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System Failure (system + failure)
Kinds of System Failure Selected AbstractsBanking System Failures in Developing and Transition Countries: Diagnosis and PredictionECONOMIC NOTES, Issue 1 2000P. Honohan First page of article [source] Set theoretic formulation of performance reliability of multiple response time-variant systems due to degradations in system componentsQUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 2 2007Young Kap Son Abstract This paper presents a design stage method for assessing performance reliability of systems with multiple time-variant responses due to component degradation. Herein the system component degradation profiles over time are assumed to be known and the degradation of the system is related to component degradation using mechanistic models. Selected performance measures (e.g. responses) are related to their critical levels by time-dependent limit-state functions. System failure is defined as the non-conformance of any response and unions of the multiple failure regions are required. For discrete time, set theory establishes the minimum union size needed to identify a true incremental failure region. A cumulative failure distribution function is built by summing incremental failure probabilities. A practical implementation of the theory can be manifest by approximating the probability of the unions by second-order bounds. Further, for numerical efficiency probabilities are evaluated by first-order reliability methods (FORM). The presented method is quite different from Monte Carlo sampling methods. The proposed method can be used to assess mean and tolerance design through simultaneous evaluation of quality and performance reliability. The work herein sets the foundation for an optimization method to control both quality and performance reliability and thus, for example, estimate warranty costs and product recall. An example from power engineering shows the details of the proposed method and the potential of the approach. Copyright © 2006 John Wiley & Sons, Ltd. [source] Assessment of high density of onsite wastewater treatment systems on a shallow groundwater coastal aquifer using PCAENVIRONMETRICS, Issue 3 2005Steven Carroll Abstract Onsite wastewater treatment systems are common throughout the world, including Australia, with approximately 17% of the Australian population relying on these systems to treat and ultimately dispose of wastewater. Systems which are properly sited, designed and managed are an effective way of providing the necessary treatment of wastewater. However, incidence of onsite system failure is common, and this is further compounded in areas where high densities of systems are established. The density of systems is not appropriately assessed in the siting and design stage. Various factors, such as site and soil characteristics and climate, can influence the treatment efficiency, and this is more critical in high density areas. Principal component analysis was used for assessing chemical and microbiological data from shallow groundwater below a high density of onsite treatment systems. The results of this study confirmed that high system densities can significantly impact shallow groundwater systems. Additionally, changes in spatial and climatic conditions, as well as the type of onsite system, can also influence the quality of groundwater. Copyright © 2004 John Wiley & Sons, Ltd. [source] Reliability modelling of uninterruptible power supply systems using fault tree analysis methodEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 6 2009Mohd Khairil Rahmat Abstract The aim of this paper is to investigate the reliability parameters estimation method for the uninterruptible power supply (UPS) systems using the Fault Tree Analysis (FTA) technique. FTA is a top,down approach to identify all potential causes leading to system failure. The computation of the system's failure probability is the main goal of this analysis, as this value can be used to calculate other important system reliability parameters such as failure rates, mean time between failures and reliability. In this paper, the FTA method was applied to five different UPS topologies and the results obtained were compared and discussed in detail. By comparing the critical fault path of the system, it was found that the inverter failures contributed most significantly to the system failure. It was also found that the probability of failure of a UPS system can be reduced by the inclusion of bypass supply, given that the failure rate of the events that causing the failure of the bypass supply should be lower compared to the ones for the main utility supply. Finally, to validate the results obtained from this method, comparisons were made to the results from other methods such as the Reliability Block Diagram, Boolean Truth Table, Probability Tree, Monte-Carlo Simulation and Field Data reliability estimation methods. Copyright © 2008 John Wiley & Sons, Ltd. [source] Numerical Modeling of Unsaturated Flow in Wastewater Soil Absorption SystemsGROUND WATER MONITORING & REMEDIATION, Issue 2 2003Deborah N. Huntzinger Beach It is common practice in the United States to use wastewater soil absorption systems (WSAS) to treat domestic wastewater. WSAS are expected to provide efficient, long-term removal of wastewater contaminants prior to ground water recharge. Soil clogging at the infiltrative surface of WSAS occurs due to the accumulation of suspended solids, organic matter, and chemical precipitates during continued wastewater infiltration. This clogging zone (CZ) creates