关键词： E. coli O157:H7   Mechanically-tenderized beef   Modeling   Kinetics  

摘要： A kinetic study was conducted to investigate the growth of Escherichia coli O157:H7 in mechanicallytenderized beef meat (MTBM) inoculated and internalized with a cocktail of 5 rifampicin-resistant (Rif(r)) or 3 arbitrarily selected wild-type strains of the bacteria. The storage was conducted at 5, 10, 15, 20, 25, and 37 degrees C. No growth was observed at 5 degrees C and the growth was minimal at 10 degrees C. Above 15 degrees C, a sigmoid trend was observed for all growth curves. Three primary growth models (modified Gompertz, Huang, and Baranyi) were used to fit the growth curves. A new Belehdradek-type secondary model was found more suitable than the traditional Ratkowsky model for describing the temperature dependence of growth rate. The statistical analysis suggested that both bacterial strains and primary growth model affect the determination of growth rates (at alpha= 0.05), with Rif(r) strains growing 10-20% slower than the wild-type strains. While there was no significant difference between the growth rates estimated by the modified Gompertz and Baranyi models, and between those of Huang and Baranyi models, the rates estimated from the Gompertz model were significantly higher than those estimated from the Huang model. The temperature dependence of growth rate of E. coli 0157:H7 in MTBM was described by both a new Belehdradek-type rate model and the Ratkowsky square-root model. While the theoretical minimum growth temperatures determined by the Ratkowsky square-root model ranged from 1.5 to 4.7 degrees C, more realistic values, varying from 6.64 to 8.76 degrees C, were estimated by the new rate model. For the Baranyi model, the average h(0) value was 2.06 +/- 0.74 and 2.15 +/- 1.14 for Rif(r) and wild-type strains of E. coli O157:H7, respectively. For the Huang and modified Gompertz models, the inverse of square-roots of lag phases was found proportional to temperature, making it possible to estimate the lag phase duration from the growth temperature. The r

关键词： 微机电系统   滑动膜阻尼   分子动力学   仿真模拟  

摘要： 本论文主要是研究在微电子机械系统（MEMS）中空气滑动膜阻尼效应对微谐振器件影响。微电子机械技术在过去的二十多年里发展非常迅速，出现了很多种微机电器件和系统，其中有一大类是利用微机械结构在固有频率处所具有的优良振动性能来工作的。缩小微机械结构与电极之间的间隙是降低驱动电压的有效方法。但是当微机械振动结构和电极之间间隙缩小到一定程度时，空气分子阻尼对微机械振动结构的能量损失影响非常显著。\n 正确预测滑动膜阻尼对于MEMS器件设计是至关重要的。当气压很低时，气体连续介质模型不再适用，只能采用分子动力学方法。基于自由分子流基础上，本文提出了一种高计算效率的分子动力学算法，可以用来计算平动和振动的滑动膜阻尼。该方法以气体分子速度分布函数生成每一分子的初始速度，通过分别单独计算每一气体分子在一个单位时间内与器件碰撞获得的动量增量，得到一个单位时间内气体分子总体动量增量，从而计算器件滑动膜阻尼系数。与已有的模型结果对比表明，本文算法具有良好的精度，而且计算量是可以接受的。

关键词： 2-Mercaptobenzothiazole   Decatungstate salts   Photodegradation   UV light   Oxygen   Photocatalysis  

摘要： The photochemical degradation of a benzothiazole derivative, 2-mercaptobenzothiazole (MBT) has been studied in aqueous solution in the presence of a polyoxometalate (POM): sodium decatungstate salts Na4W10O32 (DTA). In aerated conditions, the photodegradation rate of MBT clearly increased in the presence of DTA by a factor six when compared with the direct photolysis with k(MBT) = 0.25 h(-1) and t(1/2)(MBT)= 2.8 h. For the total comprehension of the degradation mechanism, the oxygen influence has been investigated. Oxygen appeared essential for DTA regeneration, its absence induced a three times inhibition of MBT disappearance and completely stopped the photocatalytic cycle. The main photoproducts were identified with LC-ESI-MS and LC-DAD techniques and using some calculations obtained by B3LYP/6-21G method in Gaussian 4.1 software. All the results allowed to propose a mechanistic pathway. Electron transfer and H atom abstraction processes involving W10O324-center dot excited state species were involved in the degradation. In the primary step of the degradation, the hydroxylation of the aromatic ring leading to four OH-MBT isomers and the formation of disulfide form of MBT were observed. For longer irradiation time, a secondary electron transfer permitted the oxidation of OH-MBT isomers and the formation of sulfoxide derivatives. For prolonged exposure (around 100 h), the complete mineralization was noticed in the presence of sodium decatungstate salts. (C) 2010 Elsevier B.V. All rights reserved.

关键词： Electrons  

摘要： Complementary to the semiclassical method developed in the preceding paper, here we develop a quantum-mechanical approach to characterize propagation of electron waves to large distances in photoionization microscopy of hydrogen atoms in uniform external electric fields. A formula for outgoing electron waves from the atomic source produced in photoionization has been derived. Spatial distributions of electron probability densities can be determined using the obtained formula. The electron waves that propagate to a large distance due to photoionization from the n=2 initial state of hydrogen atoms in electric fields has been calculated and the resulting probability densities are presented. Comparison with semiclassical results is made, and they are found to be in good agreement. A detailed analysis is given of strong quantum tunneling effects found in our calculations.

