• 대한전기학회:학술대회논문집
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• 대한전기학회 1989년도 하계종합학술대회 논문집
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• pp.655-658
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• 1989

The characteristics of proton-diffused $LiNbO_3$ optical waveguides with self-aligned $SiO_2$-cladding are reported. When the proton diffusion occurs, the $SiO_2$-cladding limits the lateral diffusion of protons by out-diffusion of protons in unclad region. Proton indiffusion in depth direction is promoted by inhibition of out-diffusion in clad region. Consequently, the mode profile in depth direction can be nealy symmetric. The extent of the proton exchange was observed by measuring the infrared absorption peak at about $3500cm^{-1}$. It is confirmed that proton diffusion with $SiO_2$-cladding has structural excellency.

• 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.

• 한국해양공학회지
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• 제11권2호
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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.

• Bulletin of the Korean Chemical Society
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• 제12권5호
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• pp.468-473
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• 1991

Viscoelastic properties of PET filament fibers on stress relaxation were investigated in the solvents of $H_2$O, 0.05% NaOH and 50% DMF using an Instron (UTM4-100 Tensilon) with solvent chamber. The theoretical stress relaxation equation derived by applying the Ree-Eyring's hyperbolic sine law to dashpot of three element non-Newtonian model was applied to the experimental stress relaxation curves, and the model parameters $G_1,G_2$, ${\alpha}$ and ${\beta}$ were obtained. By analyzing temperature dependency of the relaxation time, the values of activation entropy, activation enthalpy and activation free energy for flow in PET filament fiber were evaluated, the activation free energy being about 25.7 kcal/mol. The self diffusion coefficient and hole distance were obtained from parameters ${\alpha}$, ${\beta}$ and crystallite size in order to study the self diffusion and the orientation of crystallites in amorphous region and the effect of solvent.

• 대한수학회보
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• 제43권2호
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• pp.443-459
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• 2006

The prey-predator system with a single cross-diffusion pressure is known to possess a local solution with the maximal existence time $T\;{\leq}\;{\infty}$. By obtaining the bounds of $W\array_2^1$-norms of the local solution independent of T we establish the global existence of the solution. And the long-time behaviors of the global solution are analyzed when the diffusion rates $d_1\;and\;d_2$ are sufficiently large.

• 대한수학회지
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• 제48권1호
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• pp.147-158
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• 2011

In this paper, we consider a multi-dimensional diffusion process in a self-similar random environment and prove a limit theorem for the shape of the full trajectory of the diffusion by using the localization phenomenon.

• Computers and Concrete
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• 제15권5호
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• pp.847-864
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• 2015

In this paper, a reaction-diffusion model of carbonation process in self-compacting concrete (SCC) was realized with a consideration of multi-field couplings. Various effects from environmental conditions, e.g. ambient temperature, relative humidity, carbonation reaction, were incorporated into a numerical simulation proposed by ANSYS. In addition, the carbonation process of SCC was experimentally investigated and compared with a conventionally vibrated concrete (CVC). It is found that SCC has a higher carbonation resistance than CVC with a comparable compressive strength. The numerical solution analysis agrees well with the test results, indicating that the proposed model is appropriate to calculate and predict the carbonation process in SCC. The parameters sensitivity analysis also shows that the carbon dioxide diffusion coefficient and moisture field are essentially crucial to the carbonation process in SCC.

• Bulletin of the Korean Chemical Society
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• 제4권5호
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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.

• 한국건설순환자원학회논문집
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• 제10권4호
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• pp.600-608
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• 2022

이 연구는 전기영동확산시험을 이용하여 이중층수산화물(LDH)을 혼입한 균열이 있는 자기치유 시멘트 모르타르의 염화물 침투 저항성을 평가하여 LDH가 자기치유 콘크리트의 치유 효과에 미치는 영향을 고찰하였다. 실험결과에 따르면 자기치유물질만 혼입한 경우와 자기치유물질과 Ca-Al LDH를 함께 혼입한 경우 균열 발생 직후 영동확산계수는 대부분 OPC 배합에 비해 더 컸지만, 치유재령이 경과할수록 OPC 보다 더 큰 폭으로 영동확산계수가 감소하며, Ca-Al LDH를 함께 혼입한 경우가 자가치유 물질만 혼입한 경우보다 영동확산계수 감소가 더 크게 나타나 더 높은 자기치유 성능을 보였다. 이는 균열면에 자기치유 반응생성물이 증가하면서 균열 내부에서 LDH에 의한 염소이온의 구속작용이 더 커진다는 것을 시사한다.

• 대한화학회지
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• 제58권3호
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• pp.251-257
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• 2014

Poly(methyl acrylate)-poly(acrylonitrile) 공중합체의 응력완화 실험은 용매기를 부착한 인장 시험기를 사용하여 여러 온도의 공기 중, 증류수 용액에서 실행하였다. Eyring-Halsey 모델의 이론적인 응력완화식에 응력완화 실험 결과를 적용하여 여러 가지 유동 파라메타를 계산하였다. 비결정성 영역에서의 유동단위의 고찰을 위하여 유동 파라메타와 결정크기로부터 섬유고분자 물질의 자체확산, 홀 부피, 점성, 열역학파라메타 등을 계산하였다. 이들 시료의 유동 파라메타는 유동 단위의 홀부피, 자체확산, 유동 열역학 파라메타와 직접적인 연관을 갖는 것으로 규명되었다.