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.

关键词： Biology and life sciencesEngineering and technologyMaterials scienceMedicine and health sciencesPhysical sciencesResearch Article  

摘要： The link between mechanics and biology in the generation and the adaptation of bone has been well studied in context of skeletal development and fracture healing. Yet, the prediction of tissue genesis within - and the spatiotemporal healing of postnatal defects, necessitates a quantitative evaluation of mechano-biological interactions using experimental and clinical parameters. To address this current gap in knowledge, this study aims to develop a mechanistic mathematical model of tissue genesis using bone morphogenetic protein (BMP) to represent of a class of factors that may coordinate bone healing. Specifically, we developed a mechanistic, mathematical model to predict the dynamics of tissue genesis by periosteal progenitor cells within a long bone defect surrounded by periosteum and stabilized via an intramedullary nail. The emergent material properties and mechanical environment associated with nascent tissue genesis influence the strain stimulus sensed by progenitor cells within the periosteum. Using a mechanical finite element model, periosteal surface strains are predicted as a function of emergent, nascent tissue properties. Strains are then input to a mechanistic mathematical model, where mechanical regulation of BMP-2 production mediates rates of cellular proliferation, differentiation and tissue production, to predict healing outcomes. A parametric approach enables the spatial and temporal prediction of endochondral tissue regeneration, assessed as areas of cartilage and mineralized bone, as functions of radial distance from the periosteum and time. Comparing model results to histological outcomes from two previous studies of periosteum-mediated bone regeneration in a common ovine model, it was shown that mechanistic models incorporating mechanical feedback successfully predict patterns (spatial) and trends (temporal) of bone tissue regeneration. The novel model framework presented here integrates a mechanistic feedback system based on the mechanosensiti

关键词： Molecular dynamics   mechanical properties   nanowires   beta-Zn4Sb3  

摘要： Recent experimental studies reveal that beta-Zn4Sb3 nanowires have greater potential commercial application compared with conventional bulk materials. Mechanical stability of beta-Zn4Sb3 nanowires is an important foundation for their commercial application. In the present work, mechanical properties of beta-Zn4Sb3 nanowires are studied by using the molecular dynamics method, which theoretically reveals the influence mechanism of various effects (temperature, strain rate, and size effect) on the mechanical behavior of beta-Zn4Sb3 nanowires. The simulation results show that mechanical properties of beta-Zn4Sb3 nanowires decrease remarkably compared with bulk beta-Zn4Sb3. Due to the disordered Zn atoms in beta-Zn4Sb3, mechanical properties of beta-Zn4Sb3 nanowires show a weak temperature softening effect, weak strain rate hardening effect, and slight size dependence. The present simulations of beta-Zn4Sb3 nanowires represent a fundamental study and shed light on the understanding of the essential mechanical behavior of beta-Zn4Sb3 nanowires.

关键词： Copper   Lamellae   Aluminium   Dislocations   Molecular dynamics  

摘要： This paper attempts to gain an understanding of the effect of lamellar length scale on the mechanical properties of two-phase metal-intermetallic eutectic structure. We first develop a molecular dynamics model for the in-situ grown eutectic interface followed by a model of deformation of Al-Al2Cu lamellar eutectic. Leveraging the insights obtained from the simulation on the behaviour of dislocations at different length scales of the eutectic, we present and explain the experimental results on Al-Al2Cu eutectic with various different lamellar spacing. The physics behind the mechanism is further quantified with help of atomic level energy model for different length scale as well as different strain. An atomic level energy partitioning of the lamellae and the interface regions reveals that the energy of the lamellae core are accumulated more due to dislocations irrespective of the length-scale. Whereas the energy of the interface is accumulated more due to dislocations when the length-scale is smaller, but the trend is reversed when the length-scale is large beyond a critical size of about 80 nm. (C) 2014 Author(s).

关键词： 研究生   科研   职业发展   素养  

摘要： 科学研究是研究生教育的核心,而良好学术氛围是培养研究生创新能力的重要保证。为了更好地了解我国高校科学研究和学术道德状况,从而为进一步加强研究生学风建设和学术道德教育工作提供依据,本文作者通过网络等媒介,以问卷调查的形式,对上海交通大学机械与动力工程学院研究生的科学研究能力与学术道德方面开展了相关调查。通过调查,了解到学生对于良好学术氛围的渴望、读研的目的以及未来职业生涯的规划等情况,同时也发现学生中存在如学术道德不高、实习实践缺少、睡眠和健康状况差等方面的问题。本文力图通过对我国高校研究生生活状况的缩影-上海交通大学机械与动力工程学院学生的分析,寻找出我国科研工作当中存在的问题,并为进一步了解我国科研发展的情况打下基础。