关键词： Nucleotides   Transmembrane domains   empty   Active Site   Nucleosome Binding Domain   kinetic simulation   ATP-Binding Cassette Transporters   ATP Hydrolysis   Molecular Dynamics Simulation  

摘要： ATP-binding cassette transporters use the energy of ATP hydrolysis to transport substrates across cellular membranes. They have two transmembrane domains and two cytosolic nucleotide-binding domains. Biochemical studies have characterized an occluded state of the transporter in which nucleotide is tenaciously bound in one active site, whereas the opposite active site is empty or binds nucleotide loosely. Here, we report molecular-dynamics simulations of the bacterial multidrug ATP-binding cassette transporter Sav1866. In two simulations of the ATP/apo state, the empty site opened substantially by way of rotation of the nucleotide-binding domain (NBD) core subdomain, whereas the ATP-bound site remained occluded and intact. We correlate our findings with elastic network and molecular-dynamics simulation analyses of the 5av1866 NBD monomer, and with existing experimental data, to argue that the observed transition is physiological, and that the final structure observed in the ATP/apo simulations corresponds to the tight/loose state of the NBD dimer characterized experimentally.

关键词： antimony alloys   brittleness   cobalt alloys   deformation   molecular dynamics method   nanostructured materials   Poisson ratio   skutterudites   specific heat   stress-strain relations   thermal conductivity   thermal expansion   thermoelectricity   Young's modulus  

摘要： Molecular dynamics simulations have been performed to study the fundamental thermodynamic and mechanical properties of single-crystalline skutterudite CoSb3 in the nanometric scale. The several interesting thermodynamic predictions, including linear thermal expansion coefficient, specific heat capacity, thermal conductivity, and temperature dependence of elastic constants, show excellent agreement with data available in the literature. The classic mechanical tests of uniaxial tension and compression are performed respectively at constant temperatures. The CoSb3 single-crystal exhibits nonlinear elastic response during the deformation process and the sustainable stress is very high, demonstrating its outstanding stability. An interesting phenomenon occurs at compression that the stress-strain curve undergoes a transition. The cause of the transition is an atomic reconstruction, which is observed and interpreted on the basis of interatomic interactions. Both of the failure patterns under tension and compression reveal brittleness of the material. The increasing of temperature would result in a linear degradation of the effective Young's modulus and ultimate strength, but its effect on Poisson's ratio is negligible. The results provide the groundwork for future studies of service behavior of the skutterudites-based thermoelectric devices. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3598116]

关键词： Kinetics   Manganese(IV)   1,8-Bis(2-hydroxybenzamido)-3,6-diazaoctane   Glyoxylic acid  

摘要： The oxidation of glyoxylic acid (HGI) by (MnL)-L-IV {L4- = tetra deprotonated 1,8-bis(2-hydroxybenzamido)-3,6-diazaoctane) was investigated in the pH range 1.67-10.18, at 25-45 degrees C and 0.5 M ionic strength. The reaction exhibited biphasic kinetics with (MnL-)-L-III as the reactive intermediate. Mn-IV was reduced to Mn-II. The products of oxidation of HGI were identified as formic acid and CO2 in acidic medium, and oxalate in basic medium, consistent with the stoichiometry: -Delta[Mn-IV]/-Delta[HGI] = 1. In acidic medium, both (MnL)-L-IV and (MnL-)-L-III formed outer-sphere adducts with the neutral HGI {HC(OH)(2)COOH} molecule, with an association constant Q(IV) of 28 and 70 M-1, respectively. A similar adduct formation was not observed for the glyoxylate mono anion (Gl(-), CH(OH)(2)(CO2-)) and glyoxylate dianion {Gl(2-), CH(OH)(O-)CO2-}. The rate and activation parameters for the various paths are reported and an outersphere electron transfer mechanism is suggested. (C) 2011 Elsevier Ltd. All rights reserved.

