Journal of Quality and Reliability Engineering The latest articles from Hindawi Publishing Corporation © 2016 , Hindawi Publishing Corporation . All rights reserved. Preventive Maintenance Optimization in Healthcare Domain: Status of Research and Perspective Wed, 27 Jul 2016 11:28:56 +0000 Although medical equipment maintenance has been carefully managed for years, very few in-depth studies have been conducted to evaluate the effectiveness and efficiency of these implemented preventive maintenance strategies, especially after the debate about the credibility of manufacturer’s recommendations has increased in the clinical engineering community. Facing the dilemma of merely following manufactures maintenance manual or establishing an evidence-based maintenance, medical equipment maintenance could have exploited an advanced area in operations research which is maintenance optimization research. In this paper, we review and examine carefully the status of application oriented research on preventive maintenance optimization of medical devices. This study addresses preventive healthcare maintenance with a focus on factors influencing the maintenance decision making. The analysis is structured by defining different aspects necessary to construct a maintenance optimization model. We conclusively propose directions to develop suitable tools for better healthcare maintenance management. H. Mahfoud, A. El Barkany, and A. El Biyaali Copyright © 2016 H. Mahfoud et al. All rights reserved. Multicriteria FMECA Based Decision-Making for Aluminium Wire Process Rolling Mill through COPRAS-G Thu, 14 Jul 2016 17:00:47 +0000 This paper presents a multifactor decision-making approach based on “grey-complex proportional assessment (COPRAS-G) method” in a view to overcome the limitations of Failure Mode Effect and Criticality Analysis (FMECA). In this model, the scores against each failure mode are expressed in grey number instead of crisp values to evaluate the criticalities of the failure modes without uncertainty. The suggested study is carried out to identify the weights of major failure causes for bearings, gears, and shafts of aluminium wire rolling mill plant. The primary findings of the paper are that sudden impact on the rolls seems to be most critical failure cause and loss of power seems to be least critical failure cause. It is suggested to modify the current control practices with proper maintenance strategy based on achieved maintainability criticality index (MCI) for different failure causes. The outcome of study will be helpful in deriving optimized maintenance plan to maximize the performance of process industry. Nilesh Pancholi and M. G. Bhatt Copyright © 2016 Nilesh Pancholi and M. G. Bhatt. All rights reserved. Consecutive-Type Reliability Systems: An Overview and Some Applications Sun, 31 May 2015 07:27:54 +0000 The family of consecutive-type reliability systems is under investigation. More specifically, an up-to-date presentation of almost all generalizations of the well-known consecutive -out-of-: system that have been proposed in the literature is displayed, while several recent and fundamental results for each member of the aforementioned family are stated. Ioannis S. Triantafyllou Copyright © 2015 Ioannis S. Triantafyllou. All rights reserved. Variable Selection Methods for Right-Censored Time-to-Event Data with High-Dimensional Covariates Sun, 10 May 2015 09:46:49 +0000 Advancement in technology has led to greater accessibility of massive and complex data in many fields such as quality and reliability. The proper management and utilization of valuable data could significantly increase knowledge and reduce cost by preventive actions, whereas erroneous and misinterpreted data could lead to poor inference and decision making. On the other side, it has become more difficult to process the streaming high-dimensional time-to-event data in traditional application approaches, specifically in the presence of censored observations. This paper presents a multipurpose analytic model and practical nonparametric methods to analyze right-censored time-to-event data with high-dimensional covariates. In order to reduce redundant information and to facilitate practical interpretation, variable inefficiency in failure time is determined for the specific field of application. To investigate the performance of the proposed methods, these methods are compared with recent relevant approaches through numerical experiments and simulations. Keivan Sadeghzadeh and Nasser Fard Copyright © 2015 Keivan Sadeghzadeh and Nasser Fard. All rights reserved. Planning for Reliable Coal Quality Delivery Considering Geological Variability: A Case Study in Polish Lignite Mining Thu, 29 Jan 2015 16:46:46 +0000 The aim of coal quality control in coal mines is to supply power plants daily with extracted raw material within certain coal quality constraints. On the example of