• Proceedings of the Korean Operations and Management Science Society Conference
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• 2003.05a
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• pp.244-246
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• 2003

We consider an AS/RS(Automated Storage/ Retrieval System) which performs single and dual commands. In this paper, we also assume that the service times of single and dual commands are differently distributed. We transform the arrival rates of storage and retrieval commands into those of single and dual commands. Using this, we propose a non-preemptive queueing model with priority for the performance analysis of a AS/RS, and obtain approximated means of queue lengths and sojourn times.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.15 no.26
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• pp.151-157
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• 1992

This paper presents a method for analyzing the transfer lines with finite storage buffers. Each machine spends a random amount of time processing each material. This transfer line can be modeled by the tandem queueing system with finite buffers. The great dimensionality of the state space renders the analysis of such system a formidable task. We propose an efficient algorithm to obtain the marginal state probabilities based on the exact algorithm for the two-machine system. Other performance measures, such as the utilization, the blocking probability, the average sojourn time, and the average queue length, can be easily calculated.

• Archives of Plastic Surgery
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• v.44 no.6
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• pp.573-574
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• 2017

When a newly inducted plastic surgery resident embarks on maxillofacial surgery, with drills, screws, plates and burrs, it seems like a new domain altogether. As a new resident, it is truly fascinating as to how such wide variety of bony work is done without scarring over the face. Here we discuss a few practical tips which the author has learned during his surgical sojourn in residency. It is hoped that the readers who are new to maxillofacial surgery, shall find these useful.

• Journal of Korean Institute of Industrial Engineers
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• v.19 no.4
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• pp.137-146
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• 1993

We consider single server feedback queueing systems with priorities. In the model, there are J stations and job classes. Jobs of class i arrive at station i according to a Poisson process, and have a general service time distribution. We derive the generating functions of the number of jobs at each station just after a busy period and the formula for the mean sojourn time that a specific tagged job spends at station j from its arrival to departure from the system.

• Journal of the Korean Mathematical Society
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• v.35 no.1
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• pp.207-224
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• 1998

After the review of known results on the connections between selfsimilar processes with independent increments (processes of class L) and selfdecomposable distributions and between semi-selfsimilar processes with independent increments and semi-selfdecomposable distributions, dichotomy of those processes into transient and recurrent is discussed. Due to the lack of stationarity of the increments, transience and recurrence are not expressed by finiteness and infiniteness of mean sojourn times on bound sets. Comparison in transience-recurrence of the Levy process and the process of class L associated with a common distribution of class L is made.

• Journal of Korea Society of Industrial Information Systems
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• v.22 no.1
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• pp.23-32
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• 2017

In this paper, We suggest a unified approach for the analysis of discrete-time MAP/G/1 queueing system. Many researches on the D-MAP/G/1 queue have been used different approach to analyze system queue length and waiting time for the same system. Therefore, a unified framework for analyzing a system is necessary from a viewpoint of system design and management. We first derived steady-state workload distribution, and then waiting time and sojourn time are derived by the result of workload analysis. Finally, system queue length distribution is derived with generating function from the sojourn time distribution.

• Journal of the Korea Society for Simulation
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• v.23 no.3
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• pp.1-9
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• 2014

Traditional workflow time analyses have been performed treating an activity as an independent M/M/1queueing system. Using the general forms of performance measures in the M/M/1 system, various aspects of analyses can be performed. Especially, on the time analysis of an AND structure in a workflow system, the mean system sojourn time can be formalized by applying the performance measures of M/M/1 system. In the real workflow system, the AND structure cannot be described correctly under the assumption of independent M/M/1 systems. To overcome this limitation, this research makes the assumption that the all activities for a task starts simultaneously. In this situation, the theoretical solution can be derived using the performance measures of the M/G/1 system. In addition, the simulation modeling method will be proposed to analyze the AND structure of a real workflow system. Finally, some numerical results from the theoretical solutions and simulation models will be provided for verification. The main performance measures used in this research are mean queueing time and mean sojourn time.

• The Journal of the Korea Contents Association
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• v.16 no.7
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• pp.146-153
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• 2016

This work studies the equilibrium behavior of customers and optimal pricing strategies of the sever in a continuous-time M/M/1 queueing system. In this work, we consider two pricing models. The first one is called the ex-ante payment scheme where the server charges a flat price for all services, and the second one is called the ex-post payment scheme where the server charges a price that is proportional to the time a customer spends in the system. In each pricing model, the departing customer receives the reward that is inversely proportional to his/her sojourn time. The server should make the optimal pricing decisions in order to maximize its expected profit per unit time in each payment scheme. This work also investigates customer's equilibrium joining or balking behaviors under server's optimal pricing strategies. Numerical experiments are conducted to help the server best select one between two pricing models.

• Journal of KIISE:Software and Applications
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• v.26 no.11
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• pp.1288-1297
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• 1999

오늘날 많은 워크플로우 응용들은 마감 시간과 같은 시간 제약 조건들의 효율적인 관리를 요구하고 있다. 이러한 시간 제약성 워크플로우의 가장 중요한 목적들 중의 하나는 마감 시간을 만족하는 워크플로우 인스턴스의 수를 최대화하는 것이다. 시간 제약성 워크플로우 처리의 성능을 개선하기 위해서는 효과적인 액티비티들의 마감 시간 할당 방법이 요구된다. 이에 본 논문에서는 액티비티의 체재 시간과 워크플로우 제어 구조들의 특성을 고려하여 효과적인 마감 시간 할당 방법인 PST를 제안한다. PST는 기존의 방법들과 달리 워크플로우 제어 흐름을 분석하여 액티비티의 마감 시간을 할당하기 때문에 과부하에서도 높은 성능을 지원할 수 있다. 부가적으로 기존의 방법들과 성능 평가를 통해 본 논문에서 제안된 방법의 효용성을 검증한다.Abstract Nowadays, many workflow applications are requiring efficient time management such as deadline. With time-constrained workflows, one of the most important goals is to maximize the number of workflow instances that satisfy the deadline. In this regard, effective deadline assignment mechanisms should be developed to achieve high performance of time-constrained workflow processing. We propose in this paper our novel deadline assignment method called PST based on both an activity's sojourn time and the characteristics of workflow control structures. Because the method allocates the deadline to activities from analyzing the control flow of workflow, it can support good and stable workflow performance even under the high workload. In addition, we validate the usefulness of our proposed method through various experiments.

• Journal of Korea Society of Industrial Information Systems
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• v.29 no.2
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• pp.69-80
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• 2024

In this paper, we studied a discrete-time queuing system that operates under a mixed situation of D-policy and T-policy, one of the representative server control policies in queuing theory. A single server serves customers arriving by Bernoulli arrival process on a first-in, first-out basis(FIFO). If there are no customers to serve in the system, the server goes on vacation and returns, until the total service time (i.e., total amount of workload) of waiting customers exceeds predetermined workload threshold D. The operation of the system covered in this study can be used to model the efficient resource utilization of mobile devices using secondary batteries. In addition, it is significant in that the steady state waiting time and system sojourn time of the queuing system under a flexible mixed control policy were derived within a unified framework.