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초전도체 박막의 표면저항 측정용 유전체 공진기에 대한 Geometrical factor의 비교 : 전자기장 해석 대 시뮬레이션
양우일,정호상,김명수,조남순,주기남,이상영,Yang, Woo-Il,Jung, Ho-Sang,Kim, Myung-Su,Cho, Man-Soon,Choo, Kee-Nam,Lee, Sang-Young 한국초전도학회 2011 Progress in superconductivity Vol.13 No.2
유전체 공진기법을 이용하여 초전도체 박막의 표면저항을 측정할 경우, 공진기의 $Q_U$로부터 초전도체 박막의 표면저항을 구하기 위해 알아야 하는 G-factor를 시뮬레이션과 전자기장 해석을 이용해서 구한 후 두 값을 비교하였다. 시뮬레이션 과정에서 사용된 mesh 수가 증가할수록 시뮬레이션으로 구한 G-factor의 크기와 전자기장 해석을 통해 얻은 값 간의 차이가 줄어들게 됨을 확인하였다. 공진기에 따라 mesh 수 증가에 따른 G-factor의 정확도 증가가 조금씩 다르게 나타났는데, 이는 공진기와 유전체의 크기에 따라 simulation program이 계산하는 개당 mesh의 크기가 각기 다르기 때문으로 여겨진다. 19.6 GHz의 공진주파수를 지닌 사파이어 공진기의 경우 시뮬레이션과 전자기장 해석을 통해 구한 G-factor의 차이를 이용하여 표면저항의 불확도 추정치를 온도의 함수로 구했으며 $Q_U$를 2 % 이내의 상대 불확도로 측정할 경우 G-factor의 불확도 변화에 따른 표면저항의 상대 불확도 변화를 확인하였다. 본 연구 결과는 전자기장 해석이 매우 어렵거나 불가능한 구조의 유전체 공진기 (예로서 open-ended 평행판 유전체 공진기)의 G-factor를 시뮬레이션을 이용하여 구하여 초전도체 박막의 표면저항을 $Q_U$로부터 측정하고자 할 때 측정 온도 구간에서 허용되는 표면저항의 불확도를 고려하여 G-factor의 시뮬레이션 시 사용되는 mesh 수가 결정되어야 함을 보여준다. In the dielectric resonator method, which has been widely used for measuring the microwave surface resistance of superconductors, accuracies in the geometrical factors (G-factors) affect the uncertainty in the measured surface resistance. We compare the G-factors of short-ended sapphire resonator as obtained by using field analysis with those by using computer simulations: The former is obtained by using the analytic expressions for the electric and the magnetic field components inside the resonator, and the latter by using computer software. The G-factors as obtained by using the latter appear to be closer to those obtained by using the former as the resonator space is divided into larger number of sub-space, i.e., a tighter mesh, with a difference of ~8 % observed for a mesh of 14400 sub-spaces reduced to ~2 % for 114996 sub-spaces. Variations in the relative uncertainty in the surface resistance of typical $YBa_2Cu_3O_{7-\delta}$ superconductor films with those in the G-factors are studied, which provides an upper limit of the relative uncertainty in the G-factors required for realizing the target uncertainty in the surface resistance. These results could be useful in estimating the optimum number of meshes for obtaining the G-factors through computer simulations.
냉간가공한 오스테나이트계 강재의 극저온 특성에 미치는 Ni 및 N의 영향
최진일(J. I. Choe),주기남(K. N. Choo),강영환(Y. W. Kang) 한국표면공학회 2004 한국표면공학회지 Vol.37 No.1
Cryogenic characteristics of austenitic stainless steel based on 304 steel with nickel and nitrogen were investigated at room temperature and -196℃. The alloys were fabricated by vacuum arc furnace and cold working after homogenization treatment. The addition of nickel and nitrogen decreased the stability of δ-ferrite and induced the stability against the formation of martensite to result significantly in enhancing ductility at -196℃. Nitrogen reduced Md temperature, which was beneficial to the tensile strength and elongation at 25℃ and -196℃.
