Redundancy in Designs

The author contends that a previous Risk Analysis article overemphasized the pitfalls of incorporating redundancy into designs. Relevant aspects of that article are reviewed and commented upon, then the potentials and pitfalls of redundancy in systems and procedures are more broadly discussed. To provide a solid foundation for that discussion, some definitions for systems risk analysis terminology are presented. It is shown that pairs and larger sets of related failures (the physical causes of shortfalls in redundancy effectiveness) can be divided into two types: (1) cascading/induced failures and (2) common-external-cause failures. Each type has its own physical characteristics and implications for mathematical modeling. Service experience with large-commercial-airplane jet-engine propulsion systems is used to illustrate the two types of related failures. Finally, an overview is provided of event-sequence analysis, an alternative approach to systems risk analysis. When the possibility of related failures of mutually-redundant system elements must be accounted for, event-sequence analysis can usually do that better than fault-tree analysis.     

一种面向知识共享的虚拟社区模型框架

首先在分析知识共享影响因素的基础上,指出了虚拟社区是实现知识共享的有效方式之一;然后通过分析虚拟社区的内涵及其组织结构,进一步给出了一种面向知识共享的虚拟社区模型框架,并分析了该模型框架中表示层、应用层和存储层3个层面的组成部件及其功能;最后给出了实现虚拟社区的措施。所给出的虚拟社区模型框架,对于构建虚拟社区和实现有效的知识共享具有借鉴指导意义。     

Loss of Life Caused by the Flooding of New Orleans After Hurricane Katrina: Analysis of the Relationship Between Flood Characteristics and Mortality

In this article a preliminary analysis of the loss of life caused by Hurricane Katrina in the New Orleans metropolitan area is presented. The hurricane caused more than 1,100 fatalities in the state of Louisiana. A preliminary data set that gives information on the recovery locations and individual characteristics for 771 fatalities has been analyzed. One-third of the analyzed fatalities occurred outside the flooded areas or in hospitals and shelters in the flooded area. These fatalities were due to the adverse public health situation that developed after the floods. Two-thirds of the analyzed fatalities were most likely associated with the direct physical impacts of the flood and mostly caused by drowning. The majority of victims were elderly: nearly 60% of fatalities were over 65 years old. Similar to historical flood events, mortality rates were highest in areas near severe breaches and in areas with large water depths. An empirical relationship has been derived between the water depth and mortality and this has been compared with similar mortality functions proposed based on data for other flood events. The overall mortality among the exposed population for this event was approximately 1%, which is similar to findings for historical flood events. Despite the fact that the presented results are preliminary they give important insights into the determinants of loss of life and the relationship between mortality and flood characteristics.     

A Probabilistic Model of the Economic Risk to Britain's Railway Network from Bridge Scour During Floods

Scour (localized erosion by water) is an important risk to bridges, and hence many infrastructure networks, around the world. In Britain, scour has caused the failure of railway bridges crossing rivers in more than 50 flood events. These events have been investigated in detail, providing a data set with which we develop and test a model to quantify scour risk. The risk analysis is formulated in terms of a generic, transferrable infrastructure network risk model. For some bridge failures, the severity of the causative flood was recorded or can be reconstructed. These data are combined with the background failure rate, and records of bridges that have not failed, to construct fragility curves that quantify the failure probability conditional on the severity of a flood event. The fragility curves generated are to some extent sensitive to the way in which these data are incorporated into the statistical analysis. The new fragility analysis is tested using flood events simulated from a spatial joint probability model for extreme river flows for all river gauging sites in Britain. The combined models appear robust in comparison with historical observations of the expected number of bridge failures in a flood event. The analysis is used to estimate the probability of single or multiple bridge failures in Britain's rail network. Combined with a model for passenger journey disruption in the event of bridge failure, we calculate a system‐wide estimate for the risk of scour failures in terms of passenger journey disruptions and associated economic costs.     

