• Journal of the Korean Chemical Society
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• v.36 no.1
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• pp.16-23
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• 1992

High $T_c$, superconductor $(Y_{1-x}Eu_x)Ba_2Cu_3O_{7-{\delta}}$ (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) were prepared and the physical properties were observed. XRD analysis showed that the structures of all the specimen were orthorhombic and the lattice parameters a, b and c increased with the increasing x value. Electrical resistivity and magnetization measurements revealed that pure high $T_c$, superconducting phases were formed at above 90 K. The critical temperatures increased with increasing the amount of Eu. From the measurement of magnetization and the size of the grains using SEM micrographs, volume diamagnetic susceptibilities for each specimen were calculated. These values decreased with the increasing x value. The composition of Ba in the lattice site decreased as the concentration of Eu increased, and this was confirmed by EPMA. It was found out that the volume diamagnetic susceptibility of each specimen was directly influenced by the composition of Ba in the lattice site.

• Journal of the Korean Magnetics Society
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• v.23 no.1
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• pp.1-6
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• 2013

Spin-orbit coupling (SOC) effect is known to be the physical origin for various exotic magnetic phenomena in the low-dimensional systems. Recently, SOC also draws lots of attention in the study on magnetically doped thermoelectric alloys to determine their properties as the thermoelectric application as well as the topological insulator via the exact electronic structures determination near the Fermi level. In this research, aiming to investigate the spin-orbit coupling effect on the structural properties such as the lattice constants and the bulk modulus of the most widely investigated thermoelectric host material, $Bi_2Te_3$, we carried out the first-principles electronic structure calculation using the all-electron FLAPW (full-potential linearized augmented plane-wave) method. Employing both the local density approximation (LDA) and the generalized gradient approximation (GGA), the structural optimization is achieved by varying the in-plane lattice constant fixing the perpendicular lattice constant and vice versa, to find that the SOC effect increases the equilibrium lattices slightly in both directions while it markedly reduces the bulk modulus value implying the strong orientational dependence, which are attributed to the material's intrinsic structural anisotropy.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.37 no.1
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• pp.9-16
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• 2024

Using the proper orthogonal decomposition (POD) based intrusive reduced order model (ROM), the total degrees of freedom of the structural system can be significantly reduced and the critical time step satisfying the conditional stability increases in the explicit time integrations. In this study, therefore, the changes in the critical time step in the explicit time integrations are investigated using both the POD-ROM and Voronoi-cell lattice model (VCLM). The snapshot matrix is composed of the data from the structural response under the arbitrary dynamic loads such as seismic excitation, from which the POD-ROM is constructed and the predictive capability is validated. The simulated results show that the significant reduction in the computational time can be achieved using the POD-ROM with sufficiently ensuring the numerical accuracy in the seismic analyses. In addition, the validations show that the POD based intrusive ROM is compatible with the Voronoi-cell lattice based explicit dynamic analyses. In the future study, the research results will be utilized as an elemental technology for the developments of the real-time predictive models or monitoring system involving the high-fidelity simulations of structural dynamics.

• Korean Journal of Materials Research
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• v.23 no.1
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• pp.59-66
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• 2013

Opal glass samples having different chemical compositions were synthesized and transparent glass was obtained after melting. The effects of $TiO_2$, $BaF_2$, and $CeO_2$ content on the color of the opal glass were studied by observing images of the opal samples and analyzing the results via ultraviolet visible spectroscopy and color spectrometry. The aesthetic properties of the opal glass were determined by studying the transmittance of visible light in the 400 nm to 700 nm range. The basic chemical composition of opal glass was $SiO_2$ 52.9 wt%, $Al_2O_3$ 12.35 wt%, $Na_2CO_3$ 15.08 wt%, $K_2CO_3$ 10.35 wt%, $Ca_3(PO)_4$ 4.41 wt%, $MgCO_3$ 1.844 wt%, $LiCO_3$ 2.184 wt%, and $TiO_2$ 0.882 wt%. The glass samples were prepared by varying the weight percentage of $TiO_2$, $BaF_2$, and $CeO_2$. The transmittance of visible light was decreased from 95 % to 75 % in the glass samples in which $TiO_2$ content was increased from 0 to 3.882 wt%. In the blue spectrum region, as the content of $TiO_2$ increased, the reflectance value was observed to become higher. This implies that $TiO_2$ content induces more crystal formation and has an important effect on the optical properties of the glass. The opalescence of opal samples that contained $CeO_2$ or $BaF_2$ is stronger than that in the samples containing $TiO_2$. Opal glass samples comprising $TiO_2$ had tetragonal lattice structures; samples including $CeO_2$ as an additive had cubic lattice structures (FCC, $CeO_2$).

