• Journal of Microbiology and Biotechnology
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• v.23 no.8
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• pp.1123-1132
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• 2013

The removal of toxic Cr(VI) by microorganisms is a promising approach for Cr(VI) pollution remediation. In the present study, four indigenous bacteria, named LY1, LY2, LY6, and LY7, were isolated from Cr(VI)-contaminated soil. Among the four Cr(VI)-resistant isolates, strain LY6 displayed the highest Cr(VI)-removing ability, with 100 mg/l Cr(VI) being completely removed within 144 h. It could effectively remove Cr(VI) over a wide pH range from 5.5 to 9.5, with the optimal pH of 8.5. The amount of Cr(VI) removed increased with initial Cr(VI) concentration. Data from the time-course analysis of Cr(VI) removal by strain LY6 followed first-order kinetics. Based on the 16S rRNA gene sequence, strain LY6 was identified as Pseudochrobactrum asaccharolyticum, a species that had never been reported for Cr(VI) removal before. Transmission electron microscopy and energy dispersive X-ray spectroscopy analysis further confirmed that strain LY6 could accumulate chromium within the cell while conducting Cr(VI) removal. The results suggested that the indigenous bacterial strain LY6 would be a new candidate for potential application in Cr(VI) pollution bioremediation.

• Journal of Microbiology and Biotechnology
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• v.26 no.3
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• pp.540-548
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• 2016

Microbially induced calcium carbonate precipitation (CCP) is a long-standing but re-emerging environmental engineering process for production of self-healing concrete, bioremediation, and long-term storage of CO₂. CCP-capable bacteria, two Bacillus strains (JH3 and JH7) and one Sporosarcina strain (HYO08), were isolated from two samples of concrete and characterized phylogenetically. Calcium carbonate crystals precipitated by the three strains were morphologically distinct according to field emission scanning electron microscopy. Energy dispersive X-ray spectrometry mapping confirmed biomineralization via extracellular calcium carbonate production. The three strains differed in their physiological characteristics: growth at alkali pH and high NaCl concentrations, and urease activity. Sporosarcina sp. HYO08 and Bacillus sp. JH7 were more alkali- and halotolerant, respectively. Analysis of the community from the same concrete samples using barcoded pyrosequencing revealed that the relative abundance of Bacillus and Sporosarcina species was low, which indicated low culturability of other dominant bacteria. This study suggests that calcium carbonate crystals with different properties can be produced by various CCP-capable strains, and other novel isolates await discovery.

• Fire Science and Engineering
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• v.14 no.3
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• pp.1-5
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• 2000

In this paper, we analyzed the fire hazard of the ballast for fluorescent lamp used as the indoor lighting. In the result of being analyzed the ballast wire by stereo microscope, many melting points were discovered, it was impossible to judge a cause with the naked eye. In the Thermal-deteriorated ballast wire, elongation structure disappeared at above $700^{\circ}$, and it only showed the enlarged appearance of the copper particle. On the metallurgical microscope of short wire, as it was confirmed the regulation of the columnar structure and the void growth at the center of boundary-face, we found that electrical short-circuit generated. Also, it was confirmed the melted part on the analysis using SEM(scanning electron microscope). Not only CuL and Cuk line that is composition factor of copper but also OK line was observed uniformly on the spectra analysis using EDX(energy dispersive x-ray spectroscopy). It means that oxygen took part in reaction at the recombination process.

• The Journal of Advanced Prosthodontics
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• v.6 no.3
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• pp.207-214
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• 2014

PURPOSE. This study characterized the synthesis of a modified PMMA (Polymethyl methacrylate) denture acrylic loading platinum nanoparticles (PtN) and assessed its bacterial inhibitory efficacy to produce novel antimicrobial denture base material. MATERIALS AND METHODS. Polymerized PMMA denture acrylic disc ($20mm{\times}2mm$) specimens containing 0 (control), 10, 50, 100 and 200 mg/L of PtN were fabricated respectively. The obtained platinum-PMMA nanocomposite (PtNC) was characterized by TEM (transmission electron microscopy), SEM/EDX (scanning electron microscope/energy dispersive X-ray spectroscopy), thermogravimetric and atomic absorption spectrophotometer analysis. In antimicrobial assay, specimens were placed on the cell culture plate, and $100{\mu}L$ of microbial suspensions of S. mutans (Streptococcus mutans) and S. sobrinus (Streptococcus sobrinus) were inoculated then incubated at $37^{\circ}C$ for 24 hours. The bacterial attachment was tested by FACS (fluorescence-activated cell sorting) analysis after staining with fluorescent probe. RESULTS. PtN were successfully loaded and uniformly immobilized into PMMA denture acrylic with a proper thermal stability and similar surface morphology as compared to control. PtNC expressed significant bacterial anti-adherent effect rather than bactericidal effect above 50 mg/L PtN loaded when compared to pristine PMMA (P=.01) with no or extremely small amounts of Pt ion eluted. CONCLUSION. This is the first report on the synthesis and its antibacterial activity of Pt-PMMA nanocomposite. PMMA denture acrylic loading PtN could be a possible intrinsic antimicrobial denture material with proper mechanical characteristics, meeting those specified for denture bases. For clinical application, future studies including biocompatibility, color stability and warranting the long-term effect were still required.

