• 천문학회보
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• 제36권1호
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• pp.85.2-85.2
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• 2011

We investigate the driven magnetohydrodynamic (MHD) turbulence by including the effect of the expansion and collapse of background medium. The main goal is to quantify the evolution and saturation of the strength and characteristic length scales of magnetic fields in expanding and collapsing media. Our findings are as follows. First, with the expansion and collapse of background medium, the time evolution of the magnetic and kinetic energy densities depends on the nature of forcing as well as the rate of expansion and collapse. Second, at scales close to the energy injection (or driving) scale, the slope of magnetic field power spectrum shallows with expansion but steepens with collapse. Third, various characteristic length scales, relative to the energy injection scale, decrease with expansion but increase with collapse. We discuss the astrophysical implications of our results.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 추계학술대회 논문집 Vol.16
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• pp.456-459
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• 2003

In this thesis, We observed the characteristic of the diffraction efficiency according to the wave length of the chalcogenide thin films. The used an $Ag(200{\AA})/As_{40}Ge_{10}Se_{15}S_{35}$ thin film. We made grating formation by each wave length 325nm, 442nm, 632.8nm. After measure diffraction efficiency of the time. We expressed the maxium saturation value at fast time as were the short wavelength and stable characteristic. On the other hand we appeard to the by a maxium diffraction efficiency the 1.7% in 325nm, 0.8% in 442nm, 0.27% in 632.8nm. The maximum diffraction efficiency expressed high value as were the long wavelength.

• 대한전자공학회논문지SD
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• 제42권1호
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• pp.25-32
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• 2005

본 논문에서는 단 채널 GaAs MESFET과 SOI-구조의 Si JFET가 갖는 전형적인 특성: i) 드레인 전압 인가에 의한 문턱전압 roll-off, ii) 포화영역에서의 유한한 ac 출력저항, iii) 채널길이에 대한 드레인 포화전류의 의존성 약화, 등을 통합적으로 기술할 수 있는 해석적 모델을 제안하였다. 채널 방향의 전계 변화를 포함하는 새로운 형태의 가정을 기존의 GCA와 대체하고, 채널의 전류 연속성과 전계-의존 이동도를 고려하여, 공핍영역과 전도 채널에서 2차원 전위분포 식을 도출해 내었다. 이 결과, 문턱전압, 드레인 전류의 표현 식들이 동작전압전 구간의 영역에 걸쳐 비교적 정확하게 도출되었다. 또한 본 모델은 기존의 채널 shortening 모델에 비해 Early 효과에 대한 보다 더 적절한 설명을 제공하고 있음을 보이고 있다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 추계학술대회 논문집 Vol.19
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• pp.87-88
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• 2006

Recently, poly-Si TFT-LCD starts to be mass produced using excimer laser annealing (ELA) poly-Si. The main reason for this is the good quality poly-Si and large area uniformity. We report the influence of channel length and width on poly-Si TFTs performance. Transfer characteristics of p-channel poly-Si thin film transistors fabricated on polycrystalline silicon (poly-Si) thin film transistors (TFTs) with various channel lengths and widths of 2-30 ${\mu}m$ has been investigated. In this paper, we analyzed the data of p-type TFTs. We studied threshold voltage ($V_{TH}$), on/off current ratio ($I_{ON}/I_{OFF}$), saturation current ($I_{DSAT}$), and transconductance ($g_m$) of p-channel poly-Si thin film transistors with various channel lengths and widths.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2217-2221
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• 2007

Because of the ozone layer depletion and global warming, new alternative refrigerants are being developed. In this study, evaporation heat transfer characteristics of carbon dioxide flowing upward in a vertical tube have been investigated by experiment. Before the test section, a pre-heater is installed to adjust the inlet quality of the refrigerant to a desired value. A smooth tube with outer diameter of 5 mm and length of 1.44 m was selected as a test tube. The test was conducted at mass fluxes of 212 to 530 kg/$m^2s$, saturation temperature of -5 to 20$^{\circ}C$, and heat fluxes of 20 to 45 kW/$m^2$. As the vapor quality and mass fluxes increase, the heat transfer coefficients of carbon dioxide are decreased, and the heat transfer coefficients increase when the heat fluxes and saturation temperatures increase.

