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941.
过大的径向力是影响液压缸使用寿命的重要因素。该文介绍了一种低速重载液压缸,该液压缸采用辅助支承以及将活塞杆受推杆作用的作用点移至活塞与端盖上的导向套之间,能够极大地减小活塞与活塞杆所受的径向力,从而避免导向套磨损严重、拉缸、密封损坏、内泄大、端盖处有外泄等故障的发生,提高了液压缸的使用寿命。 相似文献
942.
电液负载模拟器的RBF神经网络控制 总被引:6,自引:0,他引:6
针对传统控制器自适应能力和鲁棒性差、参数调节繁琐等缺陷,提出了神经网络自适应控制方案,同时针对神经网络控制器计算复杂和稳定性证明缺乏理论依据等不足问题,在传统控制理论的基础上设计了基于PID的神经网络控制方案。根据电液负载模拟器的结构特点和目前神经网络控制的发展水平,提出了基于RBF神经网络的PID控制器,并构建了负载模拟器的神经网络控制与基于Jacobian的消扰(消除多余力)结构,仿真和试验证明其具有很好的自适应性和鲁棒性。 相似文献
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Experimental nanotips have shown significant improvement in the resolution performance of a cold field emission scanning electron microscope (SEM). Nanotip electron sources are very sharp electron emitter tips used as a replacement for the conventional tungsten field emission (FE) electron sources. Nanotips offer higher brightness and smaller electron source size. An electron microscope equipped with a nanotip electron gun can provide images with higher spatial resolution and with better signal-to-noise ratio. This could present a considerable advantage over the current SEM electron gun technology if the tips are sufficiently long-lasting and stable for practical use. In this study, an older field-emission critical dimension (CD) SEM was used as an experimental test platform. Substitution of tungsten nanotips for the regular cathodes required modification of the electron gun circuitry and preparation of nanotips that properly fit the electron gun assembly. In addition, this work contains the results of the modeling and theoretical calculation of the electron gun performance for regular and nanotips, the preparation of the SEM including the design and assembly of a measuring system for essential instrument parameters, design and modification of the electron gun control electronics, development of a procedure for tip exchange, and tests of regular emitter, sharp emitter and nanotips. Nanotip fabrication and characterization procedures were also developed. Using a "sharp" tip as an intermediate to the nanotip clearly demonstrated an improvement in the performance of the test SEM. This and the results of the theoretical assessment gave support for the installation of the nanotips as the next step and pointed to potentially even better performance. Images taken with experimental nanotips showed a minimum two-fold improvement in resolution performance than the specification of the test SEM. The stability of the nanotip electron gun was excellent; the tip stayed useful for high-resolution imaging for several hours during many days of tests. The tip lifetime was found to be several months in light use. This paper summarizes the current state of the work and points to future possibilities that will open when electron guns can be designed to take full advantage of the nanotip electron emitters. 相似文献
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949.
Comparison of friction measurements using the atomic force microscope and the surface forces apparatus: the issue of scale 总被引:1,自引:0,他引:1
Results are presented of lateral force measurements using the atomic force microscope (AFM) and the surface forces apparatus (SFA). Two different probes are used in the AFM measurements; a sharp silicon nitride tip (radius R20 nm) and a glass ball (R15 m). The lateral force is measured between the (silicon nitride or glass) probe and a mica surface which has been coated by a thin lubricant film. In the SFA, a thin lubricant film separates two molecularly smooth mica surfaces (R1 cm) which are slid relative to each other. Perfluoropolyether (PFPE) and polydimethylsiloxane (PDMS) were used as the lubricant films. In the SFA where the contact diameter is largest, the PFPE film shows much lower friction than PDMS. As the size of the probe decreases, the difference in the measured friction decreases. For sharp AFM tips, no clear distinction between the tribological properties of the films can be made. Hence, the measured coefficient of friction varies according to the length scale probed, at least for small dimensions. 相似文献
950.
J. G. Mantovani D. P. Allison R. J. Warmack T. L. Ferrell J. R. Ford R. E. Manos J. R. Thompson B. B. Reddick K. Bruce Jacobson 《Journal of microscopy》1990,158(1):109-116
We present scanning tunnelling microscope (STM) images of untreated tobacco mosaic virus (TMV) deposited on thermally evaporated and on sputter-coated palladium/gold 40:60 (Pd/Au) substrates, and imaged under ordinary atmospheric conditions. The TMV imaged on both evaporated and sputter-coated substrates was consistently several times wider than the known diameter of the virus. TMV on evaporated Pd/Au became overcoated with Pd/Au material during sample preparation and appeared elevated in STM images, whereas TMV on sputter-coated Pd/Au appeared as depressions. When naked TMV were intentionally overcoated with Pd/Au, the STM images were found to be similar to those for TMV on evaporated Pd/Au. 相似文献