• Bulletin of the Korean Chemical Society
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• v.14 no.4
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• pp.491-496
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• 1993

A class A ${\beta}$-lactamase from Staphylococcus aureus PC1 complexed with 3R,5R-clavulanate is studied. The starting geometry for the computation is the crystal structure of the ${\beta}$-lactamase. Docking of the clavulanate to the enzyme is done exploiting the requirements of electrostatic and shape complementarity between the enzyme and clavulanate. This structure is then hydrated by water molecules and refined by energy minimization and short molecular dynamics simulation. In the energy refined structure of this complex, the carboxyl group of the clavulanate is hydrogen bonded to Lys-234, and the the carbonyl carbon atom of the clavulanate is adjacent to the $O_{\gamma}$ of Ser-70. It is found that a crystallographic water molecule initially located at the oxyanion hole, which is formed by the two -NH group of Ser-70 and Gln-237, is replaced by the carbonyl oxygen atom of the 3R,5R-clavulanate after docking and energy reginement. The crystallographic water molecules are proved to be important in ligand binding. Glu-166 residue is found to be repulsive to the binding of clavulanate, which is in agreement with experimental observation. Arg-244 residue is found to be important to the binding of clavulanate as well as to interaction with C2 side chain of the clavulanate. The electron density redistribution of the clavulanate on binding to the ${\beta}$-lactamase in studied by an ab initio quantum-mechanical calculation. A significant redistribution of electron density of the clavulanate is induced by the enzyme, toward the enzyme, toward the transition state of the enzymatic reaction.

• Ceramist
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• v.21 no.4
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• pp.331-348
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• 2018

With the expectation to overcome the problem of increasing energy consumption, polymer electrolyte membrane fuel cells are getting more attention as a promising environmentally friendly and sustainable next-generation energy conversion system. In spite of the rapid improvement of polymer electrolyte membrane fuel cells(PEMFCs), there are several critical issues still need to be resolved for practical commercialization. Out of the many issues, the main hurdle comes from oxygen reduction reaction(ORR), thus development of efficient ORR electrocatalysts is the main key for enhancing PEMFC performance. Among various catalysts, 1D nanostructured catalyst is a promising candidate because it holds many advantages that come from nanostructuring while supplementing the disadvantages of other nanostructures such as nanoparticles(0D) or gyroids(3D). This review focused on diverse 1D nanostructures and talks about their advantages as catalyst for ORR. Different 1D nanostructures will be introduced while applying the structures to different materials system showing the prospects of 1D nanostructures for improving PEMFC.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.397-400
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• 2008

Traditional propellants which have a hypergolic characteristic have a high performance but also have disadvantages of toxicity and complex handling requirement. In order to replace these propellants, one of the alternatives is hydrogen peroxide which generates high temperature oxygen and water vapor after catalytic reaction. In this paper, autoignition characteristics of kerosene by decomposed hydrogen peroxide were investigated to perform fundamental research for designing a thruster using hydrogen peroxide and kerosene propellants. Contraction ratio, whether flame holder exists or not, and feeding pressure of propellants were selected as variables. From the experiments for different mixture ratio, we confirmed the ignition stability is strongly affected by a feeding pressure of propellants.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.429-434
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• 2012

Ignition delay of micro/nano aluminum particles is caused by aluminum oxide shell. The method of minimizing this ignition delay is proposed in the study. Generating and heating of particles are processed at the same time. As soon as heated particles are produced, they immediately contact with oxygen. Chemical reaction is induced on the contact surface instead of crystallization of oxide shell. Finally particles are ignited. Aluminum particles are generated by laser ablation on an aluminum plate using Nd:YAG pulse laser. Injected particles are confirmed through visualization of particles using scattering method. $CO_2$ continuous laser supplies heat to aluminum plate and generated particles. Trace of burning particles is observed in the experiment.

• Journal of Applied Biological Chemistry
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• v.64 no.3
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• pp.237-244
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• 2021

Camellia sinensis, Green tea, contains phenolic compounds that act to scavenge reactive oxygen species (ROS), such as catechin, epicatechin, etc. In contrast with the tea leaf, the bioactivity of its fruit and the fruit peels remains still unclear. This study focused on the effects of fruit and fruit peels of C. sinensis (FC and PC) against oxidative DNA damage in NIH/3T3 cells. The scavenging effects of FC and PC on ROS were assessed using 1,1-diphenyl-2-picryl hydrazyl or 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid radicals. The measurement of ROS in cellular levels was conducted by DCFDA reagent and the protein expression of γ-H2AX, H2AX, cleaved caspase-3, p53, and, p-p53 was analyzed by immunoblotting. The gene expressions of p53 and H2AX were assessed using polymerase chain reaction techniques. The major metabolites of FC and PC were quantitatively measured analyzed and the amounts of phenolic compounds and flavonoids in PC were greater than those in FC. Further, PC suppressed ROS production, which protects the oxidative stress-induced DNA damage through reducing H2AX, p53, and caspase-3 phosphorylation. These results refer that the protective effects of FC and PC are mediated by inhibition of p53 signaling pathways, probably via the bioactivity of phenolic compounds. Thus, FC and PC can serve as a potential antioxidant in DNA damage-associated diseases.

