关键词： Infinite string   Viscoelastic   Dynamic system   Contact force  

摘要： The mutual interaction between a number of multi degrees of freedom mechanical systems moving with uniform speed along an infinite taut string supported by a viscoelastic layer has been studied using the substructure synthesis method when base excitations of a common frequency are given to the mechanical systems. The mobility or impedance matrices of the string have been calculated analytically by Fourier transform method as well as wave propagation technique. The above matrices are used to calculate the response of the discrete mechanical systems. Special attention is paid to the contact forces between the discrete and the continuous systems which are estimated by numerical simulation. The effects of phase difference, the distance between the systems and different base excitation amplitudes on the collective behaviour of the mechanical systems are also studied. The present study has relevance to the coupled dynamic problem of more than one railway pantographs and an overhead catenary system where the pantographs are modelled as discrete systems and the catenary is modelled as a taut string supported by continuous viscoelastic layer. (C) 2017 Elsevier Ltd. All rights reserved.

关键词： Ceramic thin films   Deformation mechanism   Mechanical properties   Hall–Petch effect   Molecular dynamics  

摘要： The uniaxial tensile mechanical properties of polycrystalline TiN with 14 different grain sizes measuring 2.0–5.8 nm were studied via molecular dynamics with the second-nearest-neighbour modified embedded-atom method (2NN MEAM). The results show that the grain size affects the movement mechanisms of the grains and grain boundaries, and the relationship between grain size and tensile yield strength. The direct and inverse Hall-Petch formula of TiN are given. The dislocation migration of grain boundaries is the main deformation mechanism when the grain size is larger than 3.2 nm. When grains are smaller than 3.2 nm, grain rotation and grain boundary sliding are the preferred deformation mechanisms, which cause an inverse Hall–Petch effect. Polycrystalline TiN is at its hardest when the grain size ranges from 3 to 4 nm. The results can serve as theoretical basis for further doping non-metallic elements with critical grain sizes in the grain boundary produce superhard TiN composites.

摘要： The high valent Mn-V(O) (lambda(max) approximate to 407 nm) and Mn-IV(O) (lambda(max) approximate to 421 nm) species of a series of electron-rich and electron-deficient meso-tetra(aryl) porphyrins (aryl = phenyl, 2-chlorophenyl, 2-nitrophenyl, 2-methylphenyl, 2-bromophenyl, 2,6-dichlorophenyl 4-methoxyphenyl, 4-methylphenyl, 4-chlorophenyl and 4-pyridyl) were prepared through the reaction of their corresponding manganese porphyrins with oxone in dichloromethane at a relatively low temperature (273 K). While the high valent Mn(O) intermediates of the para-substituted porphyrins were significantly degraded under reaction conditions, the corresponding species of the ortho substituted porphyrins showed high oxidative stability up to 20 min. Interestingly, the high valent Mn(O) of the mono-ortho-substituted meso-tetra(phenyl) porphyrins were as stable as that of meso-tetra(2,6-dichlorophenyl) porphyrin. The presence of imidazole (ImH) was found to play crucial roles in the formation and reactivity of the high valent Mn(O) species. The kinetics and mechanism of the oxidation of olefins with the high valent Mn-V(O) porphyrin intermediate were studied and the second order rate constants were evaluated under pseudo-first-order conditions. Also, the MnIV(O) species showed a reactivity comparable with that of the corresponding Mn-V(O) species. The observation of a Hammet constant of rho = -0.48 in the oxidation of para-substituted styrenes is in accord with an electrophilic mechanism.

关键词： biosynthesis   enzymes   molecular dynamics   molecular modeling   phosphorylation  

摘要： Human a-phosphoglucomutase 1 (alpha-PGM) catalyzes the isomerization of glucose-1-phosphate into glucose-6-phosphate (G6P) through two sequential phosphoryl transfer steps with a glucose-1,6-bisphosphate (G16P) intermediate. Given that the release of G6P in the gluconeogenesis raises the glucose output levels, alpha-PGM represents a tempting pharmacological target for type 2 diabetes. Here, we provide the first theoretical study of the catalytic mechanism of human a-PGM. We performed transition-path sampling simulations to unveil the atomic details of the two catalytic chemical steps, which could be key for developing transition state (TS) analogue molecules with inhibitory properties. Our calculations revealed that both steps proceed through a concerted SN2-like mechanism, with a loose metaphosphate-like TS. Even though experimental data suggests that the two steps are identical, we observed noticeable differences: 1) the transition state ensemble has a well-defined TS region and a late TS for the second step, and 2) larger coordinated protein motions are required to reach the TS of the second step. We have identified key residues (Arg23, Ser117, His118, Lys389), and the Mg2+ ion that contribute in different ways to the reaction coordinate. Accelerated molecular dynamics simulations suggest that the G16P intermediate may reorient without leaving the enzymatic binding pocket, through significant conformational rearrangements of the G16P and of specific loop regions of the human alpha-PGM.

