• Journal of the Korean Operations Research and Management Science Society
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• v.22 no.3
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• pp.11-22
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• 1997

The aim of this paper is to develop the B & B type algorithms for globally minimizing concave function under 0-1 knapsack constraint. The linear convex envelope underestimating the concave object function is introduced for the bounding operations which locate the vertices of the solution set. And the simplex containing the solution set is sequentially partitioned into the subsimplices over which the convex envelopes are calculated in the candidate problems. The adoption of cutting plane method enhances the efficiency of the algorithm. These mean valid inequalities with respect to the integer solution which eliminate the nonintegral points before the bounding operation. The implementations are effectively concretized in connection with the branching stategys.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.13 no.2
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• pp.63-71
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• 2005

There is a concern in the aviation community that pilot schedules can lead to fatigue and increased chance of an aviation accident. Yet despite this concern, there is little empirical studies showing the relationship between pilot fatigue and commercial aviation accidents. At this point of view, countering fatigue is a challenging proposition in complex aviation operations. However, with appropriate planning, many strategies can contribute to pilot alertness and flight safety. With proper education program, sustaining a physiological fit, a right knowledge about pilot fatigue can design a safety operations. On this study, I inquire into the ways of enhancing pilot's efficiency from fatigue.

• ETRI Journal
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• v.31 no.6
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• pp.709-716
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• 2009

In this paper, we propose a novel reconfigurable processor using dynamically partitioned single-instruction multiple-data (DP-SIMD) which is able to process multimedia data. The SIMD processor and parallel SIMD (P-SIMD) processor, which is composed of a number of SIMD processors, are usually used these days. But these processors are inefficient because all processing units (PUs) should process the same operations all the time. Moreover, the PUs can process different operations only when every SIMD group operation is predefined. We propose a processor control method which can partition parallel processors into multiple SIMD-based processors dynamically to enhance efficiency. For performance evaluation of the proposed method, we carried out the inverse transform, inverse quantization, and motion compensation operations of H.264 using processors based on SIMD, P-SIMD, and DP-SIMD. Experimental results show that the DP-SIMD control method is more efficient than SIMD and P-SIMD control methods by about 15% and 14%, respectively.

• Korean Management Science Review
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• v.34 no.3
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• pp.1-14
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• 2017

This study empirically analyzes the impact of inventory management performance on the energy efficiency in Korean petrochemical companies. The concept of the distance function is used to define the energy efficiency and the estimation of the distance function is performed using the stochastic frontier analysis. The inventory turnover is selected as the variable indicating the inventory management performance of the company. The main results of this study are as follows. First, the inventory turnover has a positive impact on energy efficiency. Second, during the period over 2011~2015, while the gap in energy efficiency among the companies expanded, the average energy efficiency decreased. Third, the average energy efficiency in upstream process companies was greater than downstream process companies and the gap in energy efficiency among downstream process companies was greater than upstream process companies. Fourth, the average marginal effect of inventory turnover on energy efficiency increased gradually from 2011 to 2015. Finally, the average marginal effect of inventory turnover in downstream process companies was greater than upstream process companies, and the gap in the marginal effect of inventory turnover among downstream process companies was greater than upstream process companies. These results together imply the importance of inventory management in terms of energy efficiency.

• Journal of Navigation and Port Research
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• v.39 no.5
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• pp.393-399
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• 2015

Recently, the fierce competitions in the shipping industry and the global economic downturn have heavily influenced ports' operational strategies. In order for port authorities to remain competitive at an international level and to provide more accurate information to develop National policies, ports are required to analyse and improve operations' efficiency. In this paper, the efficiency of 19 Italian ports in 2013, handling different types of cargoes, is assessed through the application of Data Envelopment Analysis (DEA), with constant return to scale (CRS) and variable return to scale (VRS). The purpose of this study is to analyze the efficiency of Italian ports and evaluate whether differences in size and specialization of each port (or cargo handled) are directly correlated with ports' efficiency.

