• 설비공학논문집
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• 제24권11호
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• pp.792-798
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• 2012

A general concept on the definition of the second law efficiencies of thermodynamic cycles is introduced. The efficiency is defined to be proportional to the entropy generation divided by the maximum possible entropy generation. This way of definition of the cycle efficiency is clear and concise and, moreover, follows faithfully the concept of the second law of thermodynamics. This definition is applied to heat engine, refrigerator and heat pump. The second law efficiencies of heat engine and refrigeration cycles are derived, which are the same as the existing ones, respectively. The second law efficiency of heat pump, however, finds to be different from the existing one. Discussion is given about the difference and its cause.

• 한국태양에너지학회 논문집
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• 제27권4호
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• pp.87-95
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• 2007

Thermodynamic analysis of water-to-water heat pump system based on the first and second law of thermodynamics is carried out in this study. This analysis shows the distribution of irreversibilities throughout the system components and informs us of a potential improvements with the temperature condition changes. Source water temperature($T_A$), utilization water temperature($T_D$) and temperature differences (${\Delta}T_{AB}$, ${\Delta}T_{CD}$) are important factors to affect system performances such as component irreversibilities, exergetic efficiency and COPH. Advantages and disadvantages with these factors are discussed. Second law optimization phenomena with $T_A$ and ${\Delta}T_{AB}$ are also indicated.

• 한국수소및신에너지학회논문집
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• 제22권5호
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• pp.699-705
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• 2011

A combined heat and power cogeneration system driven by low-temperature sources is investigated by the first and second laws of thermodynamics. The system consists of Organic Rankine Cycle (ORC) and an additional process heater as a series circuit. Seven working fluids of R152a, propane, isobutane, butane, R11, R123, isopentane and n-pentane are considered in this work. Maximum mass flow rate of a working fluid relative to that of the source fluid is considered to extract maximum power from the source. Results indicate that the second-law efficiency can be significantly increased due to the combined heat and power generation. Furthermore, higher source temperature and lower turbine inlet pressure lead to lower second-law efficiency of ORC system but higher that of combined system. Results also show that the optimum working fluid varies with the source temperature.

• 한국콘텐츠학회논문지
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• 제14권8호
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• pp.394-405
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• 2014

본 연구는 생명보험산업의 자본시장법 시행 전 2005년부터 2008년까지의 자료와 시행 후 2009년부터 2012년까지의 자료를 토대로 첫째, 자료포락분석을 이용하여 자본시장법 시행 전 후의 효율성 분석을 하고, 대응표본 t-검정을 통해 시행 전 후의 효율성 차이를 살펴보았다. 둘째, 맘퀴스트 지수를 이용하여 자본 시장법 시행 전 후의 생산성 변화를 분석하고 대응표본 t-검정을 통해 생산성 변화 차이를 파악하였다. 셋째, 토빗 회귀분석을 이용하여 자본시장법 시행 전 후 효율성 결정요인을 분석하였다. 본 연구결과는 첫째, 자본시장법 시행 전 후 효율성 평균의 차이가 통계적으로 유의적인 차이가 없는 것으로 나타났다. 둘째, 자본시장법 시행 전 후 생산성 변화의 차이가 5% 수준에서 통계적으로 유의적인 차이가 나타나 시행 후 생산성이 증가하였음을 보여주고 있다. 셋째, 토빗 회귀분석 결과를 보면 설계사 비중이 자본시장법 시행 전 후의 효율성에 통계적으로 유의적인 정의 영향을 미치는 것으로 나타났다.

• 한국콘텐츠학회논문지
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• 제11권12호
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• pp.403-412
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• 2011

2009년 2월 4일부터 시행된 자본시장통합법은 자본시장 관련 금융 산업의 구조조정을 촉진시켜 겸업화, 통합을 통한 대형화가 가속화 될 것으로 예상되어 손해보험을 둘러싼 경쟁이 가속화 되고 있다. 이러한 상황에서 본 연구의 목적은 DEA 모형과 맘퀴스트 지수를 이용하여 생보산업의 자본시장통합법 전후 2년간의 효율성과 생산성 변화를 분석하고 더 나아가 토빗 회귀분석을 이용하여 효율성을 결정하는 요인을 추가적으로 찾아내는데 있다. 본 연구결과는 다음과 같다. 첫째 자본시장법 시행 전후의 효율성은 자본시장법 시행 전에 비하여 시행 후에 기술효율성과 순수기술효율성 및 규모효율성 모두가 유의적으로 증가한 것으로 나타났다. 둘째, 자본시장법 시행 전후의 생산성은 자본시장법 시행 전에 비하여 시행 후에 유의적으로 증가한 것으로 나타났다. 셋째, 기술효율성에 유의적인 영향을 미치는 변수는 설계사 비중, 순수기술효율성에 유의적인 영향을 미치는 변수는 자산운용률, 규모효율성에 유의적인 영향을 미치는 변수는 기업규모, 자산운용률, 설계사 비중으로 나타났다.

