• 대한조선학회지
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• 제26권4호
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• pp.3-13
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• 1989

선박이 제한수로에서 임계속도로 항진하면 solitons라는 특이한 파가 발생하여 선속보다 빠른 속도로 앞으로 전파되어 나간다. 이로인하여 선박은 급격히 증가된 조파저항을 받게되며, 또한 심한 침하와 종경사가 발생하여 때로는 수로바닥에 좌초하기도 한다. 이 문제는 선형이론으로 설명할 수 없는 비선형형상으로, 본 논문에서는 포텐셜이론에 근거하여 세장선에 대한 Matched Asymptotic Expansion 기법을 적용하여 파는 Kadomtsev-Petviashvili 방정식으로 표현할 수 있음을 보였다. 이 방정식은 선수부의 soliton 발생과 전파를, 그리고 선미부의 3차원 파를 예측하여 실험에서 발견한 현상을 반영한다. 수치계산은 soliton 발생과정을 잘 보여주고 있으며, 실험치에 유사한 조파저항, 침하 및 종경사를 제공한다.

• 한국결정성장학회지
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• 제16권2호
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• pp.49-52
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• 2006

저손실 Ti:$LiNbO_3$ 광도파로 기판에 외부전계 인가법을 사용하여 주기적으로 도메인을 반전시켰다. $LiNbO_3$의 -Z 면에 Ti 패턴 형성 후 약 $1060^{\circ}C$에서 열처리 과정을 통해 광도파로를 형성하였으며, 제작된 광도파로의 광전송 손실은 ${\sim}0.1dB/cm$ 였다. 도메인 반전을 위해 +Z면에 주기적인 전극 패턴을 형성하였으며, 외부전계의 균일한 인가를 위해 LiCl 전해 용액을 사용하여 도메인을 반전 시켰다. 선택적 화학식각을 통해, 약 $16{\mu}m$의 도메인 반전 주기를 확인 할 수 있었으며, 주기적 도메인 반전구조를 갖는 Ti : $LiNbO_3$ 도파로의 비선형 특성을 측정하였다.

• BMB Reports
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• 제32권2호
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• pp.133-139
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• 1999

Thioltransferase, also known as glutaredoxin, was previously purified and characterized from Chinese cabbage (Brassica campestris ssp. napus var. pekinensis). However, in the process of gel filtration on Sephadex G-75, there were two activity peaks. In this study, a second thioltransferase (TTase CC-2) in the minor peak of the Sephadex G-75 elution profile was further purified using affinity chromatography on an S-hexylglutathione-agarose column by eluting with buffer solution containing 2.5 mM S-hexylglutathione. It showed a single band on SDS-PAGE indicating that TTase CC-2 is electrophoretically homogeneous. The molecular weight of TTase CC-2 was estimated to be about 22,000 daltons, and its isoelectric point was determined to be 6.73. Its size appears to be atypical and much larger than that of the first thioltransferase (TTase CC-1) from Chinese cabbage, and it can utilize 2-hydroxyethyl disulfide, S-sulfocysteine, and insulin as substrates. S-sulfocysteine was found to be a superior substrate for TTase CC-2. TTase CC-2 also displayed the reducing activity for non-disulfides such as dehydroascorbic acid. Its optimum pH was 8.5, which was consistent with that of TTase CC-1. TTase CC-2 activity was greatly activated by L-cysteine and reduced glutathione, and was found to be less heat-stable compared with TTase CC-1. Molecular and physiological differences between TTase CC-1 and TTase CC-2 remain to be elucidated. Chinese cabbage is the first plant which is known to contain two kinds of thioltransferases.

• 한국항공우주학회지
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• 제32권8호
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• pp.91-100
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• 2004

경사기능재료 판에 대한 열탄성 변형과 응력 해석을 위해 Green 함수 방법이 채택되었다. 3 차원 비정상 온도분포에 대한 해는 적층판 이론에 의해 얻어진다. 열탄성 문제에 대한 기본 방정식은 각각 평면외 (out-plane) 변형과 평면내 (in-plane) 힘에 의해 유도되었다. 굽힘과 평면내 힘에 의한 열탄성 변형과 응력분포는 Galerkin 방법에 근거한 Green 함수를 이용하여 해석하였다. 열탄성 변형과 응력분포 해석을 위한 Galerkin Green 함수의 특성함수들은 사각판의 제차 경계조건을 만족시키는 허용함수들의 급수 형태로 근사화되었다. 단수지시된 사각 판에 대한 수치해석이 수행되었으며, 정사기능재료의 물성치가 판의 비정상 열탄성 거동에 미치는 영향이 검토되었다.

