窄带中频数字接收机高速信号处理技术

窄带中频数字接收机在雷达对抗侦察中得到了广泛应用，其高速信号处理技术是目前研究的重点。本文详细介绍了数字雷达告警接收机高速信号处理技术的发展现状和关键技术，最后通过对该技术的全面分析指出了值得深入研究的领域。     

A randomized voltage vector switching scheme for three-level powerinverters

In this paper, a feasibility study of a randomized space vector switching scheme for three-level inverters is reported. Based on the traditional space vector concept for pulse width modulation (PWM) inverters, the sequence of the space vector is randomized in this scheme. The overall vector, resulting from the randomization, is mathematically identical to that of the traditional space vector. It has been found that the randomized scheme can effectively spread the switching noise over a wide frequency range and at the same time keep the steady-state link capacitor voltage balanced. The proposed scheme has been implemented in real time in a digital controller and its features have been experimentally confirmed     

转移法色交换

将图Ｇ的着色由一种变为中一种，通常用Ｋｅｍｐｅ法以交换。但是，对于某些情况，用此法无效。针对这个问题，本文提出了一种转移法色交换，它适用于平面图着色，方法直观，清晰且有效。     

高功率双工旋转场移相器

旋转场移相器具有移相精度高(均方根误差可小于1°)和温度稳定性好等特点,通过改进射频传输结构,可大大提高他的功率容量。利用旋转场移相器的互易特性和铁氧体圆极化器的非互易特性,设计出高功率双工旋转场移相器。其双工特性可将收/发信号分开,实现移相器和环行器的双重功能,用于天线的收发通道等场合时,可省去一个高功率环行器,结构紧凑。分析了双工旋转场移相器的工作原理,阐述了高功率应用下的设计方法,推导出了管状铁氧体的相移量计算公式,按此方法设计了实用的器件,并给出了试验数据。     

影响喷气燃料与橡胶相容性的因素

采用几种具有不同初始物理性能及不同丙烯腈含量、不同硫化剂和硫化程度的丁腈橡胶，考察了其配方和物理性能对采用不同工艺条件生产的喷气燃料的相容性。结果表明，喷气燃料与橡胶的相容性不仅与喷气燃料的加工工艺有关，而且与橡胶的组成及其制备工艺有关。采用非加氢工艺生产的喷气燃料与橡胶的相容性好于采用加氢工艺(特别是加氢裂化工艺)生产的喷气燃料。橡胶材料的初始力学性能的好坏并不完全决定其与喷气燃料相容性的好坏，橡胶材料的耐过氧化物侵蚀能力才是影响相容性好坏的主要因素。橡胶的组成和其制备工艺决定了橡胶在喷气燃料中萃取物的数量和组成，不同萃取物的综合作用给相容性带来不同程度的影响。用硫作硫化剂的橡胶虽然原始强度低于用过氧化物作硫化剂的橡胶，但前者与喷气燃料的相容性却远好于后者。     

Process and design analysis for ultrafine-pitched wiresweep elimination in advanced copper heat spreader BGA package

The semiconductor device trend for increasing functionalities and performances yet with smaller overall feature sizes presents escalating obstacles to the decreasing form factor along with demanding thermal carrying capability required at the package level. To confront this compounding issue, ultrafine-pitch wirebond interconnect coupled with thermally enhanced copper heat spreader attached to the package are introduced. However, the additional copper heat spreader thickness introduced within the package challenges the design of the package's wire, its loop height, and the molding process control to prevent wire sweeping occurrences. This study investigates the impact of different ultrafine pitched wire types, wire loop designs, copper heat spreader structures, and mold material types on eliminating device short from occurring due to the wire sweeping phenomena. A full factorial experiment is performed using an active silicon device packaged in a thermally enhanced ball grid array (BGA) test vehicle. In addition, test characterization is carried out using x-ray and multiinsertions hot/cold continuity tests. Then, a detailed failure analysis is performed by package decapsulation and scanning electron microscopy/energy-dispersive x-ray (SEM/EDX) to confirm the experimental findings. In conclusion, the study finds that for an ultrafine-pitched thermally enhanced BGA package, wire type is insignificant to reduce wire shorting occurrences. However, mold material and copper heat spreader structure using an optimized wire loop design are significant factors in eliminating wiresweep shorting phenomena. This study concludes with a wirebond interconnect and heat slug design recommended along with an improved process parameters and assembly material sets found from the experiment.     

Crystallite growth characteristics in superfine zirconia powders and compacts

Crystallite growth characteristics of coprecipitated superfine zirconia powders have been investigated. It was found that the crystallite growth in powders follows a cubic law at 800 and 1000°C; however, the crystallite size data for compacts of both Y-TZP and YSZ cannot be fitted with a traditional parabolic or cubic law, but with a linear relation between crystallite size and the logarithm of time. In addition, it was also found that the degree of agglomeration of the powders can affect the crystallite growth.     

关于多媒体和MCAI

阐述了推广应用多媒体计算机辅助教学(MCAI)方法,对目前高等教育行业缓解师资不足、提高教学效率、改善教学效果,尤其对促进教学手段的变革和教学的现代化管理,是一种行之有效的必然途径.