改善再入通讯的化学减轻实验研究

化学减轻改善再入通讯是现实可行的技术途径,它是通过固体烧蚀和液体喷射的方法实现的。本文探讨化学减轻的机理和利用电弧风洞进行模拟实验研究的方法。实验是在H11DF电弧风洞中完成的,采用微波和探针两种诊断手段。通过大量实验确定了防热材料的烧蚀产物对流场电子密度和对电波传输的影响,以及喷射备种亲电子液体对流场电子密度的影响,为筛选防热材料及鉴定其性能提供依据。

用拉格朗日等参数单元计算应力强度因子

本文证明了在二次或三次拉格朗日等参数单元中,假使边上点和内节点移动适当的位置即可产生奇异性。在标准的拉格朗日等参单元中,使一边缩并成一点,成为三角形单元,再适当的选择边上点和内节点的位置,可以在单元的角点产生奇异性,因而,可以计算应力强度因子。在奇异元外面,适当移动边上点和内节点可以形成过渡元,可得到较精确的结果。通过几个例子表明,用这种奇异元,只要较少的单元数和节点数就能得到较精确的结果。

对振动弛豫方程的推广和讨论

<正> 一、引言 对振动弛豫方程,自1936年以来已作过广泛的研究,并在分析弛豫实验数据和研究包含弛豫过程的物理、力学现象中,得到广泛的应用。 文献中对包含简并振型的弛豫方程的使用,一直存在着含混之处。如文献[4,6,7]都在弛豫项前未加说明地引入了一些系数,这是无法理解的。又有不少人采用的是近似的甚至是包含着错误的弛豫方程。这都会对包括弛豫过程的一些物理、力学问题的理论分析带来显著的影响,并且会在处理和使用弛豫数据时造成混乱。

衍射问题的一个简化计算法

<正> 其中r为距离,k=2π/波长,c为波的傳播速度,t为时間,i=-1~(1/2).则可根据基尔霍夫公式把求任一点P的扰动的問題化为一个求面积分的問題。后来玛吉(Maggi),柯特勸(Kottler)等人又証明可把这面积分化为一个线积分,于是P点的扰动u为:

高压脉冲放电技术在金属裂纹止裂中的应用

如何产生高强度脉冲电流是应用电磁热效应遏制金属裂纹研究的一个关键问题.本文介绍了高压脉冲放电装置的工作原理;从理论上分析了充电电压、回路参数与放电电流幅值、放电周期之间的关系.在此基础上,自主设计、开发了一套高压脉冲放电装置.采用它对金属模具钢中裂纹进行了脉冲放电止裂实验.放电时裂纹尖端熔化形成堆焊和高压应力区,使裂纹尖端钝化,达到了止裂的目的.由于脉冲放电快速加热和冷却,在裂纹尖端处实现了冲击淬火,得到了超细化的隐晶马氏体和细粒碳化物等微观组织,提高了裂纹尖端处的硬度、强韧性和耐磨性,试验结果验证了该装置的有效性,本文的成果为采用电磁热效应对金属模具裂纹止裂提供了实验技术基础.

利用x射线激光干涉诊断等离子体电子密度

x射线激光探针干涉方法是诊断高温高密度激光等离子体电子密度等信息的重要工具．利用神光Ⅱ装置输出激光驱动的类镍-银x射线激光作为探针，成功地进行了马赫-曾德尔干涉法诊断实验，获得了清晰的包含等离子体信息的动态干涉条纹图像，并据此给出了待测C8H8等离子体临界面附近电子密度的空间分布。

Optimal feedback control of two-photon fluorescence in Coumarin 515 based on genetic algorithm

An optimal feedback control of two-photon fluorescence in the Coumarin 515 ethanol solution excited by shaping femtosecond laser pulses based on genetic algorithm is demonstrated experimentally. The two-photon fluorescence intensity can be enhanced by similar to 20%. Second harmonic generation frequency-resolved optical gating traces indicate that the optimal laser pulses are positive chirp, which are in favor of the effective population transfer of two-photon transitions. The dependence of the two-photon fluorescence signal on the laser pulse chirp is investigated to validate the theoretical model for the effective population transfer of two-photon transitions. The experimental results appear the potential applications in nonlinear spectroscopy and molecular physics. (c) 2005 Elsevier B.V. All rights reserved.

Formation of array microstructures on silicon by multibeam interfered ferntosecond laser pulses

We report on an optical interference method to fabricate array microstructures on the surface of silicon wafers by means of five-beam interference of femtosecond laser pulses. Optical microscope and scanning electron microscope observations revealed microstructures with micrometer-order were fabricated. The diffraction characteristics of the fabricated structures were evaluated. The present technique allows one-step realization of functional optoelectronic devices on silicon surface. (C) 2004 Elsevier B.V. All rights reserved.

Growth and spectral properties of Gd2SiO5 crystal codoped with Er and Yb

Gd2SiO5 (GSO) single crystal codoped with Yb3+ and Er3+ (Abbr. as Er:Yb:GSO) was successfully grown by the Czochralski (CZ) method for the first time and the spectral characteristics were investigated. The absorption and fluorescence spectra were measured. The emission lifetime of the I-4(13/2)-Er-level was measured to be 5.84ms and the emission cross-section at 1529nm was calculated to be 1.03 x 10(-20) cm(2). The results indicate that Er:Yb:GSO is a potential laser material at similar to 1. 55 mu m wavelength region. (c) 2006 Elsevier B.V. All rights reserved.