关键词： Polymers   Differential scanning calorimetry (DSC)   Computer modelling and simulation   Thermogravimetric analysis (TGA)   Mechanical properties  

摘要： Acrylonitrile-modified aliphatic amine adducts are often used as curing agents for room-temperature epoxy formulations (coatings, adhesives, sealants, castings, etc.), yet the curing reaction and properties of resultant epoxy systems still remain less fundamentally understood. Herein we systematically investigate our newly-developed acrylonitrile-modified multifunctional polyamine curing agent for bisphenol A epoxy resin (DGEBA): an acrylonitrile-capped poly(propyleneimine) dendrimer (PAN4). The impact of the molecular structure of PAN4 and a controlled poly(propyleneimine) dendrimer (1.0GPPI) on the curing reactivity, reaction mechanisms, thermal stability, viscoelastic response and mechanical properties of the epoxy systems are highlighted. Differential scanning calorimetry (DSC) confirms DGEBA/PAN4 shows markedly lower reactivity and reaction exotherm than DGEBA/1.0GPPI, and the model-free isoconversional kinetic analysis reveals that DGEBA/PAN4 has the generally lower reaction activation energy. To be quantitative, the progress of the isothermal cure is predicted from the dynamic cure by using the Vyazovkin equation. The isothermal kinetic prediction shows that DGEBA/PAN4 requires about 10 times longer time to achieve the same conversion than DGEBA/1.0GPPI, which agrees with the experimentally observed much longer gel time of DGEBA/PAN4. Subsequently, dynamic mechanical analysis shows that PAN4 results in the cured epoxy network with the lower β - and glass-relaxation temperatures, crosslink density, relaxation activation energy, enthalpy, entropy, but the higher damping near room temperature than 1.0GPPI. Finally, thermogravimetric analysis (TGA) demonstrates cured DGEBA/PAN4 is thermally stable up to 200 °C, and mechanical property tests substantiate that PAN4 endows the cured epoxy with much higher impact and adhesion strengths than 1.0GPPI. Our data can provide a deeper insight into acrylonitrile-modified aliphatic amine curing agents from the two good model

关键词： Mechanical properties   Relaxation   Thermal history   Aluminosilicate glass  

摘要： One of the fundamental characteristics of glass is its brittleness. The recently experienced demand for stronger and more damage resistant glasses creates opportunities for fundamental studies of the mechanical properties as a function of thermal history. This is because the properties of glassy materials are not only determined by their chemical composition, but also by their thermal history due to the non-equilibrium nature of the glassy state. Hence, understanding the relaxation behavior of the mechanical properties of glass is of great scientific and technological importance. In this paper, we have investigated the thermal history dependence of Young's modulus, Vickers hardness, and cracking behavior for an alkaline earth aluminosilicate glass composition over a wide range of fictive temperatures (approximate to 130 K). Young's modulus, hardness, and brittleness index monotonically increase with decreasing fictive temperature, whereas the crack resistance decreases. We find that all of the mechanical properties appear to follow a common underlying stretched exponential relaxation behavior, with the stretching exponent beta(m) in the range from 0.30 to 0.49 close to the Phillips value of 3/7 for structural relaxation dominated by long-range interactions. (C) 2012 Elsevier B.V. All rights reserved.

关键词： ONTOLOGY   ELECTRONIC spreadsheets   ACQUISITION of data   WEB services   COMPUTER software  

摘要： Motivation: Data collection in spreadsheets is ubiquitous, but current solutions lack support for collaborative semantic annotation that would promote shared and interdisciplinary annotation practices, supporting geographically distributed players. Results: OntoMaton is an open source solution that brings ontology lookup and tagging capabilities into a cloud-based collaborative editing environment, harnessing Google Spreadsheets and the NCBO Web services. It is a general purpose, format-agnostic tool that may serve as a component of the ISA software suite. OntoMaton can also be used to assist the ontology development process.

关键词： 粮食产量   水稻生产   机械化水平   马力   泰和县   农机化事业   农机化工作   水稻机械化  

摘要： 近年来，泰和农机化事业蓬勃发展，2008年以来，连续五年被评为全省农机化工作先进县，并被列为南方水稻机械化示范县和全国水稻机插秧示范县。目前，全县农机总量达16万余台，总动力达77．8万千瓦，形成亩均一马力的动力保有量。随着农机化步子的加快，2009年以来，粮食产量连续四年突破10亿斤，亩均产量超千斤，先后四年获全国粮食生产先进县称号。

关键词： 混合动力系统   测控系统   实验台   工程机械  

摘要： 为了研究工程机械混合动力系统的机电耦合特性和轴系的振动特性,研制了由柴油机、电动机和液压泵共轴连接组成的工程机械混合动力系统实验台。设计了由工控机、PCI总线控制卡和组态软件组成的实验台测控系统,分析测控系统输入信号和控制信号的数量与类型,确定测控系统控制策略的设计原则和开发过程。通过在柴油机输出轴的端面布置3个加速度传感器实现柴油机工作时曲轴的振动特性,对不同负载功率下柴油机曲轴的振动特性进行试验测试。测试结果表明,柴油机曲轴的振动能量集中在径向,轴向的振动能量可忽略不计;设计的测控系统能实现混合动力系统轴系振动性能测试。

关键词： 华北电力大学   人才培养机制   创新平台   机械工程学院   能源动力   国家电网公司   工程硕士   211工程  

摘要： 华北电力大学是教育部直属国家“211工程”、“985工程优势学科创新平台”重点建设高校，是教育部与国家电网公司等7家特大型电力企业集团组成的校理事会共建的全国重点大学，曾被授予国家首批工程硕士培养创新单位，在工程硕士的培养领域具：有丰富的经验和坚实的基础，也是最早培养设备监理方向工程硕士的高校之一。

关键词： 春光包装   企业   科技创新   对策研究  

摘要： 辽宁春光包装机械公司作为一家中小型企业,能成为国内同行业领军企业,其最重要的原因就是始终坚持科技创新。本文通过对这家企业的调研,感到其成功经验值得借鉴,存在的问题带有普遍性,并提出了推进中小企业发展的相应对策。

关键词： 矿用提升机   机械调速   动力学仿真   Simulink  

摘要： 根据动力学理论,建立了机械调速式提升机的数值仿真模型。根据提升机运行的条件,通过Simulink仿真软件对提升机运行过程进行动态仿真,分析了调速制动力矩对提升机调速性能的影响。

关键词： 机械弹性储能   永磁电机   非线性动力学   混沌  

摘要： 提出了一种新的基于机械弹性的储能方法,推导了永磁电机式机械弹性储能机组的非线性动力学模型,论证了机组储能过程中某些参数及运行条件下会出现混沌运动,分析了机组非线性动力学模型的线性稳定性.在此基础上,基于本实验室正在研发的0.16kWh/0.8kW机械弹性储能机组运行参数,将机组3维非线性模型降阶为带时变参数的2维投影子系统,采用坐标平面投影法研究了机组的混沌特性,分析了降维子系统平衡点位置及特征方程随时变参数的变化关系,并对机组混沌运动进行了数值验证,在一定程度上解决了解析方法,适用性较差导致对多维机电耦联系统只能仿真求解难以理论分析的问题.

关键词： 机械系统   参数化CAD   动力学  

摘要： 传统动力学求解通过对机械系统进行简化,建立动力学方程求解得到解析结果,这种方式较为繁杂且费时费力;文中通过在常用的参数化CAD软件中对机械系统动力学模型进行几何建模,然后调用CAD软件几何求解器求解,最终可以方便而快捷地解决机械系统的动力学问题。