• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.4
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• pp.77-85
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• 1999

By assuming a linearly graded depletion edge approximation in the intrinsic MOS region and by taking into account the mobility variation dependent on both lateral and vertical fields, a physics-based analytical model for a short-channel(n-channel) MOSFET is suggested. Derived expressions for the threshold voltage and the drain current of typical MOSFET is structures could be used in a unified manner for all operating range. The threshold voltage was calculated by changing following variables : channel length, drain-source voltage, source-substrate voltage, p-substrate doping level, and oxide thickness. It is shown that the threshold voltage decreases almost exponentially as the channel length decreases. In addition, the short-channel threshold voltage roll-off, the channel length modulation and the electron mobility degradation can be derived within a satisfactory accuracy.

• Aerospace Engineering and Technology
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• v.6 no.2
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• pp.87-95
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• 2007

The ocean and meteorological payloads of COMS are concerned to experience degration of image quality due to the disturbance induced by the motion of moving parts of the payloads. And thruster firings for stationkeeping and wheel offloading are expected to degrade the image quality of the optical payloads. In case of COMS, in order to keep the optical payload free from the mechanical interference from the other payload, the operation design approach has been taken. This paper introduces the operation design of COMS taken to avoid these problems. In order to meet users requirement by avoiding the degradation of image quality, the timeline of optical payloads and housekeeping are optimized, and operational constraints are applied to the mirror motion of the meteorological payload. This paper also introduces the results of time budget analysis performed to validate the operation design.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.12
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• pp.1209-1216
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• 2009

This paper presents the pose estimation of a small UAV utilizing visual information from low cost cameras installed indoor. To overcome the limitation of the outside flight experiment, the indoor flight test environment based on multi-camera systems is proposed. Computer vision algorithms for the proposed system include camera calibration, color marker detection, and pose estimation. The well-known extended Kalman filter is used to obtain an accurate position and pose estimation for the small UAV. This paper finishes with several experiment results illustrating the performance and properties of the proposed vision-based indoor flight test environment.

• Journal of Labour Economics
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• v.36 no.1
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• pp.45-62
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• 2013

In this study, we revisit an empirical literature has found that neighborhood income inequality lowers people's likelihood of contributing public goods in terms of volunteering. We contribute to the literature by explicitly addressing the issues of larger and improper neighborhood choice with a census-type data and endogenous neighborhood location with some unique features of 2009 Social Survey Data by Statistics Korea. The results have confirmed that income heterogeneity lowers people's volunteering.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.638-642
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• 2007

댐 운영이 하류하천의 하도와 생태계에 미치는 영향권 범위를 설정하고, 영향정도를 정량화하고자 하는 연구는 그 중요성에도 불구하고 상당히 미흡한 실정이다. 본 연구에서는 댐 운영이 하류 하천에 미치는 영향을 지형학적, 수리 수문학적, 환경 생태학적, 사회적 영향권으로 구분하여 다각적인 측면을 고려한 댐 하류하천 영향권 범위 설정 기준을 제시하고자 한다. 첫째, 지형학적인 영향권 범위는 댐으로 인한 유사 공급 차단, 토시공급 능력 감소와 하상변동, 하상의 장갑화 현상과 같은 하상토 대표입경의 변화 등으로 설정한다. 둘째, 수리 수문학적인 영향권 범위는 홍수파 전달, 하도의 홍수조절효과, 홍수조절비, 유황변동 등으로 설정한다. 셋째, 환경 생태학적인 영향권 범위는 수질 변화, 하도내 식생분포 변화, 어류서식처 변화 하천 코리도의 토지이용 변화 등으로 설정한다. 그리고 홍수량에 따른 댐 하류하천의 홍수범람지구 및 댐 방류로 인한 하류하천 홍수소통 장애요인 등의 요인에 의한 사회적 측면에서의 영향권 범위를 설정한다. 본 연구에서 제시하고자 하는 영향권 범위 설정방법은 정성적인 의미가 크다. 따라서 댐 운영이 하류하천에 미치는 영향요인을 세부적하고 정량화 하는 연구가 지속적으로 시행되어야 할 것이다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.9
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• pp.60-66
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• 2006

