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高精度内圆磨床采用了运行精度高、摩擦因数低、产生热变形小的液体静压导轨;作为磨床可移动部件与固定部件间的重要结合部分,液体静压导轨的刚度特性对磨床结构动态特性有着不可忽视的影响;介绍了液体静压支承的基本原理,计算了高精度内圆磨床进给系统采用液体静压闭式导轨对置油垫的刚度,并借助Matlab软件分析对置油垫刚度随供油压力、主油膜厚度、油腔宽度以及总间隙变化的规律,为液体静压导轨的刚度调整提供了理论依据。 相似文献
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钟先信 《精密制造与自动化》1980,(4)
精密磨削和超精密加工中所使用机床的主轴部件和机床导轨近年来有了很大的发展,在六十年代主要是采用液体静压轴承和静压导轨,而七十年代国外研制高精度空气静压轴承和空气静压导轨,取得了很大的进展。美国气动精密(Pneumo Precision)公司、Du Pout公司和埃克塞罗(Ex-Cell-O)公司等将高精度空气静压支承用于超精密加工的主轴部件和导轨。美国气动精密公司已经成系列地生产MSG超精密机床,包括金刚石砂轮磨削、金刚石车削、铣平面与镗孔、金刚石飞刀切削等各种机床。机床主轴和导轨全部采用空气静压 相似文献
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重点介绍静压导轨的工作原理、特.最、结构和调整,通过对闭式静压导轨主要参数的设计计算和结构分析,从而可知应用静压导轨技术的重要意义。重型卧式车床的纵、横向进给中采用静压导轨,不仅可提高进给部件的运动精度,而且也极大地降低了驱动电机的功率和扭矩,节约了能源,降低了成本,又提高了机床精度。 相似文献
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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. 相似文献
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《Measurement》2016
In current measurement theory, there are various logical and philosophical troubles, and the evaluation concepts of measurement error are various and inconsistent among different schools. This paper throws away the shackle of the current measurement theories and concepts, and re-discusses basic measurement concepts. By proving a new measurement error theory that any error is a bias and follows random distribution, this paper points out the misunderstanding of traditional measurement theory, subverts the traditional error category theory, gives out a new interpretation of measurement uncertainty concept, proposes abolishing the concept system of precision, trueness, and accuracy, and thereby achieves the united measurement concept system across all the disciplines, including geodesy, geomatics, metrology, instrumentation, and so on. 相似文献
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Y Wakayama M Inoue H Kojima M Murahashi S Shibuya H Oniki 《Microscopy research and technique》2001,55(3):154-163
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. 相似文献
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Xiuchun ZHANG 《Biocell》2019,43(4):313-319
To investigate the effects of polydatin on the proliferation, migration, and invasion of ovarian cancer, the
change of proliferative ability, migration ability, and invasive ability of human ovarian cancer cell OVCAR-3, A2780,
and HO-8910 was detected by using polydatin and up-regulating PI3K. The anticancer activity and mechanism of
polydatin in ovarian cancer were analyzed. Polydatin could effectively inhibit the proliferation, migration, and invasion
of OVCAR-3, A2780, and HO-8910, and inhibit the expression of PI3K protein. After the expression level of PI3K
protein was up-regulated, the inhibitory effect of polydatin on the proliferative ability, migration ability, and invasive
ability of OVCAR-3, A2780, and HO-8910 significantly decreased, suggesting that PI3K was the target of polydatin.
Therefore, we concluded that polydatin could inhibit the proliferation, migration, and invasion of ovarian cancer cells
by inhibiting the expression of PI3K protein, which provides an experimental basis for polydatin in the treatment of
ovarian cancer. 相似文献
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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. 相似文献
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救助打捞是国家应急保障体系的重要组成部分,承担着我国海上人命、财产、环境救助、沉船沉物打捞及其他对海上运输和海上资源开发提供安全保障等多项任务。加强救助打捞装备技术研究,是提高救助打捞综合能力的根本,是国家发展战略的重要构成。救助打捞装备专业性强,具有在高海况和大深度条件下工作可靠的适应性特点,同时又是诸多陆上装备向海上和水下发展的延伸,存在相通之处。救助打捞装备交叉机械、电气、流体、微电子、材料等多学科,其关键共性技术又不仅仅局限于救助打捞领域,在海上运输、海洋油气开发、海洋勘探、军事等领域均有应用。以救助船舶、救助飞机、海上搜寻装备、溢油处置装备等代表性的救助装备和打捞工程船、攻千斤装备、水下作业装备、饱和潜水装备、起浮装备等代表性的打捞装备为对象,分析该领域国内外发展现状和趋势,提出救助打捞装备面临的关键技术问题,为我国救助打捞装备的发展战略研究提供参考。 相似文献
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针对大压力、小压力行程的重型液压设备的结构尺寸大、油泵功率大、利用系数低、液压系统复杂等问题,提出一种压力随机可调、工作效率高、结构紧凑、性能稳定可靠的复合式高增压油缸结构。对比分析了复合缸液压机和普通单缸液压机的工作过程;论述了复合缸液压机的运行原理和设计要求;介绍了可控式增压复合油缸性能及应用。结果表明:通过增压缸将液压系统提供的压力油转换为增压油提供给主油缸,使其产生大的压力输出,可有效地减小设备主机尺寸;通过控制缸随时进行高低压转换,各阶段速度压力按需配置,实现成形工艺的最优搭配,成形周期缩短;可以提高油泵的利用系数,减小泵站装机容量;液压系统工作负荷低,性能稳定可靠,寿命长。 相似文献
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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。 相似文献
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在长期进化过程中,自然界中的多种动物、植物形成了独特的轻质、高强结构,以此来抵抗外界的复杂冲击载荷,保护自身完整,满足生存需要。生物轻质高强结构的优越性,启发了科研和工程人员采用结构仿生学的方法来对管状和板状两大类吸能结构进行设计优化和改进。对竹子、茎秆/树干、羽轴、骨骼四类管状生物结构和甲虫鞘翅、贝壳、柚子皮、龟壳四类板状生物结构进行综述,阐述了分层、多孔、螺旋、中空等多种结构与轻质高强特性之间的关系。在此基础上,对比和分析了相应的结构元素在单胞管、多胞管、嵌套管、波纹管等管状吸能结构和蜂窝夹芯板、复合材料板、混合结构板等板状吸能机构中起到的作用。进一步对当前仿生吸能领域存在的结构复杂、质量大、缺乏普适性的机理和过渡“桥梁”等问题做出了分析;最后对仿生吸能技术的形式简单化、结构轻量化、理论通用化、“形神兼备”化发展趋势做出展望。 相似文献