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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14411/18
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Article Robust Inference for Step-Stress Experiments under Interval-Censoring(Springer, 2026) Balakrishnan, Narayanaswamy; Jaenada, María; Pardo, LeandroMany moderns products have a long life before failure. Reliability analyses for such highly reliable devices therefore present a practical challenge as obtaining sufficient failure information to adequately assess lifetime behavior will require extended experimental duration. As an alternative, accelerated life testing (ALT) is commonly used to shorten the time to failure of units under test, with the results subsequently extrapolated to normal operating conditions. This paper provides a comprehensive review of robust inferential methods based on density power divergence for analyzing step-stress ALT data. Point estimates and approximate confidence intervals for model parameters, along with robust estimates of some important lifetime characteristics are developed for general lifetime distributions. Subsequently, explicit expressions are derived for four most prominent parametric lifetime distributions: exponential, Weibull, gamma, and lognormal. A semi-parametric approach based on the proportional hazards model and a competing risks scenario are also discussed as extensions of the proposed model. Throughout the manuscript, several open problems are highlighted, along with significant gaps in the literature, to motivate readers and also to promote further research in this important research area. Moreover, to illustrate the importance of step-stress ALTs and the practical utility of robust estimators, we also present some real data sets used in the literature and analyze one of them using robust methods. By analyzing real data, we demonstrate the stability of the Minimum Density Power Divergence Estimator (MDPDE) for different values of the tuning parameter in the presence of outliers. We also analyze the implications of distributional assumptions on parameter estimation. Confidence intervals, including transformed intervals, are examined, with transformed intervals resulting in confidence levels close to nominal level and also provide better interpretability. Our results highlight the importance of robust estimation techniques in the presence of data contamination and also in a careful selection of parametric models for modeling the lifetime data, as these choices significantly influence predictions of lifetime characteristics under normal operating conditions.Article Adaptation of the Food Waste Avoidance Motivation Scale into Turkish: A Validity and Reliability Study(Marmara Univ, Inst Health Sciences, 2026) Inan, Cansu Memiç; Cetiner, Özlem; Sarahman-Kahraman, Ceren; Soylu, MeltemObjective: We conducted this research to assess the psychometric properties of the Turkish version of the Food Waste Avoidance Motivation (MAFW) scale, specifically focusing on its use with adults. Methods: Between January and May 2025, data for this research were obtained via in-person interviews conducted with adults who are residents of Nigde, Turkey. The validity of the MAFW scale was examined by employing Confirmatory Factor Analysis (CFA). The internal reliability of the instrument was determined through consistency analysis; consequently, the Cronbach's alpha coefficient was derived. Results: The study's sample population comprised 268 adult subjects, with a mean age of 29.0 +/- 10.5 years. With an overall Cronbach's alpha of 0.88, the MAFW scale demonstrated strong internal consistency. The reliability coefficients for its individual subscales were observed to fall within the range of 0.82 to 0.96. The four-factor structure of the MAFW scale (environmental motivation, social motivation, financial motivation, and moral motivation) was confirmed through CFA, and the fit indices indicated a good model fit (chi & sup2;/sd=2.88; RMSEA=0.084; GFI=0.95; AGFI=0.94; CFI=0.92; TLI=0.91; SRMR=0.04). According to the convergent validity analysis, significant correlations were observed between the MAFW scale score and the Plate Clearing Tendency Scale and Household Food Security Survey Module- Short Form. Convergent validity analyses showed statistically significant but weak correlations between the MAFW scale score and both the Plate Clearing Tendency Scale and the Household Food Security Survey Module-Short Form Conclusion: Our findings indicate that the Turkish adaptation of the MAFW scale can be effectively utilized as a valid and reliable tool for measuring adult motivation to avoid food waste. The MAFW scale presents a valuable resource for subsequent studies aiming to gauge individuals' knowledge, opinions, and actions concerning food wastage.Article Citation - WoS: 1The Evaluation of System Reliability Under Dependent Shock Magnitudes(Springer, 2026) Eryilmaz, SerkanThis paper studies shock models by assuming a certain kind of dependence among shock magnitudes. In particular, discrete time extreme and run shock models are investigated when the shock magnitudes follow discrete autoregressive process of order 1. Exact expressions are obtained for the reliability functions and mean time to failure values under both models. The method for deriving the reliability characteristics is based on the use of probability generating functions. Numerical results are presented when the shocks arrive according to a Binomial process.Article Circular One/Two/Three-Dimensional Consecutive k-Type Systems(Springer, 2026) Yi, He; Balakrishnan, Narayanaswamy; Li, XiangIn this paper, several circular one/two/three-dimensional consecutive k-type systems are studied, including circular consecutive-k-out-of-n: F systems, circular l-consecutivek-out-of-n: F systems without/with overlapping, circular connected-(k(1), k(2))-outof-(n(1), n(2)): F systems, circular l-connected-(k(1), k(2))-out-of-(n(1), n(2)): F systems without/ with overlapping, circular connected-(k(1), k(2), k(3))-out-of-(n(1), n(2), n(3)): F systems, and circular