关键词： amyloid   fibril fragmentation   steered molecular dynamics (SMD)   structural defects  

摘要： We examine how the different steric packing arrangements found in amyloid fibril polymorphs can modulate their mechanical properties using steered molecular dynamics simulations. Our calculations demonstrate that for fibrils containing structural defects, their ability to resist force in a particular direction can be dominated by both the number and molecular details of the defects that are present. The simulations thereby suggest a hierarchy of factors that govern the mechanical resilience of fibrils, and illustrate the general principles that must be considered when quantifying the mechanical properties of amyloid fibres containing defects.

关键词： 轮式工程机械   串联式   混合动力  

摘要： 本文在比较了现有的轮式工程机械混合动力技术优缺点的基础上,对轮式工程机械的串联式混合动力系统进行了研究,介绍了系统的组成和工作方式,分析了串联式系统的优点,提出了串联式液压混合动力系统不但适用于轮式工程机械而且适用于频繁起停的中小型城市公交车、军用轮式汽车等车辆的行走装置。

关键词： 深层超深层钻探   夹持机械手   CATIA   ADAMS   动力学仿真  

摘要： 大陆深层超深层钻探需要可靠的钻杆自动排放系统,尤其对其中的钻杆夹持机械手有较高的要求。针对上述要求,采用CATIA建模,然后通过中间软件将模型导入到产品虚拟仿真软件ADMAS中进行动力学仿真,将仿真所得数据与理论数据进行对比,以便及时发现和解决问题,缩短设计的周期。

关键词： 人口   机械化   农村剩余劳动力   流量  

摘要： 我国农业部门还能够析出多少劳动力?本文系统分析了人口、农业劳动力需求和农村剩余劳动力的关系发现,农村劳动力供给和农业机械化是影响剩余劳动力流量的重要因素,如果农业机械化程度提高替代的劳动力低于农村劳动力供给的减少,农村剩余劳动力流量将绝对减少,机械化程度的提高将有利于从农业部门析出更多劳动力。以大庆市为例分析得出了农村剩余劳动力流量为负的结论,并提出了加大农机补贴力度和发展农机服务市场的政策建议。

关键词： 绝对坐标方法   柔性机械臂   抓取   太阳翼   仿真  

摘要： 结合绝对节点坐标方法与自然坐标方法的绝对坐标方法不仅能精确表达刚柔耦合多体系统的动力学特性而且能得到常数系统质量矩阵,便于高效计算。采用该方法研究了星载柔性机械臂在抓取漂浮目标过程中机械臂-星体-太阳翼的刚柔耦合动力学与控制问题。提出了一种间隙圆柱运动副的四点碰撞检测模型,引入一种能考虑碰撞能量耗散的连续接触模型实现了抓取过程的接触、碰撞模拟。提出了一种联合控制策略确保了抓取过程中星体姿态的稳定。该研究为实际工程应用提供一种新的星载柔性抓取机械臂-太阳翼耦合动力学与控制分析的建模与数值仿真方法。

关键词： prosthetic valve   aortic stenosis   hemodynamics   valvular heart disease  

摘要： Invasive hemodynamic evaluation in the patient with a mechanical aortic valve has in the past required transseptal or apical left ventricular puncture in order to obtain left ventricular pressure measurements. Over the last few years, several case reports have described the feasibility of using a coronary pressure-sensing guidewire to cross mechanical prosthetic aortic valves. In the current manuscript, we report four cases in which the use of a pressure-sensing guidewire was utilized for invasive hemodynamic diagnostic evaluation in patients with mechanical aortic valves. Furthermore, we present a detailed description of the technical approach to this technique and the limitations of this approach. (c) 2013 Wiley Periodicals, Inc.

关键词： Carbon nanotube   Molecular dynamics   Electron irradiation   Tension   Compression   Torsion  

摘要： Molecular dynamics simulations are carried out to investigate electron irradiation effects on mechanical properties of single-walled carbon nanotubes. Electron irradiation effects are introduced by the Monte Carlo method using the elastic collision cross section. After the irradiation, the mechanical properties, such as tensile, compressive and torsional properties, are investigated. The degradation of the mechanical strength of the nanotube irradiated at higher temperature is reduced. The simulation reveals that the recombinations of dangling bonds during irradiation and the formation of amorphous network along the cylindrical shape are the key mechanism of the robustness of the nanotubes during electron irradiation at high temperature. (C) 2013 Published by Elsevier B.V.

关键词： elastic constants   mechanical variables measurement   molecular dynamics method   molybdenum compounds   silicon compounds   stress-strain relations   temperature measurement   thermal expansion  

摘要： A new method was proposed to obtain high temperature mechanical properties with a combination of ab initio molecular dynamics and stress-strain analyses. It was applied to compounds in the Mo-Si-B ternary system, namely, T1 (Mo5Si3) and T2 (Mo5SiB2) phases. The calculated coefficient of thermal expansion, thermal expansion anisotropy, and elastic constants agree well with those from the available experiments. The method enables us to theoretically access these properties up to 2000 K. (C) 2013 Author(s).

关键词： Mixed lubrication   chemical mechanical polishing   computational fluid dynamics  

摘要： Interfacial phenomena between the wafer and the polishing pad during chemical mechanical polishing are an area of great interest as they affect post-chemical mechanical polishing wafer topographies. Traditionally, the Reynolds equation has been used to predict the fluid pressure between the wafer and the polishing pad. However, with computational fluid dynamics it is possible to predict the fluid pressure and obtain insight into the fluid motion at the leading edge and trailing edge of the wafer. Additionally, computational fluid dynamics allows for the added ability to increase the resolution of the fluid physics to the asperity scale. In this study, a model is developed to predict phenomena related to mixed lubrication chemical mechanical polishing using computational fluid dynamics. Contact mechanics between the wafer and the pad are resolved through a Winkler elastic foundation formulation. The wafer is mounted on a ball joint which allows free rotation to occur. Friction between the wafer and the polishing pad causes the wafer to assume a position which produces a sub-ambient pressure distribution similar to that obtained from experiments. The effects of different table speeds on the interfacial fluid pressure, as predicted by the computational fluid dynamics are presented.

关键词： Molecular dynamics   mechanical properties   disordered Zn atoms   nanopores   beta-Zn4Sb3  

摘要： Effects of disordered Zn atoms and nanopores on mechanical properties of beta-Zn4Sb3 are studied by using the molecular dynamics (MD) method. Due to the influence of disordered Zn atoms in beta-Zn4Sb3, the elastic modulus decreases from 90.85 GPa to 68.17 GPa, a decrease of 24.96%. The ultimate tensile stress decreases from 18.25 GPa to 9.96 GPa, a decrease of 45.42%. The fracture strain decreases from 32.7% to 20.8%, a decrease of 36.39%. Due to the influence of nanopores, the elastic modulus decreases with growing porosity, and the relationship between the elastic modulus and porosity leads to a scaling law. It seems that the porous radius and porous distribution are also important factors influencing the ultimate tensile stress and fracture strain, in addition to the porosity. However, our simulation results demonstrate that disordered Zn atoms and nanopores reduce the structural stability, dramatically decreasing the mechanical properties of beta-Zn4Sb3.