• 한국경영과학회지
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• 제30권1호
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• pp.149-159
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• 2005

In this study, we consider characteristics of stationary waiting times in single-server 2-node tandem queues with a finite buffer, a Poisson arrival process and deterministic service times. The system has two buffers: one at the first node is infinite and the other one at the second node is finite. We show that the sojourn time or departure process does not depend on the capacity of the finite buffer and on the order of nodes (service times), which are the same as the previous results. Furthermore, the explicit expressions of waiting times at the first node are given as a function of the capacity of the finite buffer and we are able to disclose a relationship of waiting times between under communication blocking and under manufacturing blocking. Some numerical examples are also given.

• International Journal of Reliability and Applications
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• 제8권1호
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• pp.67-82
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• 2007

This paper deals with the effectiveness analysis of an engineering system, which has two units of different strengths in parallel and one unit as a cold standby unit. Failure times for all the units have negative exponential distribution whereas their repair times have general distribution. Single server caters the need for the system. The effectiveness analysis of the system is done by using regenerative point technique. The different measures of effectiveness such as mean sojourn time, mean time to system failure, availability, busy period, etc, are derived. Cost factors also taken into consideration.

• 한국산업정보학회논문지
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• 제12권4호
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• pp.107-118
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• 2007

A single-server queueing model with infinite buffer and batch arrival of customers is considered. In contrast to the standard batch arrival when a whole batch arrives into the system at one epoch, we assume that the customers of an accepted batch arrive one-by one in exponentially distributed times. Service time is exponentially distributed. Flow of batches is the stationary Poisson arrival process. Batch size distribution is geometric. The number of batches, which can be admitted into the system simultaneously, is subject of control. Analysis of the joint distribution of the number batches and customers in the system and sojourn time distribution is implemented by means of the matrix technique and method of catastrophes. Effect of control on the main performance measures of the system is demonstrated numerically.

• 한국경영과학회:학술대회논문집
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• 대한산업공학회/한국경영과학회 2002년도 춘계공동학술대회
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• pp.841-844
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• 2002

Recently there has been an increasing interest in queueing models with disasters. Upon arrival of a disaster, all the customers present are noshed out. Queueing models with disasters have been applied to the problems of failure recovery in many computer networks systems, database systems and telecommunication networks in this paper, we suffest the steady state and sojourn time distributions of the M/G/l model with disaster and mass alway when the system is empty.

• 한국경영과학회:학술대회논문집
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• 대한산업공학회/한국경영과학회 2002년도 춘계공동학술대회
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• pp.923-929
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• 2002

We discuss scheduling analysis for a discrete event system with time windows of which firing or holding time delays are subject to random variation within some finite range. To do this, we propose a modified p-lime Petri net, named p+-time Petri net. We develop a condition for which a synchronized transition does not have a dead token, that is, the firing epochs do not violate the time window constraints. We propose a method of computing the feasible range of the token sojourn time at each place based on a time difference graph. We also discuss an application for analyzing wafer residency times within the process chambers for a dual-armed cluster tool for chemical vapor deposition.

• 경영과학
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• 제24권1호
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• pp.25-34
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• 2007

In this study, we consider stationary waiting times in finite-buffer 3-node single-server queues in series with a Poisson arrival process and with either constant or non-overlapping service times. We assume that each node has a finite buffer except for the first node. The explicit expressions of waiting times in all areas of the stochastic system were driven as functions of finite buffer capacities. These explicit forms show that a system sojourn time does not depend on the finite buffer sizes, and also allow one to compute and compare characteristics of stationary waiting times at all areas under two blocking rules communication and manufacturing blocking. The goal of this study is to apply these results to an optimization problem which determines the smallest buffer capacities satisfying predetermined probabilistic constraints on stationary waiting times at all nodes. Numerical examples are also provided.

• 산업경영시스템학회지
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• 제29권4호
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• pp.18-26
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• 2006

여러 형태의 고객이 외부로부터 포아송과정에 따라 각 대기행렬에 도착하고 정해진 서비스규칙에 따라 해당 서비스를 받은 후 마코비안 확률분포에 따라 시스템을 떠나거나 다른 형태의 고객으로 시스템을 다시 돌아 올 수도 있는 M/G/1 대기행렬시스템을 고려한다. 본 연구에서는 기존의 연구 모형을 확장하여 계층적 서비스 규칙을 갖는 우선순위 대기행렬모형을 제시하고 이에 대한 시스템 성능척도를 보다 체계적으로 구할 수 있는 방법을 소개한다. 이를 위하여 먼저 대기행렬시스템의 거동을 나타내는 시스템 상태를 정의하고, 바쁜기간과 서비스기간 분석을 통하여 시스템 상태의 선형 함수로 평균체제시간을 구할 수 있음을 보인다.

