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S Godoy

Publications and source records attributed to S Godoy.

8 recordsLinked to original sources
PubMed2000

Landauer equation in three-dimensional amorphous materials

We use the Boltzmann transport equation to calculate the three-dimensional (3D) version of the Landauer equation for incoherent electrons diffusing in a slab of amorphous material. We use the P1 approximation to calculate the multiple-scattering transmission coefficient as a function of the diffusion coefficient. The 3D transmission coefficient is, apart from numerical coefficients, similar to that for 1D. The result is valid only for positions far away from the boundaries and for slabs having a thickness much greater than one mean free path.

Journal Article↗
PubMed1999

Generalized Landauer equation: absorption-controlled diffusion processes.

The exact expression of the one-dimensional Boltzmann multiple-scattering coefficients, for the passage of particles through a slab of a given material, is obtained in terms of the single-scattering cross section of the material, including absorption. The remarkable feature of the result is that for multiple scattering in a metal, free from absorption, one recovers the well-known Landauer result for conduction electrons. In the case of particles, such as neutrons, moving through a weak absorbing media, Landuer's formula is modified due to the absorption cross section. For photons, in a strong absorbing media, one recovers the Lambert-Beer equation. In this latter case one may therefore speak of absorption-controlled diffusive processes.

Journal Article↗
PubMedDate not supplied

Utilisation of phytate phosphorus by rumen bacteria in a semi-continuous culture system (Rusitec) in lactating goats fed on different forage to concentrate ratios.

Experimental data on phytate phosphorus utilisation by ruminants are scarce. The aim of this study was to estimate the phytase activity of rumen micro-organisms when phytate phosphorus supply is high. A semi-continuous culture system fermentor (RUSITEC) was used. The inoculum was obtained from eight goats fed on either high or low forage level diets. Experimental buffers only differed by the nature of phosphorus monosodium phosphate vs. corn sodium phytate. The nylon bags containing 15 g DM of substrate were removed after a 48-hour incubation period. The system was maintained for 15 days: 5 days for adaptation, in order to obtain a steady state, and 10 days for sampling and recording. No significant differences were observed for DM digestibility, gas production, pH, N-NH3, and SCFA for the different treatments. Bacterial efficiency of phytate phosphorus utilisation was significantly higher (p < 0.001) with organic P, but remained lower than the data usually reported in the literature. These results may be explained by the relative saturation of bacterial phytase activity when the buffer contains a high level of phytate phosphorus.

Animal Feed↗