an impedance to flow, restricting the hydraulic conductivity and rate of infiltration. A certain degree of clogging may improve the treatment of wastewater by enhancing purification processes, in part because unsaturated flow is induced and residence times are significantly increased. However, if clogging becomes excessive, the wastewater pond height at the infiltrative surface can rise to a level where system failure occurs. The numerical model HYDRUS-2D is used to simulate unsaturated flow within WSAS to better understand the effect of CZs on unsaturated flow behavior and hydraulic retention times in sandy and silty soil. The simulations indicate that sand-based WSAS with mature CZs are characterized by a more widely distributed flow regime and longer hydraulic retention times. The impact of clogging on water flow within the silt is not as substantial. For sand, increasing the hydraulic resistance of the CZ by a factor of three to four requires an increase in the pond height by as much as a factor of five to achieve the same wastewater loading. Because the degree of CZ resistance directly influences the pond height within a system, understanding the influence of the CZ on flow regimes in WSAS is critical in optimizing system design to achieve the desired pollutant-treatment efficiency and to prolong system life. [source] Distributed object-oriented switching system software platform designINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 7 2001Hiroshi Sunaga Abstract Key technologies are presented and evaluated for establishing a distributed object-oriented switching system platform. This platform is based on CORBA, which can enhance software productivity and system scalability and is thus widely used in the information technology field. Conditions and requirements specific to switching systems, such as very high-performance and non-stop operation, are analysed and mapped to the main elements of CORBA. How to deploy and bind objects so as to minimize the processing load is clarified. Mechanisms that guarantee system reliability (saving calls in service when a system failure occurs and avoiding the spread of faults) are also presented. Evaluation of the number of dynamic program steps for systems using fully compliant CORBA, improved CORBA, and a proprietary high-speed object-request broker (ORB) shows that constructing a communication switching system by using the high-speed ORB approach is sufficient, but CORBA-compliant approaches should be used to provide an interoperable interface for communicating with external compliant systems. Copyright © 2001 John Wiley & Sons, Ltd. [source] Living donor liver transplantation for children with liver failure and concurrent multiple organ system failureLIVER TRANSPLANTATION, Issue 10 2001Cara L. Mack Liver transplantation for pediatric patients in liver failure and multiple organ system failure (MOSF) often results in poor patient survival. Progression of organ failure occurs while awaiting a cadaveric allograft. Therefore, we considered living donor liver transplantation (LDLT) in this critically ill group of children and report our initial results with comparison to a similar group who received cadaveric donation (CAD). A retrospective chart review was performed on all pediatric liver transplant recipients who met criteria for MOSF at the time of transplantation. Data collection involved pretransplantation patient profiles, as well as postoperative complications and patient survival. Eight patients in MOSF received living donor transplants and 11 patients received a cadaveric allograft. Mean wait time was 3.5 days in the LDLT group and 6.5 days in the CAD group. Pretransplantation patient profiles and postoperative complications were similar between groups. Mean cold ischemia times were 3.8 hours in the LDLT group and 7.9 hours in the CAD group (P = .0002). Thirty-day and 6-month survival rates of the LDLT group were 88% and 63% compared with 45% and 27% in the CAD group, respectively. Living donor transplant recipients in MOSF had decreased wait times to transplantation, as well as decreased cold ischemia times, compared with cadaveric transplant recipients. Patients in the LDLT group had markedly improved survival compared with the CAD group. Timely transplantation before worsening organ failure may account for these findings. [source] Chronic Pain and Obstetric Management of a Patient with Tuberous SclerosisPAIN MEDICINE, Issue 2 2007Louise M. Byrd MRCOG ABSTRACT Chronic nonmalignant pain is very disabling and carries a heavy financial strain on the individual and society as a whole. This case describes a woman with tuberous sclerosis, in her fourth pregnancy. Approximately 18 months prior to pregnancy, intractable left loin pain, thought to be secondary to hemorrhage within a tuberous lesion in the left kidney, had led to the siteing of an intrathecal morphine pump. The risks of system failure (dislodgement, dislocation), escalating dosage, infection, use in labor, and neonatal opioid withdrawal are all explored and discussed. While data are limited, with increasing use of intrathecal opioids for nonmalignant pain, such patients may be seen more regularly in obstetric clinics. With a multidisciplinary team approach, risks can be minimized and outcome for mother and baby optimized. [source] High-dose chemotherapy with autologous hematopoietic stem cell rescue for stage 4B retinoblastoma,PEDIATRIC BLOOD & CANCER, Issue 1 2010Ira J. Dunkel MD Abstract Background Stage 4b retinoblastoma (central nervous system metastatic disease) has been lethal in virtually all cases