• Journal of the Korean Magnetics Society
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• v.22 no.4
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• pp.121-124
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• 2012

We have studied electronic and magnetic structure of cubane-type Mn4 cluster using OpenMX method based on density functional method. The calculated density of states shows that the octahedron of O atoms split $e_g$ and $t_{2g}$ energy levels like bulk MnO with cubic structure. Total energy with antiferromagnetic spin configuration is lower than those of other spin configurations because of super exchange interaction. Calculated exchange interaction J between Mn atoms with anti-parallel spin is larger than between Mn atoms with parallel spin.

• Proceedings of the KSRS Conference
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• 2009.03a
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• pp.129-133
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• 2009

본 연구에서 소개할 SEBAL (Surface Energy Balance Algorithm for Land) (Bastiaanssen, 1995) 모형은 Landsat이나 NOAA 또는 MODIS 같은 원격탐사 위성으로부터 획득한 디지털 이미지 데이터(위성영상)를 이용하여, 지표에서 일어나는 증발산과 기타의 에너지 교환을 계산하는 이미지-프로세싱 모델이다. SEBAL 모형은 1995년 Bastiaanssen에 의해 처음 제안되었고, 미국의 Idaho 주립대학과 Idaho Department of Water Resources에서 NASA와 기업의 지원을 받아 활발히 연구 되었으며, 25개의 sub model들을 이용하여 지표의 증발산량과 기타 여러 에너지 교환을 계산한다. 여기서, 열적외선 방사, 표시 및 근적외선 측정은 Landsat 또는 기타 여러 위성영상을 통해 얻을 수 있으며, SEBAL 모형은 이러한 자료를 활용한다. 모형에서의 증발산량(ET)은 에너지 균형원리를 통해 pixel-by-pixel을 기준으로 계산되며, 본 연구에서 SEBAL 모형은 한강 유역 내의 경안천 유역 증발산량 map 생성을 위해 6개년도 지점 Landsat 위성영상을 이용하어 추정되었다. 연구의 목적은 SEBAL 모형을 통해 생성 된 30m 해상도의 공간 증발산량 map의 활용성 평가와 검증이며, 검증을 위해 FAO Penman-Monteith 공식을 이용하여 추정된 증발산량 값을 이용하였다. 그 결과, 오차가 2.7% 이내로 나타났다.

• Membrane Journal
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• v.31 no.4
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• pp.275-281
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• 2021

To evaluate the possibility as a separator in alkaline water electrolysis, the thermal stability, ion conductivity and durability of 5 commercially available anion exchange membranes were tested. The thermal stability of FAAM-PK-75 and FAAM-40 membrane analyzed by thermo-gravimetric analysis (TGA) showed good performance compared to the other three types of AEM, AHO, and AHA membrane. The ion conductivity of AEM membrane measured in 7 M KOH solution at 25℃ and 80℃ had a higher value of about 4~17 times compared to the other membranes. The durability of FAAM-PK-75 tested in 7 M KOH solution at 25℃ was high compared to the other membranes.

• Transactions of the Korean hydrogen and new energy society
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• v.33 no.1
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• pp.28-37
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• 2022

In this study, we synthesized a poly(pheneylene oxide) (PPO)-based organic/inorganic composite membrane having silicotungstic acid (STA) for the development of an anion exchange membrane with excellent ionic conductivity and physicochemical stability. The organic/inorganic composite membranes were prepared by introducing different STA contents (0 wt%, 10 wt%, 30 wt%, and 50 wt%) into the quaternizaed(Q)-PPO matrix. The prepared anion exchange membranes were subjected to structural analysis by proton neclear magnetic resonance and Fourier transform infrared, and thermal behavior of membranes was confirmed by thermogravimetric analysis. Among the prepared composite membranes, the ion conductivity of Q-PPO/STA-50 (40.5 mS cm^-1) showed 1.46 times compared to that of the pristine membrane (27.6 mS cm^-1). Therefore, these results demonstrated that organic/inorganic composite membranes are promising candidates for application of anion exchange membranes.

• Journal of IKEEE
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• v.11 no.4
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• pp.205-212
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• 2007

The ubiquitous sensor network consists of micro sensors with wireless communication capabilities. Compared to wired communication, wireless communication is more subject to eavesdropping as well as data variation and manipulation. Accordingly, there must be efforts to secure the information delivered over the sensor network. Providing security to the sensor network, however, requires additional energy consumption, which is an important issue since energy transformation is difficult to implement in a sensor network. This paper proposes a routing mechanism based on the energy-efficient cluster that features security functions capable of safely processing the data acquired from the sensor network. The proposed algorithm reduces energy consumption by fixing the clusters formed at the initial stage and using the pre-distribution scheme so that the cluster and node keys generated and exchanged at the initial stage are not re-generated or re-exchanged. Simulation experiments confirmed that the proposed approach reduces energy consumption compared to implementing security measures to the conventional cluster-based routing mechanism.

