• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.286-287
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• 2012

Reset-first resistive switching mechanism based on reduction reaction in HfO2-x with oxygen drift-diffusion was studied. we first report that the indirect evidence of local filamentary conductive path formation in bulk HfO2 film with local TiOx region at Ti top electrode formed during forming process and presence of anion-migration at interface between electrode and HfO2 during resistive switching through high resolution transmission electron microscopy (HRTEM), electron disperse x-ray (EDX), and electron energy loss spectroscopy (EELS) mapping. Based on forming process mechanism, we expected that redox reaction from Ti/HfO2 to TiOx/HfO2-x was responsible for an increase of initial current with increasing the post-annealing process. First-reset resistive switching in above $350^{\circ}C$ annealed Ti/HfO2 film was exhibited and the redox phenomenon from Ti/HfO2 to TiOx/HfO2-x was observed with high angle annular dark field (HAADF) - scanning transmission electron microscopy (STEM), EDX and x-ray photoelectron spectroscopy. Therefore, we demonstrated that the migration of oxygen ions at interface region under external electrical bias contributed to bipolar resistive switching behavior.

• The Journal of the Korean Society for Microbiology
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• v.21 no.3
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• pp.331-336
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• 1986

A microbiological study for the isolation and characterization of Leptospira interrogans was performed in an attempt to define the characteristics of Leptospirosis in Korea. The results are summerised as follows. Thirty-five cultures were isolated from 11 patients with leptospirosis and 24 wild rodents captured in Paju area. The isolation rate of Leptospira from wild rodents reached 23.1%. All 35 cultures were identified as Leptospira interrogans by their characteristic morphology and motility in dark field microscopy, pathogenecity in Guinea pig and sensitivity to 8-Azaguanine. Cultures formed diffuse subsurface colonies with hazy margin and were catalase, peroxidase and oxdase positive. The fifty percent lethal dose of isolate HM 4 in Guinea pig was $8.9{\times}10^4$ org. Mouse passage method was sucecssfully applied in maintenance of fresh isolates without any loss of their original virulency.

• Journal of the Korean Chemical Society
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• v.60 no.1
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• pp.34-38
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• 2016

In this paper, zinc oxide nanoparticles (ZnO NPs) were synthesized using the sonochemical method, where equimolar amounts of zinc acetate dehydrate and sodium hydroxide were separately dissolved in deionized water, and then mixed for 30 min under magnetic stirring. The resultant white gel was sonicated for 60, 120, 180, 240, and 360 min with magnetic stirring. The obtained precipitates were centrifuged, repeatedly washed with ethanol to remove ionic impurities, and dried at 50 ℃ for 24 h. The formation of pure NPs was confirmed by X-ray diffraction, and their crystallinity and crystal phases were analyzed as well. Structural investigation was carried out by field-emission scanning electron microscopy (FE-SEM). The photocatalysis behavior of the ZnO NPs was investigated in a dark room under UV irradiation, using Rhodamine B. Spherical, rod, and flower-like ZnO NPs could be obtained by adjusting the sonication time, as observed by FE-SEM. The flower-like ZnO NPs exhibited excellent photocatalytic activity.

• Korean journal of applied entomology
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• v.19 no.2 s.43
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• pp.67-72
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• 1980

A mosaic virus disease of ginger plant was investigated to determine its virus group on the basis of host range, physical and chemical properties, serological behavior and electron-microscopic morphology. The disease gave rise to yellowsih and dark-green mosaic on the leaves in the early stage and stunted all the leaves as well as rhizomes in the late stage. In the field about 43\% of the plants were observed to be diseased The disease was able to be artificially infected to the ginger plants by the sap and transmission as well as to 23 other species of plants which were known to be the CMV susceptible plants by the sap transmission; Chenopodium amaranticolar, Nicotiana tabaccum var. Havana, cow pea, cucumber, tomato,... etc. The dilution end point of the virus ranged $10^{-4}-10^{-5}$ and the thermal inactivation point $65-70^{\circ}C$. Serological test showed a positive reaction by a CMV antiserum. An electron microscopy of the purified virus showed that the virus particles were spherical with a diameter of $28-32m\mu$. Virus particles from the infected tissue were observed to be free or aggregated in the mesophyll tissue of artificially infected tobacco plant. The mosaic disease of ginger plants were conclusively suggested to the CMV group.

