• Communications of the Korean Mathematical Society
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• v.35 no.4
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• pp.1245-1254
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• 2020

The object of the present paper is to characterize Bach flat (k, 𝜇)-almost co-Kähler manifolds. It is proved that a Bach flat (k, 𝜇)-almost co-Kähler manifold is K-almost co-Kähler manifold under certain restriction on 𝜇 and k. We also characterize (k, 𝜇)-almost co-Kähler manifolds with divergence free Cotton tensor.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.4
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• pp.384-391
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• 2007

Hydrogen-blending effects in flame structure and NO emission behavior are numerically studied with detailed chemistry in methane-air counterflow diffusion flames. The composition of fuel is systematically changed from pure methane to the blending fuel of methane-hydrogen through $H_2$ molar addition up to 30%. Flame structure, which can be described representatively as a fuel consumption layer and a $H_2$-CO consumption layer, is shown to be changed considerably in hydrogen-blending methane flames, compared to pure methane flames. The differences are displayed through maximum flame temperature, the overlap of fuel and oxygen, and the behaviors of the production rates of major species. Hydrogen-blending into hydrocarbon fuel can be a promising technology to reduce both the CO and $CO_2$ emissions supposing that NOx emission should be reduced through some technologies in industrial burners. These drastic changes of flame structure affect NO emission behavior considerably. The changes of thermal NO and prompt NO are also provided according to hydrogen-blending. Importantly contributing reaction steps to prompt NO are addressed in pure methane and hydrogen-blending methane flames.

• Journal of Korea Foundry Society
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• v.8 no.3
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• pp.287-295
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• 1988

The experiment was carried out for the purpose of studying the carburization of pure iron ingot and sintered iron powder by solid carbon in the atmosphere of CO gas. The volocity of carburization was estimaed by the diffusion coefficient D calculated by carburization equation. The results obtained were as follow: 1. The higher the carburization temperature, carburization depth and carbon concentration were increased, and the melting zone which had $2.8{\sim}3.4%C$ at the $3{\sim}4mm$ from interface of carburization was formed at $1300^{\circ}C$. 2. The main carburization mechanism of pure iron ingot and the sintered iron powder were proceeded by CO gas up to $1100^{\circ}C$, solid carbon over than $1300^{\circ}C$, respectively. 3. The main carburization mechanism of pure iron ingot at $1200^{\circ}C$ was proceeded by solid carbon, and sintered iron powder was proceeded bs CO gas, however, in case the reaction time, the carburization was proceeded by solid carbon over than 5hrs. 4. The diffusion coefficient D of carbon were $0.559{\times}10^{-6}cm^2.sec^{-1}$ at $1100^{\circ}C$, $0.237{\times}10^{-6}cm^2.sec^{-1}$ at $1200^{\circ}C$, $0.087{\times}10^{-6}cm^2.sec^{-1}$ at $1300^{\circ}C$, in case of pure iron ingot carburized. 5. The diffusion coefficient D of carbon were $0.124\;cm^2.sec^{-1}$ at $1100^{\circ}C$, $0.102\;cm^2.sec^{-1}$ at $1200^{\circ}C$, $0.480\;{\times}10^{-6}cm^2.sec^{-1}$ at $1300^{\circ}C$, in the case of sintered iron carburized at the pressuring $4ton\;/\;cm^2$.

• Journal of Sensor Science and Technology
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• v.30 no.2
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• pp.94-98
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• 2021

In this study, pure and Co3O4/CoFe2O4-loaded Indium oxide (In2O3) nanofibers were synthesized by the electrospinning of an Indium/Polyvinylpyrrolidone precursor solution containing cobalt and iron bimetallic zeolitic imidazolate frameworks and subsequent heat treatment. The ethanol, toluene, p-xylene, benzene, carbon monodxide, and hydrogen gas sensing characteristics of the solution were measured at 250-400 ℃. 0.5 at%-Co3O4/CoFe2O4-loaded In2O3 nanofibers exhibited extreme response (resistance ratio - 1) to 5 ppm of ethanol (210.5) at 250 ℃ and excellent selectivity over the interfering gases. In contrast, pure In2O3 nanofibers exhibited relatively low responses to all the analyte gases and low selectivity above 250-400 ℃. The superior response and selectivity toward ethanol is explained by the catalytic roles of Co3O4 and CoFe2O4 in gas sensing reaction and the electronic sensitization induced by the formation of p (Co3O4/CoFe2O4)-n (In2O3) junctions.

• Membrane Journal
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• v.4 no.4
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• pp.197-204
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• 1994

In this study, permeation characteristics of pure $CH_4,\;CO_2$ and $CH_4/CO_2$ gas mixture were examined by permeation experiments through hollow fiber membrane module and experimental results were compared with simulation results. Permeation rate of pure gas increased with increaseing temperature in Arrhenius type. Activation energy was 6.61 kJ/mol for $CO_2$ and 25.26 kJ/mol for $CH_4$. In the permeation experiment of gas mixture, permeate flow rate and $CO_2$ concentration in permeate decreased and $CH_4$ concentration in reject increased with the increase of cut. Separation factor was in the range of 20~40 at 5~20 atm and 20% cut and it increased with pressure and against temperature Experimental values corresponded to numerical values with the deviation of 8% in permeate flow rate and $CO_2$ concentration in permeate and 15% in $CO_2$ concentration in reject.

