• Journal of the Korean Chemical Society
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• v.35 no.6
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• pp.612-616
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• 1991

Metachromatic behavior of methylene blue (MB) in solutions of aqueous sodium dodecyl sulfate (SDS), chondroitin sulfate and L-${\alpha}$-lecithin vesicle at $18~52^{\circ}$C has been studied by absorption spectroscopy. MB was clustered in the matrix of the vesicle with high concentration of L-${\alpha}$-lecithin. The metachromasy of MB was found to be independent of phase transition temperature of vesicles. These results suggest that the dyes were aggregated on the hydrophilic surfaces of vesicle. In the vesicular system, the metachromatic effect of MB was dramatically decreased in the presence of hexadecyltrimethylammonium bromide (CTAB) than SDS. It is estimated that the intercalation site of these surfactants on vesicle surfaces was different, that is, the intercalation of CTAB was more effective than that of SDS.

• Proceedings of the Korean Society of Applied Pharmacology
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• 1998.11a
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• pp.134-134
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• 1998

The modulation of glycosidase activity by inhibitors is of great interest. Such compounds have been shown to be important tools in mechanistic studies on glycohydrolase as well as having promising therapeutic application. An ${\alpha}$-glucosidase inhibitor was isolated from culture filterates of Penicillium sp. The inhibitor was active against ${\alpha}$-glucosidase isolated from yeast and porcine small intestine. However, it showed no inhibition to Aspergillus ${\alpha}$-galactosidase, Escherichia coli ${\beta}$-galactosidase, and jack bean ${\alpha}$-mannosidase. The inhibitor was highly soluble in ether, methanol and chloroform. The inhibitor was purified using silica gel, Sephadex LH-20 column chromatography and reverse-phase HPLC. The inhibitory compound designated PA-7(IC$\sub$50/=35$\mu\textrm{g}$) was obtained as white powder. The structure of PA-7 was determined with spectroscopic data of EI-MS, FAB-MS, $^1$H, and $\^$13/C NMR. The inhibitor has a diketopiperazine moiety.

• Journal of Pharmaceutical Investigation
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• v.20 no.3
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• pp.135-144
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• 1990

The effects of bile salts (BS) on the stability of dioleoylphosphatidylethanolamine (DOPE) liposomes were investigated, observing apparent absorbance of vacant liposomes and calcein release from entrapped liposomes. Unilamellar liposomes were prepared by using a small quantity of palmitoly-immunoglobulin G(IgG) ($2.5{\times}10^{-4}$ mo1/lipid mol) to stabilize the bilayer phase of the unsaturated DOPE which by itself does not form stable liposomes. The destabilization of PE immunoliposomes by papain, clearly demonstrates that the IgG is essential for stabilization of PE bilayer. Approximately 4% of the entrapped calcein was released from the PE liposomes after 1 hr from liposome formation. Calcein release and absorbance of liposomes depended on the BS/lipid ratio because of the solubilization of lipid molecule in bilayer and the formation of mixed micelles. At very low BS concentrations, the incorporation of BS induced BS/lipid aggregates in the outer vesicles monolayer, while high BS concentrations, mixed micelles were formed. Chelate and its conjugates as $3{\alpha},\;7{\alpha},\;12{\alpha}-trihydroxy$ BS induce the concentration of the $3{\alpha}$, $12{\alpha}-dihydroxy$ BS at half-maximal solubilization of immunoliposomes to approximately 2.5-, or 5-fold. Conjugation of BS with glycine or taurine slightly enhanced their capacities to perturb membranes.

