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Lim, Chaehyun,Lee, Sang-Hun,Jung, Youngmo,Son, Joo-Hiuk,Choe, Jong-Ho,Kim, Young June,Choi, Jaebin,Bae, Sukang,Kim, Jae Hun,Blick, Robert H.,Seo, Minah,Kim, Chulki Elsevier 2018 Carbon Vol.130 No.-
<P><B>Abstract</B></P> <P>The charge transfer dynamics regarding an intimate contact between graphene and single-stranded deoxyribonucleic acid (ssDNA) is investigated from DC to the THz-regime. A graphene field-effect transistor (G-FET) is immersed in ssDNA solutions where the adsorption of ssDNA is controlled in terms of absolute coverage. DC-response of the G-FET is recorded and cross-validated by observing changes in Raman spectroscopy and further investigating THz-time domain spectroscopy using a nano-slot antenna. We find very good agreement between electrical and optical approaches where the Fermi level of the ssDNA-adsorbed graphene depends on the coverage nonlinearly. The results point towards a new doping method with sub-nanoscale patterning precision on graphene and its electronic applications based on electronic junction properties.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Chaehyun Lim,Sang Hyeun Doh,Changyoung Kim 한국도시환경학회 2018 한국도시환경학회지 Vol.18 No.4
In this study, the AERMOD air diffusing model was used to estimate the range of influence of Hazardous chemicals (hydrogen fluoride) in case of small accidents in Jeju area. The impact scope were in the order of Seogwipo Fire Station, Dongbu Fire Station, Jeju Fire Station, and Seobu Fire Station. Seasonal orders were summer, spring, autumn and winter. The correlation between the meteorological factors shows a strong positive correlation with the wind speed of 0.998 and has a negative correlation with the temperature of -0.463. Through the linear regression analysis, we could estimate the equation of Impact scope = 13.922WS (Wind Speed) - 5.195 and the reliability (R2) was as high as 0.995.
Lim, Chaehyun,Kim, Changmin,Gwon, Ohhun,Jeong, Hu Young,Song, Hyun-Kon,Ju, Young-Wan,Shin, Jeeyoung,Kim, Guntae Elsevier 2018 ELECTROCHIMICA ACTA Vol.275 No.-
<P><B>Abstract</B></P> <P>Perovskite oxides have received considerable attention as useful electro-catalysts for Li-air batteries due to their properties of excellent catalytic activity, electrical conductivity, and durability. The nanostructure can enhance the electrochemical performance of perovskite oxides by enlarging the catalytic active sites. In this study, nano-size Nd<SUB>0.67</SUB>Sr<SUB>0.33</SUB>CoO<SUB>3-<I>δ</I> </SUB> (NSC) perovskite particles with a particle size of 20–50 nm and a specific surface area of 12.759 m<SUP>2</SUP> g<SUP>−1</SUP> were successfully synthesized by a microemulsion method. The NSC perovskite particles exhibit excellent electrocatalytic activity particularly in the oxygen evolution reaction (OER) with a high limiting current density of 33.68 mA cm<SUP>-2</SUP> at 0.9 V <I>vs</I>. (Hg/HgO). This excellent catalytic activity can be ascribed to the existence of Co<SUP>3+</SUP> and the enlarged surface area. Co<SUP>3+</SUP> provides catalytically active site by forming Co<SUP>3+/4+</SUP> redox couple and the enlarged surface increases active sites for reactants and catalyst particles. In this regard, nano-size NSC particles prepared by the microemulsion route provide excellent and stable electrochemical performance in the hybrid Li-air battery.