• Corrosion Science and Technology
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• 제22권6호
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• pp.457-465
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• 2023

Irradiation-assisted stress corrosion cracking (IASCC) is one of the main degradation mechanisms of austenitic stainless steels, which are used as reactor internal materials. Slow strain rate testing (SSRT) has been widely applied to evaluate the IASCC initiation characteristics of proton-irradiated tensile specimens. Tensile specimens require low surface roughness for micro-crack observation, and electropolishing is the most important specimen pre-treatment process used for this. In this study, optimal electropolishing conditions were examined through analyzing results of polarization experiments and surface roughness measurements after electropolishing. Corrosion cell and electropolishing equipment were fabricated for polarization tests and electropolishing experiments using SSRT specimens. The experimental parameters were electropolishing time, current density, electrolyte temperature, and stirring speed. The optimal electropolishing conditions for SSRT tensile specimens made of type 316 stainless steel were evaluated as a polishing time of 180 seconds, a current density of 0.15 A/cm², an electrolyte temperature of 60 ℃, and a stirring speed of 200 RPM.

• 대한원격탐사학회지
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• 제25권1호
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• pp.31-44
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• 2009

본 연구에서는 다편파 산란계 시스템을 이용하여 얻어진 후방산란계수의 연중 변화를 편파와 입사각에 따라 알아보고 벼 생육인자와의 관계를 통하여 생육인자를 추정하고자 하였다. 2007년도 국립농업과학원 시험포장에 다편파산란계 시스템(L, C, X-band 안테나, 네트워크분석기, RF cable, 입사각 $20^{\circ}{\sim}60^{\circ}$)을 제작 구축하고 벼 이앙기에서 수확기까지 산란특성을 주기적으로 관측하였으며 레이더 방정식을 이용하여 후방산란계수를 계산하여 자료 분석에 사용하였다. 모든 안테나 밴드에서 벼 생육초기(5월말$\sim$6월초)에는 VV-편파가 HH-, HV-편파보다 후방산란계수가 높게 나타났다. C-band의 경우 모든 입사각에서 벼가 자라면서 HH-편파 후방산란계수가 증가하다가 출수기(8월중순경)에 가장 높았고 그 이후 감소하는 경향이었다. X-band는 모든 편파의 후방산란계수가 벼 유수형성기(7월말경)까지 증가하다가 그 후 감소하였으며 등숙기인 9월 중순 이후 다시 증가하는 dual-peak 현상을 보였는데, 특히 VV-편파의 경우 9월 초순부터 후방산란계수 종가가 다른 편파에 비해 크게 나타났다. 파장별 밴드, 편파, 입사각도별 후방산란계수와 작물 생육과의 관계를 분석한 결과 L-band는 바이오매스와의 상관이 높게 나타났고 C-band에서는 엽면적지수와 초장과의 상관이 높게 나타났으며 X-band는 이삭 건물중과 상관이 높게 나타났다 후방산란계수를 이용하여 생육을 추정할 수 있는 회귀식을 작성하고 실측값과의 비교를 통하여 작물 생육 추정을 위한 최적 조건을 구명하였다.

• 대한원격탐사학회지
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• 제34권1호
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• pp.117-126
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• 2018

This study aims to evaluate the usability of polarimetric SAR measurements for discriminating water-covered area from other land cover types and to propose polarimetric parameters showing the better response to the flood. Flood-related changes in the polarimetric parameters were studied using the L-band PALSAR-2 quad-pol mode data acquired before and after the severe flood events occurred in Joso city, Japan. The experimental results showed that, among various polarimetric parameters, the HH-polarization intensity, the Shannon entropy, and the surfaces scattering component of model-based decomposition were found to be useful to discriminate water-covered areas from other land cover types. Particularly, an unsupervised change detection with the Shannon entropy provides the best result for an automated mapping of flood extents.

• 한국지구과학회지
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• 제34권1호
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• pp.1-12
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• 2013

채프에코는 기상레이더 영상에서 강수에코로 자주 오인된다. 본 연구에서는 채프에코를 효과적으로 제거하기 위하여 국립기상연구소 X-밴드 이중편파레이더에서 관측한 자료를 활용하여 채프에코의 반사도와 각각의 이중편파변수의 관계성을 분석하였다. 특히 본 연구는 채프에코 사례의 입체관측자료 영상에서 채프에코가 발생한 영역만을 선별하여 이중편파변수 자료들을 수집하였다. 전반적으로 이중편파변수(반사도, 차등반사도, 교차상관계수, 차등반사도 표준편차와 비차등위상차)에 대해 채프에코의 변수 값이 강수에코보다 넓은 범위를 차지하며, 채프 섬유의 공간적 배치는 레이더빔에 대해 수평적으로 놓여있는 경향이 나타났다. 일부 강수에코의 교차상관계수는 0.8 이하의 값을 갖고 있기 때문에 채프에코 값과 상당한 중첩이 나타났다. 일반적으로 교차상관계수는 강수에코와 채프에코를 효과적으로 분리하는데 좋은 변수로 고려되고 있지만, 이 연구는 교차상관계수만을 이용하여 채프에코를 제거할 경우에 일부 강수에코가 제거될 가능성이 있음을 시사한다.

• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• 제2권2호
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• pp.91-98
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• 1998

In this study, we carried out the experiments for measuring the variations of corrosion potential and current density for polarization curves with polyvinylchloride. The results exhibited especially the influence affecting the corrosion potential and various conditions (temperature, day, pH, bacteria, and added salt). The second anodic current density peak and the minimum passive current density are designated $I_P/I_0,$ respectively. The value of $I_P/I_O$ is used as a measurement for the extent of degradation of the polyvinylchloride. The potentiodpnamics parameters of the corrosion were obtained using Tafel equation.

• 천문학논총
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• 제12권1호
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• pp.1-21
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• 1997

We have obtained theoretical calibration curves to convert the amount of polarization into the strength of magnetic field, by a numerical calculation of radiation transfer for the polarized spectral line of FeI $6303{\AA}$. In our calculation, three kinds of atmospheric models (VAL-C, penumbra, umbra) have been used to make a proper calibration for an active region composed of quiet, penumbral and umbral areas. It was found that firstly, the results of our calculation depend highly on a kind of atmospheric model rather than on any other input parameters used in a model. Secondly, observed line profile showed m solar spectrum atlas proved to be very similar to the calculated profiles obtained by using a penumbra model. Finally, another method except this calibration curve should be developed to estimate correctly the distribution of magnetic field in solar active region from the observation of polarized spectral line.

• 대한화학회지
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• 제56권2호
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• pp.264-273
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• 2012

Five derivatives of phenylthiourea namely: 1-(4-methoxyphenyl)-3-phenylthiourea (1), 1-(4-methylphenyl)-3- phenylthiourea (2), 1-(4-bromophenyl)-3-phenylthiourea (3), 1-(4-chlorophenyl)-3-phenylthiourea (4) and 1-phenylthiourea (5) have been evaluated as new inhibitors for the corrosion of carbon steel in 2 M HCl solution using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. Potentiodynamic polarization measurements showed that these derivatives are mixed-type inhibitors. The inhibition efficiency was found to increase with inhibitor concentration and decreases with rise in temperature. The thermodynamic parameters of adsorption and activation were determined and discussed. Nyquist plots showed depressed semicircles with their centre below real axis. The adsorption process of studied derivatives on carbon steel surface obeys Temkin adsorption isotherm. The synergistic effect of these derivatives and some anions is discussed from the viewpoint of adsorption models. The electrochemical results are in good agreement with the calculated quantum chemical HOMO and LUMO energies of the tested molecules.

• 대한화학회지
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• 제58권2호
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• pp.160-168
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• 2014

The electrochemical behavior and corrosion inhibition of zinc in 0.5 M $H_2SO_4$ in the absence and presence of some chromones has been investigated using weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and electrochemical frequency modulation (EFM) techniques. The presence of these investigated compounds in the corrosive solutions decrease the weight loss, the corrosion current density, and double layer capacitance but increases the charge transfer resistance. Polarization studies were carried out at room temperature, and showed that all the studied compounds act as mixed type inhibitors with a slight predominance of cathodic character. The effect of temperature on corrosion inhibition has been studied and the thermodynamic activation and adsorption parameters were determined and discussed. The adsorption of the investigated compounds on zinc was found to obey Langmuir adsorption isotherm.

• 한국전자파학회:학술대회논문집
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• 한국전자파학회 2005년도 종합학술발표회 논문집 Vol.15 No.1
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• pp.289-292
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• 2005

Two planar inverted-F antenna (PIFA) arrays are proposed as an alternative model to generate input and radiation characteristics of two orthogonal oriented circular loops, which has polarization diversity, but inherent mechanical instability of two orthogonal loops, in particular, in installation and operation conditions. Two $1\times2$ PIFA sub-arrays are orthogonally placed on a ground plane and two different feeding networks are applied to control horizontal and vertical radiation current flows for each sub-array, respectively. Equivalence of scattering parameters and radiation patterns between two antennas are validated by the available commercial simulator.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 1999년도 춘계종합학술대회
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• pp.276-279
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• 1999

This paper proposes a design for microstrip patch antenna with dual resonance and dual polarization fed by proximity coupled quarter wavelength stub. The antenna characteristics are analyzed by the FDTD method with Mur's 2nd order ABC. From the simulation results based on the FDTD method, frequency characteristics of structure parameters such as the patch size and the offset feed are investigated. The numerical results are compared with the experimental results, and the comparison shows reasonable agreement for a design frequency.