理想塑性材料扩展裂纹顶端塑性区内应力场

扩展裂纹顶端弹塑性应力应变场分析是近年来断裂力学发展的重要课题。本文对弹性不可压缩的理想塑性材料中定常扩展裂纹顶端塑性区内的应力应变场进行了系统的数学分析,讨论了速度场和应力场的高阶渐近方程和解的形式,证实高阶渐近场依赖于塑性区和卸载弹性区交界线Γ_B的曲线方程。一旦Γ_3的曲线方程确定下来,高阶渐近场的解答就能确定下来。

磁流体管道中的高超声速流动特性

本文在磁雷诺数Rm=(VL/V_m)(?)1和磁作用参数N(?)1的情况下,讨论了连续磁场对可压导电介质在管道电极与绝缘体连接端面区高超声速流动的影响问题。用复变函数理论求解拉普拉斯方程,得出电流密度和洛伦茨力的解析式,并从计算中,找到了产生环电流的足够条件。导出高超声速流的扰动方程,得出扰动参量的积分公式,并对扰动方程进行数值解,揭示出与不可压介质相似的流动特性,并讨论了在各特殊点附近的流动特性。

太阳耀斑可能的储能过程

本文讨论了太阳活动区和黑子区的无力场的演化。文章分析了无力因子随时间变化的运动学含义,讨论了太阳耀斑具体的储能过程,给出了静力学无力场讨论太阳耀斑储能过程的局限性。最后,又提出了一种子午流场的储能过程。将这些“磁能的储存过程”与“适当的不稳定性导致的爆发过程”相结合起来讨论,就有可能来研究太北北阳耀斑的许多特征。

Water and salt movements in simultaneous flood-irrigation and well-drainage operations

This paper describes a new technology for solonchak soil reclamation in which surface flood irrigation of fresh water and pumped wells drainage of salty groundwater are combined. The comprehensive investigation of water and salt movement has been conducted through field test, laboratory simulation and numerical calculation. The dependence of desalination on irrigation water quantity, drainage quantity, leaching time and other parameters is obtained based on the field tests. The entire desalination process under the flood-irrigation and well-drainage operations was experimentally simulated in a vertical soil column. The water and salt movement has been numerically analysed for both the field and laboratory conditions. The present work indicates that this new technology can greatly improve the effects of desalination.

Study of the shock motion in a hypersonic shock system turbulent boundary-layer interaction

Wall pressure fluctuations and surface heat transfer signals have been measured in the hypersonic turbulent boundary layer over a number of compression-corner models. The distributions of the separation shock oscillation frequencies and periods have been calculated using a conditional sampling algorithm. In all cases the oscillation frequency distributions are of broad band, but the most probable frequencies are low. The VITA method is used for deducing large scale disturbances at the wall in the incoming boundary layer and the separated flow region. The results at present showed the existence of coherent structures in the two regions. The zero-cross frequencies of the large scale structures in the two regions are of the same order as that of the separation shock oscillation. The average amplitude of the large scale structures in the separated region is much higher than that in the incoming boundary layer. The length scale of the separation shock motion region is found to increase with the disturbance strength. The results show that the shock oscillation is of inherent nature in the shock wave/turbulent boundary layer interaction with separation. The shock oscillation is considered to be the consequence of the coherent structures in the separated region.

准定常强激波反射马赫杆突出变形准则的探讨

分析了滑移线延长线与楔面交点附近的流动特点,研究了准定常强激波反射中马赫杆的变形,建立了马赫杆突出变形消失的过渡准则,并用激波极曲线方法进行了求解.对马赫杆的变形过程进行了描述,研究了比热比、马赫数的变化对马赫杆突出变形消失条件的影响,并对突出变形消失区域与终点双马赫反射区域进行了比较.结果表明:马赫杆突出变形的消失是低比热比介质中出现的一种激波反射现象.马赫杆突出变形的消失,导致出现一种新的无射流、直马赫杆的双马赫反射结构.

