• Korea-Australia Rheology Journal
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• 제17권4호
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• pp.191-198
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• 2005

The static and dynamic rheological behavior of concentrated sodium dodecylsulfate (SDS) stabilized, deformability controllable polydimethylsiloxane (PDMS) emulsions is reported and comparisons made with silica (hard sphere) suspensions. Steady-mode measurements indicate 'hard' (viscoelastic) droplets behave as hard spheres, while 'soft' (viscous) droplets induce structural flexibility of the emulsion against shear. Dynamic-mode measurements reveal that viscoelasticity of droplets provides the great magnitude of elasticity for the 'hard' emulsion, while formation of planar films between droplets is the origin of the elasticity of 'soft' emulsions. Combination of steady and dynamic rheological behavior has enabled depiction of droplet structure evolution in relation to the shear stress applied, especially by taking advantage of the normal force that reflects the transient deformation of droplets.

• Advances in robotics research
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• 제1권1호
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• pp.61-79
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• 2014

This paper presents theoretical and experimental investigations into the dynamic modelling and characterisation of a two-link flexible manipulator incorporating payload. A planar two-link flexible manipulator that moves in a horizontal plane is considered. A dynamic model of the system is developed using a combined Euler-Lagrange and assumed mode methods, and simulated using Matlab. Experiments are performed on a lab-scaled two-link flexible manipulator for validation of the dynamic model and characterisation of the system. Two system responses namely hub angular position and deflection responses at both links are obtained and analysed in time and frequency domains. The effects of payload on the dynamic characteristics of the flexible manipulator are also studied and discussed. The results show that a close agreement between simulation and experiments is achieved demonstrating an acceptable accuracy of the developed model.

• 대한전자공학회논문지SD
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• 제40권9호
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• pp.666-672
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• 2003

본 논문에서는 광의 결합 메커니즘이 다른 ITG(integrated-twin-guide) 와 BT(butt coupled) 구조를 가지는 두 종류의 파장 가변 DBR-LD의 제작공정과 성능에 대해서 기술하였다. 두 종류의 DBR-LD는 PBH(planar buried heterostructure) 구조론 가지며, MOVPE 성장으로 제작하였다. 제작된 DBR-LD 광출력 특성을 측정한 결과 BT-DBR-LD가 ITG-DBR-LD보다 임계전류 변화폭, 광출력 변화 폭, 기울기 효율에서 2배 이상의 우수한 특성을 나타내었다. 그리고, 준 연속 파장 가변 특성은 BT-DBR-LD가 7.2nm, ITG-DBR-LD가 7.4nm 이며, SMSR이 35dB 이상으로 우수하게 나타났다. 이와 같이 BT DBR-LD가 특성이 우수한 것은 BT 구조가 ITG 구조보다 높은 결합 효율을 나타내기 때문이다.

• The Journal of the Acoustical Society of Korea
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• 제15권4E호
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• pp.14-20
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• 1996

The double mode SAW resonator filters have the serious shortcoming that out-of-band rejection above the passband is quite poor. Hence a new structure of the double mode filter is designed with the COM (Coupling Of MOdes) theory with better out-of-band rejection characteristics while keeping all the beauties of the conventional type. The second goal of the design is to reduce the planar size of the structure so that mass productivity of low frequency devices can be improved. For those purposes, several IDT's and relfector gratings are added to or subtracted from the conventional structure so that the modification can lead to better overall performance as a filter. As results of the investigation, several new double mode SAW resonator filter structures are developed. A new structure shows 10dB more out-of-band rejection that the conventional type with 25% reduced device size. Good agreement is demonstrated between the analytical results and experimental results for an illustrative 325MHz four pole resonator filter on 64°YX LiNbO3.

• 한국광학회지
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• 제21권1호
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• pp.1-5
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• 2010

본 논문에서는 실리콘 태양전지의 흡수효율 증가를 위해 도파모드 공진 특성을 이용한 격자 구조를 제안하였다. 도파모드 공진을 이용함으로써 두께를 ~200 nm 수준으로 줄이면서도 높은 흡수율을 기대할 수 있는 태양전지 설계가 가능함을 확인하였다. 제안된 구조는 은으로 된 반사경 위에 격자구조를 갖는 Poly-Si 유전체 층이 존재하는 1-D 구조로서 각 구조변수들 즉 격자의 주기, 유전체 두께, 격자 간격 및 깊이 등이 흡수 효율에 어떤 영향을 미치는지 알아보고, 변수들의 조절을 통해 최적의 구조를 찾고자 시도하였다. PSO알고리즘을 사용하여 제안된 구조의 적절성을 확인 하였으며, 이로부터 65.8%의 유효 흡수율을 얻을 수 있었다.