• 한국연소학회:학술대회논문집
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• 2001.06a
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• pp.60-66
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• 2001

Combustion using pure oxygen instead of air is an energy saving technology that can increase thermal efficiency by the improvement of burning rate and ultra high temperature flame, being used on the industrial spot. But information about it is not so enough yet. Flame figure, temperature distribution and emission concentration were measured with oxygen excess ratio and swirl number in a turbulent diffusion flame to investigate the combustion characteristics using pure oxygen. The results showed that flame figure became different as long as oxygen excess ratio varied and that concentration of NO and CO increased suddenly around ${\lambda}$=1.5.

• Journal of the Korean Electrochemical Society
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• v.10 no.3
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• pp.175-178
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• 2007

Pure iron, Fe-0.4, and 1.2 wt.%Cu alloys were examined by conducting the electrochemical techniques in the weakly alkaline solution, pH9, controlled by $Ca(OH)_2$, solution added with 0.02M NaCl. The $R_P$ measured from ac impedance, selected 10 kHz and 10mHz, in weakly alkaline solutions containing chloride ions indicated that the addition of copper up to 1.2wt.% into the pure iron significantly improved the pitting resistance of iron. In contrast to alloy, the pure iron showed the rapid pitting occurrences in drying period. During the drying period, the corrosion potential of pure iron was shifted to less noble value, pitting initiation.

• Journal of the Korean Vacuum Society
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• v.1 no.1
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• pp.106-114
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• 1992

Abstract-Quantitative surface analysis of Co-Ni and Au-Cu alloys by XPS and SIMS was studied. For Co-Ni alloy, quantitative XPS analysis could be done within 1-2% relative error with pure element standards without any correction. For Au-Cu, quantitative XPS analysis was not possible without any correction. But it could be done with standard alloys of various composition within 1-2% relative error. Without standard alloys, Au-Cu alloys could be analyzed by XPS within 10% relative error with pure element standards. For SIMS analysis of Co-Ni alloys, the relative secondary ion yields of Co+/Nit has linear relation with ratio of each composition so that quantitative SIMS analysis was possible for Co-Ni alloys. Preliminary results of XPS round robin test of VAMAS-SCA Japan Project are given.

• Applied Chemistry for Engineering
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• v.7 no.4
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• pp.605-613
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• 1996

The permeation characteristics were investigated for pure carbon dioxide and methane through asymmetric cellulose acetate(CA) membrane, composite cellulose acetate membrane and asymmetric cellulose triacetate(CTA) membrane. In particular, the effect of operating pressure on the permeation performance was examined. And the permeation behavior for a mixture of carbon dioxide and methane ($CO_2/CH_4=57.6/42.4$) was also investigated and compared to the characteristics obtained from pure gases. The experiments were run at the range of partial pressure from 25 to 125 psig, and room temperature. The permeation behaviors of the CA composite and CTA membrane were similiar to those of the CA membrane. The permeation rates of pure carbon dioxide for CA, CA composite and CTA membrane were increased slightly with an increase in upstream partial pressure, while in the case of pure methane they were independent of upstream partial pressure. For a binary mixture of carbon dioxide and methane, abnormal permeation behaviors were observed due to the plasticization of carbon dioxide and the competition effect of each gas. The separation factor and permeation rate for CTA membrane were found to be higher than those for CA membrane, but the mechanical strength of CTA membrane was very poor. And the permeation rate for CA composite membrane was higher than that for CA membrane. Consequently, it can be said that the CA composite membrane is a strong candidate for the separation of $CH_4$ and $CO_2$.

• Journal of Biomedical Engineering Research
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• v.37 no.5
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• pp.186-194
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• 2016

In this study, a co-axial flow induced microfluidic chip to fabricate pure collagen type I microfiber via the control of collagen type I and Na-alginate gelation process. The pure collagen type I microfiber was generated by selective degradation of Ca-alginate from 'Core-Shell' structured hydrogel microfiber. To make 'Core-Shell' structure, collagen type I solution was introduced into core channel and 1.5% Na-alginate solution was injected into side channel in microfluidic chip. To evaluatethe 'Core-Shell' structure, the red and green fluorescence substances were mixed into collagen type I and Na-alginate solution, respectively. The fluorescence substances were uniformly loaded into each fiber, and the different fluorescence images were dependent on their location. By immoblizing EpH4-Ras and C6 cells within collagen type I and Na-alginate solution, we sucessfully demonstrated the co-culture of EpH4-Ras and C6 cells with 'Core-Shell' like hydrogel microfiber for 5 days. Only to produce pure collagen type I hydrogel fiber, tri-sodium citrate solution was used to dissolve the shell-like Ca-alginate hydrogel fiber from 'Core-Shell' structured hydrogel microfiber, which is an excellent advantage when the fiber is employed in three-dimensional scaffold. This novel method could apply various application in tissue engineering and biomedical engineering.