• 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.

• 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.

• Journal of the Korean Society of Safety
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• v.25 no.6
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• pp.70-74
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• 2010

For each strand of wirerope sling, the international standards, ISO-8794, EN-13414 specify that the splice shall have five series of load carrying tucks. At least three of the load carrying tucks shall be made with the whole strand. And, the breaking force of the splice shall not be less than 70% or 80% of that of rope. But, There are no prescriptions for splicing types against different efficiency of each splicing type being used many workplace. In this study, analysis the work limit load efficiency according to variation of number of tucks and splicing types by experimental method As a result, the number of tucks 3+2 had the highest breaking efficiency.

• The Journal of Fisheries Business Administration
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• v.41 no.3
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• pp.45-58
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• 2010

This study estimated the technical efficiency of coastal composite fishery in Korea by using the data envelopment analysis (DEA) and the stochastic frontier analysis (SFA) methods, and the results on the respective method were compared. In the DEA method, the constant returns to scale (CRS) and the variable returns to scale (VRS) output-oriented DEA models were separated and technical efficiencies were estimated, respectively. The average estimated value of technical efficiency by the SFA method (0.633) was found to be lower than that by the VRS-DEA method (0.738), while it was higher than that by the CRS-DEA method (0.479). It was found that strong correlation exists between the SFA method and the VRS-DEA method. The method which can utilize both methods in mutually complementing way for the estimation of technical efficiency was also considered.

• 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.

• 한국정보디스플레이학회:학술대회논문집
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• 2000.01a
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• pp.115-116
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• 2000

Influence of sustain pulse-width on electro-luminous efficiency is experimentally investigated for surface discharge of AC-PDP. It is found that the firing voltage is decreased as the pulse-width is increased from $2\;{\mu}s$ to $8\;{\mu}s$ with sweeping frequency range of 10 kHz to 50 kHz. It has been found that the optimal sustain pulse-width is in the range of $3{\sim}4\;{\mu}s$ under driving frequency range of 30 kHz and 50 kHz, based on observations of memory coefficient, wall charge, and wall voltage as well as luminous efficiency.

• Journal of Korean Society for Atmospheric Environment
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• v.27 no.3
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• pp.272-280
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• 2011

A novel particle removal system for air handling unit (AHU) of subway station was evaluated experimentally. The novel system was designed in order to minimize the maintenance cost by applying axial-flow cyclones. The system consists of multiple cyclone units and dust trap. Based on our previous numerical study, it was found to be effective for removal $1\sim10{\mu}m$ sized dust particles. In this study, we manufactured the mock-up model and evaluated the model experimentally. Liquid and solid test particles were generated for evaluating collection efficiency of the system and the pressure drop was monitored. The collection efficiency was varied from 41.2% to 85.9% with increasing the sizes of particle from 1 to $6.5{\mu}m$ by particle count ratio of inlet and outlet. The pressure drop was maintained constant less than $20mmH_2O$. In addition, the collection efficiency was estimated by total mass for solid test particles. It was found that the collection efficiency was 65.7% by particle mass ratio of inlet and outlet. It shows that present system can replace current pre-filters used in subway HVAC system for removing particulate matters with minimal operational cost.

• Journal of Power System Engineering
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• v.20 no.6
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• pp.87-92
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• 2016

This research dealt with performance characteristics of OTEC system applying an ejector and additional pump. Each system using five kinds of working fluids was analyzed, and primary parameters with respect to entrainment ratio were examined: Turbine gross power, evaporation capacity, pump work, efficiency and volume flow ratio. The primary results were as following. The efficiency of ejector-pump OTEC system was dependent on entrainment of the ejector. The degree of efficiency change was different from applied working fluid, and amount of pump work was turned out to be primary factor affected system efficiency. Meanwhile, optimized entrainment ratio was different from applied working fluid since their different vapor density. System efficiency at optimized entrainmet ratio of each working fluid was around 5%, showing minor difference each other.

• Journal of Hydrogen and New Energy
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• v.27 no.2
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• pp.211-219
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• 2016

To develop an ash separator for the solid fuel chemical looping combustion system, effects of operating variables such as solid injection nozzle velocity, diameter of solid injection nozzle, gap between solid injection line and vent line, vent line inside diameter, and solid intake height on solid separation rate and solid separation efficiency were measured and discussed using heavy and coarse particle and light and fine particles mixture as bed material in an acrylic fluidized bed apparatus. The solid separation rate increased as the solid injection nozzle velocity and the diameter of solid injection nozzle increased. However, the solid separation rate decreased as the gap between solid injection line and vent line, the vent line inside diameter, and the solid intake height increased. The solid separation efficiency was in inverse proportion to the solid separation rate. In this study, we could get high solid separation rate up to 2.39 kg/hr with 91.6% of solid separation efficiency.

• Journal of Korean Society on Water Environment
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• v.30 no.3
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• pp.261-268
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• 2014

Four clays (both natural and commercial types) mainly used in Korea were tested for removal efficiency of Microcystis spp. and ecotoxicity on Daphnia magna and Vibrio fischeri. Four clays (clay A~D) were composed of 91.9~100% of sand (0.02~0.2 mm in particle size). Clay D consisted of lager particles than other clays. Major elements of the four clays were $SiO_2$ (45.3~62.8%), $Al_2O_3$ (18.5~29.7%) and $Fe_2O_3$ (5.4~7.9%). They contained kaolinite (clay mineral), quartz, muscovite, and so on. Clay C and D contained montmorillonite, one of the clay minerals improving clay-cell aggregation. For clay A, B and C, removal efficiency of Microcystis spp. was over 60% at 2 g/L. It reached about 100% at over 5 g/L. For clay D, it was over 60% and 95~100% at 5 g/L and 20 g/L respectively. After adding clays, pH decreased. The greatest drop of pH appeared at clay C. Except for addition of 100 g/L clay C, ecotoxicity on D. magna and V. fischeri didn't appeared at all dose of clays.