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Thermoelectric Properties of Bi2Te2.7Se0.3 Nanocomposites Embedded with MgO Nanoparticles
Sung-Jae Joo,Ji-Hee Son,Bok-Ki Min,이지은,Bong-Seo Kim,Byungki Ryu,Su-Dong Park,이희웅 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.69 No.8
Bi2Te2.7Se0.3 bulk materials containing x vol% MgO nanoparticles (average particle size 100 nm, x = 0, 0.5, 1.0, 1.5) were synthesized by using high-energy ball milling and plasma- activated sintering (PAS) without any special process for nanoparticle dispersion. A microstructure investigation using a scanning electron microscope (SEM) confirmed that MgO nanoparticles were properly dispersed in the Bi2Te2.7Se0.3 matrix and that the grain size was smaller in MgO-containing samples due to suppressed grain growth. The resistivity and the maximum Seebeck coefficient of Bi2Te2.7Se0.3 increased with increasing MgO content whereas the thermal conductivity decreased in the measurement temperature range of 298 K - 573 K. As a result, the maximum dimensionless figure of merit, ZTmax, increased about 8.5% in this study, from 0.806 for pristine Bi2Te2.7Se0.3 to 0.875 when x = 1.5. The ZTmax was observed to shift to lower temperature, the electron concentration to decrease, and the electron mobility to increase with increasing x, which were explained using a hypothesis that the TeBi antisite defect concentration decreased as the MgO content increased. In summary, the addition of MgO nanoparticles has been shown to be a simple and effective method to improve the low-temperature thermoelectric properties of n-type Bi2Te3 materials.
김성희,이희웅(Sung-hee Kim),Hee-woong Lee 한국정보과학회 1998 정보과학회 컴퓨팅의 실제 논문지 Vol.4 No.4
컴퓨터 그래픽스 프로그램은 그래픽 객체(graphical object)의 관리, 디스플레이(display), 그리고 객체들에 발생하는 이벤트(event)등을 처리해야 한다. 또한 다양한 그래픽스 라이브러리와 윈도우 시스템의 개발로 프로그램의 이식성(portability)이 한층 강조되고 있다. 이와 같은 기능들은 상당히 복잡할 뿐 아니라 많은 그래픽스 응용 프로그램에 공통되는 내용들이기 때문에, 이들을 하나의 툴로 개발하여 많은 응용 프로그램 개발자가 공통적으로 사용하고자 하는 시도가 계속되어져 왔다. 본 논문에서는 사용하기 편리하고, 다른 시스템으로의 이식이 용이하며, 객체 지향 기법으로 설계되었기 때문에 확장이 용이한 그래픽스 저작도구의 설계 및 구현에 대해 설명한다. Computer graphics applications require managing and displaying objects as well as handling events. There are a number of graphics libraries and window systems that can be used for these purposes. These modules are general in nature and quite complex, so it would be best if we provide these features as a toolkit or a framework to the general purpose graphics programmers. This paper presents a toolkit that is easy to use, portable, and well suited for the usual modeling and rendering tasks. The object-oriented programming techniques used in designing the toolkit make it flexible and extensible.
제일원리 계산을 이용한 rutile-TiO2의 전자구조 및 X-ray absorption spectra
오민욱 ( Min Wook Oh ),강태구 ( Tae Gu Kang ),류병기 ( Byung Ki Ryu ),이지은 ( Ji Eun Lee ),주성재 ( Sung Jae Joo ),김봉서 ( Bong Seo Kim ),민복기 ( Bok Ki Min ),이희웅 ( Hee Woong Lee ),박수동 ( Su Dong Park ) 대한금속재료학회(구 대한금속학회) 2014 대한금속·재료학회지 Vol.52 No.12
Electronic structures and X-ray absorption spectra of rutile TiO2 were obtained with the first- principles calculation. Density of states, charge density and differential charge density were obtained, from which charge transfer characteristics between Ti and O was well confirmed. Direct and indirect band gap of 1.99 and 2.03 eV were evaluated, respectively. X-ray absorption spectra of rutile TiO2 was also calculated, in which the gap between main peaks was comparable with experiment. From band structure calculations, anisotropic electrical transport properties were expected, which was in good agreement with experiment.