• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.9 no.2
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• pp.17-27
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• 2005

The problem of the onset stability in an inclined layer of dielectric viscoelastic fluid (Walter's liquid B') is studied. The analysis is made under the simultaneous action of a normal a.c. electric field and the natural convection flow due to uniformly distributed internal heat sources. The power series method used to obtain the eigen value equation which is then solved numerically to obtain the stable and unstable solutions. Numerical results are given and illustrated graphically.

• Bulletin of the Korean Chemical Society
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• v.31 no.8
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• pp.2137-2138
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• 2010

• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.286-288
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• 2003

The physical model considered here is a horizontal layer of fluid heated below and cooled above with a periodic array of evenly spaced square cylinders placed at the center of the layer, whose aspect ratio here varies from unity to six. Periodic boundary condition is employed along the horizontal direction to allow for lateral freedom for the convection cells. Two-dimensional solution for unsteady natural convection is obtained using an accurate and efficient Chebyshev spectral multi-domain methodology for a given Rayleigh numbers of $10^6$

• 한국전산유체공학회:학술대회논문집
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• 1997.10a
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• pp.10-15
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• 1997

Unsteady natural convection of an enclosed fluid has been one of the fundamental thermo-fluid problems, of which dynamic relevance is found in many engineering applications. Together with the inherent coupling between the boundary layers and the interior core, and strong interaction between flow and temperature fields, the unsteadiness poses serious hurdles for analytical and experimental approaches. With the recent development of computers and solution algorithms, computational fluid dynamics has become the prevailing tool to tackle the underlying problems. In this presentation, a few examples of numerical studies are introduced. The usefulness and potential of numerical simulations in investigating unsteady natural convection are elaborated.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.6
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• pp.154-159
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• 2018

Intentional releases occur frequently during maintenance in gas supplying companies, which may result in unpleasant odors, and the possible mistaken belief of a gas accident. Therefore, this study developed a chemical process for effective odorant removal in natural gas using an active chemical that is released intentionally during maintenance and inspection. To develop an effective treatment process for removing the odorant from released natural gas, the effluent concentrations of the odorant in the released gas were measured after a chemical oxidation reaction with a sodium hypochlorite solution in a compact gas scrubbing equipment newly devised in this study. The device was based on a mixed gas vent after the solution inject odorant in the gas through the energy of the venting gas. The cascade combination of a venturi pipe and mixing chamber was developed to remove the odorant effectively from the purposely-released natural gas using an oxidative reaction between the mercaptan compounds (odorant) and the sodium hypochlorite solution. On the other hand, the developed method could be applied limitedly to a relatively small gas release from a low-pressure source. Further studies will be needed to apply the developed process to a large-scale gas release from a high-pressure source.

• Journal of Engineering Education Research
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• v.14 no.4
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• pp.20-28
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• 2011

Writing education for the students who major in natural sciences and engineering is concentrated on just writing in liberal education. So, this article study the condition and practical solution of writing education with a focus on natural sciences and engineering. This article researches the condition of writing in these majors of Seoul National University, Massachusetts Institute of Technology and Stanford University. As a result, students keenly feel the necessity of writing in this major, but SNU does not offer such courses and few teachers that could teach it. To solve this, we propose that writing teachers of liberal education give feedback on the reports of the capstone research subject 3 or 4 times, which corresponds to 1 credit. This solution would be applicable to most universities in practice, though it is not final method.

• The Korean Fashion and Textile Research Journal
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• v.26 no.4
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• pp.411-423
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• 2024

This study examined the dyeability and functionality of silk fabrics dyed using shiitake mushroom pins discarded in large quantities on mushroom farms. FT-IR and UV-Vis spectral analyses showed that polyphenols and flavonoids were present in the hot-water extract of shiitake mushroom pins. Optimal dyeing conditions for silk fabrics were a dye concentration of 50% (v/v), dyeing temperature of 80℃, dyeing time of 60 minutes, and dyebath pH of 5.3. The post-mordant method showed a greater effect on the increase in dye uptake and color change than the pre-mordant method. Unmordanted fabrics appeared as a YR Munsell color. Except for the Cu-mordant, all post-mordanted fabrics produced a Y Munsell color. The FE-SEM/EDX analysis confirmed that the natural iron solution and mud contained various metal ions. The Fe component was found to have the greatest effect on the dye uptake and color properties. The colorfastness of the unmordanted fabrics to washing, dry cleaning, rubbing, and perspiration was excellent (above grade 4), whereas light was grade 3-4. In the case of post-mordanted fabrics with a natural iron solution, the colorfastness to washing, wet rubbing, and light improved by 0.5 grades. For post-mordanted fabrics with mud, the colorfastness to light and sweat improved by 0.5 grades. The bacterial reduction rate for staphylococcus aureus in fabrics dyed with shiitake mushroom pin extract was excellent at over 99.9%, the bacterial reduction rate for klebsiella pneumoniae was 98.1%, and the deodorization rate was excellent at 90%. These results indicate that shiitake mushroom pins can be used as a sustainable, functional natural dye.

