• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.243-246
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• 1999

The displacement current measuring system used for detecting the dynamic behavior of monolayers at the air-water interface is described. It basically consists of a film balance, a pair of electrodes connected to each other through a sensitive ammeter. Here, one electrode is suspended in air and the other electrode is the water, With Maxwll-displacement-current-measuring method, the phase transitions of Poly(λ-benzyl- L-glutamate)(PBLG) on a water surface were detected, Displacement currents generated during the compression of monolayers of PBLG on the surface of water were investigated. As results, the displacement pick was generated when the area per molecule was about 15 $\AA$$^{2}$ in low pressure, and tit was generarted when the area per molecule about 27$\AA$$^{2}$ in high pressure.

• Nuclear Engineering and Technology
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• v.47 no.6
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• pp.669-677
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• 2015

A mechanistic model for void fraction prediction with improved interfacial friction factor in nearly horizontal tubes has been proposed in connection with the development of a condensation model package for the passive auxiliary feedwater system of the Korean Advanced Power Reactor Plus. The model is based on two-phase momentum balance equations to cover various types of fluids, flow conditions, and inclination angles of the flow channel in a separated flow. The void fraction is calculated without any discontinuity at flow regime transitions by considering continuous changes of the interfacial geometric characteristics and interfacial friction factors across three typical separated flows, namely stratified-smooth, stratified-wavy, and annular flows. An evaluation of the proposed model against available experimental data covering various types of fluids and flow regimes showed a satisfactory agreement.

• Journal of Power Electronics
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• v.15 no.4
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• pp.1035-1046
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• 2015

This study presents a practical implementation of a multi-mode two-phase interleaved boost converter for fuel cell electric vehicle application. The main operating modes, which include two continuous conducting modes and four discontinuous conducting modes, are discussed. The boundaries and transitions among these modes are analyzed with consideration of the inductor parasitic resistance. The safe operational area is analyzed through a comparison of the different operating modes. The output voltage and power characteristics with open-loop or closed-loop operation are also discussed. Key performance parameters, including the DC voltage gain, input ripple current, output ripple voltage, and switch stresses, are presented and supported by simulation and experimental results.

• Journal of Power Electronics
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• v.18 no.6
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• pp.1650-1658
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• 2018

Multilevel converters are being widely used in medium-voltage high-power applications including motor drive systems, utility power transmission, and distribution systems. Selective harmonic elimination (SHE) is a well-known modulation method to generate high quality output voltage waveforms. This paper presents a new simple practical method for generating a generalized five-level waveform without selected low order harmonics. This method is based on a phase-shifted expression for the SHE problem, which can analytically calculate the exact values of switching angles and the feasible modulation index range for three-level and five-level waveforms. The proposed method automatically determines the number of transitions between levels and generates proper output waveform without solving complex trigonometric equations. Due to the simplicity of the computational burden, the real-time implementation of the proposed algorithm can be performed by a simple processor. Simulation and experiment results verify the correctness and effectiveness of the proposed method.

• Bulletin of the Korean Chemical Society
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• v.6 no.1
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• pp.40-45
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• 1985

The thermal and optical properties of two new series of thermotropic, liquid crystalline compounds were studied by differential scanning calorimetry and on the hot-stage of a polarizing microscope. The first series contained two identical mesogenic units, 4-(p-phenylbenzoyloxy) benzoate moieties, at both ends of the polymethylene spacer of varying lengths and the second series, mesogenic units with different substituents and the hexamethylene group as the central spacer. A thermodynamic analysis of the phase transitions of the compounds was made and the results were discussed in relation to their chemical structures.