• 대한설비공학회지:설비저널
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• 제3권3호
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• pp.180-184
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• 1974

From the point of view of the second law of thermodynamics, house heating and cooling systems were analysed for saving energy. The analysis provides a theoretical basis for the heat-pump application. Also the efficiency of energy use is defined more rigorously by comparing the thermodynamic availability actually consumed in heating and cooling with the minimum thermodynamic availability required to do the same heating and cooling. It was found that the present 'Ondol' heating system has a heating efficiency of around $8\%$ according to the definition described here. Several schemes to inprove the efficiency are presented.

• 한국수소및신에너지학회논문집
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• 제26권6호
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• pp.590-599
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• 2015

In this paper a performance analysis is carried out based on the first and second laws of thermodynamics for heat exchanger in organic Rankine cycle (ORC) for the recovery of low-temperature finite thermal energy source. In the analysis, effects of the selection of working fluid and pinch temperature difference are investigated on the performance of the heat exchanger including the effectiveness of the heat exchanger, exergy destruction, second-law efficiency, number of transfer unit (NTU), and pinch point. The temperature distribution are shown depending on the working fluids and the pinch temperature difference. The results show that the performance of the heat exchanger depends on the pinch temperature difference sensitively. As the pinch temperature increases, the exergy destruction in the evaporator increases but the effectiveness, second law efficiency and NTU decreases.

• 무역상무연구
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• 제53권
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• pp.315-336
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• 2012

In year 2011 export volume of South Korea surpassed 500billion USD and overall trade volume has exceeded one trillion USD. South Korea is ranked at 7th in the world by its export volume. Such an expansion of the trade volume leads to growth in customs clearance service demand. However, there are only handfuls of studies on the efficiency of customs clearance service which customs broker provide. If the efficiency in this study is not absolute, it shows relative efficiency to decision making unit. In this research survey was conducted targeting members of Korea Customs Brokers Association. Based on the survey improvement plans to enhance efficiency of customs clearances are as follows. First, rationalize the customs broker fee. Second, setup batch processing system to improve efficiency of the work process. Third, develop new area of task such as FTA and AEO certification. Forth, raise service quality by improving professionalism of customs brokers. Fifth, work efficiency of the office in the capital area will increase. Sixth, when inspecting import export cargo, customs broker should attend at the scene by their choice. Meanwhile, difference analysis on competent customs, type of office, and duration of the business was done but all the aspects were rejected. Such aspects does not influence on its effectiveness.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1996년도 한국자동제어학술회의논문집(국내학술편); 포항공과대학교, 포항; 24-26 Oct. 1996
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• pp.387-390
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• 1996

In this paper, A new PI-type reaching law for variable structure control is proposed to alleviate the chattering and improve the robustness properties in the presence of matched uncertainty. The proposed reaching law consists of a proportional term and an integral term. And the dynamics of switching function can easily be specified by using the second-order system analysis method. And also the proposed scheme has the advantages of alleviating the chattering than Gao's one and reducing the influence of uncertainties by band pass filter characteristic. The efficiency of the proposed method has been demonstrated by simulations for Dutch Roll damping in a light aircraft.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권3호
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• pp.1098-1112
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• 2018

Achievable sum rate and energy efficiency (EE) are investigated for the massive multiple-input multiple-output (Massive MIMO) downlink with channel aging in the time varying Ricean fading channel. Specifically, the expression of the achievable sum rate of the system for the maximum ratio transmission (MRT) precoder with aged channel state information (CSI) in the time varying Ricean fading channel is first presented. Based on the expression, the effect of both channel aging and the Ricean factor on the power scaling law are studied. It is found that the transmit power of base station (BS) is scaled down by $1/{\sqrt{M}}$(where M is the number of the BS antennas) when the Ricean factor K is equal to zero (i.e., time varying Rayleigh fading channel), indicating that aged CSI does not affect the power scaling law. However, the transmit power of the BS is scaled down by 1/M for the time varying Ricean fading channel (where $K{\neq}0$) indicating that the Ricean factor affects the power scaling law and sum rate, and channel aging only leads to a reduction of the sum rate. Second, the EE of the system is analyzed based on the general power consumption model. Both the theoretical analysis and the simulations show that the channel aging could degrade the sum rate and the EE of the system, and it does not affect the power scaling law.