• Journal of Microbiology and Biotechnology
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• v.13 no.4
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• pp.564-570
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• 2003

The antibacterial mechanism of enterobacter Salmonella typhimurium was studied. The rfa (Waa) gene cluster of S. typhimurium encodes the core oligosaccharide biosynthesis of lipopolysaccharide (LPS). Among the rfa gene cluster, we recently cloned the rfaE gene, which is involved in ADP-L-glycero-D-manno-heptose biosynthesis. The rfaE mutant synthesizes heptose-deficient LPS, which consists of only lipid A and 3-deoxy-D-manno-octulosonic acid (KDO), thus making an incomplete LPS and a rough phenotype mutant. S. typhimurium deep-rough mutants with the heptose region of the inner core show a reduced growth rate, sensitivity to high temperature, and hypersensitivity to hydrophobic antibiotics such as baicalin isolated from the medicinal herb of Scutellaria baicalensis Georgi. Thus, in this study, the cloned rfaE gene was added to the S. typhimurium rfaE mutant strain SL1102 (rfaE543), which makes heptose-deficient LPS and has a deep-rough phenotype. The complementation created a smooth phenotype in the SL1102 strain. The sensitivity of SL1102 to bacteriophages was also recovered to that of wild-type strain, indicating that LPS is used as the receptor for bacteriophage infection. The permeability barrier of SL1102 to hydrophobic antibiotics such as novobiocin and baicalin was restored to that of the wild-type, suggesting that antibiotic resistance of the wild-type strain is highly correlated with their LPS. Through an agar diffusion assay, the growth-inhibition activity of baicalin was fully observed in the mutant SL1102 strain. However, only a half of the inhibitory activity was detected in the rfaE complemented SL1102 strain. Furthermore, the LPS produced by the rfaE-complemented SL1102 strain was indistinguishable from LPS biosynthesis of smooth strains.

• Korean Journal of Materials Research
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• v.21 no.7
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• pp.357-363
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• 2011

In this paper, high temperature oxidation behavior of newly developed alloys, Ti-6Al-4Fe and Ti-6Al-1Fe, is examined. To understand the effect of Fe on the air oxidation behavior of the Ti-Al-Fe alloy system, thermal oxidation tests are carried out at $700^{\circ}C$ and $800^{\circ}C$ for 96 hours. Ti-6Al-4V alloy is also prepared and tested under the same conditions for comparison with the developed alloys. The oxidation resistance of the Ti-Al-Fe alloy system is superior to that of Ti-6Al-4V alloy. Ti-6Al-4V shows the worst oxidation resistance for all test conditions. This is not a result of the addition of Fe, but rather it is due to the elimination of V, which has deleterious effects on high temperature oxidation. The oxidation of the Ti-Al-Fe alloy system follows the parabolic rate law. At $700^{\circ}C$, Fe addition does not have a noticeable influence on the amount of weight gain of all specimens. However, at $800^{\circ}C$, Ti-6Al-4Fe alloy shows remarkable degradation compared to Ti-6Al-1Fe and Ti-6Al. It is discovered that the formation of $Al_2O_3$, a diffusion resistance layer, is remarkably hindered by a relative decrease of the ${\alpha}$ volume fraction. This is because Fe addition increases the volume fraction of ${\beta}$ phase within the Ti-6Al-xFe alloy system. Activities of Al, Ti, and Fe with respect to the formation of oxide layers are calculated and analyzed to explore the oxidation mechanism.

• Korean Journal of Metals and Materials
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• v.50 no.3
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• pp.256-262
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• 2012

