• Journal of the Korean Chemical Society
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• v.44 no.6
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• pp.611-624
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• 2000

In this study we analysed 3-12 grade science textbooks, many literatures and internet sites related to diffusion and dissolution concepts. From these data, we discovered that the explanations of diffusion that used in textbooks are not considered the site of collision with mediums, and confused with dissolution, state transition and effusion. In the case of dissolution, almost analysis data were short of the explanations of interaction effect. Most of all, the focus of dissolution explanations was to solve the calculation problems rather than to understand the concept. Every internet site was poor, just as the level of showing textbook contents with computer, so the only effect of using computer was the sense of sight and hearing. Chemistry must be understood nature phenomena with a view point of particle theory, but many textbooks and Internet sites didn't represent it sufficiently. We set up the correct scientific concept and linked micro world of particle theory with macro world of nature phenomena. With a use of computer which have the advantage of representing moving things, we developed the computer-assisted instruction programs related to diffusion and dissolution with the viewpoint of particle movement.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.3 no.1
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• pp.66-74
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• 1993

Potassium-Graphite Intercalation Compounds(K-GICs) have been prepared from purified natural graphite by transformed two-bulb method with variations of reaction temperature ($T_g:450^{\circ}C$, $400^{\circ}C$, $350^{\circ}C$, $300^{\circ}C$, $250^{\circ}C$).Prepared K-GICs were identified to stage transition process by X-ray diffraction data. At these results, d values of (00l) diffraction at 1 stage and 2 stage were corresponded to $5.35\AA$ and $8.73\AA$ respectively. The stage stability and energy states of K-GlCs were obtained by UV /VIS Spectrophotometric data. We found that the minimum value of reflectance was 2.67 eV(465nm) at $250^{\circ}C$and it's moved to higher energy than original graphite's. And X-ray diffraction and UV /VIS spectrophotometric datas suggest that K-GICs were formed lower stage and many charge carriers exist between C atoms of graphite. And then, these results also provide informations on the electrical and other physical properities of K-GICs.Especially, according to studied reports, d values differ from them of each author, but accurate values were established through this study.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.3
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• pp.186-191
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• 2016

The effects of $Eu^{3+}$ doping on the structural, morphological, and optical properties of $MgMoO_4:Dy^{3+},Eu^{3+}$ phosphors prepared by solid-state reaction technique were investigated. XRD patterns exhibited that all the synthesized phosphors showed a monoclinic system with a dominant (220) diffraction peak, irrespective of the content of $Eu^{3+}$ ions. The surface morphology of $MgMoO_4:Dy^{3+},Eu^{3+}$ phosphors was studied using scanning electron microscopy and the grains showed a tendency to agglomerate as the content of $Eu^{3+}$ ions increased. The excitation spectra of the phosphor powders were composed of a strong charge transfer band centered at 294 nm in the range of 230~340 nm and two intense peaks at 354 and 389 nm, respectively, arising from the $^6H_{15/2}{\rightarrow}^6P_{7/2}$ and $^6H_{15/2}{\rightarrow}^4M_{21/2}$ transitions of $Dy^{3+}$ ions. The emission spectra of the $Mg_{0.85}MoO_4$:10 mol% $Dy^{3+}$ phosphors without incorporating $Eu^{3+}$ ions revealed a strong yellow band centered at 573 nm resulting from the $^4F_{9/2}{\rightarrow}^6H_{13/2}$ transition of $Dy^{3+}$. As the content of $Eu^{3+}$ was increased, the intensity of the yellow emission was gradually decreased, while that of red emission band located at 614 nm began to appear, approached a maximum value at 10 mol%, and then decreased at 15 mol% of $Eu^{3+}$. These results indicated that white light emission could be achieved by controlling the contents of the $Dy^{3+}$ and $Eu^{3+}$ ions incorporated into the $MgMoO_4$ host crystal.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.1
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• pp.35-40
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• 2009

