The formation–distribution of condensed water in diffusion medium of proton exchange membrane fuel cells, and its tendency to reduce the local effective mass diffusivity and to influence cell performance, are studied. First the local effective mass diffusivity of a fibrous diffusion medium is determined as a function of the local porosity and local water saturation, using the network model for ...

The effect of hot water on aspen chips has been evaluated using time-domain low-field nuclear magnetic resonance (NMR) spectroscopy. At moisture contents above fiber saturation point, treated chips exhibit relaxation times of free water longer than for the control. This is consistent with the removal of hemicelluloses given the hydrophilicity of these polysaccharides. The rate of decrease in fr...

the main objective of this study is to drive a simple solution for prediction of steel fiber reinforced concrete (sfrc) behavior under four point bending test (fpbt). in this model all the force components at the beam section (before and after cracking) are formulated by applying these assumptions: a bilinear elastic-perfectly plastic stress-strain response for concrete behavior in compression,...

BACKGROUND A pilot investigation was undertaken to assess the performance of a novel fiber-optic cerebral pulse oximetry system. A fiber-optic probe designed to pass through the lumen of a cranial bolt of the type used to make intracranial pressure measurements was used to obtain optical reflectance signals directly from brain tissue. METHODS Short-duration measurements were made in six patie...

In this paper the design and performance of novel micromechanically-tunable vertical-cavity semiconductor optical amplifiers (VCSOAs) are presented. Theoretical design issues include overviews of the signal gain, wavelength tuning characteristics, saturation properties, and noise figure of these unique devices. Using general Fabry-Pérot relationships it is possible to model both the wavelength ...

Resonance properties of the all-fiber ring cavity filled with nonlinear material - saturable rare-earth-doped fiber are analyzed and experimentally investigated. Unlike earlier investigated erbium-doped at 1550nm where optical absorption photo-induced change (saturation) is observed only, ytterbium-doped 1064nm demonstrates saturation refractive index mainly. For this configuration we report ex...

In this article, the impact of input pump profile on the gain spectrum as well as the saturation behavior of one-pump fiber optical parametric amplifiers (FOPAs) is investigated. Since in practical circumstances, pump sources used for FOPAs have Lorentz-Gaussian profile instead of Gaussian, a more realistic case is considered for simulating FOPAs in this article. The results of simulations for ...