리튬 이온 전지용 리튬 코발트 산화물 양극에서의 삽입 전압과 리튬 이온 전도

김대현,김대희,서화일,김영철,Kim, Dae-Hyun,Kim, Dae-Hee,Seo, Hwa-Il,Kim, Yeong-Cheol 한국전기화학회 2010 한국전기화학회지 Vol.13 No.4

본 연구는 밀도 범함수 이론을 이용하여 Li이온전지에 사용되는 Li코발트 산화물에서의 Li이온 삽입 전압과 전도에 관한 것이다. Li이온은 Li코발트 산화물 원자구조의 각 층을 1개씩 채우거나 한 층을 다 채우고 다음 층을 채울 수 있다. 평균 삽입 전압은 3.48V로 동일하나, 전자가 후자보다 더 유리하였다. 격자상수 c는 Li농도가 0.25보다 작을 때는 증가하였으나, 0.25보다 클 때는 감소하였다. Li농도가 증가하면, Li코발트 산화물에서의 Li이온 전도를 위한 에너지 장벽은 증가하였다. Li이온전지가 방전 중 출력 전압이 낮아지는 현상은 Li농도 증가에 따른 삽입 전압의 감소와 전도 에너지 장벽의 증가로 설명할 수 있었다. We performed a density functional theory study to investigate the intercalation voltage and lithium ion conduction in lithium cobalt oxide for lithium ion battery as a function of the lithium concentration. There were two methods for the intercalation of lithium ions; the intercalation of a lithium ion at a time in the individual layer and the intercalation of lithium ions in all the sites of one layer after all the sites of another layer. The average intercalation voltage was the same value, 3.48 V. However, we found the former method was more favorable than the latter method. The lattice parameter c was increased as the increase of the lithium concentration in the range of x < 0.25 while it was decreased as increase of the lithium concentration in the range of x > 0.25. The energy barrier for the conduction of lithium ion in lithium cobalt oxide was increased as the lithium concentration was increased. We demonstrated that the decrease of the intercalation voltage and increase of the energy barrier as the increase of the lithium concentration caused lower output voltage during the discharge of the lithium ion battery.

아파트 단지 옥외공간 변천 및 요인 연구

김대현,김대수,신지훈,김순분,Kim, Dae-Hyun,Kim, Dae-Soo,Sin, Ji-Hoon,Kim, Soon-Boon 한국조경학회 2005 韓國造景學會誌 Vol.32 No.6

The purposes of this study were to classify the changing periods of apartment outdoor space in Korea and to clearly understand the specific characteristics of each period. The study has been done through on-site observation of apartment complexes, and through the analysis of housing estate planning techniques, rules and regulations affecting outdoor spaces during the rapidly developing era. The results of this study shows that three major periods with distinct characteristics were found, which were as follows: 1) The first well defined period spans from 1960 to 1990. In this period, apartment construction was rapid, and as a result, quality of housing environments were sacrificed. As little attention was given to the landscapes in apartment complex, they were constructed very simple and identical in outdoor space of apartment complex. This period can be referred to as the 'commonly universal period in apartment outdoor space'. 2) The second period spans from 1991 to 1996, during which time a housing construction project for two million residences was completed in order to significantly stimulate the provision of houses to the general public. As a result, regulations were relaxed causing housing environments to deteriorate. Although apartments were constructed very close together, there was some diversification and experimentation in outdoor styles. This period can be referred to as the 'congestion period of apartment outdoor space'. 3) The third period spans from 1997 to the present. During this time the number of unsold apartments has grown considerably throughout the country. Many different apartment complex marketing strategies have been employed to reduced the glut of unsold apartments. This experimental trend has continued and been well-received since the IMF period. The distinguishing characteristics of this period are the introduction of a rich natural landscape, the increase in communications among residents, the human oriented design, and the refined and elegant design for the outdoor street furnitures. As a result, this period can be named the "differentiation period of apartment outdoor space".

