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排序方式: 共有140条查询结果,搜索用时 56 毫秒
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H. Geßwein N. Schlechtriemen J. R. Binder J. Haußelt 《Journal of Thermal Analysis and Calorimetry》2010,100(1):33-42
A kinetic model for the reaction sintering of oxide ceramics in the system Al2O3–SiO2–ZrO2 using mixtures of intermetallic compounds is presented. A 2D finite-difference model is developed to describe the exothermic
gas-solid reactions taking place during the firing of ZrAl3/ZrSi2 powder compacts. The model accounts for the oxidation kinetics of the powder particles, as well as the consumption and diffusion
of gaseous oxygen through the porous matrix. Additionally, possible changes in the pore structure of the green body due to
the oxidation reactions and sintering effects are incorporated in the model. The resulting differential equations are coupled
with a two-dimensional Fourier heat balance equation leading to a system of nonlinear partial differential equations, which
is solved by the numerical method of lines. The influence of different processing parameters like sample composition and heating
cycle on the reaction sintering process is investigated and the model-predicted reaction behaviour is compared to experimental
results. 相似文献
35.
We report the results of experimental determinations of the triplet correlation functions of quasi-two-dimensional one-component and binary colloid suspensions in which the colloid-colloid interaction is short ranged. The suspensions studied range in density from modestly dilute to solid. The triplet correlation function of the one-component colloid system reveals extensive ordering deep in the liquid phase. At the same density the ordering of the larger diameter component in a binary colloid system is greatly diminished by a very small amount of the smaller diameter component. The possible utilization of information contained in the triplet correlation function in the theory of melting of a quasi-two-dimensional system is briefly discussed. 相似文献
36.
This paper is concerned with the syntheses of 1,8,9,16-tetrahydroxytetraphenylene derivatives and their applications as Brønsted base organocatalysts for [4+2] cycloaddition between anthrone and maleimides. The structural modifications of the catalysts and their related catalytic properties are described and discussed in details. 相似文献
37.
Appelqvist LA Addis P Björkhem I Bosset JO Caboni MF Dutta P Grandgirard A Guardiola F Hau LB Nielsen JH Hugget A Hwang LS Kumpulainen J McCluskey S Ohshima T Przbylski R Sevanian A Yan P 《Journal of AOAC International》2004,87(2):511-519
A compilation of literature data on the content of cholesterol oxidation products (COP) in various food products and in blood demonstrates a large variation in content in products or tissues of very similar nature when analyzed in different laboratories according to a large number of methods. The lack of validated, internationally recognized methodology with published accuracy and precision has so far hindered such assessments. Hence an interlaboratory comparision of methodologies of COP analysis was undertaken on egg yolk powders (EYP), whole milk powders (WMP), skim milk powders (SMP), and lard (L). Each product type had one fresh sample (low) and one aged (high) in COP contents. A total of 17 sets of results on WMP, 15 on SMP and EYP, and 13 on L were compared. Overall results (mg/kg sample) varied extensively: Fresh EYP 0.72-265, aged EYP 2.51-361; fresh WMP 0.02-18.1, aged WMP 0.02-26.9; fresh SMP 0.02-6.51, aged SMP <0.01-6.51; fresh L 0.18-97, aged L 4.15-452. Some results were questioned, viz., those from laboratories not indicating substantial differences between samples "low" and "high" in total COP. Others were excluded because of lack of verification of identity of gas chromatographic peaks by mass spectrometry. Then a more narrow range of core results (mg/kg sample) was observed: Fresh EYP 5.69-29.5 sample, aged EYP 11.8-79.0; fresh WMP 0.12-1.76, aged WMP 1.17-13.7; fresh SMP <0.30-<1.21, aged SMP 0.30-2.26; fresh L 0.18-5.07, aged L 94.4-231. At a workshop discussing the results, numerous recommendations were made toward more reliable methodology for determination of COP in foods. 相似文献
38.
Jörg Pieper Alexandra Buchsteiner Norbert A. Dencher Ruep E. Lechner Thomas Hauß 《Photochemistry and photobiology》2009,85(2):590-597
Knowledge about the dynamical properties of a protein is of essential importance for understanding the structure–dynamics–function relationship at the atomic level. So far, however, the correlation between internal protein dynamics and functionality has only been studied indirectly in steady‐state experiments by variation of external parameters like temperature and hydration. In the present study we describe a novel type of (laser‐neutron) pump‐probe experiment, which combines in situ optical activation of the biological function of a membrane protein with a time‐dependent monitoring of the protein dynamics using quasielastic neutron scattering. As a first successful application we present data obtained selectively in the ground state and in the M‐intermediate of bacteriorhodopsin (BR). Temporary alterations in both localized reorientational protein motions and harmonic vibrational dynamics have been observed during the photocycle of BR. This observation is a direct proof for the functional significance of protein structural flexibility, which is correlated with the large‐scale structural changes in the protein structure occurring during the M‐intermediate. We anticipate that functionally important modulations of protein dynamics as observed here are of relevance for most other proteins exhibiting conformational transitions in the time course of functional operation. 相似文献
39.
We present the experimental discovery of compound structures comprising solitons and vortex rings in Bose-Einstein condensates. We examine both their creation via soliton-vortex collisions and their subsequent development, which is largely governed by the dynamics of interacting vortex rings. A theoretical model in three-dimensional cylindrical symmetry is also presented. 相似文献
40.
Susann Hau Doreen M Reich Markus Scholz Wilfried Naumann Frank Emmrich Manja Kamprad Johannes Boltze 《BMC neuroscience》2008,9(1):30