• Journal of the Korean Society for Marine Environment & Energy
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• v.14 no.4
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• pp.249-256
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• 2011

Lagrangian particle transport model coupled with the EFDC have been performed to estimate the residence time and water exchange rate by release time of pollutants over a tidal cycle in Masan Bay. The modelled residence time for the whole bay was about 40 days, ranging from less than 20 days in the southern parts of Budo, to over 100 days in the upper parts of Somodo. The spatial difference of residence time was controlled by tidal residual currents and the distance to the bay channel. The area mean residence time during spring and neap tides was estimated to be about 36 days and 42 days, respectively. The time required for 30% exchange of water was calculated as ranging from 65 to 105 days by release time of pollutants.

• Journal of the Korean Institute of Gas
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• v.21 no.4
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• pp.42-46
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• 2017

As $CO_2$ emission with imprudent using fossil fuel, annual mean temperature of earth is increased in every year. Geothermal energy is inexhaustible energy resource to solve this problem. Heat pump performance and heat exchange efficiency of ground loop are important to distribute widely. Thus, this study are performed to increase heat pump performance and heat exchange efficiency of ground loop with dual expansion valves and spacer. As a results, COP of cooling & heating is obtained improvement up to 11.4% using dual expansion valves, and heat exchange efficiency is increased up to 17.5% using spacer. It will be reduced initial installation cost due to increasing heat pump performance and heat exchange efficiency of ground loop.

• Journal of the Korean Magnetics Society
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• v.20 no.2
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• pp.75-82
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• 2010

A recent progress on the prediction of the thermal stability of a nanostructured exchange-coupled trilayer is reviewed. An analytical/numerical combined method is used to calculate its magnetic energy barrier and hence the thermal stability parameter. An important feature of the method is the use of an analytical equation for the total energy that contains the magnetostatic fields. Under an assumption of the single domain state, the effective values of all the magnetostatic fields can be obtained by averaging their nonuniform values over the entire magnetic volume. In an equilibrium state, however, it is not easy to calculate the magnetostatic fields at the saddle point due to the absence of suitable methods of the accessing its magnetic configuration. This difficulty is overcome with the use of equations that link the magnetostatic fields at the saddle point and critical fields. Since the critical fields can readily be obtained by micromagnetic simulation, the present method should provide accurate results for the thermal stability of a nanostructured exchange-coupled trilayer.

• Proceedings of the Korea Contents Association Conference
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• 2017.05a
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• pp.445-446
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• 2017

신재생 에너지 분야의 산업과 기술의 발달과 함께 스마트 그리드와 에너지 저장 시스템이 주목받고 있다. 기존의 에너지 공급망에 정보통신기술(ICT)을 접목하여 에너지 공급자와 소비자가 양방향으로 실시간 정보를 교환함으로써 에너지 효율을 최적화하는 차세대 지능형 에너지망에 대한 수요가 늘고 관리기술에 대한 요구가 증가함에 따라, 다양한 에너지 공급원마다의 최적화된 운영시스템을 요구하고 있다. 본 논문에서는 산업분야에서 사용되고 있는 태양열에 기반한 시스템과 누적된 기상 데이터와 집열량에 대한 데이터를융합분석하여 수평면전일사량을 예측할 수 있는 시스템을 제안한다.

• Transactions of the Korean hydrogen and new energy society
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• v.9 no.2
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• pp.77-84
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• 1998

Hydrogen isotope exchange in mixtures of $H_2O/D_2$, $H_2O/D_2O$, or $D_2O/H_2$ can be facilitated under electrical discharge. For example, a simple DC corona discharge through the mixture creates a plasma in which the reactants are excited energetically. The reactants in such plasma, due to increase in population of excited quantum levels or due to production of radicals or ions, undergo very rapid chemical reactions even at ambient temperature. The isotope exchange reaction of hydrogen(H) and deuterium(D) produces the third kind of heavy water(HDO) and isotopic hydrogen gas(HD), as shown in $D_2+H_2O{\rightarrow}HD$ K=11.257(at $25^{\circ}C$) The reaction products can be detected with temporal resolution using the Fourier transform infrared(FTIR) absorption spectroscopy. Since $H_2O$, $D_2O$ and HDO are all infrared active with different absorption peaks, FTIR proves to be a useful tool for monitoring the reaction. Experimental results show that the electrical method is indeed a useful means to promote the reaction, showing a better efficiency than traditional catalytic methods.