• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1999년도 PROCEEDINGS OF 99 INTERNATIONAL CONFERENCE OF THE KACG AND 6TH KOREA·JAPAN EMG SYMPOSIUM (ELECTRONIC MATERIALS GROWTH SYMPOSIUM), HANYANG UNIVERSITY, SEOUL, 06월 09일 JUNE 1999
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• pp.81-114
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• 1999

The strain, surface and inerfacial energies of III-V ternary systems were calculated for three kinds of structure modes: the Frank-van der Merwe (FM) mode, the Stranski-Krastanov (SK) mode an the Volmer-Wever (VW) mode. The free energy for each mode was estimated as functions of the thickness and composition or lattice misfit. Through comparison of the free energy of each mode, it was found that the thickness-composition phase diagrams of III-V ternary systems can be determined only by considering the balance of the free energy and three kinds of structure modes appear in the phase diagrams. The SK mode appears only when the lattice misfit is large and/or the lattice layer is thick. The most stable structure of the SK mode is a cluster with four lattice layers or minimum thickness on a wetting layer of increasing lattice layers. The VW mode appears when the lattice misfit is large and the lattice layer is thin and only in the InPSb/InP and GaPSb/GaP systems which have the largest lattice misfit of III-V ternary systems. The stable region of the SK mode in the GaPSb/GaP and InPSb/InP phase diagrams is largest of all because the composition dependence of the strain energy of these systems is stronger than that of the other systems. The critical number of lattice layers below which tow-dimensional (2D) layers precede the three-dimensional (3D) nucleation in the SK mode at x=1.0 depnds on the lattice misfit.

• 한국결정성장학회지
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• 제9권4호
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• pp.387-395
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• 1999

The strain, surface and interfacial energies of III-V ternary systems were calculated for three kinds of structure modes: the Frank-van der Merwe(FM) mode, the Stanski-Krastanov(SK) mode and the Volmer-Weber(VW) mode. The free energy for each mode was estimated as functions of thickness and composition or lattice misfit. Through comparison of the free energy of each mode, it was found that the thickness-composition phase diagrams of III-V ternary systems can be determined only by considering the balance of the free energy and three kinds of structure modes appear in the phase diagrams. The SK mode appears only when the lattice misfit is large and/or the lattice layer is thick. The most stable structure of the SK mode is a cluster with four lattice layers or minimum thickness on a wetting layer of increasing lattice layers. The VW mode appears when the lattice misfit is large and the lattice layer is thin and only in the INPSb/InP and GaPSb/GaP system which have the largest lattice misfit of III-V ternary systems. The stable region of the SK mode in the GaPSb/GaP and InPSb/InP phase diagrams is largest of all because the composition dependence of the strain energy of these systems is stronger than that of the other systems. The critical number of lattice layers below which two-dimensional(2D) layers precede the three-dimensional(3D) nucleation in the SK mode at x=1.0 depends on the lattice misfit.

• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2004년도 하계학술대회
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• pp.31-34
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• 2004

본 논문에서는 현재 위성 DMB 국내 표준으로 채택되어 있는 System E 방식의 Dual Mode 신호 전송에 따른 신호변환시 Time Delay측정 방법에 대해서 제안을 하였다. 제안된 방식의 경우 아날로그 방식이 아닌 디지털 방식으로 정확한 Time Delay 측정이 가능하다. 그리고 위성 DMB Gap Filler System의 입 출력 단자를 통하여 측정이 가능함으로 측정값에 대한 신뢰성 확보가 가능하며 자동측정 방식임으로 측정시 발생될 수 있는 Human Error를 최소화 할 수 있다는 장점을 가지고 있다.

• 한국통신학회논문지
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• 제23권5호
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• pp.1282-1290
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• 1998

In this paper, the physical layer design of IMT-2000 system being developed by SK Telecom is introuduced. The outband signaling scheme and the two-pilot scheme are adopted for multimedia service and inter-cell asynchronous mode respectively. In addition, the synchronous transmission scheme is proposed to reduce the interference in the reverse link. The algorithm and simulation results of 'two-pilot scheme' for inter-cell asynchronous mode and 'reverse synchronous control' for synchronous transmission are presented.

