短波发射机寄生振荡的危害及消除

本文主要论述短波发射机工作中,高频放大单元产生的寄生振荡,通过对其产生条件和存在形式的分析,结合短波发射机防振元器件及电路,对发射机工作中寄生振荡的产生、危害及其消除进行论述。     

一条“引线”让数学课堂升温

一条引线,可能是一个知识点,也可能是一个关键词等等,我们不要小瞧它,它价值连城,是我们了解知识整体的一个引子,一个催化剂.教师要拟出一条引线作为通向数学知识学习领地的船只,悠悠小船必定摆渡更多的学生,学生对知识的呼唤也定能让课堂升温.     

教师引线，学生穿针

在课堂教学中,教师应力求将知识点的产生、发展、应用,以及与其他知识点的关联等组成一条明确的路线,使学生通过自学质疑、合作探究,在老师的精讲点拨下,完成对数学知识的理解和掌握,学会自主学习,学会将数学知识“穿针”在一起,形成数学解题通法和数学知识体系。     

用打火机制作无电池打火器

电子打火器需要用电池供电,为什么打火机却不用电池供电呢？我好奇地拆开打火机,发现原来是打火机里有一块压电陶瓷,按压点火开关,引线就会放电,点燃燃气。于是我决定用打火机做一个打火器。制作图如右图,     

Application of nonlinear fatigue damage models in power electronic module wirebond structure under various amplitude loadings

This paper presents mean fatigue lifetime predic- tion of a wire-bond structure model in power electronic module using a failure physics approach that integrates high fidelity modelling and reduced order modelling. Loading current with variable amplitudes is applied to a finite element model of simplified wirebond structures. The resulting accumulated fatigue damage due to random loads is predicted by using reduced order modelling based on failure physics, a cycle counting algorithm, and various nonlinear fatigue damage models widely used in the literature. The reduced order mod- elling approach based on failure physics uses prediction data for the electro-thermo-mechanical behaviour of the wire-bond design of a power module obtained through non-linear transient finite element simulations, in particular for the fatigue life-time of the aluminium wire attached to the silicon chip of the wire in the module. The reduced order models that capture the black box function of the accumulated plastic strain are used in pre- dicting the mean fatigue life time of the wire bond structure under random loads. One of the widely used cycle counting algorithms, rainflow counting algorithm, is used to count cycles of the temperature profile at the specific point of the wire bond structure in a power electronic module. The cycle data from the rainflow algorithm mean life time of the wire bond structure are predicted with various cumulative fatigue models. Non-linear cumulative fatigue models such as damage curve approach （DCA）, double linear damage rule （DLDR）, and double dam- age curve approach （DDCA）, and linear cumulative fatigue damage model such as Palmgren-Miner rule are used to predict the mean fatigue life of the wire bond structure, and the results are compared.     

一道竞赛题的拓展及应用

近年来,国内外数学竞赛中出现了一类关于从三角形顶点向外引线段被一点或数点分成定比的问题,为了寻找解决这类问题的一般方法,本文先建立关于这类问题的一个模型,而后再举例说明这一模型的应用.     

礼花与人生——节日随想

元宵节是整个春节的最后一天,电是我在这个春节中最兴奋的一天,因为这一天给我留下了春节最美好的记忆。元宵节,我还像以前一样醒得很晚。窗外连续不断的鞭炮声让我再也睡不着了,干脆走到窗边看热     

纱布在中学生物实验中的妙用

纱布是生物实验室常用必备的实验用具之一,其用途多种多样。笔者归纳了7种用途,现总结如下。一、做酒精灯引线纱布是做酒精灯引线的好材料。将纱布剪成15cm×7cm的长方形或一端略宽的梯形卷起即可。纱布吸引酒精的能力强而持久,且火苗旺。酒精灯是生物实验的主要加热装置,有很多生物实验都需要水