• 멤브레인
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• 제12권2호
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• pp.90-96
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• 2002

멤브레인 여과 실험에서 얻어진 데이터 처리에 간단한 수치해석을 적용하여 삼투압(osmotic pressure) 과 구배확산계수(gradient diffusion coefficient)를 도출하는 새로운 방법론을 제시하였다. 삼투압과 구배확산계수는 이론 및 실험적으로 쉽게 구할 수 없는 물리적 특성치로서 멤브레인 여과의 특성 규명에 중요하다. 모델 라텍스 콜로이드의 여과시간에 따른 투과플럭스(permeate flux) 값과 이에 대한 수치적분과 수치미분 데이터로부터 분산된 입자농도의 함수인 삼투압 관계식을 구했다. 이로부터 계산된 열역학적 계수(thermodynamic coefficient)는 입자농도가 증가할수록 감소하는 거동을 보였고, 여기에 기존에 제시되어 있는 수력학적 계수(hydrodynamic coefficient)를 도입하여 구배확산계수를 산출하였다. 아울러, 본 연구에서 계산된 입자농도에 따른 구배확산계수의 결과와 동일한 멤브레인과 라텍스 콜로이드의 여과에 대해서 기존에 통계역학적 시뮬레이션으로 예측한 결과를 비교하였다.

• 한국세라믹학회지
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• 제40권9호
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• pp.827-831
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• 2003

In proton-conducting perovskites, oxygen ions and protons make a diffusion pair for a chemical diffusion and thus lead to the transport of $H_2O$ under its chemical potential gradient. The present manuscript develops relationships between the chemical diffusion coefficient of $H_2O$ and the diffusion coefficients of protons and oxygen vacancies with an emphasis on the thermodynamic behavior of the oxygen vacancies. Depending on the degree of hydration X, two different expressions of the chemical diffusion coefficient were obtained : equation omitted and equation omitted.

• 한국공간구조학회논문집
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• 제23권3호
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• pp.87-94
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• 2023

Chloride is one of the most common threats to reinforced concrete (RC) durability. Alkaline environment of concrete makes a passive layer on the surface of reinforcement bars that prevents the bar from corrosion. However, when the chloride concentration amount at the reinforcement bar reaches a certain level, deterioration of the passive protection layer occurs, causing corrosion and ultimately reducing the structure's safety and durability. Therefore, understanding the chloride diffusion and its prediction are important to evaluate the safety and durability of RC structure. In this study, the chloride diffusion coefficient is predicted by machine learning techniques. Various machine learning techniques such as multiple linear regression, decision tree, random forest, support vector machine, artificial neural networks, extreme gradient boosting annd k-nearest neighbor were used and accuracy of there models were compared. In order to evaluate the accuracy, root mean square error (RMSE), mean square error (MSE), mean absolute error (MAE) and coefficient of determination (R2) were used as prediction performance indices. The k-fold cross-validation procedure was used to estimate the performance of machine learning models when making predictions on data not used during training. Grid search was applied to hyperparameter optimization. It has been shown from numerical simulation that ensemble learning methods such as random forest and extreme gradient boosting successfully predicted the chloride diffusion coefficient and artificial neural networks also provided accurate result.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2008년도 International Symposium on Remote Sensing
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• pp.159-162
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• 2008

This paper presents a modified mean curvature diffusion filter to smooth speckle noise in images. Mean curvature diffusion filter has already shown good results in reducing noise in images while preserving fine details. In the mean curvature diffusion, the rate of smoothing is controlled by the local value of the diffusion coefficient chosen to be a function of the local image gradient magnitude. In this paper, the diffusion coefficient is modified to be controlled adaptively by local image surface slope and heterogeneity. The local surface slope contributes to preserving details (e.g.edges) in image and the local surface heterogeneity helps the smoothing filter consider the amount of noise in both edge and non-edge area. The proposed filter's performance is demonstrated by quantitative experiments using speckle noised aerial image and TerraSAR-X satellite image.

• 한국컴퓨터산업교육학회:학술대회논문집
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• 한국컴퓨터산업교육학회 2003년도 제4회 종합학술대회 논문집
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• pp.87-94
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• 2003

Anisotropic diffusion is a selective smoothing technique that promotes smoothing within a region instead of smoothing across boundaries. In anisotropic diffusion, the rate of smoothing is controlled by the local value of the diffusion coefficient chosen to be a function of the local image gradient magnitude. El-Fallah and Gary E. Ford represented the image as a surface and proved that setting the inhomogeneous diffusion coefficient equal to the inverse of the magnitude of the surface normal results in surface evolving speed that is proportional to the mean curvature of the image surface. This model has the advantage of having the mean curvature diffusion (MCD) render invariant magnitude, thereby preserving structure and locality. In this paper, the proposed MCD model efficiently reduces diffusion coefficient at the thin edges using the smoothness of the surface.

