• Journal of the Korea Concrete Institute
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• v.15 no.1
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• pp.25-34
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• 2003

The degradation of reinforced concrete (RC) structures due to physical and chemical attacks has been a major issue in construction engineering. Deterioration of RC structures by chloride attack followed by reinforcement corrosion is one of the serious problems. An objective of this study is to develop a form of mathematical model of chloride ingress into concrete. In order to overcome some limits of the previous approaches, a chloride ingress model, consisting of chloride solution intrusion through the capillary pore and chloride ion diffusion through the pore water, was proposed. Moreover, the variability of chloride ion diffusivity due to the degree of hydration of cement, relative humidity in pore, exposure condition, and variation of chloride binding, was considered in the model. In order to verify the proposed model, the results predicted by the proposed model were compared with analysis results of Life-365, a computer program for predicting the service life of reinforced concrete structures exposed to chlorides. In conclusion, the proposed model would be promising to predict the chloride ion profile and to estimate the service life of RC structures.

• Journal of the Korean Society of Food Science and Nutrition
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• v.20 no.6
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• pp.572-581
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• 1991

For the development of a model to predict absorbed salt quantity in radish during salting, absorbed salt quantity and water content change in radish by the hour were measured at 5%, 10%, 15% brine concentration and $10^{\circ}C,\;20^{\circ}C,\;30^{\circ}C$ respectively. Absorbed salt quantity in radish by the time showed logarithmic function, absorbed salt quantity by brine concentration and temperature showed linear relation. A model to predict absorbed salt quantity in radish at each time, brine concentration and temperature was calculated by the regression program of SPSS. Apparent diffusivity of salt in radish was calculated from appropriated diffusion equation solution of Fick's second law using computer simulation. Salt diffusivity in radish increased as brine concentration increased and the effect of temperature could by expressed by Arrhenius equation. A model equation which could predict salt diffusivity was developed by regression analysis. To specify relation between salt quantity which absorbed into radish and water content which removed out of it, Flux ratio(${\Delta}W/{\Delta}S$) was calcuated. The values showed that the removed water content was greater than the absorbed salt quantity.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.7
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• pp.46-52
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• 2006

The effects of surface treatment on the hydrogen storage properties of a $Mg_2Ni$ alloy particle were investigated by the microvoltammetric technique, in which a carbon-filament microelectrode was manipulated to make electrical contact with the particle in a KOH aqueous solution. It was found that the hydrogen storage properties of $Mg_2Ni$ at room temperature were improved by the surface treatment with a nickel plating solution. The sodium salts(sodium phosphate and sodium dihydrogen citrate) contained in the nickel plating solution made the alloy form an amorphous-like state, resulting in an improved hydrogen charge/discharge capacity at room temperature as high as about 150[mAh/g] from the original value of 17[mAh/g]. Potential-step experiment was carried out to determine the apparent chemical diffusion coefficient of hydrogen atom($D_{app}$) in the alloy. Since the alloy particle we used here was a dense, conductive sphere, the spherical diffusion model was employed for data analysis. $D_{app}$ was found to vary the order between $10^{-8}{\sim}10^{-9}[cm^2/s]$ over the course of hydrogenation and dehydrogenation process.

• Computers and Concrete
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• v.15 no.1
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• pp.103-126
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• 2015

Thermal effects are significant loads for assessing concrete dam behaviour during operation. A new methodology to estimate thermal loads on concrete dams taking into account processes which were previously unconsidered, such as: the evaporative cooling, the night radiating cooling or the shades, has been recently reported. The application of this novel approach in combination with a three-dimensional finite element method to solve the heat diffusion equation led to a precise characterization of the thermal field inside the dam. However, that approach may be computationally expensive. This paper proposes the use of a new one-dimensional model based on an explicit finite difference scheme which is improved by means of the reported methodology for computing the heat fluxes through the dam faces. The improved model has been applied to a case study where observations from 21 concrete thermometers and data of climatic variables were available. The results are compared with those from: (a) the original one-dimensional finite difference model, (b) the Stucky-Derron classical one-dimensional analytical solution, and (c) a three-dimensional finite element method. The results of the improved model match well with the observed temperatures, in addition they are similar to those obtained with (c) except in the vicinity of the abutments, although this later is a considerably more complex methodology. The improved model have a better performance than the models (a) and (b), whose results present larger error and bias when compared with the recorded data.

• Journal of the Korean GEO-environmental Society
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• v.7 no.3
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• pp.43-54
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• 2006

In this paper, the uniaxial, triaxial compression tests and consolidation tests on the clay sample substituted initial pore water for pollutant were performed to evaluate the change in geotechnical properties of the contaminated clay. The contaminant transport analysis on embankment type landfill using the MT3D model was also performed to evaluate the extent of transport and diffusion. There was tendency that strength, compressibility and permeability has increased with the increase in the concentration of NaCl solution. The increase in the strength and compressibility of sample saturated with leachate was higher than samples saturated with NaCl solution, but in the permeability coefficient was lower. As the result of contaminant transport analysis, the predicted concentration was in high with the increase in the initial concentration of $Cl^-$ ion and increased in a non-linear form. The transportation distance calculated with use of regression equation between the distance from contaminant source and the concentration of $Cl^-$ ion was increased with the increase in the initial concentration.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.16 no.2
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• pp.92-102
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• 2004

In this paper, an analytical solution of calculating the excess temperature field due to a point heat source is presented in the presence of spring-neap modulation of convective alongshore flow. The basic form of the solution is identical to that given by Jung et al. (2003) but the convective term in the exponential kernel function is extended and a spring-neap variation in the horizontal eddy diffusivity is newly introduced. A set of calculations have been performed to examine the sensitivity of the heat build-up to the change in current fields and turbulent dispersion. Results indicate that the excess temperature field is confined within the tidal excursion distance, while the excess temperature field beyond the distance is mainly controlled by the horizontal diffusion. The heat build-up within the distance is considerably affected by the spring-neap variation in the horizontal eddy diffusivity; the relatively high excess temperature more than 1$^{\circ}C$ is extended further when the eddy diffusivity has spring-neap modulation.