a selected part of a lignite deposit, the problem of quality control for the run-of-mine lignite stream is discussed. The main goal is to understand potential fluctuations and deviations from production targets dependent on design options before an investment is done. A single quality parameter of the deposit is selected for this analysis—the calorific value of raw lignite. The approach requires an integrated analysis of deposit inherent variability, the extraction sequence, and the blending option during material transportation. Based on drill-hole data models capturing of spatial variability of the attribute of consideration are generated. An analysis based on two modelling approaches, Kriging and sequential Gaussian simulation, reveals advantages and disadvantages lead to conclusions about their suitability for the control of raw material quality. In a second step, based on a production schedule, the variability of the calorific value in the lignite stream has been analysed. In a third step the effect of different design options, multiple excavators and a blending bed, was investigated. Wojciech Naworyta, Szymon Sypniowski, and Jörg Benndorf Copyright © 2015 Wojciech Naworyta et al. All rights reserved. Stochastic Analysis of a Two-Unit Cold Standby System Wherein Both Units May Become Operative Depending upon the Demand Mon, 01 Dec 2014 00:10:02 +0000 The present paper analyzes a two-unit cold standby system wherein both units may become operative depending upon the demand. Initially, one of the units is operative while the other is kept as cold standby. If the operative unit fails or the demand increases to the extent that one operative unit is not capable of meeting the demand, the standby unit becomes operative instantaneously. Thus, both units may become operative simultaneously to meet the increased demand. Availability in three types of upstates is as follows: (i) when the demand is less than or equal to production manufactured by one unit; (ii) when the demand is greater than whatever produced by one unit but less than or equal to production made by two units; and (iii) when the demand is greater than the produces by two units. Other measures of the system effectiveness have also been obtained in general case as well as for a particular case. Techniques of semi-Markov processes and regenerative processes have been used to obtain various measures of the system effectiveness. Reetu Malhotra and Gulshan Taneja Copyright © 2014 Reetu Malhotra and Gulshan Taneja. All rights reserved. Design for Reliability of Complex System: Case Study of Horizontal Drilling Equipment with Limited Failure Data Sun, 30 Nov 2014 09:19:57 +0000 Reliability is an important phase in durable system designs, specifically in the early phase of the product development. In this paper, a new methodology is proposed for complex systems’ design for reliability. Specific test and field failure data scarcity is evaluated here as a challenge to implement design for reliability of a new product. In the developed approach, modeling and simulation of the system are accomplished by using reliability block diagram (RBD) method. The generic data are corrected to account for the design and environment effects on the application. The integral methodology evaluates reliability of the system and assesses the importance of each component. In addition, the availability of the system was evaluated using Monte Carlo simulation. Available design alternatives with different components are analyzed for reliability optimization. Evaluating reliability of complex systems in competitive design attempts is one of the applications of this method. The advantage of this method is that it is applicable in early design phase where there is only limited failure data available. As a case study, horizontal drilling equipment is used for assessment of the proposed method. Benchmarking of the results with a system with more available failure and maintenance data verifies the effectiveness and performance quality of presented method. Morteza Soleimani, Mohammad Pourgol-Mohammad, Ali Rostami, and Ahmad Ghanbari Copyright © 2014 Morteza Soleimani et al. All rights reserved. Interval Estimation of Stress-Strength Reliability Based on Lower Record Values from Inverse Rayleigh Distribution Sun, 16 Nov 2014 09:49:57 +0000 We consider the estimation of stress-strength reliability based on lower record values when and are independently but not identically inverse Rayleigh distributed random variables. The maximum likelihood, Bayes, and empirical Bayes estimators of are obtained and their properties are studied. Confidence intervals, exact and approximate, as well as the Bayesian credible sets for are obtained. A real example is presented in order to illustrate the inferences discussed in the previous sections. A simulation study is conducted to investigate and compare the performance of the intervals