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排序方式: 共有235条查询结果,搜索用时 31 毫秒
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We have investigated the effect of extended dislocations (0.5-3 μm) on charge distribution in GaN epilayer grown by metalorganic chemical vapor deposition on (0001) sapphire using atomic force microscopy (AFM) and scanning surface potential microscopy (SSPM). It has been observed for the surface at the extended dislocations present in undoped GaN film to be negatively charged showing 0.04-0.2 V higher potential relative to regions that contain no dislocations. In addition to the higher potential at the dislocation core, the surrounding surfaces, including the edge of the dislocations, are also negatively charged in a symmetric way around the dislocations revealing crater-shaped higher potential regions (∼0.04 V) relative to surrounding dislocation-free area. The experimental results show that the protrusion-type of dislocation is also negatively charged and its potential is dependent on the size of dislocation. 相似文献
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毫米波连续波雷达载波泄漏对消——理论分析与系统仿真 总被引:6,自引:1,他引:5
对限制连续波体制雷达系统作用距离的载波泄漏问题仔细地作了探讨,对各种连续波体制载波泄漏有源对消方法进行了理论分析,并针对毫米波宽带调频雷达实际泄漏信号的特点进行了对消环路的系统仿真。结果表明设计良好的对消系统能有效地抵消载波泄漏功率达30 ̄60dB,对进一步作实验研究提供了理论基础。 相似文献
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Dongjin Seo 《Polymer》2005,46(17):6482-6493
Foam reaction injection molding (FRIM) is one of the most popular and useful processes for producing polyurethane foam with a complex geometry. A theoretical model which includes chemical reactions, foaming, and mold filling was developed to analyze FRIM. Energy balance equation was derived by considering polyurethane reaction, water-isocyanate reaction, and evaporation of physical blowing agents. Density and viscosity model was proposed for the bubble suspension, which was assumed to be a homogeneous phase. Based on the theoretical model, three-dimensional numerical simulation for mold filling of the polyurethane foam was carried out to predict flow field, flow front advancement, and density distribution during mold filling. Mold filling of a refrigerator cavity was investigated numerically. The density and thermal conductivity of the foam in the flow front was higher than those in the initially filled region. 相似文献
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电影虚拟预演所需的三维场景搭建要求能够高效地初步将导演的构想付诸于影像,但传统计算机辅助设计工具的交互方式存在效率低的问题,限制了导演等非专业三维设计人士的场景构思.因此提出一种新的面向电影场景搭建的自然手势交互方法.根据电影虚拟预演特性和相关手势理论,设计一组有效的三维场景搭建手势集;在Unity3 D中构建基于虚拟现实的电影场景搭建徒手手势用户界面;通过用户实验对该方法进行评估,实验结果表明该方法是可行的,相比传统方法更具有自然易用性. 相似文献
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针对Galileo系统空间信号完好性监测方案中两项关键技术点做出改进,首先提出改进临界圆法,从坐标系转换角度解决最坏用户位置方位角转换的复杂度问题;其次引入“截尾概率包络”概念,改善原模型对非零均值空间信号误差值高斯分布的过分包络问题;最后在无故障、阶跃类故障、斜坡类故障3种模式下,对比分析改进方案前后系统的完好性性能;结果表明,完好性阈值对实时空间信号误差估计值的平均包络紧度由3.89米改善至2.62米,对斜坡类故障的告警更加及时。 相似文献
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Four kinds of silicon-metals (Cu, Ni, Sn)-graphite composites for anode active materials of lithium secondary batteries were
prepared by sequential employment of PECVD (Plasma enhance chemical vapor deposition) and RF(Radio-frequency)-magnetron sputtering
method. The silicon-copper-graphite composite showed the highest reversible capacity and cyclability among the silicon-metal
composite graphite samples prepared. The enhanced electrochemical performance of silicon-copper-graphite composite is attributed
to the formation of copper silicide on the surface of graphite.
The copper silicide plays an important role as a buffering layer against volume change of silicon during the intercalation/deintercalation
due to the chemical bonding of silicon and copper, and has lower interfacial impedance than that of other silicon-metal-graphite
composites which may lead to low irreversible capacity. 相似文献