reported. Here we describe a series of eight patients treated with intensive chemotherapy, defined as the intention to include high-dose chemotherapy with autologous hematopoietic stem cell rescue. Procedure Induction chemotherapy included cyclophosphamide and/or carboplatin with a topoisomerase inhibitor. High-dose chemotherapy regimens were carboplatin and thiotepa with or without etoposide (n,=,3) or carboplatin, etoposide, and cyclophosphamide (n,=,2). Results Seven patients had leptomeningeal disease and one patient had only direct extension to the CNS via the optic nerve. Three patients had stage 4b disease at the time of original diagnosis of the intra-ocular retinoblastoma; five had later onset at a median of 12 months (range 3,69 months). One patient died of toxicity (septicemia and multi-organ system failure) during induction and two had disease progression prior to high-dose chemotherapy. Five patients received high-dose chemotherapy at a median of 6 months (range 4,6) post-diagnosis of stage 4b disease. Two patients survive event-free at 40 and 101 months; one was irradiated following recovery from the high-dose chemotherapy. Conclusions Intensive multimodality therapy may be beneficial for some patients with stage 4b retinoblastoma. Longer follow-up will determine whether it has been curative. Pediatr Blood Cancer 2010;55:149,152. © 2010 Wiley-Liss, Inc. [source] Random, systematic, and common cause failure: How do you manage them?,PROCESS SAFETY PROGRESS, Issue 4 2006Michela Gentile Abstract A safety instrumented system (SIS) may fail to operate as desired when one or more of its devices fail due to random, systematic, and common cause events. IEC 61511 (ANSI/ISA 84.00.01,2004) stresses the importance of minimizing the propagation of device failure into system failure through design, operating, inspection, and maintenance practices. To fully understand the lifecycle requirements, it is first necessary to understand the types of failures and their potential effects on the SIS. Although several technical standards and other specialized literature address the topic, it is still a "fuzzy" matter, subject to misunderstanding and discussion. IEC 61511 Clause 11.9 requires that the SIL be verified using quantitative analysis, such as reliability block diagrams, fault tree analysis, and Markov modeling. This analysis includes only those dangerous failures that are random in nature. Common cause failures may or may not be included in the verification calculation depending on whether they exhibit random or systematic behavior. Any personnel assigned responsibility for verifying the SIL should understand each failure type and the strategies that can be used against it. Consequently, this article provides an overview of random, systematic, and common cause failures and clarifies the differences in their management within IEC 61511. © 2006 American Institute of Chemical Engineers Process Saf Prog, 2006 [source] The use of not logic in fault tree analysisQUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 3 2001J. D. Andrews Abstract Risk and safety assessments carried out on potentially hazardous industrial systems commonly employ fault tree analysis to predict the probability or frequency of system failure. Causes of the system failure mode are developed in an inverted tree structure where the events are linked using logic gates. The type of logic is usually restricted to AND and OR gates which makes the fault tree structure coherent. The use, directly or indirectly, of the NOT logic gate is generally discouraged as this can result in a non-coherent structure. Non-coherent structures mean that components' working states contribute to the failure of the system. The qualitative and quantitative analysis of such fault trees can present additional difficulties when compared to the coherent versions. This paper examines some of the difficulties that can occur, and what potential benefits can be derived from the incorporation of NOT logic. It is shown that the binary decision diagram (BDD) method can overcome some of the difficulties in the analysis of non-coherent fault trees. Copyright © 2001 John Wiley & Sons, Ltd. [source] Using Population Segmentation to Provide Better Health Care for All: The "Bridges to Health" ModelTHE MILBANK QUARTERLY, Issue 2 2007JOANNE LYNN The model discussed in this article divides the population into eight groups: people in good health, in maternal/infant situations, with an acute illness, with stable chronic conditions, with a serious but stable disability, with failing health near death, with advanced organ system failure, and with long-term frailty. Each group has its own definitions of optimal health and its own priorities among services. Interpreting these population-focused priorities in the context of the Institute of Medicine's six goals for quality yields a framework that could shape planning for resources, care arrangements, and service delivery, thus ensuring that each person's health needs can be met effectively and efficiently. Since this framework would guide each population segment across the institute's "Quality Chasm," it is called the "Bridges to Health" model. [source] CRIMINALIZATION OF MEDICAL ERROR: WHO DRAWS THE LINE?ANZ JOURNAL OF SURGERY, Issue 10 2007Sidney W. A. Dekker As stakeholders struggle to reconcile calls for accountability and pressures for increased patient safety, criminal prosecution of surgeons and other health-care workers for medical error seems to be on the rise. This paper examines whether legal systems can meaningfully draw a line between acceptable