~(237)Th的半衰期测量

利用 6 0MeV/u的18O离子束轰击天然铀靶 ,通过多核子转移反应生成重丰中子核素2 37Th ,由多步快速放射化学分离方法从被照射过的靶物质中分离出钍元素。观测到了2 37Th的子体2 37Paγ活性的生长及衰变行为 ,确定了2 37Th的存在 ,测得其半衰期为 (4.6 9± 0 .6 0 )min。

重丰中子同位素~(237)Th半衰期的测定

用 60 Me V/u18O离子轰击天然铀靶 ,通过多核子转移反应产生重丰中子同位素 2 3 7Th。使用改进的相对快的分离钍的放射化学流程 ,从大量铀和复杂反应产物混合物中分离钍 ,用高纯锗( HPGe)探测器联同多道分析器对化学分离的钍样品做离线 γ射线谱学研究 ,通过对 2 37Th子体 2 37Pa(半衰期 8.7min)的 853.7ke Vγ射线的生长 -衰变曲线的分析 ,确定 2 37Th的半衰期为 4 .69± 0 .60min。

A rigorous analytical method for doubly periodic cylindrical inclusions under longitudinal shear and its application

An infinite elastic solid containing a doubly periodic parallelogrammic array of cylindrical inclusions under longitudinal shear is studied. A rigorous and effective analytical method for exact solution is developed by using Eshelby's equivalent inclusion concept integrated with the new results from the doubly quasi-periodic Riemann boundary value problems. Numerical results show the dependence of the stress concentrations in such heterogeneous materials on the periodic microstructure parameters. The overall longitudinal shear modulus of composites with periodic distributed fibers is also studied. Several problems of practical importance, such as those of doubly periodic holes or rigid inclusions, singly periodic inclusions and single inclusion, are solved or resolved as special cases. The present method can provide benchmark results for other numerical and approximate methods. (C) 2003 Elsevier Ltd. All rights reserved.

分子振动的局部模和键选择化学反应的可能性

<正> 1.前言 激光这门新技术由于它的高单色性和可调谐等特点,人们一直关注它在化学领域内的应用。同位素分离和键选择性激发化学反应是最引人住目的两个问题。一般的化学反应由于不足在分子水平上进行控制的,其进程遵从统计规律,因此往往伴随着产生许多并不需要的中间产物和能量的浪费。如果人们能在分子水平上控制化学反应,即拆开需要拆开的键,组合需要组合的键,那就不但可以使反应在低温条件下进行,而且可能合成某些预

星系密度波的线性增长

本文以线性密度波局部渐近解为初值,求解二维非定常流体力学方程组和泊松方程,研究星系密度波的线性增长.数值计算结果表明,线性密度波将在几千万年时间内增长到与基态同量级,形成在中心区域具有棒形结构的螺旋图样.螺旋结构的图样速度及扰动密度的增长率随空间位置及时间变化.讨论了准稳螺旋结构假设的近似性.

φ800激波管流场参数测量

<正> 1.实验装置和测量原理 本实验使用不锈钢圆形直激波管,高压段长1.6m,内径223mm;低压及实验段内径800mm。使用氢氧燃烧驱动,驱动压力约80ata,测量支架距膜片的有效距离为14m。 我们用薄膜电阻温度计式的金膜热探头在激波管中测量②区长度和波面形状,用电探针来测量分界区与③区的交界处。它们的信号直接或经过热电模拟线路以后,输

Experimental investigation on low-temperature fatigue crack propagation in offshore structural steel A131 under random sea ice loading

An apparatus of low-temperature controlling for fatigue experiments and its crack measuring system were developed and used for offshore structural steel A131 under conditions of both low temperature and random sea ice. The experimental procedures and data processing were described, and a universal random data processing software for FCP under spectrum loading was written. Many specific features of random ice-induced FCP which differed with constant amplitude FCP behaviours were proposed and temperature effect on ice-induced FCP was pointed out with an easily neglected aspect in designing for platforms in sea ice emphasized. In the end, differences of FCP behaviours between sea ice and ocean wave were presented.

Complex stress functions and plastic zone sizes for notch cracks subjected to various loading conditions

In this paper, the conformal mapping method is used to solve the plane problem of an infinite plate containing a central lip-shaped notch subjected to biaxial loading at a remote boundary or a surface uniform pressure on the notch. The stress intensity factors KI and KII are obtained by the derived complex stress functions. The simple analytical expressions can be applied to the situation of cracks originating from a circular or an elliptical notch. The plastic zone sizes for such notch cracks are subsequently evaluated in light of the Dugdale strip yield concept. The results are consistent with available numerical data.

求解运动方程的一种不等时间步长的显式数值积分方法

在波动有限元模拟中, 若采用传统的显式数值积分方法求解运动方程, 计算时间步长需采用计算区内满足稳定条件要求的最小时间步长. 然而, 对于大部分计算区域, 这一时间步长过小, 是不必要的. 本文提出了一种不等时间步长的显式数值积分方法, 其基本思想是不同的计算区域采用满足各自稳定条件的计算时间步长. 最后, 本文通过数值试验检验了这一方法的可行性及其对数值计算精度的影响.

可压缩轴对称射流三维拟序结构的演化

采用高精度差分方法对空间发展轴对称可压缩射流流场进行直接数值模拟，计算结果显示了射流失稳后首先出现Kelvin-Helmholtz非稳定特征，流动的进一步发展，非线性效应的增长导致轴对称涡环的二次失稳和流向涡的产生，并给出了拟序结构的三维演化过程，计算结果证实了轴对称射流中二闪失稳，流向涡的产生是增强流动混合及流动产生转捩的重要机制。

冲击载荷下饱和砂土渗流和破坏的实验研究

对饱和砂土在冲击载荷下发现的变形和流动效应进行了落锤模拟实验研究，发现砂土骨架出现纵向排水通道和横向断裂等现象，对可能影响这些现象的主要因素进行了对比的实验，对上述实验现象进行了初步的解释。

冲击载荷作用下容器壳体动态响应的初步数值研究

本文针对带椭球封头的爆炸容器,黑索今(RDX)在中心处的爆炸用点爆炸模型描述,利用四阶Runge-Kutta法求解一组常微分方程得到爆炸近场的自相似解。采用有限体积形式的PPM格式求解轴对称Euler方程,得到了容器内冲击波传播及其演化的图象。以计算得到的冲击载荷为基础,修改HONDO程序,壳体弹塑性模型采用J_2流动理论描述。对冲击波和壳体的耦合作用进行了初步的数值研究。计算结果表明:容器内爆炸冲击波和壳体中应力波的传播及其演化与物理上的定性分析结果是一致的。由于应力波传播速度较冲击波快,因此,在冲击波未到达的静止流场,流场出现扰动声波,并向中心传播。封头顶点附近出现最大变形。在中等载荷作用下,可忽略壳体变形对流场的影响。

Adiabatic shear localization: occurrence, theories, and applications