• Microbiology and Biotechnology Letters
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• v.31 no.2
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• pp.171-176
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• 2003

Productivity of biosurfactant (rhamnolipid) by Pseudomonas aeuginosa F722 was investigated in the several culture conditions and culture composition. Biosurfactant production by P. aeuginosa F722 was amounted to 0.78 g/l as the result of the nitrogen sources and carbon sources without investing of optimum conditions. As for that one was investigated, biosurfactant production by P. aeruginosa F722 was amounted to 1.66 g/l. Biosurfactant production increased twofold because the composition of a modified C-medium was investigated efficiently. $NE_4$Cl or $NaNO_2$ inorganic nitrogens and yeast extract or trypton organic nitrogens were effective, but others inorganic nitrogens and organic nitrogens tested were not efficient far biosurfactant production by P. aeruginosa F722. The optimum concentration of $NH_4$Cl; inorganic nitrogen and yeast extract; organic nitrogen were 0.05% and 0.1%, respectively. In various carbon sources, others with the exception of hydrophobic property substrate (n-alkane) and hydrophilic property substrate (glucose, glycol) were not found to be effective fur biosurfactant production, and 3.0% was better in yield than other concentration of glucose. This yielded C-to-N ratios between 17 and 20. In our experiment, the highest biosurfactant production by P. aeruginosa F722 were observed in 5 days cultivation, containing glucose 3.0%, $NH_4$Cl 0.05%, and yeast extract 0.1% and C-to-N ratio was 20. Optimal pH and temperature for biosurfactant production were 7.0 and $35^{\circ}C$, respectively. Under the optimal culture conditions with glucose, biosurfactant production was amounted to 1.66 g/l. Velocity of biosurfactant production and strain growth increased after nitrogen depletion. The average surface tension of 30 mN/m after the 3 days of incubation under optimal culture condition was measured by ring tensionmeter.

• Bulletin of the Korean Mathematical Society
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• v.35 no.4
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• pp.701-707
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• 1998

An operator $T{\in} {{\mathcal L}(H)}$ is generalized k-quasihyponormal if there exist a constant M>0 such that $T^{\ast k}[M^2(T-z)^{\ast}(T-z)-(T-z)(T-z)^{\ast}]T^k{\geq}0$ for some integer $k{\geq}0$ and all $Z{\in} {\mathbf C}$. In this paper, we show that it T is a generalized k-quasihyponormal operator with the property $0{\not\in}{\sigma}(T)$, then T is subscalar of order 2. As a corollary, we get that such a T has a nontrivial invariant subspace if its spectrum has interior in C.

• Korean Journal of Mathematics
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• v.25 no.1
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• pp.117-126
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• 2017

The subnormality of some classes of operators is a very interesting property. In this paper, we prove that the weighted $Ces{\grave{a}}ro$ operator $C_h{\in}{\ell}^2(h)$ is subnormal and we described completely the set of the extended eigenvalues for the weighted $Ces{\grave{a}}ro$ operator, some other important results are also given.

• Elastomers and Composites
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• v.55 no.2
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• pp.137-146
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• 2020

Part 1 provides a theoretical introduction of the hydrolysis mechanism, while Part 2 introduces other types of reaction mechanisms after hydrolysis in elastomer and PA66 composites. We reviewed the condensation reaction, which occurs after hydrolysis in bi-functional alkoxy silane (TESPD & TESPT), and investigated its effects on the mechanical properties of the composites. We also reviewed activators such as zinc soap, which enhances the mechanical properties of silica-silane-filled elastomer composites. The interaction parameter of silica-silane-filled elastomer composites [α_C (alpha C)] were also discussed. The effects of hydrolysis on the mechanical property changes in plastic composites were compared and reviewed.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.89-90
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• 2006

Austenitic stainless steel has been used as a corrosion resistance material. However, austenitic stainless steel has poor wear resistance property due to its low hardness. In this investigation, we apply powder composite process to obtain hard layer of Stainless steel. The composite material was fabricated from planetary ball milled SUS316L stainless steel powder and WC powder and then sintered by Pulsed Current Sintering (PCS) method. We also added TiC powder as a hard particle in WC layer. Evaluations of wear properties were performed by pin-on-disk wear testing machine, and a remarkable improvement in wear resistance property was obtained.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.6
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• pp.567-573
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• 2015

This paper aims to evaluate the variation in the mechanical properties of carbon/epoxy composites under in situ low- and high-temperature environments. In situ low- and high-temperature environments were simulated with temperature ranging from $-40^{\circ}C$ to $220^{\circ}C$ using an environmental chamber and furnace. The variation in the mechanical properties of the composites was measured for longitudinal and transverse tensile properties, in-plane shear properties and interlaminar shear strength. Under the low temperature of $-40^{\circ}C$, all mechanical properties increased moderately compared to the baseline properties measured at room temperature. The changes in the longitudinal tensile properties decreased moderately with increasing temperature. However, transverse tensile properties, in-plane shear properties and interlaminar shear strength each showed a significant drop due to the glass transition behavior of the matrix after $140^{\circ}C$. Notably, the tensile property value near $100^{\circ}C$ increased compared to baseline property value, which was an unusual occurrence. This behavior was a direct result of post-curing of the epoxy resin due to its exposure to high temperature.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.5
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• pp.215-221
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• 2019

