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이동하,송재원,윤태석,Lee, D.H.,Song, J.W.,Yoon, T.S. 한국천문학회 2013 天文學論叢 Vol.28 No.3
An optical grism for education is fabricated and tested. It is composed of a transmission grating as dispersion element and a prism as diffraction angle compensation device. The transmission grating is Edmundoptics #49-584(spatial frequency 600 lines/mm, dimension $50mm{\times}50mm$). The prism is the fused silica type with angles ($41.3^{\circ}$, $-48.7^{\circ}$, $-90^{\circ}$). The grism device is fabricated by bonding the transmission grating and the prism with an optical adhesive. The zig for assembling the grism, telescope and camera is composed of an aluminum tube, an aluminum disk ring and a T-ring camera adaptor. The fabricated optical grism spectrograph is tested in laboratory using Halogen lamp and Neon lamp with DSLR camera. And the grism assembled with reflector telescope is tested in a field using stellar light. The results show good agreements with design parameters. The wavelength coverage range of the grism is 250 nm at the un-deviated wavelength of 506 nm. The wavelength resolution is 0.11 nm/pixel.
반 보존형 운동량 방정식을 이용한 SPACE 코드의 다차원 열수력 모듈 개선
이동하(D.H. Lee),이승욱(S.W. Lee),정재준(J.J. Jeong) 한국전산유체공학회 2018 한국전산유체공학회지 Vol.23 No.1
Most of nuclear thermal-hydraulic system codes, which adopt a two-fluid model for two-phase flow, use a non-conservative form of momentum equations for numerical convenience. However, it was known that the non-conservative form can cause unphysical momentum convection in some two-phase flow conditions, especially when the two-phase flow was strongly heterogeneous. In order to compensate this defect, a semi-conservative form of momentum equation is suggested, which is non-conservative in time but conservative in space. In this paper, the semi-conservative form of the two-fluid momentum equation was implemented into the multi-dimensional module of the SPACE code. Thereafter, the code was assessed by simulating two multi-dimensional two-phase flow experiments. The results showed that the semi-conservative form has better predicting capability than the non-conservative form.
Ga/(In+Ga)함량비에 따른 Cu(In,Ga)Se2 박막의 국소적 영역에서의 표면 퍼텐셜과 전류-전압 특성 연구
김지영(G. Y. Kim),정아름(A. R. Jeong),조윌렴(W. Jo),조현준(H. J. Jo),김대환(D. -H. Kim),성시준(S. -J. Sung),황대규(D. -K. Hwang),강진규(J.-K. Kang),이동하(D. H. Lee) 한국태양에너지학회 2012 한국태양에너지학회 학술대회논문집 Vol.2012 No.3
Cu(In, Ga)Se2 (CIGS) is one of the most promising photovoltaic materials because of large conversion efficiency which has been achieved with an optimum Ga/(In+Ga) composition in CuIn1-xGaxSe2 (X~0.3). The Ga/(In+Ga) content is important to determine band gap, solar cell performances and carrier behaviors at grain boundary (GB). Effects of Ga/(In+Ga) content on physical properties of the CIGS layers have been extensively studied. In previous research, it is reported that GB is not recombination center of CIGS thin-film solar cells. However, GB recombination and electron-hole pair behavior studies are still lacking, especially influence of with different X on CIGS thin-films. We obtained the GB surface potential, local current and I-V characteristic of different X (0<X<1) in CIGS thin-films by using the Kelvin probe force microscopy (KPFM) and conductive atomic force microscopy (C-AFM). From C-AFM results, we found that CIGS thin-film (X~0.3) with high conversion efficiency flows lower local current. Surface potential was smaller than 80 mV near GBs with X<0.1 and X>0.7 while X~0.3 showed higher potential than 100mV on GBs. Higher potential on GBs appears positive band bending. It can decrease recombination loss because of carrier separation. Therefore, we suggest recombination and electron-hole behaviors at GBs depending on composition of X.
정아름(Jeong, A.R.),김지영(Kim, G.Y.),조윌렴(Jo, W.),조현준(Jo, H.J.),김대환(Kim, D.H.),성시준(Sung, S.J.),강진규(Kang, J.K.),이동하(Lee, D.H.),남다현(Nam, D.H.),정현식(Cheong, H.) 한국신재생에너지학회 2011 한국신재생에너지학회 학술대회논문집 Vol.2011 No.11
We report on a direct measurement of two-dimensional chemical and electrical distribution on the surface of photovoltaic Cu(In,Ga)Se₂ thin-films using a nano-scale spectroscopic and electrical characterization, respectively. The Raman measurement reveals non-uniformed surface phonon vibration which comes from different compositional distribution and defects in the nature of polycrystalline thin-films. On the other hand, potential analysis by scanning Kelvin probe force microscopy shows a higher surface potential or a small work function on grain boundaries of the thin-films than on the grain surfaces. This demonstrates the grain boundary is positively charged and local built-in potential exist on grain boundary, which improve electron-hole separation on grain boundary. Local electrical transport measurements with scanning probe microscopy on the thin-films indicates that as external bias is increases, local current is started to flow from grain boundary and saturated over 0.3 V external bias. This accounts for carrier behavior in the vicinity of grain boundary with regard to defect states. We suggest that electron-hole separation at the grain boundary as well as chemical and electrical distribution of polycrystalline Cu(In,Ga)Se₂ thin-films.