详析接触电阻

接触电阻在实际电路中处处可见,并不陌生,但是全面、正确的解释接触电阻却不是一件容易的事情.在电磁学实验"低电阻的测量"中,尽管课本对接触电阻作了一些介绍,但是内容不太详尽,几乎每次实验都有一些学生表示疑惑.基于教学中遇到的问题,有必要对接触电阻作一详尽的分析.     

认识函数零点的三个视角

<正>函数的零点是函数与其他知识具有广泛联系的一个链接点,它从不同的角度,将数与形、函数与方程有机地联系在一起.函数的零点、方程的根、函数图象的交点,这三者之间形异质同,解题时往往需要灵活转化,因而函数的零点问题成为了近年来高考新的生长点与热点而备受青睐.笔者通过对近年来各地高考题与模考题的分析,总结了认识函数零     

大功率短波发射机风接点的改进

大功率发射机冷却取样回路中,使用风接点对风压进行采样,并送入控制和保护系统中。传统风接点鼓障率高,维护难度大,通过改进的新型风接点存在免维护、稳定性能好的优势。作者对发射机的冷却及新旧风接点的特点进行介绍,并示例说明了新型风接点的应用。     

Improving the Fatigue Performance of the Welded Joints of Ultra-Fine Grain Steel by Ultrasonic Peening

Contrast tests were carried out to study the fatigue performance of the butt joints treated by ultrasonic peening, aiming at the improvement of ultrasonic peening treatment(UPT) on welded joints of a new material. The material is a new generation of fine grain and high purity SS400 steel that has the same ingredients as the traditional low carbon steel. The specimens are in two different states:welded and ultrasonic peening conditions. The corresponding fatigue testing data were analyzed according to the regulation of the statistical method for fatigue life of the welded joints established by International Institute of Welding(IIW). Welding residual stress was considered in two different ways: the constant stress ratio R = 0.5 and the Ohta method. The nominalstress-number (σ-N) curves were corrected because of the different plate thickness compared to the standard and because there was no mismatch or angular deformation. The results indicated that: 1 ) Compared with the welded specimens, when the stress range was 200 MPa, the fatigue life of the SS400 steel specimens treated by ultrasonic peening is prolonged by over 58 times, and the fatigue strength FAT corresponding to 106 cycles is increased by about 66％; 2) As for the SS400 butt joint ( single side welding double sides molding) , after being treated by UPT, the nominal S-N curve (m = 10) of FAT 100 MPa(R =0.5) should be used for fatigue design. The standard S-N curves of FAT 100 MPa (R = 0.5, m = 10) could be used for fatigue design of the SS400 steel butt joints treated by ultrasonic peening.     

锅炉汽包水位保护系统的分析及改进

通过差压式与电接点式水位表的比较，对锅炉汽包水位测量与保护系统原理、误差及性能的分析，提出了汽包水位保护系统的改进方案，确保锅炉的安全稳定运行。     

恒温鼓风干燥箱温控电路改进

将恒温鼓风干燥箱温控装置由老式水银电接点式温控器改造成了新式的数显调节仪，收到了良好效果．     

论一种简单实用的通信告警集中监视系统

文章结合电力系统通信网操作管理维护的要求,利用通信设备告警继电器接点,给出一种简单、实用、经济的声光告警集中监视系统.     

搞好衔接 跨跃台阶──论高一物理教学中应注意的几个问题

针对初中物理教学向高中物理教学过渡过程中存在的主要问题，探寻解决好有关问题的途径和方法。通过作者多年的教学，抓住高一物理教学过程中存在的不足和弊端，剖析学生在认识上、思维上，对新知识的感知上存在的难点和弱点，提出了找好连接点，补好间断点，夯实基础，化大台阶为小台阶，滚动提高的基本思路和方法，提倡进一步密切师生关系，加强能力培养和素质教育，改善教学环境和管理机制。在教学实践中效果好，可操作性强，为广大从事高中物理教学的教师提供一个参考和借鉴。     

激活历史与现实的联系

历史学科是远离生活实践的学科，老师要善于寻找历史与现实的链接点。那么在教学中如何适时、适当、适量地激活历史与现实的联系？