Ceramic tiles, which are widely used as interior and exterior materials for construction, have recently been required to have pollution prevention function. In order to remove contaminants, many researches of ceramic tiles with hydrophilic surface property through $TiO_2$ coating and hydrophobic surface property by improving the flow of water droplets have been proceeded. Expecially, it is very important to develop a surface glaze having hydrophobicity through a sintering process above $1000^{\circ}C$ without an additional coating process and the degradation of mechanical properties. In this study, surface glaze with copper powder was applied to manufacture of ceramic tile. Contact angle of ceramic tile according to thickness of surface glaze layer was investigated after the conventional sintering process. The contact angle of the ceramic tile surface without the copper powder was shown to be $25.3^{\circ}$, which is close to hydrophilic surface. However, the contact angle was increased up to $109.8^{\circ}$ when the thickness of surface glaze with the copper powder was $150{\mu}m$. The excellent hydrophobic property of the surface glaze with copper powder was resulted from the cellular structure of copper particles on the glaze surface. In addition, the mechanical properties of the developed hydrophobic ceramic tiles such as bending strength, chemical resistance, abrasion resistance, and frost resistance were well maintained and meet the criteria of 'KS L 1001 Ceramic tile'.

• The Research Journal of the Costume Culture
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• v.24 no.5
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• pp.577-587
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• 2016

Natural dye extracted from Salicornia bigelovii was applied to silk fabrics by dip dyeing process. The dyeing properties and the functionalities of the silk fabrics were determined. Factors affecting the dyeing properties such as dyestuff concentration, temperature, time and pH were studied. The colorimetric parameters $L^*$, $a^*$, $b^*$, and H, V/C values were measured to select the optimal mordanting conditions. The color-fastnesses of the dyed and mordanted fabrics were estimated for practical use; in addition, the antibacterial property, ultraviolet protection properties were evaluated. The dyeabilities of silk increased depending on the increasing dye concentration, dyeing time, and dyeing temperature. And optimum dyeing results were achieved when dyeing with 300% (o.w.f.) of dye concentration at $90^{\circ}C$ for 100 minutes and at pH 3. The dyed silk fabrics without mordants produced yellow (Y) color and showed yellow (Y) or green yellow (GY) colors depending on the mordants type. The light fastness of dyed and Al mordanted silk fabrics were found to be excellent, and the drycleaning and rubbing fastness were good. The dyed silk fabrics showed no antibacterial property, but Al and Cu mordanted silk fabrics showed 99.9% reduction rate. The ultraviolet protection properties of the dyed silk fabric was improved. And the ultraviolet protection properties of mordanted samples showed very good ultraviolet protection properties.

• Journal of Power System Engineering
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• v.5 no.1
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• pp.89-96
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• 2001

Decorative property of chromium deposition from oxalic acid bath containing chromium oxide and ammonium sulfate, has been examined over a wide range of bath compositions and plating conditions. The followings were determined as optimum bath composition, $CrO_3\;200{\sim}250g/{\ell},\;H_2C_2O_4{\cdot}2H_2O\;500{\sim}700g/{\ell},\;(NH_4){_2}SO_4\;40{\sim}120g/{\ell}$, and operation conditions; pH $2.0{\sim}2.5$, current density of $15{\sim}250Adm^2 $ at the bath temperatures of $30{\sim}80^{\circ}C$. Bright chromium deposits were obtained over a wide range of ammonium sulfate concentration, bath temperature, and current density. The current efficiency decreased with increasing current density and bath pH, and increased with Increasing bath temperature. The highest current efficiency was obtained in the bath containing $80g/{\ell}$ of ammonium sulfate. Bright chromium deposits were not obtained at conditions of all the highest current efficiencies.

• Journal of the Korean Society of Food Science and Nutrition
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• v.29 no.5
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• pp.854-859
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• 2000

A functional yogurt was prepared from whole milk (12%) and skim milk (2%) added with green tea and mugwort tea at 3$0^{\circ}C$ for 24 hors. The yogurt product were evaluated for acid production (pH, titratable acidity), number of viable cell, viscosity, sensory property and quality-keeping property. Addition of green tea and mugwort tea remarkably accelerated acid production of yogurt. After 24 hrs incubation, titratabel acidity of green tea and mugwort tea yogurt was 1.46% and 1.62%, respectively and was higher than that (1.30%) of yogurt made with only milk. The propagation of lactic acid bacteria was not stimulated by green tea and mugwort tea and then the number of viable cell in normal (milk) yogurt green tea yogurt and mugwort tea yogurt groups, after 24 hrs incubation, was about 7.2$\times$$10^{8}$, 7.1$\times$$10^{8}$ and 7.0$\times$$10^{8}$/mL, respectively, Viscosity of green tea yogurt was slightly lower than that of milk yogurt (1,840 cps) and viscosity of mugwort tea yogurt was slightly higher than that of mild yogurt. The overall sensory score of green tea yogurt was the best of tested yogurt. When yogurt with green tea and mugwort tea was kept at 5$^{\circ}C$ for 15 days, its quality-keeping property was relatively good.