• 상하수도학회지
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• 제19권6호
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• pp.827-837
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• 2005

In this study, we derived a new non-dimensional variable including bubble size and air diffusing area by Buckingham's theorem for making a practical correlation with experimental results. Firstly, we drew a relationship between a non-dimensional variable, $NH/u_s$, which has a form of Froude number and destratification efficiency with a simple theoretical consideration. Then we derived two non-dimensional variables by Buckingham's ${\pi}$-theorem and equating them with a form of $Fr_N$ for making single parameter to correlate overall destratification efficiency. As the result, the single parameter Be number shows a correlations with destratification efficiencies obtained from laboratory and pilot experiments. Also, for the practical applications, we conducted multiple regression analysis using Be and tank area to make predictive equations about destratification efficiency. The result also shows a successful correlations with destratification efficiency ($R^2$>0.9, p<0.001). Using this equation, we proposed a new design methodology with respect to bubble diffusing area.

• 전력전자학회논문지
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• 제18권1호
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• pp.54-62
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• 2013

This paper proposes a high-efficiency DC-DC converter with improved dynamic response characteristics for modular photovoltaic power conversion. High power efficiency is achieved by reducing switching power losses of the DC-DC converter. The voltage stress of power switches is reduced at primary side. Zero-current switching of output diodes is achieved at secondary side. A modified proportional and integral controller is suggested to improve the dynamic responses of the DC-DC converter. The performance of the proposed converter is verified based on a 200 [W] modular power conversion system including the grid-tied DC-AC inverter. The proposed DC-DC converter achieves the efficiency of 97.9 % at 60 [V] input voltage for a 200 [W] output power. The overall system including DC-DC converter and DC-AC inverter achieves the efficiency of 93.0 % when 200 [W] power is supplied into the grid.

• 한국산학기술학회논문지
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• 제5권2호
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• pp.191-196
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• 2004

경영자가 가격이나 원가와 관련된 정확한 정보를 얻을 수 있다면 DEA모형을 이용하여 기술적 효율성 뿐 만 아니라 배분적 효율성과 관련된 분석이 가능해진다. 배분적 효율성을 분석하므로서 총체적 효율성을 기술적 효율성과 배분적 효율성으로 분해할 수 있고 이를 통해 보다 다양한 분석수단을 얻을 수 있다. 본 연구에서는 기본적 DEA 모형을 변형하여 배분효율성을 분석할 수 있는 DEA모형을 설계한다. 우선 예산선에 바탕을 둔 비용최소화 모형을 설계하고 이것을 다시 이익 극대화 모형으로 변환한 후 가산형의 DEA 모형으로 재설계한다. 가격정보가 주어진 경우 기술적 효율성의 범주를 벗어난 보다 다양한 형태의 효율성 분석이 가능해져 성과평가 및 그 결과의 해석 그리고 보다 현실성 있는 경영개선방안의 도출이 가능해진다.

• Environmental Engineering Research
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• 제25권3호
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• pp.439-445
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• 2020

In the estimation of the aerosol single fiber efficiency using fibrous filters, there is a size range, where the particles penetrate most effectively through the fibrous collectors, and corresponding minimum single fiber efficiency. For small particles in which the diffusion mechanism is dominant, the Cunningham slip correction factor (C_c) affects the single fiber efficiency and the most penetrating particle size (MPPS). Therefore, for accurate estimation, C_c is essential to be considered. However, many previous studies have neglected this factor because of its complexity and the associated difficulty in deriving the appropriate parameterization particularly for the MPPS. In this study, the expression for the MPPS, and the corresponding expression for the minimum single fiber efficiency are analytically derived, and the effects of C_c are determined. In order to accommodate the slip factor for all particle-size ranges, C_c is simplified and modified. Overall, the obtained analytical expression for the MPPS is in a good agreement with the exact solution.

• 한국태양에너지학회 논문집
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• 제31권2호
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• pp.120-127
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• 2011

Solar array has the following nonlinear characteristic, such as whose output current increases, output voltage is reduced. For this reason, boost converter with solar array system is always controlled to remain on the maximum power point of the solar array. In this case, we are not focused on the output of the solar array and not consider efficiency of the boost converter, which is assumed reliable. But efficiency of the converter also should be considered, which affects the total efficiency of the overall solar energy system. In this paper, efficiency calculation of the boost converter using power balance method is proposed, which will be used for a powerful reference before hardware realization.

• 한국폐기물자원순환학회지
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• 제35권7호
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• pp.600-605
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• 2018

In this study, the combustion characteristics were investigated based on the biodrying solid recovered fuel (SRF) in a 5 Ton/day scale combustion boiler. The composition of the combustion gas containing the biodrying SRF was analyzed, the particulate matter, and its HCl content was determined with the air pollutant process test method. Mass balance, carbon balance, and combustion efficiency were calculated according to the equivalence ratio (ER) method; the energy recovery efficiency of the combustion boiler was also analyzed. The overall combustion efficiency of the biodrying SRF was 97.3 % and the energy recovery efficiency was 80.2%.

