• Bulletin of the Korean Chemical Society
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• v.15 no.7
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• pp.545-549
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• 1994

Using the extended Hackel molecular orbital method in connection with the tight binding model, we have studied electronic structure and related properties of the charged cluster models relating to superconducting $YBa_{2}Cu_{3}O_{7-x}$, crystals in which O-atoms in regular sites were selectively replaced with Se atoms. In analogy to the isomorphism problem with molecules, we discuss all possible combinations of Se-substitutions in O-sites with one, two, and four Se atoms. The calculations are carried out within charged cluster models for analogues of YBa-copper oxide. Our results suggest that the electronic structure of the symmetrically Se-substituted or Se-added compound is closer to that of the YBCO superconducting compound than that obtained from the unsymmetrical substitution. This applies in particular if O is replaced with Se around the Cu(1) site. Symmetrical substitutions in the $CuO_2$ layers give rise to large variations in the electronic structure of $YBa_{2}Cu_{3}O_{7}$. This is consistent with the fact that superconductivity is very sensitive to the electronic population of the $CuO_2$ layers.

• Korean Journal of Metals and Materials
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• v.47 no.8
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• pp.461-465
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• 2009

We study the diffusion of Ag based bimetallic nanoclusters supported on graphite. Using a molecular dynamics simulation, we reveal that the Ag clusters show rapid diffusion because of their hexagonal bottom layer. In order to decrease the rate of diffusion, we added Pt and Ni to distort the structure of the alloy cluster (i.e., the alloying method). We expected Pt to provide a stronger force on Ag atoms, and Ni to shorten the bond length and thereby change the structure of Ag cluster. However, the attempt was unsuccessful, because Pt and Ni atoms formed cores inside the Ag clusters. We therefore designed a collision system where large Ag clusters collide with small Pt or Ni clusters. Upon collision with Pt clusters, the diffusion showed little change, because Pt atoms are substituted at the Ag atomic site and form a perfectly ordered structure. The collision with Ni, however, deforms the bottom layer as well as the overall cluster structure and decreases diffusion. This outcome appoints toward the possibility of further application to the manufacture of durable nanocatalysts.

• Applied Chemistry for Engineering
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• v.8 no.2
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• pp.262-266
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• 1997

The CNDO/2 calculations have been applied on cluster models for the representative hydroxyls on silica surface to get Wiberg bond orders, total energies, LUMO energies, dipole moments, and formal charge densities. The Br${\ddot{o}}$nsted acidities of suggested models for the hydroxyls were explained in terms of Wiberg bond orders. The calculated bond orders of cluster models have been changed remarkably according to the hydrogen bond. However the Lewis acidities of terminal hydroxyls on silica surface were not related to the structure of hydroxyls.

• The Korean Journal of Ecology
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• v.8 no.4
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• pp.205-214
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• 1985

At the Changnyeung natural bod, the flood in the freshwater wetland and the adaptation of the insect at this area were investigated by the species diversity index and the cluster analysis. Most dominant species was Diplonychus esakii collected at the site of the water edge and its dominance index was 0.797. This area had lower species diversity indices with the value of 0.340 to 1.712 than that of the grassland and water stream. The number of the species in this area was not rich. Some ground beetles inhabited at the flooded or wet area were important species for the pair group between the sites by the cluster analysis. The composition of the insect species at this natural wetland affected by the irregular flood was very simple and specific.

• Molecules and Cells
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• v.46 no.12
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• pp.736-742
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• 2023

NifB, a radical S-adenosylmethionine (SAM) enzyme, is pivotal in the biosynthesis of the iron-molybdenum cofactor (FeMo-co), commonly referred to as the M-cluster. This cofactor, located within the active site of nitrogenase, is essential for the conversion of dinitrogen (N₂) to NH₃. Recognized as the most intricate metallocluster in nature, FeMo-co biosynthesis involves multiple proteins and a sequence of steps. Of particular significance, NifB directs the fusion of two [Fe₄S₄] clusters to assemble the 8Fe core, while also incorporating an interstitial carbide. Although NifB has been extensively studied, its molecular mechanisms remain elusive. In this review, we explore recent structural analyses of NifB and provide a comprehensive overview of the established catalytic mechanisms. We propose prospective directions for future research, emphasizing the relevance to biochemistry, agriculture, and environmental science. The goal of this review is to lay a solid foundation for future endeavors aimed at elucidating the atomic details of FeMo-co biosynthesis.

• Journal of Environmental Impact Assessment
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• v.28 no.4
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• pp.373-386
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• 2019

In The study, is to investigate the spatial characteristics of the Miho stream, which is the main tributary of the Geum River system, and to identify the main factors influencing the water quality using water quality analysis and multivariate analysis. The survey subjects were selected as 7 main sites in the Miho stream water system, From 2012 to 2017, 16 items including weather temperature and weather data were used for multivariate analysis. As a result of the water quality analysis, the average concentration of BOD and COD for 6 years was 3grade (normal) compared with the water quality environmental standard (river) of conditions. The concentrations of nitrogen and phosphorus were highest at th upstream site, then decreased and then increased again by the hydrogeological and geomorphological effect. Cluster analysis of spatial and water quality characteristics, it was evaluated as three clusters and the pollution sources is the greatest impact. As a result of principal component analysis and factor analysis on each cluster and mainstream, three to four major components were extracted. Main stream and the Cluster 1, Cluster 3 first principal factor included nitrogen and seasonal factors,first factor of Cluster 2 included nitrogen and water temperature. Nitrogen is the principal factor which affects water quality in Miho stream.

