Analytic simulation of the backscattering of hundreds eV positrons from elemental solids

Backscattering (Bcs) coefficients for low-energy positrons (∼100 eV) from elemental solids have been simulated using an analytic approach. The model is based on the use of the transport cross-sections (TCSs) and the stopping power calculated from partial wave methods and the best-fit stopping power data of Ashley, respectively. The new result is an extension of recent calculations in the medium energy range. Comparisons, when possible, with experimental and Monte-Carlo (MC) simulation data have been made.     

一种EPR谱图模拟软件的研制

采用Microsoft Visual BASIC 4.0 for Windows 95编写了一个EPR谱图模拟软件.此软件采用鼠标控制命令按键进行程序过程.得到的图象分辨率和色彩优于用其他早期开发的BASIC语言编写的程序,打印的黑白图象质量也很好.运算时间小于20秒.这种软件可用于多种EPR模拟应用,包括自由基EPR谱图的模拟、过渡金属离子E PR谱图的模拟和二维EPR成像的模拟.EPR成像可以彩色强度图、等高线图或三维俯视图来表示.所有的模拟图象均可用激光打印机打印成黑白图片.自由基模拟程序的数据组有2560点.EPR成像的像素一般为128×128点.     

3D-solitons in a strongly magnetized plasma: Transition from flat to spherical waves of the Zakharov-Kuznetsov equation

The Zakharov-Kuznetsov equation has been used to describe ion-acoustic wave propagation in a strong magnetic plasma. An initial-value problem has been solved for this equation on the basis of a numerical method that uses the fast Fourier transform technique for calculating space derivatives and a fourth order Runge-Kutta method for the time scheme. Numerical simulations have shown that the disturbed flat solitary waves can break up into spherical ones.     

Colour in visualisation for computational fluid dynamics

Colour is used in computational fluid dynamic (CFD) simulations in two key ways. First it is used to visualise the geometry and allow the engineer to be confident that the model constructed is a good representation of the engineering situation. Once an analysis has been completed, colour is used in post-processing the data from the simulations to illustrate the complex fluid mechanic phenomena under investigation. This paper describes these two uses of colour and provides some examples to illustrate the key visualisation approaches used in CFD.     

基于简正波理论的浅海低频混响时间序列仿真

混响场时域信号序列的数值实现对主动声纳目标模拟器研制具有重要意义。本文所述适用于水平变化浅海环境混响时间序列的一种实现方法,基于现有的浅海简正波相干混响理论。所述方法的思路是通过相干散射场随机序列与发射信号的离散卷积来构成混响时域序列,文中以Pekeris均匀浅海环境为例,给出了相应的混响时间序列仿真结果,并对仿真结果的频谱特性、统计特性、强度衰减以及垂直相关特性等进行了系统检验。结果表明,由仿真混响时间序列所获得的混响特性与理论结果相符,可用于浅海混响序列的仿真。     

MuMax: A new high-performance micromagnetic simulation tool

We present MuMax, a general-purpose micromagnetic simulation tool running on graphical processing units (GPUs). MuMax is designed for high-performance computations and specifically targets large simulations. In that case speedups of over a factor 100 × can be obtained compared to the CPU-based OOMMF program developed at NIST. MuMax aims to be general and broadly applicable. It solves the classical Landau-Lifshitz equation taking into account the magnetostatic, exchange and anisotropy interactions, thermal effects and spin-transfer torque. Periodic boundary conditions can optionally be imposed. A spatial discretization using finite differences in two or three dimensions can be employed. MuMax is publicly available as open-source software. It can thus be freely used and extended by community. Due to its high computational performance, MuMax should open up the possibility of running extensive simulations that would be nearly inaccessible with typical CPU-based simulators.     

用于卵母细胞玻璃化冷冻的几种方法的传热分析

使用高冷冻速率和低浓度冷冻保护液来实现卵母细胞的玻璃化冷冻保存是目前卵母细胞低温保存的主要发展方向.文中选择四种具有代表性的用于卵母细胞玻璃化冷冻的方法:弹射法、OPS法、QMC法和Cryotop法,通过对它们传热特点的分析以及动态温度场分布的模拟计算,找出冷冻速率最高的方法.结果表明,Cryotop法的传热性能优于其...     

S=1/2体系的EPR波谱模拟

用一个以Fortran语言编制的S=1/2体系的EPR模拟谱程序.并引入了弛豫项,图谱线型得到了改善,使模拟谱与实验谱更为接近;对超超精细分裂的考虑,使该程序可适合于复杂图谱的模拟;求积分方法的近似处理,缩短了模拟谱的耗时,使复杂图谱的模拟在微机上成为现实.     