• Journal of Electrical Engineering and Technology
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• 제13권6호
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• pp.2284-2291
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• 2018

This paper deals with optimum design of surface mounted permanent magnet synchronous motor (SPMSM) for automotive component. For a compact system structure, it was designed as a motor with a 14-pole 12-slot concentrated winding and hollow shaft. The motor is a thin type structure which stator outer diameter is relatively large compared to its axial length and is designed to have a high magnetic saturation for increasing the torque density. Since the high magnetic saturation in the stator core increases the axial leakage flux, a 3-dimensional (3-D) finite element analysis (FEA) is indispensable for torque analysis. However, optimum designs using 3-D FEA is inefficient in terms of time and cost. Therefore, equivalent 2-D FEA which is able to consider axial leakage flux is applied to the optimization to overcome the disadvantages of 3-D FEA. The structure for cost reduction is proposed and optimum design using equivalent 2-D FEA has been performed.

• 한국지반공학회지:지반
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• 제7권1호
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• pp.7-14
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• 1991

시편을 통과하는 초음파의 속도를 측정 함으로써 흙의 동전단 탄성계수의 측정을 시도하였다. 초음 파의 발생 및 감지장치인 PUNDIT를 사용하였으며, 4종류의 시료에 따른 공극비 7, 포화도 7종류에 대해서 총 46개의 실험을 실시하였다. 본 연구는 시료의 공극비 및 포화도,시료의 종류등이 동전단 탄성계수에 미치는 영향에 대해서 분석하였다. 분석 결과,흙의 동전단 탄성계수는 공극비가 증가함에 따라 감소하는 경향을 보였으 며, 시료의 종류에 의 해서도 영 향을 받는다는 사실을 알 수 있었다. 또한 본 실험 장비인 PUNDIT를 사용할 경우, 시편의 길이는 5cm-8cm가 적당하였으며, 포화도의 영향은 거의 없는 것으로 판단 되었다.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2005년도 후기학술대회논문집
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• pp.240-241
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• 2005

The experiments were conducted without oil in a closed refrigerant loop which was driven by a magnetic gear pump. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater and evaporator(test section). The test section was made of a horizontal stainless steel tube with the inner diameter of 4.57 mm, and length of 4 m. The experiments were conducted at mass flux of 200 to 700 kg/$m^2s$, saturation temperature of 0$^{circ}C$ to 20$^{circ}C$, and heat flux of 10 to 30 kW/$m^2$. The test results showed the evaporation heat transfer of $CO_2$ has great effect on more nucleate boiling than convective boiling. The evaporation heat transfer coefficients of $CO_2$ are highly dependent on the vapor quality, heat flux and saturation temperature. In comparison with test results and existing correlations, correlations failed to predict the evaporation heat transfer coefficient of $CO_2$, therefore, it is necessary to develop reliable and accurate predictions determining the evaporation heat transfer coefficient of $CO_2$ in a horizontal tube.

• 한국태양에너지학회 논문집
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• 제30권1호
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• pp.34-41
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• 2010

Gas hydrates are solid solutions when water molecules are linked through hydrogen bonding and create host lattice cavities that can enclose many kinds of guest(gas) molecules. There are plenty of methane(gas) hydrate in the earth and distributed widely at offshore and permafrost. Several schemes, to produce methane hydrates, have been studied. In this study, depressurization method has been utilized for the numerical model due to it's simplicity and effectiveness. IMPES method has been used for numerical analysis to get the saturation and velocity profile of each phase and pressure profile, velocity of dissociation front progress and the quantity of produced gas. The values calculated for the sample length of 10m, show that methane hydrates has been dissolved completely in approximately 223 minutes and the velocity of dissociation front progress is 3.95㎝ per minute. The volume ratio of the produced gas in the porous media is found to be about 50%. Analysing the saturation profile and the velocity profile from the numerical results, the permeability of each phase in porous media is considered to be the most important factor in the two phase flow propagation. Consequently, permeability strongly influences the productivity of gas in porous media for methane hydrates.

• 상하수도학회지
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• 제18권2호
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• pp.235-241
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• 2004

The dissolved air flotation (DAF) process has been widely used for removing suspended solids with low density in water. It has been known as measuring the size of microbubbles precisely which move upward rapidly in contact zone is difficult. In this study particle counter monitoring (PCM) method is used to measure the rising microbubble after injection from a nozzle. Size and distribution curve of microbubbles are evaluated at different conditions such as pressure drop at intermediate valve, length of pipeline between saturation tank and nozzle and low pressure. And the efficiency is also checked when it collides with different size floc. The experimental results show the following fact. As the final pressure drop occurred closer to a nozzle, the bubble size became smaller. And small bubble collides with large floc as well as small one because of its physical characteristic. However large bubble collides well with large floc rather than small one since hydrodynamic flow in streamline interferes to collide between two. With performing computational process by mathematical model we have analyzed and verified the size effect between bubble and floc. Collision efficiency is the highest when P/B ratio shows in the range of 0.75 < P/B ratio ($R_{particle/Rbubble}$) < 2.0.