黄河三门峡一花园口“82．8”大暴雨期间水汽输送分析

通过计算１９８２年７月２９日～８月２日黄河中游三门峡一花园口间区域的水汽通量、水汽通量散度和水汽净输送等特征量，分析了这次暴雨过程的水汽源地、水汽输送的物理过程和水汽净输送量与暴雨洪水的关系。结果表明，这次暴雨的水汽主要来自东部洋面上，低空偏东风急流和三花间地区的辐合上升运动共同构成了该地区水汽输送的通道，暴雨区内水汽的缔向福合是形成暴雨水汽福合的主要过程，水汽的经向辐散则是水汽输出的主要原因，而水汽的低层辐合、高层辐散及低层水汽向高层的垂直输送是降雨增强的机制。     

1981年8～9月黄河上游强连阴雨期水汽输送分析

对黄河上游兰州以上区域１９８１年８￣９月强连阴雨期主要降水时段水汽输送的计算和分析表明，这次降雨的水汽来自孟加拉湾，由５００ｈＰａ低槽前的西南气流输送水汽；降雨区内水汽的经向辐合是水汽辐合的主要过程，纬向辐散是水汽输出的主要机制，降雨中高原地形和垂直运动也明显影响了水汽输送和降雨；该区域水汽净输送量约占实测降雨量的９２％。     

Flux pattern and fouling of membranes during ultrafiltration of some dairy products

The flux pattern of milk (whole milk, skimmed milk and buttermilk) showed a distinct contrast to whey (sweet whey and acid casein whey) systems during ultrafiltration (UF) at constant composition. For milk systems, the initial flux was lower than for whey systems, but the flux stabilised within a few minutes of operation. However, for both acid and sweet whey, the flux continued to fall with time for nearly 1 h. The fouling coefficient (FC) for buttermilk was 0.6 after 5 min, rising to 0.68 after 60 min. During this time flux did not decline, suggesting that concentration polarisation (CP), rather than fouling, was controlling the flux rate. In contrast, the FC for whey was 0.5 after 5 min with a progressive rise over the next 55 min, but the flux also fell throughout this period suggesting that flux was controlled by fouling rather than CP. The higher concentration of protein in milk systems appeared to be responsible for CP, rather than fouling, being the controlling mechanism.     

Modeling and Analysis of On-Chip Single and H-tree Distributed RLC Interconnects

This paper presents novel methods for modeling and analysis of on-chip Single and H-tree distributed resistance inductance capacitance interconnects. The matrix pade-type approximation and scaling and squaring methods are employed for the numerical estimation of delay in single interconnect, and H-tree interconnects. The proposed models, which are based on these methods, provide rational function approximation for obtaining a passive interconnect model. Multiple single input single output model approximated transfer functions are developed for H-tree interconnects structure. With the equivalent reduced order lossy interconnect transfer functions, finite ramp responses are obtained, and line delay is estimated for various line lengths, input ramp rise times, source resistances, parasitic capacitances and load capacitances. In order to demonstrate the accuracy of proposed models, the estimated 50 % delay values are compared with the standard HSPICE W-element model and are found to be in good agreement. The proposed models worst case 50 % delay errors of single interconnect are 0.27 and 0.24 % respectively, while the worst case 50 % delay errors of H-tree structure are 5.73 and 3.94 % respectively.     

Internet telephony in India

Internet telephony is a novel and cheaper method of communication and conducting business over the Internet. The paper presents an overview of Internet telephony, its methods, viz. PC-to-PC, PC-to-telephone, telephone-to-telephone and telephone-to-PC; benefits in cost advantage, simplification, consolidation, higher efficiency and reliability, etc., quality issues, protocols and drivers; challenges and regulatory framework; and status of Internet telephony in Asia Pacific region. Further, highlights its potentiality for India, implications of guidelines of Internet telephony, issues of concern, etc. Concludes that Internet telephony cannot make compromises in voice quality, reliability, scalability and manageability, and work seamlessly with telephone systems all over the world. Internet telephony will prove to be a boon for a price-sensitive market like India and rural telephony will receive an impetus. The Government of India may further deregulate the market and allow phone-to-phone telephony through the Internet and open long distance calling within the country for ISPs to realize “telecom for the common man” or “telecom for all” a reality.     