This study investigated the hydrogen storage properties of Zr-Based $AB_{2-x}M_x$ metal hybride made by HCS (Hydriding Combustion Synthesis). The materials were prepared by HCS 80 wt% $AB_2$-15 wt% Mg-5 wt% Mm, HCS 80 wt% $AB_2$-20 wt% Mg and pure Zr-Based $AB_2$, These materials were activated at 298 K under 20 bar. Both HCS 80 wt% $AB_2$-20 wt% Mg and HCS 80 wt% $AB_2$-15 wt% Mg-5 wt% Mm were absorbed within 1 minute. In the case of the $AB_2$, it was perfectly absorbed within 6 minutes. Then, the materials were evaluated to obtain P-C-T (Pressure-Composition-Temperature) curves at 298K. As a result, the hydrogen storage capacity of HCS 80 wt% $AB_2$-20 wt% Mg, HCS 80 wt% $AB_2$-15 wt% Mg-5 wt% Mm and pure Zr-Based $AB_2$ were determined to be 1.2, 1.6 and 1.74 wt%, respectively. The activation energy and rate controlling step were calculated by the Johnson-Mehl Avrami equation. The activation energies of HCS 80 wt% $AB_2$-20 wt% Mg, HCS 80 wt% $AB_2$-15 wt% Mg-5 wt% Mm and pure Zr-Based $AB_2$ were 26.91, 20.45, and 60.41 kJ/mol, respectively. Also, the values of ${\eta}$ in the Johnson-Mehl Avrami equation for HCS 80 wt% $AB_2$-20 wt% Mg, HCS 80 wt% $AB_2$-15 wt% Mg-5 wt% Mm and pure Zr-Based $AB_2$ are 0.60, 0.51, and 0.44. So, the rate controlling steps which indicate hydrogen storage mechanism are an one dimensional diffusion process.

• Korean Journal of Clinical Laboratory Science
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• v.50 no.4
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• pp.422-430
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• 2018

The inappropriate and widespread use of quinolones in humans and animals may cause accelerated emergence and spread of antimicrobial-resistant determinants. In this study, we investigated quinolone resistance mechanisms in a total of 65 nalidixic acid-resistant E. coli isolated from swine rectal swabs (N=40) and clinical specimens (N=25). Antimicrobial susceptibilities were determined by the disk diffusion method. PCR and DNA sequencing were performed for investigations of genes and mutations associated with quinolone resistance. In our study, 62 of 65 nalidixic acid-resistant E. coli harbored mutations in gyrA, parC, and/or parE genes; of the 65 isolates, 62 (95.4%) had mutations in the gyrA gene, 35 (53.8%) had mutations in the parC gene, 7 (10.8%) had mutations in the parE gene. The 35 isolates harbored mutations in two genes, gyrA and parC. Plasmid-mediated quinolone resistance (PMQR) determinants were investigated in the 65 isolates. Thirteen of 65 nalidixic acid-resistant E. coli contained the qnrS gene and 10 of those isolates had mutations in the gyrA, parC, and/or parE genes. We confirmed that an important mechanism of quinolone resistance in E. coli isolated from human and swine involves chromosomal mutations in the gyrA, parC, and/or parE genes with increasing use of quinolone for treatment or additives.

• Tunnel and Underground Space
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• v.29 no.4
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• pp.262-279
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• 2019

In the engineering barriers of high-level radioactive waste disposal, gases could be generated through a number of processes. If the gas production rate exceeds the gas diffusion rate, the pressure of the gas increases and gases could migrate through the bentonite buffer. Because people and the environment can be exposed to radioactivity, it is very important to clarify gas migration in terms of long-term integrity of the engineered barrier system. In particular, it is necessary to identify the hydro-mechanical mechanism for the dilation flow, which is a very important gas flow phenomenon only in medium containing large amounts of clay materials such as bentonite buffer, and to develop and validate new numerical approach for the quantitative evaluation of the gas migration phenomenon. Therefore, in this study, we developed a two-phase flow model considering the mechanical damage model in order to simulate the gas migration in the engineered barrier system, and validated with 1D gas flow modelling through saturated bentonite under constant volume boundary conditions. As a result of numerical analysis, the rapid increase in pore water pressure, stress, and gas outflow could be simulated when the dilation flow was occurred.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.2
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• pp.61-70
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• 2019

Geopolymer is an eco-friendly construction material that has various advantages such as reduced $CO_2$ emission, fire resistance and low thermal conductivity compared to cement. However, it has not been many studies on the thermal behavior of the surface of the geopolymer panel when flame is applied to the surface. In this study, surface characteristics of hardened geopolymer on flame exposure was investigated to observe its characteristics as heat-resistant architectural materials. External structure changes and crack due to the heat shock were not observed during the exposure on flame. According to the residue of calcite and halo pattern of aluminosilicate gel, decarboxylation and dehydration were extremely limited to the surface and, therefore, it is thought that durability of hardened geopolymer was sustained. Gehlenite and calcium silicate portion was inversely proportional to quartz and calcite and significantly directly proportional to BFS replacement ratio. Microstructure changes due to the thermal shock caused decarboxylation and dehydration of crystallization and it was developed the pore and new crystalline phase like calcium silicate and gehlenite. It is thought that those crystalline phase worked as a densification and strengthening mechanism on geopolymer panel surface.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.6
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• pp.10-16
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• 2020