关键词： 动力学方程   拉格朗日   模型简化   ADAMS  

摘要： 拉格朗日方程是通用六自由度工业机械臂进行动力学分析的常用方法。然而,当关节自由度多于三时,其动力方程的展开式相当复杂,完整地求出其表达式并不现实。考虑到通用工业机械臂的满足Pieper准则的特殊结构,只考虑机械臂的前三关节,并将腕部三个关节看作为动力效应的外部干扰,对其进行动力学分析,并通过ADAMS进行对比验证。结果表明,当只考虑机械臂前三关节时其动力学特性与考虑全部六关节相比不失一般性,且具有较小的误差。

关键词： 机械臂   轮毂打磨   并联机构   动力学分析   Lagrange方程   峰值预估模型  

摘要： 提出了一种基于2-UPS+UPU机构的5-DOF机械臂,建立了机械臂的手腕运动状态与其关节驱动参数之间的传递方程显式表达式,从而得到机械臂的伺服电机驱动参数峰值预估模型,计算出各伺服电机中的驱动转速最大理论值为25.1r/s,驱动力矩最大理论值为6.2N獉m。以一组具体的结构参数作为算例,计算出伺服电机中的驱动转速最大值为18.7r/s,驱动力矩最大值为4.73N獉m,算例伺服电机选型的预估功率为700W,证明了伺服电机峰值驱动参数预估模型的合理性。

关键词： computer modeling   crosslinking   mechanical properties   thermosets   yielding  

摘要： The influence of monomer functionality on the mechanical properties of epoxies is studied using molecular dynamics (MD) with the Reax Force Field (ReaxFF). From deformation simulations, the Young's modulus, yield point, and Poisson's ratio are calculated and analyzed. Comparison between the network structures of distinct epoxies is further advanced by the monomeric degree index (MDI). Experimental validation demonstrates the MD results correctly predict the relationship in Young's moduli. Therefore, ReaxFF is confirmed to be a useful tool for studying the mechanical behavior of epoxies. (c) 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 255-264

关键词： 草莓采摘   机械手   刚柔混联   动力学分析   柔顺控制  

摘要： 针对草莓形状不规则、组织娇嫩,容易受机械损伤,难以实现高效低损的机械化采摘作业的问题,提出一种刚柔混联的机械手结构。为了建立柔顺伪刚体模型,将柔顺构件等效为具有欠驱动关节的多刚体串联系统;采用影响系数法建立柔顺构件等效多刚体系统的动力学模型,对机械手柔性构件的动力学特性进行仿真分析与样机试验研究。仿真和试验结果表明,采用力反馈的刚柔混联机构具有良好的包络性、可控性、平稳性及速度特性,适合于草莓的柔顺抓取控制,该成果可为草莓等果蔬无损采摘机械手的设计及优化提供借鉴和参考。

关键词： 黄铜矿   机械活化   浸出   活化能  

摘要： 研究了机械活化对黄铜矿浸出率的影响并进行了动力学分析。利用X射线衍射仪、激光粒度分析仪测试了机械活化对黄铜矿晶体结构、粒度的影响。结果表明:机械活化可细化黄铜矿颗粒粒径、破坏黄铜矿晶粒完整性、降低黄铜矿活化能、提高黄铜矿反应活性。黄铜矿机械活化1h后,浸出活化能从29.27kJ/mol降低至16.87 kJ/mol。当黄铜矿与氧化剂(NaClO_2)共磨相同时间后,活化能降至12.31kJ/mol,黄铜矿反应模型从化学反应转变为扩散反应。

关键词： 多刚体系统   机械臂   运动学等效   动力学模拟   数学仿真   末端位姿   轨迹规划   运动反馈  

摘要： 在空间机器人系统应用于在轨服务、目标捕获的研究中,多自由度机械臂的动力学动特性分析是其主要困难。针对该问题,可运用D-H参数,构建坐标系统和矢量关系,搭建动力学数学模型,进行多刚体系统运动学和动力学建模的仿真研究分析,并运用SimMechanics做运动学等效和各关节的点到点的位姿解算,及动力学模拟,结合ADAMS做联合仿真对比分析。根据仿真结果,实时解算机械臂各关节以及末端抓捕工具的位姿,并做轨迹规划,以验证真实空间机械臂操作的仿真程度,更好地服务于半物理实验平台。