presented in this paper and some bootstrap intervals. Bahman Tarvirdizade and Hossein Kazemzadeh Garehchobogh Copyright © 2014 Bahman Tarvirdizade and Hossein Kazemzadeh Garehchobogh. All rights reserved. Short-Run Control Chart for Multiproducts with Multi-Items Based on Unequal Means and Variances Thu, 25 Sep 2014 06:25:51 +0000 Statistical process control (SPC) is one of the most important statistical tools for monitoring production processes. It can be effectively designed and implemented when the process or product specifications are consecutively observed from a mass production condition. Normally, short-cycle productions do not have sufficient data to implement SPC. This research introduced how to design and implement short-run control chart for batch production conditions. Monitoring critical specifications of supplied parts to automotive industry was proposed. The results revealed that unequal variables followed normal distribution and can be fluctuated over time for the purpose of monitoring multiple products for each product including multidimensions with unequal means and variances from the central line to control the chart. Out-of-control signals and nonrandom patterns can be recognized on the developed short-run control chart accordingly. Soroush Avakh Darestani and Neda Aminpour Copyright © 2014 Soroush Avakh Darestani and Neda Aminpour. All rights reserved. A Load-Share Reliability Model under the Changeable Piecewise Smooth Load Thu, 11 Sep 2014 06:10:43 +0000 A new load-share reliability model of systems under the changeable load is proposed in the paper. It is assumed that the load is a piecewise smooth function which can be regarded as an extension of the piecewise constant and continuous functions. The condition of the residual lifetime conservation, which means continuity of a cumulative distribution function of time to failure, is accepted in the proposed model. A general algorithm for computing reliability measures is provided. Simple expressions for determining the survivor functions under assumption of the Weibull probability distribution of time to failure are given. Various numerical examples illustrate the proposed model by different forms of the system load and different probability distributions of time to failure. Sergey V. Gurov and Lev V. Utkin Copyright © 2014 Sergey V. Gurov and Lev V. Utkin. All rights reserved. Performance Investigation of CMM Measurement Quality Using Flick Standard Thu, 17 Jul 2014 10:01:54 +0000 Quality of coordinate measuring machine (CMM) in dimension and form metrology is designed and performed at the NIS. The experimental investigation of CMM performance is developed by using reference Flick standard. The measurement errors of corresponding geometric evaluation algorithm (LSQ, ME, MC, and MI) and probe scanning speed (1, 2, 3, 4, and 5 mm/s) are obtained through repeated arrangement, comparison, and judgment. The experimental results show that the roundness error deviation can be evaluated effectively and exactly for CMM performance by using Flick standard. Some of influencing quantities for diameter and roundness form errors may dominate the results at all fitting algorithms under certain circumstances. It can be shown that the 2 mm/s probe speed gives smaller roundness error than 1, 3, 4, and 5 mm/s within 0.2 : 0.3 μm. It ensures that measurement at 2 mm/s is the best case to satisfy the high level of accuracy in the certain condition. Using Flick standard as a quality evaluation tool noted a high precision incremental in diameter and roundness form indication. This means a better transfer stability of CMM quality could be significantly improved. Moreover, some error formulae of data sets have been postulated to correlate the diameter and roundness measurements within the application range. Uncertainty resulting from CMM and environmental temperature has been evaluated and confirmed the quality degree of confidence in the proposed performance investigation. Salah H. R. Ali Copyright © 2014 Salah H. R. Ali. All rights reserved. Optimum Time-Censored Constant-Stress PALTSP for the Burr Type XII Distribution Using Tampered Failure Rate Model Wed, 18 Jun 2014 07:07:54 +0000 This paper presents optimum design of time-censored constant-stress partially accelerated life test sampling plan (PALTSP) in which each item runs either at use or at accelerated conditions and product life follows Burr type XII. The optimal plan consists in finding out sample proportions allocated to both use and accelerated conditions by minimizing the asymptotic variance of test statistic for deciding on acceptance/rejection of the lot such that producer’s and consumer’s interests are safeguarded. The method developed has been illustrated using an example. Sensitivity analysis has also been carried out. P. W. Srivastava and D. Sharma Copyright © 2014 P. W. Srivastava and D. Sharma. All rights