비화학양론적 Na⁺β-alumina를 위한 Mg 원자의 치환: 제일원리 계산

김대현,김대희,정용찬,서화일,김영철,Kim, Dae-Hyun,Kim, Dae-Hee,Jeong, Yong-Chan,Seo, Hwa-Il,Kim, Yeong-Cheol 한국재료학회 2010 한국재료학회지 Vol.20 No.2

$Na^+$ ion conductivity can be improved by the substitution of an Mg atom for an Al atom to form a nonstoichiometric $Na^+$ $\beta$-alumina. We performed a first principles study to investigate the most stable substitution site of an Mg atom and the resulting structural change of the nonstoichiometric $Na^+$ $\beta$-alumina. Al atoms were classified as four different layers in the spinel block that are separated by conduction planes in the nonstoichiometric $Na^+$ $\beta$-alumina. The substitution of an Mg atom for an Al atom at a tetragonal site was more favorable than that at an octahedral site. The substitution in the spinel block was more favorable than that close to the conduction plane. This result was well explained by the volume changes of the polyhedrons, by the standard deviation of the Mg-O distance, and by the comparison with bulk MgO structure. Our result indicates that the most preferable site for the Mg atom was the tetrahedral site at the spinel block in the nonstoichiometric $Na^+$ $\beta$-alumina.

$HfCl_4$와 Si (001) 표면에 결합된 두 개의 수산화기와의 상호작용: 제일원리 연구

김대현,김대희,서화일,김영철,Kim, Dae-Hyun,Kim, Dae-Hee,Seo, Hwa-Il,Kim, Yeong-Cheol 한국반도체디스플레이기술학회 2009 반도체디스플레이기술학회지 Vol.8 No.2

Density functional theory was used to investigate the adsorption and reaction of $HfCl_4$ with two hydroxyls on Si (001)-$2{\times}1$ surface in atomic layer deposition (ALD) process. We prepared a reasonable Si substrate which consisted of six inter-dimer dissociated $H_2O$ molecules and two intra-dimer dissociated $H_2O$ molecules. The $HfCl_4$must react with two hydroxyls to be a bulk-like structure. When $HfCl_4$ was adsorbed on a hydroxyl, there was energy benefit of -0.55 eV. Though there was energy loss for $HfCl_4$ to react with H of hydroxyl, thermal energy of ALD chamber would be enough to pass the energy barriers. There were five reaction pathways for $HfCl_4$ to react with two hydroxyls; inter-dimer, intra-dimer, cross-dimer, inter-row, and cross-row. Inter-row, inter-dimer and intra-dimer were relatively favorable among the five reaction pathways based on the energy difference. The electron densities between O and Hf in these three reactions were higher than the others and they had shorter Hf-O and O-O bond lengths than the other two reaction pathways.

DEMS와 H-terminated Si (001) 표면의 상호작용: 제일원리연구

김대현,김대희,박소연,서화일,이도형,김영철,Kim, Dae-Hyun,Kim, Dae-Hee,Park, So-Yeon,Seo, Hwa-Il,Lee, Do-Hyoung,Kim, Yeong-Cheol 한국세라믹학회 2009 한국세라믹학회지 Vol.46 No.4

We performed a density functional theory study to investigate the interaction of DEMS (diethoxymethylsilane) with the H-terminated Si (001) surface. The optimum structure of DEMS was first calculated by a first principles study. The dissociation probability of the O-C bond of DEMS was higher than the other seven bonds based on the bond energy calculation. When the fragmented DEMS groups reacted with the H-terminated Si (001) surface, it was the most favorable among the eight reactions to form a bond between the Si atom on the surface and the O atom of a fragmented DEMS group (($C_2H_5O$)Si($CH_3$)(H)-O-) by forming a $C_2H_6$ as by-product.

