• Journal of Korean Society of Industrial and Systems Engineering
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• v.33 no.1
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• pp.10-16
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• 2010

Mail centers are essential postal facilities that sort and dispatch postal items, and should be operated efficiently to provide customers high quality postal services. So the efficiency analysis of mail centers should be performed in order to induce better operation. But current performance evaluation system has 95 percent of predetermined and weighted non-quantitative indices. There is need to introduce objective efficiency measurement methodology. The main objectives of this study was to analyze the efficiency of 24 mail centers empirically using cone-ratio DEA and suggest the appropriate cone-ratio method. Consequently, this paper suggests that the cone-ratio DEA model integrating decision-maker's preferences is more desirable for efficiency analysis than that of using transformed data.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.6
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• pp.903-911
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• 1999

This study is discussed about the heat transfer coefficient and the fin efficiency of the heat exchanger having plate fins. A new definition for the fin efficiency of the heat exchanger is proposed. More than one hundred cases were tested numerically for the plate fins having uniform and non-uniform heat transfer coefficient. The previous models for the fin efficiency and the pure heat transfer coefficient were applicable to the heat exchanger only when the NTU is very small. It was found that the fin efficiency of the heat exchanger was nearly the same as the normalized fin temperature. The present model could estimate the pure heat transfer coefficient within a few percent in the present test range of 0＜NTU＜2.5.

• Proceedings of the KIPE Conference
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• 2001.07a
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• pp.159-162
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• 2001

This paper is proposed an efficiency optimization operation algorithm for synchronous reluctance motor (SynRM) using current phase angle control technique. The SynRM has to controlled with the optimal current phase angles with load and operation speed variation, to obtain high efficiency over the wide speed ranges. An efficiency optimization condition in SynRM which minimizes the copper and iron losses is derived based on the equivalent circuit model of the machine. The objective of the efficiency optimization control algorithm compensating the optimum current angle, is to seek a combination of d and q-axis current components which provides minimum losses at a certain operating point in steady state. The usefulness of the proposed efficiency optimization control is verified through vector-controlled inverter system with the SynRM.

• Health Policy and Management
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• v.11 no.2
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• pp.58-84
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• 2001

This study was conducted to explore the relationship between the efficiency and its organizational determinants of tile Community Mental Health Centers(CMHCs). Data are obtained from 81 personnel of 27 CMHCs from Sept. to Oct. in 1999(19 in Kyunggi province, 7 in Seoul City and 1 in Chunchon, Kangwon province). Major findings of this study are as follows. 1. DEA is a mathematical programming technique that optimizes the relative efficiency ratio of inputs over outputs for each decision-making unit(DMU). It produces a summary scalar efficiency ratio for each DMU of CMHCs. It assessed multiple inputs and multiple outputs simultaneously, and compared to specific peer group of CMHCs. 2. Organizational determinants of DEA efficiency of CMHCs we proved as advertisement(＋), location of CMHCs(in public facility)(＋), area of facility(＋), period of operation(＋), job satisfaction(＋), clarity of work-role(vague), cohesion(－), rate of certified personnel(＋), number of referral(＋), and voluntary service time(－).

• Proceedings of the Korea Society of Information Technology Applications Conference
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• 2007.11a
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• pp.108-109
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• 2007

• International Journal of Aeronautical and Space Sciences
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• v.16 no.2
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• pp.223-246
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• 2015

Structural vibration control using a piezoelectric shunt is an established control technique. This technique involves connecting a piezoelectric patch, which is bonded onto or embedded into the vibrating structure, to an electric shunt circuit. Thus, vibration energy is converted into electrical energy and is dissipated through a network of electrical components. Different configurations of shunt have been researched, among which the negative capacitance-inductance shunt has gained prominence recently. It is basically an analog, active circuit consisting of operational amplifiers and passive elements to introduce real and imaginary impedance on the vibrating structure. The present study attempts to model the behavior of a negative capacitance-inductance shunt in terms of power output and efficiency using circuit modeling software. The shunt model is validated experimentally and is used to control the structural vibration of an aluminum beam, connected to a pair of piezoelectric patches, under broadband excitation. The model is also used to determine the optimal parameters of a negative capacitance-inductance shunt to increase the efficiency and predict the voltage output limit of op-amp against the supply voltage.

