水平大气中横向风对自适应光学系统性能的影响

从理论上分析了光波在水平大气中传播时传播路径上的横向风对理想补偿系统和时间带宽 有限的自适应光学系统性能的影响,得到了自适应光学系统的Strehl比与横向风速之间关系的解析表达式,并据此得到了一批计算结果。这些结果表明横向风对自适应光学系统的补偿功能有很严重的影响，随着横向风速的增大，系统的Strehl比迅速降低。特别是对于一定接收口径的系统，当横向风速超过一定的阈值后，加了补偿的光波的成像效果比不加补偿的光波的成像效果更差。结合大气湍流的物理结构仔细分析了这种现象，并对这种现象作出了合理的解释。

太阳耀斑的运动学无力场储能机制

本文同时求解无力场方程和磁感应方程,假设无力场的磁通量管具有细长体的位形,可对半径r展开。等离子体的运动使得初始的势场演变为有电流分布的无力场,将流体的动能转变为磁场的磁能储存在磁力线管里。本文的结果,可以用来研究太阳耀斑的储能过程,在一天左右的时间内可储存10~(32)erg的能量,提供太阳耀斑爆发的需要。

Thermal stress wave and spallation induced by an electron beam

Thermal stress wave and spallation in aluminium alloy exposed to a high fluency and low energy electron beams are studied theoretically. A simple model for the study of energy deposition of electrons in materials is presented on the basis of some empirical formulae. Under the stress wave induced by energy deposition, microcracks and/or microvoids may appear in target materials, and in this case, the inelastic volume deformation should not vanish. The viscoplastic model proposed by Bodner and Partom with corresponding Gurson's yield function requires modification for this situation. The new constitutive model contains a scalar field variable description of the material damage which is taken as the void volume fraction of the polycrystalline material. Incorporation of the damage parameter permits description of rate-dependent, compressible, inelastic deformation and ductile fracture. The melting phenomenon has been observed in the experiment, therefore one needs to take into account the melting process in the intermediate energy deposition range. A three-phase equation of state used in the paper provides a more detailed and thermodynamical description of metals, particularly, in the melting region. The computational results based on the suggested model are compared with the experimental test for aluminium alloy, which is subjected to a pulsed electron beam with high fluency and low energy. (C) 1997 Elsevier Science Ltd.

On the non-linear stability theory of spinning solid bodies with liquid-filled cavities and its application to the columbus problem

In this paper, we first present a system of differential-integral equations for the largedisturbance to the general case that any arbitrarily shaped solid body with a cavity contain-ing viscous liquid rotates uniformly around the principal axis of inertia, and then develop aweakly non-linear stability theory by the Lyapunov direct approach. Applying this theoryto the Columbus problem, we have proved the consistency between the theory and Kelvin'sexperiments.

流体力学与国土安全

国土安全涉及到流体力学的广泛应用,并为其研究发展提供了诸多机遇.本评论选择列举了流体力学在反恐领域的各类课题,还建议了今后的研究方向.课题范围从防备、遏制策划中的恐怖袭击,一直到探测、应对和恢复.具体的内容则包括飞机加固,爆炸缓冲,传感器取样,爆炸物探测,微流控和芯片实验室,城市环境中化学羽流弥散以及建筑物通风等.此外,本文还讨论了蒸气羽流与远距探测,非致命武器,疾病空气传播,人员防护装备以及污染移除问题.涉及这类的应用,要求流体力学家跨越传统领域的边界,进行交叉学科研究,特别是要结合化学、生物学、气溶胶学与大气科学协同工作.

Teoría de las tres dimensiones del Desarrollo Sostenible

Actualmente existen múltiples interpretaciones del concepto de desarrollo sostenible, y muchas de ellas coinciden en que para lograrlo, las medidas a poner en marcha deberán ser económicamente viables, respetar el medio ambiente y ser socialmente equitativas. Pero a pesar de este reconocimiento de la necesidad de una interpretación integrada de estas tres dimensiones, en la práctica es necesario un cambio sustancial del enfoque de las políticas y programas en vigor.

基于强激光辐照固体锡靶产生极紫外光源的实验研究

建立了一套利用高功率YAG激光器辐照固体锡靶产生高转换效率极紫外光(extreme ultraviolet)源的实验装置.利用建立的实验装置开展了极紫外光源的强度和转换效率与抽运激光强度关系的实验研究,发现极紫外光源的转换效率随抽运激光强度的变化具有饱和效应.实验发现:当抽运激光能量达到250mJ时,极紫外光源的转换效率最高,波长为13.5nm处0.27nm带宽范围内的极紫外光源的能量转换效率为1.6%,此时对应的激光强度为1.8×1011W/cm2.