• Journal of Korean Society of Transportation
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• v.27 no.3
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• pp.49-58
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• 2009

Four alternative plans for the bus network in Daejeon metropolitan city, which have different hierarchical structure, were proposed : Alternative 1 represents a bus network without hierarchical structure, and Alternative 2, 3, and 4 represent bus networks with primary, intermediate, and advanced hierarchical structures, respectively. Efficiency of the alternative plans were evaluated based on the evaluation index including travel time cost, waiting time cost, and transition penalty cost. The travel time cost was decreased as the level of hierarchical structure gets higher until it reaches the extremely high level. As the level of hierarchical structure get higher, the waiting time cost significantly decreased while the transition penalty cost increased. Collectively, a bus network with hierarchical structure was shown to be more efficient than without it in the light of total travel cost. For the bus network with hierarchical structure, total travel cost shows a concave curve, which implies that there exists an optimal level of hierarchical structure in a bus network.

• Journal of the Korean Operations Research and Management Science Society
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• v.37 no.4
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• pp.51-65
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• 2012

Battery switching EVs are considered to be a promising alternative to overcome long charging time problems in the EV adoption. The purpose of this research is to develop integrated model for battery inventory and battery switching waiting times. Due to complexity of exact analysis, a practical approximation method is developed, which provides close results to exact values. Numerical experiments show that there exist trade-offs between the battery inventory level and the number of switching stations. The proposed model can be applied to evaluate and select the minimum cost alternative in implementing the battery switching stations.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.20 no.43
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• pp.153-162
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• 1997

M/G/1 queueing system is one of the most widely used one to model the real system. When operating a real systems, since it often takes cost, some control policies that change the operation scheme are adopted. In particular, the N-policy is the most popular among many control policies. Almost all researches on queueing system are based on the assumption that the arrival rates of customers into the queueing system is constant, In this paper, we consider the M/G/1 queueing system whose arrival rate varies according to the servers status : idle, set-up and busy states. For this study, we construct the steady state equations of queue lengths by means of the supplementary variable method, and derive the PGF(probability generating function) of them. The L-S-T(Laplace Stieltjes transform) of waiting time and average waiting time are also presented. We also develop an algorithm to find the optimal N-value from which the server starts his set-up. An analysis on the performance measures to minimize total operation cost of queueing system is included. We finally investigate the behavior of system operation cost as the optimal N and arrival rate change by a numerical study.

• Journal of Korean Society of Transportation
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• v.14 no.1
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• pp.69-80
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• 1996

In most cities, travel demand is distributed along long corridors and its destinations tend to concentrate in a central business district. For this kind of many-to-one or one-to-many travel demand pattern, a zonal operation of buses can be an efficient bus operation technique in which a long bus-demand corridor is divided into service zones and each service zone is provided with its own bus route connecting the service zone and single destination separately. This paper develops models of the total transportation costs for a single-zone operation and 2-zonal operation of buses for a long demand corridor with single destination in terms of various cost parameters, demand density, bus operation speeds, and location of the boundary between two service zones. In this study the total transportation cost is assumed to consist of the bus operation cost, passenger waiting cost and passenger travel time cost. It was proved that a zonal operation of buses can be more efficient than a single-zone operation for certain circumstances of the system and an boundary condition between two operation techniques was obtained. Also, several case studies were performed for various values of the cost parameters.

• Journal of the Korea Convergence Society
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• v.12 no.4
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• pp.217-228
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• 2021

After the integrated fare system has been applied, public transportation and transfer traffic increased. As a result, transfer passengers must be considered in the operation of the bus. Although previous studies have limitations due to utilizing deterministic mathematical models, which fails to reflect the stochastic movements of passengers and buses, in this study, a more realistic bus stop micro-simulation model is proposed. Based on the proposed simulation model, we represent the relationship between bus arrival interval and passenger wait time as a regression model and empirically show the differences between the cases with and without transfer passengers. Also, we propose a method converting passenger waiting time to cost and find optimal bus arrival interval based on the converted cost. It is expected the proposed method enables bottom-up decision making reflecting practical situation.

• Proceedings of the KSR Conference
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• 2008.11b
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• pp.1881-1888
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• 2008

As the ticket issuing methods have been diversified for the convenience of the passengers such as ticketless service(SMS ticket, e-ticket, home ticket), automatic ticket issuing machine and consignment ticket sale, maintaining the current number of ticket booth has been becoming a issue. Too many booth can cause the inefficiency of the cost of labor. According to the Charter of Customer Service of Korail, on the other hand, 95% of passengers have to purchase a train ticket within 5 minutes. This study was designed to present a decision making model for the optimum number of ticket booth which can affect an efficient operation of train station and improvement of customer convenience. And, this paper shows the proper manpower of ticket booth and the change of customer waiting time by analyzing the arrival and ticket issuing time of passengers based on 'Queueing Theory'. However, it is insufficient to be generalized due to some limitations of analysis. This study will contribute to improve customer satisfaction by reducing the waiting time at the ticket booth. In addition, presenting the optimum number of booth is expected to have an effect on the increase of productivity and cost savings.