• Korean Journal of Veterinary Research
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• v.35 no.3
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• pp.447-458
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• 1995

This study was carried out to characterize nonadrenergic, noncholinergic(NANC) relaxation of porcine retractor penis(PRP) muscle induced by electrical field stimulation(EFS) and to investigate the actions of niric oxide(NO) and vasoactive intestinal polypeptide(VIP) as candidates for NANC neurotransmitters. Biphasic relaxations of PRP muscle were induced by EFS to NANC nerve. Rapid-phase relaxation was observed at low frequency(0.5-16Hz) and slow-phase relaxation followed during high frequency(8-60Hz). Both relaxations were frequency-dependent and TTX($1{\times}10^{-6}M$)-sensitive. L-NAME($2{\times}10^{-5}M$) inhibited the rapid-phase relaxation, but not the slow-phase relaxation. The inhibition of the rapid-phase relaxation with L-NAME was reversed by L-arginine ($1{\times}10^{-3}M$) but not by D-arginine($1{\times}10^{-3}M$). Methylene blue($4{\times}10^{-5}M$) reduced the rapid-phase relaxation. Exogenous No(ExoNO, $1{\times}10^{-5}-1{\times}10^{-4}M$) induced dose-dependent relaxations of PRP muscle. Oxyhemoglobin($5{\times}1^{-5}M$) blocked the relaxation induced by ExoNO and inhibited EFS-induced relaxation. Hydroquinone($1{\times}10^{-4}M$) also abolished the relaxation induced by ExoNO, but did not affect EFS-induced relaxation. L-NAME resistant slow-phase relaxation to EFS was inhibited by ${\alpha}$-chymotrypsin(2.5 U/ml). Both methylene blue($4{\times}10^{-5}M$) and Nethylmaleimide($1{\times}10^{-4}M$) reduced the slow-phase relaxation by EFS. [4-Cl-D-$Phe^6$, $Leu^{17}$]-VIP($3{\times}10^{-6}M$) inhibited the slow-phase relaxation by EFS. External applications of VIP ($1{\times}10^{-7}M$) caused relaxations that were simillar to the L-NAME resistant slow-phase relaxations induced by EFS, and relaxant effects of exogenous VIP were blocked by ${\alpha}$-chymotrypsin(2.5 U/ml).

• Microbiology and Biotechnology Letters
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• v.17 no.5
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• pp.412-420
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• 1989

To know how the ribosomes involved in secretory protein synthesis were attached to the cytoplasmic membrane in Bacillus amyloliquefaciens, the cells were treated with puromycin combinated with magnesium at the logarithmic phase, and the variation of cell-bound and extracellular $\alpha$-amylase activity was assayed for determining the $\alpha$-amylase translocation blocking through the cytoplasmic membrane. In the abnormal $\alpha$-amylase producing mutant in which the C-terminal of the $\alpha$-amylase structure was deleted, B. umytotiquefaciens CH10-2, the $\alpha$-amylase was translocated normally through the cytoplasmic membranes, and the translocation blocking by puromycin was revealed to have a similar pattern as that in the wild type. This means that the C-terminal part of the enzyme structure may not have a signal for secretion. The cell death of the logarithmic phase cells in both strains was not affected much under 20$\mu\textrm{g}$/$m\ell$ of puromycin, however, the $\alpha$-amylase translocation was blocked markedly under less than 10$\mu\textrm{g}$/$m\ell$ of the puromycin concentration. The blocking of the enzyme secretion by puromycin may be due to the detachment of the ribosomes from cytoplasmic membranes by disturbing the nascent polypeptide synthesis. Further evidence for confirming this was that the detachment was increased in 50 mM of magnesium ion because the extracellular $\alpha$-amylase activity was decreased more under this condition. If the cells were treated with trypsin combinated with Iysozyme, the extracellular $\alpha$-amylase activity from the cultured medium was reduced markedly, however, the activity from the cells treated with trypsin only was not reduced. This means that the nascent polypeptides protruding from the cytoplasmic membrane were sensitive to the trypsin digestion, whereas the matured ones were not. Therefore, the protruding polypeptides from the cytoplasmic membranes may be truncated by trypsin before forming their final tertiary structures by folding in the cell wall layer.

