• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 춘계학술대회 논문집 유기절연재료 방전 플라즈마
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• pp.5-12
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• 2000

본 연구에서, Daubechies'Mother Wavelet를 이용한 이산 웨이블렛 변환(Discrete Wavelet Transform)에 기초한 새롭고 효과적인 특정추출방법을 제안하였다. 특정추출을 이용하여 응용방향을 설명하고 또는 통계적 파라메터의 평가를 행하였다. 본 연구에서는 다음과 같은 몇 가지 사실을 알 수 있었다. 1. 시스템에서 발생된 (인가전압이 0[V]) 노이즈라 볼 수 가있는 렌덤노이즈(Random Noise)를 디지털필터인 FIR(Finite Impulse Response)필터를 통하여 상당한 노이즈를 억제할 수가 있었다. 2. 이산 웨이블렛 변환 시 레벨 1~4까지 변환한 결과 최적의 변환상태 Level-3을 기준으로 하였다. 3. 특정추출 파라메터는 음향방출신호의 최대값, 평균값, 분산, 왜도, 첨쇄도를 특정추출파라메터로 이용하였다. 4. 특정추출 결과를 이용하여 전체 열화시간 중 대표적 음향방출신호 중 초기열화신호, 중기열화신호, 말기열화신호를 얻을 수 있었다. 이런 특정추출을 통하여 변압기열화상태를 진단할 수 있는 가능성을 확인 할 수가 있었다.

• 산업기술연구
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• 제43권1호
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• pp.1-6
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• 2023

TiO₂ is a versatile metal oxide material that is frequently used as a photo-catalyst for organic pollutant oxidation and a functional material for ultraviolet-ray protection. To improve its chemical/physical properties and widen the range of industrial application, it is demanded to control the crystalline feature and morphology precisely by applying advanced nano-synthesis methods. In this study, we prepared TiO₂ nanoparticles using the water-in-oil (W/O) microemulsion method and compared them with the particles synthesized by the conventional precipitation method. Also, we tried to find the optimum conditions for obtaining nano-sized, anatase-rich TiO₂ particles by the W/O microemulsion method. We analyzed the crystalline feature and particle size of the prepared samples using X-ray diffraction (XRD) and Transmission electron microscopy (TEM). In summary, we found the W/O microemulsion is more effective than precipitation in obtaining nano-sized TiO₂. The best result was derived when the microemulsion was formed using AOT surfactant, hydrolysis was performed under basic condition and the sample was calcined at 200℃.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2002년도 추계공동학술대회논문집
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• pp.101-105
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• 2002

F.R.P는 수지에 유리섬유를 적층하여 제작하는 방법으로 온돈 습도 등의 적층조건에 따라 기계적.물리적 특성치가 변화하며 구성성분의 함량에 따라 다양한 편차를 나타내는 특징이 있다. 강선이나 알루미늄선의 경우에는 선급의 규칙과 기타 관련규정에 적합한 규격치수의 철강재와 알루미늄을 구입하여 사용하면 되는데 반해 F.R.P는 성형을 제작하여 그 위에 유리섬유를 적층하여 건조하는 방법으로 강선 설계시의 강판의 선정 및 부재의 조합에 의한 설계방식과는 달리 재료설계와 구조설계를 동시에 행하여야 하는 특징으로 F.R.P선박의 관련 규칙은 강선에 비하여 설계자유도가 큰 반면 부재에 대한 구체적인 기준이 확정되지 못하고 잠정규정을 설정하여 사용하고 있다. 이에 본 연구에서는 선박의 길이가 12미터(M)급인 소형 F.R.P선을 기준으로 F.R.P의 재료적 특성과 강토 방향성에 따른 유리섬유의 기계적 특성을 조사하였으며 소형 F.R.P선박의 구조설계에 필요한 기초자료를 마련하였다.

• 한국방사성폐기물학회:학술대회논문집
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• 한국방사성폐기물학회 2005년도 Proceedings of The 6th korea-china joint workshop on nuclear waste management
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• pp.236-244
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• 2005

Radioactive wastes arising from a wide range of human activities are in many different physical and chemical forms, contaminated with varying radioactivity. Their common feature is the potential hazard associated with their radioactivity and the need to manage them in such a way as to protect the human environment. The geological disposal is regarded as the most reasonable and effective way to safely disposal high-level radioactive wastes in the world. The conceptual model of geological disposal in China is based on a multi-barrier system that combines an isolating geological environment with an engineered barrier system. The buffer is one of the main engineered barriers for HLW repository. The buffer material is expected to maintain its low water permeability, self-sealing property, radio nuclides adsorption and retardation property, thermal conductivity, chemical buffering property, overpack supporting property, stress buffering property over a long period of time. Benotite is selected as the main content of buffer material that can satisfy above. GMZ deposit is selected as the candidate supplier for Chinese buffer material of High Level Radioactive waste repository. This paper presents geological features of GMZ deposit and basic property of GMZ Na bentonite. GMZ bentonite deposit is a super large scale deposits with high content of Montmorillonite (about $75\%$) and GMZ-l, which is Na-bentonite produced from GMZ deposit is selected as reference material for Chinese buffer material study.

