• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.104-104
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• 2011

ZnO는 3.37 eV의 넓은 에너지 밴드갭을 갖는 투명 전도성 반도체이며 우수한 전기적, 광학적 특성으로 인해 광원소자 개발을 위한 새로운 물질로 많은 주목을 받아왔다. 더욱이, ZnO는 쉽게 나노구조 형성이 가능하기 때문에 이를 응용한 가스센서, 염료감응태양전지, 광검출기 등의 소자 개발이 활발히 이루어지고 있다. 최근에는 GaN 기반 발광다이오드 (light emitting diode, LED)의 광추출 효율을 향상시키기 위한 ZnO 나노구조 응용에 관한 연구가 보고되고 있다. GaN 기반 LED의 경우 반도체 물질과 공기 사이의 높은 굴절률 차이로 인하여 낮은 광추출 효율을 나타낸다. 이를 해결하기 위한 방법으로 표면 roughening, texturing 등 에칭공정을 이용해 광추출 효율을 개선하려는 연구들이 보고되고 있으나, 복잡한 공정과정을 필요로 하고 에칭공정에 의한 소자 표면 손상으로 전기적 특성이 나빠질 수 있다. 반면 전기화학증착법으로 성장된 ZnO 나노구조를 이용할 때, 보다 간단한 방법으로 쉽고 빠르게 나노구조를 형성할 수 있고 낮은 공정온도를 가지기 때문에 소자의 전기적 특성에 큰 영향을 주지 않는다. 수직방향으로 잘 정렬된 ZnO 나노구조를 갖는 LED의 경우 내부 Fresnel 반사 손실을 효과적으로 줄여 발광 효율을 크게 향상시킬 수 있다. 따라서, ZnO 나노구조의 성장제어 및 성장특성을 분석하는 것은 매우 중요하다. 본 연구에서는 ITO glass 위에 ZnO 나노구조를 성장하고 그 특성을 분석하였다. ITO glass 기판 위에 RF magnetron 스퍼터를 사용하여 Al 도핑된 ZnO (AZO)를 얇게 증착한 후 전기화학증착법으로 ZnO 나노구조를 성장하였다. 농도, 인가전압, 공정시간 등 다양한 공정조건을 변화시키면서 성장 메커니즘을 분석하였고, scanning electron microscope (SEM) 및 X-ray diffraction (XRD)을 통하여 구조 및 결정성 등을 분석하였다. 또한, UV-Visible-NIR spectrophotometer를 사용하여 투과율을 실험적으로 측정하여 ZnO 나노구조의 광학적 특성을 분석하였고, rigorous coupled wave analysis (RCWA) 방법을 사용하여 계면에서 발생하는 내부 반사율을 계산함으로써 나노구조의 효과를 이론적으로 분석하였다.

• 대한조선학회논문집
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• 제29권1호
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• pp.103-112
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• 1992

선박의 최종굽힘 모멘트는 설계에 적용되는 주요강도로써 이를 추정하는 여러방법들이 제안되었는데, 판과 보강재로 이루어진 구조요소의 압축 최종강도에 대한 추징에서 시작되는 것이 일반적이다. 본 논문에서는 최종굽힘 모멘트를 구하기 위해 보강판의 압축 강도추정을 지금까지 제안된 여러가지 방법을 정리하여 소개하고, 실선 설계에 적용될 수 있는 유용성 측면에서 검토하였다. 그 결과를 이용하여 3척의 살물선에 대한 신뢰성 해석을 수행하였다. 선박에 작용하는 파랑굽힘 모멘트는 선급규정에 의해 계산하였다. 본 연구의 신뢰성 해석 문제는 안전여유식의 형태가 비선형임을 고려하여 Advanced First-Order Reliability Method를 이용하였다. 몇가지의 해석예로부터 선체구조의 신뢰성 검토측면에서 최종강도 추정방법을 비교하였다.

• Journal of Ginseng Research
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• 제31권3호
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• pp.159-174
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• 2007

Pharmacology of Korean Red ginseng gives us unique possibility to develop new class of antiepileptic drugs today and to improve one's biological activity. The chemical structures of ginsenosides (GS) have some principal differences from well-known antiepileptic new generation drugs. The antiepileptic effect of GS was also demonstrated in all models of epilepsy in rats (young and adult), which have studied, in all models of epilepsy including status epilepticus (SE), induced by lithium - pilocarpine. In our experiments in rats new evidences on protective effects were exerted as a result of premedication by GS. Pre-treatment of several GS could induce decrease of the seizures severity and brain structural damage (by MRI), neuronal degeneration in hippocampus. Wave nature of severity of motor seizures during convulsive SE was observed during lithium-pilocarpine model of SE in rats (the first increase of seizures was 30 min after the beginning of SE and the second - 90 min after. The efficacy of treatment on SE by ginsenoside as expected was observed after no less 3 weeks by daily GS i.p. administration. It is blocked SE or significantly decrease the severity of seizures during SE. The implication of presented data is that combination of ginsenosides from Korean Red ginseng and ginseng cell culture Dan25 that could be applied for prevention of epileptical status development. However, a development of optimal ratio of different ginsenosides $(Rb_1$ Rc, Rg, Rf,) should consummate in the new antiepileptic drug development.

