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-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.

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.

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 $CO_2$.

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.

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.

로마제정기 그리스 세계의 파이데이아 - 제 2 소피스트론 비판을 중심으로 -

김경현 ( Kim Kyung-hyun ) 한국서양고대역사문화학회 ( 구 한국서양고대사학회 ) 2015 서양고대사연구 Vol.40 No.-

이 글은 로마 지배하의 그리스 세계, 즉 서기 2~3세기의 발칸 본토와 소아시아의 파이데이아 (교육과 문화)를 논쟁적인 방식으로 탐구한다. 논쟁의 대상은, 1969년 바워샄이 가설로 제기한 뒤, 최근까지 일군의 학자들이 보완적 연구를 통해 유력해진 이른 바 제 2 소피스트론이다. 그들에 의하면, 로마 지배 하 그리스 세계에서는 서기 2~3세기 동안 일종의 문예부흥이 일어났으며, 그 현상의 핵심은 두 가지였다. 첫째, 고전주의, 즉 고전기 아테나이 방언으로 회귀하는 언어적 순수주의(purism)와 헬레니즘 시대 이전, 즉 그리스의 영광스런 과거를 담론의 준거로 삼는 ‘의고주의’(archaism)를 문화적 코드로 공유하는 것, 둘째, 그 코드를 통해 당대 그리스 식자층이 안과 밖의 두 타자-그리스 비식자층(하층민)과 지배자 로마-에 대해 정체성을 확립하는 것. 서기 2~3세기 동안 그리스 세계에서 생산된 많은 문헌이 그 코드로 재해석되고 있지만, 그 명백한 출발점은 바워샄이 처음 그 가치를 주목한 서기 3세기의 수사학자 필로스트라투스가 쓴 『소피스트들의 전기』였다. 이 글은 제 2 소피스트론에 대해 다음과 같은 대안적 설명을 제시한다. 첫째, 필로스트라투스의 『소피스트들의 전기』는 서기 2~3세기 그리스 세계의 소피스트들에 대한 체계적이고 포괄적인 정보를 제공하지 않는다. 아울러 제 2 소피스트론이 주장하는 언어적 순수주의와 소재적 의고주의는 필로스트라투스의 전기와 큰 거리가 있다. 둘째, 서기 2~3세기 그리스 세계의 문화지형은 제 2 소피스트론이 내세우는 것처럼 ‘아테나이류’가 풍미한 것이 아니라, 한층 복합적인 것이었다. 로마지배 하 그리스 세계에서는, 헬레니즘 시대를 풍미한-그래서 공화정 말에 로마에까지 파급된-수사학의 경향 (로마인은 이를 가리켜 아시아류라 불렀다)과 기원전 1세기부터 그 대안으로 제시된, 고전기 아테나이를 모델로 삼는 신조류 외에, 웅변술보다 철학을 교육의 중심으로 삼아야 한다는 교육론 등이 공존하고 있었다. 서기 2~3세기 그리스 세계의 소피스트들은 고전문화의 부흥이라는 협소한 시각이 아니라, 이처럼 복잡한 지형 속에서 더 적절하게 이해될 수 있다. This paper attempts to understand what the Greek paideia (education and culture) was like in the eastern Roman provinces during the 2nd and 3rd centuries. It does this in a very polemical way, raising questions and opposing assumptions against the currently prevalent theory of the ‘Second Sophistic’, one that has grown into a huge academic ‘industry’ since its first proposition by G. Bowersock in 1969. According to the theory, there occurred a sort of ‘renaissance’ in the areas at issue, of which the cardinal aspects were two: ⑴ a classicism that consists of two interwoven trends, namely linguistic ‘purism’ with the Attic of the classical age (5th to 4th centuries B.C.) as the uppermost standard as well as the archaism of confining the material of discourses only to the glorious past (before the Hellenistic age); ⑵ the classicism constituted a cultural code among the Greek elite of identifying themselves in opposition to the two ‘others’, that is the lower classes lacking paideia within Greek society, and the Romans domineering over them from without. And the most indispensible evidence for this theory is Lives of Sophists written by Philostratus, a 3rd century Greek sophist, though Greek literature of the period concerned has been abundantly reinterpreted in terms of the theory. Though P. Brunt raised a dissenting voice two decades ago in view of the alarmingly gathering influence of the theory, he has remained so far ‘a lonely far cry in the wilderness’. The author of this paper, having judged him to be on the right track in principle, attempts here to reinforce his criticism with different arguments. Firstly, Philostratus’ biography does not corroborate the basic assumption of the 'Second Sophistic’ theory well. Based upon the meticulous analysis of the biographical data (birth, education and career) of about 40 odd persons recorded in the Lives, the author came to doubt its value as a reliable source upon which to base a wholesome picture of the leading sophists during the period at issue. On the contrary he gets an uneasy scent of sectarianism in the relationship among them, where Herodes Atticus of Athens and his teacher Polemo of Smyrna loom large as key figures, while the biographer himself poses as belonging to the last generation. Secondly, nowhere in the biography are the alleged trends of linguistic and rhetorical revival of classic Atticism manifest. The truth about it is that the classicism is a modern artifice conjured up from the bits and pieces strewn about in all sorts of literature from the period. In the final chapter, the author suggests an alternative picture, and it is a far more complex one compared to the simple, Atticism-centered paideia that the ‘Second Sophistic’ theory assumes. Two sorts of evidence are examined: ⑴ essays on paideia by contemporary Greek writers such as Dionysius of Halicarnassus and Plutarch; ⑵ debate on rhetorical styles among the contemporary Latin orators and writers, between so-called Asianism and Atticism. As the author finds out so far, ⑵ was a forming factor as well as a mirror effect of the contemporary topography of the Greek world of paideia. At least three different rivalling types of education co-existed in the period: the older rhetorical style, called Asianism among the Romans, a more recently emerging one self-styled as Atticism as well as the invariable exhortation of some writers such as Plutarch that philosophy rather than rhetoric should take the primacy in the upbringing of children (paides). Greek paideia during the 2nd and 3rd centuries under the Roman empire may be better understood against this complex picture than in the context of the simplified one of the ‘Second Sophistic’.