performance and negligence. By questioning essentialist assumptions behind ,crime' or ,negligence', this paper suggests that multiple overlapping and partially contradictory descriptions of the same act are always possible, and even necessary, to approximate the complexity of reality. Although none of these descriptions is inherently right or wrong, each description of the act (as negligence, or system failure, or pedagogical issue) has a fixed repertoire of responses and countermeasures appended to it, which enables certain courses of action while excluding others. Simply holding practitioners accountable (e.g. by putting them on trial) excludes any beneficial effects as it produces defensive posturing, obfuscation and excessive stress and leads to defensive medicine, silent reporting systems and interference with professional oversight. Calls for accountability are important, but accountability should be seen as bringing information about needed improvements to levels or groups that can do something about it, rather than deflecting resources into legal protection and limiting liability. We must avoid a future in which we have to turn increasingly to legal systems to wring accountability out of practitioners because legal systems themselves have increasingly created a climate in which telling each other accounts openly is less and less possible. [source] The Short-term Pulsatile Ventricular Assist Device for Postcardiotomy Cardiogenic Shock: A Clinical Trial in ChinaARTIFICIAL ORGANS, Issue 4 2009Xue-jun Xiao Abstract:, Despite the recent advances in myocardial protection, surgical techniques, intra-aortic balloon therapy, and maximal pharmacological support, postoperative ventricular dysfunction continues to occur in 0.5,1.0% of all patients undergoing cardiac surgery. Ventricular assist device (VAD) is an important therapeutic adjunct in treating patients with profound ventricular dysfunction with postcardiotomy cardiogenic shock. The purpose of this report was to describe the clinical results with the China-made Luo-Ye VAD as a short-term circulatory support. From May 1998 to December 2006, 17 patients with postcardiotomy cardiogenic shock were supported by the Luo-Ye VAD. Of these patients, 10 were males and seven were females with a mean age of 49.6 years (range 36,68 years). All cases were supported by left VAD (LVAD). Mean duration of support was 46.3 h (range 13,113 h). A criteria of insertion was established to standardize implantation criteria. Among the 17 patients treated with LVAD, eight (47.1%) patients were weaned from support and seven (41.2%) patients were discharged from hospital. Ten (58.8%) patients died while on LVAD support (nine cases) or shortly after weaning (one case). The causes of death in the entire group were cardiac (40%), renal failure (20%), neurologic (10%), sepsis (10%), and multiple organ system failure (20%). The complications were represented by bleeding, renal failure, neurologic event, infection, ventricular arrhythmias, etc. The Luo-Ye VAD functioned well and proved to be useful in patients with postcardiotomy cardiogenic shock. It carries a less-postoperative anticoagulant and a low incidence of VAD-related complications. The survival rate was encouraging in our small cohort of patients. [source] Renal autotransplantation for managing a short upper ureter or after ex vivo complex renovascular reconstructionBJU INTERNATIONAL, Issue 6 2005J. Christopher Webster Several topics related to the upper urinary tract are covered this month. Renal autotransplantation for managing a short upper ureter or after ex vivo complex renovascular reconstruction is described by authors from Florida. Percutaneous nephrolithotomy and various technical aspects associated with it are presented by authors from Germany and India. OBJECTIVE To report our contemporary experience with renal autotransplantation (AT), an established treatment for managing patients with a shortened ureter or renovascular disease, as despite its historical importance, AT remains an underused technique by urologists. PATIENTS AND METHODS All patients undergoing AT between 1997 and 2002 for a short ureter after ureteric injury and for renovascular disease were assessed by creatinine level and blood pressure before and after surgery, and antihypertensive drug use and complications. RESULTS Eleven patients had AT for renovascular disease and four for ureteric injury. There was no statistical difference in creatinine levels or blood pressure before and after surgery in either group. Eight patients treated with AT for renovascular disease required less antihypertensive medication after surgery. Minor complications occurred in both groups and included a suture abscess, chronic wound pain, and transient acute tubular necrosis. One patient in the ureteric injury group required a transplant nephrectomy after renal vein thrombosis, and one in the renovascular group died from multi-organ system failure. CONCLUSION AT remains a treatment option for patients with a short ureter after ureteric injury and in those with renovascular disease. Patients had stable renal function and blood pressure after surgery. Most patients treated for renovascular disease required less medication after AT. The procedure is associated with both minor and major complications, which must be considered before surgery. [source] REALITIES OF HEALTH POLICY IN NORTH AMERICA: GOVERNMENT IS THE PROBLEM, NOT THE SOLUTIONECONOMIC AFFAIRS, Issue 4 2008Brett J. Skinner Healthcare systems in North America are sometimes criticised as being expensive or socially irresponsible relative to