• Environmental Engineering Research
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• v.23 no.4
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• pp.345-353
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• 2018

This paper summarizes results of research on the electrochemical (EC) degradation of disinfection by-products (DBPs) and iodine-containing contrast media (ICMs), with the focus on EC reductive dehalogenation. The efficiency of EC dehalogenation of DBPs increases with the number of halogen atoms in an individual DBP species. EC reductive cleavage of bromine from parent DBPs is faster than that of chlorine. EC data and quantum chemical modeling indicate that the EC reduction of iodine-containing DBPs (I-DBPs) is characterized by the formation of active iodine that reacts with the organic substrate. The occurrence of ICMs has attracted attention due to their association with the generation of I-DBPs. Indirect EC oxidation of ICMs using anodes that produce reactive oxygen species can result in a complete degradation of these compounds yet I-DBPs are formed in the process. Reductive EC deiodination of ICMs is rapid and its overall rate is diffusion-controlled yet I-DBPs are also produced in this reaction. Further progress in practically feasible EC methods to remove DBPs, ICMs and other trace-level organic contaminants requires the development of novel electrocatalytic materials, elimination of mass transfer limitations via innovative design of 3D electrodes and EC reactors, and further progress in the understanding of intrinsic mechanisms of EC reactions of DBPs and TrOC at EC interfaces.

• Environmental Engineering Research
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• v.23 no.4
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• pp.456-461
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• 2018

The solid-state anaerobic digestion (SS-AD) has promoted the development and application for biogas production from biomass which operate a high solid content feedstock, as higher than 15% of total solids. However, the digested byproduct of SS-AD can be used as a fertilizer or as solid fuel, but it has serious problems: high moisture content and poor dewaterability. The organic residue from SS-AD has to be improved to address these problems and to make it a useful alternative energy source. Hydrothermal carbonization was investigated for conversion of the organic residue from the SS-AD of livestock waste to solid fuels. The effects of hydrothermal carbonization were evaluated by varying the reaction temperatures within the range of $180-240^{\circ}C$. Hydrothermal carbonization increased the calorific value through the reduction of the hydrogen and oxygen contents of the solid fuel, in addition to its drying performance. Therefore, after the hydrothermal carbonization, the H/C and O/C atomic ratios decreased through the chemical conversion. Thermogravimatric analysis provided the changed combustion characteristics due to the improvement of the fuel properties. As a result, the hydrothermal carbonization process can be said to be an advantageous technology in terms of improving the properties of organic waste as a solid-recovered fuel product.

• Environmental Engineering Research
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• v.24 no.2
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• pp.309-317
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• 2019

This study evaluated the kinetics of acrylamide (AM) biodegradation by mixed culture bacteria and Enterobacter aerogenes (E. aerogenes) in sequencing batch reactor (SBR) systems with AQUASIM and linear regression. The zero-order, first-order, and Monod kinetic models were used to evaluate the kinetic parameters of both autotrophic and heterotrophic nitrifications and both AM and chemical oxygen demand (COD) removals at different AM concentrations of 100, 200, 300, and 400 mg AM/L. The results revealed that both autotrophic and heterotrophic nitrifications and both AM and COD removals followed the Monod kinetics. High AM loadings resulted in the transformation of Monod kinetics to the first-order reaction for AM and COD removals as the results of the compositions of mixed substrates and the inhibition of the free ammonia nitrogen (FAN). The kinetic parameters indicated that E. aerogenes degraded AM and COD at higher rates than mixed culture bacteria. The FAN from the AM biodegradation increased both heterotrophic and autotrophic nitrification rates at the AM concentrations of 100-300 mg AM/L. At higher AM concentrations, the FAN accumulated in the SBR system inhibited the autotrophic nitrification of mixed culture bacteria. The accumulation of intracellular polyphosphate caused the heterotrophic nitrification of E. aerogenes to follow the first-order approximation.

• Current Photovoltaic Research
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• v.7 no.2
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• pp.33-37
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• 2019

In this paper, we compared the performance of $Cu(In,Ga)(S,Se)_2$ (CIGSSe) thin film solar cell with CdS buffer layer deposited by irradiating 365 nm UV light with 8 W power in Chemcial Bath Deposition (CBD) process. The effects of UV light irradiation on the thin film deposition mechanism during CBD-CdS thin film deposition were investigated through chemical and electro-optical studies. If the UV light is irradiated during the solution process, the hydrolysis of Thiourea is promoted even during the same time, thereby inhibiting the formation of the intermediate products developed in the reaction pathway and decreasing the pH of the solution. As a result, it is suggested that the efficiency of the CdS/CIGSSe solar cell is increased because the ratio of the S element in the CdS thin film increases and the proportion of the O element decreases. This is a very simple and effective approach to control the S/O ratio of the CdS thin film by the CBD process without artificially controlling the process temperature, solution pH or concentration.

• Korean Journal of Materials Research
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• v.30 no.12
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• pp.687-692
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• 2020

A zinc-air battery consists of a zinc anode, an air cathode, an electrolyte, and a separator. The active material of the positive electrode is oxygen contained in the ambient air. Therefore, zinc-air batteries have an open cell configuration. The external condition is one of the main factors for zinc-air batteries. One of the most important external conditions is temperature. To confirm the effect of temperature on the electrochemical properties of zinc-air batteries, we perform various analyses under different temperatures. Under 60 ℃ condition, the zinc-air cell shows an 84.98 % self-discharge rate. In addition, high corrosion rate and electrolyte evaporation rate are achieved at 60 ℃. Among the cells stored at various temperature conditions, the cell stored at 50 ℃ delivers the highest discharge capacity; it also shows the highest self-discharge rate (65.33 %). On the other hand, the cell stored at 30 ℃ shows only 2.28 % self-discharge rate.