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MgO-Core/ZnO-shell Nanocables Sheathed by Using the Sputtering Technique
김효성,김현우,이총무,Mesfin Abayneh Kebede,유건호,Doo Young Kim 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.5
We demonstrated the successful fabrication of MgO-core/ZnO-shell nanowires, in which the shell layers were deposited by using the sputtering technique. Transmission electron microscopy investigations revealed that core nanowires were surrounded by a ZnO shell layer. At 298 K, the photoluminescence (PL) peak intensity ratio (green/UV) decreased with increasing ZnO shell thickness. In regard to the effect of temperature, the intensity of the green emission band was progressively decreased with increasing measurement temperature. We discuss the possible associated PL emission mechanisms.
김효성,남기곤,전계록,이상욱,정두영,Kim, Hyo-Seong,Nam, Gi-Gon,Jeon, Gye-Rok,Lee, Sang-Uk,Jeong, Du-Yeong 대한전자공학회 2002 電子工學會論文誌-SP (Signal processing) Vol.39 No.1
시점을 달리하는 영상으로부터 3차원 장면 복구는 두 영상의 에피폴라 기하구조를 나타내는 F-행렬을 계산함으로서 가능하다. F-행렬을 계산하기 위해 입력으로 주어지는 두 영상의 일치점에는 잘못된 정합점과 같은 잡음을 포함하고 있기 때문에 정확한 F-행렬의 계산은 많은 오류를 가지게 된다. 따라서 본 논문에서는 에피폴라 기하구조에 영향을 미치는 잡음의 종류를 크게 outlier와 미세잡음으로 구분하였다. 상대적으로 에피폴라 기하구조에 영향을 크게 미치는 outlier를 단계적으로 제거시킴으로써 잡음 환경에서도 효과적으로 F-행렬을 계산할 수 있는 SSOR 알고리즘을 제안한다. 제안 알고리즘의 성능 평가를 위해 합성영상과 실 영상에서 실험하였으며 실험결과 제안 알고리즘이 기존의 알고리즘보다 성능이 우수함을 확인하였다. Three-Dimensional scene reconstruction from images acquired with different viewpoints is possible as estimating Fundamental matrix(F-matrix) that indicates the epipolar geometry of two images. Correspondence points required to calculate F-matrix of two images include noise such as miss matches, so generally it is hard to calculate F-matrix accurately. In this paper, we classify noise into two types; outlier and minute noise. we propose SSOR algorithm that estimate F-matrix effectively. SSOR algorithm is rejecting outlier step by step in a noise environment. To evaluate the performance of proposed algorithm we simulated with synthetic images and real images. As a result of simulation we show that proposed algorithm is better than conventional algorithms.
Comparative Study on 220V AC Feed System and 300V DC Feed System for Internet Data Centers
김효성 전력전자학회 2012 JOURNAL OF POWER ELECTRONICS Vol.12 No.1
Internet Data Centers (IDCs), which are essential facilities in the modern IT industry, typically have scores of MW of concentrated electric loads. The provision of an Uninterruptible Power Supply (UPS) is necessary for the power feed system of IDCs owing to the need for stable power. Thus, conventional IDC AC power feed systems have three cascaded power conversion stages, (AC-DC), (DC-AC), and (AC-DC), resulting in a very low conversion efficiency. In comparison, DC power feed systems require only a single power conversion stage (AC-DC) to supply AC main power to DC server loads, resulting in comparatively high conversion efficiency and reliability [4-11]. This paper compares the efficiencies of a 220V AC power feed system with those of a 300V DC power feed system under equal load conditions, as established by the Mok-Dong IDC of Korea Telecom Co. Ltd. (KT). Experimental results show that the total operation efficiency of the 300V DC power feed system is approximately 15% higher than that of the 220V AC power feed system.
A Novel Filter Design for Output LC Filters of PWM Inverters
김효성,설승기 전력전자학회 2011 JOURNAL OF POWER ELECTRONICS Vol.11 No.1
The cutoff frequency of the output LC filters of PWM inverters limits the control bandwidth of the converter system while it attenuates voltage ripples that are caused by inverter switching activities. For a selected cutoff frequency of an output LC filter,an infinite number of L-C combinations is possible. This paper analyses the characteristics of output LC filters for PWM inverters terms of the L-C combinations. Practical circuit conditions such as no-loads, full resistive-loads, and inductive-load conditions are considered in the analysis. This paper proposes a LC filter design method for PWM inverters considering both the voltage dynamics and the inverter stack size. An experimental PWM inverter system based on the proposed output LC filter design guideline is built and tested.
Filter Design for Grid-Connected Single-Phase Inverters
김효성 전력전자학회 2009 JOURNAL OF POWER ELECTRONICS Vol.9 No.4
This paper proposes a filter design guideline for grid-connected single-phase inverters. By analyzing the instantaneous voltage applied to the filter inductor, the switching ripple current through the filter inductor can be precisely calculated. Therefore, filter inductance can be designed accurately, which guaranties that the switching ripple current will be under the target value. The proposed filter design method is verified by experiment.
적외선 카메라를 이용한 에어 인터페이스 시스템(AIS) 연구
김효성,정현기,김병규,Kim, Hyo-Sung,Jung, Hyun-Ki,Kim, Byung-Gyu 한국정보처리학회 2011 정보처리학회논문지B Vol.18 No.3
본 논문에서는 기계적인 조작 장치 없이 손동작만으로 컴퓨터를 조작할 수 있는 차세대 인터페이스인 에어 인터페이스를 구현하였다. 에어 인터페이스 시스템 구현을 위해 먼저 적외선의 전반사 원리를 이용하였으며, 이후 획득된 적외선 영상에서 손 영역을 분할한다. 매 프레임에서 분할된 손 영역은 이벤트 처리를 위한 손동작 인식부의 입력으로 사용되고, 최종적으로 개별 제어 이벤트에 맵핑된 손동작 인식을 통하여 일반적인 제어를 수행하게 된다. 본 연구에서는 손영역 검출과 추적, 손동작 인식과정을 위해 구현되어진 영상처리 및 인식 기법들이 소개되며, 개발된 에어 인터페이스 시스템은 길거리 광고, 프레젠테이션, 키오스크 등의 그 활용성이 매우 클 것으로 기대된다. In this paper, we introduce non-touch style interface system technology without any touch style controlling mechanism, which is called as "Air-interface". To develop this system, we used the full reflection principle of infrared (IR) light and then user's hand is separated from the background with the obtained image at every frame. The segmented hand region at every frame is used as input data for an hand-motion recognition module, and the hand-motion recognition module performs a suitable control event that has been mapped into the specified hand-motion through verifying the hand-motion. In this paper, we introduce some developed and suggested methods for image processing and hand-motion recognition. The developed air-touch technology will be very useful for advertizement panel, entertainment presentation system, kiosk system and so many applications.