• Proceedings of the KSR Conference
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• 2004.10a
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• pp.1125-1130
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• 2004

The prestressed concrete girder bridges have been used widely at the domestic national road as well as highway because it is great in the functional and economical efficiency. Also it has the advantage of convenience of design and construction due to being given standard sections. However it could be easily verified that a standard section of P.S.C girder is excessive design, which has much more redundancy than is necessary against design loads. Thus, in this paper the formulation of the optimum design for PSC girder railway bridge is suggested and dominant design variables and constraints are inquired as performing the optimum design. The objective is adopted as total cost of PSC girder bridge ,and in order to effective optimum design, design variables are formulated as PSC girder section dimension and girder space as well. And constraints are formulated according to Korean railway design specification and considering construction-ability such as PS anchorage and girder space. Using the proposed optimum design system, optimum PSC girder bridge design has been performed. And from the results of analysis it is suggested to denote the optimum section which satisfies the structural safety ,and economical efficiency all together.

• Journal of Industrial Technology
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• v.22 no.A
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• pp.19-28
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• 2002

The Nelder-Mead simplex algorithm has been one of the most widely used methods for the nonlinear unconstrained optimization, since 1965. Recently, the new algorithm, (so-called the Fuzzy Simplex Algorithm), with fuzzy logic controllers for the expansion, reflection and contraction process of this algorithm has been proposed. In this paper, this new algorithm is developed. And, the formulation for the optimum design of the power screw's efficiency is made. And then, the developed fuzzy simplex algorithm as well as the original one is applied to this optimum design problem. The Fuzzy simplex algorithm results in a faster convergence in this problem, as reported in other study, too.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2003.04a
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• pp.201-208
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• 2003

Since the real steel box girder bridges have a large number of design variables and show complex structural behavior, it would be impractical to directly use the algorithm for its optimum design. Thus, in this study, for optimum design of real steel box girder bridge, approximated reanalysis using an higher-order Improved self-adjusted Convex Approximation (ISACA) which was newly proposed on a previous study by the author is applied for the numerical efficiency. To demonstrate the efficiency, robustness, and convergence of the approximated reanalysis technique using the ISACA, a real bridge having two continuous spans is used as an illustrative example. From the results of the numerical investigation, it may be positively stated that the efficiency, robustness, and convergence of the approximated reanalysis using an ISACA is superior compared with the previous approximated reanalysis techniques.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.2
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• pp.189-199
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• 2000

This paper investigates the thermodynamic performance of latent heat thermal energy storage system using two phase change materials(2-PCM system). The thermodynamic merit of using 2-PCM is clear in terms of exergetic efficiency, which is substantially higher than that of 1-PCM system. Optimum phase change temperature to maximize the exergetic efficiency exists for each case. The heat transfer area ratio of high temperature storage unit, X, becomes another important parameter for 2-PCM system if the phase change temperatures of given materials are different from those of optimum conditions. It is a good approximation for X$_{opt}$ to be 0.5 when optimum phase change temperatures are used. Otherwise X$_{opt}$ is determined differently as a function of given phase change temperatures.res.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.5 no.6
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• pp.1-6
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• 1982

The objective of this thesis to Provide a better insight into the effect of the amount of in-process storage has on the efficiency of production line with variable operation times. It is assumed that the material enters the line at the first work station and is then processed progressively through the line until it exits at the last work station, a finite amount of in-process storage is provided before all but the first work station of the line and the operation time of the work stations are statistically independent and follow exponential distribution. Under the above assumption, optimum allocation model is developed and following two approaches are used : 1) Given the available storage capacity, optimum allocation which minimizes the number of items in the line. 2) Given the available storage capacity, optimum allocation which. maximizes the utilization factor of the line. In a balanced three stage line, the production line efficiency is maximized under both categories when the second in-process storage is larger than the first.

