• Korean Journal of Materials Research
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• v.4 no.5
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• pp.541-549
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• 1994

The crystallization behavior and structural change of amorphous $PbTiO_{3}$ precursors prepared by coprecipitation method were investigated by XRD, Raman spectra, TEM, and RDF. The precursors were prepared at $45^{\circ}C$ and pH of 9 from a mixed solution of lead nitrate and titanium tetrachloride derived using $H_2O_2$ or $NH_4NO_3$ as an ion stabilizer. The activation energy and temperature for crystallization of the coprecipitate prepared using $NH_4NO_3$ as an ion stabilizer were lower than that derived from the solution containing $H_2O_2$ stabilizer. The amorphous coprecipitate transformed to transient phase and then to crystalline $PbTiO_{3}$. Average interatomic distances of amorphous states decreased with increasing heat-treatment temperature.

• Journal of applied mathematics & informatics
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• v.17 no.1_2_3
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• pp.605-614
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• 2005

We show that an Artinian O-sequence $h_0,h_1,{\cdots},h_{d-1},h_d\;=\;h_{d-1},h_{d+l}\;>\;h_d$ of codimension 3 is not level when $h_{d-1}\;=\;h_d\;=\;d + i\;and\;h{d+1}\;=\;d+(i+1)\;for\;i\;=\;1,\;2,\;and\;3$, which is a partial answer to the question in [9]. We also introduce an algorithm for finding noncancelable Betti numbers of minimal free resolutions of all possible Artinian O-sequences based on the theorem of Froberg and Laksov in [2].

• Journal of the Korean Ceramic Society
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• v.28 no.6
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• pp.465-470
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• 1991

AlN powder was synthesized by carbothermal reduction and nitridation of aluminum hydroxides precipitated in 5∼11 pH range from Al2(SO4)3$.$18H2O aqueous solution. Nitridation reactivity of hydroxide, which depends on precipitation pH, reaction temperature and time, was examined by XRD analysis at 1200∼1350$^{\circ}C$ and compared with that of commercial ${\alpha}$-Al2O3. Hydroxides obtained at higher pH could be more easily nitridated and, considering DTA/TG and BET results, the reason seems to be specific surface area difference of reactants depending on the content of decomposed structural water and the transition rate from transition-Al2O3 to ${\alpha}$-Al2O3.

• BMB Reports
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• v.48 no.11
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• pp.636-641
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• 2015

There are controversial findings regarding the roles of nuclear factor (erythroid-derived 2)-like 2 (Nrf2)/heme oxygenase-1 (HO-1) pathway on bone metabolism under oxidative stress. We investigated how Nrf2/HO-1 pathway affects osteoblast differentiation of MC3T3-E1 cells in response to hydrogen peroxide (H₂O₂), N-acetyl cysteine (NAC), or both. Exposing the cells to H₂O₂ decreased the alkaline phosphatase activity, calcium accumulation, and expression of osteoblast markers, such as osteocalcin and runt-related transcription factor-2. In contrast, H₂O₂ treatment increased the expression of Nrf2 and HO-1 in the cells. Treatment with hemin, a chemical HO-1 inducer, mimicked the inhibitory effect of H₂O₂ on osteoblast differentiation by increasing the HO-1 expression and decreasing the osteogenic marker genes. Pretreatment with NAC restored all changes induced by H₂O₂ to near normal levels in the cells. Collectively, our findings suggest that H₂O₂-mediated activation of Nrf2/HO-1 pathway negatively regulates the osteoblast differentiation, which is inhibited by NAC.

• Journal of the Korean Ceramic Society
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• v.31 no.8
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• pp.934-940
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• 1994

Fibers of ZrO2-SiO2 system were prepared from the hydrolysis and condensation of Si(OC2H5)4 and Zr(OnC3H7)4 with different H2O/alkoxide molar ratios. It was found that fibers could be drawn in the viscosity range of 1~100 poise from HCl catalyzed solutions with lower water contents of the mole ratio H2O/alkoxide, r 2. The fibrous gels were converted into the corresponding oxide glass fibers by heating at 80$0^{\circ}C$. Mechanical test was performed on E, A and 20ZrO2-80SiO2 glass fibers reinforced cement in order to investigate the flexural strength. The flexural strength value of 20ZrO2-80SiO2 glass fibers reinforced cement was greater than those of E and A. The chemical durability of the fibers in alkaline solutions increased with ZrO2 content. The weight loss due to the corrosion by 2N-NaOH solutions at $25^{\circ}C$ for 160 hours was about 0.31$\times$10-2 mg/dm2 for the 20ZrO2-80SiO2 glass fibers, which was superior to that of Vycor glass.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.1
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• pp.46.3-47
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• 2017