Density Functional Theory를 이용한 Si (001) 표면 위의 In 나노선 성장 연구

김대현,김대희,서화일,김영철,Kim, Dae-Hyun,Kim, Dae-Hee,Seo, Hwa-Il,Kim, Yeong-Cheol 한국재료학회 2009 한국재료학회지 Vol.19 No.3

Density functional theory was utilized to investigate the growth of an indium nanowire on a Si (001) buckled surface. A site between the edge of two Si dimers is most favorable when the first In atom is adsorbed on the surface at an adsorption energy level of 2.26 eV. The energy barriers for migration from other sites to the most favorable site are low. When the second In atom is adsorbed next to the first In atom to form an In dimer perpendicular to the Si dimer row, the adsorption energy is the highest among all adsorption sites. The third In atom prefers either of the sites next to the In dimer along the In dimer direction. The fourth In atom exhibited the same tendency showed by the second atom. The second and fourth In adsorption energy levels are higher than the first and third levels as the In atoms consume the third valence electron by forming In dimers. Therefore, the In nanowire grows perpendicular to the Si dimer row on the Si (001) surface, as it satisfies the bonding of the three valence electrons of the In atoms.

유사 특징점을 이용한 모자이킹 영상의 구성

김대현,최종수,Kim, Dae-Hyeon,Choe, Jong-Su 대한전자공학회 2001 電子工學會論文誌-SP (Signal processing) Vol.38 No.4

본 논문은 영상 시퀸스로부터 이미지 모자이킹의 구성을 위한 효율적인 알고리즘을 기술한다. 영상의 기하학적인 특징을 이용하거나 비선형 방정식을 풀었던 기존의 알고리즘과는 달리, 제안한 알고리즘은 4개의 유사특징점을 이용해 영상간 사영 변환식의 8개 파라미터를 직접 계산한다. 본 논문에서 정의된 유사특징점은 영상의 그레이레벨의 분산을 기반으로 하고, 두 영상의 중첩 영역에서만 결정된다. 또한 선택된 4개의 유사특징점에 대한 대응점 검출을 위해 카메라 이동 및 조명 변화에 의한 영상의 변화를 고려한 블록 정합 알고리즘을 적용한다. 제안된 알고리즘은 다양한 영상에 적용하여 그 성능을 평가하였다. 모의 실험 결과는 제안된 알고리즘이 기존의 알고리즘에 비해 계산량을 감소시키면서, 정확한 사영 변환식을 유도하여 모자이킹 영상을 구성하는 것을 보여주고 있다. This paper presents an efficient approach to build an image mosaics from image sequences. Unlike general panoramic stitching methods, which usually require some geometrical feature points or solve the iterative nonlinear equations, our algorithm can directly recover the 8-parameter planar perspective transforms. We use four quasi-feature points in order to compute the projective transform between two images. This feature is based on the graylevel distribution and defined in the overlap area between two images. Therefore the proposed algorithm can reduce the total amount of the computation. We also present an algorithm lot efficiently matching the correspondence of the extracted feature. The proposed algorithm is applied to various images to estimate its performance and. the simulation results present that our algorithm can find the correct correspondence and build an image mosaics.

가려짐 패턴을 이용한 가려짐 영역의 시차 교정에 관한 연구

김대현,최종수,Kim Dae-Hyun,Choi Jong-Soo 대한전자공학회 2005 電子工學會論文誌-SP (Signal processing) Vol.42 No.4

In this paper, we propose new smoothing filters, i.e., occluding patterns that can accurately correct disparities of occluded areas in the estimated disparity map. An image is composed of several layers and each layer presents similar disparity. Furthermore, the distribution of the estimated disparities has a specific direction around the boundary of the occlusion, and this distribution presents the different direction with respect to the left- and the right-based disparity map. However, typical smoothing filters, such as mean filter and median filter, did not take into account those characteristic. So, they can decrease some error, but they cannot guarantee the accuracy of the corrected disparity. On the contrary, occluding patterns can accurately correct disparities of occluded areas because they consider both the characteristic that occlusion occurs and the characteristic that disparities of the occlusion are ranged, from estimated disparity maps with respect to the left and the right images. We made experiments on occluding patterns with some real stereo image set, and as a result, we can correct disparities of occluded areas more accurately than typical smoothing filters did. 본 논문에서 우리는 추정된 시차지도에서 가려짐 영역의 시차를 교정하는 새로운 스무딩 필터인 가려짐 패턴 (occluding patterns)을 제안한다. 영상은 몇 개의 계층으로 구성되어 있고, 각각의 계층은 유사한 시차를 나타낸다. 그리고 추정된 시차들은 가려짐 영역의 경계 주변에서 특정한 방향성을 갖고 분포하며, 이러한 시차 분포의 방향성은 좌우 시차지도에 대해서 서로반대이다. 그러나 평균값 필터 또는 중간값 필터와 같은 기존의 스무딩 필터는 이러한 시차의 분포 특성을 고려하지 않고 스무딩을 수행하기 때문에 오차는 줄일 수 있으나, 교정된 시차의 정확성은 보장되지 않았다. 이와 반대로, 본 논문에서 제안하는 가려짐 패턴은 좌우 영상에서 각각 추정된 시차지도에 대해서 가려짐 영역이 발생하는 특성과 가려짐 영역에서의 시차 분포 특성을 함께 고려하여 정확하게 가려짐 영역의 시차를 교정한다. 본 논문에서 제안한 가려짐 패턴은 다양한 실험 영상에 적용하여 실험하였고, 그 결과 기존의 스무딩 방법에 비해서 정확하게 시차를 교정하는 것을 확인하였다.