• Steel and Composite Structures
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• 제44권1호
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• pp.105-117
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• 2022

Impact resistance efficiency of the newly designed sandwich beam with a laterally arched core as bio-inspired by the woodpecker is numerically investigated. The principal components of the beam comprise a dual-core system sandwiched by the top and bottom laminated CFRP skins. Different materials, including hot melt adhesive, high-density polyethylene (HDPE), acrylonitrile butadiene styrene (ABS), epoxy resin (EPON862), aluminum (Al6061), and mild carbon steel (AISI1018), are considered for the side-arched core layer of the beam for impact efficiency assessment. The aluminum honeycomb takes the role of the second core. Contact force, stress, damage formation, and impact energy for beams equipped with different materials are examined. A diversity in performance superiority is noticed in each of these indicators for different core materials. Therefore, for overall performance appraisal, the impact resistance efficiency index, which covers several chief impact performance parameters, of each sandwich beam is computed and compared. The impact resistance efficiency index of the structure equipped with the AISI1018 core is found to be the highest, about 3-10 times greater than other specimens, thus demonstrating its efficacy as the optimal material for the bio-inspired dual-core sandwich beam system.

• 한국유기농업학회지
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• 제30권4호
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• pp.499-516
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• 2022

Blueberry producers' management is failing as a result of the price decline caused by an increase in blueberry imports and the accompanying deterioration in management. Consequently, an endeavor was undertaken to verify the measurement and impact from the standpoint of efficiency and productivity of blueberry management, and to offer an indication of management improvement through analysis. Using the Rural Development Administration's income survey data, the data for twenty-four blueberry farms was analyzed. First, the management effectiveness of blueberry cultivators was evaluated. Using the CCR model (0.7297) and the BCC model (08148), the efficiency of a farm was examined. When the efficiency is one, CCR is ten and BCC is fifteen, and in overall, it was found to be ineffective, the efficiency declined from 2018 to 2019, but climbed again in 2020, according to the annual analysis. The MPI index was then used to examine productivity. T2's MPI index was 1.3338, whereas T3's MPI index was 0.8896, demonstrating a considerable decline in TC. This indicates that technological progress is not being accomplished, necessitating the need for countermeasures. In order to improve the management efficiency of blueberry producers, it is necessary to reduce costs and improve receivable prices through producer organization, and to actively introduce new technologies.

• The Journal of Asian Finance, Economics and Business
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• 제9권7호
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• pp.261-271
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• 2022

Over the last 20 years, the insurance industry in Vietnam has been rapidly growing with an average annual growth rate of 21%, one of the most active markets in Southeast Asia, raising the question of efficiency to managers, investors, and regulators. This article is one of the first research works using Data Envelopment Analysis combined with the Malmquist index over the period from 2016 to 2020 for 37 insurance firms in Vietnam to investigate the efficiency of this sector. The value-added approach is employed with total equity and operating expenses as inputs, finance income, and gross written premium as outputs. The findings reveal that most of Vietnam's insurance companies are operating quite effectively, and the non-life sector is more efficient than the life sector. There is also a regression in efficiency change, while there is a progression in technological change and total factor productivity change during the period examined. The goal of this research is to give a fundamental understanding of the overall efficiency of insurance firms in Vietnam, and help managers, investors, policyholders, and government agencies make better decisions regarding self-assessment, M&A activities, deregulation... Consequently, the insurance sector could improve in terms of efficiency and develop sustainably over time.

• The Journal of Asian Finance, Economics and Business
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• 제9권3호
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• pp.355-364
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• 2022

The effect of technological innovation on the high-quality development of the producer services industry depends on whether or not technical innovation efficiency plays a key role. This study looks at the impact of technological innovation and financial technology (fintech) on the development of high-quality producer services in Fujian Province from 2010 to 2019. The efficiency of technological innovation is measured using Data Envelopment Analysis (DEA) and the Malmquist productivity index. The mean overall innovation efficiency score is 0.639, meaning that Fujian accounts for 36.1% of resource utilization inefficiencies and that there are significant differences in technological innovation efficiency between cities. The findings show that high-quality producer services industries benefited from innovation efficiency, but that the influence of technological innovation efficiency is insignificant. This demonstrates that financial innovation has not been able to completely enhance the development level of the producer services industry. This may be due to the unreasonable output structure of technological innovation and the low industrial transformation rate of technological achievements. This study advocates that the R&D fund allocation structure be optimized. That technological innovation can improve the high-quality development of the producer services industry is a consensus within the academic community.