• 한국수소및신에너지학회논문집
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• 제18권4호
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• pp.422-431
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• 2007

Polymer electrolyte membrane fuel cell(PEMFC) is very interesting power source due to high power density, simple construction and operation at low temperature. But it has problems such as high cost, improvement of performance and effect of temperature. These problems can be approached to be solved by using mathematical models which are useful tools for analysis and optimization of fuel cell performance and for heat and water management. In this paper, the present work is to develop an electrochemical model to examine the electrochemical process inside PEM fuel cell. A complete set of considerations of mass, momentum, species and charge is developed and solved numerically with proper account of electrochemical kinetics. When depth of gas channel becomes thinner, diffusion of reactant makes well into gas diffusion layer(GDL) and the performance increases. Although at low current region there is little voltage difference between experimental data of PEM fuel cell and numerical data. When the porosity size of gas diffusion layer for PEM fuel cell is bigger, oxygen diffusion occurs well and oxygen mass fraction appears high in catalyst layer.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.2
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• pp.1176-1179
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• 2003

Low-Pressure inductively coupled RF discharge sources have important industrial applications mainly because they can provide a high-density electrodeless plasma source with low ion energy and low power loss. In an inductive discharge, the RF power is coupled to the plasma by an electromagnetic interaction with the current flowing in a coil. In this paper, the experiments have been focussed on the electric characteristic and carried out using a single Langmuir probe. The internal electric characteristics of inductively coupled Ar RF discharge at 13.56 [MHz] have been measured over a wide range of power at gas pressure ranging from $1{\sim}70$ [mTorr].

• 전자공학회논문지A
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• 제31A권5호
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• pp.106-112
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• 1994

We have developed a large area ion shower doping system with an RF plasma ion source. The ion current density (i.e., doping concentration) increases with RF power and acceleration voltage. Using this technique, we investigated the optimum condition for ion doping of phosphorus in a-Si:H and poly-Si films. The optimum acceleration voltage and doping time are 6KV and 90sec, respectively, in a-Si:H films. Under this condition the electrical conductivity of ion-doped a-Si:H film is obtained ~10$^{-3}$/cm at room temperature. The sheet resistance decreases witnh acceleration voltage in ion-doped poly-Si, and a heavily-doped layer with a sheet resistance of 920$\Omega$/ㅁ is obtained by using ion doping and subsequent activation.

• Journal of Advanced Marine Engineering and Technology
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• 제34권4호
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• pp.448-454
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• 2010

GHG 및 대기오염물질 배출 규제는 고효율 및 친환경에 적합한 새로운 선박용 동력장치의 필요성을 제기하고 있다. 최근 이와 같은 문제들을 근본적으로 해결하기 위한 지속가능한 방법으로서 연료전지를 선박의 동력발생장치로 도입하고자 하는 검토가 진행되고 있다. 본 논문은 액체연료인 메탄올을 기반으로 한 고체산화물형 연료전지시스템의 성능 특성을 분석한 것으로 공기극 입구온도 일정의 조건에서 스택의 작동온도, 전류밀도, S/C, 수소연료 이용률의 영향을 시뮬레이션으로 검토하고 있으며, 그 결과를 기체연료인 메탄의 경우와 비교하고 있다.

• Nuclear Engineering and Technology
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• 제48권3호
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• pp.773-777
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• 2016

A betavoltaic battery was prepared using radioactive $^{63}Ni$ attached to a three-dimensional single trenched P-N absorber. The optimum thickness of a $^{63}Ni$ layer was determined to be approximately $2{\mu}m$, considering the minimum self-shielding effect of beta particles. Electroplating of radioactive $^{63}Ni$ on a nickel (Ni) foil was carried out at a current density of $20mA/cm^2$. The difference of the short-circuit currents ($I_{sc}$) between the pre- and post-deposition of $^{63}Ni$ (16.65 MBq) on the P-N junction was 5.03 nA, as obtained from the I-V characteristics. An improved design with a sandwich structure was provided for enhancing performance.

