R290蒸气珠状凝结传热微尺度特性的研究

通过对自然工质R290蒸气珠状凝结传热过程的微尺度特性分析得出,在一定的过冷度、液珠半径和分形维数下,液珠的导热热阻随接触角的增大而增大,促进层的热阻在接触角为90°时最小,气液界面的热阻随着接触角的增大而减小,单个液珠的总传热热阻随着接触角的增大呈现出先减小后增大的变化规律,即存在最佳接触角,在此最佳接触角下,单个液珠的总传热热阻最小,单个液珠的传热量最大,换热表面的热流密度最高。随着液珠半径的增大,最佳接触角减小。随着过冷度的增加和分形维数的增大,换热表面液珠成核中心密度增大,表面的热流密度增加。在一定的过冷度下,液珠半径增大,液珠分布密度减少,分形维数增大,液珠的分布密度增加。在一定的分形维数和过冷度下,随着液珠半径的减小,换热表面的热流密度增大。     

双列调心凹面滚子轴承接触载荷分析

在考虑滚子与套圈、滚子与保持架以及保持架与引导套圈作用力的条件下,建立双列调心凹面滚子轴承动力学模型.以某双列调心凹面滚子轴承为研究对象,与静力学分析模型滚子最大接触载荷计算结果对比,验证了模型的正确性.并分析了工况条件(轴向载荷、径向载荷、倾覆力矩、转速)和结构参数(滚子数量、滚子长度、径向游隙)对滚子最大接触载荷的...     

Fixed-point and stratified analysis of the fine structure and composition of five gallstones with Fourier transform infrared (FT-IR) specular reflection spectroscopy

By investigating the identities, amounts, and distributions of the major components of human gallstones, the formation mechanism of calculi may be elucidated. Using FT-IR specular reflection spectroscopy, the compositions of five common types of gallstones, including cholesterol calculus, bile pigment calculus, cholesterol-bilirubin calculus, mixed calculus, and black stones, were positionally, qualitatively, and quantitatively analyzed. Several organic and inorganic substances were found in human gallstones, including cholesterol, calcium bilirubinate, calcium carbonate, calcium phosphate, and calcium stearate. Among them, cholesterol and calcium bilirubinate were the main components. The amounts of these substances varied in different types of gallstone. The distributions of cholesterol and calcium salts (with the exception of calcium bilirubinate) were also closely associated with location. In the various calculi, the amounts of cholesterol and calcium bilirubinate in the cores, the layered structures outside the cores, and the outer shells were higher than those of other substances. The identities of the major components of calculi were similar in different types of gallstones, but their amounts and distributions were significantly different. The analytical method used in this study, which was able to accurately determine the location, quality, and quantity of the major components of gallstones, would be an effective tool to study the formation mechanism of calculi.     

Histochemical and ultrahistochemical localization of heavy metals in calf organs

Cadmium, zinc, selenium, and copper were administered, singly or in combination, orally or subcutaneously. Experiment I included 32 calves of both sexes; six received Cd (two groups), Zn, Cd, and Zn, and Cd and Se (two groups) and one group was a control. In Experiment II (21 bulls), three were given Cd, Cd, and Cu, and Cd and Zn, respectively, and one group was a control. For light microscopy, in Experiment I the highest amounts of silver granules were present in the samples of liver, small intestine, and vesicular gland of all the exposed groups; in Experiment II the most affected organs were liver, kidney, and small intestine. For electron microscopy, in Experiment I, after administration of Cd and Zn, the highest amounts of granules were seen in the cytoplasm of hepatocytes and cells of the proximal and distal renal tubules and the lowest amounts were found in glandular cells of the pancreas. Administration of Cd and Se resulted in the presence of large numbers of granules in the nuclei and nucleoli of spermatogonies. In Experiment II, ingestion of Cd and Zn in feed led to the appearance of highest amounts of granules in the nucleoli, nuclei, and cytoplasm of cells in testes, kidneys, and pancreas. Following Cd intake, the highest accumulation of granules was observed in the nucleoli of hepatocytes and cells of the proximal and distal renal tubules. Combined Cd and Cu produced the highest number of granules in cells of the proximal and distal renal tubules and in the nucleoli and nuclei of germinal epithelium.     