SA508 class 3 서브머지드 아크용접부의 기계적 성질에 미치는 입열량의 영향
서윤석,고진현,김남훈,오세용,주기남,Seo Yun-seok,Koh Jin-Hyun,Kim Nam-Hoon,Oh Se-Yong,Choo Kee-Nam 대한용접접합학회 2004 대한용접·접합학회지 Vol.22 No.5
The present study is to investigate the effect of heat input on the microstructure, tensile properties and toughness of single-pass submerged arc bead-in-groove welds produced on SA508 class 3 steels. The heat input was varied in the range of 1.6, 3.2 and 5.0 kJ/mm. The toughness of weld metals was evaluated by using subsize Charpy V-notch specimens in the temperature range of -19$0^{\circ}C$ to 2$0^{\circ}C$. The weld microstructure and fractography were observed by optical and scanning electron microscopies, respectively. With increasing heat inputs, tensile strength and hardness of weld metals were decreased while elongation was increased. The poor notch toughness at 1.6 kJ/mm was attributed to the formation of ferrite with aligned second phase and banitic microstructure with high yield strength while that at 5.0 kJ/mm was due to the presence of grain boundary and polygonal ferrites. The microstructure of the intermediate energy input welds consisted of a high proportion of acicular ferrite with limited polygonal ferrites, which provide improved notch toughness.
최명환(Choi, M.H.),주기남(Choo, K.N.),조만순(Cho, M.S.),김봉구(Kim, B.G.) 한국소음진동공학회 2005 한국소음진동공학회 논문집 Vol.15 No.12
The bottom structure of an instrumented capsule is a part which is joined at the receptacle of the flow tube in the reactor in-core. A geometrical change of the bottom structure has an effect on the pressure drop and the vibration of the capsule. The out-pile test to evaluate the structural integrity of the material capsule called 04M-17U was performed by using a single channel and a half core test loop. From the pressure drop test, the optimized diameter of the cone shape's bottom structure which satisfies HANARO's flow requirement (19.6 kg/s) is 71 mm. The maximum displacement of the capsule measured at the half core test loop is lower than 1.0 mm. From the analysis results, it is found that the test hole will not be interfered with near the flow tubes because its displacement due to the cooling water is very small at 0.072 mm. The fundamental frequency of the capsule under water is 9.64 Hz. It is expected that the resonance between the capsule and the fluid flow due to the cooling water in HANARO's in-core will not occur. Also, the new bottom structure of a solid cone shape with 71 mm in diameter will be applicable to the material and special capsules in the future.
Ag계/Ni계 용가재를 이용한 STS 304L과 Inconel 600의 브레이징에 관한 연구
심규택(Kyue-Taek Shim),주기남(Kee-Nam Choo),조만순(Man-Soon Cho),박승재(Sung-Jae Park),김재훈(Jae-Hoon Kim) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
This study was carried out to develop the joining technology by nicro-brazing of STS 304L tube and the thermocouple of Inconel 600 sheath, which is used as an instrument for high-temperature irradiation in HANARO. BAg-1 and BNi-7 were used as filler materials, and AMCO 446 was selected as flux in the brazing. For evaluation of solidity of the joining, the tensile strength and the micro hardness were measured. Both the brazings of STS 304L and Inconel using BAg-1 and BNi-7 filler materials were joined firmly. Some spot flaws were found at the joining places using BNi-7 filler material, however, they turned out not to affect the strength of the materials.
중성자 조사한 4H-SiC MOSFET의 열처리에 의한 전기적 특성 변화
이태섭,안재인,김소망,박성준,조슬기,주기남,조만순,구상모,Lee, Taeseop,An, Jae-In,Kim, So-Mang,Park, Sung-Joon,Cho, Seulki,Choo, Kee-Nam,Cho, Man-Soon,Koo, Sang-Mo 한국전기전자재료학회 2018 전기전자재료학회논문지 Vol.31 No.4
In this work, we have investigated the effect of a 30-min thermal anneal at $550^{\circ}C$ on the electrical characteristics of neutron-irradiated 4H-SiC MOSFETs. Thermal annealing can recover the on/off characteristics of neutron-irradiated 4H-SiC MOSFETs. After thermal annealing, the interface-trap density decreased and the effective mobility increased in terms of the on-characteristics. This finding could be due to the improvement of the interfacial state from thermal annealing and the reduction in Coulomb scattering due to the reduction in interface traps. Additionally, in terms of the off-characteristics, the thermal annealing resulted in the recovery of the breakdown voltage and leakage current. After the thermal annealing, the number of positive trapped charges at the MOSFET interface was decreased.