Reliability Analysis Based on the Losses from Failures

The conventional reliability analysis is based on the premise that increasing the reliability of a system will decrease the losses from failures. On the basis of counterexamples, it is demonstrated that this is valid only if all failures are associated with the same losses. In case of failures associated with different losses, a system with larger reliability is not necessarily characterized by smaller losses from failures. Consequently, a theoretical framework and models are proposed for a reliability analysis, linking reliability and the losses from failures. Equations related to the distributions of the potential losses from failure have been derived. It is argued that the classical risk equation only estimates the average value of the potential losses from failure and does not provide insight into the variability associated with the potential losses. Equations have also been derived for determining the potential and the expected losses from failures for nonrepairable and repairable systems with components arranged in series, with arbitrary life distributions. The equations are also valid for systems/components with multiple mutually exclusive failure modes. The expected losses given failure is a linear combination of the expected losses from failure associated with the separate failure modes scaled by the conditional probabilities with which the failure modes initiate failure. On this basis, an efficient method for simplifying complex reliability block diagrams has been developed. Branches of components arranged in series whose failures are mutually exclusive can be reduced to single components with equivalent hazard rate, downtime, and expected costs associated with intervention and repair. A model for estimating the expected losses from early-life failures has also been developed. For a specified time interval, the expected losses from early-life failures are a sum of the products of the expected number of failures in the specified time intervals covering the early-life failures region and the expected losses given failure characterizing the corresponding time intervals. For complex systems whose components are not logically arranged in series, discrete simulation algorithms and software have been created for determining the losses from failures in terms of expected lost production time, cost of intervention, and cost of replacement. Different system topologies are assessed to determine the effect of modifications of the system topology on the expected losses from failures. It is argued that the reliability allocation in a production system should be done to maximize the profit/value associated with the system. Consequently, a method for setting reliability requirements and reliability allocation maximizing the profit by minimizing the total cost has been developed. Reliability allocation that maximizes the profit in case of a system consisting of blocks arranged in series is achieved by determining for each block individually the reliabilities of the components in the block that minimize the sum of the capital, operation costs, and the expected losses from failures. A Monte Carlo simulation based net present value (NPV) cash-flow model has also been proposed, which has significant advantages to cash-flow models based on the expected value of the losses from failures per time interval. Unlike these models, the proposed model has the capability to reveal the variation of the NPV due to different number of failures occurring during a specified time interval (e.g., during one year). The model also permits tracking the impact of the distribution pattern of failure occurrences and the time dependence of the losses from failures.     

Systems Analysis of Failures as a Quality Management Tool

Managers and quality practitioners are familiar with the linkage of the words quality and systems to denote a systematic approach to quality, as in BS5750 Quality Systems, say. There is, however, a more specialized use of the word systems that indicates the application of systems thinking and which gives rise to the adjective systemic (of, or pertaining to a system) rather than systematic (carrying out in a planned and orderly fashion). This paper examines the potential for applying systems thinking to the management of quality with particular reference to one branch of systems work: the study of failures. The paper draws comparisons between quality and systems analysis of failures and points out that some failures could equally well be described as quality problems and vice versa. The paper argues that problems at the system level are frequently overlooked or avoided by those undertaking quality improvement programmes, partly because individuals within an organization may experience only different, smaller aspects of a systemic problem and partly because the problem solvers may lack the means or motivation to tackle complex, poorly defined problem messes. It then goes on to suggest that use of a meta–method for problem analysis would enable such problems to be addressed. One such method that has been widely applied in the study of failures, the failures method, is described in detail and its application to a failure/quality problem is outlined.     

组织变革期企业的人员流动影响因素的实证研究

人才流失是我国国有企业尤其是组织变革期的企业所面临的重要问题。在回顾国内外有关员工流动主要研究成果的基础上,从个体、组织和社会3个层面,对处于变革期的一家电力企业的人员流动问题进行了实证研究,找出了影响该企业员工流动的11个因素,即年龄、党派、受教育程度、企业工龄、职称等级、所在部门、岗位性质、岗位等级、行政级别、评先进次数和培训次数,可为电力行业类似企业留人政策的制定和创新提供参考。     

Estimating the Probability of Human Error by Incorporating Component Failure Data from User-Induced Defects in the Development of Complex Electrical Systems

This article proposes a methodology for incorporating electrical component failure data into the human error assessment and reduction technique (HEART) for estimating human error probabilities (HEPs). The existing HEART method contains factors known as error-producing conditions (EPCs) that adjust a generic HEP to a more specific situation being assessed. The selection and proportioning of these EPCs are at the discretion of an assessor, and are therefore subject to the assessor's experience and potential bias. This dependence on expert opinion is prevalent in similar HEP assessment techniques used in numerous industrial areas. The proposed method incorporates factors based on observed trends in electrical component failures to produce a revised HEP that can trigger risk mitigation actions more effectively based on the presence of component categories or other hazardous conditions that have a history of failure due to human error. The data used for the additional factors are a result of an analysis of failures of electronic components experienced during system integration and testing at NASA Goddard Space Flight Center. The analysis includes the determination of root failure mechanisms and trend analysis. The major causes of these defects were attributed to electrostatic damage, electrical overstress, mechanical overstress, or thermal overstress. These factors representing user-induced defects are quantified and incorporated into specific hardware factors based on the system's electrical parts list. This proposed methodology is demonstrated with an example comparing the original HEART method and the proposed modified technique.     

