论流体运动稳定性理论的两种方法

<正> 流体运动稳定问题是流体力学理论中的一个重要课题。它以研究层流如何转变为湍流为主要目的。近一个世纪以来,理论和实验已取得很大进展,但距离最后解决问题还很远。Lin和Chandrasekhar总结了早期用简正模法研究的结果。最近,Joseph,Drazin和Reid作了进一步综述,特别总结了近年来非线性稳定理论的进展。Swinney所编《流体运动不稳定和湍流的发生》对这一研究领域最新结果作了全面评述。

有关压力传感器动态校准和动态性能评价的几个问题

在本文中,作者根据简单的线性系统分析和实践中的体会,对压力传感器的动态校准和动态性能的评价提出下列几点看法:(1)阶跃压力是较理想的动态校准压力源;激波管可以作为标准动态压力标准装置(微压传感器除外)。(2)压力传感器的主要动态性能指标为:上升时间、超调量、振荡频率或谐振频率、冲击加速度灵敏度。(3)压力传感器的校准可采用静态校准和动态校准相结合的方法,没有必要在整个量程范围内进行动态校准。用“动态灵敏度”来概括压力传感器的动态性能是不确切的。

应力波在线性磁滞体中的衰减

通过对爆炸在岩石中产生的应力波的物理分析,判断岩石应力应变关系的磁滞效应可能是应力波在岩石中衰减的主要物理机制.在线性磁滞模型下,用拉氏变换和渐近展开方法,求得应力波传播的解析解.特别是得到了应力波头以方式衰减的应力波的特解.这种解所具有的一系列特性(波形自相似,波形特征,走时和半衰期的关系,动力学和运动学参量的峰值等)与实践观测结果及已有经验公式有相当好的一致性.并表明衰减指数l仅由磁滞参数α和参数Q确定,Q为无量纲应力波头导数的绝对值.因此,这个模型可作为进一步分析物理机制和建立经验公式的基础.

On the unstable stacking criterion for ideal and cracked copper-crystals

The unstable stacking criteria for an ideal copper crystal under homogeneous shearing and for a cracked copper crystal under pure mode II loading are analysed. For the ideal crystal under homogeneous shearing, the unstable stacking energy gamma(us) defined by Rice in 1992 results from shear with no relaxation in the direction normal to the slip plane. For the relaxed shear configuration, the critical condition for unstable stacking does not correspond to the relative displacement Delta = b(p)/2, where b(p) is the Burgers vector magnitude of the Shockley partial dislocation, but to the maximum shear stress. Based on this result, the unstable stacking energy Gamma(us) is defined for the relaxed lattice. For the cracked crystal under pure mode II loading, the dislocation configuration corresponding to Delta = b(p)/2 is a stable state and no instability occurs during the process of dislocation nucleation. The instability takes place at approximately Delta = 3b(p)/4. An unstable stacking energy Pi(us) is defined which corresponds to the unstable stacking state at which the dislocation emission takes place. A molecular dynamics method is applied to study this in an atomistic model and the results verify the analysis above.

Energy conversions and storage caused by an unsteady poloidal flow in active solar regions

In this paper we discuss coupling processes between a magnetic field and an unsteady plasma motion, and analyze the features of energy storage and conversions in active region. It is pointed out that the static force-free field is insufficient for a discussion of storage processes, and also the pure unsteady plasma rotation is not a perfect approach. In order to analyze the energy storage, we must consider the addition of poloidal plasma motion. The paper shows that because the unsteady poloidal flow is added and coupling occurs between the magnetic field and both the toroidal and the poloidal plasma flows, an unsteady process is maintained which changes the force-free factor with time. Hence, the energy in the lower levels can be transferred to the upper levels, and a considerable energy can be stored in the active region. Finally, another storage process is given which is due to the pure poloidal flow. The article shows that even if there is no twisted magnetic line of force, the energy in the lower levels may still be transferred to the upper levels and stored there.

“十一五”水动力学发展规划的建议

水动力学是流体力学的一个重要分支，有着悠久的研究与发展历史，形成了比较完整的学科体系．进入21世纪以来，资源开发、环境保护、国家安全已成为世界各国普遍关注的战略问题．我国的海防建设、海洋资源开发与海洋空间利用、海岸带综合规划和水环境保护、水资源开发与利用等为水动力学研究提出了新的迫切需求．本文阐述了水动力学研究的国家需求、国内外水动力学研究的现状和发展趋势，提出了近期有待研究的主要科学问题．

Adiabatic shear localization: occurrence, theories, and applications

郭永怀先生诞辰九十周年纪念文集

目录

燃烧物理学基础

整合素-ICAM-1相互作用的二维反应动力学研究

国家自然科学基金项目(30730032)

Diffraction integral formulas of the pulsed wave field in the temporal domain

To resolve the diffraction problems of the pulsed wave field directly in the temporal domain, we extend the Rayleigh diffraction integrals to the temporal domain and then discuss the approximation condition of this diffraction formula. (C) 1997 Optical Society of America.

关于X射线同轴位相衬度成像的研究(英文)

利用模糊函数对部分相干源相X射线衬成像进行了详细的理论分析．列举了不同条件下的实验结果．通过与吸收成像相比较，相衬成像无疑对生物样品的内部结构有更高的对比度和可见度．

周期性极化铌酸锂晶体中半非共线型宽带光学参变放大理论研究

基于周期性极化铌酸锂晶体(PPLN)的准相位匹配光参变放大过程,通过倾斜周期极化铌酸锂晶体中极化域(极化光栅)一定角度,实现了介于共线匹配方式和非共线匹配方式之间的一种半非共线型准相位匹配方式,并以该匹配方式下的各光矢量几何关系得出相位匹配曲线,找到在特定抽运光和信号光波长下能获得宽带增益放大的周期极化长度。并研究其极化倾斜角度与温度特性。模拟计算表明,在合适的角度与温度条件下,该方式可以532 nm抽运光抽运的信号光在800 nm和1064 nm处均获得宽带光参变放大。

相位延迟器复合旋光器技术及其应用

提出了一种将相位延迟器复合为旋光器的技术，利用米勒矩阵对其原理与应用进行了分析。相位延迟器复合为旋光器时，将相位延迟器置于两块1／4波片之间，使两块1／4波片的快轴相互垂直且与相位延迟器的快轴分别成±45°角。利用相位延迟器复合为旋光器技术，可以将相位调制器转换为偏振方向调制器。实验验证了相位延迟器复合为旋光器和相位调制器转换为偏振方向调制器的可行性。