Oxygen diffusion, influence

Thin catalyst layers on a GC rotating disk electrode (RDE) or a rotating ring-disk electrode (RRDE) serve for studies of ORR kinetics. In order to separate the kinetic current from the measured current j, Schmidt and co-workers [Schmidt et al., 1998b] corrected the latter for the influence of oxygen diffusion in the aqueous electrolyte and in the polymer film using the foUowing equation ... 

It should be noted that in a vapour phase the liquid layer on the surface of a sensitive element of the sensor (zinc oxide) must be sufficiently thin, so that it would not produce any influence on the diffusion flux of oxygen through this layer. Possible lack of the film continuity (the presence of voids) does not prevent determination of concentration of oxygen in the bulk of the cell by the vapour - gas method. In this case, one deals with a semi-dry method. On the contrary, the presence of a thick liquid layer causes considerable errors in measuring t, because of different distribution of oxygen in a system gas - liquid layer -semiconductor film (this distribution is close to that in the system semiconductor film - liquid), in addition to substantial slowing down of oxygen diffusion in such systems. 

An assessment of the rates and duration of phenolic acid production from a residue is an important first step. Laboratory and field studies for assessing the dynamics of phenolic acid production must include considerations of the nature of the residue, soil properties, nutrient status of the system, microbial biomass interrelationships, temperature, moisture, residue placement in or on the soil, and other factors that relate to the field. Soil properties in the field are especially important when organic residues are incorporated. When soils are wet, such as those with more than -0.02 MPa water potential, oxygen diffusion is impeded and anaerobic conditions prevail, especially in soils that are high in clay content. Under these circumstances, microbial byproducts change dramatically and one result, for example, is an increase in the production of phenolic acids. Phenolic acid production is also affected by temperature (22) and soil fertility status (23). While the C H ratio of an organic residue may influence the rate of its decomposition and, hence, the rate of phenolic acid production, the... 

Bentley, T.B. and Pittman, R.N. (1997) Influence of temperature on oxygen diffusion in hamster retractor muscle. Am. J. Physiol., 272, HI 106-H1112. 

S0l., So2 and SHlo refer to the respective source terms owing to the ORR, e is the electrolyte phase potential, cGl is the oxygen concentration and cHlo is the water vapor concentration, Ke is the proton conductivity duly modified w.r.t. to the actual electrolyte volume fraction, Dsa is the oxygen diffusivity and is the vapor diffusivity. The details about the DNS model for pore-scale description of species and charge transport in the CL microstructure along with its capability of discerning the compositional influence on the CL performance as well as local overpotential and reaction current distributions are furnished in our work.25 27,67... 

Influence of Sample Thickness and 02 Diffusion. As shown above, the overall conversion of thermal degradation can depend of the sample thickness in the diffusion-controlled regime. Thus, stability comparisons are only valid for samples of comparable thickness. Let us now compare two polymers of glass transition temperatures Tgl and Tg2, oxidized at a temperature T, such that Tgl < T < Tg2. Even if the intrinsic oxidation rates are equal, polymer 1 will appear more unstable than polymer 2 because oxygen diffusion is faster above than below Tg. The thickness of the oxidized layer will be higher for polymer 1 than for polymer 2. 

There is a basis17 to assume that in the studied samples1 both the oxygen diffusion decrease, and the copper diffusion enhancement are caused by the influence of the co-segregation at dislocations. This is also consistent with the fact pointed in study15 that twin boundaries in the 123 matrix do not contribute apparently to the effective bulk oxygen diffusion. 

The equation of the rate of oxidation (unless oxygen diffusion into the polymer influence the reaction) becomes ... 

Hence, oxygen diffusion into the polymer does not influence the kinetics of radical oxidation since it is easy to see that in the case of diffusion kinetics the rate of increase of the peroxide radicals number would follow the equation ... 

Polar carotenoids present in membranes have been shown to limit molecular oxygen penetration into lipid bilayer as demonstrated by the pigment-related decrease of the oxygen diffusion-concentration product (Subczynski et al., 1991). This effect, being most probably a direct consequence of the influence ofthe carotenoids on molecular dynamics and structure of lipid membranes, appears particularly important taking into consideration the deleterious role of active oxygen species with respect to biomembranes. 

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