横流电激励CO_2激光器的二维饱和增益和输出功率

本文给出横流放电CO_2激光器中饱和增益系数的二维分布及其随辐射场的变化规律,用微观物理机制作了注释。用三种稳定振荡条件分别计算腔中的光强分布和输出功率,并予以评比,提供一种选择器件最佳设计方案的简便方法。

用自然三角形单元计算应力强度因子

<正> 用有限元法计算应力强度因子的各种奇异元中,由八节点或十二节点的四边形等参数单元所派生的奇异元最为简单,因为这种单元就是原有的等参数单元,无须程序变动,只要适当地改变裂纹顶点单元的边中点的坐标,就可使应变具有γ~(-1/2)的奇异性。这种单元是协调单元,满足收敛准则,当有人提出过渡单元概念以后,使计算结果更为精确,因此,这种单元是工程中广泛应用的一种计算应力强度因子的奇异元。与四边形等参数单元相应的一族单元是自然三角形单元。下面证明六节点的二次三角形单元和十节点的三次三角形单元,尽管它们的形状函数与上述四边形二次和三次单元通过一边收缩成一点而成的三角形单元的形状函数不同,但通过边上点取与上述等参数单元相同的位置,也可得到角点的应变具有γ~(-1/2)的奇异性。不同的是,对于六节点

小型跨声速高雷诺数实验装置

<正> (一)引言近代,随着大型飞行器的出现,飞行雷诺数大大提高;C-141飞机事件的出现更使跨声速下雷诺数效应问题成为设计先进飞机和导弹的主要问题.人们迫切需要寻找一种能实现高雷诺数的试验设备.七十年代初期,美国和北大西洋公约组织都成立了专门小组从事这项研究.从雷诺数的定义Re=ρul/μ知道,提高雷诺数有三个途径:增加模型尺度l;提高气体密

II Seminário nacional gays, lésbicas, bissexuais, travestis e transexuais : "compromisso com o respeito e a igualdade"

Seminário realizado em junho de 2005 pela Comissão de Legislação Participativa, em parceria com a Comissão de Direitos Humanos e Minorias, com a Comissão de Educação e Cultura e com a Frente Parlamentar Mista pela Livre Expressão Sexual.

纵场边值线性无力场解的唯一性

<正> 无作用力磁场在天体物理中有广泛的应用。用磁面函数讨论线性无力场,若无力因子α不等于本征值,给定纵场边值时有唯一的本征值解。文献[2]中用格林函数分析线性无力场时认为,纵场边值不能唯一确定问题的解。本文对此进行分析和讨论。

测量万瓦级CO_2激光器连续输出功率的鼠笼式能量计

<正>CO_2激光器连续输出功率可达数万瓦以上,运转时间短的仅几秒,一般的功率计很难兼顾承受高功率密度和响应时间快这两个要求.因此我们采用配有旋转盘衰减器的鼠笼式能量计进行测量.Baker给出,鼠笼能量计在不小于毫秒时间里最大可接收的能量密度为10焦耳/厘米~2.我们制作的74-6~#鼠笼能量计的实验表明,只要通过旋转盘衰减器的每个光脉冲满足上述要求,在重复频率为数十次/秒的连续光脉冲照射下,仍可实现测量.74-6~#已实测了3×10~4瓦CO_2激光器连续输出功率,它的最大功率密度已超过6×10~3

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.

Thermal-conductivity of periodic composite media with spherical inclusions

The thermal conductivity of periodic composite media with spherical inclusions embedded in a homogeneous matrix is discussed. Using Green's function, we show that the Rayleigh identity can be generalized to deal with the thermal properties of these systems. A technique for calculating effective thermal conductivities is proposed. Systems with cubic symmetries (including simple cubic, body centered cubic and face centered cubic symmetry) are investigated in detail, and useful formulae for evaluating effective thermal conductivities are derived.