• 반도체디스플레이기술학회지
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• 제15권2호
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• pp.26-31
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• 2016

The Townsend to glow discharge mode transition was investigated in the dielectric barrier discharge (DBD) helium plasma source which was powered by 20 kHz / $4.5 kV_{rms}$ high voltage at atmospheric pressure. The spatial profile of the electric field strength at each modes was measured by using the intensity ratio method of two helium emission lines (667.8 nm ($3^1D{\rightarrow}2^1P$) and 728.1 nm ($3^1S{\rightarrow}2^1P$)) and the Stark effect. ICCD images were analyzed with consideration for the electric field property. The Townsend discharge (TD) mode at the initial stage of breakdown has the light emission region located in the vicinity of the anode. The electric field of the light emitting region is close to the applied field in the system. Immediately, the light emitting region moves to the cathode and the discharge transits to the glow discharge (GD) mode. This mode transition can be understood with the ionization wave propagation. The electric field of the emitting region of GD near cathode is higher than that of TD near anode because of the cathode fall formation. This observation may apply to designing a DBD process system and to analysis of the process treatment results.

• Earthquakes and Structures
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• 제14권6호
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• pp.577-587
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• 2018

The quantitative assessment of the seismic collapse risk of a structure requires the usage of an optimal intensity measure (IM) which can adequately characterise the severity of the ground motion. Research suggests that the average spectral acceleration ($Sa_{avg}$) may be an efficient and sufficient alternate IM as compared to the more traditional first mode spectral acceleration, $Sa(T_1)$, particularly during seismic collapse risk estimation. This study primarily presents a comparative evaluation of the sufficiency of the average spectral acceleration with respect to ground motion duration, and secondarily assesses the impact of ground motion duration on collapse risk estimation. By assembling a suite of 100 historical ground motions, incremental dynamic analysis of 60 different inelastic single-degree-of-freedom (SDF) oscillators with varying periods and ductility capacities were analysed, and collapse risk estimates obtained. Linear regression models are used to comparatively quantify the sufficiency of $Sa_{avg}$ and $Sa(T_1)$ using four significant duration metrics. Results suggests that an improved sufficiency may exist for $Sa_{avg}$ when the period of the SDF system increases, particularly beyond 0.5, as compare to $Sa(T_1)$. In reference to the ground motion duration measures, results indicated that the sufficiency of $Sa_{avg}$ is more sensitive to significant duration definitions that consider almost the full wave train of an accelerogram ($SD_{a5-95}$ and $SD_{v5-95}$). In order to obtain a reduced variability of the collapse risk estimate, the 5-95% significant duration metric defined using the Arias integral ($SD_{a5-95}$) should be used for seismic collapse risk estimation in conjunction with $Sa_{avg}$.

• 천문학회보
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• 제37권2호
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• pp.115.2-115.2
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• 2012

In this study we have used the data of various instruments onboard the THEMIS spacecraft to study the characteristics of the outer radiation belt during the ascending phase of solar cycle 24. The most astonishing result is that we discovered four long-term (a month or so) periods during which the belt has nearly disappeared. The first disappearance started late 2008, followed by reappearance in ~a month, and three more similar events repeated until early 2010 when the belt has reappeared. This is well revealed at 719 keV electrons, which is the currently available uppermost energy channel from the THEMIS SST observation, but also seen at even lower energies. Overall consistent features were confirmed using the NOAA-POES observations. The vanished belt periods are associated with extremely weak solar wind conditions, low geomagnetic disturbances (in terms of Kp and AE/AL), greatly suppressed wave (ULF and chorus) activities, greatly reduced storm and substorm activities (little source particle supply), and expanded plasmapause locations. The direct observations of such events shed light on the fundamental question of the origin of the radiation belt, which is the main focus of our presentation.

• Nuclear Engineering and Technology
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• 제40권3호
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• pp.213-224
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• 2008