论工程项目进度控制

工程项目进度控制贯穿于整个工程项目的试车投产、工程施工、物资采购和勘察设计等全部过程。有效的工程项目进度控制能够大大缩短工程项目的建设工期,并保证工程项目质量,大幅度降低建设工程投资。本文首先阐述了工程项目进度控制原理;其次,重点分析了加权打分法在工程项目进度管理中的运用;最后,就工程项目进度控制措施进行了深入的探讨,具有一定的参考价值。     

Discussion on advanced manufacturing

Advanced manufacturing consists of continuity of manufacturing, its broad sense, and the core of the manufacturing process. The technology of continuous manufacturing is discussed according to both historical and modern perspectives. The relationship between human development and manufacturing technology is also discussed. Manufacturing is a continuously evolving topic. It is not only the foundation and means of imagination, conception, the science, and the technology of material change, but also the expression of national economy, national defense, and the support industries. The broad sense of manufacturing theory, which extends the concept of manufacturing, is an important development in the 20th century. The sense is analyzed in connection with design, material forming theory, synthesis of manufacturing technology, manufacturing modes, life cycle of product, hardware and software, and support environment, etc. At the same time, the core action and the development of the theory and technology of process is also discussed. At the end of this paper, the development directions of mechanical manufacturing science and technology are mentioned.     

热管废热回收蒸发器在浊水余热回收中的应用

针对污水的特性,为避免生活污水与热泵工质R22产生交叉污染,从而导致系统不能正常运行的可能性,提出在污水与热泵系统工质R22之间采用一个热管换热器,得出在系统增加了一个热管换热器的情况下,污水流量一定时,热泵制热量,性能系数COP值,热泵系统R22工质蒸发温度,污水废热回收热量随污水进口温度的增大而增大,其中热泵工质蒸发温度的增幅最大,达到65.79%,废热回收热量的增幅最小,为6.8%,污水入口温度一定时,热泵制热量,性能系数COP值,热泵工质蒸发温度,废水回收热量随着污水流量的升高而升高,但是热泵工质蒸发温度的和性能系数COP值的增幅减少,热泵制热量,热管工质蒸发温度以及废水回收热量的增幅缓慢增加.     

3500HP型钻井泵液力端的研究与展望

随着科技的发展和进步,石油、天然气和页岩气等能源已成为全球所有国家的命脉。然而想要拥有足够的能源,就必须具备先进的开采技术,因此钻井泵的发展尤为重要。钻井泵被誉为钻机的“心脏”,对于钻机来说至关重要,而对于钻井泵来说其液力端易损件的使用寿命与钻井泵的工作效率和使用寿命息息相关,因此只有提高钻井泵液力端易损件的使用寿命才能确保钻井泵的正常钻进、较高的工作效率和使用寿命。随着信息技术的发展和各行各业的相互促进与相互影响,在未来钻井泵也会向着信息化、自动化、轻量化、人性化和智能化的方向发展。     

Delta机器人综合位置误差研究及其耦合特性分析

以Delta机器人为分析对象,研究了动平台的位置误差模型,并对误差源的耦合特性进行了分析。首先,利用从动臂的位置特性,依据几何空间矢量法,建立了Delta机器人机构误差模型;其次,以数理统计与空间矢量原理为基础,推导出Delta机器人关节间隙误差模型;然后,基于空间有限元理论,在建立系统弹性动力学模型的基础上建立了其柔性误差模型;综合考虑这3种误差源,建立了Delta机器人综合位置误差模型;最后,利用Adams与Workbench联合仿真、Matlab数值计算和FARO激光跟踪仪的现场试验验证了位置误差模型的正确性,并对误差源的耦合特性进行了分析,阐述了方向位置误差与坐标轴方位之间的关系。结果表明,影响Delta机器人动平台位置误差的各个误差源间并不是简单的叠加,而是具有明显的耦合特性,并且动平台方向位置误差会随着坐标轴方位的变化而变化。     

可展开固体反射面机构设计及运动学分析

针对传统固体反射面机构主反射面型面精度和收拢率较低的问题,设计了一种可展开固体反射面机构。首先,提出4种固体反射面机构可展单元构型并对其机构自由度进行分析,对比分析构型方案优缺点确定构型方案4作为可展单元基础构型,并对其结构和展开原理进行详细设计。通过D-H坐标变换建立该机构可展单元的运动学模型,根据几何约束条件建立机构位置矢量方程,利用向量封闭投影法解出各回转角间的关系,结合MATLAB软件编程对机构的位置、速度和加速度进行分析。应用ADAMS软件建立机构仿真模型,验证了机构运动学分析的正确性。最后根据机构中回转角的限制条件和结构尺寸关系,分析回转角和结构尺寸对可展开固体反射面机构收拢率的影响,确定2.2m可展开固体反射面机构的回转角和旋转角分别为78°和30°,中心圆盘半径、铰支座一孔纵向尺寸、切换连杆横向尺寸、纵向尺寸分别为245,8,40,18mm,收拢率为0.326,从而为可展开固体反射面机构的设计提供参考。     

