다양한 온도조건과 flux 첨가량에 따른 단결정 성장용 YAG : Er³⁺ 분말 제조

박철우,강석현,박재화,김현미,최재상,강효상,심광보,Park, Cheol Woo,Kang, Suk Hyun,Park, Jae Hwa,Kim, Hyun Mi,Choi, Jae Sang,Kang, Hyo Sang,Shim, Kwang Bo 한국결정성장학회 2015 한국결정성장학회지 Vol.25 No.4

본 연구에서는 고상법 및 flux를 이용하여 $Y_3Al_5O_{12}:Er^{3+}\;(YAG:Er^{3+})$ 분말을 저온에서 성공적으로 합성하였다. 분말의 합성 여부와 분말 하소 시 온도에 따른 결정성을 분석하기 위하여 X-ray diffraction(XRD)를 측정하였다. 순수한 YAG는 일반적인 고상법으로 합성할 경우, $1400^{\circ}C$에서 12시간 동안 하소하여 순수한 YAG 상을 얻을 수 있었고, 반면에 $BaF_2$를 첨가한 결과는 상대적으로 낮은 온도($1000^{\circ}C$)에서 합성되었다. 즉, 합성온도를 약 $400^{\circ}C$ 가량 낮출 수 있는 것으로 나타났다. 또한, $BaF_2$의 최적의 농도를 찾아 첨가 후, 열처리 온도에 따라 $BaF_2$로 인한 입자의 형태 및 크기를 조사하였으며 그에 따른 발광강도에 대하여 논의하였다. In this study, using solid-state and flux, $Y_3Al_5O_{12}:Er^{3+}\;(YAG:Er^{3+})$ powders were successfully synthesized at low temperatures. To analyze the crystallinity of powders according to the synthesis or non-synthesis of powders and powder calcination temperatures, X-ray diffraction (XRD) was measured. In the case of pure YAG, when YAG was analyzed using the general solid-phase method, it was calcined for 12 hours at $1400^{\circ}C$ and pure YAG phase could be obtained. But when $BaF_2$ was added to YAG, YAG was synthesized at lower temperature (1000^{\circ}C$). It was thus found that the synthesis temperature could be lowered by about $400^{\circ}C$. Also, when BaF2 with an optimal concentration was added to $YAG:Er^{3+}$, the particle shape and size according to synthesis temperatures were surveyed, and corresponding luminous intensity was discussed.

강유전 고분자 박막의 상전이 특성

박철우,정치섭,Park, Chul-Woo,Jung, Chi-Sup 한국전기전자재료학회 2014 전기전자재료학회논문지 Vol.27 No.2

Phase transition properties of the copolymer films of polyvinylidene fluoride (PVDF) and trifluoroethylene(TrFE), P(VDF-TrFE), were studied with X-ray diffraction (XRD) and polarization modulated ellipsometry (PME). XRD studies on both Langmuir-Blodgett (LB) films and spin coated films exhibit conversions from ferroelectric phase to paraelectric phase at $108{\pm}2^{\circ}C$ on heating and paraelectric phase to ferroelectric phase at $78{\pm}2^{\circ}C$ on cooling. The presence of the ferroelectric-paraelectric phase transition is also confirmed by the PME technique for the first time in this study. PME was proved to be a very sensitive tool in the measurement of the structural changes at the nano-thickness films.

새 정부에 바란다 - '신성장동력을 중심으로'

박철우,Park, Cheol-Woo 한국과학기술단체총연합회 2013 과학과 기술 Vol.526 No.-

하악 제1대구치 단일 수복을 위한 발치 즉시 임플란트의 임상증례

박철우,Park, Cheol-Woo 대한심미치과학회 2021 Journal of the Korean Academy of Esthetic Dentistr Vol.30 No.1

Immediate implantation is widely applied as it is recognized as a useful implant treatment in dental clinic due to its various advantages as well as being able to shorten the treatment period. Immediate implant treatment was performed on 5 patients who needed extraction of the mandibular first molar for various reasons, shortening the overall treatment period, and obtaining satisfactory results. Immediate implantation after extraction is a high-level treatment that requires proper initial fixation at the exact location of the extraction socket and the surrounding soft tissues, but is considered to be a clinically very useful prosthetic restoration method 발치 즉시 임플란트는 치료 기간을 단축할 수 있을 뿐만 아니라 여러 가지 장점으로 인해서 치과임상에서 유용한 임플란트 치료법으로 인식되면서 널리 적용되고 있다. 다양한 이유로 인해서 하악 제1대구치의 발치가 필요한 5명의 환자에게 발치 즉시 임플란트 치료를 진행하여 전체 치료 기간을 단축하면서 만족스러운 결과를 얻었다. 발치 즉시 임플란트는 발치와 내 정확한 위치에 적절한 초기고정을 얻어야 하고 주위 연조직도 개선해야 하는 고난도 치료법이지만 임상적으로 매우 유용한 보철 수복 방법이라고 판단된다.