comparable systems in OECD (Organisation for Economic Co-operation and Development) countries or regions. These perceived health system failures are often mistakenly attributed to greater private sector involvement in the delivery of medical care or the provision of medical insurance in Canada and the USA. However, the exact nature and scope of state involvement in the healthcare sector in Canada and the USA is also often misunderstood and underestimated. This paper presents a fact-based context for evaluating health policy in North America. [source] Understanding the implementation of software process improvement innovations in software organizationsINFORMATION SYSTEMS JOURNAL, Issue 1 2004Karlheinz Kautz Abstract., The development of software is a complex task frequently resulting in unfinished projects, project overruns and system failures. Software process improvement (SPI) approaches have been promoted as a promising remedy for this situation. The organizational implementation of such approaches is a crucial issue and attempts to introduce SPI into software organizations often fail. This paper presents a framework to understand, and subsequently successfully perform, the implementation of SPI innovations in software organizations. The framework consists of three perspectives on innovation: an individualist, a structuralist and an interactive process perspective. Applied to SPI, they emphasize different aspects of implementing SPI innovations. While the first focuses on leadership, champions and change agents, the second focuses on organization size, departmental and task differentiation and complexity, and the third perspective views the contents of the innovation, the social context and process of the implementation as related in an interactive process. We demonstrate the framework's applicability through two cases. We show that the three perspectives supplement each other and together provide a deeper understanding of the implementation process. Such understanding is crucial for the successful uptake of SPI approaches in software organizations. [source] Improving change tolerance through Capabilities-based design: an empirical analysisJOURNAL OF SOFTWARE MAINTENANCE AND EVOLUTION: RESEARCH AND PRACTICE, Issue 2 2008Ramya Ravichandar Abstract We introduce a Capabilities-based approach for constructing large-scale systems such that they are change - tolerant. The inherent complexity of software systems increases their susceptibility to change when subjected to the vagaries of user needs, technology advances, market demands, and other change-inducing factors. Despite the inevitability of change, traditional requirements engineering strives to develop systems based on a fixed solution; a mostly unsuccessful approach as evidenced by the history of system failures. In contrast, we utilize Capabilities,functional abstractions that are neither as amorphous as user needs nor as rigid as system requirements,to architect systems that accommodate change with minimum impact. These entities are designed to exhibit the desirable characteristics of high cohesion, low coupling, and balanced abstraction levels and are generated by a two-phased process called Capabilities Engineering. Phase I mathematically exploits the structural semantics of a function decomposition graph,a representation of user needs,to formulate change-tolerant Capabilities. Phase II optimizes these Capabilities to comply with schedule and technology constraints. In this paper, we present the overall framework of this process and detail the algorithm to identify Capabilities. In addition, we empirically evaluate the change tolerance of Capabilities resulting from Phase I. For this we examine the ripple effect of needs change on a real-world Course Evaluation System based on the original requirements-based design and the corresponding Capabilities-based design. Our experimental results indicate, with statistical significance, that the Capabilities-based design is less impacted by change and thereby improves the change tolerance of the system when subjected to needs volatility. Copyright © 2008 John Wiley & Sons, Ltd. [source] Bounding the optimal burn-in time for a system with two types of failureNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 8 2004Ji Hwan Cha Abstract Burn-in is a widely used method to improve the quality of products or systems after they have been produced. In this paper, we consider the problem of determining bounds to the optimal burn-in time and optimal replacement policy maximizing the steady state availability of a repairable system. It is assumed that two types of system failures may occur: One is Type I failure (minor failure), which can be removed by a minimal repair, and the other is Type II failure (catastrophic failure), which can be removed only by a complete repair. Assuming that the underlying lifetime distribution of the system has a bathtub-shaped failure rate function, upper and lower bounds for the optimal burn-in time are provided. Furthermore, some other applications of optimal burn-in are also considered. © 2004 Wiley Periodicals, Inc. Naval Research Logistics, 2004 [source] Analysis of management actions, human behavior, and process reliability in chemical plants.PROCESS SAFETY PROGRESS, Issue 1 2008I. impact of management actions Abstract While management and engineering actions have a significant impact on process reliability, these factors have received too little attention in calculating plant risks. In this work, the focus is on understanding and modeling the influence of human behavior patterns on plant safety in