• Transactions on Electrical and Electronic Materials
• /
• 제2권3호
• /
• pp.1-6
• /
• 2001

A simulation method is proposed to study the amorphous structure of carbon nitride. The material properties of a non-uniform nitrogen distribution in an amorphous CN matrix can be studied. The cohesive energy of a group of randomly generated atoms can be minimized to find the relative positions of atoms. From the calculated configuration of atoms, many properties of amorphous carbon nitride can be calculated such as bulk modulus, P-V curve, sp$^3$/sp$^2$ ratio of carbon, and vibrational spectra. The calculation shows that the cohesive energy of non-uniform nitrogen distribution is lower than that of a uniform distribution. This may suggest that the regular structure of carbon nitride can at most be metastable. It is not easy to incorporate nitrogen atoms into a carbon matrix.

• Archives of Pharmacal Research
• /
• 제8권3호
• /
• pp.159-168
• /
• 1985

In attempt to develop a drug delivery system using serum albumin microspheres, bovine serum albumin microspheres containing antitumor agent, cytarabine, were prepared. The shape, surface characteristics, size distribution, behavior of in vitro distribution, drug release behaior, and degradation of albumin microspheres in animal liver tissue homogenate and proteolytic enzyme were investigated. The shape of albumin microspheres was spherical and the surface was smooth and compact. The size distribution of the albumin microspheres was affected by dispersion forces during emulsification and albumin concentration. Distribution of albumin mirospheres after intravenous administration in rabbit was achieved immediately. In vitro, albumin microsphere matrix was so hard that it retained most of cytarabine except initial burst during the first 10 minutes, and the level of drug release during the initial burst was affected by heating temperature, drug/albumin concentration ratio and size distribution. After drug release test, the morphology of albumin micropheres was not changed. Albumin microsphere matrix was degraded by the rabbit liver tissue homogenate and proteolytic enzyme. The degree of degradation was affected by heating temperature.

• Smart Structures and Systems
• /
• 제30권2호
• /
• pp.135-143
• /
• 2022

The object of this paper is to investigate the free vibration behavior under the effect of carbon nanotube distribution in functionally graded carbon nanotube-reinforced composite (FG-CNTRC) by using higher-order shear deformation theories. In this work, we present a novel distribution method for carbon nanotubes in the polymer matrix by using a new exponential power law distribution of carbon nanotube volume fraction. It is assumed that the SWCNTs are aligned along the beam axial direction and the distribution of the SWCNTs may vary through the thickness of the beam with different patterns of reinforcement. The rule of mixtures is used in order to obtain material properties of the CNTRC beams. Hamilton's principle is used in deriving the equations of motion. The validity of the free Vibration results is examined by comparing them with those of the known data in the literature. The results that obtained indicate that the carbon nanotube volume fraction distribution play a very important role on the free vibrations characteristics of the CNTRC beam.

• Composites Research
• /
• 제14권5호
• /
• pp.1-11
• /
• 2001

본 논문은 금속복합재료를 반용융상태로 재가열하여 Thixoforming을 하는데 필요한 소재를 제공하기 위한 장비 설계와 제조방법 등에 관한 내용을 소개하고 있다. 장비 설계에서 기지재내에 강화재가 균일하게 분산되도록 하기 위하여 강화재의 연속주입 방법과 강화재의 온도를 제어하는 방법을 소개하고 있다. 일정한 양의 강화재를 기지재료 내에 분산시키는 것은 균일 혼합을 위하여 필요한 기술이다. 또한 분산시 강화재의 수분제거를 위하여 강화재의 온도를 제어하면서 연속적으로 강제분산시키는 것은 균일분산을 위하여 필요하다. 기지재의 초정 $\alpha$의 크기가 강화재의 분산성에 크게 영향을 미치기 때문에 기지재의 초기 온도가 초정$\alpha$의 크기에 미치는 영향 등을 검토하여 복합재료 빌렛트의 제조조건에 이용하였다.

• 한국음향학회지
• /
• 제30권6호
• /
• pp.315-323
• /
• 2011

본 논문은 maximum a posteriori linear regression (MAPLR) 기반의 고속 화자적응 성능을 개선하기 위하여 사전분포를 추정하는 두 가지 방식을 제안한다. 일반적으로 MAPLR 방식에서 사용되는 변환행렬의 사전분포는 화자독립모델을 구성하는 훈련 화자들로부터 추정되어 모든 화자들에게 동등하게 적용된다. 본 논문에서는 새로운 화자에게 보다 더 적합한 사전분포를 적용하고자 적응 데이터를 이용하여 새로운 화자의 음향특성과 가까운 참조화자 집단을 선택한 후 참조화자 집단으로부터 사전분포를 추정하는 방법을 제안한다. 또한, 블록 대각 형태의 변환행렬의 사전분포를 추정하는 경우 사전분포의 평균행렬과 공분산행렬을 동일한 훈련 화자들로부터 얻어진 두 가지 형태의 변환행렬집단으로부터 각각 추정하는 방법을 제안한다. 제안된 방법의 성능 평가를 위하여 고립단어 인식실험을 통해 적응 단어의 개수에 따른 단어 인식률을 평가한다. 실험결과, 적응 단어 수가 매우 적을 때 기존의 MAPLR 방식에 비하여 통계적으로 유의미한 성능향상이 얻어짐을 보여준다.