• 대한지구과학교육학회지
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• 제1권1호
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• pp.111-118
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• 2008

This study is aimed at analyzing earth conception the nine pre service teachers who are majoring in earth science education and classifying a special feature from the ontological categories. Open ended questionnaires and semi structured interviews which meant to contribute to identifying ontological categories of concepts involving study area were designed. Pre service teachers' ontological category about earth conception most showed to dynamic and proto process. In the results show that many pre service teachers recognize simply the conception to a material, a condition and a conversion of the state changing. Most of the pre service teachers show their intermediate understanding level about the earth inner construction according to the analyzed results of the drawing tasks and interviews. The main alternative conceptions show them through a definition of the plate, a wording definition between lithosphere and asthenosphere, a feature of the plate boundary, a heat convection in the earth inner, the earth inner heat source, the earth inner structure, a physical feature of the mantle.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 압출 및 인발 심포지엄
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• pp.75-78
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• 1999

This paper is concerned with the family of parts that generally feature a central hub with radial protrusions. Typical parts that fall into this category include cross Pieces for universal joints, tube fittings, and differential gears. As opposed to conventional forward and backward extrusion, in which the material flows in a direction parallel to that of the punch or die motion, the material flows perpendicular to the punch motion in radial extrusion. In this study, the forming characteristics of radial extrusion will be considered by comparing the forces, shapes etc. The design factors during radial extrusion are investigated by the rigid-plastic FEM simulation.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 하계학술대회 논문집 Vol.5 No.2
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• pp.1270-1273
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• 2004

The combination of methane-chemical activation and Self-propagating High-temperature synthesis (SHS) has widened the possibilities for both methods. For YBCO systems the investigation showed that a short-term mechano-chemical activation of initial powders before SHS leads to single-phase and ultra-fine products. A new technique for preparation ultra-fine high-temperature superconductors of YBCO composition with a grain size d < $1{\mu}m$ is developed. The specific feature of the technique is formation of the $YBa_2Cu_3O_{7-x}$ crystalline lattice directly from an X-ray amorphous state arising as a result of mechanical activation of the original oxide mixture. The technique allows the stage of formation of any intermediate reaction products to be ruled out. X-ray and magnetic studies of ultra-fine high temperature superconductors (HTS) are carried out. Dimension effects associated with the microstructure peculiarities are revealed. A considerable enhancement of inter-grain critical currents is found to take place in the ultra-fine samples investigated.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 추계학술대회 논문집
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• pp.245-248
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• 1997

The distilled water is used for the ultrasonic wave propagating material in the measurements of broadband ultrasonic attenuation (BUA) that is applied in industrial and medical applications, The acoustic impedance of water is significantly changed with its temperature. Therefore, the quantitative evaluation of BUA with temperature and the ultrasonic wave propagating distance is highly needed. In this study, we evaluated the variation of attenuation with change in temperature. To measure the variation of BUA in the low frequency region at the temperatures, 27$^{\circ}C$, 29$^{\circ}C$, and 31$^{\circ}C$, we tested the Plyethylene, Teflon, MC-Nylon, Urethane specimens and analyzed the center frequency, frequency bandwidth, spectral peak amplitude. The results showed that BUA value appeared to be lower with increasing temperature. This may be due to the fact that the frequency feature of ultrasonic wave is affected by not only the specific gravity, acoustic impedence, but material crystalline, porosity, the distance of ultrasonic wave propagation in water.

• 소성∙가공
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• 제13권2호
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• pp.160-167
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• 2004

In order to theoretically analyze the creep behavior of high Cr steel at $600^{\circ}C$, a unified elasto-viscoplastic constitutive model based on the consideration of dislocation density is proposed. A combination of a kinetic equation describing the mechanical response of a material at a given microstructure in terms of dislocation glide and evolution equations for internal variables characterizing the microstructure provides the constitutive equations of the model. Microstructural features of the material such as the grain size and spacing between second phase particles are directly implemented in the constitutive equations. The internal variables are associated with the total dislocation density in a simple model. The model has a modular structure and can be adjusted to describe a creep behavior using the material parameters obtained from uniaxial tensile tests.

• Journal of Magnetics
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• 제16권2호
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• pp.114-119
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• 2011

This paper presents a magnetization modeling method combined with material sensitivity information to identify the unknown magnetization distribution of a hull and improve the accuracy of the predicted fields. First, based on the magnetization modeling, the hull surface was divided into three-dimensional sheet elements, where the individual remanent magnetization was assumed to be constant. For a fast search of the optimum magnetization distribution on the hull, a material sensitivity formula containing the first-order gradient information of an objective function was combined with the magnetization modeling method. The feature of the proposed method is that it can provide a stable and accurate field solution, even in the vicinity of the hull. Finally, the validity of the method was tested using a scale model ship.