• Journal of Electrical Engineering and Technology
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• v.13 no.1
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• pp.263-269
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• 2018

In this study, a selective inverter operation between a 2-level voltage source converter (VSC) and a 3-level T-type VSC (3LT VSC) is proposed to improve the efficiency of a 3LT VSC. The 3LT VSC topology, except for its neutral-point switches, has similar operations as that of the 2-level VSC. If an operation mode is changed according to efficiency, the efficiency can be improved because efficiencies of each methods are depending on current and MI (Modulation Index). The proposed method calculates the power losses of the two topologies and operates as the having lower losses. To calculate the losses, the switching and conduction losses based on the operation mode of each topology were analyzed. The controller determined the operation mode of the 2- or 3-level VSC based on the power loss calculated during every cycle. The validity of the proposed control scheme was investigated through simulation and experiments. The waveform and average efficiency of each method were compared.

• Journal of Navigation and Port Research
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• v.36 no.7
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• pp.535-544
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• 2012

In order to improve the overall ASEAN maritime transport network, each port's efficiency is regarded as a crucial factor that should be calculated periodically. This study evaluated the relative efficiency of container port operations of 32 ports belonging to 9 ASEAN nations using Data Envelopment Analysis (DEA). It found that 2 out of 32 ports in 2010 were measured as efficient ports. This study yielded two major findings. Firstly, the ports assessed as inefficient need to benchmark similar ports in size and structure from the ports that are assessed as efficient to improve their efficiency. Secondly, these results could be used to determine potential candidates and country for an international port development co-operation programme with Korea to improve the performance of the entire ASEAN port network by developing the infrastructures of ill-equipped ports.

• Management Science and Financial Engineering
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• v.19 no.2
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• pp.1-11
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• 2013

An interesting puzzle in business practices is that although many researchers emphasize the benefits of a revenue-sharing contract, a wholesale contract has remained to be the most common contractual form. By introducing the concept of unobservable efforts, we examine the contractual efficiency of a wholesale contract and a revenue-sharing contract. The multi-task agency model and experimental design approach are used to analyze the relationship between the contractual efficiency and parameters. A major finding of our study is that a wholesale contract coordinates unobservable efforts, while it fails to coordinate the order quantity decision. Because unobservable efforts have mixed effects on the contractual efficiency, the superiority of contract type depends on parameters. This finding implies that a wholesale contract can be a competitive contract, especially when unobservable efforts are heavily involved. Our conclusion is that the current popularity of a wholesale contract is manager's rational response to complex supply chain environments rather than irrational behaviors.

• Korean Management Science Review
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• v.27 no.1
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• pp.107-116
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• 2010

There are several stage in corporate's life cycle such as foundation, growth, maturity or bankruptcy. A bankruptcy is very important for corporate in the life cycle. Especially, venture business' life cycle is short compare to other type of corporate. A lot of venture businesses have emerged and bankrupted soon in the market. Venture businesses' survival or bankruptcy have been influenced by not only external environment like the rate of exchange, oil price, and foreign exchange crisis but also internal environment such as efficiency, process, human resources, finance and CEO. In this paper, we attempt to examine financial factors and efficiency that influence on the venture businesses' survival and bankruptcy. The more venture businesses have high efficiency score, the more they have high probability of survival.

• International Journal of Reliability and Applications
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• v.8 no.2
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• pp.125-135
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• 2007

In this paper, testing exponentiality against new better than used in convex average and denote by (NBUCA), or its dual (NWUCA) is investigated through the U-test. The percentiles of these tests are tabulated for samples sizes n = 5(1)40. The power estimates of the test are simulated for some commonly used distributions in reliability. Pitman's asymptotic efficiency of the test is calculated and compared. Data of 40 patients suffering from blood cancer disease (Leukemia) is considered as a practical application of the proposed test in the medical sciences.