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CD 스터드 용접의 해석 및 결함 분석 Part 1 : 공정 모델링과 해석
오현석,유중돈,Oh Hyun-Seok,Yoo Choong-D. 대한용접접합학회 2006 대한용접·접합학회지 Vol.24 No.3
The CD (Capacitor Discharge) stud welding utilizes the arc heat and pressure to attach the stud to the workpiece, which consists of the arc. ignition, arcing and pressure welding stages. In order to predict the dynamic behavior of the CD stud welding process, mechanical and electrical models are employed in this work. While the mechanical model estimates the duration of each stage, the electrical model predicts the voltage and current waveforms using the RLC circuit. Effects of process parameters such as the electric components and spring force are analyzed through simulation. It is found that the contact resistance and gap between the stud and base metal influence the tip fusing and arcing duration. The calculated results showed reasonably good agreements with the experiment results.
오현석,이준웅,Oh, Hyun-Seok,Lee, Joon-Ung 한국전기전자재료학회 2005 전기전자재료학회논문지 Vol.18 No.12
Photovoltaic effects in organic solar cell were studied in a cell configuration of ITO/PEDOT:PSS/CuPc(20 nm)/$C_{60}$(40 nm)/BCP/Al(150 nm) at room temperature. Here, the BCP layer works as an exciton blocking layer. The exciton blocking layer must transport electrons from the acceptor layer to the metal cathode with minimal increase in the total cell series resistance and should absorb damage during cathode deposition. Therefore, a proper thickness of the exciton blocking layer is required for an optimized photovoltaic cell. Several thicknesses of BCP were made between $C_{60}$ and Al. And we obtained characteristic parameters such as short-circuit current, open-circuit voltage, and power conversion efficiency of the device under the illumination of AM 1.5.
CD 스터드 용접의 해석 및 결함 분석 Part 2 : 기공 제어
오현석,유중돈,Oh Hyun-Seok,Yoo Choong-D. 대한용접접합학회 2006 대한용접·접합학회지 Vol.24 No.3
Since the voids occur at the CD stud welds, the mechanism of void formation and void reduction method are investigated in this work. It is speculated that the voids are formed because of high short-circuit current above 1000A. When the simple flow model is used to estimate the void trapping condition, the most voids are trapped at the weld mainly due to fast cooling rate of the CD stud weld. Since it is almost impossible to remove the voids completely, a method is proposed to reduce the void by decreasing the short-circuit current at the end of the arcing time. The experimental results show that the void is reduced by decreasing the short-circuit current to 1000A.
전파 망원경 수신기 전단부용 극저온 22 GHz 대역 저잡음 증폭기 모듈 설계 및 제작
오현석,이경임,양승식,염경환,제도흥,한석태,Oh Hyun-Seok,Lee Kyung-Im,Yang Seong-Sik,Yeom Kyung-Whan,Je Do-Heung,Han Seog-Tae 한국전자파학회 2006 한국전자파학회논문지 Vol.17 No.3
본 논문에서는 pHEMT(pseudo-morphic High Electron Mobility Transistor)로 구성된 저잡음 증폭기 MMIC(Monolithic Microwave Integrated Circuit)를 이용하여 극저온에서 동작하는 전파 망원경 수신기 전단부용 22 GH2 대역 저잡음 증폭기 모듈을 설계, 제작하였다. pHEMT MMIC 선정에는, 극저온에서의 동작이 입증된 pHEMT 공정을 사용하여 제작된 저잡음 증폭기 MMIC를 선택하였다. 선정된 2개의 MMIC는 박막(thin film) 세라믹 기판에 장착하여 모듈화 하였다. 모듈화 시 하우징(housing)과 캐리어(carrier) 사이의 간극을 제거하고 전파 흡수체를 사용하여 불필요한 구조에 의한 발진을 제거하였다. 또한 커넥터와 기판 사이의 부정합으로 나타나는 잡음 및 이득의 열화를 리본 조정을 통해 개선시켜 상온에서 최적의 성능을 가지도록 했다. 제작된 증폭기 모듈은 상온에서 $21.5{\sim}23.5GHz$ 대역 내 이득 $35dB{\pm}1dB$, 잡음지수 $2.37{\sim}2.57dB$를 보였다. 제작된 증폭기는 헬륨 냉각기를 이용하여 $15^{\circ}K$로 냉각 후 측정 결과, 대역 내에서 이득 35 dB 이상, 잡음온도 $28{\sim}37^{\circ}K$를 얻었다. In this paper, the cryogenically cooled low noise amplifier module for radio telescope receiver front-end using pHE-MT MMIC is designed and fabricated. In the selection of MMIC, the MMIC fabricated with the pHEMTS providing successful cryogenic operation are chosen. They are mounted in the housing using the thin film substrate. In the design of the housing, the absorber and the elimination of the gap between the carrier and the housing as well removed the unnecessary oscillations by its structure. The mismatch is improved by ribbon-tuning to provide the best performance at room temperature. The fabricated module shows the gain of $35dB{\pm}1dB$ and the noise figure of $2.37{\sim}2.57dB$ at room temperature over $21.5{\sim}23.5GHz$. In the cryogenic temperature of $15^{\circ}K$ cooled by He gas, the measured gain was above 35 dB and flatness ${\pm}2dB$ and the noise temperatures of $28{\sim}37^{\circ}K$.
최근 국내 분리 고병원성 infectious bursal disease virus의 segment A 유전자 특성
오현석,이진화,권혁무,성환우,Oh, Hyun Seok,Lee, Jin Hwa,Kwon, Hyuk Moo,Sung, Haan Woo 대한수의학회 2011 大韓獸醫學會誌 Vol.51 No.1
Infectious bursal disease virus (IBDV) is a member of the Avibirnavirus genus of the Birnaviridae family which genome consists of two segments (A and B) of double stranded RNA. Segment A gene of KNU08010 isolate, which was isolated from a 15-day-old chicken flock in 2008, was sequenced and compared with other IBDV isolates including SH/92 strain, the first Korean very virulent (vv) IBDV isolate. The amino acid sequences of segment A gene showed that KNU08010 had 99.2% homology with SH92 strain. KNU08010 isolate had specific amino acids A222, I242, I256, I294 and S299 which are highly conserved among vvIBDV strains. Phylogenetic analysis based on the nucleotide sequences of variable region of the VP2 gene of 18 IBDV strains revealed that KNU08010 was grouped with vvIBDVs and was closely related to Korean vvIBDVs isolated from wild birds.
오현석(Hyun Seok Oh) 한국농촌지도학회 1997 농촌지도와 개발 Vol.4 No.2
The purpose of this study is to examine France`s regional development policy in terms of rural development since the end of World War II. Following decentralization in 1982, France`s regional and rural development policies have been focused on the interrelated actions of government, local authorities and European authorities. The aim of their works was to extend the dispersal of industrial activities to the reorganization of the rural space. The rural development policies aimed to the agricultural modernization in the 1950s have differed in their goals, methods, and implements. France`s regional and rural development clearly illustrates the key role played by the government despite the decentralization and the challenges of the europeanization leering to a unique market of European nations. This reinforces the fad that the government is instrumental in organizing population distribution and regulating regional decision centers to harmonize both national objectives and local authorities` concerns. The French experience will be helpful as reference in the field of regional and rural development for Korea which has recently begun decentralizing.