reserved. A One-Class Classification-Based Control Chart Using the -Means Data Description Algorithm Mon, 09 Jun 2014 10:14:53 +0000 This paper aims to enlarge the family of one-class classification-based control charts, referred to as OC-charts, and extend their applications. We propose a new OC-chart using the -means data description (KMDD) algorithm, referred to as KM-chart. The proposed KM-chart gives the minimum closed spherical boundary around the in-control process data. It measures the distance between the center of KMDD-based sphere and the new incoming sample to be monitored. Any sample having a distance greater than the radius of KMDD-based sphere is considered as an out-of-control sample. Phase I and II analysis of KM-chart was evaluated through a real industrial application. In a comparative study based on the average run length (ARL) criterion, KM-chart was compared with the kernel-distance based control chart, referred to as K-chart, and the -nearest neighbor data description-based control chart, referred to as KNN-chart. Results revealed that, in terms of ARL, KM-chart performed better than KNN-chart in detecting small shifts in mean vector. Furthermore, the paper provides the MATLAB code for KM-chart, developed by the authors. Walid Gani and Mohamed Limam Copyright © 2014 Walid Gani and Mohamed Limam. All rights reserved. Simulation-Based Fuzzy Logic Approach to Assessing the Effect of Project Quality Management on Construction Performance Wed, 07 May 2014 11:27:53 +0000 This paper reports the development of an approach to integrate the appropriate modeling techniques for estimating the effect of project quality management (PQM) on construction performance. This modeling approach features a causal structure that depicts the interaction among the PQM factors affecting quality performance in a given construction operation. In addition, it makes use of fuzzy sets and fuzzy logic in order to incorporate the subjectivity and uncertainty implicit in the performance assessment of these PQM factors to discrete-event simulation models. The outcome is a simulation approach that allows experimenting with different performance levels of the PQM practices implemented in a construction project and obtaining the corresponding productivity estimates of the construction operations. These estimates are intended to facilitate the decision making regarding the improvement of a PQM system implemented in a construction project. A case study is used to demonstrate the usefulness of the proposed simulation approach for evaluating diverse performance improvement alternatives for a PQM system. Gilberto A. Corona-Suárez, Simaan M. AbouRizk, and Stanislav Karapetrovic Copyright © 2014 Gilberto A. Corona-Suárez et al. All rights reserved. Renewal and Renewal-Intensity Functions with Minimal Repair Wed, 19 Mar 2014 16:47:20 +0000 The renewal and renewal-intensity functions with minimal repair are explored for the Normal, Gamma, Uniform, and Weibull underlying lifetime distributions. The Normal, Gamma, and Uniform renewal, and renewal-intensity functions are derived by the convolution method. Unlike these last three failure distributions, the Weibull except at shape does not have a closed-form function for the n-fold convolution. Since the Weibull is the most important failure distribution in reliability analyses, the approximate renewal and renewal-intensity functions of Weibull were obtained by the time-discretizing method using the Mean-Value Theorem for Integrals. A Matlab program outputs all reliability and renewal measures. Saeed Maghsoodloo and Dilcu Helvaci Copyright © 2014 Saeed Maghsoodloo and Dilcu Helvaci. All rights reserved. Research on the Degree of Ecological Supply Chain Management Practice among Chinese Manufacturing Enterprises Thu, 06 Mar 2014 08:32:28 +0000 Based on the existing literature, this paper proposes two assumptions and designs a set of ecological supply chain performance evaluation indicators system. Because these indicators are interdependence for each other, this paper selects the analytic network process and builds the ANP network model to evaluate the degree of ecological supply chain management practice among Chinese manufacturing enterprises. The evaluation results show that there is different level indeed about the ecological supply chain management level; the better the ecological supply chain management practice degree is, the more quickly the ecological supply chain management performance levels increase. Xiaohua Chen and Guoyi Xiu Copyright © 2014 Xiaohua Chen and Guoyi Xiu. All rights reserved. Optimization Problems of Costs in a MultiState System with Imperfect Maintenance Thu, 27 Feb 2014 12:15:48 +0000 We consider optimal replacement policies with periodic imperfect maintenance actions and minimal repairs. The multistate system is minimally repaired at failure and imperfect maintenance actions are regularly