• Bulletin of the Korean Chemical Society
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• v.4 no.3
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• pp.143-148
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• 1983

Two series of thermotropic compounds were prepared and their thermal and liquid crystal properties were examined by differential scanning calorimetry and on the hot-stage of a cross-polarizing microscope. The first series of the compounds has two terminal mesogenic units based on unsubstituted and substituted p-(phenoxycarbonyl) phenyl ethers bracketing a central decamethylene spacer, and the second has 4-(p-phenylphenoxycarbonyl) phenyl ether moiety as the two terminal mesogenic units and central polymethylene spacers of varying lengths. A thermodynamic analysis of the phase transitions was made and explained in relation to structures and thermotropic behavior of the compounds.

• Bulletin of the Korean Chemical Society
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• v.19 no.9
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• pp.947-951
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• 1998

$K_2NiF_4$-type layered compounds of the ($C_nH_{2n+1}NH_3)_2SnCl_4$ (n=2, 4, 6, 8, and 10) system have been synthesized from a stoichiometric mixture of $SnCl_2$ and alkyl ammonium salt using a low temperature solution technique under the inert atmosphere condition. Their crystal structures are assigned to the orthorhombic system by X-ray powder diffraction analysis. The a and b cell parameters show small changes. However, the c parameter is varied significantly according to the increment of alkyl chains of the organic layer which is located between inorganic layers in the compounds. The conformational phase transitions of the compounds are studied by the DSC in the temperature range of 300 to 500 K. FT-IR and Raman spectra are analyzed in the ranges of 1300 to 4000 cm-1 and of 50 to 360 $cm^{-1}$ with Ar-laser (λ=514.5 nm) excitation, respectively. Photoluminescence phenomena are observed for some compounds. The bond-length of Sn-Cl is determined by the EXAFS spectroscopic analysis.

• Bulletin of the Korean Chemical Society
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• v.16 no.12
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• pp.1153-1162
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• 1995

The conformational details of β-lactose are investigated through molecular dynamics simulations in conjunction with the adiabatic potential energy map. The adiabatic energy map generated in vacuo contains five local minima. The lowest energy structure on the map does not correspond to the structure determined experimentally by NMR and the X-ray crystallography. When aqueous solvent effect is incorporated into the energy map calculation by increasing the dielectric constant, one of the local minima in the vacuum energy map becomes the global minimum in the resultant energy map. The lowest energy structure of the energy map generated in aquo is consistent with the one experimentally determined. Molecular dynamics simulations starting from those fivelocal minima on the vacuum energy map reveal that conformational transitions can take place among various conformations. Molecular dynamics simulations of the lactose and ricin B chain complex system in a stochastic boundary indicate that the most stable conformation in solution phase is bound to the binding site and that there are conformational changes in the exocyclic region of the lactose molecule upon binding.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.358-361
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• 1995

We have investigated the quasi-two-dimensional magnetism for the layered transition metal compound (C/sub n/H/sub 2n+1/NH/sub 3/)/sub 2/CuCl/sub 4/ (n=10, 14) in the high temperature regions by means of EPR (Electron Paramagnetic Resonance) and SQUID measurements. As a result, the magnetic transitions were reflected in the EPR linewidths and the magnetic suceptibilities in a sensitive manner. Fluctuations of the magnetic susceptibility and a similar variation of the .DELTA. g =(g/sub .parallel. -/g/sub .perp. /)g/sub .parallel. / value were also observed around the structural phase transition temperatures.

• Bulletin of the Korean Chemical Society
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• v.17 no.3
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• pp.274-278
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• 1996

Vanadium oxide-zirconia catalysts were prepared by dry impregnation of powdered Zr(OH)4 with aqueous solution of NH4VO3. The characterization of prepared catalysts was performed using 51V solid state NMR, XRD, and DSC. The addition of vanadium oxide up to 9 mol% to zirconia shifted the phase transitions of ZrO2 from amorphous to tetragonal toward higher temperatures due to the interaction between vanadium oxide and zirconia. On the basis of results of XRD and DSC, it is concluded that the content of V2O5 monolayer covering most of the available zirconia was 9 mol%. The crystalline V2O5 was observed only with the samples containing V2O5 content exceeding the formation of complete monolayer (9 mol%) on the surface of ZrO2.