Modeling and design of an AC to DC converter

A step-up/down single-phase AC-to-DC power converter without current sensor is proposed to achieve high performance and simple control logic. The power converter adopts a front-end diode rectifier so that only one active switch is required. The familiar state-space averaging technique for discontinuous mode DC-to-DC power converters is extended to model the proposed AC-to-DC converter. Unlike the existing model, which is valid only for a very low frequency range, namely below line frequency, the proposed model is applicable up to half switching frequency. The design of the controller is detailed. Selected experimental results are presented to verify the proposed theory     

坦克红外特征控制技术评述

坦克红外特征控制对于提高坦克的战场生存能力具有重要意义。控制的主要方法有遮障、表面处理、外形技术、主动冷却、总体设计等。坦克红外特征的控制必须与其他波段，特别是射频波段的特性控制兼容。遮障和低发射率涂料是现役坦克红外特征控制的主要措施。而对未来的主战坦克，设计应是减少其系统特性的重要途径。     

超高速电流反馈集成运放电路与特性

介绍了超高速电流反馈集成运放电路结构，基本特性以及与电压反馈集成运放在性能上的差异。     

黑白电视机的电磁兼容设计

本文结合我厂μPC三片机的设计布局,探讨黑白电视机电路的电磁兼容设计。通过理论计算,提出中放屏蔽材料选择的理论依据。     

FD—TD在分析FSS中的应用

本文讨论了用FD TD分析FSS的有关问题,提出了一种适合于在任意入射角情况下分析FSS的有效吸收边界条件,分别以单层、双层FSS为例进行了计算.数值结果和矢量模式法、谱域法的结果非常一致.     

Synthesis and transition temperatures of liquid crystals incorporating a 1,4-tetrafluorophenylene unit

Two homologous series of mesogenic materials which incorporate a 1,4-tetrafluorophenylene moiety and a terminal cyano- or nitro-substituent have been synthesized by using palladiumcatalysed coupling procedures. The compounds exhibit nematic and/or smectic A phases.     

The Cubooctahedron Shape──A Suboptimal Cell Shape for 3－Dimensional Cellular System

ＴｈｅＣｕｂｏｏｃｔａｈｅｄｒｏｎＳｈａｐｅ──ＡＳｕｂｏｐｔｉｍａｌＣｅｌｌＳｈａｐｅｆｏｒ３－ＤｉｍｅｎｓｉｏｎａｌＣｅｌｌｕｌａｒＳｙｓｔｅｍＣｈａＧｕａｎｇｍｉｎｇ；ＬｉＺｈｅｎｇｍａｏ；ＬｕＦａｎ（ＵｎｉｖｅｒｓｉｔｙｏｆＥｌｅｃｔｒｏｎｉ...     

厚膜导体的金属迁移研究

金属迁移能导致混合微电路发生灾难性失效。本文介绍一种简单易行的测试方法－水滴试验法，来测量厚膜电路的实际金属迁移率。用引方法测量时，发现Ｐｄ－Ａｇ导体的迁移率最大，Ｐｔ－Ａｕ导体的金属迁移率最小。     

Attenuation predictions at extremely low frequencies formeasurement-while-drilling electromagnetic telemetry system

Extremely low frequencies (ELFs) are employed to transmit data from underground to the ground surface in the measurement-while-drilling electromagnetic (MWD-EM) telemetry system. Based on electromagnetic field theory, the present work is aimed at predicting the receivability of the signals at the surface. A unified analytic method that is suitable for vertical, directional, or horizontal wells is presented. Attenuation properties are examined for various parameters, including the Earth's conductivity, operating frequency and the length of the drill string. The frequency dependence of the receivability in reference to a noise level is illustrated for different depths of well and different cases. It is also demonstrated that the electric field distributions at the surface have the same features for the three types of well, and that the measurements should be carried out near the well heads for any type of well. A scale model experiment is made to test the authors' theoretical results. The measured data and the computed results are comparable