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基于编码项补偿的OFDM信号SAR成像 总被引:1,自引:0,他引:1
该文探讨了正交频分复用(OFDM)波形在SAR中可能的应用,重点讨论了基于该信号体制的SAR成像。OFDM波形改变了传统线性调频信号平坦的频谱,给高分辨成像带来了新的问题。该文深入分析了OFDM波形的信号特点,推导了其2维频谱,提出了一种适合OFDM SAR精确成像的方法。该成像算法利用对编码项的补偿,实现了OFDM波形下的距离迁徙校正,有效降低了编码信号对旁瓣的影响,充分提高了OFDM波形的成像性能。仿真结果验证了所提方法的有效性。 相似文献
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在当今的社会中,人们已经离不开电子通信了,其作为了一个新兴产业,并得到了良好的应用,对各行各业起到了促进作用,同时,传统的产业收到了冲击。我国的电子通信发展较快,达到了先进的水平,不过,由于发展时间较短,存在很多不足之处,拉低了整体水平。特别是干扰问题,严重影响了电子通信的发展。本文对电子通信进行了概述,探讨了干扰要素,并且,提出了相关的应对策略。 相似文献
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介绍了一种新型固化促进剂。详述了其合成及分析过程。研究了其结构性能。指出了该化合物的应用特点,并进行了讨论。 相似文献
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对关联规则挖掘Apriori算法的进一步改进 总被引:4,自引:0,他引:4
本文对关联规则挖掘问题进行了介绍。并在分析研究了关联规则挖掘Apriori算法厦其若干改进算法的基础上,对Apriori算法做了进一步地改进,提出了RIAprlori算法。改进后的算法采用事务压缩的方法时事务集进行了更大幅度的压缩。减小了不必要的开销,从而提高了挖掘速度。 相似文献
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利用2007-2013年的COSMIC掩星数据,分析了E区与F区电离层闪烁的变化特征.发现用闪烁出现频次、闪烁发生率以及闪烁强度来表征的电离层闪烁出现规律比较相似.E区电离层闪烁在夏季半球的中纬地区最强,其次是春秋季的低纬地区和冬季半球.就经度分布来说,春秋季E区电离层闪烁呈四波结构.对F区电离层闪烁来说:南美-大西洋扇区在12月至点最为显著;非洲和太平洋扇区在6月至点最为显著;大西洋扇区在春秋分季最为显著.极区也出现中等强度的闪烁,尤其在南半球的90°E~180°E扇区较为显著.高纬E区电离层闪烁强度随太阳活动的增强而增强,而低纬和南半球的中纬E区闪烁随太阳活动的增强而减弱.高纬和低纬F区闪烁随太阳活动的增强而增强,而中纬F区电离层闪烁对太阳活动无显著依赖关系.对于赤道区来说,北半球60°W~60°E经度区闪烁强度随太阳活动的变化最为显著,其次是南半球60°E~210°E附近;而对于高纬地区来说,F区闪烁强度随太阳活动的变化最为显著的区域在南半球60°E~210°E附近. 相似文献
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Ai Bo Yang Zhi-Xing Pan Chang-Yong Zhang Tao-Tao Wang Yong Ge Jian-Hua 《Wireless Personal Communications》2006,38(4):495-507
In this paper, we focus on the Look-up Table (LUT) technique for the compensation of HPA nonlinear distortion. An improved LUT method is proposed with better performance compared with conventional LUT technique in terms of convergence speeds, BER and total degradation (TD). It can get over 8 dB gain in out-of-band spectrum re-growth suppression and about 0.3 dB BER performance gain than conventional LUT technique with the same iteration times. Also, we propose an actual application of HPA with pre-distorter in OFDM transmitter.
