볼엔드밀 가공시 이송변화에 따른 가공형상 특성

왕덕현,김원일,이윤경,임채열,우정윤,박창수 한국공작기계학회 2002 한국생산제조학회지 Vol.11 No.2

Due to the development of the CNC machine tool and CAM software, sculptured surface machining can be broadly used in die and mold industries and ball end milling process is often used for the sculptured surface machining. It is found out how feedrate affects the precision of the machining and also tried to study the most suitable feedrate in specific cutting condition. Two eddy current sensors were used for measuring tool deflections of X, Y axis, dynamometer for cutting force and roundness tester for roundness. It was found that the tool deflection is getting better as tool path is going to farther from the center of convex surface. The reason is that the cutting force is increased as the tool approaches to the center. Examining the roundness, cutting force and tool deflection characteristics, it was found that the most suitable feedrate is 90mm/min in convex surface and 120mm/min in concave surface.

AC8A-T6 알루미늄 合金材의 切削加工 特性에 關한 硏究

최현민,김경우,김우순,김용환,김동현,채왕석 한국공작기계학회 2002 한국공작기계학회 추계학술대회논문집 Vol.2002 No.-

In this study, examined the cutting characteristics of alumuminum alloy AC8A-T6 that is used to present car piston materials. And in been holding materials machining empirically escape as result that experiment comparison changing the cutting speed and feed on various condition to choose efficient machining condition. The following results can be summarized from this research. 1.As the cutting speed decreased, principal cutting force and thrust cutting force is increased, and reason that cutting force interacts greatly in the low cutting speed is thought by result by BUE's stabilization. 2.The feed speed and cutting speed increase, friction factor is decrescent and the cause appeared the thrust cutting force is fallen than cutting force relatively because chip flow according to increase of the feed rate is constraint. 3.Though specific cutting resistance grows cutting area and the feed rate are few, the cause was expose that shear angle decreases by rake face of tool gets into negative angle remarkably as wear of a cutting tool or defect part of workpiece is cut. 4.Cutting speed do greatly depth of cut is slow, surface roughness examined closely through an experiment that becomes bad, and know that it can get good surface that process cutting speed because do feed rate by 0.1㎜/rev low more than 250m/min to get good surface roughness can.

내열강의 내부품질에 따른 절삭가공 특성에 관한 연구

김동현,채왕석 韓國工作機械學會 2000 한국생산제조학회지 Vol.9 No.1

This paper is experimental study of machining characteristics about martensitic heat resisting steel STR11. Machining characteristics are different according to internal quality(chemical compositions, microscopic structure and nonetallic inclusion), mechanicla properties (tensile strength value, impact value and hardness) and dynamic cutting force Following are the results; 1. In analyzing internal quality, test materials have typical martensite structure and a minute needle-shaped structure. 2. Tensile strength and reduction of area and hardness are larger. But, valucs of elongation and impact values are smaller. Fracture surface of tensile specimen is duchile. 3. Cutting force is decreasing with cutting speed increasing. 4. Cutting force is increasing with feed speed increasing.

공구형상이 칩유동에 미치는 영향에 관한 연구

김경우,김우순,윤주식,채왕석,김동현 한국공작기계학회 2000 한국공작기계학회 추계학술대회논문집 Vol.2000 No.-

A new methodology is presented to evaluate material properties at high strain rates and high temperatures based on orthogonal metal cutting experiments and FEM simulations. Average strain rate and average temperature found in the deformation zone are computed and flow stress data at these conditions are modified until cutting forces calculated in simulations match those determined in experiments. Material properties obtained from this method were verified by additional metal cutting simulations. Derivation from cutting forces measured in experiments was less than 10%. The feasibility of tool design using FEM simulations is also demonstrated.

자동차용 피스톤소재의 금속적 특징 및 선삭 가공 특성

채왕석(Wang-Seok Chae),김경우(Kyong-Woo Kim),최현민(Hyun-Min Choi),김동현(Dong-Hyun Kim) 한국생산제조학회 2001 한국공작기계학회 추계학술대회논문집 Vol.2001 No.-

승용차용 CYLINDER ROD 소재의 밀링 절삭 특성 연구

蔡王錫(CHAE WANG SUCK),金經祐(KIM KYONG WOO),金東炫(KIM DONG HYUN) 한국생산제조학회 1996 한국공작기계학회 춘계학술대회논문집 Vol.1996 No.-

스프링과 방진고무가 융합된 제진장치의 하중-변위 관계

문주현 ( Ju-hyun Mun ),임채림 ( Chae-rim Im ),왕혜린 ( Hye-rin Wang ),양근혁 ( Keun-hyeok Yang ) 한국구조물진단유지관리공학회 2021 한국구조물진단유지관리공학회 논문집 Vol.25 No.6