Lead free positive temperature coefficient of resistivity (PTCR) ceramics based on $BaTiO_3-(Bi_{0.5}Na_{0.5})TiO_3$ solid solution were prepared by a conventional solid state reaction method. The phase structure was showed single phase with perovskite structure regardless calcinations temperature and $Ba_{1-x}(Bi_{0.5}Na_{0.5})_xTiO_3$ structure was transformed from tetragonal to orthorhombic phase at $x{\geq}0.15$ mole. The XRD peaks with $45^{\circ}{\sim}46^{\circ}$ shifted in right the influence of crystal structure change and the intensity of peak was decreased with additive $(Bi_{0.5}Na_{0.5})TiO_3$. The curie temperature risen with additive $(Bi_{0.5}Na_{0.5})TiO_3$ but disappeared for $(Bi_{0.5}Na_{0.5})TiO_3$ addition more than 0.15 mole in TMA. In relative permittivity, the curie temperature by the transform of ferroelectric phase risen with additive $(Bi_{0.5}Na_{0.5})TiO_3$ but decreased in relative permittivity. Also, the peak of new curie temperature showed the sample containing $0.025{\sim}0.045$ mole of $(Bi_{0.5}Na_{0.5})TiO_3$ near $70^{\circ}C$ caused by phase transform from ferroelectric to ferroelectric and the peak of new curie temperature disappeared at 0.045 mole of $(Bi_{0.5}Na_{0.5})TiO_3$. In our study, it was found that the PTCR in $BaTiO_3-(Bi_{0.5}Na_{0.5})TiO_3$ system was possible for $0{\sim}0.025$ mole of $(Bi_{0.5}Na_{0.5})TiO_3$ and the maximum curie temperature by phase transition showed about at $145^{\circ}C$.

• Journal of the Korean Chemical Society
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• v.48 no.6
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• pp.577-582
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• 2004

The azacrown compounds, 1,4-dioxa-7,10,13-triazacyclopentadecane-N,N',N''-triacetic acid, $N-ac_3[15]aneN_3O_2(II_a)$ and 1,4-dioxa-7,10,13-triazacyclopentadecane-N,N',N''-tripropioc acid, $N-pr_3[15]aneN_3O_2(II_b)$ were synthesized by modified methods. Potentiometry was used to determine the protonation constant of the $N-ac_3[15]aneN_3O_2\;and\;N-pr_3[15]aneN_3O_2$. The stability constants of complexes of the trivalent metal ions of $Ce^{3+},\;Eu^{3+},Gd^{3+},and\;Yb^{3+}$ and divalent metal ions of $Co^{2+},\;Ni^{2+},\;Cu^{2+},\;and\;Zn^{2+}$ with the ligands $N-ac_3[15]aneN_3O_2\;and\;N-pr_3[15]aneN_3O_2$ have been determined at $25{\pm}0.1^{\circ}C$ in 0.1 M $NaClO_4$ solution by potentiometric methods. The metal ion affinities of the two triazamacrocyclic ligands with three pendant acetate or propionate groups are compared to those obtained for the similar ligands, 1,7-dioxa-4,10,13-triazacyclopentadecane-N,N',N''-triacetic acid, and 1,7-dioxa-4,10,13- triazacyclopentadecane-N,N',N''-tripropioc acid. The trends in stability of complexes for different metal ions due to changes in the nitrogen position of the donor atoms of the ligand are discussed.

• Journal of the Korean Chemical Society
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• v.54 no.5
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• pp.515-522
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• 2010

A relation between antimicrobial activities and the formation constants of solid complexes of Cu(II), Ni(II), Co(II), Mn(II) and Fe(III) with tridentate Schiff base ligand, 4-hydroxy-3(1-{2-(benzylideneamino)-phenylimino}-ethyl)-6-methyl-2Hpyran-2-one (HL) derived from o-phenylene diamines, dehydroacetic acid (DHA) and p-chloro benzaldehyde have been studied. The ligand and metal complexes were characterized by elemental analysis, conductivity, magnetic susceptibility, thermal analysis, X-ray diffraction, IR, $^1H$-NMR, UV-vis and mass spectra. From the analytical data, the stiochiometry of the complexes was found to be 1:2 (metal:ligand) with octahedral geometry. The molar conductance values suggest the nonelectrolytic nature of metal complexes. The X-ray diffraction data suggests monoclinic crystal system for Ni(II) and orthorhombic crystal system for Cu(II) and Co(II) complexes. The IR spectral data suggest that the ligand behaves as tridentate ligand with ONN donor atoms sequence towards central metal ion. Thermal behavior (TG/DTA) and kinetic parameters calculated by Coats-Redfern method suggests more ordered activated state in complex formation. The protonation constants of the complexes were determined potentiometrically in THF:water (60:40) medium at $25^{\circ}C$ and ionic strength ${\mu}=0.1\;M$ ($NaClO_4$). Antibacterial activities in vitro were performed against Staphylococcus aureu and Escherichia coli. Antifungal activities were studied against Aspergillus Niger and Trichoderma. The effect of the metal ions and stabilities of complexes on antimicrobial activities are discussed.

