关键词： 5自由度   移动机械手   动力学   仿真  

摘要： 系统研究了5自由度轮式悬架移动机械手动力学问题.综合了拉格朗日原理和牛顿-欧拉方程,并采用笛卡尔坐标系,建立了该机械手系统的正、逆动力学模型.最后通过软件Matlab求解微分方程完成了该机械手动力学模型逆解的仿真结果.

关键词： 农用动力机械   蓄电池故障   排除方法  

摘要： 蓄电池是农用动力机械的重要构成部分，在使用中常出现这样那样的故障，其排除方法如下：

关键词： 机械密封   螺旋槽   动环   模态分析   振动特性  

摘要： 在高参数复杂工况条件下,机械密封摩擦副密封环在工作过程中产生的振动,严重影响机械密封的性能,从而引起动静环端面的磨损,使泄漏量增大。为了更清晰地描述机械密封摩擦副动环在工作过程中的动力学特性,针对带螺旋槽动环和无螺旋槽动环分别进行了模态分析,计算出了其低阶固有振动频率和主振型,以及各阶对应的最大变形量和振动应力,得到了各阶主振型图及振动应力和变形曲线的变化图;通过对比分析,带螺旋槽动环和无螺旋槽动环一阶主振型不同,其余振型基本相似,并且得到螺旋槽动环的应力和变形比无螺旋槽动环大,无螺旋槽动环的动力学性能好。

关键词： 农业   动力机械   节油  

摘要： 当前农业机械对燃油的大量消耗,不利于缓解能源紧缺的情况,为此,我们需要采取合理有效地措施,完善农业机械,减少对燃油的的使用。同时,节约农业机械用油还可以减少生产成本的开支,提高生产效率,增加居民的经济效益,,促进农业行业的健康、绿色发展。

关键词： 履带车辆   液压机械传动   转向系统   建模   仿真  

摘要： 液压机械差速转向系统是履带车辆的一种新型双功率流转向系统,在对系统构成及工作原理进行分析的基础上,运用动力学原理和模块化建模方法,建立了包含发动机、液压闭式回路系统、行星排及负载等履带车辆液压机械差速转向系统的数学模型和Simulink仿真模型。结合实例,对液压机械差速转向系统的动态响应性能进行了仿真及试验研究,对比表明所建模型能有效表达履带车辆液压机械差速转向系统性能的变化,分析了不同工况参数下系统性能的变化规律,从而为履带车辆液压机械差速转向系统的性能分析及控制研究提供理论依据。

关键词： MDM2   p53   Cancer   QSAR   Piperidinone   Library  

摘要： Tumour suppressor p53 is known to play a central role in prevention of tumour development, DNA repair, senescence and apoptosis which is in normal cells maintained by negative feedback regulator MDM2 (Murine Double Minute 2). In case of dysfunctioning of this regulatory loop, tumour development starts thus resulting in cancerous condition. Inhibition of p53-MDM2 binding would result in activation of the tumour suppressor. In this study, a novel robust fragment-based QSAR model has been developed for piperidinone derived compounds experimentally known to inhibit p53-MDM2 interaction. The QSAR model developed showed satisfactory statistical parameters for the experimentally reported dataset (r(2) = 0.9415, q(2) = 0.8958, pred_r(2) = 0.8894 and F-test = 112.7314), thus judging the robustness of the model. Low standard error values (r(2)_se = 0.3003, q(2)_se = 0.4009 and pred_r(2)_se = 0.3315) confirmed the accuracy of the developed model. The regression equation obtained constituted three descriptors (R-2-DeltaEpsilonA, R-1-RotatableBondCount and R-2-SssOCount), two of which had positive contribution while third showed negative correlation. Based on the developed QSAR model, a combinatorial library was generated and activities of the compounds were predicted. These compounds were docked with MDM2 and two top scoring compounds with binding affinities of -10.13 and -9.80 kcal/mol were selected. The binding mode of actions of these complexes were analyzed using molecular dynamics simulations. Analysis of the developed fragment-based QSAR model revealed that addition of unsaturated electronegative groups at R-2 site and groups with more rotatable bonds at R-1 improved the inhibitory activity of these potent lead compounds. The detailed analysis carried out in this study provides a considerable basis for the design and development of novel piperidinone-based lead molecules against cancer and also provides mechanistic insights into their mode of actions. (C) 2014 Elsevier In