• 생약학회지
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• 제30권4호
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• pp.377-383
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• 1999

The anti-asthmatic activities of the extract of Lonicera japonica (BuOH fraction) and its mode of action were investigated using several in vitro and in vivo models. Lonicera japonica was extracted with 30% ethanol (v/v) and successively partitioned into BuOH. The BuOH fraction reduced antigen-induced contraction of isolated trachea from sensitized guinea pigs in a concentration-dependent manner. The BuOH fraction also inhibited histamine release from rat peritoneal mast cells induced by antigen or calcium ionophore A23187 ($IC_{50}=0.26$ and 0.32mg/ml, respectively). Eosinophil infiltration into bronchoalveolar lavage fluids induced by aeroallergen challenge in passively sensitized guinea pigs was inhibited by the BuOH fraction at a dose of 800mg/kg (51.7%). In addition, the BuOH fraction inhibited leukotriene $B_4$ prodution in rat basophilic leukemia cells ($IC_{50}=0.42\;mg/ml$) as well as phosphodiesterase 4 (PDE4) isolated from rat brain ($IC_{50}=0.015\;mg/ml$). All results from this study strongly suggest that the BuOH fraction of Lonicera japonica may be useful in the treatment of asthma and its mode of action may be related with inhibition of both 5-lipoxygenase and PDE4 enzyme.

• 터널과지하공간
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• 제29권6호
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• pp.523-531
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• 2019

암석역학이나 암반공학의 여러 활용 분야 중 발파, 천공 및 기계굴착의 경우에는 파괴인성이 중요한 요소이며, 암석의 파괴인성을 측정하기 위한 여러 가지 방법들이 제안되었다. 본 연구에서는 간단히 시험편을 제작할 수 있고, 압축 하중으로 암석의 모드 I 파괴인성을 구할 수 있도록 쐐기 분열 시험편(Wedge Splitting Test Specimen)을 이용하였다. 쐐기의 작용하는 연직하중에 의한 수직 및 수평하중 모두를 고려한 균열선단의 응력상태로부터 수치해석을 통한 응력확대계수의 식을 제안하였다. 쐐기 분열 시험편에 의해 구해진 모드 I 파괴인성값을 GD와 SENB 시험편의 시험 결과와 비교하여 시험법의 타당성을 확인하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.187-187
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• 2013

양자점(Quuantum dot, QD)은 0차원 특성을 가지는 구조로 양자 구속 효과로 인하여 bulk와 는 다른 구조적, 광학적, 전기적 특성을 가지고 있다. InAs QD는 size와 barrier의 bandgap 조절을 이용하여 쉽게 bandgap을 바꿀 수 있는 장점이 있어 solar cell, semiconductor laser diode, infrared photodetector 등으로 많은 연구가 이루어지고 있다. 일반적으로 Stranski-Krastanov (SK) mode로 성장한 InAs QD는 보통 GaAs epilayer와의 lattice mismatch (7%)를 이용하여 성장을 하고 이로 인하여 strain을 가지고 있고 QD의 density와 stack이 높을수록 strain이 커진다. 하지만 sub-monolayer (SML) QD 같은 경우 wetting layer가 생기는 지점인 1.7 ML이하에서 성장되는 성장 방식으로 SK-QD보다는 작은 strain을 가지게 된다. 또 QD의 size가 작아 SK-QD보다 큰 bandgap을 가지고 있다. 본 연구에서는 분자선 에피택시(molecular beam epitaxy, MBE)를 이용하여 semi-insulating GaAs substrate 위에 InAs QD를 0.5/1/1.5/1.7/2/2.5 monolayer로 성장을 하였다. GaAs과 InAs의 성장온도와 성장속도는 각각 $590^{\circ}C$, 0.8 ML/s와 $480^{\circ}C$, 0.2 ML/s로 성장을 하였으며 적층사이의 interruption 시간은 10초로 고정하였고 10주기를 성장하였다. Photoluminescence (PL)측정 결과 SML-QD는 size에 따라서 energy가 1.328에서 1.314 eV로 약간 red shift를 하였고 SK-QD의 경우 1.2 eV의 energy정도로 0.1 eV이상 red shift 하였다. 이는 QD size에 의하여 energy shift가 있다고 사료된다. 또 wetting layer의 경우 1.41 eV의 energy를 가지는 것으로 확인 하였다. SML-QD는 SK-QD 보다 반치폭(full width at half maximum, FWHM)이 작은 것은 확인을 하였고 strain field의 감소로 해석된다. 하지만 SML-QD의 경우 SK-QD보다 상대적으로 작은 PL intensity를 가지고 있었다. 이를 개선하기 위해서는 보다 높은 QD density를 요구하게 되는데 growth temperature, V/III ratio, growth rate 등을 변화주어서 연구할 계획이다.