대기경계층 내에 놓인 자유단 원주의 형상비가 후류유동에 미치는 영향에 관한 연구

박철우,이상준,Park, Cheol-U,Lee, Sang-Jun 대한기계학회 2001 大韓機械學會論文集B Vol.25 No.12

The flow around free end of a finite circular cylinder (FC) embedded in an atmospheric boundary layer has been investigated experimentally. The experiments were carried out in a closed-return type subsonic wind tunnel with varying aspect ratio of the finite cylinder mounted vertically on a flat plate. The wakes behind a 2-D cylinder and a finite cylinder located in a uniform flow were measured for comparison. Reynolds number based on the cylinder diameter was about Re=20,000. A hot-wire anemometer was employed to measure the wake velocity and the mean pressure distributions on the cylinder surface were also measured. The flow past the FC free end shows a complicated three-dimensional wake structure and flow phenomenon is quite different from that of 2-D cylinder. The three-dimensional flow structure was attributed to the downwashing counter rotating vortices separated from the FC free end. As the FC aspect ratio decreases, the vortex shedding frequency decreases and the vortex formation length increases compared to that of 2-D cylinder. Due to the descending counter-rotating twin-vortex, near the FC free end, regular vortex shedding from the cylinder is suppressed and the vortex formation region is hardly distinguished. Around the center of the wake, the mean velocity for the FC located in atmospheric boundary layer has large velocity deficit compared to that of uniform flow.

AlN 단결정의 품질평가를 위한 molten KOH/NaOH eutectic alloy의 화학적 습식에칭

박철우,박재화,홍윤표,오동근,최봉근,이성국,심광보,Park, Cheol Woo,Park, Jae Hwa,Hong, Yoon Pyo,Oh, Dong Keun,Choi, Bong Geun,Lee, Seong Kuk,Shim, Kwang Bo 한국결정성장학회 2014 한국결정성장학회지 Vol.24 No.6

본 연구에서는 상용화되는 AlN 웨이퍼(wafer)를 이용하여 molten KOH/NaOH 화학적 습식 에칭(Wet Chemical Etching)에 따른 표면변화 특성 및 최적의 에칭 조건을 조사하였다. AlN 웨이퍼를 $350^{\circ}C$에서 5분간 에칭 시 Al-face, N-face는 서로 다른 관찰되었다. 특히, Al-face는 에치핏의 형상을 파악하여 결함특성을 관찰하였고, 이로부터 결함 밀도를 계산하여 $2{\times}10^6/cm^2{\sim}10^{10}/cm^2$의 결과를 얻었다. N-face의 경우 육각 뿔(hexagonal pyramids) 형태의 격자결함이 형성되었다. 또한 AlN 웨이퍼의 성장 시 배향을 관찰하기 위해 XRD(X-Ray Diffraction, Rigaku, JAPAN)를 이용하여 분석한 결과 육방정 AlN의 C축 방향에 해당되는 (0002) 및 (0004) 면으로 배향된 상태임을 알 수 있었고, DC-XRD(Double Crystal X-ray Diffraction, bruker, Germany)를 이용하여 rocking curve의 위치에 따라 곡률 반경을 측정했을 때 1.6~17 m의 곡률을 가지고 있는 것으로 나타났다. We investigated the optimal etching conditions and properties of the surface change due to molten KOH/NaOH chemical wet etching using an AlN wafer which has been put to practical use in the present study. Results were observed using a scanning electron microscope after 5 minutes etching at $350^{\circ}C$, was found to have a surface form of the respective other Al-face, the N-face. In particular, etch-pit in the form of a hexagon, which is observed in the Al-face appeared, It was calculated at $2{\times}10^6/cm^2{\sim}10^{10}/cm^2$ dislocation density. In the case of N-face, lattice defects in the form of the hexagonal pyramids is formed. It was discovered that in order to observe the orientation of the wafer, which corresponds to the C-axis direction of the resulting hexagonal AlN which was analyzed using XRD (0002) and is a state of being oriented in the (0004) plane. The Radius of curvature of AlN wafer was 1.6~17 m measured by DC-XRD rocking curve position.

