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551.
Patricia Bouyer Thomas Brihaye Véronique Bruyère Jean-François Raskin 《Formal Methods in System Design》2007,31(2):135-175
We study the cost-optimal reachability problem for weighted timed automata such that positive and negative costs are allowed
on edges and locations. By optimality, we mean an infimum cost as well as a supremum cost. We show that this problem is PSpace-Complete. Our proof uses techniques of linear programming, and thus exploits an important property of optimal runs: their time-transitions
use a time τ which is arbitrarily close to an integer. We then propose an extension of the region graph, the weighted discrete graph,
whose structure gives light on the way to solve the cost-optimal reachability problem. We also give an application of the
cost-optimal reachability problem in the context of timed games.
Research supported by the FRFC project “Centre Fédéré en Vérification” funded by the Belgian National Science Foundation (FNRS)
under grant nr 2.4530.02. 相似文献
552.
简述了我国现阶段的财政业务系统安全审计状况,提出了用计算机的审计技术和财政系统相结合的安全审计方案,采用基于日志的确定有穷自动机(DFA)的模型、按功能触发的形式,以及对数据库采用审计要素的方法进行审计,实现对操作系统和财政系统的审计.这不仅有利于提高财政系统的审计工作效率,而且提高了操作系统和财政系统的安全性. 相似文献
553.
554.
为提升网络流识别性能,本文提出了一种TCP流识别算法.该算法基于传输控制协议(Transmission Control Protocol,TCP)下网络通信双方的交互过程构建双向流自动机,由该自动机根据TCP协议规则和网络流当前状态判断TCP流终止,同时以基于规则的过滤机制和超时策略为辅助措施,快速识别单包流和异常中断流.该算法内存开销、计算和内存总开销均低于经典算法固定超时策略(Fixed Timeout strategy,FT)和同类代表性算法两层自适应超时策略(Two-level Self-Adaptive Timeout,TSAT),同时该算法精度高于TSAT,且仅比默认精度标准略有下降.该算法基于协议规则识别TCP流,既保证了流的准确性,又节省了流的超时等待时间,而且算法尤其适合中流、小流和不规则TCP流比重较大的情况,使得识别系统在面临DDoS攻击、蠕虫爆发等网络异常时仍能正常运行. 相似文献
555.
M.-F. Zhu W. Cao S.-L. Chen C.-P. Hong Y. A. Chang 《Journal of Phase Equilibria and Diffusion》2007,28(1):130-138
Driven by industrial demand, extensive efforts have been made to investigate microstructure evolution and microsegregation
development during solidification of multicomponent alloys. This paper briefly reviews the recent progress in modeling of
microstructures and microsegregation in solidification of multicomponent alloys using various models including micromodel,
phase field, front tracking, and cellular automaton approaches. A two-dimensional modified cellular automaton (MCA) model
coupled with phase diagram software PanEngine is presented for the prediction of microstructures and microsegregation in the
solidification of ternary alloys. The model adopts MCA technique to simulate dendritic growth. The thermodynamic data needed
for determining the dynamics of dendritic growth are calculated with PanEngine. After validating the model by comparing the
simulated values with the prediction of the Scheil model for solute profiles in the primary dendrites as a function of solid
fraction, the model was applied to simulate the microstructure and microsegregation in the solidification of Al-rich ternary
alloys. The simulation results demonstrate the capabilities of the present model not only to simulate realistic dendrite morphologies,
but also to predict quantitatively the microsegregation profiles in the solidification of multi-component alloys.
This article was presented at the Multi-Component Alloy Thermodynamics Symposium sponsored by the Alloy Phase Committee of
the joint EMPMD/SMD of The Minerals, Metals, and Materials Society (TMS), held in San Antonio, Texas, March 12-16, 2006, to
honor the 2006 William Hume-Rothery Award recipient, Professor W. Alan Oates of the University of Salford, UK. The symposium
was organized by Y. Austin Chang of the University of Wisconsin, Madison, WI, Patrice Turchi of the Lawrence Livermore National
Laboratory, Livermore, CA, and Rainer Schmid-Fetzer of the Technische Universitat Clausthal, Clauthal-Zellerfeld, Germany. 相似文献
556.
557.
摘 要:为保障医院门诊大厅人员疏散安全,开展门诊大厅人员疏散模拟与服务窗口布局优化研究。通过实地观测,统计门诊大厅的几种典型服务窗口布局以及人员数量和构成;基于调研数据,设置不同人员速度以及竞争关系,建立基于精细网络元胞自动机的医院门诊大厅疏散模型,模拟不同服务窗口布局下的人员疏散过程,并进一步提出服务窗口优化设计。研究结果表明:两侧服务窗口布局最优,疏散时间最短;服务窗口布局对运动能力越弱的人员影响越大;设置特殊窗口可以保障行动不便人群优先疏散,两侧靠近出口设置特殊窗口的疏散效率最高。研究可为门诊大厅服务窗口布局设计和人员安全疏散管理提供支撑。 相似文献
558.
The microstructural evolution of Ti-45 at.%Al alloy during directional solidification was simulated by applying a solute diffusion controlled solidification model. The obtained results have shown that under high thermal gradients the stable primary spacing can be adjusted via branching or competitive growth. For dendritic structures formed under a high thermal gradient, the secondary dendrite arms are developed not very well in many cases due to the branching mechanism under a constrained dendritic growth condition. Furthermore, it has been observed that, with increasing pulling velocity, there exists a cell/dendrite transition region consisting of cells and dendrites,which varies with the thermal gradient in a contradicting way, i.e. increase of the thermal gradient leading to the decrease of the range of the transition region. The simulations agree reasonably well with experiment results. 相似文献
559.
We consider the state complexity of compositions of regularity-preserving language operations. As our main result, we establish that determining the state complexity of an operation composed just from intersections and marked concatenations is undecidable. The proof relies on the undecidability of Hilbert's Tenth Problem. The languages used in the construction are over a fixed alphabet with at most 50 letters. We also consider some implications and generalizations, as well as discuss open problems. 相似文献
560.
G. Reinhart Ch.-A. Gandin N. Mangelinck-Noël H. Nguyen-Thi J.-E. Spinelli J. Baruchel B. Billia 《Acta Materialia》2013,61(13):4765-4777
This paper presents a comparison between the in situ and real time observation of a directional solidification experiment carried out at the European Synchrotron Radiation Facility and a direct simulation of grain structure formation in the sample using a two-dimensional cellular automaton–finite element (CA-FE) model. In situ characterization of the columnar-to-equiaxed transition in a refined Al–3.5 wt.% Ni alloy is achieved by synchrotron X-ray radiography. Two main characteristics are derived from the radiographs for each nucleated grain, namely the nucleation position in the sample and the orientation of the main trunk relative to the vertical temperature gradient. These data are then used as input for the CA-FE simulations. The CA-FE model takes into account the effects of macroscopic transport of heat, liquid momentum and solute mass on the development of the dendritic grain structure and vice versa. The influence of convection on macroscopic shape of the growth front, the grain structure, the microstructure distribution and macro-segregation is determined by a comparison between the experimental observations and results from the numerical simulations with and without fluid flow. Good qualitative agreement is obtained and limitations that are linked to the two-dimensional approximation and the need for direct tracking of the eutectic grain structure are pointed out. 相似文献