Computer simulation of atomic properties and dynamic behavior of interstitial clusters in Ni*

The atomic structure and dynamic behavior of interstitial clusters, i.e., a bundle of <110> crowdions, have been investigated in a model Ni lattice. An extended dislocation loop was obtained after full relaxation of a loop of hexagonal shape, consisting of four dislocation segments lying on {111} slip planes and two dislocation segments on {100} slip planes. The dislocation segments on {111} slip planes are extended, but the segments on {100} slip planes are not extended. By observing the motion of a dislocation loop under axially symmetrical shear stress, the Peierls stress for the dislocation loop was obtained. Also, a diamond-shaped dislocation loop was constructed in the model lattice, consisting of four dislocation segments on {111} slip planes and no segments on {100} slip planes. The Peierls stress for this diamond-shaped dislocation loop was found to be less than that for the hexagonal-shaped dislocation loop. This revised version was published online in June 2006 with corrections to the Cover Date.     

Computer simulation of amorphization phenomena in metals under irradiation

In this paper, we use a simplified model to simulate the amorphization phenomenon in metals under irradiation. The model has few parameters but can reflect the essential characteristics of the processes. Our simulation results show that the relaxation of collision cascades forms small crystal grains and the amorphization phenomenon is a result of total overlap of different grains, which depends on the irradiation temperature.     

Computer simulation of pressure sintering

The densification process during pressure sintering has been analyzed using finite element analysis. This analysis uses an iterative solution algorithm. With this the densification process in complex geometries with complex boundary conditions can be analyzed and this technique is particularly suited for tackling material nonlinearity. Evolution of dense structures with gradual closure of pores is described for two typical geometries.     

卤化银感光过程的计算机模拟

本文以光电子动力学理论为基础,采用成核生长理论模型(Nucleation&GrowthModel)和蒙特卡罗方法(Monte-CarloMethod),模拟光电子的产生、传播、衰减、直到实现潜影中心为止的感光过程.在讨论成核生长模型的基础上,把卤化银材料的感光过程分为五个阶段进行模拟,并对各个阶段的模拟算法进行了较详细的论述.     

Computer simulation of dislocation-carbon interaction in nickel

An atomistic computer model based on a rigid boundary method has been developed to estimate the interaction energy between a single edge dislocation and an impurity carbon interstitial in nickel. The simulation was carried out using the static relaxation technique on a total of 600 atoms, using an appropriate host-host pair potential. The impurity-host potential has been chosen to be a cubic function in this calculation. In the absence of the dislocation the dipole tensor for the octahedral site is seen to be spherical. Two impurity positions, one above and one below the slip plane were investigated. The carbon-dislocation interaction energies obtained were 1·4 eV and 0·7 eV respectively for the two impurity positions. The dipole tensor for the impurity in the presence of the dislocation was found to be non-diagonal.     

Computer modelling and simulation in materials science

The paper presents a brief overview of different types of modelling and simulation along with the distinguishing features between the two. Spatial as well as temporal size scales with a special reference to multiscale modelling are explained with illustrations. The paper includes a discussion on numerical experiments and their validation based on the authors’ work on FEM simulation of crack-tip blunting during ductile fracture. Attention is drawn to the use of a 3P technique involving integrated simulation of deformation (property) at microstructural level, the process at macroscopic level and the performance at the product level.     

多束相干光叠加的计算机模拟

研究了具有空间不对称分布的多束相干光的叠加问题。对参考平面上相干光产生的干涉光强分布进行理论推导和数值计算,从理论上定量地分析了多束相干光的波矢量、偏振态对干涉光强分布的影响。模拟结果表明波矢量的改变主要影响干涉光强的空间分布,激光束偏振态的改变主要影响干涉场的对比度。     

Computer simulation of defects and radiation damage

In this paper, we describe the computer simulation technique and its application to the study of radiation damage. Details of two important methods: the static and the dynamic methods have been discussed. Applications to the study of point defect formation and stability, their clusters, diffusion, dislocations and dislocation-point defect interaction are discussed drawing from our own work wherever possible. A short mention is made of the importance of the interatomic potential. Examples for the case of magnesium and other hcp metals, bcc iron and fcc Ni are cited and numbers for various quantities like formation energy, dipole tensor, interaction energy etc are quoted.     

基于LabVIEW的纳米颗粒动态散射光模拟

采用实验室虚拟仪器工程平台LabVIEW实现了纳米颗粒动态光散射信号的计算机模拟。用G语言(图形语言)设计了信号模拟的框图程序,给出了5nm, 15 nm两种粒径颗粒的模拟动态散射光信号及自相关函数。对模拟信号的粒度分析表明,这两种模拟信号产生的测量偏差分别为0.4nm和-0.6nm。     

Au量子点I－V特性的计算机模拟

基于量子力学隧穿原理，对由Au纳米粒子自组装体系构建的典型串联双隧道结模型的I－V特性进行了计算机模拟，模拟结果与实验曲线吻合。该方法对于构建纳米电子器件模型及工艺优化将具有指导意义。     

Computer simulation of ordering in bipolar nematogen H6CBP at phase transition temperature

The molecular ordering of 4-(6-hydroxyhexyloxy)-4′-cyanobiphenyl (H6CBP), a bipolar nematogen, has been carried out at nematic-isotropic transition temperature with respect to translatory and orientational motions. The complete neglect differential overlap (CNDO/2) method has been employed to compute the net atomic charge and atomic dipole moment at each atomic centre. The modified Rayleigh–Schrodinger perturbation theory with multicentred-multipole expansion method has been employed to evaluate long-range intermolecular interactions, while a 6-exp potential function has been assumed for short-range interactions. The interaction energy values obtained through these computations were used to calculate the probability of each configuration at nematic-isotropic transition temperature using the Maxwell–Boltzmann formula. On the basis of stacking, in-plane, and terminal interactions energy calculations, all possible geometrical arrangements of the molecular pair have been considered. The results are correlated with molecular parameters introduced in this article, and an attempt has been made to explain the nematic behaviour of the compound in terms of their relative order.     

