~(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。

隋唐时期东中部地区温度变化的重建(601～920年)

根据史料对隋唐时期初终霜雪、春耕、山桃开花、秋收、海冰、柑橘种植北界等现象的记载,重建了公元601～920年的东中部地区温度变化.结果发现:隋唐时期,东中部地区的气候在总体上比较温暖,与1961～2000年相比,601～920年的冬半年平均温度高约0.22℃;其中,601～820年的冬半年平均气温比现在(1961～2000年,下同)高约0.52℃,821～920年时比现在低0.42℃左右;隋唐时期的冬半年温度存在显著波动,其在100,50,30和20年尺度上的最大变幅分别达到1.05,1.38,2.02和

Reconstructing temperature change in Central East China during 601-920 AD

Chinese Academy of Sciences [KZCX2-YW-Q1-01, KZCX2-YW-315]; National Natural Science Foundation of China [40625002]

表面应力调制的微流控技术的驱动原理

发展和优化对薄膜、液滴和气泡进行流动控制操作的多功能装置,要求深入了解界面现象和微流体动力学流动.表面积/体积的大比值和低雷诺数流动是此类系统的特点.毛细数和Bond数强烈地受边界效应影响,因而可以通过各种表面处理和表面力来进行控制.本文综述了运用调制法向或切向应力,对均匀的、带化学处理条纹及拓扑结构纹理表面上的微滴和液膜进行驱动的常用技术的基本原理.

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.