Ai Bo was born in Shannxi Province in China on February 7, 1974. He received a BSc. Degree from Engineering Institute of Armed Police Force in 1997, a Master and Dr. degree from Xidian University in 2002 and 2004 in China respectively, and now working as a post dr. in Dept. of E&E, state of key lab. on microwave and digital communications in Tsinghua University in China. He has once participated in the key research project on HDTV in TEEG (Team of Engineering Expert Group) of China. He is an editorial committee member of journal of “Computer Simulations”, “Information and Electronic Engineering”, an IEEE member and a senior member of Electronics Institute of China (CIE). He has published over 60 scientific papers in his research area till now. His current interests are the research and applications of OFDM techniques with emphasis on synchronization and HPA linearization techniques.
Yang Zhi-Xing graduated from Tsinghua University, P.R. China in 1970. He is now a Professor and Deputy Director of State Key Lab. on Microwave and Digital Communication at the Department of Electronic Engineering and the Director of the DTV R&D Center in Tsinghua University. As a DTV technical expert for the Chinese government, Professor Yang has also been a member of the DTV standardization Committee of China and a leader of the DTV Standardization Harmonizing Group in Ministry of Information Industry of China. His major research interests include broadband information transmission technologies and DTV broadcasting systems.
Pan Chang-Yong received the B.S. and M.S. degrees from the Department of Electronic Engineering in Tsinghua University, P.R. China, in 1996 and 1999, respectively. He is now an associate professor in the Department of Electronic Engineering and a member of the DTV R&D Center in Tsinghua University. His research interests are in the areas of broadband wireless transmission systems and satellite communications.
Zhang Tao-Tao was born in Shandong Province in China in 1982, he received BSc. degree from Tsinghua University in 2004 and now pursing his Master degree in Dept. of E&E, state of key lab. on microwave and digital communications in Tsinghua University in China. His research interests is the power amplifier linearization techniques.
Wang Yong was born in Shannxi Province in China in 1976. He received a BSc., a Master and a Dr. Degree from Xidian University in China in 1997, 2002 and 2005, respectively, and now is an associate professor in Xidian University. He has once participated in the key research project on HDTV in TEEG (Team of Engineering Expert Group) in China and is an IEEE Member. His interests are broadband multimedia communications.
Ge Jian-Hua was born in September, 1961 in JiangSu Province in China. He received the B.Sc., Master and Ph.D. degree from Xidian University in 1982, 1985 and 1989, respectively. He is now the professor in both Xidian University in Xi’an and Shanghai Jiaotong University in Shanghai. He is the senior member of Chinese Electronics Institute. He has won lots of scientific and technical prizes in China and published many papers. His interests are transmission communications and web security. 相似文献
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An attempt is made to determine if investment in R&D and the hiring of college-educated employees result in a higher rate of inventions. The relationship between the input of R&D and inventive output is studied in two samples of Japanese factories, 34 in 1982 and 44 in 1970. These results are compared with findings in a parallel American study. The correlations between R&D and inventive output are similar in Japan and America in the 1980s, despite some differences in the management of innovation in the two nations. Moreover, the most Westernized subsample of Japanese firms in the 1970s had correlations between R&D and invention similar to those observed in the American study. Thus, it is concluded that some degree of convergence may be taking place in R&D management strategies in the two nations 相似文献
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N. A. Torkhov 《Semiconductors》2011,45(7):935-943
It is shown that changes in device characteristics and an increase in the light-to-electrical energy conversion efficiency
