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저온 분자선에피탁시 방법으로 성장시킨 GaMnAs의 planar Hall 효과
김경현,박종훈,김병두,김도진,김효진,임영언,김창수,Kim, Gyeong-Hyeon,Park, Jong-Hun,Kim, Byeong-Du,Kim, Do-Jin,Kim, Hyo-Jin,Im, Yeong-Eon,Kim, Chang-Su 한국재료학회 2002 한국재료학회지 Vol.12 No.3
Planar Hall effect of ferromagnetic GaMnAs thin films was investigated for the first time. The films were grown in an optimized growth condition via molecular beam epitaxy at low temperatures. For the optimization of the growth conditions, we used reflection high-energy electron diffraction, electrical conductivity, double crystal x-ray diffraction, and superconducting quantum interference device measurements techniques. We observed that the difference between the longitudinal resistance and the transverse resistance matches the planar Hall resistance. The ratio of the planar Hall resistance at saturation magnetic field to that at zero reached above 500%.
암모니아를 이용하여 분자선에피탁시 방법으로 AIN/Si 기판에 성장시킨 GaN의 구조적,광학적 특성
김경현,홍성의,강석준,이상현,김창수,김도진,한기평,백문철,Kim, Gyeong-Hyeon,Hong, Seong-Ui,Gang, Seok-Jun,Lee, Sang-Hyeon,Kim, Chang-Su,Kim, Do-Jin,Han, Gi-Pyeong,Baek, Mun-Cheol 한국재료학회 2002 한국재료학회지 Vol.12 No.5
A new approach of using double buffer layers of AlN and GaN for growth of GaN films on Si has been undertaken via molecular beam epitaxy using ammonia. The first buffers layer of AlN was grown using $N_2$plasma and the second of GaN was grown using ammonia. The surface roughness of the grown films was investigated by atomic force microscope and was compared with the normally grown films on sapphire. Double crystal x-ray rocking curve and low temperature photoluminescence techniques were employed for structural and optical properties examination. Donor bound exciton peak at 3.481 eV with full width half maximum of 41 meV was observed at 13K.
Al-Cu-Mu 주조합금의 피로성질에 미치는 Sn 첨가의 영향
김경현,김정대,김인배,Kim, Kyung-Hyun,Kim, Jeung-Dae,Kim, In-Bae 한국재료학회 2002 한국재료학회지 Vol.12 No.4
Effect of Sn addition on the fatigue properties of Al-Cu-Mn cast alloy was investigated by low and high cycle fatigue tests. Fatigue life showed the maximum value of 5450cycles in the Al-Cu-Mn alloy containing 0.10%Sn, but decreased rapidly beyond 0.20% of Sn additions. It was found that the fatigue strength was 132MPa and fatigue ratio was 0.31 in the alloy containing 0.10%Sn. Metallographic observation revealed that the fatigue crack initiated at the surface and propagated along the grain boundary. This propagation path was attributed to the presence of PFZ along the grain boundary. The tensile strength increased from 330MPa in 7he Sn-free Al-Cu-Mn cast alloy to 429MPa in the alloy containing 0.10%Sn. But above 0.20%Sn additions, tensile strength was decreased by the segregation of Sn.
Al-Cu-Mn 주조합금의 피로성질에 미치는 Cd 첨가의 영향
김경현,이병훈,김인배,Kim, Gyeong-Hyeon,Lee, Byeong-Hun,Kim, In-Bae 한국재료학회 2001 한국재료학회지 Vol.11 No.4
Al-Cu-Mn 주조합금의 피로성질에 미치는 Cd 첨가의 영향을 저주기 및 고주기 피로시험을 통하여 조사하였다. Cd 첨가량이 증가함에 따라 피로수명이 증가하였으며, 인장강도도 증가하였다. 고주기 피로시험결과 피로강도는 115MPa이었으며 피로비는 0.31이었다. 피로시험 결과 균열이 표면에서 발생하여 입계를 따라 전파되었는데 이러한 입계파괴는 입계를 따라 존재하는 무석출대의 영향으로 생각된다. 인장강도값은 Cd이 첨가되지 않았을 경우 330MPa이었으나 0.15%의 Cd이 첨가됨으로써 401MPa 까지 증가되었다. Effect of Cd addition on the fatigue properties of Al-Cu-Mn cast alloy was investigated by low and high cycle fatigue tests. With increasing Cd content, fatigue life and tensile strength were increased. It was found that the fatigue strength was 115MPa and the fatigue ratio was 0.31. Metallographic observation revealed that the fatigue crack initiated at the surface and propagated along the grain boundary. This propagation path was attributed to the presence of PFZ along the grain boundary. The tensile strength increased from 330MPa in the Cd-free Al-Cu- Mn cast alloy to 401MPa in the 0.15%Cd-containing alloy.
Al-10%Si-0.3%Mg 합금에서 Sr 첨가가 미세조직 및 기계적 성질에 미치는 영향
김경현,이정무,정신검 ( Kyung Hyun Kim,Jung Moo Lee,Shin Kum Jung ) 한국주조공학회 1993 한국주조공학회지 Vol.13 No.1
N/A The effects of strontium content as modifier on microstructure and mechanical properties were studied in Al-10%Si-0.3%Mg cast alloys. There were not big differences in the form of eutectic Si particle and its morphology depending on adding amount of strontium, but the alloy modified by 0.012%Sr had shown the higher values than the alloy modified 0.038%Sr in strength, elongation and impact value.