A unique event and Delphi

In this article the author describes the application of a Delphi forecast in response to a unique event—The Stockton & Darlington Railway Anniversary 1975. He illustrates the successes and failures of the survey and makes recommendations as to how failures may have been avoided. The article also includes ideas on how the Delphi approach might be used in other ways in social forecasting.     

Survival and strategy of small/micro firms

 There is no doubt that small firms have shown a great tenacity to survive despite many adverse influences. This is especially surprising in view of the apparently low profits and frequent failures. This paper aims to provide an empirical insight into the diverse problems and means of survival of small/micro firms. The research focused on the konnyaku industry, which predominantly is neither fast-growing nor prone to failure but, instead, has average performance and survival. The purpose of this article is to shed some light on the business alliances and competition in this industry in which members of a sanchi do not cooperate but compete against each other.     

Effects of maintenance policies on the productivity of flexible manufacturing cells

Flexible manufacturing cells (FMCs) often operate with increasing failure rate due to extensive utilization and wear-outs of equipment. While maintenance plans can eliminate wear-out failures, random failures are still unavoidable. This paper discusses a procedure that combines simulation and analytical models to analyze the effects of corrective, preventive, and opportunistic maintenance policies on productivity of a flexible manufacturing cell. The production output rate of an FMC, which is a function of availability, is determined under different maintenance policies and mean time between failures.     

Post-Katrina Hazard Mitigation on the Gulf Coast

The article reviews the major hazard mitigation measures considered for the Gulf Coast following hurricanes between 2005 and 2008, especially Hurricanes Katrina and Ike. Basic similarities among and between the hazard events are noted, along with a wide variety of efforts to eliminate or reduce risks from natural hazards in establishing mitigation as the major protector of affected areas. Intergovernmental collaboration, insurance reform, and public risk perception are included. Both the processes used and substantive policy options are examined. This includes attempts at system-wide solutions in dealing with the mullti-state region for recovery from devastation and providing greater resiliency toward further hazard events. Such themes as a comprehensive system approach and the use of risk informed decision making, communication of risk to the public, and the use of professional and technical expertise, are being used on the Gulf Coast. Risk informed decision making uses techniques and methods from risk analysis, scenario planning, and multi-criteria decision analysis. Stakeholders are incorporated into the development of alternatives conveyed to the public. Policy alternative include coastal restoration measures such as barrier island and shoreline restoration, structural engineering such as floodwalls and levees, and nonstructural options such as buyouts, relocation, and effective zoning and building codes. The most comprehensive approaches follow a multiple lines of defense strategy to combine the various types of risk reduction measures.     

Linking leader inclusiveness to work unit performance: The importance of psychological safety and learning from failures

Despite burgeoning interest in how groups and organizations learn from failures, little is known about how leader behavior influences these learning processes. We analyzed longitudinal data collected at a large hospital and found that leader inclusiveness was positively associated with members' perceptions of psychological safety at Time 1, and that this relationship was stronger for members in low-performing units. Unit psychological safety climate appeared to facilitate learning from failures within the work unit (Time 2), which was positively associated with subsequent unit performance (Time 3).     

