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.

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.

Phase control of gain and dispersion in an open V-type system

The control role of the relative phase between the probe and driving fields on gain, dispersion and populations in an open V-type three-level system with spontaneously generated coherence is studied. The result shows that by adjusting the value of the relative phase, the transformation between lasing with inversion and lasing without inversion (LWI) can be realized and high dispersion (refractive index) without absorption can be obtained. The shape and value range of the dispersion curve are similar to those of the gain curve, and this similarity is closely related to the relative phase. The effects of the atomic exit and injection rates and the incoherent pump rate on the control role of the relative phase are also analysed. It is found easier to get LWI by adjusting the value of the relative phase using the open system rather than the closed system, and using an incoherent pump rather than without using the incoherent pump. Moreover the open system can give a larger LWI gain than the closed system.

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。

Measurement of the wavefront of a laser diode system for intersatellite communication by a Jamin double-shearing interferometer

The frame of a laser diode transmitter for intersatellite communication is concisely introduced. A simple, novel and visual method for measuring the diffraction-limited wavefront of the transmitter by a Jamin double-shearing interferometer is proposed. To verify the validity of the measurement, the far-field divergence of beam is additionally rigorously analysed in terms of the Fraunhofer diffraction. The measurement, the necessary analyses and discussion are given in detail. By directly measuring the fringe widths and quantitatively interpreting the interference fringes, the minimum detectable wavefront height (DWH) of the wavefront is only 0.2 gimel (the distance between the perfect plane wavefront and the actual wavefront at the transmitting aperture) and the corresponding divergence is only 65.84 mu rad. This indicates that the wavefront approaches the diffraction-limited condition. The results show that this interferometer is a powerful tool for testing the semiconductor laser beam's wavefront, especially the diffraction-limited wavefront.

Double-cladding Yb3+ fiber for free-space optical communication

The experiment result of Nd:YVO4 laser pumped by laser diode that was amplified by double-cladding Yb3+ fiber is reported. Stable mode-locking pulses are obtained at repetition rate of 320 MHz and the output power is 15 mW. When laser power is amplified by Yb3+- doped double-cladding fiber amplifier, its power can get to 600 mW. Based on these, experiment of double-frequency is carried out, and green laser with power of 4 mW is obtained. (c) 2007 Wiley Periodicals, Inc.