CO_2激光脉冲探测器

<正>在CO_2脉冲激光器件应用于工业加工时,影响加工质量的非常重要的参数是光脉冲波形,在放电脉冲激光器的物理机制及等离子体研究中也是如此.因此,激光脉冲波形测量就成为必不可少的一项工作.用碲镉汞探测器测光波波型是一种类型,但该器件要在低温下工作,设备复杂,制作困难,使用也不方便.另一种则是光子牵引探测器.我们试制成功了后一种探测器件.光子牵引探测器的原理是利用半导体P型锗在激光照射下发生的光子牵引作用,根据红外光作用于半导体P型锗单晶的价带间跃迁的吸收比带内跃迁吸收强得多,当CO_2激光器所产生的红外光对P型锗单晶

径向收缩等离子体层的运动不稳定性

本文根据雪铲模型讨论了收缩效应的不稳定性问题.首先导出了具有三个方向扰动的线性化扰动方程,再运用有限时间稳定性理论来判别运动的稳定性.结果麦明,无论是z-收缩还是θ-收缩,收缩过程都是不稳定的;在加上导体壁和轴向稳定磁埸以后,也不能使z-收缩完全稳定.其次指出,对于径向运动来说,稳定性条件不仅和加速度有关,也和速度等因素有关,因此,它和平面情形的Rayleigh-Taylor不稳定性是不同的.

曲线叶栅的绕流问题

<正> 关于一般叶栅的繞流問題,現有的許多解法,如格利克(Garrick,J.E.)、馬特波尔(Murterperl,W.)和波略霍夫()等法,都以直綫叶柵的繞流問題为基礎。这些方法有个共同缺点,就是当叶片弯度較大时,計算甚繁而不准确。針对这个缺点,本文給出一系列曲綫叶棚的准确解,所用的保角变換和一般直线叶柵的保角变换一样簡單,可用來代替上述各法中的直綫叶栅部分,使它們适合于弯度較大的叶片;因为变換簡單,同时又有四个参数,故可用來調整叶棚的稠度、柵角以及叶片的進出口角度。本方法可用來計算叶柵中叶片的相互位置和形狀,尤其是弯度对于叶栅性能的影响,同时这些准确解可用來鑑定渦旋分佈法所給曲线叶棚近似解的准确度。我們应当指出:本方法所給的曲緣叶柵当稠度較大时,棚角有一定限度,所以只适

Effects of g-jitter on the critical marangoni number

A half floating zone is fixed on a vibrational deck, which supports a periodical applied acceleration to simulate the effect of g-jitter. This paper deals with the effects of g-jitter on the fluid fields and the critical Marangoni number, which describes the transition from a forced oscillation of thermocapillary convection into an instability oscillatory convection in a liquid bridge of half floating zone with top rod heated. The responses of g-jitter field on the temperature profiles and flow pattern in the liquid bridge were obtained experimentally. The results indicated that the critical Marangoni number decreases with the increasing of g-jitter effect and is slightly smaller for higher frequency of g-jitter with fixed strength of applied gravity.

A discussion about a class of stress intensity factors and its verification

In this paper, new formulae of a class of stress intensity factors for an infinite plane with two collinear semi-infinite cracks are presented. The formulae differ from those gathered in several handbooks used all over the world. Some experiments and finite element calculations have been developed to verify the new formulae and the results have shown its reliability. Finally, the new formulae and the old are listed to show the differences between them.