SF_6断路器喷口形状尺寸对烧蚀的影响及喷口设计方法探讨

本文着重分析了断路器喷口的形状尺寸,喷口内气动参数对其烧蚀的影响。根据喷口的经验数据和气流场的计算公式,总结出断路器喷口设计的估算方法。     

On the One-Step-Bracket-Generating Motion Planning Problem

We consider the general motion planning problem for a sub-Riemannian metric with one-step bracket-generating distribution. Our results generalize earlier results in the corank-one case. Mostly, we completely solve the problem in generic situation for corank smaller or equal to 3. Our results are constructive: we explicitly construct the asymptotically optimal solutions.2000 Mathematics Subject Classification. 53C17, 53C99, 93B29.The second author was partially supported by the Russian Foundation for Basic Research (project No. 0201099) and UR 03099.     

Simulation model for sizing of stand-alone solar PV system with interconnected array

Solar PV arrays made of interconnected modules are comparatively less susceptible to shadow problem and power degradation resulting from the aging of solar cells. This paper presents a simulation model for the sizing of stand-alone solar PV systems with interconnected arrays. It considers the electricity generation in the array and its storage in the battery bank serving the fluctuating load demand. The loss of power supply probability (LPSP) is used to connote the risk of not satisfying the load demand. The non-tracking (e.g., fixed and tilted) and single-axis tracking aperture arrays having cross-connected modules of single crystalline silicon solar cells in a (6×6) modular configuration are considered. The simulation results are illustrated with the help of a numerical example wherein the load demand is assumed to follow uniform probabilistic distribution. For a given load, the numbers of solar PV modules and batteries corresponding to zero values of LPSP on diurnal basis during the year round cycle of operation are presented. The results corresponding to the surplus and deficit of energy as a function of LPSP are also presented and discussed to assess the engineering design trade offs in the system components.Furthermore, a simple cost analysis has also been carried out, which indicates that for Delhi the stand-alone solar PV systems with fixed and tilted aperture arrays are better option than those with single-axis tracking aperture (with north–south oriented tracking axis) arrays.     

Constructal design of forced convection cooled microchannel heat sinks and heat exchangers

Heat transfer from arrays of circular and non-circular ducts subject to finite volume and constant pressure drop constraints is examined. It is shown that the optimal duct dimension is independent of the array structure and hence represents an optimal construction element. Solutions are presented for the optimal duct dimensions and maximum heat transfer per unit volume for the parallel plate channel, rectangular channel, elliptic duct, circular duct, polygonal ducts, and triangular ducts. Approximate analytical results show that the optimal shape is the isosceles right triangle and square duct due to their ability to provide the most efficient packing in a fixed volume. Whereas a more exact analysis reveals that the parallel plate channel array is in fact the superior system. An approximate relationship is developed which is very nearly a universal solution for any duct shape in terms of the Bejan number and duct aspect ratio. Finally, validation of the relationships is provided using exact results from the open literature.     

WINDOWS的容错能力浅析

Windows操作系统中支持的几种容错方法以及它们各自的特点和相互的差别。对于系统的恢复和数据的安全提供了良好的方法。     

On-site measurement of the performance of crystalline silicon PV arrays

A procedure for determining the rated power of crystalline silicon photovoltaic arrays from on-site measurements in the field is described. It is the outcome of several years' experience in the testing of European pilot and demonstration plants and has formed the basis of an IEC draft standard on the subject. The procedure differs significantly from that followed when measuring the rated performance of solar cells and modules. The reasons for these differences are explained.     

Costas序列在雷达信号设计中的应用研究

阐述了Costas序列的代数结构及其特点,分析了常用雷达信号,如线性调频脉冲信号、非线性调频脉冲信号等的模糊函数,文中指出当雷达信号使用Costas序列的构成方法形成跳频扩频的信号时,将获得理想的模糊函数性能,即同时获得极好的距离分辨率和速度分辨率。文中建立了多目标散射、多径衰落和加性高斯白噪声信道的数学模型,并介绍了多目标散射、多径衰落和加性高斯白噪声信道的雷达信号设计方法,最后给出了计算机仿真结果。     

Summary of HgCdTe 2D array technology in the U.K.

HgCdTe 2D arrays are needed in both medium (MW) and long (LW) wavebands for imaging, search, and track and guidance applications. Often the detector is the performance-limiting component in the system, and it is necessary to use detectors with very low excess noise and few defective pixels. Normally the detector is cooled sufficiently to freeze-out thermally generated leakage currents, so the main interest is to understand the mechanisms that determine the general detector performance and the cause of defective pixels. This paper describes the detector technology and the ion beam junction-forming process. The fundamental performance limits of homojunction HgCdTe technology and the doping levels needed to produce a detector with impact-ionization limited performance are discussed. Extensive studies have been made on defective pixels in long wavelength arrays and some technologies for reducing them are described here. Defective pixels have been found to be associated with material dislocations crossing the p-n junction and a model has been proposed for the noise-generating mechanism.     

POWER CONSUMPTION IN MECHANICALLY AGITATED CONTACTORS USING PITCHED BLADED TURBINE IMPELLERS

Power consumption was measured in mechanically agitated contactors of internal diameter 0.3 m, 0.57 m, 1.0 m and 1.5 m. Tap water was used as a liquid in all the experiments. The impeller speed was varied in the range of 0.3-13.33 r/s. Three types of impellers, namely disc turbine (DT), pitched-blade downflow turbine (PTD) and pitched blade upflow turbine (PTU) were employed. The ratio of the impeller diameter to vessel diameter (D/T) and the ratio of impeller blade width to impeller diameter (W/D) were varied over a wide range. The effects of impeller clearance from the tank bottom (C), blade angle (φ), total liquid height (H/T), number of impeller blades (n_b) and blade thickness (t_b) were studied in detail. Power consumption was measured using a torque table

Power number was found to have a strong dependence on the flow pattern generated by the impeller. Unlike, DT and PTU, the power number of PTD was found to increase with a decrease in clearance. The PTD (T/3) was found to have the lowest power number in all the vessels and the power number increased with either a decrease or an increase in the impeller diameter from T/3. The dependence of power number on impeller diameter was found to be more prominent when the D/T ratio was more than 0.3. In general, the power number was found to increase with an increase in blade angle and blade width. The effect of blade width was found to be more prominent in larger diameter vessels. A correlation has been developed for power number in the case of PTD impellers.     

简易制导航弹非线性控制

针对简易制导航弹非线性模型,运用微分几何理论和现代控制思想,提出了一种分层控制方法,即将该模型分为质心层、速度层、姿态层和角速度层,使其具有仿射型特点,然后根据各层间的关系进行控制器设计.仿真结果表明,这种分层控制器较传统控制器具有更好控制品质,且实现简单,同时满足简易制导航弹低成本要求.