On the optimal reachability problem of weighted timed automata

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.     

信息安全审计技术在财政行业的应用

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.     

低碳钢奥氏体转变为铁素体的元胞自动机模型

建立了一个在压缩变形的连续冷却作用下，低碳钢中奥氏体γ转变为铁素体α的二维元胸自动机模型，模型考虑到α相在奥氏体晶界上形核与生长，碳溶质和温度场在奥氏体和铁素体中的扩散，讨论了冷却率和应变等因素对γ→α用相变的影响。     

基于自动机的TCP流识别算法

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.     

一维水锤问题的格子气自动机

给出一维关阀断流水锤问题的时间、空间、流体完全离散的格子气自动机。     

某埋头弹机枪自动机结构设计与动力学分析

为提高大口径埋头弹机枪的射击速度,设计一种导气式自动机.以某12.7 mm埋头弹机枪为研究对象,采用升降弹膛实现开闭锁动作,对自动机的结构进行设计,利用ADAMS建立埋头弹机枪的虚拟样机模型,通过仿真获得自动机运动特性参数.仿真结果证明了该自动机结构的可行性,为大口径埋头弹机枪的设计提供一种参考方案.     

Simulation of microstructure evolution in directional solidification of Ti-45at.%Al alloy using cellular automaton method

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.     

Undecidability of state complexity

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.     

Influence of natural convection during upward directional solidification: A comparison between in situ X-ray radiography and direct simulation of the grain structure

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.     

Scale removal oxidation behavior of metal in supercritical water modeled by cellular automaton

Corrosion and oxidation of structure material in supercritical water are specific and an important issue in the nuclear industry. A scale removal cellular automaton model was proposed to investigate the development of a continuous oxide layer of Inconel 625 in supercritical water at 24.8 MPa and 600 °C. This study presented influence of the reaction behavior of oxidation, scale removal effect, and transport ratio of oxygen and metal ions on the corrosion and oxidation process with different conditions. The formation of the spinel is simulated at mesoscopic level. The developed model is also mapped with the laboratory experimental data from a supercritical water loop.