffusion in model heterogeneous porous media and (ii) continuous flow laser-polarized xenon gas. Both areas utilize the pulsed gradient spin-echo (PGSE) techniques in the gas phase, with the aim of obtaining more sophisticated information than just translational self-diffusion coefficients--a brief overview of this area is provided in the Introduction. The heterogeneous or multiple-length scale model porous media consisted of random packs of mixed glass beads of two different sizes. We focus on observing the approach of the time-dependent gas diffusion coefficient, D(t) (an indicator of mean squared displacement), to the long-time asymptote, with the aim of understanding the long-length scale structural information that may be derived from a heterogeneous porous system. We find that D(t) of imbibed xenon gas at short diffusion times is similar for the mixed bead pack and a pack of the smaller sized beads alone, hence reflecting the pore surface area to volume ratio of the smaller bead sample. The approach of D(t) to the long-time limit follows that of a pack of the larger sized beads alone, although the limiting D(t) for the mixed bead pack is lower, reflecting the lower porosity of the sample compared to that of a pack of mono-sized glass beads. The Pade approximation is used to interpolate D(t) data between the short- and long-time limits. Initial studies of continuous flow laser-polarized xenon gas demonstrate velocity-sensitive imaging of much higher flows than can generally be obtained with liquids (20-200 mm s-1). Gas velocity imaging is, however, found to be limited to a resolution of about 1 mm s-1 owing to the high diffusivity of gases compared with liquids. We also present the first gas-phase NMR scattering, or diffusive-diffraction, data, namely flow-enhanced structural features in the echo attenuation data from laser-polarized xenon flowing through a 2 mm glass bead pack. c2002 John Wiley & Sons, Ltd.

  15. The structure of hydrophobic gas diffusion electrodes.

    NASA Technical Reports Server (NTRS)

    Giner, J.

    1972-01-01

    The 'flooded agglomerate' model of the Teflon-bonded gas diffusion electrode is discussed. A mathematical treatment of the 'flooded agglomerate' model is given; it can be used to predict the performance of the electrode as a function of measurable physical parameters.

  16. Effect of foam films on gas diffusion.

    PubMed

    Quoc, P Nguyen; Zitha, Pacelli L J; Currie, Peter K

    2002-04-15

    We report an experimental investigation of the permeability to gas of systems of one or several soap films freely standing in a straight tube, using either reactive gas (NH(3)) or inert gas (argon). The series of soap films appears to be the simplest paradigm of successive lamellae arrangements encountered in foams confined in a porous medium. To conduct the experiments, we devised two novel methods for the determination of gas diffusion fluxes: one based on reactive changes of pH by NH(3) and the other on mass spectrometry. The permeability of a single film, stabilized by sodium dodecyl sulfate solution, was found to be 3.50+/-0.04 10(-2) cm/s for argon and 3.18+/-0.07 10(-4) cm/s for NH(3). The permeability value for the inert gas is in good agreement with data obtained by the diminishing-bubble method. When the number of films increases, the permeability decreases considerably as a result of cumulative film resistance effects. We also developed a simple phenomenological model based upon a combination of gas kinetic and energy barrier concepts to interpret our data. This model takes into account gas solubility and the effects of salinity, which have seemingly been ignored in previous models. The predicted film permeability decreases sharply with increase surfactant concentration, indicating the occurrence of higher adsorption and increasingly compact surfactant layers.

  17. Diffusion of Bacterial Cells in Porous Media

    PubMed Central

    Licata, Nicholas A.; Mohari, Bitan; Fuqua, Clay; Setayeshgar, Sima

    2016-01-01

    The chemotaxis signal transduction network regulates the biased random walk of many bacteria in favorable directions and away from harmful ones through modulating the frequency of directional reorientations. In mutants of diverse bacteria lacking the chemotaxis response, migration in classic motility agar, which constitutes a fluid-filled porous medium, is compromised; straight-swimming cells unable to tumble become trapped within the agar matrix. Spontaneous mutations that restore spreading have been previously observed in the enteric bacterium Escherichia coli, and recent work in other bacterial species has isolated and quantified different classes of nonchemotacting mutants exhibiting the same spreading phenotype. We present a theoretical description of bacterial diffusion in a porous medium—the natural habitat for many cell types—which elucidates how diverse modifications of the motility apparatus resulting in a nonzero tumbling frequency allows for unjamming of otherwise straight-swimming cells at internal boundaries and leads to net migration. A unique result of our analysis is increasing diffusive spread with increasing tumbling frequency in the small pore limit, consistent with earlier experimental observations but not captured by previous models. Our theoretical results, combined with a simple model of bacterial diffusion and growth in agar, are compared with our experimental measurements of swim ring expansion as a function of time, demonstrating good quantitative agreement. Our results suggest that the details of the cellular tumbling process may be adapted to enable bacteria to propagate efficiently through complex environments. For engineered, self-propelled microswimmers that navigate via alternating straight runs and changes in direction, these results suggest an optimal reorientation strategy for efficient migration in a porous environment with a given microarchitecture. PMID:26745427

  18. Forced dichotomic diffusion in a viscous media

    NASA Astrophysics Data System (ADS)

    Calisto, Hector; Bologna, Mauro; Chandía, Kristopher J.

    2017-02-01

    In this paper, we study the dynamical properties of a linear system driven by a superposition of a Gaussian white noise and a symmetric Markovian dichotomic noise operating simultaneously on the system. We find exact analytical solutions for the moment generating function and for the probability distribution function. We show analytically that the system presents characteristics belonging to the nonlinear cases, such as a nonequilibrium bimodal distribution. We infer that the white Gaussian noise smooths the two characteristics Diracs delta peaks, generated by a purely dichotomic diffusion, transforming them in two smooth maxima.

  19. Lattice Boltzmann Modeling of Gaseous Diffusion in Unsaturated Porous Media under Variable Gravity Conditions

    NASA Astrophysics Data System (ADS)

    Chau, J. F.; Or, D.; Jones, S.; Sukop, M.

    2004-05-01

    Liquid distribution in unsaturated porous media under different gravitational forces and resulting gaseous diffusion coefficients were investigated to enhance understanding of plant growth conditions in microgravity. Different fluid behavior in plant growth media under microgravity conditions as compared to earth presents a challenge to plant growth in long duration space exploration missions. Our primary objective was to provide qualitative description and quantitative measures of the role of reduced gravity on hydraulic and gaseous transport properties in simulated porous media. We implemented a multi-phase lattice Boltzmann code for equilibrium distribution of liquid in an idealized two-dimensional porous medium under microgravity and "normal" gravity conditions. The information was then used to provide boundary conditions for simulation of gaseous diffusion through the equilibrium domains (considering diffusion through liquid phase negligibly small). The models were tested by comparison with several analytical solutions to the diffusion equation, with excellent results. The relative diffusion coefficient for both series of simulations (with and without gravity) as functions of air-filled porosity was in good agreement with established models of Millington-Quirk. Liquid distribution under earth's gravity featured increased water content at the lower part of the medium relative to the distribution in reduced gravity, which resulted in decreased gas diffusion through a vertically oriented column of a porous medium. Simulation results for larger domains under various orientations will be presented.

  20. Photoacoustic-guided convergence of light through optically diffusive media.

    PubMed

    Kong, Fanting; Silverman, Ronald H; Liu, Liping; Chitnis, Parag V; Lee, Kotik K; Chen, Y C

    2011-06-01

    We demonstrate that laser beams can be converged toward a light-absorbing target through optically diffusive media by using photoacoustic-guided interferometric focusing. The convergence of light is achieved by shaping the wavefront of the incident light with a deformable mirror to maximize the photoacoustic signal, which is proportional to the scattered light intensity at the light absorber.

  1. Photoacoustic-guided convergence of light through optically diffusive media

    PubMed Central

    Kong, Fanting; Silverman, Ronald H.; Liu, Liping; Chitnis, Parag V.; Lee, Kotik K.; Chen, Y. C.

    2012-01-01

    We demonstrate that laser beams can be converged toward a light-absorbing target through optically diffusive media by using photoacoustic-guided interferometric focusing. The convergence of light is achieved by shaping the wavefront of the incident light with a deformable mirror to maximize the photoacoustic signal, which is propor tional to the scattered light intensity at the light absorber. PMID:21633446

  2. Reaction-Diffusion Patterns in Structured Media

    NASA Astrophysics Data System (ADS)

    Epstein, Irving

    I will look at pattern formation in the Belousov-Zhabotinsky (BZ) oscillating chemical reaction in media that are structured at length scales ranging from ten nanometers to a few centimeters. A reverse microemulsion consisting of nanometer diameter droplets of water containing the reactants dispersed in oil allows the physical structure (size, spacing) of the droplets and their chemical composition to be controlled independently, enabling one to generate a remarkable variety of stationary and moving patterns, including Turing structures, ordinary and antispirals, packet waves and spatiotemporal chaos. One- and two-dimensional arrays of aqueous droplets in oil generated by microfluidic techniques have diameters of the order of 100 micrometers and produce a different array of patterns that can be precisely controlled with light. In particular, circular arrays of droplets provide a testing ground for some of Turing's ideas about morphogenesis. By attaching the BZ catalyst to a polymer that shrinks and swells in response to changes in the redox state of the catalyst, one can construct gel materials that transduce chemical changes to mechanical motion, a phenomenon modeled with considerable success by the Balazs group. If time permits, I will also discuss the BZ reaction in coupled macroscopic flow reactors that mimic small neural networks.

  3. Diffusion of Lexical Change in Social Media

    PubMed Central

    Eisenstein, Jacob; O'Connor, Brendan; Smith, Noah A.; Xing, Eric P.

    2014-01-01

    Computer-mediated communication is driving fundamental changes in the nature of written language. We investigate these changes by statistical analysis of a dataset comprising 107 million Twitter messages (authored by 2.7 million unique user accounts). Using a latent vector autoregressive model to aggregate across thousands of words, we identify high-level patterns in diffusion of linguistic change over the United States. Our model is robust to unpredictable changes in Twitter's sampling rate, and provides a probabilistic characterization of the relationship of macro-scale linguistic influence to a set of demographic and geographic predictors. The results of this analysis offer support for prior arguments that focus on geographical proximity and population size. However, demographic similarity – especially with regard to race – plays an even more central role, as cities with similar racial demographics are far more likely to share linguistic influence. Rather than moving towards a single unified “netspeak” dialect, language evolution in computer-mediated communication reproduces existing fault lines in spoken American English. PMID:25409166

  4. Bibliographical review for reflectance of diffusing media

    NASA Astrophysics Data System (ADS)

    Philips-Invernizzi, Bernadette; Dupont, Daniel; Caze, Claude

    2001-06-01

    When light travels through a diffusing medium, the incident radiation is scattered and a part of it is reemitted. The reflected proportion is defined as the reflectance and provides the quantification of color sensations. Many authors have tried to derive reflectance values by various means. This bibliographical synthesis reviews the main theories on the subject, comparing them and especially their assumptions and derivations. First, the widely used theory of Kubelka and Munk--which has been proved to be a particular case of Schuster's formula-- is described, according to its terms, limits, improvements, and applications. Next, the well-known electromagnetic approach by Mie is presented, along with methods derived from radiative transfer theory, multilayer methods (the `pile of plates' due to Stokes), multiflux methods (developed by Mudgett and Richards or Volz for instance), and the corpuscular treatment proposed by Silvy. Finally, new methods are listed that allow the calculation of reflectance values, such as Monte Carlo simulations, expert systems, or neural networks. A chronological organization chart is also given to place each work or advance relative to the others.

  5. Diffusion with condensation and evaporation in porous media

    SciTech Connect

    Gu, L.; Plumb, O.A.; Ho, C.K.; Webb, S.W.

    1998-03-01

    Vapor phase transport in porous media is important in a number of environmental and industrial processes: soil moisture transport, vapor phase transport in the vadose zone, transport in the vicinity of buried nuclear waste, and industrial processes such as drying. The diffusion of water vapor in a packed bed containing residual liquid is examined experimentally. The objective is to quantify the effect of enhanced vapor diffusion resulting from evaporation/condensation in porous media subjected to a temperature gradient. Isothermal diffusion experiments in free-space were conducted to qualify the experimental apparatus and techniques. For these experiments measured diffusion coefficients are within 3.6% of those reported in the literature for the temperature range from 25 C to 40 C. Isothermal experiments in packed beds of glass beads were used to determine the tortuosity coefficient resulting in {tau} = 0.78 {+-} 0.028, which is also consistent with previously reported results. Nonisothermal experiments in packed beds in which condensation occurs were conducted to examine enhanced vapor diffusion. The interpretation of the results for these experiments is complicated by a gradual, but continuous, build-up of condensate in the packed beds during the course of the experiment. Results indicate diffusion coefficients which increase as a function of saturation resulting in enhancement of the vapor-phase transport by a factor of approximately four compared to a dry porous medium.

  6. Numerical schemes for anomalous diffusion of single-phase fluids in porous media

    NASA Astrophysics Data System (ADS)

    Awotunde, Abeeb A.; Ghanam, Ryad A.; Al-Homidan, Suliman S.; Tatar, Nasser-eddine

    2016-10-01

    Simulation of fluid flow in porous media is an indispensable part of oil and gas reservoir management. Accurate prediction of reservoir performance and profitability of investment rely on our ability to model the flow behavior of reservoir fluids. Over the years, numerical reservoir simulation models have been based mainly on solutions to the normal diffusion of fluids in the porous reservoir. Recently, however, it has been documented that fluid flow in porous media does not always follow strictly the normal diffusion process. Small deviations from normal diffusion, called anomalous diffusion, have been reported in some experimental studies. Such deviations can be caused by different factors such as the viscous state of the fluid, the fractal nature of the porous media and the pressure pulse in the system. In this work, we present explicit and implicit numerical solutions to the anomalous diffusion of single-phase fluids in heterogeneous reservoirs. An analytical solution is used to validate the numerical solution to the simple homogeneous case. The conventional wellbore flow model is modified to account for anomalous behavior. Example applications are used to show the behavior of wellbore and wellblock pressures during the single-phase anomalous flow of fluids in the reservoirs considered.

  7. Narrow groove welding gas diffuser assembly and welding torch

    DOEpatents

    Rooney, Stephen J.

    2001-01-01

    A diffuser assembly is provided for narrow groove welding using an automatic gas tungsten arc welding torch. The diffuser assembly includes a manifold adapted for adjustable mounting on the welding torch which is received in a central opening in the manifold. Laterally extending manifold sections communicate with a shield gas inlet such that shield gas supplied to the inlet passes to gas passages of the manifold sections. First and second tapered diffusers are respectively connected to the manifold sections in fluid communication with the gas passages thereof. The diffusers extend downwardly along the torch electrode on opposite sides thereof so as to release shield gas along the length of the electrode and at the distal tip of the electrode. The diffusers are of a transverse width which is on the order of the thickness of the electrode so that the diffusers can, in use, be inserted into a narrow welding groove before and after the electrode in the direction of the weld operation.

  8. Gradient Driven Flow: Lattice Gas, Diffusion Equation and Measurement Scales

    DTIC Science & Technology

    2001-01-01

    03-200 1 Journal Article (refereed) 2001 4. TITLE AND SUBTITLE Sa. CONTRACT NUMBER Gradient Driven Flow : Lattice Gas, Diffusion Equation and...time regime, the collective motion exhibits an onset of oscillation. 15. SUBJECT TERMS Diffusion; Fick’s Law; Gradient Driven Flow ; Lattice Gas 16...Form 298 (Rev. 8-98) Prescribed by ANSI Std. Z39.18 20010907 062 Gradient driven flow : lattice gas, diffusion equation and measurement scales R.B

  9. Ice Formation in Gas-Diffusion Layers

    SciTech Connect

    Dursch, Thomas; Radke, Clayton J.; Weber, Adam Z.

    2010-07-10

    Under sub-freezing conditions, ice forms in the gas-diffusion layer (GDL) of a proton exchange membrane fuel cell (PEMFC) drastically reducing cell performance. Although a number of strategies exist to prevent ice formation, there is little fundamental understanding of the mechanisms of freezing within PEMFC components. Differential scanning calorimetry (DSC) is used to elucidate the effects of hydrophobicity (Teflon® loading) and water saturation on the rate of ice formation within three commercial GDLs. We find that as the Teflon® loading increases, the crystallization temperature decreases due to a change in internal ice/substrate contact angle, as well as the attainable level of water saturation. Classical nucleation theory predicts the correct trend in freezing temperature with Teflon® loading.

  10. Transitional Gas Jet Diffusion Flames in Microgravity

    NASA Technical Reports Server (NTRS)

    Agrawal, Ajay K.; Alammar, Khalid; Gollahalli, S. R.; Griffin, DeVon (Technical Monitor)

    2000-01-01

    Drop tower experiments were performed to identify buoyancy effects in transitional hydrogen gas jet diffusion flames. Quantitative rainbow schlieren deflectometry was utilized to optically visualize the flame and to measure oxygen concentration in the laminar portion of the flame. Test conditions consisted of atmospheric pressure flames burning in quiescent air. Fuel from a 0.3mm inside diameter tube injector was issued at jet exit Reynolds numbers (Re) of 1300 to 1700. Helium mole percentage in the fuel was varied from 0 to 40%. Significant effects of buoyancy were observed in near field of the flame even-though the fuel jets were momentum-dominated. Results show an increase of breakpoint length in microgravity. Data suggest that transitional flames in earth-gravity at Re<1300 might become laminar in microgravity.

  11. Improved Modeling and Understanding of Diffusion-Media Wettability on Polymer-Electrolyte-Fuel-Cell Performance

    SciTech Connect

    Weber, Adam

    2010-03-05

    A macroscopic-modeling methodology to account for the chemical and structural properties of fuel-cell diffusion media is developed. A previous model is updated to include for the first time the use of experimentally measured capillary pressure -- saturation relationships through the introduction of a Gaussian contact-angle distribution into the property equations. The updated model is used to simulate various limiting-case scenarios of water and gas transport in fuel-cell diffusion media. Analysis of these results demonstrate that interfacial conditions are more important than bulk transport in these layers, where the associated mass-transfer resistance is the result of higher capillary pressures at the boundaries and the steepness of the capillary pressure -- saturation relationship. The model is also used to examine the impact of a microporous layer, showing that it dominates the response of the overall diffusion medium. In addition, its primary mass-transfer-related effect is suggested to be limiting the water-injection sites into the more porous gas-diffusion layer.

  12. Gas transport in unsaturated porous media: the adequacy of Fick's law

    USGS Publications Warehouse

    Thorstenson, D.C.; Pollock, D.W.

    1989-01-01

    The increasing use of natural unsaturated zones as repositories for landfills and disposal sites for hazardous wastes (chemical and radioactive) requires a greater understanding of transport processes in the unsaturated zone. For volatile constituents an important potential transport mechanism is gaseous diffusion. Diffusion, however, cannot be treated as an independent isolated transport mechanism. A complete understanding of multicomponent gas transport in porous media (unsaturated zones) requires a knowledge of Knudsen transport, the molecular and nonequimolar components of diffusive flux, and viscous (pressure driven) flux. This review presents a brief discussion of the underlying principles and interrelationships among each of the above flux mechanisms. -from Authors

  13. Anode characterisation and gas diffusion behaviour in aluminium smelting

    NASA Astrophysics Data System (ADS)

    Putri, Epma; Brooks, Geoffrey; Snook, Graeme; Eick, Ingo

    2017-01-01

    Over the past century, significant research on different aspects of the Hall-Héroult process has been conducted to increase energy efficiency. Bubble generation at the anode reaction and its contribution to the overall voltage drop in aluminium production holds significant potential for energy saving, yet the details of the gas transport mechanism for bubble nucleation behaviour are not completely understood. The multi-step electrochemical reaction releases predominantly CO2 gas along with CO gas, which is a reduction product formed by reaction of CO2 with the anode carbon. Complicating the reaction is the multiple paths by which the gas can diffuse (either through the porous anode or the electrolyte bath). There has been no detailed investigation of the correlation between gas diffusion as a function of anode and bath properties. In the present study, the porosity measurement techniques in the anode will be used to understand the relation of gas diffusion and anode properties. A porosimetric study was conducted for two different anode samples using mercury intrusion porosimetry (MIP) and hydrostatic method. The MIP method provides important anode properties information such as density, percent porosity, pore size distribution, permeability, and tortuosity factor which affect gas diffusion and anode performance. The Knudsen number obtained from MIP data shows both Knudsen diffusion and molecular diffusion need to be considered when predicting the effective diffusion.

  14. FLAMMABLE GAS DIFFUSION THROUGH SINGLE SHELL TANK (SST) DOMES

    SciTech Connect

    MEACHAM, J.E.

    2003-11-10

    This report quantified potential hydrogen diffusion through Hanford Site Single-Shell tank (SST) domes if the SSTs were hypothetically sealed airtight. Results showed that diffusion would keep headspace flammable gas concentrations below the lower flammability limit in the 241-AX and 241-SX SST. The purpose of this document is to quantify the amount of hydrogen that could diffuse through the domes of the SSTs if they were hypothetically sealed airtight. Diffusion is assumed to be the only mechanism available to reduce flammable gas concentrations. The scope of this report is limited to the 149 SSTs.

  15. High Speed, Low Cost Fabrication of Gas Diffusion Electrodes for Membrane Electrode Assemblies

    SciTech Connect

    DeCastro, Emory S.; Tsou, Yu-Min; Liu, Zhenyu

    2013-09-20

    Fabrication of membrane electrode assemblies (MEAs) depends on creating inks or pastes of catalyst and binder, and applying this suspension to either the membrane (catalyst coated membrane) or gas diffusion media (gas diffusion electrode) and respectively laminating either gas diffusion media or gas diffusion electrodes (GDEs) to the membrane. One barrier to cost effective fabrication for either of these approaches is the development of stable and consistent suspensions. This program investigated the fundamental forces that destabilize the suspensions and developed innovative approaches to create new, highly stable formulations. These more concentrated formulations needed fewer application passes, could be coated over longer and wider substrates, and resulted in significantly lower coating defects. In March of 2012 BASF Fuel Cell released a new high temperature product based on these advances, whereby our customers received higher performing, more uniform MEAs resulting in higher stack build yields. Furthermore, these new materials resulted in an “instant” increase in capacity due to higher product yields and material throughput. Although not part of the original scope of this program, these new formulations have also led us to materials that demonstrate equivalent performance with 30% less precious metal in the anode. This program has achieved two key milestones in DOE’s Manufacturing R&D program: demonstration of processes for direct coating of electrodes and continuous in-line measurement for component fabrication.

  16. Structural Measurements from Images of Noble Gas Diffusion

    NASA Astrophysics Data System (ADS)

    Cadman, Robert V.; Kadlecek, Stephen J.; Emami, Kiarash; MacDuffie Woodburn, John; Vahdat, Vahid; Ishii, Masaru; Rizi, Rahim R.

    2009-03-01

    Magnetic resonance imaging of externally polarized noble gases such as ^3He has been used for pulmonary imaging for more than a decade. Because gas diffusion is impeded by the alveoli, the diffusion coefficient of gas in the lung, measured on a time scale of milliseconds, is reduced compared to that of the same gas mixture in the absence of restrictions. When the alveolar walls decay, as in emphysema, diffusivity in the lung increases. In this paper, the relationship between diffusion measurements and the size of the restricting structures will be discussed. The simple case of diffusion in an impermeable cylinder, a structure similar to the upper respiratory airways in mammals, has been studied. A procedure will be presented by which airways of order 2 mm in diameter may be accurately measured; demonstration experiments with plastic tubes will also be presented. The additional developments needed before this technique becomes practical will be briefly discussed.

  17. A numerical assessment of cosmic-ray energy diffusion through turbulent media

    SciTech Connect

    Fatuzzo, M.; Melia, F. E-mail: fmelia@email.arizona.edu

    2014-04-01

    How and where cosmic rays are produced, and how they diffuse through various turbulent media, represent fundamental problems in astrophysics with far-reaching implications, both in terms of our theoretical understanding of high-energy processes in the Milky Way and beyond, and the successful interpretation of space-based and ground based GeV and TeV observations. For example, recent and ongoing detections, e.g., by Fermi (in space) and HESS (in Namibia), of γ-rays produced in regions of dense molecular gas hold important clues for both processes. In this paper, we carry out a comprehensive numerical investigation of relativistic particle acceleration and transport through turbulent magnetized environments in order to derive broadly useful scaling laws for the energy diffusion coefficients.

  18. SHIR competitive information diffusion model for online social media

    NASA Astrophysics Data System (ADS)

    Liu, Yun; Diao, Su-Meng; Zhu, Yi-Xiang; Liu, Qing

    2016-11-01

    In online social media, opinion divergences and differentiations generally exist as a result of individuals' extensive participation and personalization. In this paper, a Susceptible-Hesitated-Infected-Removed (SHIR) model is proposed to study the dynamics of competitive dual information diffusion. The proposed model extends the classical SIR model by adding hesitators as a neutralized state of dual information competition. It is both hesitators and stable spreaders that facilitate information dissemination. Researching on the impacts of diffusion parameters, it is found that the final density of stiflers increases monotonically as infection rate increases and removal rate decreases. And the advantage information with larger stable transition rate takes control of whole influence of dual information. The density of disadvantage information spreaders slightly grows with the increase of its stable transition rate, while whole spreaders of dual information and the relaxation time remain almost unchanged. Moreover, simulations imply that the final result of competition is closely related to the ratio of stable transition rates of dual information. If the stable transition rates of dual information are nearly the same, a slightly reduction of the smaller one brings out a significant disadvantage in its propagation coverage. Additionally, the relationship of the ratio of final stiflers versus the ratio of stable transition rates presents power characteristic.

  19. Inert-Gas Diffuser For Plasma Or Arc Welding

    NASA Technical Reports Server (NTRS)

    Gilbert, Jeffrey L.; Spencer, Carl N.; Hosking, Timothy J.

    1994-01-01

    Inert-gas diffuser provides protective gas cover for weld bead as it cools. Follows welding torch, maintaining continuous flow of argon over newly formed joint and prevents it from oxidizing. Helps to ensure welds of consistently high quality. Devised for plasma arc keyhole welding of plates of 0.25-in. or greater thickness, also used in tungsten/inert-gas and other plasma or arc welding processes.

  20. Characterization of gas diffusion electrodes for metal-air batteries

    NASA Astrophysics Data System (ADS)

    Danner, Timo; Eswara, Santhana; Schulz, Volker P.; Latz, Arnulf

    2016-08-01

    Gas diffusion electrodes are commonly used in high energy density metal-air batteries for the supply of oxygen. Hydrophobic binder materials ensure the coexistence of gas and liquid phase in the pore network. The phase distribution has a strong influence on transport processes and electrochemical reactions. In this article we present 2D and 3D Rothman-Keller type multiphase Lattice-Boltzmann models which take into account the heterogeneous wetting behavior of gas diffusion electrodes. The simulations are performed on FIB-SEM 3D reconstructions of an Ag model electrode for predefined saturation of the pore space with the liquid phase. The resulting pressure-saturation characteristics and transport correlations are important input parameters for modeling approaches on the continuum scale and allow for an efficient development of improved gas diffusion electrodes.

  1. Imaging Absorbing Structures Embedded in Thick Diffusing Media.

    NASA Astrophysics Data System (ADS)

    Dilworth, David Saunders

    Linear systems models and confocal imaging techniques are applied to the problem of imaging absorbing structures embedded in thick diffusing media. At the microscopic level, the model is linear in complex field and space variant; at the macroscopic level where spatial averaging processes are considered the model is linear in irradiance and space variant, thereby becoming mathematically more tractable. We describe the planar confocal imager, in which a small spot of light scans the front surface of a diffuser, and the light distribution on the back surface is sampled for each position of the scanning spot. A composite image is then formed by selection of one pixel from each of the 25,600 images, viz., a pixel from a spot opposite or nearly opposite from the scanning spot. The overall process is effectively a confocal imaging process. The planar system can be modified to create 3-D confocal imaging, where many stereo image pairs are created of the absorbing structures within a thick diffuser. Techniques for both planar and exfoliative deconvolution are investigated. Planar deconvolution sharpens images affected by space invariant processes in which the image point spread function is always the same. Exfoliatative deconvolution is a systematic method for sharpening images formed by space variant processes in which the point spread function varies in accordance with the depth of the embedded object. Results from planar and 3-D confocal scanning verify the linear systems model and demonstrate that the broad beam point spread function width (the point spread function formed by conventional, non-confocal imaging) can be reduced by a factor of 2. Results from planar and exfoliative deconvolution demonstrate that the confocal point spread function width can be reduced by a factor of 1.5. Preliminary optical and data processing techniques are discussed for developing a coherent confocal scanner. The image resolution from this type of scanner will be determined by the

  2. Gas mixture for diffuse-discharge switch

    DOEpatents

    Christophorou, Loucas G.; Carter, James G.; Hunter, Scott R.

    1984-01-01

    Gaseous medium in a diffuse-discharge switch of a high-energy pulse generator is formed of argon combined with a compound selected from the group consisting of CF.sub.4, C.sub.2 F.sub.6, C.sub.3 F.sub.8, n-C.sub.4 F.sub.10, WF.sub.6, (CF.sub.3).sub.2 S and (CF.sub.3).sub.2 O.

  3. Gas mixture for diffuse-discharge switch

    DOEpatents

    Christophorou, L.G.; Carter, J.G.; Hunter, S.R.

    1982-08-31

    Gaseous medium in a diffuse-discharge switch of a high-energy pulse generator is formed of argon combined with a compound selected from the group consisting of CF/sub 4/, C/sub 2/F/sub 6/, C/sub 3/F/sub 8/, n-C/sub 4/F/sub 10/, WF/sub 6/, (CF/sub 3/)/sub 2/S and (CF/sub 3/)/sub 2/O.

  4. Numerical Simulation of Gas Leaking Diffusion from Storage Tank

    NASA Astrophysics Data System (ADS)

    Zhu, Hongjun; Jing, Jiaqiang

    Over 80 percents of storage tank accidents are caused by gas leaking. Since traditional empirical calculation has great errors, present work aims to study the gas leaking diffusion under different wind conditions by numerical simulation method based on computational fluid dynamics theory. Then gas concentration distribution was obtained to determine the scope of the security zone. The results showed that gas diffused freely along the axis of leaking point without wind, giving rise to large range of hazardous area. However, wind plays the role of migrating and diluting the leaking gas. The larger is the wind speed, the smaller is the damage and the bigger is the security zone. Calculation method and results can provide some reference to establish and implement rescue program for accidents.

  5. Multicomponent Gas Diffusion and an Appropriate Momentum Boundary Condition

    NASA Technical Reports Server (NTRS)

    Noever, David A.

    1994-01-01

    Multicomponent gas diffusion is reviewed with particular emphasis on gas flows near solid boundaries-the so-called Kramers-Kistemaker effect. The aim is to derive an appropriate momentum boundary condition which governs many gaseous species diffusing together. The many species' generalization of the traditional single gas condition, either as slip or stick (no-slip), is not obvious, particularly for technologically important cases of lower gas pressures and very dissimilar molecular weight gases. No convincing theoretical case exists for why two gases should interact with solid boundaries equally but in opposite flow directions, such that the total gas flow exactly vanishes. ln this way, the multicomponent no-slip boundary requires careful treatment The approaches discussed here generally adopt a microscopic model for gas-solid contact. The method has the advantage that the mathematics remain tractable and hence experimentally testable. Two new proposals are put forward, the first building in some molecular collision physics, the second drawing on a detailed view of surface diffusion which does not unphysically extrapolate bulk gas properties to govern the adsorbed molecules. The outcome is a better accounting of previously anomalous experiments. Models predict novel slip conditions appearing even for the case of equal molecular weight components. These approaches become particularly significant in view of a conceptual contradiction found to arise in previous derivations of the appropriate boundary conditions. The analogous case of three gases, one of which is uniformly distributed and hence non-diffusing, presents a further refinement which gives unexpected flow reversals near solid boundaries. This case is investigated alone and for aggregating gas species near their condensation point. In addition to predicting new physics, this investigation carries practical implications for controlling vapor diffusion in the growth of crystals used in medical diagnosis (e

  6. 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.

  7. Physical degradation of membrane electrode assemblies undergoing freeze/thaw cycling: Diffusion media effects

    NASA Astrophysics Data System (ADS)

    Kim, Soowhan; Ahn, Byung Ki; Mench, M. M.

    In this work, the effects of properties of diffusion media (DM) (stiffness, thickness and micro-porous layer (MPL)) on the physical damage of membrane electrode assembly (MEA) subjected to freeze/thaw cycling were studied. Pressure uniformity of the diffusion media onto the catalyst layer (CL) was determined to be a key parameter to mitigate freeze-induced physical damage. Stiffer diffusion media, enabling more uniform compression under the channels and lands, can mitigate surface cracks, but flexible cloth diffusion media experienced severe catalyst layer surface damage. The thickness of the diffusion media and existence of a micro-porous layer were not observed to be major factors to mitigate freeze-damage when the catalyst layer is in contact with liquid. Interfacial delamination between diffusion media and catalyst layers, but not between the catalyst layer and membrane, was observed. This permanent deformation of the stiff diffusion media in the channel locations as well as fractures of carbon fibers increased electrical resistance, and may increase water flooding, resulting in reduced longevity and operational losses. Although use of a freeze-tolerable MEA design (negligible virgin cracked catalyst layers with thinner reinforced membrane) [S. Kim, M.M. Mench, J. Power Sources, in press] with stiff diffusion media can reduce the freeze-damage in the worst case scenario test condition of direct liquid contact, extensive irreversible damage (diffusion media/catalyst layer interfacial delamination) was not completely prevented. In addition to proper material selection, liquid water contact with the catalyst layer should be removed prior to shutdown to a frozen state to permit long-term cycling damage and facilitate frozen start.

  8. Nonequilibrium gas absorption in rotating permeable media

    NASA Astrophysics Data System (ADS)

    Baev, V. K.; Bazhaikin, A. N.

    2016-08-01

    The absorption of ammonia, sulfur dioxide, and carbon dioxide by water and aqueous solutions in rotating permeable media, a cellular porous disk, and a set of spaced-apart thin disks has been considered. The efficiency of cleaning air to remove these impurities is determined, and their anomalously high solubility (higher than equilibrium value) has been discovered. The results demonstrate the feasibility of designing cheap efficient rotor-type absorbers to clean gases of harmful impurities.

  9. Heat diffusion in the disordered electron gas

    NASA Astrophysics Data System (ADS)

    Schwiete, G.; Finkel'stein, A. M.

    2016-03-01

    We study the thermal conductivity of the disordered two-dimensional electron gas. To this end, we analyze the heat density-heat density correlation function concentrating on the scattering processes induced by the Coulomb interaction in the subtemperature energy range. These scattering processes are at the origin of logarithmic corrections violating the Wiedemann-Franz law. Special care is devoted to the definition of the heat density in the presence of the long-range Coulomb interaction. To clarify the structure of the correlation function, we present details of a perturbative calculation. While the conservation of energy strongly constrains the general form of the heat density-heat density correlation function, the balance of various terms turns out to be rather different from that for the correlation functions of other conserved quantities such as the density-density or spin density-spin density correlation function.

  10. Test Program for High Efficiency Gas Turbine Exhaust Diffuser

    SciTech Connect

    Norris, Thomas R.

    2009-12-31

    This research relates to improving the efficiency of flow in a turbine exhaust, and thus, that of the turbine and power plant. The Phase I SBIR project demonstrated the technical viability of “strutlets” to control stalls on a model diffuser strut. Strutlets are a novel flow-improving vane concept intended to improve the efficiency of flow in turbine exhausts. Strutlets can help reduce turbine back pressure, and incrementally improve turbine efficiency, increase power, and reduce greenhouse gas emmission. The long-term goal is a 0.5 percent improvement of each item, averaged over the US gas turbine fleet. The strutlets were tested in a physical scale model of a gas turbine exhaust diffuser. The test flow passage is a straight, annular diffuser with three sets of struts. At the end of Phase 1, the ability of strutlets to keep flow attached to struts was demonstrated, but the strutlet drag was too high for a net efficiency advantage. An independently sponsored followup project did develop a highly-modified low-drag strutlet. In combination with other flow improving vanes, complicance to the stated goals was demonstrated for for simple cycle power plants, and to most of the goals for combined cycle power plants using this particular exhaust geometry. Importantly, low frequency diffuser noise was reduced by 5 dB or more, compared to the baseline. Appolicability to other diffuser geometries is yet to be demonstrated.

  11. Unified Measurement System with Suction Control for Gas Transport Parameters in Porous Media

    NASA Astrophysics Data System (ADS)

    Kawamoto, K.; Rouf, M. A.; Hamamoto, S.; Sakaki, T.; Komatsu, T.; Moldrup, P.

    2010-12-01

    Pore geometric parameters including pore size distribution, total and air-filled porosities, pore tortuosity and connectivity strongly influence air flow in porous media, and, thus, characterize gas transport parameters such as gas diffusion coefficient Dp and air permeability ka. In this study, the gas transport parameters were measured for porous media with varying textures under repeated drying and wetting cycles using a newly-developed measurement system, and the hysteretic behaviors in the gas transport parameters were examined. A unified measurement system with suction control (UMS_SC) was developed for measuring soil water characteristics curve and gas transport parameters sequentially under drying and wetting cycles. It consisted of a porous plate, diffusion chamber, sample ring (15 cm in inner diameter and 12 cm in height), tensiometer, soil moisture sensor, oxygen electrodes and air pressure gauges. Soil water characteristics curve and gas transport parameters (gas diffusion coefficient Dp and air permeability ka) for differently textured materials including sand, molten slag , and a mixture material of MS and volcanic ash soil were measured under repeated drying and wetting cycles. The measurement for each porous material was initiated from a full saturation and suction head was increased/decreased in steps in the drainage/wetting cycles. Moreover, independent measurements of Dp and ka were carried out for repacked air-dried samples using a cylindrical mold (15 cm in inner diameter and 12 cm in height) in order to obtain the Dp and ka values at a full dry condition. The newly-developed UMS_SC performed well for the applied suction head less than 50 cm of water with corresponding saturation of roughly 0.3-0.5. The gas transport parameters were well measured at each suction head level under repeated drying and wetting cycles, and the measured gas transport parameters including the independent measurements were verified by literature data as well as

  12. Gas turbine engine with radial diffuser and shortened mid section

    SciTech Connect

    Charron, Richard C.; Montgomery, Matthew D.

    2015-09-08

    An industrial gas turbine engine (10), including: a can annular combustion assembly (80), having a plurality of discrete flow ducts configured to receive combustion gas from respective combustors (82) and deliver the combustion gas along a straight flow path at a speed and orientation appropriate for delivery directly onto the first row (56) of turbine blades (62); and a compressor diffuser (32) having a redirecting surface (130, 140) configured to receive an axial flow of compressed air and redirect the axial flow of compressed air radially outward.

  13. Drop Tower Setup for Dynamic Light Scattering in Dense Gas-Fluidized Granular Media

    NASA Astrophysics Data System (ADS)

    Born, Philip; Schmitz, Johannes; Bußmann, Michael; Sperl, Matthias

    2016-08-01

    Investigation of dynamics in dense granular media is challenging. Here we present a setup that facilitates gas fluidization of dense granular media in microgravity. The dynamics is characterized using diffusing wave spectroscopy. We demonstrate that agitated granular media reach a steady state within fractions of a second in drop tower flights. The intensity autocorrelation functions obtained in microgravity show a remarkable dependence on sample volume fraction and driving strength. A plateau in correlation emerges at low volume fractions and strong driving, while correlation decays only very slowly but continuously at high packing fractions. The setup allows to independently set sample volume fraction and driving strength, and thus extends the possibilities for investigations on dynamics in dense granular on ground.

  14. Gas Diffusion in Polyethylene Terepthalate By Molecular Dynamics

    NASA Astrophysics Data System (ADS)

    Butler, Simon; Adolf, David

    2006-03-01

    Molecular dynamics simulations of the diffusion of small penetrants through PET have been performed utilising the anisotropic united atom model [1] and a virtual liquid technique. [2] The accuracy and reliability of these two approaches has been assessed in terms of the improvement in equation of state behaviour and of diffusion co-efficients and solubilities. The effect of the diffusion of nitrogen, carbon dioxide, and oxygen on the local dynamics of PET have been investigated as a result. Attention has been focused on the dual mode effect [3] observed during mixed gas diffusion. [1] Molecular dynamics calculation of the equation of state of alkanes, J. Chem. Phys. 93, 6 (1990) [2] Kikuchi, Kuwajima, Fukada, Novel method to estimate the solubility of small molecules in cis-polyisoprene by molecular dynamics simulations, J. Chem. Phys, 115, 13 (2001) [3] Lewis, Duckett, Ward, Fairclough, Ryan, The barrier properties of polyethylene terephthalate to mixtures of oxygen, carbon dioxide and nitrogen, Polymer, 1631, 44 (2003)

  15. An electrochemical sensor for determining elemental iodine in gas media

    SciTech Connect

    Goffman, V.G.; Shaimerdinov, B.U.; Kotelkin, I.M.

    1993-12-01

    The possibility of using solid-electrolyte Ag, AgI/AgI/Au cells as sensors for determining the concentration of elemental iodine in gas media is investigated. It is established that the sensor parameters are independent of oxygen content and radiation dose at different relative humidities.

  16. FITTING OF THE DATA FOR DIFFUSION COEFFICIENTS IN UNSATURATED POROUS MEDIA

    SciTech Connect

    B. Bullard

    1999-05-01

    The purpose of this calculation is to evaluate diffusion coefficients in unsaturated porous media for use in the TSPA-VA analyses. Using experimental data, regression techniques were used to curve fit the diffusion coefficient in unsaturated porous media as a function of volumetric water content. This calculation substantiates the model fit used in Total System Performance Assessment-1995 An Evaluation of the Potential Yucca Mountain Repository (TSPA-1995), Section 6.5.4.

  17. Bulk and surface controlled diffusion of fission gas atoms

    SciTech Connect

    Andersson, Anders D.

    2012-08-09

    Fission gas retention and release impact nuclear fuel performance by, e.g., causing fuel swelling leading to mechanical interaction with the clad, increasing the plenum pressure and reducing the gap thermal conductivity. All of these processes are important to understand in order to optimize operating conditions of nuclear reactors and to simulate accident scenarios. Most fission gases have low solubility in the fuel matrix, which is especially pronounced for large fission gas atoms such as Xe and Kr, and as a result there is a significant driving force for segregation of gas atoms to extended defects such as grain boundaries or dislocations and subsequently for nucleation of gas bubbles at these sinks. Several empirical or semi-empirical models have been developed for fission gas release in nuclear fuels, e.g. [1-6]. One of the most commonly used models in fuel performance codes was published by Massih and Forsberg [3,4,6]. This model is similar to the early Booth model [1] in that it applies an equivalent sphere to separate bulk UO{sub 2} from grain boundaries represented by the sphere circumference. Compared to the Booth model, it also captures trapping at grain boundaries, fission gas resolution and it describes release from the boundary by applying timedependent boundary conditions to the circumference. In this work we focus on the step where fission gas atoms diffuse from the grain interior to the grain boundaries. The original Massih-Forsberg model describes this process by applying an effective diffusivity divided into three temperature regimes. In this report we present results from density functional theory calculations (DFT) that are relevant for the high (D{sub 3}) and intermediate (D{sub 2}) temperature diffusivities of fission gases. The results are validated by making a quantitative comparison to Turnbull's [8-10] and Matzke's data [12]. For the intrinsic or high temperature regime we report activation energies for both Xe and Kr diffusion in UO

  18. Diffuse hot gas in nearby face-on spiral galaxies

    NASA Astrophysics Data System (ADS)

    Doane, Nathaniel

    2007-08-01

    We present a study of the diffuse thermal emission in three nearby, face-on spiral galaxies, NGC 3631, NGC 628 and NGC 3184, using X-ray data from the Chandra X-ray Observatory and optical data from the WIYN observatory. We are able to separate out the X-ray emission from unresolved point sources from the total unresolved emission in order to study the truly diffuse X-ray emission. We find that in all cases, the spectrum of the hot gas is well fit using a two thermal-component model. In the three galaxies, we find a strong correlation between the X-ray surface brightness and regions of star formation. We also estimate the electron density, pressure and cooling time of the hot gas, finding that the pressure of the hot gas in these three galaxies is higher than the ambient Milky Way pressure. In addition to the standard two temperature spectral model of the hot-gas emission from spiral galaxies, we show a model with the hot gas at a continuum of temperatures provides an equally good fit and a more physical description of the gas. Finally, we discuss the Chandra ACIS background and our method of spectrally modeling it. We also present plots of all our spectral fits to each galaxy and its sub-regions using our background model.

  19. Soft matter in hard confinement: phase transition thermodynamics, structure, texture, diffusion and flow in nanoporous media.

    PubMed

    Huber, Patrick

    2015-03-18

    Spatial confinement in nanoporous media affects the structure, thermodynamics and mobility of molecular soft matter often markedly. This article reviews thermodynamic equilibrium phenomena, such as physisorption, capillary condensation, crystallisation, self-diffusion, and structural phase transitions as well as selected aspects of the emerging field of spatially confined, non-equilibrium physics, i.e. the rheology of liquids, capillarity-driven flow phenomena, and imbibition front broadening in nanoporous materials. The observations in the nanoscale systems are related to the corresponding bulk phenomenologies. The complexity of the confined molecular species is varied from simple building blocks, like noble gas atoms, normal alkanes and alcohols to liquid crystals, polymers, ionic liquids, proteins and water. Mostly, experiments with mesoporous solids of alumina, gold, carbon, silica, and silicon with pore diameters ranging from a few up to 50 nm are presented. The observed peculiarities of nanopore-confined condensed matter are also discussed with regard to applications. A particular emphasis is put on texture formation upon crystallisation in nanoporous media, a topic both of high fundamental interest and of increasing nanotechnological importance, e.g. for the synthesis of organic/inorganic hybrid materials by melt infiltration, the usage of nanoporous solids in crystal nucleation or in template-assisted electrochemical deposition of nano structures.

  20. An empirical formula based on Monte Carlo simulation for diffuse reflectance from turbid media

    NASA Astrophysics Data System (ADS)

    Gnanatheepam, Einstein; Aruna, Prakasa Rao; Ganesan, Singaravelu

    2016-03-01

    Diffuse reflectance spectroscopy has been widely used in diagnostic oncology and characterization of laser irradiated tissue. However, still accurate and simple analytical equation does not exist for estimation of diffuse reflectance from turbid media. In this work, a diffuse reflectance lookup table for a range of tissue optical properties was generated using Monte Carlo simulation. Based on the generated Monte Carlo lookup table, an empirical formula for diffuse reflectance was developed using surface fitting method. The variance between the Monte Carlo lookup table surface and the surface obtained from the proposed empirical formula is less than 1%. The proposed empirical formula may be used for modeling of diffuse reflectance from tissue.

  1. Using a Quasipotential Transformation for Modeling Diffusion Media inPolymer-Electrolyte Fuel Cells

    SciTech Connect

    Weber, Adam Z.; Newman, John

    2008-08-29

    In this paper, a quasipotential approach along with conformal mapping is used to model the diffusion media of a polymer-electrolyte fuel cell. This method provides a series solution that is grid independent and only requires integration along a single boundary to solve the problem. The approach accounts for nonisothermal phenomena, two-phase flow, correct placement of the electronic potential boundary condition, and multilayer media. The method is applied to a cathode diffusion medium to explore the interplay between water and thermal management and performance, the impact of the rib-to-channel ratio, and the existence of diffusion under the rib and flooding phenomena.

  2. Method of making gas diffusion layers for electrochemical cells

    DOEpatents

    Frisk, Joseph William; Boand, Wayne Meredith; Larson, James Michael

    2002-01-01

    A method is provided for making a gas diffusion layer for an electrochemical cell comprising the steps of: a) combining carbon particles and one or more surfactants in a typically aqueous vehicle to make a preliminary composition, typically by high shear mixing; b) adding one or more highly fluorinated polymers to said preliminary composition by low shear mixing to make a coating composition; and c) applying the coating composition to an electrically conductive porous substrate, typically by a low shear coating method.

  3. Gas Diffusion Studies in Steady and Nonsteady Cavities

    DTIC Science & Technology

    1987-09-01

    gaseous diffusion, turbulent entrainment, cavitating flows, gas-liquid interface, two-dimensional flows, hydrofoil I Ioscillation 19 ABSTRACT...PAS Water tunnel experiments for twoidimensional f ows were co2ducted on cavities behind a stationary and oscillating -~flat plate’ (wedge) hydrofoil ...for two-dimensional flows were conducted on cavities behind a stationary and oscillating "flat plate" (wedge) hydrofoil . It is found that the steady

  4. Ion Diffusion Within Water Films in Unsaturated Porous Media.

    PubMed

    Tokunaga, Tetsu K; Finsterle, Stefan; Kim, Yongman; Wan, Jiamin; Lanzirotti, Antonio; Newville, Matthew

    2017-04-05

    Diffusion is important in controlling local solute transport and reactions in unsaturated soils and geologic formations. Although it is commonly assumed that thinning of water films controls solute diffusion at low water contents, transport under these conditions is not well understood. We conducted experiments in quartz sands at low volumetric water contents (θ) to quantify ion diffusion within adsorbed films. At the lowest water contents, we employed fixed relative humidities to control water films at nm thicknesses. Diffusion profiles for Rb(+) and Br(-) in unsaturated sand packs were measured with a synchrotron X-ray microprobe, and inverse modeling was used to determine effective diffusion coefficients, De, as low as ∼9 × 10(-15) m(2) s(-1) at θ = 1.0 × 10(-4) m(3) m(-3), where the film thickness = 0.9 nm. Given that the diffusion coefficients (Do) of Rb(+) and Br(-) in bulk water (30 °C) are both ∼2.4 × 10(-9) m(2) s(-1), we found the impedance factor f = De/(θDo) is equal to 0.03 ± 0.02 at this very low saturation, in agreement with the predicted influence of interface tortuosity (τa) for diffusion along grain surfaces. Thus, reduced cross-sectional area (θ) and tortuosity largely accounted for the more than 5 orders of magnitude decrease in De relative to Do as desaturation progressed down to nanoscale films.

  5. Modeling Intragranular Diffusion in Low-Connectivity Granular Media

    SciTech Connect

    Ewing, Robert G.; Liu, Chongxuan; Hu, Qinhong

    2012-03-20

    Diffusive exchange of solutes between bulk water in an aquifer and water in the intragranular pores of the solid phase remains confusing after decades of study. In a previous paper, we reviewed some of the explanations, and suggested that the disparities between observation and theory were largely due to low connectivity of the intragranular pores. Low connectivity indicates that a useful conceptual framework is percolation theory, which guided our analysis. The present study was initiated to improve the finite difference (FD) model presented in the previous paper, and to test that new model rigorously against new random walk (RW) simulations of diffusion in low-connectivity porous spheres starting from non-equilibrium. The new FD model calculates diffusion separately in the infinite cluster and the finite clusters, and closely matches the new, more complex RW results. The percolation-theory based description of the new model is fairly simple, and can readily be incorporated into existing FD models. The simulations showed that the combination of low intragranular pore connectivity, and out-diffusion initiated at diffusive non-equilibrium, can produce diffusive behavior that appears as if the solute had undergone slow sorption, even in the absence of any sorption process. This mechanism may help explain some hitherto confusing aspects of intragranular diffusion.

  6. Bounded fractional diffusion in geological media: Definition and Lagrangian approximation

    NASA Astrophysics Data System (ADS)

    Zhang, Yong; Green, Christopher T.; LaBolle, Eric M.; Neupauer, Roseanna M.; Sun, HongGuang

    2016-11-01

    Spatiotemporal fractional-derivative models (FDMs) have been increasingly used to simulate non-Fickian diffusion, but methods have not been available to define boundary conditions for FDMs in bounded domains. This study defines boundary conditions and then develops a Lagrangian solver to approximate bounded, one-dimensional fractional diffusion. Both the zero-value and nonzero-value Dirichlet, Neumann, and mixed Robin boundary conditions are defined, where the sign of Riemann-Liouville fractional derivative (capturing nonzero-value spatial-nonlocal boundary conditions with directional superdiffusion) remains consistent with the sign of the fractional-diffusive flux term in the FDMs. New Lagrangian schemes are then proposed to track solute particles moving in bounded domains, where the solutions are checked against analytical or Eulerian solutions available for simplified FDMs. Numerical experiments show that the particle-tracking algorithm for non-Fickian diffusion differs from Fickian diffusion in relocating the particle position around the reflective boundary, likely due to the nonlocal and nonsymmetric fractional diffusion. For a nonzero-value Neumann or Robin boundary, a source cell with a reflective face can be applied to define the release rate of random-walking particles at the specified flux boundary. Mathematical definitions of physically meaningful nonlocal boundaries combined with bounded Lagrangian solvers in this study may provide the only viable techniques at present to quantify the impact of boundaries on anomalous diffusion, expanding the applicability of FDMs from infinite domains to those with any size and boundary conditions.

  7. Surface Diffusion Effect on Gas Transport in Nanoporous Materials

    NASA Astrophysics Data System (ADS)

    Hori, Takuma; Yoshimoto, Yuta; Takagi, Shu; Kinefuchi, Ikuya

    2016-11-01

    Polymer electrolyte fuel cells are one of the promising candidates for power sources of electric vehicles. For further improvement of their efficiency in high current density operation, a better understanding of oxygen flow inside the cells, which have micro- or nanoporous structures, is necessary. Molecular simulations such as the direct simulation of Monte Carlo (DSMC) are necessary to elucidate flow phenomena in micro- or nanostructures since the Knudsen number is close to unity. Our previous report showed that the oxygen diffusion resistance in porous structures with a characteristic pore size of 100 nm calculated by DSMC agrees well with that measured experimentally. On the other hand, when it comes to the transport in structures with much smaller pore sizes, it is expected that the surface diffusion has a significant impact on gas transport because of their higher specific surface area. Here we present the calculation of gas transport in porous structures with considering surface diffusion. The numerical porous structure models utilized in our simulations are constructed from three-dimensional imaging of materials. The effect of the distance of random walk on the total diffusion resistance in the structures is discussed. This paper is based on results obtained from a project commissioned by the New Energy and Industrial Development Organization (NEDO).

  8. A Mathematical Model of Diffusion-Limited Gas Bubble Dynamics in Tissue with Varying Diffusion Region Thickness

    NASA Technical Reports Server (NTRS)

    Srinivasan, R. Srini; Gerth, Wayne A.; Powell, Michael R.; Paloski, William H. (Technical Monitor)

    2000-01-01

    A three-region mathematical model of gas bubble dynamics has been shown suitable for describing diffusion-limited dynamics of more than one bubble in a given volume of extravascular tissue. The model is based on the dynamics of gas exchange between a bubble and a well-stirred tissue region through an intervening unperfused diffusion region previously assumed to have constant thickness and uniform gas diffusivity. As a result, the gas content of the diffusion region remains constant as the volume of the region increases with bubble growth, causing dissolved gas in the region to violate Henry's law. Earlier work also neglected the relationship between the varying diffusion region volume and the fixed total tissue volume, because only cases in which the diffusion region volume is a small fraction of the overall tissue volume were considered. We herein extend the three-region model to correct these theoretical inconsistencies by allowing both the thickness and gas content of the diffusion region to vary during bubble evolution. A postulated difference in gas diffusivity between an infinitesimally thin layer at the bubble surface and the remainder of the diffusion region leads to variation in diffusion region gas content and thickness during bubble growth and resolution. This variable thickness, differential diffusivity (VTDD) model can yield bubble lifetimes considerably longer than those yielded by earlier three-region models for given model and decompression parameters, and meets a need for theoretically consistent but relatively simple bubble dynamics models for use in studies of decompression sickness (DCS) in human subjects, Keywords: decompression sickness, gas diffusion in tissue, diffusivity

  9. Nonclassical transport in fractal media with a diffusion barrier

    SciTech Connect

    Dvoretskaya, O. A. Kondratenko, P. S.

    2013-04-15

    We investigate the impurity transport in a randomly heterogeneous fractal medium with a diffusion barrier. The barrier is due to low permeable medium surrounding the source. The transport regimes and asymptotic (large-distance) concentration distributions are found. The presence of the diffusion barrier results in the retardation of the transport regimes at short times. As regards the asymptotic concentration distribution, the barrier influence persists for long times as well.

  10. Bounded fractional diffusion in geological media: Definition and Lagrangian approximation

    USGS Publications Warehouse

    Zhang, Yong; Green, Christopher T.; LaBolle, Eric M.; Neupauer, Roseanna M.; Sun, HongGuang

    2016-01-01

    Spatiotemporal Fractional-Derivative Models (FDMs) have been increasingly used to simulate non-Fickian diffusion, but methods have not been available to define boundary conditions for FDMs in bounded domains. This study defines boundary conditions and then develops a Lagrangian solver to approximate bounded, one-dimensional fractional diffusion. Both the zero-value and non-zero-value Dirichlet, Neumann, and mixed Robin boundary conditions are defined, where the sign of Riemann-Liouville fractional derivative (capturing non-zero-value spatial-nonlocal boundary conditions with directional super-diffusion) remains consistent with the sign of the fractional-diffusive flux term in the FDMs. New Lagrangian schemes are then proposed to track solute particles moving in bounded domains, where the solutions are checked against analytical or Eularian solutions available for simplified FDMs. Numerical experiments show that the particle-tracking algorithm for non-Fickian diffusion differs from Fickian diffusion in relocating the particle position around the reflective boundary, likely due to the non-local and non-symmetric fractional diffusion. For a non-zero-value Neumann or Robin boundary, a source cell with a reflective face can be applied to define the release rate of random-walking particles at the specified flux boundary. Mathematical definitions of physically meaningful nonlocal boundaries combined with bounded Lagrangian solvers in this study may provide the only viable techniques at present to quantify the impact of boundaries on anomalous diffusion, expanding the applicability of FDMs from infinite do mains to those with any size and boundary conditions.

  11. The contribution of diffusion to gas microflow: An experimental study

    NASA Astrophysics Data System (ADS)

    Veltzke, Thomas; Baune, Michael; Thöming, Jorg

    2012-08-01

    Moderately rarefied gas flows are clearly distinguished from viscous flow in the continuum regime and from molecular diffusion at high rarefaction. They are an intermediate of the two border cases referred to as slip flow and transition regime flow. Here, we present a new pencil-and-paper approach for modeling flows in these regimes by a superposition of convection and Fickian diffusion. It allows us to predict mass flows for helium, argon, nitrogen, and carbon dioxide in microducts with parallel walls and with slightly varying cross section. The model was validated by measurement series taken from literature and by own permeation experiments on tapered microchannels. Analytical investigation of the approach showed that the diffusive flow is proportional to the cross-sectional area at the channel entrance. Hence, the mass flow in a tapered channel is unequal in both directions when diffusion dominates due to increased rarefaction. In contrary to the common Maxwellian slip approach the superposition model describes the data reliably. From this we conclude that deviations from continuum behavior in the intermediate cannot be explained by slip flow at the walls and tangential momentum accommodation, but by Fickian diffusion. Now predictions are possible without any usage of fitted parameters such as the tangential momentum accommodation coefficient.

  12. Diffusive dynamics of nanoparticles in ultra-confined media

    DOE PAGES

    Jacob, Jack Deodato; Conrad, Jacinta; Krishnamoorti, Ramanan; ...

    2015-08-10

    Differential dynamic microscopy (DDM) was used to investigate the diffusive dynamics of nanoparticles of diameter 200 400 nm that were strongly confined in a periodic square array of cylindrical nanoposts. The minimum distance between posts was 1.3 5 times the diameter of the nanoparticles. The image structure functions obtained from the DDM analysis were isotropic and could be fit by a stretched exponential function. The relaxation time scaled diffusively across the range of wave vectors studied, and the corresponding scalar diffusivities decreased monotonically with increased confinement. The decrease in diffusivity could be described by models for hindered diffusion that accountedmore » for steric restrictions and hydrodynamic interactions. The stretching exponent decreased linearly as the nanoparticles were increasingly confined by the posts. Altogether, these results are consistent with a picture in which strongly confined nanoparticles experience a heterogeneous spatial environment arising from hydrodynamics and volume exclusion on time scales comparable to cage escape, leading to multiple relaxation processes and Fickian but non-Gaussian diffusive dynamics.« less

  13. Diffusive dynamics of nanoparticles in ultra-confined media

    SciTech Connect

    Jacob, Jack Deodato; Conrad, Jacinta; Krishnamoorti, Ramanan; Retterer, Scott T.; He, Kai

    2015-08-10

    Differential dynamic microscopy (DDM) was used to investigate the diffusive dynamics of nanoparticles of diameter 200 400 nm that were strongly confined in a periodic square array of cylindrical nanoposts. The minimum distance between posts was 1.3 5 times the diameter of the nanoparticles. The image structure functions obtained from the DDM analysis were isotropic and could be fit by a stretched exponential function. The relaxation time scaled diffusively across the range of wave vectors studied, and the corresponding scalar diffusivities decreased monotonically with increased confinement. The decrease in diffusivity could be described by models for hindered diffusion that accounted for steric restrictions and hydrodynamic interactions. The stretching exponent decreased linearly as the nanoparticles were increasingly confined by the posts. Altogether, these results are consistent with a picture in which strongly confined nanoparticles experience a heterogeneous spatial environment arising from hydrodynamics and volume exclusion on time scales comparable to cage escape, leading to multiple relaxation processes and Fickian but non-Gaussian diffusive dynamics.

  14. Correlation between information diffusion and opinion evolution on social media

    NASA Astrophysics Data System (ADS)

    Xiong, Fei; Liu, Yun; Zhang, Zhenjiang

    2014-12-01

    Information diffusion and opinion evolution are often treated as two independent processes. Opinion models assume the topic reaches each agent and agents initially have their own ideas. In fact, the processes of information diffusion and opinion evolution often intertwine with each other. Whether the influence between these two processes plays a role in the system state is unclear. In this paper, we collected more than one million real data from a well-known social platform, and analysed large-scale user diffusion behaviour and opinion formation. We found that user inter-event time follows a two-scaling power-law distribution with two different power exponents. Public opinion stabilizes quickly and evolves toward the direction of convergence, but the consensus state is prevented by a few opponents. We propose a three-state opinion model accompanied by information diffusion. Agents form and exchange their opinions during information diffusion. Conversely, agents' opinions also influence their diffusion actions. Simulations show that the model with a correlation of the two processes produces similar statistical characteristics as empirical results. A fast epidemic process drives individual opinions to converge more obviously. Unlike previous epidemic models, the number of infected agents does not always increase with the update rate, but has a peak with an intermediate value of the rate.

  15. Time-resolved measurements of the optical properties of fibrous media using the anisotropic diffusion equation

    NASA Astrophysics Data System (ADS)

    Simon, Emanuel; Krauter, Philipp; Kienle, Alwin

    2014-07-01

    Transmittance and reflectance from spruce wood and bovine ligamentum nuchae as two different fibrous media are examined by time-of-flight spectroscopy for varying source detector separations and several orientations of the fibers in the sample. The anisotropic diffusion theory is used to obtain the absorption coefficient and the diffusion coefficients parallel and perpendicular to the fibers. The results are compared to those obtained with the isotropic diffusion theory. It is shown that for increasing source detector separations, the retrieved optical properties change as expected from Monte Carlo simulations performed in a previous study. This confirms that the anisotropic diffusion theory yields useful results for certain experimental conditions.

  16. Hybrid diffusion-P3 equation in N-layered turbid media: steady-state domain.

    PubMed

    Shi, Zhenzhi; Zhao, Huijuan; Xu, Kexin

    2011-10-01

    This paper discusses light propagation in N-layered turbid media. The hybrid diffusion-P3 equation is solved for an N-layered finite or infinite turbid medium in the steady-state domain for one point source using the extrapolated boundary condition. The Fourier transform formalism is applied to derive the analytical solutions of the fluence rate in Fourier space. Two inverse Fourier transform methods are developed to calculate the fluence rate in real space. In addition, the solutions of the hybrid diffusion-P3 equation are compared to the solutions of the diffusion equation and the Monte Carlo simulation. For the case of small absorption coefficients, the solutions of the N-layered diffusion equation and hybrid diffusion-P3 equation are almost equivalent and are in agreement with the Monte Carlo simulation. For the case of large absorption coefficients, the model of the hybrid diffusion-P3 equation is more precise than that of the diffusion equation. In conclusion, the model of the hybrid diffusion-P3 equation can replace the diffusion equation for modeling light propagation in the N-layered turbid media for a wide range of absorption coefficients.

  17. Verification of the integrity of barriers using gas diffusion

    SciTech Connect

    Ward, D.B.; Williams, C.V.

    1997-06-01

    In-situ barrier materials and designs are being developed for containment of high risk contamination as an alternative to immediate removal or remediation. The intent of these designs is to prevent the movement of contaminants in either the liquid or vapor phase by long-term containment, essentially buying time until the contaminant depletes naturally or a remediation can be implemented. The integrity of the resultant soil-binder mixture is typically assessed by a number of destructive laboratory tests (leaching, compressive strength, mechanical stability with respect to wetting and freeze-thaw cycles) which as a group are used to infer the likelihood of favorable long-term performance of the barrier. The need exists for a minimally intrusive yet quantifiable methods for assessment of a barrier`s integrity after emplacement, and monitoring of the barrier`s performance over its lifetime. Here, the authors evaluate non-destructive measurements of inert-gas diffusion (specifically, SF{sub 6}) as an indicator of waste-form integrity. The goals of this project are to show that diffusivity can be measured in core samples of soil jet-grouted with Portland cement, validate the experimental method through measurements on samples, and to calculate aqueous diffusivities from a series of diffusion measurements. This study shows that it is practical to measure SF{sub 6} diffusion rates in the laboratory on samples of grout (Portland cement and soil) typical of what might be used in a barrier. Diffusion of SF{sub 6} through grout (Portland cement and soil) is at least an order of magnitude slower than through air. The use of this tracer should be sensitive to the presence of fractures, voids, or other discontinuities in the grout/soil structure. Field-scale measurements should be practical on time-scales of a few days.

  18. A comparison of Fick and Maxwell-Stefan diffusion formulations in PEMFC gas diffusion layers

    NASA Astrophysics Data System (ADS)

    Lindstrom, Michael; Wetton, Brian

    2017-01-01

    This paper explores the mathematical formulations of Fick and Maxwell-Stefan diffusion in the context of polymer electrolyte membrane fuel cell cathode gas diffusion layers. The simple Fick law with a diagonal diffusion matrix is an approximation of Maxwell-Stefan. Formulations of diffusion combined with mass-averaged Darcy flow are considered for three component gases. For this application, the formulations can be compared computationally in a simple, one dimensional setting. Despite the models' seemingly different structure, it is observed that the predictions of the formulations are very similar on the cathode when air is used as oxidant. The two formulations give quite different results when the Nitrogen in the air oxidant is replaced by helium (this is often done as a diagnostic for fuel cells designs). The two formulations also give quite different results for the anode with a dilute Hydrogen stream. These results give direction to when Maxwell-Stefan diffusion, which is more complicated to implement computationally in many codes, should be used in fuel cell simulations.

  19. Slurried solid media for simultaneous water purification and carbon dioxide removal from gas mixtures

    DOEpatents

    Aines, Roger D.; Bourcier, William L.; Viani, Brian

    2013-01-29

    A slurried solid media for simultaneous water purification and carbon dioxide removal from gas mixtures includes the steps of dissolving the gas mixture and carbon dioxide in water providing a gas, carbon dioxide, water mixture; adding a porous solid media to the gas, carbon dioxide, water mixture forming a slurry of gas, carbon dioxide, water, and porous solid media; heating the slurry of gas, carbon dioxide, water, and porous solid media producing steam; and cooling the steam to produce purified water and carbon dioxide.

  20. Modeling intragranular diffusion in low-connectivity granular media

    NASA Astrophysics Data System (ADS)

    Ewing, Robert P.; Liu, Chongxuan; Hu, Qinhong

    2012-03-01

    Characterizing the diffusive exchange of solutes between bulk water in an aquifer and water in the intragranular pores of the solid phase is still challenging despite decades of study. Many disparities between observation and theory could be attributed to low connectivity of the intragranular pores. The presence of low connectivity indicates that a useful conceptual framework is percolation theory. The present study was initiated to develop a percolation-based finite difference (FD) model, and to test it rigorously against both random walk (RW) simulations of diffusion starting from nonequilibrium, and data on Borden sand published by Ball and Roberts (1991a,b) and subsequently reanalyzed by Haggerty and Gorelick (1995) using a multirate mass transfer (MRMT) approach. The percolation-theoretical model is simple and readily incorporated into existing FD models. The FD model closely matches the RW results using only a single fitting parameter, across a wide range of pore connectivities. Simulation of the Borden sand experiment without pore connectivity effects reproduced the MRMT analysis, but including low pore connectivity effects improved the fit. Overall, the theory and simulation results show that low intragranular pore connectivity can produce diffusive behavior that appears as if the solute had undergone slow sorption, despite the absence of any sorption process, thereby explaining some hitherto confusing aspects of intragranular diffusion.

  1. Digital volume imaging of the PEFC gas diffusion layer

    SciTech Connect

    Borup, Rodney L; Mukundan, Rangachary; Mukherjee, Partha; Shim, Eunkyoung

    2010-01-01

    The gas diffusion layer (GDL) plays a key role in the overall performance/durability of a polymer electrolyte fuel cell (PEFC). Of profound importance, especially in the context of water management and flooding phenomena, is the influence of the underlying pore morphology and wetting characteristics Of the GDL microstructure. In this article, we present the digital volumetric imaging (DVI) technique in order to generate the 3-D carbon paper GDL microstructure. The internal pore structure and the local microstructural variations in terms of fiber alignment and fiber/binder distributions are investigated using the several 3-D thin sections of the sample obtained from DVI.

  2. Properties of turbulence in natural gas-oxygen diffusion flames

    SciTech Connect

    Sautet, J.C.; Ditaranto, M. ); Samaniego, J.M.; Charon, O. )

    1999-07-01

    Measurements of turbulent flow field velocities, including first and second order velocity moments and the shear stress are carried out by laser Doppler velocimetry in five different, 25 kW, turbulent natural gas-oxygen diffusion flames. The mean flow behavior is described including the velocity half value radius as well as centerline velocity. Mean radial velocity profiles are fitted by a Gaussian function. According to the initial momentum ratio, different jet dynamic behaviors are pointed out by the description of the fluctuating velocity field.

  3. Gas transport in unsaturated porous media: The adequacy of Fick's law

    NASA Astrophysics Data System (ADS)

    Thorstenson, D. C.; Pollock, D. W.

    1989-02-01

    The increasing use of natural unsaturated zones as repositories for landfills and disposal sites for hazardous wastes (chemical and radioactive) requires a greater understanding of transport processes in the unsaturated zone. For volatile constituents an important potential transport mechanism is gaseous diffusion. Diffusion, however, cannot be treated as an independent isolated transport mechanism. A complete understanding of multicomponent gas transport in porous media (unsaturated zones) requires a knowledge of Knudsen transport, the molecular and nonequimolar components of diffusive flux, and viscous (pressure driven) flux. The constitutive equations relating these flux components are available from the "dusty gas" model of Mason et al. (1967). This review presents a brief discussion of the underlying principles and interrelationships among each of the above flux mechanisms. Some aspects of these transport mechanisms are, to our knowledge, generally unrecognized in the Earth science literature. The principles underlying the transport mechanisms are illustrated with binary systems; the constitutive equations are then cast in forms thought to be most useful for the study of natural unsaturated zones. The viscous and diffusive fluxes are coupled in the constitutive equations through the Knudsen diffusivities; a knowledge of Knudsen diffusivities is necessary to calculate the viscous component of flux and pressure gradients. The Knudsen diffusivities can be calculated from measurements of the Klinkenberg effect. Two examples are presented showing that in natural systems, very small pressure gradients (1 Pa/m or less) can produce viscous fluxes greater than or equal to diffusive fluxes and that, conversely, pressure gradients of this magnitude can be generated by diffusive processes. The example calculations show that major concentration gradients can be developed for stagnant (zero flux, nonreactive) gases. A method is presented for approximating the viscous and

  4. An Ohm's law analogy for the effective diffusivity of composite media

    NASA Astrophysics Data System (ADS)

    Alvarez-Ramirez, J.; Valdes-Parada, F. J.; Ibarra-Valdez, C.

    2016-04-01

    The aim of this work is to obtain an equation for the effective diffusivity of permeable composite media based on an analogy with Ohm's law of electricity. Here, particles are transported across a composite medium, which is seen as an arrangement of series and parallel resistances. Comparison with simulations of Brownian particles traveling through the successive walls of the medium showed good agreement for moderate inclusion-to-continuous medium diffusivity ratio.

  5. FAST Mapping of Diffuse HI Gas in the Local Universe

    NASA Astrophysics Data System (ADS)

    Zhu, M.; Pisano, D. J.; Ai, M.; Jiao, Q.

