• Title/Summary/Keyword: Self-diffusion coefficient

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A study on the stress dependence of diffusion coefficient at the elevated tenperature and the structural characterictics of 12% Cr rotor steel. (12% Cr강의 고온 확산계수의 응력의존성과 조직의 특성에 관한 연구)

  • 장윤석;김태형
    • Journal of Ocean Engineering and Technology
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    • v.11 no.2
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    • pp.39-47
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    • 1997
  • Creep rate the elevated temperature is known to be controller by the softening process of microstructure especially in the solid solution alloys such as 125 Cr rotor steel. The change of structure is a decreasing process of the free energy of the state including stress, diffusivity of the material, and tmeperature. This study shows that diffusion coefficient, D of 12% Cr rotor steel at 953K with 74.8 MPa is 1.084~3.140*$10^{15}mm^2sec^1$ compared to $1.658*10^{24}mm^2sec^1$at 963K without stress. During creep, the growth of martensite laths accelerates the diffusion coefficient under stress due to incoherency of interface between carbides and matrix.

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The Prediction of Solvent Mutual Diffusion Coefficient Using Vrentas-Duda's Self Diffusion Theory (Vrentas-Duda의 자기확산이론을 이용한 용매의 상호확산계수 예측)

  • 김종수;이광래;김기창
    • Membrane Journal
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    • v.10 no.1
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    • pp.19-29
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    • 2000
  • To estimatc mutual diffusion coefficient for the analysis of mass transfer phenomena in polymer/solvent system, two models are proposed and the equations are derived. The estimates of mutual diffusion coefficients are obtained by two models suggested in this work and compared with and experimental data and Vrentas-Duda's. Vrentas-Duda's self diffusion coefficient was used for the mutual diffusion coefficient. Derivative of chemical potential on solvent was derived and used using original UNIFAC-FV and modified UNIFAC-FV. However, Vrentas-Duda's equation for mutual diffusion coefficient contains Flory-Huggins parameter x. For the derivative of chemical potential term, Vrentas-Duda assumed that parameter x was constant and independent of temperatures and concentrations The assumption is one of shortcoming in vrentas-Duda's mutual diffusion coefficient. New methods proposed in this work do not have such assumptions and simplifications. For the solvent of cyclohexane, n-pentane, and n-hexane in PIB(polyisolbutylene) and PMS-BR (poly(p-methylstyrene-co-isobutylene), new methods well correlate the experimental data at various temperatures and concentrations, and predicted the experimental data much better than Vrentas-Duda's for the PIB/toluene system. It is shown that new methods are excellent tools for correlating mutual diffusion coefficient data in polymer/solvent system over wide ranges of temperature and concentration without any assumptions or simplifications.

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Development of Oxygen Diffusion Test Method for Crack Width Evaluation of Self-Healing Concrete (자기치유 콘크리트의 균열치유 성능평가를 위한 개선된 산소확산 시험방법 제안)

  • Lee, Do-Keun;Shin, Kyung-Joon
    • Journal of the Korean Recycled Construction Resources Institute
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    • v.9 no.3
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    • pp.375-382
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    • 2021
  • Self-healing concrete is in the spotlight in that it can effectively extend the lifespan of concrete structures by healing cracks in the structure by themselves without additional repairing or retrofiting actions. Currently, self-healing concrete is a field that is being actively studied around the world, but since most studies focus on the improvement of healing performance, there is a lack of methods to rationally evaluate the self-healing performance of concrete. Although the gas diffusion test method has been developed for the use in the performance evaluation of self-healing concrete, it has revealed that for gas diffusion through the matrix affect the crack diffusion coefficients depending on the environmental conditions such as the saturation of the specimen, the temperature, and humidity during the experiment. Therefore, in this study, the method has been proposed to eliminate the influence of the matrix diffusion when calculating the crack diffusion coefficient. In addition, a pre-conditioning process was introduced to shorten the experimental time. As a result, the crack width could be estimated with an error level of less than 3% in the test time of about 20 minutes.

Viscosity and Volume Effects on Convective Flows in PGSE-NMR Self-Diffusion Measurements at High Temperature

  • Seo, Ji Hye;Chung, Kee-Choo
    • Journal of the Korean Magnetic Resonance Society
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    • v.16 no.2
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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.