• Journal of the Korean Ceramic Society
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• v.32 no.12
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• pp.1392-1400
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• 1995

WC-10wt%Co-Al2O3 ceramic composites, using both the SHS (Self-propagating High Temperature Synthesis) synthesized WC powder method and commercial WC powder, were prepared by varing WC-Co/Al2O3 vol% ratio and sintering temperature (1350℃∼1650℃) for 1 hr in Ar atmosphere. Mechanical characterization has been investigated by Instron meterial testing system and Vicker's hardness test. Compositional and structural chracterizations were carried out by energy-dispersive analysis of X-ray (EDAX) data and scanning electron microscope (SEM). Electrical characterization was carried out by the electrical resistivity measurement using 4-point probe method. As sintering period increased and Al2O3 contents decreased in WC-10wt%Co-Al2O3 ceramic composite, shrinkage and relative density increased, resulting in maximum values at 1600℃. Also the major matrix phase changed with increasing Al2O3 content from 0 to 100 vol%. It was also identified by SEM, EDAX, and electrical resistivity measurement. Based on the results of analysis of flexural strength, toughness and hardness, the mechanical properties of WC-10wt%Co-Al2O3 ceramic composites using the SHS synthesized WC powder were better than those WC-10wt%Co-Al2O3 ceramic composites using commercial WC powder because WC-10wt%Co-Al2O3 ceramic composites using the SHS synthesized WC powder were sintered very well due to small initial particle size. By the addition of 40 vol% Al2O3 [60(WC=10wt%Co)-40Al2O3], it was possible to obtain a proper candidate as a superalloy.

• Korean Journal of Veterinary Service
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• v.35 no.3
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• pp.197-205
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• 2012

Despite of a long history of the sulfur on the disease healing effect, there were limited ways of applying sulfur to animal and human. We have developed the detoxified sulfur (non toxic sulfur) method to make it practical and mass production possible through laboring for many years. This study practiced scanning electron microscope (SEM), Energy dispersive X-ray spectrometer (EDS) and secondary ion mass spectrometry (SIMS) analysis to investigate the physicochemical aspect of detoxified sulfur. We also performed the oral toxicity experiment to mice, and anti-bacterial test of the detoxified sulfur. Based on the SEM, EDS and SIMS results, the united particles in the mass form with the similar component intensity with the raw sulfur were observed, and hydrogen sulfide ion (HS-) component which is regarded as a toxic matter, was decreased after detoxification. Indeed, toxicity test on the mice (10 males, 10 females) showed no clinical, histopathological changes with the 5 times amount (2,500 mg/kg) of the actual doses. However, the male-mice showed decreased in body weight by 23.6%, 24.3% in the 7th, 14th day, respectively, after detoxified sulfur. Moreover, the female-mice administered the detoxified sulfur showed decreased in body weight by 28.7% (P<0.05) than that in the control group on the 14th day. The result of antibacterial test on the detoxified sulfur showed antibacterial effect (27%) to inhibit the growth of Staphylococcus aureus. It is shown that detoxified sulfur can be used as feed additive and has an affect on the farm perfomance.

• Journal of Microbiology and Biotechnology
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• v.24 no.4
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• pp.453-464
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• 2014

