• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.8
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• pp.1022-1030
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• 1999

A numerical study was carried out to analyze the effect of flow distribution of stirred part and plug flow part on combustion efficiency at the coal gasification process in an entrained bed coal reactor. The model of computation was based on gas phase eulerian balance equations of mass and momentum. The solid phase was described by lagrangian equations of motion. The $k-{\varepsilon}$ model was used to calculate the turbulence flow and eddy dissipation model was used to describe the gas phase reaction rate. The radiation was solved using a Monte-Carlo method. One-step parallel two reaction model was employed for the devolatilization process of a high volatile bituminous Kideco coal. The computations agreed well with the experiments, but the flame front was closer to the burner than the measured one. The flow distribution of a stirred part and a plug flow part in a reactor was a function of the magnitude of recirculation zone resulted from the swirl. The combustion efficiency was enhanced with decreasing stirred part and the maximum value was found around S=1.2, having the minimum stirred part. The combustion efficiency resulted from not only the flow distribution but also the particle residence time through the hot reaction zone of the stirred part, in particular for the weak swirl without IRZ(internal recirculation zone) and the long lifted flame.

• Journal of the Korean Data and Information Science Society
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• v.17 no.3
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• pp.805-809
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• 2006

In this paper a shrinkage estimator for the measure of dispersion of the inverse Gaussian distribution with known mean is proposed. Also we compare the relative bias and relative efficiency of the proposed estimator with respect to minimum variance unbiased estimator.

• IE interfaces
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• v.11 no.1
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• pp.23-32
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• 1998

This paper presents a model for assessing the efficiency of logistics activities in distribution centers. The DEA approach is adopted to compare the relative efficiency of distribution centers, where considered as input and output factors are warehouse floor area, field storage area, average inventory level, overhead costs, number of workers, number of orders, and total value of goods handled. The artificial neural network approach is also adopted to overcome the limitation of DEA. The 12 distribution centers of Korea Telecom are studied for the validation of the model, which results in 84.9% of learning accuracy. This model can be used to identify the inefficient factors in a distribution center and to reveal changes in the degree of efficiency over time.

• Journal of Korean Society on Water Environment
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• v.37 no.4
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• pp.286-295
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• 2021

The removal efficiency of road-deposited sediment (SDR) by road sweeping was analyzed by performing particle size analysis before and after road sweeping at four highways during May to December 2019. The SDR accounted for the largest proportion in the range of 250 to 850 ㎛ and the degree of its proportion had an effect on the particle size distribution curve. The particle size distribution of the collected sediments showed a similar distribution at all sites. Below 75 ㎛, the removal efficiency of SDR showed a constant value around 40%, but above 75 ㎛, it increased as the particle size increased. The removal efficiency was 82-90% (average 86%) for gravel, 66-93% (average 79%) for coarse sand, 35-92% (average 64%) for fine sand, 29-69% (average 44%) for very fine sand, 19-58% (average 40%) for silt loading, 10-59% (average 40%) for TSP, 13-57% (average 40%) for PM10, and 15-61% (average 38%) for PM2.5. SDR removal efficiency showed an average of 69% for the four highways. It was found that if the amount of SDR was less than 100 g/m², it was affected by the road surface condition and had a large regional deviation. As such, the amount of SDR and the removal efficiency increased. The fine particles, which have relatively low removal efficiency, contained a large amount of pollutants, which is an important factor in water and air pollution. Therefore, various measures to improve the removal efficiency of fine particles in SDR by road sweeping are needed.

• Journal of the Economic Geographical Society of Korea
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• v.11 no.3
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• pp.375-388
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• 2008

