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Kim, Junghoon,Kwag, Hyon Joo,Yoo, Seung Min,Yoo, Jin Young,Chae, In-Ho,Choi, Dong-Ju,Park, Min-Jae,Vembar, Mani,Chun, Eun Ju Springer-Verlag 2018 EUROPEAN RADIOLOGY Vol.28 No.4
<P>aEuro cent PR in CCTA should be observed carefully, even if it is false positive.</P>
가스터빈용 소재 IN 738LC 합금의 미세조직 열화거동
유정훈,주성욱,신기삼,김의현,정진성,장성호,송기욱,하정수 국립7개대학공동논문집간행위원회 2002 공업기술연구 Vol.2 No.-
IN 738LC, used as gas-turbine for power generation, was heat treated at 750℃, 850℃, 950℃ for 1000, 2000, and 4000 hrs. and the microstructural evolution are examined using optical microscope, XRD, SEM/EDS. For comparison, part of gas turbine used for 18439 hours for power generation was also examined. The results showed γ´, the main strengthening elements in this alloy, was about 300 nm and was about 56% in as-cast samples. The volume fraction of γ´peaked at 2000 hours at 750℃ and then decreased at further or longer heat treatment. The average diameter of the γ´ which was about 200 nm increased to about 1㎛. Carbides were formed at dendrite, cell, or grain boundaries which was ascribed to the segregation caused by solute redistribution during solidification. It was found that the at low temperature, M_6C type carbides formed, whereas carbides of M_23C_6 type formed at higher temperature, or at longer degradation.
고에너지 전자빔 투사를 이용한 표면합금화 재료의 미세조직 연구
유정훈,신기삼,윤재홍,이찬규,허성강,오준철,이성학,어광준 국립7개대학공동논문집간행위원회 2002 공업기술연구 Vol.2 No.-
For determination of the mechanism of microstructural modification by surface alloying technique using high energy electron beam (HEEB), surface alloys of carbon steel with TiC, TiB_2 and VC were fabricated and their microstructures were analyzed using optical microscope, XRD (X-ray diffractometer), and SEM (scanning electron microscope). The surface regions of TiC and VC surface alloy consists of 1) melted, 2) interface, and 3) heat affected regions. In the TiC surface alloy precipitates of large primary and fine eutectic TiC were observed. In TiB_2 surface alloy, neither fine precipitates were present nor the TiB_2 shape was changed from the original particles, which was attributed to the high melting temperature of TiB_2. Among the three surface alloys studied, the melted region hardness of VC surface alloy was the highest.
Junghoon Lee,Hanji Park,Myeonghyun Kim,Han‑Jin Kim,Jin‑yoo Suh,Namhyun Kang 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.1
We investigated the effects of hydrogen and temperature on hydrogen embrittlement (HE) of cold-rolled equimolar CoCrFeMnNihigh-entropy alloy (HEA). The HE exhibited intergranular fracture in this HEA at 298 and 177 K. At 177 K, moretwins formed than at 298 K, and this acted as a hydrogen-diffusion path. During deformation, local stress was concentratedat the triple junction consisting of grain and twin boundaries. Hydrogen diffused predominantly along the boundary andencountered stress-concentration regions. Cracks initiated and propagated predominantly through the grain/twin boundariesby hydrogen diffusion at 298 and 177 K. Therefore, HE occurred at 298 and 177 K. At 77 K, hydrogen was distributedthroughout the specimen as twin formation was more active. The cryogenic temperature of 77 K caused the hydrogen tobecome trapped and thus not diffuse into the stress-concentration region. Thus, there was no significant HE at 77 K.
Yoo, Seunghwan,Song, Ho Young,Lee, Junghoon,Jang, Cheol-Yong,Jeong, Hakgeun The Optical Society 2012 Applied optics Vol.51 No.33
<P>In this article, we introduce a simple fabrication method for SiO(2)-based thin diffractive optical elements (DOEs) that uses the conventional processes widely used in the semiconductor industry. Photolithography and an inductively coupled plasma etching technique are easy and cost-effective methods for fabricating subnanometer-scale and thin DOEs with a refractive index of 1.45, based on SiO(2). After fabricating DOEs, we confirmed the shape of the output light emitted from the laser diode light source and applied to a light-emitting diode (LED) module. The results represent a new approach to mass-produce DOEs and realize a high-brightness LED module.</P>
DNA aptamer release from the DNA–SWNT hybrid by protein recognition
Yoo, Chang-Hyuk,Jung, Seungwon,Bae, Jaehyun,Kim, Gunn,Ihm, Jisoon,Lee, Junghoon The Royal Society of Chemistry 2016 Chemical communications Vol.52 No.13
<P>Here we show the formation of the complex between a DNA aptamer and a single-walled carbon nanotube (SWNT) and its reaction with its target protein. The aptamer, which is specifically bound with thrombin, the target protein in this study, easily wraps and disperses the SWNT by noncovalent pi-pi stacking.</P>
김정훈(Junghoon Kim),이호원(Howon Lee),이장무(Jangmoo Lee),유동호(Dongho Yoo) 한국자동차공학회 2005 한국자동차공학회 춘 추계 학술대회 논문집 Vol.2005 No.5_2
For shimmy vibration analysis, a mathematical theory model has been considered and the dynamic characteristics of full vehicle has not been considered in most researches. In this study, based on the results obtained from the quasi-static analysis of 10 dof suspension theoretical model, multi-body dynamic analysis considering shimmy vibration of the steering wheel is performed and compared with the results of MSC/ADAMS. Also, modal analysis results using front suspension system of 32 dof theoretical model agree with modal test results. Based on the results obtained from the modal test using CADA-X program, several design parameter have been found. Through simulations using MSC/ADAMS, it has been found that the shimmy vibration can be improved by changing the bush stiffness of the front suspension. In the end, the design process on the steering/suspension development is suggested for the analysis of shimmy vibration.