• Quality Improvement in Health Care
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• v.5 no.2
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• pp.202-215
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• 1998

Purpose : To shorten processing time for variety of medical affairs of the patient at the outpatient clinic of a big hospital is very important to qualify medical care of the patient. Therefore, patient's waiting time for drug delivery after doctor's prescription is often utilized as a strong tool to evaluate patient satisfaction with a medical care provided. We performed this study to investigate factors influencing patient satisfaction related with waiting time for drug delivery. Methods : The data were collected from July 21 to August 12, 1998. A total 535 patients or their families who visited outpatient clinics of Inha University Hospital were subjected to evaluate the drug delivery time and the level of their satisfaction related, which were compared with those objectively evaluated by Quality Improvement Team. The reliability of the scale was tested with Cronbach's alpha, and the data were analyzed using frequency, t-test, ANOVA, correlation analysis and multiple regression. Results : The mean drug delivery time subjectively evaluated by the patient (16.1 13.0 min) was longer than that objectively evaluated (10.9 7.6 min) by 5.2 min. Drug delivery time objectively evaluated was influenced by the prescription contents, total amount or type of drug dispensed, etc, as expected. The time discrepancy between two evaluations was influenced by several causative factors. One of those proved to be a patient's late response to the information from the pharmacy which the drug is ready to deliver. Interestingly, this discrepancy was found to be more prominent especially when waiting place for drug delivery was not less crowded. Other factors, pharmaceutical counseling at the pharmacy, emotional status or behavior of a patient while he waits for the medicine, were also found to influence the time subjectively evaluated. Regarding the degree of patient satisfaction with the drug delivery, majority of patients accepted drug delivery time with less than 10 min. It was also found to be influenced by emotional status of the patient as well as kindness or activity of pharmaceutical counselor. Conclusion : The results show that, besides prescription contents, behavior pattern or emotional status of a patient, environment of the waiting place, and quality of pharmaceutical counseling at the pharmacy, may influence the patient's subjective evaluation of waiting time for drug delivery and his satisfaction related with the service in the big hospital. In order to improve patient satisfaction related with waiting time for drug delivery, it will be cost effective to qualify pharmaceutical counseling and information system at the drug delivery site or waiting place rather than to shorten the real processing time within the pharmacy.

• Water for future
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• v.12 no.1
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• pp.60-71
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• 1979

In general, the lock structure is built at place of having great deal range for dealing with effective ships operation such as in the west coast of Korea. In Inchon harbour, the two locks of 10 KT and 50 KT tonnage class in total has been constructed for several years age, however, it has been recorded many waiting vessels at outer harbour due to the increment of oceangoing vessels & shortage of berthing facilities in accordance with beyond expectation of cargo amount increment. This paper attempts to solves the waiting vessels problem at outer harbour by simulation in applying queing theory. It is found that the simulation results such as average queue time, service time, and queue length during lock operation can be applied to find the minimum of the cost function for determination of optimum Lock Size

• IE interfaces
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• v.14 no.4
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• pp.365-373
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• 2001

It is discussed how to determine time windows for pickups and deliveries, which have been assumed to be given in all most of previous studies on traveling salesman problems with time window, vehicle routing problems with time window, vehicle scheduling and dispatching problems, and so on. First, time windows are classified into four models (DR, DA, AR, and AA) by customers‘ polices. For each model, it is shown how a time window is related to various cost terms of suppliers and customers. Under the assumption of collaborative supplier-customer relationship, an integrated cost model for both supplier and customer is constructed for determining boundaries of time windows. The cost models in this paper consists of cost terms that depend on waiting time, early arrival time, late arrival time, and rejection of receipt. A numerical example is provided and results of the sensitivity analysis for some parameters are also provided to help intuitive understanding about the characteristics of the suggested models.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.11
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• pp.5465-5480
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• 2018

Energy-efficient task scheduling on multi-core server is a fundamental issue in green cloud computing. Multi-core processors are widely used in mobile devices, personal computers, and servers. Existing energy efficient task scheduling methods chiefly focus on reducing the energy consumption of the processor itself, and assume that the cores of the processor are controlled independently. However, the cores of some processors in the market are divided into several voltage islands, in each of which the cores must operate on the same status, and the cost of the server includes not only energy cost of the processor but also the energy of other components of the server and the cost of user waiting time. In this paper, we propose a cost-aware scheduling algorithm ICAS for computation intensive tasks on multi-core server. Tasks are first allocated to cores, and optimal frequency of each core is computed, and the frequency of each voltage island is finally determined. The experiments' results show the cost of ICAS is much lower than the existing method.