한센 환자의 마비성 눈꺼풀겉말림에 시행한 강화된 가쪽 눈꺼풀판띠고정술의 효과
김경현,정인영,서성욱,Kyeong Hyeon Kim,In Young Chung,Seong Wook Seo 대한안과학회 2009 대한안과학회지 Vol.50 No.4
Purpose: To analyze the effect of the augmented lateral tarsal strip for the correction of the paralytic ectropion in leprosy patients. Methods: Ten leprosy patients (16 eyelids) with exposed keratitis and lagophthalmos from paralytic ectropion underwent surgery of the augmented lateral tarsal strip. Preoperative and postoperative vertical palpebral aperture, marginal reflex distance, lagophthalmos, and anterior segment findings were recorded at 3 and 6 months after surgery. Postoperative symptomatic and functional improvements were assessed at 6 months after surgery. Results: There was a significant reduction between preoperative and postoperative measurements for vertical palpebral aperture (3.1±0.4 mm), lower marginal reflex distance (2.1±1.0 mm), and lagophthalmos (2.0±1.2 mm). Eye irritation symptoms and lid functions were improved in all patients. In a survey, the symptomatic, functional satisfaction was achieved in 90% of patients. Conclusions: The augmented lateral tarsal strip is a sufficiently effective surgical procedure to be considered in the treatment of paralytic ectropion in leprosy patients. J Korean Ophthalmol Soc 2009;50(4):497-504
반성적 성찰활동에 기반한 사이버 학습상담이 초등학생의 학습동기 및 학습습관에 미치는 효과
김경현,도은경,Kim, Kyung-Hyun,Do, En-Kyeong 한국정보교육학회 2009 정보교육학회논문지 Vol.13 No.2
This study examines the effects of cyber learning counseling based on self-reflective activities on learning motivation and habits of elementary students. From the above processes, following findings could be drawn: First, the cyber learning counseling based on self-reflective activities turned out to have positive effects on promoting the motivation of elementary students for learning. Positive impacts were found in 4 sub-factors of motivation for learning, that are, attention, relevance, conviction and satisfaction that were enhanced after cyber counseling for learning was given. Second, the cyber learning counseling based on self-reflective activities were found to have positive effects on changing elementary students' habit of learning. After cyber learning counseling was carried out, Positive impacts were visible in sub-factors of learning habit which are the behavioral indexes of applying learning skill and student-initiated behavior.
웹 기반 문제중심학습 프로그램 개발과 학업성취에 미치는 효과 분석
김경현,정미경,최운필,Kim, Kyung-Hyun,Jung, Mi-Kyong,Choi, Un-Phil 한국정보교육학회 2005 정보교육학회논문지 Vol.9 No.1
Establishing problem-based leaning(PBL) that is one type of constitutional learning models is meaningful not only for finding the diversity of WBI types but also for being the specific example of constitutional usage of WBI. This paper shows the development of web-based and problem-based learning program for 6th grade students of elementary school and finds its effect on their studies achievement. There were two classes of traditional lessons and one class of web-based and problem-based lessons. It performed a test with the classes for science lesson. It was found that web-based and problem-based learning is more effective on the improvement of studies achievement. There was meaningful difference in studies achievement according to ICT utilization ability. Web-based and problem-based learning statistically had a meaningful effect on the improvement of ICT utilization ability.
아르곤/이산화탄소 혼합가스의 유도 결합 플라즈마를 이용한 이산화탄소 분해 연구
김경현,김관용,이효창,정진욱,Kim, Kyung-Hyun,Kim, Kwan-Yong,Lee, Hyo-Chang,Chung, Chin-Wook 한국전력공사 2015 KEPCO Journal on electric power and energy Vol.1 No.1
유도 결합 플라즈마를 활용하여 $Ar/CO_2$ 혼합가스에서 이산화탄소를 분해하는 연구이다. 고밀도 플라즈마를 발생시키기 위해 Ar 가스를 첨가하였고 이산화탄소 분해율을 측정하기 위해 광학적 광량 측정법을 사용 하였다. 유도 결합 플라즈마를 방전시키고 인가 전력, 압력, 혼합가스 비율을 변경하가며 단일 랭뮤어 프로브를 이용해 플라즈마 변수를 얻고 방출 분광기로 얻은 빛의 스펙트럼을 이용하여 분해율을 측정하였다. 측정된 플라즈마 변수로부터 $CO_2$ 유도 결합 플라즈마의 소스 특성을 확인했고 $CO_2$ 분해 메커니즘은 플라즈마 변수에 직접적인 영향을 받기 때문에 그 상관관계를 분석하였다. Decomposition of carbon dioxide is studied using $Ar/CO_2$ mixture inductively coupled plasmas (ICP). Argon gas was added to generate plasma which has high electron density. To measure decomposition rate of $CO_2$, optical emission actinometry is used. Changing input power, pressure and mixture ratio, the plasma parameters and the spectrum intensity were measured using single Langmuir probe and spectroscope. The source characteristic of Carbon dioxide ICP observed from the obtained plasma parameters. The decomposition rate is evolved depending on the reaction and discharge mode. This result is analyzed with both the measurement of the plasma parameters and the dissociation mechanism of $CO_2$.