• 전력전자학회논문지
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• 제18권5호
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• pp.492-500
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• 2013

A balanced forward-flyback converter for high efficiency and high power factor using a foward and flyback converter topologies is proposed in this paper. The conventional AC/DC flyback converter can achieve a good power factor but it has the high offset current through the transformer magnetizing inductor, which results in a large core loss and low power conversion efficiency. And, the conventional forward converter can achieve the good power conversion efficiency with the aid of the low core loss but the input current dead zone near zero cross AC input voltage deteriorates the power factor. On the other hand, since the proposed converter can operate as the forward and flyback converters during switch turn-on and turn-off periods, respectively, it cannot only perform the power transfer during an entire switching period but also achieve the high power factor due to the flyback operation. Moreover, since the current balanced capacitor can minimize the offset current through the transformer magnetizing inductor regardless of the AC input voltage, the core loss and volume of the transformer can be minimized. Therefore, the proposed converter features a high efficiency and high power factor. To confirm the validity of the proposed converter, theoretical analysis and experimental results from a prototype of 24W LED driver are presented.

• 한국환경과학회지
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• 제28권8호
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• pp.669-676
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• 2019

The purpose of this study was to evaluate the effects of different Hydraulic Retention Times (HRTs) on the contaminant removal efficiency using Aerobic Granular Sludge (AGS). A laboratory-scale experiment was performed using a sequencing batch reactor, and the Chemical Oxygen Demand (COD), nitrogen, orthophosphate removal efficiency, AGS/MLSS ratio, and precipitability in accordance with the HRT were evaluated. As a result, the COD removal efficiency was not significantly different with the reduction in HRT, and at a HRT of 6 h, the removal rate was slightly increased owing to the increase in organic loading rate. The nitrogen removal efficiency was improved by injection of influent division at a HRT of 6 h. As the HRT decreased, the MLSS and AGS tended to increase, and the sludge volume index finally decreased to 50 mL/g. In addition, the size of the AGS gradually increased to about 1.0 mm. Therefore, the control of HRT provides favorable conditions for the stable formation of AGS, and is expected to improve the contaminant removal efficiency with the selection of a proper operation strategy.

• 대한환경공학회지
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• 제27권10호
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• pp.1114-1122
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• 2005

이 연구는 초음파에 의한 1,4-dioxane(1,4-D)의 제거효율과 반응속도의 증가를 위해 초음파의 조사방식, 반응온도와 부피의 효과를 조사하였다. 초음파가 펄스방식으로 주사된 경우가 연속적으로 주사된 경우보다 약 10%의 1,4-D의 감소 효율의 증가를 보였다. 두 경우 모두 1000 mL와 반응온도가 고정되지 않은 조건에서 실시된 것으로 반응곡선은 도입단계, 가속단계, 그리고 안정화단계 등 3단계로 구분될 수 있었다. 실제로 1,4-D의 제거를 보이는 부분은 도입단계와 가속단계로 이들의 속도론적 특징은 도입단계와 가속 단계 각각 0차 반응과 유사일차반응과 부합하였다. 반면에 300 mL의 반응부피에서 온도를 고정한 경우에서는 3단계의 제거 유형을 보이지 않았다. $5^{\circ}C$로 고정한 경우만이 유사일차 반응과 부합하였고 그 이상의 온도에서는 0차 반응과 부합하였다. $20^{\circ}C$로 온도가 고정된 조건에서 반응부피 300 mL의 경우가 1000 mL 반응에서 보다 높은 분해 효율을 보였을 뿐만 아니라 단일한 제거 특성을 보였다. 이러한 반응 온도와 부피의 영향은 초음파 주사에 의해 생성되는 bubble의 강도에 영향을 주며 bubble의 강도가 높을수록 OH 라디칼의 생성이 증가되었다.

• 한국자동차공학회논문집
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• 제12권2호
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• pp.24-31
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• 2004

A cylindrical constant volume combustion bomb is used to investigate the combustion characteristics and to analyzer the heat quantity of inhomogeneous charge methane-air mixture. To analyze the heat quantity, some definitions including the CHR ratio, the UHC ratio and the HL ratio are needed and are calculated. It is shown that the effect of stratification is not significant in case of the overall excess air ratio of 1.1, mainly due to the higher heat loss and lower thermal efficiency compared to those of homogeneous condition. In the case of the overall excess air ratio of 1.4, as the initial charge pressure decreases, the CHR ratio has been decreased while the HL ratio has been increased, Generally, as the initial charge pressure increases, the amount of injection mixture has been decreased and has resulted in lower mean velocity and turbulence intensity for injection mixture. Also, the injected mixture is too rich to result in mixing deficiency in combustion chamber. From these results, it could be possible to acquire the improvement of thermal efficiency and the reduction of heat loss simultaneously through the 2-stage injection in CNG direct injection engine.

