• Journal of the Korean Operations Research and Management Science Society
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• v.24 no.2
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• pp.31-39
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• 1999

A new approximation method for finding the steady-state probabilities of the number of customers present in queueing systems with Poisson arrivals and two servers with different deterministic service times with infinite waiting room capacity is developed. The major assumption made for the approximation is that the residual service times of the servers have mutually independent uniform distributions with densities equal to the reciprocals of the respective service times. The method reflects the heterogeneity of the servers only through the ratio of their service times, irrespective of the actual magnitudes and difference. The transition probability matrix is established and the steady-state probabilities are found for a variety of traffic intensities and ratios of the two service times; also the mean number of customers present in the system and in the queue, and server utilizations are found and tabulated. The method was validated by simulation and turned out to be very sharp.

• Proceedings of the Korea Society of Information Technology Applications Conference
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• 2005.11a
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• pp.237-241
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• 2005

We present a device model for organic light emitting diodes(OLEDs) which includes charge injection, transport, recombination, and space charge effects in the organic materials. The model can describe both injection limited and space charge limited current flow and the transition between them. Calculated device current, light output, and quantum and power efficiency are presented for different cases of material and device parameters and demonstrate the improvements in device performance in bilayer devices. These results are interpreted using the calculated spatial variation of the electric field, charge density and recombination rate density in the device. We find that efficient OLEDs are possible for a proper choice of organic materials and contact parameters.

• Journal of Korean Society for Quality Management
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• v.32 no.4
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• pp.156-168
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• 2004

This research investigates the statistical efficiency of variable sampling size & sampling interval(VSSI) $\bar{X}$ charts under two assignable causes. Algorithms for calculating the average run length(ARL) and average time to signal(ATS) of the VSSI $\bar{X}$ chart are proposed by employing Markov chain method. States of the process are defined according to the process characteristics after the occurrence of an assignable cause. Transition probabilities are carefully derived from the state definition. Statistical properties of the proposed chart are also investigated. A simple procedure for designing the proposed chart is presented based on the properties. Extensive sensitivity analyses show that the VSSI $\bar{X}$ chart is superior to the VSS or VSI $\bar{X}$ chart as well as to the Shewhart $\bar{X}$ chart in statistical sense, even tinder two assignable causes.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 1996.04a
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• pp.491-494
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• 1996

주문이 매 시점마다 있는 것이 아니라 간헐적인, 즉 어느 시점에는 주문이 있고(ON) 다른시점에는 주문이 없는(OFF) 패턴에서 미래의 주문량에 대한 예측을 고려한다. 다음 시점의 예측량은 우선 주문이 있을 것인가에 대한 판단과 주문이 있다면 어느정도가 예상되는가 하는 문제의 두 가지 측면을 모두 고려해야 한다. 기존의 예측모델은 주문량 자체에 대한 고려가 일반적이며 주문시기에 대한 고려는 전무한 상태이기 때문에 이와 같은 주문패턴을 반영시키는데는 어려움이 따른다고 볼 수 있다. 본 논문에서는 이러한 주문패턴을 마코브 체인으로 모델링하고, 이러한 형태의 상태전이확률(state transition probaility) 추정식이 각각 독립적인 오목함수 (concave function)로 구성되어 있음을 보인다. 또한 확률적으로 표현되는 미래의 주문상태들에 대한 패턴을 확정시키는 알고리듬과 주문량 추정에 있어서 과거의 주문패턴을 반영시키는 모델을 제시한다.

• Journal of the Korean Professional Engineers Association
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• v.32 no.6
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• pp.148-157
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• 1999

As cultural Heritages are source of the national history and a life transition, their extinction is a fatal shock as result of cutoff the genealogy of the creative national spirit. So, we have necessarily to protect them, and to get the duty and the responsibility which the cultural inheritance hands over tnem to descendants with preserving and meaning safely at present time. In these days, the risk of fire in the Cultural Heritages building is increased because of rash changing environments from the indiscreet development of them. Accordingly, in order to get the original transmission of the Cultural Heritages, this paper involves being intensive the fire safety information of the Cultural Heritage in kyonggi-do province, analyzing their diagnoses, and studying a Fire Safety Prevention Management model to protect and to maintain them continuously. Therefore, it is to contribute from this approach to collecting fire safety information, analyzing diagnostic problems in fire accidents, and to manage the prevention method for protecting and maintaining the Cultural Heritages.

• 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.65-77
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• 1993

It is not to observe that a decision-maker frequently changes his choice strategy in the repetitive gamble choice situation. This change in risk preference attitude, however, is not well explained with the existing gamble choice models, such as Bell's disappointment-elation model which is an interesting extension of the classical MEU model. This paper shows that this change in risk preference attitude should be interpreted as a systematic transition of "d" and "e", the disappointment and elation constants of Bell's model repectively. A laboratory experiment is also performed to identify the factors which greatly affect the decision-makers' risk preference attitude change. The number of consecutive successes/failures and the amount of remaining capital found to be statistically significant factors.significant factors.

• Journal of the Korean Society for information Management
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• v.16 no.4
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• pp.53-74
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• 1999

This paper describes concept mapping techniques for eliciting and representing knowledge. Concept mapping techniques range from very informal to very formal. Informal concept mapping techniques are usually very easy to use and understand for humans, but not for computers. Formal concept mapping techniques are computational, but humans usually find them hard to understand and use. A knowledge acquisition and representation tools which handle both kinds, and the transition from informal to formal, would be very useful. It is proposed that concept maps be regarded as basic components of any knowledge-based system, complementing text and image with formal and informl active diagrams.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 1992.04b
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• pp.282-292
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• 1992

It is not rare to observe that a decision-maker frequently changes his choice strategy in the repetitive gamble choice situation. This change in risk preference attitude, however, is not well explained with the existing gamble choice models, such as Bell's disappointment-elation model which is an interesting extension of the classical MEU model. The paper shows that this change in risk preference attitude should be interpreted as a systematic transition of "d" and "e", the disappointment and elation constants of Bell's model. A laboratory experiment is also performed to identify the factors which greatly affect the decision-makers' risk preference attitude change. The number of consecutive successes/failures and the amount of remaining capital found to be statistically significant factors.significant factors.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2003.05a
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• pp.1165-1170
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• 2003

The objective of this study is to develop the simulation model of transport vehicle to analyze the required number of transport vehicle and to design the traffic pattern at automated container terminal. To model the transport vehicle, we defined the vehicle model and the traffic model using the state transition model of transport vehicle. An application of a simulation to simulate an automated container terminal with perpendicular layout is developed and described. From the results of simulation experiment, we obtained the vehicle speed and the number of vehicle under given productivity of container cranes, and analyzed the saving effect by cycle time.