Shock-induced transformation of liquid deuterium into a metallic fluid

Simultaneous measurements of shock velocity and optical reflectance at 1064, 808, and 404 nm of a high pressure shock front propagating through liquid deuterium show a continuous increase in reflectance from below 10% and saturating at approximately (40-60)% in the range of shock velocities from 12 to 20 &mgr;m/ns (pressure range 17-50 GPa). The high optical reflectance is evidence that the shocked deuterium reaches a conducting state characteristic of a metallic fluid. Above 20 &mgr;m/ns shock velocity (50 GPa pressure) reflectance is constant indicating that the transformation is substantially complete.     

On the algorithmic construction of classifying spaces and the isomorphism problem for biautomatic groups

We show that the isomorphism problem is solvable in the class of central extensions of word-hyperbolic groups,and that the isomorphism problem for biautomatic groups reduces to that for biautomatic groups with finite centre.We describe an algorithm that,given an arbitrary finite presentation of an automatic group Γ,will construct explicit finite models for the skeleta of K(Γ,1) and hence compute the integral homology and cohomology of Γ.     

A HYPERBOLIC SYSTEM OF CONSERVATION LAWS FOR FLUID FLOWS THROUGH COMPLIANT AXISYMMETRIC VESSELS

We are concerned with the derivation and analysis of one-dimensional hyperbolic systems of conservation laws modelling fluid flows such as the blood flow through compliant axisymmetric vessels.Early models derived are nonconservative and/or nonhomogeneous with measure source terms,which are endowed with infinitely many Riemann solutions for some Riemann data.In this paper,we derive a one-dimensional hyperbolic system that is conservative and homogeneous.Moreover,there exists a unique global Riemann solution for the Riemann problem for two vessels with arbitrarily large Riemann data,under a natural stability entropy criterion.The Riemann solutions may consist of four waves for some cases.The system can also be written as a 3×3 system for which strict hyperbolicity fails and the standing waves can be regarded as the contact discontinuities corresponding to the second family with zero eigenvalue.     

亚胺膦R_3PNH(R =CH_3,Cl)的极性及P-N键性质的理论研究

用从头算方法在B3LYP/ 6 31G 水平上对亚胺膦R3PNH(R =CH3,Cl)进行了理论计算研究。结果表明这两种亚胺膦的极性 ,P -N键性质及分子轨道存在明显差异 ,亚胺膦 (CH3) 3P =NH及其P -N键的极性很强 ,而Cl3P =NH的极性则较弱。与Cl3P =NH相比 (CH3) 3P =NH可能是较好的类Wittig反应试剂。     

过冷熔体中枝晶生长的相场法数值模拟

利用相场法模拟了过冷纯金属熔体中的枝晶生长过程,研究了各向导性、界面动力学、热扩散和界面能对枝晶生长的影响.结果表明,热噪声可以促发侧向分支的形成,但不影响枝晶尖端的稳态行为;随着各向异性的增加,枝晶尖端生长速度增加,尖端半径减小;当界面动力学系数减小及在界面动力学系数小于1的条件下热扩散系数减小时,枝晶尖端生长速度随之减小,而尖端半径相应增大;界面能趋于增大枝晶尺度并保持界面在扰动下的稳定,界面能越大,形成侧向分支的趋势越小 关键词： 过冷 枝晶生长 相场法 数值模拟