two settings. The first, introduced in Part I, involves a framework to estimate the impacts of management and engineering decisions, process operator performance, and processing equipment operations on the failure state of chemical plants. As examples, the impacts of poor training, maintenance problems, operator inabilities, control system failures, and excessive feed quantities, on failure states are studied. The management and engineering team and the operators are found to have significant impacts on process reliability. While the theoretical framework introduced herein is illustrated using hypothetical plant data, it should provide a basis for more quantitative safety analyses. Attempts to obtain operating data in industrial plants for validation of the framework were unsuccessful because of confidentiality and liability issues associated with industrial data. © 2007 American Institute of Chemical Engineers Process Saf Prog, 2007 [source] Management system failures identified in incidents investigated by the U.S. Chemical Safety and Hazard Investigation Board,PROCESS SAFETY PROGRESS, Issue 4 2004Angela S. Blair PE, Chemical Incident Investigator A key mission of the US Chemical Safety and Hazard Investigation Board (CSB) is to determine the root causes of incidents, report the findings, and issue recommendations to prevent similar incidents from occurring. CSB investigators respond to a variety of events occurring in a wide range of workplaces, from chemical plants and refineries to food-flavoring factories and steel mills. The details of each investigation are unique and the root causes are pertinent to each specific case. However, a common thread that emerges in CSB investigations is the inadequacy of management systems that might have prevented the incident from occurring. Examples of the systemic issues identified in CSB reports are: Lack of hazard review to predict and prevent incidents Insufficient investigation and follow-up after previous incidents Inadequate training of staff Failure to implement effective mechanical integrity programs These issues are well recognized as elements of a process safety management (PSM) program, although many incidents investigated by the CSB occurred at facilities that are not regulated by OSHA's process safety management rule.1 Indeed, a number of these incidents occurred at facilities that are well outside society's definition of "chemical plants." Please note that the opinions and conclusions expressed in this paper are those of the author, and do not necessarily represent the opinions of the Chemical Safety and Hazard Investigation Board. © 2004 American Institute of Chemical Engineers Process Saf Prog, 2004 [source] Maintenance contract assessment for aging systemsQUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 5 2008Anatoly Lisnianski Abstract This paper considers an aging system, where the system failure rate is known to be an increasing function. After any failure, maintenance is performed by an external repair team. Repair rate and cost of repair are determined by a corresponding maintenance contract with a repair team. There are many different maintenance contracts suggested by the service market to the system owner. In order to choose the best maintenance contract, a total expected cost during a specified time horizon should be evaluated for an aging system. In this paper, a method is suggested based on a piecewise constant approximation for the increasing failure rate function. Two different approximations are used. For both types of approximations, the general approach for building the Markov reward model is suggested in order to assess lower and upper bounds of the total expected cost. Failure and repair rates define the transition matrix of the corresponding Markov process. Operation cost, repair cost and penalty cost for system failures are taken into account by the corresponding reward matrix definition. A numerical example is presented in order to illustrate the approach. Copyright © 2008 John Wiley & Sons, Ltd. [source] Transient behavior of time-between-failures of complex repairable systemsQUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 4 2002J. Bert Keats Abstract It is well known for complex repairable systems (with as few as four components), regardless of the time-to-failure (TTF) distribution of each component, that the time-between-failures (TBFs) tends toward the exponential. This is a long-term or ,steady-state' property. Aware of this property, many of those modeling such systems tend to base spares provisioning, maintenance personnel availability and other decisions on an exponential TBFs distribution. Such a policy may suffer serious drawbacks. A non-homogeneous Poisson process (NHPP) accounts for these intervals for some time prior to ,steady-state'. Using computer simulation, the nature of transient TBF behavior is examined. The number of system failures until the exponential TBF assumption is valid is of particular interest. We show, using a number of system configurations and failure and repair distributions, that the transient behavior quickly drives the TBF distribution to the exponential. We feel comfortable with achieving exponential results for the TBF with 30 system failures. This number may be smaller for configurations with more components. However, at this point, we recommend 30 as the systems failure threshold for using the exponential assumption. Copyright © 2002 John Wiley & Sons, Ltd. [source] Contested hybridization of regulation: Failure of the Dutch regulatory system to protect minors from harmful mediaREGULATION & GOVERNANCE, Issue 2 2010Bärbel R. Dorbeck-Jung Abstract The hybridization of regulatory modes and instruments is currently a popular way to improve public regulation. However, it is still unclear whether combinations of hard law and soft law, co-regulation, and legally enforced self-regulation really make regulation more effective. Using the analytical framework of the "really responsive regulation" approach, in this article we explore effectiveness problems in a hybrid regulatory system that tries to protect minors from harmful media. In our analysis of low compliance rates in the context of system failures, we argue that effectiveness problems seem to arise from poorly informed staff members, lack of internal and external controls, low rule enforcement, insufficient overlap between public and private interests, poor social responsibility in the Dutch media sector, deficiencies in the institutional framework, an inconsistent regulatory strategy, and inadequate responses from responsible regulators. Furthermore, based on our case study we argue that institutional dynamics of standard-setting activities can be detrimental to regulatory goal achievement if there is no compensation at the systemic level. Ongoing "regulatory care" through control, corrective responses, and rule enforcement seems to be crucial for a hybrid regulatory system to perform well. [source] Optimal corrective maintenance contract planning for aging multi-state systemAPPLIED STOCHASTIC MODELS IN BUSINESS AND INDUSTRY, Issue 5 2009Yi Ding Abstract This paper considers an aging multi-state system, where the system failure rate varies with time. After any failure, maintenance is performed by an external repair team. Repair rate and cost of each repair are determined by a corresponding corrective maintenance contract with a repair team. The service market can provide different kinds of maintenance contracts to the system owner, which also can be changed after each specified time period. The owner of the system would like to determine a series of repair contracts during the system life cycle in order to minimize the total expected cost while satisfying the system availability. Operating cost, repair cost and penalty cost for system failures should be taken into account. The paper proposes a method for determining such optimal series of maintenance contracts. The method is based on the piecewise constant approximation for an increasing failure rate function in order to assess lower and upper bounds of the total expected cost and system availability by using Markov models. The genetic algorithm is used as the optimization technique. Numerical example is presented to illustrate the approach. Copyright © 2009 John Wiley & Sons, Ltd. [source] Limits of life in MgCl2 -containing environments: chaotropicity defines the windowENVIRONMENTAL MICROBIOLOGY, Issue 3 2007John E. Hallsworth Summary The biosphere of planet Earth is delineated by physico-chemical conditions that are too harsh for, or inconsistent with, life processes and maintenance of the structure and function of biomolecules. To define the window of life on Earth (and perhaps gain insights into the limits that life could tolerate elsewhere), and hence understand some of the most unusual biological activities that operate at such extremes, it is necessary to understand the causes and cellular basis of systems failure beyond these windows. Because water plays such a central role in biomolecules and bioprocesses, its availability, properties and behaviour are among the key life-limiting parameters. Saline waters dominate the Earth, with the oceans holding 96.5% of the planet's water. Saline groundwater, inland seas or saltwater lakes hold another 1%, a quantity that exceeds the world's available freshwater. About one quarter of Earth's land mass is underlain by salt, often more than 100 m thick. Evaporite deposits contain hypersaline waters within and between their salt crystals, and even contain large subterranean salt lakes, and therefore represent significant microbial habitats. Salts have a major impact on the nature and extent of the biosphere, because solutes radically influence water's availability (water activity) and exert other activities that also affect biological systems (e.g. ionic, kosmotropic, chaotropic and those that affect cell turgor), and as a consequence can be major stressors of cellular systems. Despite the stressor effects of salts, hypersaline environments can be heavily populated with salt-tolerant or -dependent microbes, the halophiles. The most common salt in hypersaline environments is NaCl, but many evaporite deposits and brines are also rich in other salts, including MgCl2 (several hundred million tonnes of bischofite, MgCl2·6H2O, occur in one formation alone). Magnesium (Mg) is the third most abundant element dissolved in seawater and is ubiquitous in the Earth's crust, and throughout the Solar System, where it exists in association with a variety of anions. Magnesium chloride is exceptionally soluble in water, so can achieve high concentrations (> 5 M) in brines. However, while NaCl-dominated hypersaline environments are habitats for a rich variety of salt-adapted microbes, there are contradictory indications of life in MgCl2 -rich environments. In this work, we have sought to obtain new insights into how MgCl2 affects cellular systems, to assess whether MgCl2 can determine the window of life, and, if so, to derive a value for this window. We have dissected two relevant cellular stress-related activities of MgCl2 solutions, namely water activity reduction and chaotropicity, and