• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.272-273
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• 2011

유기발광소자는 차세대 디스플레이 소자로서 빠른 응답 속도, 높은 색 재현성 및 매우 얇은 두께로 제작이 가능한 장점을 가지고 있어서 차세대 디스플레이 소자로서 많은 응용 가능성을 가지고 있다. 청색 유기발광소자는 적색 및 녹색의 유기발광소자의 발광 효율 특성보다 상대적으로 효율이 떨어지고, 색 순도가 낮으며 수명이 짧은 단점을 가지고 있어 소자 특성을 개선해야 한다. 본 논문에서는 청색 유기발광소자의 색 순도와 색 안정성 증진을 위하여 발광층을 2개의 층으로 나누어 15 nm 두께의 4,4'-Bis(2,2-diphenyl-ethen-1-yl)diphenyl (DPVBi) 형광 청색 호스트 물질에 4,4 '-Bis[4-(diphenylamino)stylyl]biphenyl (BDAVBi) 형광 청색 게스트 물질을 첨가하여 제 1 형광 발광층을 형성하고 15 nm 두께의 4,4'-Bis(carbazol-9-yl)biphenyl (CBP) 인광 호스트 물질에 bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl)iridium III (FIrpic) 인광 게스트 물질을 첨가한 제 2 인광 발광층으로 구성된 30 nm 두께의 하이브리드 발광층을 사용하여 청색 유기 발광소자를 제작하고 전기적 특성과 광학적 성질을 조사하였다. 하이브리드 발광층을 사용하여 제작된 유기발광소자는 20 mA/cm2의 전류 밀도에서 6.2 cd/A의 발광 효율을 나타내었고, 최대 밝기는 약 16,200 cd/m2로 측정 되었다. 하이브리드 발광층을 사용한 청색 유기발광소자는 전류의 흐름이 단일 발광층 유기발광소자에 비교하여 상대적으로 안정적인 전류 흐름을 가지며 발광층 내부에 더 많은 정공과 전자를 포획하여 엑시톤 형성 확률이 증가하여 발광효율과 밝기가 향상되었다. 하이브리드 발광층을 적용한 유기발광소자는 469 nm파장에서 형광 발광층의 주 전계발광 피크가 나타났고 그와 함께 인광 발광층의 부 전계발광 피크가 491 nm의 파장에서 관측되었다. 또한 전계발광 스펙트럼의 반치폭이 10 nm 감소하여 청색의 색 순도 증가에도 기여하였다. 하이브리드 발광층을 가진 청색 유기발광소자의 색 좌표는 전압 변화에 관계없이 일정한 값을 나타내었다. 이러한 결과는 형광과 인광 발광층으로 구성된 하이브리드 발광층 유기발광소자가 전기적으로 안정성을 가지며 발광 특성을 개선하고 안정적인 청색 유기 발광 디스플레이 소자로 사용 가능함을 나타내고 있다.

• Journal of the Earthquake Engineering Society of Korea
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• v.3 no.2
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• pp.1-8
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• 1999

The present paper describes an approximation for estimation of earthquake-induced hydrodynamic loads in rigid storage tank which accelerated in horizontal direction. The storage tank is vertically cylindrical, and the sectional shape may be circular, rectangular or irregular. The solution for harmonic excitation is studied based on velocity potential theory, and then the time domain solution for earthquake is obtained by using design response spectrum. As a result, earthquake load is influenced primarily by the inertia force of high frequency effective mass of the storage tank, responding to the characteristics of design response spectrum, tank sectional shape, and the ratio of tank base length to depth. Earthquake-induced hydrodynamic loads in rigid storage tank can be effectively obtained by using the high frequency approximation method in case of quite large, or small ratio of the tank base length to water depth.

• Journal of the Korean Geotechnical Society
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• v.35 no.11
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• pp.111-119
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• 2019

The high-speed railway system is mainly composed of tunnel, bridge, and viaduct to meet the straightness needed for keeping the high speed up to 400 km/s. Seismic fragility for the high-speed railway infrastructure can be assessed as two ways: one way is studying each element of infrastructure analytically or numerically, but it requires lots of research efforts due to wide range of railway system. On the other hand, empirical method can be used to access the fragility of an entire system efficiently, which requires case history data. In this study, we collect the 2004 M_W 6.6 Niigata earthquake case history data to develop empirical seismic fragility function for a railway system. Five types of intensity measures (IMs) and damage levels are assigned to all segments of target system for which the unit length is 200 m. From statistical analysis, probability of exceedance for a certain damage level (DL) is calculated as a function of IM. For those probability data points, log-normal CDF is fitted using MLE method, which forms fragility function for each damage level of exceedance. Evaluating fragility functions calculated, we observe that T=3.0 spectral acceleration (SA_T3.0) is superior to other IMs, which has lower standard deviation of log-normal CDF and low error of the fit. This indicates that long-period ground motion has more impacts on railway infrastructure system such as tunnel and bridge. It is observed that when SA_T3.0 = 0.1 g, P(DL>1) = 2%, and SA_T3.0 = 0.2 g, P(DL>1) = 23.9%.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.24 no.6
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• pp.229-236
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• 2014

A stoichiometric mixture of evaporating materials for $MnAl_2S_4$ single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, $MnAl_2S_4$ mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the Hot Wall Epitaxy (HWE) system. The source and substrate temperatures were $630^{\circ}C$ and $410^{\circ}C$, respectively. The crystalline structure of the single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). The temperature dependence of the energy band gap of the $MnAl_2S_4$ obtained from the absorption spectra was well described by the Varshni's relation, $E_g(T)=3.7920eV-5.2729{\times}10^{-4}eV/K)T^2/(T+786 K)$. In order to explore the applicability as a photoconductive cell, we measured the sensitivity (${\gamma}$), the ratio of photocurrent to dark current (pc/dc), maximum allowable power dissipation (MAPD) and response time. The results indicated that the photoconductive characteristic were the best for the samples annealed in S vapour compare with in Mn, Al, air and vacuum vapour. Then we obtained the sensitivity of 0.93, the value of pc/dc of $1.10{\times}10^7$, the MAPD of 316 mW, and the rise and decay time of 14.8 ms and 12.1 ms, respectively.