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.

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.

Al-10%Si-0.3%Mg 주조재의 보수용접에 따른 내구특성 연구

김경현,이정무 ( Kyung Hyun Kim,Jung Moo Lee ) 한국주조공학회 1994 한국주조공학회지 Vol.14 No.6

N/A The effects of weld repair on the durability in Al-10%Si-0.3%Mg castings were evaluated. The strength and fracture toughness in fusion zone were higher than those in the base metal by rapid cooling of fusion zone after welding. There were no significant differences between fatigue properties in castings and weld repaired specimen as the results of low cycle fatigue and rotating bending fatigue test. Therefore it was concluded that weld repairing did not have any significant effect on the mechanical properties of castings.

MBE로 성장된 Al_0.25Ga_0.75As/In_0.2Ga_0.8As pHEMT 에피구조의 RTA에 따른 전도 특성

김경현,홍성의,백문철,조경익,최상식,양전욱,심규환,Kim, Kyung-Hyun,Hong, Sung-Ui,Paek, Moon-Cheol,Cho, Kyung-Ik,Choi, Sang-Sik,Yang, Jeon-Wook,Shim, Kyu-Hwan 한국전기전자재료학회 2006 전기전자재료학회논문지 Vol.19 No.7

We have investigated $Al_{0.25}Ga_{0.75}As/In_{0.2}Ga_{0.8}As$ structures for pseudomorphic high electron mobility transistor(pHEMT), which were grown by molecular beam epitaxy(MBE) and consequently annealed by rapid thermal anneal(RTA), using Hall measurement, photoluminescence, and transmission electron microscopy (TEM). According to intensity and full-width at half maximum maintained stable at the same energy level, the quantized energy level in $Al_{0.25}Ga_{0.75}As/In_{0.2}Ga_{0.8}As$ quantum wells was independent of the RTA conditions. However, the Hall mobility was decreased from $6,326cm^2/V.s\;to\;2,790cm^2/V.s\;and\;2,078cm^2/V.s$ after heat treatment respectively at $500^{\circ}C\;and\;600^{\circ}C$. The heat treatment which is indispensable during the fabrication procedure would cause catastrophic degradation in electrical transport properties. TEM observation revealed atomically non-uniform interfaces, but no dislocations were generated or propagated. From theoretical consideration about the mobility changes owing to inter-diffusion, the degraded mobility could be directly correlated to the interface scattering as long as samples were annealed below $600^{\circ}C$ lot 1 min.

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 $CO_2$.

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.

Inhibitory Effects of Chimeric Decoy Oligodeoxynucleotide in the Regulation of Transcription Factors NF-κB and Sp1 in an Animal Model of Liver Cirrhosis

Kyung-Hyun Kim(김경현),Ji-Hyun Park(박지현),Soo-Jung Kim(김수정),Woo-Ram Lee(이우람),Young-Chae Chang(장영채),Hyun-Chul Kim(김현철),Kwan-Kyu Park(박관규) 한국생명과학회 2009 생명과학회지 Vol.19 No.10

간섬유화는 지속적인 간세포 손상에 대한 수복현상으로 일어나며, 급성 염증반응과 같은 손상이 주어진 후에는 간세포의 괴사 및 세포외기질의 축적이 일어나게 된다. 간섬유화에 대한 새로운 치료방법을 모색하기 위하여 본 연구에서는 간섬유화 과정에서 염증 반응과 관련된 NF-κB와 세포외기질의 축적과 관련된 Sp1전사인자를 동시에 조절하여 간섬유화 억제효과를 관찰하고자 하였다. 전사인자인 Sp1과 NF-κB를 동시에 억제하기 위하여 한 분자 내에 Sp1과 NF-κB의 전사인자와 결합하는 부위를 가지는 Chimeric (Chi) decoy oligodeoxynucleotide (ODN)을 제작하였다. Chi decoy ODN은 활성화된 간성상세포에서 간섬유화 와 관련된 유전자 발현을 억제시켰으며, 섬유화 동물모델에서도 간 조직의 염증 반응 및 섬유화 관련 인자의 발현을 현저히 억제시켰다. 따라서 Chi decoy ODN은 간섬유화 및 활성화된 간성상세포의 활성을 억제할 수 있는 유전자 치료제로 고려될 수 있을 것으로 사료된다. Liver fibrosis is a process of healing and scarring in response to chronic liver injury. Following injury, an acute inflammation response takes place resulting in moderate cell necrosis and extracellular matrix damage. To develop a novel therapeutic approach in hepatic fibrogenesis, we examined the simultaneous suppression of the transcription factors NF-κB and Sp1, which regulate acute inflammation and continuous deposition of extracellular matrix in liver fibrosis. We employed chimeric decoy oligodeoxynucleotide containing the consensus sequences of both NF-κB and Sp1 binding sites, to suppress these transcription factors simultaneously. Treatment of chimeric decoy oligodeoxynucleotide reduced the activity of hepatic stellate cells in vitro, and decreased the expression of fibrotic and proinflammatory gene responses in a mouse model of liver fibrosis. These results suggest that chimeric decoy oligodeoxynucleotide strategy can be a potential therapeutic application to prevent liver fibrosis.

로봇활용수업이 학생의 학습몰입 향상에 미치는 효과

김경현 ( Kyung Hyun Kim ) 한국컴퓨터교육학회 2011 컴퓨터교육학회 논문지 Vol.14 No.2

본 연구는 로봇활용수업이 학생의 학습몰입에 향상에 미치는 효과를 살펴보는 것이다. 본 연구의 결과, 로봇활용수업을 실시한 후의 학습몰입도 점수는 실시 전에 비해 유의미하게 향상되었으며, 학습몰입도 9개 하위요인 모두 유의미하게 향상된 것으로 나타났다. 성별에 따른 학습몰입도 점수 역시 남학생과 여학생 간에 유의미한 차이가 나타나지 않아 로봇활용수업은 학습자의 성별에 관계없이 학생의 학습몰입을 향상시키는 것으로 나타났다. 과목별 차이를 검증한 결과, 7개 과목 중에서 국어, 과학, 미술 과목에서 학생의 학습몰입을 유의미하게 향상시키는 것으로 드러났다. 이상의 결과는 첫째, 로봇활용수업이 실제적인 과제와 실천 중심의 교수·학습 환경을 바탕으로 과제에 대한 주인의식과 내적동기를 북돋우기 용이하다는 점과, 둘째, 로봇매체의 교육적 장점을 극대화하고 그에 따른 적절한 수업환경을 제공한 데서 연유한 것으로 판단된다. This paper is to explore the effects of Robot Based Instruction(RBI) on improving immersion learning. According to our research, we found out that there is significant improvement in learning immersion and there`s 9 sub-factors score after RBI was applied. Also from the result that there is no significant difference between male and female students in learning immersion score, we can found that RBI can improve the learning immersion of students regardless of the learner`s sex. The result of verification on the learning immersion is difference by subjects showed that there is significant improvement only in korean, science, art subject among 7 subjects. The above-mentioned results are based on as follows two reasons. First, RBI is efficient to improve students` internal motivation and ownership about tasks, and that is related to environment of learning and instruction focused on authentic task and practice. Second, educational advantages of robot media was reflected appropriately in RBI, also appropriate instructional environment for RBI was supported.

제정 초기(1~2세기) 로마 상류층의 혼인 및 혼외 관계: 실제와 담론

김경현 ( Kyung Hyun Kim ) 한국서양사학회 2000 西洋史論 Vol.65 No.1