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Article Citation - WoS: 11Citation - Scopus: 12A New Mixed Δ-Shock Model With a Change in Shock Distribution(Springer, 2023) Chadjiconstantinidis, Stathis; Tuncel, Altan; Eryilmaz, SerkanIn this paper, reliability properties of a system that is subject to a sequence of shocks are investigated under a particular new change point model. According to the model, a change in the distribution of the shock magnitudes occurs upon the occurrence of a shock that is above a certain critical level. The system fails when the time between successive shocks is less than a given threshold, or the magnitude of a single shock is above a critical threshold. The survival function of the system is studied under both cases when the times between shocks follow discrete distribution and when the times between shocks follow continuous distribution. Matrix-based expressions are obtained for matrix-geometric discrete intershock times and for matrix-exponential continuous intershock times, as well.Article Citation - WoS: 8Citation - Scopus: 10Nöromüsküler Hastalarda Gövde Kontrolünün Değerlendirilmesi: Gövde Bozukluk Ölçeği’nin Geçerlik ve Güvenirliği(Turkish Neurological Soc, 2018) Demir, Yasemin Parlak; Yıldırım, Sibel AksuAmaç: Çalışmamızın amacı Gövde Bozukluk Ölçeği’nin (GBÖ) erişkin nöromüsküler hastalıklarda geçerlik ve güvenirliğini araştırmaktır. Gereç ve Yöntem: Çalışmaya 66 nöromüsküler hastalık tanısı olan birey alındı. Çalışmaya dahil edilen olgulara GBÖ, Manuel Kas Testi (gövde, üst ve alt ekstremite), Motor Fonksiyon Değerlendirme Ölçeği (MFM), Fonksiyonel Bağımsızlık Ölçeği (FIM), Rivermead Mobilite İndeksi (RMI) yapıldı. Bulgular: GBÖ’nün test tekrar test, ICC güvenirlikleri mükemmel bulundu (GBÖ: 0,96 ve 0,98). Cronbach alfa katsayısı 0,82 bulundu. Yapı geçerliği için GBÖ ile MFM (r=0,29), MFM gövde (r=0,31), toplam gövde kas kuvveti (r=0,34), toplam alt ekstremite kas kuvveti (r=0,34, p<0,05), toplam kas kuvveti (gövde, alt ve üst ekstremite) (r=0,52, p<0,05) arasında anlamlı ilişki bulundu. GBÖ uyum geçerliği için FIM (r=0,32, p<0,05) ve RMI (r=0,39, p<0,05) ile ilişkili bulundu. Sonuç: Çalışmanın sonucunda GBÖ’nün erişkin kas hastalıklarında yapı ve uyum geçerliliğinin olduğu ve mükemmel güvenirliğe sahip olduğu bulundu. GBÖ rehabilitasyon kliniklerinde uygulaması kolay ve kısa zaman alan bir ölçektirArticle Citation - WoS: 13Citation - Scopus: 13Reliability Assessment of a Discrete Time Cold Standby Repairable System(Springer, 2021) Kan, Cihangir; Eryilmaz, SerkanThis paper is concerned with the study of a discrete time repairable system consisting of one active and one standby component. The lifetime and repair time are assumed to have discrete phase-type distributions. The system's lifetime is represented as a compound random variable. A matrix-based expression for the probability generating function of the system's lifetime is obtained based on the phase characteristics of lifetime and repair time distributions. The probability generating function is then used to obtain the distribution of the system's lifetime. Reliability and hazard rate functions are computed and evaluated for some particular choices of lifetime and repair time distributions. The limiting behavior of the hazard rates is also investigated.Article Citation - WoS: 9Citation - Scopus: 12The Behavior of Warm Standby Components With Respect To a Coherent System(Elsevier Science Bv, 2011) Eryilmaz, SerkanThis paper is concerned with a coherent system consisting of active components and equipped with warm standby components. In particular, we study the random quantity which denotes the number of surviving warm standby components at the time of system failure. We represent the distribution of the corresponding random variable in terms of system signature and discuss its potential utilization with a certain optimization problem. (C) 2011 Elsevier B.V. All rights reserved.Article Citation - WoS: 3Citation - Scopus: 3On the Mean Number of Remaining Components in Three-State k-out-of-n< System(Elsevier Science Bv, 2015) Eryilmaz, Serkan; Eryılmaz, Serkan; Eryılmaz, Serkan; Industrial Engineering; Industrial EngineeringA three-state k-out-of-n system with n independent components is considered, where the vector k of integers is determined by given fixed scalars k(1) and k(2) such that k(1), k(2) <= n. The mean number of components of each type either in a perfect functioning state or in a partially working state at the time of the system failure and at a time while the system is working are studied. An optimization problem concerned with the most economical value of n is also formulated. (C) 2015 Elsevier B.V. All rights reserved.Article Citation - WoS: 11Citation - Scopus: 12Discrete Time Shock Models Involving Runs(Elsevier Science Bv, 2015) Eryilmaz, SerkanIn this paper, three different discrete time shock models are studied. In the first model, the failure occurs when the additively accumulated damage exceeds a certain level while in the second model the system fails upon the local damage caused by the consecutively occurring shocks. The third model is a mixed model and combines the first and second models. The survival functions of the systems under these models are obtained when the occurrences of the shocks are independent, and when they are Markov dependent over the periods. (C) 2015 Elsevier B.V. All rights reserved.Article Citation - WoS: 3Citation - Scopus: 3Validity and Reliability of Turkish Version the Family Inventory of Needs-Pediatric Ii: an Inventory To Identify Care Needs of Parents of Children With Cancer(Kare Publ, 2019) Boztepe, Handan; Ay, Ayşe; Monterosso, Leanne; Ayşe, A.Y.OBJECTIVEThis study was conducted to translate and adapt the Family Inventory of Needs-Pediatric II (FIN-PEDII) into the Turkish language and investigate its validity and reliability for parents of children with cancer.METHODSA self-administered questionnaire and Family Inventory of Needs-Pediatric II was completed by 180parents whose children (0-18 years old) were diagnosed with leukemia, solid tumors, and central nervous system tumors. FIN-PED II was translated into Turkish and then back-translated and then evaluated by three experts for face validity. For construct validity, exploratory factor analysis was applied andfor reliability, internal consistency analysis was employed.RESULTSAs a result of exploratory factor analysis, it was observed that percentages of explaining total variancewere 74.787%, 68.649%, and 72.746% for sections of the importance of care needs, the need fulfilment,and the need for further information, respectively. As a result of Cronbach’s Alpha reliability analysis,the reliabilities of the sections on the importance of care needs, need fulfilment, and the need for furtherinformation for FIN-PED II was 0.814, 0.906, and 0.915.CONCLUSIONAlthough the Turkish version of FIN-PED II needs further psychometric testing, it is an effective, validand reliable tool to find out the care needs of parents of children with cancer.Article Citation - WoS: 25Citation - Scopus: 33Dynamic Behavior of k-out-of-n< Systems(Elsevier, 2011) Eryilmaz, Serkan; Erylmaz, SerkanIn this paper, we study the distribution and expected value of the number of working components at time t in usual and weighted k-out-of-n:G systems under the condition that they are working at time t. We evaluate the distribution of the corresponding conditional random variable and compute its expected value for the systems consisting of independent but nonidentical components. Illustrative examples are presented and an optimization problem which makes use of the conditional random variable is also formulated and solved numerically. (c) 2011 Elsevier B.V. All rights reserved.Article Citation - WoS: 8Citation - Scopus: 8On δ-shock model with a change point in intershock time distribution(Elsevier, 2024) Chadjiconstantinidis, Stathis; Eryilmaz, SerkanIn this paper, we study the reliability of a system that works under o-shock model. That is, the system failure occurs when the time between two successive shocks is less than a given threshold o. In a traditional setup of the o shock model, the intershock times are assumed to have the same distribution. In the present setup, a change occurs in the distribution of the intershock times due to an environmental effect. Thus, the distribution of the intershock times changes after a random number of shocks. The reliability of the system is studied under this change point setup.Article Citation - WoS: 11Citation - Scopus: 15Optimal Age Replacement Policy for Discrete Time Parallel Systems(Springer, 2023) Eryilmaz, Serkan; Tank, FatihIn the case of discrete age replacement policy, a system whose lifetime is measured by the number cycles is replaced preventively after a specific number of cycles or correctively at failure, whichever occurs first. Under the discrete setup, the policy has been mostly considered for single unit systems. In this paper, a discrete time age replacement policy is studied for a parallel system that consists of components having discretely distributed lifetimes. In particular, the necessary conditions for the unique and finite replacement cycle that minimize the expected cost rate are obtained. The theoretical results are illustrated with numerical examples to observe the effect of the cost values and the mean lifetime of the components on the optimal replacement cycle.
