Application of Markov renewal theory and semi-Markov decision processes in maintenance modeling and optimization of multi-unit systems

In this paper, a condition-based maintenance model for a multi-unit production system is proposed and analyzed using Markov renewal theory. The units of the system are subject to gradual deterioration, and the gradual deterioration process of each unit is described by a three-state continuous time homogeneous Markov chain with two working states and a failure state. The production rate of the system is influenced by the deterioration process and the demand is constant. The states of the units are observable through regular inspections and the decision to perform maintenance depends on the number of units in each state. The objective is to obtain the steady-state characteristics and the formula for the long-run average cost for the controlled system. The optimal policy is obtained using a dynamic programming algorithm. The result is validated using a semi-Markov decision process formulation and the policy iteration algorithm. Moreover, an analytical expression is obtained for the calculation of the mean time to initiate maintenance using the first passage time theory.     

Another manifestation of cyber conflict: attaining military objectives through cyber avenues of approach

Cyberspace is an avenue of approach through which a military force can attain objectives of value. Through these cyber avenues of approach, military forces can engage, vet, organize, and direct human agents to accomplish specific activities. Although the objectives of these activities could differ from traditional military objectives, they still have military relevance. This particular manifestation of cyber conflict is neither a new domain of war nor something outside of warfare. Rather, it can be viewed as an emerging avenue of approach in the larger context of military operations, auguring benefits in the integration of cyber activities with operations.     

Information security: Designing a stochastic‐network for throughput and reliability

Todas information and communication network requires a design that is secure to tampering. Traditional performance measures of reliability and throughput must be supplemented with measures of security. Recognition of an adversary who can inflict damage leads toward a game‐theoretic model. Through such a formulation, guidelines for network designs and improvements are derived. We opt for a design that is most robust to withstand both natural degradation and adversarial attacks. Extensive computational experience with such a model suggests that a Nash‐equilibrium design exists that can withstand the worst possible damage. Most important, the equilibrium is value‐free in that it is stable irrespective of the unit costs associated with reliability vs. capacity improvement and how one wishes to trade between throughput and reliability. This finding helps to pinpoint the most critical components in network design. From a policy standpoint, the model also allows the monetary value of information‐security to be imputed. © 2009 Wiley Periodicals, Inc. Naval Research Logistics, 2009     

基于表面电荷法的像管静电场计算

与传统的有限差分法和有限元法相比,表面电荷法可降低单元剖分难度并能处理开放边界,更适于计算静电透镜的静电场。针对轴对称及非轴对称两类结构,采用样条函数及奇异形状函数改进电极表面的电荷密度估计,讨论了二维及三维表面电荷法的实现。与具有解析解的单位圆盘进行比较,分析了表面电荷法的电位计算精度,并用于轴对称及非轴对称像管计算。结果表明：对轴对称系统,在文中给定步长下,二维及三维表面电荷法与有限差分法计算相对误差不超过10^-3,且二维方法精度整体高于三维方法,二维、三维表面电荷法对3种像面位置的计算结果与有限差分法结果相比,最大误差不超过0.6mm;对非轴对称系统,3种方案下轴外电子运行轨迹的差异明显,非对称因素所产生的干涉场影响是不可忽略的。     

静电放电抗扰度试验中辐射场若干特性的试验研究

国际标准IEc61000-4—2中对静电放电抗扰度试验方法和试验布局进行了规定,但是对间接静电放电（ESD）产生的辐射场没有进行描述。根据标准IEc61000—4—2,首先对水平耦合板和垂直耦合板放电时垂直耦合板上的场分布进行了分析,然后对几种医疗设备进行静电放电抗扰度试验。试验得出：1）对两种耦合板放电时,水平耦合板上电场强度和磁场强度随测试距离的变化趋势不同;2）试验结果对ESD模拟器的种类有着依赖关系。这些结果为研究电子设备静电放电抗扰度试验新方法、新标准和新的试验平台及诊断评估方法提供了参考依据。     

海浪水压场正态性及参数模型

在对不同海域、不同海况和不同水深下测的大量海浪水压场数据分析的基础上,采用Epps-Pulley检验方法对海浪水压场信号的正态性进行了检验,进而利用Box-Jenkins方法对海浪水压场信号服从何种线性模型进行了辨识。结果表明,在100 s时间内,海浪水压场信号服从或近似服从正态分布,并可利用AR模型对其进行描述。     

镜像法求解导体球外点电荷电场的代数解

用代数法求解了导体球外点电荷在空间产生的静电场。得到了能反映导体球中自由电荷性质的新解该结果既符合唯一性定理,又有明确的物理含义。     

创新消防现代警务机制思考

加强消防警务机制建设是促进消防工作规范化、制度化、法制化和社会化建设的有力保障,是保证社会经济发展、社会和谐稳定的基本条件。近年来消防部队在警务机制改革方面迈出了可喜的步伐,但是由于社会发展机制和体制的限制,消防力量不足、勤务实战演练效果不理想、信息化建设水平偏低等问题依旧存在,有待于在创新现代消防警务机制建设中加以解决。     

一种改进的云评估方法

在现有云评估方法的基础上,将云概念化和逆向云发生器引入其中,对原有评估方法进行改进。利用改进后的评估方法对C4ISR系统效能进行评估,使评语的各个数字特征由训练数据得到而非人为确定,进一步消除了评估过程的主观性。     

基于加权D-S证据理论的辐射源目标识别

在目标识别中D-S证据理论应用较为广泛,该理论要求各传感器的重要程度相同,与作战使用相矛盾.就此提出了基于加权D-S证据理论的时空域目标识别方法,突出了不同传感器在目标识别中的地位和作用,使目标识别结果更接近作战实际.