    2016-02-01

    We propose to use the Five hundred meter Aperture Spherical radio Telescope (FAST) to map the diffuse intergalactic HI gas in the local universe at column densities of NHI=1018 cm-2 and below. The major science goal is to study gas accretion during galaxy evolution, and trace cosmic web features in the local universe. We disuss the technical feasibilty of such a deep survey, and have conducted test observations with the Arecibo 305 m telescope. Our preliminary results shows that, with about a few thousand hours of observing time, FAST will be able to map several hundred square degree regions at 1 σ of NHI=2×1017 cm-2 level out to a distance of 5-10 Mpc, and with a volume 1000 larger than that of the Local Group.

  6. Liquid water transport characteristics of porous diffusion media in polymer electrolyte membrane fuel cells: A review

    NASA Astrophysics Data System (ADS)

    Liu, Xunliang; Peng, Fangyuan; Lou, Guofeng; Wen, Zhi

    2015-12-01

    Fundamental understanding of liquid water transport in gas diffusion media (GDM) is important to improve the material and structure design of polymer electrolyte membrane (PEM) fuel cells. Continuum methods of two-phase flow modeling facilitate to give more details of relevant information. The proper empirical correlations of liquid water transport properties, such as capillary characteristics, water relative permeability and effective contact angle, are crucial to two phase flow modeling and cell performance prediction. In this work, researches on these properties in the last decade are reviewed. Various efforts have been devoted to determine the water transport properties for GDMs. However, most of the experimental studies are ex-situ measurements. In-situ measurements for GDMs and extending techniques available to study the catalyst layer and the microporous layer will be further challenges. Using the Leverett-Udell correlation is not recommended for quantitative modeling. The reliable Leverett-type correlation for GDMs, with the inclusion of the cosine of effective contact angle, is desirable but hard to be established for modeling two-phase flow in GDMs. A comprehensive data set of liquid water transport properties is needed for various GDM materials under different PEM fuel cell operating conditions.

  7. Measuring adsorption, diffusion and flow in chemical engineering: applications of magnetic resonance to porous media

    NASA Astrophysics Data System (ADS)

    Gladden, Lynn F.; Mitchell, Jonathan

    2011-03-01

    Magnetic resonance (MR) techniques are increasingly used to improve our understanding of the multi-component, multi-phase processes encountered in chemical engineering. This review brings together many of the MR techniques used, and often developed specifically, to study chemical engineering systems and, in particular, processes occurring within porous media. Pulse sequences for relaxometry, pulsed field gradient measurements of diffusion, imaging and velocimetry measurements are described. Recent applications of these MR pulse sequences to microporous, mesoporous and macroporous structures are then reviewed. Considering the microporous and mesoporous systems, we focus attention on studies of rock cores, manufactured materials such as cement and gypsum plaster, and catalysts. When considering macroporous structures, the transport through packed beds of particles typical of fixed-bed catalytic reactors is reviewed; a brief overview of the increasing research interest in gas-solid fluidized beds is also presented. We highlight the field of sparse k-space sampling as an area that is in its infancy and suggest that, combined with Bayesian methods, it will offer new opportunities in both extending the application of high-field MR techniques to chemical engineering and increasing the range of measurements that can be carried out using low-field hardware.

  8. Variations between Dust and Gas in the Diffuse Interstellar Medium. II. Search for Cold Gas

    NASA Astrophysics Data System (ADS)

    Reach, William T.; Heiles, Carl; Bernard, Jean-Philippe

    2017-01-01

    The content of interstellar clouds, in particular the inventory of diffuse molecular gas, remains uncertain. We identified a sample of isolated clouds, approximately 100 M⊙ in size, and used the dust content to estimate the total amount of gas. In Paper I, the total inferred gas content was found significantly larger than that seen in 21 cm emission measurements of H i. In this paper we test the hypothesis that the apparent excess “dark” gas is cold H i, which would be evident in absorption but not in emission due to line saturation. The results show that there is not enough 21 cm absorption toward the clouds to explain the total amount of “dark” gas.

  9. Diffuse-Interface Modelling of Flow in Porous Media

    NASA Astrophysics Data System (ADS)

    Addy, Doug; Pradas, Marc; Schmuck, Marcus; Kalliadasis, Serafim

    2016-11-01

    Multiphase flows are ubiquitous in a wide spectrum of scientific and engineering applications, and their computational modelling often poses many challenges associated with the presence of free boundaries and interfaces. Interfacial flows in porous media encounter additional challenges and complexities due to their inherently multiscale behaviour. Here we investigate the dynamics of interfaces in porous media using an effective convective Cahn-Hilliard (CH) equation recently developed in from a Stokes-CH equation for microscopic heterogeneous domains by means of a homogenization methodology, where the microscopic details are taken into account as effective tensor coefficients which are given by a Poisson equation. The equations are decoupled under appropriate assumptions and solved in series using a classic finite-element formulation with the open-source software FEniCS. We investigate the effects of different microscopic geometries, including periodic and non-periodic, at the bulk fluid flow, and find that our model is able to describe the effective macroscopic behaviour without the need to resolve the microscopic details.

  10. Quenched Large Deviations for Interacting Diffusions in Random Media

    NASA Astrophysics Data System (ADS)

    Luçon, Eric

    2017-03-01

    The aim of the paper is to establish a large deviation principle (LDP) for the empirical measure of mean-field interacting diffusions in a random environment. The point is to derive such a result once the environment has been frozen (quenched model). The main theorem states that a LDP holds for every sequence of environment satisfying appropriate convergence condition, with a rate function that does not depend on the disorder and is different from the rate function in the averaged model. Similar results concerning the empirical flow and local empirical measures are provided.

  11. Innovative discharge geometries for diffusion-cooled gas lasers

    NASA Astrophysics Data System (ADS)

    Lapucci, Antonio

    2004-09-01

    Large area, narrow discharge gap, diffusion cooled gas lasers are nowadays a well established technology for the construction of industrial laser sources. Successful examples exist both with the slab (Rofin-Sinar) or coaxial (Trumpf) geometry. The main physical properties and the associated technical problems of the transverse large area RF discharge, adopted for the excitation of high power diffusion cooled gas lasers, are reviewed here. The main problems of this technology are related to the maintenance of a uniform and stable plasma excitation between closely spaced large-area electrodes at high power-density loading. Some practical solutions such as distributed resonance of the discharge channel proved successful in the case of square or rectangular cross-sections but hardly applicable to geometries such as that of coaxial electrodes. In this paper we present some solutions, adopted by our group, for the development of slab and annular CO2 lasers and for CO2 laser arrays with linear or circular symmetry. We will also briefly mention the difficulties encountered in the extraction of a good quality beam from an active medium with such a cross section. A problem that has also seen some interesting solutions.

  12. Effects of buoyancy on gas jet diffusion flames

    NASA Technical Reports Server (NTRS)

    Bahadori, M. Yousef; Edelman, Raymond B.

    1993-01-01

    The objective of this effort was to gain a better understanding of the fundamental phenomena involved in laminar gas jet diffusion flames in the absence of buoyancy by studying the transient phenomena of ignition and flame development, (quasi-) steady-state flame characteristics, soot effects, radiation, and, if any, extinction phenomena. This involved measurements of flame size and development, as well as temperature and radiation. Additionally, flame behavior, color, and luminosity were observed and recorded. The tests quantified the effects of Reynolds number, nozzle size, fuel reactivity and type, oxygen concentration, and pressure on flame characteristics. Analytical and numerical modeling efforts were also performed. Methane and propane flames were studied in the 2.2 Second Drop Tower and the 5.18-Second Zero-Gravity Facility of NASA LeRC. In addition, a preliminary series of tests were conducted in the KC-135 research aircraft. Both micro-gravity and normal-gravity flames were studied in this program. The results have provided unique and new information on the behavior and characteristics of gas jet diffusion flames in micro-gravity environments.

  13. Radiation from Gas-Jet Diffusion Flames in Microgravity Environments

    NASA Technical Reports Server (NTRS)

    Bahadori, M. Yousef; Edelman, Raymond B.; Sotos, Raymond G.; Stocker, Dennis P.

    1991-01-01

    This paper presents the first demonstration of quantitative flame-radiation measurement in microgravity environments, with the objective of studying the influences and characteristics of radiative transfer on the behavior of gas-jet diffusion flames with possible application to spacecraft fire detection. Laminar diffusion flames of propane, burning in quiescent air at atmospheric pressure, are studied in the 5.18-Second Zero-Gravity Facility of NASA Lewis Research Center. Radiation from these flames is measured using a wide-view angle, thermopile-detector radiometer, and comparisons are made with normal-gravity flames. The results show that the radiation level is significantly higher in microgravity compared to normal-gravity environments due to larger flame size, enhanced soot formation, and entrapment of combustion products in the vicinity of the flame. These effects are the consequences of the removal of buoyancy which makes diffusion the dominant mechanism of transport. The results show that longer test times may be needed to reach steady state in microgravity environments.

  14. Frequency behavior of coherent random lasing in diffusive resonant media

    NASA Astrophysics Data System (ADS)

    Tiwari, Anjani Kumar; Uppu, Ravitej; Mujumdar, Sushil

    2012-10-01

    We investigate diffusive propagation of light and consequent random lasing in an amplifying medium comprising resonant spherical scatterers. A Monte-Carlo calculation based on photon propagation via three-dimensional random walks is employed to obtain the dwell-times of light in the system. We compare the inter-scatterer and intra-scatterer dwell-times for representative resonant and non-resonant wavelengths. Our results show that more efficient random lasing, with intense coherent modes, is obtained for a system with intra-scatterer gain. This is also coupled with a larger reduction in frequency fluctuations. We find that such a system can yield almost thresholdless random lasing. Inspired by these results, we discuss a possible practical situation, based on a monodisperse aerosol, wherein frequency controlled coherent random lasing can be obtained. Since our analysis essentially investigates transport of intensity, the results are relevant to coherent random lasers under nonresonant feedback.

  15. Predicting release and transport of pesticides from a granular formulation during unsaturated diffusion in porous media

    NASA Astrophysics Data System (ADS)

    Paradelo, Marcos; Soto-Gómez, Diego; Pérez-Rodríguez, Paula; Pose-Juan, Eva; López-Periago, J. Eugenio

    2014-03-01

    The release and transport of active ingredients (AIs) from controlled-release formulations (CRFs) have potential to reduce groundwater pesticide pollution. These formulations have a major effect on the release rate and subsequent transport to groundwater. Therefore the influence of CRFs should be included in modeling non-point source pollution by pesticides. We propose a simplified approach that uses a phase transition equation coupled to the diffusion equation that describes the release rate of AIs from commercial CRFs in porous media; the parameters are as follows: a release coefficient, the solubility of the AI, and diffusion transport with decay. The model gives acceptable predictions of the pesticides release from commercial CRFs in diffusion cells filled with quartz sand. This approach can be used to study the dynamics of the CRF-porous media interaction. It also could be implemented in fate of agricultural chemical models to include the effect of CRFs.

  16. Glitters of warm H2 in cold diffuse molecular gas

    NASA Astrophysics Data System (ADS)

    Falgarone, Edith; Boulanger, Francois; Combes, Francoise; Pineau Des Forets, Guillaume; Verstraete, Laurent

    2007-05-01

    Cold molecular hydrogen, a dominant gas fraction in galaxies, does not radiate due to the symmetry of the molecule. The only tracers of cold H2, the rotational lines of CO and dust thermal emission operate only in metal-rich environments. By detecting the lowest rotational lines of H2 at unexpected levels in the cold diffuse medium of the Galaxy, ISO-SWS has challenged the traditional view of the interstellar medium (ISM) by possibly revealing the existence of tiny gas fractions within the cold ISM, warm enough to excite H2 lines. The heating source of H2 there is the intermittent dissipation of supersonic turbulence, pervading the entire ISM. These glitters of H2 line emission may become the unique tracers of cold H2 in low metallicity environments. Given the fundamental importance of probing large hidden masses of gas in galaxies, for their implication on galaxy dynamics, star formation thresholds in metal-poor environments, and the hypothesis of H2 as baryonic dark matter in galaxies, the present SST/IRS proposal is dedicated to further search of this still elusive emission. The proposed observations consist in several IRS LL pointings along the major axis of two external galaxies with massive HI disks extending far beyond their optical radius, and for which the HI rotation curve cannot be accounted for by the stellar and visible gas components. These spectra also observed in the direction of the galaxy nuclei, are meant to allow the separation between the H2 emission with stellar-type excitation from that originating in gas heated by turbulence dissipation. The goal of the proposal is to strenghten the existence of pockets of warm H2 disseminated in the cold diffuse medium of galaxies. These glitters of warm H2 would be a new tracer of hitherto undetected amounts of cold H2 in low metallicity environments, and, as a more exploratory facet, might probe the presence of large amounts of baryonic dark matter in galaxies in the form of cold molecular hydrogen.

  17. A new model for thermal contact resistance between fuel cell gas diffusion layers and bipolar plates

    NASA Astrophysics Data System (ADS)

    Sadeghifar, Hamidreza; Djilali, Ned; Bahrami, Majid

    2014-11-01

    A new analytical model is developed to predict the thermal contact resistance (TCR) between fibrous porous media such as gas diffusion layers (GDLs) of polymer electrolyte membrane fuel cells (PEMFCs) and flat surfaces (bipolar plates). This robust model accounts for the salient geometrical parameters of GDLs, mechanical deformation, and thermophysical properties of the contacting bodies. The model is successfully validated against experimental data, and is used to perform in a comprehensive parametric study to investigate the effects of fiber parameters such as waviness and GDL properties on the TCR. Fiber waviness, diameter and surface curvature, as well as GDL porosity, are found to have a strong influence on TCR whereas fiber length does not affect the TCR when the porosity is kept constant. Such findings provide useful guidance for design and manufacturing of more effective GDLs for PEMFC heat management. The analytic model can be readily implemented in simulation and modeling of PEMFCs, and can be extended with minor modifications to other fibrous porous media such as fibrous catalysts, insulating media and sintered metals.

  18. Survival probability and order statistics of diffusion on disordered media.

    PubMed

    Acedo, L; Yuste, S B

    2002-07-01

    We investigate the first passage time t(j,N) to a given chemical or Euclidean distance of the first j of a set of N>1 independent random walkers all initially placed on a site of a disordered medium. To solve this order-statistics problem we assume that, for short times, the survival probability (the probability that a single random walker is not absorbed by a hyperspherical surface during some time interval) decays for disordered media in the same way as for Euclidean and some class of deterministic fractal lattices. This conjecture is checked by simulation on the incipient percolation aggregate embedded in two dimensions. Arbitrary moments of t(j,N) are expressed in terms of an asymptotic series in powers of 1/ln N, which is formally identical to those found for Euclidean and (some class of) deterministic fractal lattices. The agreement of the asymptotic expressions with simulation results for the two-dimensional percolation aggregate is good when the boundary is defined in terms of the chemical distance. The agreement worsens slightly when the Euclidean distance is used.

  19. The impact of thermal conductivity and diffusion rates on water vapor transport through gas diffusion layers

    NASA Astrophysics Data System (ADS)

    Burlatsky, Sergei F.; Atrazhev, Vadim V.; Gummalla, Mallika; Condit, Dave A.; Liu, Fuqiang

    Proper water management in a hydrogen-fueled polymer electrolyte membrane (PEM) fuel cell is critical for performance and durability. A mathematical model has been developed to elucidate the effect of thermal conductivity and water vapor diffusion coefficient in the gas diffusion layers (GDLs). The fraction of product water removed in the vapor phase through the GDL as a function of GDL properties/set of material and component parameters and operating conditions has been calculated. The current model enables identification of conditions wherein condensation occurs in each GDL component. The model predicts the temperature gradient across various components of a PEM fuel cell, providing insight into the overall mechanism of water transport in a given cell design. The water condensation conditions and transport mode in the GDL components depend on the combination of water vapor diffusion coefficients and thermal conductivities of the GDL components. Different types of GDLs and water transport scenarios are defined in this work, based on water condensation in the GDL and fraction of water that the GDL removes through the vapor phase, respectively.

  20. Effect of pore structure on gas trapping in porous media

    NASA Astrophysics Data System (ADS)

    Mohammadian, Sadjad; Geistlinger, Helmut; Vogel, Hans-Jörg

    2014-05-01

    Capillary trapping of nonwetting phase in porous media plays an important role in many geological processes. For example, large portions of hydrocarbons cannot be extracted from reservoirs due to capillary forces, while in carbon sequestration processes; capillary trapping might improve the storage efficiency. An important case is when the wetting phase (mostly water) displaces a low-viscosity low-density fluid. In such cases, like water encroachment into gas reservoirs or rising of water table in soils, competition of gravity, viscous, and capillary forces determines the final configuration of the fluids in invaded zone. The trapped nonwetting phase and its distribution within the porous media will affect many other processes such as flow of the other fluids and mass transfer phenomena. Thus, investigating the parameters affecting phase trapping and distribution, especially their relation to pore structure, which controls the capillary action, is required. The aim is to predict gas trapping from structural properties of the material. We conducted a series of column experiments, in which water displaces air at a range of flow rates in different glass-bead packs. The final 3D configuration and morphology of fluids was observed using X-Ray Computed Tomography (CT). We extracted 3D structure of porous media as well as of the trapped gas phase, and quantified them in terms of volume ratios, interfacial area, and morphology. Then we investigated the relations of the trapped phase to capillary forces (pore structure) and viscous forces (front velocity). The results give us new insights to explore the flow and dissolution processes: We found no systematic dependency of the front velocity of the invading water phase in the velocity range from 0.1 to 0.6 cm/min what corresponds to capillary numbers from 2 to 12 ×10^-6. Our experimental results indicate that the capillary trapping mechanism is controlled by the local pore structure and local connectivity and not by

  1. Analysis of porous media heterogeneities using the diffusion of pressure waves

    NASA Astrophysics Data System (ADS)

    Rigord, P.; Caristan, Y.; Hulin, J. P.

    1993-06-01

    We present an experimental study and a model of the diffusion of sinusoidal pressure waves through porous media. We show that measurements of the hydraulic admittance A(omega) in the sine wave mode allow us to probe the structure of porous samples with an adjustable investigation depth depending on the frequency omega. The variations of A(omega) in heterogeneous media with a percolationlike geometry are modeled numerically on 2D percolation networks. One obtains a transition from normal diffusion at low frequencies to anomalous diffusion at higher frequencies. At the transition, the penetration depth of the wave is of the order of the percolation correlation length. The hydraulic admittance and transmittance of 20 percent porosity pressed calcite have been investigated experimentally with sine wave excitations at pulsations omega between 2 x 10 exp -4 and 0.42 rad/s. Both the modulus and the phase of the complex admittance A(omega) display normal diffusive variations as omega increases. Increasing the viscosity reduces the frequency above which the diffusive behavior is observed. The measured diffusion coefficient is 25 percent higher than that computed from permeability and compressibility values measured independently; this difference may be associated with nonconnected porosity.

  2. Diffusion of colloidal fluids in random porous media.

    PubMed

    Chávez-Rojo, M A; Juárez-Maldonado, R; Medina-Noyola, M

    2008-04-01

    The diffusive relaxation of a colloidal fluid adsorbed in a porous medium depends on many factors, including the concentration and composition of the adsorbed colloidal fluid, the average structure of the porous matrix, and the nature of the colloid-colloid and colloid-substrate interactions. A simple manner to describe these effects is to model the porous medium as a set of spherical particles fixed in space at random positions with prescribed statistical structural properties. Within this model one may describe the relaxation of concentration fluctuations of the adsorbed fluid by simply setting to zero the short-time mobility of one species (the porous matrix) in a theory of the dynamics of equilibrium colloidal mixtures, or by extending such dynamic theory to explicitly consider the porous matrix as a random external field, as recently done in the framework of mode coupling theory [V. Krakoviack, Phys. Rev. Lett. 94, 065703 (2005)]. Here we consider the first approach and employ the self-consistent generalized Langevin equation (SCGLE) theory of the dynamics of equilibrium colloidal mixtures, to describe the dynamics of the mobile component. We focus on the short- and intermediate-time regimes, which we compare with Brownian dynamics simulations involving a binary mixture with screened Coulomb interactions for two models of the average static structure of the matrix: a porous matrix constructed by quenching configurations of an equilibrium mixture in which both species were first equilibrated together, and a preexisting matrix with prescribed average structure, in which we later add the mobile species. We conclude that in both cases, if the correct static structure factors are provided as input, the SCGLE theory correctly predicts the main features of the dynamics of the permeating fluid.

  3. Gas depletion through single gas bubble diffusive growth and its effect on subsequent bubbles

    NASA Astrophysics Data System (ADS)

    Moreno Soto, Alvaro; Prosperetti, Andrea; Lohse, Detlef; van der Meer, Devaraj; Physics of Fluid Group Collaboration; MCEC Netherlands CenterMultiscale Catalytic Energy Conversion Collaboration

    2016-11-01

    In weakly supersaturated mixtures, bubbles are known to grow quasi-statically as diffusion-driven mass transfer governs the process. In the final stage of the evolution, before detachment, there is an enhancement of mass transfer, which changes from diffusion to natural convection. Once the bubble detaches, it leaves behind a gas-depleted area. The diffusive mass transfer towards that region cannot compensate for the amount of gas which is taken away by the bubble. Consequently, the consecutive bubble will grow in an environment which contains less gas than for the previous one. This reduces the local supersaturation of the mixture around the nucleation site, leading to a reduced bubble growth rate. We present quantitative experimental data on this effect and the theoretical model for depletion during the bubble growth rate. This work was supported by the Netherlands Center for Multiscale Catalytic Energy Conversion (MCEC), an NWO Gravitation programme funded by the Ministry of Education, Culture and Science of the government of the Netherlands.

  4. Diffusion of high-frequency energy in fluid-saturated porous media

    NASA Astrophysics Data System (ADS)

    Savin, Eric

    2004-05-01

    The modern mathematical theory of microlocal analysis shows that the energy associated with the high-frequency solutions of hyperbolic partial differential equations (such as the wave or the Navier equations) satisfy Liouville-type transport equations, or radiative transfer equations for randomly heterogeneous media. For long propagation times the latter can be approached by diffusion equations. Some classical results of the structural acoustics literature about the heat conduction analogy and the statistical energy analysis of structural dynamics at higher frequencies are recovered in this process. The purpose of this communication is to focus on such a diffusive regime for isotropic, fluid-saturated porous media. More specifically, we have derived the diffusion parameters (transport mean-free path and diffusion constant) for such media. Our model considers Biot's equations of poroelasticity, where thermal and viscous effects are modelized by dynamic tortuosity and compressibility with singular memory kernels. The macroscopic bulk modulus and density of the dry solid phase are assumed to be homogeneous random processes, while tortuosity and porosity remain constant.

  5. A Search for Hot, Diffuse Gas in Superclusters

    NASA Technical Reports Server (NTRS)

    Boughn, Stephen P.

    1998-01-01

    The HEA01 A2 full sky, 2-10 keV X-ray map was searched for diffuse emission correlated with the plane of the local supercluster of galaxies and a positive correlation was found at the 99% confidence level. The most obvious interpretation is that the local supercluster contains a substantial amount of hot (10(exp 8) OK), diffuse gas, i.e. ionized hydrogen, with a density on the order of 2 - 3 x 10(exp -6) ions per cubic centimeter. This density is about an order of magnitude larger than the average baryon density of the universe and is consistent with a supercluster collapse factor of 10. The implied total mass is of the order of 10(exp 16) times the mass of the sun and would constitute a large fraction of the baryonic matter in the local universe. This result supports current thinking that most of the ordinary matter in the universe is in the form of ionized hydrogen; however, the high temperature implied by the X-ray emission is at the top of the range predicted by most theories. The presence of a large amount of hot gas would leave its imprint on the Cosmic Microwave Background (CMB) via the Sunyaev-Zel'dovich (SZ) effect. A marginal decrement (-17 muK) was found in the COBE 4-year 53 GHz CMB map coincident with the plane of the local supercluster. Although the detection is only 1beta, the level is consistent with the SZ effect predicted from the hot gas. If these results are confirmed by future observations they will have important implications for the formation of large-scale structure in the universe. Three other projects related directly to the HEAO 1 map or the X-ray background in general benefited from this NASA grant. They are: (1) "Correlations between the Cosmic X-ray and Microwave Backgrounds: Constraints on a Cosmological Constant"; (2) "Cross-correlation of the X-ray Background with Radio Sources: Constraining the Large-Scale Structure of the X-ray Background"; and (3) "Radio and X-ray Emission Mechanisms in Advection Dominated Accretion Flow".

  6. Effect of transition from slip to free molecular flow on gas transport in porous media

    NASA Astrophysics Data System (ADS)

    Bravo, Maria Cecilia

    2007-10-01

    Traditional models, such as the advection-diffusion and the dusty gas models, overlook the contribution of the transition flow regime between the slip and the free molecular flow, on the gas transport in porous media. In this work we demonstrate that, due to the existence of this intermediate regime, the Klinkenberg [Drill. & Prod. Prac. 1941, 200 (1941)] parameter b depends on the pressure. Reported experiments were used to corroborate such an effect and a formulation that extends the Klinkenberg equation—to include the effect of a region at pore scale where both molecule-molecule and molecule-wall interactions are important—was developed. The mathematical form of the extended Klinkenberg equation remains the same, but the slippage Klinkenberg's parameter b is now a generalized parameter that is a function of Knudsen's number. It was demonstrated that the widely accepted relation between the parameter b and the Knudsen diffusion coefficient is a good approximation just for Knudsen numbers corresponding to the free molecular flow regime. The model proposed in this paper reproduces the experimental data and predicts practical situations where important errors on total flow rate can be expected if the transition flow regime is neglected in the formalism.

  7. Thermal characterization of semi-transparent media: measurement of phononic diffusivity of glass and silica

    NASA Astrophysics Data System (ADS)

    Lazard, M.; André, S.; Maillet, D.

    2003-09-01

    Materials such as glasses, insulated foams, polymers are semi-transparent. In order to measure the phononic diffusivity of such media in which the heat transfer is both conductive and radiative it is necessary to develop a complete methodology. The technique, we propose here, is an extension of the Flash method with the use of a semi-analytical combined model. It permits to determine the diffusivity of materials such as glass and silica for a large range of temperature (from 300K to 700K).

  8. A novel rumor diffusion model considering the effect of truth in online social media

    NASA Astrophysics Data System (ADS)

    Sun, Ling; Liu, Yun; Zeng, Qing-An; Xiong, Fei

    2015-12-01

    In this paper, we propose a model to investigate how truth affects rumor diffusion in online social media. Our model reveals a relation between rumor and truth — namely, when a rumor is diffusing, the truth about the rumor also diffuses with it. Two patterns of the agents used to identify rumor, self-identification and passive learning are taken into account. Combining theoretical proof and simulation analysis, we find that the threshold value of rumor diffusion is negatively correlated to the connectivity between nodes in the network and the probability β of agents knowing truth. Increasing β can reduce the maximum density of the rumor spreaders and slow down the generation speed of new rumor spreaders. On the other hand, we conclude that the best rumor diffusion strategy must balance the probability of forwarding rumor and the probability of agents losing interest in the rumor. High spread rate λ of rumor would lead to a surge in truth dissemination which will greatly limit the diffusion of rumor. Furthermore, in the case of unknown λ, increasing β can effectively reduce the maximum proportion of agents who do not know the truth, but cannot narrow the rumor diffusion range in a certain interval of β.

  9. A Bloch-Torrey Equation for Diffusion in a Deforming Media

    SciTech Connect

    Rohmer, Damien; Gullberg, Grant T.

    2006-12-29

    Diffusion Tensor Magnetic Resonance Imaging (DTMRI)technique enables the measurement of diffusion parameters and therefore,informs on the structure of the biological tissue. This technique isapplied with success to the static organs such as brain. However, thediffusion measurement on the dynamically deformable organs such as thein-vivo heart is a complex problem that has however a great potential inthe measurement of cardiac health. In order to understand the behavior ofthe Magnetic Resonance (MR)signal in a deforming media, the Bloch-Torreyequation that leads the MR behavior is expressed in general curvilinearcoordinates. These coordinates enable to follow the heart geometry anddeformations through time. The equation is finally discretized andpresented in a numerical formulation using implicit methods, in order toget a stable scheme that can be applied to any smooth deformations.Diffusion process enables the link between the macroscopic behavior ofmolecules and themicroscopic structure in which they evolve. Themeasurement of diffusion in biological tissues is therefore of majorimportance in understanding the complex underlying structure that cannotbe studied directly. The Diffusion Tensor Magnetic ResonanceImaging(DTMRI) technique enables the measurement of diffusion parametersand therefore provides information on the structure of the biologicaltissue. This technique has been applied with success to static organssuch as the brain. However, diffusion measurement of dynamicallydeformable organs such as the in-vivo heart remains a complex problem,which holds great potential in determining cardiac health. In order tounderstand the behavior of the magnetic resonance (MR) signal in adeforming media, the Bloch-Torrey equation that defines the MR behavioris expressed in general curvilinear coordinates. These coordinates enableus to follow the heart geometry and deformations through time. Theequation is finally discretized and presented in a numerical formulationusing

  10. Development of an Internet accessible software: optics and spectroscopy of gas-aerosol media

    NASA Astrophysics Data System (ADS)

    Voitsekhovskaya, O. K.; Kashirskii, D. E.; Egorov, O. V.

    2015-11-01

    A description of an Internet accessible software «Optics and spectroscopy of gas-aerosol media» is represented. The new software is focused on research in the field of direct and inverse problems of optics and spectroscopy of gas-aerosol media.

  11. Modeling heating curve for gas hydrate dissociation in porous media.

    PubMed

    Dicharry, Christophe; Gayet, Pascal; Marion, Gérard; Graciaa, Alain; Nesterov, Anatoliy N

    2005-09-15

    A method for modeling the heating curve for gas hydrate dissociation in porous media at isochoric conditions (constant cell volume) is presented. This method consists of using an equation of state of the gas, the cumulative volume distribution (CVD) of the porous medium, and a van der Waals-Platteeuw-type thermodynamic model that includes a capillary term. The proposed method was tested to predict the heating curves for methane hydrate dissociation in a mesoporous silica glass for saturated conditions (liquid volume = pore volume) and for a fractional conversion of water to hydrate of 1 (100% of the available water was converted to hydrate). The shape factor (F) of the hydrate-water interface was found equal to 1, supporting a cylindrical shape for the hydrate particles during hydrate dissociation. Using F = 1, it has been possible to predict the heating curve for different ranges of pressure and temperature. The excellent agreement between the calculated and experimental heating curves supports the validity of our approach.

  12. Diffusion of a Rouse chain in porous media: A mode-coupling-theory study

    NASA Astrophysics Data System (ADS)

    Ding, Huai; Jiang, Huijun; Zhao, Nanrong; Hou, Zhonghuai

    2017-01-01

    We use a kinetic mode-coupling theory (MCT) combining with generalized Langevin equation (GLE) to study the diffusion and conformational dynamics of a bead-spring Rouse chain (RC) dissolved in porous media. The media contains fluid particles and immobile matrix ones wherein the latter leads to the lack of translational invariance. The friction kernel ζ (t ) used in the GLE can be obtained directly by adopting a simple density-functional approach in which the density correlators calculated by MCT equations of porous media serve as inputs. Due to cage effects generated by surrounding particles, ζ (t ) shows a very long tail memory in the high volume fraction of fluid and matrix. It is found that the long-time center-of-mass diffusion constant DCM of the RC decreases with the increment of volume fraction, influencing more strongly by the matrix particles than by the fluid ones. The auto-correlation function (ACF) of the end-to-end distance fluctuation can also be calculated theoretically based on GLE. Of particular interest is that the power-law region of ACF has a nearly fixed length in logarithmic scale when it shifts to longer time range, with increasing the volume fraction of media particles. Moreover, the effect of lack of translational invariance has been investigated by comparing the results between fluid-matrix and pure fluid cases under identical total volume fraction.

  13. Gas diffusivity and permeability through the firn column at Summit, Greenland: measurements and comparison to microstructural properties

    NASA Astrophysics Data System (ADS)

    Adolph, A. C.; Albert, M. R.

    2014-02-01

    The physical structure of polar firn plays a key role in the mechanisms by which glaciers and ice sheets preserve a natural archive of past atmospheric composition. This study presents the first measurements of gas diffusivity and permeability along with microstructural information measured from the near-surface firn through the firn column to pore close-off. Both fine- and coarse-grained firn from Summit, Greenland are included in this study to investigate the variability in firn caused by seasonal and storm-event layering. Our measurements reveal that the porosity of firn (derived from density) is insufficient to describe the full profiles of diffusivity and permeability, particularly at porosity values above 0.5. Thus, even a model that could perfectly predict the density profile would be insufficient for application to issues involving gas transport. The measured diffusivity profile presented here is compared to two diffusivity profiles modeled from firn air measurements from Summit. Because of differences in scale and in firn processes between the true field situation, firn modeling, and laboratory measurements, the results follow a similar overall pattern but do not align; our results constitute a lower bound on diffusive transport. In comparing our measurements of both diffusivity and permeability to previous parameterizations from numerical 3-D lattice-Boltzmann modeling, it is evident that the previous relationships to porosity are likely site-specific. We present parameterizations relating diffusivity and permeability to porosity as a possible tool, though use of direct measurements would be far more accurate when feasible. The relationships between gas transport properties and microstructural properties are characterized and compared to existing relationships for general porous media, specifically the Katz-Thompson (KT), Kozeny-Carman (KC), and Archie's law approximations. While those approximations can capture the general trend of gas transport

  14. Detachment of Liquid-Water Droplets from Gas-Diffusion Layers

    SciTech Connect

    Das, Prodip K.; Grippin, Adam; Weber, Adam Z.

    2011-07-01

    A critical issue for optimal water management in proton-exchange-membrane fuel cells at lower temperatures is the removal of liquid water from the cell. This pathway is intimately linked with the phenomena of liquid-water droplet removal from surface of the gas-diffusion layer and into the flow channel. Thus, a good understanding of liquid-water transport and droplet growth and detachment from the gas-diffusion layer is critical. In this study, liquid-water droplet growth and detachment on the gas-diffusion layer surfaces are investigated experimentally to improve the understating of water transport through and removal from gas-diffusion layers. An experiment using a sliding-angle measurement is designed and used to quantify and directly measure the adhesion force for liquid-water droplets, and to understand the droplets? growth and detachment from the gas-diffusion layers.

  15. A hybrid transport-diffusion model for radiative transfer in absorbing and scattering media

    NASA Astrophysics Data System (ADS)

    Roger, M.; Caliot, C.; Crouseilles, N.; Coelho, P. J.

    2014-10-01

    A new multi-scale hybrid transport-diffusion model for radiative transfer is proposed in order to improve the efficiency of the calculations close to the diffusive regime, in absorbing and strongly scattering media. In this model, the radiative intensity is decomposed into a macroscopic component calculated by the diffusion equation, and a mesoscopic component. The transport equation for the mesoscopic component allows to correct the estimation of the diffusion equation, and then to obtain the solution of the linear radiative transfer equation. In this work, results are presented for stationary and transient radiative transfer cases, in examples which concern solar concentrated and optical tomography applications. The Monte Carlo and the discrete-ordinate methods are used to solve the mesoscopic equation. It is shown that the multi-scale model allows to improve the efficiency of the calculations when the medium is close to the diffusive regime. The proposed model is a good alternative for radiative transfer at the intermediate regime where the macroscopic diffusion equation is not accurate enough and the radiative transfer equation requires too much computational effort.

  16. Diffusion and decay chain of radioisotopes in stagnant water in saturated porous media.

    PubMed

    Guzmán, Juan; Alvarez-Ramirez, Jose; Escarela-Pérez, Rafael; Vargas, Raúl Alejandro

    2014-09-01

    The analysis of the diffusion of radioisotopes in stagnant water in saturated porous media is important to validate the performance of barrier systems used in radioactive repositories. In this work a methodology is developed to determine the radioisotope concentration in a two-reservoir configuration: a saturated porous medium with stagnant water is surrounded by two reservoirs. The concentrations are obtained for all the radioisotopes of the decay chain using the concept of overvalued concentration. A methodology, based on the variable separation method, is proposed for the solution of the transport equation. The novelty of the proposed methodology involves the factorization of the overvalued concentration in two factors: one that describes the diffusion without decay and another one that describes the decay without diffusion. It is possible with the proposed methodology to determine the required time to obtain equal injective and diffusive concentrations in reservoirs. In fact, this time is inversely proportional to the diffusion coefficient. In addition, the proposed methodology allows finding the required time to get a linear and constant space distribution of the concentration in porous mediums. This time is inversely proportional to the diffusion coefficient. In order to validate the proposed methodology, the distributions in the radioisotope concentrations are compared with other experimental and numerical works.

  17. Compressed air energy storage in depleted natural gas reservoirs: effects of porous media and gas mixing

    NASA Astrophysics Data System (ADS)

    Oldenburg, C. M.; Pan, L.

    2015-12-01

    Although large opportunities exist for compressed air energy storage (CAES) in aquifers and depleted natural gas reservoirs, only two grid-scale CAES facilities exist worldwide, both in salt caverns. As such, experience with CAES in porous media, what we call PM-CAES, is lacking and we have relied on modeling to elucidate PM-CAES processes. PM-CAES operates similarly to cavern CAES. Specifically, working gas (air) is injected through well(s) into the reservoir compressing the cushion gas (existing air in the reservoir). During energy recovery, high-pressure air from the reservoir flows first into a recuperator, then into an expander, and subsequently is mixed with fuel in a combustion turbine to produce electricity, thereby reducing compression costs. Energy storage in porous media is complicated by the solid matrix grains which provide resistance to flow (via permeability in Darcy's law); in the cap rock, low-permeability matrix provides the seal to the reservoir. The solid grains also provide storage capacity for heat that might arise from compression, viscous flow effects, or chemical reactions. The storage of energy in PM-CAES occurs variably across pressure gradients in the formation, while the solid grains of the matrix can release/store heat. Residual liquid (i.e., formation fluids) affects flow and can cause watering out at the production well(s). PG&E is researching a potential 300 MW (for ten hours) PM-CAES facility in a depleted gas reservoir near Lodi, California. Special considerations exist for depleted natural gas reservoirs because of mixing effects which can lead to undesirable residual methane (CH4) entrainment and reactions of oxygen and CH4. One strategy for avoiding extensive mixing of working gas (air) with reservoir CH4 is to inject an initial cushion gas with reduced oxygen concentration providing a buffer between the working gas (air) and the residual CH4 gas. This reduces the potential mixing of the working air with the residual CH4

  18. Buoyancy induced extinction of laminar gas jet diffusion flames

    NASA Technical Reports Server (NTRS)

    Altenkirch, R. A.; Eichhorn, R.; Brancic, A. B.

    1977-01-01

    The behavior of laminar gas jet diffusion flames subjected to elevated gravity in order to investigate the role of buoyancy in such flames has been studied experimentally. Higher than earth normal gravity was achieved using a 1.83 m diameter centrifuge. Methane, ethane, propane and hydrogen air flames were stabilized at the exit of small tubular burners ranging in size from .05 to .21 cm in diameter. The experimental arrangement was such that the flames were burnt vertically upward. Following a shortening of the flame and a decrease in luminosity with increasing gravity level, further increases in gravity caused the hydrocarbon flames to separate from the rim and eventually extinguish. The extinction gravity levels appear to correlate with the parameter g alpha (u)/S to the 3rd (u), which should be a constant for buoyancy controlled extinction. This parameter is developed by a rudimentary analysis of the heat loss from the premixed stabilizing flame in the lifted flame base. When the loss is excessive, the flame is extinguished.

  19. Electrochemical disinfection using the gas diffusion electrode system.

    PubMed

    Xu, Wenying; Li, Ping; Dong, Bin

    2010-01-01

    A study on the electrochemical disinfection with H2O2 generated at the gas diffusion electrode (GDE) from active carbon/polytetrafluoroethylene was performed in a non-membrane cell. The effects of Pt load and the pore-forming agent content in GDE, and operating conditions were investigated. The experimental results showed that nearly all bacterial cultures inoculated in the secondary effluent from wastewater treatment plant could be inactivated within 30 min at a current density of 10 mA/cm2. The disinfection improved with increasing Pt load. Addition of the pore-forming agent NH4HCO3 improved the disinfection, while a drop in the pH value resulted in a rapid rise of germicidal efficacy and the disinfection time was shortened with increasing oxygen flow rate. Adsorption was proved to be ineffective in destroying bacteria, while germicidal efficacy increased with current density. The acceleration rate was different, it initially increased with current density. Then decreased, and finally reached a maximum at a current density of 6.7 mA/cm2. The disinfection also improved with decreasing total bacterial count. The germicidal efficacy in the cathode compartment was approximately the same as in the anode compartment, indicating that the contribution of direct oxidation and the indirect treatment of bacterial cultures by hydroxyl radical was similar to the oxidative indirect effect of the generated H2O2.

  20. Stability analysis of an encapsulated microbubble against gas diffusion.

    PubMed

    Katiyar, Amit; Sarkar, Kausik

    2010-03-01

    Linear stability analysis is performed for a mathematical model of diffusion of gases from an encapsulated microbubble. It is an Epstein-Plesset model modified to account for encapsulation elasticity and finite gas permeability. Although bubbles, containing gases other than air, are considered, the final stable bubble, if any, contains only air, and stability is achieved only when the surrounding medium is saturated or oversaturated with air. In absence of encapsulation elasticity, only a neutral stability is achieved for zero surface tension, the other solution being unstable. For an elastic encapsulation, different equilibrium solutions are obtained depending on the saturation level and whether the surface tension is smaller or higher than the elasticity. For an elastic encapsulation, elasticity can stabilize the bubble. However, imposing a non-negativity condition on the effective surface tension (consisting of reference surface tension and the elastic stress) leads to an equilibrium radius which is only neutrally stable. If the encapsulation can support a net compressive stress, it achieves actual stability. The linear stability results are consistent with our recent numerical findings. Physical mechanisms for the stability or instability of various equilibriums are provided.

  1. Multimodel analysis of anisotropic diffusive tracer-gas transport in a deep arid unsaturated zone

    USGS Publications Warehouse

    Green, Christopher T.; Walvoord, Michelle Ann; Andraski, Brian J.; Striegl, Robert G.; Stonestrom, David A.

    2015-01-01

    Gas transport in the unsaturated zone affects contaminant flux and remediation, interpretation of groundwater travel times from atmospheric tracers, and mass budgets of environmentally important gases. Although unsaturated zone transport of gases is commonly treated as dominated by diffusion, the characteristics of transport in deep layered sediments remain uncertain. In this study, we use a multimodel approach to analyze results of a gas-tracer (SF6) test to clarify characteristics of gas transport in deep unsaturated alluvium. Thirty-five separate models with distinct diffusivity structures were calibrated to the tracer-test data and were compared on the basis of Akaike Information Criteria estimates of posterior model probability. Models included analytical and numerical solutions. Analytical models provided estimates of bulk-scale apparent diffusivities at the scale of tens of meters. Numerical models provided information on local-scale diffusivities and feasible lithological features producing the observed tracer breakthrough curves. The combined approaches indicate significant anisotropy of bulk-scale diffusivity, likely associated with high-diffusivity layers. Both approaches indicated that diffusivities in some intervals were greater than expected from standard models relating porosity to diffusivity. High apparent diffusivities and anisotropic diffusivity structures were consistent with previous observations at the study site of rapid lateral transport and limited vertical spreading of gas-phase contaminants. Additional processes such as advective oscillations may be involved. These results indicate that gases in deep, layered unsaturated zone sediments can spread laterally more quickly, and produce higher peak concentrations, than predicted by homogeneous, isotropic diffusion models.

  2. Diffusion Dominant Solute Transport Modelling in Fractured Media Under Deep Geological Environment - 12211

    SciTech Connect

    Kwong, S.; Jivkov, A.P.

    2012-07-01

    Deep geologic disposal of high activity and long-lived radioactive waste is gaining increasing support in many countries, where suitable low permeability geological formation in combination with engineered barriers are used to provide long term waste contaminant and minimise the impacts to the environment and risk to the biosphere. This modelling study examines the solute transport in fractured media under low flow velocities that are relevant to a deep geological environment. In particular, reactive solute transport through fractured media is studied using a 2-D model, that considers advection and diffusion, to explore the coupled effects of kinetic and equilibrium chemical processes. The effects of water velocity in the fracture, matrix porosity and diffusion on solute transport are investigated and discussed. Some illustrative modelled results are presented to demonstrate the use of the model to examine the effects of media degradation on solute transport, under the influences of hydrogeological (diffusion dominant) and microbially mediated chemical processes. The challenges facing the prediction of long term degradation such as cracks evolution, interaction and coalescence are highlighted. The potential of a novel microstructure informed modelling approach to account for these effects is discussed, particularly with respect to investigating multiple phenomena impact on material performance. The GRM code is used to examine the effects of media degradation for a geological waste disposal package, under the combined hydrogeological (diffusion dominant) and chemical effects in low groundwater flow conditions that are typical of deep geological disposal systems. An illustrative reactive transport modelling application demonstrates the use of the code to examine the interplay of kinetic controlled biogeochemical reactive processes with advective and diffusive transport, under the influence of media degradation. The initial model results are encouraging which show the

  3. Diffusion of dilute gas in arrays of randomly distributed, vertically aligned, high-aspect-ratio cylinders.

    PubMed

    Szmyt, Wojciech; Guerra, Carlos; Utke, Ivo

    2017-01-01

    In this work we modelled the diffusive transport of a dilute gas along arrays of randomly distributed, vertically aligned nanocylinders (nanotubes or nanowires) as opposed to gas diffusion in long pores, which is described by the well-known Knudsen theory. Analytical expressions for (i) the gas diffusion coefficient inside such arrays, (ii) the time between collisions of molecules with the nanocylinder walls (mean time of flight), (iii) the surface impingement rate, and (iv) the Knudsen number of such a system were rigidly derived based on a random-walk model of a molecule that undergoes memoryless, diffusive reflections from nanocylinder walls assuming the molecular regime of gas transport. It can be specifically shown that the gas diffusion coefficient inside such arrays is inversely proportional to the areal density of cylinders and their mean diameter. An example calculation of a diffusion coefficient is delivered for a system of titanium isopropoxide molecules diffusing between vertically aligned carbon nanotubes. Our findings are important for the correct modelling and optimisation of gas-based deposition techniques, such as atomic layer deposition or chemical vapour deposition, frequently used for surface functionalisation of high-aspect-ratio nanocylinder arrays in solar cells and energy storage applications. Furthermore, gas sensing devices with high-aspect-ratio nanocylinder arrays and the growth of vertically aligned carbon nanotubes need the fundamental understanding and precise modelling of gas transport to optimise such processes.

  4. Diffusion of dilute gas in arrays of randomly distributed, vertically aligned, high-aspect-ratio cylinders

    PubMed Central

    Guerra, Carlos

    2017-01-01

    In this work we modelled the diffusive transport of a dilute gas along arrays of randomly distributed, vertically aligned nanocylinders (nanotubes or nanowires) as opposed to gas diffusion in long pores, which is described by the well-known Knudsen theory. Analytical expressions for (i) the gas diffusion coefficient inside such arrays, (ii) the time between collisions of molecules with the nanocylinder walls (mean time of flight), (iii) the surface impingement rate, and (iv) the Knudsen number of such a system were rigidly derived based on a random-walk model of a molecule that undergoes memoryless, diffusive reflections from nanocylinder walls assuming the molecular regime of gas transport. It can be specifically shown that the gas diffusion coefficient inside such arrays is inversely proportional to the areal density of cylinders and their mean diameter. An example calculation of a diffusion coefficient is delivered for a system of titanium isopropoxide molecules diffusing between vertically aligned carbon nanotubes. Our findings are important for the correct modelling and optimisation of gas-based deposition techniques, such as atomic layer deposition or chemical vapour deposition, frequently used for surface functionalisation of high-aspect-ratio nanocylinder arrays in solar cells and energy storage applications. Furthermore, gas sensing devices with high-aspect-ratio nanocylinder arrays and the growth of vertically aligned carbon nanotubes need the fundamental understanding and precise modelling of gas transport to optimise such processes. PMID:28144565

  5. A lattice-Boltzman model for noble gas diffusion

    NASA Astrophysics Data System (ADS)

    Cassata, W. S.; Huber, C.; Renne, P. R.

    2010-12-01

    Thermochronometry by the 40Ar/39Ar, 4He/3He, and (U-Th)/He techniques provides insights into a array of planetary processes that span immense time and temperature regimes, from rapid and high temperature asteroid impact events to mountain uplift occurring over plate tectonic timescales at near surface temperatures. Thermal modeling has expanded from simple calculations for quantifying diffusion from a single spherical domain or log normal distributions of domains to include crystals having discrete domain distributions, fast diffusion pathways, diffusive anisotropy, complex crystal geometries, alpha damage, and alpha ejection. Despite these advances, our understanding of diffusion within crystals that have complex microstructural features (e.g., exsolution and diffusive sinks) or highly asymmetric concentration gradients remains fragmentary. Improved computational speeds now enable thermochronologists to quantitatively explore many such problems. We have developed a code based on the lattice-Boltzmann (LB) method to model diffusion from a variety of complex 2-D geometries having isotropic, temperature-independent anisotropic, and temperature-dependent anisotropic diffusivity. We utilize the LB diffusion code to examine the effects of non-zero concentration boundaries, fast diffusion pathways, diffusive sinks, exsolution lamellae, asymmetrical concentration distributions, and temperature gradients on calculated diffusion parameters, age data, and inferred thermal histories. Animations and geological examples illustrate the applicability of the code to natural settings.

  6. Diffused waveguiding capillary tube with distributed feedback for a gas laser

    NASA Technical Reports Server (NTRS)

    Elachi, C. (Inventor)

    1976-01-01

    For use in a waveguide gas laser, a capillary tube of glass or ceramic has an inner surface defining a longitudinal capillary opening through which the laser gas flows. At least a portion of the inner surface is corrugated with corrugations or channels with a periodicity Lambda where Lambda = 1/2 Lambda, Lambda being the laser gas wavelength. The tube includes a diffused region extending outwardly from the opening. The diffused region of a depth d on the order of 1 Lambda to 3 Lambda acts as a waveguide for the waves, with the corrugations producing distributed feedback. The evanescent component of the waves traveling in the diffused region interact with the laser gas in the opening, gaining energy, and thereby amplifying the waves travelling in the diffused region, which exit the diffused region, surrounding the opening, as a beam of wavelength Lambda.

  7. Lattice Boltzmann simulation of the gas-solid adsorption process in reconstructed random porous media.

    PubMed

    Zhou, L; Qu, Z G; Ding, T; Miao, J Y

    2016-04-01

    The gas-solid adsorption process in reconstructed random porous media is numerically studied with the lattice Boltzmann (LB) method at the pore scale with consideration of interparticle, interfacial, and intraparticle mass transfer performances. Adsorbent structures are reconstructed in two dimensions by employing the quartet structure generation set approach. To implement boundary conditions accurately, all the porous interfacial nodes are recognized and classified into 14 types using a proposed universal program called the boundary recognition and classification program. The multiple-relaxation-time LB model and single-relaxation-time LB model are adopted to simulate flow and mass transport, respectively. The interparticle, interfacial, and intraparticle mass transfer capacities are evaluated with the permeability factor and interparticle transfer coefficient, Langmuir adsorption kinetics, and the solid diffusion model, respectively. Adsorption processes are performed in two groups of adsorbent media with different porosities and particle sizes. External and internal mass transfer resistances govern the adsorption system. A large porosity leads to an early time for adsorption equilibrium because of the controlling factor of external resistance. External and internal resistances are dominant at small and large particle sizes, respectively. Particle size, under which the total resistance is minimum, ranges from 3 to 7 μm with the preset parameters. Pore-scale simulation clearly explains the effect of both external and internal mass transfer resistances. The present paper provides both theoretical and practical guidance for the design and optimization of adsorption systems.

  8. Multifrequency radiation diffusion equations for homogeneous, refractive, lossy media and their interface conditions

    SciTech Connect

    Shestakov, Aleksei I.

    2013-06-15

    We derive time-dependent multifrequency diffusion equations for homogeneous, refractive lossy media. The equations are applicable for a domain composed of several materials with distinct refractive indexes. In such applications, the fundamental radiation variable, the intensity I, is discontinuous across material interfaces. The diffusion equations evolve a variable ξ, the integral of I over all directions divided by the square of the refractive index. Attention is focused on boundary and internal interface conditions for ξ. For numerical solutions using finite elements, it is shown that at material interfaces, the usual diffusion coefficient 1/3κ of the multifrequency equation, where κ is the opacity, is modified by a tensor diffusion term consisting of integrals of the reflectivity. Numerical results are presented. For a single material simulation, the ξ equations yield the same result as diffusion equations that evolve the spectral radiation energy density. A second simulation solves a test problem that models radiation transport in a domain comprised of materials with different refractive indexes. Results qualitatively agree with those previously published.

  9. Theory and simulation of time-fractional fluid diffusion in porous media

    NASA Astrophysics Data System (ADS)

    Carcione, José M.; Sanchez-Sesma, Francisco J.; Luzón, Francisco; Perez Gavilán, Juan J.

    2013-08-01

    We simulate a fluid flow in inhomogeneous anisotropic porous media using a time-fractional diffusion equation and the staggered Fourier pseudospectral method to compute the spatial derivatives. A fractional derivative of the order of 0 < ν < 2 replaces the first-order time derivative in the classical diffusion equation. It implies a time-dependent permeability tensor having a power-law time dependence, which describes memory effects and accounts for anomalous diffusion. We provide a complete analysis of the physics based on plane waves. The concepts of phase, group and energy velocities are analyzed to describe the location of the diffusion front, and the attenuation and quality factors are obtained to quantify the amplitude decay. We also obtain the frequency-domain Green function. The time derivative is computed with the Grünwald-Letnikov summation, which is a finite-difference generalization of the standard finite-difference operator to derivatives of fractional order. The results match the analytical solution obtained from the Green function. An example of the pressure field generated by a fluid injection in a heterogeneous sandstone illustrates the performance of the algorithm for different values of ν. The calculation requires storing the whole pressure field in the computer memory since anomalous diffusion ‘recalls the past’.

  10. Diffusion in Homogeneous and in Inhomogeneous Media: A New Unified Approach.

    PubMed

    Mercier Franco, Luís Fernando; Castier, Marcelo; Economou, Ioannis G

    2016-11-08

    We propose a new method to calculate the diffusion coefficient within molecular dynamics simulations for either homogeneous or inhomogeneous fluids. We formulate such method by solving analytically the Smoluchowski equation for a linear potential of mean force within a thin layer with absorbing boundary conditions. The bulk, or homogeneous, fluid diffusion emerges as a particular case in this approach. We apply this method to bulk liquid water at atmospheric pressure and different temperatures using the SPC/E water force field. We show that our method gives results as accurate as the traditional Einstein-Smoluchowski method, avoiding the fitting procedure required in the traditional method. We also apply this method for molten sodium chloride showing its applicability for multicomponent systems. The water vapor-liquid interface is studied as an example of an inhomogeneous system. We calculate all the components of the diffusion tensor at the interface. We observe the same anisotropy between the perpendicular and the parallel components at the interface as it has been noted in the literature. We also calculate the perpendicular self-diffusion coefficient of methane near the calcite surface showing that this coefficient is much lower than the parallel diffusion coefficients. We believe that this new unified approach is a very promising technique for both bulk and confined media.

  11. Characterization of highly scattering media by measurement of diffusely backscattered polarized light

    DOEpatents

    Hielscher, Andreas H.; Mourant, Judith R.; Bigio, Irving J.

    2000-01-01

    An apparatus and method for recording spatially dependent intensity patterns of polarized light that is diffusely backscattered from highly scattering media are described. These intensity patterns can be used to differentiate different turbid media, such as polystyrene-sphere and biological-cell suspensions. Polarized light from a He-Ne laser (.lambda.=543 nm) is focused onto the surface of the scattering medium, and a surface area of approximately 4.times.4 cm centered on the light input point is imaged through polarization analysis optics onto a CCD camera. A variety of intensity patterns may be observed by varying the polarization state of the incident laser light and changing the analyzer configuration to detect different polarization components of the backscattered light. Experimental results for polystyrene-sphere and Intralipid suspensions demonstrate that the radial and azimuthal variations of the observed pattern depend on the concentration, size, and anisotropy factor, g, of the particles constituting the scattering medium. Measurements performed on biological cell suspensions show that intensity patterns can be used to differentiate between suspensions of cancerous and non-cancerous cells. Introduction of the Mueller-matrix for diffusely backscattered light, permits the selection of a subset of measurements which comprehensively describes the optical properties of backscattering media.

  12. Characterization of highly scattering media by measurement of diffusely backscattered polarized light

    SciTech Connect

    Hielscher, A.H.; Mourant, J.R.; Bigio, I.J.

    2000-01-04

    An apparatus and method for recording spatially dependent intensity patterns of polarized light that is diffusely backscattered from highly scattering media are described. These intensity patterns can be used to differentiate different turbid media, such as polystyrene-sphere and biological-cell suspensions. Polarized light from a He-Ne laser ({lambda} = 543 nm) is focused onto the surface of the scattering medium, and a surface area of approximately 4 x 4 cm centered on the light input point is imaged through polarization analysis optics onto a CCD camera. A variety of intensity patterns may be observed by varying the polarization state of the incident laser light and changing the analyzer configuration to detect different polarization components of the backscattered light. Experimental results for polystyrene-sphere and intralipid suspensions demonstrate that the radial and azimuthal variations of the observed pattern depend on the concentration, size, and anisotropy factor, g, of the particles constituting the scattering medium. Measurements performed on biological cell suspensions show that intensity patterns can be used to differentiate between suspensions of cancerous and non-cancerous cells. Introduction of the Mueller-matrix for diffusely backscattered light, permits the selection of a subset of measurements which comprehensively describes the optical properties of backscattering media.

  13. Imaging diffuse clouds: bright and dark gas mapped in CO

    NASA Astrophysics Data System (ADS)

    Liszt, H. S.; Pety, J.

    2012-05-01

    Aims: We wish to relate the degree scale structure of galactic diffuse clouds to sub-arcsecond atomic and molecular absorption spectra obtained against extragalactic continuum background sources. Methods: We used the ARO 12 m telescope to map J = 1-0 CO emission at 1' resolution over 30' fields around the positions of 11 background sources occulted by 20 molecular absorption line components, of which 11 had CO emission counterparts. We compared maps of CO emission to sub-arcsec atomic and molecular absorption spectra and to the large-scale distribution of interstellar reddening. Results: 1) The same clouds, identified by their velocity, were seen in absorption and emission and atomic and molecular phases, not necessarily in the same direction. Sub-arcsecond absorption spectra are a preview of what is seen in CO emission away from the continuum. 2) The CO emission structure was amorphous in 9 cases, quasi-periodic or wave-like around B0528+134 and tangled and filamentary around BL Lac. 3) Strong emission, typically 4-5 K at EB - V ≤ 0.15 mag and up to 10-12 K at EB - V ≲ 0.3 mag was found, much brighter than toward the background targets. Typical covering factors of individual features at the 1 K km s-1 level were 20%. 4) CO-H2 conversion factors as much as 4-5 times below the mean value N(H2)/WCO = 2 × 1020 H2 cm-2 (K km s-1)-1 are required to explain the luminosity of CO emission at/above the level of 1 K km s-1. Small conversion factors and sharp variability of the conversion factor on arcminute scales are due primarily to CO chemistry and need not represent unresolved variations in reddening or total column density. Conclusions: Like Fermi and Planck we see some gas that is dark in CO and other gas in which CO is overluminous per H2. A standard CO-H2 conversion factor applies overall owing to balance between the luminosities per H2 and surface covering factors of bright and dark CO, but with wide variations between sightlines and across the faces of

  14. Additive manufacturing of liquid/gas diffusion layers for low-cost and high-efficiency hydrogen production

    SciTech Connect

    Mo, Jingke; Zhang, Feng -Yuan; Dehoff, Ryan R.; Peter, William H.; Toops, Todd J.; Green, Jr., Johney Boyd

    2016-01-14

    The electron beam melting (EBM) additive manufacturing technology was used to fabricate titanium liquid/gas diffusion media with high-corrosion resistances and well-controllable multifunctional parameters, including two-phase transport and excellent electric/thermal conductivities, has been first demonstrated. Their applications in proton exchange membrane eletrolyzer cells have been explored in-situ in a cell and characterized ex-situ with SEM and XRD. Compared with the conventional woven liquid/gas diffusion layers (LGDLs), much better performance with EBM fabricated LGDLs is obtained due to their significant reduction of ohmic loss. The EBM technology components exhibited several distinguished advantages in fabricating gas diffusion layer: well-controllable pore morphology and structure, rapid prototyping, fast manufacturing, highly customizing and economic. In addition, by taking advantage of additive manufacturing, it possible to fabricate complicated three-dimensional designs of virtually any shape from a digital model into one single solid object faster, cheaper and easier, especially for titanium. More importantly, this development will provide LGDLs with control of pore size, pore shape, pore distribution, and therefore porosity and permeability, which will be very valuable to develop modeling and to validate simulations of electrolyzers with optimal and repeatable performance. Further, it will lead to a manufacturing solution to greatly simplify the PEMEC/fuel cell components and to couple the LGDLs with other parts, since they can be easily integrated together with this advanced manufacturing process

  15. Additive manufacturing of liquid/gas diffusion layers for low-cost and high-efficiency hydrogen production

    DOE PAGES

    Mo, Jingke; Zhang, Feng -Yuan; Dehoff, Ryan R.; ...

    2016-01-14

    The electron beam melting (EBM) additive manufacturing technology was used to fabricate titanium liquid/gas diffusion media with high-corrosion resistances and well-controllable multifunctional parameters, including two-phase transport and excellent electric/thermal conductivities, has been first demonstrated. Their applications in proton exchange membrane eletrolyzer cells have been explored in-situ in a cell and characterized ex-situ with SEM and XRD. Compared with the conventional woven liquid/gas diffusion layers (LGDLs), much better performance with EBM fabricated LGDLs is obtained due to their significant reduction of ohmic loss. The EBM technology components exhibited several distinguished advantages in fabricating gas diffusion layer: well-controllable pore morphology and structure,more » rapid prototyping, fast manufacturing, highly customizing and economic. In addition, by taking advantage of additive manufacturing, it possible to fabricate complicated three-dimensional designs of virtually any shape from a digital model into one single solid object faster, cheaper and easier, especially for titanium. More importantly, this development will provide LGDLs with control of pore size, pore shape, pore distribution, and therefore porosity and permeability, which will be very valuable to develop modeling and to validate simulations of electrolyzers with optimal and repeatable performance. Further, it will lead to a manufacturing solution to greatly simplify the PEMEC/fuel cell components and to couple the LGDLs with other parts, since they can be easily integrated together with this advanced manufacturing process« less

  16. Hybridized wavefront shaping for high-speed, high-efficiency focusing through dynamic diffusive media

    NASA Astrophysics Data System (ADS)

    Hemphill, Ashton S.; Tay, Jian Wei; Wang, Lihong V.

    2016-12-01

    One of the prime limiting factors of optical imaging in biological applications is the diffusion of light by tissue, which prevents focusing at depths greater than the optical diffusion limit (typically ˜1 mm). To overcome this challenge, wavefront shaping techniques that use a spatial light modulator (SLM) to correct the phase of the incident wavefront have recently been developed. These techniques are able to focus light through scattering media beyond the optical diffusion limit. However, the low speeds of typically used liquid crystal SLMs limit the focusing speed. Here, we present a method using a digital micromirror device (DMD) and an electro-optic modulator (EOM) to measure the scattering-induced aberrations, and using a liquid crystal SLM to apply the correction to the illuminating wavefront. By combining phase modulation from an EOM with the DMD's ability to provide selective illumination, we exploit the DMD's higher refresh rate for phase measurement. We achieved focusing through scattering media in less than 8 ms, which is sufficiently short for certain in vivo applications, as it is comparable to the speckle correlation time of living tissue.

  17. Quantifying the properties of two-layer turbid media with frequency-domain diffuse reflectance.

    PubMed

    Pham, T H; Spott, T; Svaasand, L O; Tromberg, B J

    2000-09-01

    Noncontact, frequency-domain measurements of diffusely reflected light are used to quantify optical properties of two-layer tissuelike turbid media. The irradiating source is a sinusoidal intensity-modulated plane wave, with modulation frequencies ranging from 10 to 1500 MHz. Frequency-dependent phase and amplitude of diffusely reflected photon density waves are simultaneously fitted to a diffusion-based two-layer model to quantify absorption (mu(a)) and reduced scattering (mu(s)') parameters of each layer as well as the upper-layer thickness (l). Study results indicate that the optical properties of two-layer media can be determined with a percent accuracy of the order of +/-9% and +/-5% for mu(a) and mu(s)', respectively. The accuracy of upper-layer thickness (l) estimation is as good as +/-6% when optical properties of upper and lower layers are known. Optical property and layer thickness prediction accuracy degrade significantly when more than three free parameters are extracted from data fits. Problems with convergence are encountered when all five free parameters (mu(a) and mu(s)' of upper and lower layers and thickness l) must be deduced.

  18. Improvement of oxygen diffusion characteristic in gas diffusion layer with planar-distributed wettability for polymer electrolyte fuel cell

    NASA Astrophysics Data System (ADS)

    Koresawa, Ryo; Utaka, Yoshio

    2014-12-01

    Mass transfer characteristics of gas diffusion layer (GDL) are closely related to performance of polymer electrolyte fuel cells. Therefore, it is necessary to clarify the characteristics of water distribution relating to the microscopic conformation and oxygen diffusivity of GDL. A hybrid type carbon paper GDL with planar-distributed wettability is investigated for control of liquid water movement and distribution due to hydrophobic to hydrophilic areas that provide wettability differences in GDL and to achieve enhancement of both oxygen diffusion and moisture retention. Hybrid GDLs with different PTFE content were fabricated in an attempt to improve the oxygen diffusion characteristics. The effects of different PTFE contents on the oxygen diffusivity and water distribution were simultaneously measured and observed using galvanic cell oxygen absorber and X-ray radiography. The PTFE distribution was observed using scanning electron microscopy. The formation of oxygen diffusion paths was confirmed by X-ray radiography, where voids in the hybrid GDL were first formed in the hydrophobic regions and then spread to the untreated wetting region. Thus, the formation of oxygen diffusion paths enhanced the oxygen diffusion. In addition, the effects of local PTFE content in the hydrophobic region and the optimal amount of PTFE for hybrid GDL were elucidated.

  19. Predicting Partitioning and Diffusion Properties of Nonpolar Chemicals in Biotic Media and Passive Sampler Phases by GC × GC.

    PubMed

    Nabi, Deedar; Arey, J Samuel

    2017-02-14

    The chemical parameters needed to explain and predict bioavailability, biodynamics, and baseline toxicity are not readily available for most nonpolar chemicals detected in the environment. Here, we demonstrate that comprehensive two-dimensional gas chromatography (GC × GC) retention times can be used to predict 26 relevant properties for nonpolar chemicals, specifically: partition coefficients for diverse biotic media and passive sampler phases; aquatic baseline toxicity; and relevant diffusion coefficients. The considered biotic and passive sampler phases include membrane and storage lipids, serum and muscle proteins, carbohydrates, algae, mussels, polydimethylsiloxane, polyethylene, polyoxymethylene, polyacrylate, polyurethane, and semipermeable membrane devices. GC × GC-based chemical property predictions are validated with a compilation of 1038 experimental property data collected from the literature. As an example application, we overlay a map of baseline toxicity to fathead minnows onto the separated analyte signal of a polychlorinated alkanes (chlorinated paraffins) technical mixture that contains 7820 congeners. In a second application, GC × GC-estimated properties are used to parametrize multiphase partitioning models for mammalian tissues and organs. In a third example, we estimate chemical depuration kinetics for mussels. Finally, we illustrate an approach to screen the GC × GC chromatogram for nonpolar chemicals of potentially high concern, defined based on their GC × GC-estimated biopartitioning properties, diffusion properties, and baseline toxicity.

  20. Photon diffusion near the point-of-entry in anisotropically scattering turbid media

    PubMed Central

    Vitkin, Edward; Turzhitsky, Vladimir; Qiu, Le; Guo, Lianyu; Itzkan, Irving; Hanlon, Eugene B.; Perelman, Lev T.

    2012-01-01

    From astronomy to cell biology, the manner in which light propagates in turbid media has been of central importance for many decades. However, light propagation near the point-of-entry (POE) in turbid media has never been analytically described, until now. Here we report a straightforward and accurate method that overcomes this longstanding, unsolved problem in radiative transport. Our theory properly treats anisotropic photon scattering events and takes the specific form of the phase function into account. As a result, our method correctly predicts the spatially dependent diffuse reflectance of light near the POE for any arbitrary phase function. We demonstrate that the theory is in excellent agreement with both experimental results and Monte Carlo simulations for several commonly used phase functions. PMID:22158442

  1. Lattice Boltzmann Method for Diffusion-Reaction-Transport Processes in Heterogeneous Porous Media

    NASA Astrophysics Data System (ADS)

    Xu, You-Sheng; Zhong, Yi-Jun; Huang, Guo-Xiang

    2004-07-01

    Based on the lattice Boltzmann method and general theory of fluids flowing in porous media, a numerical model is presented for the diffusion-reaction-transport (DRT) processes in porous media. As a test, we simulate a DRT process in a two-dimensional horizontal heterogeneous porous medium. The influence of gravitation in this case can be neglected, and the DRT process can be described by a strongly heterogeneous diagnostic test strip or a thin confined piece of soil with stochastically distributing property in horizontal directions. The results obtained for the relations between reduced fluid saturation S, concentration c1, and concentration c2 are shown by using the visualization computing technique. The computational efficiency and stability of the model are satisfactory.

  2. Inexact Picard iterative scheme for steady-state nonlinear diffusion in random heterogeneous media.

    PubMed

    Mohan, P Surya; Nair, Prasanth B; Keane, Andy J

    2009-04-01

    In this paper, we present a numerical scheme for the analysis of steady-state nonlinear diffusion in random heterogeneous media. The key idea is to iteratively solve the nonlinear stochastic governing equations via an inexact Picard iteration scheme, wherein the nonlinear constitutive law is linearized using the current guess of the solution. The linearized stochastic governing equations are then spatially discretized and approximately solved using stochastic reduced basis projection schemes. The approximation to the solution process thus obtained is used as the guess for the next iteration. This iterative procedure is repeated until an appropriate convergence criterion is met. Detailed numerical studies are presented for diffusion in a square domain for varying degrees of nonlinearity. The numerical results are compared against benchmark Monte Carlo simulations, and it is shown that the proposed approach provides good approximations for the response statistics at modest computational effort.

  3. Modelling neutron transport in planetary media via analytical multigroup diffusion theory

    NASA Astrophysics Data System (ADS)

    Panfili, P.; Luciani, A.; Furfaro, R.; Ganapol, B. D.; Mostacci, D.

    A novel analytical solution to the 1D, steady-state, multi-slab, multi-group diffusion equation is proposed as a mean to compute the energy-dependent galactic cosmic ray-induced neutron fluxes established in planetary media. More specifically, the proposed algorithm is implemented to allow fast and highly accurate determination of low-energy cosmic ray neutrons inside the Earth's surface and atmosphere. Two sets of experimental measurements have been considered to validate our model. In both cases, a good agreement between the calculated and observed neutron fluxes is achieved. Subsequently, neutron diffusion calculations have been performed for various Earth-based scenarios comprising (a) two-slab (air-soil) configuration and (b) three-slab (air-soil-ice) configuration to investigate the functional relationship between soil composition and neutron spatial distribution.

  4. Scaling method for fast Monte Carlo simulation of diffuse reflectance spectra from multilayered turbid media.

    PubMed

    Liu, Quan; Ramanujam, Nirmala

    2007-04-01

    A scaling Monte Carlo method has been developed to calculate diffuse reflectance from multilayered media with a wide range of optical properties in the ultraviolet-visible wavelength range. This multilayered scaling method employs the photon trajectory information generated from a single baseline Monte Carlo simulation of a homogeneous medium to scale the exit distance and exit weight of photons for a new set of optical properties in the multilayered medium. The scaling method is particularly suited to simulating diffuse reflectance spectra or creating a Monte Carlo database to extract optical properties of layered media, both of which are demonstrated in this paper. Particularly, it was found that the root-mean-square error (RMSE) between scaled diffuse reflectance, for which the anisotropy factor and refractive index in the baseline simulation were, respectively, 0.9 and 1.338, and independently simulated diffuse reflectance was less than or equal to 5% for source-detector separations from 200 to 1500 microm when the anisotropy factor of the top layer in a two-layered epithelial tissue model was varied from 0.8 to 0.99; in contrast, the RMSE was always less than 5% for all separations (from 0 to 1500 microm) when the anisotropy factor of the bottom layer was varied from 0.7 to 0.99. When the refractive index of either layer in the two-layered tissue model was varied from 1.3 to 1.4, the RMSE was less than 10%. The scaling method can reduce computation time by more than 2 orders of magnitude compared with independent Monte Carlo simulations.

  5. Diffusion-controlled startup of a gas-loaded liquid-metal heat pipe

    NASA Astrophysics Data System (ADS)

    Ponnappan, R.; Boehman, L. I.; Mahefkey, E. T.