• 한국지역지리학회지
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• 제16권3호
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• pp.275-294
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• 2010

세계화와 더불어 최근 국제인구이동의 한 경향은 단순기능인력뿐만 아니라 전문직 종사자의 초국적 이주 또한 증가하고 있다는 점이다. 우리나라도 예외가 아니어서 2000년 이후 전문직 이주자의 수가 지속적으로 증가하고 있으며, 2009년 현재 그 수가 5만여 명에 이른다. 이러한 외국인 전문직 이주자 증가의 또 하나의 특징은 단기체류자에 비해 장기체류자가 늘고 있다는 점이다. 유형별로는 외국어 강사가 가장 많고 그 다음으로는 기업투자, 특정직업 등 기업활동과 관련된 전문직 이주자가 많다. 연예 스포츠 관련 전문직 이주자도 적지 않지만 2003년 이후 그 수가 급격히 감소하였다. 출신지역은 지리적으로 근접한 아시아가 가장 많지만, 외국어 강사의 경우 북미 지역 출신이 많은 것처럼 유형에 따라 다소 차이가 있다. 이들의 거주지역은 거의 대부분 대도시로 특히 서울을 비롯한 수도권의 비중이 크고 공업지역인 거제도와 같은 남동연안지역에도 적지 않게 분포한다. 적응이란 관점에서 보았을 때, 전문직 이주자의 한국인과의 교류는 거주지역보다는 직장을 중심으로 이루어지는 경향이며 한국에 영구정착 의지가 크지 않은 편이다. 또한 정책적으로도 이주노동자나 결혼이주자에 비해 이들은 상대적 사각지대에 있다.

• Journal of Preventive Medicine and Public Health
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• 제39권4호
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• pp.346-352
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• 2006

Objectives: The purposes of this study were to propose a screening schedule for the early detection of breast cancer among Korean women, as based on the statistical model, and to compare the efficacy of the proposed screening schedule with the current recommendations. Methods: The development of the screening schedule for breast cancer closely followed the work of Lee and Zelen (1998). We calculated the age-specific breast cancer incidence rate from the Korea Central Cancer Registry (2003), and then we estimated the scheduling of periodic examinations for the early detection of breast cancer, using mammography, and based on the threshold method. The efficacy of the derived screening schedule was evaluated by the schedule sensitivity. Results: For estimating the screening schedule threshold method, we set the threshold value as the probability of being in the preclinical stage at age 35, the sensitivity of mammography as 0.9 and the mean sojourn time in the preclinical stage as 4 years. This method generated 14 examinations within the age interval [40, 69] of 40.0, 41.3, 42.7, 44.1, 45.4, 46.7, 48.0, 49.3, 51.0, 53.2, 55.3, 57.1, 59.0 and 63.6 years, and the schedule sensitivity was 75.4%. The proposed screening schedule detected 85.2% (74.5/87.4) of the cases that could have been detected by annual screening, but it required only about 48.7% (14.0/30.0) of the total number of examinations. We also examined the threshold screening schedules for a range of sensitivities of mammography and the mean sojourn time in the preclinical stage. Conclusions: The proposed screening schedule for breast cancer with using the threshold method will be helpful to provide guidelines for a public health program for choosing an effective screening schedule for breast cancer among Korean women.

• 한국정보과학회논문지:정보통신
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• 제35권4호
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• pp.355-366
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• 2008

본 논문에서는 3G 이동통신망과 WiBro 망간 수직 핸드오버 지원을 위한 mobile SCTP (mSCTP) 핸드오버 기법 적용방안을 제안한다. 제안하는 이종망간 mSCTP 핸드오버 기법의 성능분석을 위해 이동 단말에서 mSCTP 핸드오버를 자동적으로 지원하는 시스템을 개발하였다. 리눅스 기반 테스트베드 실험을 통해 핸드오버 지연 관점에서 성능을 분석하고 실험결과를 Mobile IP 핸드오버 기법과 비교하였다. 실험결과, 이종망간 중첩영역에서 이동 단말의 체류시간이 충분히 클 때 mSCTP 핸드오버 지연시간이 상당히 감소될 수 있고, 또한 Mobile IP 보다 상대적으로 더 좋은 핸드오버 성능을 보여주고 있음을 알 수 있었다.