• Bulletin of the Korean Chemical Society
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• v.31 no.9
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• pp.2497-2502
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• 2010

Arg13 is a conserved active-site residue in all known Pi class glutathione S-transferases (GSTs) and in most Alpha class GSTs. To evaluate its contribution to substrate binding and catalysis of this residue, three mutants (R13A, R13K, and R13L) were expressed in Escherichia coli and purified by GSH affinity chromatography. The substitutions of Arg13 significantly affected GSH-conjugation activity, while scarcely affecting glutathione peroxidase or steroid isomerase activities. Mutation of Arg13 into Ala largely reduced the GSH-conjugation activity by approximately 85 - 95%, whereas substitutions by Lys and Leu barely affected activity. These results suggest that, in the GSH-conjugation activity of hGST P1-1, the contribution of Arg13 toward catalytic activity is highly dependent on substrate specificities and the size of the side chain at position 13. From the kinetic parameters, introduction of larger side chains at position 13 results in stronger affinity (Leu > Lys, Arg > Ala) towards GSH. The substitutions of Arg13 with alanine and leucine significantly affected $k_{cat}$, whereas substitution with Lys was similar to that of the wild type, indicating the significance of a positively charged residue at position 13. From the plots of log ($k_{cat}/{K_m}^{CDNB}$) against pH, the $pK_a$ values of the thiol group of GSH bound in R13A, R13K, and R13L were estimated to be 1.8, 1.4, and 1.8 pK units higher than the $pK_a$ value of the wild-type enzyme, demonstrating the contribution of the Arg13 guanidinium group to the electrostatic field in the active site. From these results, we suggest that contribution of Arg13 in substrate binding is highly dependent on the nature of the electrophilic substrates, while in the catalytic mechanism, it stabilizes the GSH thiolate through hydrogen bonding.

• Korean Journal of Environmental Agriculture
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• v.29 no.3
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• pp.273-281
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• 2010

Concentration of antibiotics including a tetracycline group (TCs) of tetracycline (TC), chlortetracycline (CTC), and oxytetracycline (OTC), a sulfonamide group (SAs) of sulfamethoxazole (SMX), sulfathiazole (STZ), and sulfamethazine (SMT), an ionophore group (IPs) of lasalocid (LSL), monensin (MNS), and salinomycin (SLM), and a macrolide group (MLs) of tylosin (TYL) was determined from samples collected from the agricultural soil, stream water, and sediment. For the agricultural soil samples, the concentration of TCs had the highest value among all tested antibiotic's groups due to its high accumulation rate on the surface soils. The lower concentrations of SAs in the agricultural soils may be resulted from its lower usage and lower distribution coefficient (Kd) compared to TCs. The concentration of TCs in stream water was significantly increased through June to September. It would be likely due to soil loss during an intensive rainfall event and a reduction of water level after the monsoon season. A significant amount of TCs in the sediment was also detected due to its accumulation from runoff, which occurred by complexation of divalent cations, ion exchange, and hydrogen bonding among humic acid molecules. To ensure environmental or human safety, continuous monitoring of antibiotics residues in surrounding ecosystems and systematic approach to the occurrence mechanism of antibiotic resistant bacteria are required.

• Journal of the Korea Concrete Institute
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• v.21 no.5
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• pp.589-597
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• 2009

High Performance Fiber-reinforced Cement Composite (HPFRCC) shows the multiple crack and damage tolerance capacity due to the interfacial bonding of the fibers to the cement matrix. For practical application, it is needed to investigate the fractural behavior of HPFRCC and understand the micro-mechanism of cement matrix with reinforcing fiber. This study is devoted to the investigation of the AE signals in HPFRCC under monotonic and cyclic uniaxial compressive loading, and total four series were tested. The major experimental parameters include the type and volume fraction of fiber (PE, PVA, SC), the hybrid type and loading pattern. The test results showed that the damage progress by compressive behavior of the HPFRCC is a characteristic for the hybrid fiber type and volume fraction. It is found from acoustic emission (AE) parameter value, that the second and third compressive load cycles resulted in successive decrease of the amplitude as compared with the first compressive load cycle. Also, the AE Kaiser effect existed in HPFRCC specimens up to 80% of its ultimate strength. These observations suggested that the AE Kaiser effect has good potential to be used as a new tool to monitor the loading history of HPFRCC.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.27-27
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• 2011

