Coupling the finite element method and molecular dynamics in the framework of the heterogeneous multiscale method for quasi-static isothermal problems

Multiscale models are designed to handle problems with different length scales and time scales in a suitable and efficient manner. Such problems include inelastic deformation or failure of materials. In particular, hierarchical multiscale methods are computationally powerful as no direct coupling between the scales is given. This paper proposes a hierarchical two-scale setting appropriate for isothermal quasi-static problems: a macroscale treated by continuum mechanics and the finite element method and a microscale modelled by a canonical ensemble of statistical mechanics solved with molecular dynamics. This model will be implemented into the framework of the heterogeneous multiscale method. The focus is laid on an efficient coupling of the macro- and micro-solvers. An iterative solution algorithm presents the macroscopic solver, which invokes for each iteration an atomistic computation. As the microscopic computation is considered to be very time consuming, two optimisation strategies are proposed. Firstly, the macroscopic solver is chosen to reduce the number of required iterations to a minimum. Secondly, the number of time steps used for the time average on the microscale will be increased with each iteration. As a result, the molecular dynamics cell will be allowed to reach its state of thermodynamic equilibrium only in the last macroscopic iteration step. In the preceding iteration steps, the molecular dynamics cell will reach a state close to equilibrium by using considerably fewer microscopic time steps. This adapted number of microsteps will result in an accelerated algorithm (aFE-MD-HMM) obtaining the same accuracy of results at significantly reduced computational cost. Numerical examples demonstrate the performance of the proposed scheme.     

Application of structured lighting sensor for online measurement

On the background of increasing request for stringent quality improvement and rising productivity, requirements for online measurement systems are growing as well. Among all the measurement tools, the vision system is considered as the most appropriate tool to provide proper accuracy, high speed, low cost, and 100% online inspection. Structure lighting sensor is the most popular method used in vision system. In this paper, the theory of vision system based on structure lighting is introduced. The measurement application to the seamless steel tube is introduced particularly. Another typical application, the online measurement on car body using structure lighting, is also illustrated.     

A general strategy for designing seamless multiscale methods

We present a new general framework for designing multiscale methods. Compared with previous work such as Brandt’s systematic up-scaling, the heterogeneous multiscale method (HMM) and the “equation-free” approach, this new framework has the distinct feature that it does not require reinitializing the microscale model at each macro time step or each macro iteration step. In the new strategy, the macro- and micro-models evolve simultaneously using different time steps (and therefore different clocks), and they exchange data at every step. The micro-model uses its own appropriate time step. The macro-model runs at a slower pace than required by accuracy and stability considerations for the macroscale dynamics, in order for the micro-model to relax. Examples are discussed and application to modeling complex fluids is presented.     

电厂高压锅炉用15CrMoG无缝钢管中钼分析方法研究

15CrMoG无缝钢管是一种大量使用的高压锅炉钢管。本文基于钼与硫氰酸钠的显色反应,建立了光度法测定15CrMoG无缝钢管样品中钼的方法。采用硫酸-磷酸混合酸溶解试样,在硫酸-高氯酸介质中以氯化亚锡为还原剂,钼与硫氰酸钠生成橙红色络合物,测量其吸光度,吸光度与钼含量在质量分数0.11%—0.89%范围内呈线性关系。本法采用更接近于真实样品的标钢溶液建立校准曲线,实验表明,该方法准确、简便。测定了不同厂家15CrMoG无缝钢管中的钼,测定结果满意。     

Optimal seamless self-assembly of files in linear networks

A file F is sited at one end (the root) of a path in some network. Each non-root node in the path is able to cache part or all of F, and each node may also have a client wanting to download F. Links between neighbors on the path have given transmission delays associated with them, but the delay from a node to its own client, if it has one, is zero. In the seamless, self-assembly paradigm all clients issue requests simultaneously at time 0, each starts to receive segments of F immediately, and continues to receive them until F is fully downloaded. The process must be implemented by means of a distributed self-assembly protocol which is unaware of network structure beyond links to immediate neighbors. We exhibit such a protocol, and show how to assign segments of F to the node caches in such a way that, no matter which nodes are chosen as clients, seamless self-assembly is realized and, simultaneously, the total cache size achieves a lower bound determined solely by the link delays. The paper concludes with a brief discussion of the many open problems arising in systems requiring seamless, or nearly seamless, self assembly of files.     

An optical MEMS-based dynamic capacity allocation scheme for handoff using moving extended cells in radio-over-fiber networks

We demonstrate a Dynamic Capacity Allocation scheme for the realization of Moving Extended Cells in Radio-over-Fiber networks. Our scheme exploits a reconfigurable MEMS-based Central Office architecture for routing of and switching between six data carrying wavelengths, forming in this way cell clusters that transmit the same information content and can move with the mobile user. Error free transmission through 25 km SMF is presented for a 5-cell MEC structure, with each optical channel carrying 500 Mb/s data subcarrier-modulated at 8.5 GHz.     

新型节能BT下载协议的设计与验证

随着因特网普及,因上网而消耗的能源迅速上升,逐渐成为世界能源消耗的主要部分之一.这些能源绝大部分消耗在终端计算机上,包括用户的个人电脑和大型数据中心的服务器等.将重点考虑用户在P2P下载(如BT下载)中,因个人电脑必须处在长期工作状态而导致的能耗.我们设计了一种新型的BT下载协议,引入一种新的BT协议的网络结构,从而在不牺牲用户BT下载的速度的情况下,允许用户的个人电脑在一定时间内待机或关机,以此大量降低BT下载协议的能耗.对该协议用实验进行了验证,实验证明新型BT下载协议最高可以减少95%的能耗,同时还能缩短文件的平均下载时间.