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 Introduc...

The dusty gas model constitutive relationships were incorporated into a numerical model for three-phase, multicomponent flow and transport in porous media. The dusty gas model properly accounts for interactions between all gas-phase species in multicomponent gas mixtures. The model also included Knudsen diffusion, which becomes important in very fine grained soils. The dusty gas model results w...

Using a novel NMR scheme we observed persistence in 1-D gas diffusion. Analytical approximations and numerical simulations have indicated that for an initially random array of spins undergoing diffusion, the probability p(t) that the average spin magnetization in a given region has not changed sign (i.e., “persists”) up to time t follows a power law t−θ, where θ depends on the dimensionality of...

Aktrrct-Aqueous-phase oxidation of SO, occurs via a sequence of steps consisting of gas-phase diffusion, mass transfer at the gas-water interface, hydrolysis and ionization of the dissolved sulfur-IV, aqueous-phase diffusion, and oxidation reaction. Expressions are given for the characteristic times of these several processes for reaction in aqueous droplets. Readily applicable crite.ria are de...

During short-term maximal exercise, horses have impaired pulmonary gas exchange, manifested by diffusion limitation and arterial hypoxemia, without marked ventilation-perfusion (VA/Q) inequality. Whether gas exchange deteriorates progressively during prolonged submaximal exercise has not been investigated. Six thoroughbred horses performed treadmill exercise at approximately 60% of maximal oxyg...

Using a novel NMR scheme we observed persistence in 1D gas diffusion. Analytical approximations and numerical simulations have indicated that for an initially random array of spins undergoing diffusion, the probability p(t) that the average spin magnetization in a given region has not changed sign (i.e., "persists") up to time t follows a power law t(-straight theta), where straight theta depen...

A measurement system for current distribution mapping for a PEFC has been developed. The segmented anode is constructed so as to have high thermal conductivity in order to prevent the formation of large temperature gradients between the electrodes. The construction is therefore feasible for use at high current densities. Both segmented and unsegmented gas diffusion layers are used. The effect o...

A model for the simulation of the steady-state impedance response of a polymer electrolyte membrane fuel cell ~PEMFC! cathode is presented. The catalyst layer of the electrode is assumed to consist of many flooded spherical agglomerate particles surrounded by a small volume fraction of gas pores. Stefan-Maxwell equations are used to describe the multicomponent gas-phase transport occurring in b...

Introduction Phase contrast MRI which is commonly used to map blood [1]has been applied more recently to map gas velocities using hyperpolarized tracers[2, 3].The bipolar gradient used to induce a phase shift proportional to velocity also introduces diffusion weighting. This can be safely neglected considering diffusion coefficients of liquids. However, for a gas, diffusion can no longer be neg...

We present a combined analytical and numerical approach based on the Mori projection operator formalism and Monte Carlo simulations to study surface diffusion within the lattice-gas model. In the present theory, the average jump rate and the susceptibility factor appearing are evaluated through Monte Carlo simulations, while the memory functions are approximated by the known results for a Langm...