伺服放大器的研究与改进

本文介绍的伺服放大器采用集成触发器与双向可控硅构成零电流交流开关,具有制造工艺简单、维修方便、射频干扰小和可靠性高等优点。文中对目前大量使用的电动执行器中的伺放电路进行了分析,介绍了改进电路的工作原理。     

基于KJ008的新型伺服放大器的研制

在分析ＤＤＺ－ Ⅱ、Ⅲ型电动执行器伺服放大器电路的基础上,研制开发了一种采用ＫＪ００８ 集成触发器的新型伺服放大器,阐述了其工作原理及电路。经调试、使用,性能优异     

DFC伺服放大器在控制系统中的应用

本文对电动执行机构的主要部件之一──Ｄ Ｆ Ｃ伺服放大器的结构、性能、工作原理及试车投运等作了简要的说明，并绘制了多套使用伺服放大器组成的自动控制系统的方框图。     

一种双端输入的直流差动对数放大器的研制

本文介绍了一种实用的双端输入的直流差动对数放大器。文中给出了该放大器的数学模式;对电路结构、主要技术指标和测试方法作了简单描述;一些主要测试数据和数据处理方法被给出。同时对该放大器的特点、制作等有关的问题进行了初步地探讨。     

解决影响放大器增益的方法

本文介绍了在使用测量放大器的过程中，通过采用模拟开关换档，有效解决放大器增益的方法，并通过对所设计电路的分析说明，得出推导公式。     

基于Multisim的伺服放大器的特性分析

介绍伺服放大器的原理，并应用Multisim强大的电路仿真功能，对伺服放大器的特性进行分析，并对电路进行实物测试，实验证明与仿真结果相符。     

检测仪表微伏信号的直流放大

介绍微伏模拟信号的精密放大电路。讨论了对高精密，低漂移的集成运算放大器的选择要求，探讨了温度和干扰对小信号精密放大电路的影响问题。     

IRM红外线分析仪前置放大器的原理及设计原则

本文对IRM红外线分析仪前置放大器的工作原理及设计原则作了较系统的分析。首先从转换灵敏度的概念和推导的计算公式出发,讨论了提高前置级灵敏度和稳定性的方法。对噪声的产生原因、抑制方法及对关键元件参数的要求也作了介绍。文章较多地介绍了调制法前置级的工作原理及设计原则,不仅对常见的调频型和调幅型电路作了介绍,而且还介绍了一种脉冲调宽型电路可供科研、生产部门的技术人员参考。     

运算放大器应用电路

概述过去,作为模拟计算机的基本元件是用电子管或晶体管等独立元件组成的运算放大器,因为这种放大器成本高,故一般不太应用。随着单块集成技术的发展,性能高、成本低的集成式运算放大器试制成功后,在控制设备、仪表及其他领域里已广泛地使用着运算放大器。运算放大器可控制DC～10KHz左右的频率的信号,在模拟电路上几乎全部可以应用,因为分立电路,不需要复杂的偏电路,所以很容易使用。因为实际电路和计算电路非常一致,这样就可以简化电路的设计。采用运算放大器709型的μPC55A及741型的μPC151A的实际电路作以下介绍。     

伺放特性改进和执行器反向制动

本文介绍了一种对ＤＤＺ—Ⅱ、Ⅲ电动伺服放大器进行改进的电路。在改进了伺放输出特性的同时,还具备了执行器反向制动功能。１电动执行器的反向制动在ＤＫＪ型角行程电动执行器中,为了保证断电时迅速制动,在执行器电动机上设计了刹车装置。在投自动时,为防止执行器惯...     

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.     

Localization of sarcoglycan, neuronal nitric oxide synthase, beta-dystroglycan, and dystrophin molecules in normal skeletal myofiber: triple immunogold labeling electron microscopy.

