• Computers and Concrete
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• v.8 no.2
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• pp.125-142
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• 2011

In the present paper, a numerical simulation method based on mesoscopic composite structure of concrete, the truss network model, is developed to evaluate the diffusivity of concrete in order to account for the microstructure of concrete, the binding effect of chloride ions and the chloride concentration dependence. In the model, concrete is described as a three-phase composite, consisting of mortar, coarse aggregates and the interfacial transition zones (ITZs) between them. The advantage of the current model is that it can easily represent the movement of mass (e.g. water or chloride ions) through ITZs or the potential cracks within concrete. An analytical method to estimate the chloride diffusivity of mortar and ITZ, which are both treated as homogenious materials in the model, is introduced in terms of water-to-cement ratio (w/c) and sand volume fraction. Using the newly developed approaches, the effect of cracking of concrete on chloride diffusion is reflected by means of the similar process as that in the test. The results of calculation give close match with experimental observations. Furthermore, with consideration of the binding capacity of chloride ions to cement paste and the concentration dependence for diffusivity, the one-dimensional nonlinear diffusion equation is established, as well as its finite difference form in terms of the truss network model. A series of numerical analysises performed on the model find that the chloride diffusion is substantially influenced by the binding capacity and concentration dependence, which is same as that revealed in some experimental investigations. This indicates the necessity to take into account the binding capacity and chloride concentration dependence in the durability analysis and service life prediction of concrete structures.

• Journal of the Microelectronics and Packaging Society
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• v.23 no.2
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• pp.57-63
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• 2016

We developed a flexible and micro-thick electromagnetic interference (EMI) shielding nanofabric layer that also functions as a water resisting and heat sinking material. Electrospinning followed by a simple heat treatment process was carried on to produce the EMI-shielding Ni/C hybrid nanofibers. The ambient oxygen partial pressure ($pO_2$ = 0.1, 0.7, 1.3 Torr) applied during the heat treatment was varied in order to optimize the effectiveness of EMI-shielding by modifying the size and crystallinity of the magnetic Ni nanoparticles distributed throughout the C nanofibers. Permittivity and permeability of the nanofibers under the electromagnetic (EM) wave frequency range of 300 MHz~1 GHz were measured, which implied the EMI-shielding effectiveness (SE) optimization at $pO_2$ = 0.7 Torr during the heat treatment. The materials' heat diffusivity for both in-plane direction and vertical direction was measured to confirm the anisotropic thermal diffusivity that can effectively deliver and sink the local heat produced during device operations. Also, the nanofibers were aged at room temperature in oxygen ambient for water resisting function.

• Korean Journal of Soil Science and Fertilizer
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• v.17 no.1
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• pp.12-17
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• 1984

In order to find out the effects of soil conditioner treatment on the water movement in sandy loam and silt loam soils were treated with two different kinds of soil conditioners, hydrophobic Bitumen 0.4% or hydrophillic Uresol 0.6%, and the changes of wetting angle (soil-water contact angle), penetrability and diffusivity were measured. The results were summarized as follows: 1. Uresol 0.6% treatment decreased the wetting angle of sandy loam more than $10^{\circ}$, but there was no big difference in silt loam. 2. Sandy loam soil was changed to almost hydrophobic and the wetting angle of silt loam soil was increased to $84.9^{\circ}$ as compared to $76.0^{\circ}$ of untreated soil by Bitumen 0.4% treatment. 3. By Uresol treatment, penetrability of sandy loam was doubled but there was not difference in silt loam, and it was decreased to half in two soils by Bitumen treatment. 4. A significant positive correlation between penetrability and the cosine of wetting angle was recognized. 5. Soil water diffusivity was greatly changed by soil conditioner treatment, and the big differences were appeared at lower soil moisture content.

• Journal of the Korea Concrete Institute
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• v.15 no.6
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• pp.778-784
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• 2003

The carbonation of concrete is one of the major factors that cause durability problems in concrete structures. The rate of carbonation depends largely upon the diffusivity of carbon dioxide in concrete. The purpose of this study is to identify the diffusion coefficients of carbon dioxide for various concrete mixtures. To this end, several series of tests have been planned and conducted. The test results indicate that the diffusion of carbon dioxide reached the steady-state within about five hours after exposure. The diffusion coefficient increases with the increase of water-cement ratio and decreases with the increase of relative humidity at the same water-cement ratio. The content of aggregates also influences the diffusivity of carbon dioxide in concrete. It was found that the diffusion coefficient of cement paste is larger than that of concrete or mortar. The experimental study of carbon dioxide diffusivity in this study will allow more realistic assessment of carbonation depth in concrete structures.

• Journal of the Korean Chemical Society
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• v.37 no.1
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• pp.22-35
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• 1993

The transport phenomena of the free amino acids through poly(hydroxyethyl methacrylate)[P(HEMA)] have been investigated with and without various kinds of surfactants solution and in the mixed surfactants solution. Glutamine has the highest diffusivity among 4 amino acids at 1CMC of cetyldimethylethylammonium bromide(CTABr) surfactant. Glutamic acid is not affected by the concentration of CTABr. Methionine and Lysine shows slight decreased diffusivity at 0.5 CMC, but increase its diffusivity at 1CMC and 2CMC due to the structure change of membrane and the viscosity change of surfactant solution. Glutamic acid has the highest diffusivity among four amino acids at sodium dodecyl sulfate(SDS) and Triton X-100 surfactant. In mixed surfactant solution, each amino acids shows high diffusivity through 45% water content membrane at the 0.5 mole fraction of SDS in the SDS/TX-100 surfactant mixtures. It has been found that not only the property of membrane but also the effects of solute-solvent interactions and solvent effect are very important as the permeation of amino acids occurs through P(HEMA) membrane. The diffusivities of free amino acids through membrane depend upon their molecular shape, size and charge.