• Archives of Pharmacal Research
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• v.27 no.11
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• pp.1177-1182
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• 2004

The effect of poly[2-methacryloyloxyethyl phosphorylcholine] (pMPC) on the skin permeation property was investigated by performing in vitro skin permeation study of a model drug, nicotinic acid (NA). Effect of pMPC polymer in donor solution on skin permeation rates was evaluated using side-by-side diffusion cells. Also, the structural alterations in the stratum corneum (SC), inter-lamellar bilayer (ILB) and dermis layers in pMPC-treated and -untreated skin sections were investigated with transmission electron microscopy (TEM). The permeation profile of NA without pMPC in donor solution showed biphasic mode: initial $1^{st} phase and 2^{nd}$ hydration phase. The sudden, more than 10-fold increase in flux from the initial steady state (43.5 $\mu g/cm^2$/hr) to the $2^{nd}$ hydration phase (457.3 $\mu g/cm^2$/hr) suggests the disruption of skin barrier function due to extensive hydration. The permeation profile of NA with 3% pMPC in the donor solution showed monophasic pattern: the steady state flux (10.9 $\mu g/cm^2$/hr) without abrupt increase of the flux. The degree of NA permeation rate decreased in a concentration-dependent manner of pMPC. TEM of skin equilibrated with water or 2% pMPC for 12 h showed that corneocytes are still cohesive and epidermis is tightly bound to dermis in 2% pMPC-treated skin, while wider separation between corneocytes and focal dilations in inter-cellular spaces were observed in water-treated skin. This result suggests that pMPC could protect the barrier property of the stratum corneum by preventing the disruption of ILB structure caused by extensive skin hydration during skin permeation study.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.3
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• pp.129-138
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• 1993

In this study, the applicability of finite analytic method (FAM) is studied by selecting linearized-Burgers equation and Burgers equation which have convective and diffusive behaviors as the model equation of Navier-Stokes equations and by comparing numerical solution of finite difference method (FDM) and finite analytic method. The results are as follows. It is shown that the convergence of FAM for steady-state analytic solution of linearized-Burgers equation and Burgers equation is better than that of FDM under the same criteria. Also the accuracy of FAM for transient solution of Burgers equation is excellent. Especially, it is shown that oscillation phenomenon due to dispersion errors which occur according to the choice of grid size in FDM does not occur in FAM at all. So, it can be thought that FAM is numerically very stable scheme, which is free from dispersion errors.

• Applied Chemistry for Engineering
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• v.24 no.6
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• pp.621-627
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• 2013

In order to apply eco-friendly poly(propylene carbonate) (PPC) into barrier packaging materials, six different PPC/exfoliated graphite (EFG) nanocomposite films with different EFG were successfully prepared by a solution blending method. Their water sorption behavior was gravimetrically investigated as a function of the EFG content and interpreted with respect to their chemical structure and morphology. The water sorption isotherms were reasonably well fitted by Fickian diffusion model, regardless of morphological heterogeneities. With increasing the EFG content, the diffusion coefficient and water uptake decreased from $12.5{\times}10^{-10}cm^2sec^{-1}$ to $7.2{\times}10^{-10}cm^2sec^{-1}$ and from 8.9 wt% to 4.2 wt%, respectively, which indicates that the moisture resistance capacity of PPC was greatly enhanced by incorporating EFG into PPC. The enhanced water barrier property of the PPC/EFG nanocomposite films with the high aspect ratio EFG makes them potential candidates for versatile packaging applications. However, to maximize the performance of the nanocomposite films, further researches are required to increase the compatibility of EFG in the PPC matrix.

• Journal of Pharmaceutical Investigation
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• v.36 no.2
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• pp.97-102
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• 2006

The aim of this study was to investigate the feasibility and optimize permeability of slim patch type as a transdermal delivery system of caffein. Slim patch type was formulated and tested in modified Franz diffusion cell across cellulose membrane and hairless mouse skin in pH 5.8 phosphate buffer solution (PBS). The effect of $Pharmsolv^{\circledR}$ and drug concentration on permeation at four model, 1,2% $Pharmsolv^{\circledR}$ with $0.12\;mg/cm^2$ caffein and 0.12, $1.2\;mg/cm^2$ caffein with 2% $Pharmsolv^{\circledR}$ through hairless mouse skin was studied in vitro. The release of caffein from slim patch with various loading was fitted by the Higuchi's diffusion equation. The result showed that chemical $Pharmsolv^{\circledR}$ produced a large and significant increase of permeation. The effect of 2% $Pharmsolv^{\circledR}$ on permeation of caffein was greater about 10-fold greater than 1% $Pharmsolv^{\circledR}$ in first 60 minutes. The effect of drug concentration, however, was lower than that produced by chemical $Pharmsolv^{\circledR}$. Within the tested system, the most efficient combination for caffein slim patch type was $0.12\;mg/cm^2$ caffein with 2% $Pharmsolv^{\circledR},$ although $1.2\;mg/cm^2$ caffein with 2% $Pharmsolv^{\circledR}$ showed highest amounts permeation, because permeated percentages were significantly lower about $1/4{\sim}1/5$ times.