Sol-gel modification of mesoporous alumina membranes is a very successful technique to improve gas separation performance. Due to the formed microporous top layer, the membranes show activated transport and molecular sieve-like separation factors. This paper concentrates on the mechanism of activated transport (also often referred to as micropore diffusion or molecular sieving). Based on a theo...

Disturbances in the relationship of ventilation and perfusion may result in hypoxemia, a deficiency of oxygen in the blood. The four major causes of hypoxemia are hypoventilation, alveolar-capillary diffusion impairment, shunt, and ventilation perfusion mismatch.1 In this article factors which determine ventilation and gas exchange will be identified and abnormalities leading to hypoxemia will ...

A mathematical model is presented to explain the regulation of nitrogenase electron allocation to N2 fixation (EAC) in legume nodules. The model is based on two assumptions: (a) that H2 inhibits N2 fixation in a competitive manner; and (b) that O2, H2, and N2 move into and out of nodules by diffusion and their movement is impeded by a diffusion barrier, the permeability of which is controlled t...

In diffusion, gases (or liquids) move from an area of high concentration (partial pressure) to areas of low concentration (partial pressure). If there is a mixture of gases in a container, the pressure of each gas (partial pressure or concentration) is equal to the pressure that each gas would produce if it occupied the container alone. This applies equally well to the concentration of a gas in...

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 gas substances through a membrane. By using a new portable FIA system equipped with a gas-diffusion unit, a highly sensitive and on-site determination of total carbonate in aqueous sol...

Gas diffusion layers (GDLs) are commonly known as one of the critical water management components in polymer electrolyte fuel cells with significant impact on electrochemical cell performance. Increasing levels liquid saturation GDLs, especially during high-current-density operation, limit gas transport from flow field channels to catalyst layer surfaces and hence reduce To provide GDL material...

intrapulmonary shunt is miniscule is further confirmed by a recent study reporting venous admixture in very fit athletes during exercise breathing pure O 2 (18). During 100% oxygen breathing, alveolar PO 2 is elevated to such an extent that ventilation-perfusion inequality and diffusion limitation no longer contribute to the AaDO 2 —it can be explained only by right to left shunting (18). In th...