l-connected-(k(1), k(2), k(3))-out-of-(n(1), n(2), n(3)): F systems without/with overlapping. Reliability functions of these systems are studied using finite Markov chain imbedding approach (FMCIA). Some illustrative examples are provided, and possible applications and generalizations of the established results are also mentioned.Article A General Type of Linear Consecutive-K Systems(Springer, 2026) Yi, He; Balakrishnan, Narayanaswamy; Li, XiangIn this paper, some well-known consecutive k-type systems, including linear consecutive-k-out-of-n: F systems and linear l-consecutive-k-out-of-n: F systems without/with overlapping, are generalized by using more general failure patterns. Finite Markov chain imbedding approach (FMCIA) is applied in a new way for evaluating reliabilities of these generalized new systems. Some illustrative examples are provided for demonstrating the theoretical results established here and also for showing the efficiency of the computational process. Finally, some possible applications and generalizations are mentioned.Article Nonparametric Tests for Comparing Reliabilities of Coherent Systems at Specific Mission Time(IEEE-Inst Electrical Electronics Engineers Inc, 2026) Xu, Xuan; Zhu, Xiaojun; Balakrishnan, Narayanaswamy; Ng, Hon Keung TonyReliability analysis of coherent systems is critical for evaluating the performance of systems whose functionality depends on the reliability of their components. Traditional parametric methods for comparing reliabilities of coherent systems assume a specific probability distribution for component lifetimes, which may result in inaccurate results when these model assumptions are violated. This article introduces nonparametric procedures using system-level data with known signatures to compare the reliabilities of systems. The proposed methodology avoids parametric distributional assumptions for component lifetimes while relying on the standard assumption in signature-based reliability analysis. Specifically, a two-sample likelihood ratio test procedure is proposed to demonstrate a component or system with superior reliability. Monte Carlo simulations are performed to evaluate the performance of the proposed methods. Furthermore, we examine the effect of system structure on test power and determine favourable structures to enhance the power performance of the test. Practical examples are used to illustrate the proposed test procedures.Article Citation - WoS: 1Citation - Scopus: 1A Class of Shock Models for a System That Is Equipped With a Protection Block With an Application to Wind Turbine Reliability(Wiley, 2025) Eryilmaz, SerkanThis paper studies a class of shock models for a system that is equipped with a protection block that has its own failure rate. Under the considered class, the system exposed to shocks at random times is protected by the protection block, and the probability of the shock damaging the system varies depending on whether the protection block operates or not. The system failure criteria is defined based on the pattern of the critical/damaging shocks. Exact expressions for the reliability and mean time to failure of the system are obtained, and detailed computations are presented for the run shock model, which is included in the class. The application of the extreme shock model, which is included in the relevant class, to wind turbine reliability is also discussed.Article Citation - Scopus: 1The Distribution of Wind Power from a Dispersed Array of Wind Turbine Generators and Its Reliability Based Applications(Elsevier, 2026) Eryilmaz, Serkan; Kan, Cihangir; Devrim, YilserIn this paper, the probability distribution of wind power from a dispersed array of wind turbine sites is studied considering forced outage rates of wind turbines. The wind speeds at distinct sites are assumed to be dependent and the dependence is modeled by copulas. In particular, the probability distribution of the aggregate power from two sites is exactly derived. The probability distribution of the aggregate power is also derived under the particular case when site 1 consists of n1 identical wind turbines of type 1 and site 2 consists of n2 identical wind turbines of type 2. Numerical results are presented to illustrate the theoretical findings for a chosen copula function.Article Citation - WoS: 10Citation - Scopus: 10Reliability and Optimal Age-Based Replacement Policy for Consecutive 2-Out System Equipped With Protection Blocks(Pergamon-Elsevier Science Ltd, 2025) Eryilmaz, SerkanThis paper concerns the reliability evaluation and optimal age-based replacement policy for the linear consecutive 2-out-of-n:G system whose two consecutive components are protected by a block that has its own failure rate. Two alternative methods are proposed to compute the reliability of the system. The first method is based on direct probabilistic approach and uses the reliability of the ordinary consecutive 2-outof-n:G system. The second method is based on the concept of survival signature. Closed form equations for the system reliability and the mean number of failed components within the system are obtained. The optimal age-based replacement policy is also defined and studied. Extensive numerical results are presented to illustrate the findings.Article Citation - WoS: 8Citation - Scopus: 8On Reliability of Consecutive k-out-of-n:G System Equipped With Protection Blocks(Taylor & Francis Ltd, 2026) Eryilmaz, SerkanThe linear consecutive k-out-of-n:G system consists of n linearly ordered components such that the system works properly when there exists at least k consecutively working components. This paper is concerned with the reliability evaluation of the linear consecutive k-out-of-n: G system equipped with protection blocks. Protection blocks which have their failure rates are used to increase the system reliability. The closed-form expressions for the system reliability when $ 2k\geq n $ 2k >= n are obtained when the most critical components, i.e. the components that have the highest importance levels are involved by the protection blocks. Numerical examples are provided to illustrate the closed-form reliability equations.