Lognormal Approximations of Fault Tree Uncertainty Distributions

Fault trees are used in reliability modeling to create logical models of fault combinations that can lead to undesirable events. The output of a fault tree analysis (the top event probability) is expressed in terms of the failure probabilities of basic events that are input to the model. Typically, the basic event probabilities are not known exactly, but are modeled as probability distributions: therefore, the top event probability is also represented as an uncertainty distribution. Monte Carlo methods are generally used for evaluating the uncertainty distribution, but such calculations are computationally intensive and do not readily reveal the dominant contributors to the uncertainty. In this article, a closed‐form approximation for the fault tree top event uncertainty distribution is developed, which is applicable when the uncertainties in the basic events of the model are lognormally distributed. The results of the approximate method are compared with results from two sampling‐based methods: namely, the Monte Carlo method and the Wilks method based on order statistics. It is shown that the closed‐form expression can provide a reasonable approximation to results obtained by Monte Carlo sampling, without incurring the computational expense. The Wilks method is found to be a useful means of providing an upper bound for the percentiles of the uncertainty distribution while being computationally inexpensive compared with full Monte Carlo sampling. The lognormal approximation method and Wilks’s method appear attractive, practical alternatives for the evaluation of uncertainty in the output of fault trees and similar multilinear models.     

树木崇拜与民俗文化

中华民族有着丰富的民俗文化,其中,有许多是与树木有关的,文章就此探讨了树木崇拜及其引发的社会行为。     

论间接故意与过于自信的过失 --理论与实际的矛盾

间接故意与过于自信的过失是犯罪构成中主观方面最容易混淆的两种罪过,本文对这两种罪过进行了系统的比较,并对两者的实际操作中所体现的矛盾进行了分析,最后文章对矛盾提出了解决的方案。     

论缔约过失责任制度——兼评合同自由与合同正义

缔约过失责任制度的产生与发展是 19世纪下半叶尤其是 2 0世纪以来合同法走向现代化的重要标志之一。缔约过失责任制度的价值论基础 ,就在于诚实信用原则所体现的正义价值与合同自由原则所体现的自由价值构成相倚的两极 ,产生相互亲和的张力。加强对我国缔约过失责任制度的深入研究 ,评析其得失 ,有助于进一步完善我国缔约过失责任制度     

基于规则的MCD磨粒信息诊断专家系统

研究了一种用于发动机磨损状态监测与故障诊断的MCD磨粒信息诊断专家系统 (ES)。首先讨论了诊断知识的获取与规则表示方法 ,接着根据面向对象模板化设计思想 ,研究了一种知识库、推理机和人机界面的一体化构造策略 ,并在此基础上引入深度优先搜索、反向引导正向控制的启发性推理机制     

A Tabu Search Heuristic for the Location of Multi-Type Protection Devices on Electrical Supply Tree Networks

The problem of determining the number of multi-type protection devices and their locations on electrical supply tree networks with subtree dependency is investigated. The aim is to reduce the amount of inconvenience caused to customers that are affected by any given fault on the networks. An appropriate implementation of tabu search is proposed. We exploit a variable neighborhood and a soft aspiration level, and we embed a data structure and reduction tests into the search to speed up the process. Computational tests are performed on randomly generated electrical tree networks varying in size and branch complexity with encouraging results.     

Wide Diameters of Cartesian Product Graphs and Digraphs

In graph theory and study of fault tolerance and transmission delay of networks, connectivity and diameter of a graph are two very important parameters and have been deeply studied by many authors. Wide diameter combining connectivity with diameter is a more important parameter to measure fault tolerance and efficiency of parallel processing computer networks and has received much attention in the recent years. Diameter with width k of a graph G is defined as the minimum integer d for which between any two distinct vertices in G there exist at least k internally disjoint paths of length at most d. In the present paper, the tight upper bounds of wide diameter of the Cartesian product graphs are obtained. Some known results can be deduced or improved from ours.     

套管的失效分析

通过收集石油套管现场失效数据资料,以套管失效为顶事件建立了石油套管的故障树,该故障树共考虑了47个不同的基本事件。通过对套管故障树的分析,得到了套管失效故障树的一阶最小割集27个,二阶最小割集29个,四阶最小割集1个,确立了套管的主要失效形式为潜在损坏、套管挤毁、套管断裂及严重腐蚀,并提出了提高套管可靠性的措施。     

Soft Classification Trees

An extension of soft classification trees to multinomial outcomes is presented. Estimates of the method's predictive accuracy, as well as average tree size and tree depths, are systematically compared to those of the conventional Classification and Regression Tree (CART) approach by the means of simulations. A similar comparison is performed on real datasets. Results point to an advantage in favor of the soft tree.     

基于支持向量机的管理信息系统故障识别模型研究

管理信息系统故障影响着企业信息工程的开展。及时识别故障,能够为企业争取更多时间处理故障。因此,管理信息系统故障识别有着重要的研究意义和实践意义。基于支持向量机,构建管理信息系统故障识别模型,通过把样本应用于该模型,结果表明该模型具有较好的准确性,能有效识别管理信息系统故障。