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151.
浅析在“夷陵杯”评选过程中发现的一些建筑电气安装中存在的质量问题,并提出防控措施,供创优质精品工程的电气安装工程技术人员共同探讨,同时也希望引起建设、施工、监理单位乃至质量监督部门的高度重视。 相似文献
152.
通过铸造和300℃热加压制备细晶Mg-6Zn-4Y合金,利用XRD、OM、SEM和TEM研究合金组织,并测试其室温拉伸性能。结果表明,合金主要由α-Mg和W相两相组成,挤压态合金具有双峰晶粒尺寸分布;细小晶粒为动态再结晶晶粒,平均尺寸为1.2μm;粗大晶粒(占面积分数的23%)为未再结晶区域,并沿挤压方向被拉长。合金的极限抗拉强度、屈服强度和伸长率分别为(371±10)MPa,(350±5)MPa和(7±2)%,其工程应力—应变曲线有明显的屈服点。合金高强度归因于晶粒细化和W相、纳米沉淀颗粒及强基面织构的增强作用。 相似文献
153.
铝合金阳极氧化膜的制备和研究 总被引:1,自引:0,他引:1
用直流叠加脉冲方波制备了铝合金阳极氧化膜,对礤性能和光谱选择特性进行了测试和研究,并提出了结构模型,从微观角度讨论了影响阳极氧化膜品质的几个关键因素。 相似文献
154.
《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2011,659(1):428-433
Detecting and monitoring emissions from flaring gamma-ray sources in the very-high-energy (VHE, > 100 GeV) band is a very important topic in gamma-ray astronomy. The ARGO-YBJ detector is characterized by a high duty cycle and a wide field of view. Therefore, it is particularly capable of detecting flares from extragalactic objects. Based on fast reconstruction and analysis, real-time monitoring of 33 selected VHE extragalactic sources is implemented. Flares exceeding a specific threshold are reported timely, hence enabling the follow-up observation of these objects using more sensitive detectors, such as Cherenkov telescopes. 相似文献
155.
156.
This work aims to determine the characteristic PN junction diode, subject to a reverse polarization, while I (breakdown voltage) of the inverse current in a GaAs specifying the parameters that influence the breakdown voltage of the diode. In this work, we simulated the behavior of the ionization phenomenon by impact breakdown by avalanche of the PN junctions, subject to an inverse polarization. We will take into account both the trapping model in a stationary regime in the P+N structure using like material of basis the Ⅲ-Ⅴ compounds and mainly the GaAs semi-insulating in which the deep centers have in important densities. We are talking about the model of trapping in the space charge region (SCR) and that is the trap density donor and acceptor states. The carrier crossing the space charge region (SCR) of W thickness creates N electron-hole pairs: for every created pair, the electron and the hole are swept quickly by the electric field, each in an opposite direction, which comes back, according to an already accepted reasoning, to the crossing of the space charge region (SCR) by an electron or a hole. So the even N pair created by the initial particle provoke N2 ionizations and so forth. The study of the physical and electrical behaviour of semiconductors is based on the influence of the presence of deep centers on the characteristic I(V) current-tension, which requires the calculation of the electrostatic potential, the electric field, the integral of ionization, the density of the states traps, the diffusion current of minority in the regions (1) and (3), the current thermal generation in the region (2), the leakage current in the surface, and the breakdown voltage. 相似文献
157.
为了将代理模型应用于核工程反应堆热工水力现象中,以再淹没现象为研究对象,构建代理模型,并通过控制实验参数的数量,来化解精度与效率之间的矛盾。首先使用拉丁超立方方法抽取输入样本,并通过RELAP5建模获取输出样本,由MATLAB分别构建RBF神经网络代理模型和Kriging代理模型,对包壳峰值温度(PCT)进行拟合。然后分析比较了2种代理模型的拟合结果,发现2种代理模型的相对误差值均小于0.15%,均适用于再淹没现象;Kriging代理模型的拟合精度高于RBF神经网络代理模型。 相似文献
158.
159.
Fourier spectral method can achieve exponential accuracy both on the approximation level and for solving partial differential equations if the solutions are analytic. For a linear PDE with discontinuous solutions, Fourier spectral method will produce poor point-wise accuracy without post-processing, but still maintains exponential accuracy for all moments against analytic functions. In this note we assess the accuracy of Fourier spectral method applied to nonlinear conservation laws through a numerical case study. We have found out that the moments against analytic functions are no longer very accurate. However the numerical solution does contain accurate information which can be extracted by a Gegenbauer polynomial based post-processing.Research supported by ARO Grant DAAL03-91-G-0123 and DAAH04-94-G-0205, NSF Grant DMS-9211820, NASA Grant NAG1-1145 and contract NAS1-19480 while the first author was in residence at ICASE, NASA Langley Research Center, Hampton, Virginia 23681-0001, and AFOSR Grant 93-0090. 相似文献
160.
The introduction of an HVDC system into the trunk power supply system requires transmitting as much dc power as possible for improving the whole ac/dc system stability. The continued operation scheme of an HVDC system which makes it possible to operate even under very low commutation bus voltage is adopted to cope with such system requirement. Further stability improvement can be achieved by adding damping control which modulates converter active and/or reactive power. To take full advantage of these control effects, it is essential that the HVDC system can maintain stable operation during the ac system faults and reclosing. Particular attention should be given to a repetitive commutation failure following the unbalanced ac transmission line faults. This paper discusses first the cause of the repetitive commutation failure when supplied with unbalanced ac system voltage based on an experiment using the CRIEPI AC-DC Power System Simulator. Then a stabilization control scheme with an on-line extinction angle estimation is proposed and the effect is verified by digital simulation. 相似文献