关键词： Molecular dynamics   PMMA   Ag nanoparticle   Mechanical property   Modeling   Simulation  

摘要： The molecular dynamics simulation (MD) was carried out to investigate the mechanical properties of pristine polymethylmethacrylate (PMMA) and the composites of PMMA mixed with the silver nanoparticles (PMMA/AgNPs) at two AgNP weight fractions at 0.60 and 1.77 wt%. From the stress-strain profiles by the tensile process, it can be seen that the improvement on Young's modulus is insignificant at these lower AgNP fractions. The tensile strength of pristine PMMA can be slightly improved by the embedded AgNPs at 1.77 wt%, because the local density and strength of PMMA in the vicinity of AgNP surface within about 8.2 are improved. For the temperature effect on the mechanical properties of pristine PMMA and PMMA/AgNP composite, the Young's moduli and strength of pristine PMMA and PMMA/AgNP composite significantly decrease at temperatures of 450 and 550 K, which are close to the predicted melting temperature of pristine PMMA about 460 K. At these temperatures, the PMMA materials become more ductile and the AgNPs within the PMMA matrix display higher mobility than those at 300 K. When the tensile strain increases, the AgNPs tend to get closer and the fracture appears at the PMMA part, leading to the close values of Young's modulus and ultimate strength for pristine PMMA and PMMA/AgNP composite at 450 and 550 K.

关键词： haptic memory   electronic skin   resistive random access memory   triboelectric nanogenerator   bioinspired  

摘要： Haptic memory, from the interaction of skin and brain, can not only perceive external stimuli but also memorize it after removing the external stimuli. For the mimicry of human sensory memory, a self-powered artificial tactile memorizing system was developed by coupling bionic electronic skin and nonvolatile resistive random access memory (RRAM). The tribotronic nanogenerator is utilized as electronic skin to transform the touching signal into electric pulse, which will be programmed into the artificial brain: RRAM. Because of the advanced structural designs and accurate parameter matching, including the output voltages and the resistances in different resistive states, the artificial brain can be operated in self-powered mode to memorize the touch stimuli with the responsivity up to 20 times. For demonstrating the application potential of this system, it was fabricated as an independently addressed matrix to realize the memorizing of motion trace in two-dimensional space. The newly designed self-powered nonvolatile system has broad applications in next-generation high-performance sensors, artificial intelligence, and bionics.

关键词： dye adsorption   hydrogels   mechanical properties   rheology   structure-property relations  

摘要： Chitosan (CS) hydrogels are receiving growing attention as adsorbents for water purification purposes. The conditions of preparation of this class of materials play a crucial in the determination of their performances;however, this aspect is often neglected in the literature. In this study, we deal with this issue, focusing on the structure-property relationships of CS hydrogels obtained by phase inversion method. We show that the concentration of the starting solution determines the density and strength of intermolecular interactions, and that the gelation kinetics dictates the hydrogel structure at the microscale. Consequently, even subtle changes in the preparation protocol can cause significant differences in the performances of CS hydrogels in terms of mechanical properties and dye adsorption capacity. The observed trends are often neither trivial nor monotonic. Nonetheless, we demonstrate that they can be interpreted looking at the CS network structure, which can be inferred by rheological measurements. (c) 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1843-1849

关键词： Palladium   Ceria   Three-way catalyst   Light-off   Oxidation   Carbon monoxide   Propylene  

摘要： The light-off (ignition) and steady-state behavior for individual oxidation and co-oxidation of CO and propylene under near-stoichiometric conditions was studied using Pd/Al2O3 and Pd/CeO2-ZrO2 monolith catalysts. CO and propylene are shown to be self- and mutually-inhibiting, with inhibition mitigated by the promotional effect of CeO2-ZrO2. Oxidation is enhanced at low temperatures for CO, and at intermediate and high temperatures for propylene. Light-off behavior during CO and propylene co-oxidation is similarly improved at low and high temperatures. Steady-state differential kinetics measurements using Pd/Al2O3 show reaction orders of similar to-1 with respect to CO and propylene. Using Pd/CeO2-ZrO2, the reaction order with respect to CO shifts towards zero and the activation energy decreases, suggesting an alternate reaction mechanism for CO oxidation when enough ceria is present. Mechanisms for CO and propylene oxidation that are consistent with the kinetics and inhibition trends are presented. (C) 2017 Elsevier B.V. All rights reserved.

