LD泵浦Nd∶YVO4与Nd∶GdVO4腔内倍频绿光激光器的对比研究

报道了LD端面分别泵浦Nd∶YVO4、Nd∶GdVO4晶体,腔内Ⅱ类相位匹配KTP倍频的绿光激光器.通过对激光材料热透镜效应的分析,得出优化的谐振腔参数,在泵浦功率为6.1 W时得到的绿光激光器的光-光转化效率分别为15.5%、10.7%.从实验结果中,得到两种激光晶体的一些性能差异,为以后的研究提供一些参考.     

Transient Modeling and Analysis of Pulse-Width Modulated Z-Source Inverter

The newly proposed Z-Source inverter has been proven in the literature to exhibit both steady-state voltage buck and boost capabilities using a unique LC impedance network coupled between the power source and converter circuit. This paper now presents transient modeling and analysis of a voltage-type Z-source inverter. These aspects are found to be challenging and they need to be carefully investigated before attempting to design advanced control algorithms for controlling the Z-source inverter. Through detailed analysis, the paper identifies several phenomena on the dc and ac-sides of the inverter, which would result in the inverter having a non-minimum-phase transient response. The dc-side phenomenon is associated with the Z-source impedance network, which is shown through small-signal and signal-flow-graph analyses to be having a right-half-plane zero in its control-to-output transfer function. Also, the ac-side phenomenon is shown through space vector analysis to depend on the time intervals of inverter states used for reconstructing the desired inverter output voltage. Based on the ac vectorial analysis, a method for improving the inverter transient response is also presented. Last, simulation results obtained using a switching-functional model and experimental results obtained using a laboratory prototype are presented for validating the described theoretical concepts     

Field Measurements with a 5.25 GHz Broadband MIMO-OFDM Communication System

Theoretical capacity calculations and corresponding simulations show significant capacity/throughput gains from MIMO systems. Whether these gains are achievable in a real system, deployed in a practical environment, depends on a variety of factors, such as the choice of the communication algorithms, analog impairments and the "quality" of the wireless channel to sustain MEMO communications. In this paper, a 5.25 GHz broadband MIMO-OFDM testbed is described along with field measurements conducted with it. The MIMO-OFDM communication algorithms and also the impact of analog impairments on the performance of the system are described. Detailed system calibration results are described which serve as a baseline for results of field measurements. The results of wireless measurements are compared with the theoretical capacity, computed with the channel estimates obtained during the demodulation process. The average achievable capacity in the indoor wireless environment is shown to be 9.97 bps/Hz (bits per sec per Hz) while the capacity loss due to analog impairments and the choice of algorithms is about 2.33 bps/Hz. Also, field measurements conducted with the system in various environments are presented comparing the average throughput/capacity achieved in each of these environments.     

浅谈网络安全

介绍了网络建设中的安全问题 ,并从两个方面提出了相应的解决措施。     

Sensitivity and Coding of Opportunistic ALOHA in Sensor Networks with Mobile Access

We consider a distributed medium access protocol, Opportunistic ALOHA, for reachback in sensor networks with mobile access points (AP). We briefly discuss some properties of the protocol, like throughput and transmission control for an orthogonal CDMA physical layer. We then consider the incorporation of necessary side information like location into the transmission control and numerically demonstrate the loss in throughput in the absence of such information. Through simulations, we discuss the robustness and sensitivity of the protocol under various modeling errors and propose strategies to allow for errors in estimation of some parameters without reduction in the throughput. For networks, where the sensors are allowed to collaborate, we consider three coding schemes for reliable transmission: spreading code independent, spreading code dependent transmission and coding across sensors. These schemes are compared in terms of achievable rates and random coding error exponents. The coding across sensors scheme has comparable achievable rates to the spreading code dependent scheme, but requires the additional transmission of sensor ID. However, the scheme does not require the mobile AP to send data through the beacon unlike the other two schemes. The use of these coding schemes to overcome sensitivity is demonstrated through simulations. Parvathinathan Venkitasubramaniam was born in India in 1981. He received his B.Tech. degree from the department of Electrical Engineering, Indian Institute of Technology, Madras in 2002. He joined the School of Electrical and Computer Engineering, Cornell University, Ithaca, NY, in 2002 and he is working toward his Ph.D. degree. He is a recipient of the 2004 Leonard G. Abraham Award (with S. Adireddy and L. Tong) from the IEEE Communications Society. His research interests include random-access protocols,sensor networks, and information theory. Srihari Adireddy was born in India in 1977. He received the B.Tech. degree from the Department of Electrical Engineering, Indian Institute of Technology, Madras, and M.S. and Ph. D. degrees from the School of Electrical and Computer Engineering, Cornell University, Ithaca, NY in 2001 and 2003 respectively. Currently, he is working at Silicon Laboratories, Austin, TX. He is a recipient of the 2004 Leonard G. Abraham Award (with P. Venkitasubramaniam and L. Tong) from the IEEE Communications Society. His research interests include signal processing, information theory, and random-access protocols. Lang Tong received the B.E. degree from Tsinghua University, Beijing, China, in 1985, and M.S. and Ph.D. degrees in electrical engineering in 1987 and 1990, respectively, from the University of Notre Dame, Notre Dame, Indiana. He was a Postdoctoral Research Affiliate at the Information Systems Laboratory, Stanford University in 1991. Currently, he is a Professor in the School of Electrical and Computer Engineering, Cornell University, Ithaca, New York. Dr. Tong received Young Investigator Award rom the Office of Naval Research in 1996, and the Outstanding Young Author Award from the IEEE Circuits and Systems Society in 1991, the 2004 IEEE Signal Processing Society Best Paper Award (with M. Dong), the 2004 Leonard G. Abraham Prize Paper Award from the IEEE Communications Society (with P. Venkitasubramaniam and S. Adireddy). His areas of interest include statistical signal processing, adaptive receiver design for communication systems, signal processing for communication networks, and information theory.     