In order to investigate the mode of existence of the sarcoglycan complex, neuronal nitric oxide synthase (nNOS), beta-dystroglycan, and dystrophin in the normal skeletal myofiber, we examined the ultrastructural localization and mutual spatial relationship of nNOS, beta-dystroglycan, dystrophin, and the individual components of the sarcoglycan complex by using triple immunogold labeling electron microscopy. Each molecule of alpha-, beta-, gamma- and delta-sarcoglycans is located intracellularly or extracellularly near the muscle plasma membrane mostly in accordance with the sarcoglycan antigenic sites against which the antibodies were generated. The association of different two and/or three sarcoglycan molecules out of alpha-, beta-, gamma- and delta-sarcoglycan molecules was frequently observed. Each molecule of nNOS, beta-dystroglycan, and dystrophin was ultrastructurally noted along the cell surface of normal skeletal myofibers. Moreover, the close relation of a sarcoglycan molecule with beta-dystroglycan and dystrophin, and the association of nNOS with dystrophin were also confirmed ultrastructurally. Thus, this study demonstrated that the constituting molecules of the sarcoglycan complex, nNOS, beta-dystroglycan, and dystrophin existed in the form of a cluster at the normal muscle plasma membrane. The association of nNOS with dystrophin and its associated glycoproteins may form a macromolecular signaling complex at the muscle plasma membrane.     

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。     

Review on microbial metabolomics of probiotics and pathogens: Methodologies and applications

In recent years, microbial metabolomics, a new field that has attracted wide attention, provides a map of metabolic pathways and clarifies the interaction mechanism between microorganisms and hosts. Many microorganisms are found in the human intestine, oral cavity, vagina, etc. Probiotics could maintain the good health of the host, while pathogens and an imbalance of bacterial flora lead to a series of diseases of the body and mind. Metabolomics is a science for qualitative and quantitative analysis of all metabolites in an organism or biological system, which could provide key information to understand the related metabolic pathways and associated changes. This approach analyzes the final products of cellular regulatory processes, the level of which can be regarded as the ultimate response of the biological system to genetic or environmental changes. Microbial metabolomics has been widely used in different research fields, such as microbial phenotypic classification, mutant screening, metabolic pathways, microbial metabolic engineering, fermentation engineering monitoring and optimization, microbial environmental pollution, and so on. However, there are only a few reviews on microbial metabolomics of probiotics and pathogens. This review summarizes the main methodologies, including sample preparation, identification of metabolites, data processing, and analysis. Recent applications in microbial metabolomics of probiotics and pathogens are also described. This paper first summarized the research progress and application of microbial metabolomics from two aspects: probiotics and pathogenic bacteria. Probiotics and pathogenic bacteria do not exist independently most of the time; hence, these were reviewed in the research field of coexistence of probiotics and pathogenic bacteria, which was subdivided into important microbial research fields closely related to human health, including the human gut, oral cavity, food, and nutrition-related microorganisms. Then, the main problems and trends associated with microbial metabolomics are discussed.     

基于FLUENT的液体动静压轴承的动态特性分析

应用计算流体力学软件FLUENT对超高速磨削用五腔动静压轴承进行动态特性研究,得到动静压轴承内部压力场和温度场分布;计算轴承的承载力、温度、刚度、阻尼等动态参数,分析这些动态参数与偏心率以及转速之间的关系。结果表明:在保持供油压力和轴承偏心率不变的情况下,随着转速的提高,油温上升,轴承承载力及偏位角不断增大;在保持供油压力和主轴转速不变的情况下,随着偏心率的增大,轴承流量有所减少,轴承的承载能力不断增大,偏位角基本保持不变。     

热喷涂宽温域耐磨自润滑涂层研究现状与展望

在航空、航天、冶金、电力、石化、矿采等领域,零件高温摩擦磨损特性是影响装备寿命的重要因素,在关重零部件表面设计制备宽温域耐磨自润滑涂层是装备零件强化改性和再制造修复的重要手段。首先阐述了宽温域耐磨自润滑涂层设计中过渡层、基础相、增强相的材料选择依据;其次针对单一固体润滑剂适用温度范围窄的问题,梳理了从低温润滑剂发生氧化反应原位生成高温润滑剂,低温润滑剂与高温润滑剂长时协同作用,添加抑制剂减缓润滑相的损耗退化等三种宽温域耐磨自润滑涂层材料设计方法;而后总结了宽温域耐磨自润滑涂层的制备工艺,分析了不同喷涂工艺的技术特点和涂层制备实例,介绍了宽温域耐磨自润滑涂层在军事装备和工业设备上的典型应用;最后在此基础上对宽温域耐磨自润滑涂层的未来发展方向进行了展望。     

