• Journal of Electrical Engineering and Technology
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• 제3권2호
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• pp.276-279
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• 2008

We report on the enhancement of cathode-luminescence in an $In_xGa_{1-x}N/In_yGa_{1-y}$ green light emitting diode structure using two-dimensional photonic crystals. The square lattice arrays of photonic crystals with diameter/periodicity of 200/500 nm were fabricated by electron beam lithography. Inductively coupled plasma dry etching was used to etch and define photonic crystals. Three samples with different etch depths, i.e., 170, 95, and 65 nm, were constructed. Field emission scanning electron microscope analysis shows that air holes of photonic crystal structure with inverted-cone shapes were fabricated after dry etching. Cathode-luminescence measurement indicated that up to 30-fold enhancement of cathode-luminescence intensity has been achieved.

• Ecology and Resilient Infrastructure
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• 제2권1호
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• pp.33-41
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• 2015

본 연구는 어류서식적합도 향상을 위해 유전자알고리즘을 이용한 하천의 구조개선 방안을 제시하였다. 하천구조 개선에 의한 수리특성의 변화에 따른 어류 서식적합도와 물리적 교란양상과의 상관특성을 분석하였다. 원주천의 하천 환경조사와 어류의 군집특성을 이용하여 수중 생태계를 대표할 수 있는 복원 목표어종으로 참갈겨니를 선택하였다. 참갈겨니의 서식적합지수를 사용한 서식적합도 분석은 PHABSIM 모형을 이용하였다. HEC-RAS를 이용한 수리특성 분석과 하천교란 평가방법을 이용하여 물리적 교란평가를 수행하였다. 서식적합도 향상을 위한 최적의 저수로 폭의 개선방안을 제시하였다. 하천구조의 개선에 의한 수리특성의 변화에 따른 서식적합도와 물리적 교란의 상관성을 분석하여 어류 서식적합도와 물리적 교란 평가점수의 향상이 있음을 확인하였다. 서식적합도 향상을 위한 하천의 구조 개선은 물리적 교란의 평가점수의 향상을 가져옴을 확인하였다.

• 전기전자학회논문지
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• 제11권4호
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• pp.307-314
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• 2007

In this paper, we propose an image contrast enhancement algorithm for an LCD TV. The proposed algorithm consists of two processes: the image segmentation process and the tone curve control process. The first process uses an automatic threshold technique to decompose an input image into two regions and then utilizes a hierarchical structure for real-time processing. The second process generates a gray level tone curve for contrast enhancement using a weighted sum of average tone curves for two segmented regions. Experimental result shows that the proposed algorithm outperforms the conventional contrast enhancement methods for an LCD TV.

• Current Optics and Photonics
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• 제7권1호
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• pp.97-103
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• 2023

In this paper, we propose Babinet-principle-inspired metasurfaces for strong resonant enhancement of local magnetic fields. The metasurfaces are designed as complementary structures of original metasurfaces supporting the local enhancement of electric fields. We show numerically that the complementary structures can support spoof magnetic surface plasmons that induce strong local magnetic fields without sacrificing the deep sub-wavelength-thick nature of the metasurface. By introducing a periodic array of metallic rods in the proximity of the metasurfaces, we demonstrate that a resonant enhancement of the local magnetic fields, more than 80 times the amplitude of an incident magnetic field, can emerge from a resonance of the spoof magnetic surface plasmons.

• Journal of Information Processing Systems
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• 제19권4호
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• pp.465-473
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• 2023

An image enhancement algorithm and image defogging method are studied in this paper. The formation of fog and the characteristics of fog image are analyzed, and the fog image is preprocessed by histogram equalization method; then the additive white noise is removed by foggy image attenuation model, the atmospheric scattering physical model is constructed, the image detail characteristics are enhanced by image enhancement method, and the visual effect of defogging image is enhanced by guided filtering method. The proposed method has a good defogging effect on the image. When the number of training iterations is 3,000, the peak signal-to-noise ratio of the proposed method is 43.29 dB and the image structure similarity is 0.9616, indicating excellent image defogging effect.

• 한국막학회:학술대회논문집
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• 한국막학회 2003년도 추계 총회 및 학술발표회
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• pp.55-57
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• 2003

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2013년도 춘계학술대회 논문집
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• pp.665-666
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• 2013

• Journal of Electrical Engineering and Technology
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• 제10권3호
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• pp.1131-1137
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• 2015

Gallium nitride (GaN) is a promising material for next-generation high-power applications due to its wide bandgap, high breakdown field, high electron mobility, and good thermal conductivity. From a structure point of view, the vertical device is more suitable to high-power applications than planar devices because of its area effectiveness. However, it is challenging to obtain a completely upright vertical structure due to inevitable sidewall slope in anisotropic etching of GaN. In this letter, we design and analyze the enhancement-mode n-channel vertical GaN MOSFET with variation of sidewall gate angle by two-dimensional (2D) technology computer-aided design (TCAD) simulations. As the sidewall slope gets closer to right angle, the device performances are improved since a gradual slope provides a leakage current path through the bulk region.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.314.2-314.2
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• 2014

To improve the optical and electrical properties of commercialized GaN-based light-emitting diodes (LEDs), many methods are suggested. In recent years, great efforts have been made to improve the internal quantum efficiency and light extraction efficiency (LEE) and promising approaches are suggested using a patterned sapphire substrate (PSS), V-pit embedded LED structures, and silica nanostructures. In this study, we report on the enhancement of photoluminescence (PL) intensity in GaN-based LED structures by using the combination of SiO2 (silica) nanospheres and polystyrene/SiO2 core-shell nanospheres. The SiO2 nanospheres-coated LED structure shows the slightly increased PL intensity. Moreover the polystyrene/SiO2 core-shell nanospheres-coated structure shows the more increase of PL intensity comparing to that of only SiO2 spheres-coated structure and the conventional structure without coating of nanospheres. The Finite-difference time-domain (FDTD) simulation results show corresponding result with experimentally observed results. The mechanism of enhancement of PL intensity using the coating of polystyrene/SiO2 core-shell nanospheres on LED surface can be explained by the improvement in extraction efficiency by both increasing the probability of light escape by reducing Fresnel reflection and by multiple scattering within the core-shell nanospheres.

• 한국자동차공학회논문집
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• 제21권1호
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• pp.36-42
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• 2013

Recently, the automobile of the future will be able to substitute an electric vehicle for an internal combustion engine, so the following research is actively in the process of advancing. A traction motor is one of the core parts which compose the electric vehicle. Especially, it is difficult to connect cooling water piping to an in-wheel motor because the in-wheel motor is located within the wheel structure. This structure has disadvantage for closed type and air cooling, so the cooling design of motor housing and internal in-wheel motor is important. In this study, thermo-flow analysis of the in-wheel motor for vehicles was performed in consideration of ram air effect. In order to improve cooling efficiency of the motor, we variously changed geometries of housing and internal shape. As a result, we found that the cooling efficiency was most excellent, in case the cooling groove direction was same with air flow direction and arranged densely. Furthermore, we investigated the cooling performance enhancement with respect to variable geometries of internal in-wheel motor.