Co2+,Er3+:Y3Al5O12晶体的生长及其吸收特性

应用中频感应提拉法成功生长出新型的Co2+,Er3+:Y3Al5O12晶体.研究了室温下晶体的吸收光谱性能.结合Er3+:Y3Al5O12晶体的光谱,并利用调Q判据对Co2+,Er3+:Y3Al5O12晶体调Q特性进行了简单的分析.结果表明Co2+,Er3+:YAG晶体是一种很有潜力的自调Q激光晶体.     

Analysis and Optimization of the Energy Efficiency in the 802.11 DCF

This paper introduces an analytical model to investigate the energy efficiency of the IEEE 802.11 distributed coordinated function (DCF). This model not only accounts for the number of contending nodes, the contention window, but also the packet size, and the channel condition. Based on this model, we identify the tradeoff in choosing optimum parameters to optimize the energy efficiency of DCF in the error-prone environment. The effects of contention window and packet size on the energy efficiency are examined and compared for both DCF basic scheme and DCF with four-way handshaking. The maximum energy efficiency can be obtained by combining both the optimal packet size and optimal contention window. To validate our analysis, we have done extensive simulations in ns-2, and simulation results seem to match well with the presented analytical results. The Ohio Board of Regents Doctoral Enhancements Funds and the National Science Foundation under Grant CCR 0113361 have supported this work. Xiaodong Wang received his B.S. degree in communication engineering from Beijing Information Technical Institute of China in 1995, and his M.S. degree in electric engineering from Beijing University of Aeronautics and Astronautics of China in 1998. He joined China Telecom in 1998 where he worked on communication protocols for telecommunication. From June 2000 to July 2002, he worked on GSM base station software development at Bell-labs China, Beijing, China. Currently he is a Ph.D. student in Computer Engineering at University of Cincinnati. His research activities include wireless MAC protocols, energy saving for wireless sensor networks. He is a student member of the IEEE. Jun Yin received the BS degree in automatic control from Dalian Railway Institute of China in 1997, and the MS degree in flight control from Beijing University of Aeronautics and Astronautics of China in 2001. Since 2001 she has been a Ph.D. student in the OBR Research Center for Distributed and Mobile Computing at the University of Cincinnati. Her research interests include performance evaluation of 802.11 MAC protocol, wireless ad hoc networks and sensor networks. She is a student member of the IEEE. Dharma P.Agrawal IEEE Fellow, 1987; ACM Fellow, 1998; AAAS Fellow, 2003 Dr. Agrawal is the Ohio Board of Regents Distinguished Professor of Computer Science and Computer Engineering in the department of Electrical and Computer Engineering and Computer Science, University of Cincinnati, OH. He has been a faculty member at Wayne State University, (1977–1982) and North Carolina State University (1982–1998). He has been a consultant to the General Dynamics Land Systems Division, Battelle, Inc., and the U. S. Army. He has held visiting appointment at AIRMICS, Atlanta, GA, and the AT&T Advanced Communications Laboratory, Whippany, NJ. He has published a number of papers in the areas of Parallel System Architecture, Multi computer Networks, Routing Techniques, Parallelism Detection and Scheduling Techniques, Reliability of Real-Time Distributed Systems, Modeling of C-MOS Circuits, and Computer Arithmetic. His recent research interest includes energy efficient routing, information retrieval, and secured communication in ad hoc and sensor networks, effective handoff handling and multicasting in integrated wireless networks, interference analysis in piconets and routing in scatternet, use of smart directional antennas (multibeam) for enhanced QoS, Scheduling of periodic real-time applications and automatic load balancing in heterogeneous workstation environment. He has four approved patents and three patent filings in the area of wireless cellular networks.     

智能交通视频监控系统双向认证架构研究

随着城市智能交通系统和交通视频监控系统的发展,监控数据传输的安全性必将成为需要重视的问题。视频监测数据在采集和传输过程中可能受到篡改、泄露、窃听等安全威胁,研究一种提高交通视频监控系统数据安全性的方法能够有效解决这一问题。文章提出了一种基于可信模块的双向安全认证架构,不仅解决了用户和终端的身份认证,而且认证了服务器端的身份,有效提高了视频监控数据的安全性。     

Flexible and Highly Sensitive Pressure Sensors Based on Bionic Hierarchical Structures

The rational design of high‐performance flexible pressure sensors attracts attention because of the potential applications in wearable electronics and human–machine interfacing. For practical applications, pressure sensors with high sensitivity and low detection limit are desired. Here, ta simple process to fabricate high‐performance pressure sensors based on biomimetic hierarchical structures and highly conductive active membranes is presented. Aligned carbon nanotubes/graphene (ACNT/G) is used as the active material and microstructured polydimethylsiloxane (m‐PDMS) molded from natural leaves is used as the flexible matrix. The highly conductive ACNT/G films with unique coalescent structures, which are directly grown using chemical vapor deposition, can be conformably coated on the m‐PDMS films with hierarchical protuberances. Flexible ACNT/G pressure sensors are then constructed by putting two ACNT/G/PDMS films face to face with the orientation of the ACNTs in the two films perpendicular to each other. Due to the unique hierarchical structures of both the ACNT/G and m‐PDMS films, the obtained pressure sensors demonstrate high sensitivity (19.8 kPa^?1, <0.3 kPa), low detection limit (0.6 Pa), fast response time (<16.7 ms), low operating voltage (0.03 V), and excellent stability for more than 35 000 loading–unloading cycles, thus promising potential applications in wearable electronics.     

