• East Asian mathematical journal
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• v.24 no.1
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• pp.45-55
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• 2008

We consider an M/G/1 queue with $P^M_{\lambda}$-service policy, which is a two-stage service policy. The server starts to serve with rate 1 if a job arrives to the sever in idle state. If the workload of the system upcrosses $\lambda$, then the service rate is changed to M and this rate continues until the system is empty. It costs to change the service rate to M and maintaining the rate. When the expectation of the stationary workload is supposed to be less than a given value, we derive the optimal value of M.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2010.11a
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• pp.188-191
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• 2010

The study investigated the optimal configuration of SVC (Scalable Video Coding) to apply to the satellite broadcasting service, and compared the performance of the SVC with that of the AVC (Advanced Video Coding). To get the optimal configuration, we analyzed the optimal bit rate allocation between the layers and the optimal scalability which requires the least bit rate for the required PSNR for various kinds of contents using JSVM. As a result of investigation, we found that the optimal bit rate allocation occurs when the bit rate of the base layer is minimum, and the spatial scalability shows the best performance. The performance of SVC is similar to that of AVC for spatial scalability, but it depends on contents.

• Journal of the Korea Society for Simulation
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• v.13 no.1
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• pp.41-50
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• 2004

The purpose of this paper is to analyse the manager's policy to maximize the profit in a multiple-server queueing facility with a limited queue capacity. We assume that the level of advertizing effects on the arrival rate of customers to the facility. The model without ‘word of mouth effect’ is assumed that the arrival rate is independent on the qualify of service level. We estimate the service quality by the balking rate of customers from system. We extend this to the model with ‘word of mouth effect’. To achieve the maximum profit, the most important factor is the considerably high utilization of facility for both models. Given service rate, we should maintain an effective arrival rate to some extent. To this end, among the available options, an increase of advertizing effort is more desirable than reducing the fee if the service value of customers remains unchanged. We also investigate whether the variability of service time has a significant impact on determining the optimal policy. The cost of service variability is not so expensive as that in a single server model due to the reduced variability of service times in a multiple-server model.

• Journal of Korea Port Economic Association
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• v.32 no.2
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• pp.137-156
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• 2016

This study analyzes the optimal service levels of exclusive container terminals in terms of the optimal berth occupancy rate and the ships' waiting ratios, based on the number of berths. We develop a simulation model using berth throughput data from pier P, Busan New Port, a representative port in Korea, and apply the simulation results to different numbers of berths. In addition to the above results, we analyze the financial data and costs of delayed ships and delayed cargoes for the past three years from the viewpoints of the terminal operation company (TOC), shipping companies, and shippers to identify the optimal service level for berth occupancy rates that generate the highest net profit. The results show that the optimal levels in the container terminal are a 63.4% berth occupancy rate and 10.6% ship waiting ratio in berth 4,66.0% and 9.6% in berth 5, and 69.0% and 8.5% in berth 6. However, the results of the 2013 study by the Ministry of Maritime Affairs and Fisheries showed significantly different optimal service levels: a 57.1% berth occupancy rate and 7.4% ship waiting ratio in berth 4; 63.4% and 6.6% in berth 5; and 66.6% and 5.6% in berth 6. This suggests that optimal service level could change depending on when the analysis is performed. In other words, factors affecting the optimal service levels include exchange rates, revenue, cost per TEU, inventory cost per TEU, and the oil price. Thus, optimal service levels can never be fixed. Therefore, the optimal service levels for container terminals need to be able to change relatively quickly, depending on factors such as fluctuations in the economy, the oil price, and exchange rates.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.6 no.8
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• pp.93-103
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• 1983

In this paper, we study an optimal service policy of the M/M/2/K queueing system with two types of customers. The incurred costs consist of waiting cost, service cost and incurred costs consist of waiting cost, service cut and changeover cost. The changeover cost occurs when a server who assigned to serve a particular type of customers reassigned to the other types of customers. Two servers serve two types of customers who arrive to the two separate queues. The two types of customers differ in respect of their arrival rate, service rate, waiting cost, and service cost. The servers require a policy, for determining when they should change their service type, which minimizes the long run expected total cost. The policy is obtained by a Markov decision process model that consists of a finite number of states and actions. In order to find the optimal service policy, we define states and actions of the system, compute onestep transition probabilities, and apply to the successive approximations algorithm.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.5A
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• pp.574-582
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• 2004

This paper shows the performance comparisons of several different rate scheduling schemes for non-real time data service over the uplink of burst switching-based direct sequencecode division multiple access (DS/CDMA) system to support the integrated voice/data service. The closed-form solution of optimal scheduling formulation, which minimizes average transmission delay when all of the active data users are transmitting simultaneously, is presented and mathematical analyses with other rate scheduling schemes, which provide efficiency criterion of transmission delay for rate scheduling schemes, are performed. Numerical results show the analyses explicitly.