• Current Photovoltaic Research
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• v.8 no.3
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• pp.94-101
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• 2020

This study was trying to focus on achieving high efficiency of multi junction solar cell with thin film silicon solar cells. The proposed thin film Si-Ge/c-Si tandem junction solar cell concept with a combination of low-cost thin-film silicon solar cell technology and high-efficiency c-Si cells in a monolithically stacked configuration. The tandem junction solar cells using amorphous silicon germanium (a-SiGe:H) as an absorption layer of upper sub-cell were simulated through ASA (Advanced Semiconductor Analysis) simulator for acquiring the optimum structure. Graded Ge composition - effect of E_g profiling and inserted buffer layer between absorption layer and doped layer showed the improved current density (J_sc) and conversion efficiency (η). 13.11% conversion efficiency of the tandem junction solar cell was observed, which is a result of showing the possibility of thin film Si-Ge/c-Si tandem junction solar cell.

• Journal of Mechanical Science and Technology
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• v.17 no.1
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• pp.122-128
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• 2003

This paper presents a thermodynamic analysis of heat pump system using water as a heat source and heat sink. The primary object in this study is the optimization of exergetic efficiency. Two different systems, 2-stream and 1-stream system, are analyzed in detail. Mass flow ratio (the ratio of mass flow rate of water through evaporator to that through condenser) is identified as the most important parameter to be optimized. It is shown that there exists an optimum mass flow ratio to maximize exergetic efficiency. The variation of optimum exergetic efficiency of 2-stream system is quite small and the value lies between 0.2∼0.23 for the range of investigation in this study. However, far better performance can be obtained from 1-stream system. This means considerable irreversibilities are generated through condenser of the 2-stream system. The effects of adiabatic efficiency of compressor-motor unit on the overall system performance are also examined in the analysis.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.6
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• pp.52-61
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• 1996

In this paper, harmonic-tuning method to achieve the maximum efficiency is proposed. Harmonic tuning method is applied to the optimum load impedance of a class B amplifier, which is extracted by using the modified cripps method. High efficiency power amplifier utilizing GaAs MESFET is designed and fabricated in the 835MHz band. The performance of th eamplifier is presented by having output power of 30.8dBm, drain efficiency of 80.5% and power added efficiency of 66% with an associated power gain of 7.4dB.

• Asia-Pacific Journal of Business
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• v.5 no.1
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• pp.1-11
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• 2014

The study provides new empirical evidence on the level of profit efficiency and returns to scale of the Bangladesh banking sector. We employ the Slack-Based Data Envelopment Analysis (SBM-DEA) method to assess the level of profit efficiency of individual banks over the years 2004 to 2011. The empirical findings indicate that the Bangladesh banking sector has exhibited the highest and lowest level of profit efficiency during years 2004 and 2011 respectively. We find that only eight banks have been profit efficient throughout the period under study. The empirical findings seem to suggest that most of the Bangladesh banks have been experiencing economies of scale due to being at less than the optimum size, or diseconomies of scale due to being at more than the optimum size. Thus, decreasing or increasing the scale of production could result in cost savings or efficiencies.

• Journal of Korean Society for Atmospheric Environment
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• v.9 no.2
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• pp.125-131
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• 1993

Electrostatic Precipitator has been widely used to get high efficiency which is required for collection of fine particles. In order to provide collection efficiency and size distribution data for a pilot electrostatic precipitator, a pilot study has been conducted on fly ash from pulverized coal burning apparatus. The aims of this study are to investigate characteristics of electric charge, to measure collection efficiency varied with the applied voltage, to get an optimum current and current density. Optimum current density was obtained to 0.7mA/$cm^2$ at the average electric field strength 2.33kV/cm in this experiment. Maximum particle collection efficiency was indicated 99.21% at the applied voltage 7kV. Finally, particle size distribution is also compared with photographic results. Both coarse and fine particles at the range of 0.5$\sim$2$\mu$m and 3$\sim$10 SEM $\mu$m were clearly removed by increasing applied voltage.