• 대한산업공학회지
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• 제36권2호
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• pp.108-116
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• 2010

The maintenance of a deteriorating system is often imperfect. Previous studies have shown that the imperfect preventive maintenance (PM) can reduce the wear out and aging effects of deteriorating systems to a certain level between the conditions of as good as new and as bad as old. In this paper, we employ the concept of the improvement factor in investigating two optimal PM policies; failure limit policy and periodic PM policy. We redefine the improvement factor model as a function of the cost of PM, using this concept, we derive the conditions of optimal PM policies and formulate expressions to compute the expected cost rate. Based on this information, the determination of the maintenance policies which minimize the cost rate is examined. Numerical examples for the Weibull distribution case are also given.

• East Asian mathematical journal
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• 제24권1호
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• pp.45-55
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• 2008

We consider an M/G/1 queue with $P^M_{\lambda}$-service policy, which is a two-stage service policy. The server starts to serve with rate 1 if a job arrives to the sever in idle state. If the workload of the system upcrosses $\lambda$, then the service rate is changed to M and this rate continues until the system is empty. It costs to change the service rate to M and maintaining the rate. When the expectation of the stationary workload is supposed to be less than a given value, we derive the optimal value of M.

• Management Science and Financial Engineering
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• 제15권1호
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• pp.33-49
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• 2009

We examine the effectiveness of the conventional (Q, r) model in managing production-inventory systems with finite capacity, stochastic demand, and stochastic order processing times. We show that, for systems with finite production capacity, order replenishment lead times are highly sensitive to loading and order quantity. Consequently, the choice of optimal order quantity and optimal reorder point can vary significantly from those obtained under the usual assumption of a load-independent lead time. More importantly, we show that for a given (Q, r) policy the conventional model can grossly under or over-estimate the actual cost of the policy. In cases where a setup time is associated with placing a production order, we show that the optimal (Q, r) policy derived from the conventional model can, in fact, be infeasible.

• 대한안전경영과학회지
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• 제6권1호
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• pp.61-70
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• 2004

In this paper, a group replacement policy based on a failure count is analysed. For a group of identical repairable units, a maintenance policy is performed with two phase considerations: a repair interval phase and a waiting interval phase. Each unit undergoes minimal repair at failure during the repair interval. Beyond the interval, no repair is made until a number of failures. The expected cost rate expressions under the policy is derived. A method to obtain the optimal values of decision variables are explored. Numerical examples are given to demonstrate the results.

• 한국국방경영분석학회지
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• 제17권1호
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• pp.61-83
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• 1991

There has been a great deal of research dealing with the optimal replacement of stochastically deteriorating equipment and research in queueing systems with a finite calling population. However. there has been a lack of research which combines these two areas to deal with optimal replacement for a fixed number of machines and a limited number of repairmen. In this research, an optimal control policy for replacement involving two machines and one repairman is developed by investigating a class of age replacement policies in the context of controlling a G/M/1 queueing system with a finite calling population. The control policy to be imposed on this problem is an age-dependent control policy, described by the control limit $t^{\ast}$. The control limit is operational only when the repairman is idle; that is. if both machines are working, as soon as a machine reaches the age $t^{\ast}$ it is taken out of service for replacememt. We obtain the ${\epsilon}$-optimal control age which will minimize the long-run average system cost. An algorithm is developed that is applicable to general failure time distributions and cost functions. The algorithm does not require the condition of unimodality for implementation.

• 국제지역연구
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• 제15권1호
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• pp.59-86
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• 2011

본고는 공급측면(비용)의 비대칭정보가 존재할 때, 일국의 외국 독점기업에 부과하는 최적관세 정책에 관한 내용이다. 즉, 한 나라의 후생관점에서 시장 지배력을 가진 외국독점기업에 대한 최적관세의 결정 문제를 비용측면의 비대칭정보하에서 분석하는 것이 이 논문의 목적이다. 따라서 비대칭정보하에서의 전략적 최적관세가 도출되고 그 함축성이 논의된다. 주요 결과는 외국기업의 독점렌트를 이전하기 위한 최적관세의 크기가 완전정보하에서 보다 비대칭정보하에서 더 커진다는 것이다. 또한 외국독점렌트를 이전하기 위한 전략적 무역정책이 비대칭정보하에서 유동적임이 드러난다. 이 연구는 문헌적으로 기존의 전략적 무역정책을 보완하며 특히 이 분야의 선구적 이론인 브랜더-스펜서의 결과(1984)를 이론적으로 확장하는 의미를 가진다.

• 대한산업공학회지
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• 제26권2호
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• pp.81-87
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• 2000

As for M/G/1 queueing system, we use various control policies, with which we can optimize the system. Up to now the most widely adopted policies are N-Policy, T-Policy, D-Policy, and so on. The existing researches are largely concerned to find an optimal operation condition or to optimize the system under single policy in M/G/1 system. There are, however, few literatures dealing with multiple control policies at once to enhance the flexibility of the model. In this study, we consider M/G/1 system adopting N-Policy and T-Policy simultaneously. If one of two conditions is satisfied, then, the server starts the service. We call this Min(N,T)-Policy. We find the probability distribution of the number of customers and mean waiting time in steady state and derive a cost function. Next, we seek the $N^*$, optimal threshold under various N values. Finally, we reveal the characteristics of cost function.

