???? The International of Journal of Performability Engineering has completed six years of its publication and has entered the seventh year of its publication in the year 2011. A brief report on IJPE is available below. During this period, we have taken special care that our readers are exposed to new emerging topics and areas in all the constituents of performability engineering and it is heartening to see that NSD – an international scientific data base of Norway (http://dbh.nsd.uib.no/kanaler/) has rated this journal higher than some of the international journals in the allied areas. We would keep the standard of this journal very high and continue to provide high quality papers to our readers. Not to mention that we take utmost care to get the papers submitted to our journal refereed by competent reviewers and papers are often revised to see that they present the main idea of the paper in a compact form. We discourage publishing verbose articles in IJPE.

A Brief Report on IJPE

The details of IJPE issues published during this period (July 2005-Nov. 2010) are as follows:

Contributing Countries:

The following countries (in alphabetic order) contributed papers to the IJPE during this period:
Abu Dhabi, Australia, Brazil, Canada, China, Czech Republic, Denmark, Egypt, Finland, France, Germany, Greece, Holland, Hong Kong, Hungary, India, Iran, Israel, Italy, Japan, Jordan, Korea (South), Malaysia, Morocco, New Zealand, Norway, Oman, Poland, Portugal, Romania, Singapore, South Africa, Spain, Sweden, Switzerland, Taiwan, United Kingdom, United States of America, Venezuela.

Major contributing countries were:

Australia, China, Canada, France, India, Israel, Italy, Japan, Norway, Sweden, South Korea, Taiwan, U.K., U.S.A. (The highest number of papers published were from U.S.A.).

Areas of Performability Engineering represented:

Our effort has been to emphasize and to ensure a balanced representation of all constituent areas of Performability Engineering (viz., Quality, Reliability, Maintainability, Safety, Risk and Sustainability) through the IJPE issues and we did bring out at least one special issue in all these constituent areas during this period. However, the numbers of papers published during this period were largely from Reliability, Safety, Risk and Maintainability (and Maintenance Engineering and Management) areas (in order of their numbers). However, there were not very many contributions from sustainability and quality areas. These areas need to be strengthened in future. Never-the-less, management and human factors and design for environment were adequately represented in each of these areas.

We had special issue devoted to Prognostics & Health Management and special sections on Six Sigma and Data Mining. In forthcoming issues, we are going to have special issues/sections planned on some of the frontier areas like Reliability Growth Models, Multi-state systems, e-maintenance, Performance and Dependability models of Dynamic Systems, Dependability of Wireless and Systems and Networks. In short we keep our readers updated with the latest developments in the area of perfomability Engineering.

In traditional methods for reliability analysis, one complex system is often considered as being composed by some subsystems in series. Usually, the failure of any subsystem would be supposed to lead to the failure of the entire system. However, some subsystems’ lifetimes are long enough and even never fail during the life cycle of the entire system. Moreover, such subsystems’ lifetimes will not be influenced equally under different circumstances. In practice, such interferences will affect the model’s accuracy, but it is seldom considered in traditional analysis. To address these shortcomings, this paper presents a new approach to do reliability analysis for complex systems. Here a certain fraction of the subsystems is defined as a “cure fraction” under the consideration that such subsystems’ lifetimes are long enough and even never fail during the life cycle of the entire system. By introducing environmental covariates and the joint power prior, the proposed model is developed within the Bayesian survival analysis framework, and thus the problem for censored (or truncated) data in reliability tests can be resolved. In addition, a Markov chain Monte Carlo computational scheme is implemented and a numeric example is discussed to demonstrate the proposed model.
Received on March 30, 2010, revised on August 08, 2010
References: 18

Traditional approaches to assess the performability of airports ignore the needs of consumers in terms of the ability to move both passengers and cargo in a timely fashion, instead focusing on the airport as an economic entity. These approaches focus on the ability to generate throughput based upon the available assets at the airport. In this paper, we explore the ability to generate timely throughputs of flights based upon both the assets of the airport and the way those assets are used. We employ widely accepted data envelopment analysis (DEA) to measure performability of the 45 largest airports in the United States using data spanning an eight-year period. The result of these models is a new aviation system diagnostic that identifies weaknesses throughout the entire national airspace to highlight specific areas for improvement and investment for reliable timely throughput. To illustrate the methodology, we present two case studies.
Received on March 31, 2010, revised on August 07, 2010
References: 27

Fault diagnostics systems are incorporated to determine the health of the system they monitor. There are however times when the diagnostics system reports faults which do not exist. This situation commonly arises at system start-up when high vibration levels exist and the systems are not performing in the same way as when they are operational. Unnecessary shutdowns can occur due to transient behaviour of the system. On autonomous vehicles, such as Unmanned Aerial Vehicles (UAVs), information about the health of the system can be used to support the decision making process and to plan the future system operation. When faults are reported on autonomous systems, where there is no pilot to interpret the conditions reported, a method is needed to establish whether the reported faults do exist. Utilizing a fault propagation modeling technique deviations in system variables can be propagated through the system until further evidence of fault presence is observed. If some evidence that contradicts the fault presence is found, the fault can be cancelled and unnecessary shutdowns can be avoided.