analysed signatures of life at different concentrations of MgCl2 in a natural environment, namely the 0.05,5.05 M MgCl2 gradient of the seawater : hypersaline brine interface of Discovery Basin , a large, stable brine lake almost saturated with MgCl2, located on the Mediterranean Sea floor. We document here the exceptional chaotropicity of MgCl2, and show that this property, rather than water activity reduction, inhibits life by denaturing biological macromolecules. In vitro, a test enzyme was totally inhibited by MgCl2 at concentrations below 1 M; and culture medium with MgCl2 concentrations above 1.26 M inhibited the growth of microbes in samples taken from all parts of the Discovery interface. Although DNA and rRNA from key microbial groups (sulfate reducers and methanogens) were detected along the entire MgCl2 gradient of the seawater : Discovery brine interface, mRNA, a highly labile indicator of active microbes, was recovered only from the upper part of the chemocline at MgCl2 concentrations of less than 2.3 M. We also show that the extreme chaotropicity of MgCl2 at high concentrations not only denatures macromolecules, but also preserves the more stable ones: such indicator molecules, hitherto regarded as evidence of life, may thus be misleading signatures in chaotropic environments. Thus, the chaotropicity of MgCl2 would appear to be a window-of-life-determining parameter, and the results obtained here suggest that the upper MgCl2 concentration for life, in the absence of compensating (e.g. kosmotropic) solutes, is about 2.3 M. [source] Building community knowledge systems: an empirical study of IT-support for sharing best practices among managersKNOWLEDGE AND PROCESS MANAGEMENT: THE JOURNAL OF CORPORATE TRANSFORMATION, Issue 3 2003Jørgen P. Bansler The paper reports a field study of knowledge sharing in a large and complex organization. The objective of the study was to gain an in-depth understanding of the implementation and use of a web-based knowledge sharing system designed to facilitate the circulation of best practices among middle managers. We followed the system from its introduction in early 1997 until it was abandoned in the beginning of 2000. We focused on the way the system was introduced in the organization, how it changed, and how the intended group of users received (and eventually rejected) the system. Based on our interviews and observations we identify five reasons for the systems failure. We close the paper by some reflections on the use of the concept of ,shared practice' in the development of IT-supported knowledge sharing systems. Copyright © 2003 John Wiley & Sons, Ltd. [source] Low temperature-induced systems failure in Escherichia coli: Insights from rescue by cold-adapted chaperonesPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 1 2006Massimo Strocchi Abstract The growth of Escherichia coli cells is impaired at temperatures below 21°C and stops at 7.5°C; however, growth of a transgenic strain producing the cold-adapted chaperones Cpn60 and Cpn10 from the psychrophilic bacterium Oleispira antarctica is good at low temperatures. The E.,coli,cpn+ transgene offers a novel opportunity for examining the essential protein for cell viability at low temperatures. By screening a large-scale protein map (proteome) of cells of K-12 and its Cpn+ transgene incubated at 4°C, we identified 22,housekeeping proteins involved in systems failure of E.,coli when confronted with low temperature. Through co-immunoprecipitation of Cpn60, Northern blot, and in vitro refolding, we systematically identified that protein,chaperone interactions are key determinants of their protein functions at low temperatures. Furthermore, chromosomal gene deletion experiments suggest that the mechanism of cold-induced systems failure in E.,coli is cold-induced inactivation of the GroELS chaperonins and the resulting failure to refold cold-inactivated Dps, ClpB, DnaK and RpsB proteins. These findings: (1),indicate the potential importance of chaperones in cold sensitivity, cold adaptation and cold tolerance in cellular systems, and (2),suggest the identity of a few key cold-sensitive chaperone-interacting proteins that get inactivated and ultimately cause systems failure in E.,coli cells at low temperatures. [source] Mortality related to anaesthesia in France: analysis of deaths related to airway complications,ANAESTHESIA, Issue 4 2009Y. Auroy Summary Death certificates from the French national mortality database for the calendar year 1999 were reviewed to analyse cases in which airway complications had contributed to peri-operative death. Respiratory deaths (and comas) found in a previous national 1978,82 French survey (1 : 7960; 95% CI 1 : 12 700 to 1 : 5400) were compared with the death rate found in the present one: 1 : 48 200 (95% CI 1 : 140 000 to 1 : 27 500). In 1999, deaths associated with failure of the breathing circuit and equipment were no longer encountered and no death was found to be related to undetected hypoxia in the recovery unit. Deaths related to difficult intubation also occurred at a lower rate than in the previous report (1 : 46 000; 95% CI 1 : 386 000 to 1 : 13 000) in 1978,82 vs 1 : 176 000 (95% CI 1 : 714 000 to 1 : 46 000) in 1999, a fourfold reduction. In most cases, there were both inadequate practice and systems failure (inappropriate communication between staff, inadequate supervision, poor organisation). This large French survey shows that deaths associated with respiratory complications during anaesthesia have been strikingly reduced during this 15-year period. [source] | ||||||||||||||||||||||||||||