Relationship between Crack Width and Gas Diffusion Coefficient of Cracked Acrylic Specimens (균열 아크릴 시편의 기체 확산계수와 균열폭의 관계)

  • Lee, Do-Keun;Lim, Min-Hyuk;Shin, Kyung-Jun
    • Journal of the Korean Recycled Construction Resources Institute
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    • v.6 no.4
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    • pp.245-251
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    • 2018
  • Recently, as the importance of structural maintenance has been increased, studies on self - healing concrete technology are being actively carried out. On the other hand, test for evaluating the self-healing performance is not standardized yet. Although visual test is used as a basic method for measuring crack widths, it is difficult to observe the crack width inside the specimen, and there is a disadvantage that only the local measurement of the surface can be measured due to the inhomogeneous cracking characteristics. Although permeability test has been widely used as an indirect method for measuring crack width, there is a problem due to the viscosity of water, and also a possibility that the internal material of the specimen may be eluted during the test. In this study, we propose a crack width evaluation method using gas diffusion characteristics. Idealized straight cracks were fabricated by acrylic and the diffusion coefficients of specimens were analyzed with respect to crack width and thickness. The experimental results show that the crack width and the diffusion coefficient are in a linear relationship and that the thickness and diffusion coefficient are inversely related.

A Modified Enskog-Like Equation of Self-Diffusion Coefficients for Penetrable-Sphere Model Fluids

  • Suh, Soong-Hyuck;Liu, Hong-Lai
    • Bulletin of the Korean Chemical Society
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    • v.32 no.4
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    • pp.1336-1340
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    • 2011
  • Molecular dynamics simulations have been performed to investigate the transport properties of self-diffusion coefficients in the penetrable-sphere model system. The resulting simulation data for the product of the packing fraction and the self-diffusion coefficient exhibit a transition from an increasing function of density in lower repulsive systems, where the soft-type collisions are dominant, to a decreasing function in higher repulsive systems, where most particle collisions are the hard-type reflections due to the low-penetrability effects. A modified Enskog-like equation implemented by the effective packing fraction with the mean-field energy correction is also proposed, and this heuristic approximation yields a reasonably good result even in systems of high densities and high repulsive energy barriers.

Molecular Dynamics Study of the Self-Diffusion Coefficient and Velocity Autocorrelation Function of a Polymer Molecule in Solution

  • Kang, Hong-Seok;Lee, Young-Seek;Ree, Tai-kyue
    • Bulletin of the Korean Chemical Society
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    • v.4 no.5
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    • pp.223-227
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    • 1983
  • A molecular dynamic computer experiment was performed on a system of 108 particles composed of a single polymer chain and solvent molecules. The state considered was in the immediate neighborhood of the triple point of the system. The polymer itself is an analog of a freely jointed chain. The Lennard-Jones potential was used to represent the interactions between all particles except for that between the chain elements forming a bond in the polymer chain, for which the interaction was expressed by a harmonic potential. The self-diffusion coefficient and velocity autocorrelation function (VACF) of a polymer were calculated at various chain lengths $N_p$, and various interaction strengths between solvent molecules and a polymer chain element. For self-diffusion coefficients D, the Einstein relation holds good; as chain length $N_p$ increases the D value decreases, and D also decreases as ${\varepsilon}_{cs}$ (the interaction parameter between the chain element and solvent molecules) increases. The relaxation time of velocity autocorrelation decreases as ${\varepsilon}_{cs}$ increases, and it is constant for various chain lengths. The diffusion coefficients in various conditions reveal that our systems are in a free draining limit as is well known from the behavior of low molecular weight polymers, this also agrees with the Kirkwood-Riesman theory.

Temperature Dependence on Structure and Self-Diffusion of Water: A Molecular Dynamics Simulation Study using SPC/E Model

  • Lee, Song Hi
    • Bulletin of the Korean Chemical Society
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    • v.34 no.12
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    • pp.3800-3804
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    • 2013
  • In this study, molecular dynamics simulations of SPC/E (extended simple point charge) model have been carried out in the canonical NVT ensemble over the range of temperatures 300 to 550 K with and without Ewald summation. The quaternion method was used for the rotational motion of the rigid water molecule. Radial distribution functions $g_{OO}(r)$, $g_{OH}(r)$, and $g_{HH}(r)$ and self-diffusion coefficients D for SPC/E water were determined at 300-550 K and compared to experimental data. The temperature dependence on the structural and diffusion properties of SPC/E water was discussed.

LONG-TIME PROPERTIES OF PREY-PREDATOR SYSTEM WITH CROSS-DIFFUSION

  • Shim Seong-A
    • Communications of the Korean Mathematical Society
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    • v.21 no.2
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    • pp.293-320
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    • 2006
  • Using calculus inequalities and embedding theorems in $R^1$, we establish $W^1_2$-estimates for the solutions of prey-predator population model with cross-diffusion and self-diffusion terms. Two cases are considered; (i) $d_1\;=\;d_2,\;{\alpha}_{12}\;=\;{\alpha}_{21}\;=\;0$, and (ii) $0\;<\;{\alpha}_{21}\;<\;8_{\alpha}_{11},\;0\;<\;{\alpha}_{12}\;<\;8_{\alpha}_{22}$. It is proved that solutions are bounded uniformly pointwise, and that the uniform bounds remain independent of the growth of the diffusion coefficient in the system. Also, convergence results are obtained when $t\;{\to}\;{\infty}$ via suitable Liapunov functionals.