• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.10
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• pp.89-96
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• 2015

Explicit numerical integration methods for power system transient stability simulation require very small time steps to avoid numerical instability. The EXST1 exciter model is a primary source of fast dynamics in power system transients. In case of the EXST1, the required small integration time step for entire system simulation increases the computational demands in terms of running time and storage. This paper presents a practical exciter model reduction approach which allows the increase of the required step size and thus the method can decrease the computational demands. The fast dynamics in the original EXST1 are eliminated in the reduced exciter model. The use of a larger time step improves the computational efficiency. This paper describes the way to eliminate the fast dynamics from the original exciter model based on linear system theory. In order to validate the performance of the proposed method, case studies with the GSO-37 bus system are provided. Comparisons between the original and reduced models are made in simulation accuracy and critical clearing time.

• The Journal of the Korea Contents Association
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• v.20 no.4
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• pp.159-168
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• 2020

This study aims to utilize DEA, analyze the efficiency of Korean coffee franchises, look into the factors that affect efficiency, and improve the efficiency of Korean coffee franchises. The main results of this study are as follows. First, according to CCR model standards, there are a total of 9 efficient coffee franchises and according to BCC model standards, there are a total of 12 efficient coffee franchises. A total of three of the inefficient DMUs were found to have a value of 1 for BCC, while the other 25 were found to be inefficient for both technology and scale. Second, of 28 franchises, 11 were analyzed to be decreasing return to scale and through future increased investments of optimum levels, business performance can be improved and efficiency can be enhanced. Analysis showed that 9 franchises appeared as CRS and it is most ideal to maintain the yield of future output elements at current levels and the work efficiency of 8 franchises in increasing returns to scale states expands as production scales increase according to specialization and role division and yield can relatively improve a lot. Third, the analysis of factors affecting the efficiency of franchises through the Tobit regression analysis showed that the number of franchises and operating periods had a positive (+) effect on efficiency. Based on this study, the efficiency of coffee franchises should be analyzed to establish strategies to maximize efficiency. Based on this study, the efficiency of coffee franchises should be analyzed to establish strategies to maximize efficiency.

• Journal of Korean Society on Water Environment
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• v.25 no.2
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• pp.268-280
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• 2009

Oncheon basin which are located in Busan is divided into 43 basin on the basis of main pipe, constructed with Storm Water Management Model (SWMM). Occurrence situation for Outflow and pollutant loads by long-term continuous rainfall is examined for treatment district and river analysis point of Oncheon basin and a reduction vs effectiveness table for effective CSOs managements is made for each of treatment districts according to each of managements. In case that treatment equipment is located at the discharge point of CSO, treatment efficiency is analysed. It is supposed that treatment equipment have an efficiency on the basis of a concentration and runoff discharge over a critical flow is discharged with it untreated and treating runoff discharge with treatment equipment at each of runoff discharge points and treating it gathered at sewage treatment plant (STP) through trunk sewer is compared for a relative treatment efficiency.

• JSTS:Journal of Semiconductor Technology and Science
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• v.9 no.4
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• pp.216-224
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• 2009

The endless scaling down of the semiconductor process made the impact of the power network noise on the performance of the state-of-the-art chip a serious design problem. This paper compares the performances of two popular circuit reduction approaches used to improve the efficiency of power network noise analysis: moment matching-based model order reduction (MOR) and node elimination-based MOR. As the benchmarks, we chose PRIMA and R2Power as the matching-based MOR and the node elimination-based MOR. Experimental results indicate that the accuracy, efficiency, and memory requirement of both methods very strongly depend on the structure of the given circuit, i.e., numbers of the nodes and sources, and the number of moments to preserve for PRIMA. PRIMA has higher accuracy in general, while the error of R2Power is also in the acceptable range. On the other hand, PRIMA has the higher efficiency than R2Power, only when the numbers of nodes and sources are small enough. Otherwise, R2Power clearly outperforms PRIMA in efficiency. In the memory requirement, the memory size of PRIMA increases very quickly as the numbers of nodes, sources, and preserved moments increase.