关键词： Si/a-Si core-shell nanowires   Elastic modulus   Molecular dynamics  

摘要： The nanomechanical properties of Si/a-Si core-shell NWs are investigated using molecular dynamics simulations with EDIP model. Under uniaxial compressive and tensile loading, the computed Young's modulus increases as the radius of crystalline core increases and decreases as the thickness of amorphous shell increases. Whereas the critical strains are found to be independent of the size of crystalline cores and amorphous shells. For the nonaxial torsional and bending strains, both torsional stiffness and bending stiffness increase as the thickness of amorphous shell increases and also as the radius of crystalline core increases. In addition, the critical torsion angle rapidly decreases as the thickness of amorphous shells increases and also as the radius of crystalline core increases. However, the critical bending angles are independent of the size of crystalline cores and amorphous shells. These results show that the amorphous shell has significant effects on the mechanical properties of Si/a-Si core-shell NWs under external loadings. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.

关键词： Alzheimer Disease/metabolism   Amyloid beta-Protein/chemistry   Amyloid beta-Protein/metabolism   Flavonoids/chemistry   Flavonoids/metabolism   Humans   Molecular Dynamics Simulation   Peptide Fragments/chemistry   Peptide Fragments/metabolism   Protein Binding   Protein Stability  

摘要： Alzheimer's disease is a progressive, neurodegenerative disorder that is the leading cause of senile dementia, afflicting millions of individuals worldwide. Since the identification of the amyloid beta-peptide (A beta) as the principal toxic entity in the progression of Alzheimer's disease, numerous attempts have been made to reduce endogenous A beta production and deposition, including designing inhibitors of the proteases that generate the peptide, generating antibodies against A beta aggregates, utilizing metal chelators, and identifying small molecules that target the peptide during the aggregation pathway. The last approach is particularly attractive, as A beta is normally present in vivo, but aggregation is a purely pathological event. Studies conducted in vitro and in vivo have suggested that administration of flavonoids, compounds naturally present in many foods, including wine and tea, can prevent and reverse A beta aggregation, but mechanistic details are lacking. In this work, we employ atomistic, explicit-solvent molecular dynamics (MD) simulations to identify the mechanism of A beta fibril destabilization by morin, one of the most effective anti-aggregation flavonoids, using a model of the mature A beta fibril. Through the course of 24 simulations totaling 4.3 mu s, we find that morin can bind to the ends of the fibrils to block the attachment of an incoming peptide and can penetrate into the hydrophobic core to disrupt the Asp23-Lys28 salt bridges and interfere with backbone hydrogen bonding. The combination of hydrophobicity, aromaticity, and hydrogen bonding capacity of morin imparts the observed behavior.

标准号: NF U64-055/IN1-2010

关键词： ADAMS软件   搬运机械手   动力学仿真   运动学   仿真分析   虚拟样机技术   机械手设计   动力学相  

摘要： 基于虚拟样机技术,利用ADAMS软件对搬运机械手进行建模,并对其进行运动学及动力学仿真,检查机械手在运动工作过程中的正确性和准确性。同时获得各部件的运动学及动力学相应曲线,分析机械手结构设计及其受力情况是否合理,为机械手设计提供参考。

标准号: NF E56-003-2-2010

摘要： La présente norme précise les exigences de sécurité pour les étançons et vérins lorsqu'ils sont utilisés tel que spécifié par le fabricant ou son mandataire. Les exemples couverts par la norme comprennent les étançons, les vérins de soutènement et les vérins comprenant des extensions mécaniques, les soupapes internes et les dispositifs de protection, les joints d'étanchéité, les raccords hydrauliques (y compris le premier tuyau flexible ou la soupape de type B, voir partie 3) et leurs points de levage, mais à l'exclusion des tuyaux et gaines à cuir de protection), les soupapes externes, ainsi que les unités de commande hydrauliques et é*** présente norme s'applique aux étançons, vérins de soutènement et vérins utilisés à des températures ambiantes comprises entre - 10 oC et 60 *** présente norme identifie et tient compte :- des risques potentiels pouvant résulter de l'utilisation des étançons, vérins de soutènement et vérins ;- des zones et des conditions d'utilisation susceptibles de créer de tels risques ;- des situations dangereuses susceptibles d'entraîner des blessures ou pouvant affecter la santé. Cette norme décrit des méthodes de réduction de ces phénomènes *** liste des phénomènes dangereux couverts est donnée à l'article *** présente norme s'applique à tous les étançons, vérins de soutènement et vérins commercialisés pour la première fois après leur fabrication qui suit la date de publication de la présente *** présente norme européenne ne définit pas d'exigences supplémentaires concernant :- les milieux environnants particulièrement corrosifs ;- les risques dus à la construction, au transport et à la mise hors service ;- les tremblements de terre.

标准号: NF E56-003-2/IN1-2010