• Journal of Korea Spatial Information System Society
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• v.3 no.2 s.6
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• pp.5-19
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• 2001

We are able to construct and utilize DEM(Digital Elevation Model) throughout the NGIS(National Geographic Information System) project. It is important that interpolation methods and appreciate size of grid for the construction of accurate DEM(Digital Elevation Model). There were several references related to the DEM(Digital Elevation Model) construction method, however they couldn't consider various topographical characteristics in the korea. In this study, we recommended that suitable interpolation method for each topographic element. After dividing Poonggi area into mountain, hill, urban, agricultural land, we constructed DEM(Digital Elevation Model) with various interpolation methods and grid size using 1:5,000 digital map. Then evaluated accuracy using elevation data which extracted from air-photo. The interpolation methods were analyzed and compared for various topographical conditions. As a result, Kriging method was superior to TIN method for all the topographical conditions. Another experiment was performed to examine optimal grid space for DEM with each topographical condition. 10m grid space was most suitable for mountain area and hilly districts, while 30m grid space was most suitable for urban area and farm land.

• Proceedings of the KSRS Conference
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• 2007.03a
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• pp.251-256
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• 2007

FY-2C 위성은 2004년 10월 발사되어 동경 105도 에 서 운영 중인 중국의 정지 궤도 기상위성 이며 관측 영상은 한반도 지역을 포함하고 있다. 현재 FY-2C S-VISSR2.0[l]에 대한 Navigation 알고리즘이 공개되어 있지 않으며，Navigation을 위하여 S-VISSR2.0에 포함되어 있는 Simplified Mapping Block 정보를 사용하여야 한다. Simplified Mapping Block은 5도 간격의 정보만을 제 공하므로 관측 지 역 의 모든 좌표에 대한 Navigation 정보를 얻기 위해서는 보간볍을 사용하여야 한다. 그러나 보간법은 기준 점에서 멀어질수록 오차가 크게 나타날 수 있다. 따라서 본 논문에서는 모든 좌표에 대한 Navigation 정보를 얻을 수 있는 MTSAT Image Navigation 알고리즘을 FY-2C S-VISSR2.0에 적용하여 Simplified Mapping Block과의 차이를 분석하였다. 분석 방법은 Simplified Mapping Block과 MTSAT Image Navigation[2] 알고리즘을 5도 간격의 격자 점(위경도)에서 Column 및 Line 값 비교， Geo-location된 영상의 품질 비교，WDB2 Map Data의 Coast Line과의 비교를 수행하였다. 분석 결과 격자 점에서의 Column, Line 값은 0.5 이내의 차이 값을 나타내었다. 그리고 Geo-location된 영상 비교에서는 격자 점 주변에서 영상의 차이가 없으나 격자 점에서 멸어질수록 영상의 품질은 MTSAT Image Navigation 알고리즘으로 생성한 영상이 더 우수하였다. WDB2 Map Data의 Coast Line과의 비교에서 오차는 동일하게 발생하였으며，영상의 Column 축에 대한 오차는 평균 1.847 Pixel, 최대 6 Pixel, 최소 oPixel 이며， Line 축에 대한 오차는 평균 0.135 Pixel, 최대 4 Pixel, 최소 0 Pixel을 나타내었다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.15 no.3
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• pp.190-195
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• 2003

For many coastal problems, such as wave transformation, tidal circulation, sediment transports and diffusion phenomena, we resort to numerical techniques. The representative numerical techniques are the method of finite differences and finite elements. The approximate algebraic equations, referred to as finite difference equations(FDEs), are subsequently solved at discrete grid points within the domain of interests. Therefore, a set of grid points within the domain, as well as the boundaries of the domain, must be specified. The generation of grids for FDEs, with uniform spacing, is very simple compared to that of finite elements. However, within a very complex domain, there are few grid generation tools we can use conveniently. Unfortunately, most of the commercial grid generation programs are developed only for finite element method. In this paper, grid generation method using digitizer, with uniform rectangular spacing, are introduced in detail. Didger and Surfer programs by Golden Software are necessary to produce comparatively accurate and simple depth data.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.192.2-192.2
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• 2015

본 논문에서는 사파이어 기판 표면에 레이저 처리를 통해 격자 구조(레이저 격자 구조)를 제작하고 InGaN/GaN 발광다이오드(Light-Emitting Diodes, LED) 박막을 성장 한 시료에서 Bowing 특성 변화를 논의한다. 그리고 Bowing 정도에 따른 InGaN/GaN LED의 광학 및 전기적 특성을 Photoluminescence (PL)와 Electroluminescence (EL) Mapping 법을 이용하여 상호 비교 분석하였다. 2-인치 사파이어 기판 상에 레이저 격자 구조의 간격은 1 mm (GS1-LED), 2 mm (GS2-LED), 3 mm (GS3-LED) 로 제작하였으며, 격자 구조가 없는 LED를 기준 시료(C-LED)로 사용하였다. GS1-LED, GS2-LED, GS3-LED의 Bowing 정도는 C-LED 대비 각각 8%, 7.6%, 6.4% 감소하였다. PL Mapping 결과, GS-LED의 발광 파장의 분포 균일도가 C-LED 보다 개선되는 것을 확인하였고, 파장이 C-LED 대비 단파장으로 이동하였다. 또한, GS-LED시료의 PL 강도는 C-LED보다 증가하였고, 특히 GS2-LED의 PL 강도는 C-LED 대비 6.9% 증가 하였다. EL mapping 결과, GS-LED 발광 파장의 분포 균일도는 PL 결과와 유사하게 측정되었으며, 2인치 기판 전체 면적에 대한 GS-LED의 주요 동작전압 및 출력 전력 수율이 C-LED대비 현저히 개선되었다. 사파이어 기판 표면에 제작한 레이저 격자 구조에 따른 InGaN/GaN LED의 광학적, 전기적 특성을 Bowing의 개선과 응력 완화 현상으로 논의 할 예정이다.

