Pressure effects on the structural, elastic , electronic and optical properties of ZnO from first-principles calculations

First-principles calculations of the structural, electronic, optical and elastic properties of ZnO as a function of the pressure have been performed within density functional theory using Ultra soft pseudo potentials and generalized gradient approximation (GGA) for the exchange and correlation energy. Through our results, we note that the lattice constants decrease with the pressure increasing. Also, the elastic constants C11, C12, C13 and C33 and  the bulk modulus B increase with the pressure increasing. However, the elastic constants C44, the Shear modulus (G) and  Young’s modulus (E) decrease slowly with  increasing pressure, the band gap increases with the pressure increasing and ZnO has direct band. As pressure increases, the static dielectric constants ɛ1(0) and static refraction index n(0) decrease. Our calculated results are in good agreement with experimental data and other theoretical calculations.Keywords: DFT calculation, electronic, optical, elastic, under pressur

Non-additivity of feedstuffs examined in vitro and the influence of incubation medium pH.

Contributed to: Proceedings of the British Society of Animal Science 2001, p.133. (York, Reino Unido, April 9-11, 2001)Non-additivity occurs when the nutritive value of a mixture of feedstuffs differs from that of the sum of its components. It is most commonly observed when one dietary constituent influences, either positively or negatively, the apparent digestibility of another under conditions where components such as nitrogen and sulphur are non-limiting. In general negative effects occur due to the depression of rumen pH or substrate competition, while positive effects have been identified when readily fermentable fibre sources such as sugar beet pulp have been included in rations containing poorly fermented forages such as cereal straw. With the increasing use of in vitro systems, not just to examine feed degradation characteristics but to derive parameters such as microbial protein yield, the following study was conducted to determine whether such interactions could be identified in vitro.Peer reviewe