• 전기화학회지
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• 제5권1호
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• pp.27-29
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• 2002

본 연구는 메탄올과 공기를 이용하여 상온, 상압에서 전기를 발생시키는 휴대폰용 전원공급 장치의 개발에 관한 것이다. 이 장치는 직접 메탄을 연료전지(DMFC)와 Back-up전지가 병렬로 연결되어 있어, 통화시 소요 전력의 최대 $50\%$ DMFC가 공급하고 나머지 부분은 Back-up 전지가 공급한다. 또한 통화 대기시에는 DMFC가 $100\%$ 필요 전력을 공급하고, 잉여 전력으로 Back-up전지를 충전한다. 상기 DMFC는 유효면적이 $9cm^2$인 8개의 단위전지가 직렬로 연결되어 있으며, 휴대폰의 작동 전압 범위인 2.5-3.9V의 전압을 출력한다.

• Journal of Electrical Engineering and Technology
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• 제7권6호
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• pp.869-875
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• 2012

Because of the nature of wind, the output power of wind turbines fluctuates according to wind speed variation. Therefore, many countries have set up wind-turbine interconnection standards usually named as Grid-Code to regulate the output power of wind farms to improve power system reliability and power quality. This paper proposes three operation modes of wind farms such as maximum power point tracking (MPPT) mode, single wind turbine control mode and wind farm control mode to control the output power of wind turbines as well as overall wind farms. This paper also proposes an operation scheme of wind farm to alleviate power fluctuation of wind farm by choosing the appropriate control mode and coordinating multiple wind turbines in consideration of grid conditions. The performance of the proposed scheme is verified via simulation studies in PSCAD/EMTDC with doubly-fed induction generator (DFIG) based wind turbine models.

• Mass Spectrometry Letters
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• 제2권2호
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• pp.41-44
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• 2011

Molecular compositions of two types of heavy oil were studied using positive atmospheric pressure photoionization (APPI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Vacuum gas oil (VGO) was generated from vacuum distillation of atmospheric residual oil (AR), and slurry oil (SLO) was generated from catalytic cracking of AR. These heavy oils have similar boiling point ranges in the range of 210-$650^{\circ}C$, but they showed different mass ranges and double-bond equivalent (DBE) distributions. Using DBE and carbon number distributions, aromatic ring distributions, and the extent of alkyl side chains were estimated. In addition to the main aromatic hydrocarbon compounds, those containing sulfur, nitrogen, and oxygen heteroatoms were identified using simple sample preparation and ultra-high mass resolution FT-ICR MS analysis. VGO is primarily composed of mono- and di-aromatic hydrocarbons as well as sulfur-containing hydrocarbons, whereas SLO contained mainly polyaromatic hydrocarbons and sulfur-containing hydrocarbons. Both heavy oils contain polyaromatic nitrogen components. SLO inludes shorter aromatic alkyl side chains than VGO. This study demonstrates that APPI FT-ICR MS is useful for molecular composition characterization of petroleum heavy oils obtained from different refining processes.