이 연구의 목적은 천장구조재의 내진성능향상을 위해 개발된 제진장치(seismic dampingㆍisolation unit, 이하 SDI 유닛)의 압축 및 인장하중상태의 하중-변위 관계를 평가하고 축하중 설계를 위한 기초자료를 구축하는데에 있다. 주요변수는 스프링의 유무, 방진고무의 적층수와 스프링과 방진고무의 결합을 위해 설치된 볼트의 프리스트레스력의 크기 그리고 재하방법이다. 실험결과 볼트의 프리스트레스력의 크기가 클수록, 반복하중 보다는 단조하중에서, 그리고 스프링이 있는 SDI 유닛은 하중-변위관계에서 탄성한계점까지의 강성증가 뿐만 아니라 최대 하중 이후의 연성거동에 유리하였다. 결과적으로 에너지 소산능력은 스프링이 있으면서, 3층의 방진고무 및 볼트 항복강도의 10%의 프리스트레스력을 갖는 SDI 유닛에서 가장 높았다. 개발된 SDI 유닛의 인장내력에 대해 JIS B 2704-1(2018) 및 KDS 31 00(2019)의 기준은 단조상태에서는 안전측에서 평가된 반면, 반복하중상태에서 약 10% 높게 평가되었다. The objective of this study is to establish the fundamental design data for axial load-displacement relationship under axial monotonic or cyclic responses of seismic damping·isolation (SDI) units developed for ceiling structures. The main parameters include the installation of a spring, the number of rubber layer, prestress stress of bolts for connector between the spring and rubbers, and loading type. Test results showed that SDI units with a spring in the core and higher prestress stress of bolts tended to be higher stiffness at the ascending branch and more ductile behavior at the descending branch. This trends more notable for the specimens under monotonic load rather than cyclic loads. Consequently, the energy dissipation of SDI unit can be optimally designed with the following conditions: installation of a spring within 3-layer rubbers and prestress applied to the bolts at 10% of their yielding strength . When compared with the experimental tension capacity of the developed SDI units, the predictions by JIS B 2704-1 and KDS 31 00 are conservative under monotonic loading but higher by approximately 10% under cyclic loading.

Decreased level and defective function of circulating endothelial progenitor cells in children with moyamoya disease

Kim, Jin Hyun,Jung, Ji-Hye,Phi, Ji Hoon,Kang, Hyun-Seung,Kim, Jeong Eun,Chae, Jong Hee,Kim, Sang-Jeong,Kim, Young-Hoon,Kim, Young Yim,Cho, Byung-Kyu,Wang, Kyu-Chang,Kim, Seung-Ki Wiley Subscription Services, Inc., A Wiley Company 2010 JOURNAL OF NEUROSCIENCE RESEARCH - Vol.88 No.3

<P>Circulating endothelial progenitor cells (EPCs) play an important role in physiological and pathological neovascularization and may be involved in attenuating ischemic diseases. This study aimed to characterize circulating EPCs in moyamoya disease (MMD), one of the most common pediatric cerebrovascular diseases. Twenty-eight children with MMD prior to any surgical treatment and 12 healthy volunteers were recruited. Peripheral blood mononuclear cells (PBMNCs) were isolated and cultured in endothelial cell growth medium. Temporal change of phenotype of cells was analyzed on days 0 and 7. The formation of EPC clusters was evaluated on day 7. The CD34<SUP>+</SUP>, CD133<SUP>+</SUP>, and KDR<SUP>+</SUP> cells, and the number of EPC clusters was significantly reduced in children with MMD. In controls, CD34<SUP>+</SUP> cells were significantly decreased on day 7 compared with day 0, but in MMD they were only slightly decreased. The change in KDR<SUP>+</SUP> cells on day 7 compared with day 0 was the reverse of that for CD34<SUP>+</SUP> cells. Functional assay of EPC demonstrated less tube formation and increased senescent-like phenotype in children with MMD. Analysis of the circulating EPCs of MMD children reveals decreased level and defective function. This study suggests that circulating EPCs may be associated with MMD pathogenesis. © 2009 Wiley-Liss, Inc.</P>

텍스트 마이닝을 활용한 한국어 학습자의 핵심 어휘 및 문법 사용 양상 연구

채윤미(Yunmi Chae),길호현(Ho hyun Kil),왕연(Yan Wang) 우리말교육현장학회 2022 우리말교육현장연구 Vol.16 No.2

