销钉机筒挤出机内销钉附近物料流场分析及功率计算

采用当量粘度的方法，基于牛顿流体模型，提出销钉机筒挤出机内销钉附近流场的应力及速度分布数学模型和销钉消耗功率的计算方法。用NR／炭黑混炼胶进行的挤出过程中销钉消耗功率的研究结果表明，实测值与计算值的相对误差只有4％。     

三相单级全桥PFC电压尖峰机理分析与抑制

介绍了一种基于全桥结构的三相单级功率因数校正(PFC)变换器,该变换器工作于电感电流断续模式(DCM),电感电流即输入电流的峰值自动跟踪输入电压,可实现功率因数校正.建立了桥臂开关对臂导通时变换器的简化模型,并分析了该阶段变压器原边电压尖峰的产生机理.分析结果表明,由于变压器漏感的存在,变压器原边于桥臂开关对臂导通期间将产生很大的电压尖峰,该电压尖峰大小由变压器原边的漏感、电流与并联电容三个参数决定.最后,结合电路的工作原理,提出了一种变压器原边无源缓冲电路来抑制该电压尖峰.实验结果表明,变压器原边的电压尖峰得到了有效抑制.     

Formation mechanism of aerodynamic drag of high-speed train and some reduction measures

Aerodynamic drag is proportional to the square of speed. With the increase of the speed of train, aerodynamic drag plays an important role for high-speed train. Thus, the reduction of aerodynamic drag and energy consumption of high-speed train is one of the essential issues for the development of the desirable train system. Aerodynamic drag on the traveling train is divided into pressure drag and friction one. Pressure drag of train is the force caused by the pressure distribution on the train along the reverse running direction. Friction drag of train is the sum of shear stress, which is the reverse direction of train running direction. In order to reduce the aerodynamic drag, adopting streamline shape of train is the most effective measure. The velocity of the train is related to its length and shape. The outer wind shields can reduce train’s air drag by about 15%. At the same time, the train with bottom cover can reduce the air drag by about 50%, compared with the train without bottom plate or skirt structure. Foundation item: Project(2001AA505000) supported by the National High-Tech Research and Development of China     

一种多级跨域访问控制管理模型

访问控制管理为维护访问控制策略的安全、一致提供了重要保障。针对现有访问控制管理模型存在指派关系复杂、扩展性差、缺乏对跨域访问管理有效支撑的问题,结合多级跨域系统特性和访问控制管理的细粒度要求,文章提出了多级跨域访问控制管理模型,给出了模型的基本元素、元素关系、约束条件和管理规则。与现有研究相比,该模型具有良好的可扩展性,支持细粒度的管理操作,能够有效支撑多级跨域环境下安全、统一的访问控制管理。     

物联网位置数据安全策略研究

在物联网技术中,基于位置的服务在定位技术的推动下得到长足发展,在给用户带来便利的同时,也给用户位置信息的暴露提供了极大可能。文章研究了位置数据保护的主要技术和研究进展,分析了各类隐私保护方法,为位置隐私数据保护研究研究提供了一定的借鉴。     

溶胶-凝胶涂膜法制备片状TiO2的研究

以Ti（OC4H9）4为原料，采用溶胶-凝胶涂膜法制备片状TiO2，探讨了溶胶的性质、涂膜过程、煅烧温度等参数对片TiO2性能的影响，结果表明：反应温度为30℃，水与Ti（OC4H9）4的摩尔比为2～4，Ti（OC4H9）。与无水乙醇的摩尔比为7～10，pH值为1～3，反应时间为15min的条件下，通过溶胶涂膜、干燥、剥片及400℃煅烧2h，可得到具有明显片状结构的TiO2。制得的片状TiO2为锐钛矿型，粒径约为30～60μm，厚度约为2μm。径厚比约为15～30。     

基于层次分析法的高校贫困生灰色综合认定方法

针对高校家庭经济困难学生资格认定的问题,提出了运用层次分析法来确定评定指标权重;引入灰色系统理论,建立了科学的高校家庭经济困难学生资格等级认定方法,以期实现对学生经济困难程度的准确判定.     

Preparation of Y2O3：Eu^3＋ phosphor by molten salt assisted method

A kind of fine and quasi-spherical Y2O3：Eu^3＋ phosphor was prepared by firing a preparative precursor at 1 200 ℃ for 2 h with the molten salts of Na2CO3, S and NaCl. The precursor was obtained by homogeneous precipitation of yttrium and europium with oxalic acid when using EDTA, citric acid or starch as complexant. The structure and morphology of the phosphors were characterized by XRD and SEM, respectively. The influence of complexing environment, firing temperature and molten salts on formation of the phosphor Y2O3：Eu^3＋ was discussed. The result show that the prepared Y2O3：Eu^3＋ phosphor is of quasi-spherical structure with size of 2-3 μm. Its luminescent intensity is 30% higher than that of the same phosphor prepared by the same procedure but without molten salts, and is 5% higher than that of commercial Y2O3：Eu^3＋ red phosphor.     

渐开线零齿差机构啮合原理与强度条件

零齿差机构的突出问题是齿轮的干涉与强度。在导出避免干涉的条件后，建立新的强度公式，给出各项检验指标，并提出切齿过程中保证精度的具体措施。     

基于AFM的纳米测试技术在机械领域中的应用

简要介绍了AFM的基本原理及操作模式。系统地阐述了AFM在国内外机械领域的发展现状，并进行了展望。