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A nano-structured perovskite oxide catalyst, Nd<SUB>0.67</SUB>Sr<SUB>0.33</SUB>CoO<SUB>3-<I>δ</I> </SUB> was successfully synthesized <I>via</I> inverse micro-emulsion method. </LI> <LI> The microemulsion method not only provides exensive surface area, but also increases Co<SUP>3+</SUP> and adsorbed oxygen species. </LI> <LI> The extended surface area and increased Co<SUP>3</SUP> <SUP>+</SUP> and adsorbed oxygen species enhace the electro-catalytic activity. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Lim, Chaehyun,Jun, Areum,Jo, Hongil,Ok, Kang Min,Shin, Jeeyoung,Ju, Young-Wan,Kim, Guntae The Royal Society of Chemistry 2016 Journal of Materials Chemistry A Vol.4 No.17
<▼1><▼1><P>We investigated the phase transition and its correlated electrical and electro-chemical properties of a novel double perovskite series, PrBa1−xCaxCo2O5+δ.</P></▼1><▼2><P>Layered perovskite oxides with the formula LnBaCo2O5+δ (Ln = Pr, Nd, Sm and Gd) have received attention as promising cathode materials for solid oxide fuel cells (SOFCs) because of their high oxygen diffusion and surface exchange coefficients. Recently, many researchers have reported that substituting barium with strontium or calcium can increase the structural stability, electrical conductivity, and catalytic activity of LnBaCo2O5+δ. In this study, we investigated the effect of Ca doping on the structural, electrical, and electrochemical properties of PrBa1−xCaxCo2O5+δ (<I>x</I> = 0, 0.1, 0.2, 0.3 and 0.4). Increasing the amount of Ca dopant changed the structure of PrBa1−xCaxCo2O5+δ from a layered perovskite to a simple perovskite. At <I>x</I> = 0.3, co-existence of the simple and the layered perovskite structure is observed. Electrical conductivity and electro-chemical performance were improved with increasing amount of Ca in the layered perovskite structure and declined with increasing amount of the simple perovskite phase.</P></▼2></▼1>
Lim, Chaehyun,Sengodan, Sivaprakash,Jeong, Donghwi,Shin, Jeeyoung,Kim, Guntae Elsevier 2019 International journal of hydrogen energy Vol.44 No.2
<P><B>Abstract</B></P> <P>Layered perovskites can be considered as promising cathode materials for intermediate-temperature solid oxide fuel cell because of their fast oxygen kinetics compared to simple perovskites. Among them, the cobalt-based layered perovskites are considered as very promising cathode materials due to its high conductivity and fast oxygen kinetics, but they are unstable under operating condition. Doping other transition metal such as Fe, Mn, Cu, and Ni can be considered to solve the instability of the cobalt-based layered perovskites.</P> <P>In this paper, we investigated Fe doped cobalt-based layered perovskite, PrBa<SUB>0.8</SUB>Ca<SUB>0.2</SUB>Co<SUB>2-<I>x</I> </SUB>Fe<SUB> <I>x</I> </SUB>O<SUB>5+<I>δ</I> </SUB> (<I>x</I> = 0, 0.5, and 1.0), as prospective cathode materials in terms of their crystal structures, thermal expansion behavior, electro- and electro-chemical properties. The PrBa<SUB>0.8</SUB>Ca<SUB>0.2</SUB>Co<SUB>1.5</SUB>Fe<SUB>0.5</SUB>O<SUB>5+<I>δ</I> </SUB> shows improved maximum power density of 1.89 W cm<SUP>−2</SUP> and polarization resistance of 0.080 Ω cm<SUP>2</SUP> at 600 °C as compared with un-doped PrBa<SUB>0.8</SUB>Ca<SUB>0.2</SUB>Co<SUB>2</SUB>O<SUB>5+<I>δ</I> </SUB> while maintaining suppressed thermal expansion. Based on these results, PrBa<SUB>0.8</SUB>Ca<SUB>0.2</SUB>Co<SUB>1.5</SUB>Fe<SUB>0.5</SUB>O<SUB>5+<I>δ</I> </SUB> can be considered as a promising cathode material for intermediate-temperature solid oxide fuel cell.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Electrochemical properties and stability of the Ca doped PrBaCo<SUB>2</SUB>O<SUB>5+<I>δ</I> </SUB> can be improved by Fe doping. </LI> <LI> The stronger [Fe–O] bonding strength increases the mobile oxygen species in the Ln-O layer of layered perovskites. </LI> <LI> The increased mobile oxygen improves the catalytic activity and thermal stability. </LI> <LI> Fe doped PrBa<SUB>0.8</SUB>Ca<SUB>0.2</SUB>Co<SUB>2</SUB>O<SUB>5+<I>δ</I> </SUB> can be considered as a promising cathode material. </LI> </UL> </P>