For the design of real applicable molecular devices, current-voltage properties through molecular nanostructures such as metal-molecule-metal junctions (molecular junctions) have been studied extensively. In thiolate monolayers on the gold electrode, the chemical bonding of sulfur to gold and the van der Waals interactions between the alkyl chains of neighboring molecules are important factors in the formation of well-defined monolayers and in the control of the electron transport rate. Charge transport through the molecular junctions depends significantly on the energy levels of molecules relative to the Fermi levels of the contacts and the electronic structure of the molecule. It is important to understand the interfacial electron transport in accordance with the increased film thickness of alkyl chains that are known as an insulating layer, but are required for molecular device fabrication. Thiol-tethered RuII terpyridine complexes were synthesized for a voltage-driven molecular switch and used to understand the switch-on mechanism of the molecular switches of single metal complexes in the solid-state molecular junction in a vacuum. Electrochemical voltammetry and current-voltage (I-V) characteristics are measured to elucidate electron transport processes in the bistable conducting states of single molecular junctions of a molecular switch, Ru(II) terpyridine complexes. (1) On the basis of the Ru-centered electrochemical reaction data, the electron transport rate increases in the mixed self-assembled monolayer (SAM) of Ru(II) terpyridine complexes, indicating strong electronic coupling between the redox center and the substrate, along the molecules. (2) In a low-conducting state before switch-on, I-V characteristics are fitted to a direct tunneling model, and the estimated tunneling decay constant across the Ru(II) terpyridine complex is found to be smaller than that of alkanethiol. (3) The threshold voltages for the switch-on from low- to high-conducting states are identical, corresponding to the electron affinity of the molecules. (4) A high-conducting state after switch-on remains in the reverse voltage sweep, and a linear relationship of the current to the voltage is obtained. These results reveal electron transport paths via the redox centers of the Ru(II) terpyridine complexes, a molecular switch.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.2
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• pp.61-69
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• 2011

Fiber Reinforced Plastic (FRP) sheets have been widely used to retrofit and rehabilitate RC structures, while in case of retrofitting steel structures, there are no codes and researches. It stems from configuration of member and characteristics of bonding behavior. This study focused on the static behavior of steel beams reinforcement by AFRP sheets. The main objective of the experimental programme was the evaluation of the force transfer mechanism, the increment of the beam load carrying capacity and the bending stiffness. A bending test was conducted on a H-shaped steel beam, with aramid FRP sheets bonded to its flanges. The mid-span deflection and the strain from three points along AFRP sheets were recorded Test results exhibit that the increment of the load-carrying capacity with reference to a mid-span deflection level of 15 mm(1/125mm of the clear span) was equal to 9.4% and for the two layers case, an elastic stiffness increment is slightly higher than one layer case.

• Korean Journal of Optics and Photonics
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• v.3 no.4
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• pp.258-265
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• 1992

A low loss optical waveguide of $P_{2}O_{5}-SiO_{2}$on Si substrate is produced by using the chemical vapour deposition method of $SiO_2$ thin films used in Si technology. Propagation loss of the waveguide layer was 1.65 dB/cm as produced and reduced down to 0.1 dB/cm after heat treatment at $1100^{\circ}C$. By using laser lithography and reactive ion etching method $P_{2}O_{5}-SiO_{2}$ waveguide was produced and subsequently annealed at $1100^{\circ}C$.As a result of this annealing the shape of the waveguide core was changed from rectangular to semi-circular form, and the propagation loss was reduced as down to 0.03 dB/cm at 0.6328$\mu$m and 0.04dB/cm at 1.53$\mu$m. We think that the mechanism of the reduction in propagation loss during the heat treatment is the following: 1) The hydrogen bonding in waveguide layer, which causes absorption loss, is dissociated and diffused out. 2) The roughness of the interface and the micro-structure of the waveguide layer is removed. 3) The irregularities in the cross-sectional shape of the waveguide which was induced during the lithographic process were disappeared by flowing of the waveguide core.

• Journal of the Korean Chemical Society
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• v.29 no.6
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• pp.565-574
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• 1985

The rates of reaction between 4-substituted-2,6-dinitrochlorobenzenes with para-substituted anilines in methanol-acetonitrile mixtures were measured by conductometry. It was observed that the rate constant increases in the order of X = 4-$NO_2 {\gg}4-CN {\gg}4- CF_3$, where X is a substituent in the substrate. The rate constant also increases in the order of Y = p-O$CH_3{\gg}p- CH_3{\gg}H {\gg}p-Cl{\gg}m- NO_2$, where Y is a substituent in the aniline ring. Kinetic studies in the methanol-acetonitrile solvent system with various nucleophiles showed that the N-C bond forming step is making a great contribution to the overall second order rate constant. The electrophilic catalysis by methanol probably consists of the hydrogen bonding between alcoholic hydrogen and leaving chloride in the transition state. The nucleophilic catalysis by methanol may be ascribed to the formation of hydrogen bonds between alcoholic oxygen and hydrogens of amines in the transition state. All these experimental facts are supporting the operation of $S_N$Ar machanism with the second step being the rate determining. This mechanism can be successfully fitted to the PES model.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.59-59
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• 2010

