• 대한기계학회논문집
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• 제18권11호
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• pp.2860-2870
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• 1994

When crack are detected in aged turbine rotors of power plants, information on fracture resistance of the aged material at operating temperature is needed for determination of critical loading condition and residual life of the turbine. In this study, fracture toughness (J$_lc$) and tearing modulus(T$_mat$) of virgin and thermally degraded 1Cr-1Mo-0.25V steel, which is one of the most widely used rotor steels, were measured at 538.deg. C according to ASTM E813 and ASTM E1152, respectively. Five kinds of specimen with different degradation levels were prepared by isothermal aging heat treatment at $630^{\circ}C.$ It was observed that J$_lc$ and T$_mat$ value decreased as the degradation level increased. Analysis of microstructures using a scanning electron microscope showed that the decrement of J$_lc$ is related to segregation of impurities at grain boundaries. It was also verified that the DC electric potential drop method is accurate and reliable for crack length monitoring at elevated temperature.

• 조명전기설비학회논문지
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• 제18권2호
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• pp.23-28
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• 2004

전기 임피던스 단층촬영법(electrical impedance tomography, EIT)은 미지의 내부 저항률 분포를 갖는 물체 주위에 특수하게 제작된 전극을 여러 개 배치하고 적절하게 설계된 전류를 주입하여 이에 따른 인가전압을 물체 경계에서 측정한 후 이를 근거로 EIT의 영상복원 알고리즘에서 물체 내부의 미지의 저항률 분포를 재구성하는 기술이다. 전기 임피던스 단층촬영법의 영상복원 과정은 비선형 방정식으로 기술되며, 그 해석적인 해를 구하기가 매우 어려우므로 수치적인 방법으로 근사해를 구한다. 본 논문에서는 EIT 영상복원 방법으로 동시 인자변환 확률적 근사화(simultaneous perturbation stochastic approximation, SPSA) 방법을 제안한다. SPSA 방법을 이용한 EIT 영상복원의 성능을 컴퓨터시뮬레이션을 통해 살펴보고 기존의 mNR 방법에 의해 얻어진 결과와 비교 분석하도록 한다.

• 한국통신학회논문지
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• 제19권3호
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• pp.515-522
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• 1994

원뿔형 컬러게이트 급전 혼의 복사특성을 가우시안 빔 모드이론으로 해석한다. 혼 개구면의 전계를 Gaussian-Laguerre모드로 전개하며, 이 모드가 파동방정식의 해임을 밝히고, 모드 확장계수에 의하여 개구면의 전개를 계산함으로써, 종래의 기본모드에 의한 복사특성 해석의 오차를 줄일 수 있게 한다. C-밴드, Ku-밴드 및 밀리미터파 대역에서 동작하는 컬러게이트 혼 안테나의 복사패턴을 계산하였다. 각 벤드에 대하여 계산한 복사패턴은 벡터 포텐실 적분법에 의하여 구한 복사패턴 및 6.175GHz에서의 실측치 등과 잘 일치한다.

• 한국세라믹학회지
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• 제45권12호
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• pp.796-801
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• 2008

$LaGaO_3$ thin film was prepared on Ni-Fe metal porous substrate by Pulsed Laser Deposition method. By the thermal reduction, the dense $NiO-{Fe_3}{O_4}$ substrate is changed to a porous Ni-Fe metal substrate. The volumetric shrinkage and porosity of the substrate are controlled by the reduction temperature. It was found that a thermal expansion property of the Ni-Fe porous metal substrate is almost the same with that of $LaGaO_3$ based oxide. $LaGaO_3$ based electrolyte films are prepared by the pulsed laser deposition (PLD) method. The film composition is sensitively affected by the deposition temperature. The obtained film is amorphous state after deposition. After post annealing at 1073K in air, the single phase of $LaGaO_3$ perovskite was obtained. Since the thermal expansion coefficient of the film is almost the same with that of LSGM film, the obtained metal support LSGM film cell shows the high tolerance against a thermal shock and after 6 min startup from room temperature, the cell shows the almost theoretical open circuit potential.

• 한국수자원학회논문집
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• 제30권1호
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• pp.63-73
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• 1997

본 연구는 지하심부에 유류를 저장할 때 널리 이용되는 수막시설의 설치에 따른 공동주변의 흐름해석을 모의하기 위한 유한요소모형의 확립에 관한 것이다. 최종 행렬방정식의 대칭형 전체전도행렬을 풀기위해 벡터저장방식의 Choleski법을 이용하였으며, 전기상사법의 결과와 비교하여 모형을 검증하였다. 모형을 실제 비축기지에 적용하였으며, 대표적인 횡단면에 대해 요소망을 구성하여 공동내부의 압력과 수평수막설치에 따른 포텐션과 유속의 변화 등을 비교하고, 종단면에 대한 분석을 통해 연직수막설치에 따른 포텐셜의 변화와 인접공동간의 영향을 비교 분석한 결과 본 연구에서 확립된 모형은 공동주변 흐름해석에 유용하게 이용될 수 있는 것으로 확인되었다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.1
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• pp.123-126
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• 2003