关键词： Molecular dynamics   mechanics   nanopore   vacancy   Bi2Te3  

摘要： The effects of nanopores and vacancies on the mechanical properties of Bi2Te3 have been studied. Cuboid single-crystal bulk Bi2Te3 with atoms removed was chosen for molecular dynamics simulations. The mechanisms of action of the two defects can be distinguished by their specific effects on the crystal structure of the bulk Bi2Te3. The mechanical properties of the nanoporous Bi2Te3 are affected by porosity (I center dot), surface-to-volume ratio (rho), and minimum cross-section length (L (min)). The elastic modulus remains unchanged at 52.86 GPa for constant porosity of 0.7% whereas the ultimate stress and fracture strain gradually decrease with growing rho or decreasing L (min). The lattice stability of Bi2Te3 gradually weakens as the proportion of vacancies increases;this leads to increasing potential energy and poorer mechanical properties of Bi2Te3. When the proportion of Bi vacancies is increased from 0% to 8%, the elastic modulus decreases from 57.17 GPa to 36.32 GPa, a reduction of 36.47%, the ultimate stress decreases from 6.40 GPa to 3.61 GPa, a reduction of 43.59%, and the fracture strain decreases from 22.4% to 13.8%, a reduction of 38.39%.

关键词： Skutterudites   mechanical properties   molecular dynamics   nanopores  

摘要： The effects of nanometer-size pores on the uniaxial tensile mechanical properties of single-crystal bulk CoSb3 were investigated by classical molecular dynamics simulation. The pores were assumed to be cylindrical and uniformly distributed along two vertical principal crystallographic directions of a square lattice. The dependence of the effects of pores on pore diameter and porosity was examined separately, by varying pore diameter and porosity in the ranges a (0)-6a (0) and 0.1-5%, respectively, where a (0) is the lattice constant of CoSb3. The results from simulation indicate that, at constant porosity, Young's modulus remains almost constant whereas ultimate strength decreases as pore diameter increases. At constant pore diameter, Young's modulus decreases monotonically as porosity increases exponentially;interestingly, variation of the ultimate strength is negligible. Numerically, the mechanical performance of systems containing nanopores is still desirable, although no better than that of the no-pore system. The results provide useful information for realistic application of skutterudites.

关键词： Differential cross sections   GPU   H + NH   H2   Nitrogen   State-to-state   Wave packet  

摘要： State-to-state time-dependent quantum dynamics calculations have been carried out to study the abstraction processes in the title reaction for the first time. The ab initio potential energy surface of the lowest quartet electronic state of the system recently reported by Zhai et al. (J Chem Phys 135:104314/1-104314/7, ) is employed in this investigation. Influences of the collision energy on the product state-resolved differential cross sections (DCSs) are calculated and discussed. For low collision energies, we find that reactive collisions along the collinear pathway result in the H product backward scattering. In the case of high collision energy, the stripping collisions with larger impact parameters tend to produce sideways scattering and furnish a high internal excitation of the H. The product H is found to have an inverted rotational distribution and no inversion in vibrational distributions. Moreover, the state-to-state DCSs provide a global perspective of the reaction mechanisms and their contribution to the final H internal energy states. A reaction model is built and works well for our calculated results. [ABSTRACT FROM AUTHOR]

关键词： Molecular dynamics simulation   mechanical properties   Mg2Si   vacancy  

摘要： The mechanical properties of single-crystal bulk Mg2Si have been investigated using the molecular dynamics simulation method, in which a many-body potential energy function including bond and angle interactions is adopted to predict the mechanical properties. Virtual tension tests of specimens under different conditions, including Mg vacancy and temperature effects, were carried out by controlling the strain along the principal crystallographic direction. The simulation results show that single-crystal bulk Mg2Si exhibits a nonlinear elastic stress-strain response and the mechanical properties degrade significantly with increasing vacancy content. Moreover, the effect of temperature on the mechanical properties of single-crystal bulk Mg2Si is also discussed in detail.