• Corrosion Science and Technology
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• v.4 no.1
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• pp.19-22
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• 2005

Two Au-Ag-Cu-Pd dental casting alloys (Au:12% and 20%) used. The test solutions used 0.9 % NaCl solution (isotonic sodium chloride solution), 0.9 % NaCl solution containing 1 % lactic acid, and 0.9 % NaCl solution containing 1 % lactic acid and 0.1 mol $dm^{-3}$ $Na_2S$. The surface of two samples in three sample solutions was not natural discoloration during one year. The alloy containing 12 % gold was easily alloyed and the composition was uniform comparing with the alloy containing 20 % gold. The rest potentials have not a little effect after three months. The kinds of metals could not definitely from the oxidation and reduction waves of metal on the cyclic voltammograms. The dissolutions of gold and palladium were 12 % Au sample in the 0.9 % NaCl solution containing 1 % lactic acid and 0.1 mol $dm^{-3}$ $Na_{2}S$. The pH of solution had an affect on dissolution of copper, and sulfur ion had an affect on dissolution of silver. The copper dissolved amount from 20 % gold sample was about 26 times comparing with that of 12 % gold sample in the 0.9 % solution containing 1 % lactic acid. Corrosion products were silver chloride and copper chloride in NaCl solution, and silver sulfide and copper sulfide in NaCl solution containing $Na_{2}S$.

• Journal of Korean Biological Nursing Science
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• v.17 no.2
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• pp.150-158
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• 2015

Purpose: This study aimed to evaluate the effects of gargling with S-solution and gargling with A-solution on salivary pH, coated tongue, and dental plaque index in preschool children. Methods: Non-equivalent control group pretest-posttest design was used to select the participants. 99 preschool children were divided into three groups. Dependent variables were recorded at baseline, 30 minutes, and 7 days after the first treatment was given. The data were analyzed using $X^2$-test, ANOVA, and repeated measures of ANOVA. Results: There were no significant differences in dependent variables in pre-test. However, the salivary pH in the S-solution group had significantly increased after 30 minutes (p<.05) and then again 7 days (p<.01) after the first treatment. Also, the S-solution and A-solution groups had greater decrease in dental plaque index after 30 minutes and again 7 days after the first treatment (p<.001) than the control group. With respect to coated tongue, there were no significant differences among the three groups. Conclusion: The results of this study indicate that essential oil gargling after brushing is helpful in improving oral health due to auxiliary oral hygiene effects with natural products. Specifically, gargling with S-solution is more effective than A-solution on oral health in preschool children by neutralizing salivary pH and reducing dental plaque index.

• Reproductive and Developmental Biology
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• v.28 no.3
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• pp.173-179
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• 2004

This study was conducted to investigate the toxi-cological effects of different vitrification solution on development of immature porcine oocytes in vitro. Oocytes were exposed to EFS solution [40% ethylene glycol (EG) + 18% Ficoll + 0.3M sucrose], ES solution (5.5M EG + 1.0M sucrose) or GE solution [10% glycol (G) + 20% EG], and these oocytes were transferred to sucrose solution directly. Maturation rates were significantly (P<0.05) higher in the ES solution (44.5%) and control (57.6%) than in the EFS solution (38.8%) and GE solution (22.4%). No differences among three solution were found in fertilization rates. Cleavage rates was significantly (P<0.05) higher in the ES solution (47.1%) and control (65.9%) than in the EFS solution (21.9%) and GE solution (19.0%), but no difference among three solutions was found in the blastocyst formation rates. These results indicate that combination of EG and sucrose solutions had effects on development of immature porcine oocytes.