• Journal of the Korean Operations Research and Management Science Society
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• v.4 no.1
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• pp.51-67
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• 1979

This paper considers the problem of determining an optimal dynamic operating policy for a two-stage tandem queueing service system in which the service facilities (or stages) can be operated at more than one service rate. At each period of the system's operation, the system manager must specify which of the available service rates is to be employed at each stage. The cost structure includes an operating cost for running each stage and a service facility profit earned when a service completion occurs at Stage 2. We assume that the system has a finite waiting capacity in front of each station and each customer requires two services which must be done in sequence, that is, customers must pass through Stage 1 and Stage 2 in that order. Processing must be in the order of arrival at each station. The objective is to minimize the total discounted expected cost in a two-stage tandem queueing service system, which we formulate as a Discrete-Time Markov Decision Process. We present analytical and numerical results that specify the form of the optimal dynamic operating policy for a two-stage tandem queueing service system.

• Korean Journal of Veterinary Service
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• v.15 no.1
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• pp.1-6
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• 1992

A survey on the dosage optimal time for the bovine fascioliasis was carried out from Jan. 1987 to Dec. 1990. The results were summarized as follows ; 1. The mean infection rate was 27.7% (1,662 heads were infected out of 3,247 heads In 205 herds). A seasonal infection rate was winter (34.6%) >spring(32.5%) >summer(24.7%) > autumn(22.8%) 2. In the density of the fasciola spp. egg of infected bovine feces remarks 79.6% on the range below 10. 3. The density of fasciola spp. egg is not directly proportinal to the infection rate, and remarks on the range from 5 to 20. 4. In the herds dosed vermifuge the appearance of the fasciola spp. egg is as follows ; 1∼3 months show 3.8% and 4∼6 months 8.5% 5. The dosage optimal time for the bovine fasciliasis is as follows ; 1) According to the monthly infection rate the first dosage optimal time is Dec and Feb and the second-Jun and Aug. 2) In the herd dosed vermifuge the dosage optimal time is to dose twice by 60 days interval after 3∼4 months from previous dosage.

• Proceedings of the Korean Statistical Society Conference
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• 2003.10a
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• pp.189-194
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• 2003

We consider an M/G/1 queueing system under P$_{\lambda}^{M}$-service policy. As soon as the workload exceeds threshold ${\lambda}$ > 0, the service rate is increased from 1 to M ${\geq}$ 1 and is kept until the system becomes empty. After assigning several costs, we show that there exists a unique M minimizing the long-run average cost per unit time.

• Health Policy and Management
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• v.11 no.4
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• pp.88-108
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• 2001

Separation of prescribing and dispensing practice in Korea has changed the service pattern of the pharmacy. The prescription dispensing activities, however, are concentrated excessively on the pharmacies near hospitals or clinics. Thus this study was conducted to estimate the number of optimal dispensing cases for the community pharmacy. Forty-six pharmacies were selected using systematic stratified random sampling method, and ninety-five pharmacists were interviewed on their workload of dispensing and other activities at pharmacies. One hundred and seventy prescriptions were chosen based on the length of drug administration and drug dosage form, and the dispensing time was measured by time-watch method. Also pharmacy benefit claims data were analyzed to identify the characteristics of the pharmacies which performed more than optimal dispensing cases. According to the study results, the average work time per pharmacist per day was found to be 10hours 32minutes and the dispensing activities occupied 7hours 36minutes. It took 5.72minutes on average for each dispensing case. The optimal dispensing case was estimated as 75 cases under the condition of 10hours 32minutes work time and 6% allowance rate. Even though the pharmacies near hospitals or clinics participated dispensing services actively, only pharmacies near clinics dealt with more than optimal dispensing cases. For the pharmacies near hospitals they dealt with less than optimal cases, but drug administration period per prescription was almost 3 times longer than that of pharmacies near clinics. Thus the intensity of dispensing activities such as drug administration period is to be considered to estimate optimal dispensing cases more accurately.