• 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.

• 한국결정성장학회지
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• 제10권4호
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• pp.297-301
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• 2000

H와 Li의 양자교환법에 의해 평면도파로와 channel도파로를 $LiNbO_3$단결정 기판위에 구현하였다. 양자원으로 피로인산을 사용하였고 평면도파로의 모드들에 대한 유효굴절률을 측정하였으며 반응시간과 반응온도로부터 광도파로의 깊이와 계단형 형태의 굴절률 변화에 대한 식을 구하였다. 이 식에서 구한 단일모드 도파 조건으로 channel 도파로를 제작하였고 입사광의 제한 효과를 관찰하였다.

• 한국연소학회지
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• 제19권1호
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• pp.29-38
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• 2014

This paper described an experimental investigations of combustion instability mode in a lean premixed dual swirl combustor for micro-gasturbine system. When such the instability occurs, a strong coupling between pressure oscillations and unsteady heat release excites a self-sustained acoustic wave which results in a loud, annoyed sound and may also lead a structural damage to the combustion chamber. The detailed period of flame behavior and heat release in combustion instability mode have been examined with high speed OH and CH-PLIF system and $CH^*$ chemiluminescence measurement, flame tomography with operated at 10 kHz and 6 kHz each. Experiment results suggest that unstable flame behavior has a specific frequency with 200 Hz and this frequency is accords with about 1/2 sub-harmonic of combustor resonance frequency, not fundamental frequency. This is very interesting phenomenon that have not reported yet from other previous works. Therefore, when a thermo-acoustic instability with Rayleigh criterion occurs, the fact that the period of heat release and flame behavior are different each other was proposed for the first time through this work.

• 대한토목학회논문집
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• 제28권6A호
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• pp.827-833
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• 2008

이 논문은 elastica형 아치의 자유진동에 관한 연구이다. Elastica형 아치의 선형은 항상 일정한 곡선길이를 갖는 후좌굴 기둥의 정확탄성곡선을 이용하였다. 이 Elastica형 아치의 곡률항을 일반아치의 자유진동을 지배하는 미분방정식에 적용하여 고유진동수 및 진동형을 산출하였다. 수치해석 예에서는 회전-회전, 회전-고정 및 고정-고정의 지점조건을 고려하였다. 회전관성이 고유진동수에 미치는 영향을 분석하고, 아치의 높이비 및 세장비와 고유진동수와의 관계를 그림에 나타내었다. Elastica형 아치와 포물선형 아치의 고유진동수를 비교한 결과, elastica형 아치의 고유진동수가 포물선 아치의 고유진동수보다 매우 크게 나타나는 동적 특성을 보였다. 진동형의 전형적인 예를 그림에 나타내었다.

• Bulletin of the Korean Chemical Society
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• 제29권8호
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• pp.1533-1538
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• 2008

Porphyrins generally bind DNA in two different ways with respect to the mixing ratio; monomeric binding at a low mixing ratio and outside stacking at a high mixing ratio. In the present study, CTDNA binding property of a planar structured porphyrin, 5,10,15,20-tetrakis(N-methyl-4-pyridin-4-yl-phenyl)porphyrin (referred to as B-TMPyP) was investigated using absorption, CD, LD, and $LD^r$ spectroscopies. B-TMPyP produced a bisignate CD band, even at the lowest mixing ratio, indicating that B-TMPyP may not have a monomeric binding mode. From the observations of the spectral changes to the absorption, CD, and LD spectra in mixing ratio dependent titrations, B-TMPyP seems to have a quite different stacking type compared to that for the binding of $H_2$TMPyP. Moreover, B-TMPyP produced a CD band of opposite shape in the Soret band region. A qualitative explanation for the observed optical differences is also given.