Diffusion and viscosity equations of state for a Lennard-Jones fluid obtained from molecular dynamics simulations

Equilibrium molecular dynamics simulations were performed for a Lennard-Jones fluid at 171 conditions spanning the range 0≤p ⁺≤1.0 and 0.8≤T ⁺≤4.0. The Einstein or, mean-squared-displacement (MSD) formula was used to compute the self-diffusion coefficient and a recently suggested, modified MSD equation was used to compute the shear viscosity at each condition. Analytical equations for the self-diffusion and viscosity coefficients were then fitted to the simulated data as polynomial functions ofp ⁺ andT ⁺. The resultant smoothing equations correlate the simulated data quite well and agree with argon experimental data within the uncertainty of the data.     

(t,s,S)库存系统的计算机优化仿真

分析了(t,s,S)库存系统定量优化的难点,提出计算机仿真是这一难点的解决方法之一.详细介绍了以Visual Basic 6为平台所开发的软件实现(t,s,S)库存优化的具体步骤.指出该软件较好地实现了参数交互输入与模拟数据的图形输出,具有较宽的应用范围,模拟结果符合实际,具有一定的应用价值.     

Healing substrates with mobile, particle-filled microcapsules: designing a ‘repair and go’ system

We model the rolling motion of a fluid-driven, particle-filled microcapsule along a heterogeneous, adhesive substrate to determine how the release of the encapsulated nanoparticles can be harnessed to repair damage on the underlying surface. We integrate the lattice Boltzmann model for hydrodynamics and the lattice spring model for the micromechanics of elastic solids to capture the interactions between the elastic shell of the microcapsule and the surrounding fluids. A Brownian dynamics model is used to simulate the release of nanoparticles from the capsule and their diffusion into the surrounding solution. We focus on a substrate that contains a damaged region (e.g. a crack or eroded surface coating), which prevents the otherwise mobile capsule from rolling along the surface. We isolate conditions where nanoparticles released from the arrested capsule can repair the damage and thereby enable the capsules to again move along the substrate. Through these studies, we establish guidelines for designing particle-filled microcapsules that perform a ‘repair and go’ function and thus, can be utilized to repair damage in microchannels and microfluidic devices.     

断裂动力学有限元程序的开发及在天然气管道裂纹扩展问题上的应用

许多工程问题是由于流(气)体压力导致了结构开裂,裂纹迅速扩展或者止裂,这被认为是断裂动力学最前沿的研究领域。本文描述了应用于分析流体/结构/断裂耦合作用问题的计算程序PFRAC(Pipeline FRacture Analysis Code),和它在天然气管道裂纹迅速扩展问题上的应用。基于断裂动力学的模式,提出了裂纹扩展和止裂的判据。对于裂纹驱动力的计算,给出了节点力释放技术和能量平衡方法的具体应用。根据实际管道开裂试验的数据,提出了便于非耦合作用计算的裂纹后面气体压力衰减模式。针对钢制和塑料制天然气工程管道,给出了部分计算和试验的结果。     

POLYCHAR-9 Worldwide Forum on Polymer Applications and Theory in 2001

Profile of POLYCHAR conferences is briefly defined. An introduction to the following papers presented at the POLYCHAR-9 conference in January 2001 is provided. Prizes awarded at the POLYCHAR-9 Forum and the composition of the Prize Committee are listed. Electronic Publication     

POLYCHAR-10 World Forum on Polymer Applications &; Theory in 2002

A report from POLYCHAR-10 is provided. An introduction to the following papers presented at the POLYCHAR-10 Forum is given. A small selection of the authors and titles of the papers presented is listed. Prizes awarded are listed along with the composition of the Prize Committee. Some research groups of high activity which are represented at POLYCHAR every year are named. Electronic Publication     

Generation of polymeric structures on a computer

Our simulations of mechanical and tribological behavior of polymeric materials rely on the creation of realistic materials on a computer. They follow previous work with one- and two-phase two-dimensional materials [9, 10, 11]. We now report a procedure of creation of three-dimensional polymers. Related issues are those of characterization in terms of the average chain length and the average end-to-end distance and also of visualization of the structures before, during and after a tribological or mechanical simulated "experiment." Electronic Publication     

Fold and flexibility: what can proteins' mechanical properties tell us about their folding nucleus?

The determination of a protein''s folding nucleus, i.e. a set of native contacts playing an important role during its folding process, remains an elusive yet essential problem in biochemistry. In this work, we investigate the mechanical properties of 70 protein structures belonging to 14 protein families presenting various folds using coarse-grain Brownian dynamics simulations. The resulting rigidity profiles combined with multiple sequence alignments show that a limited set of rigid residues, which we call the consensus nucleus, occupy conserved positions along the protein sequence. These residues'' side chains form a tight interaction network within the protein''s core, thus making our consensus nuclei potential folding nuclei. A review of experimental and theoretical literature shows that most (above 80%) of these residues were indeed identified as folding nucleus member in earlier studies.     

Towards a taxonomy for multiscale methods in computational mechanics: building blocks of existing methods

Existing multiscale methods in computational mechanics are analyzed with respect to their computational building blocks, considering methods in both solid and fluid mechanics. From this analysis, a step towards a taxonomy for multiscale methods in computational mechanics is taken. The present article is not intended as a closed story; it is rather hoped that it may provide some basis for future discussions. Moreover, it might even provide a point of view to more clearly identify differences and similarities in the variety of multiscale methods currently existing or being developed in the future. The methods or their building blocks, respectively, are investigated with a view on their multiscale features regarding the underlying problem, spatial scale processing, and temporal scale processing. As expected, it turns out that the mechanics of the underlying problem strongly influences the necessary building blocks of an adequate multiscale method.     

Thermal and fluid mechanical problems in space flight

In this paper the basic research activities being carried out in the Institute of Space and Aeronautical Sciences, University of Tokyo and other establishments have been discussed. Four problems of space flight, namely, thermal design of spacecraft, thermal protection during. planetary entry, surface contamination of spacecraft and microgravity effects in space have been specifically highlighted.     

He原子在金属Ti中的第一性原理计算

本文用基于量子化学基本原理的密度泛函理论,研究He原子在金属Ti中的几何结构和能量变化。计算得到单个He原子在完美Ti晶体中最可几占位为八面体间隙,两个He原子互相靠近时会形成稳定的原子对。进一步分析了体系优化后的能带结构和电子态密度分布。分析得出在没有缺陷存在的完美晶体中,He原子会聚集形成团簇。     

On statistical mechanics of vortex lines

An ensemble of a large number of vortex lines in cylindrical bounded domain is being considered. A system of equations determining the statistical characteristics of vortex line motion is derived from the assumption that this motion is ergodic and vortex lines are sufficiently smooth. The smoothness of vortex lines is characterized by vortex diffusivity. Both cases of finite and infinite vortex diffusivity are discussed. The continuum limit equations are obtained.