• Journal of Korean Institute of Industrial Engineers
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• v.19 no.1
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• pp.61-71
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• 1993

We focus on a way of combining the Monte Calro methods of antithetic variates and control variates to reduce the variance of the estimator of the mean response in a simulation experiment. Combined Method applies antithetic variates (partially) for driving approiate stochastic model components to reduce the vaiance of estimator and utilizes the correlations between the response and control variates. We obtain the variance of the estimator for the response analytically and compare Combined Method with control variates method. We explore the efficiency of this method in reducing the variance of the estimator through the port operations model. Combined Method shows a better performance in reducing the variance of estimator than methods of antithetic variates and control variates in the range from 6% to 8%. The marginal efficiency gain of this method is modest for the example considered. When the effective set of control variates is small, the marginal efficiency gain may increase. Though these results are from the limited experiments, Combined Method could profitably be applied to large-scale simulation models.

• Journal of the Korean Operations Research and Management Science Society
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• v.29 no.3
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• pp.41-61
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• 2004

The purpose of this paper is to construct $\ulcorner$CIDEAR(Cross Impact-DEA-AR)$\lrcorner$ model which evaluates proposed R&D projects considering cross impact among them and selects proper projects to utilize resources efficiently as well as to maximize efficacy of investments. For this purpose, $\ulcorner$CIDEAR$\lrcorner$ model is designed as the following six steps. $\ulcorner$Decision Theory Evaluation Model$\lrcorner$ is for setting and selecting the evaluation items according to the structured procedure of evaluation system. The priority of items is decided at $\ulcorner$AR Decision Model$\lrcorner$$\ulcorner$Cross Impact Estimation Model$\lrcorner$ is for computing the final probability of success and the result is used to revise the evaluation results of $\ulcorner$Decision Theory Evaluation Model$\lrcorner$. $\ulcorner$Resource Performance Analysis Model$\lrcorner$ classifies the proposed R&D projects on the basis of required resources and expected performance. Consequently, the possibility of bias of project selection can be prevented. $\ulcorner$Priority Oder Decision Model$\lrcorner$ is for computing the efficacy of proposed projects. Finally, $\ulcorner$Efficacy-Efficiency Cause Analysis Model$\lrcorner$ analyzes the structure of efficacy and efficiency of the projects. The major findings and significances of this study are summarized as follows: (1) $\ulcorner$CIDEAR$\lrcorner$ model can deal with the affairs of R&D projects having the characteristics of mutual independence as well as mutual dependence in the point of efficacy and efficiency. Hence, it is possible to evaluate and select R&D projects more accurately. (2) It can be possible to raise the possibility of projects success. R&D manager can use the information for project management because the efficacy-efficiency structure of selected projects can be analyzed. (3) We proved the usefulness of the constructed $\ulcorner$CIDEAR$\lrcorner$ model using an case about twenty-one R&D projects of a leading company of electronic industry in Korea.

• Journal of the military operations research society of Korea
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• v.35 no.2
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• pp.99-117
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• 2009

Energy is essential factor of production for a firm to produce goods and services. If so, what is the condition of maintaining profit of a firm when energy price is going up? In conclusion, the condition is that the rate of productivity improvement should be greater than the rate of energy price increase. To put this concretely, when the elasticity of energy price as to the productivity improvement is greater than the weight of the energy cost on to the total revenue of the firm, the firm can escape the negative effect of energy price increase. This is that, saying that once more, the firm have to reduce the energy cost or promote energy efficiency to maintain appropriate or sufficient profit when energy price is going up fast. Therefore, in this study we will analyze the effect of the oil price increase on the energy saving investment and that of energy saving investment on the energy efficiency in the field of Korean manufacturing industry. In doing so, this study could show that the effect of energy price increase on the energy efficiency of the firm and the factor of that mechanism.

• Spatial Information Research
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• v.10 no.1
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• pp.61-76
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• 2002

Mobile map services using PDA are prevailing because of the rapid developments of techniques of the internet and handhold devices recently. While the volume of spatial data is tremendous and the spatial operations are time-intensive, the PDA has small size memory and a low performance processor. Therefore, the spatial index for PDA should be small size and efficiently filter out the candidate objects of spatial operation as well. This paper proposes a spatial index far PDA called MHF(Multilevel Hashing File). The MHF has simple structure for storage efficiency and uses a hashing technique, which is direct search method, for search efficiency. This paper also designs a compression technique for MBR. which occupies almost 80% of index data in the two dimensional case. We call it HMBR. Although the HMBR technique reduces the MB\ulcorner size to almost a third, it shows good filtering efficiency because of no information loss by quantization in case of small objects that occupy a major portion. Our experimental tests show that the proposed MHF index using HMBR technique is appropriate for PDA in terms of the size of index, the Number of MBR comparisons, the filtering efficiency and the execution time of spatial operations.