Computer simulation of deformation and fracture of small crystals by molecular dynamics method

Body-centred cubic iron whiskers having [100] and [110] axes were pulled in a molecular dynamics simulation using a supercomputer. The upper yield stress close to the theoretical strength was found. Above the upper yield stress, phase transformation was observed; at the same time the stress was greatly reduced. A new possible mechanism of twinning is proposed. The whiskers were pulled until they had broken into two pieces. Copper small crystals with and without a notch were sheared. It was observed that the edge dislocations were created at the surface and moved through and escaped from the crystals. Copper small single crystals with a notch were pulled. A half-dislocation was created near the tip of the notch. Sharp yield stress was observed. In medium deformation dislocations on different slip planes were created. Due to the cutting of dislocations the tensile stress increased.     

Atomic-scale computer simulation of primary irradiation damage effects in metals

Molecular dynamics (MD) has been used extensively to simulate displacement cascades in metals; and this paper contains a summary of the progress made to date. It includes results dealing with the effect of primary knock-on atom energy and irradiation temperature on defect formation in a variety of metals. It is shown that in addition to data on the number of defects produced, quantitative information is available on the distribution of defects created in clusters. Thus, the nature of the primary damage state is now clear. The successful development of multiscale models to describe the evolution of radiation damage microstructure and its impact on material performance requires detailed atomic-level information about the stability, motion and interaction of defects. This is starting to be obtained by MD and some recent results are discussed. The place of atomic-scale modelling in the multiscale problem of radiation damage is shown. This revised version was published online in July 2006 with corrections to the Cover Date.     

氩色谱分析仪的使用和改进

针对DHP-06型氩色谱分析仪在分析使用过程中存在高纯氩载气使用量大和分析工操作时间长等矛盾,介绍了采用氩储槽内的氩净化后做载气的改造方案.     

Ab initio molecular dynamics studies of metal clusters

We present results of ourab initio molecular dynamics simulations on the atomic and electronic structure of clusters of divalent metals, aluminum and antimony, which exhibit a range of bonding characteristics e.g. non-metal-metal transition, metallic and covalent respectively. Results of these studies have been used to develop icosahedral AI₁₂X (X = C, Si and Ge) superatoms with 40 valence electrons which correspond to a filled electronic shell. It is found that the doping leads to a large gain in the binding energy as compared to Al₁₃, suggesting this to be a novel way of developing species for cluster assembled materials. Further studies of adsorption of Li, Si and Cl atoms on Al₇ and Al₁₃ clusters show marked variation in the adsorption behaviour of clusters as a function of size and the adsorbate. Silicon reconstructs both the clusters and induces covalency in Al-Al bonds. We discuss the adsorption behaviour in terms of the superatom-atom interactions.     

关于Ar馏份气体成分分析的讨论

从工艺角度看,Ａｒ馏份中分析Ａｒ和分析Ｏ２是一样的,但从分析仪器的角度看,分析Ａｒ比分析Ｏ２更合理。这主要考虑到了大气压力变化对气体分析仪器讯号输出有影响。     

TE10波在矩形波导管中传播的计算机测量及动态反馈模拟

通过应用计算机驱动步进电机控制驻波测量线的移动和可变衰减器的转动,结合放大电路及模数转换卡,实现了自动测量矩形波导管内微波的工作状态。同时将测量得到的数据通过计算机软件进行分析,利用编程模拟绘制出当前时刻TE10波的动画图像,即通过入射波与反射波的叠加,确定出当前为匹配状态、驻波状态或混波状态。通过计算机自动测量及动态反馈模拟,使实验效果、实验精度得到显著提高,实践应用效果甚好。     

Synthesis and properties of novel materials at high pressure and temperature—molecular dynamics simulation studies

Molecular dynamics simulations, in combination with lattice dynamics studies, based on semiempirical interatomic potentials, have been very useful in the study of properties of complex novel materials at high temperature and pressure. Various properties such as the equation of state, elastic and thermodynamic properties, phase transitions and melting have been studied. These studies help in understanding the synthesis of important new and novel materials, especially the amorphous materials, compounds with unusually coordinated atoms, (e.g. with five-coordinated silicon atoms), materials with controlled thermal expansion, etc. A few examples will be discussed from our recent studies.     

Electronic properties of chemically produced silver clusters: grain morphology studies

Abstract

The electronic properties of silver clusters formed on the surface of reduction- sensitized octahedral and cubic AgBr emulsions were studied. Prior to sensitization with dimethylamineborane, SnCl₂ or high pH, these emulsions had the same efficiency. The results suggest that the octahedral emulsion has more potential to achieve a higher maximum speed increase. This difference may be due to fewer available sites for silver cluster formation on cubic surfaces. Gelatin concentration studies showed that the gelatin and/or impurities do play a role in silver cluster formation by high pH treatment. The precise role of OH^? is uncertain.     

Computer simulation for quality and reliability engineering

Computer simulation has been used widely in many industries for many applications. A simulation model mimics a real world system, enabling an investigation of its operation. More recently simulation models have incorporated a visual display and interactive features to aid understanding and enhance the investigation. Computer simulation has many potential uses in quality and reliability engineering, for instance, modelling equipment failures, quality control strategies, maintenance requirements and operational logistics. A case study shows how simulation has been used to study the throughput, flexibility and robustness of a manufacturing plant design. Alternative simulation software packages are briefly discussed.