爆轰试验用新型射频连接器的结构设计

针对目前爆轰试验中使用的机械密封射频连接器存在的问题.设计了基于玻璃封接技术的新型密封射频连接器结构,并进行了射频反射补偿计算和强度分析.本项研究为爆轰条件下新型密封射频连接器的研制提供了设计依据.     

Impulse breakdown voltages of triggered multistage vacuum gap

Several sealed-off triggered vacuum gaps are connected in series to improve hold-off voltage. The characteristics of impulse breakdown voltage of these series-connected gaps are investigated experimentally. The sum hold-off voltage of series-connected gaps decreases to a unit hold-off voltage when the maximum value of voltage division ratio across the gaps increases to unity. Self-breakdown probability of the series-connected gaps is always higher than that of a single gap under the same conditions. Hence, stage efficiency of the multistage gap decreases with increasing number of stages. Its value is 90 percent with 2-stage gap and 75 percent with 5-stage gap, respectively, under the same voltage division ratio and the same gap length (2.0 mm) in each stage. Triggered breakdown voltage of 2- or 3- stage gap is several hundred volts when all gaps are triggered simultaneously at the peak of the main impulse wave and a working voltage range is nearly 100 percent in this case. The working voltage range decreases with number of stages. Its value is 45 percent with 3-stage gap and 15 percent with 5-stage gap, respectively, when one triggered gap is fired for switching.     

Zooplankton population in the river tigris: Effects of samarra impoundment

The influences of the Samarra impoundment on the ecology of the downstream sector of the river Tigris are investigated. Zooplankton were collected monthly from July 1987 to July 1988. It was found that zooplankton were most abundant during high river discharges in March. During the month of low river discharge, September, the zooplankton population was greatly reduced immediately below the barrage and remained so to the last downstream station. Several factors seem to explain such differences. The high discharge from the impoundment was found to be the dominating factor and may flush the small backwaters in which zooplankton were abundant, thus increasing the population in the river. Zooplankton species vary in their ability to sustain populations in the river, variations which are due mainly to species-specific characteristics.     

浅析上海市建筑防水材料近况

本文浅析了上海市建筑防水材料的生产、质量及应用情况,并对防水工程的发展提出了建议。     

Maximum power density for an endoreversible carnot heat engine

An analysis using maximum power-density criteria has been carried out for an endoreversible Carnot heat engine. The results have been compared with known results on maximum power analysis. The design parameters at maximum power density lead to smaller and more efficient endoreversible Carnot heat engines than those working at maximum power output.     

龙桥碾压混凝土双曲拱坝施工质量管理

龙桥水电站碾压混凝土双曲拱坝施工速度快,采取了一系列强化质量管理措施,施工质量优良,重点介绍质量管理的具体做法.     

创业家与企业家的相关内涵思辨

学术界和实践界对entrepreneur和entrepreneurship的内涵界定不清晰，缺少概念基础，从而限制了《创业学》的发展。分析了创业与创新的本质；区别了活跃在企业创立和成长阶段、致力于创造生产函数的创业家和扮演“权威”、致力于改变函数自变量的企业家；界定了在不同语境中创业家与企业家的含义。最后，强调了需要根据上下文来判断它们的内涵。     

Lyapunov‐stable discrete‐time model reference adaptive control

Discrete‐time model reference adaptive control (MRAC) is considered with both least squares and projection algorithm parameter identification. For both cases complete Lyapunov proofs are given for stability and convergence. The results extend the approach of Johansson (Int. J. Control 1989; 50 (3):859–869) to include Lyapunov stability for MRAC when the normalized projection algorithm is used for parameter identification. Copyright © 2005 John Wiley & Sons, Ltd.