• Journal of the Korean Ceramic Society
• /
• v.44 no.1 s.296
• /
• pp.32-36
• /
• 2007

Zinc gallate $(ZnGa_2O_4)$ thin film phosphors have been formed on ITO glass substrates by a sol-gel spinning coating method. For the formation of the film phosphors, the starting materials of zinc acetate dihydrate, gallium nitrate hydrate and 2-methoxyethanol as a solution were used. The thin films deposited were firstly dried at $100^{\circ}C$ and fired at $500^{\circ}C\;or\;600^{\circ}C$ for 30 min and then, annealed $500^{\circ}C\;or\;600^{\circ}C$ at for 30 min under an annealing atmosphere of 3% $H_2/Ar$. The thin films deposited on ITO glass plates showed the (220), (222), (400), (422), (511), and (440) peaks of spinel structure as well as the (311) peak indicating a standard powder diffraction pattern. The surface morphologies of the thin film phosphors were observed with a firing and an annealing condition. The $ZnGa_2O_4$ film phosphors showed the blue emission spectra around 410 nm as well as the emission spectra in the UV region (360-380 nm).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2003.07b
• /
• pp.732-734
• /
• 2003

A solvothermal synthetic method to $BaTiO_3$ nanoparticle has been investigated in toluene solution with $BaTi(OR)_6$ as precursor. A precursor prepared from barium metal with toluene, isopropanol and titanium isopropoxide was used as a starting material. Weight ratio of precursor to solvent prepared in the mixture are 5/100, 10/100, 20/100 and 50/100wt%. At the weight ratio of 50/100wt%, $BaTiO_3$ butterfly twin crystalline(${\fallingdotseq}100nm$) was obtained after synthesis at $250^{\circ}C$ for 20hrs in an autoclave. X-ray diffraction and transmission electron microscopy showed that the product of 50/100wt% has crystallization. At 5/100, 10/100, and 20/100wt%, however, red colloidal solution was obtained after synthesis and crystalline phase of $BaTiO_3$ was not produced.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.10 no.2
• /
• pp.59-65
• /
• 1990

This study investigates the effects of human impact and precipitation on groundwater flow conditions at a small area in Dejima Upland using a transient three-dimensional simulation. To show the utility of the transient three-dimensional model, the results of the numerical model are compared with those of Theis problem for which analytical solution is available. It appears that over the time period studied, the results of the model agree well with the analytical solution. Simulation is undertaken for a period of 30days starting from May 1st, when irrigation starts. Groundwater flow patterns determined by a numerical model are presented in the form of plotted potential lines and discussed. Results of simulation clearly indicate that the groundwater flow system should be analysed using a transient three-dimensional model, especially for the region which is effected by human impact.

• Journal of the Korean Electrochemical Society
• /
• v.8 no.1
• /
• pp.42-46
• /
• 2005

It has been known that the synthesis of the cathode materials for the lithium rechargeable batteries by the sol-gel process has many advantages over the conventional solid-state method. It has been, however, a continuing issue that new additional steps should be introduced to commercialize this process. In this work, spray drying was introduced to the existing sol-gel process as a continuous mass production method of the pre-heat treatment precursor materials. The precursors of $LiCoO_2$ and $LiNi_{0.8}Co_{0.2}O_2$ were continuously produced through spray drying from the solution containing stoichiometric amount of lithium, cobalt, and nickel sources as well as a chelating agent. The process variables, such as pH of the starting solution, spray drying conditions, and calcination conditions were optimized. The XRD pattern for the synthesized material indicated a good crystallinity with a layered structure.

• Journal of the Korean Applied Science and Technology
• /
• v.31 no.1
• /
• pp.50-58
• /
• 2014

A novel fullerene derivative with photoresponsive azobenzene group was designed and synthesized, and its photoresponsive properties were reported. Starting from 4-nitrophenol, compound 1, which is containing fullerene moiety connected to azobenzene group through covalent linkage was synthesized by 5 steps. All the intermediates and the final compound were characterized by $^1H$, $^{13}C$-NMR, FAB-Mass or elemental analysis. Compound 1 exhibited the expected photoresponsive behavior. Chloroform solution($10^{-5}M$) of it served to maximize the absorption at 351 nm corresponding to the trans-azobenzene chromophore. Irradiation of this solution with 365 nm light resulted in photoisomerization to cis-azobenzene, as evidenced by decrease in the absorbance at 351 nm and an increase in absorbance at 450nm. A photostationary state was reached within about 150 s. Thermal reversion to the original spectrum was observed over the course of about 6 h at room temperature in the dark. However, exposure to bright sun light for about 5 s also effect almost complete reversion to the trans-isomer. This indicates that there is no strong steric influence on the trans-cis reversible isomerization of compound 1.