본 연구는 외국인 한국어 학습자가 생산한 내러티브 텍스트의 언어적 표현에 대한 사용 양상을 한국어 모어 화자의 텍스트와 비교하여 살펴보고, 객관적인 방법으로 그 특징을 밝히고자 하였다. 이를 위해 기존에 이루어졌던 분석 방법과 차별화를 두어 텍스트 마이닝의 언어 네트워크 기법을 활용하였다. 통계학적으로 유의미하다고 판단되는 어휘와 문법적 요소를 추출한 후, 텍스트 구조에 따라 어휘와 시제·상의 사용이 어떻게 다르게 나타나는지 살펴보았다. 두 집단은 대부분 도입부, 사건 전개부, 결말부 구조에 따라 글을 전개하였으며 큰 차이를 보이지 않았다. 구조별 핵심 어휘와 어휘 간 관계성을 살펴본 결과 도입부, 사건전개부, 결말부에서 두 집단은 주제에 따른 내용의 차이를 보였으며 외국인 학습자의 경우 도입부에서 1인칭 대명사를 과도하게 사용하는 특징이 나타났다. 또한 각 구조에 나타난 시제·상의 사용 양상을 살펴본 결과 외국인 학습자는 한국인 모어 화자에 비해 시제와 상, 그리고 양태성을 지닌 문법 요소에 대해서도 다양하게 활용하지 못한다는 점이 확인되었다. 이는 학습자가 초급에서 배운 문법 사용에 익숙해져 있으며 시제와 상과 관련한 습득은 아직 불완전한 것으로 보여 이에 대한 학습이 요구된다는 것을 알 수 있었다. 본 연구는 정성적인 연구 방법을 통해서는 확인하기 어려웠던 언어적 특징을 전산화하여 명시적으로 파악하고 결과를 도출하려고 했다는 점에서 의의가 있다. This study aims to examine the usage patterns of linguistic expressions in narrative texts produced by foreign Korean learners compared with the text of Korean native speakers, and to reveal their characteristics objectively. To this end, the semantic network technique of text mining was used to differentiate it from the existing analysis methods. After extracting the words and grammatical elements considered statistically significant, we examined how the use of word, tense, and aspect differed according to the text structure. Korean native speakers and foreign Korean learners mostly developed their writings according to the structure of the introduction, events, and conclusion, and there was no significant difference. As a result of examining the relationship between key words and words for each structure, the two groups showed differences in content according to the topic in the introduction, events, and conclusion. Foreign learners displayed a characteristic of excessive use of first-person pronouns. In addition, as a result of examining the usage patterns of tenses and expressions in each structure, it was confirmed that foreign learners were unable to utilize the grammatical elements with tenses, aspect, and modalities as variedly as native Korean speakers did. This shows that the learner is accustomed to using grammar learned at the beginner level, and the acquisition related to tense and phase is still incomplete; hence, learning is required. This study is meaningful in that it attempted to computerize and explicitly identify linguistic features that were difficult to confirm through qualitative research methods to derive at results.

Large-scale synthesis of van der Waals 1-dimensional material Mo₆S₃I₆ by using a MoI₂ precursor

Oh, Seungbae,Chae, Sudong,Choi, Kyung Hwan,Kim, Bum Jun,Lee, Sang Hoon,Wang, Cong,Liu, Zhixiang,Jeon, Jiho,Lee, Jae-Hyun,Yu, Hak Ki,Choi, Jae-Young Elsevier 2019 JOURNAL OF ALLOYS AND COMPOUNDS Vol.803 No.-

<P><B>Abstract</B></P> <P>By using a MoI<SUB>2</SUB> precursor, a one-dimensional linear chain material, Mo<SUB>6</SUB>S<SUB>3</SUB>I<SUB>6</SUB>, was synthesized on a centimeter scale. As MoI<SUB>2</SUB> can be used to form Mo<SUB>6</SUB>S<SUB>3</SUB>I<SUB>6</SUB> through a gas-phase reaction, a larger amount of single crystals can be synthesized; moreover, these crystals are significantly longer than those synthesized by using Mo, S, and I powder. The synthesized Mo<SUB>6</SUB>S<SUB>3</SUB>I<SUB>6</SUB> exhibited the characteristics of paramagnetic semiconductors with excellent thermal stability and a low bandgap. Furthermore, Mo<SUB>6</SUB>S<SUB>3</SUB>I<SUB>6</SUB> can be separated into long nanometer-scale chains by a solution dispersion process.</P> <P><B>Highlights</B></P> <P> <UL> <LI> First synthesis of cm scale synthesize of vdW 1D material Mo<SUB>6</SUB>S<SUB>3</SUB>I<SUB>6</SUB>. </LI> <LI> Superior material properties based on high crystallinity. </LI> <LI> Atomic level (nm) dispersion for ideal 1D materials. </LI> </UL> </P>