• Progress in Superconductivity
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• v.9 no.2
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• pp.177-182
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• 2008

[ $MgB_2$ ] thin films were fabricated using hybrid physical-chemical vapor deposition (HPCVD) method on silicon substrates with buffers of alumina grown by using atomic layer deposition method. The growth war in a range of temperatures $500\;{\sim}\;600^{\circ}C$ and under the reactor pressures of $25\;{\sim}\;50\;Torr$. There are some interfacial reactions in the as-grown films with impurities of mostly $Mg_2Si$, $MgAl_2O_4$, and other phases. The $T_c$'s of $MgB_2$ films were observed to be as high as 39 K, but the transition widths were increased with growth temperatures. The magnetization was measured as a function of temperature down to the temperature of 5 K, but the complete Meissner effect was not observed, which shows that the granular nature of weak links is prevailing. The formation of mostly $Mg_2Si$ impurity in HPCVD process is discussed, considering the diffusion and reaction of Mg vapor with silicon substrates.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.232-233
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• 2006

In recent years the interest in organic/inorganic hybrid materials has increased at a fast rate. Nano organic-inorganic hybrid composites have shown advantages for preparing hard coating layers. Especially, nano hybrid composite has low environmental pollution. It has high transparency, hardness, toughness, thermal dissociation temperature, hydrophobicity by using nano sized inorganic material. There are many ways in which these materials may be synthesized, a typical one being the use of silica and silanes using the sol-gel process. The structure of sol-gel silica evolves as a result of these successive hydrolysis and condensation reactions and the subsequent drying and curing. The sol-gel reactions are catalyzed by acids and produce silica sol solutions. The silica sol grows until they reach a size where a gel transition occurs and a solid-like gel is formed. Colloidal silica(CS)/silane sol solutions were synthesized in variation with parameters such as different acidity and reaction time. In order to understand their physical and chemical properties, sol-gel coating films were fabricated on glass. From all sol-gel solutions, seasoning effect of sol-gel coating layer on glass was observed.

• Journal of Microbiology
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• v.39 no.3
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• pp.149-153
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• 2001

The electron transfer reaction is one of the most essential processes of life. Not only does it provide the means of transforming solar and chemical energy into a utilizable form for all living organisms, it also extends into a range of metabolic processes that support the life of a cell. Thus, it is of great interest to understand the physical basis of the rates and reduction potentials of these reactions. To identify the major determinants of reduction potentials in redox proteins, we have chosen the simplest electron transfer protein, rubredoxin, a small (52-54 residue) iron-sulfur protein family, widely distributed in bacteria and archaea. Rubredoxins can be grouped into two classes based on the correlation of their reduction potentials with the identity of residue 44; those with Ala44 (ex: Pyrococcus furiosus) have reduction potentials that are ∼50 mV higher than those with Va144 (ex: Clostridium pasteurianum). Based on the crystal structures of rubredoxins from C. pasteurianum and P. furiosus, we propose the identity of residue 44 alone determines the reduction potential by the orientation of the electric dipole moment of the peptide bond between 43 and 44. Based on 1.5 $\AA$ resolution crystal structures and molecular dynamics simulations of oxidized and reduced rubredoxins from C. pasteurianum, the structural rearrangements upon reduction suggest specific mechanisms by which electron transfer reactions of rubredoxin should be facilitated.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.9
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• pp.897-902
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• 2011

Chemical reactions occurring in a PEMFC are dominated by the physical conditions and interface properties, and the reactions are expressed in terms of impedance. The performance of a PEMFC can be simply diagnosed by examining the impedance because impedance characteristics can be expressed by an equivalent electrical circuit. In this study, the characteristics of a PEMFC are assessed using the AC impedance and various equivalent circuits such as a simple equivalent circuit, equivalent circuit with a CPE, equivalent circuit with two RCs, and equivalent circuit with two CPEs. It was found in this study that the characteristics of a PEMFC could be assessed using impedance and an equivalent circuit, and the accuracy was highest for an equivalent circuit with two CPEs.

• Advances in materials Research
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• v.4 no.2
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• pp.113-132
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• 2015

The phenomena of high-voltage polarization and conductivity in oriented vinylidenefluoride and tetrafluoroethylene copolymer films have been investigated. It was shown that under certain electric fields, injection of carriers from the material of electrodes appears The barrier for holes injection in the copolymer was found to be lower than that for electrons. It results in more effective screening of the external field near the anode than near cathode. Electrones, ejected from cathode, creating negative charge by trapping on the surface. It is shown that the electrons injected from cathodes create a negative homocharge on the copolymer surface and then become captured on the surface shallow traps. Their nature has been studied by the x-ray photoelectron spectroscopy. It was shown that these traps may consist of chemical defects in the form of new functional groups formed by reactions of surface macromolecules with sputtered atoms of aluminum. The asymmetric shape of hysteresis curves was explained by the difference in mobility of injected holes and electrons. These factors caused appearance of "non-closed" hysteresis curves for fluorine-containing polymer ferroelectrics. Hysteresis phenomena observed at low electric fields (below coercive ones) are to associate with the behavior of the domains localized in the ordered regions formed during secondary crystallization of copolymers.