• Structural Engineering and Mechanics
• /
• v.38 no.2
• /
• pp.211-229
• /
• 2011

In this paper, we present a new explicit procedure using periodic cubic B-spline interpolation polynomials to solve linear and nonlinear dynamic equation of motion governing single degree of freedom (SDOF) systems. In the proposed approach, a straightforward formulation was derived from the approximation of displacement with B-spline basis in a fluent manner. In this way, there is no need to use a special pre-starting procedure to commence solving the problem. Actually, this method lies in the case of conditionally stable methods. A simple step-by-step algorithm is implemented and presented to calculate dynamic response of SDOF systems. The validity and effectiveness of the proposed method is demonstrated with four examples. The results were compared with those from the numerical methods such as Duhamel integration, Linear Acceleration and also Exact method. The comparison shows that the proposed method is a fast and simple procedure with trivial computational effort and acceptable accuracy exactly like the Linear Acceleration method. But its power point is that its time consumption is notably less than the Linear Acceleration method especially in the nonlinear analysis.

• Journal of the Korean Ceramic Society
• /
• v.37 no.7
• /
• pp.665-672
• /
• 2000

The ferroelectric YMnO3 thin films were prepared by MOD(metal-organic decomposition) method with Y- and Mn-acetylacetonate as starting materials. Thin films were grown on various substrates by spin-coating technique. The crystalline phases of the thin films were identified by X-ray diffractometer as a function of heat-treatment temperature, pH of coating solution and substrate. In addition, the effect of Mn/Y molar ratio(0.8~1.2) on the formation of hexagonal-YMnO3 phase was investigated. In forming highly c-axisoriented hexagonal-YMnO3 single phase, the Pt coated Si substrate was more effective than the bare Si substrate, and the optimum heat-treatment condition was at 82$0^{\circ}C$ for 30 min. Higher Mn/Y molar ratio within 0.8~1.2 and pH of YMnO3 precursor solution within 0.5~2.5 favored formation of ferroelectric hexagonal phase rather than orthorhombic phase. Leakage current density of the hexagonal-YMnO3 thin film formed on Pt(111)/TiO2/SiO2/Si substrate was low enough as 0.4~4.0$\times$10-8(A/$\textrm{cm}^2$) at 5 V and its remanent polarization(Pr), calculated from the P-E hysteresis loop, was 3 nC/$\textrm{cm}^2$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2007.11a
• /
• pp.339-339
• /
• 2007

Metal coating on ceramic powder has long been attracting interest for various applications such as superconductor where the brittle nature of high temperature ceramic superconductor was complemented by silver coating and metalloceramics where mechanical property improvement was achieved via electroless plating. More recently it has become of great interest in embedded passive device applications since metal coating on ceramic particles may result in the enhancement of the dielectric properties of ceramic-polymer composite capacitors. In our study, nickel ion-containing solution was used for coating commercial capacitor-grade $BaTiO_3$ powder. After filtering process, the powder was dried and heat-treated in 5% forming gas at $900^{\circ}C$. XRD and TEM were utilized for the observation of crystallization behavior and morphology of the particles. It was found that the nickel coating characteristics were strongly dependent on the several parameters and processing variables, such as starting $BaTiO_3$ particle size, nickel source, solution chemistry, coating temperature and time. In this paper, the effects of these variables on the coating characteristics will be presented in some detail.

• Information Systems Review
• /
• v.5 no.2
• /
• pp.183-202
• /
• 2003

In this paper, we designed an interoperability evaluation system based on technical reference model, HanTRM (Technical Reference Model) and the information technology architecture methodology, TAProcess (Technical Architecture Process). TAProcess provides standardized procedure and methodology for the efficient installation, management and operation of information technology. HanTRM can be used as a referencial basic framework for all organizations which are starting to make technical reference model. We propose a method that utilize HanTRM and a procedure that evaluates interoperability between information systems to design interoperbility evaluation system. So, this interoperbility evaluation system will be more usefully applied to organizations.

• Bulletin of the Korean Chemical Society
• /
• v.12 no.1
• /
• pp.61-67
• /
• 1991

Conformational free energy calculations using an empirical potential function and the hydration shell model (a program CONBIO) were carried out on the neutral L-ascorbic acid (AA) in the unhydrated and hydrated states. The conformational energy was minimized from starting conformations which included possible conformations of six torsion angles in the molecule. The conformational entropy of each low energy conformation in both states was computed using a harmonic approximation. From the analysis of conformational free energies for AA in both states, intramolecular hydrogen bonds (HBs) are proved to be an essential factor in stabilizing the overall conformations, and cause the conformations in both states to be quite different from those in crystal. In the case of hydrated AA, there is a competition between HBs and hydration, and the hydration around the two hydroxyl groups attached to the acyclic side chain forces the molecule to form less stable HBs. The hydration affects strongly the conformational energy surfaces of AA. Several feasible conformations obtained in this work indicate that there exists an ensemble of several conformations in aqueous solution. The calculated probable conformations for the rotation about the C5-C6 bond of the acyclic side chain are trans and gauche +, which are in good agreement with results of NMR experiment.