基于2007-2013年COSMIC掩星数据的电离层振幅闪烁研究

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.     

Fourth quarter 2009 IEEE communications surveys and tutorials

Welcome to the fourth issue of 2009 of the IEEE Communications Surveys and Tutorials. Paper in this issue survey the research effort in several areas such mobility in Wimax, mobility models in VANET, handoff in cellular networks, admission control in MANETS, physical impairments in optical networks, physical layer issues in the 802.11n standard as well as jamming in wireless sensor networks     

Inventive payoff from R&D in Japanese industry: convergencewith the West

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     

Effect of photovoltage on current flow in metal-semiconductor schottky-barrier contacts

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.     

开放体系下云母表面纳米气泡的制备与观察

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.     

Improved LUT Technique for HPA Nonlinear Pre-Distortion in OFDM Systems

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.     

A Strategy for Broad-Band Network Introduction in Italy

Studies are being carried out in Italy concerning the strategy for the introduction in the 1990's of optical fiber systems in the distribution network, in order to supply customers with broad-band services (in particular with video services). This paper deals with some of the main choices that are being done, in particular in view of a field trial which is planned in Rome in 1988.     

Changes in hemoglobin and ferritin biosynthesis in leukemias detected by M?ssbauer spectroscopy

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.     

Photovoltaics in architecture in The Netherlands: an architect's view

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.     

微孔无铜原因分析与改善

文章主要分析了PCB制造过程中微孔出现孔无铜的各类原因以及改善预防措施,并且详细介绍了对于火山灰堵孔造成的微孔孔无铜的原因分析。