• Journal of the Korean Chemical Society
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• v.53 no.3
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• pp.266-271
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• 2009

In the recently synthesized rare earth transition metal carbide $La_7O_{s4}C_9$ one finds one-dimensional organometallic $[O_{s4}C_9]^{21-}$ polymers embedded in a $La^{3+}$ ionic matrix. The electronic structure of the polymeric $[O_{s4}C_9]^{21-}$ chain was investigated by density of states (DOS) and crystal orbital overlap population (COOP), using the extended Huckel algorithm. A fragment molecular orbital analysis is used to study the bonding characteristics of the $C_2$ units in $La_7O_{s4}C_9$ containing $C_2$ units and single C atoms as well. The title compound contains partially filled Os and carbon bands leading to metallic conductivity. As the observed distances already indicated, the calculations show extensive Os-C interactions. The C-C bond distance in the diatomic $C_2$ units ($d_{C-C}$=131 pm) in the solid is significantly increased relative to $${C_2}^{2-}$$ or acetylene, because antibonding $1{\pi}_g$ orbitals are partially filled by the Os-$C_2(1\;{\pi}_g)$ bonding contribution found at and below the Fermi level.

• Mycobiology
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• v.43 no.4
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• pp.458-466
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• 2015

Oak tree death caused by symbiosis of an ambrosia beetle, Platypus koryoensis, and an ophiostomatoid filamentous fungus, Raffaelea quercus-mongolicae, has been a nationwide problem in Korea since 2004. In this study, we surveyed the yeast species associated with P. koryoensis to better understand the diversity of fungal associates of the beetle pest. In 2009, a total of 195 yeast isolates were sampled from larvae and adult beetles (female and male) of P. koryoensis in Cheonan, Goyang, and Paju; 8 species were identified by based on their morphological, biochemical and molecular analyses. Meyerozyma guilliermondii and Candida kashinagacola were found to be the two dominant species. Among the 8 species, Candida homilentoma was a newly recorded yeast species in Korea, and thus, its mycological characteristics were described. The P. koryoensis symbiont R. quercusmongolicae did not show extracelluar CM-cellulase, xylanase and avicelase activity that are responsible for degradation of wood structure; however, C. kashinagacola and M. guilliermondii did show the three extracellular enzymatic activities. Extracelluar CM-cellulase activity was also found in Ambrosiozyma sp., C. homilentoma, C. kashinagacola, and Candida sp. Extracelluar pectinase activity was detected in Ambrosiozyma sp., C. homilentoma, Candida sp., and M. guilliermondii. All the 8 yeast species displayed compatible relationships with R. quercus-mongolicae when they were co-cultivated on yeast extract-malt extract plates. Overall, our results demonstrated that P. koryoensis carries the yeast species as a symbiotic fungal associate. This is first report of yeast diversity associated with P. koryoensis.

• 한국균학회소식:학술대회논문집
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• 2016.05a
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• pp.33-33
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• 2016

Mycotoxins are toxic secondary metabolites produced by fungi. They can be present in where agricultural-based commodities are contaminated with toxigenic fungi. These mycotoxins cause various toxicoses in human and livestock when consumed. Small grains including corn, barley, rice or wheat are frequently contaminated with mycotoxins due to infection mainly by toxigenic Fusarium species and/or under environment favorable to fungal growth. One of the most well-known Fusarium toxin groups in cereals is trichothecenes consisting of many toxic compounds. Deoxynivalenol (DON), nivalenol (NIV), T-2 toxin, and various derivatives belong to this group. Zearalenone and fumonisin (FB) are also frequently produced by many species of the same genus. In order to monitor Korean cereals for contamination with Fusarium and other mycotoxigenic fungal species as well, barley, corn, maize, rice grains, and soybean were collected from fields at harvest or during storage for several years. The fungal colonies outgrown from the grain samples were identified based on morphological and molecular characteristics. Trichothecene chemotypes of Fusarium species or presence of FB biosynthetic gene were determined using respective diagnostic PCR to predict possible toxin production. Heavy grain contamination with fungi was detected in barley, rice and wheat. Predominant fungal genus of barley and wheat was Alternaria (up to 90%) while that of rice was Fusarium (~40%). Epicoccum also appeared frequently in barley, rice and wheat. While frequency of Fusarium species in barley and wheat was less than 20%, the genus mainly consisted of Fusarium graminearum species complex (FGSC) which known to be head blight pathogen and mycotoxin producer. Fusarium composition of rice was more diverse as FGSC, Fusarium incarnatum-equiseti species complex (FIESC), and Fusarium fujikuroi species complex (FFSC) appeared all at considerable frequencies. Prevalent fungal species of corn was FFSC (~50%), followed by FGSC (<30%). Most of FFSC isolates of corn tested appeared to be FB producer. In corn, Fusarium graminearum and DON chemotype dominate within FGSC, which was different from other cereals. Soybeans were contaminated with fungi less than other crops and Cercospora, Cladosporium, Alternaria, Fusarium etc. were detected at low frequencies (up to 14%). Other toxigenic species such as Aspergillus and Penicillium were irregularly detected at very low frequencies. Multi-year survey of small grains revealed dominant fungal species of Korea (barley, rice and wheat) is Fusarium asiaticum having NIV chemotype.