• Korean Journal of Mineralogy and Petrology
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• v.33 no.1
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• pp.19-28
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• 2020

Ranciéte is a hexagonal phyllomanganate mineral containing random Mn(IV) vacancies with hydrated Ca²⁺ cations charged balanced as interlayer cations. Its Mn²⁺ analogue is called takanelite, and ranciéite and takanelite are regarded as end-members of a solid solution series of (Ca²⁺,Mn²⁺)Mn₄O₉·nH₂O. Because the minerals are found as very small particles associated with other minerals, the crystal structures of the solid solution series have yet to be defined. In this research, we conducted classical molecular dynamics (MD) simulations of ranciéite and takanelite by varying the Mn²⁺/Ca²⁺ interlayer cation ratio to find relations between the interlayer cations and mineral structures. MD simulation results of chalcophanite group minerals are compared with experimental results to verify our method applied. Then, lattice parameters of ranciéite and takanelite models are presented along with detailed interlayer structures as to the distribution and coordination of cations and water molecules. This study shows the potentials of MD simulations in entangling complicated phyllomanganates structures.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.5
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• pp.182-187
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• 2015

The growth and characterization of micro sized AlGaN array structures selectively grown by metal organic chemical vapor deposition (MOCVD) on GaN stripes are reported. The shape of the AlGaN array structures depends on the size of exposed area for selective growth. The AlGaN array structures grown selectively on relatively large exposed area have regular shapes resembling those of the GaN stripes on the substrate, while samples selectively grown on relatively small exposed area have irregular shapes. The phonon frequency of the AlGaN array structures increases with increasing Al composition in the AlGaN structure. However, at relatively high Al composition (x = 0.28 in this research), the phonon frequency decreases slightly from the expected value not only because of large tensile strain associated with large differences between the lattice constants of the AlGaN structure and underlying GaN stripes but also changes of crystal facet direction during the selective growth.

• Bulletin of the Korean Chemical Society
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• v.29 no.6
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• pp.1157-1161
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• 2008

2,6-Dinitrophenol (2,6-DNP) complexes with lanthanide series including yttrium (except Pm, Tm, and Lu) have been synthesized and their crystal structures have been analyzed by X-ray diffraction methods. Singlecrystal X-ray structure determinations have been performed at 296 K on the Ce$\rightarrow$Yb species and shown them to be isomorphous, triclinic, P1, a = 8.6558(2)$\rightarrow$8.5605(3) $\AA$, b = 11.8813(3)$\rightarrow$11.6611(4) $\AA$, c = 13.9650(3) $\rightarrow$13.8341(5) $\AA$, $\alpha$ = 73.785(1)$\rightarrow$73.531(2)o, $\beta$ = 74.730(1)→74.903(2)${^{\circ}}$, $\gamma$ = 69.124(1)→ 69.670 $(2){^{\circ}}$, V = 1266.86(5)→1221.53(7) $$\AA^{3}$$, Z = 2. In Ln(III) complexes, three 2,6-DNP ligands coordinate directly to the metal ion in the bidentate fashion. The nine coordinated Ln(III) ion forms slightly distorted tri-capped trigonal prism. There are no water molecules in the crystal lattice. The dependences of metal to ligand bond lengths are discussed on the atomic number of lanthanide elements. The thermal properties of lanthanide complexes of 2,6- DNP have also studied by TG-DTG and DSC thermal analysis methods.