Mice embryology: A microscopic overview

In this work, we studied the embryology of mice of 12, 14, and 18 days of gestation by gross observation, light microscopy, and scanning electron microscopy. Grossly, the embryos of 12 days were observed in C‐shaped region of the brain, eye pigmentation of the retina, first, second, and third pharyngeal arches gill pit nasal region on the fourth ventricle brain, cervical curvature, heart, liver, limb bud thoracic, spinal cord, tail, umbilical cord, and place of the mesonephric ridge. Microscopically, the liver, cardiovascular system and spinal cord were observed. In the embryo of 14 days, we observed structures that make up the liver and heart. At 18 days of gestation fetuses, it was noted the presence of eyes, mouth, and nose in the cephalic region, chest and pelvic region with the presence of well‐developed limbs, umbilical cord, and placenta. Scanning electron microscopy in 18 days of gestation fetuses evidenced head, eyes closed eyelids, nose, vibrissae, forelimb, heart, lung, kidney, liver, small bowel, diaphragm, and part of the spine. The results obtained in this work describe the internal and external morphology of mice, provided by an integration of techniques and review of the morphological knowledge of the embryonic development of this species, as this animal is of great importance to scientific studies. Microsc. Res. Tech. 2012. © 2012 Wiley Periodicals, Inc.     

具有微织构形貌的结合面法向接触刚度分形模型的研究

研究微织构结合面上的表面形貌参数对结合面法向接触刚度的影响。根据微织构表面的形貌特征,将微织构表面分为织构前表面和织构区域两部分,由分形接触理论计算出织构前表面上微凸体的基本参数,忽略织构区域底部未接触部分,将微凸体在接触载荷作用下的变形分为三个阶段:弹性阶段、弹塑性阶段、塑性阶段。由接触力学理论,首先建立织构前表面上单个微凸体的法向接触刚度模型。然后由微观到宏观,结合微织构表面的织构形貌特征,构造整个宏观微织构结合面的法向接触刚度计算模型,研究不同的表面形貌参数对于微织构界面上法向接触载荷、微凸体因载荷产生的变形以及法向接触刚度的影响。经过仿真分析之后,结果表明,当微织构结合面的法向接触载荷不断增大时,结合面的法向接触刚度总体呈单调上升趋势;并且随着织构密度的增加,结合面上由于织构形貌的存在,使得一部分微凸体未产生变形,从而减小结合面的法向接触刚度,并且当法向载荷增加时,这种效果会更加明显;在相同的接触载荷下,塑性指数越高,处于塑性变形状态的微凸体就越多,从而使具有微织构形貌的结合面的法向接触刚度变大。     

超低能耗电子电路系统设计原则

超低功耗电子电路系统设计,需要对电路的整个功耗进行仔细的分析研究,影响电路系统功耗的因素有负载能力、电源电压、工作频率、集成度、输出电平等,加强对这些因素的软件、硬件控制,通过分析影响功耗的因素,从而仔细分析设计超低功耗电子电路系统的设计原则,有效实现降低整个系统功耗的目的。     

ICP-MS顺次分析鸡蛋壳中微量元素

本研究基于顺次电离质谱分析技术,发展了一种直接质谱分析方法分析鸡蛋蛋壳中微量元素.在仅需少量样品预处理的条件下,分别用水和5％稀硝酸作为洗脱液,对鸡蛋壳中水溶性微量元素组分和酸溶性微量元素组分进行顺次提取,然后在线传输至ICP-MS进行分析.该方法可在10 min内实现单个样品中15种微量元素水溶性组分和酸溶性组分的顺...     

