• 한국경영과학회지
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• 제4권1호
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• pp.51-67
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• 1979

This paper considers the problem of determining an optimal dynamic operating policy for a two-stage tandem queueing service system in which the service facilities (or stages) can be operated at more than one service rate. At each period of the system's operation, the system manager must specify which of the available service rates is to be employed at each stage. The cost structure includes an operating cost for running each stage and a service facility profit earned when a service completion occurs at Stage 2. We assume that the system has a finite waiting capacity in front of each station and each customer requires two services which must be done in sequence, that is, customers must pass through Stage 1 and Stage 2 in that order. Processing must be in the order of arrival at each station. The objective is to minimize the total discounted expected cost in a two-stage tandem queueing service system, which we formulate as a Discrete-Time Markov Decision Process. We present analytical and numerical results that specify the form of the optimal dynamic operating policy for a two-stage tandem queueing service system.

• Communications for Statistical Applications and Methods
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• 제25권4호
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• pp.443-451
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• 2018

$P^M_{\lambda}$-service policy is a workload dependent hysteretic policy. The policy has two service states comprised of the ordinary stage and the fast stage. An ordinary service stage is initiated by the arrival of a customer in an idle state. When the workload of the server surpasses threshold ${\lambda}$, the ordinary service stage changes to the fast service state, and it continues until the system is empty. These service stages alternate in this manner. When the cost of changing service stages is high, the hysteretic policy is more efficient than the threshold policy, where a service stage changes immediately into the other service stage at either case of the workload's surpassing or crossing down a threshold. $P^M_{\lambda}$-service policy is a modification of $P^M_{\lambda}$-policy proposed to control finite dams, and also an extension of the well-known D-policy. The distributions of the stationary workload of $P^M_{\lambda}$-service policy and its variants are studied well. However, there is no known result on the sojourn time distribution. We prove that there is a relation between the sojourn time of a customer and the first up-crossing time of the workload process over the threshold ${\lambda}$ after the arrival of the customer. Using the relation and the duality of M/G/1 and G/M/1 queues, we obtain conditional sojourn time distributions in M/G/1 and G/M/1 queues under the policy.

• 한국시뮬레이션학회논문지
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• 제20권3호
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• pp.29-39
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• 2011

예약시스템은 고객들이 서비스에 효과적으로 접근하는 것을 용이하게 하는 방법으로 의료 등의 서비스 산업에서 많이 사용되고 있다. 예약시스템의 중요성 때문에 서비스 제공 환경 별로 효과적인 예약정책 수립에 대한 연구가 많이 진행되고 있지만 대부분의 연구는 단일 서버, 단일 단계로 구성된 서비스 시스템만을 고려하고 있다. 본 논문은 다수의 서버로 구성된 두 단계 서비스 시스템에서 다양한 예약정책을 평가하여 효과적인 예약정책을 수립하는 것을 목적으로 한다. 2단계의 서버가 개별적으로 고객 예약을 수립하는 환경을 고려하여 본 연구에서는 교차예약정책을 제시하였다. 시뮬레이션 연구를 통하여 기존의 전통적인 예약정책과 비교하여 고객대기시간, 서버의 유휴시간, 예약보다 지연 도착하는 고객의 수 등에서 교차예약정책이 우수한 결과를 제공하는 것을 제시하였다.

• 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.

• 한국통계학회:학술대회논문집
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• 한국통계학회 2004년도 학술발표논문집
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• pp.295-300
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• 2004

We consider a G/M/1 queue with two-stage service policy. The server starts to serve with rate of ${\mu}1$ customers per unit time until the number of customers in the system reaches A. At this moment, the service rate is changed to that of ${\mu}2$ customers per unit time and this rate continues until the system is empty. We obtain the stationary distribution of the number of customers in the system.

• Journal of the Korean Data and Information Science Society
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• 제24권4호
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• pp.941-948
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• 2013

We introduce the $P^M_{{\lambda},{\tau}}$ service policy, as a generalized two-stage service policy of the $P^M_{\lambda}$ policy of Bae et al. (2002) for an M/G/1 queueing system. By using the level crossing theory and solving the corresponding integral equations, we obtain the explicit expression for the stationary distribution of the workload in the system.

• 보건행정학회지
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• 제25권3호
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• pp.152-161
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• 2015

We analyze the determinants of obesity and the chronic diseases using the Korea Health Panel data. Also we analyze the effect of obesity and the chronic diseases on the health care expenditures. Through this study, to reduce the health care expenditures, we suggest the policy implication that might curb the obesity and the chronic diseases. We estimate the determinants of obesity, the chronic diseases, and the health care expenditures using 2SLS (two stage least squares) estimation method under the simultaneous equations framework. Result says that obesity and chronic diseases significantly have positive effects on the health care expenditures. Also the determinants of the health care expenditures that have positive effects are age, income and health care utilization variables.