Coupling characteristics of high birefringence dual-core As2S3 rectangular lattice photonic crystal fiber

A type of As2S3 chalcogenide glass mid-infrared dual-core photonic crystal fiber has been proposed.The dualcore photonic crystal fiber(PCF) consists of two asymmetric cores.The high polarization property and the coupling characteristics have been studied by using the finite element method and mode coupling theory.Numerical results show that the birefringence at wavelength λ = 10 μm is up to 0.01386 and the coupling length can reach wavelength λ = 5 μm,261 μm and 271.44 μm for x-polarized mode and y-polarized mode,respectively.It demonstrates that a 6.786-mm-long fiber can exhibit an extinction ratio of better than 10 dB and a bandwidth of 180 nm.     

Ti<Superscript>3+</Superscript>-doped TiO<Subscript>2</Subscript> hollow sphere with mixed phases of anatase and rutile prepared by dual-frequency atmospheric pressure plasma jet

A novel method of synthesizing Ti³⁺-doped TiO₂ was proposed. Ti³⁺-doped TiO₂ hollow spheres were prepared with different thickness of carbon shell by using atmospheric pressure plasma jet generated by dual-frequency power sources. The as-synthesized Ti³⁺-doped TiO₂ hollow microspheres were characterized by X-ray diffraction (XRD) pattern, scanning electron microscope (SEM) images, high-resolution transmission electron microscopy (HRTEM) images, Raman spectra, X-ray photoelectron spectroscopy (XPS), and UV–vis spectra. These results indicated that these samples had mixed phases of anatase and rutile and the structure of hollow sphere varied with different thickness of carbon shell. The Ti-O-C chemical bond was the connection between the TiO₂ hollow sphere and carbon layer. Amount of Ti³⁺ ions were found, which were accompanied with the formation of oxygen vacancies. Meantime, the as-synthesized catalysts also display strong absorption in the visible light region and have a narrow band energy gap. Optical emission spectroscopy (OES) was used to observe different excited species in the discharge area. These results showed that the oxygen content had a significant impact on the number of oxygen vacancies. Finally, the photocatalytic activities of as-prepared samples were evaluated by decomposition of rhodamine B aqueous solution, which showed better photocatalytic activity under UV–vis light irradiation.     

红外单站被动定位技术速度更新算法研究

针对红外单站被动定位技术中空中机动目标的运动速度不断变化这一实际情况,提出了一种基于红外相机运动特性的对目标的运动速度进行实时更新的校正算法.该算法克服了大多基于匀速直线运动这一空间模型的红外单站被动定位方案目标速度不变的缺点,客观地反映了空中机动目标的实际运动状况,不仅能对目标的运动速度进行实时准确的更新校正,而且可推演出一种新的红外单站被动定位算法,对推动红外单站被动定位技术的工程实用化进程具有重要的意义.     

基于AHP-Entropy方法的科技成果转化绩效评价

科技成果的转化绩效优劣需要从多个层次、多个视角进行考核,本文从转化成果的经济效益、社会效益、环境效益和扩散效应等四个方面对科技成果转化绩效进行评价,评价体系的建立力求突出指标的精炼性和数据的可获性,借助AHP-Entropy方法并结合调查数据开展实证分析,阐述了评价方法的操作步骤且验证了评价体系的科学性和实践可行性。     

Parallel difference schemes with interface extrapolation terms for quasi-linear parabolic systems

In this paper some new parallel difference schemes with interface extrapolation terms for a quasi-linear parabolic system of equations are constructed. Two types of time extrapolations are proposed to give the interface values on the interface of sub-domains or the values adjacent to the interface points, so that the unconditional stable parallel schemes with the second accuracy are formed. Without assuming heuristically that the original boundary value problem has the unique smooth vector solution, the existence and uniqueness of the discrete vector solutions of the parallel difference schemes constructed are proved. Moreover the unconditional stability of the parallel difference schemes is justified in the sense of the continuous dependence of the discrete vector solution of the schemes on the discrete known data of the original problems in the discrete W2(2,1) (Q△) norms. Finally the convergence of the discrete vector solutions of the parallel difference schemes with interface extrapolation terms to the unique generalized solution of the original quasi-linear parabolic problem is proved. Numerical results are presented to show the good performance of the parallel schemes, including the unconditional stability, the second accuracy and the high parallelism.