关键词： redundant constraint forces   redundant actuators   singularity   penalty technique   actuating and passive constraints   forward and inverse dynamics  

摘要： Redundancy in the constraining of mechanical systems achieves more stability and larger load capacity for the system, while in actuation it provides better robustness against singularities and higher maneuverability. Few techniques have been developed with the aim to handle redundancy and singularities in dynamics analysis, and further research is still needed in this area. In this paper, we illustrate the concept of actuating and passive constraints. Then, we expand on the existing penalty techniques by incorporating the concept of actuating and passive constraints to present a penalty formulation that is capable of efficiently handling singularities and redundancy in constraining and actuation and can carry out either forward or inverse dynamics analysis of mechanical systems. As such, the proposed approach is referred to as the actuating-passive constraints penalty approach. [DOI: 10.1115/1.4002510]

关键词： anthropometric measurements   passenger vehicle   width of the optimal space  

摘要： This paper discusses a new way of modelling the width of the space that accommodates the drivers of passenger vehicles. The fact that there is a more or less fixed zero point, which is the origin of the coordinates of the man-vehicle system makes it possible to determine the mechanical-mathematical co-dependence in this system more accurately. The space is determined by taking extreme pairs of the dimensions and a series of anthropometric measurements to which the vehicle needs to be adjusted as the measurement limits. These were determined by analysis which includes both the theory of mechanisms and vehicle mechanics. In this way the method of adapting the vehicle to accommodate a range from the 5th-percentile woman to the 95th-percentile man has finally been surpassed. The paper demonstrates a methodology for designing the interior space of a passenger vehicle based on the fact that, in a range of anthropometric measurements of equal total lengths, each measurement has segments of different lengths, because people with the same leg lengths have different upper- and lower-leg lengths. Therefore the interior space of the vehicle is designed to accommodate extreme measurements and to allow for limitations caused by movement and the physical laws derived from seeing the anthropometric measurement mechanism as a mechanical mechanism. The paper offers a design for the space behind the windscreen, the position of the steering wheel, and the position of the foot controls together with the total space which the driver occupies, primarily from the aspect of anthropometric limitations, concluding that the maximum width for accommodation of the driver at the lowest level of a seat along the x axis is 169 mm, and along the y axis is 1013 mm.

关键词： Neural controller   Mechanical coupling   Visuomotor tracking   Stability   Sensitivity  

摘要： Coupled human balancing tasks are investigated based on both pseudo-neural controllers characterized by time-delayed feedback with random gain and natural human balancing tasks. It is shown numerically that, compared to single balancing tasks, balancing tasks coupled by mechanical structures exhibit enhanced stability against balancing errors in terms of both amplitude and velocity and also improve the tracking ability of the controllers. We then perform an experiment in which numerical pseudo-neural controllers are replaced with natural human balancing tasks carried out using computer mice. The results reveal that the coupling structure generates asymmetric tracking abilities in subjects whose tracking abilities are nearly symmetric in their single balancing tasks.

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。