Stress analysis of spontaneous Sn whisker growth

Spontaneous Sn whisker growth is a surface relief phenomenon of creep, driven by a compressive stress gradient. No externally applied stress is required for the growth, and the compressive stress is generated within, from the chemical reaction between Sn and Cu to form the intermetallic compound Cu₆Sn₅ at room temperature. To obtain the compressive stress gradient, a break of the protective oxide on the Sn surface is required because the free surface of the break is stress-free. Thus, spontaneous Sn whisker growth is unique that stress relaxation accompanies stress generation. One of the whisker challenging issues in understanding and in finding effective methods to prevent spontaneous Sn whisker growth is to develop accelerated tests of whisker growth. Use of electromigration on short Sn stripes can facilitate this. The stress distribution around the vicinity and the root of a whisker can be obtained by using the micro-beam X-ray diffraction utilizing synchrotron radiation. A discussion of how to prevent spontaneous Sn whisker growth by blocking both stress generation and stress relaxation is given.     

Characteristics of Milk Powders Produced by Spray Freeze Drying

Skim and whole milk powders were manufactured at lab scale by spray freeze drying (SFD), using liquid nitrogen as the cryogen. The polydispersity of droplet/particle sizes was limited using an encapsulator nozzle to atomize the feed. Particle morphology was examined using a scanning electron microscope. Samples were compared with equivalent spray-dried powders in tests of wettability and dissolution in water. The spray freeze-dried powders were found to be highly porous, with a uniform structure of pores throughout the entire particles. When tested in water, SFD skim milk powders wetted roughly three times as fast as industrially spray-dried agglomerated skim milk powders and were observed to dissolve rapidly by breaking down into smaller particles.     

风管摩擦阻力的直接计算方法

提出用高精度的反映密度、黏度和温度关系的经验公式和Colebrook公式计算风管摩擦阻力系数的方法。分析和算例表明，用该方法计算，计算结果比采用常用工程设计方法更为准确，为应用计算机进行风道设计提供了直接、简便的方法。     

论我国高校科技成果转化的制度建设

高校科技成果转化是当今世界各国政府、产业界、学术界共同关注的课题,也是世界经济与科技、教育相结合的成功经验.在以往对该问题的研究中,人们较多地关注技术创新,而新制度经济学的研究表明,技术创新与制度创新之间是一个交互决定的动态演进过程.制度创新在作为技术创新实现的前提条件的意义上,对技术创新起着先决性的决定作用.基于以上认识,我们有必要从一个新的视角对高校科技成果的转化进行研究,注重高校科技成果转化过程中的制度建设.     

镁钴铝类水滑石催化合成安息香甲醚

采用共沉淀法制备了镁钴铝类水滑石化合物(MgCoAl-HTLcs),并用 X 射线衍射、扫描电子显微镜、NH_3程序升温脱附等方法对 MgCoAl-HTLcs 进行了表征,并以 MgCoAl-HTLcs 为催化剂催化苯甲醛与甲醇反应合成安息香甲醚,研究了n(Mg):n(Co):n(Al)、催化剂用量、原料配比、反应温度、反应时间对合成反应的影响。表征结果显示,MgCoAl-HTLcs 的晶相完整,表面主要为弱酸、弱碱性。催化合成安息香甲醚的适宜条件为:MgCoAl-HTLcs 催化剂用量0.10 g(约为原料总质量的0.23%),n(Mg):n(Co):n(Al)=0.4:1.6:1.0,V(苯甲醛):V(甲醇)=3:50,反应温度50℃,反应时间150 min。在此条件下,苯甲醛的平衡转化率达77.49%,安息香甲醚选择性接近100%。为洁净合成安息香甲醚开辟了一条新的途径。     

Cr-Mo solid solutions forced by high-energy ball milling

Mixtures of Cr and Mo elemental powders, with the nominal compositions Cr₂₅Mo₇₅, Cr₅₀Mo₅₀, and Cr₇₅Mo₂₅, are processed by high-energy ball milling at ambient temperature. Milling is observed to force the mixing of the immiscible bcc elements Cr and Mo into solid solutions. The lattice parameter of these solid solutions, measured by X-ray diffraction (XRD), displays the expected positive deviation from Vegard’s law. These deviations are compared to the ones predicted by Eshelby’s inclusion model for dilute alloys. The conventional Williamson-Hall approach is shown to fail to determine the grain size in as-milled samples, probably due to the high density of dislocations. Annealing at 700 °C for 10 hours under argon leads to a large reduction in structural defect density, without inducing any significant decomposition. The mixing measured in Cr-Mo is discussed in the broader context of the mechanical mixing forced by ball milling in moderately immiscible systems.     

分置式牛津型斯特林制冷机的数值分析与实验验证

对分置式牛津型斯特林制冷机进行了数值计算 ,介绍了计算模型考虑到的众多不可逆因素。通过对计算结果与实验结果的对比 ,验证了本文数值计算的准确性 ,说明本文计算模型与数值处理方法是切实可行的     

全方位治理城市交通,促进城市可持续发展

城市交通对城市的社会经济活动和生态资源环境具有双向作用,是城市功能中最活跃的因素.目前城市交通问题突出表现在交通阻塞和汽车尾气污染两个方面,已成为困扰着大中城市发展的主要问题.交通堵塞不仅给人们的生活和工作带来不便,而且增加了城市经济运行的时间成本,影响到城市功能的发挥和城市的健康发展,同时又进一步加剧了能源的消耗.可见城市交通问题是关系到城市可持续发展的关键问题之一.     

新型复合弹簧的研究

提出一种金属圆锥弹簧与橡胶圆锥弹簧复合而成的弹簧．分析表明：它可以应用于弹性耦合激励振动筛和座式直线振动筛。