in metal-semiconductor Schottky barrier contacts are associated with a peripheral electric field built into the contact. For
contacts with longer perimeters, variations in device characteristics and the light-to-electrical energy conversion efficiency
are significantly larger. Since the photovoltage and peripheral electric fields in the contact region are codirected with
the intrinsic electric field of the space-charge region, contact illumination results in a larger increase in the “dead” zone
in forward portions of current-voltage characteristics, a larger decrease in the effective Schottky barrier height, and an
increase in the field electron emission. An increase in the reverse field emission under photovoltage leads to an increase
in the recombination current in the space-charge region, which provides dc photocurrent flow in the circuit. 相似文献
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T. H. Reijenga 《Progress in Photovoltaics: Research and Applications》1996,4(4):279-294
The Netherlands has a programme for the integration of photovoltaic (PV) modules in the built environment. The aim of this programme is to realize 250 MWp in PV systems by the year 2010. Within this programme the integration of PV modules in architecture has an important role, presenting opportunities for architects. New Technology and materials are an invitation for new design. BEAR Architecten is involved in several low-energy, bio-climatic building projects, amongst them are a few PV projects: De Kleine Aarde, an Environmental Education Centre with transparent PV panels in the glass roof; roof retrofit with PV modules in five houses in Leiden; facade integration with PV shading in 22 houses in Dordrecht; roof integration in row houses in Enschede; roof integration in a utility building in Geldermalsen. Information about these projects is given, but also the possibilities and the problems are discussed here. A general conclusion is that custom-made modules are often necessary to make well-designed buildings. 相似文献
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固/液界面纳米气泡的存在已经得到证实,并成为界面科学研究的一个焦点.在原子力显微镜液体池内制备纳米气泡的基础上,本研究建立了在开放体系中进行醇水替换,制备纳米气泡的方法.原子力显微镜观察显示.开放体系中进行醇水替换,也可以在水/云母界面上稳定地生成纳米气泡.将不同环境下制备的纳米气泡进行比较,统计结果显示,在开放体系下制备的纳米气泡密度较低,形态也较小.不同环境下醇水替换产生的纳米气泡数量和形态的差异,为纳米气泡形成的机制提供了新的佐证.开放体系下纳米气泡制备方法的建立拓展了纳米气泡的制备条件,揭示了纳米气泡存在的普遍性,同时也为纳米气泡性质研究提供了新的途径. 相似文献
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The primary results of the study of hemoglobin and ferritin in erythrocytes in leukemia are considered in the light of the M?ssbauer spectroscopy data. The quantitative changes in hemoglobin and ferritin during differentiation of cells in the Friend erythroleukemia are shown. The qualitative changes in iron electronic structure of oxyhemoglobin in different forms of human leukemias are shown. 相似文献
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I G Kovalenko 《Eksperimental?nai?a onkologii?a》1986,8(2):60-63
Changes in biosynthesis of cholesterol and free fatty acids from 2-14C-acetate in the host liver and tumour tissue as well as concentrations of various classes of lipids in blood were determined in rats bearing the transplanted Pliss lymphosarcoma. The transplantation of the tumour stimulates cholesterol biosynthesis de novo in the liver, but produces no changes in the fatty acid synthesis. Tumour growth is accompanied by a progressive increase in the content of triglycerides and beta-lipoproteins with a parallel drop in the alpha-cholesterol level in the animal blood. The concentration of total cholesterol is of phasic character depending on the stage of tumour growth. The possible mechanisms determining such alterations in lipids metabolism are discussed. 相似文献
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大别山南山岭和碧溪岭石榴橄榄岩中的橄榄石具有不同的显微构造特征,前者基本不发育位错,而后者的位错比较普遍。碧溪岭橄榄石的微观晶形可分为球形颗粒和多面块体两类。球形颗粒内位错密度极低,是局部重结晶作用的结果,表明样品曾受到瞬间高温的作用;而多面块体内则分布着较高密度(~2×10^8/cm^2)的位错,其中有些微区的位错已显著扩展,形成层错,而另外一些区域中位错依然保持全位错的构形,表明各微区的层错能可能不同。层错能的差异最可能源于各微区成分的不同,实验结果显示Mg含量较高的微区,易形成层错。多面块体内的位错有明显运动迹象,表明样品曾受到长期、和缓的温度与差应力的联合作用。据此推测,碧溪岭地区板块间曾发生长期的相互挤压作用和不均匀的塑性变形,并最终发生瞬时激烈碰撞,由此产生的热量导致一些变形严重的微区发生重结晶形成球形颗粒,而未发生重结晶区域的位错则基本保持碰撞之前的组态。本文为碧溪岭地区板块俯冲和折返的超高压变质过程和演化历史及南山岭岩体形成于碰撞造山后的认识提供了流变学的证据。 相似文献