carried out for preventive maintenance. The discrete modified Weibull distribution is introduced and some cost functions applied to this distribution are defined in order to be minimized. Moreover, we assume that the costs of preventive maintenance depend on the degree of repair via a Kijima type 2 model. For illustrative purpose, the obtained results are applied on sets of simulated data. Soufiane Gasmi and Nizar Mannai Copyright © 2014 Soufiane Gasmi and Nizar Mannai. All rights reserved. An Integrated Procedure for Bayesian Reliability Inference Using MCMC Tue, 14 Jan 2014 11:55:25 +0000 The recent proliferation of Markov chain Monte Carlo (MCMC) approaches has led to the use of the Bayesian inference in a wide variety of fields. To facilitate MCMC applications, this paper proposes an integrated procedure for Bayesian inference using MCMC methods, from a reliability perspective. The goal is to build a framework for related academic research and engineering applications to implement modern computational-based Bayesian approaches, especially for reliability inferences. The procedure developed here is a continuous improvement process with four stages (Plan, Do, Study, and Action) and 11 steps, including: (1) data preparation; (2) prior inspection and integration; (3) prior selection; (4) model selection; (5) posterior sampling; (6) MCMC convergence diagnostic; (7) Monte Carlo error diagnostic; (8) model improvement; (9) model comparison; (10) inference making; (11) data updating and inference improvement. The paper illustrates the proposed procedure using a case study. Jing Lin Copyright © 2014 Jing Lin. All rights reserved. Reliability and Fatigue Analysis in Cantilever-Based MEMS Devices Operating in Harsh Environments Sun, 12 Jan 2014 00:00:00 +0000 The microelectromechanical system (MEMS) is one of the most diversified fields of microelectronics; it is rated to be the most promising technology of modern engineering. MEMS can sense, actuate, and integrate mechanical and electromechanical components of micro- and nano sizes on a single silicon substrate using microfabrication techniques. MEMS industry is at the verge of transforming the semiconductor world into MEMS universe, apart from other hindrances; the reliability of these devices is the focal point of recent research. Commercialization is highly dependent on the reliability of these devices. MEMS requires a high level of reliability. Several technological factors, operating conditions, and environmental effects influencing the performances of MEMS devices must be completely understood. This study reviews some of the major reliability issues and failure mechanisms. Specifically, the fatigue in MEMS is a major material reliability issue resulting in structural damage, crack growth, and lifetime measurements of MEMS devices in the light of statistical distribution and fatigue implementation of Paris' law for fatigue crack accumulation under the influence of undesirable operating and environmental conditions. Mohammad Tariq Jan, Nor Hisham Bin Hamid, Mohd Haris Md Khir, Khalid Ashraf, and Mohammad Shoaib Copyright © 2014 Mohammad Tariq Jan et al. All rights reserved. Acceptance Sampling Plans from Life Tests Based on Percentiles of Half Normal Distribution Wed, 04 Dec 2013 10:33:18 +0000 The design of acceptance sampling plans is developed under truncated life testing based on the percentiles of half normal distribution. The minimum sample size necessary to ensure the specified life percentile is obtained under a given consumer’s risk. The operating characteristic values of the sampling plans as well as the producer’s risk are presented. The results are illustrated by examples. B. Srinivasa Rao, Ch. Srinivasa Kumar, and K. Rosaiah Copyright © 2013 B. Srinivasa Rao et al. All rights reserved. A Start-Up Demonstration Test Involving Distant Failures Thu, 28 Nov 2013 10:28:06 +0000 A new procedure for determining the acceptance or rejection of a system that undergoes a start-up demonstration set of tests is presented. It is a generalization of the recently introduced CSDF model (consecutive successes distant failures). According to the new total successes consecutive successes total failures distant failures (TSCSTFDF) procedure, a unit is accepted when either a total number of successful tests or a specified number of consecutive successes are observed before a total number of failures or the occurrence of near failures which are too close to each other. The practical advantage of this new procedure is the significant reduction in the expected number of required tests together with improved second-order statistics (standard deviation). Amos E. Gera Copyright © 2013 Amos E. Gera. All rights reserved. Differential Importance Measure for Components Subjected to Aging Phenomena Tue, 08 Oct 2013 08:34:20 +0000 The paper refers to the evaluation of the unavailability of systems made