    1990-07-01

    Liquid-metal heat pipes have exhibited difficulties starting up from a frozen-state. Inert gas loading is a possible solution to the frozen-state startup problem. The present study deals with the diffusion-controlled startup analysis and testing of an argon-loaded, 2-m-long, stainless steel-sodium heat pipe of the double-walled type with artery channel and long adiabatic section. A two-dimensional, quasi-steady state, binary vapor-gas diffusion model determined the energy transport rate of vapor at the diffusion front. The analytical solution to the diffusion problem provided the vapor flux, which in turn was used in the one-dimensional transient thermal model of the heat pipe to predict the time rate-of-change of temperature and position of the hot front. The experimental test results successfully demonstrated the startup of a gas-loaded sodium heat pipe and validated the diffusion model of the startup.

  6. [Electrochemical disinfection using the gas diffusion electrode system].

    PubMed

    Xu, Wen-Ying; Li, Ping; Dong, Bin

    2010-01-01

    Study on the electrochemical disinfection with the H2O2 produced at the gas diffusion electrode (GDE) prepared from active carbon/ poly-tetrafluoroethylene (PTFE) was performed in the non-membrane cell. The effects of PTFE mass fraction W(PTFE) and content of the pore-forming agent in GDE m(NH4CO3), operating conditions such as pH value and oxygen flow rate Q(o2)) on disinfection were investigated, respectively. The experimental results showed that H2 O2 reached peak production at W(PTFE) of 0.5 in GDE. Addition of the pore-forming agent in the appropriate amount improved the disinfection, and this phenomenon was more obvious at neutral pH than at acidic pH. BET specific area analysis indicated that the average pore size in the membrane electrode first decreased significantly with the increasing amount of pore-forming agent, and then increased moderately. This helped the mass transfer of oxygen at the GDE. Adsorption made little or no progress to kill the bacteria during the electrolysis. Drop of pH value resulted in a rapid rise of the germicidal efficacy. This system had a broad pH coverage: when total bacterial count in raw water was 10(6) CFU x mL(-1), pH 3-10,the germicidal efficacy was greater than 80% after 30 min electrolysis using the GDE with W(Pt) of 3 per thousand as cathode. Increase of the oxygen flow rate Q(o2) within limits had little influence on the production of H2 O2 and the succeeding disinfection. On one hand, resistance of the solution and energy consumption on the disinfection increased at high oxygen flow rate, which gave rise to an increase in the operating cost of disinfection with the GDE system; on the other hand, treatment time could be reduced reasonably at high oxygen flow rate, which leads to reduction of equipment investment. Killing mechanism study showed that the direct oxidation and formation of the free radicals at the anode played a greater role in the beginning, and then the oxidative indirect effect of the generated H2 O2 at

  7. A new in-situ method to determine the apparent gas diffusion coefficient of soils

    NASA Astrophysics Data System (ADS)

    Laemmel, Thomas; Paulus, Sinikka; Schack-Kirchner, Helmer; Maier, Martin

    2015-04-01

    Soil aeration is an important factor for the biological activity in the soil and soil respiration. Generally, gas exchange between soil and atmosphere is assumed to be governed by diffusion and Fick's Law is used to describe the fluxes in the soil. The "apparent soil gas diffusion coefficient" represents the proportional factor between the flux and the gas concentration gradient in the soil and reflects the ability of the soil to "transport passively" gases through the soil. One common way to determine this coefficient is to take core samples in the field and determine it in the lab. Unfortunately this method is destructive and needs laborious field work and can only reflect a small fraction of the whole soil. As a consequence insecurity about the resulting effective diffusivity on the profile scale must remain. We developed a new in-situ method using new gas sampling device, tracer gas and inverse soil gas modelling. The gas sampling device contains several sampling depths and can be easily installed into vertical holes of an auger, which allows for fast installation of the system. At the lower end of the device inert tracer gas is injected continuously. The tracer gas diffuses into the surrounding soil. The resulting distribution of the tracer gas concentrations is used to deduce the diffusivity profile of the soil. For Finite Element Modeling of the gas sampling device/soil system the program COMSOL is used. We will present the results of a field campaign comparing the new in-situ method with lab measurements on soil cores. The new sampling pole has several interesting advantages: it can be used in-situ and over a long time; so it allows following modifications of diffusion coefficients in interaction with rain but also vegetation cycle and wind.

  8. 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

    2016-09-01

    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.

  9. An in situ method for real-time monitoring of soil gas diffusivity

    NASA Astrophysics Data System (ADS)

    Laemmel, Thomas; Maier, Martin; Schack-Kirchner, Helmer; Lang, Friederike

    2016-04-01

    Soil aeration is an important factor for the biogeochemistry of soils. Generally, gas exchange between soil and atmosphere is assumed to be governed by molecular diffusion and by this way fluxes can be calculated using by Fick's Law. The soil gas diffusion coefficient DS represents the proportional factor between the gas flux and the gas concentration gradient in the soil and reflects the ability of the soil to "transport passively" gas through the soil. One common way to determine DS is taking core samples in the field and measuring DS in the lab. Unfortunately this method is destructive and laborious and it can only reflect a small fraction of the whole soil. As a consequence, uncertainty about the resulting effective diffusivity on the profile scale, i.e. the real aeration status remains. We developed a method to measure and monitor DS in situ. The set-up consists of a custom made gas sampling device, the continuous injection of an inert tracer gas and inverse gas transport modelling in the soil. The gas sampling device has seven sampling depths (from 0 to -43 cm of depth) and can be easily installed into vertical holes drilled by an auger, which allows for fast installation of the system. Helium (He) as inert tracer gas was injected continuously at the lower end of the device. The resulting steady state distribution of He was used to deduce the DS depth distribution of the soil. For Finite Element Modeling of the gas-sampling-device/soil system the program COMSOL was used. We tested our new method both in the lab and in a field study and compared the results with a reference lab method using soil cores. DS profiles obtained by our in-situ method were consistent with DS profiles determined based on soil core analyses. Soil gas profiles could be measured with a temporal resolution of 30 minutes. During the field study, there was an important rain event and we could monitor the decrease in soil gas diffusivity in the top soil due to water infiltration. The effect

  10. Time-resolved diffusion tomographic 2D and 3D imaging in highly scattering turbid media

    NASA Technical Reports Server (NTRS)

    Alfano, Robert R. (Inventor); Cai, Wei (Inventor); Liu, Feng (Inventor); Lax, Melvin (Inventor); Das, Bidyut B. (Inventor)

    1999-01-01

    A method for imaging objects in highly scattering turbid media. According to one embodiment of the invention, the method involves using a plurality of intersecting source/detectors sets and time-resolving equipment to generate a plurality of time-resolved intensity curves for the diffusive component of light emergent from the medium. For each of the curves, the intensities at a plurality of times are then inputted into the following inverse reconstruction algorithm to form an image of the medium: ##EQU1## wherein W is a matrix relating output at source and detector positions r.sub.s and r.sub.d, at time t, to position r, .LAMBDA. is a regularization matrix, chosen for convenience to be diagonal, but selected in a way related to the ratio of the noise, to fluctuations in the absorption (or diffusion) X.sub.j that we are trying to determine: .LAMBDA..sub.ij =.lambda..sub.j .delta..sub.ij with .lambda..sub.j =/<.DELTA.Xj.DELTA.Xj> Y is the data collected at the detectors, and X.sup.k is the kth iterate toward the desired absoption information. An algorithm, which combines a two dimensional (2D) matrix inversion with a one-dimensional (1D) Fourier transform inversion is used to obtain images of three dimensional hidden objects in turbid scattering media.

  11. Time-resolved diffusion tomographic 2D and 3D imaging in highly scattering turbid media

    NASA Technical Reports Server (NTRS)

    Alfano, Robert R. (Inventor); Cai, Wei (Inventor); Gayen, Swapan K. (Inventor)

    2000-01-01

    A method for imaging objects in highly scattering turbid media. According to one embodiment of the invention, the method involves using a plurality of intersecting source/detectors sets and time-resolving equipment to generate a plurality of time-resolved intensity curves for the diffusive component of light emergent from the medium. For each of the curves, the intensities at a plurality of times are then inputted into the following inverse reconstruction algorithm to form an image of the medium: wherein W is a matrix relating output at source and detector positions r.sub.s and r.sub.d, at time t, to position r, .LAMBDA. is a regularization matrix, chosen for convenience to be diagonal, but selected in a way related to the ratio of the noise, to fluctuations in the absorption (or diffusion) X.sub.j that we are trying to determine: .LAMBDA..sub.ij =.lambda..sub.j .delta..sub.ij with .lambda..sub.j =/<.DELTA.Xj.DELTA.Xj> Y is the data collected at the detectors, and X.sup.k is the kth iterate toward the desired absorption information. An algorithm, which combines a two dimensional (2D) matrix inversion with a one-dimensional (1D) Fourier transform inversion is used to obtain images of three dimensional hidden objects in turbid scattering media.

  12. Impact of compression on gas transport in non-woven gas diffusion layers of high temperature polymer electrolyte fuel cells

    NASA Astrophysics Data System (ADS)

    Froning, Dieter; Yu, Junliang; Gaiselmann, Gerd; Reimer, Uwe; Manke, Ingo; Schmidt, Volker; Lehnert, Werner

    2016-06-01

    Gas transport in non-woven gas diffusion layers of a high-temperature polymer electrolyte fuel cell was calculated with the Lattice Boltzmann method. The underlying micro structure was taken from two sources. A real micro structure was analyzed in the synchrotron under the impact of a compression mask mimicking the channel/rib structure of a flow field. Furthermore a stochastic geometry model based on synchrotron X-ray tomography studies was applied. The effect of compression is included in the stochastic model. Gas transport in these micro structures was simulated and the impact of compression was analyzed. Fiber bundles overlaying the micro structure were identified which affect the homogeneity of the gas flow. There are significant deviations between the impact of compression on effective material properties for this type of gas diffusion layers and the Kozeny-Carman equation.

  13. Mathematical model of diffusion-limited evolution of multiple gas bubbles in tissue

    NASA Technical Reports Server (NTRS)

    Srinivasan, R. Srini; Gerth, Wayne A.; Powell, Michael R.

    2003-01-01

    Models of gas bubble dynamics employed in probabilistic analyses of decompression sickness incidence in man must be theoretically consistent and simple, if they are to yield useful results without requiring excessive computations. They are generally formulated in terms of ordinary differential equations that describe diffusion-limited gas exchange between a gas bubble and the extravascular tissue surrounding it. In our previous model (Ann. Biomed. Eng. 30: 232-246, 2002), we showed that with appropriate representation of sink pressures to account for gas loss or gain due to heterogeneous blood perfusion in the unstirred diffusion region around the bubble, diffusion-limited bubble growth in a tissue of finite volume can be simulated without postulating a boundary layer across which gas flux is discontinuous. However, interactions between two or more bubbles caused by competition for available gas cannot be considered in this model, because the diffusion region has a fixed volume with zero gas flux at its outer boundary. The present work extends the previous model to accommodate interactions among multiple bubbles by allowing the diffusion region volume of each bubble to vary during bubble evolution. For given decompression and tissue volume, bubble growth is sustained only if the bubble number density is below a certain maximum.

  14. Diffuse optical 3D-slice imaging of bounded turbid media using a new integro-differential equation.

    PubMed

    Pattanayak, D; Yodh, A

    1999-04-12

    A new integro-differential equation for diffuse photon density waves (DPDW) is derived within the diffusion approximation. The new equation applies to inhomogeneous bounded turbid media. Interestingly, it does not contain any terms involving gradients of the light diffusion coefficient. The integro-differential equation for diffusive waves is used to develop a 3D-slice imaging algorithm based the on angular spectrum representation in the parallel plate geometry. The algorithm may be useful for near infrared optical imaging of breast tissue, and is applicable to other diagnostics such as ultrasound and microwave imaging.

  15. Relative role of convective and diffusive mixing in the miscible Rayleigh-Taylor instability in porous media

    NASA Astrophysics Data System (ADS)

    Gopalakrishnan, S. S.; Carballido-Landeira, J.; De Wit, A.; Knaepen, B.

    2017-01-01

    The relative role of convection and diffusion is characterized both numerically and experimentally for porous media flows due to a Rayleigh-Taylor instability of a horizontal interface between two miscible solutions in the gravity field. We show that, though globally convection dominates over diffusion during the nonlinear regime, diffusion can locally be as important as convection and even dominates over lateral convection far away from the fingertips. Our experimental and numerical computations of the temporal evolution of the mixing length, the width of the fingers, and their wavelength are in good agreement and show that the lateral evolution of fingers is governed by diffusion.

  16. Transport of methane and noble gases during gas push-pull tests in variably saturated porous media.

    PubMed

    Gómez, Katherine; Gonzalez-Gil, Graciela; Schroth, Martin H; Zeyer, Josef

    2008-04-01

    The gas push-pull test (GPPT) is a single-well gas-tracer method to quantify in situ rates of CH4 oxidation in soils. To improve the design and interpretation of GPPT field experiments, gas component transport during GPPTs was examined in abiotic porous media over a range of water saturations (0.0 < or = Sw < or = 0.61). A series of GPPTs using He, Ne, and Ar as tracers for CH4 were performed at two injection/extraction gas flow rates (approximately 200 and approximately 700 mL min(-1)) in a laboratory tank. Extraction phase breakthrough curves and mass recovery curves of the gaseous components became more similar at higher Sw as water in the pore space restricted diffusive gas-phase transport. Diffusional fractionation of the stable carbon isotopes of CH4 during the extraction period of GPPTs also decreased with increasing Sw (particularly when Sw > 0.42). Gas-component transport during GPPTs was numerically simulated using estimated hydraulic parameters for the porous media and no fitting of data for the GPPTs. Numerical simulations accurately predicted the relative decline of the gaseous components in the breakthrough curves, but slightly overestimated recoveries at low Sw (< or = 0.35) and underestimated recoveries at high Sw (> or = 0.49). Comparison of numerical simulations considering and not considering air-water partitioning indicated that removal of gaseous components through dissolution in pore water was not significant during GPPTs, even at Sw = 0.61. These data indicate that Ar is a good tracer for CH4 physical transport over the full range of Sw studied, whereas, at Sw > 0.61, any of the tracers could be used. Greater mass recovery at higher Sw raises the possibility to reduce gas flow rates, thereby extending GPPT times in environments such as tundra soils where low activity due to low temperatures may require longer test times to establish a quantifiable difference between reactant and tracer breakthrough curves.

  17. Effects of diffusion in magnetically inhomogeneous media on rotating frame spin-lattice relaxation

    NASA Astrophysics Data System (ADS)

    Spear, John T.; Gore, John C.

    2014-12-01

    In an aqueous medium containing magnetic inhomogeneities, diffusion amongst the intrinsic susceptibility gradients contributes to the relaxation rate R1ρ of water protons to a degree that depends on the magnitude of the local field variations ΔBz, the geometry of the perturbers inducing these fields, and the rate of diffusion of water, D. This contribution can be reduced by using stronger locking fields, leading to a dispersion in R1ρ that can be analyzed to derive quantitative characteristics of the material. A theoretical expression was recently derived to describe these effects for the case of sinusoidal local field variations of a well-defined spatial frequency q. To evaluate the degree to which this dispersion may be extended to more realistic field patterns, finite difference Bloch-McConnell simulations were performed with a variety of three-dimensional structures to reveal how simple geometries affect the dispersion of spin-locking measurements. Dispersions were fit to the recently derived expression to obtain an estimate of the correlation time of the field variations experienced by the spins, and from this the mean squared gradient and an effective spatial frequency were obtained to describe the fields. This effective spatial frequency was shown to vary directly with the second moment of the spatial frequency power spectrum of the ΔBz field, which is a measure of the average spatial dimension of the field variations. These results suggest the theory may be more generally applied to more complex media to derive useful descriptors of the nature of field inhomogeneities. The simulation results also confirm that such diffusion effects disperse over a range of locking fields of lower amplitude than typical chemical exchange effects, and should be detectable in a variety of magnetically inhomogeneous media including regions of dense microvasculature within biological tissues.

  18. Derivation and Solution of Multifrequency Radiation Diffusion Equations for Homogeneous Refractive Lossy Media

    SciTech Connect

    Shestakov, A I; Vignes, R M; Stolken, J S

    2010-01-05

    Starting from the radiation transport equation for homogeneous, refractive lossy media, we derive the corresponding time-dependent multifrequency diffusion equations. Zeroth and first moments of the transport equation couple the energy density, flux and pressure tensor. The system is closed by neglecting the temporal derivative of the flux and replacing the pressure tensor by its diagonal analogue. The system is coupled to a diffusion equation for the matter temperature. We are interested in modeling annealing of silica (SiO{sub 2}). We derive boundary conditions at a planar air-silica interface taking account of reflectivities. The spectral dimension is discretized into a finite number of intervals leading to a system of multigroup diffusion equations. Three simulations are presented. One models cooling of a silica slab, initially at 2500 K, for 10 s. The other two are 1D and 2D simulations of irradiating silica with a CO{sub 2} laser, {lambda} = 10.59 {micro}m. In 2D, we anneal a disk (radius = 0.4, thickness = 0.4 cm) with a laser, Gaussian profile (r{sub 0} = 0.5 mm for 1/e decay).

  19. VARIATIONS BETWEEN DUST AND GAS IN THE DIFFUSE INTERSTELLAR MEDIUM

    SciTech Connect

    Reach, William T.; Heiles, Carl; Bernard, Jean-Philippe

    2015-10-01

    Using the Planck far-infrared and Arecibo GALFA 21 cm line surveys, we identified a set of isolated interstellar clouds (approximately degree-sized on the sky and comprising 100 solar masses) and assessed the ratio of gas mass to dust mass. Significant variations of the gas/dust ratio are found both from cloud to cloud and within regions of individual clouds; within the clouds, the atomic gas per unit dust decreases by more than a factor of 3 compared with the standard gas/dust ratio. Three hypotheses are considered. First, the apparently low gas/dust ratio could be due to molecular gas. Comparing to Planck CO maps, the brightest clouds have a H{sub 2}/CO ratio comparable to Galactic plane clouds, but a strong lower limit is placed on the ratio for other clouds, such that the required amount of molecular gas is far higher than would be expected based on the CO upper limits. Second, we consider self-absorbed 21 cm lines and find that the optical depth must be ∼3, significantly higher than found from surveys of radio sources. Third, grain properties may change within the clouds: they become more emissive when they are colder, while not utilizing heavy elements that already have their cosmic abundance fully locked into grains. It is possible that all three processes are active, and follow-up studies will be required to disentangle them and measure the true total gas and dust content of interstellar clouds.

  20. Mathematical model of diffusion-limited gas bubble dynamics in unstirred tissue with finite volume

    NASA Technical Reports Server (NTRS)

    Srinivasan, R. Srini; Gerth, Wayne A.; Powell, Michael R.

    2002-01-01

    Models of gas bubble dynamics for studying decompression sickness have been developed by considering the bubble to be immersed in an extravascular tissue with diffusion-limited gas exchange between the bubble and the surrounding unstirred tissue. In previous versions of this two-region model, the tissue volume must be theoretically infinite, which renders the model inapplicable to analysis of bubble growth in a finite-sized tissue. We herein present a new two-region model that is applicable to problems involving finite tissue volumes. By introducing radial deviations to gas tension in the diffusion region surrounding the bubble, the concentration gradient can be zero at a finite distance from the bubble, thus limiting the tissue volume that participates in bubble-tissue gas exchange. It is shown that these deviations account for the effects of heterogeneous perfusion on gas bubble dynamics, and are required for the tissue volume to be finite. The bubble growth results from a difference between the bubble gas pressure and an average gas tension in the surrounding diffusion region that explicitly depends on gas uptake and release by the bubble. For any given decompression, the diffusion region volume must stay above a certain minimum in order to sustain bubble growth.

  1. Water Transport in the Micro Porous Layer and Gas Diffusion Layer of a Polymer Electrolyte Fuel Cell

    NASA Astrophysics Data System (ADS)

    Qin, C.; Hassanizadeh, S. M.

    2015-12-01

    In this work, a recently developed dynamic pore-network model is presented [1]. The model explicitly solves for both water pressure and capillary pressure. A semi-implicit scheme is used in updating water saturation in each pore body, which considerably increases the numerical stability at low capillary number values. Furthermore, a multiple-time-step algorithm is introduced to reduce the computational effort. A number of case studies of water transport in the micro porous layer (MPL) and gas diffusion layer (GDL) are conducted. We illustrate the role of MPL in reducing water flooding in the GDL. Also, the dynamic water transport through the MPL-GDL interface is explored in detail. This information is essential to the reduced continua model (RCM), which was developed for multiphase flow through thin porous layers [2, 3]. C.Z. Qin, Water transport in the gas diffusion layer of a polymer electrolyte fuel cell: dynamic pore-network modeling, J Electrochimical. Soci., 162, F1036-F1046, 2015. C.Z. Qin and S.M. Hassanizadeh, Multiphase flow through multilayers of thin porous media: general balance equations and constitutive relationships for a solid-gas-liquid three-phase system, Int. J. Heat Mass Transfer, 70, 693-708, 2014. C.Z. Qin and S.M. Hassanizadeh, A new approach to modeling water flooding in a polymer electrolyte fuel cell, Int. J. Hydrogen Energy, 40, 3348-3358, 2015.

  2. An advanced passive diffusion sampler for the determination of dissolved gas concentrations

    NASA Astrophysics Data System (ADS)

    Gardner, P.; Solomon, D. K.

    2009-06-01

    We have designed and tested a passive headspace sampler for the collection of noble gases that allows for the precise calculation of dissolved gas concentrations from measured gas mixing ratios. Gas permeable silicon tubing allows for gas exchange between the headspace in the sampler volume and the dissolved gases in the adjacent water. After reaching equilibrium, the aqueous-phase concentration is related to the headspace concentration by Henry's law. Gas exchange between the water and headspace can be shut off in situ, preserving the total dissolved gas pressure upon retrieval. Gas samples are then sealed in an all metal container, retaining even highly mobile helium. Dissolved noble gas concentrations measured in these diffusion samplers are in good agreement with traditional copper tube aqueous-phase samples. These significantly reduce the laboratory labor in extracting the gases from a water sample and provide a simple and robust method for collecting dissolved gas concentrations in a variety of aqueous environments.

  3. Free and Forced Convection in High Permeability Porous Media: Impact on Gas Flux at the Earth-atmosphere Interface

    NASA Astrophysics Data System (ADS)

    Weisbrod, N.; Levintal, E.; Dragila, M. I.; Kamai, T.

    2015-12-01

    Gas movement within the earth's subsurface and its exchange with the atmosphere is one of the principal elements contributing to soil and atmospheric function. As the soil permeability increases, gas circulation by convective mechanisms becomes significantly greater than the diffusion. Two of the convective mechanisms, which can be of great importance, are being explored in this research. The first one is thermal convection venting (TCV), which develops when there are unstable density gradients. The second mechanism is wind induced convection (WIC), which develops due to surface winds that drive air movement. Here, we report the results of a study on the relationships between the porous media permeability and particle size, and the development and magnitude of TCV and WIC with the development of thermal differences and surface winds. The research included large high-permeability column experiments carried out under highly controlled laboratory conditions, using well-defined single-sized spherical particles while surface winds and thermal differences were forced and monitored. CO2 enriched air, functioned as a tracer, was used to quantify the impact of TCV and WIC on gas migration in the porous media. Results show that in homogenous porous media a permeability range of 10-7 to 10-6 m2 is the threshold value for TCV onset under standard atmospheric conditions. Adding surface wind with an average velocity of 1.5 m s-1 resulted in WIC effect to a depth of -0.3 m in most experimental settings; however, it did not caused additional air circulation at the reference depth of -0.9 m. Furthermore, given the appropriate conditions, a combined effect of TCV and WIC did significantly increase the overall media ventilation. Simulations of temperature profiles in soil under that permeability, showed that as the thermal gradient changes with depth and is a continuous function, TCV cells can be developed in local sections of the profile, not necessarily reaching the atmosphere.

  4. Interplay between oxygen demand reactions and kinetic gas-water transfer in porous media.

    PubMed

    Oswald, Sascha E; Griepentrog, Marco; Schirmer, Mario; Balcke, Gerd U

    2008-08-01

    Gas-water phase transfer associated with the dissolution of trapped gas in porous media is a key process that occurs during pulsed gas sparging operations in contaminated aquifers. Recently, we applied a numerical model that was experimentally validated for abiotic situations, where multi-species kinetic inter-phase mass transfer and dissolved gas transport occurred during pulsed gas penetration-dissolution events [Balcke, G.U., Meenken, S., Hoefer, C. and Oswald, S.E., 2007. Kinetic gas-water transfer and gas accumulation in porous media during pulsed oxygen sparging. Environmental Science & Technology 41(12), 4428-4434]. Here we extend the model by using a reactive term to describe dissolved oxygen demand reactions via the formation of a reaction product, and to study the effects of such an aerobic degradation process on gas-water mass transfer and dissolution of trapped gas in porous media. As a surrogate for microbial oxygen reduction, first-order oxygen demand reactions were based on the measured oxidation of alkaline pyrogallol in column experiments. This reaction allows for adjusting the rate to values close to expected biodegradation rates and detection of the reaction product. The experiments and model consistently demonstrated accelerated oxygen gas-water mass transfer with increasing oxygen demand rates associated with an influence on the partitioning of other gases. Thus, as the oxygen demand accelerates, less gas phase residues, consisting mainly of nitrogen, are observed, which is in general beneficial to the performance of field biosparging operations. Model results additionally predict how oxygen demand influences oxygen mass transfer for a range of biodegradation rates. A typical field case scenario was simulated to illustrate the observed coupling of oxygen consumption and gas bubble dissolution. The model provides a tool to improve understanding of trapped gas behavior in porous media and contributes to a model-assisted biosparging.

  5. Hydrogen production in a microbial electrolysis cell with nickel-based gas diffusion cathodes

    NASA Astrophysics Data System (ADS)

    Manuel, M.-F.; Neburchilov, V.; Wang, H.; Guiot, S. R.; Tartakovsky, B.

    Gas diffusion cathodes with Ni alloy and Ni catalysts manufactured by chemical deposition were tested for H 2 production in a microbial electrolysis cell (MEC). In a continuous flow MEC, multi-component cathodes containing Ni, Mo, Cr, and Fe, at a total catalyst load of 1 mg cm -2 on carbon support demonstrated stable H 2 production at rates of 2.8 - 3.7 L LR-1 d-1 with only 5% methane in the gas stream. Furthermore, a Ni-only gas diffusion cathode, with a Ni load of 0.6 mg cm -2, demonstrated a H 2 production rate of 4.1 L LR-1 d-1 . Overall, H 2 production was found to be proportional to the Ni load implying that inexpensive gas diffusion cathodes prepared by chemical deposition of Ni can be successfully used for continuous production of H 2 in a MEC.

  6. Derivation of effective fission gas diffusivities in UO2 from lower length scale simulations and implementation of fission gas diffusion models in BISON

    SciTech Connect

    Andersson, Anders David Ragnar; Pastore, Giovanni; Liu, Xiang-Yang; Perriot, Romain Thibault; Tonks, Michael; Stanek, Christopher Richard

    2014-11-07

    This report summarizes the development of new fission gas diffusion models from lower length scale simulations and assessment of these models in terms of annealing experiments and fission gas release simulations using the BISON fuel performance code. Based on the mechanisms established from density functional theory (DFT) and empirical potential calculations, continuum models for diffusion of xenon (Xe) in UO2 were derived for both intrinsic conditions and under irradiation. The importance of the large XeU3O cluster (a Xe atom in a uranium + oxygen vacancy trap site with two bound uranium vacancies) is emphasized, which is a consequence of its high mobility and stability. These models were implemented in the MARMOT phase field code, which is used to calculate effective Xe diffusivities for various irradiation conditions. The effective diffusivities were used in BISON to calculate fission gas release for a number of test cases. The results are assessed against experimental data and future directions for research are outlined based on the conclusions.

  7. In situ bioremediation: A network model of diffusion and flow in granular porous media

    SciTech Connect

    Griffiths, S.K.; Nilson, R.H.; Bradshaw, R.W.

    1997-04-01

    In situ bioremediation is a potentially expedient, permanent and cost- effective means of waste site decontamination. However, permeability reductions due to the transport and deposition of native fines or due to excessive microorganism populations may severely inhibit the injection of supplemental oxygen in the contamination zone. To help understand this phenomenon, we have developed a micro-mechanical network model of flow, diffusion and particle transport in granular porous materials. The model differs from most similar models in that the network is defined by particle positions in a numerically-generated particle array. The model is thus widely applicable to computing effective transport properties for both ordered and realistic random porous media. A laboratory-scale apparatus to measure permeability reductions has also been designed, built and tested.

  8. Isotopic mass-dependence of noble gas diffusion coefficients inwater

    SciTech Connect

    Bourg, I.C.; Sposito, G.

    2007-06-25

    Noble gas isotopes are used extensively as tracers inhydrologic and paleoclimatic studies. These applications requireknowledge of the isotopic mass (m) dependence of noble gas diffusioncoefficients in water (D), which has not been measured but is estimatedusing experimental D-values for the major isotopes along with an untestedrelationship from kinetic theory, D prop m-0.5. We applied moleculardynamics methods to determine the mass dependence of D for four noblegases at 298 K, finding that D prop m-beta with beta<0.2, whichrefutes the kinetic theory model underlying all currentapplications.

  9. A diffuse interface approach to injection-driven flow of different miscibility in heterogeneous porous media

    NASA Astrophysics Data System (ADS)

    Chen, Ching-Yao; Yan, Pei-Yu

    2015-08-01

    Miscible and immiscible injection flows in heterogeneous porous media, for which the permeability is characterized by a log Gaussian distribution, are simulated by a robust diffuse-interface formulation. The robust numerical method enables direct qualitative and quantitative comparisons regarding pattern formations in various fluid miscibility conditions. For miscible injections, the typical size of fingering structures depends strongly on the correlation length and forms tapered fingers with sharper tips. On the other hand, the typical size of immiscible fingers is affected less significantly by the permeability heterogeneity, and wide spreading tips are retained in the fingering patterns. Prominence of fingering instability is quantitatively evaluated by the channeling width and the interfacial length. The channeling width shows strong and monotonic dependences on the heterogeneous variance. On the contrary, maximum channeling width occurs at intermediate correlation length due to local resonant effect between the faster penetrating fingers and permeability heterogeneity. On the other hand, effects of the correlation length and the permeability variance on the interfacial lengths are generally consistent. Longer interfacial length is perturbed by smaller correlation length or higher variance. Interesting invariant evolutions of interfacial lengths are revealed regardless of the permeability variance in sufficiently large correlation length under all miscibility conditions. In addition, the regime of slower growth of interfacial length at later times experimentally observed in homogeneous miscible injection is verified in heterogeneous porous media as well.

  10. Trapped bubbles keep pumice afloat and gas diffusion makes pumice sink

    NASA Astrophysics Data System (ADS)

    Fauria, Kristen E.; Manga, Michael; Wei, Zihan

    2017-02-01

    Pumice can float on water for months to years - long enough for pumice to travel across oceans and facilitate the spread of species. Long-lived pumice floatation is unexpected, however, because pumice pores are highly connected and water wets volcanic glass. As a result, observations of long floating times have not been reconciled with predictions of rapid sinking. We propose a mechanism to resolve this paradox - the trapping of gas bubbles by water within the pumice. Gas trapping refers to the isolation of gas by water within pore throats such that the gas becomes disconnected from the atmosphere and unable to escape. We use X-ray microtomography to image partially saturated pumice and demonstrate that non-condensable gas trapping occurs in both ambient temperature and hot (500 °C) pumice. Furthermore, we show that the size distribution of trapped gas clusters matches predictions of percolation theory. Finally, we propose that diffusion of trapped gas determines pumice floatation time. Experimental measurements of pumice floatation support a diffusion control on pumice buoyancy and we find that floatation time τ scales as τ ∝ L2/Dθ2 where L is the characteristic length of pumice, D is the gas-water diffusion coefficient, and θ is pumice water saturation. A mechanistic understanding of pumice floatation is a step towards understanding how pumice is partitioned into floating and sinking components and provides an estimate for the lifetime of pumice rafts in the ocean.

  11. Diffusion of methane and other alkanes in metal-organic frameworks for natural gas storage

    SciTech Connect

    Borah, B; Zhang, HD; Snurr, RQ

    2015-03-03

    Diffusion of methane, ethane, propane and n-butane was studied within the micropores of several metal organic frameworks (MOFs) of varying topologies, including the MOFs PCN-14, NU-125, NU-1100 and DUT-49. Diffusion coefficients of the pure components, as well as methane/ethane, methane/ propane and methane/butane binary mixtures, were calculated using molecular dynamics simulations to understand the effect of the longer alkanes on uptake of natural gas in MOB. The calculated self diffusion coefficients of all four components are on the order of 10(-8) m(2)/s. The diffusion coefficients of the pure components decrease as a function of chain length in all of the MOFs studied and show different behaviour as a function of loading in different MOB. The self-diffusivities follow the trend DPCN-14 < DNU-125 approximate to DNU-1100 < DDUT-49, which is exactly the reverse order of the densities of the MOFs: PCN-14 > NU-125 approximate to NU-1100 > DUT-49. By comparing the diffusion of pure methane and methane mixtures vvith the higher alkancs, it is observed that the diffusivity of methane is unaffected by the presence of the higher alkanes in the MOFs considered, indicating that the diffusion path of methane is not blocked by the higher alkanes present in natural gas. (C) 2014 Elsevier Ltd. All rights reserved.

  12. Enhanced Vapor-Phase Diffusion in Porous Media - LDRD Final Report

    SciTech Connect

    Ho, C.K.; Webb, S.W.

    1999-01-01

    As part of the Laboratory-Directed Research and Development (LDRD) Program at Sandia National Laboratories, an investigation into the existence of enhanced vapor-phase diffusion (EVD) in porous media has been conducted. A thorough literature review was initially performed across multiple disciplines (soil science and engineering), and based on this review, the existence of EVD was found to be questionable. As a result, modeling and experiments were initiated to investigate the existence of EVD. In this LDRD, the first mechanistic model of EVD was developed which demonstrated the mechanisms responsible for EVD. The first direct measurements of EVD have also been conducted at multiple scales. Measurements have been made at the pore scale, in a two- dimensional network as represented by a fracture aperture, and in a porous medium. Significant enhancement of vapor-phase transport relative to Fickian diffusion was measured in all cases. The modeling and experimental results provide additional mechanisms for EVD beyond those presented by the generally accepted model of Philip and deVries (1957), which required a thermal gradient for EVD to exist. Modeling and experimental results show significant enhancement under isothermal conditions. Application of EVD to vapor transport in the near-surface vadose zone show a significant variation between no enhancement, the model of Philip and deVries, and the present results. Based on this information, the model of Philip and deVries may need to be modified, and additional studies are recommended.

  13. Time-resolved diffusion tomographic imaging in highly scattering turbid media

    NASA Technical Reports Server (NTRS)

    Alfano, Robert R. (Inventor); Cai, Wei (Inventor); Liu, Feng (Inventor); Lax, Melvin (Inventor); Das, Bidyut B. (Inventor)

    1998-01-01

    A method for imaging objects in highly scattering turbid media. According to one embodiment of the invention, the method involves using a plurality of intersecting source/detectors sets and time-resolving equipment to generate a plurality of time-resolved intensity curves for the diffusive component of light emergent from the medium. For each of the curves, the intensities at a plurality of times are then inputted into the following inverse reconstruction algorithm to form an image of the medium: X.sup.(k+1).spsp.T =?Y.sup.T W+X.sup.(k).spsp.T .LAMBDA.!?W.sup.T W+.LAMBDA.!.sup.-1 wherein W is a matrix relating output at detector position r.sub.d, at time t, to source at position r.sub.s, .LAMBDA. is a regularization matrix, chosen for convenience to be diagonal, but selected in a way related to the ratio of the noise, to fluctuations in the absorption (or diffusion) X.sub.j that we are trying to determine: .LAMBDA..sub.ij =.lambda..sub.j .delta..sub.ij with .lambda..sub.j =/<.DELTA.Xj.DELTA.Xj> Here Y is the data collected at the detectors, and X.sup.k is the kth iterate toward the desired absoption information.

  14. Experimental studies and model analysis of noble gas fractionation in porous media

    USGS Publications Warehouse

    Ding, Xin; Kennedy, B. Mack.; Evans, William C.; Stonestrom, David A.

    2016-01-01

    The noble gases, which are chemically inert under normal terrestrial conditions but vary systematically across a wide range of atomic mass and diffusivity, offer a multicomponent approach to investigating gas dynamics in unsaturated soil horizons, including transfer of gas between saturated zones, unsaturated zones, and the atmosphere. To evaluate the degree to which fractionation of noble gases in the presence of an advective–diffusive flux agrees with existing theory, a simple laboratory sand column experiment was conducted. Pure CO2 was injected at the base of the column, providing a series of constant CO2 fluxes through the column. At five fixed sampling depths within the system, samples were collected for CO2 and noble gas analyses, and ambient pressures were measured. Both the advection–diffusion and dusty gas models were used to simulate the behavior of CO2 and noble gases under the experimental conditions, and the simulations were compared with the measured depth-dependent concentration profiles of the gases. Given the relatively high permeability of the sand column (5 ´ 10−11 m2), Knudsen diffusion terms were small, and both the dusty gas model and the advection–diffusion model accurately predicted the concentration profiles of the CO2 and atmospheric noble gases across a range of CO2 flux from ?700 to 10,000 g m−2 d−1. The agreement between predicted and measured gas concentrations demonstrated that, when applied to natural systems, the multi-component capability provided by the noble gases can be exploited to constrain component and total gas fluxes of non-conserved (CO2) and conserved (noble gas) species or attributes of the soil column relevant to gas transport, such as porosity, tortuosity, and gas saturation.

  15. Turbine exhaust diffuser with region of reduced flow area and outer boundary gas flow

    DOEpatents

    Orosa, John

    2014-03-11

    An exhaust diffuser system and method for a turbine engine. The outer boundary may include a region in which the outer boundary extends radially inwardly toward the hub structure and may direct at least a portion of an exhaust flow in the diffuser toward the hub structure. At least one gas jet is provided including a jet exit located on the outer boundary. The jet exit may discharge a flow of gas downstream substantially parallel to an inner surface of the outer boundary to direct a portion of the exhaust flow in the diffuser toward the outer boundary to effect a radially outward flow of at least a portion of the exhaust gas flow toward the outer boundary to balance an aerodynamic load between the outer and inner boundaries.

  16. Ultrasonic imaging of highly scattering media from local measurements of the diffusion constant: Separation of coherent and incoherent intensities

    NASA Astrophysics Data System (ADS)

    Aubry, Alexandre; Derode, Arnaud

    2007-02-01

    As classical imaging fails with diffusive media, one way to image a multiple-scattering medium is to achieve local measurements of the dynamic transport properties of a wave undergoing diffusion. This paper presents a method to obtain local measurements of the diffusion constant D in a multiple-scattering medium. The experimental setup consists in an array of programmable transducers placed in front of the multiple-scattering medium to be imaged. By achieving Gaussian beamforming both at emission and reception, an array of virtual sources and receivers located in the near field is constructed. The time evolution of the incoherent component of the intensity backscattered on this virtual array is shown to represent directly the growth of the diffusive halo as Dt . A matrix treatment is proposed to separate the incoherent intensity from the coherent backscattering peak. Once the incoherent contribution is isolated, a local measurement of the diffusion constant is possible. The technique is applied to image the long-scale variations of D in a random-scattering sample made of two parts with a different concentration of cylindrical scatterers. This experimental result is obtained with ultrasonic waves around 3MHz . It illustrates the possibility of imaging diffusive media from local measurements of the diffusion constant, based on coherent Gaussian beamforming and a matrix “antisymmetrization,” which creates a virtual antireciprocity.

  17. Modelling of diffusion-limited retardation of contaminants in hydraulically and lithologically nonuniform media

    NASA Astrophysics Data System (ADS)

    Liedl, Rudolf; Ptak, Thomas

    2003-11-01

    A new reactive transport modelling approach and examples of its application are presented, dealing with the impact of sorption/desorption kinetics on the spreading of solutes, e.g. organic contaminants, in groundwater. Slow sorption/desorption is known from the literature to be strongly responsible for the retardation of organic contaminants. The modelling concept applied in this paper quantifies sorption/desorption kinetics by an intra-particle diffusion approach. According to this idea, solute uptake by or release from the aquifer material is modelled at small scale by a "slow" diffusion process where the diffusion coefficient is reduced as compared to the aqueous diffusion coefficient due to (i) the size and shape of intra-particle pores and (ii) retarded transport of solutes within intra-particle pores governed by a nonlinear sorption isotherm. This process-based concept has the advantage of requiring only measurable model parameters, thus avoiding fitting parameters like first-order rate coefficients. In addition, the approach presented here allows for modelling of slow sorption/desorption in lithologically nonuniform media. Therefore, it accounts for well-known experimental findings indicating that sorptive properties depend on (i) the grain size distribution of the aquifer material and (ii) the lithological composition (e.g. percentage of quartz, sandstone, limestone, etc.) of each grain size fraction. The small-scale physico-chemical model describing sorption/desorption is coupled to a large-scale model of groundwater flow and solute transport. Consequently, hydraulic heterogeneities may also be considered by the overall model. This coupling is regarded as an essential prerequisite for simulating field-scale scenarios which will be addressed by a forthcoming publication. This paper focuses on mathematical model formulation, implementation of the numerical code and lab-scale model applications highlighting the sorption and desorption behavior of an organic

  18. On the validity of a Fickian diffusion model for the spreading of liquid infiltration plumes in partially saturated heterogeneous media

    SciTech Connect

    Pruess, K.

    1994-01-01

    Localized infiltration of aqueous and -non-aqueous phase liquids (NAPLs) occurs in many circumstances. Examples include leaky underground pipelines and storage tanks, landfill and disposal sites, and surface spills. Because of ever-present heterogeneities on different scales such infiltration plumes are expected to disperse transversally and longitudinally. This paper examines recent suggestions that liquid plumes are being dispersed from medium heterogeneities in a manner that is analogous to Fickian diffusion. Numerical simulation experiments on liquid infiltration in heterogeneous media are performed to study the dispersive effects of small-scale heterogeneity. It is found that plume spreading indeed tends to be diffusive. Our results suggest that, as far as infiltration of liquids is concerned, broad classes of heterogeneous media behave as dispersive media with locally homogeneous (albeit anisotropic) permeability.

  19. FEA for damping of structures having elastic bodies, viscoelastic bodies, porous media and gas

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Takao; Kurosawa, Yoshio; Matsumura, Shuuji

    2007-01-01

    A numerical method is proposed to calculate damping properties for soundproof structures involving solid bodies, porous media and air in two-dimensional regions. Both effective density and bulk modulus have complex quantity to represent damped sound fields in the porous media. Particle displacements in the media are discretized using finite element method. For damped solid bodies, displacements are formulated using conventional finite elements including complex modulus of elasticity. Displacement vectors as common unknown variables are solved under coupled condition between solid bodies, porous media and gas. Further, by applying asymptotic method to complex eigenvalue problem, explicit expressions of modal loss factor for the mixed structures are derived. The proposed methods yield appropriate results for some typical problems and this method diminish computational time for large-scaled finite element models concerning the mixed structure. Moreover, it is found that damping can be coupled in the mixed structures between solid bodies, porous media and air.

  20. Experimental Investigation of Laminar Gas Jet Diffusion Flames in Zero Gravity

    NASA Technical Reports Server (NTRS)

    Cochran, Thomas H.

    1972-01-01

    An experimental program was conducted to study the burning of laminar gas jet diffusion flames in a zero-gravity environment. The tests were conducted in a 2.2-Second-Zero-Gravity Facility and were a part of a continuing effort investigating the effects of gravity on basic combustion processes. The photographic results indicate that steady state gas jet diffusion flames existed in zero gravity but they were geometrically quite different than their normal-gravity counterparts. Methane-air flames were found to be approximately 50 percent longer and wider in zero gravity than in normal gravity.

  1. Hybrid model of light propagation in random media based on the time-dependent radiative transfer and diffusion equations

    NASA Astrophysics Data System (ADS)

    Fujii, Hiroyuki; Okawa, Shinpei; Yamada, Yukio; Hoshi, Yoko

    2014-11-01

    Numerical modeling of light propagation in random media has been an important issue for biomedical imaging, including diffuse optical tomography (DOT). For high resolution DOT, accurate and fast computation of light propagation in biological tissue is desirable. This paper proposes a space-time hybrid model for numerical modeling based on the radiative transfer and diffusion equations (RTE and DE, respectively) in random media under refractive-index mismatching. In the proposed model, the RTE and DE regions are separated into space and time by using a crossover length and the time from the ballistic regime to the diffusive regime, ρDA 10 / μt‧ and tDA 20 / v μt‧ where μt‧ and v represent a reduced transport coefficient and light velocity, respectively. The present model succeeds in describing light propagation accurately and reduces computational load by a quarter compared with full computation of the RTE.

  2. Ballistic and Diffuse Ultrafast Laser Pulses Propagation in Model Random Media and Biological Tissues

    NASA Astrophysics Data System (ADS)

    Liu, Feng

    The goal of this thesis is to study light scattering and ultrashort laser pulse propagation in the model discrete random media and biological tissues. The temporal profiles of the scattered ultrashort laser pulses were measured by using ultrashort laser pulses, streak camera with 10 ps time response and the femtosecond cross correlation technique. The intensity of the diffuse pulse is found to be preferentially reduced by the absorption with respect to the intensity of the ballistic light because the diffuse light on the average travel through a longer path than the ballistic light. A simple experiment was performed to demonstrate that one can image through a highly scattering medium by increasing the absorption in the medium. The speed of the ballistic pulse was measured by the femtosecond second harmonic cross correlation method and was found to be reduced by the scattering. This speed reduction can be accounted for by the volume fraction combination of the indices of refraction of the scatterers and the water or by the coherent interference between the scattered waves and the primary wave. No distinct ballistic pulse was observed when the laser pulse transmitted through a thin tissue. The continuous random variation of the dielectric constant in tissue may account for the lack of a distinct ballistic pulse. Nevertheless, the early arriving portion of the transmitted pulse was shown to carry image information. The earlier arriving photons were found to produce image of the hidden object with better quality. The intensity of the early arriving transmitted photons was found to decay exponentially with increasing tissue thickness. The earlier the photons arrive, the quicker their intensity decay. Diffusion theory was found to describe the overall transmitted pulse profiles well, but it underestimates the intensity of the early arriving photons. Compressing tissue was found not to change the key optical parameters of the tissue. The scattered laser pulse profile in

  3. On molecular transport effects in real gas laminar diffusion flames at large pressure

    NASA Astrophysics Data System (ADS)

    Palle, Sridhar; Nolan, Christopher; Miller, Richard S.

    2005-10-01

    Direct numerical simulations are conducted of unsteady, exothermic and one-dimensional laminar diffusion flames at large pressures. The simulations are used to assess the impact of molecular diffusion and real gas effects under high pressure conditions with simplified chemical kinetics. The formulation includes the fully compressible form of the governing equations, real gas effects modeled by the cubic Peng-Robinson equation of state, and a generalized form of the Soret and Dufour mass and heat diffusion vectors derived from nonequilibrium thermodynamics and fluctuation theory. The cross diffusion fluxes are derived for a ternary species system and include the effects of both heat and mass diffusion in the presence of temperature, concentration and pressure gradients (i.e., Soret and Dufour diffusion). The ternary species formulation is applied to a simplified single step reaction elucidating molecular and thermodynamic effects apparent in general combustion. Realistic models for pressure, temperature and species dependent heat capacities, viscosities, thermal conductivities and mass diffusivities are also included. Three different model reactions are simulated both including and neglecting Soret and Dufour cross diffusion. The simulation results show that Soret and Dufour effects are negligible for reactions comprised of species with equal or near equal molecular weights. However, Soret diffusion effects are apparent when species with nonequal molecular weights are involved in the reaction and result in reductions of the peak flame temperature. In addition, it is shown that neglect of cross diffusion leads to deviations in the predicted flame thicknesses, with under predictions for a hydrogen-oxygen system and over predictions for a heavy hydrocarbon reaction. These effects are explained in detail through examinations of the individual heat and mass flux vectors as well as through associated thermodynamic properties. A parametric study addresses the effects of

  4. Porous liquids: A promising class of media for gas separation

    SciTech Connect

    Zhang, Jinshui; Chai, Song -Hai; Qiao, Zhen -An; Mahurin, Shannon M.; Chen, Jihua; Fang, Youxing; Wan, Shun; Nelson, Kimberly; Zhang, Pengfei; Dai, Sheng

    2014-11-17

    In porous liquids with empty cavities we successfully has been successfully fabricated by surface engineering of hollow structures with suitable corona and canopy species. By taking advantage of the liquid-like polymeric matrices as a separation medium and the empty cavities as gas transport pathway, this unique porous liquid can function as a promising candidate for gas separation. A facile synthetic strategy can be further extended to other types of nanostructure-based porous liquid fabrication, opening up new opportunities for preparation of porous liquids with attractive properties for specific tasks.

  5. Dimethylether: a low velocity, low diffusion drift chamber gas

    SciTech Connect

    Villa, F.

    1983-01-01

    There are two main motivations to look for a low electron mobility gas: the first is that a low drift velocity relaxes the need to measure drift times with nanosecond (or even subnanosecond) precision; the second is that (in an ideal drift geometry), the capability of resolving two closely spaced tracks depends upon the ratio of electron mobility to ion mobility ..mu../sub e//..mu../sub i/. Since ..mu../sub i/ is rather constant, the way to separate two tracks is to slow down the electrons. Many other properties are required besides low mobility and low drifting electron temperature: the gas should have a large (> 10/sup 3/) stable gain; it must be chemically stable and not oxic; it should not attack materials commonly used to fabricate drift chambers, etc. With these requirements in mind, we have tried a few promising (on paper) gases, either pure or in admixture with Argon. One of the gases examined, dimethylether ((CH/sub 3/)/sub 2/)), has shown interesting characteristics.

  6. Determination of spatially-resolved porosity, tracer distributions and diffusion coefficients in porous media using MRI measurements and numerical simulations.

    PubMed

    Marica, Florea; Jofré, Sergio Andrés Bea; Mayer, K Ulrich; Balcom, Bruce J; Al, Tom A

    2011-07-01

    This work is focused on measuring the concentration distribution of a conservative tracer in a homogeneous synthetic porous material and in heterogeneous natural sandstone using MRI techniques, and on the use of spatially resolved porosity data to define spatially variable diffusion coefficients in heterogeneous media. The measurements are made by employing SPRITE, a fast MRI method that yields quantitative, spatially-resolved tracer concentrations in porous media. Diffusion experiments involving the migration of H(2)O into D(2)O-saturated porous media are conducted. One-dimensional spatial distributions of H(2)O-tracer concentrations acquired from experiments with the homogeneous synthetic calcium silicate are fitted with the one-dimensional analytical solution of Fick's second law to confirm that the experimental method provides results that are consistent with expectations for Fickian diffusion in porous media. The MRI-measured concentration profiles match well with the solution for Fick's second law and provide a pore-water diffusion coefficient of 1.75×10(-9)m(2)s(-1). The experimental approach was then extended to evaluate diffusion in a heterogeneous natural sandstone in three dimensions. The relatively high hydraulic conductivity of the sandstone, and the contrast in fluid density between the H(2)O tracer and the D(2)O pore fluid, lead to solute transport by a combination of diffusion and density-driven advection. The MRI measurements of spatially distributed tracer concentration, combined with numerical simulations allow for the identification of the respective influences of advection and diffusion. The experimental data are interpreted with the aid of MIN3P-D - a multicomponent reactive transport code that includes the coupled processes of diffusion and density-driven advection. The model defines local diffusion coefficients as a function of spatially resolved porosity measurements. The D(e) values calculated for the heterogeneous sandstone and used to

  7. Influence of gas law on ultrasonic behaviour of porous media under pressure.

    PubMed

    Griffiths, S; Ayrault, C

    2010-06-01

    This paper deals with the influence of gas law on ultrasonic behaviour of porous media when the saturating fluid is high pressured. Previous works have demonstrated that ultrasonic transmission through a porous sample with variations of the static pressure (up to 18 bars) of the saturating fluid allows the characterization of high damping materials. In these studies, the perfect gas law was used to link static pressure and density, which is disputable for high pressures. This paper compares the effects of real and perfect gas laws on modeled transmission coefficient for porous foams at these pressures. Direct simulations and a mechanical parameters estimation from minimization show that results are very similar in both cases. The real gas law is thus not necessary to describe the acoustic behaviour of porous media at low ultrasonic frequencies (100 kHz) up to 20 bars.

  8. WETTABILITY ALTERATION OF POROUS MEDIA TO GAS-WETTING FOR IMPROVING PRODUCTIVITY AND INJECTIVITY IN GAS-LIQUID FLOWS

    SciTech Connect

    Abbas Firoozabadi

    2003-12-01

    Wettability alteration to intermediate gas-wetting in porous media by treatment with FC-759, a fluoropolymer polymer, has been studied experimentally. Berea sandstone was used as the main rock sample in our work and its wettability before and after chemical treatment was studied at various temperatures from 25 to 93 C. We also studied recovery performance for both gas/oil and oil/water systems for Berea sandstone before and after wettability alteration by chemical treatment. Our experimental study shows that chemical treatment with FC-759 can result in: (1) wettability alteration from strong liquid-wetting to stable intermediate gas-wetting at room temperature and at elevated temperatures; (2) neutral wetting for gas, oil, and water phases in two-phase flow; (3) significant increase in oil mobility for gas/oil system; and (4) improved recovery behavior for both gas/oil and oil/water systems. This work reveals a potential for field application for improved gas-well deliverability and well injectivity by altering the rock wettability around wellbore in gas condensate reservoirs from strong liquid-wetting to intermediate gas-wetting.

  9. Pyrolysis Gas Flow in Thermally Ablating Media Using Time-Implicit Discontinuous Galerkin Methods

    DTIC Science & Technology

    2011-01-01

    dynamics of flow of pyrolysis gas in a charring ablating media. We have benchmarked our results with the published data. The protective coating of... Dynamics Laboratory and Test Facility,Department of Mechanical and Aerospace Engineering,Gainesville,FL,32611 8. PERFORMING ORGANIZATION REPORT NUMBER 9...Gas flow Code, which is a family of our in-house finite element modules, and has been used to solve problems in plasma dynamics like low pressure

  10. Subdiffusion, Anomalous Diffusion and Propagation of a Particle Moving in Random and Periodic Media

    NASA Astrophysics Data System (ADS)

    Mishra, Shradha; Bhattacharya, Sanchari; Webb, Benjamin; Cohen, E. G. D.

    2016-02-01

    We investigate the motion of a single particle moving on a two-dimensional square lattice whose sites are occupied by right and left rotators. These left and right rotators deterministically rotate the particle's velocity to the right or left, respectively and flip orientation from right to left or from left to right after scattering the particle. We study three types of configurations of left and right rotators, which we think of as types of media, through with the particle moves. These are completely random (CR), random periodic (RP), and completely periodic (CP) configurations. For CR configurations the particle's dynamics depends on the ratio r of right to left scatterers in the following way. For small r˜eq 0, when the configuration is nearly homogeneous, the particle subdiffuses with an exponent of 2/3, similar to the diffusion of a macromolecule in a crowded environment. Also, the particle's trajectory has a fractal dimension of d_f˜eq 4/3, comparable to that of a self-avoiding walk. As the ratio increases to r˜eq 1, the particle's dynamics transitions from subdiffusion to anomalous diffusion with a fractal dimension of d_f˜eq 7/4, similar to that of a percolating cluster in 2-d. In RP configurations, which are more structured than CR configurations but also randomly generated, we find that the particle has the same statistic as in the CR case. In contrast, CP configurations, which are highly structured, typically will cause the particle to go through a transient stage of subdiffusion, which then abruptly changes to propagation. Interestingly, the subdiffusive stage has an exponent of approximately 2/3 and a fractal dimension of d_f˜eq 4/3, similar to the case of CR and RP configurations for small r.

  11. Study of Gas Flow Characteristics in Tight Porous Media with a Microscale Lattice Boltzmann Model

    NASA Astrophysics Data System (ADS)

    Zhao, Jianlin; Yao, Jun; Zhang, Min; Zhang, Lei; Yang, Yongfei; Sun, Hai; An, Senyou; Li, Aifen

    2016-09-01

    To investigate the gas flow characteristics in tight porous media, a microscale lattice Boltzmann (LB) model with the regularization procedure is firstly adopted to simulate gas flow in three-dimensional (3D) digital rocks. A shale digital rock and a sandstone digital rock are reconstructed to study the effects of pressure, temperature and pore size on microscale gas flow. The simulation results show that because of the microscale effect in tight porous media, the apparent permeability is always higher than the intrinsic permeability, and with the decrease of pressure or pore size, or with the increase of temperature, the difference between apparent permeability and intrinsic permeability increases. In addition, the Knudsen numbers under different conditions are calculated and the results show that gas flow characteristics in the digital rocks under different Knudsen numbers are quite different. With the increase of Knudsen number, gas flow in the digital rocks becomes more uniform and the effect of heterogeneity of the porous media on gas flow decreases. Finally, two commonly used apparent permeability calculation models are evaluated by the simulation results and the Klinkenberg model shows better accuracy. In addition, a better proportionality factor in Klinkenberg model is proposed according to the simulation results.

  12. Study of Gas Flow Characteristics in Tight Porous Media with a Microscale Lattice Boltzmann Model

    PubMed Central

    Zhao, Jianlin; Yao, Jun; Zhang, Min; Zhang, Lei; Yang, Yongfei; Sun, Hai; An, Senyou; Li, Aifen

    2016-01-01

    To investigate the gas flow characteristics in tight porous media, a microscale lattice Boltzmann (LB) model with the regularization procedure is firstly adopted to simulate gas flow in three-dimensional (3D) digital rocks. A shale digital rock and a sandstone digital rock are reconstructed to study the effects of pressure, temperature and pore size on microscale gas flow. The simulation results show that because of the microscale effect in tight porous media, the apparent permeability is always higher than the intrinsic permeability, and with the decrease of pressure or pore size, or with the increase of temperature, the difference between apparent permeability and intrinsic permeability increases. In addition, the Knudsen numbers under different conditions are calculated and the results show that gas flow characteristics in the digital rocks under different Knudsen numbers are quite different. With the increase of Knudsen number, gas flow in the digital rocks becomes more uniform and the effect of heterogeneity of the porous media on gas flow decreases. Finally, two commonly used apparent permeability calculation models are evaluated by the simulation results and the Klinkenberg model shows better accuracy. In addition, a better proportionality factor in Klinkenberg model is proposed according to the simulation results. PMID:27587293

  13. DEVELOPMENT OF LOW-DIFFUSION FLUX-SPLITTING METHODS FOR DENSE GAS-SOLID FLOWS

    EPA Science Inventory

    The development of a class of low-diffusion upwinding methods for computing dense gas-solid flows is presented in this work. An artificial compressibility/low-Mach preconditioning strategy is developed for a hyperbolic two-phase flow equation system consisting of separate solids ...

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

    SciTech Connect

    McGill U; Gostick, J. T.; Gunterman, H. P.; Weber, A. Z.; Newman, J. S.; Kienitz, B. L.; MacDowell, A. A.

    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.

  15. Engineered Water Highways in Fuel Cells: Radiation Grafting of Gas Diffusion Layers.

    PubMed

    Forner-Cuenca, Antoni; Biesdorf, Johannes; Gubler, Lorenz; Kristiansen, Per Magnus; Schmidt, Thomas Justus; Boillat, Pierre

    2015-11-04

    A novel method to produce gas diffusion layers with patterned wettability for fuel cells is presented. The local irradiation and subsequent grafting permits full design flexibility and wettability tuning, while modifying throughout the whole material thickness. These water highways have improved operando performance due to an optimized water management inside the cells.

  16. Nonlinear diffusion-wave equation for a gas in a regenerator subject to temperature gradient

    NASA Astrophysics Data System (ADS)

    Sugimoto, N.

    2015-10-01

    This paper derives an approximate equation for propagation of nonlinear thermoacoustic waves in a gas-filled, circular pore subject to temperature gradient. The pore radius is assumed to be much smaller than a thickness of thermoviscous diffusion layer, and the narrow-tube approximation is used in the sense that a typical axial length associated with temperature gradient is much longer than the radius. Introducing three small parameters, one being the ratio of the pore radius to the thickness of thermoviscous diffusion layer, another the ratio of a typical speed of thermoacoustic waves to an adiabatic sound speed and the other the ratio of a typical magnitude of pressure disturbance to a uniform pressure in a quiescent state, a system of fluid dynamical equations for an ideal gas is reduced asymptotically to a nonlinear diffusion-wave equation by using boundary conditions on a pore wall. Discussion on a temporal mean of an excess pressure due to periodic oscillations is included.

  17. Porous Media Combustors for Clean Gas Turbine Engines

    DTIC Science & Technology

    2007-11-02

    emissions , no cooling requirement for the! combustor itself and the potential to operate free from combustion- induced noise. The reduced combustion...that the combustor operates in a "super-adiabatic" mode, with low emissions . Intrinsic pressure loss is within values, commonly accepted for propulsion...principles for low emissions turbulent flame gas turbine combustors are well established. The preferred strategy remains lean burn, often with staging to

  18. General slip regime permeability model for gas flow through porous media

    NASA Astrophysics Data System (ADS)

    Zhou, Bo; Jiang, Peixue; Xu, Ruina; Ouyang, Xiaolong

    2016-07-01

    A theoretical effective gas permeability model was developed for rarefied gas flow in porous media, which holds over the entire slip regime with the permeability derived as a function of the Knudsen number. This general slip regime model (GSR model) is derived from the pore-scale Navier-Stokes equations subject to the first-order wall slip boundary condition using the volume-averaging method. The local closure problem for the volume-averaged equations is studied analytically and numerically using a periodic sphere array geometry. The GSR model includes a rational fraction function of the Knudsen number which leads to a limit effective permeability as the Knudsen number increases. The mechanism for this behavior is the viscous fluid inner friction caused by converging-diverging flow channels in porous media. A linearization of the GSR model leads to the Klinkenberg equation for slightly rarefied gas flows. Finite element simulations show that the Klinkenberg model overestimates the effective permeability by as much as 33% when a flow approaches the transition regime. The GSR model reduces to the unified permeability model [F. Civan, "Effective correlation of apparent gas permeability in tight porous media," Transp. Porous Media 82, 375 (2010)] for the flow in the slip regime and clarifies the physical significance of the empirical parameter b in the unified model.

  19. Pyrolysis gas-liquid chromatography of the genus Bacillus: effect of growth media on pyrochromatogram reproducibility.

    PubMed

    Oxborrow, G S; Fields, N D; Puleo, J R

    1977-04-01

    Pyrolysis gas-liquid chromatography was performed on dried Bacillus microorganisms to evaluate the effects of growth media. Six cultures of Bacillus and six lot numbers of Trypticase soy agar (BBL) were used to test the hypothesis that a microorganism grown on various lot numbers of the same chromatogram. Also tested was the effect of three different media on chromatogram reproduction using the same six cultures. Results show little or no differences observed between the chromatograms of the individual Bacillus spp. grown on the six lot numbers of Trypticase soy agar. When chromatograms of the three different media were compared, several differences were observed, particularly in the areas most characteristic of individual species. Pryolysis gas-liquid chromatography can be a useful tool for the characterization or identification of the genus Bacillus if the chromatographic and cultural conditions are maintained.

  20. Fractional and fractal dynamics approach to anomalous diffusion in porous media: application to landslide behavior

    NASA Astrophysics Data System (ADS)

    Martelloni, Gianluca; Bagnoli, Franco

    2016-04-01

    Richardson's treatise on turbulent diffusion in 1926 [24] and today, the list of system displaying anomalous dynamical behavior is quite extensive. We only report some examples: charge carrier transport in amorphous semiconductors [25], porous systems [26], reptation dynamics in polymeric systems [27, 28], transport on fractal geometries [29], the long-time dynamics of DNA sequences [30]. In this scenario, the fractional calculus is used to generalized the Fokker-Planck linear equation -∂P (x,t)=D ∇2P (x,t), ∂t (3) where P (x,t) is the density of probability in the space x=[x1, x2, x3] and time t, while D >0 is the diffusion coefficient. Such processes are characterized by Eq. (1). An example of Eq. (3) generalization is ∂∂tP (x,t)=D∇ αP β(x,t) - ∞ < α ≤ 2 β > - 1 , (4) where the fractional based-derivatives Laplacian Σ(∂α/∂xα)i, (i = 1, 2, 3), of non-linear term Pβ(x,t) is taken into account [31]. Another generalized form is represented by equation ∂∂tδδP(x,t)=D ∇ αP(x,t) δ > 0 α ≤ 2 , (5) that considers also the fractional time-derivative [32]. These fractional-described processes exhibit a power law patters as expressed by Eq. (2). This general introduction introduces the presented work, whose aim is to develop a theoretical model in order to forecast the triggering and propagation of landslides, using the techniques of fractional calculus. The latter is suitable for modeling the water infiltration (i.e., the pore water pressure diffusion in the soil) and the dynamical processes in the fractal media [33]. Alternatively the fractal representation of temporal and spatial derivative (the fractal order only appears in the denominator of the derivative) is considered and the results are compared to the fractional one. The prediction of landslides and the discovering of the triggering mechanism, is one of the challenging problems in earth science. Landslides can be triggered by different factors but in most cases the trigger is an

  1. Compilation and evaluation of gas phase diffusion coefficients of reactive trace gases in the atmosphere: volume 1. Inorganic compounds

    NASA Astrophysics Data System (ADS)

    Tang, M. J.; Cox, R. A.; Kalberer, M.

    2014-09-01

    Diffusion of gas molecules to the surface is the first step for all gas-surface reactions. Gas phase diffusion can influence and sometimes even limit the overall rates of these reactions; however, there is no database of the gas phase diffusion coefficients of atmospheric reactive trace gases. Here we compile and evaluate, for the first time, the diffusivities (pressure-independent diffusion coefficients) of atmospheric inorganic reactive trace gases reported in the literature. The measured diffusivities are then compared with estimated values using a semi-empirical method developed by Fuller et al. (1966). The diffusivities estimated using Fuller's method are typically found to be in good agreement with the measured values within ±30%, and therefore Fuller's method can be used to estimate the diffusivities of trace gases for which experimental data are not available. The two experimental methods used in the atmospheric chemistry community to measure the gas phase diffusion coefficients are also discussed. A different version of this compilation/evaluation, which will be updated when new data become available, is uploaded online (diffusion"target="_blank">https://sites.google.com/site/mingjintang/home/diffusion).

  2. Purging of a multilayer insulation with dacron tuft spacer by gas diffusion

    NASA Technical Reports Server (NTRS)

    Sumner, I. E.; Fisk, W. J.

    1976-01-01

    The time and purge gas usage required to purge a multilayer insulation (MLI) panel with gaseous helium by means of gas diffusion to obtain a condensable gas (nitrogen) concentration of less than 1 percent within the panel are stipulated. Two different, flat, rectangular MLI panels, one incorporating a butt joint, were constructed of of 11 double-aluminized Mylar (DAM) radiation shields separated by Dacron tuft spacers. The DAM/Dacron tuft concept is known commercially as Superfloc. The nitrogen gas concentration as a function of time within the MLI panel could be adequately predicted by using a simple, one dimensional gas diffusion model in which the boundary conditions at the edge of the MLI panel were time dependent. The time and purge gas usage required to achieve 1 percent nitrogen gas concentration within the MLI panel varied from 208 to 86 minutes and 34.1 to 56.5 MLI panel purge volumes, respectively, for gaseous helium purge rates from 10 to 40 MLI panel volumes per hour.

  3. Diffuse gas emissions at the Ukinrek Maars, Alaska: Implications for magmatic degassing and volcanic monitoring

    USGS Publications Warehouse

    Evans, William C.; Bergfeld, D.; McGimsey, R.G.; Hunt, A.G.

    2009-01-01

    Diffuse CO2 efflux near the Ukinrek Maars, two small volcanic craters that formed in 1977 in a remote part of the Alaska Peninsula, was investigated using accumulation chamber measurements. High CO2 efflux, in many places exceeding 1000 g m-2 d-1, was found in conspicuous zones of plant damage or kill that cover 30,000-50,000 m2 in area. Total diffuse CO2 emission was estimated at 21-44 t d-1. Gas vents 3-km away at The Gas Rocks produce 0.5 t d-1 of CO2 that probably derives from the Ukinrek Maars basalt based on similar ??13C values (???-6???), 3He/4He ratios (5.9-7.2 RA), and CO2/3He ratios (1-2 ?? 109) in the two areas. A lower 3He/4He ratio (2.7 RA) and much higher CO2/3He ratio (9 ?? 1010) in gas from the nearest arc-front volcanic center (Mount Peulik/Ugashik) provide a useful comparison. The large diffuse CO2 emission at Ukinrek has important implications for magmatic degassing, subsurface gas transport, and local toxicity hazards. Gas-water-rock interactions play a major role in the location, magnitude and chemistry of the emissions.

  4. Evaluation of porosity and thickness on effective diffusivity in gas diffusion layer

    NASA Astrophysics Data System (ADS)

    Gao, Yuan; Montana, Angel; Chen, Fengxiang

    2017-02-01

    Porosity and thickness are two key properties of GDL and both affect the transport properties of porous media. This paper focuses on the influence of the GDL microstructure on its transport properties, which will be analyzed from different samples. The results show that thickness affects permeability through the principal flow direction more than through non-principal directions, thus it is necessary to increase the anisotropic characteristics of the material. Moreover, it is ascertained that permeability is more affected by the number of fibers than by the thickness. For the variable porosity sample groups, the simulation results are coincident with the fractal model in principal and non-principal flow directions, and water saturation inside the GDL samples has been evaluated. They are shown several cases of the GDL model to illustrate the fluid flow along through-plane and in-plane directions as well as the conditions at inlet and outlet boundaries. These results have a strong potential to gain deeper understanding of the microscopic flow phenomenon within the porous structures and to determine the influence the microstructure has on the macroscopic transport properties, thus leading to notable improvements of fuel cell performance.

  5. Time-independent hybrid enrichment for finite element solution of transient conduction–radiation in diffusive grey media

    SciTech Connect

    Mohamed, M. Shadi; Seaid, Mohammed; Trevelyan, Jon; Laghrouche, Omar

    2013-10-15

    We investigate the effectiveness of the partition-of-unity finite element method for transient conduction–radiation problems in diffusive grey media. The governing equations consist of a semi-linear transient heat equation for the temperature field and a stationary diffusion approximation to the radiation in grey media. The coupled equations are integrated in time using a semi-implicit method in the finite element framework. We show that for the considered problems, a combination of hyperbolic and exponential enrichment functions based on an approximation of the boundary layer leads to improved accuracy compared to the conventional finite element method. It is illustrated that this approach can be more efficient than using h adaptivity to increase the accuracy of the finite element method near the boundary walls. The performance of the proposed partition-of-unity method is analyzed on several test examples for transient conduction–radiation problems in two space dimensions.

  6. Risk assessment of failure modes of gas diffuser liner of V94.2 siemens gas turbine by FMEA method

    NASA Astrophysics Data System (ADS)

    Mirzaei Rafsanjani, H.; Rezaei Nasab, A.

    2012-05-01

    Failure of welding connection of gas diffuser liner and exhaust casing is one of the failure modes of V94.2 gas turbines which are happened in some power plants. This defect is one of the uncertainties of customers when they want to accept the final commissioning of this product. According to this, the risk priority of this failure evaluated by failure modes and effect analysis (FMEA) method to find out whether this failure is catastrophic for turbine performance and is harmful for humans. By using history of 110 gas turbines of this model which are used in some power plants, the severity number, occurrence number and detection number of failure determined and consequently the Risk Priority Number (RPN) of failure determined. Finally, critically matrix of potential failures is created and illustrated that failure modes are located in safe zone.

  7. 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.

  8. Effect of advective flow in fractures and matrix diffusion on natural gas production

    SciTech Connect

    Karra, Satish; Makedonska, Nataliia; Viswanathan, Hari S.; Painter, Scott L.; Hyman, Jeffrey D.

    2015-10-12

    Although hydraulic fracturing has been used for natural gas production for the past couple of decades, there are significant uncertainties about the underlying mechanisms behind the production curves that are seen in the field. A discrete fracture network based reservoir-scale work flow is used to identify the relative effect of flow of gas in fractures and matrix diffusion on the production curve. With realistic three dimensional representations of fracture network geometry and aperture variability, simulated production decline curves qualitatively resemble observed production decline curves. The high initial peak of the production curve is controlled by advective fracture flow of free gas within the network and is sensitive to the fracture aperture variability. Matrix diffusion does not significantly affect the production decline curve in the first few years, but contributes to production after approximately 10 years. These results suggest that the initial flushing of gas-filled background fractures combined with highly heterogeneous flow paths to the production well are sufficient to explain observed initial production decline. Lastly, these results also suggest that matrix diffusion may support reduced production over longer time frames.