Deterioration of reinforced concrete structure caused by chloride ingress is the main issue and regrading this, many studies have been investigated with both experiments and computational modelling. In addition to chloride diffusion, chloride sorption should be considered as a chloride transport mechanism in concrete structure and cracks formed in concrete structures are the main variable to evaluate the performance of the structures. In this study, after making two types of cracks width (0.1 and 0.3 mm) in reinforced concretes, chloride absorption tests were performed. Weight change and colour change using 0.1 AgNO3 solution from the samples were performed to measure chloride ingress. Image processing was also carried out to quantify range of colour change in carck face. From the result, it were confirmed that the amount of chloride absorption increases with exposure time and increasing crack width, and chlorides reached at steel depth within 1 hour. It would be possible that chloride can move through interface bewteen steel and concrete, thereby further study regarding this is required.

• Journal of the Microelectronics and Packaging Society
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• v.29 no.2
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• pp.81-89
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• 2022

The in-situ electromigration(EM) and annealing test were performed at 110, 130, and 150℃ with a current density of 1.3×10⁵ A/cm² conditions to investigate the effect of non-conductive film (NCF) on growth kinetics of intermetallic compound (IMC) in Cu/Ni/Sn-2.5Ag microbump. As a result, the activation energy of the Ni₃Sn₄ IMC growth in the annealing and EM conditions according to the NCF application was about 0.52 eV, and there was no significant difference. This is because the growth rate of Ni-Sn IMC is much slower than that of Cu-Sn IMC, and the growth behavior of Ni-Sn IMC increases linearly with the square root of time, so it has the same reaction mechanism dominated by diffusion. In addition, there is no difference in the activation energy of the Ni₃Sn₄ IMC growth because the EM resistance effect of the back stress according to the NCF application is not large.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.6
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• pp.230-237
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• 2022

It is essential that service life of reinforced concrete structures in economic and safety aspects should be secured. It is well-known that chloride attack is a typical deterioration mechanism in field concrete structures. To prevent serious accidents like collapse, many studies have been conducted to increase resistance of chloride ingress using concrete mixed with GGBS. The usage of GGBS concrete is nowadays mandatory. Since most concretes in the field are unsaturated, study regarding chloride absorption is necessary, but many studies have focused on the chloride diffusion phenomenon. Methods for evaluating chloride absorption are cost and improper in the field. It is necessary to develop a simple method for evaluating chloride absorption in practice. This study evaluated resistance of chloride ingress in GGBS concretes with impedance measurement and absorption test. From the results, it was confirmed that the contents of absorbed chloride were linearly correlated with the measured electrical resistivities (or conductivities) in the concrete. At the end of the test, the electrical conductivities were 250.8 S/m (w/b=0.4) and 303.1 S/m (w/b=0.6) for PC concretes, and 2.6 S/m (w/b=0.4) and 64.4 S/m (w/b=0.6) for GGBS concretes, respectively. Considering influencing factors for chloride absorption and impedance measurement, chloride ingress into concrete is mainly affected by pore structures due to replacement of GGBS. Especially, formations of pore structure are different with binder, thereby binders should be considered in building reinforced concrete structures exposed to chloride environments.

• Tunnel and Underground Space
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• v.34 no.2
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• pp.89-103
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• 2024

In the disposal environment, gases can be generated at the interface between canister and buffer due to various factors such as anaerobic corrosion, radiolysis, and microbial degradation. If the gas generation rate exceeds the diffusion rate, the gas within the buffer may compress, resulting in physical damage to the buffer due to the increased pore pressure. In particular, the rapid movement of gases, known as gas breakthroughs, through the dilatancy pathway formed during this process may lead to releasing radionuclide. Therefore, understanding these gas generation and movement mechanism is essential for the safety assessment of the disposal systems. In this study, an experimental apparatus for investigating gas migration within buffer was constructed based on a literature review. Subsequently, a gas injection experiment was conducted on a compacted bentonite block made of Bentonile WRK (Clariant Ltd.) powder. The results clearly demonstrated a sharp increase in stress and pressure typically observed at the onset of gas breakthrough within the buffer. Additionally, the range of stresses induced by the swelling phenomenon of the buffer, was 4.7 to 9.1 MPa. The apparent gas entry pressure was determined to be approximately 7.8 MPa. The equipment established in this study is expected to be utilized for various experiments aimed at building a database on the initial properties of buffer and the conditions during gas injection, contributing to understanding the gas migration phenomena.