• 비파괴검사학회지
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• 제34권6호
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• pp.457-466
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• 2014

This paper presents an analytic and numerical simulation of the generation and propagation of pico-second ultrasound with nano-scale wavelength, enabling the production of bulk waves in thin films. An analytic model of laser-matter interaction and elasto-dynamic wave propagation is introduced to calculate the elastic strain pulse in microstructures. The model includes the laser-pulse absorption on the material surface, heat transfer from a photon to the elastic energy of a phonon, and acoustic wave propagation to formulate the governing equations of ultra-short ultrasound. The excitation and propagation of acoustic pulses produced by ultra-short laser pulses are numerically simulated for an aluminum substrate using the finite-difference method and compared with the analytical solution. Furthermore, Fourier analysis was performed to investigate the frequency spectrum of the simulated elastic wave pulse. It is concluded that a pico-second bulk wave with a very high frequency of up to hundreds of gigahertz is successfully generated in metals using a 100-fs laser pulse and that it can be propagated in the direction of thickness for thickness less than 100 nm.

• 한국추진공학회지
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• 제18권5호
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• pp.87-94
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• 2014

고성능 연소추진 시스템의 고주파 연소불안정 현상을 이해하기 위해서는 연소 열발생과 유동 섭동간의 에너지 교환 메커니즘 이해가 필수적이다. 화염의 동적 특성 변화를 인위적인 섭동을 통해 화염전달함수로 표현하고 이해하고자 하는 다수의 실험적 연구가 진행되어 왔다. 이 가운데 특히 연소기 입구 유동에 섭동을 가진하여 축 방향 섭동에 대한 화염반응을 살펴보는 연구가 활발히 진행되었다. 최근에는 실제 연소시스템에서 발생하는 횡 방향 음향모드를 모의하는 연구들이 진행되고 있다.

• Journal of Information Display
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• 제2권3호
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• pp.13-17
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• 2001

The manganese-doped magnesium tin oxide with spinel structure was selected as a green phosphor for FED application and was synthesized by the solid state reaction. Its luminescence properties were investigated under low-voltage electron excitation. The $Mg_2SnO_4$:Mn phosphor showed green emission with the spectrum centered at 500 nm due to energy transfer from $^4T_1$ to $^6A_1$ of $Mn^{2+}$ ion. Optimum Mn concentration was 0.6 mole % and the decay time was shorter than 10 ms.

• 한국전기전자재료학회논문지
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• 제23권8호
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• pp.627-631
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• 2010

ZnS:Mn yellow phosphors doped with Cu for white light emitting diodes were synthesized by solid state reaction method. The optical properties and structures of ZnS:Mn,Cu phosphors were investigated by x-ray diffraction, photoluminescence, and scanning electro microscopy. Photoluminescence excitation spectra originated from $Mn^{2+}$ were ranged from 450 nm to 500 nm. The yellow emission at around 580 nm was associated with $^4T_1{\rightarrow}^6A_1$ transition of $Mn^{2+}$ ions in ZnS:Mn,Cu phosphors. The highest photoluminescence intensity of the phosphors under 405 nm excitation was obtained at Cu concentration of 0.02 mol%. The enhanced photoluminescent intensity in the ZnS:Mn,Cu phosphors was interpreted by energy transfer from Cu to Mn.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 춘계학술대회논문집
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• pp.567-571
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• 2005

The slender rectangular cantilever beam has vef interesting to study dynamic behaviors of the harmonic base excitation of a cantilever beam shows many nonlinear dynamics due to unstability , energy transfer and mode coupling. Nonlinear phenomenon shows superharmonic, subharmonic, super subharmonic and chaotic motions of the cantilever beam. Experimental observation and verification of these phenomenon carry much importance for the theoretical study as well as in it self. In the experimental cantilever beam, the chaotic motions of the beam appear as a pink noise signal in FFT analysis and as a torus structure in the oscilloscope analyzed to eventually give information of chaotic motions of the cantilever beam.

• 한국소음진동공학회논문집
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• 제14권12호
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• pp.1314-1321
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• 2004

The non-linear responses of a slender rectangular cantilever beam subjected to lateral harmonic base-excitation are investigated by the 2-channel FFT analyzer. Both linear and nonlinear behaviors of the cantilever beam are compared with each other. Bending mode, torsional mode, and transverse mode are coupled in such a way that the energy transfer between them are observed. Especially, superharmonic, subharmonic, and chaotic motions which result from the unstable inertia terms in the transverse mode are analyzed by the FFT analyzer The aim is to give the explanations of the route to chaos, i.e., harmonic motion \longrightarrow superharmonic motion \longrightarrow subharmonic motion \longrightarrow chaos.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2006년도 6th International Meeting on Information Display
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• pp.1355-1359
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• 2006

Due to its efficient red emission, $Eu^{3+}$ ion has been doped in various host materials. $GdCa_4B_3O_{10}:Eu^{3+}$ phosphor for red emission has been prepared by solid state reaction. Photoluminescence properties for the phosphor under UV and VUV excitation were investigated. The $GdCa_4B_3O_{10}:Eu^{3+}$ phosphor under both excitation conditions shows typical red emission spectrum centered at 611 nm with several weak peaks due to energy transfer from $^5D_O\;to\;^7F_J(J=1,2,3,4)$ of $Eu^{3+}$ ion. On the other hand, the activator content exhibiting the concentration quenching under UV and VUV irradiation is 10 mole% and 2.5 mole%, respectively.

• Journal of Photoscience
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• 제1권1호
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• pp.75-82
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• 1994

General features of the fluorescence depolarization are briefly reviewed. Molecular rotations and electronic excitation transports are considered to account for the fluorescence depolarization. Various molecular systems studied by the fluorescence depolarization are described. The FiSrster theory which forms a basis for the energy transfer is revisited. Several theoretical treatments for the fluorescence depolarization in liquid and solid phases such as classical hydrodynamics, probability distribution function, Green's function formalism, molecular dynamics simulation and Monte Carlo methods are introduced.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2008년도 International Meeting on Information Display
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• pp.1509-1512
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• 2008

Monomer and aggregate of $Bebq_2$ give fluorescence at 492 and 511 nm at 12 K, respectively. Intense T1 emission with vibronic structure was observed from $Bebq_2$ and $Alq_3$ below 70 K by heavily doping with phosphorescent $Ir(ppy)_3$. Energy transfer from $Ir(ppy)_3$ was clarified by photoluminescence excitation spectra.

• 한국광학회:학술대회논문집
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• 한국광학회 2007년도 하계학술발표회 논문집
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• pp.107-107
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• 2007