Moisture-induced failures of adhesive flip chip interconnects

Adhesive flip chip interconnect has been recognized as a promising substitute for solder interconnection due to its fine-pitch, lead-free, and low-temperature processing capabilities. As adhesives are made of polymers, moisture absorption by the polymeric resin remains as one of the principal contributors to adhesive joint failure mechanisms. In this research, the reliability performance of the adhesive flip chip in the pressure cooker test and moisture sensitivity test conditions was investigated. The failure modes were found to be interfacial delamination and bump/pad opening which may eventually lead to total loss of electrical contact. Different sizes of bump/pad opening in the interconnections were discussed in the context of the significance of mismatch in coefficient of moisture expansion (CME) between adhesive and other components in the package, which induces a hygroscopic swelling stress. The effect of moisture diffusion in the package and the CME mismatch were also evaluated from the standpoint of finite element modeling. In this study, it is concluded that hygroscopic swelling assisted by loss of adhesion strength upon moisture absorption is responsible for the moisture-induced failures in these adhesive flip chip interconnects.     

Improvement of pixel electrode circuit for active-matrix OLED by application of reversed-biased voltage

In this paper, an improved ac pixel electrode circuit for active-matrix organic light-emitting display (AMOLED) has been proposed by adding a thin-film transistor. This circuit can provide an ac driving mode for AMOLED and makes the OLED in a reversed-biased voltage during the reverse cycle. And a circuit design for understanding ac driving mode was presented. The circuit simulation results indicate that this circuit is feasible. The circuit structure is practical for the AMOLED pixel driver; it can improve the performance of OLED.     

一种自偏置低压共源共栅带隙基准电路设计

随着CMOS工艺的发展,器件尺寸逐渐缩小,短沟道效应的影响日益突出。共源共栅电流源可以很好地抑制小尺寸效应,但其消耗的电压余度较大,偏置电路设计繁琐。因此介绍了一种采用自偏置低压共源共栅电流源的带隙基准电路结构,用两个电阻代替了偏置电路。仿真结果显示,该带隙基准电路的最低电源电压约为2.98V,相对于普通的共源共栅结构,降低了2个MOSFET阈值电压;工作在最低电源电压下,功耗约为270μW,相对于带偏置电路的结构,降低约75μW。仿真结果证明,该电路能够简化共源共栅电路的设计和调试,并减少低压共源共栅电路的功耗。     

Joint channel and symbol estimation by oblique projections

The problem of simultaneous blind channel and symbol estimation of a single-input multiple-output (SIMO) communication channel is considered. It is shown that the outer product of the channel vector and the channel input sequence can be obtained by a linear estimator that has the finite sample convergence property. Furthermore, this estimator can be obtained by the use of oblique projections. An order detection algorithm that avoids the use of subjective thresholding is also proposed. Applications to multiuser detection are also considered     

含UPFC电力系统的潮流计算研究

柔性交流输电技术可灵活地控制和调节电力系统的运行状态;统一潮流控制器是ＦＡＣＴＳ的重要构成元件之一;为此着重介绍了含ＵＰＦＣ的电力系统潮流计算的数学模型和计算方法,并给出相应算例。