• Journal of the Korean Ceramic Society
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• v.42 no.9 s.280
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• pp.602-606
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• 2005

[ $LiCoO_{2}$ ] is the most common cathode electrode materials in Lithium-ion batteries. $LiCo_{0.97}Mg_{0.03}O_2$ was synthesized by the solid-state reaction method. We investigated crystal structures, electrical conductivities and electrochemical properties. The crystal structure of $LiCo_{0.97}Mg_{0.03}O_2$ was analyzed by X-ray powder diffraction and Rietveld refinement. The material showed a single phase of a layered structure with the space group R-3m. The lattice parameter(a, c) of $LiCo_{0.97}Mg_{0.03}O_2$ was larger than that of $LiCoO_2$. The electrical conductivity of sintered samples was measured by the Van der Pauw method. The electrical conductivities of $LiCoO_2$ and $LiCo_{0.97}Mg_{0.03}O_2$ were $2.11{\times}10^{-4}\;S/cm$ and $2.41{\times}10^{-1}\;S/cm$ at room temperature, respectively. On the basis of the Hall effect analysis, the increase in electrical conductivities of $LiCo_{0.97}Mg_{0.03}O_2$ is believed due to the increased carrier concentrations, while the carrier mobility was almost invariant. The electrochemical performance was investigated by coin cell test. $LiCo_{0.97}Mg_{0.03}O_2$ showed improved cycling performance as compared with $LiCoO_2$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.237-238
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• 2006

The electrical properties such as dielectric constants and dielectric losses in the spinel samples of $LiGaTiO_4$, Li(Ga,Eu)$TiO_4$, $Li(Ga.Yb)TiO_4$ have been characterized by varying measuring temperature and frequency. The long range order structures are analyzed by rietveld refinement method. and local atomic disorder structures are analyzed by MEM (maximum entropy method). The relation between the crystal structure and dielectric properties are discussed. $LiGaTiO_4$ spinel has the IMMA with lattice constant, a = 5.86333, b=17.5872. c = 8.28375 ${\AA}$, Li-sites are partially substituted by Ga or Ti. Two crystallographic oxygen sites are partially occupied(40~50%). The dielectric constants of $LiGaTiO_4$, $LiYbTiO_4$, and $LiGa_{2/6}Eu_{1/6}Ti_{1.5}O_4$ ceramics were 127, 75 and 272, respectively at 100 kHz. The dielectric relaxation were observed in the $LiGaTiO_3$ ceramics and the temperature where dielectric loss shows maximum was $390^{\circ}C$ at 1 kHz and increased with increasing the measuring frequency.

• Advances in aircraft and spacecraft science
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• v.4 no.4
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• pp.353-369
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• 2017

Flutter is a dangerous phenomenon encountered in flexible structures subjected to aerodynamic forces. This includes aircraft, buildings and bridges. Flutter occurs as a result of interactions between aerodynamic, stiffness, and inertia forces on a structure. In an aircraft, as the speed of the flow increases, there may be a point at which the structural damping is insufficient to damp out the motion which is increasing due to aerodynamic energy being added to the structure. This vibration can cause structural failure, and therefore considering flutter characteristics is an essential part of designing an aircraft. Scientists and engineers studied flutter and developed theories and mathematical tools to analyze the phenomenon. Strip theory aerodynamics, beam structural models, unsteady lifting surface methods (e.g., Doublet-Lattice) and finite element models expanded analysis capabilities. Periodic Structures have been in the focus of research for their useful characteristics and ability to attenuate vibration in frequency bands called "stop-bands". A periodic structure consists of cells which differ in material or geometry. As vibration waves travel along the structure and face the cell boundaries, some waves pass and some are reflected back, which may cause destructive interference with the succeeding waves. This may reduce the vibration level of the structure, and hence improve its dynamic performance. In this paper, for the first time, we analyze the flutter characteristics of a wing with a periodic change in its sandwich construction. The new technique preserves the external geometry of the wing structure and depends on changing the material of the sandwich core. The periodic analysis and the vibration response characteristics of the model are investigated using a finite element model for the wing. Previous studies investigating the dynamic bending response of a periodic sandwich beam in the absence of flow have shown promising results.