关键词： 机械动力   格局   变化  

摘要： 分析了21世纪以来黑龙江省农业机械动力变化,以地方和农垦总局进行对比,总结二者不同机械动力格局的构成。介绍了农垦总局大马力拖拉机状况。

关键词： Solid-liquid reactions   Kinetics   Leaching   Mass transfer   Morphology  

摘要： A systematic approach was developed to consider liquid-solid reactions with rough solid particles and shrinking particle model. The model is able to predict the reactivities of both non-porous and porous solid particles;the reaction order with respect to the solid material varies from zero (non-porous slab) to one (porous particle). As a model system, leaching of zinc sulphide (sphalerite) with ferric iron in an acidic environment was considered. The modelling was based on experimental data obtained in a batch reactor system, for which both conventional mixing and ultrasound was applied. Rival models based on plausible reaction mechanisms were derived and discriminated qualitatively and with regression analysis. The best model described the leaching reaction as a stepwise process, where ferricions react with solid zinc sulphide in consecutive surface reaction steps. Shrinking particle model a long with the surface roughness approach was used. The model predicts first order behaviour with respect to zinc sulphide, while the reaction order with respect to ferric iron varies from one to two as there action progresses. This is in accordance with experimental observations. The intrinsic kinetics, liquid-solid mass transfer and the effect of ultrasound were well described by the best kinetic model. (C) 2010 Elsevier Ltd. All rights reserved.

关键词： 分子机械   模拟   动力学   建模  

摘要： 从纳米尺度了解结构和材料的动力学性能有着重要的意义,对分子机械动力学的研究现状进行了概括和总结,介绍了目前常用的分析模型,展望了未来的研究方向和热点。

关键词： 并联机械手   动力性能   尺度综合  

摘要： 研究一种二平动自由度高速并联机械手的动力尺度综合方法.在建立逆刚体动力学模型基础上,提出一种基于单轴最大驱动力矩全域最大值最小的动力学性能评价指标,该指标可表示为系统尺度和惯性参数及位形的显函数形式,可直接用于观察奇异位形的出现条件.建立雅可比矩阵奇异值的显式,提出一组兼顾速度、精度和刚度的传递角约束方程,通过考察奇异值与运动学性能的关系,可将传递角约束方程转化为性能约束方程,同时配以工作空间/机构尺度等约束条件,利用工程实例研究性能约束对尺度参数和动力学性能评价指标的影响规律,由此综合出在满足上述约束条件下使得系统动力学性能最优的尺度参数.

关键词： 工程机械   发动机   供应商   中国   潍柴动力股份有限公司   市场地位   获奖产品   颁奖典礼  

摘要： 3月29日，2009年中国工程机械年度产品TOP50评选颁奖典礼在北京举行，本次活动评选出了2009年中国工程机械市场各方面表现优异的50个产品，无论在技术创新、市场表现或应用贡献方面，这些获奖产品均在各自领域有着极高的市场地位，受到专家、用户及媒体代表的高度认可。在发动机产品评选项目中，潍柴动力股份有限公司作为唯一获奖企业，被评为“2009年中国工程机械年度发动机供应商”。

关键词： 微构件   振动模型   固有频率   动力学分析  

摘要： 微电子机械系统中的微构件如定子、转子,结构尺寸微小,一般在数百微米量级。制造微构件的材料主要是硅,硅具有优良的机械性能,能够满足微结构对材料力学性能的要求。机械(力学)理论基础如弹性体基本方程、运动学方程、动力学方程、弹性梁基本方程、振动理论等对微构件依然适用。笔者对一种新型微电机的驱动机理进行了研究。基于振动学理论,建立了微机械构件的振动数学模型,计算了自由振动固有频率以及推导出激励下的振动方程,并在此基础上进行了运动学和动力学分析。

关键词： 机械动力学   有限元法   试验模态分析   综合性实验  

摘要： 针对目前机械动力学课程中悬臂梁结构模态分析实验存在的问题,引导学生将学习过的CAD/CAE软件操作知识运用于该实验,弥补了实验仪器和实验装置的不足,也提高了学生做实验的主动性和创新性,大大提升了实验效果。

关键词： Molecular dynamics simulation   Mechanical properties   Bismuth telluride   Thermoelectric material   Nanofilm  

摘要： A molecular dynamics (MD) simulation has been carried out to evaluate the mechanical properties of Bi2Te3 nanofilm, and all the simulation results are compared with that of Bi2Te3 bulk. After the stable free-relaxation state has been obtained, the radial distribution function of Bi2Te3 nanofilm is computed to validate its crystal structure. The distributions of potential energy and stress along the thickness direction are obtained. It is found that the surface atoms possess high potential energy;the surface of the nanofilm undergoes tensile stress, while the inside undergoes compressive stress. Tension simulations have been conducted to evaluate the mechanical properties (including Young's modulus, ultimate strength and failure strain) of the nanofilm. The effects of surface, size, and temperature on the calculating results of Bi2Te3 nanofilm are discussed in detail. (C) 2010 Elsevier B.V. All rights reserved.

关键词： Model comparison   Maximum caliber   Organic matter dynamics   Litter decomposition   Mineral nitrogen   Microbial biomass   C-13 labelling   Priming effect  

摘要： First order kinetics characterize most models of soil organic matter dynamics. Although first order kinetics often provide a good description of litter decomposition, their general applicability has recently been challenged by numerous observations of priming effects. A priming effect can be defined as a change in native soil organic matter decomposition rate following the addition of some labelled exogenous substrate. Recently two new formalisms were developed which predict a priori the existence of priming effects, whether positive or negative. The Extended Mass Action (EMA) formalism is a generalization of enzyme kinetics at the microbial scale. The Maximum Caliber (MAXCAL) formalism describes the most probable dynamics of a system that arises when the multiple ways feasible macroscopic dynamics can be realized at the microscopic particle scale are accounted for. Here those two formalisms were applied to a common soil compartimentation scheme and their predictions confronted with an appropriate set of priming observations. We show that the two formalisms generate distinct, testable predictions and that the MAXCAL formalism performed better than the EMA formalism. We discuss the determinants of priming effects as predicted by the Maximum Caliber formalism. (c) 2010 Elsevier Ltd. All rights reserved.

关键词： Nanostructured intermetallics   Phase transformation   Twinning   Work hardening   Simulations   atomistic  

摘要： The asymmetric stress strain behavior under tension/compression in an initial < 100 > B-2-NiAl nanowire is investigated considering two different surface configurations i.e., < 100 >/(0 1 0) (0 0 1) and < 100 >/(0 1 1) (0 - 1 1). This behavior is attributed to two different deformation mechanisms namely a slip dominated deformation under compression and a known twinning dominated deformation under tension. It is also shown that B2 -> BCT (body-centered-tetragonal) phase transformation under tensile loading is independent of the surface configurations for an initial < 100 > oriented NiAl nanowire. Under tensile loading, the nanowire undergoes a stress-induced martensitic phase transformation from an initial B2 phase to BCT phase via twinning along {110} plane with failure strain of similar to 0.30. On the other hand, a compressive loading causes failure of these nanowires via brittle fracture after compressive yielding, with a maximum failure strain of similar to-0.12. Such brittle fracture under compressive loading occurs via slip along {110} plane without any phase transformations. Softening/hardening behavior is also reported for the first time in these nanowires under tensile/compressive loadings, which cause asymmetry in their yield strength behavior in the stress strain space. Result shows that a sharp increase in energy with increasing strain under compressive loading causes hardening of the nanowire, and hence, gives improved yield strength as compared to tensile loading. (C) 2010 Elsevier Ltd. All rights reserved.