• 대한미생물학회지
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• 제11권1호
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• pp.1-11
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• 1976

Escherichia coli(ATCC 11115)에 실험실등에서 상용하는 여러가지 항균제를 시간별로 처리, 그 변화양상을 전자현미경으로 관찰한 바 그 결과를 요약하면 다음과 같다. 1) 대조군은 3층의 단일막으로 형성된 세포벽에 둘러쌓여 있으며 세포질은 전자밀도가 낮은 nucleoid와 ribosme들이 산재하여 있음을 관찰할 수 있었다. 2) 70% ethanol용액 처리군은 핵물질을 관찰할 수 없었고 세포질은 세포 중앙부로 응집되어 있었으며 세포벽의 외부에서는 bleb 들을 관찰 할 수 있었다. 3) 3% $H_2O_2$ 용액 처리군은 세포내용물의 변화는 70% ethanol 처리군과 대동소이(大同小異)하였으나 세포벽에서는 심한 굴곡현상이 관찰되었다. 4) 5% lysol 용액처리군은 세포질 및 핵물질 부위가 완전히 구분되어 나타났으며 세포질내의 ribosome과립들은 시간이 경과할수록 그 응집현상이 심하였고 세포 외부에는 ribosome 양 과립들이 부착하고 있음이 관찰되었다. 5) 1% DDEGH 용액 처리군은 세포질의 응집 및 세포막과 세포벽이 뚜렷이 관찰되지 않았으며 세포외부에 세포내용물과 동일한 물질로 생각되는 물질이 부착되어 있음을 관찰할 수 있었다. 6) 고압멸균 처리군은 세포막 및 세포벽의 파괴, 탈락 및 세포내용물의 유출현상이 관찰되었다.

• 한국재료학회지
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• 제4권4호
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• pp.466-471
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• 1994

타이타니움이소프로폭사이드의 가수분해로 타이타니아 졸용액을 제조하고 그 특성을 조사하였다. 용매, 촉매 그리고 물의 양이 졸의 안정도에 미치는 영향을 조\ulcorner고, 서로 다른 온도에서 졸용액의 전단점도를 측정하여 그 각각의 gel time을 알아보았다. 안정한 조성의 졸용액을 이용하여 광학적으로 투명하고 균일한 타이타니아 박막을 제조할 수 있었다. 또한, 이차비선형 활성단을 도입한 후에도 좋은 박막을 제조할 수 있었다. 제조된 박막은 3~5kV, 50~$100^{\circ}C$ 온도범위에서 코로나 분극처리 하였다. 632.8nm He-Ne레이저를 이용하여 측정한 일차 전기 광학 상수, $r_{33}$는 1.5~5pm/V로서 경시 안정성을 나타내었다.

• 한국재료학회지
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• 제20권4호
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• pp.217-222
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• 2010

Zirconium diboride (ZrB2) and mixed diboride of (Zr0.7Ta0.3)B2 containing 30 vol.% silicon carbide (SiC) composites were prepared by hot-pressing at $1800^{\circ}C$. XRD analysis identified the high crystalline metal diboride-SiC composites at $1800^{\circ}C$. The TaB2 addition to ZrB2-SiC showed a slight peak shift to a higher angle of 2-theta of ZrB2, which confirmed the presence of a homogeneous solid solution. Elastic modulus, hardness and fracture toughness were slightly increased by addition of TaB2. A volatility diagram was calculated to understand the oxidation behavior. Oxidation behavior was investigated at $1500^{\circ}C$ under ambient and low oxygen partial pressure (pO2~10-8 Pa). In an ambient environment, the TaB2 addition to the ZrB2-SiC improved the oxidation resistance over entire range of evaluated temperatures by formation of a less porous oxide layer beneath the surface SiO2. Exposure of metal boride-SiC at low pO2 resulted in active oxidation of SiC due to the high vapor pressure of SiO (g), and, as a result, it produced a porous surface layer. The depth variations of the oxidized layer were measured by SEM. In the ZrB2-SiC composite, the thickness of the reaction layer linearly increased as a function of time and showed active oxidation kinetics. The TaB2 addition to the ZrB2-SiC composite showed improved oxidation resistance with slight deviation from the linearity in depth variation.