• Bulletin of the Korean Chemical Society
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• v.4 no.3
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• pp.128-132
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• 1983

The self-diffusion experiment of water was performed across two series of tactic poly(2-hydroxyethyl methacrylate), P(HEMA) membranes prepared by crosslinking with various amount of hexamethylene diisocyanate (HMDIC). The tagging material was tritium hydroxide (THO) and the efflux of THO was counted on a Liquid Scintillation Counter. The transport data of THO show that the permeability decreases as the amount of HMDIC increased from 2.5 to 10 mole % and the self-diffusions coefficient shows a parallel trend with it. The diffusivity data was discussed in terms of the change of water structural orderliness within membranes. Using the relation between viscosities and diffusivities derived from Eyring's absolute rate theory, the corresponding viscosities of water within two series of tactic P(HEMA) membranes were obtained. From this, it is seen that the viscosity of water within tactic P(HEMA) membranes may have the same values with those of supercooling water whose temperature ranges from -28 to -$36^{\circ}C.$.

• Journal of Korean Society on Water Environment
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• v.32 no.3
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• pp.243-252
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• 2016

In cases of water pollution accidents, accurate prediction for arrival time and concentration of contaminants in a river is essential to take proper measures and minimize their impact on downstream water intake facilities. It is critical to fully understand the behavior characteristics of contaminants on river surface, especially in case of oil spill accidents. Therefore, in this study, the effects of main parameters of advection and diffusion of contaminants were analyzed and validated by comparing the results of Lagrangian particle tracking (LPT) simulation of Environmental Fluid Dynamic Code (EFDC) model with those of Global Position System (GPS)-equipped drifter experiment. Prevention scenario modeling was accomplished by taking cases of movable weir operation into account. The simulated water level and flow velocity fluctuations agreed well with observations. There was no significant difference in the speed of surface particle movement between 5 and 10 layer modeling. Therefore, 5 layer modeling could be chosen to reduce computational time. It was found that full three dimensional modeling simulated wind effects on surface particle movements more sensitively than depth-averaged two dimensional modeling. The diffusion range of particles was linearly proportional to horizontal diffusivity by sensitivity analysis. Horizontal diffusivity estimated from the results of GPS-equipped drifter experiment was 0.096 m²/sec, which was considered to be valid for applying the LPT module in this area. Finally, the scenario analysis results showed that particle movements could be stagnant when discharge from the upstream weir was reduced, implying the possibility of securing time for mitigation actions such as oil boom installation and wiping oil contaminants. The outcomes of this study can help improve the prediction accuracy of particle tracking simulation to establish the most suitable mitigation plan considering the combination of movable weir operation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.11
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• pp.689-695
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• 2016

The performance of proton exchange membrane fuel cells (PEMFC) is strongly related to the water flow and accumulation in the gas diffusion layer (GDL) and catalyst layer. Understanding the behavior of fluid from the characteristics of the media is crucial for the improvement of the performance and design of the GDL. In this paper, a numerical method is proposed to calculate the design parameters of the GDL, i.e., permeability, tortuosity, and effective diffusivity. The fluid flow in a channel filled with randomly packed hard spheres is simulated to validate the method. The flow simulation was performed by lattice Boltzmann method with bounce back condition for the solid volume fraction in the porous media, with different values of porosities. Permeability, which affects the flow, was calculated from the average pressure drop and the velocity in the porous media. Tortuosity, calculated by the ratio the average path length of the randomly injected massless particles to the thickness of the porous media, and the resultant effective diffusivity were in good agreement with the theoretical model. The suggested method can be used to calculate the parameters of real GDL accurately without any modification.

• 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.

• Korean Journal of Environmental Agriculture
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• v.26 no.2
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• pp.171-178
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• 2007

Diffusion and accumulation of ethoprophos in fruit such as apple and two types of pears were examined by dipping them into the solution of ethoprophos. The effective diffusivities of ethoprophos at the skin and flesh of apple and pear were determined by simulation their experimental accumulation curves with calculated ones from the model assuming consecutive diffusion of ethoprophos from skin to flesh. Its effective diffusivity at the flesh with higher content of water were higher, $\sim10^{-10}\;m^2/s$, regardless of the types of fruits, while that at the skin was small, $\sim10^{-12}\;m^2/s$ and increased with the order of 'Niitaka' pear < 'Whangkeumbae' pear < 'Fuji' apple. The variation in the concentration of ethoprophos in its solution did not induce any change in affecting its effective diffusivity at the flesh of 'Whangkeumbae' pear, but the increase in the concentration caused the increase in its effective diffusivity at the skin. The penetration rate of ethoprophos at the skin was an important factor in determining its accumulation rate in fruit.