• Journal of Powder Materials
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• v.12 no.3
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• pp.186-191
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• 2005

A formation of aluminum hydroxide by hydrolysis of nano and micro aluminum powder has been studied. The nano aluminum powder of 80 to 100 nm in diameter was fabricated by a pulsed wire evaporation (PWE) method. The micro powder was commercial product with more than $10\;{\mu}m$ in diameter. The hydroxide type and morphology depending on size of the aluminum powder were examined by several analyses such as XRD, TEM, and BET. The hydrolysis procedure of micro aluminum powder was different from that of nano aluminum powder. The nano aluminum powder after immersing in the water was transformed rapidly to a nano fibrous boehmite, accompanying with a remarkable temperature increase, and then further transformed slowly to a stable bayerite. However, the micro powder was changed to the stable bayerite slowly and directly. The formation of fibrous aluminum hydroxide from nano aluminum powder might be due to the fine cracks which were formed by hydrogen gas pressure on the surface hydroxide layer during hydrolysis. The nano powder with large specific surface area and small size reacted more actively and faster than the micro powder, and transformed to meta-stable hydroxide in relatively short reaction time. Therefore, the formation of fibrous boehmite is special characteristic of hydrolysis of nano aluminum powder.

• Journal of Powder Materials
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• v.24 no.1
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• pp.1-5
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• 2017

We have investigated the washing method of as-synthesized CdSe/ZnS core/shell structure quantum dots (QDs) and the effective surface passivation method of the washed QDs using PMMA. The quantum yield (QY%) of as-synthesized QDs decreases with time, from 79.3% to 21.1%, owing to surface reaction with residual organics. The decreased QY% is restored to the QY% of as-synthesized QDs by washing. However, the QY% of washed QDs also decreases with time, owing to the absence of surface passivation layer. On the other hand, the PMMA-treated QDs maintained a relatively higher QY% after washing than that of the washed QDs that were kept in toluene solution for 30 days. Formation of the PMMA coating layer on CdSe/ZnS QD surface is confirmed by HR-TEM and FT-IR. It is found that the PMMA surface coating, when combined with washing, is useful to be applied in the storage of QDs, owing to its long-term stability.

• Journal of Powder Materials
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• v.24 no.1
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• pp.11-16
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• 2017

In this study, simple chemical synthesis of green emitting Cd-free InP/ZnS QDs is accomplished by reacting In, P, Zn, and S precursors by one-pot process. The particle size and the optical properties were tailored, by controlling various experimental conditions, including [In]/[MA] (MA: myristic acid) mole ratio, reaction temperature and reaction time. The results of ultraviolet-visible spectroscopy (UV-vis), and of photoluminescence (PL), reveal that the exciton emission of InP was improved by surface coating, with a layer of ZnS. We report the correlation between each experimental condition and the luminescent properties of InP/ZnS core/shell QDs. Transmission electron microscopy (TEM), and X-ray powder diffraction (XRD) techniques were used to characterize the as-synthesized QDs. In contrast to core nanoparticles, InP/ZnS core/shell treated with surface coating shows a clear ultraviolet peak. Besides this work, we need to study what clearly determines the shell kinetic growth mechanism of InP/ZnS core shell QDs.

• Journal of Microbiology and Biotechnology
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• v.28 no.10
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• pp.1654-1663
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• 2018

Finding a safe and broad-spectrum medication is a goal of scientists, pharmacists, and physicians, but developing and fabricating the right medicine can be challenging. The current study describes the formation of silver nanoparticles (AgNPs) by Fusarium mangiferae. It involves the antibiofilm activity of the nanoparticles against Staphylococcus aureus. It also involves cytotoxic effect against mammalian cell lines. Well-dispersed nanoparticles are formed by F. mangiferae. The sizes of the nanoparticles were found to range from 25 to 52 nm, and UV-Vis scan showed absorption around 416-420 nm. SEM, TEM, and AFM results displayed spherical and oval shapes. Furthermore, the FTIR histogram detected amide I and amide II compounds responsible for the stability of AgNPs in an aqueous solution. AgNPs were observed to decrease the formation of biofilm at 75% (v/v). DNA reducing, smearing, and perhaps fragmentation were noticed after treating the bacterial cells with 50% (v/v). Additionally, cell lysis was detected releasing proteins in the supernatant. It was also observed that the AgNPs have the ability to cause 59% cervical cancer cell line (HeLa) deaths at 25% (v/v), however, they showed about 31% toxicity against rat embryo fibroblast transformed cell lines (REF). The results of this study prove the efficiency of AgNPs as an antibiofilm against S. aureus, suggesting that AgNPs could be an alternative to antibiotics. It must also be emphasized that AgNPs displayed cytotoxic behavior against mammalian cell lines. Further studies are needed for assessing risk in relation to the possible benefit of prescribing AgNPs.