Lee, Junghoon,Jang, Moonjeong,Lee, Sang Myeon,Yoo, Dohyuk,Shin, Tae Joo,Oh, Joon Hak,Yang, Changduk American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.22
<P>Over the past few years, one of the most remarkable advances in the field of polymer solar cells (PSCs) has been the development of fluorinated 2,1,3-benzothiadiazole (BT)-based polymers that lack the solid working principles of previous designs, but boost the power conversion efficiency. To assess a rich data set for the influence of the fluorinated BT units on the charge-transport characteristics in organic field-effect transistors (OFETs), we synthesized two new polymers (<B>PDPP-FBT</B> and <B>PDPP-2FBT</B>) incorporating diketopyrrolopyrrole (DPP) and either single- or double-fluorinated BT and thoroughly investigated them via a range of techniques. Unlike the small differences in the absorption properties of <B>PDPP-FBT</B> and its nonfluorinated analogue (<B>PDPP-BT</B>), the introduction of doubly fluorinated BT into the polymer backbone induces a noticeable change in its optical profiles and energy levels, which results in a slightly wider bandgap and deeper HOMO for <B>PDPP-2FBT</B>, relative to the others. Grazing incidence X-ray diffraction (GIXD) analysis reveals that both fluorinated polymer films have long-range orders along the out-of-plane direction, and π–π stacking in the in-plane direction, implying semicrystalline lamellar structures with edge-on orientations in the solid state. Thanks to the strong intermolecular interactions and highly electron-deficient π-systems driven by the inclusion of F atoms, the polymers exhibit electron mobilities of up to 0.42 and 0.30 cm<SUP>2</SUP> V<SUP>–1</SUP> s<SUP>–1</SUP> for <B>PDPP-FBT</B> and <B>PDPP-2FBT</B>, respectively, while maintaining hole mobilities higher than 0.1 cm<SUP>2</SUP> V<SUP>–1</SUP> s<SUP>–1</SUP>. Our results highlight that the use of fluorinated BT blocks in the polymers is a promising molecular design strategy for improving electron transporting performance without sacrificing their original hole mobility values.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-22/am505925w/production/images/medium/am-2014-05925w_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am505925w'>ACS Electronic Supporting Info</A></P>
Topology optimization of the permanent magnet type MRI considering the magnetic field homogeneity
Lee, Junghoon,Yoo, Jeonghoon Elsevier 2010 Journal of magnetism and magnetic materials Vol.322 No.9
<P>This study is to suggest a concept design of the permanent magnet (PM) type magnetic resonance imaging (MRI) device based on the topology optimization method. The pulse currents in the gradient coils in the MRI device will introduce the effect of eddy currents in ferromagnetic material and it may worsen the quality of imaging. To equalize the magnetic flux in the PM type MRI device for good imaging, the eddy current effect in the ferromagnetic material must be reduced. This study attempts to use the topology optimization scheme for equalizing the magnetic flux in the measuring domain of the PM type MRI device using that the magnetic flux can be calculated directly by a commercial finite element analysis package. The density method is adopted for topology optimization and the sensitivity of the objective function is computed according to the density change of each finite element in the design domain. As a result, optimal shapes of the pole of the PM type MRI device can be obtained. The commercial package, ANSYS, is used for analyzing the magnetic field problem and obtaining the resultant magnetic flux. (C) 2009 Elsevier B. V. All rights reserved.</P>
Seonghoon Yoo,Byungrok Moon,Myeonghwan Choi,Xian Guo,Junghoon Lee,Namhyun Kang 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.11
In this study, the effect of the Ti/N ratio on the coarsening behaviour of (Ti, Nb)(C, N) precipitates and prior austenite grainsize (PAGS) in the coarse-grained heat-affected zone (CGHAZ) during the welding process was investigated. Oscillationand tandem electro-gas welding (EGW) were simulated using the finite element method to calculate the thermal history ofthe CGHAZ. The calculated thermal history was applied to the Gleeble specimens to simulate the CGHAZ of tandem EGW. As the Ti/N ratio decreased to ~1.5, and the amount of N increased, finer and more (Ti, Nb)(C, N) precipitates existed inthe as-rolled and CGHAZ specimens (peak temperature ~ 1335 °C), thereby producing a small PAGS. Comparing with theprevious studies regarding to the isothermal kinetics conducted by isothermal heat treatment of Ti(C,N), the athermal kinetics(simulation of tandem EGW) of (Ti,Nb)(C,N) showed the insignificant growth of PAGS. Furthermore, Nb-rich precipitateswere dissolved in the matrix above 1000 °C, and they did not contribute to the PAGS growth of the CGHAZ.