• The Korean Journal of Mycology
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• v.48 no.3
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• pp.329-335
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• 2020

From 2008 to 2017, Korean azalea (Rhododendron yedoense f. poukhanense) showing angular, necrotic leaf spots were found in Jeju and Hongcheon, Korea. The lesions occurred frequently, detracting from the beauty of the glossy green leaves of the plant and causing premature defoliation. Therefore, to identify the fungus associated with the lesions, morphological characterization and molecular phylogenetic analysis of actin (Act), translation elongation factor 1-alpha (EF), internal transcribed spacer (ITS), 28S nrDNA (LSU), and RNA polymerase II encoding the second largest subunit (RPB2) of the two representative isolates were performed. The phylogenetic tree inferred from the neighbor-joining method showed the isolates clustering in the Sphaerulina azaleae group. Therefore, the fungus associated with the angular leaf spots on the Korean azalea was identified as Sphaerulina azaleae.

• Mycobiology
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• v.48 no.4
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• pp.288-295
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• 2020

Species of Laccaria (Hydnangiaceae, Agaricales, and Basidiomycota) are well-known ectomycorrhizal symbionts of a broad range of hosts. Laccaria species are characterized by brown, orange, or purple colored basidiocarps, and globose or oblong, echinulate and multinucleate basidiospores. While some Laccaria species are easily identified at the species level using only the morphological characteristics, others are hard to distinguish at the species level due to small differences in morphology. Heretofore, ten Laccaria species have been reported in Korea. While studying the fungal diversity in the National Parks of Korea, two new Laccaria species were discovered. Species identification was done based on molecular analyses (ITS, 28S rDNA, rpb2, and tef1), then were confirmed by their corresponding morphologies. The two newly discovered Laccaria species are proposed here as Laccaria macrobasidia and Laccaria griseolilacina. The unique morphological characters of L. macrobasidia that distinguish it from its closely related species are orange-brown colored basidiocarp, long basidia and the absence of cheilocystidia. L. griseolilacina is characterized by a light grayish lavender-colored pileus and the absence of cheilocystidia. Two new species are described and illustrated in the present paper.

• Journal of the Korea Society of Computer and Information
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• v.15 no.12
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• pp.175-180
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• 2010

In this paper, we have investigated ultrahigh frequency nano-mechanical resonators, made of DWCNTs with various wall lengths, via classical molecular dynamics simulations. We have aimed our analysis on the frequency variations of these resonators with the DWCNT wall lengths. The results show that the variations can be well fitted by either the Pearson VII function when the resonant frequency of normalized by its maximum frequency is plotted as a function of the inner/outer wall length ratio L5/L10 for different values of the outer wall length L10, and the Gauss distribution function when the resonant frequency of normalized by its maximum frequency is plotted as a function of the outer/inner wall length ratio for different values of the inner wall length.

