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991.
论述了透视仿射对应理论及该理论在解决工程实际问题方面的应用,并举例论述了,透视仿射对应理论在画法几何的相交问题中的应用。为工程技术人员图解相交问题中的交点、交线提供了一种新的方法。  相似文献   
992.
Cavitation caused by insufficient suction is a major factor that influences the life of aircraft pumps. Currently, pressurizing the tank can solve the cavitation problem under steady large-flow conditions. However, this method is not always effective under transient conditions (from zero flow to full flow in a very short time). Moreover, to apply and design other measures, such as a boost impeller, the suction dynamics during the transient period must be investigated. In this paper, a novel approach based on the pressure wave propagation theory is proposed for predicting the inlet pressure of an aircraft pump under transient conditions. First, a dynamic model of a typical aircraft pump is established in the form of differential equations. Then, the transient flow model of the inlet line is described using momentum and continuity equations, and the governing equations are discretized by the method of characteristics and the finite difference method. The simulated results are in good agreement with the results from verification tests. Further simulation analysis indicates that the wave velocity and transient time may influence the inlet and reservoir pressure as well as the size of the inlet line. Finally, solutions for upgrading the inlet pressure are discussed. These solutions provide guidelines for designing inlet installations.  相似文献   
993.
如何正确提取团块位置以实现自动跟踪对图像理解有重要意义。由于团块在图像中出现频繁且位置不确定,位置提取困难。针对一个二值图像识别系统提出了基于集合变换(即数学形态学和二值有序统计)的团块位置提取方法。即,首先对图像进行二值化,其次对二值化图像进行形态学变换,最后对变换的结果图像进行统计分析,由分析结果得出团块的位置信息。用本方法对地图中九种团块线型作了实验,表明该方法运算简单,并行性高。  相似文献   
994.
Extensive experimental studies on the heat transfer characteristics of two rows of aligned jet holes impinging on a concave surface in a wing leading edge were conducted, where50000 Rej 90000, 1.74 H/d 27.5, 66° a 90°, and 13.2 r/d 42.03. The finding was that the heat transfer performance at the jet-impingement stagnation point with two rows of aligned jet holes was the same as that with a single row of jet holes or the middle row of three-row configurations when the circumferential angle of the two jet holes was larger than 30°. The attenuation coefficient distribution of the jet impingement heat transfer in the chordwise direction was so complicated that two zones were divided for a better analysis. It indicated that: the attenuation coefficient curve in the jet impingement zone exhibited an approximate upside-down bell shape with double peaks and a single valley; the attenuation coefficient curve in the non-jet impingement zone was like a half-bell shape, which was similar to that with three rows of aligned jet holes; the factors,including Rej, H/d and r/d, affected the attenuation coefficient value at the valley significantly.When r/d was increased from 30.75 to 42.03, the attenuation rates of attenuation coefficient increased only by 1.8%. Consequently, experimental data-based correlation equations of the Nusselt number for the heat transfer at the jet-impingement stagnation point and the distributionof the attenuation coefficient in the chordwise direction were acquired, which play an important role in designing the wing leading edge anti-icing system with two rows of aligned jet holes.  相似文献   
995.
SN 1006 is one of the supernova remnants (SNRs) with relatively low-temperature electrons, considering the young age of just 1000 years. We carried out SN 1006 mapping observations with the X-ray Imaging Spectrometers (XIS) and the Hard X-ray Detector (HXD) onboard Suzaku, the fifth Japanese X-ray satellite. Thanks to the excellent spectral resolution of XIS in the soft X-ray band, H-like and He-like oxygen emission lines were clearly detected, and we could make a map of the line intensity, and as well as a flux and the photon index of nonthermal component. We found that these parameters have spatial dependences from region to region in the SNR; the north region is bright in nonthermal, while dim in thermal; the east region is bright in both nonthermal and thermal; the inner region shows dim nonthermal and bright thermal emission. The photon index is the smallest in the north region.  相似文献   
996.
根据**飞机上,CW-1002和Ⅱ-5的试飞结果,对两种产品的性能做了对比分析;对飞行中大气温度的获取方法提出了的新意见。  相似文献   
997.
The problem of a spacecraft orbiting the Neptune–Triton system is presented. The new ingredients in this restricted three body problem are the Neptune oblateness and the high inclined and retrograde motion of Triton. First we present some interesting simulations showing the role played by the oblateness on a Neptune’s satellite, disturbed by Triton. We also give an extensive numerical exploration in the case when the spacecraft orbits Triton, considering Sun, Neptune and its planetary oblateness as disturbers. In the plane a × I (a = semi-major axis, I = inclination), we give a plot of the stable regions where the massless body can survive for thousand of years. Retrograde and direct orbits were considered and as usual, the region of stability is much more significant for the case of direct orbit of the spacecraft (Triton’s orbit is retrograde). Next we explore the dynamics in a vicinity of the Lagrangian points. The Birkhoff normalization is constructed around L2, followed by its reduction to the center manifold. In this reduced dynamics, a convenient Poincaré section shows the interplay of the Lyapunov and halo periodic orbits, Lissajous and quasi-halo tori as well as the stable and unstable manifolds of the planar Lyapunov orbit. To show the effect of the oblateness, the planar Lyapunov family emanating from the Lagrangian points and three-dimensional halo orbits are obtained by the numerical continuation method.  相似文献   
998.
通过大量的事实,阐述了在企业不断深化改革过程中,开创社会化计量测试的基础,条件及基本做法。  相似文献   
999.
没有农业的现代化就没有中国农业生产现代化,通过分析我国农业现代化的基本现状和存在的问题,提出了只有提高农业劳动生产率,开拓现代农业新领域,调整产业结构,发挥比较优势,坚持科教兴农,走集约化农业发展道路,我国农业的现代化和社会主义新农村建设才能取得更大的成效。  相似文献   
1000.
中小企业群是目前国际上产业规划的流行模式。我国中小企业群具有生产运用战略纵向一体化,原材料供应方式灵活多变,经营方式专业化以及制造技术相对落后等特征。建立供需链管理模式下的地方网络体系,实施大规模定制的生产运作模式,一方面可以提高中小企业自身的管理与运作水平,还能把不同的具有产业关联的中小企业联结成一个整体,形成资源合力,加速中小企业发展,提升中小企业群的核心竞争力。  相似文献   
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