• Korean Journal of Environmental Biology
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• v.38 no.1
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• pp.61-70
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• 2020

A eukaryotic microalga was isolated from seawater in Janghang Harbor, Korea and its morphological, molecular, and physiological characteristics were investigated. Due to its simple morphology, no distinctive characters were found by morphological observation, such as light microscope or scanning/transmission electron microscopy (S/TEM). However, molecular phylogenetic evidence inferred from the concatenated small subunit (SSU) 18S rRNA and internal transcribed spacer (ITS) sequence data indicated that the isolate belonged to the newly described Micractinium singularis. Furthermore, it was clustered with Antarctic Micractinium strains and it also showed a psychrotolerant property, surviving at temperatures as low as 5℃. However, its optimal growth temperatures range from 15℃ to 25℃, indicating that this microalga is a mesophile. Additionally, gas chromatography-mass spectrometry (GC/MS) analysis showed that the isolate was rich in nutritionally important omega-3 polyunsaturated fatty acid, and high-performance liquid chromatography analysis (HPLC) revealed that the high-value antioxidant lutein was biosynthesized as an accessory pigment by this microalga, with glucose as the major monosaccharide. Therefore, in this study, a Korean marine M. singularis species was discovered, characterized, and described. It was subsequently added to the national culture collections.

• Journal of Sensor Science and Technology
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• v.24 no.1
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• pp.41-46
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• 2015

In this work, pure hierarchical ZnO structure was prepared using a simple hydrothermal method, and Ag nanoparticles doped hierarchical ZnO structure was synthesized uniformly through photochemical route. The reduced graphene oxide (rGO) has been synthesized by typical Hummer's method and reduced by hydrazine. Prepared Ag/ZnO nanostructures are uniformly dispersed on the surface of rGO sheets using ultrasonication process. The synthesized samples were characterized by SEM, TEM, EDS, XRD and PL spectra. The average size of prepared ZnO microspheres was around $2{\sim}3{\mu}m$ and showed highly uniform. The average size of doped-Ag nanoparticles was 50 nm and decorated into ZnO/rGO network. The $C_2H_2$ gas sensing properties of as-prepared products were investigated using resistivity-type gas sensor. Ag/ZnO-rGO based sensors exhibited good performances for $C_2H_2$ gas in comparison with the Ag/ZnO. The $C_2H_2$ sensor based on Ag/ZnO-rGO had linear response property from 3~1000 ppm of $C_2H_2$ concentration at working temperature of $200^{\circ}C$. The response values with 100 ppm $C_2H_2$ at $200^{\circ}C$ were 22% and 78% for Ag/ZnO and Ag/ZnO-rGO, respectively. In additions, the sensor still shows high sensitivity and quick response/recovery to $C_2H_2$ under high relative humidity conditions. Moreover, the device shows excellent selectivity towards to $C_2H_2$ gas at optimal working temperature of $200^{\circ}C$.

• Korean Journal of Veterinary Service
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• v.36 no.3
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• pp.171-180
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• 2013

This study was carried out to investigate the antimicrobial resistance pattern and distribution of resistance gene in 44 Enterobacteriaceae and 21 Pseudomonas (P) aeruginosa isolated from hospitalized dogs and cats in animal hospital from 2010 to 2011 in Daegu. Among Enterobacteriaceae, Escherichia (E) coli was highly resistant to ampicillin (56.7%), followed by tetracycline (53.3%), cephalothin, streptomycine, sulfamethoxazole/trimethoprim, gentamicin and norfloxacin (40.0~43.3%). The remaining isolates of Enterobacteriaceae had high resistance to ampicillin (64.3%) and streptomycin (42.9%). Whereas, P. aeruginosa was low resistant to all antimicrobials tested (less than 15%). int I 1 gene was detected in 20 (57.1%) of 35 antimicrobial resistant Enterobacteriaceae and 2 (9.5%) of 21 P. aeruginosa., but int I 2 gene was not detected in all isolates. The eight resistance genes were found either alone or combination with other gene (s): $bla_{TEM}$, aadA, strA-strB, clmA, tetA, tetB, sul I and sul II. About 78% of integron-positive isolates were resistance to more than four antimicrobial agents. The findings suggest that class I integrons are widely distributed in E. coli among Enterobacteriaceae from dogs and cats and multi-drug resistance related to the presence of class I integrons. The prudent use of antimicrobials and continuous monitoring for companion animals are required.