• Proceedings of the Korean Institute Of Construction Engineering and Management
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• autumn
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• pp.401-404
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• 2002

To manage a construction project efficiently, it is essential to ensure the practical usage in construction management. The purpose of this study is to develop a practical model, which will increase the efficiency of management. The followings are the method of this study: (1) Establishing a breakdown structure based on integration of CBS and WBS which is well acquainted (2) Developing and systemizing managerial standards and processes on such activities as calculating and marking progress rates & schedule, summarizing cost by activities level, making out project analysis reports. This study shall contribute to raising the efficiency in construction management after being verified in a pilot project and being developed into construction management system.

• Journal of the Korean BIBLIA Society for library and Information Science
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• v.8 no.1
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• pp.197-227
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• 1997

The main purpose of this study is ① to settle and to analyze the classification of the Internet Search Engine comparitively, and ② to build the compatible model of Internet Search Engine classification in order to seek information on the Internet resources. specially in the branch of the Computers and Internet areas. For this study, four Internet Search Engine (Excite, 1-Detect, Simmany, Yahoo Korea!), Inspec Classification and two distionaries were used. The major findings and result of analysis are summarized as follows : 1. The basis of the classification is the scope of topics, the system logic, the clearness, the efficiency. 2. The scope of topics is analyzed comparitively by the number of items from each Search Engine. In the result, Excite is the most superior of the four 3. The system logic is analyzed comparitively by the casuality balance and consistency of the items from each Search Engine. In the result, Excite is the most superior of the four 4. The clearness is analyzed comparitively by the clearness and accuracy of items, the recognition of the searchers. In the result, Excite is the most superior of the four. 5 The efficiency is analyzed comparitively by the exactness of indexing and decreasing the effort of the searchers. In the result, Yahoo Korea！ is the most superior of the four. 6 The compatible model of Internet Search Engine classification is estavlished to uplift the scope of topics, the system logic, the clearness, and the efficiency. The model divides the area mainly based upon the topics and resources using‘bookmark’and‘shadow’concept.

• Journal of Power Electronics
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• v.18 no.5
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• pp.1489-1500
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• 2018

Partial shading analysis of large-scale photovoltaic (PV) arrays has recently become a theoretically and numerically challenging issue, and it is necessary for PV system designers. The main contributions of this study are the following: 1) A PSIM-based macro-model was employed because it is remarkably fast, has high precision, and has no convergence issues. 2) Three types of equivalent macro-models were developed for the transformation of a small PV sub-array with uniform irradiance to a new macro-model. 3) On the basis of the proposed new macro-model, a tearing method was established, which can divide a large-scale PV array into several small sub-arrays to significantly improve the efficiency improvement of a simulation. 4) Three platforms, namely, PSIM, PSpice, and MATLAB, were applied to evaluate the proposed tearing method. The proposed models and methods were validated, and the value of this research was highlighted using an actual large-scale PV array with 2420 PV modules. Numerical simulation demonstrated that the tearing method can remarkably improve the simulation efficiency by approximately thousands of times, and the method obtained a precision of nearly 6.5%. It can provide a useful tool to design the optimal configuration of a PV array with a given shading pattern as much as possible.

• The Journal of Asian Finance, Economics and Business
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• v.5 no.3
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• pp.19-29
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• 2018

This research examined the alternatives of Jensen's alpha (α) estimation models in the Capital Asset Pricing Model, discussed by Treynor (1961), Sharpe (1964), and Lintner (1965), using the robust maximum likelihood type m-estimator (MM estimator) and Bayes estimator with conjugate prior. According to finance literature and practices, alpha has often been estimated using ordinary least square (OLS) regression method and monthly return data set. A sample of 50 securities is randomly selected from the list of the S&P 500 index. Their daily and monthly returns were collected over a period of the last five years. This research showed that the robust MM estimator performed well better than the OLS and Bayes estimators in terms of efficiency. The Bayes estimator did not perform better than the OLS estimator as expected. Interestingly, we also found that daily return data set would give more accurate alpha estimation than monthly return data set in all three MM, OLS, and Bayes estimators. We also proposed an alternative market efficiency test with the hypothesis testing Ho: α = 0 and was able to prove the S&P 500 index is efficient, but not perfect. More important, those findings above are checked with and validated by Jackknife resampling results.