• Journal of the Institute of Convergence Signal Processing
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• v.8 no.2
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• pp.84-90
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• 2007

In this paper, the demonstration of a 130-channel optical demultiplexer based on the cascaded volume holographic gratings is presented. By serially adding the second holographic grating, which has different grating period, slant angle, and center wavelength compared to those of the first grating, the operating wavelength range of the optical demultiplexer could be expanded, and therefore, the number of channels of the holographic demultiplexer is increased by twice. As a result of the experiment, a 0.4-nm-spaced demultiplexer with the channel uniformity of 3.5 dB, the 3dB-bandwidth of 0.12nm, and the channel crosstalk of -20dB is experimentally achieved.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.1
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• pp.53-62
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• 2017

The forced convection heat transfer performance of a twist-vane spacer grid for a dual-cooled annular fuel assembly was examined experimentally. The twist-vane spacer grid was uniquely designed to enhance mixing inside subchannels and mixing between adjacent subchannels. For testing, a $4{\times}4$ square-arrayed rod bundle with narrow gaps between rods was prepared as the dual-cooled annular fuel assembly to be simulated. The pitch-to-rod diameter ratio of simulated dual-cooled annular fuel assembly was 1.08. The experiments were performed under the following conditions: axial bulk velocity, 1.5 m/s and heat flux, $26kW/m^2$. With regard to the circumferential temperature distribution, the lowest rod-wall temperatures upstream and downstream were measured at the subchannel center and the position toward the tip of twist-vane, respectively. With regard to the axial temperature distribution, behind the twist-vane spacer grid, the rod-wall temperature decreased drastically, and the Nusselt number was enhanced by up to 56 %. The present measured data indicate that the twist-vane spacer grid can effectively improve the forced convection heat transfer in the dual-cooled annular fuel assembly with narrow gaps.

• Journal of Radiation Protection and Research
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• v.28 no.4
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• pp.311-319
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• 2003

We developed a grid-based Gaussian plume model to evaluate tracer release data measured at Young Gwang nuclear site in 1996. Downwind distance was divided into every 10m from 0.1km to 20km, and crosswind distance was divided into every 10m centering released point from -5km to 5km. We determined dispersion factors, ${\sigma}_y\;and\;{\sigma}_z$ using Pasquill-Gifford method computed by atmospheric stability. Forecasting ability of the grid-based Gaussian plume model was better at the 3km away from the source than 8km. We confirmed that dispersion band must be modified if receptor is far away from the source, otherwise P-G method is not appropriate to compute diffusion distance and diffusion strength in case of growing distance. So, we developed an empirical equation using linear programming. An objective function was designed to minimize sum of the absolute value between observed and computed values. As a result of application of the modified dispersion equation, prediction ability was improved rather than P-G method.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.42 no.7 s.337
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• pp.13-20
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• 2005

We propose an erbium-doped fiber ring laser whose multi-wavelength oscillation is tunable and switchable by tuning fiber bragg gratings. By applying axial pressure on the fiber bragg grating, the wavelength spacing of the proposed laser can be tuned continuously. And by adjusting a polarization controller(PC), the proposed laser can be switched among dual-, triple- and four-wavelength lasing operations.

• Proceedings of the Korean Society Of Semiconductor Equipment Technology
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• 2006.05a
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• pp.127-130
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• 2006

사파이어 기판위에 MOCVD (metal organic chemical vapor deposition)를 이용하여 8주기의 InGaN/GaN 다중양자우물(multiple quantum well : MQW)구조가 성장되어졌고 이 구조 위에 p-GaN층이 형성됐다. 다시 p-GaN 위에 200nm의 두께를 갖는 PMMU 박막을 도포하고 electron beam lithography system을 이용하여 직경이 150nm가 되도록 나노단위의 삼각격자 구조를 가진 구멍을 패턴하고 inductively coupled plasma(ICP)를 이용하여 식각을 하여 광결정을 제작하였다. 광결정은 두께가 26nm이고 격자간격은 460nm로서 파장이 450nm인 파란빛을 나노회절 시켜서 photoluminescence(PL)의 세기를 강화시킨다.

• Korean Journal of Optics and Photonics
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• v.4 no.1
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• pp.36-46
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• 1993

The formula of the diffraction patterns which were made by the grating with the variable periods were derived. The diffraction patterns which had the various data value of the variable periods were simulated by the IBM PC., and the characteristics of the patterns were discussed. The purposes of this study was to find the periods of the real grating and their degree of variation by using the results of the experiment.