27,607 research outputs found
Electronic structure of Zr-Ni-Sn systems: role of clustering and nanostructures in Half-Heusler and Heusler limits
Half-Heusler and Heusler compounds have been of great interest for several
decades for thermoelectric, magnetic, half-metallic and many other interesting
properties. Among these systems, Zr-Ni-Sn compounds are interesting
thermoelectrics which can go from semiconducting half-Heusler (HH) limit,
ZrNiSn, to metallic Heusler (FH) limit, ZrNiSn. Recently Makogo et al. [J.
Am. Chem. Soc. 133, 18843 (2011)] found that dramatic improvement in the
thermoelectric power factor of HH can be achieved by putting excess Ni into the
system. This was attributed to an energy filtering mechanism due to the
formation of FH nanostructures in the HH matrix. Using density functional
theory we have investigated clustering and nanostructure formation in
HHFH systems near the HH and FH ends and found that excess Ni atoms
in HH tend to stay close to each other and form nanoclusters of FH. On the
other hand, there is competing interaction between Ni-vacancies in FH which
prevent them from forming HH nano clusters. Effects of nano inclusions on the
electronic structure at both HH and FH ends will be discussed.Comment: Published in J. Phys.: Condens. Matte
Effects of adsorbed phase on diffusion of subcritical hydrocarbons in activated carbon at low pressures
Diffusions of free and adsorbed molecules of subcritical hydrocarbons in activated carbon were investigated to study the influence of adsorbed molecules on both diffusion processes at low pressures. A collision reflection factor, defined as the fraction of molecules undergoing collision to the solid surface over reflection from the surface, is incorporated into Knudsen diffusivity and surface diffusivity in meso/macropores. Since the porous structure of activated carbon is bimodal in nature, the diffusion of adsorbed molecules is contributed by that of weakly adsorbed molecules on the meso/macropore surfaces and that of strongly adsorbed molecules in the small confinement of micropores. The mobility of adsorbed molecules on the meso/macropore surface is characterized by the surface diffusivity D-mu 2, while that in the micropore is characterized by D-mu 1. In our study with subcritical hydrocarbons, we have found that the former increases almost linearly with pressure, while the latter exhibits a sharp increase at a very low-pressure region and then decreases beyond a critical pressure. This critical pressure is identified as a pressure at which the micropores are saturated
Orientações sobre boas práticas de fabricação (BPF) para unidades processadoras de leite de cabra.
Edificações e instalações; Controle de pragas e vetores; Abastecimento de água; ResÃduos; Equipamentos e utensÃlios; Manipuladores; Processamento do leite; Rotulagem e armazenamento do produto final; Controle de qualidade do produto final; Transporte do produto final.bitstream/CNPC/20708/1/cot76.pd
Avaliacao da produtividade e do teor proteico de acessos de Stylosanthes.
Avaliacao de acessos de Stylosanthes, visando a selecao de materiais adaptados e produtivos.bitstream/item/97564/1/PAND800001.pd
Testing for periodicities in near-IR light curves of Sgr A
We present the results of near-infrared (2 μm) monitoring of Sgr A*-IR with 1 minute time sampling using laser guide star adaptive optics (LGS AO) system at the Keck II
telescope. Sgr A*-IR was observed continuously for up to three hours on each of seven nights, between 2006 May and 2007 August. Sgr A*-IR is detected at all times and is continuously variable. These observations allow us to investigate Nyquist sampled periods ranging from
about 2 minutes to an hour. Of particular interest are periods of ~20 min, which corresponds to a quasi-periodic (QPO) signal claimed based upon previous near-infrared observations and interpreted as the orbit of a ’hot spot’ at or near the last stable orbit of a spinning black hole.
We investigate these claims by comparing periodograms of the light curves with models for red noise and find no significant deviations that would indicate QPO activity at any time scale probed in the study. We find that the variability of Sgr A* is consistent with a model based on
correlated noise with a power spectrum having a frequency dependence of ~ f^(2.5), consistent with that observed in AGNs. Furthermore, the periodograms show power down to the minimum sampling time of 2 min, well below the period of the last stable orbit of a maximally spinning black hole, indicating that the Sgr A*-IR light curves observed in this study is unlikely to be from the Keplerian motion of a single ’hot spot’ of orbiting plasma
- …