The electrophoretic deposition method using the suspension solution with additives under the electric potential was applied for the fabrication of YBCO superconductor wire. This method was able to simplify the fabrication facilities, and produce an uniform and dense thick film. To improve the critical current density of deposited films, the additive PEGs(Poly Ethylene Glycole) with the molecular weight of 600, 1000 and 3400, were used as chemical binders for the suspension solution. The organic additive PEG showed better effects to the properties of YBCO superconductor wire. The PEG improved the adhesion between superconductor particles and suppressed the crack on the surface, which enhanced the surface uniformity and density of YBCO deposited film. It was found that acetone suspension solution showed better deposition properties than the others. The samples fabricated in the solution with the additive, 8 vol.% of 1% PEG(1000), showed the highest critical current density measured as $2300{\sim}2400\;Acm^2$ at 77 K, 0 T.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 춘계학술대회 논문집 유기절연재료 전자세라믹 방전플라즈마 일렉트렛트 및 응용기술
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• pp.132-137
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• 2002

The mold transformers have been widely used in underground substations in large building and have some advantages in comparison to oil-transformer, that is low fire risk, excellent environmental compatibility, compact size and high reliability. In addition, the application of mold transformer for outdoor is possible due to development of epoxy resin. The mold transformer generally has cooling duct between low voltage coil and high voltage coil. A mold transformer made by one body molding method has been developed for small size and low loss. The life of transformer is significantly dependent on the thermal behavior in windings. To analyse winding temperature rise, many transformer designer have calculated temperature distribution and hot spot point by finite element method(FEM). Recently, numerical analyses of transformer are studied for optimum design, that is electric field analysis, magnetic field, potential vibration, thermal distribution and thermal stress. In this paper, the temperature distribution of 50 kVA pole mold transformer for power distribution are investigated by FEM program and the temperature rise test of designed mold transformer carried out and test result is analyzed compare to simulation data. In this result, the designed mold transformer is satisfied to limit value of temperature and the other property is good such as voltage ratio, winding resistance, no-load loss, load loss, impedance voltage and percent regulation.

• Rapid Communication in Photoscience
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• 제2권3호
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• pp.79-81
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• 2013

A novel method of fabricating polythiophene-gold nanoparticle composite film electrodes for photoelectric conversion is demonstrated. The method includes electrodeposition of gold and electropolymerization of 2,2'-bithiophene onto an indium-tin-oxide (ITO) electrode. First, electrodeposition of gold onto the ITO electrode was carried out with various repetition times of pulsed applied potential (0.25 s at -2.0 V vs. Ag/AgCl) in an aqueous solution of $HAuCl_4$. Significant progress of the number density of deposited gold nanoparticles was confirmed from scanning electron micrographs, from 4 (1 time) to 25% (15 times). Next, electropolymerization of 2,2'-bithiophene onto the above ITO electrode was performed under controlled charge condition (+1.4 V vs. Ag wire, 15 $mC/cm^2$). Structural characterization of as-fabricated films were carried out by spectroscopic and electron micrographic methods. Photocurrent responses from the sample film electrodes were investigated in the presence of electron acceptors (methyl viologen and oxygen). Photocurrent intensities increased with increasing the density of deposited gold nanoparticles up to ~10%, and tended to decrease above it. It suggests that the surplus gold nanoparticles exhibit quenching effects rather than enhancement effects based on localized electric fields induced by surface plasmon resonance of the deposited gold nanoparticles.

• Journal of the Optical Society of Korea
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• 제15권2호
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• pp.196-201
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• 2011

Near-field properties of light emanated from a subwavelength double slit of finite length in a thin metal film, which is essential for understanding fundamental physical mechanisms for near-field optical beam manipulations and various potential nanophotonic device applications, is investigated by using a three-dimensional finite-difference time-domain method. Near-field intensity distribution along the propagation direction of light after passing through the slit has been obtained from the phase relation of transverse electric and magnetic fields and the wave impedance. It is found that the near field of emerged light from the both slits is evanescent, that is consistent with conventional surface plasmon localization near the metal surface. Due to the finite of the slit, the amplitude of this evanescent field does not monotonically approach to than of the infinite slit as the slit length increases, i.e. the near-field of the longer slit along the center line can be weaker than that of the shorter one.

• 제어로봇시스템학회논문지
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• 제9권1호
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• pp.50-56
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• 2003

In electrical impedance tomography(EIT), various image reconstruction algorithms have been used in order to compute the internal resistivity distribution of the unknown object with its electric potential data at the boundary. Mathematically the EIT image reconstruction algorithm is a nonlinear ill-posed inverse problem. This paper presents a new combined method based on genetic algorithm(GA) and modified Newton-Raphson(mNR) algorithm via two-step approach for the solution of the static EIT inverse problem. In the first step, each mesh is classified into three mesh groups: target, background, and temporary groups. The mNR algorithm can be used to determine the region of group. In the second step, the values of these resistivities are determined using genetic algorithm. Computer simulations with the 32 channels synthetic data show that the spatial resolution of reconstructed images by the proposed scheme is improved compared to that of the mNR algorithm at the expense of increased computational burden.