• KDI Journal of Economic Policy
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• 제13권4호
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• pp.141-153
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• 1991

본고(本稿)에서는 재정당국(財政當局)과 통화당국(通貨當局)를 포괄하는 통합정부(統合政府)의 최적재원조달(最適財源調達)의 관점에서 재정정책(財政政策)과 통화정책간(通貨政策間)의 체계적(體系的)인 연관(聯關)의 존재 여부와 그 내용을 재정우위(財政優位)모델의 이론적 결과에 입각하여 실증적(實證的)으로 고찰하였다. 재정우위(財政優位)모델에서는 통화(通貨)에 의한 직접적(直接的) 재원조달(財源調達) 경로(經路)로서의 seigniorage의 확보와, 간접적(間接的) 경로(經路)로서의 인플레적 편의(偏倚)를 모델화하여 정부예산제약하(政府豫算制約下)에서 최적(最適) 인플레이션율(率) 조세부담율(租稅負擔率)의 선택문제를 다루고 있으며, 이 모델에서 밝혀진 재정(財政) 통화정책(通貨政策)의 적정관계(適正關係)는 최적 인플레이션율(率)/조세부담률(租稅負擔率) 비율(比率)과 한계수입비율간(限界收入比率間)의 정(正)의 상관관계(相關關係)와, 인플레이션율(率)과 조세부담률간(租稅負擔率間)의 정(正)의 상관관계(相關關係)로 함축된다. 1970~80년대 한국경제(韓國經濟)의 거시경제정책영역(巨視經濟政策領域)의 성격 규명을 위한 가설검정(假說檢定) 결과는 이 기간의 재정(財政) 통화변수(通貨變數)의 추이가 통화에 의한 직접적 재원조달측면(財源調達側面)을 강조하는 재정우위(財政優位)의 최적화(最適化) 과정(過程)의 이론적(理論的) 결과(結果)와 부합됨을 보여주고 있다. 본(本) 연구결과(硏究結果)는 한국(韓國)의 거시경제정책기조(巨視經濟政策基調) 설명(說明)에 있어 재정우위(財政優位)의 최적화(最適化)모델이 유용할 수 있으며 재정(財政) 통화정책변수(通貨政策變數)들이 기대되는 수준 이상으로 체계적인 연관을 가지고 있음을 보여주고 있다. 또한 재정우위(財政優位)모델의 이론적 결과의 엄밀한 해석을 통하여 통화공급(通貨供給)과 물가(物價)의 설명변수(說明變數)로서의 재정(財政)의 중요성과 그 구체적 내용을 보여주고 있다.

• 산학경영연구
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• 제6권
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• pp.135-152
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• 1993

The optional market segmentation pricing policy for rooms of hotels are investigated under the assumption of a linear demand function, and for four different situations: (1) single price market, (2) optimal segmentation of the unused capacity of a single-price-maeket, (3) optimal segmantation for all rooms, and (4) opimal segmentation for infiltration from higher priced to adjacent lower priced segments. The purpose of tis study is th show that with proper pricing policy, it would be possible to increase profits considerably. Such a profit increase might be achived by market segmentation coupled with product differentiation, where the different market segments are identified, sperated, and in each segment a different price per room is called for. The different prices are determined based on the specific price elasticity typical for each market segment and the relavant costs. The pricing model implied in this study is based on basic economic pricing theory and optimization techniques. While somewhat complex in its mathmatical solution, it can be easily programmed for use by practitioners, avoiding the need to cope with the technical aspects of the solution. In section II-1, the optimal single-market Single-price policy is evaluated. The optimal strategy under the constraint that only the previously unutilized rooms are segmented is analysed in section II-2, while the optimal strategy without this constraint is determined in section II-3. In section II-4, the optimal market-segmentation pricing policy is derived for the case in which market seperation is allowed for all the rooms under the assumption of custtomer infiltration from each market segment to the adjacent lower priced segment Finally, some considerations relating to the practicality of the model as a decision support tool and the requirements for its implementation are discussed in section III.

• 품질경영학회지
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• 제31권3호
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• pp.185-192
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• 2003

In this paper, the properties on the optimal replacement policies for the general failure model are developed. In the general failure model, two types of system failures may occur : one is Type I failure (minor failure) which can be removed by a minimal repair and the other, Type II failure (catastrophic failure) which can be removed only by complete repair. It is assumed that, when the unit fails, Type I failure occurs with probability 1-p and Type II failure occurs with probability p, $0\leqp\leq1$. Under the model, the system is minimally repaired for each Type I failure, and it is repaired completely at the time of the Type II failure or at its age T, whichever occurs first. We further assume that the repair times are non-negligible. It is assumed that the minimal repair times in a renewal cycle consist of a strictly increasing geometric process. Under this model, we study the properties on the optimal replacement policy minimizing the long-run average cost per unit time.