具有隐藏故障的多状态竞争失效系统检测策略研究

复杂工业系统的故障中有40%属于隐藏故障,若隐藏故障得不到及时消除,则可能导致巨大的经济损失。本文针对具有隐藏故障的多状态竞争失效系统,在考虑不完全检测的基础上,对其进行了维修建模。首先,基于制定的视情维修策略,分析了系统的更新情形;然后,基于所推导出的各种系统更新情形的发生概率,建立了以期望成本率为目标函数,以检测间隔时间为决策变量的维修模型。最后,以电容器组为例对所构建维修模型的适用性和有效性进行了验证,研究结果表明,检测质量对检测策略的制定有重要影响,因此研究具有隐藏故障的多状态竞争失效系统的检测策略时,有必要考虑检测误差。本文提出的维修建模方法不仅能在一定程度上丰富多状态竞争失效系统的维修策略理论与方法,还能为工程实际中复杂工业系统的维修工作提供理论基础与决策依据。     

考虑代销商保鲜努力的农产品委托代销策略研究

农业服务市场发展壮大推动了农产品销售服务模式创新。但是，作为经销模式有益补充的委托代销模式在我国农产品产销对接中还极少被采用。在代销商的保鲜努力影响农产品鲜度和损耗的假设条件下，构建了生产商和代销商的主从博弈模型，比较分析了支付服务费和视同买断两种委托代销方式的最优产品定价、代销期和保鲜努力水平，以及生产商和代销商的委托代销方式选择和达成委托代销协议的条件。结论表明，服务佣金和协议价是影响农产品委托代销策略的关键因素。若协议价足够高，生产商和代销商倾向于采用支付服务费委托代销方式；若协议价处于中间水平，生产商和代销商倾向于采用视同买断委托代销方式；若协议价过低，生产商和代销商不能达成委托代销协议，但是协议谈判的结果更可能向视同买断方式靠拢。此外，服务佣金契约和协议价契约不能协调农产品供应链。     

Too Big to Learn: The Effects of Major Acquisition Failures on Subsequent Acquisition Divestment

We examine whether firms learn from their major acquisition failures. Drawing from a threat‐rigidity theoretical framework, we suggest that firms do not learn from their major acquisition failures. Furthermore, we hypothesize that host‐country experience reinforces the negative effects of major acquisition failures. Our research hypotheses are tested using an event history analysis of 741 acquisitions undertaken by French listed and non‐listed firms in the USA between January 1988 and December 2008. We use failure divestment (divestment resulting from acquisition failure) as a proxy for acquisition performance. Consistent with our theoretical framework, we find that major acquisition failures have a negative impact on future acquisition performance. Furthermore, we find that such negative effects are reinforced by firms’ host‐country experience.     

面向相继故障的复杂网络上袭击策略研究

针对复杂网络遭遇随机故障和蓄意攻击引发的相继故障问题,采用网络中节点j上的初始负荷为Lj=βkjα(这里kj表示为节点j的度,α和β是可调参数),并基于崩溃节点负荷局域择优重新分配的原则,提出了一个带有可调参数的相继故障模型.通过度量网络鲁棒性的一个新的指标,即:关键阈值Tc,对比了两种袭击策略下网络上的全局相继故障现象.数值模拟得到了一些有趣而又违背直觉的结论:一方面,当模型中的可调参数α<1时,袭击网络中度最小的节点比袭击度最大的节点更易导致相继故障;而另一方面,当α=1时,两种袭击对网络的破坏几乎是相同的.此外,数值模拟结果也得到了理论解析的验证.     

A Mathematical Model of Service Failure and Recovery Strategies*

Understanding the nature of service failures and their impact on customer responses and designing cost‐effective recovery strategies have been recognized as important issues by both service researchers and practitioners. We first propose a conceptual framework of service failure and recovery strategies. We then transform it into a mathematical model to assist managers in deciding on appropriate resource allocations for outcome and process recovery strategies based on customer risk profiles and the firm's cost structures. Based on this mathematical model we derive optimal recovery strategies, conduct sensitivity analyses of the optimal solutions for different model parameters, and illustrate them through numerical examples. We conclude with a discussion of managerial implications and directions for future research.     

The social role theory of unethical leadership

Challenging the standard reasoning regarding leaders' ethical failures, we argue that a potent contributor to these failures is the social role expectations of leaders. We maintain that leaders' central role expectation of goal achievement contributes to the over-valuing of group goals and greater moral permissibility of the means used to achieve these goals. In studies 1 and 2 we demonstrated that the role of leader, relative to group member, is associated with an increased appraisal of group goals which is predicted by the leaders' role expectations and not driven by the psychological effects of power. Next, we experimentally demonstrated the importance of both role expectations of leadership and group goal importance in leaders' justification to engage in morally questionable behavior to achieve group goals. Finally, we supported the social role predictions in a laboratory experiment by assigning people to roles and assessing goal importance and unethical decision-making and behaviors.