In this paper a propagation table method is developed to model fault propagation through a system. The system is broken down into its constituent components and each model shows how process variables depend not only on the state of the component but also on the state of the entire system. The outputs of the two-way fault propagation modeling are values of process variables at different locations in the system. These values can be compared with the symptoms observed and used to cancel or confirm faults. This comparison process is accomplished at each phase that the system goes through during its defined mission. The illustration of the fault propagation methodology is given using an example system, and its application for the fault cancellation process is discussed.
Received on October 27, 2009, revised on August 04, 2010
References: 14

In this paper, redundancy allocation problem for system reliability has been presented with entropy as objective function. This model using entropy has been used to account for the lack of expert’s information. The goal of entropy redundancy allocation problem is to find out optimal level of redundancies at each subsystem in a way that maximizes reliability and entropy of the system subject to specified system cost. Intuitionistic fuzzy optimization technique is used to analyze an entropy based reliability redundancy optimization problem. Numerical examples have been provided to illustrate the model.
Received on September 22, 2009, revised on September 4, 2010
References: 37

Reversed hazard rate (RHR) is a useful tool in the area of maintenance management, particularly for condition monitoring. Its typical behaviour makes it suitable for the assessment of waiting time and hidden failures. Nature of reversed hazard rate is therefore, analytically and numerically investigated, for the standard distributions and presented in this paper. It is shown that RHR is a decreasing function for important statistical distributions, which rather makes it viable to be used in the field of maintenance engineering. Required data was simulated in MATLAB version 7.0. The results are discussed and presented in the paper.
Received on October 19, 2009, revised on September 12, 2010
References: 8

Use of eco-friendly composites has recently gained importance due to their light weight, and moderate strength. The favourable environmental impact of synthetic fibers has forced many researchers to look for alternative materials. In this paper, we have studied the effect of chemical treatment on mechanical properties of randomly mixed hybrid fiber composites for varying fiber percentage weight (wt %). The fibers of banana and kenaf were treated with 2.0% of sodium hydroxide (NaOH) solution for 3 hrs and composites are prepared with different fiber wt% ratio keeping the overall ratio of fibers as equal. Composites made with treated fibers exhibited superior mechanical properties i.e., tensile strength, flexural strength and impact strength. After treatment, the tensile strength, flexural strength and impact strength were increased to 36.4 MPa, 25.2 MPa and 0.6 kJ/m2, respectively due to the removal of impurities from the fiber surface. The fractured surfaces of composites were investigated using scanning electron microscopy.
Received on November 16, 2009, revised on April 1, 2010
References: 11

The paper presents a reliability analysis of an identical two-unit parallel CC plant system. Each unit consists of two identical 150 ton electrically operated overhead travelling (EOT) cranes operative at fully installed capacity. Failure in any crane of a unit brings the unit to a complete halt, and the inspection is carried out to detect the type of failure. Four years maintenance data from a steel production plant have been used for this purpose. Three major failures were noted in the system, viz., repairable, replaceable, and reconditioning/reinstallation. The real failure situations as depicted in the data have been considered for analysis. Optimized reliability indices of the system effectiveness are estimated numerically by using semi-Markov processes and regenerative point techniques.
Received on September 13, 2009, revised on September 12, 2010
References: 3

In general, downtime of a system can be attributed due to multiple failure categories and repair costs for each failure categories can be different. Many of these failure types are repaired to a state which can be called as bad as old and such repair actions are termed as “minimal repair”. Many system or components are replaced after a certain number of such minimal repair actions. In this study, we intend to prove that if the system failure process can be described by NHPP (Non Homogenous Poisson Process), then each failure category can also be modelled by NHPP. Based on this, a cost model is developed by using the decomposition of the NHPP and renewal theory. Using the cost model, a model is developed to obtain the optimal number of minimum repair action every failure category. Since it is not possible to find any analytical solution, solution to the renewal function, an approximate approach is introduced to obtain numerical solution. Finally, a numerical example is presented to demonstrate the method.
Received on September 6, 2009, revised on August 9, 2010
References: 15

In this paper, we discuss an often-ignored, but very important issue, i.e., how to recover slow replicas quickly in a fault tolerant system. Despite the fact that the replicas are deployed in identically-equipped computing nodes, under heavy load, some replicas would lag behind due to various reasons. Quickly recovering slow replicas is important because not doing so could result in reduced throughput, high jitters in end-to-end latency, and reduced replication degree.
Received on July 14, 2010, revised on November 10, 2010
References: 5

The “invariants” in a process are the non-changing parts. In this paper, invariants in determining the redundancy allocation to optimize system reliability and maintainability are exploited. This article demonstrates how recognizing the computational invariants can lead to efficient system assessments.
Received on August 9, 2010, revised on October 11, 2010
References: 5