北京自由电子激光最近进展──实现饱和振荡

北京自由电子激光(BFEL)装置于1993年底在10.68μm处实现了饱和振荡.输出激光能量为3mJ,饱和平顶宽度2μs.对应饱和振荡平均功率为210kW(宏脉冲),峰值功率约为20MW,比自发辐射高8个量级,单程小讯号净增益为24%,转换效率为0.45%,与理论预期结果相符.光束质量接近衍射极限.目前装置可工作于9-11μm.     

有序分组资料的线性趋势检验的确切概率计算

有序分组资料的线性趋势检验主要用于检验几个二项总体反应率的线性趋势；在医学与生物学中最典型的用途是研究剂量和反应的关系． 如果用Ｚ检验来代替通常在本检验中所用的卡方检验，就可容易地导出本检验的确切概率计算方法，和其他２×Ｃ有序列联表有着相同的形式．本文给出了该检验的确切概率计算方法．     

Limit distribution of the number of consecutive records

A succinct series expression is derived for describing the limit distribution of the number of times r consecutive elements are all records (in a sequence of independent and identically distributed random variables with a common continuous distribution) for all r ≥ 2. Previously, only the limit distributions for r = 1, 2, and 3 were known. © 2005 Wiley Periodicals, Inc. Random Struct. Alg., 2005     

Cd-Sn(0.2)-Zn三元合金高压相图的测定

 为了验证三元合金高压相图的计算结果，本文采用高压DTA方法，测定了Cd-Sn-Zn三元系中x_Sn=20 at.%截面的高压垂直截面相图，实验压力为0、0.5、1.0、1.5 GPa。测得的常压相图（p=0 GPa）中其液相线与H. J. Bray的实验结果完全相符，所得高压相图与常压相图比较，在p=1.5 GPa时低共晶点上移了大约35 K，共析组成向富锌端移动了大约8%。     

原伊鲁烷型倍半萜醇芳香酸酯的碳谱研究

作者自人工发酵得到的蜜环菌Armillaria mellea (Vahl.ex Fr.) Quel.菌丝体中分离出十七个原伊鲁烷型倍半萜醇芳香酸翻,在研究这些化合物的化学结构中,对其全去偶碳谱,偏共振谱或INEPT谱,C-H COSY谱和远程C-H COSY谱进行比较仔细地分析,指定了每个化合物各碳的归属,讨论了其碳谱的特征,并指出¹³C NMR谱是对新的该类型化合物结构测定的有效方法.     

Effects of barium on the nonlinear electrical characteristics and dielectric properties of SnO2-based varistors

The effects of barium on electrical and dielectric properties of the SnO_2·Co_2O_3·Ta_2O_5 varistor system sintered at 1250℃ for 60min were investigated. It is found that barium significantly improves the nonlinear properties. The breakdown electrical field increases from 378.0 to 2834.5V/mm, relative dielectric constant (at 1kHz) falls from 1206 to 161 and the resistivity (at 1kHz) rises from 60.3 to 1146.5kΩ·cm with an increase of BaCO_3 concentration from 0mol% to 1.00mol%. The sample with 1.00mol% barium has the best nonlinear electrical property and the highest nonlinear coefficient (α=29.2). A modified defect barrier model is introduced to illustrate the grain-boundary barrier formation of barium-doped SnO_{2}-based varistors.     

A Novel and Efficient Catalytic System for Aerobic Oxidative Coupling of 2-Naphthol Derivatives

The paper reported a novel and efficient aerobic oxidative coupling reaction of 2-naphthol derivatives catalyzed by CuCu (Ⅰ or Ⅱ)N-alkylimidazole complexes in excellent yields. The crystal structure of CuCu(Ⅱ)N-methylimidazole complex to be determined by X-Ray.     

A projection method for solving incompressible viscous flows on domains with moving boundaries

In this paper, a projection method is presented for solving the flow problems in domains with moving boundaries. In order to track the movement of the domain boundaries, arbitrary‐Lagrangian–Eulerian (ALE) co‐ordinates are used. The unsteady incompressible Navier–Stokes equations on the ALE co‐ordinates are solved by using a projection method developed in this paper. This projection method is based on the Bell's Godunov‐projection method. However, substantial changes are made so that this algorithm is capable of solving the ALE form of incompressible Navier–Stokes equations. Multi‐block structured grids are used to discretize the flow domains. The grid velocity is not explicitly computed; instead the volume change is used to account for the effect of grid movement. A new method is also proposed to compute the freestream capturing metrics so that the geometric conservation law (GCL) can be satisfied exactly in this algorithm. This projection method is also parallelized so that the state of the art high performance computers can be used to match the computation cost associated with the moving grid calculations. Several test cases are solved to verify the performance of this moving‐grid projection method. Copyright © 2004 John Wiley Sons, Ltd.     

等厚双层涂层材料受集中力作用的平面问题理论解

界面应力的正确评价是分析薄膜涂层材料力学特性的难题之一。利用镜像点法和Dirichlet等值性原理，本文推导了等厚双层薄膜涂层材料受表面集中力作用的平面问题理论解。该显式理论解是以固定在各镜像点上的局部坐标系下的Goursat应力函数的形式给出的。对应于高阶镜像点的应力函数，可通过递推的方法，从对应于低阶镜像点的应力函数求得，而且也易于计算机编程。随着镜像点阶数的增大，它与界面的距离也越来越大，因而相对应的应力函数对界面应力的影响越来越小。最后的算例表明，只需考虑前面有限个镜像点，便可获得足够精度的解。该理论解可作为格林函数，以求解复杂问题的理论解，也可用作边界元法的基本解，提高数值计算的精度和效率。