• 산업경영시스템학회지
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• 제45권4호
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• pp.53-60
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• 2022

In a group-testing method, instead of testing a sample, for example, blood individually, a batch of samples are pooled and tested simultaneously. If the pooled test is positive (or defective), each sample is tested individually. However, if negative (or good), the test is terminated at one pooled test because all samples in the batch are negative. This paper considers a queueing system with a two-stage group-testing policy. Samples arrive at the system according to a Poisson process. The system has a single server which starts a two-stage group test in a batch whenever the number of samples in the system reaches exactly a predetermined size. In the first stage, samples are pooled and tested simultaneously. If the pooled test is negative, the test is terminated. However, if positive, the samples are divided into two equally sized subgroups and each subgroup is applied to a group test in the second stage, respectively. The server performs pooled tests and individual tests sequentially. The testing time of a sample and a batch follow general distributions, respectively. In this paper, we derive the steady-state probability generating function of the system size at an arbitrary time, applying a bulk queuing model. In addition, we present queuing performance metrics such as the offered load, output rate, allowable input rate, and mean waiting time. In numerical examples with various prevalence rates, we show that the second-stage group-testing system can be more efficient than a one-stage group-testing system or an individual-testing system in terms of the allowable input rates and the waiting time. The two-stage group-testing system considered in this paper is very simple, so it is expected to be applicable in the field of COVID-19.

• 보건행정학회지
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• 제1권1호
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• pp.3-18
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• 1991

On the stage of transition from highly centralized government to local self-government in Korea, administrating practice characteristics of the directors of Health Centers is essentially required to be found. This study was conducted in order to find the administration patte군 of the directors of Health Centers in Korea and their opinion on the environment of health administration including personnel management regime for them. The materials were collected from 149 directors of Health Centers with a structured questionaire by mailing. The major findings of this study were as follows. 1. About two-thirds of the directors(69.1%) make plan through the consensus between public service perosonnel in programme department and them in budgt control department. And 75.0% of the directors maintain the planed by the predecessor. 2. More than two-thirds of the directors (71.1%) take subordinates opinion into consideration in case of the programmes facing objections. 3. When the directors face obstacles in pursuing health programmes they usually consult other public service personnel than inhabitants. 4. Only 10.8% of the directors were satisfied with the support of the Ministry of Internal Affairs for health administration while more than half of them were satisfied with the support of health institution in higher level. 5. The directors evaluated the job attitude of the public service personnel in low level as more favorable than that of there higher level public service personnel who work for central government. 6. Only 18.1% of the idrectors were satisfied with their saley. And more than half of them expect the promotion of their position. On the ground of this result the administration attitude of the directors of Health Centers would be evaluated as improved and as more positive than that of other public service personnel in health authorities. However, they are required to consult the inhabitants more frequently for health administration. An the public service personnel in high level who work for central government are required to improve their job attitude.

• 수산경영론집
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• 제35권1호
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• pp.57-85
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• 2004

To develop an blue tourism website(BTW) for electronic commerce(EC), information requirements of BTW are defined firstly. We defined information requirements of BTW from two aspects, i.e., front office and back office. Information requirements for front office were derived by consumer purchasing decision process. And information requirements for back office were derived by tourism value chain. Total 29 functions are identified as critical EC related functions of BTW. Among them, 25 functions were investigated into BTW. BTWs were searched by search engines - Yahoo and Empas - to Korean websites. There are 12 specialized BTWs, except one cyber museum website. For 12 websites, 25 functions were probed. By the results, in need recognition stage of blue tourism, only weather information was provided in most websites. In information search stage of blue tourism, package recommendation and various contents were provided in most websites. In consumption stage of blue tourism, traffic information were provided in most websites. And in after - sales service stage of blue tourism, bulletin board function was implemented in most websites. The rest of the functions were scarcely implemented. On the whole, it was concluded that most EC related functions of BTW in Korea were not implemented properly. To improve the status quo, it is expected in the dimension of individual website, that marketing planning, customized service, intelligent service, reinforcing purchasing assistance functions, customer relationship management, and escrow service etc. need to be implemented. And it is expected in the dimension of blue tourism industry, that standardizing product catalog, security assistance policy, information sharing by industrial database, finding referral model of BTW, elevating information mind, revising related laws etc. are needed.