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고정형(Stationary-gantry) 희소뷰(Sparse-view) CT 보안검색시스템의 공간분해능 평가
김영조,최광윤,정춘호,박형규,YoungJo Kim,KwangYoon Choi,Chunhe Zheng,HyeongKyu Park 한국방사선산업학회 2023 방사선산업학회지 Vol.17 No.4
In this study, the image quality assessment, especially spatial resolution evaluation, for Sparse-view CT reconstructed images was performed. The main goal of the experiment is to evaluate Modulation Transfer Function by using American Standard Method for Measurement of Computed Tomography System Performance(ASTM E1695-95) which uses the edge test object. To compare with the ASTM method, a different method, the radial-type edge profile, to measure MTF using the edge method also performed. Both approaches were tested on the same image acquired by the stationary-gantry sparse-view CT security-screening system using cylindrical test phantom manufactured in accordance with ANSI 42.45. Both of the spatial resolutions at 10% modulation are 0.195, 0.203lp pixel<sup>-1</sup>, respectively. The method implemented by ASTM E1695-95 showed higher reliability and had a relatively more accurate spatial resolution result than the radial-type edge profile method.
방열 특성에 따른 집광형 태양전지의 광전변환효율 변화에 관한 실험적 연구
김강호(Kangho Kim),정상현(Sang Hyun Jung),김영조(Youngjo Kim),김창주(Chang Zoo Kim),전동환(Dong Hwan Jun),신현범(Hyun-Beom Shin),이재진(Jaejin Lee),강호관(Ho Kwan Kang) 한국태양광발전학회 2014 Current Photovoltaic Research Vol.2 No.4
Under concentrated illuminations, the solar cells show higher efficiencies mainly due to an increase of the open circuit voltage. In this study, InGaP/InGaAs/Ge triple-junction solar cells have been grown by a low pressure metalorganic chemical vapor deposition. Photovoltaic characteristics of the fabricated solar cells are investigated with a class A solar simulator under concentrated illuminations from 1 to 100 suns. Ideally, the open circuit voltage should increase with the current level when maintained at the same temperature. However, the fabricated solar cells show degraded open circuit voltages under high concentrations around 100 suns. This means that the heat sink design is not optimized to keep the cell temperature at 25°C. To demonstrate the thermal degradation, changes of the device performance are investigated with different bonding conditions and heat sink materials.
InGaP/GaAs 이중접합 기반의 고효율 플렉시블 태양전지 제조기술 연구
문승필(Seungpil Moon),김영조(Youngjo Kim),김강호(Kangho Kim),김창주(Chang Zoo Kim),정상현(Sang Hyun Jung),신현범(Hyun-Beom Shin),박경호(Kyung Ho Park),박원규(Won-Kyu Park),안연식(Yeon-Shik Ahn),강호관(Ho Kwan Kang) 한국태양광발전학회 2016 Current Photovoltaic Research Vol.4 No.3
III-V compound semiconductor based thin film solar cells promise relatively higher power conversion efficiencies and better device reliability. In general, the thin film III-V solar cells are fabricated by an epitaxial lift-off process, which requires an AlxGa1-xAs (x≥0.8) sacrificial layer and an inverted solar cell structure. However, the device performance of the inversely grown solar cell could be degraded due to the different internal diffusion conditions. In this study, InGaP/GaAs double-junction solar cells are inversely grown by MOCVD on GaAs (100) substrates. The thickness of the GaAs base layer is reduced to minimize the thermal budget during the growth. A wide band gap p-AlGaAs/n-InGaP tunnel junction structure is employed to connect the two subcells with minimal electrical loss. The solar cell structures are transferred on to thin metal films formed by Au electroplating. An AlAs layer with a thickness of 20 nm is used as a sacrificial layer, which is removed by a HF:Acetone (1:1) solution during the epitaxial lift-off process. As a result, the flexible InGaP/GaAs solar cell was fabricated successfully with an efficiency of 27.79% under AM1.5G illumination. The efficiency was kept at almost the same value after bending tests of 1,000 cycles with a radius of curvature of 10 mm.
황종선(Hwang jongsun),이달형(Lee dalhyung),김영조(Kim youngjo),이상진(Lee sangjin),김재준(Kim jaejoon) 대한전기학회 2009 대한전기학회 학술대회 논문집 Vol.2009 No.4
1970년대부터 극저주파전자계가 인체건강에 유해한지에 대한 궁금증이 중가하고 있는 실정이다. 또한 그 시기로부터 중요한 이슈에 대한 해결방안과 향후 연구방향에 대한 지표설정을 위해 많은 연구가 행해져 왔다. 본 고에서는 세계보건기구(WHO)가 2007년 극저주파전자계와 인체건강의 관계 검토를 마무리한 공식보고서(Fact sheet No.322) 결과를 고찰해보고자 한다.