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니켈기 초내열 합금의 천이액상확산접합 특성에 미치는 접합 온도 및 가열 속도의 영향
최우혁,김성욱,김종현,김길영,이창희,Choi Woo-Hyuk,Kim Sung-Wook,Kim Jong-Hyun,Kim Gil-Young,Lee Chang-Hee 대한용접접합학회 2005 대한용접·접합학회지 Vol.23 No.2
This study was carried out to investigate the effect of bonding temperature and heating rate on transient liquid phase diffusion bonding of Ni-base superalloy. The heating rate was varied by $0.1^{\circ}C$/sec, $1^{\circ}C$/sec, $10^{\circ}C$/sec to the bonding temperatures $1100^{\circ}C,\;1150^{\circ}C,\;1200^{\circ}C$ under vacuum. As bonding temperature increased, maximum dissolution width of base metal increased, but a dissolution finishing time decreased. The eutectic width of insert metal in the bonded interlayer decreased linearly in proportion to the square root of holding time during isothermal solidification stage. The bonding temperature was raised, isothermal solidification rate slightly increased. As the heating rate decreased and the bonding temperature increased, the completion time of dissolution after reaching bonding temperature decreased. When the heating rate was very slow, the solidification proceeded before reaching bonding temperature and the time required for the completion of isothermal solidification became reduced.
초음파 진단영상 대조도 개선을 위한 확률 경계 맵을 이용한 연구
최우혁,박원환,박성윤,Choi, Woo-hyuk,Park, Won-hwan,Park, Sungyun 대한한의진단학회 2016 大韓韓醫診斷學會誌 Vol.20 No.1
Ultrasonic imaging is the most widely modality among modern imaging device for medical diagnosis. Nevertheless, medical ultrasound images suffer from speckle noise and low contrast. In this paper, we propose probabilistic edge map for ultrasound image edge enhancement using automatic alien algorithm. The proposed method used applied speckle reduced ultrasound imaging for edge improvement using sequentially acquired ultrasound imaging. To evaluate the performance of method, the similarity between the reference and edge enhanced image was measured by quantity analysis. The experimental results show that the proposed method considerably improves the image quality with region edge enhancement.
부분용적효과를 고려한 확산텐서영상에 대한 관심영역 분석 연구
최우혁,윤의철,Choi, Woohyuk,Yoon, Uicheul 대한의용생체공학회 2016 의공학회지 Vol.37 No.2
In this study, we proposed ameliorated method for region of interest (ROI) study to improve its accuracy using partial volume effect (PVE). PVE which arose in volumetric images when more than one tissue type occur in a voxel, could be used to reduce an amount of gray matter and cerebrospinal fluid within ROI of diffusion tensor image (DTI). In order to define ROIs, individual b0 image was spatially aligned to the JHU DTI-based atlas using linear and non-linear registration (http://cmrm.med.jhmi.edu/). Fractional anisotropy (FA) and mean diffusivity (MD) maps were estimated by fitting diffusion tensor model to each image voxel, and their mean values were computed within each ROI with PVE threshold. Participants of this study consisted of 20 healthy controls, 27 Alzheimer's disease and 27 normal-pressure hydrocephalus patients. The result showed that the mean FA and MD of each ROI were increased and decreased respectively, but standard deviation was significantly decreased when PVE was applied. In conclusion, the proposed method suggested that PVE was indispensable to improve an accuracy of DTI ROI study.