Now, on developing COMS(Communication, Ocean and Meteorological Satellite) has solar panel on the south panel only. Therefore, the wheel off-loading has to be performed periodically to reduce a induced momentum energy by a asymmetric solar panel. One of two East/West station keeping maneuver to correct simultaneously longitude and eccentricity, orbit corrections may be performed during one of the two wheel off-loading manoeuvres per day to get enough observation time for meteorological and ocean sensor. In this paper, we applied a linearized orbit maneuver equation to acquire maneuver time and delta-V. Nonlinear simulation for the station keeping is performed and compared with general station keeping strategy for fuel reduction.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.549-549
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• 2013

고전압 펄스 플라즈마를 액체 속에서 발생시켜 수소 스펙트럼의 광학적 특성을 연구하였다. 고전압 펄스 발생 장치인 막스 제네레이터는 용량이 $0.5{\mu}F$인 축전기 5개로 이루어져 있다. 각각의 축전기는 전원 장치를 이용하여 저항을 통해 병렬로 충전되며, 방전 시에는 불꽃 방전 스위치에 의해 동시에 직렬로 연결되어 고전압을 발생시킨다. 따라서, 출력 전압과 전류는 40kV, 3 kA이며 총 에너지는 약 125 J이다. 직육면체 모양의 폴리카보네이트 용기 내부의 양쪽면에는 탐침 모양의 전극이 구성되어 있으며 전극 사이에서 고전압을 가진 플라즈마가 형성된다. 실험에서 액체로는 증류수를 사용하였다. 액체 방전 시 발생하는 수소 스펙트럼을 관측하기 위해 초점거리 30 cm의 monochromator를 이용하였고, 수소 알파선의 656.3 nm와 수소 베타선의 434.1 nm를 관측하였다. 전자 밀도의 측정법으로는 Stark broadening법을 이용하여 측정하였으며, 전자 온도는 Stark profile의 상대적인 전자 밀도의 비를 이용하여 계산하였다. 전자밀도는 실험조건에서 약 $3{\times}10^{15}cm^{-3}$, 전자온도는 약 2.5 eV가 측정되었다.

• Journal of Astronomy and Space Sciences
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• v.14 no.1
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• pp.150-157
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• 1997

A precise determination of the fuel efficiency is important because North/South station keeping, which controls the inclination of the geostationary orbit, consumes most of the satellie fuel. We estimate the amount of fuel required during the lifetime of the KOREASAT when MFT(Minimum Fuel Target) technique is adopted, and the result is compared to those when MCT(Maximum Compensation Target) and TBCT(Track-Back Chord Target) technique are applied. From this computation, we find that if MFT technique is adopted, the lifetime of the satellite can be extended at least 45 and 15 days, respectively, compared to those consumed with MCT and TBCT technique.

• Journal of the Korean GEO-environmental Society
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• v.13 no.6
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• pp.41-50
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• 2012

In general, it is critical that grout consistency permit the complete filling of void space without segregation of ingredients. Recently, the antiwashout agent is used on underwater grout materials for preventing the grout from the segregation in water. This study introduces a new type of antiwashout underwater and flowable grout material using viscous modifiers and its characteristics comparing with conventional grout materials in fresh and sea water. It is found that the antiwashout underwater grout both in fresh and sea water has enough strength and good resistance to segregation.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.3
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• pp.292-302
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• 1998

In this study, 14 refrigerant mixtures composed of R32, R125, R134a, R143a, R152a, and R1270(Propylene) were tested in a breadboard heat pump in an attempt to replace R22 used in most of the residential air conditioners and heat pumps. The heat pump was of 1 ton capacity and water was employed as the secondary heat transfer fluids. All tests were conducted under ARI test A condition. Ternary mixtures composed of R32, R125, and R134a were shown to have 4∼5% higher COP and capacity than R22 and hence they seem to be very promising candidates to replace R22. On the other hand, ternary mixtures containing R125, R134a, and R152a have lower COP and capacity than R22. R32/R134a binary mixtures show a 7% increase in COP and have the similar capacity to that of R22 and hence they are also good candidates to replace R22. Special care must be exercised when a suction line heat exchanger is used with these mixtures in air conditioners. Finally, the compressor discharge temperatures of all mixtures tested were lower than those of R22 by 15.g∼34.7t, which indicates that these mixtures would offer better system reliability and longer life time than R22.