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排序方式: 共有1111条查询结果,搜索用时 15 毫秒
1.
中国互联网协会将具有以下特点的邮件定义垃圾邮件:(1)收件人事先没有提出要求或者同意接收的广告、电子刊物、各种形式的宣传品等宣传性的电子邮件;(2)收件人无法拒收的电子邮件;(3)隐藏发件人身份、地址、标题等信息的电子邮件;(4)含有虚假的信息源、发件人、路由等信息的电子邮件。 相似文献
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图1所示的弹性管联轴节,多用于传递力矩小于50g·cm的传动系统中。这种弹性管联轴节,具有结构简单,装配方便,无空回误差,能吸收冲击、振动等特点。在电子工业产品中,设计师们大多喜欢采用。加工弹性管联轴节的关键工序尺寸是A、B和t,即螺旋槽的切削成形。我们根据铣削和车削两种加工工艺特点,吸取了它们的长处,在c616普通车床上成功地加工出了弹性管联轴节。在车床上加工弹性管联轴节,需要设计制造一副简易工装(见如图2)。其中α角等于联轴节螺旋升角,即tgα=t/(πd),螺杆的螺距等于联轴节的螺距t。这副简易工装固定在刀架上。 相似文献
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Hierarchical streamline bundles 总被引:2,自引:0,他引:2
Yu H Wang C Shene CK Chen JH 《IEEE transactions on visualization and computer graphics》2012,18(8):1353-1367
Effective 3D streamline placement and visualization play an essential role in many science and engineering disciplines. The main challenge for effective streamline visualization lies in seed placement, i.e., where to drop seeds and how many seeds should be placed. Seeding too many or too few streamlines may not reveal flow features and patterns either because it easily leads to visual clutter in rendering or it conveys little information about the flow field. Not only does the number of streamlines placed matter, their spatial relationships also play a key role in understanding the flow field. Therefore, effective flow visualization requires the streamlines to be placed in the right place and in the right amount. This paper introduces hierarchical streamline bundles, a novel approach to simplifying and visualizing 3D flow fields defined on regular grids. By placing seeds and generating streamlines according to flow saliency, we produce a set of streamlines that captures important flow features near critical points without enforcing the dense seeding condition. We group spatially neighboring and geometrically similar streamlines to construct a hierarchy from which we extract streamline bundles at different levels of detail. Streamline bundles highlight multiscale flow features and patterns through clustered yet not cluttered display. This selective visualization strategy effectively reduces visual clutter while accentuating visual foci, and therefore is able to convey the desired insight into the flow data. 相似文献
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Holland CK Apfel RE 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1989,36(2):204-208
An approximate analytical formulation is presented that allows for the calculation of acoustic pressure thresholds for transient cavitation over a variety of frequencies and host fluid parameters. Specifically, R.E. Apfel's (1986) theory is extended to include an estimate of the time delay associated with the Laplace pressure, 2sigma/R(0), where sigma is the surface tension and R(0) is the initial radius. Also presented is a correction factor for the time-averaged pressure difference, across the bubble wall during growth. An optimum size distribution of nuclei for the predisposition of a sample to microcavitation is exhibited. The role of transient cavitation in medical ultrasound is discussed. 相似文献
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Smith PM Campbell CK 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1989,36(1):10-15
A study of low-loss surface-acoustic-wave (SAW) interdigitated interdigital transducer (IIDT) structures is presented. A model based on mixed scattering matrices was used in the analysis. It is shown that the inherent comb frequency response of the IIDT can be smoothed by slanting the transducers in the structure. Alternatively, the combs can be enhanced to produce a compact low-loss feedback element for potential application in multimode oscillators. Experimental verification of the analysis is provided by a 3:2 slanted-finger IIDT filter with a 10% relative bandwidth of 5.9-dB insertion loss, and a comb filter with 13.4-dB insertion loss and comb spacing of about 3 MHz. The measured responses agree quite well with the theory. 相似文献
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