Gas phase and surface reaction kinetics of CVD diamond growth

학위논문(박사)--서울대학교 대학원 :금속공학과,1996.Docto

Calculation of Fe-Ni-O Ternary Phase Diagram

Fe-Ni-O에서 존재하는 여러상들의 자유에너지에 대한 수식적 표현을 검토하였다. 이들중 spinel상은 Schmalzried등이 제안한 식으로, 그리고 ε상과 ι상은 아정규용액 모형으로 잘 설명되었다. 이들 용액모형을 이용하여 계산된 1273K 등온단면도와 상안정도는 실험자료와 잘 부합하였다.The analytical expressions for the free energies of various phases existed in the Fe-Ni-O system were dicussed. Among them, the spinel phase is well fitted in the expression proposed by Schmalzried et al., and the εand the ιphases are well described by the subregular solution model. The isothermal section and stability diagram which are calculated using these solution models at 1237K are in good agreement with the experimental data.The analytical expressions for the free energies of various phases existed in the Fe-Ni-O system were dicussed. Among them, the spinel phase is well fitted in the expression proposed by Schmalzried et al., and the εand the ιphases are well described by the subregular solution model. The isothermal section and stability diagram which are calculated using these solution models at 1237K are in good agreement with the experimental data

The Effects of Hydrogen Contents in Al Melt on the Porosity of Al Castings

Al 주물의 기공발생 원인을 이론적으로 규명하고, Al 용탕 중의 수소함량을 직접 측정하여 탈가스의 효과와 주물품의 미세조직변화를 관찰하였다. 그 결과, 다이캐스팅용 합금으로 많이 사용되는 Al-7.5%Si-0.4%Mg 합금에서 기공이 전혀 발생하지 않을 용탕 중의 최소수소농도는 0.1㎤/100g이며, 용탕 중의 수소는 장입물 속의 수분에 의해서라기 보다는 주로 용해 중의 분위기로부터 침투한다는 사실을 알았다. 또한 탈가스 효과는 초기 수소농도가 높을수록, 용탕의 온도가 낮을수록 더 좋다는 결론을 얻었다.We studied theoretically the formation of porosities in Al castings, and observered by experimentally the hydrogen contents in Al melts and the changes of microstructures in Al castings. As results, we know that the minimun hydrogen content which will not generate the porosity in Al-7.5%Si-0.4%Mg diecasting alloy is 0.1㎤/100g and, the hydrogen penetrates into the Al melts by the melting atmospheres rather than by the moistures in Al scrap. Also, we know the facts that the initial hydrogen contents are higher and the temperature of melts are lower, the effect of degassing is supenor.We studied theoretically the formation of porosities in Al castings, and observered by experimentally the hydrogen contents in Al melts and the changes of microstructures in Al castings. As results, we know that the minimun hydrogen content which will not generate the porosity in Al-7.5%Si-0.4%Mg diecasting alloy is 0.1㎤/100g and, the hydrogen penetrates into the Al melts by the melting atmospheres rather than by the moistures in Al scrap. Also, we know the facts that the initial hydrogen contents are higher and the temperature of melts are lower, the effect of degassing is supenor

Coherent 한 방해전파를 제거하기 위한 병렬처리 적응 어레이 시스템에 관한 연구

학위논문(박사) - 한국과학기술원 : 전기 및 전자공학과, 1989.8, [ xii, 161 p. ]The main objective of this dissertation is to develop an adaptive beamformer which is highly fast and numerically stable, and is capable of nulling out coherent interferences. Signal reception using an array of sensor elements is currently the subject of considerable interest because an array antenna system affords the means of break-throughs overcoming the directivity and resolution limitations of a single sensor element. The beam pattern of the adaptive array is automatically adjusted to create nulls in the directions of interfering signals, while passing a desired, look-direction signal with minimum distortion. Conventional beamformers so far studied require the assumption that interfering signals are not correlated with the desired signal. When this underlying assumption is no longer valid, the adaptive beamformer not only generates false nulls, but also tends to cancel the look-direction signal completely, resulting in a poor performance. In order to cope with the performance degradations due to the coherence between the desired signal and interferences, the spatial smoothing technique has been used. Although the method is found to be effective in combatting coherent interferences, it is disadvantageous in that the method significantly reduce the effective array aperture. To use the array aperture efficiently, the modified spatial smoothing technique has been developed. But, the method still forms covariance matrices as is the case of the original spatial smoothing technique, which difficulties when the wordlength is finite. Accordingly, to prevent the numerical instability caused by the spatial smoothing technique and its variations, one must have twice as long wordlength as the original data set particularly when the given data is ill-conditioned. In this dissertation, we present a data-domain modified spatial smoothing (DMSS) technique, by which the inter-signal correlation can be removed, and the formation of covariance matrices can be avoided. Since t...한국과학기술원 : 전기 및 전자공학과

Development of a simulator for the integrated voice/data packet communications network

학위논문(석사) - 한국과학기술원 : 전기 및 전자공학과, 1984.2, [ iv, 95 p. ]본 논문은 음성과 data가 집적된 packet통신망의 성능을 예측하기 위한 simulator의 개발에 대하여 연구되었다. 본 논문에서 구현된 simulator는 data protocol은 물론 음성 packet의 송 수신 과정을 model화 하였으며 또한 한 전송선에 data packet과 음성 packet을 통계적으로 다중화하는 link제어 과정을 model화 하였다. 따라서 이 simulator는 data terminal과 host사이의 data교환 과정은 물론, 음성 terminal사이의 음성 통화 과정까지 simulation 할 수 있다. 본 논문에서는 simulator의 구현 방법중 실제 system과 가장 유사하게 model화 할 수 있는 process interaction 방법을 사용하였으며 simulation언어로는 GPSS를 선택하였다. 한편 simulator의 run time효율을 높이기 위하여 GPSS-V의 link blok을 응용하므로써 조건적 event에 대한 event scan수를 줄이는 방법을 사용하였다. 본 논문은 먼저 run time효율을 높이기 위해 사용된 event scan감축 방법 및 simulator의 model에 대하여 설명하였고 이어서 구현된 simulator로부터 얻어진 몇가지 결과에 대하여 검토하였다.한국과학기술원 : 전기 및 전자공학과

Development of a Packet-Switched Public computer Communication Network -PART 1: KORNET Overview and Development of Network Management Center

본 론문은 packet 교환 방식의 computer 통신망인 KORNET 개발에 판한 4편의 논문중 제1부로서 KORNET의 전체적인 개요와 network management center(NMC)의 개발에 관하여 기술하였다. NMC는 operator dialogue를 통하여 network내 여러 소자의 상태를 감지 하고 가입자와 network의 운용을 담당하며 routing의 관리를 담당하는등 network의 중추적 기능을 구행한다 본 KORNET의 구현에 있어서 통신 protocol은 CCITT의 권고사항을 충실히 따랐으며 NMC의 응용 software인 operator interface, prinary/secondary부, session layer차 packet level adaptor는 자체적으로 개발하였고, packet, link 및 physical level protocol은 Data Goner각사에서 개발한 XODIAC X.25를 응용하여 개발하였다