• Clean Technology
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• v.12 no.2
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• pp.95-100
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• 2006

Fractionation and hydrodealkylation (HDA) units, subparts of BTX plant, were thermodynamically analyzed using the notion of exergy. Exergy values were calculated as the sum of physical and chemical exergies due to the existence of chemical reactions. The analysis was based on the simulation results with the aid of real operating data. Driving and material exergy losses were separately defined and quantified. Locations and the reason of major exergy losses were identified and improvement strategies were suggested. It was noted that the exergy analysis could provide a sound base for adopting the concept of industrial ecology and developing loss prevention schemes.

• Journal of the Korean Chemical Society
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• v.33 no.2
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• pp.238-246
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• 1989

1,3-Oxathiolane sulfoxide 4 in which the sulfoxide oxygen and the 2-methyl group are on the same face of the oxathiolane ring undergoes a sigmatropic rearrangement to produce a ring expansion product. The structure of this product would be dihydro-1,4-oxathiin 6 or isomeric exo compound 7. This paper describes physical and chemical methods to determine the correct structure of the two alternatives. Thus, $^1HNMR$, UV spectroscopies, and mass spectrometry showed that the product actually obtained had the structure 6. It was also found that from deuteration reactions of the product the compound 7 was initaly formed and then tautomerized to endo compound 6.

• Journal of Environmental Science International
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• v.19 no.9
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• pp.1119-1127
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• 2010

The behavior of copper throughout the whole process of wastewater treatment plant that uses the activated sludge process to treat the wastewater of petrochemical industry that contains low concentration of copper was investigated. Total inflow rate of wastewater that flows into the aeration tank was $697\;m^3$/day with 0.369 mg/L of copper concentration, that is, total copper influx was 257.2 g/day. The ranges of copper concentrations of the influent to the aeration tank and effluent from the one were 0.315 ~ 0.398 mg/L and 0.159 ~ 0.192 mg/L, respectively. The average removal rate of copper in the aeration tank was 50.8 %. The bioconcentration factor (BCF) of copper by microbes in the aeration tank was 3,320. The accumulated removal rate of copper throughout the activated sludge process was 71.3%, showing a high removal ratio by physical and chemical reactions in addition to biosorption by microbes. The concentration of copper in the solid dehydrated by filter press ranged from 74.8 mg/kg to 77.2 mg/kg and the concentration of copper by elution test of waste was 2.690 ~ 2.920 mg/L. It was judged that the copper concentration in dehydrated solid by bioconcentration could be managed with the control of that in the influent.

• Elastomers and Composites
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• v.36 no.4
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• pp.268-277
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• 2001

The MDI(4,4'-diphenyl methane diisocyanate) was mixed with PPG, PEG and trimethylolpropane(TMP) respectively to prepare polyurethane resin. The various physical properties were measured for the mixtures. The gel-time was shortened by adding of PEG and TMP The molecular weight made a greater influence on the gel-time than the number of functional groups. The NCO-OH reaction was more active and faster than the NCO-NCO reaction. The hardness was influenced by crosslinking-density and molecular structure. The NCO-OH reactions yielded the flexible films and the NCO-NCO reactions yielded the brittle films. The increase of crystallinity and shrinkage induced the low adhesion ratio but the adding of TMP induced the high adhesion ratio. The flame-retardancy was influenced by quantity and kinds of flame-retardant. IXOL B-251 was the most excellent among the flame-retardants employed in this study. TCCP was partially separated because of the lack of solubility.

• Journal of Soil and Groundwater Environment
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• v.25 no.2_spc
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• pp.86-100
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• 2020

Analyzing and monitoring environmental contaminants based on geophysical exploration techniques have become important and it is now widely applied to delineate spatial distribution geophysical characteristics in wide area. Among the techniques, induced polarization (IP) method, which measures polarization effects on electrical potential distribution, has drawn much attention as an effective tool for environmental monitoring since IP is sensitive to changes in biochemical reactions. However, various reactions stemming from the presence of multiple contaminants have greatly enhanced heterogeneity of polluted sites to result in highly variable electrical characteristics of the site. Those contaminants influence chemical and physical state of soil and groundwater to alter electrical double layer, which in turn influences polarization of the media. Since biochemical reactions between microbes and contaminants result in various IP effects, IP laboratory experiments were conducted to investigate IP responses of the contaminated soil samples under various conditions. Field IP surveys can delineate the spatial distribution of contamination, while providing additional information about electrical properties of a target medium, together with DC resistivity. Reviewing IP effects of contaminants as well as IP surveys can serve as a good starting point for the application of IP survey in site assessment for environmental remediation.