• Journal of the Korean Society for Heat Treatment
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• v.27 no.3
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• pp.115-120
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• 2014

Microstructural features were comparatively investigated in AZ91 (Mg-9%Al-1%Zn) and AZ91-0.5%Sn alloys, in order to clarify the reason for the enhancement in room temperature tensile properties by the addition of small amount of Sn in Mg-Al-based alloy. In as-cast state, the Sn-containing alloy showed increased YS, UTS and elongation than the Sn-free alloy. The microstructural examination revealed that various factors including finer cell size, reduction of lamellar (${\alpha}+{\beta}$) phase and morphological change of bulky ${\beta}$ phase from partially divorced shape to fully divorced shape, are likely to be responsible for the improvement in tensile properties for the Sn-containing alloy. It is noted that two alloys showed similar tensile properties after solution treatment. This implies that microstructural evolution related to the ${\beta}$ phase plays a key role in better tensile properties in the Sn-containing alloy.

• Journal of international Conference on Electrical Machines and Systems
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• v.3 no.3
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• pp.264-271
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• 2014

Virtual synchronous generator (VSG) in single-phase to interface distributed renewable energy resources is investigated in this paper. Mathematical models and numerical analysis are utilized to illustrate the features of the VSG. Enhanced control strategy is presented to ensure the performance of the VSG. Besides, a second order generalized integer (SOGI) is employed to calculate the instantaneous output power of the VSG in virtual ${\alpha}{\beta}$ frame. By the means of a phase-locked loop based scheme, the VSG can seamlessly transform between islanded and grid-tied modes, which can meet the requirements of micro-grid. At last, the validation and the proposed approach are verified by the simulated results using PSCAD/EMTDC.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.482-483
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• 2006

Synthesis of iron nanopowder by room-temperature electrochemical reduction process of ${\alpha}-Fe_2O_3$ nanopowder was investigated in terms of phase evolution and microstructure. As process variables, reduction time and applied voltage were changed in the range of $1{\sim}20$ h and $30{\sim}40$ V, respectively. From XRD analyses, it was found that volume of Fe phase increased with increasing reduction time and applied voltage, respectively. The crystallite size of Fe phase in all powder samples was less than 30 nm, implying that particle growth was inhibited by the reaction at room temperature. Based on the distinct equilibrium shape of crystalline particle, phase composition of nanoparticles was identified by TEM observation.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.3
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• pp.135-139
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• 2018

In this study, we report the effect of VI/III ratio on ${\alpha}-Ga_2O_3$ epilayer on sapphire substrate by halide vapor phase epitaxy. The surface of ${\alpha}-Ga_2O_3$ epilayer grown with various VI/III ratios was flat and crack-free. To analyze the optical properties of the ${\alpha}-Ga_2O_3$ epilayers, the transmittance and an optical band gap were measured. The optical band gap was shown to be around 5 eV and showed a proportional increase in VI/III ratios. To determine the crystal quality of alpha gallium oxide grown with a ratio of 23, closed to the theoretical optical band gap, the FWHM was measured by HR-XRD. The calculated dislocation density of screw and edge were $1.5{\times}10^7cm^{-2}$ and $5.4{\times}10^9cm^{-2}$, respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.32 no.5
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• pp.426-431
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• 2019

In this study, we report the effect of pre-treatment of alpha-$Ga_2O_3$ grown on a sapphire substrate by halide vapor phase epitaxy (HVPE). During the pre-treatment process, 10 sccm of GaCl gas was injected to the sapphire substrate at $470^{\circ}C$. The surface morphologies of the alpha-$Ga_2O_3$ layers grown with various pre-treatment time (3, 5, and 10 min) were flat and crack-free. The transmittance of the alpha-$Ga_2O_3$ epi-layers was measured to analyze their optical properties. The transmittance was over 80% within the range of visible light. The strain in the alpha-$Ga_2O_3$ grown with a pre-treat 5 min was measured, and was found to be close to the theoretical XRD peak position. This can be explained by the reduction of strain having caused a lattice mismatch between the alpha-$Ga_2O_3$ layer and sapphire substrate. The calculated dislocation density of the screw and edge were $2.5{\times}10^5cm^{-2}$ and $8.8{\times}10^9cm^{-2}$, respectively.