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Fe- 및 Co-질산염을 이용한 Fe-50 wt% Co 나노분말의 합성 및 특성 평가
류도형,오승탁,Riu, Doh-Hyung,Oh, Sung-Tag 한국재료학회 2010 한국재료학회지 Vol.20 No.10
The optimum route to fabricate nano-sized Fe-50 wt% Co and hydrogen-reduction behavior of calcined Fe-/Conitrate was investigated. The powder mixture of metal oxides was prepared by solution mixing and calcination of Fe-/Co-nitrate. A DTA-TG and microstructural analysis revealed that the nitrates mixture by the calcination at $300^{\circ}C$ for 2 h was changed to Fe-oxide/$Co_3O_4$ composite powders with an average particle size of 100 nm. The reduction behavior of the calcined powders was analyzed by DTA-TG in a hydrogen atmosphere. The composite powders of Fe-oxide and Co3O4 changed to a Fe-Co phase with an average particle size of 40 nm in the temperature range of $260-420^{\circ}C$. In the TG analysis, a two-step reduction process relating to the presence of Fe3O4 and a CoO phase as the intermediate phase was observed. The hydrogen-reduction kinetics of the Fe-oxide/Co3O4 composite powders was evaluated by the amount of peak shift with heating rates in TG. The activation energies for the reduction, estimated by the slope of the Kissinger plot, were 96 kJ/mol in the peak temperature range of $231-297^{\circ}C$ and 83 kJ/mol of $290-390^{\circ}C$, respectively. The reported activation energy of 70.4-94.4 kJ/mol for the reduction of Fe- and Co-oxides is in reasonable agreement with the measured value in this study.
분자량이 조절된 폴리카보실란으로부터 제조한 SiC Fiber의 특성분석
류도형,김영희,박홍식,김현이,신동근,김형래 한국세라믹학회 2005 한국세라믹학회지 Vol.42 No.8
Polycarbosilane was synthesized by the Kumada rearrangement of polydimethylsilane in the presence of zeolite (ZSM-5) as a catalyst at 350℃. The prepared polycarbosilane had very low molecular weight distribution (Mw=500), so that it was not suitable to fabricate SiC fiber by melt spinning. Further polymerization of PCS was conducted around 400℃ to obtain spinnable polycarbosilane. After polymerization, the polycarbosilanes were isolated by distillation according to the molecular weight distributions. The PCS with a controlled molecular weight distribution was spun into continuous polycarbosilane green fibers. The PCS green fiber was successfully transformed into silicon oxycarbide fiber. The room temperature strength of the SiC fiber was around 1.5-1.8 GPa. The oxidation behavior and the tensile strength after oxidation were also evaluated. SiC 섬유를 제조하기 위하여 제올라이트를 촉매로 사용하여 350℃에서 6시간 반응시켜 폴리카보실란을 제조하였다. 제조된 폴리카보실란은 80%이상의 높은 수율을 보였으나 분자량 500이하의 올리고머로서 SiC 섬유를 제조하기에 적합한 방사성을 갖지는 못했다. 따라서, 400℃의 온도범위에서 재중합을 실시하여 분자량 분포를 스피닝에 적합하도록 조절하였다. 중합된 폴리카보실란을 분별증류하여 분자량별로 분류한 후 분자량에 따른 스피닝특성 및 SiC 섬유화 특성에 대하여 분석하였다. 제조된 SiC 섬유의 상온 인장강도는 1.5-1.8 GPa 이었으며 1200oC 산화시험 후에는 섬유의 표면에 약 350 nm 의 산화층이 생성되었으나 상온강도의 저하는 없었다.
능동형 커먼 모드 전압 감쇄기를 통한 유도 전동기의 고주파 누설전류 억제
류도형(Do-Hyung Lyu),홍순일(Soon-Il Hong),박성준(Sung-Jun Parb),김철우(Cheul-U Kim) 전력전자학회 2000 전력전자학술대회 논문집 Vol.2000 No.11
This paper propose a "Active common-mode voltage damper circuit" that is capable of a suppression of a common-mode voltage produced in the PWM VSI. The four level half-bridge PWM inverter circuit and common-mode transformer are incorporated into the "Active common-mode voltage damper", the resign<br/> method of which is presented. Effect of "Active<br/> common-mode voltage damper" in this paper verifies a propriety and effectiveness in 2.2[kw] induction motor drive using IGBT inverter. Experimental results show that "common-mode voltage damper" makes contributions to reducing a high frequency leakage current and common-mode voltage.
류도형(Ryu Do Hyung) 한국영어어문교육학회 2017 영어어문교육 Vol.23 No.2
When learning English as a foreign language, receptive learning tends to come first, followed by the practical application of productive learning. However, learners of a foreign language should be exposed to both receptive learning and productive learning simultaneously. Productive learning processes should not be used later than receptive learning. This study explores whether productive use of word combinations is more effective than input-based receptive learning. For the experiment, a productive activity using PowerPoint was designed by modifying an existing ‘unscramble’ activity using TED talks material. 82 Korean college students were divided into experimental and control groups, a productive learning group and a receptive learning group. They were taught in 24 class sessions for one semester. These two groups were assessed using three tests (two L1→L2 translation tests in mid-term and final tests, three delayed receptive tests, three output tests), and in open-ended reports from the experimental group students. The results showed that the experimental group outperformed the other group in acquiring word combinations productively. The findings of this study indicate that the students’ productive use of word combinations tends to result in better memorization and the acquisition of productive and receptive vocabulary.
Definitions of Routines Revisited
류도형(Do Hyung Ryu) 한국영어어문교육학회 2014 영어어문교육 Vol.20 No.4
The purpose of this paper is to reconsider current definitions and research directions about routines. In this paper, a problem statement about scholars' research findings about routines is made. It is pointed out that their interpretations of routines lack psychological reality. They believe that routines would be perceived as single language units which are then useful in communication. However, it could be said that people don't use routines because of their usefulness; the use of routines is habitual and natural and they are used regardless of usefulness. Based on a literature review of recent research, how routines are generated and developed will be considered. Also the new concept of routines will be proposed as the relationship between lexical units and chunks. Lastly, in regard to educational implication, it is suggested to teach English with movies to maximize the social features and developmental effects of routines. Movies are a kind of society in which there exist social values. To discover social values in movies is to get close to routines, which leads to language development. Further research should be undertaken in order to learn more about the relationship between language users and the routines they use.
영어 단어결합체(Word Combinations)와 청킹화(Chunking): 블록(Block)개념의 적용
류도형 ( Ryu Do Hyung ) 대한언어학회 2018 언어학 Vol.26 No.2
There is agreement that many word combinations are multiword units stored in long-term memory and retrieved as chunks. There is also increasing evidence that these formulaic language units are integral to first and second language acquisition. This is based on the view of chunking in the cognitive process, which can be utilized to overcome the limitations of working memory and increase its capacity. This study suggests that the chunking process should be the core basis of the learning and teaching of English in classrooms. The present study describes the -chunking process, word combinations, and the block concept of computer languages, based on block-based coding. A block puzzle activity was developed to use chunking with word combinations, an approach applied from the concept of block coding. The purpose of this study is to investigate the possibility and effectiveness of facilitating memorization of word combinations by a block puzzle activity based on the chunking process. The experiment results indicate that students recalled expressions of word combinations better. The findings have implications for EFL teaching and activity design purposes.