不同因素对汽车传动离合器接合过程影响分析

离合器是汽车传动系统的重要组成部分,其接合过程直接影响到车辆起步性能和动力传递,并影响系统各单元的使用寿命。针对离合器接合过程的特点,对滑摩状态和接合状态进行动力学分析,建立系统的动力学模型;从滑摩功和冲击度两个方面对离合器接合过程进行评价,获取影响换挡品质的评价指标因素;根据动力模型和数学模型,基于Simulink建立离合器接合过程的分析模型;研究不同坡度及载重等因素对离合器接合过程中摩擦片的角速度、滑摩功及冲击度的影响,获取各因素的影响规律。结果可知:随着油门开度和油门变化率的逐渐增大,离合器接合角速度和接合时间都有所增大,接合过程产生的滑摩功也不断增多;随着起步坡度、载重的增大,离合器接合角速度逐渐减小,接合时间逐渐增大,接合过程产生的滑摩功也不断增多;分析过程和结果为此类设计提供参考。     

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影响,结果表明:随轴向载荷增大,一列滚子受力增大,另一列滚子受力减小;随径向载荷增大,滚子最大接触载荷增大;随倾覆力矩增大,2列滚子接触载荷几乎不变;随转速增大,滚子最大接触载荷增大;随滚子数量增多和滚子长度增加,滚子最大接触载荷减小;随径向游隙增大,滚子最大接触载荷呈先减小后增大趋势。     

A screening test for anti-wear additives in a modified four-ball test

Modern engine tests that evaluate the anti-wear properties of automotive engine oils are increasingly sophisticated and expensive, and often have relatively poor precision. The development of a simple, inexpensive, and reliable bench test to screen the anti-wear properties of fully formulated engine oils prior to their testing in engines is therefore very attractive. Numerous methods already exist, but they typically measure wear only at the end of the test by measuring the consequences of wear. The present paper describes an alternative approach, its purpose being the comparative evaluation of the anti-wear performance of lubricants throughout the test under variable load. A four-ball machine was used as a test rig for this work, and was equipped with instruments allowing study of the oil bath temperature, load applied to the balls, and the displacement of the load lever arm. The work presented focuses on a test procedure containing the following important elements: pre-ageing of oils, test start-up at very low load, incremental increases in load, stepwise increase in load, with each step sufficiently long to allow system equilibrium. Recording and analysis of the temperature and arm displacement curves permit the recognition of two distinct forms of wear: slow and gradual abrasive wear, and sudden and intense adhesive wear (scuffing). The presence and the intensity of the latter were found to have a direct relation with the anti-wear performance of candidate oils in the API Sequence VE engine test. The procedure ranked oils correctly in relation to their dithiophosphate concentration, correctly distinguished secondary and primary zinc dithiophosphates and, more interestingly, predicted the positive effects of some ashless anti-wear additives in accordance with results obtained in the Sequence VE.     

湿式离合器液压缸活塞密封圈改进设计及仿真分析

O形密封圈具有结构紧凑、便于安装等优势,被广泛的应用于湿式离合器。工作过程中,作动部件由静止开始做变速运动,受动静摩擦力共同作用,而关于该过程研究较少。按照国家标准对湿式离合器液压缸活塞密封圈进行设计,通过workbench建立密封圈模型,根据密封圈接触应力及等效应力云图对密封圈、活塞沟槽尺寸及材料硬度进行优化仿真。由仿真分析可知,优化后密封圈及沟槽结构尺寸更加合理,且密封圈材料IRHD硬度应在70~80之间选取。同时获得液压缸运动过程中密封圈动静摩擦力变化曲线,该曲线为湿式离合器响应时间及控制策略研究奠定了基础。