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Modified View Factor를 이용한 인공위성 분자오염 역류확률 예측법
이진원(Jin-Won Lee),이재달(Jae-Dal Lee),이민영(Min-young Yi),한동인(Dong-In Han),이창호(Chang-ho Lee),이상률(S. R. Lee) 한국항공우주학회 2005 韓國航空宇宙學會誌 Vol.33 No.4
인공위성의 outgassing 분자에 대한 역류오염 해석에는 BGK 또는 DSMC 등의 방법이 사용되어 왔으나, 이들은 해석이 복잡하고 시간이 오래 걸리는 등의 비효율성이 문제이다. 본 논문에서는 분자들의 충돌간 평균자유행로가 위성체의 크기에 비해 매우 길고, 동시에 위성체의 속도가 분자들의 열속도보다 매우 크다는 점을 이용하여, 간단한 근사모델을 도입함으로써 일반적인 view factor 법과 비슷한 편리성과 간편성을 가지면서 DSMC 법과 정확하게 일치하는 결과를 주는 modified view factor 법을 개발, 제안한다. Satellite contamination from back-scattered molecules has long been analyzed using the BGK theory or the DSMC technique which are rather inefficient in that they are complicated or take a long time in the analysis. This study presents a new technique of estimating the back-scattering contamination, which is very simple and easy to use like the view factor method and also very accurate. This method, called the modified view factor method, is equivalent to the DSMC in so far as the molecular thermal velocity is much smaller than the satellite velocity and the mean free path much longer than the satellite.
Zn<SUB>1−x</SUB>Fe<SUB>x</SUB>O의 뫼스바우어 분광학적 연구
김성진(S. J. Kim),이상률(S. R. Lee),박철수(C. S. Park),김응찬(E. C. Kim),조영걸(Y. G. Joh),김동호(D. H. Kim) 한국자기학회 2008 韓國磁氣學會誌 Vol.18 No.2
Recently, the - semiconductor ZnO, normally n-type, doped with magnetic impurities was reported to be ferromagnetic above room temperature. Since ZnO is optically transparent, ferromagnetic Zno should a transparent magnet as well. The purpose of this study was to carry out Mossbauer, X-ray and magnetic-susceptibility measurements on ZnO<SUB>0.99</SUB>Fe<SUB>0.01</SUB>O to examine its magnetic properties and to separate the contributions of the ferromagnetic and the paramagnetic phases to the magnetization. The X-ray diffraction (XRD) data for Zn<SUB>0.99</SUB>Fe<SUB>0.01</SUB>O showed a typical hexagonal structure, with no indication of a secondary phase. The magnetic hysteresis (M-H) curve at room temperature showed an obvious ferromagnetic behaviour, and the magnetic moment per Fe atom under an applied field of 0.8 T was estimated to be about 2 μB, suggesting a low spin configuration of Fe ions. Mossbauer spectra of Zno<SUB>0.99</SUB>Fe<SUB>0.01</SUB>O have been taken at various temperatures ranging from 100 to 300 K. The Mossbauer spectrum of Zn<SUB>0.99</SUB>Fe<SUB>0.01</SUB>O consists of a ferromagnetic (six-Lorentzian) and a paramagnetic phase (doublet).
Ti-Getter가 Ti<SUB>0.96</SUB>Co<SUB>0.02</SUB>Fe<SUB>0.02</SUB>O₂의 자기적 특성에 미치는 영향
남효덕(H. D. Nam),김성진(S. J. Kim),백종근(J. K. Baek),이상률(S. R. Lee),박철수,김응찬(E. C. Kim) 한국자기학회 2008 韓國磁氣學會誌 Vol.18 No.3
The samples were synthesized by using a solid state reaction. The X-ray diffraction pattern for Ti<SUB>0.96</SUB>Co<SUB>0.02</SUB>Fe<SUB>0.02</SUB>O₂ showed a pure rutile phase with tetragonal structure, Mixtures of the proper proportions of the elements sealed in evacuated quartz ampoule were heated at 870~930 ℃ for one day and then slowly cooled down to room temperature at a rate of 10 ℃/h. In order to obtain single phase material, it was necessary to grind the sample after the first firing and to press the powders into pellets before annealing them for a second time in evacuated and sealed quartz ampoule. Magnetic properties have been investigated using the vibrating sample magnetometer (VSM). Room temperature magnetic hysteresis (M-H) curve showed an obvious ferromagnetic behavior and the magnetic moment per Fe atom under the applied of 0.8 T was estimated to be about 1.5 μB/CoFe. But the magnetic moment per Fe atom under the applied of 0.8 T was estimated to be about 0.02 μB/CoFe without Ti-getter. Size of particles is about 1 ㎛ using the transmission electron microscope (TEM). The ingredients of sample are distributed irregular in particles. Only Fe get shown on the surface of particles.