Distribution curves of sectional areas through some families of convex particles

We outline the results of a computer program which calculates frequency distributions of functions of cross-sectional regions of convex planar-faced polyhedra, ‘sphero-polyhedra’, and populations of perturbed polyhedra. This is done by ‘cutting’ a computer representation of the figure by a large number of random planes. The procedure is applied to cubes, dodecahedra, truncated octahedra, and approximate β-tetrakaidecahedra. Certain aspects of the shape of the object, e.g. sharpness of corners, angularity, compactness, and degree of symmetry are related to aspects of the shape of the distribution curves, e.g. beginning and ending points of the curves, rate of rise of the peak, relative location of the peak, and height and width of the peak.     

干燥带对绝缘子温度场影响的研究

对干燥带对污秽绝缘子温度场分布进行了研究,介绍了绝缘子干燥带形成原因,利用绘图软件,绘制了绝缘子分析模型; 然后分析了干燥带的产生过程; 最后运用ANSYS软件电热耦合的方法,从干燥带产生位置、干燥带产生条数、干燥带产生长度、干燥带产生宽度4个方面,分析污秽绝缘子径向温度分布情况。研究结果表明,干燥带产生位置、干燥带产生长度、干燥带产生宽度、干燥带产生条数不同,绝缘子径向温度分布特征差异较大。     

基于正交试验的旋转轴唇形密封可靠性影响因素研究

为探讨多因素相互作用对油封可靠性的影响,以某减速器中输入轴与轴承端盖间的油封为研究对象,基于有限元软件获得不同结构参数时油封的静态压力分布曲线和影响系数矩阵,并将分析结果集成到油封的混合数值计算模型,分析并计算油侧唇角、空气侧唇角、理论接触宽度、过盈量、弹簧劲度系数、腰厚、腰长7个结构参数对油封泵送率和摩擦扭矩值的影响;将油封的7个结构参数作为变量因素,以油封泵送率和摩擦扭矩作为响应目标进行正交试验,研究各结构参数对油封密封可靠性的灵敏性。结果表明:各因素对油封泵送率敏感性影响程度由大到小依次为油侧唇角、理论接触宽度、空气侧唇角、腰厚、过盈量、腰长、弹簧劲度系数,各因素对摩擦扭矩的敏感性影响程度由大到小依次为油侧唇角、理论接触宽度、腰厚、弹簧劲度系数、过盈量、空气侧唇角、腰长,表明油侧唇角和理论接触宽度是影响油封可靠性的最主要因素。确定油封参数的最优组合,油封优化后的摩擦扭矩比优化前的更低,因而能够减少油封工作时的摩擦生热量,从而延长油封的使用寿命。     

基于高等教育服务消费者视角的大学生权利

高等教育服务是高等学校的基本产出,大学生是高等教育服务的消费者。基于这种消费者身份,源自对高等教育服务消费自由、正义与效率的追求,大学生应该享有知情权、选择权、参与管理权、消费条件权、损害求偿权、公平消费权、维护尊严权、消费教育权、维权结社权等消费权利。这些权利的实现需要进行权利的合法设定,保障客观物质条件,发挥社会中介组织作用,建立高等教育问责制度,增强消费者自己的权利意识和维权能力。在消费者权利受到侵犯时,可以通过与学校协商、向学校申诉、向教育行政主管部门申诉、申请行政复议、调解、仲裁、司法审查、舆论监督等途径寻求救济。     

基于组态技术的自动控制系统仿真研究

随着集散式工业控制系统的不断发展,在各种控制设备之间进行数据、命令的传输与交换的要求,促使工业控制装置的联网与通讯不断地发展。基于参与老师的一个关于金山电厂水源监测系统设计的项目研究的成果,本文简单介绍了KingView软件,详细讲述了应用"组态王6.53"的强大功能开发系统的方法,尤其详细讲述了几个重要部分的开发过程,画面制作、趋势曲线、数据报表和报警功能的具体实施方法,以及如何利用KingView软件中的仿真PLC对系统进行仿真,并给出了主要程序加以说明。将自动化技术、计算机技术、通信技术融为一体,计算精度高,性能稳定、实用性强,可以提高工作效率。     

机翼结构质量分配方法探讨

在进行飞机设计时,机翼结构的重量的分配十分重要。但是机翼结构的质量分配需要考虑诸多因素,提出一种机翼结构的质量分配方法。进行机翼结构的质量分配时,一般将其按照一定比例分配到承剪结构、承弯结构、起落架结构、气动荷载结构、燃油结构、前后缘结构以及其他一些附属结构等。需要对机翼结构的质量分配的方法进行探讨,分析质量分配方法的合理性和有效性。