Understanding Community Resilience from a PRA Perspective Using Binary Decision Diagrams

Probabilistic risk assessment (PRA) is a useful tool to assess complex interconnected systems. This article leverages the capabilities of PRA tools developed for industrial and nuclear risk analysis in community resilience evaluations by modeling the food security of a community in terms of its built environment as an integrated system. To this end, we model the performance of Gilroy, CA, a moderate‐size town, with regard to disruptions in its food supply caused by a severe earthquake. The food retailers of Gilroy, along with the electrical power network, water network elements, and bridges are considered as components of a system. Fault and event trees are constructed to model the requirements for continuous food supply to community residents and are analyzed efficiently using binary decision diagrams (BDDs). The study also identifies shortcomings in approximate classical system analysis methods in assessing community resilience. Importance factors are utilized to rank the importance of various factors to the overall risk of food insecurity. Finally, the study considers the impact of various sources of uncertainties in the hazard modeling and performance of infrastructure on food security measures. The methodology can be applicable for any existing critical infrastructure system and has potential extensions to other hazards.     

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.     

Toward an Application Guide for Safety Integrity Level Allocation in Railway Systems

The work in the article presents the development of an application guide based on feedback and comments stemming from various railway actors on their practices of SIL allocation to railway safety‐related functions. The initial generic methodology for SIL allocation has been updated to be applied to railway rolling stock safety‐related functions in order to solve the SIL concept application issues. Various actors dealing with railway SIL allocation problems are the intended target of the methodology; its principles will be summarized in this article with a focus on modifications and precisions made in order to establish a practical guide for railway safety authorities. The methodology is based on the flowchart formalism used in CSM (common safety method) European regulation. It starts with the use of quantitative safety requirements, particularly tolerable hazard rates (THR). THR apportioning rules are applied. On the one hand, the rules are related to classical logical combinations of safety‐related functions preventing hazard occurrence. On the other hand, to take into account technical conditions (last safety weak link, functional dependencies, technological complexity, etc.), specific rules implicitly used in existing practices are defined for readjusting some THR values. SIL allocation process based on apportioned and validated THR values is finally illustrated through the example of “emergency brake” subsystems. Some specific SIL allocation rules are also defined and illustrated.     

花木租赁行业的市场初探

随着经济不断发展和环境意识的增强 ,花木租赁市场空间越来越大。前景看好。花木租赁行业是近年来出现的一个新兴行业 ,通过对中国部分花木城市租赁行业调查了解 ,在具有广大养花爱好者及经济持续高速发展的中国 ,花木租赁行业的兴起将带动整个花卉市场的规模生产及成为花木市场销量的主流     

从《道路交通安全法》看强制责任保险的发展对策

《道路交通安全法》的开始实施,使机动车第三者责任强制保险的法律地位得到认可。本文以此为出发点,探讨了强制责任保险的性质、目前的发展情况和面临的问题以及解决这些问题的对策,以期准确了解和完善该制度并促进其在我国的发展。     

Survival trees with time-dependent covariates: Application to estimating changes in the incubation period of AIDS

Tree-structured methods for exploratory data analysis have previously been extended to right-censored survival data. We further extend these methods to allow for truncation and time-dependent covariates. We apply the new methods to a data set on incubation times of acquired immunodeficiency syndrome (AIDS), using calendar time as a time-dependent covariate. Contrary to expectation, we find that rates of progression to AIDS appear to be faster after August 1989 than before.     

基于任务模块的实时软件可靠性模型

根据实时多任软件的特征和各任务所占系统时间的非均匀分布，以任务模块为基本测试单元，提出一种实时多任务软件可靠性评价模型。由于任务周期、任务切换方式、切换频率以及任务故障率等基本参数易于分析和测试，因此该模型具有良好的可实现性和可扩充性，为实时多任务软件的可靠性评价开辟了一条新途径     

远程通信铁路机车运用状态实时监测系统的研究

铁路机车运用状态实时监测系统将机车的运行信息、故障信息及机车的参数信息通过远程移动通信技术直接传输到地面监测系统，解决了长期以来铁路地面无法实时采集机车数据的问题，从而实现了对机车的远程实时监测。利用电子地图技术实现对运行机车自动跟踪、定位、轨迹实时显示；采用故障诊断专家系统设计思想对实时故障进行诊断处理、指导司机操作，确保行车安全；对机车参数信息进行存储、分析、；12总，为机车操纵人员和维修人员提供决策依据，为状态修提供原始数据。主要阐述了系统的总体架构及各模块的设计思想，可以为其他远程监测系统提供很好的解决方案。     

基于案例推理的压力容器故障维修方法

针对目前压力容器故障维修依赖经验知识的程度高,智能知识库利用率低的问题,提出基于案例推理的压力容 器故障维修方法。通过定义对应故障特征关键词字典,优化案例库案例存储与索引机制,对故障案例信息进行结构化和 知识化;并采用结合最近相邻法和灰色关联度算法的案例相似度匹配方法,提高案例匹配精度。经应用实例验证,从案 例库中匹配相似案例速度快、可靠度高,可供原故障案例参考。因此,该方法在实际使用中有效降低了经验知识的依赖 程度,较好地利用智能知识库,为压力容器全生命周期的维护、修理和操作( MRO)提供便利。     

基于ARM9的无线数据传输终端的设计

设计了1个基于ARM9与GPRS模块的工程机械无线数据传输终端。该终端以samsung公司的s3c2440a微处理器为控制核心，利用BenQ M22模块进行GPRS无线传输，克服了工业、军事等领域一些设备工作环境受地域限制数据传输不便的问题。实现实时监控，为机械设备故障诊断与维修提供了依据。