关键词： Mechanical properties   Diamond nanowires   Strain rates   Size effects   Temperature dependent properties   Molecular dynamics   Atomistic methods  

摘要： Using molecular dynamics simulations, strain rate, temperature and size dependent mechanical properties of < 001 > orientation diamond nanowires are investigated. It is found that, for the same cross-sectional areas, strain rates have almost no effect on yield strength and Young's modulus, provided strain rates are within the range from 0.001 to 0.025 ps(-1). Our calculated results have also indicated that, at the temperature ranging from 100 to 500 K, diamond nanowires' yield strength, Young's modulus, fracture strength and fracture strain are all decreasing with increasing temperature. Furthermore, at the temperature of 300 K, yield strength, Young's modulus, fracture strength and fracture strain increase dramatically with increasing cross sectional area. Finally, orientation dependent diamond nanowires mechanical properties are studied. (C) 2011 Elsevier B.V. All rights reserved.

关键词： superresolution imaging   cell division   centrosomal protein of 55 kDa   mitotic kinesin-like protein 1   Madin-Darby canine kidney cells  

摘要： The final stage of cytokinesis is abscission, the cutting of the narrow membrane bridge connecting two daughter cells. The endosomal sorting complex required for transport (ESCRT) machinery is required for cytokinesis, and ESCRT-III has membrane scission activity in vitro, but the role of ESCRTs in abscission has been undefined. Here, we use structured illumination microscopy and time-lapse imaging to dissect the behavior of ESCRTs during abscission. Our data reveal that the ESCRT-I subunit tumor-susceptibility gene 101 (TSG101) and the ESCRT-III subunit charged multivesicular body protein 4b (CHMP4B) are sequentially recruited to the center of the intercellular bridge, forming a series of cortical rings. Late in cytokinesis, however, CHMP4B is acutely recruited to the narrow constriction site where abscission occurs. The ESCRT disassembly factor vacuolar protein sorting 4 (VPS4) follows CHMP4B to this site, and cell separation occurs immediately. That arrival of ESCRT-III and VPS4 correlates both spatially and temporally with the abscission event suggests a direct role for these proteins in cytokinetic membrane abscission.

关键词： Molecular dynamics   Simulation and modeling   Alzheimer's disease   Amyloid proteins   Hydrogen bonding   Leucine   Alanine   Strong interaction  

摘要： Alzheimer's disease (AD) pathogenesis is associated with formation of amyloid fibrils caused by polymerization of the amyloid beta-peptide (A beta), which is a process that requires unfolding of the native helical structure of A beta. According to recent experimental studies, stabilization of the A beta central helix is effective in preventing A beta polymerization into toxic assemblies. To uncover the fundamental mechanism of unfolding of the A beta central helix, we performed molecular dynamics simulations for wild-type (WT), V18A/F19A/F20A mutant (MA), and V18L/F19L/F20L mutant (ML) models of the A beta central helix. It was quantitatively demonstrated that the stability of the alpha-helical conformation of both MA and ML is higher than that of WT, indicating that the alpha-helical propensity of the three nonpolar residues (18, 19, and 20) is the main factor for the stability of the whole A beta central helix and that their hydrophobicity plays a secondary role. WT was found to completely unfold by a three-step mechanism: 1) loss of alpha-helical backbone hydrogen bonds, 2) strong interactions between nonpolar sidechains, and 3) strong interactions between polar sidechains. WT did not completely unfold in cases when any of the three steps was omitted. MA and ML did not completely unfold mainly due to the lack of the first step. This suggests that disturbances in any of the three steps would be effective in inhibiting the unfolding of the A beta central helix. Our findings would pave the way for design of new drugs to prevent or retard AD.

关键词： 工程模式   专业实验室   建设   实践  

摘要： 本文探讨了邵阳学院动力机械专业实验室面向市场科学确定实验室学术方向、采用与现代工程发展相适应的建设模式,坚持创新实验与生产实际相结合、实现教学、科研与社会服务多功能效应的动力机械专业实验室建设理念及其实践效果。为培养和造就高素质的创新型应用型人才提供优化的实践环境和学习空间。

关键词： 冲击   振动   周期运动   分岔  

摘要： 建立了一类冲击钻进机械系统的动力学模型,分析了系统周期冲击运动的类型,给出判定系统发生钻进运动的条件,并采用数值计算的方法分析了系统的动力学行为和系统参数对系统钻进效果的影响。结果表明:擦边分岔处是系统两种截然不同运动的"分界线","擦边"运动导致p/n运动转迁为(p-1)/n运动或形成复杂的长周期运动或混沌;当激振频率ω在q=1/1周期运动的冲击速度峰值附近时,系统具有最大冲击速度和最佳钻进量。

关键词： 长行程动力头钻机   增量式光电编码器   瞬时机械钻速   检测  

摘要： 瞬时机械钻速是孔内工况分析的一个重要指标,其检测的难点是在复杂工况下精确测量微单位时间内动力头的线性位移。对于长行程动力头钻机,由于动力头行程长,常规位移传感器很难全行程监测动力头微量线性位移。介绍了一种采用增量式光电编码器测量动力头线性位移的新方法,通过测量角位移换算成线位移,不仅精度高,而且不受动力头行程的限制,同时对编码器的选型、现场信号分析及信号采集进行了研究。

关键词： 轮式悬架   移动刚体机械手   动力学   瞬态稳定性  

摘要： 研究了2杆轮式悬架移动刚体机械手（平面）在其末端执行器跟踪给定轨迹工况下的动力学瞬态稳定性。在进行系统动力学模型分析的基础上，综合考虑了轮胎与路面作用力，给出了系统瞬态动力学稳定性评价准则，并进行了数值仿真，仿真结果真实反映了系统在执行任务时动力学瞬态稳定性分布情况及悬架对系统整体稳定性的影响。该准则适用于移动机械手轨迹跟踪工况下的稳定性评价，或以该准则为约束条件，进行系统多目标优化。

关键词： 发动机   配气相位   可变机构   气门升程  

摘要： 针对某量产汽油机设计了一款机械式连续可变气门升程（CVVL）机构,介绍了该CVVL机构的结构及原理,进行了动力学仿真计算,分析了其运动特性及主要零件的受力状况,结果表明：控制轴转角在10~140°间调节时,该机构气门升程为0.12~7.88 mm,开启持续期相应在80~247°曲轴转角（CA）间变化。控制轴转角140°时,全转速范围内的气门落座速率〈0.60 m/s;零件间接触紧密,未发生飞脱;最大气门升程随转速上升而上升,并在5000 r/min时形成拐点。

关键词： 设计研究院   技术创新   企业理念   机械工业   动力源   节能减排   节约资源   保护环境  

摘要： 节能减排、节约资源、低碳资金、保护环境是我们中机六院一贯倡导的企业理念和追求的目标，这是我们做设计的一贯宗旨。我们采取的措施是强化技术创新、加快技术的开发和推广。