  9. Effect of advective flow in fractures and matrix diffusion on natural gas production

    DOE PAGES

    Karra, Satish; Makedonska, Nataliia; Viswanathan, Hari S.; ...

    2015-10-12

    Although hydraulic fracturing has been used for natural gas production for the past couple of decades, there are significant uncertainties about the underlying mechanisms behind the production curves that are seen in the field. A discrete fracture network based reservoir-scale work flow is used to identify the relative effect of flow of gas in fractures and matrix diffusion on the production curve. With realistic three dimensional representations of fracture network geometry and aperture variability, simulated production decline curves qualitatively resemble observed production decline curves. The high initial peak of the production curve is controlled by advective fracture flow of freemore » gas within the network and is sensitive to the fracture aperture variability. Matrix diffusion does not significantly affect the production decline curve in the first few years, but contributes to production after approximately 10 years. These results suggest that the initial flushing of gas-filled background fractures combined with highly heterogeneous flow paths to the production well are sufficient to explain observed initial production decline. Lastly, these results also suggest that matrix diffusion may support reduced production over longer time frames.« less

  10. Inverse gas chromatography. V - Computer simulation of diffusion processes on the column

    NASA Technical Reports Server (NTRS)

    Hattam, Paul; Munk, Petr

    1988-01-01

    The elution behavior of low molecular weight probes on inverse gas chromatography (IGC) columns is simulated using a computer. The IGC model is based on a polymer stationary phase of uniform thickness with a nonnegligible resitance to probe penetration. Three characteristic numbers are found to determine the whole process: Z(p) characterizing the distribution of the probe between phases, Z(f) describing the diffusion in the polymer phase, and Z(g) related to diffusion in the gaseous phase. For situations when Z(p)/Z(f) is less than 2, the standard evaluation procedures are virtually useless. The actual behavior of such systems is described.

  11. Oxygen diffusion measurements in porous media on the ISS: One piece of the puzzle for optimal root zone performance

    NASA Astrophysics Data System (ADS)

    Jones, Scott; Heinse, Robert; Or, Dani; Topham, T. Shane; Podolsky, Igor; Bingham, Gail

    Optimization of Root Zone Substrates (ORZS) are currently being researched to expand plantbased bio-regenerative life support systems. This NASA funded research investigates the effect of reduced-gravity on porous media fluid management at the root-module and pore scale, necessitated by current limitations in root zone management that may have led to stunted, often unexplained plant vigor. Among them, alterations in substrate water retention and oxygen diffusion are restraining optimal support of plant growth. Our work explores the effect of gravity on the distribution and flow of fluids in porous media. These effects demonstrate unanticipated behavior in fluid transport with fluid distribution in pursuit of a capillary equilibrium within the hysteretic, contingent energy potential of water and continuity of phases for the supply of plant resources to the root. We investigate how accounts of fluid transport are part of a larger story of fluid distribution when gravitational and capillary forces are shifting. We now have data from the International Space Station that were collected in a novel experimental setup developed and tested for measurement of oxygen diffusion in partially saturated porous media under microgravity conditions with a sealed dual-chamber diffusion cell. The experiment flew on the International Space Station between July and September 2007 as part of the ORZS- MIS experimental flight package. In comparing oxygen diffusion measurements in microgravity with earth-based data, results point to enhanced hysteresis in oxygen diffusion dependency on air-filled porosity in microgravity. This indicates altered water distribution patterns relative to earth-based measurements. Considering air invasion during drainage, we hypothesize that a critical air-filled pathway forms at higher saturation in microgravity due to the absence of hydrostatic water distribution. A shift in the critical air-filled porosity in microgravity would require adjustment in plant

  12. Onset of convection in a gravitationally unstable diffusive boundary layer in porous media

    NASA Astrophysics Data System (ADS)

    Riaz, A.; Hesse, M.; Tchelepi, H. A.; Orr, F. M.

    2006-02-01

    We present a linear stability analysis of density-driven miscible flow in porous media in the context of carbon dioxide sequestration in saline aquifers. Carbon dioxide dissolution into the underlying brine leads to a local density increase that results in a gravitational instability. The physical phenomenon is analogous to the thermal convective instability in a semi-infinite domain, owing to a step change in temperature at the boundary. The critical time for the onset of convection in such problems has not been determined accurately by previous studies. We present a solution, based on the dominant mode of the self-similar diffusion operator, which can accurately predict the critical time and the associated unstable wavenumber. This approach is used to explain the instability mechanisms of the critical time and the long-wave cutoff in a semi-infinite domain. The dominant mode solution, however, is valid only for a small parameter range. We extend the analysis by employing the quasi-steady-state approximation (QSSA) which provides accurate solutions in the self-similar coordinate system. For large times, both the maximum growth rate and the most dangerous mode decay as t^{1/4}. The long-wave and the short-wave cutoff modes scale as t^{1/5} and t^{4/5}, respectively. The instability problem is also analysed in the nonlinear regime by high-accuracy direct numerical simulations. The nonlinear simulations at short times show good agreement with the linear stability predictions. At later times, macroscopic fingers display intense nonlinear interactions that significantly influence both the front propagation speed and the overall mixing rate. A dimensional analysis for typical aquifers shows that for a permeability variation of 1—3000 mD, the critical time can vary from 2000 yrs to about 10 days while the critical wavelength can be between 200 m and 0.3 m.

  13. Effect of dynamic diffusion of air, nitrogen, and helium gaseous media on the microhardness of ionic crystals with juvenile surfaces

    NASA Astrophysics Data System (ADS)

    Klyavin, O. V.; Fedorov, V. Yu.; Chernov, Yu. M.; Shpeizman, V. V.

    2015-09-01

    The load dependences of the microhardness of surface layers of NaCl and LiF ionic single crystals with juvenile surfaces and surfaces exposed to air for a long time measured in the air, nitrogen, and helium gaseous media have been investigated. It has been found that there is a change in the sign of the derivative of the microhardness as a function of the load for LiF crystals indented in helium and after their aging in air, as well as a weaker effect of the nitrogen and air gaseous media on the studied dependences as compared to NaCl crystals. It has also been found that, after the aging of the surface of NaCl crystals in air, there is a change in the sign of the derivative of the microhardness in the nitrogen and air gaseous media, as well as a pronounced change in the microhardness as a function of the time of aging the samples in air as compared to the weaker effect of the gaseous medium for LiF crystals. The obtained data have been analyzed in terms of the phenomenon of dislocation-dynamic diffusion of particles from the external medium into crystalline materials during their plastic deformation along the nucleating and moving dislocations. It has been shown that this phenomenon affects the microhardness through changes in the intensity of dislocation multiplication upon the formation of indentation rosettes in different gaseous media. The performed investigation of the microhardness of the juvenile surface of NaCl and LiF crystals in different gaseous media has revealed for the first time a different character of dislocation-dynamic diffusion of these media in a "pure" form.

  14. Investigations of Air Perfusion through Porous Media and Super-Hydrophobic Surface Active Gas Replenishment

    NASA Astrophysics Data System (ADS)

    Perlin, Marc; Gose, James W.; Golovin, Kevin; Ceccio, Steven L.; Tuteja, Anish

    2015-11-01

    Super-hydrophobic (SH) materials have been used successfully to generate reduced skin-friction in laminar flows. Success in the laminar regime has led researchers to try SH materials in turbulent flows. More often than not, this has been unsuccessful at providing meaningful skin-friction drag reduction, and has even generated increased drag. This failure is frequently attributed to the wetting of an SH surface or equivalently the transition from the Cassie-Baxter to the Wenzel state. The result is fluid flow over an essentially roughened surface. In this investigation the researchers aim to perfuse small amounts of gas through porous media, including sintered and foam metals, to attain skin-friction drag reduction in a fully-developed turbulent channel flow. As air is perfused through porous media, the solid - liquid interaction at the interface transitions to a solid - liquid - gas interaction. This can result in an interface that functions similarly to SH materials. Controlled air perfusion that provides the necessary replenishment of lost gas at the interface might prevent wetting, and thus eliminate or reduce the effect of the roughness on the flow. This latter possibility is investigated by perfusing small amounts of gas through porous media with and without SH coatings. To quantify the effectiveness of this method, pressure drop is used to infer friction drag along the surface in a fully-developed turbulent channel flow. The authors recognize the support of ONR.

  15. Connecting the molecular scale to the continuum scale for diffusion processes in smectite-rich porous media

    SciTech Connect

    Bourg, I.C.; Sposito, G.

    2009-12-01

    In this paper, we address the manner in which the continuum-scale diffusive properties of smectite-rich porous media arise from their molecular- and pore-scale features. Our starting point is a successful model of the continuum-scale apparent diffusion coefficient for water tracers and cations which decomposes it as a sum of pore-scale terms describing diffusion in macropore and interlayer 'compartments.' We then apply molecular dynamics (MD) simulations to determine molecular-scale diffusion coefficients D{sub interlayer} of water tracers and representative cations (Na{sup +}, Cs{sup +}, Sr{sup 2+}) in Na-smectite interlayers. We find that a remarkably simple expression relates D{sub interlayer} to the pore-scale parameter {delta}{sub nanopore} {<=} 1, a constrictivity factor that accounts for the lower mobility in interlayers as compared to macropores: {delta}{sub nanopore} = D{sub interlayer}/D{sub 0}, where D{sub 0} is the diffusion coefficient in bulk liquid water. Using this scaling expression, we can accurately predict the apparent diffusion coefficients of tracer H{sub 2}O, Na{sup +}, Sr{sup 2+} and Cs{sup +}+ in compacted Na-smectite-rich materials.

  16. Effects of gas composition in headspace and bicarbonate concentrations in media on gas and methane production, degradability, and rumen fermentation using in vitro gas production techniques.

    PubMed

    Patra, Amlan Kumar; Yu, Zhongtang

    2013-07-01

    Headspace gas composition and bicarbonate concentrations in media can affect methane production and other characteristics of rumen fermentation in in vitro gas production systems, but these 2 important factors have not been evaluated systematically. In this study, these 2 factors were investigated with respect to gas and methane production, in vitro digestibility of feed substrate, and volatile fatty acid (VFA) profile using in vitro gas production techniques. Three headspace gas compositions (N2+ CO2+ H2 in the ratio of 90:5:5, CO2, and N2) with 2 substrate types (alfalfa hay only, and alfalfa hay and a concentrate mixture in a 50:50 ratio) in a 3×2 factorial design (experiment 1) and 3 headspace compositions (N2, N2 + CO2 in a 50:50 ratio, and CO2) with 3 bicarbonate concentrations (80, 100, and 120 mM) in a 3×3 factorial design (experiment 2) were evaluated. In experiment 1, total gas production (TGP) and net gas production (NGP) was the lowest for CO2, followed by N2, and then the gas mixture. Methane concentration in headspace gas after fermentation was greater for CO2 than for N2 and the gas mixture, whereas total methane production (TMP) and net methane production (NMP) were the greatest for CO2, followed by the gas mixture, and then N2. Headspace composition did not affect in vitro digestibility or the VFA profile, except molar percentages of propionate, which were greater for CO2 and N2 than for the gas mixture. Methane concentration in headspace gas, TGP, and NGP were affected by the interaction of headspace gas composition and substrate type. In experiment 2, increasing concentrations of CO2 in the headspace decreased TGP and NGP quadratically, but increased the concentrations of methane, NMP, and in vitro fiber digestibility linearly, and TMP quadratically. Fiber digestibility, TGP, and NGP increased linearly with increasing bicarbonate concentrations in the medium. Concentrations of methane and NMP were unaffected by bicarbonate concentration, but

  17. Lattice-Boltzmann Simulations of Multiphase Flows in Gas-Diffusion-Layer (GDL) of a PEM Fuel Cell

    SciTech Connect

    Mukherjeea, Shiladitya; Cole, J Vernon; Jainb, Kunal; Gidwania, Ashok

    2008-11-01

    Improved power density and freeze-thaw durability in automotive applications of Proton Exchange Membrane Fuel Cells (PEMFCs) requires effective water management at the membrane. This is controlled by a porous hydrophobic gas-diffusion-layer (GDL) inserted between the membrane catalyst layer and the gas reactant channels. The GDL distributes the incoming gaseous reactants on the catalyst surface and removes excess water by capillary action. There is, however, limited understanding of the multiphase, multi-component transport of liquid water, vapor and gaseous reactants within these porous materials. This is due primarily to the challenges of in-situ diagnostics for such thin (200 -“ 300 {microns}), optically opaque (graphite) materials. Transport is typically analyzed by fitting Darcy's Law type expressions for permeability, in conjunction with capillary pressure relations based on formulations derived for media such as soils. Therefore, there is significant interest in developing predictive models for transport in GDLs and related porous media. Such models could be applied to analyze and optimize systems based on the interactions between cell design, materials, and operating conditions, and could also be applied to evaluating material design concepts. Recently, the Lattice Boltzmann Method (LBM) has emerged as an effective tool in modeling multiphase flows in general, and flows through porous media in particular. This method is based on the solution of a discrete form of the well-known Boltzmann Transport Equation (BTE) for molecular distribution, tailored to recover the continuum Navier-Stokes flow. The kinetic theory basis of the method allows simple implementation of molecular forces responsible for liquid-gas phase separation and capillary effects. The solution advances by a streaming and collision type algorithm that makes it suitable to implement for domains with complex boundaries. We have developed both single and multiphase LB models and applied them to

  18. Imaging in diffusing media with a neural net formulation: a problem in large-scale computation

    NASA Astrophysics Data System (ADS)

    Schlereth, Fred H.; Fossaceca, John A.; Keckler, Andrew D.; Barbour, Randall L.

    1992-05-01

    Attempts to recover images from objects which diffuse radiation pose an especially challenging problem in terms of defining a suitable reconstruction algorithm and with regard to identifying an appropriate computing environment for efficient processing. In this paper we consider both issues and, in particular, describe results of an algebraic technique for imaging the interior of objects which diffuse penetrating radiation using a new multicomputer environment. Two important issues which arise when considering the numerical solution of ultra large problems are the numerical precision achieved and the overall computing efficiency. Our interest in this problem concerns the possibility of obtaining 3-D optical images of tissue which could identify the availability of oxygen by evaluating oxygen- dependent changes in the near infrared spectrum of hemoglobin. These studies were motivated by recent reports from our group and others, which showed promising results for imaging in dense scattering media given only diffusely scattered signals. In our model we assume the use of an NIR laser to provide the input radiation and suitable detectors to measure both transmission and backscatter. In our present work we assume a simple Markov process model for the way in which the energy travels in the medium, but it should be noted that the reconstruction technique we propose can use any model, including nonlinear as well as linear effects, and higher order processes. Current simulations are in 2-D but the methods are easily extended to 3-D. The algorithms we propose are more closely related to algebraic reconstruction algorithms such as ART, SIRT, and SART than to algorithms based on the Born and Rytov approximations such as used for tomographic imaging with diffracting sources. Our algorithms are a significant departure from those based on these standard algebraic methods. We assume only a probabilistic knowledge of the path of the radiation, and minimal knowledge of the absorption

  19. Report on simulation of fission gas and fission product diffusion in UO2

    SciTech Connect

    Andersson, Anders David; Perriot, Romain Thibault; Pastore, Giovanni; Tonks, Michael R.; Cooper, Michael William; Liu, Xiang-Yang; Goyal, Anuj; Uberuaga, Blas P.; Stanek, Christopher Richard

    2016-07-22

    In UO2 nuclear fuel, the retention and release of fission gas atoms such as xenon (Xe) are important for nuclear fuel performance by, for example, reducing the fuel thermal conductivity, causing fuel swelling that leads to mechanical interaction with the clad, increasing the plenum pressure and reducing the fuel–clad gap thermal conductivity. We use multi-­scale simulations to determine fission gas diffusion mechanisms as well as the corresponding rates in UO2 under both intrinsic and irradiation conditions. In addition to Xe and Kr, the fission products Zr, Ru, Ce, Y, La, Sr and Ba have been investigated. Density functional theory (DFT) calculations are used to study formation, binding and migration energies of small clusters of Xe atoms and vacancies. Empirical potential calculations enable us to determine the corresponding entropies and attempt frequencies for migration as well as investigate the properties of large clusters or small fission gas bubbles. A continuum reaction-­diffusion model is developed for Xe and point defects based on the mechanisms and rates obtained from atomistic simulations. Effective fission gas diffusivities are then obtained by solving this set of equations for different chemical and irradiation conditions using the MARMOT phase field code. The predictions are compared to available experimental data. The importance of the large XeU3O cluster (a Xe atom in a uranium + oxygen vacancy trap site with two bound uranium vacancies) is emphasized, which is a consequence of its high mobility and high binding energy. We find that the XeU3O cluster gives Xe diffusion coefficients that are higher for intrinsic conditions than under irradiation over a wide range of temperatures. Under irradiation the fast-­moving XeU3O cluster recombines quickly with irradiation-induced interstitial U ions, while this mechanism is less important for intrinsic conditions. The net result is higher

  20. An adaptive streamline diffusion finite element method for hyperbolic systems in gas dynamics

    NASA Astrophysics Data System (ADS)

    Zhou, Guohui

    1992-09-01

    The paintwise error analysis of the streamline diffusion method for two dimensional stationary problem with constant coefficients is extended to the time dependent problem. The purpose of the study is to justify a local mesh refinement strategy. The one dimensional Euler equations coming from the shock tube and Riemann's problem in gas dynamics are used. The gas is assumed to be at rest on both sides of the membrane, with pressure and density different on each side. The case where the problem is scalar and linear is discussed. Linear systems of hyperbolic type in one space variable and nonlinear scalar problems are studied.

  1. 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.

  2. Selective determination of chlorine dioxide using gas diffusion flow injection analysis

    SciTech Connect

    Hollowell, D.A.; Pacey, G.E.; Gordon, G.

    1985-12-01

    An automated absorbance technique for the determination of aqueous chlorine dioxide has been developed by utilizing gas diffusion flow injection analysis. A gas diffusion membrane is used to separate the donor (sampling) stream from the acceptor (detecting) stream. The absorbance of chlorine dioxide is monitored at 359 nm. The first method uses distilled water as the acceptor stream and gives a detection limit of 0.25 mg/L chlorine dioxide. This system is over 550 times more selective for chlorine dioxide than chlorine. To further minimize chlorine interference, oxalic acid is used in the acceptor stream. The detection limit for this system is 0.45 mg/L chlorine dioxide. This second system is over 5400 times more selective for chlorine dioxide than chlorine. Both methods show excellent selectivity for chlorine dioxide over iron and manganese compounds, as well as other oxychlorinated compounds such as chlorite and perchlorate ions. 18 references, 7 figures, 3 tables.

  3. Random Vibration Tests for Prediction of Fatigue Life of Diffuser Structure for Gas Dynamic Laser

    NASA Astrophysics Data System (ADS)

    Maurer, O. F.; Banaszak, D. L.

    1980-01-01

    Static and dynamic strain measurements which were taken during test stand operations of the gas dynamic laser (GDL) for the AF Airborne Laser Laboratory indicated that higher than expected vibrational stress levels may possibly limit the fatigue life of the laser structure. Particularly the diffuser sidewall structure exhibited large amplitude random vibrations which were excited by the internal gas flow. The diffuser structure consists of two layers of brazed stainless steel, AISI-347, panels. Cooling ducts were milled into the outer face sheet. These in turn are backed by the inner face sheet. So called T-rail stiffeners silver-brazed to the outer face sheets add the required stiffness and divide the sidewall into smaller rectangular plate sections.

  4. Selective chlorine dioxide determination using gas-diffusion flow injection analysis with chemiluminescent detection

    SciTech Connect

    Hollowell, D.A.; Gord, J.R.; Gordon, G.; Pacey, G.E.

    1986-06-01

    An automated chemiluminescent technique has been developed utilizing the advantages of gas-diffusion flow injection analysis. A gas-diffusion membrane separates the donor (sampling) stream from the acceptor (detecting) stream and removes ionic interferences. A novel chemiluminescence flow-through detector cell is used to measure the concentration of chlorine dioxide as a function of the intensity of the chemiluminescence produced from its reaction with luminol. The chemiluminescent reagent merges with the analyte directly in front of the photomultiplier tube in order to maximize the sensitivity of the system. The detection limit for chlorine dioxide is approximately 5 ppb. The method is over 1500 times more selective for chlorine dioxide than for chlorine on a mole basis. This method eliminates interference from iron and manganese compounds, as well as other oxychlorinated compounds such as chlorite ion and chlorate ion.

  5. Turbine exhaust diffuser with a gas jet producing a coanda effect flow control

    DOEpatents

    Orosa, John; Montgomery, Matthew

    2014-02-11

    An exhaust diffuser system and method for a turbine engine includes an inner boundary and an outer boundary with a flow path defined therebetween. The inner boundary is defined at least in part by a hub structure that has an upstream end and a downstream end. The outer boundary may include a region in which the outer boundary extends radially inward toward the hub structure and may direct at least a portion of an exhaust flow in the diffuser toward the hub structure. The hub structure includes at least one jet exit located on the hub structure adjacent to the upstream end of the tail cone. The jet exit discharges a flow of gas substantially tangential to an outer surface of the tail cone to produce a Coanda effect and direct a portion of the exhaust flow in the diffuser toward the inner boundary.

  6. Pore Network Modeling of Multiphase Transport in Polymer Electrolyte Membrane Fuel Cell Gas Diffusion Layers

    NASA Astrophysics Data System (ADS)

    Fazeli, Mohammadreza

    In this thesis, pore network modeling was used to study how the microstructure of the polymer electrolyte membrane (PEM) fuel cell gas diffusion layer (GDL) influences multiphase transport within the composite layer. An equivalent pore network of a GDL was used to study the effects of GDL/catalyst layer condensation points and contact quality on the spatial distribution of liquid water in the GDL. Next, pore networks extracted from synchrotron-based micro-computed tomography images of compressed GDLs were employed to simulate liquid water transport in GDL materials over a range of compression pressures, and favorable GDL compression values for preferred liquid water distributions were found for two commercially available GDL materials. Finally, a technique was developed for calculating the oxygen diffusivity in carbon paper substrates with a microporous layer (MPL) coating through pore network modeling. A hybrid network was incorporated into the pore network model, and effective diffusivity predictions of MPL coated GDL materials were obtained.

  7. Simulation of radiation driven fission gas diffusion in UO2, ThO2 and PuO2

    NASA Astrophysics Data System (ADS)

    Cooper, M. W. D.; Stanek, C. R.; Turnbull, J. A.; Uberuaga, B. P.; Andersson, D. A.

    2016-12-01

    Below 1000 K it is thought that fission gas diffusion in nuclear fuel during irradiation occurs through atomic mixing due to radiation damage. Here we present a molecular dynamics (MD) study of Xe, Kr, Th, U, Pu and O diffusion due to irradiation. It is concluded that the ballistic phase does not sufficiently account for the experimentally observed diffusion. Thermal spike simulations are used to confirm that electronic stopping remedies the discrepancy with experiment and the predicted diffusivities lie within the scatter of the experimental data. Our results predict that the diffusion coefficients are ordered such that DO* > DKr* > DXe* > DU*. For all species >98.5% of diffusivity is accounted for by electronic stopping. Fission gas diffusivity was not predicted to vary significantly between ThO2, UO2 and PuO2, indicating that this process would not change greatly for mixed oxide fuels.

  8. Development and optimization of porous carbon papers suitable for gas diffusion electrodes. Final report, December 2000

    SciTech Connect

    Fleming, Gerald J.; Fleming, Patrick J.

    2001-01-16

    This final report details results from the program to optimize porous carbon gas diffusion electrodes for use in fuel cells. Efforts focused on isolating discrete paper properties through a custom-made matrix, then fuel cell testing each variant to correlate properties to performance. Resulting reduced cost material was manufactured on production equipment and made available to DOE industry partners. The resulting product is suitable for continuous production, which will be evaluated in future work.

  9. Measurements of Plasma Expansion due to Background Gas in the Electron Diffusion Gauge Experiment

    SciTech Connect

    Kyle A. Morrison; Stephen F. Paul; Ronald C. Davidson

    2003-08-11

    The expansion of pure electron plasmas due to collisions with background neutral gas atoms in the Electron Diffusion Gauge (EDG) experiment device is observed. Measurements of plasma expansion with the new, phosphor-screen density diagnostic suggest that the expansion rates measured previously were observed during the plasma's relaxation to quasi-thermal-equilibrium, making it even more remarkable that they scale classically with pressure. Measurements of the on-axis, parallel plasma temperature evolution support the conclusion.

  10. Effects of Buoyancy on Laminar, Transitional, and Turbulent Gas Jet Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Bahadori, M. Yousef; Stocker, Dennis P.; Vaughan, David F.; Zhou, Liming; Edelman, Raymond B.

    1993-01-01

    Gas jet diffusion flames have been a subject of research for many years. However, a better understanding of the physical and chemical phenomena occurring in these flames is still needed, and, while the effects of gravity on the burning process have been observed, the basic mechanisms responsible for these changes have yet to be determined. The fundamental mechanisms that control the combustion process are in general coupled and quite complicated. These include mixing, radiation, kinetics, soot formation and disposition, inertia, diffusion, and viscous effects. In order to understand the mechanisms controlling a fire, laboratory-scale laminar and turbulent gas-jet diffusion flames have been extensively studied, which have provided important information in relation to the physico-chemical processes occurring in flames. However, turbulent flames are not fully understood and their understanding requires more fundamental studies of laminar diffusion flames in which the interplay of transport phenomena and chemical kinetics is more tractable. But even this basic, relatively simple flame is not completely characterized in relation to soot formation, radiation, diffusion, and kinetics. Therefore, gaining an understanding of laminar flames is essential to the understanding of turbulent flames, and particularly fires, in which the same basic phenomena occur. In order to improve and verify the theoretical models essential to the interpretation of data, the complexity and degree of coupling of the controlling mechanisms must be reduced. If gravity is isolated, the complication of buoyancy-induced convection would be removed from the problem. In addition, buoyant convection in normal gravity masks the effects of other controlling parameters on the flame. Therefore, the combination of normal-gravity and microgravity data would provide the information, both theoretical and experimental, to improve our understanding of diffusion flames in general, and the effects of gravity on the

  11. Theoretical and experimental correlations of gas dissolution, diffusion, and thermodynamic properties in determination of gas permeability and selectivity in supported ionic liquid membranes.

    PubMed

    Gan, Quan; Zou, Yiran; Rooney, David; Nancarrow, Paul; Thompson, Jillian; Liang, Lizhe; Lewis, Moira

    2011-05-11

    Supported ionic liquid membranes (SILMs) has the potential to be a new technological platform for gas/organic vapour separation because of the unique non-volatile nature and discriminating gas dissolution properties of room temperature ionic liquids (ILs). This work starts with an examination of gas dissolution and transport properties in bulk imidazulium cation based ionic liquids [C(n)mim][NTf2] (n=2.4, 6, 8.10) from simple gas H(2), N(2), to polar CO(2), and C(2)H(6), leading to a further analysis of how gas dissolution and diffusion are influenced by molecular specific gas-SILMs interactions, reflected by differences in gas dissolution enthalpy and entropy. These effects were elucidated again during gas permeation studies by examining how changes in these properties and molecular specific interactions work together to cause deviations from conventional solution-diffusion theory and their impact on some remarkably contrasting gas perm-selectivity performance. The experimental perm-selectivity for all tested gases showed varied and contrasting deviation from the solution-diffusion, depending on specific gas-IL combinations. It transpires permeation for simpler non-polar gases (H(2), N(2)) is diffusion controlled, but strong molecular specific gas-ILs interactions led to a different permeation and selectivity performance for C(2)H(6) and CO(2). With exothermic dissolution enthalpy and large order disruptive entropy, C(2)H(6) displayed the fastest permeation rate at increased gas phase pressure in spite of its smallest diffusivity among the tested gases. The C(2)H(6) gas molecules "peg" on the side alkyl chain on the imidazulium cation at low concentration, and are well dispersed in the ionic liquids phase at high concentration. On the other hand strong CO(2)-ILs affinity resulted in a more prolonged "residence time" for the gas molecule, typified by reversed CO(2)/N(2) selectivity and slowest CO(2) transport despite CO(2) possess the highest solubility and

  12. DYNAMIC S0 GALAXIES. II. THE ROLE OF DIFFUSE HOT GAS

    SciTech Connect

    Li Jiangtao; Chen Yang; Daniel Wang, Q.; Li Zhiyuan

    2011-08-10

    Cold gas loss is thought to be important in star formation quenching and morphological transition during the evolution of S0 galaxies. In high-density environments, this gas loss can be achieved via many external mechanisms. However, in relatively isolated environments, where these external mechanisms cannot be efficient, the gas loss must then be dominated by some internal processes. We have performed Chandra analysis of hot gas in five nearby isolated S0 galaxies, based on the quantitative subtraction of various stellar contributions. We find that all the galaxies studied in the present work are X-ray faint, with the luminosity of the hot gas (L{sub X} ) typically accounting for {approx}< 5% of the expected Type Ia supernova (SN) energy injection rate. We have further compared our results with those from relevant recent papers, in order to investigate the energy budget, cold-hot gas relation, and gas removal from S0 galaxies in isolated environments. We find that elliptical and S0 galaxies are not significantly different in L{sub X} at the low-mass end (typically with K-band luminosity L{sub K} {approx}< 10{sup 11} L{sub sun,K}). However, at the high-mass end, S0 galaxies tend to have significantly lower L{sub X} than elliptical galaxies of the same stellar masses, as already shown in previous observational and theoretical works. We further discuss the potential relationship of the diffuse X-ray emission with the cold (atomic and molecular) gas content in the S0 and elliptical galaxies included in our study. We find that L{sub X} /L{sup 2}{sub K} tends to correlate positively with the total cold gas mass (M{sub H{sub 2}+H{sub i}}) for cold-gas-poor galaxies with M{sub H{sub 2}+H{sub i}}{approx}<10{sup 8} M{sub sun}, while they anti-correlate with each other for cold-gas-rich galaxies. This cold-hot gas relationship can be explained in a scenario of early-type galaxy evolution, with the leftover cold gas from the precursor star-forming galaxy mainly removed by the

  13. Monte Carlo simulation with fixed steplength for diffusion processes in nonhomogeneous media

    NASA Astrophysics Data System (ADS)

    Ruiz Barlett, V.; Hoyuelos, M.; Mártin, H. O.

    2013-04-01

    Monte Carlo simulation is one of the most important tools in the study of diffusion processes. For constant diffusion coefficients, an appropriate Gaussian distribution of particle's steplengths can generate exact results, when compared with integration of the diffusion equation. It is important to notice that the same method is completely erroneous when applied to non-homogeneous diffusion coefficients. A simple alternative, jumping at fixed steplengths with appropriate transition probabilities, produces correct results. Here, a model for diffusion of calcium ions in the neuromuscular junction of the crayfish is used as a test to compare Monte Carlo simulation with fixed and Gaussian steplength.

  14. The Vertical Structure of Diffuse Ionized Gas in Galactic Spiral Arms

    NASA Astrophysics Data System (ADS)

    Krishnarao, Dhanesh; Haffner, L. Matthew; Benjamin, Robert A.

    2017-01-01

    The Wisconsin H-Alpha Mapper provides the most sensitive velocity resolved observations of diffuse Hα, [S II] λ6716, and [N II] λ6584 emission in the Galaxy, tracing the warm (~8000K) ionized component of the interstellar medium. The vertical extent of this diffuse gas can directly impact the midplane pressure, influencing cold molecular clouds and star formation in the disk. Here, we analyze the vertical structure of the warm ionized medium around multiple spiral arm components of the Galaxy. Diffuse halo emission is isolated using longitude varying velocity channels guided by CO emission tracing cold molecular gas in the disk. We find exponential electron density squared (or emission measure) scale heights and analyze its behavior as a function of Galactocentric radius and the presence of cold molecular clouds and star forming regions in the disk. Statistical analysis of the behavior of [S II]/Hα and [N II]/Hα line ratios along some of these spiral arms disentangle the complex physical conditions of the warm ionized gas as a function of height and in-situ electron density. Some spiral arm sections, in particular the far Carina arm, have significantly larger (>3x) scale heights than previously studied arms that tend to increase as a function of Galactocentric radius.

  15. Surfactant shedding and gas diffusion during pulsed ultrasound through a microbubble contrast agent suspension.

    PubMed

    O'Brien, Jean-Pierre; Stride, Eleanor; Ovenden, Nicholas

    2013-08-01

    Interest in coated microbubbles as agents for therapeutic and quantitative imaging applications in biomedical ultrasound has increased the need for their accurate theoretical characterization. Effects such as gas diffusion, variation in the properties of the coating and the resulting changes in bubble behavior under repeated exposure to ultrasound pulses are, however, still not well understood. In this study, a revised equation for microbubble motion is proposed that includes the effects of gas diffusion, as well as adsorption, desorption and shedding of a surfactant from the bubble surface. This is incorporated into a nonlinear wave propagation model to account for these additional time dependent effects in the response of microbubble populations. The results from the model indicate there can be significant changes in both bubble behavior and the propagated pulse over time. This is in agreement with existing experimental data but is not predicted by existing propagation models. The analysis indicates that changes in bubble dynamics are dominated by surfactant shedding on the timescale of a diagnostic ultrasound pulse and gas diffusion over the timescale of the pulse repetition frequency. The implications of these results for the development of more accurate algorithms for quantitative imaging and for therapeutic applications are discussed.

  16. Numerical scheme to complete a compressible gas flow in variable porosity media

    NASA Astrophysics Data System (ADS)

    Rochette, D.; Clain, S.; Buffard, T.

    2005-05-01

    We present an approximate Riemann solver coupled with a finite volume method to compute non conservative Euler equations in variable porosity media using ideal gas state law. The non conservative term is numerically taken into account from an original idea of LeRoux (1998) but here Riemann problems at each interface of the mesh are linearized using a VFRoe approach. The main goal is the resolution of the non conservative system even if the porosity is discontinuous. Stationary solutions are determined with continuous and discontinuous porosity in order to test the numerical scheme and computations of gas shock subsonic wave moving in a non continuous porosity medium are presented.

  17. Influence of the Gas-Water Interface on Transport of Microorganisms through Unsaturated Porous Media

    PubMed Central

    Wan, Jiamin; Wilson, John L.; Kieft, Thomas L.

    1994-01-01

    In this article, a new mechanism influencing the transport of microorganisms through unsaturated porous media is examined, and a new method for directly visualizing bacterial behavior within a porous medium under controlled chemical and flow conditions is introduced. Resting cells of hydrophilic and relatively hydrophobic bacterial strains isolated from groundwater were used as model microorganisms. The degree of hydrophobicity was determined by contact-angle measurements. Glass micromodels allowed the direct observation of bacterial behavior on a pore scale, and three types of sand columns with different gas saturations provided quantitative measurements of the observed phenomena on a porous medium scale. The reproducibility of each break-through curve was established in three to five repeated experiments. The data collected from the column experiments can be explained by phenomena directly observed in the micromodel experiments. The retention rate of bacteria is proportional to the gas saturation in porous media because of the preferential sorption of bacteria onto the gas-water interface over the solid-water interface. The degree of sorption is controlled mainly by cell surface hydrophobicity under the simulated groundwater conditions because of hydrophobic forces between the organisms and the interfaces. The sorption onto the gas-water interface is essentially irreversible because of capillary forces. This preferential and irreversible sorption at the gas-water interface strongly influences the movement and spatial distribution of microorganisms. Images PMID:16349180

  18. Application of gas diffusion biocathode in microbial electrosynthesis from carbon dioxide.

    PubMed

    Bajracharya, Suman; Vanbroekhoven, Karolien; Buisman, Cees J N; Pant, Deepak; Strik, David P B T B

    2016-11-01

    Microbial catalysis of carbon dioxide (CO2) reduction to multi-carbon compounds at the cathode is a highly attractive application of microbial electrosynthesis (MES). The microbes reduce CO2 by either taking the electrons or reducing the equivalents produced at the cathode. While using gaseous CO2 as the carbon source, the biological reduction process depends on the dissolution and mass transfer of CO2 in the electrolyte. In order to deal with this issue, a gas diffusion electrode (GDE) was investigated by feeding CO2 through the GDE into the MES reactor for its reduction at the biocathode. A combination of the catalyst layer (porous activated carbon and Teflon binder) and the hydrophobic gas diffusion layer (GDL) creates a three-phase interface at the electrode. So, CO2 and reducing equivalents will be available to the biocatalyst on the cathode surface. An enriched inoculum consisting of acetogenic bacteria, prepared from an anaerobic sludge, was used as a biocatalyst. The cathode potential was maintained at -1.1 V vs Ag/AgCl to facilitate direct and/or hydrogen-mediated CO2 reduction. Bioelectrochemical CO2 reduction mainly produced acetate but also extended the products to ethanol and butyrate. Average acetate production rates of 32 and 61 mg/L/day, respectively, with 20 and 80 % CO2 gas mixture feed were achieved with 10 cm(2) of GDE. The maximum acetate production rate remained 238 mg/L/day for 20 % CO2 gas mixture. In conclusion, a gas diffusion biocathode supported bioelectrochemical CO2 reduction with enhanced mass transfer rate at continuous supply of gaseous CO2. Graphical abstract ᅟ.

  19. Non-universal tracer diffusion in crowded media of non-inert obstacles.

    PubMed

    Ghosh, Surya K; Cherstvy, Andrey G; Metzler, Ralf

    2015-01-21

    We study the diffusion of a tracer particle, which moves in continuum space between a lattice of excluded volume, immobile non-inert obstacles. In particular, we analyse how the strength of the tracer-obstacle interactions and the volume occupancy of the crowders alter the diffusive motion of the tracer. From the details of partitioning of the tracer diffusion modes between trapping states when bound to obstacles and bulk diffusion, we examine the degree of localisation of the tracer in the lattice of crowders. We study the properties of the tracer diffusion in terms of the ensemble and time averaged mean squared displacements, the trapping time distributions, the amplitude variation of the time averaged mean squared displacements, and the non-Gaussianity parameter of the diffusing tracer. We conclude that tracer-obstacle adsorption and binding triggers a transient anomalous diffusion. From a very narrow spread of recorded individual time averaged trajectories we exclude continuous type random walk processes as the underlying physical model of the tracer diffusion in our system. For moderate tracer-crowder attraction the motion is found to be fully ergodic, while at stronger attraction strength a transient disparity between ensemble and time averaged mean squared displacements occurs. We also put our results into perspective with findings from experimental single-particle tracking and simulations of the diffusion of tagged tracers in dense crowded suspensions. Our results have implications for the diffusion, transport, and spreading of chemical components in highly crowded environments inside living cells and other structured liquids.

  20. Diffusion of Social Media among County 4-H Programs in Tennessee

    ERIC Educational Resources Information Center

    Bowen, Rebekah D.; Stephens, Carrie A.; Childers, Courtney C.; Avery, Elizabeth J.; Stripling, Christopher T.

    2013-01-01

    Over the past decade, Cooperative Extension and 4-H professionals have been faced with the decision of whether to adopt new communication technologies such as social media. Research on social media and Cooperative Extension has identified risks and barriers to adoption; however, many Cooperative Extension professionals believe that social media…

  1. Relative importance of gas-phase diffusive and advective tichloroethene (TCE) fluxes in the unsaturated zone under natural conditions.

    PubMed

    Choi, Jee-Won; Tillman, Fred D; Smith, James A

    2002-07-15

    It was hypothesized that atmospheric pressure changes can induce gas flow in the unsaturated zone to such an extent that the advective flux of organic vapors in unsaturated-zone soil gas can be significant relative to the gas-phase diffusion flux of these organic vapors. To test this hypothesis, a series of field measurements and computer simulations were conducted to simulate and compare diffusion and advection fluxes at a trichloroethene-contaminated field site at Picatinny Arsenal in north-central New Jersey. Moisture content temperature, and soil-gas pressure were measured at multiple depths (including at land surface) and times for three distinct sampling events in August 1996, October 1996, and August 1998. Gas pressures in the unsaturated zone changed significantly over time and followed changes measured in the atmosphere. Gas permeability of the unsaturated zone was estimated using data from a variety of sources, including laboratory gas permeability measurements made on intact soil cores from the site, a field air pump test, and calibration of a gas-flow model to the transient, one-dimensional gas pressure data. The final gas-flow model reproduced small pressure gradients as observed in the field during the three distinct sampling events. The velocities calculated from the gas-flow model were used in transient, one-dimensional transport simulations to quantify advective and diffusive fluxes of TCE vapor from the subsurface to the atmosphere as a function of time for each sampling event. Effective diffusion coefficients used for these simulations were determined from independent laboratory measurements made on intact soil cores collected from the field site. For two of the three sampling events (August 1996 and August 1998), the TCE gas-phase diffusion flux at land surface was significantly greater than the advection flux over the entire sampling period. For the second sampling event (October 1996), the advection flux was frequently larger than the

  2. Experimental characterization of in-plane permeability of gas diffusion layers

    NASA Astrophysics Data System (ADS)

    Feser, J. P.; Prasad, A. K.; Advani, S. G.

    Recent studies indicate that PEM fuel cell performance may be strongly influenced by in-plane permeability of the gas diffusion layer (GDL). The current study employs a radial flow technique for obtaining in-plane permeability of GDLs, using either gas or liquid as the impregnating fluid. A model has been developed and experimentally verified to account for compressibility effects when permeability measurements are conducted using a gas. Permeability experiments are performed on samples of woven, non-woven, and carbon fiber-based GDL at various levels of compression using air as the impregnating fluid. Woven and non-woven samples are measured to have significantly higher in-plane permeability compared to carbon fiber paper at similar solid volume fractions.

  3. Gas detection and migration in geological media: lessons learned from the Roselend Natural Laboratory (Invited)

    NASA Astrophysics Data System (ADS)

    Pili, E.; Guillon, S.; Agrinier, P.; Sabroux, J.; Adler, P. M.

    2013-12-01

    The Roselend Natural Laboratory (French Alps) is a unique facility for studying gas transport in the subsurface and across the geosphere-atmosphere interface. At 55 m depth, a sealed cavity allows for gas release experiments across fractured porous rocks in the unsaturated zone. While many parameters controlling the state of the geological system are known, analogous gas-tracer experiments were conducted at the field-scale with SF6 and 3He. Water infiltration, permeability and the concentrations of many gases, naturally occurring or injected, are recorded via long-term and high-resolution monitoring. The fracture network is characterized thanks to extensive drilling, logging and modeling. These experiments are used to determine the physical and chemical processes that would control the noble gas source term after an underground nuclear explosion in the framework of the Comprehensive nuclear-Test-Ban Treaty (CTBT) and to develop and validate the corresponding numerical models. The Roselend Natural Laboratory also provides a test bed for sampling protocols and instrument developments. Detection of gases relevant to CTBT issues requires that their baseline concentration is understood. Experiments and subsequent modeling demonstrated that baselines are a highly dynamical process resulting from gas sources, sinks and modulation by barometric pressure and water movements. Gas migration from underground cavities occurs as early venting through fractures due to advection driven by gas overpressure. It is associated with very large dilution which requires very low detection limits. Late-time seepage occurs through fractured porous media thanks to barometric pumping, which is only efficient for a narrow window of parameter values. Full calculation for real fractured porous media is now available.

  4. Measuring diffusivity in supercooled liquid nanoscale films using inert gas permeation. I. Kinetic model and scaling methods.

    PubMed

    Smith, R Scott; Matthiesen, Jesper; Kay, Bruce D

    2010-11-07

    We describe in detail a diffusion model used to simulate inert gas transport through supercooled liquid overlayers. In recent work, the transport of the inert gas has been shown to be an effective probe of the diffusivity of supercooled liquid methanol in the experimentally challenging regime near the glass transition temperature. The model simulations accurately and quantitatively describe the inert gas permeation desorption spectra. The simulation results are used to validate universal scaling relationships between the diffusivity, overlayer thickness, and the temperature ramp rate for isothermal and temperature programmed desorption. From these scaling relationships we derive simple equations from which the diffusivity can be obtained using the peak desorption time or temperature for an isothermal or set of TPD experiments, respectively, without numerical simulation. The results presented here demonstrate that the permeation of gases through amorphous overlayers has the potential to be a powerful technique to obtain diffusivity data in deeply supercooled liquids.

  5. Controls on the physical properties of gas-hydrate-bearing sediments because of the interaction between gas hydrate and porous media

    USGS Publications Warehouse

    Lee, Myung W.; Collett, Timothy S.

    2005-01-01

    Physical properties of gas-hydrate-bearing sediments depend on the pore-scale interaction between gas hydrate and porous media as well as the amount of gas hydrate present. Well log measurements such as proton nuclear magnetic resonance (NMR) relaxation and electromagnetic propagation tool (EPT) techniques depend primarily on the bulk volume of gas hydrate in the pore space irrespective of the pore-scale interaction. However, elastic velocities or permeability depend on how gas hydrate is distributed in the pore space as well as the amount of gas hydrate. Gas-hydrate saturations estimated from NMR and EPT measurements are free of adjustable parameters; thus, the estimations are unbiased estimates of gas hydrate if the measurement is accurate. However, the amount of gas hydrate estimated from elastic velocities or electrical resistivities depends on many adjustable parameters and models related to the interaction of gas hydrate and porous media, so these estimates are model dependent and biased. NMR, EPT, elastic-wave velocity, electrical resistivity, and permeability measurements acquired in the Mallik 5L-38 well in the Mackenzie Delta, Canada, show that all of the well log evaluation techniques considered provide comparable gas-hydrate saturations in clean (low shale content) sandstone intervals with high gas-hydrate saturations. However, in shaly intervals, estimates from log measurement depending on the pore-scale interaction between gas hydrate and host sediments are higher than those estimates from measurements depending on the bulk volume of gas hydrate.

  6. Portable vapor diffusion coefficient meter

    DOEpatents

    Ho, Clifford K.

    2007-06-12

    An apparatus for measuring the effective vapor diffusion coefficient of a test vapor diffusing through a sample of porous media contained within a test chamber. A chemical sensor measures the time-varying concentration of vapor that has diffused a known distance through the porous media. A data processor contained within the apparatus compares the measured sensor data with analytical predictions of the response curve based on the transient diffusion equation using Fick's Law, iterating on the choice of an effective vapor diffusion coefficient until the difference between the predicted and measured curves is minimized. Optionally, a purge fluid can forced through the porous media, permitting the apparatus to also measure a gas-phase permeability. The apparatus can be made lightweight, self-powered, and portable for use in the field.

  7. Similarity Solution for Gas Production From Dissociating Hydrates in Geologic Media

    NASA Astrophysics Data System (ADS)

    Moridis, G. J.; Reagan, M. T.

    2007-12-01

    By using the Boltzman transformation, the nonlinear partial differential equations governing multicomponent mass flow, energy transport and phase changes in a geologic system involving methane hydrate dissociation can be reduced to simpler ordinary differential equations, without resorting to simplifications or approximations that require removal of any of the nonlinearities. This capability indicates that the problem admits a similarity solution, which results in invariance of any of the parameters (e.g., pressure, temperature, phase saturations) with respect to the similarity variable r/t1/2. The similarity solution is confirmed in test problems involving gas production from hydrate deposits undergoing dissociation by depressurization and thermal stimulation. The existence of the similarity solution provides a robust estimator of the gas production potential of natural hydrate accumulations, in addition to a reliable tool for the evaluation of the validity of numerical simulators of gas hydrate behavior in porous media.

  8. Calculation of effective transport properties of partially saturated gas diffusion layers

    NASA Astrophysics Data System (ADS)

    Bednarek, Tomasz; Tsotridis, Georgios

    2017-02-01

    A large number of currently available Computational Fluid Dynamics numerical models of Polymer Electrolyte Membrane Fuel Cells (PEMFC) are based on the assumption that porous structures are mainly considered as thin and homogenous layers, hence the mass transport equations in structures such as Gas Diffusion Layers (GDL) are usually modelled according to the Darcy assumptions. Application of homogenous models implies that the effects of porous structures are taken into consideration via the effective transport properties of porosity, tortuosity, permeability (or flow resistance), diffusivity, electric and thermal conductivity. Therefore, reliable values of those effective properties of GDL play a significant role for PEMFC modelling when employing Computational Fluid Dynamics, since these parameters are required as input values for performing the numerical calculations. The objective of the current study is to calculate the effective transport properties of GDL, namely gas permeability, diffusivity and thermal conductivity, as a function of liquid water saturation by using the Lattice-Boltzmann approach. The study proposes a method of uniform water impregnation of the GDL based on the "Fine-Mist" assumption by taking into account the surface tension of water droplets and the actual shape of GDL pores.

  9. Evaluation of a fast single-photon avalanche photodiode for measurement of early transmitted photons through diffusive media.

    PubMed

    Mu, Ying; Valim, Niksa; Niedre, Mark

    2013-06-15

    We tested the performance of a fast single-photon avalanche photodiode (SPAD) in measurement of early transmitted photons through diffusive media. In combination with a femtosecond titanium:sapphire laser, the overall instrument temporal response time was 59 ps. Using two experimental models, we showed that the SPAD allowed measurement of photon-density sensitivity functions that were approximately 65% narrower than the ungated continuous wave case at very early times. This exceeds the performance that we have previously achieved with photomultiplier-tube-based systems and approaches the theoretical maximum predicted by time-resolved Monte Carlo simulations.

  10. Tomographic imaging of absolute optical absorption coefficient in turbid media using combined photoacoustic and diffusing light measurements.

    PubMed

    Yin, Lu; Wang, Qiang; Zhang, Qizhi; Jiang, Huabei

    2007-09-01

    We present a new method that can provide high resolution images of absolute optical absorption coefficient in heterogeneous turbid media. In this method, acoustic measurements in conventional photoacoustic tomography are combined with diffusing light measurements to separate the product of absorption coefficient and optical fluence or photon density. We validate this method using a series of tissuelike phantom experiments. The experimental results show that targets as small as 0.5 mm in diameter with optical absorption contrasts as low as 1.5 relative to a 50 mm diameter scattering background medium can be clearly detected.

  11. A field study to estimate the vertical gas diffusivity and permeability of compacted MSW using a barometric pumping analytical model.

    PubMed

    Larson, Judd; Kumar, Sendhil; Gale, S Adrian; Jain, Pradeep; Townsend, Timothy

    2012-03-01

    The measurement of vertical gas diffusivity and permeability of compacted municipal solid waste (MSW) using an analytical gas flow and transport model was evaluated. A series of pressure transducers were buried in a MSW landfill and in situ pressures were modelled using an algorithm that predicts soil-gas pressures based on field-measured barometric pressure data and vertical diffusivity. The vertical gas diffusivity that represented the best-fit of the measured pressures was estimated at 20 locations and ranged from 0.002 to 0.052 m2 s(-1). The vertical gas permeability ranged from 3.3 × 10(-14) to 4.5 × 10(-12) m2 for the upper-most 3 to 6 m of compacted MSW. The shortfalls of applying this method to landfill conditions are also discussed.

  12. Description of gas/particle sorption kinetics with an intraparticle diffusion model: Desorption experiments

    USGS Publications Warehouse

    Rounds, S.A.; Tiffany, B.A.; Pankow, J.F.

    1993-01-01

    Aerosol particles from a highway tunnel were collected on a Teflon membrane filter (TMF) using standard techniques. Sorbed organic compounds were then desorbed for 28 days by passing clean nitrogen through the filter. Volatile n-alkanes and polycyclic aromatic hydrocarbons (PAHs) were liberated from the filter quickly; only a small fraction of the less volatile ra-alkanes and PAHs were desorbed. A nonlinear least-squares method was used to fit an intraparticle diffusion model to the experimental data. Two fitting parameters were used: the gas/particle partition coefficient (Kp and an effective intraparticle diffusion coefficient (Oeff). Optimized values of Kp are in agreement with previously reported values. The slope of a correlation between the fitted values of Deff and Kp agrees well with theory, but the absolute values of Deff are a factor of ???106 smaller than predicted for sorption-retarded, gaseous diffusion. Slow transport through an organic or solid phase within the particles or preferential flow through the bed of particulate matter on the filter might be the cause of these very small effective diffusion coefficients. ?? 1993 American Chemical Society.

  13. Effect of gas diffusion layer and membrane properties in an annular proton exchange membrane fuel cell

    NASA Astrophysics Data System (ADS)

    Khazaee, I.; Ghazikhani, M.; Esfahani, M. Nasr

    2012-01-01

    A complete three-dimensional and single phase computational dynamics model for annular proton exchange membrane (PEM) fuel cell is used to investigate the effect of changing gas diffusion layer and membrane properties on the performances, current density and gas concentration. The proposed model is a full cell model, which includes all the parts of the PEM fuel cell, flow channels, gas diffusion electrodes, catalyst layers and the membrane. Coupled transport and electrochemical kinetics equations are solved in a single domain; therefore no interfacial boundary condition is required at the internal boundaries between cell components. This computational fluid dynamics code is used as the direct problem solver, which is used to simulate the two-dimensional mass, momentum and species transport phenomena as well as the electron- and proton-transfer process taking place in a PEMFC that cannot be investigated experimentally. The results show that by increasing the thickness and decreasing the porosity of GDL the performance of the cell enhances that it is different with planner PEM fuel cell. Also the results show that by decreasing the thickness of the membrane the performance of the cell increases.

  14. Investigating the Diffuse Ionized Gas in the Magellanic Stream with Mapped WHAM Observations

    NASA Astrophysics Data System (ADS)

    Smart, Brianna; Haffner, L. Matthew; Barger, Kathleen; Hernandez, Mike

    2016-01-01

    We present early stages of an Hα survey of the Magellanic Stream using the Wisconsin H-Alpha Mapper (WHAM). While the neutral component of the Stream may extend 200° across the sky (Nidever et al. 2010), its ionized gas has not yet been studied in detail. Fox et al. 2014 find that the tidal debris in the Magellanic System contains twice as much ionized gas as neutral and may extend 30° away from the H I emission. However, such absorption-line studies are not sensitive to the overall morphology of the ionized gas. Using targeted Hα emission observations of the Magellanic Stream, Barger et al. 2015 find that although the warm ionized gas tracks the neutral gas, it often spans a few degrees away from the H I emission at slightly offset velocities. Using WHAM's unprecedented sensitivity to diffuse emission (~ 10s of mR) and its velocity resolution (12 km/s) to isolate Stream emission, we are now conducting the first full Hα survey of its ionized component. Here we present early results, including spatial and kinematic comparisons to the well-established neutral profile of the Stream. WHAM research and operations are supported through NSF Award AST-1108911.

  15. Dynamic behaviors of liquid droplets on a gas diffusion layer surface: Hybrid lattice Boltzmann investigation

    NASA Astrophysics Data System (ADS)

    Wu, Jie; Huang, Jun-Jie

    2015-07-01

    Water management is one of the key issues in proton exchange membrane fuel cells. Fundamentally, it is related to dynamic behaviors of droplets on a gas diffusion layer (GDL) surface, and consequently they are investigated in this work. A two-dimensional hybrid method is employed to implement numerical simulations, in which the flow field is solved by using the lattice Boltzmann method and the interface between droplet and gas is captured by solving the Cahn-Hilliard equation directly. One or two liquid droplets are initially placed on the GDL surface of a gas channel, which is driven by the fully developed Poiseuille flow. At a fixed channel size, the effects of viscosity ratio of droplet to gas ( μ ∗ ), Capillary number (Ca, ratio of gas viscosity to surface tension), and droplet interaction on the dynamic behaviors of droplets are systematically studied. By decreasing viscosity ratio or increasing Capillary number, the single droplet can detach from the GDL surface easily. On the other hand, when two identical droplets stay close to each other or a larger droplet is placed in front of a smaller droplet, the removal of two droplets is promoted.

  16. Dependence of ion drift velocity and diffusion coefficient in parent gas on its temperature

    NASA Astrophysics Data System (ADS)

    Maiorov, Sergey; Golyatina, Rusudan

    2016-09-01

    The results of Monte Carlo calculations of the ion drift characteristics are presented: ions of noble gases and Ti, Fe, Co, Cs, Rb, W and mercury ions in case of constant and uniform electric field are considered. The dependences of the ion mobility on the field strength and gas temperature are analyzed. The parameters of the drift velocity approximation by the Frost formula for gas temperatures of 4.2, 77, 300, 1000, and 2000 K are presented. A universal drift velocity approximation depending on the reduced electric field strength and gas temperature is obtained. In the case of strong electric fields or low gas temperatures, the deviation of the ion distribution function from the Maxwellian one (including the shifted Maxwellian one) can be very significant. The average energies of chaotic motion of ions along and across the electric field can also differ significantly. It is analyzed the kinetic characteristics of ion drift in own gas: ion diffusion coefficient along the field and across the field; thermal spread of velocities (temperature) along the field and across the field. The unexpected and nontrivial fact takes place: collision with backscattering represent only 10-50% of the total number of collisions. This calculation can be used when analyzing experiments with dusty plasma under cryogenic discharge, ultracold plasma. The work was supported by the Russian Science Foundation (grant RNF 14-19-01492).

  17. Automation of flow injection gas diffusion-ion chromatography for the nanomolar determination of methylamines and ammonia in seawater and atmospheric samples

    PubMed Central

    Gibb, Stuart W.; Wood, John W.; Fauzi, R.; Mantoura, C.

    1995-01-01

    The automation and improved design and performance of Flow Injection Gas Diffusion-Ion Chromatography (FIGD-IC), a novel technique for the simultaneous analysis of trace ammonia (NH3) and methylamines (MAs) in aqueous media, is presented. Automated Flow Injection Gas Diffusion (FIGD) promotes the selective transmembrane diffusion of MAs and NH3 from aqueous sample under strongly alkaline (pH > 12, NaOH), chelated (EDTA) conditions into a recycled acidic acceptor stream. The acceptor is then injected onto an ion chromatograph where NH3 and the MAs are fully resolved as their cations and detected conductimetrically. A versatile PC interfaced control unit and data capture unit (DCU) are employed in series to direct the selonoid valve switching sequence, IC operation and collection of data. Automation, together with other modifications improved both linearily (R2 > 0.99 MAs 0-100 nM, NH3 0-1000 nM) and precision (<8%) of FIGD-IC at nanomolar concentrations, compared with the manual procedure. The system was successfully applied to the determination of MAs and NH3 in seawater and in trapped particulate and gaseous atmospheric samples during an oceanographic research cruise. PMID:18925047

  18. Diffusion-driven growth of a spherical gas bubble in gelatin gels supersaturated with air

    NASA Astrophysics Data System (ADS)

    Shirota, Eriko; Ando, Keita

    2016-11-01

    We experimentally and theoretically study diffusion-driven growth of laser-induced gas bubbles in gelatin gels supersaturated with air. The supersaturation in the gels is realized by using a large separation between heat and mass diffusion rates. An optical system is developed to induce bubble nucleation by laser focusing and visualize the subsequent bubble growth. To evaluate the effect of the gel elasticity on the bubble growth rate, we propose the extended Epstein-Plesset theory that considers bubble pressure modifications due to linear/nonlinear elasticity (in addition to Laplace pressure). From comparisons between the experiments and the proposed theory, the bubble growth rate is found to be hindered by the elasticity. This study is supported by JSPS KAKENHI Grant Number 25709008.

  19. Alveolar ventilation to perfusion heterogeneity and diffusion impairment in a mathematical model of gas exchange

    NASA Technical Reports Server (NTRS)

    Vidal Melo, M. F.; Loeppky, J. A.; Caprihan, A.; Luft, U. C.

    1993-01-01

    This study describes a two-compartment model of pulmonary gas exchange in which alveolar ventilation to perfusion (VA/Q) heterogeneity and impairment of pulmonary diffusing capacity (D) are simultaneously taken into account. The mathematical model uses as input data measurements usually obtained in the lung function laboratory. It consists of two compartments and an anatomical shunt. Each compartment receives fractions of alveolar ventilation and blood flow. Mass balance equations and integration of Fick's law of diffusion are used to compute alveolar and blood O2 and CO2 values compatible with input O2 uptake and CO2 elimination. Two applications are presented. The first is a method to partition O2 and CO2 alveolar-arterial gradients into VA/Q and D components. The technique is evaluated in data of patients with chronic obstructive pulmonary disease (COPD). The second is a theoretical analysis of the effects of blood flow variation in alveolar and blood O2 partial pressures. The results show the importance of simultaneous consideration of D to estimate VA/Q heterogeneity in patients with diffusion impairment. This factor plays an increasing role in gas alveolar-arterial gradients as severity of COPD increases. Association of VA/Q heterogeneity and D may produce an increase of O2 arterial pressure with decreasing QT which would not be observed if only D were considered. We conclude that the presented computer model is a useful tool for description and interpretation of data from COPD patients and for performing theoretical analysis of variables involved in the gas exchange process.

  20. Determination of acetaldehyde in saliva by gas-diffusion flow injection analysis.

    PubMed

    Ramdzan, Adlin N; Mornane, Patrick J; McCullough, Michael J; Mazurek, Waldemar; Kolev, Spas D

    2013-07-05

    The consumption of ethanol is known to increase the likelihood of oral cancer. In addition, there has been a growing concern about possible association between long term use of ethanol-containing mouthwashes and oral cancer. Acetaldehyde, known to be a carcinogen, is the first metabolite of ethanol and it can be produced in the oral cavity after consumption or exposure to ethanol. This paper reports on the development of a gas-diffusion flow injection method for the online determination of salivary acetaldehyde by its colour reaction with 3-methyl-2-benzothiazolinone hydrazone (MBTH) and ferric chloride. Acetaldehyde samples and standards (80 μL) were injected into the donor stream containing NaCl from which acetaldehyde diffused through the hydrophobic Teflon membrane of the gas-diffusion cell into the acceptor stream containing the two reagents mentioned above. The resultant intense green coloured dye was monitored spectrophotometrically at 600 nm. Under the optimum working conditions the method is characterized by a sampling rate of 9h(-1), a linear calibration range of 0.5-15 mg L(-1) (absorbance=5.40×10(-2) [acetaldehyde, mg L(-1)], R(2)=0.998), a relative standard deviation (RSD) of 1.90% (n=10, acetaldehyde concentration of 2.5 mg L(-1)), and a limit of detection (LOD) of 12.3 μg L(-1). The LOD and sampling rate of the proposed method are superior to those of the conventional gas chromatographic (GC) method (LOD=93.0 μg L(-1) and sampling rate=4 h(-1)). The reliability of the proposed method was illustrated by the fact that spiked with acetaldehyde saliva samples yielded excellent recoveries (96.6-101.9%), comparable to those obtained by GC (96.4-102.3%) and there was no statistically significant difference at the 95% confidence level between the two methods when non-spiked saliva samples were analysed.

  1. An Experimental and Computational Evaluation of the Importance of Molecular Diffusion in Gas Gravity Currents

    NASA Astrophysics Data System (ADS)

    Herman, Jeremy J.

    The accidental release of hazardous, denser-than-air gases during their transport or manufacture is a vital area of study for process safety researchers. This project examines the importance of molecular diffusion on the developing concentration field of a gas gravity current released into a calm environment. Questions which arose from the unexpectedly severe explosion in 2005 at Buncefield, England were of particular interest. The accidental overfilling of a large tank with gasoline on a completely calm morning led to a massive open air explosion. Forensic evidence showed that at the time of ignition, a vapor cloud, most of which now appears to have been within the flammability limits, covered approximately 120,000 m2. Neither the severity of the explosion, nor the size of the vapor cloud would have been anticipated. Experiments were conducted in which carbon dioxide was released from a sunken source into a one meter wide channel devoid of any wind. These experiments were designed in such a way as to mitigate the formation of a raised head at the front of the gravity current which would have resulted in turbulent entrainment of air. This was done to create a flow in which molecular diffusion was the controlling form of mixing between the carbon dioxide and air. Concentration measurements were taken using flame ionization detection at varying depths and down channel locations. A model of the experiments was developed using COMSOL Multiphysics. The only form of mixing allowed between carbon dioxide and air in the model was molecular diffusion. In this manner the accuracy of the assertion that molecular diffusion was controlling in our experiments was checked and verified. Experimental measurements showed a large variation of gas concentration with depth of the gravity current at the very beginning of the channel where the gas emerged up from the sunken source and began flowing down channel. Due to this variation, molecular diffusion caused the vertical concentration

  2. The diffusion of {sup 14}CO{sub 2} through engineered barrier media

    SciTech Connect

    Bauer, L.R.; Landolt, R.R.

    1988-12-31

    The diffusion of {sup 14}CO{sub 2} through crushed tuff, bentonite and a crushed tuff/bentonite mixture was measured for two diffusion lengths. The ability of {sup 14}CO{sub 2} to penetrate a microsilica-containing cement proposed for repository use was also examined. The specimens were subjected to uniaxially-applied compressive loads prior to the diffusion tests to simulate the onset of environmentally-induced microcracks. The results suggest that the presence of a tuff- or bentonite-based backfill would not significantly affect {sup 14}CO{sub 2} release rates from a repository. Conversely, {sup 14}CO{sub 2} diffusion through simulated cement seals can apparently only occur after severe physical damage has been induced. These results may have implications for the ability of a repository to comply with the applicable regulatory release limits for C-14.

  3. Numerical modeling of two-phase behavior in the PEFC gas diffusion layer

    SciTech Connect

    Mukherjee, Partha Pa223876; Kang, Qinjun; Mukundan, Rangachary; Borup, Rod L

    2009-01-01

    A critical performance limitation in the polymer electrolye fuel cell (PEFC) is attributed to the mass transport loss originating from suboptimal liquid water transport and flooding phenomena. Liquid water can block the porous pathways in the fibrous gas diffusion layer (GDL) and the catalyst layer (CL), thus hindering oxygen transport from the flow field to the electrochemically actives sites in the catalyst layer. In this paper, the study of the two phase behavior and the durability implications due to the wetting characteristics in the carbon paper GDL are presented using a pore-scale modeling framework.

  4. The Massive Stellar Population in the Diffuse Ionized Gas of M33

    NASA Technical Reports Server (NTRS)

    Hoopes, Charles G.; Walterbos, Rene A. M.

    1995-01-01

    We compare Far-UV, H alpha, and optical broadband images of the nearby spiral galaxy M33, to investigate the massive stars associated with the diffuse ionized gas. The H-alpha/FUV ratio is higher in HII regions than in the DIG, possibly indicating that an older population ionizes the DIG. The broad-band colors support this conclusion. The HII region population is consistent with a young burst, while the DIG colors resemble an older population with constant star formation. Our results indicate that there may be enough massive field stars to ionize the DIG, without the need for photon leakage from HII regions.

  5. Binary and ternary gas mixtures with temperature enhanced diffuse glow discharge characteristics for use in closing switches

    DOEpatents

    Christophorou, L.G.; Hunter, S.R.

    1988-06-28

    An improvement to the gas mixture used in diffuse glow discharge closing switches is disclosed which includes binary and ternary gas mixtures which are formulated to exhibit decreasing electron attachment with increasing temperature. This increases the efficiency of the conductance of the glow discharge and further inhibits the formation of an arc. 11 figs.

  6. Binary and ternary gas mixtures with temperature enhanced diffuse glow discharge characteristics for use in closing switches

    DOEpatents

    Christophorou, Loucas G.; Hunter, Scott R.

    1990-01-01

    An improvement to the gas mixture used in diffuse glow discharge closing switches is disclosed which includes binary and ternary gas mixtures which are formulated to exhibit decreasing electron attachment with increasing temperature. This increases the efficiency of the conductance of the glow discharge and further inhibits the formation of an arc.

  7. Binary and ternary gas mixtures with temperature enhanced diffuse glow discharge characteristics for use in closing switches

    DOEpatents

    Christophorou, L.G.; Hunter, S.R.

    1990-06-26

    An improvement to the gas mixture used in diffuse glow discharge closing switches is disclosed which includes binary and ternary gas mixtures which are formulated to exhibit decreasing electron attachment with increasing temperature. This increases the efficiency of the conductance of the glow discharge and further inhibits the formation of an arc. 11 figs.

  8. Transport characteristics of gas phase ozone in unsaturated porous media for in-situ chemical oxidation.

    SciTech Connect

    Choi, H.; Lim, H-N; Kang, J-W; Hwang, T-M; Kim, J.; Environmental Research; Kwangju Inst. of Science and Technology; Yonsei Univ.

    2002-07-01

    Laboratory column experiments were conducted by employing various porous media to delineate the characteristics of gaseous ozone transport in the unsaturated zone under various conditions. Water content, soil organic matter (SOM), and metal oxides (MOs) were found to be the factors most influential in the fate and transport of gaseous ozone in unsaturated porous media. The migration velocity of the gaseous ozone front was inversely proportional to the MO content of the porous media. Increased water content at fixed gas flux decreased the ozone breakthrough time proportionally as a result of reduced gas pore volume (PV) in the column, and increased pore water interfered with reactions of gaseous ozone with SOM and MOs on the surface of porous media. The feasibility of in-situ ozone injection for the remediation of unsaturated soils contaminated with either phenanthrene or diesel-range organics (DROs) was investigated under various conditions. The maximum removal after 1 h of ozone injection was achieved in columns packed with baked sand, followed, in descending order, by glass beads and by sand, indicating that catalytic ozone decomposition with MOs in columns packed with baked sand enhanced hydroxyl radical formation and resulted in increased contaminant removal. Overall removal efficiency of multicomponent C{sub 10}-C{sub 24} DROs after 14 h of ozonation was 78.7%. Ozone transport was retarded considerably because of the high ozone demand of DROs, requiring more than 6 h for the gaseous ozone to initially break through the soil column under the experimental conditions tested in this study. Overall, gaseous ozone was readily delivered and transported to remediate unsaturated soils contaminated with phenanthrene and DROs.

  9. Anomalous diffusion of fluid momentum and Darcy-like law for laminar flow in media with fractal porosity

    NASA Astrophysics Data System (ADS)

    Balankin, Alexander S.; Valdivia, Juan-Carlos; Marquez, Jesús; Susarrey, Orlando; Solorio-Avila, Marco A.

    2016-08-01

    In this Letter, we report experimental and theoretical studies of Newtonian fluid flow through permeable media with fractal porosity. Darcy flow experiments were performed on samples with a deterministic pre-fractal pore network. We found that the seepage velocity is linearly proportional to the pressure drop, but the apparent absolute permeability increases with the increase of sample length in the flow direction L. We claim that a violation of the Hagen-Poiseuille law is due to an anomalous diffusion of the fluid momentum. In this regard we argue that the momentum diffusion is governed by the flow metric induced by the fractal topology of the pore network. The Darcy-like equation for laminar flow in a fractal pore network is derived. This equation reveals that the apparent absolute permeability is independent of L, only if the number of effective spatial degrees of freedom in the pore-network ν is equal to the network fractal (self-similarity) dimension D, e.g. it is in the case of fractal tree-like networks. Otherwise, the apparent absolute permeability either decreases with L, if ν < D, e.g. in media with self-avoiding fractal channels, or increases with L, if ν > D, as this is in the case of the inverse Menger sponge.

  10. A macroscopic model for slightly compressible gas slip-flow in homogeneous porous media

    NASA Astrophysics Data System (ADS)

    Lasseux, D.; Parada, F. J. Valdes; Tapia, J. A. Ochoa; Goyeau, B.

    2014-05-01

    The study of gas slip-flow in porous media is relevant in many applications ranging from nanotechnology to enhanced oil recovery and in any situation involving low-pressure gas-transport through structures having sufficiently small pores. In this paper, we use the method of volume averaging for deriving effective-medium equations in the framework of a slightly compressible gas flow. The result of the upscaling process is an effective-medium model subjected to time- and length-scale constraints, which are clearly identified in our derivation. At the first order in the Knudsen number, the macroscopic momentum transport equation corresponds to a Darcy-like model involving the classical intrinsic permeability tensor and a slip-flow correction tensor that is also intrinsic. It generalizes the Darcy-Klinkenberg equation for ideal gas flow, and exhibits a more complex form for dense gas. The component values of the two intrinsic tensors were computed by solving the associated closure problems on two- and three-dimensional periodic unit cells. Furthermore, the dependence of the slip-flow correction with the porosity was also verified to agree with approximate analytical results. Our predictions show a power-law relationship between the permeability and the slip-flow correction that is consistent with other works. Nevertheless, the generalization of such a relationship to any configuration requires more analysis.

  11. High Pressure Gas Permeation and Liquid Diffusion Studies of Coflon and Tefzel Thermoplastics. Revision

    NASA Technical Reports Server (NTRS)

    Morgan, G. J.; Campion, R. P.