• 대한기계학회논문집B
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• 제27권11호
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• pp.1548-1562
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• 2003

This paper is the first of several companion papers which compare the methods of Air-fuel ratio determination. There are many methods which calculate Air-Fuel ratio from exhaust emission. Most of them are based on the simple chemical equations, which use balance of atom, and the error of the calculation is negligible as far as the instrumentation accuracy is guaranteed. They assume homogeneous mixture and complete combustion to the extent of oxygen availability. Because of these simple assumptions, they cannot offer the information about the fuel distribution state and the malfunction of instrument. For these limitations, Eltinge offered new one based on stricter mathematical model. This result coincides with the others very well and gives more information about the mixture state and instrumentation. Consequently this might be a general solution for Air-fuel ratio determination and exhaust composition. The objects of the calculation, however, were not commercial fuels except gasoline and the compensation method of unburned hydrocarbon was not appropriate to recent analyzer. Moreover he did not consider the fuel which contains oxygen, such as methanol, ethanol and blend of gasoline-alcohol. In this paper, Eltinge chart is expanded to the arbitrary fuel composition as the reference exhaust compositions for the purpose of further discussions about Air-fuel ratio determination methods and the charts fur gasoline, diesel, methanol, M85, liquefied petroleum gas(LPG), natural gas(NG), propane, butane are illustrated.

• Earthquakes and Structures
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• 제14권4호
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• pp.313-322
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• 2018

The present study is dedicated to investigate the SH body-as well as Love-waves propagation effects in porous media with uncertain porosity and permeability. A unified formulation of the governing equations for one-dimensional (1-D) wave propagation in anisotropic porous layered media is presented deterministically. The uncertainties around the above two cited parameters are taken into account by random fields with the help of Monte Carlo Simulations (MCS). Random samples of the porosity and the permeability are generated according to the normal and lognormal distribution functions, respectively, with a mean value and a coefficient of variation for each one of the two parameters. After performing several thousands of samples, the mathematical expectation (mean) of the solution of the wave propagation equations in terms of amplification functions for SH waves and in terms of dispersion equation for Love-waves are obtained. The limits of the Love wave velocity in a porous soil layer overlaying a homogeneous half-space are obtained where it is found that random variations of porosity change the zeros of the wave equation. Also, the increase of uncertainties in the porosity (high coefficient of variation) decreases the mean amplification function amplitudes and shifts the fundamental frequencies. However, no effects are observed on both Love wave dispersion and amplification function for random variations of permeability. Lastly, the present approach is applied to a case study in the Adapazari town basin so that to estimate ground motion accelerations lacked in the fast-growing during the main shock of the damaging 1999 Kocaeli earthquake.

• 한국분말재료학회지
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• 제20권5호
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• pp.359-365
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• 2013

In this study, we fabricated $Nd_2Fe_{14}B$ hard magnetic powders with various sizes via spray drying combined with reduction-diffusion process. Spray drying is widely used to produce nearly spherical particles that are relatively homogeneous. Thus, the precursor particles were prepared by spray drying using the aqueous solution containing Nd salts, Fe salts and boric acid with the target stoichiometric composition of $Nd_2Fe_{14}B$. The mean particle sizes of the spray-dried powders are in the range from one to seven micrometer, which are adjusted by controlling the concentrations of precursor solutions. After debinding the as-prepared precursor particles, ball milling was also conducted to control the particle sizes of Nd-Fe-B oxide powders. The resulting particles with different sizes were subjected to subsequent treatments including hydrogen reduction, Ca reduction and washing for CaO removal. The size effect of Nd-Fe-B oxide particles on the formation of $Nd_2Fe_{14}B$ phase and magnetic properties was investigated.