1인 가구 환경에서 프라이버시 보호 영상을 활용한 위험 행동 인식에 관한 연구
임채현(ChaeHyun Lim),김명호(Myung Ho Kim) 한국컴퓨터정보학회 2022 韓國컴퓨터情報學會論文誌 Vol.27 No.5
최근 딥러닝 기술의 발달로 사람의 행동을 인식하는 연구가 진행 중에 있다. 본 논문에서는 딥러닝 기술을 활용하여 1인 가구 환경에서 발생할 수 있는 위험 행동을 인식하는 연구를 진행하였다. 1인 가구의 특성상 개인의 프라이버시 보호가 필요하다. 본 논문에서는 개인의 프라이버시 보호를 위해 가우시안 블러 필터가 적용된 프라이버시 보호 영상에서 사람의 위험 행동을 인식한다. 위험 행동 인식 방법은 객체 검출 모델인 YOLOv5 모델을 활용하여 영상에서 사람 객체 검출 및 전처리 방법을 적용한 후 행동 인식 모델의 입력값으로 활용하여 위험 행동을 인식한다. 실험에는 ResNet3D, I3D, SlowFast 모델을 사용하였고, 실험 결과 SlowFast 모델이 프라이버시 보호 영상에서 95.7%로 가장 높은 정확도를 달성하였다. 이를 통해 개인의 프라이버시를 보호하면서 1인 가구 환경에서 사람의 위험 행동을 인식하는 것이 가능하다. Recently, with the development of deep learning technology, research on recognizing human behavior is in progress. In this paper, a study was conducted to recognize risky behaviors that may occur in a single-person household environment using deep learning technology. Due to the nature of single-person households, personal privacy protection is necessary. In this paper, we recognize human dangerous behavior in privacy protection video with Gaussian blur filters for privacy protection of individuals. The dangerous behavior recognition method uses the YOLOv5 model to detect and preprocess human object from video, and then uses it as an input value for the behavior recognition model to recognize dangerous behavior. The experiments used ResNet3D, I3D, and SlowFast models, and the experimental results show that the SlowFast model achieved the highest accuracy of 95.7% in privacy-protected video. Through this, it is possible to recognize human dangerous behavior in a single-person household environment while protecting individual privacy.
Kwon, Ohhun,Sengodan, Sivaprakash,Lim, Chaehyun,Jeong, Hu Young,Shin, Jeeyoung,Ju, Young-Wan,Kim, Guntae The Electrochemical Society 2016 Journal of the Electrochemical Society Vol.163 No.9
<P>In this work, we report on a BaZrO3 (BZO) modified NiO-YSZ anode fabricated by co-sintering of NiO-YSZ and BaCO3 for SOFCs. The BZO modified Ni-YSZ anode shows stable electrochemical performance in H-2 fuel containing a high level of 100 ppm sulfur for more than 100 hours. On the other hand, an unmodified Ni-YSZ anode degrades significantly in 100 ppm sulfur containing H-2 fuel. The obtained results demonstrate that the BZO in the Ni-YSZ is an excellent catalyst for enhancing the sulfur tolerance of the conventional Ni-YSZ anode. Moreover, the surface modification strategy is simple and cost-effective, and thereby can promote commercialization of Ni-YSZ anode supported cells. (C) 2016 The Electrochemical Society. All rights reserved.</P>
Matching Pursuit 방식을 이용한 OFDM 시스템의 채널 추정
최재환(Jaehwan Choi),임채현(Chaehyun Lim),한동석(Dongseog Han),윤대중(Daejung Yoon) 한국방송·미디어공학회 2004 한국방송공학회 학술발표대회 논문집 Vol.2004 No.-
본 논문에서는 직교 주파수 분할 다중 접속 (orthogonal frequency division multiplexing, OFDM) 시스템에서 matching pursuit (MP) 알고리듬을 이용하는 이동 채널 추정법을 제안한다. 기존의 OFDM 시스템에서 채널추정 알고리듬으로 쓰이는 zero-forcing (ZF) 알고리듬은 잡음의 영향으로 채널 추정 오류의 가능성을 가지고 있다. 제안한 알고리듬에서는 MP 알고리듬을 이용하여 스파스(sparse)형태의 채널을 추정함으로써 다중경로가 없다고 가정되는 시간영역의 채널구간에서 발생될 수 있는 잡음에 의한 영향을 줄인다. 또한 연속적으로 전송되는 파일럿 정보를 이용하여 실시간으로 채널의 변화를 추정한다. 제안한 알고리듬으로 채널을 추정하고 등화를 했을 경우 ZF 알고리듬보다 우수한 성능을 보임을 실험에서 확인한다.