Search results for " diffusion"

Impact of cyclic mechanical stress on the electrical contact resistance between gas diffusion layer and bipolar plates in Polymer Electrolyte Membran…

2018

WHEC 2018, 22nd edition of the WORLD HYDROGEN ENERGY CONFERENCE, Rio de Janeiro, BRESIL, 17-/06/2018 - 22/06/2018; and collisions) and the mechanical clamping stress applied during the stack assembly. The internal stresses come from the shrinking and the swelling of the membrane caused by water content and the difference between the thermal expansion coefficients of the cell components. These mechanical stresses have an impact on the global fuel cell's performance and one of the most sensitive cell's components to this pressure is the Gas Diffusion Layer (GDL). This layer, assembled with the membrane electrode assembly, provides the reactant gases, evacuates the produced heat and …

Diffusive equilibrium properties of O2 in amorphous SiO2 nanoparticles probed via dependence of concentration on size and pressure

2014

An experimental study on the diffusive equilibrium value of interstitial O2 in silica nanoparticles was carried out on samples with average particles diameter 40, 14, and 7 nm. The investigation was performed by measuring the concentration of interstitial O2 by Raman and photoluminescence techniques. The dependence of diffusive equilibrium concentration on pressure and temperature was investigated in the pressure range from 0.2 to 76 bar and in the temperature range from 98 to 244 °C. The equilibrium concentration of interstitial O2 follows Henry’s law at pressures below 13 bar whereas a departure from this model is observed at higher pressures. In particular, O2 concentration saturates abo…

Selective chlorine determination by gas diffusion in a tandem flow assembly and spectrophotometric detection with o-dianisidine

2001

Abstract A fast, selective, sensitive and automated method for determination of free chlorine in industrial formulations and water samples is proposed. The automation of the flow assembly is based on the “tandem flow” approach, which uses a set of solenoid valves acting as independent switches. The operating cycle for obtaining a typical analytical transient signal can easily be programmed by means of friendly software running in the Windows environment. The manifold is provided with a gas diffusion unit which permits the removal of interfering species as well as concentrating the chlorine. The determination of chlorine is performed on the basis of the oxidation of o-dianisidine as the colo…

Stability analysis for stochastic hybrid systems: A survey

2014

This survey addresses stability analysis for stochastic hybrid systems (SHS), which are dynamical systems that combine continuous change and instantaneous change and that also include random effects. We re-emphasize the common features found in most of the models that have appeared in the literature, which include stochastic switched systems, Markov jump systems, impulsive stochastic systems, switching diffusions, stochastic impulsive systems driven by renewal processes, diffusions driven by Lévy processes, piecewise-deterministic Markov processes, general stochastic hybrid systems, and stochastic hybrid inclusions. Then we review many of the stability concepts that have been studied, inclu…

Oxygen Diffusion in Alumina. Application to Synthetic and Thermally Grown Al<sub>2</sub>O<sub>3</sub>

2005

S. Chevalier, B. Lesage, C. Legros, G. Borchardt, G. Strehl, M. Kilo Laboratoire de Recherches sur la Reactivite des Solides, CNRS UMR 5613, Universite de Bourgogne, F-21078 Dijon, France Laboratoire d’Etudes des Materiaux Hors Equilibre, CNRS UMR 8647, Universite Paris XI, F-91405 Orsay, France. Institut fur Metallurgie, TU Clausthal, Robert Koch Strasse 42, D38678 Clausthal-Zellerfeld, Germany. * sebastien.chevalier@u-bourgogne.fr

Analytic solutions of the diffusion-deposition equation for fluids heavir than atmospheric air

2008

A steady-state bi-dimensional turbulent diffusion equation was studied to find the concentration distribution of a pollutant near the ground. We have considered the air pollutant emitted from an elevated point source in the lower atmosphere in adiabatic conditions. The wind velocity and diffusion coefficient are given by power laws. We have found analytical solutions using or the Lie Group Analysis or the Method of Separation of Variables. The classical diffusion equation has been modified introducing the falling term with non-zero deposition velocity. Analytical solutions are essential to test numerical models for the great difficulty in validating with experiments.

Modification of Ce oxidation state by thermal treatments in controlled atmosphere of Ce-Ti-Eu doped SiO2 glasses

2010

A velocity–diffusion method for a Lotka–Volterra system with nonlinear cross and self-diffusion

2009

The aim of this paper is to introduce a deterministic particle method for the solution of two strongly coupled reaction-diffusion equations. In these equations the diffusion is nonlinear because we consider the cross and self-diffusion effects. The reaction terms on which we focus are of the Lotka-Volterra type. Our treatment of the diffusion terms is a generalization of the idea, introduced in [P. Degond, F.-J. Mustieles, A deterministic approximation of diffusion equations using particles, SIAM J. Sci. Stat. Comput. 11 (1990) 293-310] for the linear diffusion, of interpreting Fick's law in a deterministic way as a prescription on the particle velocity. Time discretization is based on the …

PET/PEN Blends of Industrial Interest as Barrier Materials. Part I. Many-Scale Molecular Modeling of PET/PEN Blends

2006

Mesoscale molecular simulations, based on parameters obtained through atomistic molecular dynamics and Monte Carlo calculations, have been used for modeling and predicting the behavior of PET/PEN blends. Different simulations have been performed in order to study and compare pure homopolymer blends with blends characterized by the presence of PET/PEN block copolymers acting as compatibilizer. A many-scale molecular modeling strategy was devised to evaluate PET/PEN blend characteristics, simulate phase segregation in pure PET/PEN blends, and demonstrate the improvement of miscibility due to the presence of the transesterification reaction products. The behavior of distribution densities and …

La distribution des tuiles estampillées de la VIIIe légion Augusta autour de Mirebeau-sur-Bèze (Côte-d'Or, France)

2011

The 8th Augustan Legion was installed at Mirebeau-sur-Bèze (Côte-d'Or) after 70 AD following the troubles that arose with the Lingons. It remained there until the time of Domitian, a period of roughly twenty years, during which time the soldiers produced tiles stamped with the name of the legion. Analysis of the dispersion of the tiles in the region around Mirebeau shows that they followed the communication routes. Consideration of the contexts in which these tiles were used, their number on each site and the resources necessary to manufacture them reveals that the 8th Legion may have played a significant role in the diffusion and adoption of tiled roofs, a construction technique that was t…