• Proceedings of the Plant Resources Society of Korea Conference
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• 2018.04a
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• pp.93-93
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• 2018

This study disclosed the aqueous fruits extract of Rubus coreanus as a sustainable agent for the synthesis of Rubus coreanus zinc oxide nanoparticle (Rc-ZnO Nps) using as a reducing and capping precursor for co-precipitation method. The development of Rc-ZnO was assured by white precipitated powder and analyzed by spectroscopic and analytical instruments. The UV-visible (UV-Vis) studies indicate the maximum absorbance at 357nm which confirmed the formation of ZnO Nps and the purity, functional group and monodispersity were assured by field emission transmission electron microscopy (FE-TEM), Fourier Transform Infrared (FTIR) Spectroscopy and dynamic light scattering (DLS). The X-ray powder diffraction (XRD) data revealed the Nps is 23.16 nm in size, crystalline in nature and possess hexagonal wurtzite structure. The Rc-ZnO Nps were subjected for catalytic studies. The Malachite Green dye was degraded by Rc- ZnO NPs in both dark and light (100 W tungsten) conditions and it degraded about 90% at 4 hours observation in both cases. The biodegradable, low cost Rc-ZnO NPs can be a better weapon for waste water treatment.

• Korean Journal of Materials Research
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• v.24 no.7
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• pp.370-374
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• 2014

Inorganic pigments have high thermal stability and chemical resistance at high temperature. For these reasons, they are used in clay, paints, plastic, polymers, colored glass and ceramics. $CoAl_2O_4$ nano-powder was synthesized by reverse-micelle processing the mixed precursor(consisting of $Co(NO_3)_2$ and $Al(NO_3)_3$). The $CoAl_2O_4$ was prepared by mixing an aqueous solution at a Co:Al molar ratio of 1:2. The average particle size, and the particle-size distribution, of the powders synthesized by heat treatment (at 900; 1,000; 1,100; and $1,200^{\circ}C$ for 2h) were in the range of 10-20 nm and narrow, respectively. The average size of the synthesized nano-particles increased with increasing water-to-surfactant molar ratio. The synthesized $CoAl_2O_4$ powders were characterized by X-ray diffraction analysis(XRD), field-emission scanning electron microscopy(FE-SEM) and color spectrophotometry. The intensity of X-ray diffraction of the synthesized $CoAl_2O_4$ powder, increased with increasing heating temperature. As the heating temperature increased, crystal-size of the synthesized powder particles increased. As the R-value(water/surfactant) and heating temperature increased, the color of the inorganic pigments changed from dark blue-green to cerulean blue.

• Journal of Surface Science and Engineering
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• v.50 no.5
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• pp.339-344
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• 2017

Highly corrosion resistance performance of CrAlSiN coatings were obtained by applying ultrathin $Al_2O_3$ thin films using atomic layer deposition (ALD) method. CrAlSiN coatings were prepared on Cr adhesion layer/SUS304 substrates by a hybrid coating system of arc ion plating and high power impulse magnetron sputtering (HiPIMS) method. And, ultrathin $Al_2O_3$ passivation layer was deposited on the CrAlSiN/Cr adhesion layer/SUS304 sample to protect CrAlSiN coatings by encapsulating the whole surface defects of coating using ALD. Here, the high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and energy dispersive X-ray spectrometry (EDX) analysis revealed that the ALD $Al_2O_3$ thin films uniformly covered the inner and outer surface of CrAlSiN coatings. Also, the potentiodynamic and potentiostatic polarization test revealed that the corrosion protection properties of CrAlSiN coatings/Cr/SUS304 sample was greatly improved by ALD encapsulation with 50 nm-thick $Al_2O_3$ thin films, which implies that ALD-$Al_2O_3$ passivation layer can be used as an effect barrier layer of corrosion.

• Mycobiology
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• v.36 no.3
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• pp.143-147
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• 2008