Graphene is a 2-D sheet of $sp^2$-bonded carbon arranged in a honeycomb lattice. This material has attracted major interest, and there are many ongoing efforts in developing graphene devices because of its high charge mobility and crystal quality. Therefore clear understanding of the substrate effect and mechanism of synthesis of graphene is important for potential applications and device fabrication of graphene. In a published paper in J. Phys. Chem. C (2008), the effect of substrate on the atomic/electronic structures of graphene is negligible for graphene made by mechanical cleavage. However, nobody shows the interaction between Ni substrate and graphene. Therefore, we have studied this interaction. In order to studying these effect between graphene and Ni substrate, We have observed graphene synthesized on Ni substrate and graphene transferred on $SiO_2$/Si substrate through Raman spectroscopy. Because Raman spectroscopy has historically been used to probe structural and electronic characteristics of graphite materials, providing useful information on the defects (D-band), in-plane vibration of sp2 carbon atoms (G-band), as well as the stacking orders (2D-band), we selected this as analysis tool. In our study, we could not observe the doping effect between graphene and Ni substrate or between graphene and $SiO_2$/Si substrate because the shift of G band in Raman spectrum was not occurred by charge transfer. We could noticed that the bonding force between graphene and Ni substrate is more strong than Van de Waals force which is the interaction between graphene and $SiO_2$/Si. Furthermore, the synthesized graphene on Ni substrate was in compressive strain. This phenomenon was observed by 2D band blue-shift in Raman spectrum. And, we consider that the graphene is incommensurate growth with Ni polycrystalline substrate.

• Journal of Radiation Industry
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• v.9 no.4
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• pp.217-221
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• 2015

When reactor coolant leaks occur due to cracks of a steam generator's tube, radioactive materials contained in the primary cooling water in nuclear power plant are forced out toward the secondary systems. At this time the secondary water purification resin in the ion exchange resin tower of the steam generator blowdown system is contaminated by the radioactivity of the leaked radioactive materials, so we pack this in special containers and store temporarily because we could not dispose it by ourselves. If steam generator tube leakage occurs, it produces contaminated spent resins annually about 5,000~7,000 liters. This may increase the amount of nuclear waste productions, a disposal working cost and a unit price of generating electricity in the plant. For this reasons, it is required to develop a decontamination process technique for reducing the radioactive level of these resins enough to handle by the self-disposal method. In this research, First, Investigated the structure and properties of the ion exchange resin used in a steam generator blowdown system. Second, Checked for a occurrence status of contaminated spent resin and a disposal technology. Third, identified the chemical characteristics of the waste radionuclides of the spent resin, and examined ionic bonding and separation mechanism of radioactive nuclear species and a spent resin. Finally, we carried out the decontamination experiment using chemicals, ultrasound, microbubbles, supercritical carbon dioxide to process these spent resin. In the case of the spent resin decontamination method using chemicals, the higher the concentration of the drug decontamination efficiency was higher. In the ultrasound method, foreign matter of the spent resin was removed and was found that the level of radioactivity is below of the MDA. In the microbubbles method, we found that the concentration of the radioactivity decreased after the experiment, so it can be used to the decontamination process of the spent resin. In supercritical carbon dioxide method, we found that it also had a high decontamination efficiency. According to the results of these experiments, almost all decontamination method had a high efficiency, but considering the amounts of the secondary waste productions and work environment of the nuclear power plant, we judged the ultrasound and supercritical carbon dioxide method are suitable for application to the plant and we established the plant applicable decontamination process system on the basis of these two methods.

• Tunnel and Underground Space
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• v.31 no.6
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• pp.623-646
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• 2021

As the demand for electric power increases with acceleration of electrification at home and abroad, the needs for coal-fired electrical power plant are accordingly increased. However, these coal-fired electrical power plants induce also many environmental problems such as increase of air pollutants, increase of possibility of land contamination by reclamation of coal ash, even though these power plants have a good economical efficiency. In case of a by-product of coal-fired electrical power plants, only 70% of them are recycled and the remaining 30% of by-product are fully buried in surrounding ground. Consequently, this study deals with coal ash backfilling mechanism in abandoned mine openings for the purposes of increasing the coal ash recycling rate as well as securing the mine area stability. In order to analyze the backfill and ground reinforcement by interaction between rock mass and backfills, the copying samples of discontinuous surface with different roughnesses were produced for bond strength tests and direct shear tests. And statistical analysis was also conducted to decide the characteristics of bond and shear behavior with joint roughness and their curing day. Numerical simulations were also analyzed for examining the effect of interface behavior on ground stability.