    1997-01-01

    The life of fluid-carrying flexible or umbilical pipes during service at elevated temperatures and pressures depends inter alia on their resistance to attack by the fluids present and the rate at which these fluids are absorbed by the pipe lining materials. The consequences of fluid ingress into the thermoplastic lining could mean a) a reduction in its mechanical strength, to increase chances of crack formation and growth and thus a loss of integrity, b) the occurrence of permeation right through the lining material, with pressure build- up in the outer pipe wall construction (of flexible pipes) or chemical attack (from a hostile permeant) on outer layers of reinforcements. Therefore it is important within this project to have relevant permeation data for Coflon and Tefzel thermoplastics: the former is plasticised, the latter is not. A previous report (CAPP/M.2) described experimental equipment and techniques used by MERL when measuring high pressure (up to 5000 psi) gas permeation and liquid diffusion through thermoplastic samples cut from extruded bar or pipe, and provided the basic theory involved. Norsk Hydro are also performing gas permeation tests on pipe sections, at up to 100 bars (1450 psi) pressure or so, and reporting separately. Some comparisons between data from Norsk Hydro and MERL have been made herein. The tests should be considered as complementary, as the Norsk Hydro test has the obvious benefit of using complete pipe sections, whilst MERL can test at much higher pressures, up to 1000 bar if necessary. The sophisticated analytical measuring equipment of Norsk Hydro can distinguish the individual components of mixed gases and hence the various permeation-linked coefficients whereas MERL, in using pressure increase at constant volume to determine permeation rate, is limited to obtaining single gas data, or apparent (or representative) coefficients for a mixed gas as a whole. Except for the initial fluid diffusion data for Tefzel described in CAPP

  12. Derivatization in gas chromatographic determination of phenol and aniline traces in aqueous media

    NASA Astrophysics Data System (ADS)

    Gruzdev, I. V.; Zenkevich, I. G.; Kondratenok, B. M.

    2015-06-01

    Substituted anilines and phenols are the most common hydrophilic organic environmental toxicants. The principles of gas chromatographic determination of trace amounts of these compounds in aqueous media at concentrations <=0.1 μg litre-1 based on synthesis of their derivatives (derivatization) directly in the aqueous phase are considered. Conversion of relatively hydrophilic analytes into more hydrophobic derivatives makes it possible to achieve such low detection limits and optimize the protocols of extractive preconcentration and selective chromatographic detection. Among the known reactions, this condition is best met by electrophilic halogenation of compounds at the aromatic moiety. The bibliography includes 177 references.

  13. Testing of a Hydrogen Diffusion Flame Array Injector at Gas Turbine Conditions

    SciTech Connect

    Weiland, Nathan T.; Sidwell, Todd G.; Strakey, Peter A.

    2013-07-03

    High-hydrogen gas turbines enable integration of carbon sequestration into coal-gasifying power plants, though NO{sub x} emissions are often high. This work explores nitrogen dilution of hydrogen diffusion flames to reduce thermal NO{sub x} emissions and avoid problems with premixing hydrogen at gas turbine pressures and temperatures. The burner design includes an array of high-velocity coaxial fuel and air injectors, which balances stability and ignition performance, combustor pressure drop, and flame residence time. Testing of this array injector at representative gas turbine conditions (16 atm and 1750 K firing temperature) yields 4.4 ppmv NO{sub x} at 15% O{sub 2} equivalent. NO{sub x} emissions are proportional to flame residence times, though these deviate from expected scaling due to active combustor cooling and merged flame behavior. The results demonstrate that nitrogen dilution in combination with high velocities can provide low NO{sub x} hydrogen combustion at gas turbine conditions, with significant potential for further NO{sub x} reductions via suggested design changes.

  14. Flame-in-gas-shield and miniature diffusion flame hydride atomizers for atomic fluorescence spectrometry: optimization and comparison

    NASA Astrophysics Data System (ADS)

    Marschner, Karel; Musil, Stanislav; Dědina, Jiří

    2015-07-01

    A detailed optimization of relevant experimental parameters of two hydride atomizers for atomic fluorescence spectrometry: flame-in-gas-shield atomizer with a two-channel shielding unit and a standard atomizer for atomic fluorescence spectrometry, miniature diffusion flame, was performed. Arsine, generated by the reaction with NaBH4 in a flow injection arrangement, was chosen as the model hydride. Analytical characteristics of both the atomizers (sensitivity, noise, limits of detection) were compared. Under optimum conditions sensitivity obtained with flame-in-gas-shield atomizer was approximately twice higher than with miniature diffusion flame. The additional advantage of flame-in-gas-shield atomizer is significantly lower flame emission resulting in a better signal to noise ratio. The resulting arsenic limits of detection for miniature diffusion flame and flame-in-gas-shield atomizer were 3.8 ng l- 1 and 1.0 ng l- 1, respectively.

  15. The effect of diffusion and susceptibility differences on T2 measurements for fluids in porous media and biological tissues.

    PubMed

    Borgia, G C; Brown, R J; Fantazzini, P

    1996-01-01

    A number of features of T2 measurements for fluids in porous media have shown behavior contrary to that suggested by intuition developed in other areas. For porous media with relatively uniform pore spaces the following have been observed, in each case for certain ranges only of Xv (susceptibility difference times frequency), D (diffusion coefficient), a (a pore dimension), porespace shape and distribution, echo-time t for single echoes and half-echo-spacing tau for CPMG): (1) In S(t) for FID (free induction decay, S for signal) with constant slope after an initial period of increasing slope; (2) In Ss(t) for single (subscript s) echoes linear (instead of cubic) in t after an initial period; (3) for CPMG R(tau) = 1/T2(tau) - 1/T2(tau-->0) linear in tau over a substantial range; (4) slope of R(tau) independent of D and alpha for this range; (5) slope R(s) of In Ss(t) independent of D and a, and (6) R(s)(t) and R(tau) at long times linear (instead of quadratic) in Xv. These features appear to be compatible with the assumption of a truncated Cauchy-Lorentz distribution of the local magnetic fields due to susceptibility differences. The statistics of repeated sampling of local fields in different parts of the porespace during diffusion lead to a suppression, after a short time, of the effects of diffusion on the FID decay rate and the single-echo decay rate over significant ranges of the parameters. Data are presented to extend the range of parameters studied previously.

  16. Quantitative gas chromatographic analysis of volatile fatty acids in spent culture media and body fluids.

    PubMed Central

    van den Bogaard, A E; Hazen, M J; Van Boven, C P

    1986-01-01

    Gas chromatographic analysis of volatile fatty acids for identification of obligately anaerobic bacteria and for presumptive diagnosis of anaerobic infections is now widely practiced. However, it is difficult to compare data because only a qualitative analysis is done or only chromatograms are presented instead of quantitative data on volatile fatty acid production. We compared three stationary phases for volatile fatty acid analysis of aqueous solutions and four methods of pretreating samples for gas chromatography. Quantitative analysis could be done accurately by using Carbowax as the stationary phase after pretreatment of spent culture media with Dowex columns. If only qualitative analysis is required (e.g., for presumptive diagnosis of anaerobic infections), ether extraction and headspace analysis are equally suitable. The overall variation coefficient for volatile fatty acid production by four reference strains of obligately anaerobic bacteria after 24 h of incubation was approximately 10%. PMID:3958144

  17. Generation of tunable octave-spanning mid-infrared pulses by filamentation in gas media.

    PubMed

    Cheng, Mark; Reynolds, Anthony; Widgren, Heather; Khalil, Munira

    2012-06-01

    The continued development of femtosecond mid-infrared (IR) sources with ultrabroad spectral width is critical for probing and controlling complex molecular structural dynamics on an ultrafast timescale. We report on a sub-20 fs, coherent mid-IR source with an octave-spanning spectral bandwidth (>2000 cm(-1)) tunable from 2-8 micrometers (37.5-150 THz), with energy >0.4 μJ/pulse at 1 kHz. The mid-IR pulses are generated by four-wave mixing during the filamentation of intense 800 nm and 400 nm pulses in various gas media. Spectral tunability is achieved by the choice of gas, pressure and input 800 nm pulse energy.

  18. The transition from silicon to gas detection media in nuclear physics

    NASA Astrophysics Data System (ADS)

    Pollacco, Emanuel C.

    2016-06-01

    Emerging radioactive beams and multi petawatt laser facilities are sturdily transforming our base concepts in instruments in nuclear physics. The changes are fuelled by studies of nuclei close to the drip-line or exotic reactions. This physics demands high luminosity, wide phase space cover with good resolution in energy, time, position and sampled waveform. By judiciously modifying the micro-world of the particle or space physics instruments (Double Sided Strip Si Detectors, Micro-Pattern Gas Amplifiers, microelectronics), we are on the path to initiate dream experiments. In the following a brief status in the domain is reported for selected instruments that highlight the present trends with silicon and the growing shift towards gas media for charged particle detection.

  19. Finite Element Analysis of Poroelastic Composites Undergoing Thermal and Gas Diffusion

    NASA Technical Reports Server (NTRS)

    Salamon, N. J. (Principal Investigator); Sullivan, Roy M.; Lee, Sunpyo

    1995-01-01

    A theory for time-dependent thermal and gas diffusion in mechanically time-rate-independent anisotropic poroelastic composites has been developed. This theory advances previous work by the latter two authors by providing for critical transverse shear through a three-dimensional axisymmetric formulation and using it in a new hypothesis for determining the Biot fluid pressure-solid stress coupling factor. The derived governing equations couple material deformation with temperature and internal pore pressure and more strongly couple gas diffusion and heat transfer than the previous theory. Hence the theory accounts for the interactions between conductive heat transfer in the porous body and convective heat carried by the mass flux through the pores. The Bubnov Galerkin finite element method is applied to the governing equations to transform them into a semidiscrete finite element system. A numerical procedure is developed to solve the coupled equations in the space and time domains. The method is used to simulate two high temperature tests involving thermal-chemical decomposition of carbon-phenolic composites. In comparison with measured data, the results are accurate. Moreover unlike previous work, for a single set of poroelastic parameters, they are consistent with two measurements in a restrained thermal growth test.

  20. Killing of total heterotrophic bacteria using the gas diffusion electrode system.

    PubMed

    Xu, W Y; Li, P

    2012-06-01

    This study focused on the disinfection of dual electrodes with a gas diffusion cathode using total heterotrophic bacteria as indicator microorganisms. Batch tests were performed to study the effects of platinum load W(Pt) and the pore-forming agent content WNH4HCO3 in gas diffusion electrodes on the germicidal efficacy eta and H2O2 yield. The results showed that the disinfection improved with W(Pt), but its efficiency at W(Pt) of 3 per thousand was equivalent to W(Pt) of 4 per thousand. The right amount of the pore-forming agent improved disinfection. Continuous tests were performed to study residence times (RTs), pH and oxygen flow rates Qo2 on the germicidal efficacy and H2O2 yield. The results indicated that at the steady state total heterotrophic bacteria in the outlet stream were completely inactivated under our experimental conditions. Disinfection improved with increasing RT. This phenomenon was more significant when RT < 20 min. A drop in pH value resulted in the rapid rise of germicidal efficacy, while disinfection shortened with an increasing oxygen flow rate Qo2. The operating costs are high. Further research is required to fully understand all parameters and reduce operating costs.

  1. Study of effective transport properties of fresh and aged gas diffusion layers

    NASA Astrophysics Data System (ADS)

    Bosomoiu, Magdalena; Tsotridis, Georgios; Bednarek, Tomasz

    2015-07-01

    Gas diffusion layers (GDLs) play an important role in proton exchange membrane fuel cells (PEMFCs) for the diffusion of reactant and the removal of product water. In the current study fresh and aged GDLs (Sigracet® GDL34BC) were investigated by X-ray computed tomography to obtain a representative 3D image of the real GDL structure. The examined GDL samples are taken from areas located under the flow channel and under the land. Additionally, a brand new Sigracet® GDL34BC was taken as a reference sample in order to find out the impact of fuel cell assembly on GDL. The produced 3D image data were used to calculate effective transport properties such as thermal and electrical conductivity, diffusivity, permeability and capillary pressure curves of the dry and partially saturated GDL. The simulation indicates flooding by product water occurs at contact angles lower than 125° depending on sample porosity. In addition, GDL anisotropy significantly affects the permeability as well as thermal and electrical conductivities. The calculated material bulk properties could be next used as input for CFD modelling of PEM fuel cells where GDL is usually assumed layer-like and homogeneous. Tensor material parameters allow to consider GDL anisotropy and lead to more realistic results.

  2. Helium Ionization in the Diffuse Ionized Gas Surrounding UCH ii Regions

    NASA Astrophysics Data System (ADS)

    Anish Roshi, D.; Churchwell, E.; Anderson, L. D.

    2017-04-01

    We present measurements of the singly ionized helium-to-hydrogen ratio ({n}{{He}+}/{n}{{{H}}+}) toward diffuse gas surrounding three ultracompact H ii (UCH ii) regions: G10.15-0.34, G23.46-0.20, and G29.96-0.02. We observe radio recombination lines of hydrogen and helium near 5 GHz using the GBT to measure the {n}{{He}+}/{n}{{{H}}+} ratio. The measurements are motivated by the low helium ionization observed in the warm ionized medium and in the inner Galaxy diffuse ionized regions. Our data indicate that the helium is not uniformly ionized in the three observed sources. Helium lines are not detected toward a few observed positions in sources G10.15-0.34 and G23.46-0.20, and the upper limits of the {n}{{He}+}/{n}{{{H}}+} ratio obtained are 0.03 and 0.05, respectively. The selected sources harbor stars of type O6 or hotter as indicated by helium line detection toward the bright radio continuum emission from the sources with mean {n}{{He}+}/{n}{{{H}}+} value 0.06 ± 0.02. Our data thus show that helium in diffuse gas located a few parsecs away from the young massive stars embedded in the observed regions is not fully ionized. We investigate the origin of the nonuniform helium ionization and rule out the possibilities (a) that the helium is doubly ionized in the observed regions and (b) that the low {n}{{He}+}/{n}{{{H}}+} values are due to additional hydrogen ionizing radiation produced by accreting low-mass stars. We find that selective absorption of ionizing photons by dust can result in low helium ionization but needs further investigation to develop a self-consistent model for dust in H ii regions.

  3. Diffusion of latex and DNA chains in 2D confined media.

    PubMed

    Mathé, Jérôme; Di Meglio, Jean-Marc; Tinland, Bernard

    2008-06-01

    We report a study on the dynamics of latex polystyrene beads and of DNA molecules confined in two dimensions, using fluorescence video-microscopy. We particularly focus on the character of the confined objects (hard or soft) and on the nature of the confinement: liquid (in a soap film) or solid (between two glass plates). For weak confinements, whatever the nature of confinement, we observe that DNA molecules and latex beads behave very similarly: the tighter the confinement, the slower the diffusion with a good agreement with theory. For strong confinements between solid walls (thickness of confinement smaller than the bulk radius of gyration), DNA coils are not immobilized and still diffuse. We show in this case that the conformation of DNA chains is in good agreement with the predictions of De Gennes and Brochard (radius approximately e (-1/4), with e the confinement gap); on the other hand, we cannot really check the theoretical predictions for the diffusion coefficient. Interestingly, strong confinement of latex beads in a soap film leads to a anomalous slow diffusion, certainly associated with an additional viscous drag generated by the interfaces.

  4. Non-equilibrium chemistry and cooling in the diffuse interstellar medium - II. Shielded gas

    NASA Astrophysics Data System (ADS)

    Richings, A. J.; Schaye, J.; Oppenheimer, B. D.

    2014-08-01

    We extend the non-equilibrium model for the chemical and thermal evolution of diffuse interstellar gas presented in Richings et al. to account for shielding from the UV radiation field. We attenuate the photochemical rates by dust and by gas, including absorption by H I, H2, He I, He II and CO where appropriate. We then use this model to investigate the dominant cooling and heating processes in interstellar gas as it becomes shielded from the UV radiation. We consider a one-dimensional plane-parallel slab of gas irradiated by the interstellar radiation field, either at constant density and temperature or in thermal and pressure equilibrium. The dominant thermal processes tend to form three distinct regions in the clouds. At low column densities, cooling is dominated by ionized metals such as Si II, Fe II, Fe III and C II, which are balanced by photoheating, primarily from H I. Once the hydrogen-ionizing radiation becomes attenuated by neutral hydrogen, photoelectric dust heating dominates, while C II becomes dominant for cooling. Finally, dust shielding triggers the formation of CO and suppresses photoelectric heating. The dominant coolants in this fully shielded region are H2 and CO. The column density of the H I-H2 transition predicted by our model is lower at higher density (or at higher pressure for gas clouds in pressure equilibrium) and at higher metallicity, in agreement with previous photodissociation region models. We also compare the H I-H2 transition in our model to two prescriptions for molecular hydrogen formation that have been implemented in hydrodynamic simulations.

  5. Multicomponent effective medium-correlated random walk theory for the diffusion of fluid mixtures through porous media.

    PubMed

    Bonilla, Mauricio R; Bhatia, Suresh K

    2012-01-10

    Molecular transport in nanoconfined spaces plays a key role in many emerging technologies for gas separation and storage, as well as in nanofluidics. The infiltration of fluid mixtures into the voids of porous frameworks having complex topologies is common place to these technologies, and optimizing their performance entails developing a deeper understanding of how the flow of these mixtures is affected by the morphology of the pore space, particularly its pore size distribution and pore connectivity. Although several techniques have been developed for the estimation of the effective diffusivity characterizing the transport of single fluids through porous materials, this is not the case for fluid mixtures, where the only alternatives rely on a time-consuming solution of the pore network equations or adaptations of the single fluid theories which are useful for a limited type of systems. In this paper, a hybrid multicomponent effective medium-correlated random walk theory for the calculation of the effective transport coefficients matrix of fluid mixtures diffusing through porous materials is developed. The theory is suitable for those systems in which component fluxes at the single pore level can be related to the potential gradients of the different species through linear flux laws and corresponds to a generalization of the classical single fluid effective medium theory for the analysis of random resistor networks. Comparison with simulation of the diffusion of binary CO(2)/H(2)S and ternary CO(2)/H(2)S/C(3)H(8) gas mixtures in membranes modeled as large networks of randomly oriented pores with both continuous and discrete pore size distributions demonstrates the power of the theory, which was tested using the well-known generalized Maxwell-Stefan model for surface diffusion at the single pore level.

  6. Coupling between geochemical reactions and multicomponent gas and solute transport in unsaturated media: A reactive transport modeling study

    NASA Astrophysics Data System (ADS)

    Molins, S.; Mayer, K. U.

    2007-05-01

    The two-way coupling that exists between biogeochemical reactions and vadose zone transport processes, in particular gas phase transport, determines the composition of soil gas. To explore these feedback processes quantitatively, multicomponent gas diffusion and advection are implemented into an existing reactive transport model that includes a full suite of geochemical reactions. Multicomponent gas diffusion is described on the basis of the dusty gas model, which accounts for all relevant gas diffusion mechanisms. The simulation of gas attenuation in partially saturated landfill soil covers, methane production, and oxidation in aquifers contaminated by organic compounds (e.g., an oil spill site) and pyrite oxidation in mine tailings demonstrate that both diffusive and advective gas transport can be affected by geochemical reactions. Methane oxidation in landfill covers reduces the existing upward pressure gradient, thereby decreasing the contribution of advective methane emissions to the atmosphere and enhancing the net flux of atmospheric oxygen into the soil column. At an oil spill site, methane oxidation causes a reversal in the direction of gas advection, which results in advective transport toward the zone of oxidation both from the ground surface and the deeper zone of methane production. Both diffusion and advection contribute to supply atmospheric oxygen into the subsurface, and methane emissions to the atmosphere are averted. During pyrite oxidation in mine tailings, pressure reduction in the reaction zone drives advective gas flow into the sediment column, enhancing the oxidation process. In carbonate-rich mine tailings, calcite dissolution releases carbon dioxide, which partly offsets the pressure reduction caused by O2 consumption.

  7. Coupling between geochemical reactions and multicomponent gas and solute transport in unsaturated media: A reactive transport modeling study

    USGS Publications Warehouse

    Molins, S.; Mayer, K.U.

    2007-01-01

    The two-way coupling that exists between biogeochemical reactions and vadose zone transport processes, in particular gas phase transport, determines the composition of soil gas. To explore these feedback processes quantitatively, multicomponent gas diffusion and advection are implemented into an existing reactive transport model that includes a full suite of geochemical reactions. Multicomponent gas diffusion is described on the basis of the dusty gas model, which accounts for all relevant gas diffusion mechanisms. The simulation of gas attenuation in partially saturated landfill soil covers, methane production, and oxidation in aquifers contaminated by organic compounds (e.g., an oil spill site) and pyrite oxidation in mine tailings demonstrate that both diffusive and advective gas transport can be affected by geochemical reactions. Methane oxidation in landfill covers reduces the existing upward pressure gradient, thereby decreasing the contribution of advective methane emissions to the atmosphere and enhancing the net flux of atmospheric oxygen into the soil column. At an oil spill site, methane oxidation causes a reversal in the direction of gas advection, which results in advective transport toward the zone of oxidation both from the ground surface and the deeper zone of methane production. Both diffusion and advection contribute to supply atmospheric oxygen into the subsurface, and methane emissions to the atmosphere are averted. During pyrite oxidation in mine tailings, pressure reduction in the reaction zone drives advective gas flow into the sediment column, enhancing the oxidation process. In carbonate-rich mine tailings, calcite dissolution releases carbon dioxide, which partly offsets the pressure reduction caused by O2 consumption.

  8. Characterization techniques for gas diffusion layers for proton exchange membrane fuel cells - A review

    NASA Astrophysics Data System (ADS)

    Arvay, A.; Yli-Rantala, E.; Liu, C.-H.; Peng, X.-H.; Koski, P.; Cindrella, L.; Kauranen, P.; Wilde, P. M.; Kannan, A. M.

    2012-09-01

    The gas diffusion layer (GDL) in a proton exchange membrane fuel cell (PEMFC) is one of the functional components that provide a support structure for gas and water transport. The GDL plays a crucial role when the oxidant is air, especially when the fuel cell operates in the higher current density region. There has been an exponential growth in research and development because the PEMFC has the potential to become the future energy source for automotive applications. In order to serve in this capacity, the GDL requires due innovative analysis and characterization toward performance and durability. It is possible to achieve the optimum fuel cell performance only by understanding the characteristics of GDLs such as structure, pore size, porosity, gas permeability, wettability, thermal and electrical conductivities, surface morphology and water management. This review attempts to bring together the characterization techniques for the essential properties of the GDLs as handy tools for R&D institutions. Topics are categorized based on the ex-situ and in-situ characterization techniques of GDLs along with related modeling and simulation. Recently reported techniques used for accelerated durability evaluation of the GDLs are also consolidated within the ex-situ and in-situ methods.

  9. Identifying Extraplanar Diffuse Ionized Gas in a Sample of MaNGA Galaxies

    NASA Astrophysics Data System (ADS)

    Hubbard, Ryan J.; Diamond-Stanic, Aleksandar M.; MaNGA Team

    2016-01-01

    The efficiency with which galaxies convert gas into stars is driven by the continuous cycle of accretion and feedback processes within the circumgalactic medium. Extraplanar diffuse ionized gas (eDIG) can provide insights into the tumultuous processes that govern the evolution of galactic disks because eDIG emission traces both inflowing and outflowing gas. With the help of state-of-the-art, spatially-resolved spectroscopy from MaNGA (Mapping Nearby Galaxies at Apache Point Observatory), we developed a computational method to identify eDIG based on the strength of and spatial extent of optical emission lines for a diverse sample of 550 nearby galaxies. This sample includes roughly half of the MaNGA galaxies that will become publicly available in summer 2016 as part of the Thirteenth Data Release of the Sloan Digital Sky Survey. We identified signatures of eDIG in 8% of the galaxies in this sample, and we found that these signatures are particularly common among galaxies with active star formation and inclination angles >45 degrees. Our analysis of the morphology, incidence, and kinematics of eDIG has important implications for current models of accretion and feedback processes that regulate star formation in galaxies. We acknowledge support from the Astrophysics REU program at the University of Wisconsin-Madison, the National Astronomy Consortium, and The Grainger Foundation.

  10. A numerical study of the effects of ambipolar diffusion on the collapse of magnetic gas clouds

    NASA Technical Reports Server (NTRS)

    Black, D. C.; Scott, E. H.

    1982-01-01

    The gravitational collapse of isothermal, nonrotating magnetic gas clouds have been calculated numerically, including the effects of ambipolar diffusion. The fractional ionization in the clouds is approximated by a power-law function of the gas density, f = K/n to the q-power, where K and q are adjustable parameters. Eleven numerical experiments were run, and the results indicate that the asymptotic character of collapse is determined mainly by the value of q and is largely independent of the other parameters characterizing a cloud (e.g., K, cloud mass). In particular, there is nearly a one-to-one correspondence between q and the slope, x, of the central magnetic field strength-gas density relationship. If q is no more than 0.8, a cloud collapses asymptotically, as though the magnetic field were 'frozen' to the neutral matter. The magnetic field strength at the center of a collapsing cloud is strongly amplified during collapse even for values of q of about 1, despite extremely low values of fractional ionization. A discussion of the theoretical basis for this unexpected behavior is given. Possible implications of our results for the problems of magnetic braking of rotating protostars and star formation in general are also presented.

  11. Performance enhancement of polymer electrolyte fuel cells by combining liquid removal mechanisms of a gas diffusion layer with wettability distribution and a gas channel with microgrooves

    NASA Astrophysics Data System (ADS)

    Utaka, Yoshio; Koresawa, Ryo

    2016-08-01

    Although polymer electrolyte fuel cells (PEFCs) are commercially available, there are still many problems that need to be addressed to improve their performance and increase their usage. At a high current density, generated water accumulates in the gas diffusion layer and in the gas channels of the cathode. This excess water obstructs oxygen transport, and as a result, cell performance is greatly reduced. To improve the cell performance, the effective removal of the generated water and the promotion of oxygen diffusion in the gas diffusion layer (GDL) are necessary. In this study, two functions proposed in previous reports were combined and applied to a PEFC: a hybrid GDL to form an oxygen diffusion path using a wettability distribution and a gas separator with microgrooves to enhance liquid removal. For a PEFC with a hybrid GDL and a gas separator with microgrooves, the concentration overvoltage of the PEFC was reduced, and the current density limit and maximum power density were increased compared with a conventional PEFC. Moreover, the stability of the cell voltage was markedly improved.

  12. Localization and diffusion of tracer particles in viscoelastic media with active force dipoles

    NASA Astrophysics Data System (ADS)

    Yasuda, Kento; Okamoto, Ryuichi; Komura, Shigeyuki; Mikhailov, Alexander S.

    2017-02-01

    Optical tracking in vivo experiments reveal that diffusion of particles in biological cells is strongly enhanced in the presence of ATP and the experimental data for animal cells could previously be reproduced within a phenomenological model of a gel with myosin motors acting within it (Fodor É. et al., EPL, 110 (2015) 48005). Here, the two-fluid model of a gel is considered where active macromolecules, described as force dipoles, cyclically operate both in the elastic and the fluid components. Through coarse-graining, effective equations of motions for idealized tracer particles displaying local deformations and local fluid flows are derived. The equation for deformation tracers coincides with the earlier phenomenological model and thus confirms it. For flow tracers, diffusion enhancement caused by active force dipoles in the fluid component, and thus due to metabolic activity, is found. The latter effect may explain why ATP-dependent diffusion enhancement could also be observed in bacteria that lack molecular motors in their skeleton or when the activity of myosin motors was chemically inhibited in eukaryotic cells.

  13. Perturbation model to predict the effect of spatially varying absorptive inhomogeneities in diffusing media.

    PubMed

    De Nicola, S; Esposito, R; Lepore, M

    2003-08-01

    We develop a perturbation model to predict the effect of a spatially varying absorptive inhomogeneities in a diffusing slab. The model is based on a perturbation solution of diffusion equation derived for a refractive index mismatch between the scattering slab and the surrounding medium, through the use of the extrapolated boundary conditions. We show that the model allows to compute the time-dependent relative change in the transmitted signal resulting from the presence of the inclusion. We derive simplified expressions for the perturbed time-resolved transmittance that allows to implement an efficient fitting procedure for obtaining the optical properties of the absorptive inclusion. The accuracy of the predictions of the model was investigated through comparison with the results of the Finite Element Method to solve the time-dependent diffusion equation numerically. The procedure is used to obtain the absorption perturbation parameter of an absorptive inclusion characterized by spatially dependent Gaussian distribution of its absorption coefficient located at the midplane of a scattering slab.

  14. Factors affecting gas migration and contaminant redistribution in heterogeneous porous media subject to electrical resistance heating.

    PubMed

    Munholland, Jonah L; Mumford, Kevin G; Kueper, Bernard H

    2016-01-01

    A series of intermediate-scale laboratory experiments were completed in a two-dimensional flow cell to investigate gas production and migration during the application of electrical resistance heating (ERH) for the removal of dense non-aqueous phase liquids (DNAPLs). Experiments consisted of heating water in homogeneous silica sand and heating 270 mL of trichloroethene (TCE) and chloroform (CF) DNAPL pools in heterogeneous silica sands, both under flowing groundwater conditions. Spatial and temporal distributions of temperature were measured using thermocouples and observations of gas production and migration were collected using front-face image capture throughout the experiments. Post-treatment soil samples were collected and analyzed to assess DNAPL removal. Results of experiments performed in homogeneous sand subject to different groundwater flow rates showed that high groundwater velocities can limit subsurface heating rates. In the DNAPL pool experiments, temperatures increased to achieve DNAPL-water co-boiling, creating estimated gas volumes of 131 and 114 L that originated from the TCE and CF pools, respectively. Produced gas migrated vertically, entered a coarse sand lens and subsequently migrated laterally beneath an overlying capillary barrier to outside the heated treatment zone where 31-56% of the original DNAPL condensed back into a DNAPL phase. These findings demonstrate that layered heterogeneity can potentially facilitate the transport of contaminants outside the treatment zone by mobilization and condensation of gas phases during ERH applications. This underscores the need for vapor phase recovery and/or control mechanisms below the water table during application of ERH in heterogeneous porous media during the co-boiling stage, which occurs prior to reaching the boiling point of water.

  15. Factors affecting gas migration and contaminant redistribution in heterogeneous porous media subject to electrical resistance heating

    NASA Astrophysics Data System (ADS)

    Munholland, Jonah L.; Mumford, Kevin G.; Kueper, Bernard H.

    2016-01-01

    A series of intermediate-scale laboratory experiments were completed in a two-dimensional flow cell to investigate gas production and migration during the application of electrical resistance heating (ERH) for the removal of dense non-aqueous phase liquids (DNAPLs). Experiments consisted of heating water in homogeneous silica sand and heating 270 mL of trichloroethene (TCE) and chloroform (CF) DNAPL pools in heterogeneous silica sands, both under flowing groundwater conditions. Spatial and temporal distributions of temperature were measured using thermocouples and observations of gas production and migration were collected using front-face image capture throughout the experiments. Post-treatment soil samples were collected and analyzed to assess DNAPL removal. Results of experiments performed in homogeneous sand subject to different groundwater flow rates showed that high groundwater velocities can limit subsurface heating rates. In the DNAPL pool experiments, temperatures increased to achieve DNAPL-water co-boiling, creating estimated gas volumes of 131 and 114 L that originated from the TCE and CF pools, respectively. Produced gas migrated vertically, entered a coarse sand lens and subsequently migrated laterally beneath an overlying capillary barrier to outside the heated treatment zone where 31-56% of the original DNAPL condensed back into a DNAPL phase. These findings demonstrate that layered heterogeneity can potentially facilitate the transport of contaminants outside the treatment zone by mobilization and condensation of gas phases during ERH applications. This underscores the need for vapor phase recovery and/or control mechanisms below the water table during application of ERH in heterogeneous porous media during the co-boiling stage, which occurs prior to reaching the boiling point of water.

  16. Specific features of diffuse photon migration in highly scattering media with optical properties of biological tissues

    SciTech Connect

    Proskurin, S G; Potlov, A Yu; Frolov, S V

    2015-06-30

    Specific features of motion of photon density normalised maximum (PDNM) of pulsed radiation in highly scattering media with optical properties of biological tissues are described. A numerical simulation has confirmed that, when the object is a homogeneous cylinder, PDNM always moves to its geometric centre. In the presence of an absorbing inhomogeneity, PDNM moves towards the point symmetric to the geometric centre of the inhomogeneity with respect to the centre of the cylindrical object. In the presence of a scattering inhomogeneity, PDNM moves towards its geometric centre. (radiation scattering)

  17. Buoyancy Effects on Flow Transition in Hydrogen Gas Jet Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Albers, Burt W.; Agrawal, Ajay K.; Griffin, DeVon (Technical Monitor)

    2000-01-01

    Experiments were performed in earth-gravity to determine how buoyancy affected transition from laminar to turbulent flow in hydrogen gas jet diffusion flames. The jet exit Froude number characterizing buoyancy in the flame was varied from 1.65 x 10(exp 5) to 1.14 x 10(exp 8) by varying the operating pressure and/or burner inside diameter. Laminar fuel jet was discharged vertically into ambient air flowing through a combustion chamber. Flame characteristics were observed using rainbow schlieren deflectometry, a line-of-site optical diagnostic technique. Results show that the breakpoint length for a given jet exit Reynolds number increased with increasing Froude number. Data suggest that buoyant transitional flames might become laminar in the absence of gravity. The schlieren technique was shown as effective in quantifying the flame characteristics.

  18. Gas diffusion electrode setup for catalyst testing in concentrated phosphoric acid at elevated temperatures

    SciTech Connect

    Wiberg, Gustav K. H. E-mail: m.arenz@chem.ku.dk; Fleige, Michael; Arenz, Matthias E-mail: m.arenz@chem.ku.dk

    2015-02-15

    We present a detailed description of the construction and testing of an electrochemical cell setup allowing the investigation of a gas diffusion electrode containing carbon supported high surface area catalysts. The setup is designed for measurements in concentrated phosphoric acid at elevated temperature, i.e., very close to the actual conditions in high temperature proton exchange membrane fuel cells (HT-PEMFCs). The cell consists of a stainless steel flow field and a PEEK plastic cell body comprising the electrochemical cell, which exhibits a three electrode configuration. The cell body and flow field are braced using a KF-25 vacuum flange clamp, which allows an easy assembly of the setup. As demonstrated, the setup can be used to investigate temperature dependent electrochemical processes on high surface area type electrocatalysts, but it also enables quick screening tests of HT-PEMFC catalysts under realistic conditions.

  19. Application of gas diffusion electrodes in bioelectrochemical syntheses and energy conversion.

    PubMed

    Horst, Angelika E W; Mangold, Klaus-Michael; Holtmann, Dirk

    2016-02-01

    Combining the advantages of biological components (e.g., reaction specificity, self-replication) and electrochemical techniques in bioelectrochemical systems offers the opportunity to develop novel efficient and sustainable processes for the production of a number of valuable products. The choice of electrode material has a great impact on the performance of bioelectrochemical systems. In addition to the redox process at the electrodes, interactions of biocatalysts with electrodes (e.g., enzyme denaturation or biofouling) need to be considered. In recent years, gas diffusion electrodes (GDEs) have proved to be very attractive electrodes for bioelectrochemical purposes. GDEs are porous electrodes, that posses a large three-phase boundary surface. At this interface, a solid catalyst supports the electrochemical reaction between gaseous and liquid phase. This mini-review discusses the application of GDEs in microbial and enzymatic fuel cells, for microbial electrolysis, in biosensors and for electroenzymatic synthesis reactions.

  20. Carbon film coating on gas diffusion layer for proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Lin, Jui-Hsiang; Chen, Wei-Hung; Su, Shih-Hsuan; Liao, Yuan-Kai; Ko, Tse-Hao

    This study discusses a novel process to increase the performance of proton exchange membrane fuel cells (PEMFC). In order to improve the electrical conductivity and reduce the surface indentation of the carbon fibers, we modified the carbon fibers with pitch-based carbon materials (mesophase pitch and coal tar pitch). Compared with the gas diffusion backing (GDB), GDB-A240 and GDB-MP have 32% and 33% higher current densities at 0.5 V, respectively. Self-made carbon paper with the addition of a micro-porous layer (MPL) (GDL-A240 and GDL-MP) show improved performance compared with GDB-A240 and GDB-MP. The current densities of GDL-A240 and GDL-MP at 0.5 V increased by 37% and 31% compared with GDL, respectively. This study combines these two effects (carbon film and MPL coating) to promote high current density in a PEMFC.

  1. Thermally induced gas flows in ratchet channels with diffuse and specular boundaries

    PubMed Central

    Shahabi, Vahid; Baier, Tobias; Roohi, Ehsan; Hardt, Steffen

    2017-01-01

    A net gas flow can be induced in the gap between periodically structured surfaces held at fixed but different temperatures when the reflection symmetry along the channel axis is broken. Such a situation arises when one surface features a ratchet structure and can be augmented by altering the boundary conditions on different parts of this surface, with some regions reflecting specularly and others diffusely. In order to investigate the physical mechanisms inducing the flow in this configuration at various Knudsen numbers and geometric configurations, direct simulation Monte Carlo (DSMC) simulations are employed using transient adaptive subcells for collision partner selection. At large Knudsen numbers the results compare favorably with analytical expressions, while for small Knudsen numbers a qualitative explanation for the flow in the strong temperature inhomogeneity at the tips of the ratchet is provided. A detailed investigation of the performance for various ratchet geometries suggests optimum working conditions for a Knudsen pump based on this mechanism. PMID:28128309

  2. Thermally induced gas flows in ratchet channels with diffuse and specular boundaries

    NASA Astrophysics Data System (ADS)

    Shahabi, Vahid; Baier, Tobias; Roohi, Ehsan; Hardt, Steffen

    2017-01-01

    A net gas flow can be induced in the gap between periodically structured surfaces held at fixed but different temperatures when the reflection symmetry along the channel axis is broken. Such a situation arises when one surface features a ratchet structure and can be augmented by altering the boundary conditions on different parts of this surface, with some regions reflecting specularly and others diffusely. In order to investigate the physical mechanisms inducing the flow in this configuration at various Knudsen numbers and geometric configurations, direct simulation Monte Carlo (DSMC) simulations are employed using transient adaptive subcells for collision partner selection. At large Knudsen numbers the results compare favorably with analytical expressions, while for small Knudsen numbers a qualitative explanation for the flow in the strong temperature inhomogeneity at the tips of the ratchet is provided. A detailed investigation of the performance for various ratchet geometries suggests optimum working conditions for a Knudsen pump based on this mechanism.

  3. Defect Detection in Fuel Cell Gas Diffusion Electrodes Using Infrared Thermography

    SciTech Connect

    Ulsh, Michael; Porter, Jason M.; Bittinat, Daniel C.; Bender, Guido

    2016-04-01

    Polymer electrolyte membrane fuel cells are energy conversion devices that offer high power densities and high efficiencies for mobile and other applications. Successful introduction into the marketplace requires addressing cost barriers such as production volumes and platinum loading. For cost reduction, it is vital to minimize waste and maximize quality during the manufacturing of platinum-containing electrodes, including gas diffusion electrodes (GDEs). In this work, we report on developing a quality control diagnostic for GDEs, involving creating an ex situ exothermic reaction on the electrode surface and using infrared thermography to measure the resulting temperature profile. Experiments with a moving GDE containing created defects were conducted to demonstrate the applicability of the diagnostic for real-time web-line inspection.

  4. Thermodynamic Properties of a Trapped Bose Gas:. a Diffusion Monte Carlo Study

    NASA Astrophysics Data System (ADS)

    Datta, S.

    We investigate the thermodynamic properties of a trapped Bose gas of Rb atoms interacting through a repulsive potential at low but finite temperature (kBT < μ < Tc) by Quantum Monte Carlo method based upon the generalization of Feynman-Kac method1-3 applicable to many-body systems at T=0 to finite temperatures. In this paper, we report temperature variation of condensation fraction, chemical potential, density profile, total energy of the system, release energy, frequency shifts and moment of inertia within the realistic potential model (Morse type) for the first time by diffusion Monte Carlo technique. The most remarkable success was in achieving the same trend in the temperature variation of frequency shifts as was observed in JILA4 for both m=2 and m=0 modes. For other things, we agree with the work of Giorgini et al.,5 Pitaevskii et al.6 and Krauth.7

  5. Outflowing Diffuse Gas in the Active Galactic Nucleus of NGC 1068

    NASA Astrophysics Data System (ADS)

    Geballe, T. R.; Mason, R. E.; Oka, T.

    2015-10-01

    Spectra of the archetypal Type II Seyfert galaxy NGC 1068 in a narrow wavelength interval near 3.7 μm have revealed a weak absorption feature due to two lines of the molecular ion {{{H}}}3+. The observed wavelength of the feature corresponds to a velocity of -70 km s-1 relative to the systemic velocity of the galaxy, implying an outward flow from the nucleus along the line of sight. The absorption by H{}3+ along with the previously known broad hydrocarbon absorption at 3.4μm are probably formed in diffuse gas that is in close proximity to the continuum source, i.e., within a few tens of parsecs of the central engine. Based on that conclusion and the measured H{}3+ absorption velocity and with the assumption of a spherically symmetric wind we estimate a rate of mass outflow from the active galactic nucleus of ˜1 M⊙ yr-1.

  6. A new quasi-steady method to measure gas permeability of weakly permeable porous media

    NASA Astrophysics Data System (ADS)

    Jannot, Yves; Lasseux, Didier

    2012-01-01

    A new quasi-steady method for the determination of the apparent gas permeability of porous materials is presented in this paper along with the corresponding interpretative physical model derived from the unsteady flow equations. This method is mainly dedicated to the measurement of very low permeability of thin porous media, although thicker but more permeable samples may also be analyzed. The method relies on quasi-steady flow resulting from a (quasi) constant pressure maintained at the inlet face of the sample. Gas flow-rate, as low as 3 × 10-10 m3/s, is determined from the record of pressure increase in a reservoir connected to the outlet face of the sample. An estimate of the characteristic time, tc, to reach quasi-steady flow after imposing a constant pressure at the inlet is derived. It is validated by direct numerical simulations of the complete unsteady flow, clearly defining the required experimental duration for the method to apply. Experimental results obtained on rather permeable and thick rock samples are reported showing an excellent agreement of the measured permeability with that determined independently on the same sample whereas the experimental value of tc is also in very good agreement with the predicted one. The method is further employed on a composite material sheet allowing the identification of an apparent gas permeability of about 10-23 m2.

  7. Comparison of kinetic and equilibrium reaction models insimulating gas hydrate behavior in porous media

    SciTech Connect

    Kowalsky, Michael B.; Moridis, George J.

    2006-11-29

    In this study we compare the use of kinetic and equilibriumreaction models in the simulation of gas (methane) hydrate behavior inporous media. Our objective is to evaluate through numerical simulationthe importance of employing kinetic versus equilibrium reaction modelsfor predicting the response of hydrate-bearing systems to externalstimuli, such as changes in pressure and temperature. Specifically, we(1) analyze and compare the responses simulated using both reactionmodels for natural gas production from hydrates in various settings andfor the case of depressurization in a hydrate-bearing core duringextraction; and (2) examine the sensitivity to factors such as initialhydrate saturation, hydrate reaction surface area, and numericaldiscretization. We find that for large-scale systems undergoing thermalstimulation and depressurization, the calculated responses for bothreaction models are remarkably similar, though some differences areobserved at early times. However, for modeling short-term processes, suchas the rapid recovery of a hydrate-bearing core, kinetic limitations canbe important, and neglecting them may lead to significantunder-prediction of recoverable hydrate. The use of the equilibriumreaction model often appears to be justified and preferred for simulatingthe behavior of gas hydrates, given that the computational demands forthe kinetic reaction model far exceed those for the equilibrium reactionmodel.

  8. Metal based gas diffusion layers for enhanced fuel cell performance at high current densities

    NASA Astrophysics Data System (ADS)

    Hussain, Nabeel; Van Steen, Eric; Tanaka, Shiro; Levecque, Pieter

    2017-01-01

    The gas diffusion layer strongly influences the performance and durability of polymer electrolyte fuel cells. A major drawback of current carbon fiber based GDLs is the non-controlled variation in porosity resulting in a random micro-structure. Moreover, when subjected to compression these materials show significant reduction in porosity and permeability leading to water management problems and mass transfer losses within the fuel cell. This study investigated the use of uniform perforated metal sheets as GDLs in conjunction with microchannel flowfields. A metal sheet design with a pitch of 110 μm and a hole diameter of 60 μm in combination with an MPL showed superior performance in the high current density region compared to a commercially available carbon paper based GDL in a single cell environment. Fuel cell testing with different oxidants (air, heliox and oxygen) indicate that the metal sheet offers both superior diffusion and reduced flooding in comparison to the carbon based GDL. The presence of the MPL has been found to be critical to the functionality of the metal sheet suggesting that the MPL design may represent an important optimisation parameter for further improvements in performance.

  9. Fabrication of stainless steel mesh gas diffusion electrode for power generation in microbial fuel cell.

    PubMed

    You, Shi-Jie; Wang, Xiu-Heng; Zhang, Jin-Na; Wang, Jing-Yuan; Ren, Nan-Qi; Gong, Xiao-Bo

    2011-01-15

    This study reports the fabrication of a new membrane electrode assembly by using stainless steel mesh (SSM) as raw material and its effectiveness as gas diffusion electrode (GDE) for electrochemical oxygen reduction in microbial fuel cell (MFC). Based on feeding glucose (0.5 g L(-1)) substrate to a single-chambered MFC, power generation using SSM-based GDE was increased with the decrease of polytetrafluoroethylene (PTFE) content applied during fabrication, reaching the optimum power density of 951.6 mW m(-2) at 20% PTFE. Repeatable cell voltage of 0.51 V (external resistance of 400 Ω) and maximum power density of 951.6 mW m(-2) produced for the MFC with SSM-based GDE are comparable to that of 0.52 V and 972.6 mW m(-2), respectively obtained for the MFC containing typical carbon cloth (CC)-made GDE. Besides, Coulombic efficiency (CE) is found higher for GDE (SSM or CC) with membrane assembly than without, which results preliminarily from the mitigation of Coulombic loss being associated with oxygen diffusion and substrate crossover. This study demonstrates that with its good electrical conductivity and much lower cost, the SSM-made GDE suggests a promising alternative as efficient and more economically viable material to conventional typical carbon for power production from biomass in MFC.

  10. Stochastic diffusion interactions and coarsening in a system of droplets growing from a supersaturated gas mixture.

    PubMed

    Pines, V; Zlatkowski, M; Chait, A

    2005-01-15

    In this work we study diffusion interactions among liquid droplets growing in stochastic population by condensation from supersaturated binary gas mixture. During the postnucleation transient regime collective growth of liquid droplets competing for the available water vapor decreases local supersaturation leading to the increase of critical radius and the onset of coarsening process. In coarsening regime the growth of larger droplets is prevailing noticeably broadening the droplet size-distribution function when the condensation process becomes more intensive than the supersaturation yield. Modifications in the kinetic equation are discussed and formulated for a stochastic population of liquid droplets when diffusional interactions among droplets become noteworthy. The kinetic equation for the droplet size-distribution function is solved together with field equations for the mass fraction of disperse liquid phase, mass fraction of water vapor component of moist air, and temperature during diffusion-dominated regime of droplet coarsening. The droplet size and mass distributions are found as functions of the liquid volume fraction, showing considerable broadening of droplet spectra. It is demonstrated that the effect of latent heat of condensation considerably changes coarsening process. The coarsening rate constant, the droplet density (number of droplets per unit volume), the screening length, the mean droplet size, and mass are determined as functions of the temperature, pressure, and liquid volume fraction.

  11. Tracer test for the measurement of gas diffusion and non-aqueous phase liquid (NAPL) saturation in soil.

    PubMed

    Van De Steene, Joke; Höhener, Patrick

    2009-01-01

    During soil bioremediation, the diffusion of oxygen into the soil is an important prerequisite for aerobic biodegradation, and the decrease of petroleum products is the ultimate goal. Both processes need to be monitored. The aim of this work was to develop a gas tracer test that yields information on both, gas diffusion and residual saturation with non-aqueous phase liquids (NAPLs) in unsaturated soil heaps. One conservative tracer (methane) and 4 partitioning gas tracers (diethylether, methyl tert-butyl ether, chloroform and n-heptane) were injected as vapors into laboratory columns filled with unsaturated sand with increasing NAPL saturation. Breakthrough curves of gaseous compounds were measured at two points and compared to analytical solutions of an analytical diffusive-reactive transport equation. By fitting of methane data, robust results for effective diffusivity (tortuosity) were obtained. NAPL saturation was most accurately measured by the moderately water soluble tracers (ethers and chloroform). The hydrophobic tracer n-heptane did not partition into water-immersed NAPL. An easy and accurate way to assess air-NAPL partitioning constants from gas chromatography retention times is furthermore reported. It is concluded that gas tracer tests have the potential for measuring two important properties in soil bioremediation systems easily and quickly.

  12. Simulation of radiation driven fission gas diffusion in UO2, ThO2 and PuO2

    DOE PAGES

    Cooper, Michael William D.; Stanek, Christopher Richard; Turnbull, James Anthony; ...

    2016-12-01

    Below 1000 K it is thought that fission gas diffusion in nuclear fuel during irradiation occurs through atomic mixing due to radiation damage. Here we present a molecular dynamics (MD) study of Xe, Kr, Th, U, Pu and O diffusion due to irradiation. It is concluded that the ballistic phase does not sufficiently account for the experimentally observed diffusion. Thermal spike simulations are used to confirm that electronic stopping remedies the discrepancy with experiment and the predicted diffusivities lie within the scatter of the experimental data. Here, our results predict that the diffusion coefficients are ordered such that D*0 >more » D*Kr > D*Xe > D*U. For all species >98.5% of diffusivity is accounted for by electronic stopping. Fission gas diffusivity was not predicted to vary significantly between ThO2, UO2 and PuO2, indicating that this process would not change greatly for mixed oxide fuels.« less

  13. The Transport Equation in Optically Thick Media: Discussion of IMC and its Diffusion Limit

    SciTech Connect

    Szoke, A.; Brooks, E. D.

    2016-07-12

    We discuss the limits of validity of the Implicit Monte Carlo (IMC) method for the transport of thermally emitted radiation. The weakened coupling between the radiation and material energy of the IMC method causes defects in handling problems with strong transients. We introduce an approach to asymptotic analysis for the transport equation that emphasizes the fact that the radiation and material temperatures are always different in time-dependent problems, and we use it to show that IMC does not produce the correct diffusion limit. As this is a defect of IMC in the continuous equations, no improvement to its discretization can remedy it.

  14. Optical measurements of absorption changes in two-layered diffusive media

    NASA Astrophysics Data System (ADS)

    Fabbri, Francesco; Sassaroli, Angelo; Henry, Michael E.; Fantini, Sergio

    2004-04-01

    We have used Monte Carlo simulations for a two-layered diffusive medium to investigate the effect of a superficial layer on the measurement of absorption variations from optical diffuse reflectance data processed by using: (a) a multidistance, frequency-domain method based on diffusion theory for a semi-infinite homogeneous medium; (b) a differential-pathlength-factor method based on a modified Lambert-Beer law for a homogeneous medium and (c) a two-distance, partial-pathlength method based on a modified Lambert-Beer law for a two-layered medium. Methods (a) and (b) lead to a single value for the absorption variation, whereas method (c) yields absorption variations for each layer. In the simulations, the optical coefficients of the medium were representative of those of biological tissue in the near-infrared. The thickness of the first layer was in the range 0.3-1.4 cm, and the source-detector distances were in the range 1-5 cm, which is typical of near-infrared diffuse reflectance measurements in tissue. The simulations have shown that (1) method (a) is mostly sensitive to absorption changes in the underlying layer, provided that the thickness of the superficial layer is ~0.6 cm or less; (2) method (b) is significantly affected by absorption changes in the superficial layer and (3) method (c) yields the absorption changes for both layers with a relatively good accuracy of ~4% for the superficial layer and ~10% for the underlying layer (provided that the absorption changes are less than 20-30% of the baseline value). We have applied all three methods of data analysis to near-infrared data collected on the forehead of a human subject during electroconvulsive therapy. Our results suggest that the multidistance method (a) and the two-distance partial-pathlength method (c) may better decouple the contributions to the optical signals that originate in deeper tissue (brain) from those that originate in more superficial tissue layers.

  15. Spectral characterization of diffusion in porous media by the modulated gradient spin echo with CPMG sequence

    NASA Astrophysics Data System (ADS)

    Stepišnik, Janez; Lasič, Samo; Mohorič, Aleš; Serša, Igor; Sepe, Ana

    2006-10-01

    Carr-Purcell-Meiboom-Gill train of radiofrequency pulses applied to spins in the constant magnetic field gradient is an efficient variant of the modulated magnetic field gradient spin echo method, which provides information about molecular diffusion in the frequency-domain instead in the time-domain as with the two-pulse gradient spin echo. The frequency range of novel technique is broad enough to sample the power spectrum of displacement fluctuation in water-saturated pulverized silica (SiO 2) and provides comprehensive information about the molecular restricted motion as well as about the structure of medium.

  16. Diffusion approximation with polarization and resonance effects for the modelling of seismic waves in strongly scattering small-scale media

    NASA Astrophysics Data System (ADS)

    Margerin, Ludovic

    2013-01-01

    This paper presents an analytical study of the multiple scattering of seismic waves by a collection of randomly distributed point scatterers. The theory assumes that the energy envelopes are smooth, but does not require perturbations to be small, thereby allowing the modelling of strong, resonant scattering. The correlation tensor of seismic coda waves recorded at a three-component sensor is decomposed into a sum of eigenmodes of the elastodynamic multiple scattering (Bethe-Salpeter) equation. For a general moment tensor excitation, a total number of four modes is necessary to describe the transport of seismic waves polarization. Their spatio-temporal dependence is given in closed analytical form. Two additional modes transporting exclusively shear polarizations may be excited by antisymmetric moment tensor sources only. The general solution converges towards an equipartition mixture of diffusing P and S waves which allows the retrieval of the local Green's function from coda waves. The equipartition time is obtained analytically and the impact of absorption on Green's function reconstruction is discussed. The process of depolarization of multiply scattered waves and the resulting loss of information is illustrated for various seismic sources. It is shown that coda waves may be used to characterize the source mechanism up to lapse times of the order of a few mean free times only. In the case of resonant scatterers, a formula for the diffusivity of seismic waves incorporating the effect of energy entrapment inside the scatterers is obtained. Application of the theory to high-contrast media demonstrates that coda waves are more sensitive to slow rather than fast velocity anomalies by several orders of magnitude. Resonant scattering appears as an attractive physical phenomenon to explain the small values of the diffusion constant of seismic waves reported in volcanic areas.

  17. Molecular dynamics simulation of framework flexibility effects on noble gas diffusion in HKUST-1 and ZIF-8

    DOE PAGES

    Parkes, Marie V.; Demir, Hakan; Teich-McGoldrick, Stephanie L.; ...

    2014-03-28

    Molecular dynamics simulations were used to investigate trends in noble gas (Ar, Kr, Xe) diffusion in the metal-organic frameworks HKUST-1 and ZIF-8. Diffusion occurs primarily through inter-cage jump events, with much greater diffusion of guest atoms in HKUST-1 compared to ZIF-8 due to the larger cage and window sizes in the former. We compare diffusion coefficients calculated for both rigid and flexible frameworks. For rigid framework simulations, in which the framework atoms were held at their crystallographic or geometry optimized coordinates, sometimes dramatic differences in guest diffusion were seen depending on the initial framework structure or the choice of frameworkmore » force field parameters. When framework flexibility effects were included, argon and krypton diffusion increased significantly compared to rigid-framework simulations using general force field parameters. Additionally, for argon and krypton in ZIF-8, guest diffusion increased with loading, demonstrating that guest-guest interactions between cages enhance inter-cage diffusion. No inter-cage jump events were seen for xenon atoms in ZIF-8 regardless of force field or initial structure, and the loading dependence of xenon diffusion in HKUST-1 is different for rigid and flexible frameworks. Diffusion of krypton and xenon in HKUST-1 depends on two competing effects: the steric effect that decreases diffusion as loading increases, and the “small cage effect” that increases diffusion as loading increases. Finally, a detailed analysis of the window size in ZIF-8 reveals that the window increases beyond its normal size to permit passage of a (nominally) larger krypton atom.« less

  18. Molecular dynamics simulation of framework flexibility effects on noble gas diffusion in HKUST-1 and ZIF-8

    SciTech Connect

    Parkes, Marie V.; Demir, Hakan; Teich-McGoldrick, Stephanie L.; Sholl, David S.; Greathouse, Jeffery A.; Allendorf, Mark D.

    2014-03-28

    Molecular dynamics simulations were used to investigate trends in noble gas (Ar, Kr, Xe) diffusion in the metal-organic frameworks HKUST-1 and ZIF-8. Diffusion occurs primarily through inter-cage jump events, with much greater diffusion of guest atoms in HKUST-1 compared to ZIF-8 due to the larger cage and window sizes in the former. We compare diffusion coefficients calculated for both rigid and flexible frameworks. For rigid framework simulations, in which the framework atoms were held at their crystallographic or geometry optimized coordinates, sometimes dramatic differences in guest diffusion were seen depending on the initial framework structure or the choice of framework force field parameters. When framework flexibility effects were included, argon and krypton diffusion increased significantly compared to rigid-framework simulations using general force field parameters. Additionally, for argon and krypton in ZIF-8, guest diffusion increased with loading, demonstrating that guest-guest interactions between cages enhance inter-cage diffusion. No inter-cage jump events were seen for xenon atoms in ZIF-8 regardless of force field or initial structure, and the loading dependence of xenon diffusion in HKUST-1 is different for rigid and flexible frameworks. Diffusion of krypton and xenon in HKUST-1 depends on two competing effects: the steric effect that decreases diffusion as loading increases, and the “small cage effect” that increases diffusion as loading increases. Finally, a detailed analysis of the window size in ZIF-8 reveals that the window increases beyond its normal size to permit passage of a (nominally) larger krypton atom.

  19. Structural, thermal and dielectric properties of cobaltous malonate single crystals grown in limited diffusion media

    NASA Astrophysics Data System (ADS)

    Lincy, A.; Mahalakshmi, V.; Tinto, A. J.; Thomas, J.; Saban, K. V.

    2010-11-01

    Well-faceted crystals of cobaltous malonate (C 6 H 12 Co 2 O 12) have been grown by the controlled diffusion of ionic species in hydrosilica gel. Single crystal X-ray diffraction studies show that the crystal belongs to the monoclinic system with space group C2/m. The unit cell dimensions are a=12.6301(9) Å, b=7.3857(9) Å, c=7.2945(7) Å, α= γ=90°, β=120.193(9)°. The functional groups, elucidated from the FT-IR spectrum, are in conformity with the information derived from the X-ray diffraction studies. The thermal behaviour of the material has been investigated using TG-DTA in the temperature range 30-1050 °C. The optical band gap of the sample is estimated using diffuse reflectance spectroscopy (DRS). The dielectric constant and dielectric loss of the crystal have been studied over wide temperature and frequency ranges. AC conductivity measurements reveal a thermally activated process and the mechanism behind the conduction process has been discussed.

  20. Organics and Halocarbons in Volcanic Gas Emissions: Sampling, Analysis, and Estimates of Source Strengths for Diffuse and Fumarolic Gas Emissions

    NASA Astrophysics Data System (ADS)

    Schwandner, F. M.; Seward, T. M.; Giże, A. P.; Hall, K.

    2003-12-01

    The well-established interest in organic compounds in volcanic emissions, emerging in the early 1800?s and continuing through modern times, has led to a long history of method development for the analysis of trace organics in volcanic gases. Both the sampling and analysis techniques have often been hampered by strong matrix effects, such as interferences by aerosol and ash scattering in spectroscopy, or the adverse impact of sulfur, acids and water on chromatographic and wet chemical techniques. Established methods exist for the ground-based sampling of fumaroles and diffuse degassing structures, whereas remote OP-FTIR spectroscopy appears promising for the detection and quantification of organic compounds during dangerous eruptive phases. The most successful collection techniques are based on a multiple-fold enrichment of the analytes during sampling, either by the absorption flask technique (''Giggenbach bottle''), or by in-line separation of water and sulfur from the analytes with subsequent trapping onto solid adsorbents. For organic analytes present at relatively high concentrations (e.g., C1-C6 hydrocarbons), the first technique has been used extensively. For labile and trace compounds (pptv to ppbv abundance), the latter technique has proven more reliable provided that the gas is dried sufficiently during sampling and that suitable dry gas volumes are sampled. A poor choice of sampling technique, or its incorrect application, may lead to erroneous results. These are often obvious by the finding of near-air concentrations, since volcanic gases are strongly enriched with respect to ambient air for a large range of compounds. Quantitative and independent testing of the air fraction possibly entrained during sampling must be performed in order to achieve reliable results. By using gas chromatography coupled with mass spectrometric detection (GC-MS), unambiguous simultaneous identification of compounds can be achieved by two independent analytical techniques

  1. Diffuse Ionized Gas in the Magellanic System: Early Results from WHAM-South

    NASA Astrophysics Data System (ADS)

    Haffner, L. Matthew; Madsen, G. J.

    2011-01-01

    From its new vantage point at CTIO, the Wisconsin Hα Mapper is poised to explore the full distribution and kinematics of diffuse plasma in extended gaseous structures near the Magellanic Clouds. Shaped by the interaction between the Clouds and the Milky Way, the Bridge, Stream, and Leading Arm gas complexes have been studied extensively in 21 cm emission and optical/UV absorption. With spectral resolution of 12 km/s, WHAM is able to separate optical emission from these structures and brighter local gas near vLSR 0 km/s. Combined with its unprecedented sensitivity to the limit of atmospheric line confusion ( 10s of mR), we are embarking on a survey of the ionized component of the Magellanic System with WHAM. With observations of the southern component of our all-sky survey nearly completed, we have begun to examine some emission features toward the Magellanic System. Here we present a sample of several regions observed recently with WHAM in Hα. WHAM was built and continues to operate with ongoing support from NSF. The research presented here is currently funded by award AST-0607512 and an International Program Development Fund from the University of Sydney.

  2. A dedicated compression device for high resolution X-ray tomography of compressed gas diffusion layers

    SciTech Connect

    Tötzke, C.; Manke, I.; Banhart, J.; Gaiselmann, G.; Schmidt, V.; Bohner, J.; Müller, B. R.; Kupsch, A.; Hentschel, M. P.; Lehnert, W.

    2015-04-15

    We present an experimental approach to study the three-dimensional microstructure of gas diffusion layer (GDL) materials under realistic compression conditions. A dedicated compression device was designed that allows for synchrotron-tomographic investigation of circular samples under well-defined compression conditions. The tomographic data provide the experimental basis for stochastic modeling of nonwoven GDL materials. A plain compression tool is used to study the fiber courses in the material at different compression stages. Transport relevant geometrical parameters, such as porosity, pore size, and tortuosity distributions, are exemplarily evaluated for a GDL sample in the uncompressed state and for a compression of 30 vol.%. To mimic the geometry of the flow-field, we employed a compression punch with an integrated channel-rib-profile. It turned out that the GDL material is homogeneously compressed under the ribs, however, much less compressed underneath the channel. GDL fibers extend far into the channel volume where they might interfere with the convective gas transport and the removal of liquid water from the cell.

  3. Superhydrophobic PAN nanofibers for gas diffusion layers of proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Salahuddin, Mohammad; Hwang, Gisuk; Asmatulu, Ramazan

    2016-04-01

    Proton exchange membrane (PEM) fuel cells are considered to be the promising alternatives of natural resources for generating electricity and power. An optimal water management in the gas diffusion layers (GDL) is critical to high fuel cell performance. Its basic functions include transportation of the reactant gas from flow channels to catalyst effectively, draining out the liquid water from catalyst layer to flow channels, and conducting electrons with low humidity. In this study, polyacrylonitrile (PAN) was dissolved in a solvent and electrospun at various conditions to produce PAN nanofibers prior to the stabilization at 280 °C for 1 hour in the atmospheric pressure and carbonization at 850 °C for 1 hour. The surface hydrophobicity values of the carbonized PAN nanofibers were adjusted using superhydrophobic and hydrophilic agents. The thermal, mechanical, and electrical properties of the new GDLs depicted much better results compared to the conventionally used ones. The water condensation tests on the surfaces (superhydrophobic and hydrophilic) of the GDL showed a crucial step towards improved water managements in the fuel cell. This study may open up new possibilities for developing high- performing GDL materials for future PEM fuel cell applications.

  4. Transient behavior of simultaneous flow of gas and surfactant solution in consolidated porous media

    SciTech Connect

    Baghdikian, S.Y.; Handy, L.L.

    1991-07-01

    The main objective of this experimental research was to investigate the mechanisms of foam generation and propagation in porous media. Results obtained give an insight into the conditions of foam generation and propagation in porous media. The rate of propagation of foam is determined by the rates of lamellae generation, destruction, and trapping. Several of the factors that contribute to foam generation have studied with Chevron Chaser SD1000 surfactant. Interfacial tension (IFT) measurements were performed using a spinning drop apparatus. The IFT of two surfactant samples of different concentrations were measured with dodecane and crude oil from the Huntington Beach Field as a function of temperature and time. Foam was used as an oil-displacing fluid. However, when displacing oil, foam was not any more effective than simultaneous brine and gas injection. A series of experiments was performed to study the conditions of foam generation in Berea sandstone cores. Results show that foam may be generated in sandstone at low flow velocities after extended incubation periods. The effect of pregenerating foam before injection into the sandstone was also studied. The pressure profiles in the core were monitored using three pressure taps along the length of the core. A systematic study of foaming with different fluid velocities and foam qualities provides extensive data for foam flow conditions. 134 refs., 57 figs., 2 tabs.

  5. Study of heat transfer characteristics during dissociation of gas hydrates in porous media

    SciTech Connect

    Kamath, V.A.

    1984-01-01

    An experimental technique was developed to measure the rate of formation and dissociation of hydrates in porous media. In the first phase of the work, hydrates of propane and methane were studied. Propane hydrate cores were formed by contacting liquid propane with compacted porous ice cores at 274 K for 24 to 100 hours, whereas the formation of methane hydrates was achieved by contacting ice cores with gaseous methane at about 7000 kPa and 274 K, for 24 to 200 hours. These hydrate cores were dissociated by circulating warm water over the top of the core, under controlled temperatures and pressures. The major findings of these experiments are as follows: 1) the phenomena of dissociation of hydrates to liquid water and gas is similar to nucleate boiling of liquids; 2) the rate of dissociation of hydrates at constant ..delta..T, is directly proportional to the area of hydrates exposed to the warm fluid or the composition of hydrates in the core; and 3) the rate of heat transfer and dissociation increase with increase in pressure and the rate of circulation of the warm fluid. Unified correlations for heat transfer and dissociation rates were successfully obtained for both methane and propane hydrate dissociation. These correlations will be useful to predict the rate of dissociation and gas production in hydrate reservoirs. In the second phase of his work, in order to simulate the conditions of hydrate dissociation in the earth, methane hydrates were formed and dissociated in unconsolidated cores of sand. The results of these experiments have demonstrated that the heat transfer resistance of the media (rock) plays an important role in dissociation of hydrates in earth.

  6. Elimination of a spiral wave pinned at an obstacle by a train of plane waves: Effect of diffusion between obstacles and surrounding media.

    PubMed

    Tanaka, Masanobu; Hörning, Marcel; Kitahata, Hiroyuki; Yoshikawa, Kenichi

    2015-10-01

    In excitable media such as cardiac tissue and Belousov-Zhabotinsky reaction medium, spiral waves tend to anchor (pin) to local heterogeneities. In general, such pinned waves are difficult to eliminate and may progress to spatio-temporal chaos. Heterogeneities can be classified as either the absence or presence of diffusive interaction with the surrounding medium. In this study, we investigated the difference in the unpinning of spiral waves from obstacles with and without diffusive interaction, and found a profound difference. The pacing period required for unpinning at fixed obstacle size is larger in case of diffusive obstacles. Further, we deduced a generic theoretical framework that can predict the minimal unpinning period. Our results explain the difference in pacing periods between for the obstacles with and without diffusive interaction, and the difference is interpreted in terms of the local decrease of spiral wave velocity close to the obstacle boundary caused in the case of diffusive interaction.

  7. Elimination of a spiral wave pinned at an obstacle by a train of plane waves: Effect of diffusion between obstacles and surrounding media

    SciTech Connect

    Tanaka, Masanobu; Hörning, Marcel; Kitahata, Hiroyuki; Yoshikawa, Kenichi

    2015-10-15

    In excitable media such as cardiac tissue and Belousov-Zhabotinsky reaction medium, spiral waves tend to anchor (pin) to local heterogeneities. In general, such pinned waves are difficult to eliminate and may progress to spatio-temporal chaos. Heterogeneities can be classified as either the absence or presence of diffusive interaction with the surrounding medium. In this study, we investigated the difference in the unpinning of spiral waves from obstacles with and without diffusive interaction, and found a profound difference. The pacing period required for unpinning at fixed obstacle size is larger in case of diffusive obstacles. Further, we deduced a generic theoretical framework that can predict the minimal unpinning period. Our results explain the difference in pacing periods between for the obstacles with and without diffusive interaction, and the difference is interpreted in terms of the local decrease of spiral wave velocity close to the obstacle boundary caused in the case of diffusive interaction.

  8. Interactions between liquid-water and gas-diffusion layers in polymer-electrolyte fuel cells

    SciTech Connect

    Das, Prodip K.; Santamaria, Anthony D.; Weber, Adam Z.

    2015-06-11

    Over the past few decades, a significant amount of research on polymer-electrolyte fuel cells (PEFCs) has been conducted to improve performance and durability while reducing the cost of fuel cell systems. However, the cost associated with the platinum (Pt) catalyst remains a barrier to their commercialization and PEFC durability standards have yet to be established. An effective path toward reducing PEFC cost is making the catalyst layers (CLs) thinner thus reducing expensive Pt content. The limit of thin CLs is high gas-transport resistance and the performance of these CLs is sensitive to the operating temperature due to their inherent low water uptake capacity, which results in higher sensitivity to liquid-water flooding and reduced durability. Therefore, reducing PEFC's cost by decreasing Pt content and improving PEFC's performance and durability by managing liquid-water are still challenging and open topics of research. An overlooked aspect nowadays of PEFC water management is the gas-diffusion layer (GDL). While it is known that GDL's properties can impact performance, typically it is not seen as a critical component. In this work, we present data showing the importance of GDLs in terms of water removal and management while also exploring the interactions between liquid-water and GDL surfaces. The critical interface of GDL and gas-flow-channel in the presence of liquid-water was examined through systematic studies of adhesion forces as a function of water-injection rate for various GDLs of varying thickness. GDL properties (breakthrough pressure and adhesion force) were measured experimentally under a host of test conditions. Specifically, the effects of GDL hydrophobic (PTFE) content, thickness, and water-injection rate were examined to identify trends that may be beneficial to the design of liquid-water management strategies and next-generation GDL materials for PEFCs.

  9. Interactions between liquid-water and gas-diffusion layers in polymer-electrolyte fuel cells

    DOE PAGES

    Das, Prodip K.; Santamaria, Anthony D.; Weber, Adam Z.

    2015-06-11

    Over the past few decades, a significant amount of research on polymer-electrolyte fuel cells (PEFCs) has been conducted to improve performance and durability while reducing the cost of fuel cell systems. However, the cost associated with the platinum (Pt) catalyst remains a barrier to their commercialization and PEFC durability standards have yet to be established. An effective path toward reducing PEFC cost is making the catalyst layers (CLs) thinner thus reducing expensive Pt content. The limit of thin CLs is high gas-transport resistance and the performance of these CLs is sensitive to the operating temperature due to their inherent lowmore » water uptake capacity, which results in higher sensitivity to liquid-water flooding and reduced durability. Therefore, reducing PEFC's cost by decreasing Pt content and improving PEFC's performance and durability by managing liquid-water are still challenging and open topics of research. An overlooked aspect nowadays of PEFC water management is the gas-diffusion layer (GDL). While it is known that GDL's properties can impact performance, typically it is not seen as a critical component. In this work, we present data showing the importance of GDLs in terms of water removal and management while also exploring the interactions between liquid-water and GDL surfaces. The critical interface of GDL and gas-flow-channel in the presence of liquid-water was examined through systematic studies of adhesion forces as a function of water-injection rate for various GDLs of varying thickness. GDL properties (breakthrough pressure and adhesion force) were measured experimentally under a host of test conditions. Specifically, the effects of GDL hydrophobic (PTFE) content, thickness, and water-injection rate were examined to identify trends that may be beneficial to the design of liquid-water management strategies and next-generation GDL materials for PEFCs.« less

  10. The diffusion of radiation in moving media. IV. Flux vector, effective opacity, and expansion opacity

    NASA Astrophysics Data System (ADS)

    Wehrse, R.; Baschek, B.; von Waldenfels, W.

    2003-04-01

    For a given velocity and temperature field in a differentially moving 3D medium, the vector of the radiative flux is derived in the diffusion approximation. Due to the dependence of the velocity gradient on the direction, the associated effective opacity in general is a tensor. In the limit of small velocity gradients analytical expression are obtained which allow us to discuss the cases when the direction of the flux vector deviates from that of the temperature gradient. Furthermore the radiative flux is calculated for infinitely sharp, Poisson distributed spectral lines resulting in simple expressions that provide basic insight into the effect of the motions. In particular, it is shown how incomplete line lists affect the radiative flux as a function of the velocity gradient. Finally, the connection between our formalism and the concept of the expansion opacity introduced by Karp et al. (\\cite{karp}) is discussed.

  11. Interpretation of tracer surface diffusion experiments on UO2 — roles of gas and solid transport processes

    SciTech Connect

    Olander, D. R.

