• 응용통계연구
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• 제23권6호
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• pp.1147-1156
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• 2010

본 논문에서는 비 재생무료교체-수리보증이 종료된 이후의 수리가 가능한 시스템에 대한 교체정책을 제안한다. 이를 위해서, 비 재생무료교체-수리보증을 정의하고, 사용자 측면에서 비 재생무료교체-수리보증이 종료된 이후의 보전모형이 고려된다. 최적의 보전정책을 결정하기 위한 기준으로는 사용자 측면의 단위시간당 기대비용이 고려되고, 보증 기간이 종료된 이후에 발생되는 시스템의 유지비용은 사용자가 모두 지불하게 된다. 즉, 시스템의 운영기간 동안 사용자가 지불하여야 할 비용들이 주어져 있을 때, 비 재생무료교체-수리보증이 종료된 이후의 최적의 보전주기를 결정한다. 마지막으로 본 논문에서 제안된 보존정책을 설명하기 위해서 수치적 예를 살펴본다.

• 한국신뢰성학회지:신뢰성응용연구
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• 제13권2호
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• pp.77-86
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• 2013

Recently, an extended warranty of a system following the expiration of the basic warranty is becoming increasingly popular to the user. In this respect, we suggest a replacement model following the expiration of extended warranty with minimal repair warranty from the user's point of view in this paper. Under extended warranty, the failed system is minimally repaired by the manufacturer at no cost to the user during the original extended warranty period. As a criterion of the optimality, we utilize the expected cost rate per unit time during the life cycle from the user's perspective and suggest the optimal replacement period after extended warranty. Finally, a few numerical examples are given for illustrative purpose.

• 대한산업공학회지
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• 제34권1호
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• pp.98-107
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• 2008

The purpose of this paper is to present an optimization scheme that aims at minimizing the expected cost per unittime. This study considers a linear connected-(r, s)-ouI-of-(m, n):f lattice system whose components are orderedlike the elements of a linear (m, n)-matrix. We assume that all components are in the state 1 (operating) or 0(failed) and identical and s-independent. The system fails whenever at least one connected (r, s)-submatrix offailed components occurs. To find the optimal threshold of maintenance intervention, we use a simulatedannealing(SA) algorithm for the cost optimization procedure. The expected cost per unit time is obtained byMonte Carlo simulation. We also has made sensitivity analysis to the different cost parameters. In this study,utility maintenance model is constructed so that minimize the expense under full equipment policy throughcomparison for the full equipment policy and preventive maintenance policy. The full equipment cycle and unitcost rate are acquired by simulated annealing algorithm. The SA algorithm is appeared to converge fast inmulti-component system that is suitable to optimization decision problem.

• 대한산업공학회지
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• 제22권4호
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• pp.651-662
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• 1996

This paper concerns with preventive replacement under periodic inspections for an item (system) which is in a state of preparedness. The item is subject to wear. The item fails randomly but the failure rate depends on the accumulated wear. The item is preventively replaced if it survives a certain wear limit at periodic inspections. The foiled item is, however, replaced at periodic inspections. Given the costs for replacements and inspections, and the penalty cost of the time elapsed between failure und its detection, the optimal wear limit according to the long-run expected cost per unit time criterion is derived. It has been proved that the optimal wear limit is unique if an item has increasing weer-dependent failure rate. A numerical example for a stationary gamma wear process with Weibull distributed failure is given to show its applicability.

• 산업경영시스템학회지
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• 제44권4호
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• pp.154-168
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• 2021

COVID-19 has been spreading all around the world, and threatening global health. In this situation, identifying and isolating infected individuals rapidly has been one of the most important measures to contain the epidemic. However, the standard diagnosis procedure with RT-PCR (Reverse Transcriptase Polymerase Chain Reaction) is costly and time-consuming. For this reason, pooled testing for COVID-19 has been proposed from the early stage of the COVID-19 pandemic to reduce the cost and time of identifying the COVID-19 infection. For pooled testing, how many samples are tested in group is the most significant factor to the performance of the test system. When the arrivals of test requirements and the test time are stochastic, batch-service queueing models have been utilized for the analysis of pooled-testing systems. However, most of them do not consider the false-negative test results of pooled testing in their performance analysis. For the COVID-19 RT-PCR test, there is a small but certain possibility of false-negative test results, and the group-test size affects not only the time and cost of pooled testing, but also the false-negative rate of pooled testing, which is a significant concern to public health authorities. In this study, we analyze the performance of COVID-19 pooled-testing systems with false-negative test results. To do this, we first formulate the COVID-19 pooled-testing systems with false negatives as a batch-service queuing model, and then obtain the performance measures such as the expected number of test requirements in the system, the expected number of RP-PCR tests for a test sample, the false-negative group-test rate, and the total cost per unit time, using the queueing analysis. We also present a numerical example to demonstrate the applicability of our analysis, and draw a couple of implications for COVID-19 pooled testing.