• 한국응용과학기술학회지
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• 제19권4호
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• pp.339-348
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• 2002

Self-diffusion coefficients of colloidal ass9Ciation structures in the aqueous solutions of anionic ammonium dodecyl sulfate (ADS) and cationic octadecyltrimethylammonium chloride (OTAC) surfactants were measured by pulsed-gradient spin echo NMR. The results were interpreted on the basis of the ADS/OTAC/water phase diagram. Crossing the phase boundaries, significant changes in self diffusion coefficients were observed and well correlated to the phase diagram. For the micelles their apparent radii were obtained from Stokes-Einstein equation. Their values were 15 for the ADS micelles and 54 ${{\AA}}$ for the OTAC micelles, respectively. For vesicles which were formed spontaneously at different relative amounts of the surfactants and total surfactant concentrations, the radius was measured as 50 to 200 nm. This result is in fair agreement with those by TEM and light scattering.

• 해양환경안전학회지
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• 제20권5호
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• pp.511-525
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• 2014

본 연구는 반폐쇄성 해역인 마산만을 대상으로 eco-hydrodynamic model을 이용하여 해역의 물리적 구조를 분석하여, 물리적 안정도를 나타내는 수직확산계수를 산정하고, 생태계 모델에 적용하여 그 타당성을 평가하는 것이다. 해역의 물리적 구조는 EFDC모델을 사용하여 구하였으며, 수직 확산계수는 수층간의 밀도차이가 커질수록 감소하도록 산정하였다. 산정된 수직 확산계수를 Stella프로그램을 이용하여 구축한 생태계모델에 적용하여, 용존산소 재현성으로 그 타당성을 평가하였다. 수직확산계수 변화를 추정하여 적용한 모델의 결과는 2008년의 $R^2$값은 0.529~0.700으로 나타났으며, 2009년 $R^2$값은 0.542~0.791로 나타났다. 계산값은 관측값과 유사한 경향을 나타내었으며, 만 내측의 빈산소수괴를 잘 재현하였다. 본 연구에서 적용된 수직확산계수는 해역의 밀도성층과 물리적 안정도를 의미하는데, 향후 폐쇄성 내만해역의 빈산소수괴 발생 예측에 유용하게 활용될 것으로 판단된다.

• 한국자기공명학회논문지
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• 제16권2호
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• pp.122-132
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• 2012

The effects of the sample viscosity and volume on the convective flows induced by temperature gradient in PGSE-NMR self-diffusion measurements at high temperature have been investigated. The experimental results showed that the viscosity of the liquid sample strongly affects the magnitude of the convective flows as well as the diffusion coefficient itself. It was also found that the convective flows increase as the sample volume increase.

• 한국GIS학회:학술대회논문집
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• 한국GIS학회 2004년도 GIS/RS 공동 춘계학술대회 논문집
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• pp.523-528
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• 2004

본 연구는 원격탐사 영상분류 과정에 이방성 분산 복원의 적용을 제안하고 있다. 수정 이방성 분산 복원은 많은 원격탐사 영상에 나타나는 지리적 연결성을 대표하는 Markov random field에 기반한 확률적 모형을 사용하고 있고 반복적인 확산과정을 통해 영상복원을 수행한다. 제안 확산과정은 지리적 연결성과 연관된 응집력 계수를 위하여 brightness gradient의 함수를 사용하며 매 반복단계마다 adaptive하게 추정한다. 한반도의 위성 원격탐사 자료에 대한 실험을 실시하였고 제안된 수정 이방성 분산 복원의 적용은 실제 관측 자료에도 매우 효과적임을 알 수 있었다.

• 한국자기공명학회논문지
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• 제12권1호
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• pp.51-59
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• 2008

Convection effect in liquids has been one of the main targets to be overcome in pulsed-field-gradient NMR measurements of self-diffusion coefficients since the temperature gradient along the sample tube generated by the heating and/or cooling process causes the effect, resulting in additional diffusion. It is known that the capillary is the most appropriate tube type for diffusion experiments at variable temperatures since the narrower tube suppresses convection effectively. For evaluating the properties of hydrogen bonding, diffusion coefficients of the $K^+$-complexed and free valinomycin in a micro tube have been determined at various temperatures. From the analysis of the obtained diffusion coefficient values, we could conclude that the intramolecular hydrogen bonding in both of the $K^+$ complexed and free valinomycin in a non-polar solvent is preserved over the observed temperature range, and the temperature dependence of hydrogen bonding is more pronounced in free valinomycin. It is also thought that there is no big change in the radius of the $K^+$-complexed as temperature is varied, and the ratio of overall radius, $r_{complex}/r_{free}$ is slightly decreased as temperature rises.