    1981-02-01

    In this paper, the spreading of a tracer from an enriched needle source which contacts the surface of a depleted pellet sink is analyzed rigorously. It is shown that volume diffusion in both the needle and the pellet need to be considered because only by this process is sufficient radioactivity accumulated for measurement after the anneal. Parasitic gas phase processes are of two types: evaporative loss of solid if a flowing gas is used, or molecular diffusion from enriched portions of the surface to depleted zones if the couple is in a closed vessel with a stagnant gas. A complete numerical solution including surface diffusion, solid diffusion, evaporative loss and contact resistance is applied to the UO2 tracer study of Marlowe and Kazanoff at 1915°C. Based upon UO2 evaporation experiments, the analysis shows that the evaporative loss effect is not important in these experiments. Finally, the UO2 surface diffusion coefficient deduced from analysis of these data is 0.2 ± 0.1 cm2/s at 1915°C, which is 104 times larger than that predicted by extrapolation of values obtained by mass transfer techniques.

  12. Linking basin-scale and pore-scale gas hydrate distribution patterns in diffusion-dominated marine hydrate systems: DIFFUSION-DRIVEN HYDRATE GROWTH IN SANDS

    DOE PAGES

    Nole, Michael; Daigle, Hugh; Cook, Ann E.; ...

    2017-02-01

    The goal of this study is to computationally determine the potential distribution patterns of diffusion-driven methane hydrate accumulations in coarse-grained marine sediments. Diffusion of dissolved methane in marine gas hydrate systems has been proposed as a potential transport mechanism through which large concentrations of hydrate can preferentially accumulate in coarse-grained sediments over geologic time. Using one-dimensional compositional reservoir simulations, we examine hydrate distribution patterns at the scale of individual sand layers (1 to 20 m thick) that are deposited between microbially active fine-grained material buried through the gas hydrate stability zone (GHSZ). We then extrapolate to two- dimensional and basin-scalemore » three-dimensional simulations, where we model dipping sands and multilayered systems. We find that properties of a sand layer including pore size distribution, layer thickness, dip, and proximity to other layers in multilayered systems all exert control on diffusive methane fluxes toward and within a sand, which in turn impact the distribution of hydrate throughout a sand unit. In all of these simulations, we incorporate data on physical properties and sand layer geometries from the Terrebonne Basin gas hydrate system in the Gulf of Mexico. We demonstrate that diffusion can generate high hydrate saturations (upward of 90%) at the edges of thin sands at shallow depths within the GHSZ, but that it is ineffective at producing high hydrate saturations throughout thick (greater than 10 m) sands buried deep within the GHSZ. As a result, we find that hydrate in fine-grained material can preserve high hydrate saturations in nearby thin sands with burial.« less

  13. Gradation of mechanical properties in gas-diffusion electrode. Part 2: Heterogeneous carbon fiber and damage evolution in cell layers

    NASA Astrophysics Data System (ADS)

    Poornesh, K. K.; Cho, C. D.; Lee, G. B.; Tak, Y. S.

    In PEM fuel cell, gas-diffusion electrode (GDE) plays very significant role in force transmission from bipolar plate to the membrane. This paper investigates the effects of geometrical heterogeneities of gas-diffusion electrode layer (gas-diffusion layer (GDL) and catalyst layer (CL)) on mechanical damage evolution and propagation. We present a structural integrity principle of membrane electrode assembly (MEA) based on the interlayer stress transfer capacity and corresponding cell layer material response. Commonly observable damages such as rupture of hydrophobic coating and breakage of carbon fiber in gas-diffusion layer are attributed to the ductile to brittle phase transition within a single carbon fiber. Effect of material inhomogeneity on change in modulus, hardness, contact stiffness, and electrical contact resistance is also discussed. Fracture statistics of carbon fiber and variations in flexural strength of GDL are studied. The damage propagation in CL is perceived to be influenced by the type of gradation and the vicinity from which crack originates. Cohesive zone model has been proposed based on the traction-separation law to investigate the damage propagation throughout the two interfaces (carbon fiber/CL and CL/membrane).

  14. Characterization of internal wetting in polymer electrolyte membrane gas diffusion layers

    NASA Astrophysics Data System (ADS)

    Cheung, Perry; Fairweather, Joseph D.; Schwartz, Daniel T.

    Capillary pressure vs. saturation (P C(S L)) curves are fundamental to understanding liquid water transport and flooding in PEM gas diffusion layers (GDLs). P C(S L) curves convolute the influence of GDL pore geometry and internal contact angles at the three-phase liquid/solid/gas boundary. Even simple GDL materials are a spatially non-uniform mixture of carbon fiber and binder, making a Gaussian distribution of contact angles likely, based on the Cassie-Baxter equation. For a given Gaussian contact angle distribution with mean (θ Mean) and standard deviation (σ), a realistic P C(S L) curve can be computed using a bundle of capillaries model and GDL pore size distribution data. As expected, computed P C(S L) curves show that θ Mean sets the overall hydrophilic (θ Mean < 90°) or hydrophobic (θ Mean > 90°) character of the GDL (i.e., liquid saturation level at a given capillary pressure), and σ affects the slope of the P C(S L) curve. The capillary bundle model also can be used with (θ Mean, σ) as unknown parameters that are best-fit to experimentally acquired P C(S L) and pore size distribution data to find (θ Mean, σ) values for actual GDL materials. To test this, pore size distribution data was acquired for Toray TGP-H-090 along with hysteretic liquid and gas intrusion capillary pressure curve data. High quality best-fits were found between the model and combined datasets, with GDL liquid intrusion showing fairly neutral internal surface wetting properties (θ Mean = 92° and σ = 10°) whereas gas intrusion displayed a hydrophilic character (θ Mean = 52° and σ = 8°). External liquid advancing and receding contact angles were also measured on this same material and they also showed major hysteresis. The new methods described here open the door for better understanding of the link between GDL material processing and the wetting properties that affect flooding.

  15. Dust and gas jets: Evidence for a diffuse source in Halley's coma

    NASA Technical Reports Server (NTRS)

    Clairemidi, Jacques; Rousselot, Philippe; Vernotte, F.; Moreels, Guy

    1992-01-01

    The distribution of dust-scattered intensity in Halley's inner coma is measured with the Vega three-channel spectrometer at three selected wavelengths: 377, 482, and 607 nm. The variation along a cometo-centric radius may be described by a p(sup -s) law where p is the distance between nucleus and optical axis and s is an exponent which is equal to 1 except in an intermediate 3000 less than p less than 7000 km region where s = 1.5. The shape of the radial distribution may be explained with a model including solar radiation pressure effect and quantum scattering efficiencies calculated from Mie theory. Monochromatic images inside an angular sector having its apex at the nucleus show evidence of two dust jets which extend to 40,000 Km. The pixel-to-pixel ratio of two images of dust intensity at 377 and 482 nm shows that the scattered intensity presents an excess of blue coloration in a zone located around the jets between 10,000 and 25,000 km. This coloration is interpreted as being due to a population of sub-micronic grains which result of the fragmentation of dust particles transported in the jets. It is suggested that the diffuse source where an additional quantity of CO was detected might be connected with the presence of a dust jet. In the present scheme, grain particles with a size of several micron or 10 micron would be transported inside a dust jet to distances of several 10,000 km where they would suffer fragmentation and produce sub-micronic particles and a release of gas which would be at the origin of the diffuse source.

  16. Interacting biochemical and diffusive controls on trace gas sources in unsaturated soils

    NASA Astrophysics Data System (ADS)

    Rubol, S.; Manzoni, S.; Bellin, A.; Porporato, A. M.

    2011-12-01

    Microbes react to environmental conditions on different timescales. When conditions improve (e.g., rewetting, substrate amendment), the residing population exits the dormant state, becomes active and starts synthesizing extra-cellular enzymes. If substrate availability, and hence energy, is sufficient, microbes may start to reproduce and increase the size of their population. These dynamics make it complicated to interpret measured relationships between microbial activity (e.g., respiration, denitrification, N mineralization) and environmental conditions. In particular, the relationship between bacterial activity and soil moisture, which is derived by incubating soil samples at constant soil moisture levels, seems to vary under dynamic hydrological conditions. This may be related to both soil physical properties and the resilience of bacteria to adapt to rapid changes in soil moisture. We present a process-based model that includes both the above effects and test the hypothesis that the ratio of the time scale of biological versus physical factors determines the shape describing the relationship between microbial activity and soil moisture. In particular, we focus on the role of oxygen dynamics, which regulate the prevalence of aerobic versus anaerobic conditions and thus the prevalence of nitrification versus denitrification. We identify and compare the time scale of the biological oxygen consumption with the time scale of physical diffusion. Starting from well-aerated conditions, as bacteria consume O2 in solution, more oxygen dissolves from the atmosphere - depending on gas-filled porosity. If water dynamics or tillage limits re-aeration, this can affect the equilibrium between the aqueous and the gaseous phase and thus alter the time scale of the reactions. This balance between consumption and re-aeration by diffusion ultimately controls the water quality as well the production of trace gases.

  17. Hyperpolarized Gas Diffusion MRI for the Study of Atelectasis and Acute Respiratory Distress Syndrome

    PubMed Central

    Cereda, Maurizio; Xin, Yi; Kadlecek, Stephen; Hamedani, Hooman; Rajaei, Jennia; Clapp, Justin; Rizi, Rahim R.

    2014-01-01

    Considerable uncertainty remains about the best ventilator strategies for the mitigation of atelectasis and associated airspace stretch in patients with acute respiratory distress syndrome (ARDS). In addition to several immediate physiological effects, atelectasis increases the risk of ventilator-associated lung injury (VALI), which has been shown to significantly worsen ARDS outcomes. A number of lung imaging techniques have made substantial headway in clarifying the mechanisms of atelectasis. This paper reviews the contributions of CT, PET, and conventional MRI to understanding this phenomenon. In doing so, it also reveals several important shortcomings inherent to each of these approaches. Once these shortcomings have been made apparent, we describe how hyperpolarized gas magnetic resonance imaging (HP MRI)—a technique that is uniquely able to assess responses to mechanical ventilation and lung injury in peripheral airspaces—is poised to fill several of these knowledge gaps. The HP-MRI-derived apparent diffusion coefficient (ADC) quantifies the restriction of 3He diffusion by peripheral airspaces, thereby obtaining pulmonary structural information at an extremely small scale. Lastly, this paper reports the results of a series of experiments that measured ADC in mechanically ventilated rats in order to investigate (i) the effect of atelectasis on ventilated airspaces; (ii) the relationship between positive end-expiratory pressure (PEEP), hysteresis, and the dimensions of peripheral airspaces; and (iii) the ability of PEEP and surfactant to reduce airspace dimensions after lung injury. An increase in ADC was found to be a marker of atelectasis-induced overdistension. With recruitment, higher airway pressures were shown to reduce stretch rather than worsen it. Moving forward, HP MRI has significant potential to shed further light on the atelectatic processes that occur during mechanical ventilation. PMID:24920074

  18. Inelastic gas: An experimental study of vibro-fluidized dilute granular media

    NASA Astrophysics Data System (ADS)

    Feitosa, Klebert Bezerra

    We conduct an experimental study of a two dimensional vibro-fluidized dilute granular medium. The system is composed of spherical beads confined to move in a vertical plane and excited by intense vertical vibrations. We perform full-field tracking of positions and orientations of the spheres by high speed photography. In steady-state, the motion of the grains resembles that of a molecular gas, thus the name granular gas. We study the distribution of linear velocities in the granular gas. The investigation shows that the distributions are non-gaussian, best fitted by the function P(v) ˜ exp(-beta| v|/sigma)1.5), and insensitive to number density, driving parameters and particle inelasticity. The distribution is a one parameter distribution, parameterized by the mean square velocity; which defines a granular temperature. T = ½ . We study binary mixtures of the granular media. We find that, in general, the granular temperature is not equal for the two types of spheres. However, the temperature ratio is constant in the bulk. The ratio depends strongly on the mass ratio of the spheres, but not on their inelasticity. The ratio is also insensitive to compositional parameters of the mixture such as number fraction and number density. We also investigate the statistics of the power flux into a subsystem of the granular gas. The power shows large fluctuations, including frequent large negative fluctuations. The relative probabilities of positive and negative fluctuations in the power flux are in close accord with the Fluctuation Theorem of Gallavotti and Cohen (Gallavotti & Cohen, 1995b). We also compare the effective temperature that emerges from this analysis to the kinetic granular temperature. Finally, we study the rotational dynamics of the granular gas. We find that the granular temperature is not equipartitioned between translational and rotational degrees of freedom. We also demonstrate that the ratio of rotational to translational energy is independent of the

  19. Passage of a shock wave through inhomogeneous media and its impact on gas-bubble deformation

    NASA Astrophysics Data System (ADS)

    Nowakowski, A. F.; Ballil, A.; Nicolleau, F. C. G. A.

    2015-08-01

    The paper investigates shock-induced vortical flows within inhomogeneous media of nonuniform thermodynamic properties. Numerical simulations are performed using a Eulerian type mathematical model for compressible multicomponent flow problems. The model, which accounts for pressure nonequilibrium and applies different equations of state for individual flow components, shows excellent capabilities for the resolution of interfaces separating compressible fluids as well as for capturing the baroclinic source of vorticity generation. The developed finite volume Godunov type computational approach is equipped with an approximate Riemann solver for calculating fluxes and handles numerically diffused zones at flow component interfaces. The computations are performed for various initial conditions and are compared with available experimental data. The initial conditions promoting a shock-bubble interaction process include weak to high planar shock waves with a Mach number ranging from 1.2 to 3 and isolated cylindrical bubble inhomogeneities of helium, argon, nitrogen, krypton, and sulphur hexafluoride. The numerical results reveal the characteristic features of the evolving flow topology. The impulsively generated flow perturbations are dominated by the reflection and refraction of the shock, the compression, and acceleration as well as the vorticity generation within the medium. The study is further extended to investigate the influence of the ratio of the heat capacities on the interface deformation.

  20. Testing a Dynamical Equilibrium Model of the Extraplanar Diffuse Ionized Gas in NGC 891

    NASA Astrophysics Data System (ADS)

    Boettcher, Erin; Zweibel, Ellen G.; Gallagher, J. S., III; Benjamin, Robert A.

    2016-12-01

    The observed scale heights of extraplanar diffuse ionized gas (eDIG) layers exceed their thermal scale heights by a factor of a few in the Milky Way and other nearby edge-on disk galaxies. Here, we test a dynamical equilibrium model of the eDIG layer in NGC 891, where we ask whether the thermal, turbulent, magnetic field, and cosmic-ray pressure gradients are sufficient to support the layer. In optical emission-line spectroscopy from the SparsePak integral field unit on the WIYN 3.5 m telescope, the Hα emission in position-velocity space suggests that the eDIG is found in a ring between galactocentric radii of {R}\\min ≤slant R≤slant 8 {kpc}, where {R}\\min ≥slant 2 {kpc}. We find that the thermal ({σ }{th}=11 km s-1) and turbulent ({σ }{turb}=25 km s-1) velocity dispersions are insufficient to satisfy the hydrostatic equilibrium equation given an exponential electron scale height of {h}z=1.0 {kpc}. Using a literature analysis of radio continuum observations from the CHANG-ES survey, we demonstrate that the magnetic field and cosmic-ray pressure gradients are sufficient to stably support the gas at R≥slant 8 kpc if the cosmic rays are sufficiently coupled to the system ({γ }{cr}=1.45). Thus, a stable dynamical equilibrium model is viable only if the eDIG is found in a thin ring around R = 8 kpc, and nonequilibrium models such as a galactic fountain flow are of interest for further study.

  1. Constraining Gas Diffusivity-Soil Water Content Relationships in Forest Soils Using Surface Chamber Fluxes and Depth Profiles of Multiple Trace Gases

    NASA Astrophysics Data System (ADS)

    Dore, J. E.; Kaiser, K.; Seybold, E. C.; McGlynn, B. L.

    2012-12-01

    Forest soils are sources of carbon dioxide (CO2) to the atmosphere and can act as either sources or sinks of methane (CH4) and nitrous oxide (N2O), depending on redox conditions and other factors. Soil moisture is an important control on microbial activity, redox conditions and gas diffusivity. Direct chamber measurements of soil-air CO2 fluxes are facilitated by the availability of sensitive, portable infrared sensors; however, corresponding CH4 and N2O fluxes typically require the collection of time-course physical samples from the chamber with subsequent analyses by gas chromatography (GC). Vertical profiles of soil gas concentrations may also be used to derive CH4 and N2O fluxes by the gradient method; this method requires much less time and many fewer GC samples than the direct chamber method, but requires that effective soil gas diffusivities are known. In practice, soil gas diffusivity is often difficult to accurately estimate using a modeling approach. In our study, we apply both the chamber and gradient methods to estimate soil trace gas fluxes across a complex Rocky Mountain forested watershed in central Montana. We combine chamber flux measurements of CO2 (by infrared sensor) and CH4 and N2O (by GC) with co-located soil gas profiles to determine effective diffusivity in soil for each gas simultaneously, over-determining the diffusion equations and providing constraints on both the chamber and gradient methodologies. We then relate these soil gas diffusivities to soil type and volumetric water content in an effort to arrive at empirical parameterizations that may be used to estimate gas diffusivities across the watershed, thereby facilitating more accurate, frequent and widespread gradient-based measurements of trace gas fluxes across our study system. Our empirical approach to constraining soil gas diffusivity is well suited for trace gas flux studies over complex landscapes in general.

  2. Advanced control of liquid water region in diffusion media of polymer electrolyte fuel cells through a dimensionless number

    SciTech Connect

    Wang, Yun; Chen, Ken S.

    2016-03-21

    In the present study, a three-dimension (3-D) model of polymer electrolyte fuel cells (PEFCs) is employed to investigate the complex, non-isothermal, two-phase flow in the gas diffusion layer (GDL). Phase change in gas flow channels is explained, and a simplified approach accounting for phase change is incorporated into the fuel cell model. It is found that the liquid water contours in the GDL are similar along flow channels when the channels are subject to two-phase flow. Here, analysis is performed on a dimensionless parameter Da0 introduced in our previous paper and the parameter is further evaluated in a realistic fuel cell. We found that the GDL's liquid water (or liquid-free) region is determined by the Da0 number which lumps several parameters, including the thermal conductivity and operating temperature. By adjusting these factors, a liquid-free GDL zone can be created even though the channel stream is two-phase flow. Such a liquid-free zone is adjacent to the two-phase region, benefiting local water management, namely avoiding both severe flooding and dryness.

  3. Advanced control of liquid water region in diffusion media of polymer electrolyte fuel cells through a dimensionless number

    NASA Astrophysics Data System (ADS)

    Wang, Yun; Chen, Ken S.

    2016-05-01

    In the present work, a three-dimension (3-D) model of polymer electrolyte fuel cells (PEFCs) is employed to investigate the complex, non-isothermal, two-phase flow in the gas diffusion layer (GDL). Phase change in gas flow channels is explained, and a simplified approach accounting for phase change is incorporated into the fuel cell model. It is found that the liquid water contours in the GDL are similar along flow channels when the channels are subject to two-phase flow. Analysis is performed on a dimensionless parameter Da0 introduced in our previous paper [Y. Wang and K. S. Chen, Chemical Engineering Science 66 (2011) 3557-3567] and the parameter is further evaluated in a realistic fuel cell. We found that the GDL's liquid water (or liquid-free) region is determined by the Da0 number which lumps several parameters, including the thermal conductivity and operating temperature. By adjusting these factors, a liquid-free GDL zone can be created even though the channel stream is two-phase flow. Such a liquid-free zone is adjacent to the two-phase region, benefiting local water management, namely avoiding both severe flooding and dryness.

  4. Advanced control of liquid water region in diffusion media of polymer electrolyte fuel cells through a dimensionless number

    DOE PAGES

    Wang, Yun; Chen, Ken S.

    2016-03-21

    In the present study, a three-dimension (3-D) model of polymer electrolyte fuel cells (PEFCs) is employed to investigate the complex, non-isothermal, two-phase flow in the gas diffusion layer (GDL). Phase change in gas flow channels is explained, and a simplified approach accounting for phase change is incorporated into the fuel cell model. It is found that the liquid water contours in the GDL are similar along flow channels when the channels are subject to two-phase flow. Here, analysis is performed on a dimensionless parameter Da0 introduced in our previous paper and the parameter is further evaluated in a realistic fuelmore » cell. We found that the GDL's liquid water (or liquid-free) region is determined by the Da0 number which lumps several parameters, including the thermal conductivity and operating temperature. By adjusting these factors, a liquid-free GDL zone can be created even though the channel stream is two-phase flow. Such a liquid-free zone is adjacent to the two-phase region, benefiting local water management, namely avoiding both severe flooding and dryness.« less

  5. EOS7CA Version 1.0: TOUGH2 Module for Gas Migration in Shallow Subsurface Porous Media Systems

    SciTech Connect

    Oldenburg, Curtis M.

    2015-06-22

    EOS7CA is a TOUGH2 module for mixtures of a non-condensible gas (NCG) and air (with or without a gas tracer), an aqueous phase, and water vapor. The user can select the NCG as being CO2, N2, or CH4. EOS7CA uses a cubic equation of state with a multiphase version of Darcy’s Law to model flow and transport of gas and aqueous phase mixtures over a range of pressures and temperatures appropriate to shallow subsurface porous media systems. The limitation to shallow systems arises from the use of Henry’s Law for gas solubility which is appropriate for low pressures but begins to over-predict solubility starting at pressures greater than approximately 1 MPa (10 bar). The components modeled in EOS7CA are water, brine, NCG, gas tracer, air, and optional heat.

  6. Fabrication of gas diffusion electrodes via electrophoretic deposition for high temperature polymer electrolyte membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Felix, Cecil; Jao, Ting-Chu; Pasupathi, Sivakumar; Linkov, Vladimir M.; Pollet, Bruno G.

    2014-07-01

    The Electrophoretic Deposition (EPD) method was adapted to fabricate Gas Diffusion Electrodes (GDEs) for Membrane Electrode Assemblies (MEA) for High Temperature Polymer Electrolyte Membrane Fuel Cells (HT-PEMFC) operating at 160 °C. Suspensions containing the Pt/C catalyst, polytetrafluoroethylene (PTFE) and NaCl were studied. Stable catalyst suspensions were observed when the NaCl concentrations were ≤0.1 mM. Mercury intrusion porosity analysis showed that the GDEs obtained via the EPD method had higher porosity (30.5 m2 g-1) than the GDEs fabricated by the ultrasonic spray method (25.2 m2 g-1). Compared to the ultrasonically sprayed MEA, the EPD MEA showed ∼12% increase in peak power at a slightly lower (∼4 wt %) Pt loading. Electrochemical Impedance Spectroscopy (EIS) analysis showed a lower charge transfer resistance for the EPD MEA compared to the ultrasonically sprayed MEA while Cyclic Voltammetry (CV) analysis showed ∼16% higher Electrochemical Surface Area (ECSA) for the EPD MEA compared to the ultrasonically sprayed MEA. These observations were attributed to the higher porosity and better catalyst particle size distribution of the EPD GDEs. A comparison between PTFE and Nafion® ionomer in the Catalyst Layers (CL) of two EPD MEAs revealed that PTFE yielded MEAs with better performance and is therefore more suitable in HT-PEMFCs.

  7. Wire rod coating process of gas diffusion layers fabrication for proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Kannan, A. M.; Sadananda, S.; Parker, D.; Munukutla, L.; Wertz, J.; Thommes, M.

    Gas diffusion layers (GDLs) were fabricated using non-woven carbon paper as a macro-porous layer substrate developed by Hollingsworth & Vose Company. A commercially viable coating process was developed using wire rod for coating micro-porous layer by a single pass. The thickness as well as carbon loading in the micro-porous layer was controlled by selecting appropriate wire thickness of the wire rod. Slurry compositions with solid loading as high as 10 wt.% using nano-chain and nano-fiber type carbons were developed using dispersion agents to provide cohesive and homogenous micro-porous layer without any mud-cracking. The surface morphology, wetting characteristics and pore size distribution of the wire rod coated GDLs were examined using FESEM, Goniometer and Hg porosimetry, respectively. The GDLs were evaluated in single cell PEMFC under various operating conditions (temperature and RH) using hydrogen and air as reactants. It was observed that the wire rod coated micro-porous layer with 10 wt.% nano-fibrous carbon based GDLs showed the highest fuel cell performance at 85 °C using H 2 and air at 50% RH, compared to all other compositions.

  8. Next-generation polymer-electrolyte-membrane fuel cells using titanium foam as gas diffusion layer.

    PubMed

    Choi, Hyelim; Kim, Ok-Hee; Kim, Minhyoung; Choe, Heeman; Cho, Yong-Hun; Sung, Yung-Eun

    2014-05-28

    In spite of their high conversion efficiency and no emission of greenhouse gases, polymer electrolyte membrane fuel cells (PEMFCs) suffer from prohibitively high cost and insufficient life-span of their core component system, the membrane electrode assembly (MEA). In this paper, we are proposing Ti foam as a promising alternative electrode material in the MEA. Indeed, it showed a current density of 462 mA cm(-2), being ca. 166% higher than that with the baseline Toray 060 gas diffusion layer (GDL) (278 mA cm(-2)) with 200 ccm oxygen supply at 0.7 V, when used as the anode GDL, because of its unique three-dimensional strut structure promoting highly efficient catalytic reactions. Furthermore, it exhibits superior corrosion resistance with almost no thickness and weight changes in the accelerated corrosion test, as opposed to considerable reductions in the weight and thickness of the conventional GDL. We believe that this paper suggests profound implications in the commercialization of PEMFCs, because the metallic Ti foam provides a longer-term reliability and chemical stability, which can reduce the loss of Pt catalyst and, hence, the cost of PEMFCs.

  9. Gas diffusion-type oxygen electrode using perovskite-type oxides for metal-air batteries

    SciTech Connect

    Hyodo, Takeo; Miura, Norio; Yamazoe, Noboru

    1995-12-31

    In order to develop an air cathode of metal-air batteries, oxygen reduction behavior of gas diffusion-type carbon electrodes loaded with perovskite-type oxides, La{sub 1{minus}x}A{prime}{sub x}FeO{sub 3} (A{prime} = Ca, Sr, Ba, 0 {le} x {le} 1.0), was examined in 8 M KOH at 60 C. Among the oxide catalysts tested, La{sub 0.5}Sr{sub 0.5}FeO{sub 3} (specific surface area: 21.5 m{sup 2}{center_dot}g{sup {minus}1}) gave the highest electrode performance. On the basis of electrode reaction kinetics, H{sub 2}O{sub 2} decomposition rates, and temperature programmed desorption of oxygen, it was concluded that such a performance was attributable to the active sites of the oxide for the direct 4-electron reduction of oxygen. Moreover, the electrode using La{sub 0.5}Sr{sub 0.5}FeO{sub 3} was found to be rather stable in a short-term operation for 90 h at 300 mA{center_dot}cm{sup {minus}2}.

  10. Study on gas diffusion emitted from different height of point source.

    PubMed

    Yassin, Mohamed F

    2009-01-01

    The flow and dispersion of stack-gas emitted from different elevated point source around flow obstacles in an urban environment have been investigated, using computational fluid dynamics models (CFD). The results were compared with the experimental results obtained from the diffusion wind tunnel under different conditions of thermal stability (stable, neutral or unstable). The flow and dispersion fields in the boundary layer in an urban environment were examined with different flow obstacles. Gaseous pollutant was discharged in the simulated boundary layer over the flat area. The CFD models used for the simulation were based on the steady-state Reynolds-Average Navier-Stoke equations (RANS) with kappa-epsilon turbulence models; standard kappa-epsilon and RNG kappa-epsilon models. The flow and dispersion data measured in the wind tunnel experiments were compared with the results of the CFD models in order to evaluate the prediction accuracy of the pollutant dispersion. The results of the CFD models showed good agreement with the results of the wind tunnel experiments. The results indicate that the turbulent velocity is reduced by the obstacles models. The maximum dispersion appears around the wake region of the obstacles.

  11. Two-phase behavior and compression effects in the PEFC gas diffusion medium

    SciTech Connect

    Mukherjee, Partha P; Kang, Qinjun; Schulz, Volker P; Wang, Chao - Yang; Becker, Jurgen; Wiegmann, Andreas

    2009-01-01

    A key performance limitation in the polymer electrolyte fuel cell (PEFC), manifested in terms of mass transport loss, originates from liquid water transport and resulting flooding phenomena in the constituent components. A key contributor to the mass transport loss is the cathode gas diffusion layer (GDL) due to the blockage of available pore space by liquid water thus rendering hindered oxygen transport to the active reaction sites in the electrode. The GDL, therefore, plays an important role in the overall water management in the PEFC. The underlying pore-morphology and the wetting characteristics have significant influence on the flooding dynamics in the GDL. Another important factor is the role of cell compression on the GDL microstructural change and hence the underlying two-phase behavior. In this article, we present the development of a pore-scale modeling formalism coupled With realistic microstructural delineation and reduced order compression model to study the structure-wettability influence and the effect of compression on two-phase behavior in the PEFC GDL.

  12. Thin liquid/gas diffusion layers for high-efficiency hydrogen production from water splitting

    DOE PAGES

    Mo, Jingke; Retterer, Scott T.; Cullen, David A.; ...

    2016-06-13

    Liquid/gas diffusion layers (LGDLs) play a crucial role in electrochemical energy technology and hydrogen production, and are expected to simultaneously transport electrons, heat, and reactants/products with minimum voltage, current, thermal, interfacial, and fluidic losses. In addition, carbon materials, which are typically used in proton exchange membrane fuel cells (PEMFCs), are unsuitable for PEM electrolyzer cells (PEMECs). In this study, a novel titanium thin LGDL with well-tunable pore morphologies was developed by employing nano-manufacturing and was applied in a standard PEMEC. The LGDL tests show significant performance improvements. The operating voltages required at a current density of 2.0 A/cm2 were asmore » low as 1.69 V, and its efficiency reached a report high of up to 88%. The new thin and flat LGDL with well-tunable straight pores has been demonstrated to remarkably reduce the ohmic, interfacial and transport losses. In addition, well-tunable features, including pore size, pore shape, pore distribution, and thus porosity and permeability, will be very valuable for developing PEMEC models and for validation of its simulations with optimal and repeatable performance. The LGDL thickness reduction from greater than 350 μm of conventional LGDLs to 25 μm will greatly decrease the weight and volume of PEMEC stacks, and represents a new direction for future developments of low-cost PEMECs with high performance.« less

  13. Thin liquid/gas diffusion layers for high-efficiency hydrogen production from water splitting

    SciTech Connect

    Mo, Jingke; Retterer, Scott T.; Cullen, David A.; Toops, Todd J.; Green, Jr, Johney Boyd; Zhang, Feng-Yuan

    2016-06-13

    Liquid/gas diffusion layers (LGDLs) play a crucial role in electrochemical energy technology and hydrogen production, and are expected to simultaneously transport electrons, heat, and reactants/products with minimum voltage, current, thermal, interfacial, and fluidic losses. In addition, carbon materials, which are typically used in proton exchange membrane fuel cells (PEMFCs), are unsuitable for PEM electrolyzer cells (PEMECs). In this study, a novel titanium thin LGDL with well-tunable pore morphologies was developed by employing nano-manufacturing and was applied in a standard PEMEC. The LGDL tests show significant performance improvements. The operating voltages required at a current density of 2.0 A/cm2 were as low as 1.69 V, and its efficiency reached a report high of up to 88%. The new thin and flat LGDL with well-tunable straight pores has been demonstrated to remarkably reduce the ohmic, interfacial and transport losses. In addition, well-tunable features, including pore size, pore shape, pore distribution, and thus porosity and permeability, will be very valuable for developing PEMEC models and for validation of its simulations with optimal and repeatable performance. The LGDL thickness reduction from greater than 350 μm of conventional LGDLs to 25 μm will greatly decrease the weight and volume of PEMEC stacks, and represents a new direction for future developments of low-cost PEMECs with high performance.

  14. Gas-diffusion microextraction coupled with spectrophotometry for the determination of formaldehyde in cork agglomerates.

    PubMed

    Brandão, Pedro F; Ramos, Rui M; Valente, Inês M; Almeida, Paulo J; Carro, Antonia M; Lorenzo, Rosa A; Rodrigues, José A

    2017-04-01

    In this work, a simple methodology was developed for the extraction and determination of free formaldehyde content in cork agglomerate samples. For the first time, gas-diffusion microextraction was used for the extraction of volatile formaldehyde directly from samples, with simultaneous derivatization with acetylacetone (Hantzsch reaction). The absorbance of the coloured solution was read in a spectrophotometer at 412 nm. Different extraction parameters were studied and optimized (extraction temperature, sample mass, volume of acceptor solution, extraction time and concentration of derivatization reagent) by means of an asymmetric screening. The developed methodology proved to be a reliable tool for the determination of formaldehyde in cork agglomerates with the following suitable method features: low LOD (0.14 mg kg(-1)) and LOQ (0.47 mg kg(-1)), r (2) = 0.9994, and intraday and interday precision of 3.5 and 4.9%, respectively. The developed methodology was applied to the determination of formaldehyde in different cork agglomerate samples, and contents between 1.9 and 9.4 mg kg(-1) were found. Furthermore, formaldehyde was also determined by the standard method EN 717-3 for comparison purposes; no significant differences between the results of both methods were observed. Graphical abstract Representation of the GDME system and its main components.

  15. Purging of a tank-mounted multilayer insulation system by gas diffusion

    NASA Technical Reports Server (NTRS)

    Sumner, I. E.

    1978-01-01

    The investigation was conducted on a multilayer insulation (MLI) system mounted on a spherical liquid hydrogen propellant tank. The MLI consisted of two blankets of insulation each containing 15 double-aluminized Mylar radiation shields separated by double silk net spacers. The gaseous nitrogen initially contained within the MLI system and vacuum chamber was purged with gaseous helium introduced both underneath the MLI and into the vacuum chamber. The MLI panels were assumed to be purged primarily by means of gas diffusion. Overall, test results indicated that nitrogen concentrations well below 1 percent could be achieved everywhere within the MLI system. Typical times to achieve 1 percent nitrogen concentration within the MLI panels ranged from 69 minutes at the top of the tank to 158 minutes at the bottom of the tank. Four space-hold thermal performance tests indicated no significant thermal degradation of the MLI system had occurred due to the purge tests conducted. The final measured heat input attributed to the MLI was 7.23 watts as compared to 7.18 watts for the initial baseline thermal performance test.

  16. Comparisons of diffusive and advective fluxes of gas phase volatile organic compounds (VOCs) in unsaturated zones under natural conditions

    NASA Astrophysics Data System (ADS)

    You, Kehua; Zhan, Hongbin

    2013-02-01

    Diffusive flux is traditionally treated as the dominant mechanism of gas transport in unsaturated zones under natural conditions, and advective flux is usually neglected. However, some researchers have found that pressure-driven and density-driven advective flux may also be significant under certain conditions. This article compares the diffusive, pressure-driven and density-driven advective fluxes of gas phase volatile organic compound (VOCs) in unsaturated zones under various natural conditions. The presence of a less or more permeable layer at ground surface in a layered unsaturated zone is investigated for its impact on the net contribution of advective and diffusive fluxes. Results show although the transient advective flux can be greater than the diffusive flux, under most of the field conditions the net contribution of the advective flux is one to three orders of magnitude less than the diffusive flux, and the influence of the density-driven flux is undetectable. The advective flux contributes comparably with the diffusive flux only when the gas-filled porosity is less than 0.05. The presence of a less permeable layer at ground surface slightly increases the total flux in the underlying layer, while the presence of a more permeable layer at ground surface significantly increases the total flux in it. When the magnitude of water table fluctuation is less than 1 cm, and the period is greater than 0.5 day, the fluctuation of the water table can be simulated by fixing the water table position and setting a fluctuating moving velocity at the water table.

  17. Dual gas-diffusion membrane- and mediatorless dihydrogen/air-breathing biofuel cell operating at room temperature

    NASA Astrophysics Data System (ADS)

    Xia, Hong-qi; So, Keisei; Kitazumi, Yuki; Shirai, Osamu; Nishikawa, Koji; Higuchi, Yoshiki; Kano, Kenji

    2016-12-01

    A membraneless direct electron transfer (DET)-type dihydrogen (H2)/air-breathing biofuel cell without any mediator was constructed wherein bilirubin oxidase from Myrothecium verrucaria (BOD) and membrane-bound [NiFe] hydrogenase from Desulfovibrio vulgaris Miyazaki F (MBH) were used as biocatalysts for the cathode and the anode, respectively, and Ketjen black-modified water proof carbon paper (KB/WPCC) was used as an electrode material. The KB/WPCC surface was modified with 2-aminobenzoic acid and p-phenylenediamine, respectively, to face the positively charged electron-accepting site of BOD and the negatively charged electron-donating site of MBH to the electrode surface. A gas-diffusion system was employed for the electrodes to realize high-speed substrate supply. As result, great improvement in the current density of O2 reduction with BOD and H2 reduction with MBH were realized at negatively and postively charged surfaces, respectively. Gas diffusion system also suppressed the oxidative inactivation of MBH at high electrode potentials. Finally, based on the improved bioanode and biocathode, a dual gas-diffusion membrane- and mediatorless H2/air-breathing biofuel cell was constructed. The maximum power density reached 6.1 mW cm-2 (at 0.72 V), and the open circuit voltage was 1.12 V using 1 atm of H2 gas as a fuel at room temperature and under passive and quiescent conditions.

  18. Effects of milling media on the mechanical properties of gas pressure sintered α/β-SiAlON

    NASA Astrophysics Data System (ADS)

    Chun, Sungsu; Min, Bong-Ki; Kim, Sukyoung

    2014-11-01

    Three types of milling media, alumina, zirconia and cemented tungsten carbide (CTC), were used for the solid-state preparation of SiAlON from Si3N4 using Y2O3-Al2O3-AlN as sintering aids. Fully densified α and β dual-phase SiAlON composites were obtained by gas pressure sintering (GPS) at 1750 °C for 1.5 hrs. The relative contents of α- and β-SiAlON and grain boundary phases in the sintered samples were affected by the type of milling media, where the main grain boundary phases were α-, β-SiAlON and melilite (Y2Si3O3N4). Zirconium nitride was observed at the grain boundaries of the samples prepared using zirconia media, and WC and CO3W3C were observed with the sample prepared using CTC media due to contamination from the milling media. As a result, the overall mechanical properties, color, and microstructure of SiAlON were affected by the grain boundary phases and the α- to β-SiAlON ratio. The SNZ sample prepared using ZrO2 media showed better mechanical properties than the SNA and SNW samples. These results were compared with those obtained by spark plasma sintering, which was reported previously.

  19. Gas exchange dependency on diffusion coefficient: direct /sup 222/Rn and /sup 3/He comparisons in a small lake

    SciTech Connect

    Torgersen, T.; Mathieu, G.; Hesslein, R.H.; Broecker, W.S.

    1982-01-20

    A direct field comparison was conducted to determine the dependency of gas exchange coefficient (k/sub x/) on the diffusion coefficient (D/sub x/). The study also sought to confirm the enhanced vertical exchange properties of limnocorrals and similar enclosures. Gas exchange coefficients for /sup 222/Rn and /sup 3/He were determined in a small northern Ontario lake, using a /sup 226/Ra and /sup 3/H spike to gain the necessary precision. The results indicate that the gas exchange coefficient is functionally dependent on the diffusion coefficient raised to the 1.22/sub -35//sup + > 12/ power (k/sub x/ = f(D/sub x//sup 1.22)), clearly supporting the stagnant film model of gas exchange. Limnocorrals were found to have gas exchange rates up to 1.7 times higher than the whole lake in spite of the observation of more calm surface conditions in the corral than in the open lake. 33 references, 6 figures, 8 tables.

  20. Laser absorption spectroscopy of water vapor confined in nanoporous alumina: wall collision line broadening and gas diffusion dynamics.

    PubMed

    Svensson, Tomas; Lewander, Märta; Svanberg, Sune

    2010-08-02

    We demonstrate high-resolution tunable diode laser absorption spectroscopy (TDLAS) of water vapor confined in nanoporous alumina. Strong multiple light scattering results in long photon pathlengths (1 m through a 6 mm sample). We report on strong line broadening due to frequent wall collisions (gas-surface interactions). For the water vapor line at 935.685 nm, the HWHM of confined molecules are about 4.3 GHz as compared to 2.9 GHz for free molecules (atmospheric pressure). Gas diffusion is also investigated, and in contrast to molecular oxygen (that moves rapidly in and out of the alumina), the exchange of water vapor is found very slow.

  1. On the asymptotic preserving property of the unified gas kinetic scheme for the diffusion limit of linear kinetic models

    SciTech Connect

    Mieussens, Luc

    2013-11-15

    The unified gas kinetic scheme (UGKS) of K. Xu et al. (2010) [37], originally developed for multiscale gas dynamics problems, is applied in this paper to a linear kinetic model of radiative transfer theory. While such problems exhibit purely diffusive behavior in the optically thick (or small Knudsen) regime, we prove that UGKS is still asymptotic preserving (AP) in this regime, but for the free transport regime as well. Moreover, this scheme is modified to include a time implicit discretization of the limit diffusion equation, and to correctly capture the solution in case of boundary layers. Contrary to many AP schemes, this method is based on a standard finite volume approach, it does neither use any decomposition of the solution, nor staggered grids. Several numerical tests demonstrate the properties of the scheme.

  2. Effective diffusivity in partially-saturated carbon-fiber gas diffusion layers: Effect of local saturation and application to macroscopic continuum models

    NASA Astrophysics Data System (ADS)

    García-Salaberri, Pablo A.; Gostick, Jeff T.; Hwang, Gisuk; Weber, Adam Z.; Vera, Marcos

    2015-11-01

    Macroscopic continuum models are an essential tool to understand the complex transport phenomena that take place in gas diffusion layers (GDLs) used in polymer electrolyte fuel cells (PEFCs). Previous work has shown that macroscopic models require effective properties obtained under uniform saturation conditions to get a consistent physical formulation. This issue, mostly unappreciated in the open literature, is addressed in detail in this work. To this end, lattice Boltzmann simulations were performed on tomographic images of dry and water-invaded carbon-paper GDL subsamples with nearly uniform porosity and saturation distributions. The computed effective diffusivity shows an anisotropic dependence on local porosity similar to that reported for morphologically analogous GDLs. In contrast, the dependence on local saturation is rather isotropic, following a nearly quadratic power law. The capability of the local correlations to recover the layer-scale properties obtained from inhomogeneous GDLs is checked by global averaging. Good agreement is found between the upscaled results and the diffusivity data of the GDL from which the present subsamples were taken, as well as other global data presented in the literature. A higher blockage effect of local saturation is, however, expected for the under-the-rib region in operating PEFCs.

  3. Relative gas diffusivity as a controller of soil N2 and N2O fluxes

    NASA Astrophysics Data System (ADS)

    Clough, Tim; Balaine, Nimlesh; Beare, Mike; Thomas, Steve

    2015-04-01

    Animal grazing may induce soil compaction and has been shown to enhance emissions of the greenhouse gas nitrous oxide (N2O). The dominant substrate for N2O production is urea, supplied to the soil in ruminant urine. While studies have examined the effects of water-filled pore space on N2O emissions there has been less attention paid to the role of soil physical properties, such as relative gas diffusivity (Dp/Do), on N2O emissions and associated emissions of dinitrogen (N2). Three experiments were performed on soil cores maintained at a range of soil bulk densities (1.1 to 1.5 Mg/m3) and soil matric potentials (-10 to -0.2 kPa). These soil cores received urea at 700 kg N/ha to simulate a urine deposition event. Using the 15N tracer technique we measured N2 and N2O fluxes in order to investigate the role of soil Dp/Do as a controlling factor the magnitude of N2 and N2O fluxes and the reduction of N2O. As soil compaction and soil moisture contents increased soil Dp/Do declined. This in turn resulted in slower rates of nitrification. The mean cumulative fluxes of N2O, as a percentage of N applied, ranged from <1 to 16% after 35 days. Cumulative N2 fluxes as a percentage of N applied, ranged from <1 to 60% after 35 days. Soil compaction and soil matric potential interacted to influence Dp/Do which in turn was seen to be a strong determinant of the magnitude of both N2O and N2 fluxes. As Dp/Do values decreased a critical value was reached where N2O fluxes rapidly switched from being at a maximum to a minimum while at the same time N2 production intensified. This was also reflected in the N2:N2O ratios, based on cumulative fluxes, which ranged from <1 to 25. When compared with water-filled pore space the Dp/Do variable proved to be a better predictor of the switch from N2O production to N2 production.

  4. An experimental investigation of gas-particle flows through diffusers in the freeboard region of fluidized beds

    SciTech Connect

    Kale, S.R.; Eaton, J.K.

    1985-09-01

    Results reported in Kale and Eaton showed that very-wide-angle diffusers located in the freeboard above a fluidized bed substantially reduce elutriation--a resul that was contrary to intuition. The present experiment was designed to explain these results. One set of measurements was made with the bed in place and a second set with the bed material removed. The flow structure was drastically altered by the presence of the fluidized bed below the diffuser. A simple analysis suggests that suspended particles in the diffuser flow are responsible for the change in the flow structure. Momentum loss from the gas to the suspended particles reduces the pressure gradient, thereby eliminating the tendency to separate.

  5. Influence of environmental variables on diffusive greenhouse gas fluxes at hydroelectric reservoirs in Brazil.

    PubMed

    Rogério, J P; Santos, M A; Santos, E O

    2013-11-01

    For almost two decades, studies have been under way in Brazil, showing how hydroelectric reservoirs produce biogenic gases, mainly methane (CH4) and carbon dioxide (CO2), through the organic decomposition of flooded biomass. This somewhat complex phenomenon is due to a set of variables with differing levels of interdependence that directly or indirectly affect greenhouse gas (GHG) emissions. The purpose of this paper is to determine, through a statistical data analysis, the relation between CO2, CH4 diffusive fluxes and environmental variables at the Furnas, Itumbiara and Serra da Mesa hydroelectric reservoirs, located in the Cerrado biome on Brazil's high central plateau. The choice of this region was prompted by its importance in the national context, covering an area of some two million square kilometers, encompassing two major river basins (Paraná and Tocantins-Araguaia), with the largest installed power generation capacity in Brazil, together accounting for around 23% of Brazilian territory. This study shows that CH4 presented a moderate negative correlation between CO2 and depth. Additionally, a moderate positive correlation was noted for pH, water temperature and wind. The CO2 presented a moderate negative correlation for pH, wind speed, water temperature and air temperature. Additionally, a moderate positive correlation was noted for CO2 and water temperature. The complexity of the emission phenomenon is unlikely to occur through a simultaneous understanding of all the factors, due to difficulties in accessing and analyzing all the variables that have real, direct effects on GHG production and emission.

  6. Agar disk diffusion (Bauer-Kirby) tests with various fastidious and nonfastidious reference (ATCC) strains: comparison of several agar media.

    PubMed

    Traub, W H; Leonhard, B

    1994-01-01

    Several agar media (Mueller-Hinton agar, MHA; diagnostic sensitivity test agar, DSTA; Schaedler agar, SchA; Todd-Hewitt agar with added yeast extract, THYA; Wilkins-Chalgren agar, WCA) were compared using the Bauer-Kirby agar disk diffusion test against six nonfastidious quality control strains: Staphylococcus aureus ATCC 25923 and ATCC 29213, Escherichia coli ATCC 25922 and ATCC 35218, Pseudomonas aeruginosa ATCC 27853, and Enterococcus faecalis ATCC 29212. MHA, DSTA, and THYA yielded essentially comparable inhibition zones. However, WCA and SchA antagonized cotrimoxazole and aminoglycoside antibiotics; furthermore, SchA antagonized polymyxin B, and both WCA and SchA antagonized imipenem against the P. aeruginosa strain, but not against the E. coli strains. Sheep blood-MHA (Bl-MHA), WCA, THYA, and DSTA were examined with Streptococcus pyogenes ATCC 19615, Streptococcus agalactiae ATCC 13813, and Streptococcus pneumoniae ATCC 6306. In comparison with Bl-MHA, both WCA and THYA yielded comparable inhibition zones against S. pyogenes; DSTA afforded suboptimal growth. DSTA yielded larger inhibition zones with the majority of antimicrobial drugs against S. agalactiae, whereas WCA and THYA enhanced the activity of oxacillin and penicillin G against this strain. S. pneumoniae strain ATCC 6306 grew well on Bl-MHA, yielded suboptimal growth on WCA and faint growth on THYA, and failed to grow on DSTA. Chocolate-supplemented sheep blood-MHA (CHOC-MHA) was compared with Haemophilus test medium (HTM), WCA with added NAD, and THYA with added hematin and NAD against Haemophilus influenzae strains ATCC 35056 and ATCC 49247. The activities of doxycycline and rifampin were enhanced against both strains by HTM, WCA+NAD, and THYA+hematin+NAD. Only WCA+NAD antagonized cotrimoxazole against both H. influenzae strains, an effect due to thymidine; however, HTM antagonized cotrimoxazole against S. aureus ATCC 25923 and E. coli ATCC 25922. It was concluded that Bl-MHA performed best for

  7. 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.

  8. A diffusion-kinetic model for pulverized-coal combustion and heat-and-mass transfer in a gas stream

    SciTech Connect

    E.A. Boiko; S.V. Pachkovskii

    2008-12-15

    A diffusion-kinetic model for pulverized-coal combustion and heat-and-mass transfer in a gas stream is proposed, and the results of numerical simulation of the burnout dynamics of Kansk-Achinsk coals in the pulverized state at different treatment conditions and different model parameters are presented. The mathematical model describes the dynamics of thermochemical conversion of solid organic fuels with allowance for complex physicochemical phenomena of heat-and-mass exchange between coal particles and the gaseous environment.

  9. Anisotropic diffusion filter based edge enhancement for the segmentation of carotid intima-media layer in ultrasound images using variational level set method without re-initialisation.

    PubMed

    Sumathi, K; Anandh, K R; Mahesh, V; Ramakrishnan, S

    2014-01-01

    In this work an attempt has been made to enhance the edges and segment the boundary of intima-media layer of Common Carotid Artery (CCA) using anisotropic diffusion filter and level set method. Ultrasound B mode longitudinal images of normal and abnormal images of common carotid arteries are used in this study. The images are subjected to anisotropic diffusion filter to generate edge map. This edge map is used as a stopping boundary in variational level set method without re-initialisation to segment the intima-media layer. Geometric features are extracted from this layer and analyzed statistically. Results show that anisotropic diffusion filtering is able to extract the edges in both normal and abnormal images. The obtained edge maps are found to have high contrast and sharp edges. The edge based variational level set method is able to segment the intima-media layer precisely from common carotid artery. The extracted geometrical features such as major axis and extent are found to be statistically significant in differentiating normal and abnormal images. Thus this study seems to be clinically useful in diagnosis of cardiovascular disease.

  10. ICP-MS analysis of fission product diffusion in graphite for High-Temperature Gas-Cooled Reactors

    NASA Astrophysics Data System (ADS)

    Carter, Lukas M.

    Release of radioactive fission products from nuclear fuel during normal reactor operation or in accident scenarios is a fundamental safety concern. Of paramount importance are the understanding and elucidation of mechanisms of chemical interaction, nuclear interaction, and transport phenomena involving fission products. Worldwide efforts to reduce fossil fuel dependence coupled with an increasing overall energy demand have generated renewed enthusiasm toward nuclear power technologies, and as such, these mechanisms continue to be the subjects of vigorous research. High-Temperature Gas-Cooled Reactors (HTGRs or VHTRs) remain one of the most promising candidates for the next generation of nuclear power reactors. An extant knowledge gap specific to HTGR technology derives from an incomplete understanding of fission product transport in major core materials under HTGR operational conditions. Our specific interest in the current work is diffusion in reactor graphite. Development of methods for analysis of diffusion of multiple fission products is key to providing accurate models for fission product release from HTGR core components and the reactor as a whole. In the present work, a specialized diffusion cell has been developed and constructed to facilitate real-time diffusion measurements via ICP-MS. The cell utilizes a helium gas-jet system which transports diffusing fission products to the mass spectrometer using carbon nanoparticles. The setup was designed to replicate conditions present in a functioning HTGR, and can be configured for real-time release or permeation measurements of single or multiple fission products from graphite or other core materials. In the present work, we have analyzed release rates of cesium in graphite grades IG-110, NBG-18, and a commercial grade of graphite, as well as release of iodine in IG-110. Additionally we have investigated infusion of graphite samples with Cs, I, Sr, Ag, and other surrogate fission products for use in release or

  11. Spectral Apparatus with a Cryogenic, High-Throughput, Multipass Gas Cell for Studies of Absorption of Radiation by Gaseous Media

    NASA Astrophysics Data System (ADS)

    Moskalenko, N. I.; Mirumyants, S. O.; Parzhin, S. N.; Dodov, I. R.

    2016-11-01

    Spectral systems with an MKhK-6 cryogenic, high-throughput, multipass gas cell for studying the absorption spectra of gaseous media with high spectral resolution in the 0.1-6 μm range at pressures of 100 to 5·106 Pa and temperatures of 180-300 K are discussed. Their use in measurements of spectral absorption coefficients, temperature dependences of the spectral transmission function, and parameters of spectral absorption lines is examined.

  12. Effect of the PTFE content in the gas diffusion layer on water transport in polymer electrolyte fuel cells (PEFCs)

    NASA Astrophysics Data System (ADS)

    Mortazavi, Mehdi; Tajiri, Kazuya

    2014-01-01

    The dynamic behavior of a liquid water droplet emerging and detaching from the surface of the gas diffusion layer (GDL) is investigated. The droplet growth and detachment are studied for different polytetrafluoroethylene (PTFE) contents within the GDL and for different superficial gas velocities flowing in the gas channel. To simulate the droplet behavior in the cathode and anode of an operating polymer electrolyte fuel cell, separate experiments are conducted with air and hydrogen being supplied in the gas channel, respectively. Both the superficial gas velocity and the PTFE content within the GDL are found to impact the droplet detachment diameter. Increasing the superficial gas velocity increases the drag force applied on the droplet sitting on the GDL surface. It is observed that the droplet detaches at a smaller diameter for higher superficial gas velocities. The droplets also detach at smaller diameters from GDLs with a higher amount of PTFE. Such observation is justified according to two different points of view: (1) heterogeneous through-plane PTFE distribution through the GDL and (2) reduced GDL surface roughness caused by PTFE loading.

  13. 'Averaged' Diffusion of Radiation in Spectral Lines intra Interjacent Plasma-Gas Layer

    SciTech Connect

    Demura, A. V.; Demchenko, G. V.

    2008-10-22

    The approximate model of 'averaged diffusion' for resonance radiation transfer is introduced. It allows to reduce computational efforts preserving satisfactory accuracy while modeling divertor plasmas.

  14. Gas Phase Spectroscopy of Cold PAH Ions: Contribution to the Interstellar Extinction and the Diffuse Interstellar Bands

    NASA Technical Reports Server (NTRS)

    Biennier, L.; Salama, F.; Allamandola, L. J.; Scherer, J. J.; OKeefe, A.

    2002-01-01

    Polycyclic Aromatic Hydrocarbon molecules (PAHs) are ubiquitous in the interstellar medium (ISM) and constitute the building blocks of interstellar dust grains. Despite their inferred important role in mediating the energetic and chemical processes in thc ISM, their exact contribution to the interstellar extinction, and in particular to the diffuse interstellar bands (DIBs) remains unclear. The DIBs are spectral absorption features observed in the line of sight of stars that are obscured by diffuse interstellar clouds. More than 200 bands have been reported to date spanning from the near UV to the near IR with bandwidths ranging from 0.4 to 40 Angstroms (Tielens & Snow 1995). The present consensus is that the DIBs arise from free flying, gas-phase, organic molecules and/or ions that are abundant under the typical conditions reigning in the diffuse ISM. PAHs have been proposed as possible carriers (Allamandola et al. 1985; Leger & DHendecourt 1985). The PAH hypothesis is consistent with the cosmic abundance of Carbon and Hydrogen and with the required photostability of the DIB carriers against the strong VUV radiation field in the diffuse interstellar clouds. A significant fraction of PAHs is expected to be ionized in the diffuse ISM.

  15. Development of a miniaturized diffusive sampler for true breathing-zone sampling and thermal desorption gas chromatographic analysis.

    PubMed

    Lindahl, Roger; Levin, Jan-Olof; Sundgren, Margit

    2009-07-01

    Exposure measurements should be performed as close as possible to the nose and mouth for a more correct assessment of exposure. User-friendly sampling equipment, with a minimum of handling before, during and after measurement, should not affect ordinary work. In diffusive (passive) sampling, no extra equipment as sampling pumps is needed, making the measurements more acceptable to the user. The diffusive samplers are normally attached on a shoulder, on a breast-pocket or on the lapel. There are, however, difficulties if true breathing-zone sampling is to be performed, since available diffusive samplers normally cannot be arranged close to the nose/mouth. The purpose of this work was to study the performance of a miniaturized tube type diffusive sampler attached to a headset for true breathing-zone sampling. The basis for this miniaturization was the Perkin Elmer ATD tube. Both the size of the tube and the amount of adsorbent was decreased for the miniaturized sampler. A special tube holder to be used with a headset was designed for the mini tube. The mini tube is thermally desorbed inside a standard PE tube. The new sampler was evaluated for the determination of styrene, both in laboratory experiments and in field measurements. As reference method, diffusive sampling with standard Perkin Elmer tubes, thermal desorption and gas chromatographic (GC) analysis was used. The sampling rate was determined to 0.356 mL min(-1) (CV 9.6%) and was not significantly affected by concentration, sampling time or relative humidity.

  16. Linking basin-scale and pore-scale gas hydrate distribution patterns in diffusion-dominated marine hydrate systems

    NASA Astrophysics Data System (ADS)

    Nole, Michael; Daigle, Hugh; Cook, Ann E.; Hillman, Jess I. T.; Malinverno, Alberto