• Journal of the military operations research society of Korea
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• v.34 no.1
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• pp.61-77
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• 2008

Data Envelopment Analysis(DEA) is a promising methodology to evaluate the relative efficiency of the decision-making units. We have compared the efficiency of six electric power generation companies in Korea using DEA. The analysis results by input-oriented CCR and BCC models are summarized as follows: first, different results were acquired between using input factors as total capacity of generators and as sub-totals of generator capacity based on primary energy sources. It is the result influenced by input factors which are characterized by the proportion of fixed costs(generating facilities) and variable costs(generation costs for primary energy), Second, the efficiency will be increased if the input factors selected, according to primary energy sources discussed in this research, are used during long-term expansion of electric power capacity plans. It is expected that this approach can give a feedback for management of electric power generation companies.

• Journal of Korea Multimedia Society
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• v.19 no.2
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• pp.352-359
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• 2016

This paper presents high efficiency 5A synchronous DC-DC buck converter. The proposed DC-DC buck converter works from 4.5V to 18V input voltage range, and provides up to 5A of continuous output current and output voltage adjustable down to 0.8V. This chip is packaged MCP(multi-chip package) with control chip, top side P-CH switch, and bottom side N-CH switch. This chip is designed in a 25V high voltage CMOS 0.35um technology. It has a maximum power efficiency of up to 94% and internal 3msec soft start and fixed 500KHz PWM(Pulse Width Modulation) operations. It also includes cycle by cycle current limit function, short and thermal shutdown protection circuit at 150℃. This chip size is 2190um*1130um includes scribe lane 10um.

• Korean Management Science Review
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• v.22 no.2
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• pp.77-97
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• 2005

The traditional measures of a container port (or terminal) efficiency such as crane productivity, cargo throughput, etc. were generally presenting the partial efficiency since they evaluated only each individual factor and based on cross-sectional data. To overcome this problem, and in an effort to help port authorities develop a winning strategy in the increasingly competitive container transportation market, this Paper develops a meaningful set of benchmarks that will set the standard for best practices. In particular, this paper proposed a combined method to merge the DEA and simulation technique over time. To illustrate the usefulness of the proposed combined DEA/simulation model, this paper used the panel data of the four Gwangyang container terminals and seven Busan container terminals in Korea over the four-year period of 1999 through 2002.

• Journal of Korea Society of Industrial Information Systems
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• v.25 no.4
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• pp.49-63
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• 2020

Municipal governments today are facing increasingly complex issues while resources continue to be constraint but the service quality expectation from citizen is more demanding. They must develop and implement tools that help manage operations more efficiently. While Lean Six Sigma principle and tools have been widely applied to profit organizations, the extant literature has not provided many cases of such application to local governments. This research presents a case study of applying Lean Six Sigma approaches and tools to a municipal government of a small town in USA to improve process efficiency, quality performance, and citizen satisfaction. In this case study, DMAIC (Define, Measure, Analyze, Implement, and Control) is used as a tool to define current issues, develop, and measure performance metrics, and recommend action plans. The result of this case study shows that applying the principles and tools of Lean Six Sigma provides an excellent way to improve the process efficiency and quality of providing public work services at a local government.

• Fashion & Textile Research Journal
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• v.16 no.6
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• pp.979-986
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• 2014

This study establishes basic data for operations management by organizing processes and measuring time in the mini line for female jackets to improve productivity, ensure competitiveness, and maintain operator competency and the line process flow balance between apparel manufacturing companies. The results of this study are as follows. Sewing operations are divided into preparation functions, arrangement, partial tasks, and assembly that consist of 84 processes. The results from time measurement indicate that 3238.41seconds (sec) were required to produce a single jacket and that the average time required for operators was 231.32 sec. A control limit was established to increase the reliability of the measured value for net time. After outside values were removed, the operation time was measured to be 3176.35 sec. This accounted for 98.08% of the total operation time, with net time decreasing by 62.06. Skill and effort level coefficients were applied to measure the operator performance, the total real time was calculated to be 3415. The requirement for preparation and arrangement operations were 1233.35 sec, and 2182.22 sec for partial tasks and assembly operations. Process separation and organization were performed after the bottleneck operation was selected to identify the maximum line balance. Consequently, process efficiency of preparation and arrangement operations increased from 79.19% to 93.00%, and the partial tasks and assembly operations increased from 62.36% to 90.93%.

• ETRI Journal
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• v.30 no.6
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• pp.871-873
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• 2008

In this letter, we investigate the spectral efficiency of IEEE 802.22 wireless regional area network (WRAN) spectrum overlay when it is used in TV white space. Since 2004, when the FCC published the notice of proposed rule making 04-186 to make use of unused TV spectrum, the IEEE 802.22 working group has been standardizing specifications for WRAN operations. There have been a few papers investigating the spectral efficiency of this, but their analyses were limited to the cases for various guard distances between WRAN base stations. Since WRAN base station (BS) power for WRAN service may differ from country to country, it is important to analyze the spectral efficiency for various WRAN BS powers. In this letter, we analyze the spectral efficiency of WRAN spectrum overlay as a function of the power of WRAN BSs. The simulation results show that spectral efficiency decreases as the power of WRAN BSs and guard distances increase.