• 한국전기전자재료학회논문지
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• 제26권12호
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• pp.878-881
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• 2013

In this study, we have fabricated the dye sensitized solar cell (DSSC) composed by a transparent conductive oxide (TCO), a nanocrystalline semiconductor film usually $TiO_2$, a sensitizer adsorbed on the surface of the semiconductor, an electrolyte containing a redox mediator and a counter electrode. The $TiO_2$ nanopowder was prepared by sol-gel methode. The HCl (hydrochloric acid) and TBAOH (Tetrabutyl amonium hydroxide) was added for improving the catalyst and distributed properties of $TiO_2$ nanopowder. Ammonium hydroixde was added in order to control the morphology and size of $TiO_2$ nano crystal. A $TiO_2$ paste for working electrode was prepared with the addition of HPC (hydroxypropyl cellulos) used as a binder of which volume was controled as 1.3, 1.5, 1.7, and 2.0%. The measured I-V curves of assembled DSSC showed that the cell with 1.7% HPC binder had the best efficiency of 6.79%.

• International Journal of Air-Conditioning and Refrigeration
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• 제15권3호
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• pp.108-113
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• 2007

The performance of a solar water heater incorporating evacuated tubes was evaluated using a transient simulation program, TRNSYS. Simulations were performed for $60^{\circ}C$ of hot water load temperature and for 280 liter of daily hot water volumes and three 400 liter of storage tank volumes. Three patterns of daily hot water consumption profile were used in the present study (morning, lunch and evening). The results show that the increase in solar fraction depends on the load profile, as well as the collector efficiency coefficient. Hot water draw profile has a large effect on the performance of the SDHWS, the morning load profile has the highest solar fraction. The annual solar fraction of the system, at the weather conditions of Jinju is approximately 84% at lunch load pattern, the 280 kg of load volume, 400 kg of tank volume and the $60^{\circ}C$ of load temperature.

• Tribology and Lubricants
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• 제36권2호
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• pp.96-104
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• 2020

The electric vehicle industry is rapidly developing because of enforced environmental regulations, and several studies have been conducted on the multispeed transmission to improve the fuel efficiency of electric vehicles. Among these studies, research on the power density improvement of electric vehicle transmission is critical. Thus, the optimal design of the gear train is necessary to enhance transmission efficiency. In this study, an optimal design methodology for the lightweight two-speed transmission of electric vehicles is proposed. Because a multispeed transmission has many operating conditions and equality and inequality constraints, a new gear design method that combines analytical and iterative methods is applied without using complex optimization algorithms. Sets of possible design variables are generated considering the operating conditions and various design variables. The modules and face width ratios of each stage gear that satisfy the corresponding operating conditions are analytically calculated. The volume of the gear train is calculated, evaluated, and arranged using these values to determine the optimal solution for minimizing the volume, and the proposed methodology is applied to the actual model to verify its effectiveness. The design of a two-speed transmission with multiple operating conditions and constraints without complicated optimization algorithms can be optimized.

• 대한전기학회논문지:전력기술부문A
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• 제51권12호
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• pp.630-637
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• 2002

This paper proposed a new diffusion model considering DSM rebate program's support conditions. The proposed method used some aspects of the rebate program such as support qualifications, annual support volume, and support level per appliance as following : The support qualifications were limited as the consumer which can get the rebate program's benefit, the annual support volume was constrained as the fixing budget and the support level per appliance was considered by high-efficient appliance actuality price. This paper also proposed a new method that used neural network as its parameter estimation moth[,4 for the diffusion model. The diffusion model and its parameter estimation method are expected to be able to analyze the diffusion characteristics of high-efficient appliance through the rebate program and the effects of rebate program's support conditions. Also, these will be able to evaluate the impacts and to analyze the cost-effectiveness of Energy Efficiency Demand-Side Management(EEDSM) resources. The case study is performed on the high-efficient lighting appliance rebate program of Korea by using the suggested diffusion model and estimation method and thus verified its validity.

• 한국의학물리학회:학술대회논문집
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• 한국의학물리학회 2002년도 Proceedings
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• pp.83-85
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• 2002

Yonsei Cancer Center introduced an IMRT System at the beginning of February, 2002. The system consists of CORVUS(NOMOS) inverse planning machine, LANTIS(SIEMENS), PRIMEVIEW and PRIMART Linac(SIEMENS). The optimization of CORVUS planning system with PRIMART is an important work to get an efficient treatment plan. So, we studied two Finite Size Pencil Beams, 1.0 x 1.0 cm$^2$ and 0.5 x 1.0 cm$^2$, and four leaf transmission sets, 5%, 10%, 20%, 33%. We compared the dose distribution of target volume and delivery efficiency of the plan results.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.83-86
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• 2009

The field of the large volume heat exchanger for wasted heat recovery ventilation system is being expanded enormously seeing as the fact that the quantity of reducing energies are huge due to the large volume heat exchanger for wasted heat recovery system at large buildings and factories, which consume large amount of energies while it has been arising huge amount of losses in Korea because of the lack of technology.