연구논문 : 빔 블랭크 연속주조시 공기틈 형성에 의한 열전달과 응고층 변형거동의 연결해석

김경현(Kyung Hyun Kim),한흥남(Heung Nam Han),여태정(Tae Jung Yeo),이용기(Yong Gi Lee),오규환(Kyu Hwan Oh),이동녕(Dong Nyung Lee) 대한금속재료학회(구 대한금속학회) 1995 금속제련 학술회의 Vol.- No.-

서양고대세계의 개인숭배

김경현(Kim Kyung-hyun) 한국서양고대역사문화학회 2010 서양고대사연구 Vol.26 No.-

This paper aims to survey the varieties of personality cult in the ancient western world. Three major historical periods are dealt with: the archaic and classical ages of Greek poleis, the Hellenistic age, and the Republican and Imperial ages of Roman history. In the course of the three periods two discrete types of personality cult loom large: hero??cult and ruler??cult. And the related phenomenon of divine kingship, particularly exemplified in ancient Egypt and Mosopotamia, are juxtaposed as to throw them into relief first of all. but also in consideration of the possibility of its influence upon the ruler??cults that appeared in the periods under discussion. In the final analysis, it is revealed that the two forms of cult were exclusive to each other when they became predominant in a particular period of history. Hero??cult was the typical form of personality cult in the societies of relatively moderate size like Greek poleis, and it played the role of a monument embodying public values and aspiration of entire community. In contrast, ruler??cult (including emperor worship) was prevalent in territorial kingdoms or imperial powers where the appearance of despotic sovereign was by and large inevitable. There, subject communities tended to organize by themselves the ruler??cult as a token of gratitude and/or allegiance to the ruler, and it was very rare that ruler should attempt to deify himself and/or impose the worship of himself on an official base. And ancient Egypt remained always the exception where there had developed the theology of solar diety incarnated as paraoh, and it happened that when it was subjugated by the Macedonians and Romans, the foreign rulers simply stepped into the native predecessors. And the author suggests further that the final results of analysis on personality cults in the ancient world are approximate to the theorems the Italian political scientist E. Gentile has deduced from the data the contemporary totalitarian as well as democratic states provide in relation with the same subject. Namely, two ways of ‘sanctifications of politics’ (‘political religion’ and ‘civic religion’) correspond generally to hero??cult and ruler??cult in the ancient western societies. This comparison awakens us to the fact that personality cult is timeless phenomenon of the humanity and that the cult is the religious translation of politico-social relations.