by repairable binary independent components subjected to aging phenomena. Exponential, exponential-linear, and Weibull distributions are assumed for the components failure times. We assume that components failure rate increases only slightly during the maintenance period, but we recognize the effectiveness of preventive maintenance only in presence of aging phenomena. Importance measures allow the ranking of the input variables. We propose analytical equations that allow the estimation of the first-order Differential Importance Measure (DIM) on the basis of the Birnbaum measures of components, under the hypothesis of uniform percentage changes of parameters. Without further information than that used for the estimation of “DIM for components,” “DIM for parameters” allows considering separately the importance of random failures, aging phenomena, and preventive and corrective maintenance. A two-step process is proposed for the system improvement, by increasing the components reliability and maintainability performance as much as possible (within the applicable technological limits) and then by optimizing preventive maintenance on them. Some examples taken from the scientific literature are solved in order to verify the correctness of the analytical equations and to show their use. Stefano La Rovere, Paolo Vestrucci, Maria Sperandii, and Claudia Mandurino Copyright © 2013 Stefano La Rovere et al. All rights reserved. A Procedure for the Selection of Single Sampling Plans by Variables Based on Pareto Distribution Sun, 22 Sep 2013 11:17:01 +0000 Product control in statistical quality control is the methodology that deals with procedures for taking decisions about one or more lots of finished products manufactured by production processes. Sampling inspection by variables is one of the major classifications of product control and comprises procedures for deciding about the disposition of a lot of individual units based on sample measurements of units on a quality characteristic under study. These procedures are defined under the assumption that the quality characteristic is measurable on a continuous scale, and the functional form of the probability distribution must be known. Inspection procedures which have been developed under the implicit assumption that the quality characteristic is distributed as normal with the related properties are found in the literature of product control. The assumption of normality may not be realized often in practice, and it becomes indispensable to investigate the properties of sampling plans based on nonnormal distributions. In this paper, a single sampling plan by variables is formulated and evaluated when the quality characteristic is assumed to be distributed according to a Pareto distribution. A procedure is developed for determining the parameters of the plan for specified requirements to ensure protection to both the producer and consumer. Geetha Sathya Narayanan and Vijayaraghavan Rajarathinam Copyright © 2013 Geetha Sathya Narayanan and Vijayaraghavan Rajarathinam. All rights reserved. Productivity Improvement of a Special Purpose Machine Using DMAIC Principles: A Case Study Thu, 12 Sep 2013 15:01:48 +0000 Six Sigma is one of the popular methodologies used by the companies to improve the quality and productivity. It uses a detailed analysis of the process to determine the causes of the problem and proposes a successful improvement. Various approaches are adopted while following Six Sigma methodologies and one of them is DMAIC. The successful implementation of DMAIC and FTA is discussed in this paper. In this study, the major problem was of continuous rework up to 16%, which was leading to wastage of man hours and labor cost. Initially, fault tree analysis (FTA) was used to detect the key process input variables (KPIVs) affecting the output. Multivariable regression analysis was performed to know the possible relationship between the KPIVs and the output. The DMAIC methodology was successfully implemented to reduce the rework from 16% bores per month to 2.20% bores per month. The other problem of nonuniform step bores was also reduced significantly. Sunil Dambhare, Siddhant Aphale, Kiran Kakade, Tejas Thote, and Atul Borade Copyright © 2013 Sunil Dambhare et al. All rights reserved. Reliability Analysis of the Engineering Systems Using Intuitionistic Fuzzy Set Theory Wed, 11 Sep 2013 11:35:41 +0000 The present paper investigates the reliability analysis of industrial systems by using vague lambda-tau methodology in which information related to system components is uncertain and imprecise in nature. The uncertainties in the data are handled with the help of intuitionistic fuzzy set (IFS) theory rather than fuzzy set theory. Various reliability parameters are addressed for strengthening the analysis in terms of degree of acceptance and rejection of IFS. Performance as well as sensitivity analysis of the