    2017-02-01

    The goal of this study is to computationally determine the potential distribution patterns of diffusion-driven methane hydrate accumulations in coarse-grained marine sediments. Diffusion of dissolved methane in marine gas hydrate systems has been proposed as a potential transport mechanism through which large concentrations of hydrate can preferentially accumulate in coarse-grained sediments over geologic time. Using one-dimensional compositional reservoir simulations, we examine hydrate distribution patterns at the scale of individual sand layers (1-20 m thick) that are deposited between microbially active fine-grained material buried through the gas hydrate stability zone (GHSZ). We then extrapolate to two-dimensional and basin-scale three-dimensional simulations, where we model dipping sands and multilayered systems. We find that properties of a sand layer including pore size distribution, layer thickness, dip, and proximity to other layers in multilayered systems all exert control on diffusive methane fluxes toward and within a sand, which in turn impact the distribution of hydrate throughout a sand unit. In all of these simulations, we incorporate data on physical properties and sand layer geometries from the Terrebonne Basin gas hydrate system in the Gulf of Mexico. We demonstrate that diffusion can generate high hydrate saturations (upward of 90%) at the edges of thin sands at shallow depths within the GHSZ, but that it is ineffective at producing high hydrate saturations throughout thick (greater than 10 m) sands buried deep within the GHSZ. Furthermore, we find that hydrate in fine-grained material can preserve high hydrate saturations in nearby thin sands with burial.Plain Language SummaryThis study combines one-, two-, and three-dimensional simulations to explore one potential process by which methane dissolved in water beneath the seafloor can be converted into solid methane hydrate. This work specifically</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014PhDT.......376B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014PhDT.......376B"><span>The effects of inlet temperature and turbulence characteristics on the flow development inside a <span class="hlt">gas</span> turbine exhaust <span class="hlt">diffuser</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bomela, Christian Loangola</p> <p></p> <p>The overall industrial <span class="hlt">gas</span> turbine efficiency is known to be influenced by the pressure recovery in the exhaust system. The design and, subsequently, the performance of an industrial <span class="hlt">gas</span> turbine exhaust <span class="hlt">diffuser</span> largely depend on its inflow conditions dictated by the turbine last stage exit flow state and the restraints of the <span class="hlt">diffuser</span> internal geometry. Recent advances in Computational Fluid Dynamics (CFD) tools and the availability of computer hardware at an affordable cost made the virtual tool a very attractive one for the analysis of fluid flow through devices like a <span class="hlt">diffuser</span>. In this backdrop, CFD analyses of a typical industrial <span class="hlt">gas</span> turbine hybrid exhaust <span class="hlt">diffuser</span>, consisting of an annular <span class="hlt">diffuser</span> followed by a conical portion, have been carried out with the purpose of improving the performance of these thermal devices using an open-source CFD code "OpenFOAM". The first phase in the research involved the validation of the CFD approach using OpenFOAM by comparing CFD results against published benchmark experimental data. The numerical results closely captured the flow reversal and the separated boundary layer at the shroud wall where a steep velocity gradient has been observed. The standard k --epsilon turbulence model slightly over-predicted the mean velocity profile in the casing boundary layer while slightly under-predicted it in the reversed flow region. A reliable prediction of flow characteristics in this region is very important as the presence of the annular <span class="hlt">diffuser</span> inclined wall has the most dominant effect on the downstream flow development. The core flow region and the presence of the hub wall have only a minor influence as reported by earlier experimental studies. Additional simulations were carried out in the second phase to test the veracity of other turbulence models; these include RNG k--epsilon, the SST k--o, and the Spalart-Allmaras turbulence models. It was found that a high resolution case with 47.5 million cells using the SST k</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/834362','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/834362"><span>WETTABILITY ALTERATION OF POROUS <span class="hlt">MEDIA</span> TO <span class="hlt">GAS</span>-WETTING FOR IMPROVING PRODUCTIVITY AND INJECTIVITY IN <span class="hlt">GAS</span>-LIQUID FLOWS</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Abbas Firoozabadi</p> <p>2001-10-15</p> <p>The wettability of Berea and chalk samples for <span class="hlt">gas</span>-oil and <span class="hlt">gas</span>-water fluids were altered from strong liquid-wetting to intermediate <span class="hlt">gas</span>-wetting. Two polymers, FC-722 and FC-759, were used to alter the wettability. FC-759 is soluble in water and some 20 times less expensive than FC-722. <span class="hlt">Gas</span> and liquid relative permeabilities were measured before and after wettability alteration. The results demonstrate a significant increase in liquid-phase relative permeability. <span class="hlt">Gas</span>-phase relative permeability for a fixed saturation may increase or decrease. However, because of the very high liquid mobility and reduced liquid saturation, the <span class="hlt">gas</span> mobility also increases for a fixed pressure drop. A number of liquid injectivity tests were also carried out. The results reveal that the liquid-phase mobility can increase significantly when the wettability of rocks is altered from strong liquid-wetting to intermediate <span class="hlt">gas</span>-wetting. All the results show clearly that the application of wettability alteration to intermediate <span class="hlt">gas</span>-wetting may significantly increase deliverability in <span class="hlt">gas</span> condensate reservoirs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1330173','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1330173"><span>Milestone report: The simulation of radiation driven <span class="hlt">gas</span> <span class="hlt">diffusion</span> in UO<sub>2</sub> at low temperature</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Cooper, Michael William; Kuganathan, Navaratnarajah; Burr, Patrick A; Rushton, Michael J.; Grimes, Robin W; Turbull, James Anthony; Stanek, Christopher Richard; Andersson, Anders David</p> <p>2016-10-24</p> <p>Below 1000 K it is thought that fission <span class="hlt">gas</span> <span class="hlt">diffusion</span> in nuclear fuel during irradiation occurs through atomic mixing due to radiation damage. This is an important process for nuclear reactor performance as it affects fission <span class="hlt">gas</span> release, particularly from the periphery of the pellet where such temperatures are normal. Here we present a molecular dynamics study of Xe and Kr <span class="hlt">diffusion</span> due to irradiation. Thermal spikes and cascades have been used to study the electronic stopping and ballistic phases of damage, respectively. Our results predict that O and Kr exhibit the greatest <span class="hlt">diffusivity</span> and U the least, while Xe lies in between. It is concluded that the ballistic phase does not sufficiently account for the experimentally observed <span class="hlt">diffusion</span>. Preliminary thermal spike calculations indicate that the electronic stopping phase generates greater fission <span class="hlt">gas</span> displacement than the ballistic phase, although further calculation must be carried out to confirm this. A good description of the system by the empirical potentials is important over the very wide temperatures induced during thermal spike and damage cascade simulations. This has motivated the development of a parameter set for <span class="hlt">gas</span>-actinide and <span class="hlt">gas</span>-oxygen interactions that is complementary for use with a recent many-body potential set. A comprehensive set of density functional theory (DFT) calculations were used to study Xe and Kr incorporation at a number of sites in CeO<sub>2</sub>, ThO<sub>2</sub>, UO<sub>2</sub> and PuO<sub>2</sub>. These structures were used to fit a potential, which was used to generate molecular dynamics (MD) configurations incorporating Xe and Kr at 300 K, 1500 K, 3000 K and 5000 K. Subsequent matching to the forces predicted by DFT for these MD configurations was used to refine the potential set. This fitting approach ensured weighted fitting to configurations that are thermodynamically significant over a broad temperature range, while avoiding computationally expensive DFT-MD calculations</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/pages/biblio/1343742-linking-basin-scale-pore-scale-gas-hydrate-distribution-patterns-diffusion-dominated-marine-hydrate-systems','SCIGOV-DOEP'); return false;" href="https://www.osti.gov/pages/biblio/1343742-linking-basin-scale-pore-scale-gas-hydrate-distribution-patterns-diffusion-dominated-marine-hydrate-systems"><span>Linking basin-scale and pore-scale <span class="hlt">gas</span> hydrate distribution patterns in <span class="hlt">diffusion</span>-dominated marine hydrate systems</span></a></p> <p><a target="_blank" href="http://www.osti.gov/pages">DOE PAGES</a></p> <p>Nole, Michael; Daigle, Hugh; Cook, Ann E.; ...</p> <p>2017-02-07</p> <p>The goal of this study is to computationally determine the potential distribution patterns of <span class="hlt">diffusion</span>-driven methane hydrate accumulations in coarse-grained marine sediments. <span class="hlt">Diffusion</span> of dissolved methane in marine <span class="hlt">gas</span> hydrate systems has been proposed as a potential transport mechanism through which large concentrations of hydrate can preferentially accumulate in coarse-grained sediments over geologic time. Using one-dimensional compositional reservoir simulations, we examine hydrate distribution patterns at the scale of individual sand layers (1 to 20 m thick) that are deposited between microbially active fine-grained material buried through the <span class="hlt">gas</span> hydrate stability zone (GHSZ). We then extrapolate to two- dimensional and basin-scalemore » three-dimensional simulations, where we model dipping sands and multilayered systems. We find that properties of a sand layer including pore size distribution, layer thickness, dip, and proximity to other layers in multilayered systems all exert control on <span class="hlt">diffusive</span> methane fluxes toward and within a sand, which in turn impact the distribution of hydrate throughout a sand unit. In all of these simulations, we incorporate data on physical properties and sand layer geometries from the Terrebonne Basin <span class="hlt">gas</span> hydrate system in the Gulf of Mexico. We demonstrate that <span class="hlt">diffusion</span> can generate high hydrate saturations (upward of 90%) at the edges of thin sands at shallow depths within the GHSZ, but that it is ineffective at producing high hydrate saturations throughout thick (greater than 10 m) sands buried deep within the GHSZ. As a result, we find that hydrate in fine-grained material can preserve high hydrate saturations in nearby thin sands with burial.« less</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_19 --> <div id="page_20" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="381"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1998PhDT........93A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1998PhDT........93A"><span>Scalar measurements and analysis of hydrogen <span class="hlt">gas</span> jet <span class="hlt">diffusion</span> flames in normal and microgravity</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Al-Ammar, Khalid Nasser</p> <p></p> <p>The quantitative Rainbow Schlieren Deflectometry (RSD) technique was used for the first time to measure scalar profiles in laminar and transitional hydrogen <span class="hlt">gas</span>-jet <span class="hlt">diffusion</span> flames burning in quiescent air in normal and microgravity. The angular deflection data obtained across the field-of-view by the RSD technique were used with Abel inversion to find the refractive index of the reacting mixture. The refractive index was related to the temperature and oxygen mole using the conserved scalar approach, combined with chemical equilibrium. Probe measurements of temperature and oxygen mole fraction were taken to validate the RSD technique. Good agreement was reached between the probe and RSD measurements in the fuel-lean side of the flame surface. The RSD measurements in the fuel-rich side of the flame were less reliable, in part, because of the measurement uncertainty and the assumption of chemical equilibrium. Contour plots of angular deflection reveal higher radial gradients in normal gravity compared to those in microgravity. Temperature profiles during transition from normal to microgravity in the drop tower were obtained to determine the extent of steady-state microgravity conditions achieved in experiments. The results show that the high temperature regions e.g., the flame surface, reached steady-state prior to the lower temperature regions e.g., the schlieren boundary. The time to reach steady-state decreased as the jet exit Reynolds number was increased. The schlieren boundary did not reach steady-state at low jet exit Reynolds numbers because of the greater influence of gravity. Effects of burner diameter and jet exit Reynolds number on flame shape and scalar profiles in normal and microgravity were evaluated. It was confirmed that the flame height varies linearly with Reynolds number in the laminar cases. Further, the flame height was shown to be independent of gravity within the range of jet-exit Reynolds numbers used (40 to 70). At a given jet</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012PhDT.......308B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012PhDT.......308B"><span><span class="hlt">Gas</span> <span class="hlt">Diffusion</span> Barriers Using Atomic Layer Deposition: A New Calcium Test and Polymer Substrate Effects</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bertrand, Jacob Andrew</p> <p></p> <p>The increasing demand on available energy resources has led to a desire for more energy efficient devices. The wide use of displays in consumer electronics, such as televisions, cell phones, cameras and computers makes them an ideal target for improvement. Organic light-emitting diodes (OLEDs) are a good candidate to replace traditional Si based devices. However, the low work function metals typically used as electrodes in OLEDs are very reactive with water and oxygen. Ultralow permeability <span class="hlt">gas</span> <span class="hlt">diffusion</span> barriers with water vapor transmission rates (WVTRs) as low as <10-6g/(m2*day) are required on the polymers used to fabricate organic electronic and thin film photovoltaic devices. Atomic Layer Deposition (ALD) uses self-limiting surface reactions to deposit thin conformal films. ALD is capable of depositing thin, conformal, high quality barriers. WVTR values as low as ˜5 x 10-5 g/(m2*day) have been measured for Al2O3 ALD films at 38 °C/85% RH using the Ca test with optical transmission probing. The Ca test is a technique with very high sensitivity to measure ultralow WVTRs. This test relies on measuring the oxidation of a Ca metal film by monitoring the change in its optical or electrical properties. However, glass lid control experiments have indicated that the WVTRs measured by the Ca test are limited by H2O permeability through the epoxy seals. Varying results have been reported in the literature using the electrical conductance of Ca to measure permeation. In this work, two approaches were applied to overcome the epoxy edge seal limitations. The first approach was to deposit Al2O 3 ALD barriers directly on Ca metal. While the Al 2O3 ALD barriers were successfully deposited, the measurement of an accurate WVTR was limited by barrier pinholes. The presence of pinholes in the Al2O3 ALD barrier on Ca results in the localized oxidation of the Ca sensor. Heterogeneous degradation of the Ca causes inaccuracies in the conductance of the film. As oxidation regions</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JPS...320..153Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JPS...320..153Y"><span>Microscale characterisation of stochastically reconstructed carbon fiber-based <span class="hlt">Gas</span> <span class="hlt">Diffusion</span> Layers; effects of anisotropy and resin content</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yiotis, Andreas G.; Kainourgiakis, Michael E.; Charalambopoulou, Georgia C.; Stubos, Athanassios K.</p> <p>2016-07-01</p> <p>A novel process-based methodology is proposed for the stochastic reconstruction and accurate characterisation of Carbon fiber-based matrices, which are commonly used as <span class="hlt">Gas</span> <span class="hlt">Diffusion</span> Layers in Proton Exchange Membrane Fuel Cells. The modeling approach is efficiently complementing standard methods used for the description of the anisotropic deposition of carbon fibers, with a rigorous model simulating the spatial distribution of the graphitized resin that is typically used to enhance the structural properties and thermal/electrical conductivities of the composite <span class="hlt">Gas</span> <span class="hlt">Diffusion</span> Layer materials. The model uses as input typical pore and continuum scale properties (average porosity, fiber diameter, resin content and anisotropy) of such composites, which are obtained from X-ray computed microtomography measurements on commercially available carbon papers. This information is then used for the digital reconstruction of realistic composite fibrous matrices. By solving the corresponding conservation equations at the microscale in the obtained digital domains, their effective transport properties, such as Darcy permeabilities, effective <span class="hlt">diffusivities</span>, thermal/electrical conductivities and void tortuosity, are determined focusing primarily on the effects of medium anisotropy and resin content. The calculated properties are matching very well with those of Toray carbon papers for reasonable values of the model parameters that control the anisotropy of the fibrous skeleton and the materials resin content.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/18809078','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/18809078"><span>Flow injection conductometric system with <span class="hlt">gas</span> <span class="hlt">diffusion</span> separation for the determination of Kjeldahl nitrogen in milk and chicken meat.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Junsomboon, Jaroon; Jakmunee, Jaroon</p> <p>2008-10-10</p> <p>A simple flow injection (FI) conductometric system with <span class="hlt">gas</span> <span class="hlt">diffusion</span> separation was developed for the determination of Kjeldahl nitrogen (or proteins) in milk and chicken meat. The sample was digested according to the Kjeldahl standard method and the digest was diluted and directly injected into the donor stream consisting of 4M NaOH. In alkaline medium, ammonium was converted to ammonia, which <span class="hlt">diffused</span> through the PTFE membrane to dissolve in an acceptor stream (water). Dissociation of ammonia caused a change in conductance of the acceptor solution, which was linearly proportional to the concentration of ammonium originally present in the injected solution. A conductometric flow through cell and an amplifier circuit was fabricated, which helped improve sensitivity of the conductometric detection system. With using a plumbing Teflon tape as a <span class="hlt">gas</span> <span class="hlt">diffusion</span> membrane and without thermostating control of the system, a linear calibration graph in range of 10-100mgL(-1) N-NH(4) was obtained, with detection limit of 1mgL(-1) and good precision (relative standard deviation of 0.3% for 11 replicate injections of 50mgL(-1) N-NH(4)). The developed method was validated by the standard Kjeldahl distillation/titration method for the analysis of milk and chicken meat samples. The proposed system had sample throughput of 35h(-1) and consumed much smaller amounts of chemical than the standard method (275mg vs 17.5g of NaOH per analysis, respectively).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JPS...342..393I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JPS...342..393I"><span>Application of a self-supporting microporous layer to <span class="hlt">gas</span> <span class="hlt">diffusion</span> layers of proton exchange membrane fuel cells</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ito, Hiroshi; Heo, Yun; Ishida, Masayoshi; Nakano, Akihiro; Someya, Satoshi; Munakata, Tetsuo</p> <p>2017-02-01</p> <p>The intrinsic effect of properties of a self-supporting microporous layer (MPL) on the performance of proton exchange membrane fuel cells (PEMFCs) is identified. First, a self-supporting MPL is fabricated and applied to a <span class="hlt">gas</span> <span class="hlt">diffusion</span> layer (GDL) of a PEMFC, when the GDL is either an integrated sample composed of a <span class="hlt">gas</span> <span class="hlt">diffusion</span> backing (GDB, i.e., carbon paper) combined with MPL or a sample with only MPL. Cell performance tests reveal that, the same as the MPL fabricated by the coating method, the self-supporting MPL on the GDB improves the cell performance at high current density. Furthermore, the GDL composed only of the MPL (i.e., GDB-free GDL) shows better performance than does the integrated GDB/MPL GDL. These results along with literature data strongly suggest that the low thermal conductivity of MPL induces a high temperature throughout the GDL, and thus vapor <span class="hlt">diffusion</span> is dominant in the transport of product water through the MPL.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/11759510','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/11759510"><span>Highly sensitive determination method for total carbonate in water samples by flow injection analysis coupled with <span class="hlt">gas-diffusion</span> separation.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Oshima, M; Wei, Y; Yamamoto, M; Tanaka, H; Takayanagi, T; Motomizu, S</p> <p>2001-11-01</p> <p>A spectrophotometric method for the determination of total carbonate in water samples was developed. The method is based on the color change of an acid-base indicator in relation to the concentration of permeable <span class="hlt">gas</span> substances through a membrane. By using a new portable FIA system equipped with a <span class="hlt">gas-diffusion</span> unit, a highly sensitive and on-site determination of total carbonate in aqueous solutions was investigated. A new color-change system with 4-(2',4'-dinitrophenylazo)-1-naphthol-5-sulfonic acid (DNN5S) was developed. Absorbance changes of the reagent solution were measured at 450 nm with a light-emitting diode (LED) as a light source. A new type of <span class="hlt">gas-diffusion</span> unit was used, and was constructed with double tubing: the inner tubing was a micro porous PTFE (polytetrafluoroethylene) tubing (1.0 mm inner diameter and 1.8 mm outer diameter, pore size 2 microns, porosity 50%); the outer tubing was made of glass with 2.0 mm inner diameter. The optimized system conditions were as follows: the sample size was 200 microliters, the temperature of the air bath for the <span class="hlt">gas-diffusion</span> unit was 25 degrees C, and the length of the <span class="hlt">gas-diffusion</span> unit was 15 cm; each flow rate was 0.3 ml min-1. For measuring carbonate at low concentrations, a method for preparing water with less carbonate was proposed: the carbonate content of the water was decreased down to 5 x 10(-7) M. The calibration graph was rectilinear from 1 x 10(-6) M to 10(-3) M, and the detection limit (corresponding to a signal-to-noise ratio of 3) was 1 x 10(-6) M of carbonate. The relative standard deviation (RSD) of ten measurements of 2.3 x 10(-5) M Na2CO3 solution was 1.9%. The total carbonate in various kinds of water (such as river, sea, rain, distilled and ultra purified) was determined.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19950005461','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19950005461"><span>Analysis and design of numerical schemes for <span class="hlt">gas</span> dynamics. 2: Artificial <span class="hlt">diffusion</span> and discrete shock structure</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Jameson, Antony</p> <p>1994-01-01</p> <p>The effect of artificial <span class="hlt">diffusion</span> on discrete shock structures is examined for a family of schemes which includes scalar <span class="hlt">diffusion</span>, convective upwind and split pressure (CUSP) schemes, and upwind schemes with characteristics splitting. The analysis leads to conditions on the <span class="hlt">diffusive</span> 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 <span class="hlt">diffusion</span>. 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009APS..DMP.Y1118M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009APS..DMP.Y1118M"><span>Probing sub-alveolar length scales with hyperpolarized-<span class="hlt">gas</span> <span class="hlt">diffusion</span> NMR</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Miller, Wilson; Carl, Michael; Mooney, Karen; Mugler, John; Cates, Gordon</p> <p>2009-05-01</p> <p><span class="hlt">Diffusion</span> MRI of the lung is a promising technique for detecting alterations of normal lung microstructure in diseases such as emphysema. The length scale being probed using this technique is related to the time scale over which the helium-3 or xenon-129 <span class="hlt">diffusion</span> is observed. We have developed new MR pulse sequence methods for making <span class="hlt">diffusivity</span> measurements at sub-millisecond <span class="hlt">diffusion</span> times, allowing one to probe smaller length scales than previously possible in-vivo, and opening the possibility of making quantitative measurements of the ratio of surface area to volume (S/V) in the lung airspaces. The quantitative accuracy of simulated and experimental measurements in microstructure phantoms will be discussed, and preliminary in-vivo results will be presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22606993','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22606993"><span>Improved characterization of <span class="hlt">gas</span>-particle partitioning for per- and polyfluoroalkyl substances in the atmosphere using annular <span class="hlt">diffusion</span> denuder samplers.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ahrens, Lutz; Harner, Tom; Shoeib, Mahiba; Lane, Douglas A; Murphy, Jennifer G</p> <p>2012-07-03</p> <p><span class="hlt">Gas</span>-phase perfluoroalkyl carboxylic acids (PFCAs) sorb strongly on filter material (i.e., GFF, QFF) used in conventional high volume air samplers, which results in an overestimation of the particle-phase concentration. In this study, we investigated an improved technique for measuring the <span class="hlt">gas</span>-particle partitioning of per- and polyfluoroalkyl substances (PFASs) using an annular <span class="hlt">diffusion</span> denuder sampler. Samples were analyzed for 7 PFAS classes [i.e., PFCAs, perfluoroalkane sulfonic acids (PFSAs), fluorotelomer alcohols (FTOHs), fluorotelomer methacrylates (FTMACs), fluorotelomer acrylates (FTACs), perfluorooctane sulfonamides (FOSAs), and perfluorooctane sulfonamidoethanols (FOSEs)]. The measured particulate associated fraction (Φ') using the <span class="hlt">diffusion</span> denuder sampler generally followed the trend FTACs (0%) < FTOHs (~8%) < FOSAs (~21%) < PFSAs (~29%) < FOSEs (~66%), whereas the Φ' of the C(8)-C(18) PFCAs increased with carbon chain length, and ranged from 6% to 100%. The ionizability of some PFASs, when associated with particles, is an important consideration when calculating the <span class="hlt">gas</span>-particle partitioning coefficient as both ionic and neutral forms can be present in the particles. Here we differentiate between a <span class="hlt">gas</span>-particle partitioning coefficient for neutral species, K(p), and one that accounts for both ionic and neutral species of a compound, K(p)'. The measured K(p)' for PFSAs and PFCAs was 4-5 log units higher compared to the interpolated K(p) for the neutral form only. The measured K(p)' can be corrected (to apply to the neutral form only) with knowledge of the pK(a) of the chemical and the pH of the condensed medium ("wet" particle or aqueous aerosol). The denuder-based sampling of PFASs has yielded a robust data set that demonstrates the importance of atmospheric pH and chemical pK(a) values in determining <span class="hlt">gas</span>-particle partitioning of PFASs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/18587976','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/18587976"><span>Control of interspecies electron transfer flow during anaerobic digestion: dynamic <span class="hlt">diffusion</span> reaction models for hydrogen <span class="hlt">gas</span> transfer in microbial flocs.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ozturk, S S; Palsson, B O; Thiele, J H</p> <p>1989-02-05</p> <p>Dynamic reaction <span class="hlt">diffusion</span> models were used to analyze the consequences of aggregation for syntrophic reactions in methanogenic ecosystems. Flocs from a whey digestor were used to measure all model parameters under the in situ conditions of a particular defined biological system. Fermentation simulations without adjustable parameters could precisely predict the kinetics of H(2) <span class="hlt">gas</span> production of digestor flocs during syntrophic methanogenesis from ethanol. The results demonstrated a kinetic compartmentalization of H(2) metabolism inside the flocs. The interspecies electron transfer reaction was mildly <span class="hlt">diffusion</span> controlled. The H(2) <span class="hlt">gas</span> profiles across the flocs showed high H (2) concentrations inside the flocs at any time. Simulations of the syntrophic metabolism at low substrate concentrations such as in digestors or sediments showed that it is impossible to achieve high H(2) <span class="hlt">gas</span> turnovers at simultaneously low steady-state H(2) concentrations. This showed a mechanistic contradiction in the concept of postulated low H(2) microenvironments for the anaerobic digestion process. The results of the computer experiments support the conclusion that syntrophic H(2) production may only be a side reaction of H(2) independent interspecies electron transfer in methanogenic ecosystems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3933172','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3933172"><span>A multiscale MD–FE model of <span class="hlt">diffusion</span> in composite <span class="hlt">media</span> with internal surface interaction based on numerical homogenization procedure</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Kojic, M.; Milosevic, M.; Kojic, N.; Kim, K.; Ferrari, M.; Ziemys, A.</p> <p>2014-01-01</p> <p>Mass transport by <span class="hlt">diffusion</span> within composite materials may depend not only on internal microstructural geometry, but also on the chemical interactions between the transported substance and the material of the microstructure. Retrospectively, there is a gap in methods and theory to connect material microstructure properties with macroscale continuum <span class="hlt">diffusion</span> characteristics. Here we present a new hierarchical multiscale model for <span class="hlt">diffusion</span> within composite materials that couples material microstructural geometry and interactions between <span class="hlt">diffusing</span> particles and the material matrix. This model, which bridges molecular dynamics (MD) and the finite element (FE) method, is employed to construct a continuum <span class="hlt">diffusion</span> model based on a novel numerical homogenization procedure. The procedure is general and robust for evaluating constitutive material parameters of the continuum model. These parameters include the traditional bulk <span class="hlt">diffusion</span> coefficients and, additionally, the distances from the solid surface accounting for surface interaction effects. We implemented our models to glucose <span class="hlt">diffusion</span> through the following two geometrical/material configurations: tightly packed silica nanospheres, and a complex fibrous structure surrounding nanospheres. Then, rhodamine 6G <span class="hlt">diffusion</span> analysis through an aga-rose gel network was performed, followed by a model validation using our experimental results. The microstructural model, numerical homogenization and continuum model offer a new platform for modeling and predicting mass <span class="hlt">diffusion</span> through complex biological environment and within composite materials that are used in a wide range of applications, like drug delivery and nanoporous catalysts. PMID:24578582</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2548071','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2548071"><span>Determination of total carbon dioxide in beer and soft drinks by <span class="hlt">gas</span> <span class="hlt">diffusion</span> and flow injection analysis</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Ljunggren, Esbjörn; Karlberg, Bo</p> <p>1995-01-01</p> <p>A <span class="hlt">gas</span> <span class="hlt">diffusion</span> FIA method for determination of total CO2 in beer and in soft drinks is described. The composition of the acceptor stream for <span class="hlt">diffused</span> carbon dioxide is critical. Bromocresol purple has been selecled among a large number of tested pH indicators and if the detection is made at a wavelength of 430 nm, stable baseline conditions and positive deflections of the resulting FIA peaks are obtained. The selected indicator is combined with a linear pH buffer. A simple and practical graphical method for determining a suitable starting pH of the acceptor stream, as well as the expected dynamic range and the linearity of the calibration graph, is presented. PMID:18925022</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012EGUGA..1411390T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012EGUGA..1411390T"><span><span class="hlt">Gas</span> transport processes in sea ice: How convection and <span class="hlt">diffusion</span> processes might affect biological imprints, a challenge for modellers</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tison, J.-L.; Zhou, J.; Thomas, D. N.; Rysgaard, S.; Eicken, H.; Crabeck, O.; Deleu, F.; Delille, B.</p> <p>2012-04-01</p> <p>Recent data from a year-round survey of landfast sea ice growth in Barrow (Alaska) have shown how O2/N2 and O2/Ar ratios could be used to pinpoint primary production in sea ice and derive net productivity rates from the temporal evolution of the oxygen concentration at a given depth within the sea ice cover. These rates were however obtained surmising that neither convection, nor <span class="hlt">diffusion</span> had affected the <span class="hlt">gas</span> concentration profiles in the ice between discrete ice core collections. This paper discusses examples from three different field surveys (the above-mentioned Barrow experiment, the INTERICE IV tank experiment in Hamburg and a short field survey close to the Kapisilit locality in the South-East Greenland fjords) where convection or <span class="hlt">diffusion</span> processes have clearly affected the temporal evolution of the <span class="hlt">gas</span> profiles in the ice, therefore potentially affecting biological signatures. The INTERICE IV and Barrow experiment show that the initial equilibrium dissolved <span class="hlt">gas</span> entrapment within the skeletal layer basically governs most of the profiles higher up in the sea ice cover during the active sea ice growth. However, as the ice layers age and cool down under the temperature gradient, bubble nucleation occurs while the concentration in the ice goes well above the theoretical one, calculated from brine equilibrium under temperature and salinity changes and observed brine volumes. This phase change locks the gases within the sea ice structure, preventing "degassing" of the ice, as is observed for salts under the mushy layer brine convection process. In some cases, mainly in the early stages of the freezing process (first 10-20 cm) where temperature gradients are strong and the ice still permeable on its whole thickness, repeated convection and bubble nucleation can actually increase the <span class="hlt">gas</span> concentration in the ice above the one initially acquired within the skeletal layer. Convective processes will also occur on ice decay, when ice permeability is restored and the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2001GeCoA..65.2723Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2001GeCoA..65.2723Z"><span>Experimental investigation on the carbon isotope fractionation of methane during <span class="hlt">gas</span> migration by <span class="hlt">diffusion</span> through sedimentary rocks at elevated temperature and pressure</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, Tongwei; Krooss, Bernhard M.</p> <p>2001-09-01</p> <p>Molecular transport (<span class="hlt">diffusion</span>) of methane in water-saturated sedimentary rocks results in carbon isotope fractionation. In order to quantify the <span class="hlt">diffusive</span> isotope fractionation effect and its dependence on total organic carbon (TOC) content, experimental measurements have been performed on three natural shale samples with TOC values ranging from 0.3 to 5.74%. The experiments were conducted at 90°C and fluid pressures of 9 MPa (90 bar). Based on the instantaneous and cumulative composition of the <span class="hlt">diffused</span> methane, effective <span class="hlt">diffusion</span> coefficients of the 12CH 4 and 13CH 4 species, respectively, have been calculated. Compared with the carbon isotopic composition of the source methane (δ 13C 1 = -39.1‰), a significant depletion of the heavier carbon isotope ( 13C) in the <span class="hlt">diffused</span> methane was observed for all three shales. The degree of depletion is highest during the initial non-steady state of the <span class="hlt">diffusion</span> process. It then gradually decreases and reaches a constant difference (Δ δ = δ 13C diff -δ 13C source) when approaching the steady-state. The degree of the isotopic fractionation of methane due to molecular <span class="hlt">diffusion</span> increases with the TOC content of the shales. The carbon isotope fractionation of methane during molecular migration results practically exclusively from differences in molecular mobility (effective <span class="hlt">diffusion</span> coefficients) of the 12CH 4 and 13CH 4 entities. No measurable solubility fractionation was observed. The experimental isotope-specific <span class="hlt">diffusion</span> data were used in two hypothetical scenarios to illustrate the extent of isotopic fractionation to be expected as a result of molecular transport in geological systems with shales of different TOC contents. The first scenario considers the progression of a <span class="hlt">diffusion</span> front from a constant source (<span class="hlt">gas</span> reservoir) into a homogeneous "semi-infinite" shale caprock over a period of 10 Ma. In the second example, <span class="hlt">gas</span> <span class="hlt">diffusion</span> across a 100 m caprock sequence is analyzed in terms of absolute quantities</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007MicST..19...22S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007MicST..19...22S"><span>Effect of micro gravity on the product selectivity of dichlorodifluoromethane electrolysis at metal supported <span class="hlt">gas</span> <span class="hlt">diffusion</span> electrodes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sonoyama, Noriyuki</p> <p>2007-12-01</p> <p>The micro gravity effect on the product selectivity of electrochemical reduction of CCl2 F2 (CFC-12) was studied using the metal supported <span class="hlt">gas</span> <span class="hlt">diffusion</span> electrodes (GDEs). Under the micro gravity, the current efficiency for methane formation (the final product) increased, whereas that for CHClF2formation (a intermediate product) decreased at the Cu-supported GDE compared with the result under the normal gravity. This result suggests that the convection has an influence on the product selectivity for electrochemical reaction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2001CPL...348..175B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2001CPL...348..175B"><span>Time evolution analysis of a 2D solid <span class="hlt">gas</span> equilibrium: a model system for molecular adsorption and <span class="hlt">diffusion</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Berner, S.; Brunner, M.; Ramoino, L.; Suzuki, H.; Güntherodt, H.-J.; Jung, T. A.</p> <p>2001-11-01</p> <p>The adsorption of sub-phthalocyanine molecules on Ag(1 1 1) has been studied by means of scanning tunneling microscopy (STM). The molecules are observed in different two-dimensional (2D) phases of adsorption which coexist in thermodynamic equilibrium. In the condensed phase the molecules form well-ordered islands with a honeycomb pattern. In the <span class="hlt">gas</span> phase single molecules can be discriminated in single scan lines by characteristic tip excursions which occur randomly. The energy barrier for surface <span class="hlt">diffusion</span> as well as the condensation energy to form 2D islands is estimated and discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009APS..MARZ26005R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009APS..MARZ26005R"><span>Effects of inhomogeneous partial absorption and the geometry of the boundary on the population evolution of molecules <span class="hlt">diffusing</span> in general porous <span class="hlt">media</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ryu, Seungoh; Johnson, David L.</p> <p>2009-03-01</p> <p>We consider the <span class="hlt">diffusion</span>-relaxation dynamics in porous <span class="hlt">media</span> with partially absorbing boundary conditions. Spectral analysis of Helmholtz equation for the uniform boundary condition has been widely used as a probe of geometry of the medium. The NMR relaxation of the fluid magnetization, for example, is used for a variety of <span class="hlt">media</span> such as rocks, cement, bones, and cheese. While direct relationship between their geometry and the spectrum forms the basis for such applications, little attention has been paid to the spatial variation of the boundary condition. We report on the way the geometry and such inhomogeneity become intertwined and affect the spectrum. It is often impossible to gauge how severe such interference is in the biological or geophysical experiments. We develop a perturbative theory and numerical techniques and test for cases for which exact solution is obtained.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA538078','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA538078"><span>Experimental and Computational Investigation of a <span class="hlt">Gas</span> Laser Pressure Recovery System <span class="hlt">Diffuser</span></span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>2011-02-08</p> <p>device. In many cases a passive supersonic <span class="hlt">diffuser</span> followed by a steam-driven ejector is used to increase the pressure. In a supersonic <span class="hlt">diffuser</span>, the...5 10 I- CFD Analysis Results , Pexit-1Otorr I • Experimental Data, Pexit=1 0.0 torr .. / ~ ~ ~ ’-I;"" 15 20 Position (in) 25 30 35 Figure 10...cavity boundary layers. 35 30 25 ’F 20 g ~ ::J .. .. ~ 15 Q. 10 o ~ . V~ ••• ~ .... . 10 l- eFD Analysis Results , Pexit=20torr I</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/379955','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/379955"><span>Experimental and numerical investigation of shock wave propagation through complex geometry, <span class="hlt">gas</span> continuous, two-phase <span class="hlt">media</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Liu, James Chien-Chih</p> <p>1993-01-01</p> <p>The work presented here investigates the phenomenon of shock wave propagation in <span class="hlt">gas</span> continuous, two-phase <span class="hlt">media</span>. The motivation for this work stems from the need to understand blast venting consequences in the HYLIFE inertial confinement fusion (ICF) reactor. The HYLIFE concept utilizes lasers or heavy ion beams to rapidly heat and compress D-T targets injected into the center of a reactor chamber. A segmented blanket of failing molten lithium or Li<sub>2</sub>BeF<sub>4</sub> (Flibe) jets encircles the reactors central cavity, shielding the reactor structure from radiation damage, absorbing the fusion energy, and breeding more tritium fuel.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006JPS...160.1041Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006JPS...160.1041Z"><span>Effects of porosity distribution variation on the liquid water flux through <span class="hlt">gas</span> <span class="hlt">diffusion</span> layers of PEM fuel cells</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhan, Zhigang; Xiao, Jinsheng; Li, Dayong; Pan, Mu; Yuan, Runzhang</p> <p></p> <p>Flooding of the membrane electrode assembly (MEA) and dehydrating of the polymer electrolyte membrane have been the key problems to be solved for polymer electrolyte membrane fuel cells (PEMFCs). So far, almost no papers published have focused on studies of the liquid water flux through differently structured <span class="hlt">gas</span> <span class="hlt">diffusion</span> layers (GDLs). For <span class="hlt">gas</span> <span class="hlt">diffusion</span> layers including structures of uniform porosity, changes in porosity (GDL with microporous layer (MPL)) and gradient change porosity, using a one-dimensional model, the liquid saturation distribution is analyzed based on the assumption of a fixed liquid water flux through the GDL. And then the liquid water flux through the GDL is calculated based on the assumption of a fixed liquid saturation difference between the interfaces of the catalyst layer/GDL and the GDL/<span class="hlt">gas</span> channel. Our results show that under steady-state conditions, the liquid water flux through the GDL increases as contact angle and porosity increase and as the GDL thickness decreases. When a MPL is placed between the catalyst layer and the GDL, the liquid saturation is redistributed across the MPL and GDL. This improves the liquid water draining performance. The liquid water flux through the GDL increases as the MPL porosity increases and the MPL thickness decreases. When the total thickness of the GDL and MPL is kept constant and when the MPL is thinned to 3 μm, the liquid water flux increases considerably, i.e. flooding of MEA is difficult. A GDL with a gradient of porosity is more favorable for liquid water discharge from catalyst layer into the <span class="hlt">gas</span> channel; for the GDLs with the same equivalent porosity, the larger the gradient is, the more easily the liquid water is discharged. Of the computed cases, a GDL with a linear porosity 0.4 x + 0.4 is the best.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_20 --> <div id="page_21" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="401"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006SPIE.6367E..0KC','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006SPIE.6367E..0KC"><span>DSA laser measurements and atmospheric <span class="hlt">diffusion</span> models for the estimation of the <span class="hlt">gas</span> emission flux by spot source fields: methods and experimental results</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cuccoli, Fabrizio; Facheris, Luca; Vaselli, Orlando</p> <p>2006-09-01</p> <p>A simple method for estimating the <span class="hlt">gas</span> emission flux by spot source fields based on IR laser measurements and atmospheric <span class="hlt">diffusion</span> models is presented. The method is based on a proper arrangement of the optical links around the emission area, over which the determination of the <span class="hlt">gas</span> integral concentration is required. The first objective of such measurements is to tune the parameters of a basic <span class="hlt">diffusion</span> model in order to estimate, as second objective, the <span class="hlt">gas</span> emission flux by applying the tuned model to experimental measurements. After discussing the proposed model and method, experimental data obtained from some CO II-rich natural discharges in Tuscany (Central Italy) are presented</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1991PhDT........20B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1991PhDT........20B"><span>Determination of <span class="hlt">diffusion</span> parameters of thermal neutrons for non-moderator <span class="hlt">media</span> by a pulsed method and a time independent method</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Boufraqech, A.</p> <p>1991-02-01</p> <p>Two methods for determining the <span class="hlt">diffusion</span> parameters of thermal neutrons for non-moderator and non-multiplicator <span class="hlt">media</span> have been developed. The first one, which is a pulsed method, is based on thermal neutrons relaxation coefficients measurement in a moderator, with and without the medium of interest that plays the role of reflector. For the experimental results interpretation using the <span class="hlt">diffusion</span> theory, a corrective factor which takes into account the neutron cooling by <span class="hlt">diffusion</span> has been introduced. Its dependence on the empirically obtained relaxation coefficients is in a good agreement with the calculations made in P3L2 approximation. The difference between linear extrapolation lengths of the moderator and the reflector has been taken into account, by developing the scalar fluxes in Bessel function series which automatically satisfy the boundary conditions at the extrapolated surfaces of the two <span class="hlt">media</span>. The obtained results for iron are in a good agreement with those in the literature. The second method is time independent, based on the 'flux albedo' measurements interpretation (concept introduced by Amaldi and Fermi) by P3 approximation in the one group transport theory. The independent sources are introduced in the Marshak boundary conditions. An angular albedo matrix has been used to deal with multiple reflections and to take into account the distortion of the current vector when entering a medium, after being reflected by this latter. The results obtained by this method are slightly different from those given in the literature. The analysis of the possible sources causing this discrepancy, particulary the radial distribution of flux in cylindrical geometry and the flux depression at medium-black body interface, has shown that the origin of this discrepancy is the neutron heating by <span class="hlt">diffusion</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26938707','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26938707"><span>Benchmarking Rapid TLES Simulations of <span class="hlt">Gas</span> <span class="hlt">Diffusion</span> in Proteins: Mapping O2 Migration and Escape in Myoglobin as a Case Study.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Shadrina, Maria S; English, Ann M; Peslherbe, Gilles H</p> <p>2016-04-12</p> <p>Standard molecular dynamics (MD) simulations of <span class="hlt">gas</span> <span class="hlt">diffusion</span> consume considerable computational time and resources even for small proteins. To combat this, temperature-controlled locally enhanced sampling (TLES) examines multiple <span class="hlt">diffusion</span> trajectories per simulation by accommodating multiple noninteracting copies of a <span class="hlt">gas</span> molecule that <span class="hlt">diffuse</span> independently, while the protein and water molecules experience an average interaction from all copies. Furthermore, <span class="hlt">gas</span> migration within a protein matrix can be accelerated without altering protein dynamics by increasing the effective temperature of the TLES copies. These features of TLES enable rapid simulations of <span class="hlt">gas</span> <span class="hlt">diffusion</span> within a protein matrix at significantly reduced (∼98%) computational cost. However, the results of TLES and standard MD simulations have not been systematically compared, which limits the adoption of the TLES approach. We address this drawback here by benchmarking TLES against standard MD in the simulation of O2 <span class="hlt">diffusion</span> in myoglobin (Mb) as a case study since this model system has been extensively characterized. We find that 2 ns TLES and 108 ns standard simulations map the same network of <span class="hlt">diffusion</span> tunnels in Mb and uncover the same docking sites, barriers, and escape portals. We further discuss the influence of simulation time as well as the number of independent simulations on the O2 population density within the <span class="hlt">diffusion</span> tunnels and on the sampling of Mb's conformational space as revealed by principal component analysis. Overall, our comprehensive benchmarking reveals that TLES is an appropriate and robust tool for the rapid mapping of <span class="hlt">gas</span> <span class="hlt">diffusion</span> in proteins when the kinetic data provided by standard MD are not required. Furthermore, TLES provides explicit ligand <span class="hlt">diffusion</span> pathways, unlike most rapid methods.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JMagR.273..124B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JMagR.273..124B"><span><span class="hlt">Diffusion</span>-mediated 129Xe <span class="hlt">gas</span> depolarization in magnetic field gradients during continuous-flow optical pumping</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Burant, Alex; Branca, Rosa Tamara</p> <p>2016-12-01</p> <p>The production of large volumes of highly polarized noble gases like helium and xenon is vital to applications of magnetic resonance imaging and spectroscopy with hyperpolarized (HP) <span class="hlt">gas</span> in humans. In the past ten years, 129Xe has become the <span class="hlt">gas</span> of choice due to its lower cost, higher availability, relatively high tissue solubility, and wide range of chemical shift values. Though near unity levels of xenon polarization have been achieved in-cell using stopped-flow Spin Exchange Optical Pumping (SEOP), these levels are currently unmatched by continuous-flow SEOP methods. Among the various mechanisms that cause xenon relaxation, such as persistent and transient xenon dimers, wall collisions, and interactions with oxygen, relaxation due to <span class="hlt">diffusion</span> in magnetic field gradients, caused by rapidly changing magnetic field strength and direction, is often ignored. However, during continuous-flow SEOP production, magnetic field gradients may not have a negligible contribution, especially considering that this methodology requires the combined use of magnets with very different characteristics (low field for spin exchange optical pumping and high field for the reduction of xenon depolarization in the solid state during the freeze out phase) that, when placed together, inevitably create magnetic field gradients along the <span class="hlt">gas</span>-flow-path. Here, a combination of finite element analysis and Monte Carlo simulations is used to determine the effect of such magnetic field gradients on xenon <span class="hlt">gas</span> polarization with applications to a specific, continuous-flow hyperpolarization system.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27825066','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27825066"><span><span class="hlt">Diffusion</span>-mediated (129)Xe <span class="hlt">gas</span> depolarization in magnetic field gradients during continuous-flow optical pumping.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Burant, Alex; Branca, Rosa Tamara</p> <p>2016-12-01</p> <p>The production of large volumes of highly polarized noble gases like helium and xenon is vital to applications of magnetic resonance imaging and spectroscopy with hyperpolarized (HP) <span class="hlt">gas</span> in humans. In the past ten years, (129)Xe has become the <span class="hlt">gas</span> of choice due to its lower cost, higher availability, relatively high tissue solubility, and wide range of chemical shift values. Though near unity levels of xenon polarization have been achieved in-cell using stopped-flow Spin Exchange Optical Pumping (SEOP), these levels are currently unmatched by continuous-flow SEOP methods. Among the various mechanisms that cause xenon relaxation, such as persistent and transient xenon dimers, wall collisions, and interactions with oxygen, relaxation due to <span class="hlt">diffusion</span> in magnetic field gradients, caused by rapidly changing magnetic field strength and direction, is often ignored. However, during continuous-flow SEOP production, magnetic field gradients may not have a negligible contribution, especially considering that this methodology requires the combined use of magnets with very different characteristics (low field for spin exchange optical pumping and high field for the reduction of xenon depolarization in the solid state during the freeze out phase) that, when placed together, inevitably create magnetic field gradients along the <span class="hlt">gas</span>-flow-path. Here, a combination of finite element analysis and Monte Carlo simulations is used to determine the effect of such magnetic field gradients on xenon <span class="hlt">gas</span> polarization with applications to a specific, continuous-flow hyperpolarization system.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012CoTPh..58..891M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012CoTPh..58..891M"><span><span class="hlt">Diffusive</span> Thermal Conductivity of Superfluid Fermi <span class="hlt">Gas</span> in p-Wave State at Low Temperatures</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>M. Khademi, Dehkordi; Nasirimoghadam, S.; Nabipoor, F.; M. A., Shahzamanian</p> <p>2012-12-01</p> <p>The <span class="hlt">diffusive</span> thermal conductivity tensor of p-wave superfluid at low temperatures is calculated by using the Boltzmann equation approach. We use the Sykes and Brooker procedure and show that Kxx is equal to Kyy and these are related to T-1, also Kzz is proporated to T-3.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/834363','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/834363"><span>WETTABILITY ALTERATION OF POROUS <span class="hlt">MEDIA</span> TO <span class="hlt">GAS</span>-WETTING FOR IMPROVING PRODUCTIVITY AND INJECTIVITY IN <span class="hlt">GAS</span>-LIQUID FLOWS</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Abbas Firoozabadi</p> <p>2002-10-21</p> <p>The authors have performed a number of imbibition tests with the treated and untreated cores in nC{sub 10}, nC{sub 14}, and nC{sub 16} and a natural <span class="hlt">gas</span> condensate liquid. Imbibition tests for nC{sub 14} and nC{sub 16} were also carried out at elevated temperatures of 100 C and 140 C. An experimental polymer synthesized for the purpose of this project was used in core treatment. Imbibition results are very promising and imply liquid condensate mobility enhancement in the treated core. They also performed flow tests to quantify the increase in well deliverability and to simulate flow under realistic field conditions. In the past we have performed extensive testing of wettability alteration in intermediate <span class="hlt">gas</span> wetting for polymer FC759 at temperatures of 24 C and 90 C. The results were promising for the purpose of <span class="hlt">gas</span> well deliverability improvement in <span class="hlt">gas</span> condensate wells. We used FC759 to lower the surface energy of various rocks. The model fluids nC{sub 10}, and nC{sub 14} were used to represent condensate liquid, and air was used as the <span class="hlt">gas</span> phase. A new (L-16349) polymer, which has been recently synthesized for the purpose of the project, was used in the work to be presented here. L-16349 is a water-soluble fluorochemical polymer, with low order, neutral PH and very low volatile organic compound (VOC < 9.1 g/l). It is light yellow in appearance and density in 25% solution is 1.1 g/cc. Polymer L-16349 is very safe from environmental considerations and it is economical for our purpose. In this work, in addition to nC{sub 10}, and nC{sub 14}, we used two other liquids nC{sub 16}, and a liquid condensate in order to study the effect of wettability alteration with a broader range of fluids.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JPS...243...40F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JPS...243...40F"><span>Optimisation of electrophoretic deposition parameters for <span class="hlt">gas</span> <span class="hlt">diffusion</span> electrodes in high temperature polymer electrolyte membrane fuel cells</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Felix, Cecil; Jao, Ting-Chu; Pasupathi, Sivakumar; Pollet, Bruno G.</p> <p>2013-12-01</p> <p>Electrophoretic deposition (EPD) method was used to fabricate <span class="hlt">gas</span> <span class="hlt">diffusion</span> electrodes (GDEs) for high temperature polymer electrolyte membrane fuel cells (HT PEMFC). Parameters related to the catalyst suspension and the EPD process were studied. Optimum suspension conditions are obtained when the catalyst particles are coated with Nafion® ionomer and the pH is adjusted to an alkaline range of about 8-10. These suspensions yield good stability with sufficient conductivity to form highly porous catalyst layers on top of the <span class="hlt">gas</span> <span class="hlt">diffusion</span> layers (GDLs). GDEs were fabricated by applying various electric field strengths of which 100 V cm-1 yields the best membrane electrode assembly (MEA) performance. Compared to an MEA fabricated by the traditional hand sprayed (HS) method, the EPD MEA shows superior performance with a peak power increase of about 73% at similar platinum (Pt) loadings. Electrochemical Impedance Spectroscopy (EIS) analysis shows lower charge transfer resistance for the MEA fabricated via the EPD method compared to the HS MEA. The EPD GDE exhibits a greater total pore area (22.46 m2 g-1) compared to the HS GDE (13.43 m2 g-1) as well as better dispersion of the Pt particles within the catalyst layer (CL).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JPS...336...40L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JPS...336...40L"><span>A critical review on <span class="hlt">gas</span> <span class="hlt">diffusion</span> micro and macroporous layers degradations for improved membrane fuel cell durability</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lapicque, Francois; Belhadj, Mariem; Bonnet, Caroline; Pauchet, Joël; Thomas, Yohann</p> <p>2016-12-01</p> <p>Formerly considered as a secondary component of fuel cell, <span class="hlt">gas</span> <span class="hlt">diffusion</span> layers (GDLs) have been shown to have a key role in <span class="hlt">gas</span> transport to the catalyst layers and in water management: in particular, the microporous layer (MPL) deposited on the <span class="hlt">diffusion</span> substrate has an active part in water distribution in the membrane electrode assembly and in its efficient removal from the cell. In addition to its perfect design for the targeted application and in combination with the macroporous substrate (MPS), the MPL structure and physicochemical properties have to contribute to the cell durability, which is still considered as insufficient for larger, massive commercialisation of this energy conversion system. The paper is aimed at reviewing the main knowledge gained on the role of the MPL on GDL operation and durability, with investigation of degradation phenomena of both MPL and MPS, together with the role played by the MPL in mitigating the occurrence of degradation phenomena that can occur in the whole fuel cell. In addition to the reviewing purpose, original data on ex-situ degradation of GDL are presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22102214','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22102214"><span>Changes in liquid water alter nutrient bioavailability and <span class="hlt">gas</span> <span class="hlt">diffusion</span> in frozen antarctic soils contaminated with petroleum hydrocarbons.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Harvey, Alexis Nadine; Snape, Ian; Siciliano, Steven Douglas</p> <p>2012-02-01</p> <p>Bioremediation has been used to remediate petroleum hydrocarbon (PHC)-contaminated sites in polar regions; however, limited knowledge exists in understanding how frozen conditions influence factors that regulate microbial activity. We hypothesized that increased liquid water (θ(liquid) ) would affect nutrient supply rates (NSR) and <span class="hlt">gas</span> <span class="hlt">diffusion</span> under frozen conditions. If true, management practices that increase θ(liquid) should also increase bioremediation in polar soils by reducing nutrient and oxygen limitations. Influence of θ(liquid) on NSR was determined using diesel-contaminated soil (0-8,000 mg kg(-1)) from Casey Station, Antarctica. The θ(liquid) was altered between 0.007 and 0.035 cm(3) cm(-3) by packing soil cores at different bulk densities. The nutrient supply rate of NH 4+ and NO 3-, as well as <span class="hlt">gas</span> <span class="hlt">diffusion</span> coefficient, D(s), were measured at two temperatures, 21°C and -5°C, to correct for bulk density effects. Freezing decreased NSR of both NH 4+ and NO 3-, with θ(liquid) linked to nitrate and ammonia NSR in frozen soil. Similarly for D(s), decreases due to freezing were much more pronounced in soils with low θ(liquid) compared to soils with higher θ(liquid) contents. Additional studies are needed to determine the relationship between degradation rates and θ(liquid) under frozen conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004JPS...137..183H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004JPS...137..183H"><span>Performance equations for cathodes in polymer electrolyte fuel cells with non-uniform water flooding in <span class="hlt">gas</span> <span class="hlt">diffusers</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hsuen, Hsiao-Kuo</p> <p></p> <p>The performance equations for cathodes of polymer electrolyte fuel cells (PEFCs) that describe the dependence of cathode potential on current density are developed. Formulation of the performance equations starts from the reduction of a one-dimensional model that considers, in detail, the potential losses pertinent to the limitations of electron conduction, oxygen <span class="hlt">diffusion</span>, proton migration, and the oxygen reduction reaction. In particular, non-uniform accumulation of liquid water in the <span class="hlt">gas</span> <span class="hlt">diffuser</span>, which partially blocks the <span class="hlt">gas</span> channels and imposes a greater resistance for oxygen transport, is taken into account. Reduction of the one-dimensional model is implemented by approximating the oxygen concentration profile in the catalyst layer with a parabolic polynomial or a piecewise parabolic one determined by the occurrence of oxygen depletion. The final forms of the equations are obtained by applying the method of weighted residuals over the catalyst layer. The weighting function is selected in such a way that the weighted residuals can be analytically integrated. Potential losses caused by the various limiting processes can be quantitatively estimated by the performance equations. Thus, they provide a convenient diagnostic tool for the cathode performance. Computational results reveal that the performance equations agree well with the original one-dimensional model over an extensive range of parameter values. This indicates that the present performance equations can be used as a substitute for the one-dimensional model to provide quantitatively correct predictions for the cathode performance of PEFCs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26987282','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26987282"><span>CAD/CAM-designed 3D-printed electroanalytical cell for the evaluation of nanostructured <span class="hlt">gas-diffusion</span> electrodes.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Chervin, Christopher N; Parker, Joseph F; Nelson, Eric S; Rolison, Debra R; Long, Jeffrey W</p> <p>2016-04-29</p> <p>The ability to effectively screen and validate <span class="hlt">gas-diffusion</span> electrodes is critical to the development of next-generation metal-air batteries and regenerative fuel cells. The limiting electrode in a classic two-terminal device such as a battery or fuel cell is difficult to discern without an internal reference electrode, but the flooded electrolyte characteristic of three-electrode electroanalytical cells negates the prime function of an air electrode-a void volume freely accessible to gases. The nanostructured catalysts that drive the energy-conversion reactions (e.g., oxygen reduction and evolution in the air electrode of metal-air batteries) are best evaluated in the electrode structure as-used in the practical device. We have designed, 3D-printed, and characterized an air-breathing, thermodynamically referenced electroanalytical cell that allows us to mimic the Janus arrangement of the <span class="hlt">gas-diffusion</span> electrode in a metal-air cell: one face freely exposed to gases, the other wetted by electrolyte.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016Nanot..27q4002C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016Nanot..27q4002C"><span>CAD/CAM-designed 3D-printed electroanalytical cell for the evaluation of nanostructured <span class="hlt">gas-diffusion</span> electrodes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chervin, Christopher N.; Parker, Joseph F.; Nelson, Eric S.; Rolison, Debra R.; Long, Jeffrey W.</p> <p>2016-04-01</p> <p>The ability to effectively screen and validate <span class="hlt">gas-diffusion</span> electrodes is critical to the development of next-generation metal-air batteries and regenerative fuel cells. The limiting electrode in a classic two-terminal device such as a battery or fuel cell is difficult to discern without an internal reference electrode, but the flooded electrolyte characteristic of three-electrode electroanalytical cells negates the prime function of an air electrode—a void volume freely accessible to gases. The nanostructured catalysts that drive the energy-conversion reactions (e.g., oxygen reduction and evolution in the air electrode of metal-air batteries) are best evaluated in the electrode structure as-used in the practical device. We have designed, 3D-printed, and characterized an air-breathing, thermodynamically referenced electroanalytical cell that allows us to mimic the Janus arrangement of the <span class="hlt">gas-diffusion</span> electrode in a metal-air cell: one face freely exposed to gases, the other wetted by electrolyte.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1001648','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1001648"><span>Injection, flow, and mixing of CO2 in porous <span class="hlt">media</span> with residual <span class="hlt">gas</span>.</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Oldenburg, C.M.; Doughty, C.A.</p> <p>2010-09-01</p> <p>Geologic structures associated with depleted natural <span class="hlt">gas</span> reservoirs are desirable targets for geologic carbon sequestration (GCS) as evidenced by numerous pilot and industrial-scale GCS projects in these environments world-wide. One feature of these GCS targets that may affect injection is the presence of residual CH{sub 4}. It is well known that CH{sub 4} drastically alters supercritical CO{sub 2} density and viscosity. Furthermore, residual <span class="hlt">gas</span> of any kind affects the relative permeability of the liquid and <span class="hlt">gas</span> phases, with relative permeability of the <span class="hlt">gas</span> phase strongly dependent on the time-history of imbibition or drainage, i.e., dependent on hysteretic relative permeability. In this study, the effects of residual CH{sub 4} on supercritical CO{sub 2} injection were investigated by numerical simulation in an idealized one-dimensional system under three scenarios: (1) with no residual <span class="hlt">gas</span>; (2) with residual supercritical CO{sub 2}; and (3) with residual CH{sub 4}. We further compare results of simulations that use non-hysteretic and hysteretic relative permeability functions. The primary effect of residual <span class="hlt">gas</span> is to decrease injectivity by decreasing liquid-phase relative permeability. Secondary effects arise from injected <span class="hlt">gas</span> effectively incorporating residual <span class="hlt">gas</span> and thereby extending the mobile <span class="hlt">gas</span> plume relative to cases with no residual <span class="hlt">gas</span>. Third-order effects arise from <span class="hlt">gas</span> mixing and associated compositional effects on density that effectively create a larger plume per unit mass. Non-hysteretic models of relative permeability can be used to approximate some parts of the behavior of the system, but fully hysteretic formulations are needed to accurately model the entire system.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/20338231','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/20338231"><span>Perfusion and <span class="hlt">diffusion</span> limitations in middle ear <span class="hlt">gas</span> exchange: the exchange of CO2 as a test case.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Marcusohn, Yael; Ar, Amos; Dirckx, Joris J J</p> <p>2010-06-14</p> <p>A long standing debate on perfusion/<span class="hlt">diffusion</span> limitations in the context of middle ear (ME) <span class="hlt">gas</span> exchange was revisited using data obtained from previous iso-pressure <span class="hlt">gas</span>-exchange measurements in different mammals. We tried to determine whether the exchange of CO(2) in the ME is limited by perfusion or by <span class="hlt">diffusion</span> by comparing the mass specific cardiac output (msQ) and the mass specific initial CO(2) flow rate into air-washed MEs (msV(i) CO(2)) of rabbits and rats. Based on previously published allometry at rest, the msQ was 0.154 mL/(min g) in rabbits (mean body weight: 2800 g) and 0.259 mL/(min g) in rats (mean body weight: 179.1 g); msV(i) CO(2) (Delta t=0) was 0.109+/-0.047 microL/(h g) in rabbits (n=16) and 0.170+/-0.094 microL/(h g) in rats (n=9). Similar ratios were found when an allometric comparison was made between the ratio of msV(i) CO(2) (Delta t=0) (approximately 0.64), and the ratio of msQs (approximately 0.59) in rabbits and rats. If the active mucosal surface areas of MEs of rabbits and rats are directly proportional to their masses as are the masses of their hearts and if their msQs are proportional to the rates of blood flows in the ME mucosa, these results support the assumption that the exchange of CO(2) in the ME of mammals is mainly perfusion (and not <span class="hlt">diffusion</span>) dependent.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27074933','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27074933"><span>Peclet number analysis of cross-flow in porous <span class="hlt">gas</span> <span class="hlt">diffusion</span> layer of polymer electrolyte membrane fuel cell (PEMFC).</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Suresh, P V; Jayanti, Sreenivas</p> <p>2016-10-01</p> <p>Adoption of hydrogen economy by means of using hydrogen fuel cells is one possible solution for energy crisis and climate change issues. Polymer electrolyte membrane (PEM) fuel cell, which is an important type of fuel cells, suffers from the problem of water management. Cross-flow is induced in some flow field designs to enhance the water removal. The presence of cross-flow in the serpentine and interdigitated flow fields makes them more effective in proper distribution of the reactants on the reaction layer and evacuation of water from the reaction layer than <span class="hlt">diffusion</span>-based conventional parallel flow fields. However, too much of cross-flow leads to flow maldistribution in the channels, higher pressure drop, and membrane dehydration. In this study, an attempt has been made to quantify the amount of cross-flow required for effective distribution of reactants and removal of water in the <span class="hlt">gas</span> <span class="hlt">diffusion</span> layer. Unit cells containing two adjacent channels with <span class="hlt">gas</span> <span class="hlt">diffusion</span> layer (GDL) and catalyst layer at the bottom have been considered for the parallel, interdigitated, and serpentine flow patterns. Computational fluid dynamics-based simulations are carried out to study the reactant transport in under-the-rib area with cross-flow in the GDL. A new criterion based on the Peclet number is presented as a quantitative measure of cross-flow in the GDL. The study shows that a cross-flow Peclet number of the order of 2 is required for effective removal of water from the GDL. Estimates show that this much of cross-flow is not usually produced in the U-bends of Serpentine flow fields, making these areas prone to flooding.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009JPS...194..328K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009JPS...194..328K"><span>Uneven <span class="hlt">gas</span> <span class="hlt">diffusion</span> layer intrusion in <span class="hlt">gas</span> channel arrays of proton exchange membrane fuel cell and its effects on flow distribution</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kandlikar, S. G.; Lu, Z.; Lin, T. Y.; Cooke, D.; Daino, M.</p> <p></p> <p>Intrusion of the <span class="hlt">gas</span> <span class="hlt">diffusion</span> layer (GDL) into <span class="hlt">gas</span> channels due to fuel cell compression has a major impact on the <span class="hlt">gas</span> flow distribution, fuel cell performance and durability. In this work, the effect of compression resulting in GDL intrusion in individual parallel PEMFC channels is investigated. The intrusion is determined using two methods: an optical measurement in both the in-plane and through-plane directions of GDL, as well as an analytical fluid flow model based on individual channel flow rate measurements. The intrusion measurements and estimates obtained from these methods agree well with each other. An uneven distribution of GDL intrusion into individual parallel channels is observed. A non-uniform compression force distribution derived from the clamping bolts causes a higher intrusion in the end channels. The heterogeneous GDL structure and physical properties may also contribute to the uneven GDL intrusion. As a result of uneven intrusion distribution, severe flow maldistribution and increased pressure drop have been observed. The intrusion data can be further used to determine the mechanical properties of GDL materials. Using the finite element analysis software program ANSYS, the Young's modulus of the GDL from these measurements is estimated to be 30.9 MPa.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017ApJ...838..165V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017ApJ...838..165V"><span>Thermal Pressure in <span class="hlt">Diffuse</span> H2 <span class="hlt">Gas</span> Measured by Herschel [C II] Emission and FUSE UV H2 Absorption</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Velusamy, T.; Langer, W. D.; Goldsmith, P. F.; Pineda, J. L.</p> <p>2017-04-01</p> <p>UV absorption studies with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite have made important observations of H2 molecular <span class="hlt">gas</span> in Galactic interstellar translucent and <span class="hlt">diffuse</span> clouds. Observations of the 158 μm [C ii] fine-structure line with Herschel trace the same H2 molecular <span class="hlt">gas</span> in emission. We present [C ii] observations along 27 lines of sight (LOSs) toward target stars of which 25 have FUSE H2 UV absorption. Two stars have only HST STIS C ii λ2325 absorption data. We detect [C ii] 158 μm emission features in all but one target LOS. For three target LOSs that are close to the Galactic plane, | {\\text{}}b| < 1°, we also present position–velocity maps of [C ii] emission observed by Herschel Heterodyne Instrument in the Far Infrared (HIFI) in on-the-fly spectral-line mapping. We use the velocity-resolved [C ii] spectra observed by the HIFI instrument toward the target LOSs observed by FUSE to identify [C ii] velocity components associated with the H2 clouds. We analyze the observed velocity integrated [C ii] spectral-line intensities in terms of the densities and thermal pressures in the H2 <span class="hlt">gas</span> using the H2 column densities and temperatures measured by the UV absorption data. We present the H2 <span class="hlt">gas</span> densities and thermal pressures for 26 target LOSs and from the [C ii] intensities derive a mean thermal pressure in the range of ∼6100–7700 K cm‑3 in <span class="hlt">diffuse</span> H2 clouds. We discuss the thermal pressures and densities toward 14 targets, comparing them to results obtained using the UV absorption data for two other tracers C i and CO. Our results demonstrate the richness of the far-IR [C ii] spectral data which is a valuable complement to the UV H2 absorption data for studying <span class="hlt">diffuse</span> H2 molecular clouds. While the UV absorption is restricted to the directions of the target star, far-IR [C ii] line emission offers an opportunity to employ velocity-resolved spectral-line mapping capability to study in detail the clouds’ spatial and velocity</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/18947990','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/18947990"><span>Textural characterization of <span class="hlt">media</span> composed of compacted pieces of cardboard and polyethylene using a <span class="hlt">gas</span> tracer method.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kacem, M; Salvador, S; Quintard, M</p> <p>2009-02-01</p> <p>The aim of this work is the experimental determination of effective transport properties of porous <span class="hlt">media</span> consisting of compacted pieces of cardboard and polyethylene (PE). The proposed method itself is more general and can be applied to many different materials and contexts. Three major transport properties were determined: porosity, tortuosity factor and permeability. Three parameters characterizing the <span class="hlt">media</span> were varied over a wide range: the bulk density, the size of the elements entering the mix, and the proportion of cardboard and PE in the mix. The properties were measured by means of a specially designed experimental device based on miscible <span class="hlt">gas</span> tracing. The porosity and tortuosity factor were simultaneously determined by parametric identification, based on the experimental sample output response to an inlet <span class="hlt">gas</span> concentration step change compared to the results of a direct numerical model. Permeability was calculated in the standard way from the measurement of the pressure drop across the sample. The reproducibility of the measurements was very good. It was found that changing the material density of the medium significantly affects all three structural properties. When the bulk density is varied between 300 and 900 kg m(-3), the tortuosity factor varies in a range as large as 18-8 and the permeability decreases by a ratio of 2-3. The tortuosity factor shows unusual variation, characterized by a decrease when density is increased above 500 kg m(-3). The size of the elements does not significantly affect the structural properties of the medium in the range of parameters studied.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009PhRvE..80b6109R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009PhRvE..80b6109R"><span>Effects of inhomogeneous partial absorption and the geometry of the boundary on population evolution of molecules <span class="hlt">diffusing</span> in general porous <span class="hlt">media</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ryu, Seungoh</p> <p>2009-08-01</p> <p>We consider aspects of the population dynamics, inside a bound domain, of <span class="hlt">diffusing</span> agents carrying an attribute which is stochastically destroyed upon contact with the boundary. The normal mode analysis of the relevant Helmholtz equation under the partially absorbing, but uniform, boundary condition provides a starting framework in understanding detailed evolution dynamics of the attribute in the time domain. In particular, the boundary-localized depletion has been widely employed in practical applications that depend on geometry of various porous <span class="hlt">media</span> such as rocks, cement, bones, and cheese. While direct relationship between the pore geometry and the <span class="hlt">diffusion</span>-relaxation spectrum forms the basis for such applications and has been extensively studied, relatively less attention has been paid to the spatial variation in the boundary condition. In this work, we focus on the way the pore geometry and the inhomogeneous depletion strength of the boundary become intertwined and thus obscure the direct relationship between the spectrum and the geometry. It is often impossible to gauge experimentally the degree to which such interference occurs. We fill this gap by perturbatively incorporating classes of spatially varying boundary conditions and derive their consequences that are observable through numerical simulations or controlled experiments on glass bead packs and artificially fabricated porous <span class="hlt">media</span>. We identify features of the spectrum that are most sensitive to the inhomogeneity, apply the method to the spherical pore with a simple hemispherical binary distribution of the depletion strength, and obtain bounds for the induced change in the slowest relaxation mode.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_21 --> <div id="page_22" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="421"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JMagR.271...21S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JMagR.271...21S"><span>Finite element modeling of 129Xe <span class="hlt">diffusive</span> <span class="hlt">gas</span> exchange NMR in the human alveoli</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stewart, Neil J.; Parra-Robles, Juan; Wild, Jim M.</p> <p>2016-10-01</p> <p>Existing models of 129Xe <span class="hlt">diffusive</span> exchange for lung microstructural modeling with time-resolved MR spectroscopy data have considered analytical solutions to one-dimensional, homogeneous models of the lungs with specific assumptions about the alveolar geometry. In order to establish a model system for simulating the effects of physiologically-realistic changes in physical and microstructural parameters on 129Xe exchange NMR, we have developed a 3D alveolar capillary model for finite element analysis. To account for the heterogeneity of the alveolar geometry across the lungs, we have derived realistic geometries for finite element analysis based on 2D histological samples and 3D micro-CT image volumes obtained from ex vivo biopsies of lung tissue from normal subjects and patients with interstitial lung disease. The 3D alveolar capillary model permits investigation of the impact of alveolar geometrical parameters and <span class="hlt">diffusion</span> and perfusion coefficients on the in vivo measured 129Xe CSSR signal response. The heterogeneity of alveolar microstructure that is accounted for in image-based models resulted in considerable alterations to the shape of the 129Xe <span class="hlt">diffusive</span> uptake curve when compared to 1D models. Our findings have important implications for the future design and optimization of 129Xe MR experiments and in the interpretation of lung microstructural changes from this data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5141475','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5141475"><span>Unified rheology of vibro-fluidized dry granular <span class="hlt">media</span>: From slow dense flows to fast <span class="hlt">gas</span>-like regimes</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Gnoli, Andrea; Lasanta, Antonio; Sarracino, Alessandro; Puglisi, Andrea</p> <p>2016-01-01</p> <p>Granular <span class="hlt">media</span> take on great importance in industry and geophysics, posing a severe challenge to materials science. Their response properties elude known soft rheological models, even when the yield-stress discontinuity is blurred by vibro-fluidization. Here we propose a broad rheological scenario where average stress sums up a frictional contribution, generalizing conventional μ(I)-rheology, and a kinetic collisional term dominating at fast fluidization. Our conjecture fairly describes a wide series of experiments in a vibrofluidized vane setup, whose phenomenology includes velocity weakening, shear thinning, a discontinuous thinning transition, and gaseous shear thickening. The employed setup gives access to dynamic fluctuations, which exhibit a broad range of timescales. In the slow dense regime the frequency of cage-opening increases with stress and enhances, with respect to μ(I)-rheology, the decrease of viscosity. <span class="hlt">Diffusivity</span> is exponential in the shear stress in both thinning and thickening regimes, with a huge growth near the transition. PMID:27924928</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016NatSR...638604G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016NatSR...638604G"><span>Unified rheology of vibro-fluidized dry granular <span class="hlt">media</span>: From slow dense flows to fast <span class="hlt">gas</span>-like regimes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gnoli, Andrea; Lasanta, Antonio; Sarracino, Alessandro; Puglisi, Andrea</p> <p>2016-12-01</p> <p>Granular <span class="hlt">media</span> take on great importance in industry and geophysics, posing a severe challenge to materials science. Their response properties elude known soft rheological models, even when the yield-stress discontinuity is blurred by vibro-fluidization. Here we propose a broad rheological scenario where average stress sums up a frictional contribution, generalizing conventional μ(I)-rheology, and a kinetic collisional term dominating at fast fluidization. Our conjecture fairly describes a wide series of experiments in a vibrofluidized vane setup, whose phenomenology includes velocity weakening, shear thinning, a discontinuous thinning transition, and gaseous shear thickening. The employed setup gives access to dynamic fluctuations, which exhibit a broad range of timescales. In the slow dense regime the frequency of cage-opening increases with stress and enhances, with respect to μ(I)-rheology, the decrease of viscosity. <span class="hlt">Diffusivity</span> is exponential in the shear stress in both thinning and thickening regimes, with a huge growth near the transition.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6121621','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6121621"><span>Solar cells made by laser-induced <span class="hlt">diffusion</span> directly from phosphine <span class="hlt">gas</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Turner, G.B.; Tarrant, D.; Pollock, G.; Pressley, R.; Press, R.</p> <p>1981-12-15</p> <p>A new method for making p-n junctions based on immersion in a transparent dopant <span class="hlt">gas</span> followed by irradiation with a pulsed laser is presented. An alexandrite laser was used, operating at 0.73 ..mu..m where photolysis of the dopant <span class="hlt">gas</span> PH/sub 3/ does not occur. Multiple pulses of 2.2--2.7 J/cm/sup 2/ were used to make Si solar cells with total area efficiencies up to 8.6% without benefit of antireflection coatings.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2852445','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2852445"><span>Monitoring of hemodynamic changes induced in the healthy breast through inspired <span class="hlt">gas</span> stimuli with MR-guided <span class="hlt">diffuse</span> optical imaging</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Carpenter, C. M.; Rakow-Penner, R.; Jiang, S.; Pogue, B. W.; Glover, G. H.; Paulsen, K. D.</p> <p>2010-01-01</p> <p>Purpose: The modulation of tissue hemodynamics has important clinical value in medicine for both tumor diagnosis and therapy. As an oncological tool, increasing tissue oxygenation via modulation of inspired <span class="hlt">gas</span> has been proposed as a method to improve cancer therapy and determine radiation sensitivity. As a radiological tool, inducing changes in tissue total hemoglobin may provide a means to detect and characterize malignant tumors by providing information about tissue vascular function. The ability to change and measure tissue hemoglobin and oxygenation concentrations in the healthy breast during administration of three different types of modulated <span class="hlt">gas</span> stimuli (oxygen∕carbogen, air∕carbogen, and air∕oxygen) was investigated. Methods: Subjects breathed combinations of gases which were modulated in time. MR-guided <span class="hlt">diffuse</span> optical tomography measured total hemoglobin and oxygen saturation in the breast every 30 s during the 16 min breathing stimulus. Metrics of maximum correlation and phase lag were calculated by cross correlating the measured hemodynamics with the stimulus. These results were compared to an air∕air control to determine the hemodynamic changes compared to the baseline physiology. Results: This study demonstrated that a <span class="hlt">gas</span> stimulus consisting of alternating oxygen∕carbogen induced the largest and most robust hemodynamic response in healthy breast parenchyma relative to the changes that occurred during the breathing of room air. This stimulus caused increases in total hemoglobin and oxygen saturation during the carbogen phase of <span class="hlt">gas</span> inhalation, and decreases during the oxygen phase. These findings are consistent with the theory that oxygen acts as a vasoconstrictor, while carbogen acts as a vasodilator. However, difficulties in inducing a consistent change in tissue hemoglobin and oxygenation were observed because of variability in intersubject physiology, especially during the air∕oxygen or air∕carbogen modulated breathing protocols</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014PhDT.........6E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014PhDT.........6E"><span>Improved Experimental and Mathematical Techniques for Measurement of Solvent <span class="hlt">Gas</span> <span class="hlt">Diffusivity</span> in Heavy Oils</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Elliott, Ethan Robert</p> <p></p> <p>This dissertation describes the first experimental measurement of the energy and interaction dependent shear viscosity eta and bulk viscosity zeta in the hydrodynamic expansion of a two-component Fermi <span class="hlt">gas</span> near a broad collisional (Feshbach) resonance. This expansion also provides a precise test of scale invariance and an examination of local thermal equilibrium as a function of interaction strength. After release from an anisotropic optical trap, we observe that a resonantly interacting <span class="hlt">gas</span> obeys scale-invariant hydrodynamics, where the mean square cloud size <r2 = < x2> + <y2> + <z2> expands ballistically (like a noninteracting <span class="hlt">gas</span>) and the energy-averaged bulk viscosity is consistent with zero, $0.00(0.04) ℎ n, with n the density. In contrast, the aspect ratios of the cloud exhibit anisotropic "elliptic"flow with an energy-dependent shear viscosity. Tuning away from resonance, we observe conformal symmetry breaking, where <r2> deviates from ballistic flow. We find that eta has both a quadratic and a linear dependence on the interaction strength 1/(kFIa ), where a is the s-wave scattering length and kFI is the Fermi wave vector for an ideal <span class="hlt">gas</span> at the trap center. At low energy, the minimum is less than the resonant value and is significantly shifted toward the BEC side of resonance, to 1/(k FIa) = 0.2.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19790006578','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19790006578"><span><span class="hlt">Gas</span> <span class="hlt">diffusion</span> liquid storage bag and method of use for storing blood</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bank, H.; Cleland, E. L. (Inventor)</p> <p>1979-01-01</p> <p>The shelf life of stored whole blood may be doubled by adding a buffer which maintains a desired pH level. However, this buffer causes the generation of CO2 which, if not removed at a controlled rate, causes the pH value of the blood to decrease, which shortens the useful life of the blood. A blood storage bag is described which permits the CO2 to be <span class="hlt">diffused</span> out at a controlled rate into the atmosphere, thereby maintaining the desired pH value and providing a bag strong enough to permit handling.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/20015487','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/20015487"><span>Determination of the optimum conditions for boric acid extraction with carbon dioxide <span class="hlt">gas</span> in aqueous <span class="hlt">media</span> from colemanite containing arsenic</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Ata, O.N.; Colak, S.; Copur, M.; Celik, C.