• Asian-Australasian Journal of Animal Sciences
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• v.31 no.8
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• pp.1141-1149
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• 2018

Objective: Cluster of differentiation 4 protein (CD4) gene is an important immune related gene which plays a significant role in T cell development and host resistance during viral infection. Methods: In order to unravel the relationship of CpG island methylation level of CD4 gene with its gene expression and T lymphocyte subpopulation traits, we used one typical Chinese indigenous breed (Dapulian, DP) and one commercial breed (Landrace), then predicted the CpG island of CD4 gene, determined the methylation status of CpG sites by bisulfite sequencing polymerase chain reaction (BSP), and carried out the correlation analyses of methylation frequencies of CpG sites with mRNA expression and T lymphocyte subpopulation traits. Results: There was one CpG island predicted in the upstream -2 kb region and exon one of porcine CD4 gene, which located 333 bp upstream from the start site of gene and contained nine CpG sites. The correlation analysis results indicated that the methylation frequency of CpG_2 significantly correlated with CD4 mRNA expression in the DP and Landrace combined population, though it did not reach significance level in DP and Landrace separately. Additionally, 15 potential binding transcription factors (TFs) were predicted within the CpG island, and one of them (Jumonji) contained CpG_2 site, suggesting that it may influence the CD4 gene expression through the potential binding TFs. We also found methylation frequency of CpG_2 negatively correlated with T lymphocyte subpopulation traits CD4+CD8-CD3-, CD4-CD8+CD3- and CD4+/CD8+, and positively correlated with CD4-CD8+CD3+ and CD4+CD8+CD3+ (for all correlation, p<0.01) in DP and Landrace combined population. Thus, the CpG_2 was a critical methylation site for porcine CD4 gene expression and T lymphocyte subpopulation traits. Conclusion: We speculated that increased methylation frequency of CpG_2 may lead to the decreased expression of CD4, which may have some kind of influence on T lymphocyte subpopulation traits and the immunity of DP population.

• Korean journal of applied entomology
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• v.49 no.2
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• pp.105-113
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• 2010

Moths were collected using a 22W UV black light trap in June through September in 2005 and May, June, August and September in 2006. The study sites were Namsan (Mt. Nam), Jirisan (Mt. Jiri), Woraksan (Mt. Worak) which are part of the Korean National Long Term Ecological Research (KNLTER). There were two common forest communities, Quercus mongolica and Pinus densiflora. The purpose of this study was to compare species diversity of the major plant feeding Lepidoptera in the two forest types at the regional KNLTER sites. We collected a total of 435 species from the KLTER sites in 2005 and 2006. Abundance of moths was highest at Woraksan (Mt. Worak) followed by Jirisan (Mt. Jiri). The Namsan (Mt. Nam) site had the lowest, with five families (Arctiidae, Geometridae, Noctuidae, Notodontidae, and Pyralidae). Analysis of variance (ANOVA) showed statistically significant differences at sampling date in species abundance as a response variable and at site in species richness as another response variable. Although we expected a distinct cluster with the forest type at each study site, one of ordination analyses, nonmetric multidimensional scaling (NMS), showed distinct clusters with the moth assemblages at each site only but NMS did not show any distinct cluster with the different forest types at each site as we expected.

• Applied Biological Chemistry
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• v.48 no.3
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• pp.189-200
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• 2005

Biological nitrogen fixation is an important process for academic and industrial aspects. This review will briefly compare industrial and biological nitrogen fixation and cover the characteristics of biological nitrogen fixation studied in Azotobacter vinelandii. Various organisms can carry out biological nitrogen fixation and recently the researches on the reaction mechanism were concentrated on the free-living microorganism, A. vinelandii. Nitrogen fixation, which transforms atmospheric $N_2$ into ammonia, is chemically a reduction reaction requiring electron donation. Nitrogenase, the biological nitrgen fixer, accepts electrons from biological electron donors, and transfers them to the active site, FeMo-cofactor, through $Fe_4S_4$ cluster in Fe protein and P-cluster in MoFe protein. The electron transport and the proton transport are very important processes in the nitrogenase catalysis to understand its reaction mechanism, and the interactions between FeMo-cofactor and nitrogen molecule are at the center of biological nitrogen fixation mechanism. Spectroscopic studies including protein X-ray crystallography, EPR and $M{\ddot{o}}ssbauer$, biochemical approaches including substrate and inhibitor interactions as well as site-directed mutation study, and chemical approach to synthesize the FeMo-cofactor model compounds were used for biological nitrogen fixation study. Recent research results from these area were presented, and finally, a new nitrogenase reaction mechanism will be proposed based on the various research results.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.10
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• pp.386-393
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• 2018

The Korean military supplies industry tends to become limited in terms of its development to specific areas in line with strategic promotion policies of the local private direct industrial site. However, the relation between base and small cluster is getting lower of the local industrial site. In this study, information related to authorized test reports for munitions was collected through the military quality information system and subjected to social network analysis(SNA). SNA was performed through the relationships among defense quality assurance agencies, test institutions, contracts and cooperative firms through UCINET's Two-Mode Network. In the field of weapon systems, the median technology industry, and the test analysis dependent are high in Seoul, so the analysis revealed that strengthening the infrastructure for test analysis is needed. Also, it was deemed necessary for government-driven political support. Besides, the field support system was efficiently utilizing a relatively local test analysis. It was analyzed that they are overcoming the regional boundaries of small clusters by strategically changing their contract and cooperative firms' status. The research found some spatial inconsistencies between base and small clusters in the military supplies industry, and it was judged that a political suggestion was needed.