We have detected the slime mold, Diachea leucopodia (GNU06-10) in a strawberry greenhouse located in Sancheong-gun, Gyeongnam. Typical fruiting bodies had developed gregariously on the strawberry leaves, petioles, and plant debris on ground soil habitat, and also surprisingly on plastic pipes and a vinyl covering. Field samples were examined via stereomicroscopy, light microscopy, and SEM for the determination of morphological characteristics. Dark-brown to black spores formed gregariously within the stipitate cylindrical sporangium, and were covered by an iridescent peridium, which may be intact at maturity, or may have disintegrated. The upper portion of the peridium generally breaks up to expose the spores, whereas the lower portion was usually persistent. The results of energy dispersive X-ray spectrometer (EDS) analysis showed that lime was present in the stalk and columella but absent from the spores, capillitium, and peridium. The above characteristics confirm its taxonomic position in the genus Diachea. However, this genus is intermediate in character between the Physarales and Stemonitales of the Myxogastromycetidae. Hence, this genus had been classified as a member of the Stemonitales until the mid-1970's, on the basis of its iridescent peridium and noncalcareous capillitial system, similar to Comatricha of the Stemonitaceae. By way of contrast, emphasis on morphological characteristics, most notably the calcareous stalk and typical columella, places Diachea within the order Physarales. The presence of a phaneroplasmodium during the trophic stage and lime deposition in its sporophores, as was confirmed in this work, supported the inclusion of Diachea in the Physarales, and the noncalcareous capillitial system verified its identification as a member of the Didymiaceae. Further characteristics of the species D. leucopodia include the following: phaneroplasmodium, spore globose 7.5 ${\mu}m$ in diameter, very minutely roughened; sporangia $500{\mu}m\times1mm$, more or less cylindrical, gregarious, stalked 1.2mm; stalk and columella white.

• Journal of Periodontal and Implant Science
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• v.30 no.1
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• pp.111-120
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• 2000

Purpose We designed this study for the purpose of determining the relationship between periodontal disease activity and PLBW, using the evaluation of probing pocket depth, loss of attachment, gingival index, gingival crevicular fluid amount and subgingival microflora. Methods A total of 100 volunteer mothers(mean age 30.44) at the Department of Obstetrics and Gynecology Seoul National University Hospital were selected for this study.Pregnancy outcomes were categorized into cases and controls in two ways. our definition was based on the following; Group 1 : Any PLBW cases Vs. All NBW controls Group 2 : PLBW cases Vs. NBW controls A periodontal exam was performed on the Ramfjord( #16, 21, 24, 36, 41, 44) teeth and Clinical evaluation consisted of probing pocket depth, loss of attachment, gingival index and gingival crevicular fluid amount. Subgingival plaque samples were collected by three sterile #35 paper points. The total number of anaerobic colonies and aerobic bacteria were enumerated after incubation. Antisera to P. gingivalis, P. intermedia, A. actinomycetemcomitans were produced in white rabbits with live whole cells suspensions. The specific fluorescent bacteria obtained by immunofluorescence and total cell counts obtained by dark-field microscopy were counted on four fields. The percent of each specific microorganism in the total cell count was determined. Results Any PLBW and PLBW cases showed significantly greater probing depth and attachment loss than all NBW and NBW controls. Cases group had significantly increased anaerobic bacterial counts compared with control group and no differences in the other microbes. This study confirmed that periodontal disease is a statistically significant risk factor for PLBW by investigating clinical parameters and subgingival plaque analysis.

• Journal of the Korean Chemical Society
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• v.59 no.5
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• pp.397-406
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• 2015

ZnO, II-VI group inorganic compound semi-conductor, has been receiving much attention due to its wide applications in various fields. Since the ZnO has 3.37 eV of a wide band gap and 60 meV of big excitation binding energy, it is well-known material for various uses such the optical property, a semi-conductor, magnetism, antibiosis, photocatalyst, etc. When applied in the field of photocatalyst, many research studies have been actively conducted regarding magnetic materials and the core-shell structure to take on the need of recycling used materials. In this paper, magnetic core-shell ZnFe₂O₄@SiO₂ nanoparticles (NPs) have been successfully synthesized through three steps. In order to analyze the structural characteristics of the synthesized substances, X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FT-IR) were used. The spinel structure of ZnFe₂O₄ and the wurtzite structure of ZnO were confirmed by XRD, and ZnO production rate was confirmed through the analysis of different concentrations of the precursors. The surface change of the synthesized materials was confirmed by SEM. The formation of SiO₂ layer and the synthesis of ZnFe₂O₄@ZnO@SiO₂ NPs were finally verified through the bond of Fe-O, Zn-O and Si-O-Si by FT-IR. The magnetic property of the synthesized materials was analyzed through the vibrating sample magnetometer (VSM). The increase and decrease in the magnetism were respectively confirmed by the results of the formed ZnO and SiO₂ layer. The photocatalysis effect of the synthesized ZnFe₂O₄ @ZnO@SiO₂ NPs was experimented in a black box (dark room) using methylene blue (MB) under UV irradiation.