溴代聚苯乙烯机械特性的模拟计算

介绍使用计算机模拟软件,建立的聚苯乙烯和溴代聚苯乙烯非晶态高分子模型.选择适于有机高分子的DREIDING分子力场,根据模型的原子类型,参照文献数据修改其力场参数.在此力场下对模型进行能量优化,使模型尽量符合实际材料.然后,使用分子模拟法中的机械特性模拟,选择一定的计算方法和力学参量,模拟玻璃态物质在外张力下的形变,并计算出其力学特性参数,如体积模量、杨氏模量、泊松比等,给出了PS的应力-应变曲线以及各力学特性随溴代量变化情况.     

Simulation of pressure-space-time history in underwater explosions

Pressure-space-time history of shock waves due to the detonation of explosive charge in water is obtained by simulating the numerical integration of shock trajectory with the variation of fluid parameters behind the shock front. Results are compared with those obtained experimentally elsewhere.     

Comparison between fixed and Gaussian steplength in Monte Carlo simulations for diffusion processes

We analyze the different degrees of accuracy of two Monte Carlo methods for the simulation of one-dimensional diffusion processes with homogeneous or spatial dependent diffusion coefficient that we assume correctly described by a differential equation. The methods analyzed correspond to fixed and Gaussian steplengths. For a homogeneous diffusion coefficient it is known that the Gaussian steplength generates exact results at fixed time steps Δt. For spatial dependent diffusion coefficients the symmetric character of the Gaussian distribution introduces an error that increases with time. As an example, we consider a diffusion coefficient with constant gradient and show that the error is not present for fixed steplength with appropriate asymmetric jump probabilities.     

Learning in innovation networks: Some simulation experiments

According to the organizational learning literature, the greatest competitive advantage a firm has is its ability to learn. In this paper, a framework for modeling learning competence in firms is presented to improve the understanding of managing innovation. Firms with different knowledge stocks attempt to improve their economic performance by engaging in radical or incremental innovation activities and through partnerships and networking with other firms. In trying to vary and/or to stabilize their knowledge stocks by organizational learning, they attempt to adapt to environmental requirements while the market strongly selects on the results. The simulation experiments show the impact of different learning activities, underlining the importance of innovation and learning.     

局部热力学平衡状态下的等离子体电导率计算

在Zollweg & Liebermann模型（Z&L模型）的基础上,结合高温条件下的量子机理作用,考虑了电子与中性粒子的碰撞关系,最终得出修正后的电导率模型,并对局部热力学平衡状态下的水中放电等离子体的粒子数密度及电导率进行了模拟计算.计算结果表明压力为定值的情况下,水中放电等离子体的总粒子数密度随温度变化呈下降趋势,温度达到15000 K时,一次电离达最大值.电导率随温度增加总体呈上升趋势,温度低于12000 K时,电子与中性粒子的碰撞起主导作用,而温度高于25000 K时,电子与离子的碰撞起主导作用.     

Computer simulation of acoustic nonlinear parameter tomography

I.IntroductionUltrasonicimaginghasbcenwide1yusedinthcfie1dofclinicaldiagnosis,becauseitcanvisualizethetissuetharacterizationandinternalstructureofbiologicalobjectsbyacousticwave.Usingconventionalultrasonicimagingtechnique,theimagesofacousticlinearparameterssuchassoundve1ocity,acousticimpedenccandattenuationcoefficientmaybeobtained.Thesehavebecometheeffectivemethodsofu1trasonicdiagnosis.How-ever,inordertoobscrvctheearlystageofcanccr,weintendtoobtainmoreaccurateandmorecompleteinformationaboutth…     

Effect of viscosity on ultrasound wave reflection from a solid/liquid interface

A study of the simulated reflection of a wideband ultrasound shear wave from the solid/viscous fluid interface is presented. Various parameters affecting reflection factors including the material properties of the solid, fluid properties like density and viscosity, and the operating frequency are discussed. Simulated ultrasonic response waveforms are compared with the experimentally obtained data for NIST traceable calibration standards of viscosity. A good agreement was observed between the simulated and experimental waveforms at various viscosities and for different solid substrates.     

蒙特卡罗计算机模拟应用一例

通过圆周率的计算，说明蒙特卡罗计算机模拟方法的应用过程