• 소성∙가공
• /
• 제12권2호
• /
• pp.102-109
• /
• 2003

In the manufacturing process of metal matrix composites parts, thixoforging is one of the most effective forming processes. The major purpose of the current study is to provide the proper conditions such as the die shape, the forging velocity, the forging time, the forging pressure and reinforcement injection velocity and pressure on various defects in thixoforged cylinder liner, filling tests were performed by MAGMA S/W. In order to evaluate the effectiveness of the calculated conditions which is given by computer aided engineering, A357, A380 and SiC$_{p}$/A380 cylind~5$mu extrm{m}$r liner were fabricated under the calculated conditions. SiC$_{p}$/A380 composite billets were fabricated by both the mechanical stirring and electrical magnetic stirring process. Incase fo SiC$_{p}$/A380 composite cylinder liner, reinforcement distribution and effect of reinforcement(SiC$_{p}$) content(10~20 vol. %)and size(5.5~14${\mu}{\textrm}{m}$) on the mechanical properties were investigatedstigated.

• 한국주조공학회지
• /
• 제16권6호
• /
• pp.523-536
• /
• 1996

This paper relates to fabrication processing analysis of metal matrix composites by the injection of liquid metal into a fibrous preforms. One dimensional heat transfer analysis during squeeze infiltration process of aluminum base composites has been studied. An analysis method was investigated for the temperature distribution, infiltration velocity and melt infiltration characteristics with the commercial preform with short fiber array. When molten metal is infiltrated in a fibrous preform with random orientation, phase transformation will be occurred in a region such as molten metal, solidified region, preform region and infiltration composites region. a mathematical modelling for a solidification phenomena in fabrication process of metal matrix composites using a squeeze infiltration technique was investigated by the basic relations for liquid metal into a fibrous preform. The temperature distribution of theoretical results was compared with experimental data.

• 한국공작기계학회논문집
• /
• 제10권6호
• /
• pp.42-47
• /
• 2001

In this study, fatigue limit of ductile cast iron is evaluated based on phenomena of the microscopic observation, such as matrix structure, spheroidal ratio, size of graphite and distribution. Three different ferrite-pearlite matrix structure, GCD 45-), GCD 50, GCD 60 series, all of which contain more than 70% spheroidal ratio of graphite, were used to obtain the correlation between maximum size of graphite and fatigue strength. It was concluded as fellows. (1) In Ductile cast iron of ferrite-pearlite matrix, the fatigue limit of GCD 60 series with 73% pearlite structure was the highest. (2) From observation of the starting point of crack of all specimens, it is noted that the crack initiates, in graphite, goes through ferrite and propagates into pearlite. (3) A good quality of Ductile cast iron used in this experiment can be checked from uniformly distributed graphite. The negligible interaction effect between graphites was verified by microscopic observation and fracture mechanics investigation in surface and interior of the specimen.

• 대한전기학회논문지
• /
• 제41권5호
• /
• pp.459-467
• /
• 1992

This paper presents a new algorithm for the countermeasure to alleviate the line overloads due to contingency without shedding loads in a power system. This method for relieving the line overloads by line switching is based on obtaining the kine outage distribution factors-the linear sensitivity factors, which give the amount of change in the power flow of each line due to the removal of a line in a power system. There factors are made up of the elements of sparse bus reactance matrix and brach reactances. In this paper a fast algorithm and program is presented for obtaining only the required bus reactance elements which corresponds to a non-zero elements of bus admittance matrix, and elements of columns which correspond to two terminal buses of the overloaded(monitored) line. The proposed algorithm has been validated in tests on a 6-bus and the 30-bus test system.

• 대한전자공학회논문지SP
• /
• 제40권5호
• /
• pp.357-364
• /
• 2003

기본행렬(fundamental matrix)을 정확하게 추정하기 위해서는 대상 스테레오 영상간의 일치점 정보에 존재하는 아웃라이어(outlier)에 의한 영향을 줄여야 한다. 계산된 기본행렬은 일치점 집합의 선택에 의해 많이 영향 받으며, 정확한 기본행렬을 구하기 위해서는 일치점 정보에서 아웃라이어를 제거해야 한다. 본 논문에서는 고르게 분포하는 일치점을 선택함으로써 보다 정화하게 기본행렬을 추정할 수 있음을 보이며, 이를 바탕으로 대상 영상 내에 고르게 분포하는 일치점들의 집합들을 효과적으로 선택하는 새로운 방법이 제안된다. 제안된 방법은 대상 영상을 균일한 부영역(subregion)으로 분할한 다음, 각 영역 상에 존재하는 대응점의 개수 및 각 영역의 면적을 고려하여 기본행렬 계산에 적합한 일치점 집합을 선택한다. 합성 및 실제 영상을 대상으로 일치점들의 분포를 고려하는 제안된 알고리즘이 보다 정확한 기본행렬을 구함을 확인하였다.