关键词： theta-Fe3C   o-Fe7C3   h-Fe7C3   MEAM   Classical MD  

摘要： Structural, mechanical and thermal properties of theta-Fe3C cementite, o-Fe7C3 and h-Fe7C3, the common carbides in steels and earth's inner core, are calculated upto 450 GPa pressure and 2000 K temperature range using classical molecular dynamic (MD) simulations. A thorough evaluation of phase stability and elastic properties of several iron-carbides (gamma'-FeC, eta-Fe2C, zeta-Fe2C, h-Fe7C3, o-Fe7C3, chi-Fe5C2, theta-Fe3C, gamma'-Fe4C, gamma ''-Fe4C and alpha'-F16C2) is performed using four MD potentials (namely, MEAM, Tersoff and EAM/ FS) for broad comparison of these potentials at static condition. The MD calculated pressure-volume, pressure-elastic constants and volume-temperature relations for theta-Fe3C, o-Fe7C3 and h-Fe7C3 phases are thoroughly compared with available experimental and first principles calculated values to assess the range of applicability and deficiencies of these interatomic potentials. Our enthalpy calculations suggest that o-Fe7C3 is more stable than Eckstrom-Adcock hexagonal iron carbide (h-Fe7C3) upto 450 GPa and 2000 K (Earth's core condition) which is in agreement with recent experiment. Our MD calculated longitudinal sound velocities match well with experiments (within 2%) upto 75 GPa and starts deviating from Birch's law at high pressures due to nonlinear interaction of phonon modes. The MD calculated pressure-volume-temperature relation of theta-Fe3C phase reproduces experimental values and pressurevolume- temperature relation of o-Fe7C3 phase is predicted upto 200 GPa and 2000 K. The MD calculated melting temperatures of theta-Fe3C and Fe7C3 using two-phase simulations match well with experimental values within their errorbars at 50 GPa and higher pressures. (C) 2017 Elsevier B.V. All rights reserved.

关键词： 产品销售   工程机械   市场占有率   叉车行业   产品平台   发动机   装载机   机动力  

摘要： 今年上半年,潍柴共计销售各类型工程机械用发动机同比增长近70%,其中,在传统优势市场,潍柴装载机动力产品市场占有率超过80%.除了在装载机市场拥有不可撼动的行业地位以外,潍柴积极利用全系列产品平台优势拓展更广阔的市场.在叉车行业,潍柴叉车动力产品销售大幅增长.在压路机配套方面,潍柴发动机市场占有率从2013年的4%提高到2017年的30%,其中国Ⅲ占有率接近40%,同比去年实现翻番增长,潍柴WP6发动机正在成为行业内的主流发动机.

关键词： 研究生课堂教学   现状调查   统计分析  

摘要： 运用问卷调查和统计方法评估研究生课堂教学的现实状况,并借图表直观呈现。研究表明,其课堂教学总体秩序良好,教师责任心强,教学效果良好;问题在于教材前沿性不够、教学灵活性不足、学生学习积极性尚需提高,建议通过加强教师教学工作及其监管不断改进。

关键词： 微创外科手术机器人   人机交互   力矩控制   重力补偿   虚拟工具   术前规划   顺应控制   主动关节   被动关节  

摘要： 为了实现微创外科手术机器人的主动手术姿态调整,针对微创手术机械臂的RCM机构特点以及主被动关节相结合的摆位方式,本文提出了基于关节力矩的虚拟工具控制算法以实现操作者与手术机械臂之间的力交互过程。该算法以在关节处安装力矩传感器的方式进行交互力的采集,并结合采样数据提出了一套完整的重力矩补偿方法。根据关节处的受力情况,力控制模型能够实时调整模型参数以响应主动力摆位不同阶段的动态要求。在自行研制的微创外科手术机器人样机上进行相关的实验验证,实验结果表明:各关节的重力矩补偿模型效果明显,基于关节力矩的虚拟工具模型能够实现柔顺自然的人机交互过程,并具有较高的可控性和稳定性,可以较好地完成微创外科手术机械臂的手术位姿调整。

关键词： 安全工程   建筑机械   系统动力学   建筑机械设备   事故演变   Vensim模型   动态模拟  

摘要： 为研究建筑机械设备在突发事故情景下的事故演变趋势和差异、定量评估建筑机械设备的事故风险,基于系统动力学原理及方法的系统论、信息论、结构论、控制论和协同论特点及Vensim软件的仿真模拟功能,以建筑布局、作业环境与操作、设备自身和安全管理为核心状态变量,以多个影响因素指标为辅助变量来进一步补充和完善,构建了系统图并模拟了3种不同事故的后期变化。仿真模拟结果表明:建筑机械的设备成本和设备更新速率及监控预警是保障机械设备安全性的重要影响因素,这三者直接决定建筑机械设备的后期状态;事故危险性在事故前期非常大,在后期大致分为3类情况,即超额恢复、基本恢复和完全报废。灵敏度分析表明,建筑机械设备成本、监控预警和安全管理水平及应急处置能力与建筑机械设备的综合状态正相关,设备更新速率与建筑机械设备的综合状态负相关,正负相关的影响效果都非常明显。

关键词： 大头瓦磨损   故障机理   接触碰撞模型   多体动力学   往复式机械  

摘要： 大头瓦磨损故障是往复式机械严重故障之一,故障激励响应复杂,导致其难以早期预警。基于多体动力学理论,依据非线性碰撞模型和非线性摩擦模型,建立了大头瓦磨损故障的动力学模型;通过改变曲轴与大头瓦的间隙大小模拟大头瓦磨损故障的劣化过程;分析大头瓦磨损故障劣化过程接触碰撞力的变化规律及往复式机械的响应特征,提出了对应的早期预警和诊断方法。