Multiuser MIMO OFDM Based TDD/TDMA for Next Generation Wireless Communication Systems

Multiple-input multiple-output (MIMO) wireless technology in combination with orthogonal frequency division multiplexing (MIMO OFDM) is an attractive air-interface solution for next-generation wireless local area networks (WLANs), wireless metropolitan area networks (WMANs), and fourth-generation mobile cellular wireless systems. In this paper, one multiuser MIMO OFDM systems with TDD/TDMA was proposed for next-generation wireless mobile communications, i.e., TDD/TDMA 4G, which can avoid or alleviate the specific limitations of existing techniques designed for multiuser MIMO OFDM systems in broadband wireless mobile channel scenarios, i.e., bad performance and extreme complexity of multiuser detectors for rank-deficient multiuser MIMO OFDM systems with CDMA as access modes, extreme challenges of spatial MIMO channel estimators in rank-deficient MIMO OFDM systems, and exponential growth complexity of optimal sub-carrier allocations for OFDMA-based MIMO OFDM systems. Furthermore, inspired from the Steiner channel estimation method in multi-user CDMA uplink wireless channels, we proposed a new design scheme of training sequence in time domain to conduct channel estimation. Training sequences of different transmit antennas can be simply obtained by truncating the circular extension of one basic training sequence, and the pilot matrix assembled by these training sequences is one circular matrix with good reversibility. A novel eigenmode transmission was also given in this paper, and data symbols encoded by space–time codes can be steered to these eigenmodes similar to MIMO wireless communication systems with single-carrier transmission. At the same time,, an improved water-filling scheme was also described for determining the optimal transmit powers for orthogonal eigenmodes. The classical water-filling strategy is firstly adopted to determine the optimal power allocation and correspondent bit numbers for every eigenmode, followed by a residual power reallocation to further determine the additional bit numbers carried by every eigenmode. Compared with classical water-filling schemes, it can also obtain larger throughputs via residual power allocation. At last, three typical implementation schemes of multiuser MIMO OFDM with TDMA, CDMA and OFDMA, i.e., TDD/TDMA 4G, VSF-OFCDM and FuTURE B3G TDD, were tested by numerical simulations. Results indicated that the proposed multiuser MIMO OFDM system schemes with TDD/TDMA, i.e., TDD/TDMA 4G, can achieve comparable system performance and throughputs with low complexity and radio resource overhead to that of DoCoMo MIMO VSF-OFCDM and FuTURE B3G TDD.     

基于推挽式带伪直流母线拓扑的光伏逆变器设计

针对中小功率光伏并网发电系统的特点,在分析比较常用拓扑方案的基础上,采用推挽式带伪直流母线的拓扑结构作为光伏并网逆变器的主电路。文中重点阐述了主电路的工作原理和关键电路元件的参数设计,并对整流二极管的缓冲和工频逆变器的控制进行了相应的探讨。最后通过实验结果验证了理论分析的正确性。     

几种数据压缩算法的比较

对几种数据压缩算法进行了总结,并针对实验数据表对其压缩率进行了比较。     

Analytical expressions for intermodulation distortion of a MESFET small-signal amplifier using the nonlinear Volterra series

Using the nonlinear Volterra series representation, analytical expressions for the third-order intermodulation distortion power and intercept point for a MESFET small-signal amplifier are derived when its equivalent circuit is bilateral and includes the gate-to-drain capacitance (C_gd) explicitly as a nonlinear element. Previously developed analytical expressions treated C_gd as a linear element or incorporated it as a part of gate-to-source and drain-to-source capacitances (C_gs and C_ds). These new analytical expressions are then compared with experimental data and good agreement is obtained. The analytical expressions are also used to study the variation of intermodulation distortion with input power and frequency, and the effect of the individual nonlinear elements in the MESFET’s equivalent circuit.