• Proceedings of the Korean Operations and Management Science Society Conference
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• 1993.10a
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• pp.118-118
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• 1993

We consider a discrete event dynamic system called periodic job shop, where an identical mixture of items called minimal part set(MPS) is repetitively produced in the same processing order and the primary performance measure is the cycle time. The precedence relationships among events(starts of operations) are represented by a directed graph with rocurront otructure. When each operation starts as soon as all its preceding operations complete(called earliest starting), the occurrences of events are modeled in a linear system using a special algebra called minimax algebra. By investigating the eigenvalues and the eigenvectors, we develop conditions on the directed graph for which a stable steady state or a finite eigenvector exists. We demonstrate that each finite eigenvector, characterized as a finite linear combination of a class of eigenvalue, is the minimum among all the feasible schedules and an identical schedule pattern repeats every MPS. We develop an efficient algorithm to find a schedule among such schedules that minimizes a secondary performance measure related to work-in-process inventory. As a by-product of the linear system approach, we also propose a way of characterizing stable steady states of a class of discrete event dynamic systems.

• Journal of the Korean Operations Research and Management Science Society
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• v.16 no.2
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• pp.128-147
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• 1991

We propose a dynamic incidence matrix (DIM) for reflecting states and time conditions of a timed Petri net (TPN) explicitly. Since a DIM consists of a conventional incidence matrix, two time-related vectors and two state-related vectors, we can get the advantages inherent in the conventional incidence matrix of describing a static structure of a system as well as another advantage of expressing time dependent state transitions. We introduce an algorithm providing the DIM with a state transition mechanism. Because the algorithm is, in fact, an algorithmic model for discrete event simulation of TPN models, we provide a theoretical basis of model transformation of a TPN model into a DEVS(Discrete Event system Specification) model. By executing the algorithm we can carry out performance analysis of computer communication protocols which are represented TPN models.

• Journal of the Korean Operations Research and Management Science Society
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• v.18 no.3
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• pp.1-12
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• 1993

Several alternative manufacturing control strategies are under study in the literature. They are, specifically, push system, pull system, conwip system, and as a special case, infinite buffer system. We focus on modeling, comparison analysis and design of these systems. The event epoch sequences of each system are generated which also enable us to compare their performance. Then the stochastic monotonicity of these enent epoch sequences in several important design parameters are established through the structure of the generalized semi-Markov schemes on which they are based. Finally, we solve the stochastic optimization problem which minimizes these event epochs. Our results supplement the applicability of some previously known results in the literature.

• Proceedings of the Safety Management and Science Conference
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• 2000.05a
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• pp.339-349
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• 2000

Inchon Port is the second largest import-export port of Korea, and has the point at issue such as the excessive logistics cost because of the limits of handling capacity and the chronic demurrage. There are few research activities on the analysis and improvement of the whole port operation, because Inchon Port not only has the dual dock system and various facilities but also handles a various kind of cargo. The purpose of this paper is to develop the simulation program as a long-term strategic support tool, considering the dual dock system and the TU(Terminal Operation Company) system executed since March, 1997 in Inchon Port. The basic input parameters such as arrival intervals, cargo tons, service rates are analyzed and the probability density functions for these parameters are estimated. The main mechanism of simulation model is the discrete event-driven simulation and the next-event time advancing. The program is executed based on the knowledge base and database. From the simulation model, it is possible to estimate the demurrage status through analyzing various scenarios and to establish the long-term port strategic plan.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2006.05a
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• pp.1765-1770
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• 2006

본 논문에서는 반도체 fab 라인의 물류 설비를 event graph로 모델링 하는 방법론을 제안하고 있다. 최근 반도체 fab 라인 같은 대표적인 자본 집약적 제조라인에서는 운영단계에서 투입 계획, PM schedule 및 operation rule 등을 변화시켜 가며 평가 및 검증해 볼 수 있는 what-if simulation을 위한 line simulator의 필요성이 점점 높아지고 있다. 그러나 상용 simulator는 각 제조라인의 특성에 맞게 customization하는데 많은 시간과 비용이 소요될 뿐만 아니라 특성을 반영하는데 한계가 있다. 따라서 이러한 line simulator를 개발할 때 근간이 되는 설비의 simulation model이 필요하다. 이 때 설비들은 생산(processing) 및 물류(handling) 설비로 나눌 수 있는데, 본 논문에서는 반도체 fab 라인의 물류 설비 모델링 방법을 제시하고 실제 물류 설비를 모델링 해 봄으로써 그 효용성을 알아본다.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2002.05a
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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.

• Journal of the Korean Operations Research and Management Science Society
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• v.40 no.4
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• pp.123-144
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• 2015

Through the event study methodology and the case study on the Company T and its subsidiaries, this study analyzes the effect of credit rating downgrade in the Korean stock market. Our empirical results cast some doubts on whether credit rating agencies made adequate credit rating adjustments on the Chaebol companies, and suggest that little information was provided to the bond market investors. This study provides some policy implications by recommending that regulators encourage credit rating agencies to provide more accurate and appropriate information to market participants.

• Journal of the Korea Safety Management & Science
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• v.9 no.1
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• pp.23-35
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• 2007

Present time there are many risk analysis method in the world. A hazard is an exposure that has the potential to induce and adverse event. Risk is the probability of an adverse event given exposure to hazard. The evaluation of scientific information on the hazardous properties of environmental agents and the extent of exposure to these agents. But operation risk analysis method is not enough for manufacturing industry even if it is existence, it will be separated to improve Safety. In this paper, I will develop the AHP Weighted operation risk analysis method to improve Safety.

• Proceedings of the Safety Management and Science Conference
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• 2011.11a
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• pp.583-591
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• 2011

A number of Brain-Computer Interface (BCI) studies have been performed to assess the cognitive status through EEG signal. However, there are a few studies trying to prevent user from unexpected safety-accident in BCI study. The EEGs were collected from 19 subjects who participated in two experiments (rest & event-related potential measurement). There was significant difference in EEG changes of both spontaneous and event-related potential. Beta power and P300 latency may be useful as a biomarker for prevention of response to safety-accident.

• Proceedings of the KSR Conference
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• 2005.11a
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• pp.72-76
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• 2005

This event recorder system, owing to the advancement of communication technology, is independently installed in most on-board electronics and given integrated management by on-board monitoring equipments. However, since the safety oriented equipments such as signalling devices, train protection systems, and train radios have been mounted on trains recently" the existing on-board monitoring device is no longer reliable enough for permanent preservation of data from train crashes or fires. This study has pointed out the problems mentioned above and described the designing concept of the fault recording system for high-speed trains for effective utilization of the train management program.