EH36-TM강의 대입열 EGW 용접부 저온 인성에 미치는 미세 조직의 영향
최우혁,조성규,최원규,고상기,한종만,Choi, Woo-Hyuk,Cho, Sung-Kyu,Choi, Won-Kyu,Ko, Sang-Gi,Han, Jong-Man 대한용접접합학회 2012 대한용접·접합학회지 Vol.30 No.1
The characteristics of high heat input (342kJ/cm) EG (Electro Gas Arc) welded joint of EH36-TM steel has been investigated. The weld metal microstructure consisted of fine acicular ferrite (AF), a little volume of polygonal ferrite (PF) and grain boundary ferrite (GBF). Charpy impact test results of the weld metal and heat affected zone (HAZ) met the requirement of classification rule (Min. 34J at $-20^{\circ}C$). In order to evaluate the relationship between the impact toughness property and the grain size of HAZ, the austenite grain size of HAZ was measured. The prior austenite grain size in Fusion line (F.L+0.1 mm) was about $350{\mu}m$. The grain size in F.L+1.5 mm was measured to be less than $30{\mu}m$ and this region was identified as being included in FGHAZ(Fine Grain HAZ). It is seen that as the austenite grain size decreases, the size of GBF, FSP (Ferrite Side Plate) become smaller and the impact toughness of HAZ increases. Therefore, the CGHAZ was considered to be area up to 1.3mm away from the fusion line. Results of TEM replica analysis for a welded joint implied that very small size ($0.8\sim1.2{\mu}m$) oxygen inclusions played a role of forming fine acicular ferrite in the weld metal. A large amount of (Ti, Mn, Al)xOy oxygen inclusions dispersed, and oxides density was measured to be 4,600-5,300 (ea/mm2). During the welding thermal cycle, the area near a fusion line was reheated to temperature exceeding $1400^{\circ}C$. However, the nitrides and carbides were not completely dissolved near the fusion line because of rapid heating and cooling rate. Instead, they might grow during the cooling process. TiC precipitates of about 50 ~ 100nm size dispersed near the fusion line.
EXIF정보를 이용한 위치기반 디지털사진 앨범의 설계 및 구현
최우혁 ( Woo-hyuk Choi ),김진호 ( Jin-ho Kim ),김진일 ( Jin-il Kim ) 한국정보처리학회 2008 한국정보처리학회 학술대회논문집 Vol.15 No.2
본 논문에서는 디지털사진의 효율적인 관리를 위하여 EXIF정보를 이용한 위치 기반의 디지털사진 앨범을 설계하고 구현한다. 촬영된 디지털사진을 과거에 일어난 사건으로 정의하고, 인간이 사건의 인지에 시간적 배경인 시간정보와 공간적 배경인 공간정보를 사용하고 있는 점을 착안하여 이를 기반으로 한 앨범의 설계와 제작을 보인다. 시스템은 대표적인 디지털사진 파일의 포맷으로 사용되는 JPEG/EXIF 포맷의 EXIF정보에 포함된 사진촬영 날짜와 GPS정보를 이용하여 설계되어 기존의 사진 관리시스템보다 효율적인 사용자 상호작용이 가능하다.
이온성 액체 기반의 고분자 물질의 합성 및 특성과 그 응용
최우혁 ( U Hyeok Choi ),이민재 ( Min Jae Lee ) 한국공업화학회 2016 공업화학전망 Vol.19 No.4
이온성 액체 기반의 이온성 고분자 물질(PILs)은 이온성 액체 모노머(imidazolium, pyridinium, pyrrolidinium, piperidinium, ammonium, phosphonium 등) 또는 그와 유사한 구조로부터 합성된 이온성 고분자 물질이며, 다양한 용도의 고체 전해질로 적용이 가능하다. 이 글에서는 이러한 기능성 고분자 물질의 다양한 종류, 합성방법 및 구조의 변화에 따른 특성에 대하여 기술하고자 한다. 또한 이온성 고분자 물질에서의 이온 전도성과 이온거동에 대하여, 그리고 마지막으로 이러한 이온성 액체 기반의 고분자 물질의 전해질로서의 적용 가능분야에 대하여 기술하고자 한다. 이온성 액체 기반의 고분자 물질의 특성으로부터의 향상된 이온전도성, 기계적 강도, 안정성 등이 확보된 고분자 전해질에 대한 연구가 지속적으로 보고되고 있고, 미래 에너지 소재로서의 다양한 분야에 적용될 수 있을 것이다.