高温超导体Bi2223中掺杂对结构和输运性质的影响

用固相反应法制备了化学计量比为Bi1.8Pb0.4Sr2-xKxCa2-yNdyCu3Oz(x=0,0.02;y=0,0.02)的样品。通过X射线衍射(XRD)技术,扫描电子显微镜(SEM),电阻率,磁性和拉曼测量对样品的结构和物性做了表征。随着掺杂的不同,样品的超导转变温度Tconset从99K变化到110K。与x=y=0的样品相比,x=0.02,y=0的样品其超导电性和临界电流密度都有了明显改善。     

平面运动链类型综合的基杆构形树法

在对平面机构闭式运动链结构组成进行研究后,提出运动链类型综合的基杆构形树法。首先,针对给定的构件数与自由度,基于缩杆邻接矩阵综合出运动链连杆序列、缩杆序列、构件度序列以及基杆联结度序列等恒量序列。然后,归纳出基于缩杆邻接矩阵对运动链进行类型综合的方法与步骤,定义了基杆构形树,并用基杆构形树综合出运动链的基杆构形矩阵,进一步研究了综合运动链联结矩阵的缩杆匹配方法。由于基杆构形树法在综合过程中按杆的级别、运动副数目以及联结关系等结构不变量将运动链进行了分类细化,因此综合规律性强、效率高,有利于减少后续刚性子链消除与运动链同构识别的计算量,尤其适合于多杆多自由度平面机构闭式运动链的计算机自动综合,并在12杆以下平面机构闭式运动链的类型综合中得到成功的应用。同时,以10杆单自由度机构运动链的类型综合为例进行了实例分析。     

建筑物地基裂缝成因初探

山东省某矿区的主要建筑物包括采矿车间、选矿 车间、办公楼和生活区建筑物，1991年建成，1993年开 始使用，1998年发现地面及建筑物裂缝、沉陷.为了采 取更有效的工程措施控制沉降，保证建筑物的安全，针 对工程区沉降和地基裂缝成因进行了勘察研究. 1工程概况 面坡降约3一4.5     

Laser diode intersatellite links: Communications subsystem

This paper analyzes the critical areas in optical communications systems, placing particular emphasis on the modulation/demodulation techniques used in the ISL communications subsystem design for the ESA/PSDE programme. A 4-PPM/QPM demodulator has been designed, and problems of implementing the system at high data rates have been addressed. Maximum likelihood demodulation techniques and slot and frame synchronization were used. An attempt was made to devise a way to achieve synchronization tracking without using unique words along data patterns. Finally, for the optical ISL the use of coding is suggested as a way to relax link budget requirements. Coding could reduce problems caused by pointing subsystem instabilities. The use of on-board soft decoding without system bandwidth expansion is also foreseen.     

RObust Header Compression (ROHC) Performance for Multimedia Transmission over 3G/4G Wireless Networks

