稀薄气体二维外部柱体绕流特性研究

本文采用直接模拟蒙特卡罗方法对稀薄气体二维外部柱体绕流问题进行了数值模拟。结果表明:外部绕流问题,在特定情况下会产生激波,激波的产生,不仅与气体的稀薄程度有关,还与来流马赫数有关。而气流与壁面之间的换热,随来流马赫数增加而增加,随气体稀薄程度增加而减小。     

绕圆柱体自由表面磁流体流动和传热的研究

本文对在不同雷诺数下,绕圆柱体的磁流体自由表面流动及传热进行了模拟,分析了磁场对绕流圆柱尾迹和涡分离的影响,获得了两种雷诺数下的电磁力密度、流场和温度场分布。结果表明,磁场不仅影响了流动的形态,而且对湍流有抑制作用,降低了自由表面的更新机制,从而减少了传热能力;在相同的Hartmann数下,相比低雷诺数下的流动换热情况,高雷诺数下的湍流不能被完全抑制,自由表面与尾迹的相互作用也较强,因而自由表面换热也较强。     

Insight into the extractability of metals from soils using an implementation of the linear adsorption isotherm model

This paper deals with an often overlooked artifact in sequential and single extraction of metals from soils, viz. the volume to mass (V/m) ratio as a potential source for inadequate extraction yields. We offer a theoretical framework to get a grip on this intricate parameter and came up with a model based on a linear adsorption isotherm to derive the correct maximal metal extractability for a certain extractant. We verified the model experimentally using 0.1 mol l⁻¹ nitric acid for extraction of seven metals (Cr, Co, Cu, Cd, Pb, Ni and Zn) from an urban soil sample, and concluded that commonly used V/m ratios in the range of 10-40 ml g⁻¹ may give as much as 50% too low extraction yields. Thus, a strong caveat is in place as to be very critical what V/m ratios to use and preferably apply the model derived to obtain the correct maximal extractability using a variable V/m ratio method.     

Numerical Study on the Coagulation and Breakage of Nanoparticles in the Two-Phase Flow around Cylinders

The Reynolds averaged N-S equation and dynamic equation for nanoparticles are numerically solved in the two-phase flow around cylinders, and the distributions of the concentration M₀ and geometric mean diameter d_g of particles are given. Some of the results are validated by comparing with previous results. The effects of particle coagulation and breakage and the initial particle concentration m₀₀ and size d₀ on the particle distribution are analyzed. The results show that for the flow around a single cylinder, M₀ is reduced along the flow direction. Placing a cylinder in a uniform flow will promote particle breakage. For the flow around multiple cylinders, the values of M₀ behind the cylinders oscillate along the spanwise direction, and the wake region in the flow direction is shorter than that for the flow around a single cylinder. For the initial monodisperse particles, the values of d_g increase along the flow direction and the effect of particle coagulation is larger than that of particle breakage. The values of d_g fluctuate along the spanwise direction; the closer to the cylinders, the more frequent the fluctuations of d_g values. For the initial polydisperse particles with d₀ = 98 nm and geometric standard deviation σ = 1.65, the variations of d_g values along the flow and spanwise directions show the same trend as for the initial monodisperse particles, although the differences are that the values of d_g are almost the same for the cases with and without considering particle breakage, while the distribution of d_g along the spanwise direction is flatter in the case with initial polydisperse particles.     

过渡金属络合物成键本质分析的常用方法

过渡金属络合物中过渡金属与配体间所形成的化学键的成键本质,可以在理论化学基础上,采用定量的方法进行分析。本文重点以铁羰基络合物为例,对常用的分析方法,如自然键轨道方法(NBO)、电荷分解分析(CDA)、分子中的原子(AIM)拓扑分析方法以及ETS和EDA能量分解方法等,在应用中的优缺点进行了分析和评述。借助于这些方法提供的电荷、能量和电子密度等配分项可以深刻认识和理解过渡金属-配体间形成的化学键的成键本质。     

A bump triangular dynamic factorization algorithm for the simplex method

A dynamic factorization algorithm is developed which algebraically partitions the basis inverse in such a manner so that the simplex method can be executed from a series of small inverses and the basis itself. This partition is maintained dynamically so that the additional memory required to represent the basis inverse reduces to this series of small inverses for in-core implementations.The algorithm is intended for use in solving general large-scale linear programming problems. This new method of basis representation should permit rather large problems to be solved completely in-core.Preliminary computational experience is presented and comparisons are made with Reid's sparsity-exploiting variant of the Bartels—Golub decomposition for linear programming bases. The computational experience indicated that a significant reduction in memory requirements can usually be obtained using the dynamic factorization approach with only a slight (up to about 20%) degradation of execution time.This research was supported in part by the Air Force Office of Scientific Research, Air Force System Command, USAF, under AFOSR Contract/Grant Number AFOSR-74-2715.     

order and disorder lines in systems with competing interactions: II. The IRF model

Systems with competing interactions can be often exactly solved on a restricted subspace of the parameter space, called an order or disorder trajectory. A simple method introduced within the transfer matrix formalism allows for the calculation of the free energy and spin-spin correlation functions along the order and disorder lines of the Ising model with all possible interactions around a face of the square lattice (IRF model). The general eight-vertex model is thoroughly examined and shows full analogy with the quantum spin chain results of the previous paper.On leave from and address after September 1, 1982: Institute for Theoretical Physics, Eötvös University, 1088 Budapest, Puskin U. 5–7, Hungary.     

Study of electron solvation in polar solvents using path integral calculations

A path-integral Monte Carlo algorithm for the simulation of electrons solvated in polar liquids is briefly outlined, and results are presented for the electron solvated in liquid water.