• Applied Science and Convergence Technology
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• v.24 no.3
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• pp.47-52
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• 2015

The correlation between admittance and dielectric spectroscopy of dielectric relaxation in lead scandium noibate, have been investigated. Lead scandium niobate, with composition $PbSc_{0.5}Nb_{0.5}O_3$, was prepared by conventional solid state synthesis. Conductance Y'(G), susceptance Y"(B) and capacitance C of lead scandium niobate as a function of frequency and temperature were measured. From the temperature-dependence of RLC circuit, insight into physical significance of the dielectric properties of lead scandium niobate is obtained. The relative strong frequency dependent of dielectric properties in lead scandium niobate is observed, and the phase transition occurred at a broad temperature region. Also, the value of critical exponent ${\gamma}$=1.6 showed on heating process. The long relaxation times part enlarged diffuse by conductivity effects with increasing temperature, and the ordering between $Sc^{3+}$ and $Nb^{5+}$ in PSN influences complex admittance and dielectric properties. Confirmed the typical characteristic of lead-type relaxor in the Raman spectra of lead scandium niobate and major ranges are between 400 and $900cm^{-1}$.

• The KSFM Journal of Fluid Machinery
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• v.11 no.4
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• pp.7-13
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• 2008

The computational investigation is performed to find out the interaction of arc plasmas with surrounding materials and the thermal flow characteristics in a PASB (Puffer-Assisted Self-Blast) chamber, which is one of new breaking concepts in $SF_6$ switchgears. It is very important to define the flow and mass transfer happened during the full arcing history for further understanding complex physics inside the chamber. In this study, we have considered two diffusion processes by the hot arc plasma, one is PTFE nozzle ablation and the other is Cu electrode evaporation, simultaneously. It was found that the principle of the pressure-rise inside the chamber is confirmed by the computational results and the increase of the electrical conductivity of the residual gas near current zero is critical to the chamber design.

• Journal of the Korean Ceramic Society
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• v.47 no.1
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• pp.47-53
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• 2010

Ceramics with perovskite-type structure are interesting functional materials for several energy conversion processes due to their flexible structure and a variety of properties. Prominent examples are electrode materials in fuel cells and batteries, thermoelectric converters, piezoelectrics, and photocatalysts. The very attractive physical-chemical properties of perovskite-type phases can be modified in a controlled way by changing the composition and crystallographic structure in tailor-made soft chemistry synthesis processes. Improved thermoelectric materials such as cobaltates with p-type conductivity and n-type manganates are developed by following theoretical predictions and tested to be applied in oxidic thermoelectric converters.

• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.144-145
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• 2003

A feasibility study on the alternating jet flow under the static electromagnetic field was carried out. When a fluid with electrical conductivity lies in the static electromagnetic field and moves electric current occurs in the fluid. Due to the electromagnetic field and the electric current, lorentz force generates in the fluid, which undergo the 'breaking' effect to the fluid. In order to simulate the complex fluid flow in the magnetic field, electromagnetic and fluid flow analysis need to be solved simultaneously. In the present study, a SOLA (SOLution Algorithm) scheme was used in order to calculate electromagnetic and fluid flow field. Jet flow without an electromagnetic field was compared with analytical solution in order to validate the flow analysis scheme. Effect of jet velocity on the flow pattern down the jet was investigated.

• Journal of the Korean Chemical Society
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• v.25 no.3
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• pp.177-182
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• 1981

Benzoylpyridinium and lutidinium salts containing$ [MoO(NCS)_5]^{2-}$ have been synthesized. The complexes have been characterized by spectroscopic, magnetic susceptibility and conductivity studies. Benzoylpyridinium and lutidinium oxopentaisothiocyanatomolybdates(Ⅴ) arise from d-d and charge transfer transitions. The magnetic moments of the complexes are close to the spin-only values. The complex anions are mononuclear containing N-bonded $NCS^-$ ligand.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.255.2-255.2
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• 2014

Electrode erosion is indispensable for atmospheric plasma systems, as well as for switching devices, due to the high heat flux transferred from arc plasmas to contacts, but experimental and theoretical works have not identified the characteristic phenomena because of the complex physical processes. Our investigation is concerned with argon free-burning arcs with anode erosion at atmospheric pressure by computational fluid dynamics (CFD) analysis. We are also interested in the energy flux and temperature transferring to the anode with a simplified unified model of arcs and their electrodes. In order to determine two thermodynamic quantities such as temperature and pressure and flow characteristics we have modified Navier-Stokes equations to take into account radiation transport, electrical power input and the electromagnetic driving forces with the relevant Maxwell equations. From the simplified self-consistent solution the energy flux to the anode can be derived.

• Proceedings of the Korean Fiber Society Conference
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• 2003.10b
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• pp.34-37
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• 2003

The development and improvement of advanced fuel cell systems is a major topic of current research, since fuel cells are considerably more efficient than other energy converters$^1$. In proton exchange membrane fuel cell and direct methanol fuel cell the polymer membrane represents a key component. The membrane materials fulfill complex requirements. It has to combine electrochemical stability, workability, high ionic conductivity, low permeation of the reactants (methanol etc.) (omitted)

• Journal of the Optical Society of Korea
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• v.20 no.3
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• pp.431-434
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• 2016

Tris-HCl buffer solution is extensively used in biochemistry and molecular biology to maintain a stable pH for biomolecules such as nucleic acids and proteins. Here we report on the high-precision THz dielectric spectroscopy of a 10 mM Tris-HCl buffer. Using a double Debye model, including conductivity of ionic species, we measured the complex dielectric functions of Tris-HCl buffer. The fast relaxation time of water molecules in Tris-HCl buffer is ~20% longer than that in pure water while the slow relaxation time changes little. This means that the reorientation dynamics of Tris-HCl buffer with such a low Tris concentration is quite different from that of pure water.

• Journal of the Korean Solar Energy Society
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• v.23 no.4
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• pp.63-70
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• 2003

It is very important to improve the insulation performance of curtain wall anchoring unit since it is composed of materials with high thermal conductivity, such as aluminium, steel and so on. This study aims to evaluate the heating energy performance and economical efficiency of various alternatives which are different in position and material of insulation. As results, alternative of inserting the urethane washer & pad and coating the anchoring unit with urethane foam can improve the heating energy performance and L.C.C(Life Cycle Cost) by 6.33% and 0.95%, respectively, as compared with the existing case.

• Journal of the Korean Ceramic Society
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• v.43 no.12 s.295
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• pp.758-763
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• 2006

Perovskites with nominal compositions $Ln_{0.8}Sr_{0.2}CoO_{3-\delta}$ (Ln=Gd, Nd, Pr, Sm, or Yb) were fabricated as cathode materials using a solid-state reaction method for low-temperature operating Solid-Oxide Fuel Cells (SOFCs). X-ray diffraction analysis and microstructure observation for the sintered samples were performed. The ac complex impedance was measured in the temperature range of $600-900^{\circ}C$ in air and fitted with a Solartron ZView program. The crystal structure, microstructure, electrical conductivity, and polarization resistance of $Ln_{0.8}Sr_{0.2}CoO_{3-\delta}$ were characterized systematically.