system parameter has been investigated for accessing the impact of taking wrong combinations on its performance. Finally results are compared with the existing traditional crisp and fuzzy methodologies results. The technique has been demonstrated through a case study of bleaching unit of a paper mill. Harish Garg, Monica Rani, and S. P. Sharma Copyright © 2013 Harish Garg et al. All rights reserved. A Heuristic Methodology for Efficient Reduction of Large Multistate Event Trees Mon, 10 Jun 2013 15:07:55 +0000 This work proposes a new methodology for the management of event tree information used in the quantitative risk assessment of complex systems. The size of event trees increases exponentially with the number of system components and the number of states that each component can be found in. Their reduction to a manageable set of events can facilitate risk quantification and safety optimization tasks. The proposed method launches a deductive exploitation of the event space, to generate reduced event trees for large multistate systems. The approach consists in the simultaneous treatment of large subsets of the tree, rather than focusing on the given single components of the system and getting trapped into guesses on their structural arrangement. Eftychia C. Marcoulaki Copyright © 2013 Eftychia C. Marcoulaki. All rights reserved. Robust Control Charts for Monitoring Process Mean of Phase-I Multivariate Individual Observations Sun, 09 Jun 2013 13:16:06 +0000 Hoteling's control charts are widely used in industries to monitor multivariate processes. The classical estimators, sample mean, and the sample covariance used in control charts are highly sensitive to the outliers in the data. In Phase-I monitoring, control limits are arrived at using historical data after identifying and removing the multivariate outliers. We propose Hoteling's control charts with high-breakdown robust estimators based on the reweighted minimum covariance determinant (RMCD) and the reweighted minimum volume ellipsoid (RMVE) to monitor multivariate observations in Phase-I data. We assessed the performance of these robust control charts based on a large number of Monte Carlo simulations by considering different data scenarios and found that the proposed control charts have better performance compared to existing methods. Asokan Mulayath Variyath and Jayasankar Vattathoor Copyright © 2013 Asokan Mulayath Variyath and Jayasankar Vattathoor. All rights reserved. A Review of Quality Criteria Supporting Supplier Selection Thu, 06 Jun 2013 09:03:53 +0000 This paper presents a review of decision criteria reported in the literature for supporting the supplier selection process. The review is based on an extensive search in the academic literature. After a literature review of decision criteria, we discuss the most important criteria: quality. Then different methods and factors for assessing the quality of supplier are discussed. Results showed that all methods and factors mentioned in this paper are not appropriate tools for quality evaluation. Moreover, we propose a novel method (using loss functions) in order to assess the quality of suppliers. Mohammad Abdolshah Copyright © 2013 Mohammad Abdolshah. All rights reserved. Statistical Inferences and Applications of the Half Exponential Power Distribution Wed, 05 Jun 2013 14:09:10 +0000 We investigate the statistical inferences and applications of the half exponential power distribution for the first time. The proposed model defined on the nonnegative reals extends the half normal distribution and is more flexible. The characterizations and properties involving moments and some measures based on moments of this distribution are derived. The inference aspects using methods of moment and maximum likelihood are presented. We also study the performance of the estimators using the Monte Carlo simulation. Finally, we illustrate it with two real applications. Wenhao Gui Copyright © 2013 Wenhao Gui. All rights reserved. On Stress-Strength Reliability with a Time-Dependent Strength Wed, 05 Jun 2013 14:05:13 +0000 The study of stress-strength reliability in a time-dependent context needs to model at least one of the stress or strength quantities as dynamic. We study the stress-strength reliability for the case in which the strength of the system is decreasing in time and the stress remains fixed over time; that is, the strength of the system is modeled as a stochastic process and the stress is considered to be a usual random variable. We present stochastic ordering results among the lifetimes of the systems which have the same strength but are subjected to different stresses. Multicomponent form of the aforementioned stress-strength interference is also considered. We illustrate the results for the special case when the strength is modeled by a Weibull process. Serkan Eryilmaz Copyright © 2013 Serkan Eryilmaz. All rights reserved.