• 응용통계연구
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• 제15권1호
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• pp.107-117
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• 2002

본 논문에서는 혼합보증기간이 있는 수리 가능한 시스템에 대하여 보증기간이 종료된 이후의 교체정책을 고려한다. 이러한 교체정책은 보증기간이 재생되는 재생혼합보증과 재생되지 않는 비재생혼합보증에 대하여 고려되며, 최적의 교체정책을 설정하기 위 해서 단위 시간당 기대비용을 사용한다. 재생혼합보증과 비재생혼합보증이 있는 시스템에 대하여 소비자 관점에서의 단위 시간당 기대비용을 구하고, 이를 최소화하는 최적의 보전기간을 결정한다 그리고, 시스템의 고장시간이 와이블분포일 때 수치적 예를 통해서 제안된 최적의 교체정책을 설명한다.

• Journal of the Korean Data and Information Science Society
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• 제13권1호
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• pp.55-65
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• 2002

In this paper we present a Bayesian approach for determining an optimal maintenance policy following the expiration of warranty for a repairable system. We consider two types of warranty policies : non-renewing free replacement warranty (NFRW) and non-renewing pro-rata warranty (NPRW). The mathematical formula of the expected cost rate per unit time is obtained for NFRW and NPRW, respectively. When the failure time is Weibull distribution with uncertain parameters, a Bayesian approach is established to formally express and update the uncertain parameters for determining an optimal maintenance policy. We illustrate the use of our approach with simulated data.

• Communications for Statistical Applications and Methods
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• 제9권1호
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• pp.21-31
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• 2002

This paper considers a Bayesian approach to determine an optimal replacement policy for a repairable system with warranty period. The mathematical formula of the expected cost rate per unit time is obtained for two cases : RFRW(renewing free-replacement warranty) and RPRW(renewing pro-rata warranty). When the failure time is Weibull distribution with uncertain parameters, a Bayesian approach is established to formally express and update the uncertain parameters for determining an optimal replacement policy. Some numerical examples are presented for illustrative purpose.

• 조명전기설비학회논문지
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• 제23권4호
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• pp.47-55
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• 2009

본 논문에서는 해석적방법론에 의한 산업용 수용가의 공급지장비를 산정할 수 있는 방법론을 개발하기 위해 산업용 수용가 1,026호를 방문하여 설문조사를 수행하는 미시적 접근법을 사용하여 산업용 수용가의 종별 공급지장비를 표준산업분류에 의한 18개의 업종으로 조사하였다. 얻어진 조사결과를 계층화의사 결정법(AHP; Analytic Hierarchy Process)으로 최적의 공급지장비용 함수(SCDF; Sector Customer Demage Function)를 선정하였다. 이를 통하여 배전계통에서의 신뢰도 가치평가(VBDRA; Value Based Distribution Reliability Assessment)를 위해서 주어진 배전계통 예상 공급지장에너지(EENS; Expected Energy Not Supply), 정전비용기대치(ECOST; Expected Interruption Cost), 차단에너지비율(IEAR; Interrupted Energy Assessment Rate)을 계산하여 그 가치를 평가하였다. 이를 배전계통에 적용하기 위해서 사례연구로 적용하고 공급지장비용을 도출하여 그 특성을 분석하였다.

• 품질경영학회지
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• 제43권4호
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• pp.471-488
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• 2015

Purpose: Double sampling $T^2$ chart is a useful tool for detecting a relatively small shift in process mean when the process is controlled by multiple variables. This paper finds the optimal design of the double sampling $T^2$ chart in both economical and statistical sense under Weibull failure model. Methods: The expected cost function is mathematically derived using recursive equation approach. The optimal designs are found using a genetic algorithm for numerical examples and compared to those of single sampling $T^2$ chart. Sensitivity analysis is performed to see the parameter effects. Results: The proposed design outperforms the optimal design of the single sampling $T^2$ chart in terms of the expected cost per unit time and Type-I error rate for all the numerical examples considered. Conclusion: Double sampling $T^2$ chart can be designed to satisfy both economic and statistical requirements under Weibull failure model and the resulting design is better than the single sampling counterpart.