The pumping of coolant in a liquid metal fast reactor may be performed with an annular linear induction electro-magnetic (EM) pump. Linear induction pumps use a traveling magnetic field wave created by poly-phase currents, and the induced currents and their associated magnetic field generate a Lorentz force, whose effect can be the pumping of the liquid metal. The flow behaviors in the pump are very complex, including a time-varying Lorentz force and pressure pulsation, because an induction EM pump has time-varying magnetic fields and the induced convective currents that originate from the flow of the liquid metal. These phenomena lead to an instability problem in the pump arising from the changes of the generated Lorentz forces along the pump's geometry. Therefore, a magneto-hydro-dynamics (MHD) analysis is required for the design and operation of a linear induction EM pump. We have developed a time-harmonic 2-dimensional axisymmetry MHD analysis method based on the Maxwell equations. This paper describes the analysis and numerical method for obtaining solutions for some MHD parameters in an induction EM pump. Experimental test results obtained from an induction EM pump of CLIP-150 at the STC "Sintez," D.V. Efremov Institute of Electro-physical Apparatus in St. Petersburg were used to validate the method. In addition, we investigated some characteristics of a linear induction EM pump, such as the effect of the convective current and the double supply frequency (DSF) pressure pulsation. This simple model overestimated the convective eddy current generated from the sodium flow in the pump channel; however, it had a similar tendency for the measured data of the pump performance through a comparison with the experimental data. Considering its simplicity, it could be a base model for designing an EM pump and for evaluating the MHD flow in an EM pump.

• International Journal of Naval Architecture and Ocean Engineering
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• 제5권1호
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• pp.161-177
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• 2013

High-speed vessels require good resistance and seakeeping performance for safe operations in rough seas. The resistance and seakeeping performance of high-speed vessels varies significantly depending on their hull forms. In this study, three planing hulls that have almost the same displacement and principal dimension are designed and the hydrodynamic characteristics of those hulls are estimated by high-speed model tests. All model ships are deep-V type planing hulls. The bows of no.2 and no.3 model ships are designed to be advantageous for wave-piercing in rough water. No.2 and no.3 model ships have concave and straight forebody cross-sections, respectively. And length-to-beam ratios of no.2 and no.3 models are larger than that of no.1 model. In calm water tests, running attitude and resistance of model ships are measured at various speeds. And motion tests in regular waves are performed to measure the heave and pitch motion responses of the model ships. The required power of no.1 (VPS) model is smallest, but its vertical motion amplitudes in waves are the largest. No.2 (VWC) model shows the smallest motion amplitudes in waves, but needs the greatest power at high speed. The resistance and seakeeping performance of no.3 (VWS) model ship are the middle of three model ships, respectively. And in regular waves, no.1 model ship experiences 'fly over' phenomena around its resonant frequency. Vertical accelerations at specific locations such as F.P., center of gravity of model ships are measured at their resonant frequency. It is necessary to measure accelerations by accelerometers or other devices in model tests for the accurate prediction of vertical accelerations in real ships.

• 한국수소및신에너지학회논문집
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• 제25권4호
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• pp.378-385
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• 2014

In this research, we investigate electrical performance and electrochemical properties of graphene supported Pt (Pt/G) and PtM (M = Ni and Y) alloy catalysts (PtM/Gs) that are synthesized by modified polyol method. With the PtM/Gs that are adopted for oxygen reduction reaction (ORR) as cathode of proton exchange membrane fuel cells (PEMFCs), their catalytic activity and ORR performance and electrical performance are estimated and compared with one another. Their particle size, particle distribution and electrochemically active surface (EAS) area are measured by TEM and cyclic voltammetry (CV), respectively. On the other hand, regarding ORR activity and electrical performance of the catalysts, (i) linear sweeping voltammetry by rotating disk electrode and rotating ring-disk electrode and (ii) PEMFC single cell tests are used. The TEM and CV measurements demonstrate particle size and EAS of PtM/Gs are compatible with those of Pt/G. In case of PtNi/G, its half-wave potential, kinetic current density, transferred electron number per oxygen molecule and $H_2O_2$ production % are excellent. Based on data obtained by half-cell test, when PEMFC singlecell tests are carried out, current density measured at 0.6V and maximum power density of the PEMFC single cell employing PtNi/G are better than those employing Pt/G. Conclusively, PtNi/Gs synthesized by modified polyol shows better ORR catalytic activity and PEMFC performance than other catalysts.

• 한국전자파학회논문지
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• 제28권8호
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• pp.646-652
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• 2017

큰 부피의 플라즈마를 발생시키기 위하여 플라즈마 층을 포함하는 유전체 장벽 방전 구조(dielectric barrier discharge)를 제안하고, 발생기 동작 유무에 따른 모노스태틱 레이다 단면적(mono-static radar cross section)을 측정함으로써 대기압 플라즈마가 전자기파에 미치는 영향을 분석하였다. 다수의 전극을 평면으로 평행 배열함으로써 플라즈마 층의 부피를 증가시켰으며, 전극 배열과 수직인 방향의 전기장을 포함하는 전자기파를 입사시킴으로써 발생기와의 원치 않는 커플링을 최소화 시켰다. 실험 결과, 모노스태틱 레이다 단면적을 2 GHz부터 25 GHz까지 측정하였을 때, K band에서 최대 8 dB까지 감소하는 것을 확인하였다. 또한, 고전압 발생기의 인가 전압을 최대 20 kV까지 변화시킴으로써 원하는 주파수에서 플라즈마로 인한 감소치를 유연하게 조절 가능함을 보였다.