The current research was focused on the extracellular biosynthesis of bactericidal silver nanoparticles (AgNPs) using cell-free supernatant of a local isolate previously identified as a novel Streptomyces aegyptia NEAE 102. The biosynthesis of silver nanoparticles by Streptomyces aegyptia NEAE 102 was quite fast and required far less time than previously published strains. The produced particles showed a single surface plasmon resonance peak at 400 nm by UV-Vis spectroscopy, which confirmed the presence of AgNPs. Response surface methodology was chosen to evaluate the effects of four process variables ($AgNO_3$ concentration, incubation period, pH levels, and inoculum size) on the biosynthesis of silver nanoparticles by Streptomyces aegyptia NEAE 102. Statistical analysis of the results showed that the linear and quadratic effects of incubation period, initial pH, and inoculum size had a significant effect (p < 0.05) on the biosynthesis of silver nanoparticles by Streptomyces aegyptia NEAE 102. The maximum silver nanoparticles biosynthesis (2.5 OD, at 400 nm ) was achieved in runs number 5 and 14 under the conditions of 1 mM $AgNO_3$ (1-1.5% (v/v)), incubation period (72-96 h), initial pH (9-10), and inoculum size (2-4% (v/v)). An overall 4-fold increase in AgNPs biosynthesis was obtained as compared with that of unoptimized conditions. The biosynthesized silver nanoparticles were characterized using UV-VIS spectrophotometer and Fourier transform infrared spectroscopy analysis, in addition to antimicrobial properties. The biosynthesized AgNPs significantly inhibited the growth of medically important pathogenic gram-positive (Staphylococcus aureus) and gram-negative bacteria (Pseudomonas aeruginosa) and yeast (Candida albicans).

• Corrosion Science and Technology
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• v.19 no.4
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• pp.189-195
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• 2020

Two air vents situated on a heat transport pipe in district heating system were exposed to the same environment for 10 years. However, one air vent was more corroded than the other. It also had a hole on the top of the front-end pipe. Comparative analysis was performed for these air vents to identify the cause of corrosion and establish countermeasures. Through experimental observation of the damaged part and analyses of powders sampled from air vents, it was found that corrosion was initiated at the top of the front-end pipe. It then spread to the bottom. Energy dispersive X-ray spectroscopy results showed that potassium and chlorine were measured from the corroded product in the damaged air vent derived from rainwater and insulation, respectively. The temperature of the damaged air vent was maintained at 75 ~ 120 ℃ by heating water. Rainwater-soaked insulation around the front-end pipe had been hydrolyzed. Therefore, the damaged air vent was exposed to an environment in which corrosion under insulation could be facilitated. In addition, ion chromatography and inductively coupled plasma measurements indicated that the matrix of the damaged front-end pipe contained a higher manganese content which might have promoted corrosion under insulation.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.22 no.2
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• pp.119-127
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• 2012

Objectives: The aim of this study is to identify concentration characteristics of indoor and outdoor airborne total fiber particles and asbestos in Gyeongnam Provinces. Methods: This study investigated concentration characteristics of indoor fiber particles from 748 schools and 38 public facilities as well as outdoor particles from 11 sites through PCM (phase contrast microscope). SEM/EDX (scanning electron microscope/energy dispersive using X-ray analysis) was used to obtain physicochemical information of asbestos fiber particles. The study identified asbestos rate in the 15 samples from indoor and outdoor airborne total fiber particles. Results: 1. The average indoor airborne concentrations of total fiber particles were $0.0011{\pm}0007$ f/cc in schools and $0.0015{\pm}0007$ f/cc in public facilities by PCM. Over 90% of the fiber particles were identified as single fibers. 2. The average outdoor airborne concentrations of total fiber particles were $0.0007{\pm}0002$ f/cc, and they were lower than those of indoor airborne concentrations. 3. The results showed that the form of asbestiform was diverse as skein of thread like form and long needle, which was relatively narrower than that of glass fiber and rock wool. 4. The results of SEM/EDX analysis of 15 areas where total fiber particle was relatively high showed that the form was rather similar to that of asbestos, but chemical composition was proven to be non-asbestos. Conclusions: The concentration of indoor and outdoor airborne total fiber particles of Gyeongnam Provinces satisfied the IAQ (Indoor air quality) level of 0.01 f/cc and asbestos was not found in most of the samples by SEM/EDX.

• Journal of the Korean Society of Safety
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• v.34 no.4
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• pp.1-5
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• 2019

In the field of combined cycle power generation, thermal barrier coating(TBC) protects the super-heat-resistant alloy, which forms the core component of the gas turbine, from high temperature exposure. As the turbine inlet temperature(TIT) increases, TBC is more important and durability performance is also important when considering maintenance cost and safety. Therefore, studies have been made on the fabrication method of TBC and super-heat-resistant alloy in order to improve the performance of the TBC. In recent years, due to excellent properties such as high temperature creep resistance and high temperature strength, turbine blade material have been replaced by a single crystal superalloy, however there is a lack of research on TBC applied to single crystal superalloy. In this study, to understand the isothermal degradation performance of the TBC applied to the single crystal superalloy, isothermal exposure test was conducted at various temperature to derive the delamination life. The growth curve of thermally grown oxide(TGO) layer was predicted to evaluate the isothermal degradation performance. Also, microstructural analysis was performed by scanning electron microscope(SEM) and energy dispersive X-ray spectroscopy (EDS) to determine the effect of mixed oxide formation on the delamination life.