关键词： Thermoset   Molecular dynamics   Glass transition   Conversion degree  

摘要： We use molecular dynamics (MD) to perform an extensive characterization of the thermo-mechanical response of a thermoset polymer composed of epoxy EPON862 and curing agent DETDA. Our simulations, with no adjustable parameters, show that atomistic simulation can capture non-trivial behavior of amorphous thermosets including the role of polymerization degree, thermal history, strain rate and temperature on the glass transition temperature (T-g) and mechanical response (including ultimate properties) and lead to predictions in quantitative agreement with experiments. We find a significant increase in T-g, Young's modulus and yield stress with degree of polymerization while yield strain is significantly less sensitive to it. For structures cured beyond the gel point (percolation of a 3D network) conversion degree and temperature affect yield stress in a similar way with yield stress linearly dependent on T T-g: however, we find non-linear and non-universal relationship below the gel point. Our results show that a relative small variation in polymerization degree (similar to 5%) can explain the spread in experimental measurements of T-g and elastic constants available in the literature. (c) 2011 Elsevier Ltd. All rights reserved.

关键词： 机械密封   瞬态特性   启停   密封性能   泄漏  

摘要： 启停过程顺利与否直接关系到机械密封的可靠和长寿命运行。考虑密封端面流固力耦合作用、微观空化及端面接触的影响,通过建立机械密封瞬态启停动力学模型,计算瞬态启停过程中密封浮动环的轴向位移、密封端面液膜厚度变化、端面接触力及泄漏率等密封参量,研究了机械密封启停过程中的瞬态密封行为,分析了动环轴向跳动等对机械密封性能的影响。结果表明:受轴向跳动和启停过程速度变化的影响,密封参量呈现瞬态扰动现象,且轴向跳动越大,扰动越大。该模型和计算方法对完善机械密封设计方法、评价机械密封设计合理性具有一定的参考价值。

关键词： 工程机械   柴油机   特性  

摘要： 随着我国科学技术水平的提高，我国工程机械市场需求不断增长，但由于其在作业时带来的对环境的污染如灰尘、噪声等，各地政府根据国家政策法规，根据本地实际情况，也纷纷出台了工程机械作业的相关政策，这些产业政策有力的推动了国内工程机械市场的发展，从而也使得工程机械迎来了发展的春天。另一个方面由于我国经济建设的步伐加快以及国家一些诸如新农村建设、高铁建设、西电东送、灾后重建等重大项目的投资也促使工程机械市场有力发展。

关键词： 机械式变速器   换挡控制   换挡品质   遗传算法  

摘要： 分析了无动力中断机械式变速器的换挡原理,建立了换挡过程的动力学模型,设计了针对该变速器的基于离合器扭矩容量预先控制的换挡策略.基于Matlab/Simulink软件,建立了该变速器的仿真模型,并以包括冲击度和滑磨功两个参量在内的最优换挡品质为目标,应用单纯形法和遗传算法等对换挡过程中节气门开度的控制参数进行了优化.仿真结果表明,采用所设计的控制策略和优化后的控制参数,无动力中断机械式变速器换挡过程中的换挡冲击和离合器滑磨可得到良好控制,实现动力的持续和平稳输出.

关键词： 浮选机   稳流板   定子   动力学  

摘要： 通过在机械搅拌式浮选机槽体上增加稳流板,改变定子通道面积、形状,寻求机械搅拌式浮选机的最优动力学参数。通过调整叶轮转速、浸没深度来比较稳流板及定子通道对浮选机动力学的影响。试验结果显示,增加稳流板和改变定子通道形状可明显改善槽内浮选环境。

关键词： 工程机械   动力转向系统   故障诊断  

摘要： 主要介绍了在公路工程施工生产中的一些工程机械液压动力转向系统的故障诊断

关键词： 工程机械   无级变速技术   液压混合动力   应用   附加能量   重力势能   制动机构   有用功  

摘要： 1 前言 工程机械除了完成特定工作所必需消耗的能量即有用功以外，还必须提供附加的能量来完成工作循环，包括重力势能与运动动能，附加能量通常通过制动机构消耗掉了。比如挖掘机，重达几顿的转台要频繁的起停，动臂和斗杆需要不断的上升下降；