Two-phase flow and pool boiling heat transfer in microgravity

Researches on two-phase flow and pool boiling heat transfer in microgravity, which included groundbased tests, flight experiments, and theoretical analyses, were conducted in the National Microgravity Laboratory/CAS. A semi-theoretical Weber number model was proposed to predict the slug-to-annular flow transition of two-phase gas–liquid flows in microgravity, while the influence of the initial bubble size on the bubble-to-slug flow transition was investigated numerically using the Monte Carlo method. Two-phase flow pattern maps in microgravity were obtained in the experiments both aboard the Russian space station Mir and aboard IL-76 reduced gravity airplane. Mini-scale modeling was also used to simulate the behavior of microgravity two-phase flow on the ground. Pressure drops of two-phase flow in microgravity were also measured experimentally and correlated successfully based on its characteristics. Two space experiments on pool boiling phenomena in microgravity were performed aboard the Chinese recoverable satellites. Steady pool boiling of R113 on a thin wire with a temperature-controlled heating method was studied aboard RS-22, while quasi-steady pool boiling of FC-72 on a plate was studied aboard SJ-8. Ground-based experiments were also performed both in normal gravity and in short-term microgravity in the drop tower Beijing. Only slight enhancement of heat transfer was observed in the wire case, while enhancement in low heat flux and deterioration in high heat flux were observed in the plate case. Lateral motions of vapor bubbles were observed before their departure in microgravity. The relationship between bubble behavior and heat transfer on plate was analyzed. A semi-theoretical model was also proposed for predicting the bubble departure diameter during pool boiling on wires. The results obtained here are intended to become a powerful aid for further investigation in the present discipline and development of two-phase systems for space applications.

钙质砂的胶结性及对力学性质影响的实验研究

对南海钙质砂进行了三轴实验研究, 重点针对不同胶结情况下的力学性质,如不同胶结材料和含量的变化对强度和应力应变特性的影响等.研究表明,钙质砂具有与陆源砂不同的性质,它的内摩擦角高达48°,远大于一般陆源砂的35°左右;在低围压下钙质砂表现出剪胀性,但随围压增加剪胀性降低;利用硅酸盐水泥作为胶结材料效果较好;随着水泥含量的增加,钙质砂试样的强度增加.

Spectral narrowing of negatively chirped femtosecond pulse by cross-phase modulation in a single-mode optical fiber

We demonstrate theoretically that the negatively chirped femtosecond laser pulse can be spectrally narrowed by cross-phase modulation. The new view is well Supported by numerical simulation. The negative chirp method in fibers might be useful in all optical wavelength switching applications. (c) 2005 Elsevier B.V. All rights reserved.

飞秒激光所致金纳米粒子析出的玻璃非线性吸收

依据Z-scan技术，使用波长532nm的纳秒脉冲，研究了通过聚焦的飞秒脉冲诱导并辅以热处理得到的金纳米粒子析出的玻璃的非线性吸收．观察到金纳米粒子析出的玻璃具有饱和吸收特性．根据局域场效应，对实验结果拟合，得到在接近表面等离子体共振激发情况下，金纳米粒子三阶极化率虚部分别为Imχm^(3)=5．7×10^-7esu．玻璃样品中金纳米粒子的非线性响应主要起源于热电子贡献。

激光二极管抽运的Yb：GSO连续锁模激光

作为发射在1μm波段的二极管抽运全固态激光器的增益介质，掺Yb离子的晶体备受关注。掺Yb晶体具有能级结构简单，量子缺陷低（〈0．1），量子效率高等优点。目前成功使用掺Yb的晶体作为增益介质的飞秒激光振荡器已有很多报道，如Yb：BOYSE，Yb：KYW，Yb：SYSE等。

掺铈硅酸钆闪烁晶体的研究进展与发展方向

本文综述了铈离子掺质硅酸钆(Ce：Gd2SiO5)闪烁晶体的结构、闪烁性能、闪烁机理及晶体生长的研究现状，重点讨论了Ce：GsO闪烁晶体生长的研究进展；提出了硅酸钆闪烁晶体未来研究发展的几个方向为：大尺寸晶体的生长、高光输出的研究、混合型硅酸钆晶体的研究等。

LBO晶体上ZrO2薄膜的显微结构和光学性质

用电子柬蒸发方法在三种不同取向的三硼酸锂（LiB3O3，简称LBO）晶体上沉积了ZrO2薄膜。采用分光光度计和X射线衍射技术对LBO晶体基底结构对薄膜光学性质和显微结构的影响进行了研究。实验结果表明：基底结构对薄膜的显微结构和光学性质具有明显影响，即X-LBO，Y-LBO和Z-LBO上沉积的ZrO3薄膜分别沿m（-212），m（021）和o（130）择优生长，且m（021）择优取向的ZrO3薄膜具有最高的折射率和最小的晶格不匹配。