• Management & Information Systems Review
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• v.35 no.2
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• pp.119-136
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• 2016

The purpose of this study are as follows : First, This study conceptually provide an insight of reasons that organizations seek to create, acquire, store and distribute knowledge at the level of an organization and of process how they can transform or evolve to knowledge based organizations. Second, this study confirms examine what theories can be used to knowledge management, how such theories can be useful to analyse knowledge management and provide a theoretical foundation for knowledge management research. Applied to the theories of knowledge based and resource based view and institutional theory, the essence of knowledge management confirms that the organization finds job-related knowledge and know-how retained by individual of organizational members systematically and shares common knowledge within the organization and explains knowledge creation, multi-dimensional knowledge transition and share in all dimension of individual, group, and organization. As a result of comparative analysis of theory of organizational knowledge creation theory, In knowledge management, building of knowledge-creative culture, transitional process of explicit knowledge and tacit knowledge, knowledge creation and knowledge operation are important. In the basis on these study results, we discussed how the organizational knowledge creation theory can be used to manage knowledge in the organization, and also proposed hypotheses based on some arguments against the universal acceptance of the theory.

• Journal of the Korea Society for Simulation
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• v.21 no.3
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• pp.79-88
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• 2012

Recently, the study in efficient operation, maintenance, and equipment-design have been growing rapidly in military industry to meet the required missions. Through out these studies, the importance of Concurrent Spare Parts(CSP) are emphasized. The CSP, which is critical to the operation and maintenance to enhance the availability, is offered together when a equipment is delivered. Despite its significance, th responsibility for determining the range and depth of CSP are done from administrative decision rather than engineering analysis. The purpose of the paper is to optimize the number of CSP per item using simulation and multiple regression. First, the result, as the change of operational availability, was gained from changing the number of change in simulation model. Second, mathematical regression was computed from the input and output data, and the number of CSP was optimized by multiple regression and linear programming; the constraint condition is the cost for optimization. The advantage of this study is to respond with the transition of constraint condition quickly. The cost per item is consistently altered in the development state of equipment. The speed of analysis, that simulation method is continuously performed whenever constraint condition is repeatedly altered, would be down. Therefore, this study is suitable for real development environment. In the future, the study based on the above concept improves the accuracy of optimization by the technical progress of multiple regression.

• Elastomers and Composites
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• v.34 no.2
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• pp.121-127
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• 1999

Characteristics of high molecular weight styrene-butadiene rubber(HM-SBR)/low molecular weight styrene-butadiene rubber(LM-SBR) mixtures were studied to investigate how to modify the processability and the mechanical properties of styrene-butadiene rubber (SBR). Mooney viscosity of the HM-SBR/LM-SBR mixtures and torque increase due to the vulcanization decreased by increasing the LM-SBR content of the mixtures. Shore A hardness and rebound properties were decreased by increasing the LM-SBR content of the mixtures. It was found that the value of tan ${\delta}$ of the mixtures in rubbery state was increased, while glass transition temperatures of the vulcanized blends were constant by increasing the LM-SBR content of the mixtures. It was postulated that the decrease of Mooney viscosity by increasing the LM-SBR content of the blends was due to plasticizing effects of the LM-SBR and the increased polydispersity of the mixtures. Change of mechanical properties of the vulcanized HM-SBR/LM-SBR mixtures was attributed to the decreased crosslink densities of the mixtures by increasing the LM-SBR content of the mixtures.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.30 no.3
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• pp.103-109
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• 2020

The effect of La₂O₃ addition on the crystalline phase, microstructure, and dielectric properties of BaTiO₃ has been studied as a function of the amounts of La₂O₃. 0.3 mol% TiO₂-excess BaTiO₃ powder was synthesized by solid-state reaction, and then the powder compacts with various amounts of La₂O₃ were sintered at 1250℃ for 2 hours. Room temperature XRD showed changes in the lattice parameters and a decrease of tetragonality (c/a) as the amounts of La₂O₃ increased. It can be explained that the phase transition from tetragonal to cubic phase occurred because La³⁺ replaced Ba²⁺ site, which increased the instability of the tetragonal phase. As La₂O₃ was added over 0.1 mol%, the critical driving force for growth (Δg_c) increased over maximum driving force (Δg_max). As the result, the grain size decreased with La₂O₃ addition. Dielectric constant decreased as the amounts of La₂O₃ increased, which was analyzed with crystal structure and microstructure.