Kinetic Flux–Vector Splitting for the Navier–Stokes Equations

Before a hybrid scheme can be developed combining the direct simulation Monte Carlo (DSMC) method and a Navier–Stokes (NS) representation, one must have access to compatible kinetic-split fluxes from the NS portion of the hybrid scheme. The kinetic theory basis is given for the development of the required fluxes from the Chapman–Enskog velocity distribution function for a simple gas; and these are then extended to a polyatomic gas by use of the Eucken approximation. The derived fluxes are then used to implement boundary conditions at solid surfaces that are based on concepts associated with kinetic theory and the DSMC method. This approach is shown to lead to temperature slip and velocity slip as a natural outcome of the new formulation, a requirement for use in the near-continuum regime where DSMC and NS must be joined. Several different flows, for which solid boundaries are not present, are computed using the derived fluxes, together with a second-order finite-volume scheme, and the results are shown to agree well with several established numerical schemes for the NS equations.     

Engineerable compression of ultrashort pulses by use of second-harmonic generation in chirped-period-poled lithium niobate

We demonstrate the use of an aperiodic quasi-phase-matching (QPM) grating to generate second-harmonic pulses that are stretched or compressed relative to input pulses at the fundamental frequency. We frequency doubled an externally chirped erbium-doped fiber laser generating 17-ps (FWHM) pulses at 1560nm to produce near-transform-limited 110-fs (FWHM) pulses at 780nm by use of a 5-cm-long lithium niobate crystal poled with a QPM grating chirped from an 18.2- to a 19.8-microm period.     

二不能压缩气体的分片合流运动

本文求出规定二不能压缩气体的分片合流运动时,速度与质量密度分布的微分方程式。假定两种气体的密度不同但温度则相等。不能压缩的定义是每单位体积中的两种气体分子数的和不变。本文只讨论一平面守恒注中所需要的微分方程式。粘滞流体运动中之边界近似法仍可应用。同样方法亦可用到守恒圆柱体注,半注及气体中温度不同诸问题。     

Modeling of superscalar instruction scheduling and analysis of a heuristic scheduling algorithm

The problem of superscalar instruction scheduling is studied and an analysis of a heuristic scheduling algorithm is presented. First, a superscalar architecture is characterized byk, the number of types of functional units employed,m _i , the number of typei functional units,P _ij , thejth functional unit of typei, andz, the maximal number of delay cycles incurred by the execution of instructions. A program trace to be scheduled is modeled by a directed acyclic graph with delay on precedence relations. These two models reflect most of the flavor of the superscalar instruction scheduling problem. A heuristic scheduling algorithm called the ECG-algorithm is designed by compiling two scheduling guidelines. The performance of the ECG-algorithm is evaluated through worst-case analysis. Lettingw _ECG denote the length of an ECG-schedule andw _opt the length of an optimal schedule, we established the boundwv _ECG /w _opt k+1–2/[max{m _i }(z+1)], which is smaller than other known bounds.     

辐照聚甲醛聚合机理、结构与形态的研究——Ⅰ.三聚甲醛晶体结构的精确测定及其聚合机理

用Co~(60)γ射线辐照三聚甲醛晶体固相聚合得到高分子量的聚甲醛。我们精确测定了三聚甲醛的晶体结构,利用三聚甲醛晶体结构模型,可以很好地阐明三聚甲醛在受到γ射线辐照后开环聚合的机理,由三聚甲醛晶体固相聚合得到的聚三聚甲醛,应该有两种不同取向的分子链,一种与三聚甲醛的c轴平行;另一种与c轴成75°37′的交角。     

t,F显著性检验应用中的一个问题

文章就ｔ，Ｆ显著性检验在同一个问题上检验判断的不一致性，提出在对一种分析结果（或测试结果）实施鉴定时，有必要同时进行ｔ，Ｆ的联合检验，而只有当联合检验一同被接受之后，所作用出的判定结论才是完整和可信赖的。