</p> <p>2000-02-01</p> <p>The Taguchi method was used to determine optimum conditions for the boric acid extraction from colemanite ore containing As in aqueous <span class="hlt">media</span> saturated by CO{sub 2} <span class="hlt">gas</span>. After the parameters were determined to be efficient on the extraction efficiency, the experimental series with two steps were carried out. The chosen experimental parameters for the first series of experiments and their ranges were as follows: (1) reaction temperature, 25--70 C; (2) solid-to-liquid ratio (by weight), 0.091 to 0.333; (3) <span class="hlt">gas</span> flow rate (in mL/min), 66.70--711; (4) mean particle size, {minus}100 to {minus}10 mesh; (5) stirring speed, 200--600 rpm; (6) reaction time, 10--90 min. The optimum conditions were found to be as follows: reaction temperature, 70 C; solid-to-liquid ratio, 0.091; <span class="hlt">gas</span> flow rate, 711 (in mL/min); particle size, {minus}100 mesh; stirring speed, 500 rpm; reaction time, 90 min. Under these optimum conditions, the boric acid extraction efficiency from the colemanite containing As was approximately 54%. Chosen experimental parameters for the second series of experiments and their ranges were as follows: (1) reaction temperature, 60--80 C; (2) solid-to-liquid ratio (by weight), 0.1000 to 0.167; (3) <span class="hlt">gas</span> pressure (in atm), 1.5; 2.7; (4) reaction time, 45--120 min. The optimum conditions were found to be as follows: reaction temperature, 70 C; solid-to-liquid ratio, 0.1; <span class="hlt">gas</span> pressure, 2.7 atm; reaction time, 120 min. Under these optimum conditions the boric acid extraction efficiency from the colemanite ore was approximately 75%. Under these optimum conditions, the boric acid extraction efficiency from calcined colemanite ore was approximately 99.55%.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/784396','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/784396"><span>An Effective Continuum Model for the Liquid-to-<span class="hlt">Gas</span> Phase Change in a Porous Medium Driven by Solute <span class="hlt">Diffusion</span>: II. Constant Liquid Withdrawal Rates</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Tsimpanogiannis, Ioannis N.; Yortsos, Yanis C.</p> <p>2001-08-15</p> <p>This report describes the development of an effective continuum model to describe the nucleation and subsequent growth of a <span class="hlt">gas</span> phase from a supersaturated, slightly compressible binary liquid in a porous medium, driven by solute <span class="hlt">diffusion</span>.This report also focuses on the processes resulting from the withdrawal of the liquid at a constant rate. As before, the model addresses two stages before the onset of bulk <span class="hlt">gas</span> flow, nucleation and <span class="hlt">gas</span> phase growth. Because of negligible gradients due to gravity or viscous forces, the critical <span class="hlt">gas</span> saturation, is only a function of the nucleation fraction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011GeCoA..75.2170H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011GeCoA..75.2170H"><span>A lattice Boltzmann model for noble <span class="hlt">gas</span> <span class="hlt">diffusion</span> in solids: The importance of domain shape and <span class="hlt">diffusive</span> anisotropy and implications for thermochronometry</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Huber, Christian; Cassata, William S.; Renne, Paul R.</p> <p>2011-04-01</p> <p>Thermochronometry based on radiogenic noble gases is critically dependent upon accurate knowledge of the kinetics of <span class="hlt">diffusion</span>. With few exceptions, complex natural crystals are represented by ideal geometries such as infinite sheets, infinite cylinders, or spheres, and <span class="hlt">diffusivity</span> is assumed to be isotropic. However, the physical boundaries of crystals generally do not conform to ideal geometries and <span class="hlt">diffusion</span> within some crystals is known to be anisotropic. Our failure to incorporate such complexities into <span class="hlt">diffusive</span> models leads to inaccuracies in both thermal histories and <span class="hlt">diffusion</span> parameters calculated from fractional release data. To address these shortcomings we developed a code based on the lattice Boltzmann (LB) method to model <span class="hlt">diffusion</span> from complex 3D geometries having isotropic, temperature-independent anisotropic, and temperature-dependent anisotropic <span class="hlt">diffusivity</span>. In this paper we outline the theoretical basis for the LB code and highlight several advantages of this model relative to more traditional finite difference approaches. The LB code, along with existing analytical solutions for <span class="hlt">diffusion</span> from simple geometries, is used to investigate the affect of intrinsic crystallographic features (e.g., crystal topology and <span class="hlt">diffusion</span> anisotropy) on calculated <span class="hlt">diffusion</span> parameters and a novel method for approximating thermal histories from crystals with complex topologies and <span class="hlt">diffusive</span> anisotropy is presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1156914','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1156914"><span>Atomistic modeling of intrinsic and radiation-enhanced fission <span class="hlt">gas</span> (Xe) <span class="hlt">diffusion</span> in UO2 +/- x: Implications for nuclear fuel performance modeling</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Giovanni Pastore; Michael R. Tonks; Derek R. Gaston; Richard L. Williamson; David Andrs; Richard Martineau</p> <p>2014-03-01</p> <p>Based on density functional theory (DFT) and empirical potential calculations, the <span class="hlt">diffusivity</span> of fission <span class="hlt">gas</span> atoms (Xe) in UO2 nuclear fuel has been calculated for a range of non-stoichiometry (i.e. UO2x), under both out-of-pile (no irradiation) and in-pile (irradiation) conditions. This was achieved by first deriving expressions for the activation energy that account for the type of trap site that the fission <span class="hlt">gas</span> atoms occupy, which includes the corresponding type of mobile cluster, the charge state of these defects and the chemistry acting as boundary condition. In the next step DFT calculations were used to estimate migration barriers and internal energy contributions to the thermodynamic properties and calculations based on empirical potentials were used to estimate defect formation and migration entropies (i.e. pre-exponentials). The <span class="hlt">diffusivities</span> calculated for out-of-pile conditions as function of the UO2x nonstoichiometrywere used to validate the accuracy of the <span class="hlt">diffusion</span> models and the DFT calculations against available experimental data. The Xe <span class="hlt">diffusivity</span> is predicted to depend strongly on the UO2x non-stoichiometry due to a combination of changes in the preferred Xe trap site and in the concentration of uranium vacancies enabling Xe <span class="hlt">diffusion</span>, which is consistent with experiments. After establishing the validity of the modeling approach, it was used for studying Xe <span class="hlt">diffusion</span> under in-pile conditions, for which experimental data is very scarce. The radiation-enhanced Xe <span class="hlt">diffusivity</span> is compared to existing empirical models. Finally, the predicted fission <span class="hlt">gas</span> <span class="hlt">diffusion</span> rates were implemented in the BISON fuel performance code and fission <span class="hlt">gas</span> release from a Risø fuel rod irradiation experiment was simulated. 2014 Elsevier B.V. All rights</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JNuM..451..225A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JNuM..451..225A"><span>Atomistic modeling of intrinsic and radiation-enhanced fission <span class="hlt">gas</span> (Xe) <span class="hlt">diffusion</span> in UO2±x: Implications for nuclear fuel performance modeling</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Andersson, D. A.; Garcia, P.; Liu, X.-Y.; Pastore, G.; Tonks, M.; Millett, P.; Dorado, B.; Gaston, D. R.; Andrs, D.; Williamson, R. L.; Martineau, R. C.; Uberuaga, B. P.; Stanek, C. R.</p> <p>2014-08-01</p> <p>Based on density functional theory (DFT) and empirical potential calculations, the <span class="hlt">diffusivity</span> of fission <span class="hlt">gas</span> atoms (Xe) in UO2 nuclear fuel has been calculated for a range of non-stoichiometry (i.e. UO2±x), under both out-of-pile (no irradiation) and in-pile (irradiation) conditions. This was achieved by first deriving expressions for the activation energy that account for the type of trap site that the fission <span class="hlt">gas</span> atoms occupy, which includes the corresponding type of mobile cluster, the charge state of these defects and the chemistry acting as boundary condition. In the next step DFT calculations were used to estimate migration barriers and internal energy contributions to the thermodynamic properties and calculations based on empirical potentials were used to estimate defect formation and migration entropies (i.e. pre-exponentials). The <span class="hlt">diffusivities</span> calculated for out-of-pile conditions as function of the UO2±x non-stoichiometry were used to validate the accuracy of the <span class="hlt">diffusion</span> models and the DFT calculations against available experimental data. The Xe <span class="hlt">diffusivity</span> is predicted to depend strongly on the UO2±x non-stoichiometry due to a combination of changes in the preferred Xe trap site and in the concentration of uranium vacancies enabling Xe <span class="hlt">diffusion</span>, which is consistent with experiments. After establishing the validity of the modeling approach, it was used for studying Xe <span class="hlt">diffusion</span> under in-pile conditions, for which experimental data is very scarce. The radiation-enhanced Xe <span class="hlt">diffusivity</span> is compared to existing empirical models. Finally, the predicted fission <span class="hlt">gas</span> <span class="hlt">diffusion</span> rates were implemented in the BISON fuel performance code and fission <span class="hlt">gas</span> release from a Risø fuel rod irradiation experiment was simulated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1981ApPhL..39..967T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1981ApPhL..39..967T"><span>Solar cells made by laser-induced <span class="hlt">diffusion</span> directly from phosphine <span class="hlt">gas</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Turner, G. B.; Tarrant, D.; Pollock, G.; Pressley, R.; Press, R.</p> <p>1981-12-01</p> <p>A method for making p-n junctions is presented, which is based on immersion in a transparent dopant <span class="hlt">gas</span> followed by irradiation with a pulsed laser. An alexandrite laser operating at 0.73 micron is used where photolysis of the dopant <span class="hlt">gas</span> PH3 does not occur, and multiple pulses of 2.2-2.7 J/sq cm are used to make Si solar cells with a total area efficiency up to 8.6% without benefit of anti-reflection coatings. Use of other gases should allow p-type doping, and the spatial localization inherent in the process could make the method applicable to structures such as interdigitated solar cells, transistors, and integrated circuits.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/587721','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/587721"><span>Experimental and numerical investigation of shock wave propagation through complex geometry, <span class="hlt">gas</span> continuous, two-phase <span class="hlt">media</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Chien-Chih Liu, James</p> <p>1993-01-01</p> <p>The work presented here investigates the phenomenon of shock wave propagation in <span class="hlt">gas</span> continuous, two-phase <span class="hlt">media</span>. The motivation for this work stems from the need to understand blast venting consequences in the HYLIFE inertial confinement fusion (ICF) reactor. The HYLIFE concept utilizes lasers or heavy ion beams to rapidly heat and compress D-T targets injected into the center of a reactor chamber. A segmented blanket of falling molten lithium or Li<sub>2</sub>BeF<sub>4</sub> (Flibe) jets encircles the reactor`s central cavity, shielding the reactor structure from radiation damage, absorbing the fusion energy, and breeding more tritium fuel. X-rays from the fusion microexplosion will ablate a thin layer of blanket material from the surfaces which face toward the fusion site. This generates a highly energetic vapor, which mostly coalesces in the central cavity. The blast expansion from the central cavity generates a shock which propagates through the segmented blanket - a complex geometry, <span class="hlt">gas</span>-continuous two-phase medium. The impulse that the blast gives to the liquid as it vents past, the <span class="hlt">gas</span> shock on the chamber wall, and ultimately the liquid impact on the wall are all important quantities to the HYLIFE structural designers.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.sciencedirect.com/science/article/pii/S0169772211000805','USGSPUBS'); return false;" href="http://www.sciencedirect.com/science/article/pii/S0169772211000805"><span>Role of back <span class="hlt">diffusion</span> and biodegradation reactions in sustaining an MTBE/TBA plume in alluvial <span class="hlt">media</span></span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Rasa, Ehsan; Chapman, Steven W.; Bekins, Barbara A.; Fogg, Graham E.; Scow, Kate M.; Mackay, Douglas M.</p> <p>2011-01-01</p> <p>A methyl tert-butyl ether (MTBE) / tert-butyl alcohol (TBA) plume originating from a gasoline spill in late 1994 at Vandenberg Air Force Base (VAFB) persisted for over 15 years within 200 feet of the original spill source. The plume persisted until 2010 despite excavation of the tanks and piping within months after the spill and excavations of additional contaminated sediments from the source area in 2007 and 2008. The probable history of MTBE concentrations along the plume centerline at its source was estimated using a wide variety of available information, including published details about the original spill, excavations and monitoring by VAFB consultants, and our own research data. Two-dimensional reactive transport simulations of MTBE along the plume centerline were conducted for a 20-year period following the spill. These analyses suggest that MTBE <span class="hlt">diffused</span> from the thin anaerobic aquifer into the adjacent anaerobic silts and transformed to TBA in both aquifer and silt layers. The model reproduces the observation that after 2004 TBA was the dominant solute, <span class="hlt">diffusing</span> back out of the silts into the aquifer and sustaining plume concentrations much longer than would have been the case in the absence of such <span class="hlt">diffusive</span> exchange. Simulations also suggest that aerobic degradation of MTBE or TBA at the water table in the overlying silt layer significantly affected concentrations of MTBE and TBA by limiting the chemical mass available for back <span class="hlt">diffusion</span> to the aquifer.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3267905','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3267905"><span>Role of back <span class="hlt">diffusion</span> and biodegradation reactions in sustaining an MTBE/TBA plume in alluvial <span class="hlt">media</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Rasa, Ehsan; Chapman, Steven W.; Bekins, Barbara A.; Fogg, Graham E.; Scow, Kate M.; Mackay, Douglas M.</p> <p>2012-01-01</p> <p>A methyl tert-butyl ether (MTBE) / tert-butyl alcohol (TBA) plume originating from a gasoline spill in late 1994 at Vandenberg Air Force Base (VAFB) persisted for over 15 years within 200 feet of the original spill source. The plume persisted until 2010 despite excavation of the tanks and piping within months after the spill and excavations of additional contaminated sediments from the source area in 2007 and 2008. The probable history of MTBE concentrations along the plume centerline at its source was estimated using a wide variety of available information, including published details about the original spill, excavations and monitoring by VAFB consultants, and our own research data. Two-dimensional reactive transport simulations of MTBE along the plume centerline were conducted for a 20-year period following the spill. These analyses suggest that MTBE <span class="hlt">diffused</span> from the thin anaerobic aquifer into the adjacent anaerobic silts and transformed to TBA in both aquifer and silt layers. The model reproduces the observation that after 2004 TBA was the dominant solute, <span class="hlt">diffusing</span> back out of the silts into the aquifer and sustaining plume concentrations much longer than would have been the case in the absence of such <span class="hlt">diffusive</span> exchange. Simulations also suggest that aerobic degradation of MTBE or TBA at the water table in the overlying silt layer significantly affected concentrations of MTBE and TBA by limiting the chemical mass available for back <span class="hlt">diffusion</span> to the aquifer. PMID:22115089</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://cfpub.epa.gov/si/si_public_record_report.cfm?dirEntryId=129153&keyword=AIDS&actType=&TIMSType=+&TIMSSubTypeID=&DEID=&epaNumber=&ntisID=&archiveStatus=Both&ombCat=Any&dateBeginCreated=&dateEndCreated=&dateBeginPublishedPresented=&dateEndPublishedPresented=&dateBeginUpdated=&dateEndUpdated=&dateBeginCompleted=&dateEndCompleted=&personID=&role=Any&journalID=&publisherID=&sortBy=revisionDate&count=50&CFID=78777631&CFTOKEN=33796782','EPA-EIMS'); return false;" href="http://cfpub.epa.gov/si/si_public_record_report.cfm?dirEntryId=129153&keyword=AIDS&actType=&TIMSType=+&TIMSSubTypeID=&DEID=&epaNumber=&ntisID=&archiveStatus=Both&ombCat=Any&dateBeginCreated=&dateEndCreated=&dateBeginPublishedPresented=&dateEndPublishedPresented=&dateBeginUpdated=&dateEndUpdated=&dateBeginCompleted=&dateEndCompleted=&personID=&role=Any&journalID=&publisherID=&sortBy=revisionDate&count=50&CFID=78777631&CFTOKEN=33796782"><span>CRITICAL EVALUATION OF THE <span class="hlt">DIFFUSION</span> HYPOTHESIS IN THE THEORY OF POROUS <span class="hlt">MEDIA</span> VOLATILE ORGANIC COMPOUND (VOC) SOURCES AND SINKS</span></a></p> <p><a target="_blank" href="http://oaspub.epa.gov/eims/query.page">EPA Science Inventory</a></p> <p></p> <p></p> <p>The paper proposes three alternative, <span class="hlt">diffusion</span>-limited mathematical models to account for volatile organic compound (VOC) interactions with indoor sinks, using the linear isotherm model as a reference point. (NOTE: Recent reports by both the U.S. EPA and a study committee of the...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1813878L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1813878L"><span>Automatic semi-continuous accumulation chamber for <span class="hlt">diffuse</span> <span class="hlt">gas</span> emissions monitoring in volcanic and non-volcanic areas</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lelli, Matteo; Raco, Brunella; Norelli, Francesco; Virgili, Giorgio; Continanza, Davide</p> <p>2016-04-01</p> <p>Since various decades the accumulation chamber method is intensively used in monitoring activities of <span class="hlt">diffuse</span> <span class="hlt">gas</span> emissions in volcanic areas. Although some improvements have been performed in terms of sensitivity and reproducibility of the detectors, the equipment used for measurement of <span class="hlt">gas</span> emissions temporal variation usually requires expensive and bulky equipment. The unit described in this work is a low cost, easy to install-and-manage instrument that will make possible the creation of low-cost monitoring networks. The Non-Dispersive Infrared detector used has a concentration range of 0-5% CO2, but the substitution with other detector (range 0-5000 ppm) is possible and very easy. Power supply unit has a 12V, 7Ah battery, which is recharged by a 35W solar panel (equipped with charge regulator). The control unit contains a custom programmed CPU and the remote transmission is assured by a GPRS modem. The chamber is activated by DataLogger unit, using a linear actuator between the closed position (sampling) and closed position (idle). A probe for the measure of soil temperature, soil electrical conductivity, soil volumetric water content, air pressure and air temperature is assembled on the device, which is already arranged for the connection of others external sensors, including an automatic weather station. The automatic station has been tested on the field at Lipari island (Sicily, Italy) during a period of three months, performing CO2 flux measurement (and also weather parameters), each 1 hour. The possibility to measure in semi-continuous mode, and at the same time, the <span class="hlt">gas</span> fluxes from soil and many external parameters, helps the time series analysis aimed to the identification of <span class="hlt">gas</span> flux anomalies due to variations in deep system (e.g. onset of volcanic crises) from those triggered by external conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140000685','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140000685"><span>Multiphase Transport in Porous <span class="hlt">Media</span>: <span class="hlt">Gas</span>-Liquid Separation Using Capillary Pressure Gradients International Space Station (ISS) Flight Experiment Development</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Wheeler, Richard R., Jr.; Holtsnider, John T.; Dahl, Roger W.; Deeks, Dalton; Javanovic, Goran N.; Parker, James M.; Ehlert, Jim</p> <p>2013-01-01</p> <p>Advances in the understanding of multiphase flow characteristics under variable gravity conditions will ultimately lead to improved and as of yet unknown process designs for advanced space missions. Such novel processes will be of paramount importance to the success of future manned space exploration as we venture into our solar system and beyond. In addition, because of the ubiquitous nature and vital importance of biological and environmental processes involving airwater mixtures, knowledge gained about fundamental interactions and the governing properties of these mixtures will clearly benefit the quality of life here on our home planet. The techniques addressed in the current research involving multiphase transport in porous <span class="hlt">media</span> and <span class="hlt">gas</span>-liquid phase separation using capillary pressure gradients are also a logical candidate for a future International Space Station (ISS) flight experiment. Importantly, the novel and potentially very accurate Lattice-Boltzmann (LB) modeling of multiphase transport in porous <span class="hlt">media</span> developed in this work offers significantly improved predictions of real world fluid physics phenomena, thereby promoting advanced process designs for both space and terrestrial applications.This 3-year research effort has culminated in the design and testing of a zero-g demonstration prototype. Both the hydrophilic (glass) and hydrophobic (Teflon) <span class="hlt">media</span> Capillary Pressure Gradient (CPG) cartridges prepared during the second years work were evaluated. Results obtained from ground testing at 1-g were compared to those obtained at reduced gravities spanning Martian (13-g), Lunar (16-g) and zero-g. These comparisons clearly demonstrate the relative strength of the CPG phenomena and the efficacy of its application to meet NASAs unique <span class="hlt">gas</span>-liquid separation (GLS) requirements in non-terrestrial environments.LB modeling software, developed concurrently with the zero-g test effort, was shown to accurately reproduce observed CPG driven <span class="hlt">gas</span>-liquid separation</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19860057896&hterms=Chemical+Quantitative+Analysis&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DChemical%2BQuantitative%2BAnalysis','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19860057896&hterms=Chemical+Quantitative+Analysis&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DChemical%2BQuantitative%2BAnalysis"><span>Thermofluid analysis of the SSME preburner using a <span class="hlt">gas-gas</span> <span class="hlt">diffusion</span> model for oxygen and hydrogen combustion at supercritical pressures</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Prakash, C.; Singhal, A. K.; Shafer, C.</p> <p>1986-01-01</p> <p>The paper discusses the thermofluid analysis of the Space Shuttle Main Engine (SSME) fuelside preburner. The governing equations have been solved numerically to predict flow, heat transfer, mixing, and combustion. A two-fluid approach is adopted in which oxygen is regarded as one fluid and hydrogen is regarded as the other fluid. The chemical kinetics is assumed to be very fast so that combustion is primarily controlled by the rate of mixing between oxygen and hydrogen. The preburner pressure is much greater than the critical pressures of oxygen and hydrogen; hence, a <span class="hlt">gas-gas</span> <span class="hlt">diffusion</span> model (rather than an evaporation model) has been developed to compute the rate of interphase mixing. Empirical correlations have been incorporated to account for the effect of slip on the interphase exchange. A sensitivity study has been performed with various model parameters. It is observed that the model can predict possibility of incomplete combustion and local regions of high temperatures under steady operating conditions. Some of these anomalies have been observed in actual tests, and the numerical model is useful for understanding possible causes and remedies. At least some measurements are needed for quantitative verification of the model.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_22 --> <div id="page_23" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="441"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22492430','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22492430"><span>Lateral <span class="hlt">gas</span> phase <span class="hlt">diffusion</span> length of boron atoms over Si/B surfaces during CVD of pure boron layers</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Mohammadi, V. Nihtianov, S.</p> <p>2016-02-15</p> <p>The lateral <span class="hlt">gas</span> phase <span class="hlt">diffusion</span> length of boron atoms, L{sub B}, along silicon and boron surfaces during chemical vapor deposition (CVD) using diborane (B{sub 2}H{sub 6}) is reported. The value of L{sub B} is critical for reliable and uniform boron layer coverage. The presented information was obtained experimentally and confirmed analytically in the boron deposition temperature range from 700 °C down to 400 °C. For this temperature range the local loading effect of the boron deposition is investigated on the micro scale. A L{sub B} = 2.2 mm was determined for boron deposition at 700 °C, while a L{sub B} of less than 1 mm was observed at temperatures lower than 500 °C.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PhDT.......128G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PhDT.......128G"><span>X-Ray-Based Imaging for Characterizing Heterogeneous <span class="hlt">Gas</span> <span class="hlt">Diffusion</span> Layers for Polymer Electrolyte Membrane Fuel Cells</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>George, Michael G.</p> <p></p> <p>Characterization of <span class="hlt">gas</span> <span class="hlt">diffusion</span> layers (GDLs) for polymer electrolyte membrane (PEM) fuel cells informs modeling studies and the manufacturers of next generation fuel cell materials. Identifying the physical properties related to the primary functions of the modern GDL (thermal, electrical, and mass transport) is necessary for understanding the impact of GDL design choices. X-ray micro-computed tomographic reconstructions of GDLs were studied to isolate GDL surface morphologies. Surface roughness was measured for a wide variety of samples and a sensitivity study highlighted the scale-dependence of surface roughness measurements. Furthermore, a spatially resolved distribution map of polytetrafluoroethylene (PTFE) in the microporous layer (MPL), critical for water management and mass transport, was identified and the existence of PTFE agglomerations was highlighted. Finally, the impact of accelerated degradation on GDL wettability and water transport increases in liquid water accumulation and oxygen mass transport resistance were quantified as a result of accelerated GDL degradation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008JPS...182..112S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008JPS...182..112S"><span>Effect of capillary pressure on liquid water removal in the cathode <span class="hlt">gas</span> <span class="hlt">diffusion</span> layer of a polymer electrolyte fuel cell</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shi, Wanyuan; Kurihara, Eru; Oshima, Nobuyuki</p> <p></p> <p>In order to investigate the effect of capillary pressure on the transport of liquid water in the cathode <span class="hlt">gas</span> <span class="hlt">diffusion</span> layer (GDL) of a polymer electrolyte fuel cell, a one-dimensional steady-state mathematical model was developed, including the effect of temperature on the capillary pressure. Numerical results indicate that the liquid water saturation significantly increases with increases in the operating temperature of the fuel cell. An elevated operating temperature has an undesirable influence on the removal of liquid water inside the GDL. A reported peculiar phenomenon in which the flooding of the fuel cell under a high operating temperature and an over-saturated environment is more serious in a GDL combined with a micro-porous layer (MPL) than in a GDL without an MPL [Lim and Wang, Electrochim. Acta 49 (2004), 4149-4156] is explained based on the present analysis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011MeScT..22j5409B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011MeScT..22j5409B"><span>A Loschmidt cell combined with holographic interferometry for binary <span class="hlt">diffusion</span> experiments in <span class="hlt">gas</span> mixtures including first measurements on the argon-neon system</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Buttig, D.; Vogel, E.; Bich, E.; Hassel, E.</p> <p>2011-10-01</p> <p>A new variant of the Loschmidt technique has been developed for measuring binary <span class="hlt">diffusion</span> coefficients in <span class="hlt">gas</span> mixtures in a temperature range from 10 to 80 °C and for pressures between 0.1 and 1 MPa. The two half cells of the thermostatted <span class="hlt">diffusion</span> cell have a rectangular cross section and are fixed one upon the other. They can be connected and separated by means of a sliding plate provided with a pneumatically operated seal. The concentration in both half cells is determined simultaneously during the <span class="hlt">diffusion</span> process using an optical system for holographic interferometry for each. The change in the refractive index results in an interference pattern which is recorded as a function of time. The concentrations of the <span class="hlt">diffusing</span> components are derived by means of the Lorentz-Lorenz equation. The binary <span class="hlt">diffusion</span> coefficients are calculated via the integrated ideal <span class="hlt">diffusion</span> equation for the complete mole fraction range performing only a unique <span class="hlt">diffusion</span> experiment. The performance of the apparatus is demonstrated on first measurements on the argon-neon system at 293.15 K. Separate refractive index measurements are carried out leading to values for the first refractivity virial coefficient of the pure gases with an estimated uncertainty of ±0.1%. This low uncertainty is required for the aimed uncertainty of ±0.5...1% for the <span class="hlt">diffusion</span> measurements to determine the concentration and density dependences of the binary <span class="hlt">diffusion</span> coefficient.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012PhDT........34N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012PhDT........34N"><span>Two studies of <span class="hlt">diffuse</span> <span class="hlt">gas</span> interactions in the Magellanic System and instrumentation for suppressing satellite signal interference in radio telescopes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nigra, Lou Michael</p> <p>2012-05-01</p> <p>I present observational evidence of processes taking place in two <span class="hlt">diffuse</span> environments of the Magellanic System important to the ultimate fate of accreting material in general and its impact on a host galaxy. Using optical and radio data, I show that initial formation of NGC 602's massive stars and subsequent chain of triggered star formation in a <span class="hlt">diffuse</span> environment likely resulted from colliding structures of expanding remnants of supernova- or wind-driven shells. The process could take place in any gaseous interaction remnant of sufficient density as a result of large scale turbulence energized by the interaction itself. The young stars produced in an accreting remnant in this fashion would eventually contribute to the diversity of the host galaxy's stellar population. I also provide all unprecedented, direct observational glimpse into the ablation processes acting on the periphery of an accreting gaseous remnant that ultimately will determine its fate, consumption by the host's halo or reaching the disk as star-formation fuel. Using novel spatial averaging methods I found that in the interaction zone between warm MS <span class="hlt">gas</span> and hot Halo <span class="hlt">gas</span>, a Turbulent Mixing Layer is strongly indicated. Such an interaction can significantly moderate the ablation rate of the cloud into the Halo. Finally, I describe a Radio Frequency Interference (RFI) Suppression subsystem for insertion into radio telescope hardware systems that is capable of reconstructing and directly subtracting replicas of multiple interfering signals of Global Positioning System (GPS) and other navigation satellites, including the unique and troublesome GPS L3 signal. The subsystem provides important enhancements over prior approaches and allows handling of the complex signaling of L3. The subsystem is designed to easily "plug in" to virtually any radio telescope system and operate autonomously. Its essential function has been simulated, demonstrating its ability to identify and characterize actual</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015APS..DFDR25006G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015APS..DFDR25006G"><span>A Study of the Influence of Numerical <span class="hlt">Diffusion</span> on <span class="hlt">Gas</span>-Solid Flow Predictions in Fluidized Beds</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ghandriz, Ronak; Sheikhi, Reza</p> <p>2015-11-01</p> <p>In this work, an investigation is made of the influence of numerical <span class="hlt">diffusion</span> on the accuracy of <span class="hlt">gas</span>-solid flow predictions in fluidized beds. This is an important issue particularly in bubbling fluidized beds since numerical error greatly affects the dynamics of bubbles and their associated mixing process. A bed of coal (classified as Geldart A) is considered which becomes fluidized as the velocity of nitrogen stream into the reactor is gradually increased. The fluidization process is simulated using various numerical schemes as well as grid resolutions. Simulations involve Eulerian-Eulerian two-phase flow modeling approach and results are compared with experimental data. It is shown that higher order schemes equipped with flux limiter give favorable prediction of bubble and particle dynamics and hence, the mixing process within the reactor. The excessive numerical <span class="hlt">diffusion</span> associated with lower order schemes results in unrealistic prediction of bubble shapes and bed height. Comparison is also made of computational efficiency of various schemes. It is shown that the Monotonized Central scheme with down wind factor results in the shortest simulation time because of its efficient parallelization on distributed memory platforms.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010JPS...195.4350W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010JPS...195.4350W"><span>Silver nanoparticle-decorated carbon nanotubes as bifunctional <span class="hlt">gas-diffusion</span> electrodes for zinc-air batteries</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, T.; Kaempgen, M.; Nopphawan, P.; Wee, G.; Mhaisalkar, S.; Srinivasan, M.</p> <p></p> <p>Thin, lightweight, and flexible <span class="hlt">gas-diffusion</span> electrodes (GDEs) based on freestanding entangled networks of single-walled carbon nanotubes (SWNTs) decorated with Ag nanoparticles (AgNPs) are tested as the air-breathing cathode in a zinc-air battery. The SWNT networks provide a highly porous surface for active oxygen absorption and <span class="hlt">diffusion</span>. The high conductivity of SWNTs coupled with the catalytic activity of AgNPs for oxygen reduction leads to an improvement in the performance of the zinc-air cell. By modulating the pH value and the reaction time, different sizes of AgNPs are decorated uniformly on the SWNTs, as revealed by transmission electron microscopy and powder X-ray diffraction. AgNPs with sizes of 3-5 nm double the capacity and specific energy of a zinc-air battery as compared with bare SWNTs. The simplified, lightweight architecture shows significant advantages over conventional carbon-based GDEs in terms of weight, thickness and conductivity, and hence may be useful for mobile and portable applications.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017MNRAS.466.3217Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017MNRAS.466.3217Z"><span>SDSS-IV MaNGA: the impact of <span class="hlt">diffuse</span> ionized <span class="hlt">gas</span> on emission-line ratios, interpretation of diagnostic diagrams and <span class="hlt">gas</span> metallicity measurements</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, Kai; Yan, Renbin; Bundy, Kevin; Bershady, Matthew; Haffner, L. Matthew; Walterbos, René; Maiolino, Roberto; Tremonti, Christy; Thomas, Daniel; Drory, Niv; Jones, Amy; Belfiore, Francesco; Sánchez, Sebastian F.; Diamond-Stanic, Aleksandar M.; Bizyaev, Dmitry; Nitschelm, Christian; Andrews, Brett; Brinkmann, Jon; Brownstein, Joel R.; Cheung, Edmond; Li, Cheng; Law, David R.; Roman Lopes, Alexandre; Oravetz, Daniel; Pan, Kaike; Storchi Bergmann, Thaisa; Simmons, Audrey</p> <p>2017-04-01</p> <p><span class="hlt">Diffuse</span> ionized <span class="hlt">gas</span> (DIG) is prevalent in star-forming galaxies. Using a sample of 365 nearly face-on star-forming galaxies observed by Mapping Nearby Galaxies at APO, we demonstrate how DIG in star-forming galaxies impacts the measurements of emission-line ratios, hence the interpretation of diagnostic diagrams and <span class="hlt">gas</span>-phase metallicity measurements. At fixed metallicity, DIG-dominated low ΣHα regions display enhanced [S II]/Hα, [N II]/Hα, [O II]/Hβ and [O I]/Hα. The gradients in these line ratios are determined by metallicity gradients and ΣHα. In line ratio diagnostic diagrams, contamination by DIG moves H II regions towards composite or low-ionization nuclear emission-line region (LI(N)ER)-like regions. A harder ionizing spectrum is needed to explain DIG line ratios. Leaky H II region models can only shift line ratios slightly relative to H II region models, and thus fail to explain the composite/LI(N)ER line ratios displayed by DIG. Our result favours ionization by evolved stars as a major ionization source for DIG with LI(N)ER-like emission. DIG can significantly bias the measurement of <span class="hlt">gas</span> metallicity and metallicity gradients derived using strong-line methods. Metallicities derived using N2O2 are optimal because they exhibit the smallest bias and error. Using O3N2, R23, N2 = [N II]/Hα and N2S2Hα to derive metallicities introduces bias in the derived metallicity gradients as large as the gradient itself. The strong-line method of Blanc et al. (IZI hereafter) cannot be applied to DIG to get an accurate metallicity because it currently contains only H II region models that fail to describe the DIG.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1329908','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1329908"><span>Simulation of radiation driven fission <span class="hlt">gas</span> <span class="hlt">diffusion</span> in UO<sub>2</sub>, ThO<sub>2</sub> and PuO<sub>2</sub></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Cooper, Michael William D.; Stanek, Christopher Richard; Turnbull, James Anthony; Uberuaga, Blas P.; Andersson, David Anders</p> <p>2016-12-01</p> <p>Below 1000 K it is thought that fission <span class="hlt">gas</span> <span class="hlt">diffusion</span> in nuclear fuel during irradiation occurs through atomic mixing due to radiation damage. Here we present a molecular dynamics (MD) study of Xe, Kr, Th, U, Pu and O <span class="hlt">diffusion</span> due to irradiation. It is concluded that the ballistic phase does not sufficiently account for the experimentally observed <span class="hlt">diffusion</span>. Thermal spike simulations are used to confirm that electronic stopping remedies the discrepancy with experiment and the predicted <span class="hlt">diffusivities</span> lie within the scatter of the experimental data. Here, our results predict that the <span class="hlt">diffusion</span> coefficients are ordered such that D*<sub>0</sub> > D*<sub>Kr</sub> > D*<sub>Xe</sub> > D*<sub>U</sub>. For all species >98.5% of <span class="hlt">diffusivity</span> is accounted for by electronic stopping. Fission <span class="hlt">gas</span> <span class="hlt">diffusivity</span> was not predicted to vary significantly between ThO<sub>2</sub>, UO<sub>2</sub> and PuO<sub>2</sub>, indicating that this process would not change greatly for mixed oxide fuels.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20010074030','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20010074030"><span>Large Eddy Simulation of Gravitational Effects on Transitional and Turbulent <span class="hlt">Gas</span>-Jet <span class="hlt">Diffusion</span> Flames</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Givi, Peyman; Jaberi, Farhad A.</p> <p>2001-01-01</p> <p>The basic objective of this work is to assess the influence of gravity on "the compositional and the spatial structures" of transitional and turbulent <span class="hlt">diffusion</span> flames via large eddy simulation (LES), and direct numerical simulation (DNS). The DNS is conducted for appraisal of the various closures employed in LES, and to study the effect of buoyancy on the small scale flow features. The LES is based on our "filtered mass density function"' (FMDF) model. The novelty of the methodology is that it allows for reliable simulations with inclusion of "realistic physics." It also allows for detailed analysis of the unsteady large scale flow evolution and compositional flame structure which is not usually possible via Reynolds averaged simulations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20040053510','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20040053510"><span>Large Eddy Simulation Of Gravitational Effects In Transitional And Turbulent <span class="hlt">Gas</span>-Jet <span class="hlt">Diffusion</span> Flames</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Jaberi, Farhad A.; Givi, Peyman</p> <p>2003-01-01</p> <p>The influence of gravity on the spatial and the compositional structures of transitional and turbulent hydrocarbon <span class="hlt">diffusion</span> flames are studies via large eddy simulation (LES) and direct numerical simulation (DNS) of round and planar jets. The subgrid-scale (SGS) closures in LES are based on the filtered mass density function (FMDF) methodology. The FMDF represents the joint probability density function (PDF) of the SGS scalars, and is obtained by solving its transport equation. The fundamental advantage of LES/FMDF is that it accounts for the effects of chemical reaction and buoyancy exactly. The methodology is employed for capturing some of the fundamental influences of gravity in equilibrium flames via realistic chemical kinetic schemes. Some preliminary investigation of the gravity effects in non-equilibrium flames is also conducted, but with idealized chemical kinetics models.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19800013479','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19800013479"><span>Effect of scenedesmus acuminatus green algae extracts on the development of Candida lipolytic yeast in <span class="hlt">gas</span> condensate-containing <span class="hlt">media</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bilmes, B. I.; Kasymova, G. A.; Runov, V. I.; Karavayeva, N. N.</p> <p>1980-01-01</p> <p>Data are given of a comparative study of the growth and development as well as the characteristics of the biomass of the C. Lipolytica yeast according to the content of raw protein, protein, lipids, vitamins in the B group, and residual hydrocarbons during growth in <span class="hlt">media</span> with de-aromatized <span class="hlt">gas</span>-condensate FNZ as the carbon source with aqueous and alcohol extracts of S. acuminatus as the biostimulants. It is shown that the decoction and aqueous extract of green algae has the most intensive stimulating effect on the yeast growth. When a decoction of algae is added to the medium, the content of residual hydrocarbons in the biomass of C. lipolytica yeast is reduced by 4%; the quantity of protein, lipids, thamine and inositol with replacement of the yeast autolysate by the decoction of algae is altered little.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/15089316','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/15089316"><span>Time-resolved contrast function and optical characterization of spatially varying absorptive inclusions at different depths in <span class="hlt">diffusing</span> <span class="hlt">media</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>De Nicola, S; Esposito, R; Lepore, M; Indovina, P L</p> <p>2004-03-01</p> <p>The role of a spatially varying absorptive inhomogeneity located at different depths within a turbid material has been investigated. This inhomogeneity has been characterized by a spatially dependent Gaussian distribution of its absorption coefficient. The present study has been performed calculating the time-resolved contrast function in the framework of the first-order perturbative approach to the <span class="hlt">diffusion</span> equation for a slab geometry and a coaxial measurement scheme. The model has allowed us to take into account different locations of the inclusion along the source-detector axis. The accuracy of time-resolved contrast predictions has been analyzed through comparisons with results of the finite element method that has been used to numerically solve the <span class="hlt">diffusion</span> equation. Recovery of the absorption perturbation parameter of the inhomogeneity for different axial positions has also been investigated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5056907','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5056907"><span>Method for estimating closed-form solutions of the light <span class="hlt">diffusion</span> equation for turbid <span class="hlt">media</span> of any boundary shape</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Alqasemi, Umar; Salehi, Hassan S.; Zhu, Quing</p> <p>2016-01-01</p> <p>This paper reports a method of estimating an approximate closed-form solution to the light <span class="hlt">diffusion</span> equation for any type of geometry involving Dirichlet’s boundary condition with known source location. It is based on estimating the optimum locations of multiple imaginary point sources to cancel the fluence at the extrapolated boundary by constrained optimization using a genetic algorithm. The mathematical derivation of the problem to approach the optimum solution for the direct-current type of <span class="hlt">diffuse</span> optical systems is described in detail. Our method is first applied to slab geometry and compared with a truncated series solution. After that, it is applied to hemispherical geometry and compared with Monte Carlo simulation results. The method provides a fast and sufficiently accurate fluence distribution for optical reconstruction. PMID:26831771</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015SPIE.9538E..0GA','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015SPIE.9538E..0GA"><span>Light propagation through weakly scattering <span class="hlt">media</span>: a study of Monte Carlo vs. <span class="hlt">diffusion</span> theory with application to neuroimaging</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ancora, Daniele; Zacharopoulos, Athanasios; Ripoll, Jorge; Zacharakis, Giannis</p> <p>2015-07-01</p> <p>One of the major challenges within Optical Imaging, photon propagation through clear layers embedded between scattering tissues, can be now efficiently modelled in real-time thanks to the Monte Carlo approach based on GPU. Because of its nature, the photon propagation problem can be very easily parallelized and ran on low cost hardware, avoiding the need for expensive Super Computers. A comparison between <span class="hlt">Diffusion</span> and MC photon propagation theory is presented in this work with application to neuroimaging, investigating low scattering regions in a mouse-like phantom. Regions such as the Cerebral Spinal Fluid, are currently not taken into account in the classical computational models because of the impossibility to accurately simulate light propagation using fast <span class="hlt">Diffusive</span> Equation approaches, leading to inaccuracies during the reconstruction process. The goal of the study presented here, is to reduce and further improve the computation accuracy of the reconstructed solution in a highly realistic scenario in the case of neuroimaging in preclinical mouse models.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://cfpub.epa.gov/si/si_public_record_report.cfm?dirEntryId=150663&keyword=helium&actType=&TIMSType=+&TIMSSubTypeID=&DEID=&epaNumber=&ntisID=&archiveStatus=Both&ombCat=Any&dateBeginCreated=&dateEndCreated=&dateBeginPublishedPresented=&dateEndPublishedPresented=&dateBeginUpdated=&dateEndUpdated=&dateBeginCompleted=&dateEndCompleted=&personID=&role=Any&journalID=&publisherID=&sortBy=revisionDate&count=50&CFID=84682432&CFTOKEN=96870979','EPA-EIMS'); return false;" href="http://cfpub.epa.gov/si/si_public_record_report.cfm?dirEntryId=150663&keyword=helium&actType=&TIMSType=+&TIMSSubTypeID=&DEID=&epaNumber=&ntisID=&archiveStatus=Both&ombCat=Any&dateBeginCreated=&dateEndCreated=&dateBeginPublishedPresented=&dateEndPublishedPresented=&dateBeginUpdated=&dateEndUpdated=&dateBeginCompleted=&dateEndCompleted=&personID=&role=Any&journalID=&publisherID=&sortBy=revisionDate&count=50&CFID=84682432&CFTOKEN=96870979"><span>ANALYSIS OF A <span class="hlt">GAS</span>-PHASE PARTITIONING TRACER TEST CONDUCTED THROUGH FRACTURED <span class="hlt">MEDIA</span></span></a></p> <p><a target="_blank" href="http://oaspub.epa.gov/eims/query.page">EPA Science Inventory</a></p> <p></p> <p></p> <p>The <span class="hlt">gas</span>-phase partitioning tracer method was used to estimate non-aqueous phase liquid (NAPL), water, and air saturations in the vadose zone at a chlorinated-solvent contaminated field site in Tucson, AZ. The tracer test was conducted in a fractured clay system that is the confin...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AGUFM.P21A0224B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUFM.P21A0224B"><span>Mineral Precipitation in Porous <span class="hlt">Media</span>: Laboratory <span class="hlt">Diffusion</span> Experiments as Analogues for Concretion Formation in Utah and on Mars</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Barge, L. M.; Petruska, J.; Potter, S.; Cho, J.; Chan, M.; Nealson, K.</p> <p>2007-12-01</p> <p>We present results of laboratory gel <span class="hlt">diffusion</span> experiments designed to simulate the precipitation of iron minerals in natural systems. Liesegang bands and crystals of various iron minerals were formed in aqueous gels, "mini- concretions" of mineral precipitate were formed in both sand and a sand/agarose mixture, and the formation of hollow mineral spheres was observed in gel precipitation experiments where organics were introduced. These mineral structures are analogous to concretion forms observed in the Navajo Sandstone region of Utah, which have been suggested as terrestrial analogs for the "blueberry" hematite concretions on Mars. Iron mineral precipitates (perhaps with a gel precursor) occur in many forms in the Navajo Sandstone, including "mini- concretions" (solid concretions 1-2 mm in diameter), "rind-like" concretions (hollow spheres of hematite several cm in diameter, surrounding a region of sandstone), and Liesegang banding (banded patterns that form at reaction fronts through <span class="hlt">diffusion</span> of ions from one reservoir to another). On Mars only small (4-5mm) and mini-concretions (~ 1mm) have been observed; Liesegang bands or large rind-like concretions have not yet been discovered. The varying conditions that give rise to each of these mineral structures in the laboratory indicate that the small, spheroidal types of iron precipitates found in the Utah and Martian environments may be diagnostic of the <span class="hlt">diffusion</span> medium, presence of organics, and characteristics of fluid in that region.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JPS...320..222R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JPS...320..222R"><span>Measurement of effective bulk and contact resistance of <span class="hlt">gas</span> <span class="hlt">diffusion</span> layer under inhomogeneous compression - Part II: Thermal conductivity</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Roy Chowdhury, Prabudhya; Vikram, Ajit; Phillips, Ryan K.; Hoorfar, Mina</p> <p>2016-07-01</p> <p>The <span class="hlt">gas</span> <span class="hlt">diffusion</span> 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 <span class="hlt">gas</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JPS...341..302S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JPS...341..302S"><span>Eliminating micro-porous layer from <span class="hlt">gas</span> <span class="hlt">diffusion</span> electrode for use in high temperature polymer electrolyte membrane fuel cell</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Su, Huaneng; Xu, Qian; Chong, Junjie; Li, Huaming; Sita, Cordellia; Pasupathi, Sivakumar</p> <p>2017-02-01</p> <p>In this work, we report a simple strategy to improve the performance of high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) by eliminating the micro-porous layer (MPL) from its <span class="hlt">gas</span> <span class="hlt">diffusion</span> electrodes (GDEs). Due to the absence of liquid water and the general use of high amount of catalyst, the MPL in a HT-PEMFC system works limitedly. Contrarily, the elimination of the MPL leads to an interlaced micropore/macropore composited structure in the catalyst layer (CL), which favors <span class="hlt">gas</span> transport and catalyst utilization, resulting in a greatly improved single cell performance. At the normal working voltage (0.6 V), the current density of the GDE eliminated MPL reaches 0.29 A cm-2, and a maximum power density of 0.54 W cm-2 at 0.36 V is obtained, which are comparable to the best results yet reported for the HT-PEMFCs with similar Pt loading and operated using air. Furthermore, the MPL-free GDE maintains an excellent durability during a preliminary 1400 h HT-PEMFC operation, owing to its structure advantages, indicating the feasibility of this electrode for practical applications.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28090766','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28090766"><span><span class="hlt">Gas</span> <span class="hlt">Diffusion</span> Barriers Prepared by Spatial Atmospheric Pressure Plasma Enhanced ALD.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Hoffmann, Lukas; Theirich, Detlef; Pack, Sven; Kocak, Firat; Schlamm, Daniel; Hasselmann, Tim; Fahl, Henry; Räupke, André; Gargouri, Hassan; Riedl, Thomas</p> <p>2017-02-01</p> <p>In this work, we report on aluminum oxide (Al2O3) <span class="hlt">gas</span> permeation barriers prepared by spatial ALD (SALD) at atmospheric pressure. We compare the growth characteristics and layer properties using trimethylaluminum (TMA) in combination with an Ar/O2 remote atmospheric pressure plasma for different substrate velocities and different temperatures. The resulting Al2O3 films show ultralow water vapor transmission rates (WVTR) on the order of 10(-6) gm(-2)d(-1). In notable contrast, plasma based layers already show good barrier properties at low deposition temperatures (75 °C), while water based processes require a growth temperature above 100 °C to achieve equally low WVTRs. The activation energy for the water permeation mechanism was determined to be 62 kJ/mol.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_23 --> <div id="page_24" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li class="active"><span>24</span></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="461"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016MNRAS.461.4505J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016MNRAS.461.4505J"><span><span class="hlt">Diffuse</span> <span class="hlt">gas</span> in retired galaxies: nebular emission templates and constraints on the sources of ionization</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Johansson, Jonas; Woods, Tyrone E.; Gilfanov, Marat; Sarzi, Marc; Chen, Yan-Mei; Oh, Kyuseok</p> <p>2016-10-01</p> <p>We present emission-line templates for passively-evolving (`retired') galaxies, useful for investigation of the evolution of the interstellar medium in these galaxies, and characterization of their high-temperature source populations. The templates are based on high signal-to-noise (>800) co-added spectra (3700-6800 Å) of ˜11 500 <span class="hlt">gas</span>-rich Sloan Digital Sky Survey galaxies devoid of star formation and active galactic nuclei. Stacked spectra are provided for the entire sample and sub-samples binned by mean stellar age. In our previous paper, Johansson et al., these spectra provided the first measurements of the He II 4686 Å line in passively-evolving galaxies, and the observed He II/Hβ ratio constrained the contribution of accreting white dwarfs (the `single-degenerate' scenario) to the Type Ia supernova rate. In this paper, the full range of unambiguously detected emission lines are presented. Comparison of the observed [O I] 6300 Å/Hα ratio with photoionization models further constrains any high-temperature single-degenerate scenario for Type Ia supernovae (with 1.5 ≲ T/105 K ≲ 10) to ≲3-6 per cent of the observed rate in the youngest age bin (i.e. highest SN Ia rate). Hence, for the same temperatures, in the presence of an ambient population of post-asymptotic giant branch stars, we exclude additional high-temperature sources with a combined ionizing luminosity of ≈1.35 × 1030 L⊙/M⊙,* for stellar populations with mean ages of 1-4 Gyr. Furthermore, we investigate the extinction affecting both the stellar and nebular continuum. The latter shows about five times higher values. This contradicts isotropically distributed dust and <span class="hlt">gas</span> that renders similar extinction values for both cases.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1013261','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1013261"><span>Experimentally Measured Interfacial Area during <span class="hlt">Gas</span> Injection into Saturated Porous <span class="hlt">Media</span>: An Air Sparging Analogy</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Crandall, Dustin; Ahmadi, Goodarz; Smith, Duane H., Bromhal, Grant</p> <p>2010-01-01</p> <p>The amount of interfacial area (awn) between air and subsurface liquids during air-sparging can limit the rate of site remediation. Lateral movement within porous <span class="hlt">media</span> could be encountered during air-sparging operations when air moves along the bottom of a low-permeability lens. This study was conducted to directly measure the amount of awn between air and water flowing within a bench-scale porous flow cell during the lateral movement of air along the upper edge of the cell during air injections into an initially water-saturated flow cell. Four different cell orientations were used to evaluate the effect of air injection rates and porous <span class="hlt">media</span> geometries on the amount of awn between fluids. Air was injected at flow rates that varied by three orders of magnitude, and for each flow cellover this range of injection rates little change in awn was noted. A wider variation in awn was observed when air moved through different regions for the different flow cell orientations. These results are in good agreement with the experimental findings of Waduge et al. (2007), who performed experiments in a larger sand-pack flow cell, and determined that air-sparging efficiency is nearly independent of flow rate but highly dependent on the porous structure. By directly measuring the awn, and showing that awn does not vary greatly with changes in injection rate, we show that the lack of improvement to remediation rates is because there is a weak dependence of the awn on the air injection rate.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFMNS51B1832G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFMNS51B1832G"><span>Fractional <span class="hlt">Diffusion</span> Analysis of the Electromagnetic Field In Fractured <span class="hlt">Media</span> Part II: 2.5-D Approach</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ge, J.; Everett, M. E.; Weiss, C. J.</p> <p>2012-12-01</p> <p>A 2.5D finite difference (FD) frequency-domain modeling algorithm based on the theory of fractional <span class="hlt">diffusion</span> of electromagnetic (EM) fields generated by a loop source lying above a fractured geological medium is addressed in this paper. The presence of fractures in the subsurface, usually containing highly conductive pore fluids, gives rise to spatially hierarchical flow paths of induced EM eddy currents. The <span class="hlt">diffusion</span> of EM eddy currents in such formations is anomalous, generalizing the classical Gaussian process described by the conventional Maxwell equations. Based on the continuous time random walk (CTRW) theory, the <span class="hlt">diffusion</span> of EM eddy currents in a rough medium is governed by the fractional Maxwell equations. Here, we model the EM response of a 2D subsurface containing fractured zones, with a 3D loop source, which results the so-called 2.5D model geometry. The governing equation in the frequency domain is converted using Fourier transform into k domain along the strike direction (along which the model conductivity doesn't vary). The resulting equation system is solved by the multifrontal massively parallel solver (MUMPS). The data obtained is then converted back to spatial domain and the time domain. We find excellent agreement between the FD and analytic solutions for a rough halfspace model. Then FD solutions are calculated for a 2D fault zone model with variable conductivity and roughness. We compare the results with responses from several classical models and explore the relationship between the roughness and the spatial density of the fracture distribution.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/890709','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/890709"><span>Comparison of Kinetic and Equilibrium Reaction Models inSimulating the Behavior of <span class="hlt">Gas</span> Hydrates in Porous <span class="hlt">Media</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Kowalsky, Michael B.; Moridis, George J.</p> <p>2006-05-12</p> <p>In this study we compare the use of kinetic and equilibrium reaction models in the simulation of <span class="hlt">gas</span> (methane) hydrates in porous <span class="hlt">media</span>. Our objective is to evaluate through numerical simulation the importance of employing kinetic versus equilibrium reaction models for predicting the response of hydrate-bearing systems to external stimuli, such as changes in pressure and temperature. Specifically, we (1) analyze and compare the responses simulated using both reaction models for production in various geological settings and for the case of depressurization in a core during extraction; and (2) examine the sensitivity to factors such as initial hydrate saturation, hydrate reaction surface area, and numerical discretization. We find that for systems undergoing thermal stimulation and depressurization, the calculated responses for both reaction models are remarkably similar, though some differences are observed at early times. Given these observations, and since the computational demands for the kinetic reaction model far exceed those for the equilibrium reaction model, the use of the equilibrium reaction model often appears to be justified and preferred for simulating the behavior of <span class="hlt">gas</span> hydrates.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24688828','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24688828"><span>Reliable recovery of the optical properties of multi-layer turbid <span class="hlt">media</span> by iteratively using a layered <span class="hlt">diffusion</span> model at multiple source-detector separations.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Liao, Yu-Kai; Tseng, Sheng-Hao</p> <p>2014-03-01</p> <p>Accurately determining the optical properties of multi-layer turbid <span class="hlt">media</span> using a layered <span class="hlt">diffusion</span> model is often a difficult task and could be an ill-posed problem. In this study, an iterative algorithm was proposed for solving such problems. This algorithm employed a layered <span class="hlt">diffusion</span> model to calculate the optical properties of a layered sample at several source-detector separations (SDSs). The optical properties determined at various SDSs were mutually referenced to complete one round of iteration and the optical properties were gradually revised in further iterations until a set of stable optical properties was obtained. We evaluated the performance of the proposed method using frequency domain Monte Carlo simulations and found that the method could robustly recover the layered sample properties with various layer thickness and optical property settings. It is expected that this algorithm can work with photon transport models in frequency and time domain for various applications, such as determination of subcutaneous fat or muscle optical properties and monitoring the hemodynamics of muscle.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008A%26A...489..217P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008A%26A...489..217P"><span>Imaging galactic <span class="hlt">diffuse</span> <span class="hlt">gas</span>: bright, turbulent CO surrounding the line of sight to NRAO150</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pety, J.; Lucas, R.; Liszt, H. S.</p> <p>2008-10-01</p> <p>Aims: To understand the environment and extended structure of the host galactic <span class="hlt">gas</span> whose molecular absorption line chemistry, we previously observed along the microscopic line of sight to the blazar/radiocontinuum source NRAO150 (aka B0355+508). Methods: We used the IRAM 30 m Telescope and Plateau de Bure Interferometer to make two series of images of the host <span class="hlt">gas</span>: i) 22.5'' resolution single-dish maps of 12CO J = 1-0 and 2-1 emission over a 220'' by 220'' field; ii) a hybrid (interferometer+singledish) aperture synthesis mosaic of 12CO J = 1-0 emission at 5.8'' resolution over a 90''-diameter region. Results: At 22.5'' resolution, the CO J = 1-0 emission toward NRAO150 is 30-100% brighter at some velocities than seen previously with 1' resolution, and there are some modest systematic velocity gradients over the 220'' field. Of the five CO components seen in the absorption spectra, the weakest ones are absent in emission toward NRAO150 but appear more strongly at the edges of the region mapped in emission. The overall spatial variations in the strongly emitting <span class="hlt">gas</span> have Poisson statistics with rms fluctuations about equal to the mean emission level in the line wings and much of the line cores. The J = 2-1/J = 1-0 line ratios calculated pixel-by-pixel cluster around 0.7. At 6'' resolution, disparity between the absorption and emission profiles of the stronger components has been largely ameliorated. The 12CO J = 1-0 emission exhibits i) remarkably bright peaks, {T}_mb = 12-13 K, even as 4'' from NRAO150; ii) smaller relative levels of spatial fluctuation in the line cores, but a very broad range of possible intensities at every velocity; and iii) striking kinematics whereby the monotonic velocity shifts and supersonically broadened lines in 22.5'' spectra are decomposed into much stronger velocity gradients and abrupt velocity reversals of intense but narrow, probably subsonic, line cores. Conclusions: CO components that are observed in absorption at a moderate</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016SPIE.9864E..0QW','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016SPIE.9864E..0QW"><span>A sequential method for measuring the optical properties of two-layer <span class="hlt">media</span> with spatially-resolved <span class="hlt">diffuse</span> reflectance: simulation study</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Aichen; Lu, Renfu; Xie, Lijuan</p> <p>2016-05-01</p> <p>A sequential method for estimating the optical properties of two-layer <span class="hlt">media</span> with spatially-resolved <span class="hlt">diffuse</span> reflectance was proposed and validated using Monte Carlo-generated reflectance profiles. The relationship between the penetration depth of detected photons and source-detector separation was first studied. Photons detected at larger source-detector separations generally penetrated deeper into the medium than those detected at small source-detector separations. The effect of each parameter (i.e., the absorption and reduced scattering coefficients (μa and μs') of each layer, and the thickness of top layer) on reflectance was investigated. It was found that the relationship between the optical properties and thickness of top layer was a critical factor in determining whether photons would have sufficient interactions with the top layer and also penetrate into the bottom layer. The constraints for the proposed sequential estimation method were quantitatively determined by the curve fitting procedure coupled with error contour map analyses. Results showed that the optical properties of top layer could be determined within 10% error using the semi-infinite <span class="hlt">diffusion</span> model for reflectance profiles with properly selected start and end points, when the thickness of top layer was larger than two times its mean free path (mfp'). And the optical properties of the bottom layer could be estimated within 10% error by the two-layer <span class="hlt">diffusion</span> model, when the thickness of top layer was less than 16 times its mfp'. The proposed sequential estimation method is promising for improving the estimation of the optical properties of two-layer tissues from the same spatially-resolved reflectance.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27505816','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27505816"><span>Mapping the energy density of shaped waves in scattering <span class="hlt">media</span> onto a complete set of <span class="hlt">diffusion</span> modes.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ojambati, Oluwafemi S; Mosk, Allard P; Vellekoop, Ivo M; Lagendijk, Ad; Vos, Willem L</p> <p>2016-08-08</p> <p>We study the energy density of shaped waves inside a quasi-1D disordered waveguide. We find that the spatial energy density of optimally shaped waves, when expanded in the complete set of eigenfunctions of the <span class="hlt">diffusion</span> equation, is well described by considering only a few of the lowest eigenfunctions. Taking into account only the fundamental eigenfunction, the total internal energy inside the sample is underestimated by only 2%. The spatial distribution of the shaped energy density is very similar to the fundamental eigenfunction, up to a cosine distance of about 0.01. We obtain the energy density of transmission eigenchannels inside the sample by numerical simulation of the scattering matrix. Computing the transmission-averaged energy density over all transmission channels yields the ensemble averaged energy density of shaped waves. From the averaged energy density, we reconstruct its spatial distribution using the eigenfunctions of the <span class="hlt">diffusion</span> equation. The results of our study have exciting applications in controlled biomedical imaging, efficient light harvesting in solar cells, enhanced energy conversion in solid-state lighting, and low threshold random lasers.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23188803','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23188803"><span>A mathematical model of fluid and <span class="hlt">gas</span> flow in nanoporous <span class="hlt">media</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Monteiro, Paulo J M; Rycroft, Chris H; Barenblatt, Grigory Isaakovich</p> <p>2012-12-11</p> <p>The mathematical modeling of the flow in nanoporous rocks (e.g., shales) becomes an important new branch of subterranean fluid mechanics. The classic approach that was successfully used in the construction of the technology to develop oil and <span class="hlt">gas</span> deposits in the United States, Canada, and the Union of Soviet Socialist Republics becomes insufficient for deposits in shales. In the present article a mathematical model of the flow in nanoporous rocks is proposed. The model assumes the rock consists of two components: (i) a matrix, which is more or less an ordinary porous or fissurized-porous medium, and (ii) specific organic inclusions composed of kerogen. These inclusions may have substantial porosity but, due to the nanoscale of pores, tubes, and channels, have extremely low permeability on the order of a nanodarcy (~109-²¹ m² ) or less. These inclusions contain the majority of fluid: oil and <span class="hlt">gas</span>. Our model is based on the hypothesis that the permeability of the inclusions substantially depends on the pressure gradient. At the beginning of the development of the deposit, boundary layers are formed at the boundaries of the low-permeable inclusions, where the permeability is strongly increased and intensive flow from inclusions to the matrix occurs. The resulting formulae for the production rate of the deposit are presented in explicit form. The formulae demonstrate that the production rate of deposits decays with time following a power law whose exponent lies between -1/2 and -1. Processing of experimental data obtained from various oil and <span class="hlt">gas</span> deposits in shales demonstrated an instructive agreement with the prediction of the model.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3528606','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3528606"><span>A mathematical model of fluid and <span class="hlt">gas</span> flow in nanoporous <span class="hlt">media</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Monteiro, Paulo J. M.; Rycroft, Chris H.; Barenblatt, Grigory Isaakovich</p> <p>2012-01-01</p> <p>The mathematical modeling of the flow in nanoporous rocks (e.g., shales) becomes an important new branch of subterranean fluid mechanics. The classic approach that was successfully used in the construction of the technology to develop oil and <span class="hlt">gas</span> deposits in the United States, Canada, and the Union of Soviet Socialist Republics becomes insufficient for deposits in shales. In the present article a mathematical model of the flow in nanoporous rocks is proposed. The model assumes the rock consists of two components: (i) a matrix, which is more or less an ordinary porous or fissurized-porous medium, and (ii) specific organic inclusions composed of kerogen. These inclusions may have substantial porosity but, due to the nanoscale of pores, tubes, and channels, have extremely low permeability on the order of a nanodarcy () or less. These inclusions contain the majority of fluid: oil and <span class="hlt">gas</span>. Our model is based on the hypothesis that the permeability of the inclusions substantially depends on the pressure gradient. At the beginning of the development of the deposit, boundary layers are formed at the boundaries of the low-permeable inclusions, where the permeability is strongly increased and intensive flow from inclusions to the matrix occurs. The resulting formulae for the production rate of the deposit are presented in explicit form. The formulae demonstrate that the production rate of deposits decays with time following a power law whose exponent lies between and . Processing of experimental data obtained from various oil and <span class="hlt">gas</span> deposits in shales demonstrated an instructive agreement with the prediction of the model. PMID:23188803</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JEOS....8E3081G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JEOS....8E3081G"><span>Polishing of Optical <span class="hlt">Media</span> by Dielectric Barrier Discharge Inert <span class="hlt">Gas</span> Plasma at Atmospheric Pressure</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gerhard, C.; Weihs, T.; Luca, A.; Wieneke, S.; Viöl, W.</p> <p>2013-12-01</p> <p>In this paper, surface smoothing of optical glasses, glass ceramic and sapphire using a low-power dielectric barrier discharge inert <span class="hlt">gas</span> plasma at atmospheric pressure is presented. For this low temperature treatment method, no vacuum devices or chemicals are required. It is shown that by such plasma treatment the micro roughness and waviness of the investigated polished surfaces were significantly decreased, resulting in a decrease in surface scattering. Further, plasma polishing of lapped fused silica is introduced. Based on simulation results, a plasma physical process is suggested to be the underlying mechanism for initialising the observed smoothing effect.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/12175277','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/12175277"><span>Optical rotation and linear and circular depolarization rates in <span class="hlt">diffusively</span> scattered light from chiral, racemic, and achiral turbid <span class="hlt">media</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Hadley, Kevin C; Vitkin, I Alex</p> <p>2002-07-01</p> <p>The polarization properties of light scattered in a lateral direction from turbid <span class="hlt">media</span> were studied. Polarization modulation and synchronous detection were used to measure, and Mueller calculus to model and derive, the degrees of surviving linear and circular polarization and the optical rotation induced by turbid samples. Polystyrene microspheres were used as scatterers in water solutions containing dissolved chiral, racemic, and achiral molecules. The preservation of circular polarization was found to exceed the linear polarization preservation for all samples examined. The optical rotation induced increased with the chiral molecule concentration only, whereas both linear and circular polarizations increased with an increase in the concentrations of chiral, racemic, and achiral molecules. This latter effect was shown to stem solely from the refractive index matching mechanism induced by the solute molecules, independent of their chiral nature.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25678320','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25678320"><span>A novel multiple headspace extraction <span class="hlt">gas</span> chromatographic method for measuring the <span class="hlt">diffusion</span> coefficient of methanol in water and in olive oil.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Zhang, Chun-Yun; Chai, Xin-Sheng</p> <p>2015-03-13</p> <p>A novel method for the determination of the <span class="hlt">diffusion</span> coefficient (D) of methanol in water and olive oil has been developed. Based on multiple headspace extraction <span class="hlt">gas</span> chromatography (MHE-GC), the methanol released from the liquid sample of interest in a closed sample vial was determined in a stepwise fashion. A theoretical model was derived to establish the relationship between the <span class="hlt">diffusion</span> coefficient and the GC signals from MHE-GC measurements. The results showed that the present method has an excellent precision (RSD<1%) in the linear fitting procedure and good accuracy for the <span class="hlt">diffusion</span> coefficients of methanol in both water and olive oil, when compared with data reported in the literature. The present method is simple and practical and can be a valuable tool for the determination of the <span class="hlt">diffusion</span> coefficient of volatile analyte(s) into food simulants from food and beverage packaging material, both in research studies and in actual applications.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/15006862','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/15006862"><span>Delineation of Fast Flow Paths in Porous <span class="hlt">Media</span> Using Noble <span class="hlt">Gas</span> Tracers</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Hudson, G B; Moran, J E</p> <p>2002-03-21</p> <p>Isotopically enriched xenon isotopes are ideal for tracking the flow of relatively large volumes of groundwater. Dissolved noble <span class="hlt">gas</span> tracers behave conservatively in the saturated zone, pose no health risk to drinking water supplies, and can be used with a large dynamic range. Different Xe isotopes can be used simultaneously at multiple recharge sources in a single experiment. Results from a tracer experiment at a California water district suggests that a small fraction of tracer moved from the recharge ponds through the thick, unconfined, coarse-grained alluvial aquifer to high capacity production wells at a horizontal velocity of 6 m/day. In contrast, mean water residence times indicate that the average rate of transport is 0.5 to 1 m/day.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5075678','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5075678"><span><span class="hlt">Gas</span> transport during in vitro and in vivo preclinical testing of inert <span class="hlt">gas</span> therapies</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Katz, Ira; Palgen, Marc; Murdock, Jacqueline; Martin, Andrew R.; Farjot, Géraldine; Caillibotte, Georges</p> <p>2016-01-01</p> <p>New <span class="hlt">gas</span> therapies using inert gases such as xenon and argon are being studied, which require in vitro and in vivo preclinical experiments. Examples of the kinetics of <span class="hlt">gas</span> transport during such experiments are analyzed in this paper. Using analytical and numerical models, we analyze an in vitro experiment for <span class="hlt">gas</span> transport to a 96 cell well plate and an in vivo delivery to a small animal chamber, where the key processes considered are the wash-in of test <span class="hlt">gas</span> into an apparatus dead volume, the <span class="hlt">diffusion</span> of test <span class="hlt">gas</span> through the liquid <span class="hlt">media</span> in a well of a cell test plate, and the pharmacokinetics in a rat. In the case of small animals in a chamber, the key variable controlling the kinetics is the chamber wash-in time constant that is a function of the chamber volume and the <span class="hlt">gas</span> flow rate. For cells covered by a liquid <span class="hlt">media</span> the <span class="hlt">diffusion</span> of <span class="hlt">gas</span> through the liquid <span class="hlt">media</span> is the dominant mechanism, such that liquid depth and the <span class="hlt">gas</span> <span class="hlt">diffusion</span> constant are the key parameters. The key message from these analyses is that the transport of <span class="hlt">gas</span> during preclinical experiments can be important in determining the true dose as experienced at the site of action in an animal or to a cell. PMID:27826419</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27826419','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27826419"><span><span class="hlt">Gas</span> transport during in vitro and in vivo preclinical testing of inert <span class="hlt">gas</span> therapies.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Katz, Ira; Palgen, Marc; Murdock, Jacqueline; Martin, Andrew R; Farjot, Géraldine; Caillibotte, Georges</p> <p>2016-03-01</p> <p>New <span class="hlt">gas</span> therapies using inert gases such as xenon and argon are being studied, which require in vitro and in vivo preclinical experiments. Examples of the kinetics of <span class="hlt">gas</span> transport during such experiments are analyzed in this paper. Using analytical and numerical models, we analyze an in vitro experiment for <span class="hlt">gas</span> transport to a 96 cell well plate and an in vivo delivery to a small animal chamber, where the key processes considered are the wash-in of test <span class="hlt">gas</span> into an apparatus dead volume, the <span class="hlt">diffusion</span> of test <span class="hlt">gas</span> through the liquid <span class="hlt">media</span> in a well of a cell test plate, and the pharmacokinetics in a rat. In the case of small animals in a chamber, the key variable controlling the kinetics is the chamber wash-in time constant that is a function of the chamber volume and the <span class="hlt">gas</span> flow rate. For cells covered by a liquid <span class="hlt">media</span> the <span class="hlt">diffusion</span> of <span class="hlt">gas</span> through the liquid <span class="hlt">media</span> is the dominant mechanism, such that liquid depth and the <span class="hlt">gas</span> <span class="hlt">diffusion</span> constant are the key parameters. The key message from these analyses is that the transport of <span class="hlt">gas</span> during preclinical experiments can be important in determining the true dose as experienced at the site of action in an animal or to a cell.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1016934','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1016934"><span>Simulation of Infrared Laser Heating of Silica Using Heat Conduction and Multifrequency Radiation <span class="hlt">Diffusion</span> Equations Adapted for Homogeneous Refractive Lossy <span class="hlt">Media</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Shestakov, A I; Matthews, M J; Vignes, R M; Stolken, J S</p> <p>2010-10-28</p> <p>Localized, transient heating of materials using micro-scale, highly absorbing laser light has been used in many industries to anneal, melt and ablate material with high precision. Accurate modeling of the relative contributions of conductive, convective and radiative losses as a function of laser parameters is essential to optimizing micro-scale laser processing of materials. In bulk semi-transparent materials such as silicate glass melts, radiation transport is known to play a significantly larger role as the temperature increases. Conventionally, radiation is treated in the frequency-averaged <span class="hlt">diffusive</span> limit (Rosseland approximation). However, the role and proper treatment of radiative processes under rapidly heated, high thermal gradient conditions, often created through laser-matter interactions, is at present not clear. Starting from the radiation transport equation for homogeneous, refractive lossy <span class="hlt">media</span>, they derive the corresponding time-dependent multi-frequency <span class="hlt">diffusion</span> equations. Zeroth and first moments of the transport equation couple the energy density, flux and pressure tensor. The system is closed by neglecting the temporal derivative of the flux and replacing the pressure tensor by its diagonal analogue. The radiation equations are coupled to a <span class="hlt">diffusion</span> equation for the matter temperature. They are interested in modeling infrared laser heating of silica over sub-millimeter length scales, and at possibly rapid rates. Hence, in contrast to related work, they retain the temporal derivative of the radiation field. They derive boundary conditions at a planar air-silica interface taking account of reflectivities obtained from the Fresnel relations that include absorption. The effect of a temperature-dependent absorption index is explored through construction of a multi-phonon dielectric function that includes mode dispersion. The spectral dimension is discretized into a finite number of intervals yielding a system of multigroup <span class="hlt">diffusion</span> equations</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1082175','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1082175"><span>Isothermal Ice Crystallization Kinetics in the <span class="hlt">Gas-Diffusion</span> Layer of a Proton-Exchange-Membrane Fuel Cell</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Dursch, Thomas J.; Ciontea, Monica A.; Radke, Clayton J.; Weber, Adam Z.</p> <p>2011-12-01</p> <p>Nucleation and growth of ice in the fibrous <span class="hlt">gas-diffusion</span> layer (GDL) of a proton-exchange membrane fuel cell (PEMFC) are studied using isothermal differential scanning calorimetry (DSC). Isothermal crystallization rates and pseudo-steady-state nucleation rates are obtained as a function of subcooling from heat-flow and induction-time measurements. Kinetics of ice nucleation and growth are studied at two polytetrafluoroethylene (PTFE) loadings (0 and 10 wt %) in a commercial GDL for temperatures between 240 and 273 K. A nonlinear ice-crystallization rate expression is developed using Johnson–Mehl–Avrami–Kolmogorov (JMAK) theory, in which the heat-transfer-limited growth rate is determined from the moving-boundary Stefan problem. Induction times follow a Poisson distribution and increase upon addition of PTFE, indicating that nucleation occurs more slowly on a hydrophobic fiber than on a hydrophilic fiber. The determined nucleation rates and induction times follow expected trends from classical nucleation theory. Finally, a validated rate expression is now available for predicting ice-crystallization kinetics in GDLs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26036588','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26036588"><span>Enhanced hydroxyl radical generation in the combined ozonation and electrolysis process using carbon nanotubes containing <span class="hlt">gas</span> <span class="hlt">diffusion</span> cathode.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wu, Donghai; Lu, Guanghua; Zhang, Ran; Lin, Qiuhong; Yan, Zhenhua; Liu, Jianchao; Li, Yi</p> <p>2015-10-01</p> <p>Combination of ozone together with electrolysis (ozone-electrolysis) is a promising wastewater treatment technology. This work investigated the potential use of carbon nanotube (CNT)-based <span class="hlt">gas</span> <span class="hlt">diffusion</span> cathode (GDC) for ozone-electrolysis process employing hydroxyl radicals (·OH) production as an indicator. Compared with conventional active carbon (AC)-polytetrafluoroethylene (PTFE) and carbon black (CB)-PTFE cathodes, the production of ·OH in the coupled process was improved using CNTs-PTFE GDC. Appropriate addition of acetylene black (AB) and pore-forming agent Na2SO4 could enhance the efficiency of CNTs-PTFE GDC. The optimum GDC composition was obtained by response surface methodology (RSM) analysis and was determined as CNTs 31.2 wt%, PTFE 60.6 wt%, AB 3.5 wt%, and Na2SO4 4.7 wt%. Moreover, the optimized CNT-based GDC exhibited much more effective than traditional Ti and graphite cathodes in Acid Orange 7 (AO7) mineralization and possessed the desirable stability without performance decay after ten times reaction. The comparison tests revealed that peroxone reaction was the main pathway of ·OH production in the present system, and cathodic reduction of ozone could significantly promote ·OH generation. These results suggested that application of CNT-based GDC offers considerable advantages in ozone-electrolysis of organic wastewater.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24077341','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24077341"><span>Analysis of petroleum-contaminated soils by <span class="hlt">diffuse</span> reflectance spectroscopy and sequential ultrasonic solvent extraction-<span class="hlt">gas</span> chromatography.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Okparanma, Reuben N; Coulon, Frederic; Mouazen, Abdul M</p> <p>2014-01-01</p> <p>In this study, we demonstrate that partial least-squares regression analysis with full cross-validation of spectral reflectance data estimates the amount of polycyclic aromatic hydrocarbons in petroleum-contaminated tropical rainforest soils. We applied the approach to 137 field-moist intact soil samples collected from three oil spill sites in Ogoniland in the Niger Delta province (5.317°N, 6.467°E), Nigeria. We used sequential ultrasonic solvent extraction-<span class="hlt">gas</span> chromatography as the reference chemical method. We took soil <span class="hlt">diffuse</span> reflectance spectra with a mobile fibre-optic visible and near-infrared spectrophotometer (350-2500 nm). Independent validation of combined data from studied sites showed reasonable prediction precision (root-mean-square error of prediction = 1.16-1.95 mg kg(-1), ratio of prediction deviation = 1.86-3.12, and validation r(2) = 0.77-0.89). This suggests that the methodology may be useful for rapid assessment of the spatial variability of polycyclic aromatic hydrocarbons in petroleum-contaminated soils in the Niger Delta to inform risk assessment and remediation.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li class="active"><span>24</span></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_24 --> <div id="page_25" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li class="active"><span>25</span></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="481"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22133053','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22133053"><span>Isothermal ice crystallization kinetics in the <span class="hlt">gas-diffusion</span> layer of a proton-exchange-membrane fuel cell.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Dursch, T J; Ciontea, M A; Radke, C J; Weber, A Z</p> <p>2012-01-17</p> <p>Nucleation and growth of ice in the fibrous <span class="hlt">gas-diffusion</span> layer (GDL) of a proton-exchange membrane fuel cell (PEMFC) are investigated using isothermal differential scanning calorimetry (DSC). Isothermal crystallization rates and pseudo-steady-state nucleation rates are obtained as a function of subcooling from heat-flow and induction-time measurements. Kinetics of ice nucleation and growth are studied at two polytetrafluoroethylene (PTFE) loadings (0 and 10 wt %) in a commercial GDL for temperatures between 240 and 273 K. A nonlinear ice-crystallization rate expression is developed using Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory, in which the heat-transfer-limited growth rate is determined from the moving-boundary Stefan problem. Induction times follow a Poisson distribution and increase upon addition of PTFE, indicating that nucleation occurs more slowly on a hydrophobic fiber than on a hydrophilic fiber. The determined nucleation rates and induction times follow expected trends from classical nucleation theory. A validated rate expression is now available for predicting ice-crystallization kinetics in GDLs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28116624','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28116624"><span>Chemical characterization of diesel and hydrotreated vegetable oil (HVO) soot after reactive <span class="hlt">gas</span> probing using <span class="hlt">diffuse</span> reflectance FTIR spectroscopy (DRIFTS).</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Tapia, A; Salgado, M S; Martín, M P; Rodríguez-Fernández, J; Rossi, M J; Cabañas, B</p> <p>2017-01-23</p> <p>A chemical characterization of diesel and hydrotreated vegetable oil (HVO) soot has been developed using <span class="hlt">diffuse</span> reflectance infrared Fourier transform spectroscopy (DRIFTS) before and after the reaction with different probe gases. Samples were generated under combustion conditions corresponding to an urban operation mode of a diesel engine and were reacted with probe <span class="hlt">gas</span>-phase molecules in a Knudsen flow reactor. Specifically, NH2OH, O3 and NO2 were used as reactants (probes) and selected according to their reactivities towards specific functional groups on the sample surface. Samples of previously ground soot were diluted with KBr and were introduced in a DRIFTS accessory. A comparison between unreacted and reacted soot samples was made in order to establish chemical changes on the soot surface upon reaction. It was concluded that the interface of diesel and HVO soot before reaction mainly consists polycyclic aromatic hydrocarbons, nitro and carbonyl compounds, as well as ether functionalities. The main difference between both soot samples was observed in the band of the C=O groups that in diesel soot was observed at 1719 cm(-1) but not in HVO soot. After reaction with probe gases, it was found that nitro compounds remain on the soot surface, that the degree of unsaturation decreases for reacted samples, and that new spectral bands such as hydroxyl groups are observed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004PhST..108..124P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004PhST..108..124P"><span>Hydrogen <span class="hlt">Gas</span> Driven Permeation through Asymmetric Membranes in <span class="hlt">Diffusion</span> Limited and Surface Limited Regimes: Interplay between Analytical and Numerical Calculations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pisarev, A.; Bacherov, A.</p> <p></p> <p>Validity of analytical solutions for the <span class="hlt">gas</span> driven permeation of H in the <span class="hlt">Diffusion</span> Limited Regime (DLR) and Surface Limited Regime (SLR) is analyzed by comparison with numerical calculations. Margins for analytical formulas have been established in terms of the permeation factors W = KLSp1/2/D on the inlet (W1) and outlet (W2) sides of the membrane. The DLR analytical formula gives perfect result (error less than 0.5%) if both W2 ≥ 104 and W1 ≥ 102 conditions are satisfied simultaneously. Decrease of both margins by two orders of magnitude leads to 10% error. The SLR analytical formula gives a very good result (error less than 0.5%) if both W1 ≤ 10-2 and W2W1 ≤ 10-3 conditions are satisfied simultaneously. Increase of both margins by two orders of magnitude leads to 10% error. It has been shown that the inlet side and the outlet side conditions are different in their importance for validity of the analytical formulas. In DLR the condition is softer on the inlet side and more rigid on the outlet side, while in SLR the condition is softer on the outlet side and more rigid on the inlet side.</p> </li>