The early studies on the cultural industries had mainly emphasized the viewpoint of "efficiency" based on the "flexible specialization" theory, but they have gradually shed light on the viewpoint of "creativity": creative human resources and various networks generating creative energies. Despite the importance of these studies, it is impossible to explain every cultural industrial agglomeration phenomena from specific and few viewpoints due to the diversity of each cultural industry. This study describes the dissimilarity of agglomeration factors between the Japanese animation and home video game industries which form salient agglomeration in the same region. Both industries share similar characteristics with industrial agglomeration of SMEs in Tokyo and close inter-firm relationships. However, they differ in their historical development paths and each firm's behavior and strategy because of their own distribution systems and production processes. In particular, the difference in distribution systems clearly affects whether a company values "efficiency" factors of agglomeration advantage or "creativity" factors of that in case of locational choice. The distribution sector of the cultural industry, compared with the production sector, has a tendency to value profitability rather than creation itself. Therefore, a cultural industry with the strong distribution sector tends to form the industrial system emphasizing profitability. The Japanese animation firm is apt to choose its location from the perspective of efficiency, which easily contributes to profitability, because television broadcasting stations are strong distribution sector. Conversely, the Japanese game firm chooses its location from the perspective of creativity due to the absence of strong distribution sector.

• Journal of the Korean Operations Research and Management Science Society
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• v.24 no.4
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• pp.95-109
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• 1999

We propose a series of methodologies that can evaluate relative efficiency of logistics units(centers) in three categories; managerial, cost, and operational efficiency. Inputs and outputs of logistics systems are first defined. Appropriate quantitative and qualitative measures for the three categories are then selected. Employed also are Analytic Hierarchy Process, Weighted Scoring Method, Stochastic Frontier Model, and Data Envelopment Analysis for the development of a comprehensive assessment scheme. Our scheme not only assesses the degree of relative efficiency of logistics units but also identify the sources of inefficiency in each unit The methodologies are applied to a large telecommunications company which operates 12 distribution centers nation wide. Relative efficiencies of the centers are compared using 1995-1997 performance data. Summarized are the level of efficiency of each distribution center for each of the three categories. The degree and sources of inefficiency of each distribution center are also discussed.

• Information Systems Review
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• v.15 no.2
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• pp.75-90
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• 2013

This research was undertaken to find out how effectively ERP has been employed by the enterprises through comparing and analyzing the management performance of each enterprise after introducing ERP to Retail and Distribution Industry using DEA technique. According to the research results, efficiency evaluation for each site was calculated through input and output factors to find out comparative ERP system usage efficiency of 10 Retail and Distribution Industry Companies in terms of such factors as employee, quick assets, inventories, sales revenue, operating income. This paper confirms that the companies having launched management innovation by aggressively adopting ERP saw their management efficiency improving consistently, and in the distribution industry, it took at least 3 years before the effect of ERP introduction on enhancing management efficiency became visible. Furthermore, this paper also reveals that, unlike the manufacturing industry which was the subject of the previous study, efficiency was not necessarily proportional to the size of company in the service industry including distribution and export which was the subject of this paper.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.5
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• pp.732-738
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• 2015

In ac discharge, emission efficiency shows an time-varying characteristics during discharge. The phenomenon is caused by the potential distribution changes during the discharge, which indicates that a specific potential distribution can contribute to a high improvement of the emission efficiency. To create an artificial environment for a potential distribution favorable to emission efficiency, we used the asymmetric electrode structure and proved the capability. Our results showed that the ratio of the area of anode to cathode became larger, the emission efficacy was greatly improved.

• Journal of the Korean Statistical Society
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• v.33 no.4
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• pp.449-458
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• 2004

Data envelopment analysis (DEA) estimators have been widely used in productivity analysis. The asymptotic distribution of DEA estimator derived by Kneip et al. (2003) is too complicated and abstract for analysts to use in practice, though it should be appreciated in its own right. This paper provides another way to express the limit distribution of the DEA estimator in a tractable way.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.7
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• pp.20-25
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• 2010

With the diversification of distribution facilities, existing distributed generation can be subdivided into Microgrids, which are smaller units for application. These Microgrids, subdivided as such and connected to distribution systems, should operate under driving plans that will ensure their economic efficiency and, accordingly, the configuration of those distribution systems that include Microgrids should also be changed. The perception of the necessity to secure the economic efficiency of distribution systems is gradually increasing and studies intended to assess the economic efficiency of Microgrids and Smartgrids are ongoing. In this paper, the power generation capacity of an economically operative Microgrid was calculated using the MonteCarlo simulation, which is a method based on the probability theory considering the power generation cost of Microgrids linked with power supply systems and reverse sales costs, etc., and an optimum distribution systems was configured based on the results of these calculation.