RObust Header Compression (ROHC) has recently been proposed to reduce the large protocol header overhead when transmitting voice and other continuous media over IP based protocol stacks in wireless networks. In this paper we evaluate the real-time transmission of GSM encoded voice and H.26L encoded video with ROHC over a wireless link. For the voice transmission we examine the impact of ROHC on the consumed bandwidth, the voice quality, and the delay jitter in the voice signal. We find that for a wide range of error probabilities on the wireless link, ROHC roughly cuts the bandwidth required for the transmission of GSM encoded voice in half. In addition, ROHC improves the voice quality compared to transmissions without ROHC, especially for large bit error probabilities on the wireless link. The improvement reaches 0.26 on the 5-point Mean Opinion Score for a bit error probability of 10^–3. For the video transmission we examine the impact of ROHC on the consumed bandwidth. We find that the bandwidth savings with ROHC depend on the quantization scale used for the video encoding and the video content and ranges between 5–40% for typical scenarios.Frank H.P. Fitzek is an Associate Professor in the Department of Communication Technology, University of Aalborg, Denmark heading the Future Vision group. He received his diploma (Dipl.-Ing.) degree in electrical engineering from the University of Technology – Rheinisch-Westflische Technische Hochschule (RWTH) – Aachen, Germany, in 1997 and his Ph.D. (Dr.-Ing.) in Electrical Engineering from the Technical University Berlin, Germany in 2002. As a visiting student at the Arizona State University he conducted research in the field of video services over wireless networks. He co-founded the start-up company acticom GmbH in Berlin in 1999. In 2002 he was Adjunct Professor at the University of Ferrara, Italy giving lectures on wireless communications and conducting research on multi-hop networks. His current research interests are in the areas of 4G wireless communication, QoS support for multimedia services, access techniques, security for wireless communication, and the integration of multi hop networks in cellular systems. Dr. Fitzek serves on the Editorial Board of the IEEE Communications Surveys and Tutorials. He is the program chair for the International Conference on Advances in Computer Entertainment Technology (ACE2004) and serves in the program committee for VTC2003, VTC2004, ACE2004, and IEEE MWN2004.Stephan Rein studied Electrical Engineering at the Technical University of Aachen, Germany, and the Technical University of Berlin (TUB), Germany. He received the Dipl.-Ing. degree in electrical engineering from the TUB in 2003. From March 2003 to October 2003 he visited the multimedia networking group in the Department of Electrical Engineering at Arizona State University, Tempe. He is currently pursuing the Ph.D. degree at the Institute for Energy and Automation Technology, Technical University of Berlin. His current research interests include data compression and digital signal processing with emphasis on wavelet theory.Patrick Seeling received the Dipl.-Ing. degree in industrial engineering and management (specializing in electrical engineering) from the Technical University of Berlin (TUB), Germany, in 2002. Since 2003 he has been a Ph.D. student in the Department of Electrical Engineering at Arizona State University. His research interests are in the area of video communications in wired and wireless networks. He is a student member of the IEEE and the ACM.Martin Reisslein is an Assistant Professor in the Department of Electrical Engineering at Arizona State University, Tempe. He received the Dipl.-Ing. (FH) degree from the Fachhochschule Dieburg, Germany, in 1994, and the M.S.E. degree from the University of Pennsylvania, Philadelphia, in 1996. Both in electrical engineering. He received his Ph.D. in systems engineering from the University of Pennsylvania in 1998. During the academic year 1994–1995 he visited the University of Pennsylvania as a Fulbright scholar. From July 1998 through October 2000 he was a scientist with the German National Research Center for Information Technology (GMD FOKUS), Berlin. While in Berlin he was teaching courses on performance evaluation and computer networking at the Technical University Berlin. He is editor-in-chief of the IEEE Communications Surveys and Tutorials and has served on the Technical Program Committees of IEEE Infocom, IEEE Globecom, and the IEEE International Symposium on Computer and Communications. He has organized sessions at the IEEE Computer Communications Workshop (CCW). He maintains an extensive library of video traces for network performance evaluation, including frame size traces of MPEG-4 and H.263 encoded video, at . He is co-recipient of the Best Paper Award of the SPIE Photonics East 2000 – Terabit Optical Networking conference. His research interests are in the areas of Internet Quality of Service, video traffic characterization, wireless networking, and optical networking.     

基于不均匀系数的水环境容量计算方法探讨

基于不均匀系数的水环境容量计算方法 ,以及混合区的概念及其允许范围 ,提出不均匀系数求解思路 ,并应用二维水量、水质数学模型进行求解。着重探讨不均匀系数的取值范围。作为实例 ,对广东鉴江非感潮河流 ,选取河宽为最重要因素来表征河流大小 ,求其不均匀系数。     

Spin glass state in high-temperature superconductors

The glass state of high-temperature superconductors in the models of Josephson weak links is studied. Reversibility phenomena in weak magnetic fields are outlined.     

一些组合三角的生成递推式

本文通过对递推式 R(λ,μ)=R(λ-1,μ)+R(λ,μ-1)的研究重新得到杨辉三角、双进组合三角;发现了又一种新的组合三角——非对称双进组合三角;利用非对称双进组合三角,简化了不定积分dx/sln~mxcos~nx(m,n 是奇正整数)的计算并初等地推导出二项式级数1,2,……)。     

Priority-oriented reservation multiple access scheme for data communication through satellites

A multi-access scheme is proposed for handling priority-based messages in data communication systems through satellites. The different schemes by which time slots are alloted by the satellite are based on a ‘priority index’. The performance characteristics of the system using these schemes under different traffic conditions are discussed.     

Taxonomy of parallel processing and definitions

This paper presents a simple taxonomy for the interconnected computer systems by using the address space or buffer type as the key identifying element. The main aim of this classification is to distinguish the major difference between multicomputer and multiprocessor systems and to derive the definitions for the same.