TiO₂/ITO 나노구조체 광전극의 합성 및 염료감응 태양전지에의 적용

김대현,박경수,최영진,최헌진,박재관,Kim, Dae-Hyun,Park, Kyung-Soo,Choi, Young-Jin,Choi, Heon-Jin,Park, Jae-Gwan 한국세라믹학회 2011 한국세라믹학회지 Vol.48 No.1

A Sn-doped $In_2O_3$ (ITO) nanowire photoelectrode was produced using a simple metal evaporation method at low synthesis temperature (< $540^{\circ}C$). The nanowire electrodes have large surface area compared with that of flat ITO thin film, and show low electrical resistivity of $5.6{\times}10^{-3}{\Omega}cm$ at room temperature. In order to apply ITO nanowires to the photoelectrodes of dye-sensitized solar cell (DSSC), those surfaces were modified by $TiO_2$ nanoparticles using a chemical bath deposition (CBD) method. The conversion efficiency of the fabricated $TiO_2$/ITO nanostructure-based DSSC was obtained at 1.4%, which was increased value by a factor of 6 than one without ITO nanowires photoelectrode. This result is attributed to the large surface area and superior electrical property of the ITO nanowires photoelectrode, as well as the structural advantages, including short diffusion length of photo-induced electrons, of the fabricated $TiO_2$/ITO nanostructure-based DSSC.

An Efficient Feature Point Detection for Interactive Pen-Input Display Applications

김대현,김명준,Kim Dae-Hyun,Kim Myoung-Jun Korean Institute of Information Scientists and Eng 2005 정보과학회논문지 : 시스템 및 이론 Vol.32 No.11

There exist many feature point detection algorithms that developed in pattern recognition research . However, interactive applications for the pen-input displays such as Tablet PCs and LCD tablets have set different goals; reliable segmentation for different drawing styles and real-time on-the-fly fieature point defection. This paper presents a curvature estimation method crucial for segmenting freeHand pen input. It considers only local shape descriptors, thus, peforming a novel curvature estimation on-the-fly while drawing on a pen-input display This has been used for pen marking recognition to build a 3D sketch-based modeling application. 패턴 인식 연구 분야에서 많은 특징점 추출 알고리즘들이 개발되었지만, 태블릿 PC나 LCD 태블릿과 같은 펜-입력 디스플레이를 위한 인터액티브 애플리케이션들은 기존과는 다른 요구사항을 가진다. 사용자 마다 다른 다양한 스케치 스타일의 대해서 세그멘테이션 및 특징점 추출을 그림을 그리는 동안 실시간에 안정적으로 수행하여야 한다. 본 논문은 사용자로부터 자유로이 입력된 펜 입력을 분할(segmentation)하기 위해 필수적인 곡률(curvature) 측정 방법을 제안한다. 이 방법은 국소적인 모양 정보(shape descriptors)만을 사용하므로 펜 입력동안 곧바로(on-the-fly) 곡률을 측정할 수 있다. 본 알고리즘은 3차원 스케치 기반 모델링 애플리케이션에서 펜 마킹 인식을 위해서 사용되었다.