• Journal of the Korean Wood Science and Technology
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• v.17 no.4
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• pp.57-69
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• 1989

Roughage feeds were produced from Hyun-aspen (Populus alba $\times$ p. glandulosa) by steaming-defibration and steaming-explosion. The objectives of this work were to find proper conditions for the treatment of Hyun-aspen by analyzing the compositional change and digestibility and to investigate the change of physical properties of exploded woods. The results of this work were as follows; 1. The method of steaming-de fibration gave the best producing rate of feedstuffs when the chips were steamed (9kg/$cm^2$ under the pressure) for 10 minutes. The yield and the digestibility of feedstuffs were 84.2% and 38.1%, respectively. It is the merit of this method that feedstuffs manufactured by this method was uniformity in particle size, and facilities of fiberboard factory could be used directly, 2. For defibration of the chip by explosion, the proper condition was steamed under the pressure (20kg/$cm^2$) for 4 minutes. The yield and the digestibility of feedstuffs were 93.4% and 68.1%, respectively. The feedstuffs produced under these conditions had higher nutritional quality than rice straw and this method was considered as the best for making feedstuffs from Hyun-aspen chip. But it is defect that exploded feedstuffs was ununiformity in particle size and had unique odor. The physical properties of the feedstuffs were investigated by a light microscope and a TEM. The feedstuffs produced under the low pressure (20 kg/$cm^2$) still maintained the structure of fibers. However, the feedstuffs produced under the high pressure (28 kg/$cm^2$) resulted in higher de fib ration than these prepared under the low pressure. The highly defibrated feedstuffs recombined with solublized lignin. The crystallinity of feedstuffs was increased by 10% and micelle width increased double after treatment.

• Journal of the Korean Society for Heat Treatment
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• v.4 no.3
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• pp.13-20
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• 1991

The present work was aimed to examine the variation of precipitations and mechanical properties by thermomechanical treatments (TMT) in Al-2.19 wt%Li and Al-2.0 wt%Li-0.11 wt%Zr alloys. This study was performed by TEM, SEM observation, DSC, electrical resistance measurement, hardness and tensile strength measurement. First peak of resistivity aged at $90^{\circ}C$ was caused by precipitation of ${\delta}^{\prime}$-precursor phase, and second peak was caused by precipitation of ${\delta}^{\prime}$ phase. According to this result, the precipitation process of Al-2.19 wt%Li alloy was as follow : $SSSS{\rightarrow}{\delta}^{\prime}$-precursor phase ${\rightarrow}{\delta}^{\prime}$ (Coherent ${\rightarrow}$ Semi-coherent) ${\rightarrow}{\delta}$. In a Al-2.0 wt%Li-0.11 wt%Zr ternary alloy, the first peak of resistivity was appeared at initial aging heat-treatment. It is result from exsistant of ${\delta}^{\prime}$-precursor phase. The effect acceleration in a binary alloy was not appeared and the over-aging ternary alloy was accelerated with increase of the reduction rate. It is caused by combination effect of ${\delta}^{\prime}$ and composite phase.

• Journal of the Korean Society for Heat Treatment
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• v.22 no.3
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• pp.155-161
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• 2009

An investigation of the deformation behavior of ${\gamma}'-Ni_3Al$ single crystals containing fine dispersion of disordered ${\gamma}$ particles was performed for several different crystal orientations. Deformation structures were observed by the weak-beam method of transmission electron microscopy (TEM). The critical resolved shear stress (CRSS) for (111) [$\bar{1}$01] slie. increases with increasing temperature in the temperature range where (111) slip operates. The CRSS for (111) [$\bar{1}$01] slip is dependent on crystal orientation in the corresponding temperature range. The temperature where the strenjlth reaches a maximum is dependent on crystal orientation; the higher the ratio of the Schmid factors of (010) [$\bar{1}$01] to that of (111) [$\bar{1}$01], the higher the peak temperature. The peak temperatures were increased by the precipitation of y particles for the samples of all orientations. Electron microscopy of deformation induced dislocation arrangements under peak temperature has revealed that most of dislocations are straight screw dislocations. The mobility of screw dislocations decreases with increasing temperature. Above the peak temperature, dislocations begin to cross slip from the (111) [$\bar{1}$01] slip system to the (010) [$\bar{1}$01] slip system, thus decreasing the strength.