다공성 방풍펜스 후방에 놓인 삼각프리즘의 표면압력특성에 관한 풍공학적 연구

박철우,이상준,Park, Cheol-U,Lee, Sang-Jun 대한기계학회 1997 大韓機械學會論文集B Vol.21 No.11

The effects of porous wind fence on the pressure characteristics around a 2-dimensional prism model of triangular cross-section were investigated experimentally. The fence and prism model were embedded in a neutral atmospheric surface boundary layer over the city suburb. In this study, various fences of different porosity, back fence, inclination angle of prism and location of additional back prisms were tested to investigate their effects on the pressure and wall shear stress of the prism surface. The fence and prism had the same height of 40 mm and Reynolds number based on the model height was Re=3.9*10$^{4}$. The porous fence with porosity 40% was found to be the best wind fence for decreasing the mean and pressure fluctuations on the prism surface. By installing the fence of porosity 40%, the wall shear stress on the windward surface of prism was largely decreased up to 1/3 of that without the fence. This indicates that the porous fence is most effective to abate the wind erosion. Pressure fluctuations on the model surface were decreased more than half when a back fence was located behind the prism in addition to the front fence. With locating several back prisms and decreasing the inclination angle of triangular prism, the pressure fluctuations on the model surface were increased on the contrary.

몬테 카를로 시뮬레이션을 통한 발사관 구조 안전성 분석

박철우,이온수,신효섭,박진용,이동주,Park, Chul-Woo,Lee, Onsoo,Shin, Hyo-Sub,Park, Jin-Yong,Lee, Dong-Ju 한국시뮬레이션학회 2018 한국시뮬레이션학회 논문지 Vol.27 No.4

Launching system is designed to store the payload, withstand the rigors, and prevent it from rusting and damaging. The behavior during initial deployment of the missile is determined by production, assembly and insertion condition of a launching tube and a missile. The purpose of this research is to confirm the safety of a launching tube by statistically analyzing behavior of the missile, during initial deployment stage. Error parameters which effect initial behavior of the missile are selected and analyzed through Monte-Carlo Simulation. Based on the result of simulation, tip-off and stress distribution between rail and shoe is predicted by using the commercial analysis program called Recurdyn. Lastly, the safety factor is calculated based on yield strength of the material and maximum stress of the rail during the process of launching. The safety of the launching system is verified from the result of the safety factors. 발사관은 탑재물을 보관하고 외부 환경으로부터 부식 및 파손되는 것을 방지하는 역할을 한다. 발사관과 유도탄의 제작, 조립 그리고 장입 상태에 따라 발사할 때 유도탄의 초기 거동을 결정하게 된다. 본 연구의 목적은 유도탄이 발사관에서 사출될 때 유도탄의 초기 거동을 결정하는 요소를 통계적으로 분석하여 발사관의 안전성을 확인하는 것이다. 유도탄이 발사될 때 거동에 영향을 주는 오차 요소들을 선정한 후 Monte-Carlo 시뮬레이션을 수행하여 통계적으로 분석하였다. 시뮬레이션 결과를 바탕으로, 각 오차 요소들을 고려한 다물체 동역학 해석을 상용프로그램인 Recurdyn을 이용하여 동역학 해석을 수행하여 유도탄 발사할 때 발생하는 중력 침하 및 레일과 슈 사이에 발생하는 응력을 구하였다. 해당 결과를 바탕으로 현재 설계된 발사관에 대한 안전성을 검증하였다.

한국산업기술대학교의 산학일체형 교육제도

박철우,Park, Cheol-U 한국대학교육협의회 2004 大學敎育 Vol.127 No.-

시멘트 콘크리트 포장의 발전을 위한 국내외 콘크리트 포장의 시공 및 배합에 대한 검토(III) - 유럽형 고성능 콘크리트 포장 배합특성 분석

박철우,윤경구,Park, Cheol-U,Yun, Gyeong-Gu 한국도로학회 2009 한국도로학회지 Vol.11 No.4