• Applied Microscopy
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• 제39권1호
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• pp.73-77
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• 2009

Contaminative artifacts such as carbonaceous materials on carbon-coated microgrids are unavoidable, which is induced by electron beam exposure inside electron microscopes. This phenomenon raise a source to produce confusing information to the samples investigated by analytical TEM, which should be alleviated as much as possible. As experimental precautions for reducing this unwanted effect, the use of $LN_2$ cooled anti-contaminator and pre-illumination of electron beam at low magnification can be helpful. Nevertheless, we should be cautious to set an illumination condition for microanalysis because the contaminative effect is dependent with the types of irradiation situations, which is well known to be a decisive factor for causing the carbonaceous artifacts. Accordingly, it is necessary that optimal illumination to minimize the contaminative effect should be selected for improving the accuracy of microanalysis. In this paper, we introduce the practical method to determine the optimal illumination condition by evaluating the contaminative effect as a function of instrumental spot size, which is directly linked with electron current density.

• 한국초전도ㆍ저온공학회논문지
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• 제17권1호
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• pp.36-39
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• 2015

Many studies are being conducted to implement wireless charging, for example, for cellular phones or electronic tooth brushes, via wireless power transmission technique. However, the magnetic induction method had a very short transmission distance. To solve this problem, the team of Professor Marin Soljacic proposed a magnetic resonance system that used two resonance coils with the same resonance frequency. It had an approximately 40% efficiency at a 2m distance. The system improved the low efficiency and short distance problems of the existing systems. So it could also widen the application range of wireless power transmission. Many studies on the subject are underway. In this paper, the superconductor coil was used to improve the efficiency of magnetic resonance wireless power transmission. The resonance wireless power transmission system had a source coil, a load coil, and resonance coils (a transmitter and a receiver). The efficiency and distance depended on the characteristics of the transmitter and receiver coils that had the same resonance frequency. Therefore, two resonance coils were fabricated by superconductors. The current density of the superconductor was higher than that of the normal conductor coil. Accordingly, it had a high quality-factor and improved efficiency.

• 반도체디스플레이기술학회지
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• 제13권3호
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• pp.39-43
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• 2014

The effect of electrode charging on the ion energy distribution (IED) was investigated in the dual-frequency capacitively coupled plasma source which was powered of 100 MHz RF at the top electrode and 400 kHz bias on the bottom electrode. The charging property was analyzed with the distortion of the measured current and voltage waveforms. The capacitance and the resistance of electrode sheath can change the property of ion and electron charging on the electrode so it is sensitive to the plasma density which is controlled by the main power. The ion energy distribution was estimated by equivalent circuit model, being compared with the measured distribution obtained from the ion energy analyzer. Results show that the low frequency bias power changes effectively the low energy population of ion in the energy distribution.

• Journal of Welding and Joining
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• 제34권2호
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• pp.67-72
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• 2016

Aluminum alloy is one of light weight material and it is used to make LNG tank and ship. However, in order to weld aluminum alloy high density heat source is needed. In this paper, I-butt welding of Al 5083 with 6mm thickness using Plasma-MIG welding was carried out. The experiment was performed to investigate the influence of plasma-MIG welding parameters such as plasma current, wire feeding rate, MIG-welding voltage and welding speed on the tensile strength of weld. In addition we suggested 3 strength estimation models which are second order polynomial regression model, multiple nonlinear regression model and neural network model. The estimation performance of 3 models was evaluated in terms of average error rate (AER) and their values were 0.125, 0.238, and 0.021 respectively. Neural network model which has training concept and reflects non -linearity was best estimation performance.

• 한국태양에너지학회:학술대회논문집
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• 한국태양에너지학회 2009년도 추계학술발표대회 논문집
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• pp.350-355
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• 2009

The crysralline silicon solar cell where the solar cell market grows rapidly is occupying of about 85% or more high efficiency and low cost endeavors many crystalline solar cells. The fabricaion process of high efficiency crystalline silicon solar cells necessitate complicated fabrication processes and Ti/Pd/AG contact, This metal contacts have only been used in limited areas in spite of their good srability and low contact resistance because of expensive materials and process. Commercial solar cells with screen-printed solar cells formed by using Ag paste suffer from loe fill factor and high contact resistance and low aspect ratio. Ni and Cu metal contacts have been formed by using electroless plating and light-induced electro plating techniques to replace the Ti/Pd/Ag and screen-printed Ag contacts. Copper and Silver can be plated by electro & light-induced plating method. Light-induced plating makes use the photovoltaic effect of solar cell to deposit the metal on the front contact. The cell is immersed into the electrolytic plating bath and irradiated at the front side by light source, which leads to a current density in the front side grid. Electroless plated Ni/ Electro&light-induced plated Cu/ Light-induced plated Ag contact solar cells result in an energy conversion efficiency of 16.446 % on 0.2~0.6${\Omega}$ cm, $20{\times}20mm^2$, CZ(Czochralski) wafer.