• Journal of Korean Institute of Industrial Engineers
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• v.31 no.4
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• pp.277-288
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• 2005

The proliferation of the internet technologies and applications has intensified business activities on the Internet. This study considered the price competition between two shopping channels, one on-line seller and the other traditional off-line retailer. Based on the Hotelling's linear market model, we derive the Nash and Stackelberg equilibria as a function of the cost parameters which represent the characteristics of the online and off-line channels. By analyzing the equilibrium solutions, the following significant findings were obtained. First, pricing by Stackelberg equilibrium always outperformed that of Nash equilibrium. However the value of the cost parameters played a crucial role in determining both channels' preferred position (price leader or follower). Second, the online seller could benefit more in terms of profit by lowering its efficiency when its efficiency belongs to a certain interval. Third, when the online seller's efficiency is low, lowering its delivery cost has no contribution to its profit. To benefit more from lowering its delivery cost, increasing its channel efficiency to a certain level should be preceded.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.780_781
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• 2009

This paper proposes efficiency optimization control of IPMSM drive using hybrid intelligent controller(HIC). The design of the speed controller based on fuzzy-neural network that is implemented using fuzzy control and neural network. The design of the current based on adaptive fuzzy control using model reference and the estimation of the speed based on neural network using ANN controller. In order to maximize the efficiency in such applications, this paper proposes the optimal control method of the armature current. The optimal current can be decided according to the operating speed and the load conditions. This paper proposes speed control of IPMSM using ALM-FNN, current control of model reference adaptive fuzzy control(MTC) and estimation of speed using ANN controller. The proposed control algorithm is applied to IPMSM drive system controlled HIC, the operating characteristics controlled by efficiency optimization control are examined in detail.

• Journal of Technology Innovation
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• v.12 no.1
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• pp.25-48
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• 2004

The relative efficiency of loan projects of information technology promotion fund is measured using Data Envelopment Analysis. Information technology promotion project is supervised by the Ministry of Information and Communication and is managed by the Institute of Information Technology Assessment. Among all the projects of information technology supported by this fund, this study deals with the themes that have been completed from 2000 to 2002. With multiple input and output data including the amount of fund, the period of study, the rate of increase in revenue, the increase in the amount of export and the increase in the number of patent, the relative efficiency scores of all the 119 subjects were calculated in CCR and BCC models of DEA. From the reference sets of some inefficient Decision Making Units, the causes of their inefficiency were analyzed. To compare the relative efficiencies among various DMUs, Super-Efficiency Ranking Method and Logistic Regression Model were used. As the result of this study, it was shown that W promotion funds in the fields related to mobile technology, visual equipment and communication device were used most efficiently.

• The Korean Journal of Applied Statistics
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• v.22 no.6
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• pp.1167-1176
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• 2009

Few studies have investigated the quantitative relationship between port ownership structure and port efficiency with mixed results. This paper therefore contributes to the empirical literature by investigating the impact of port privatization on port efficiency using sample data drawn from the world's major ports. Moreover, this study applies the Bayesian approach to estimate the impact of port ownership on port efficiency. We fit Bayesian stochastic frontier model which is introduced by Griffin and Steel (2007) by WinBUGS. World's 25 main ports data are used for analysis. Based on MCMC sampling, we estimate parameters of the model and efficiency index of each ports. Moreover, we add estimates from package Frontier 4.1c in order to compare them with Bayesian results.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.1
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• pp.51-56
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• 2012

This paper reports the generation efficiency and the thermal performance of a thermoelectric generator (TEG) harvesting energy from the waste heat of high power electronic components. A thermoelectric (TE) model containing thermal boundary resistances is used to predict generation efficiency and junction temperature of a high power electronic component. The predicted results are verified with measured values, and the discrepancy between prediction and measurement is seen to be moderate. The verified TE model predicts generation efficiencies, junction temperatures of the component, and temperature differences across a TEG at various source heat flows associated with various electrical load resistances. This study explores effects of the load resistance on the generation efficiency, the temperature difference across a TEG, and the junction temperature.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.8
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• pp.448-455
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• 2009

A performance analysis of the regenerative gas turbine system with afterfogging is carried out. Because of the high temperature at the outlet of air compressor, afterfogging has a potential of improved recuperation of exhaust heat than inlet fogging. Thermodynamic analysis model of the gas turbine system is developed by using an ideal gas assumption. Using the model, the effects of pressure ratio, water injection ratio, and ambient temperature are investigated parametrically on thermal efficiency and specific power of the cycle. The dependency of pressure ratio giving peak thermal efficiency is also investigated. The results of numerical computation for the typical cases show that the regenerative gas turbine system with afterfogging can make a notable enhancement of thermal efficiency and specific power. In addition, the peak thermal efficiency is shown to decrease almost linearly with ambient temperature.