• Archives of Pharmacal Research
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• v.28 no.4
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• pp.443-450
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• 2005

In the present study, we have characterized the choline transport system and examined the influence of various amine drugs on the choline transporter using a conditionally immortalized rat brain capillary endothelial cell line (TR-BBB) in vitro. The cell-to-medium (C/M) ratio of $[^3{H}]choline$ in TR-BBB cells increased time-dependently. The initial uptake rate of $[^3{H}]choline$ was concentration-dependent with a Michaelis-Menten value, $K_{m}$, of $26.2\pm2.7{\mu}M$. The $[^3{H}]choline$ uptake into TR-BBB was $Na^{+}-independent$, but was membrane potential-dependent. The $[^3{H}]choline$ uptake was susceptible to inhibition by hemicholinium-3, and tetraethy-lammonium (TEA), which are organic cation transporter substrates. Also, the uptake of $[^3{H}]choline$ was competitively inhibited with $K_{i}$ values of $274 {\mu}M, 251 {\mu}M and 180 {\mu}M$ in the presence of donepezil hydrochloride, tacrine and $\alpha-phenyl-n-tert-butyl nitrone$ (PBN), respectively. These characteristics of choline transport are consistent with those of the organic cation transporter (OCT). OCT2 mRNA was expressed in TR-BBB cells, while the expression of OCT3 or choline transporter (CHT) was not detected. Accordingly, these results suggest that OCT2 is a candidate for choline transport at the BBB and may influence the BBB permeability of amine drugs.

• The Journal of Natural Sciences
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• v.6 no.1
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• pp.103-108
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• 1993

Zeolites were discovered as a natural mineral more than two hundred ago. In the beginning, the mineral was used as ion-exchange material and adsorbent. After the end of World War II , however, a variety of zeolites have become available in large amounts because of the establishment of low temperature synthesis and the discobery of natural zeolite deposits of sedimentary origin. Various uses of xeolite were developed utilizing the unique crystal strucrure and function of these minerals. In connection with this development remakable progress has also been made in basic stuides on the related geology and mineralogy, crystallization from sols and gels, structure, ion exchange, adsorption and cataiysis. As a result, zeolites, which had been known only as mineral specimens displayed in museums. established a firm position among the high-technology masterials with excellent functional capabilities.

• Korean Journal of Food Science and Technology
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• v.35 no.4
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• pp.545-550
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• 2003

The effect of ${\beta}-glucan$ on gelatinization of barley starch was studied. By the rapid visco-analyzer measurement, gelatinization of starch became rapid and viscosity increased largely on the RVA pattern by addition of ${\beta}-glucan$ to starch. The results of differential scanning calorimeter showed that molecular structure of starch was getting stabilized through shifting up of gelatinization temperature and increase in enthalpy by addition of ${\beta}$-glucan. X-ray diffraction pattern also showed the same results as differential scanning calorimeter. But it was revealed that addition of ${\beta}$-glucan to starch didn't affect characteristics such as microscopic observation, solubility, swelling power, and iodine binding properties during gelatinization of starch.

• Journal of Life Science
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• v.17 no.11
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• pp.1453-1463
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• 2007

This study presents a molecular phylogenetic analysis of the harmful dinoflagellate Cochlodinium polykrikoides, by use of partial sequence of small subunit (SSU) rRNA gene from most of the major taxa(24 species) in dinoflagellates. The class Dinophyceae clade formed a strong monophyletic relationship with C. polykrikoides and several taxa. On the basis of deeper nodes, the phylogenetic relationships placed C. polykrikoides closer to the order Prorocentrales rather than to the order Gymnodiniales, which was supported by a strong bootstrap value (100%) in the analyses of Neighbor-Joining and Parsimony methods. There is strong support for C. polykrikoides being placed in the same branch as Gymnodiniaceae and being connected in a clade with Prororcentrum micans among Prorocentrales. Morphological data show that C. polykrikoides is well associated with the genus Gyrodinium; however, this species is genetically closer to Gymnodinium than to Gyrodinium. The placement of C. polykrikoides always formed an independent branch separated from other dinoflagellates. In conclusion, planktonic P. micans plays an important role as an ancestor of Gymnodinium, whereas C. polykrikoides appears to be used an intermediate position between P. micans and Gymnodinium based on evolution.