We performed simultaneous VLBI observations of H2O 616-523 (22.2 GHz) and SiO v=1, 2, J=1-0 (43.1, 42.8 GHz) and v=1, J=2-1, J=3-2 (86.2, 129.3 GHz) masers toward VX Sagittarius using the Korean VLBI Network (KVN). The astrometrically registered maps of the 22.2 GHz H2O and 43.1, 42.8, 86.2 SiO masers were successfully obtained at two epochs of 2016 February 27 and 2016 March 27 by adopting the Source Frequency Phase Referencing (SFPR) method. In addition we detected 129.3 Ghz SiO maser at second epoch. These results make it possible to determine the accurate position of central star as a dynamical center of 22.2 GHz H2O maser and relative locations of 43.1, 42.8, 86.2, 129.3 GHz SiO masers. In addition, it is possible to investigate the morphological and kinematic variations of clumpy structures from SiO maser to H2O maser regions in future together with the development of asymmetric structure of H2O maser region.

• Proceedings of the KIEE Conference
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• 1997.07d
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• pp.1537-1539
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• 1997

In this study, the dielectric properties of $Pb(Mg_{1/3}Nb_{2/3})O_3-PbTiO_3$ Ceramics have been investigated as a addition of the amount of $MnO_2(0{\leq}x{\leq}0.9wt%)$. The Temperature-dependant dielectric characteristics of 0.9PMN-0.1PT relaxor ferroelectric system were improved by enhencing the extent of the diffuse phase transition(DPT). The maximum dielectric permittivity decreased by substitution $MnO_2$ and the dielectric loss decreased with increasing $MnO_2$ substitution amount. It is expected decreasing in inner heat energy for temperature with increasing $MnO_2$ substitution.

• Journal of the Korean Ceramic Society
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• v.44 no.9
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• pp.471-476
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• 2007

The hydration mechanism of the $3CaO{\cdot}Al_2O_3-CaSO_4{\cdot}2H_2O$ system in the presence of alkali sulfates has been investigated. The early hydration rate of $3CaO{\cdot}Al_2O_3$ was accelerated by the addition of $Na_2SO_4$ and $K_2SO_4$. This is closely related to the formation of syngenite $(CaSO_4{\cdot}K_2SO_4{\cdot}H_2O)$, and the U-phase added $K_2SO_4$ and $Na_SO_4$ in the $3CaO{\cdot}Al_2O_3-CaSO_4{\cdot}2H_2O$ system, respectively. The formation of the rigid syngenite and U-phase structure led to rapid setting and decreases the sulfate content in the liquid phase of the hydrating cement to the extent that it cannot adequately retard the hydration of $3CaO{\cdot}Al_2O_3$. In case of the alkali sulfate not added to the $3CaO{\cdot}Al_2O_3-CaSO_4{\cdot}2H_2O$ system, the ettringite was transformed to monosulfoaluminate immediately after the consumption of gypsum. However, when the alkali sulfates were added to this system, the ettringite did not transform to monosulfoaluminate immediately even though the gypsum was completely consumed. There was a stagnation period to transform to the monosufoaluminate after the consumption of gypsum because the syngenite and U-phase remained as the sulfate source.

• Journal of the Korean Chemical Society
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• v.44 no.1
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• pp.52-59
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• 2000

The reaction gel mixtures of molar composition (0.3${\sim}$2.1) $SiO_2:\;(0.10{\sim}0.50)\;CTABr:\;0.15{\sim}0.23)\;TMAOH:\;(20{\sim}100)\;H_2O$ we prepared and then aged at room temperature for a definite duration. The aged gel is reacted hydrothermally at $150^{\circ}C$ for 2 days. The pH of reaction gel during synthesis is strongly influenced by the concentration of TMAOH and silica source. The pH change affects the phase of product, which is monitored by X-ray diffractometer. With increasing the TMAOH ratio from 0.19 to 0.23, the gel becomes more basic, and the product involves more lamellar phase. At TMAOH ratio lower than 0.19, the hexagonal phase is lower with decrease of pH. The content of the lamellar phase increases at a lower $SiO_2$ concentration, and higher concentrations have a clear detrimental effect on the crystallinity ofMCM-41 due to an excess silica source. The best quality MCM-41 is synthesized from a reaction gel composition of $1.0\;SiO_2:\;0.27\;CTABr:\;0.19\;TMAOH:\;40\;H_2O$. The pH values of this gel, aged one for 24 hr, and reacted one at $150^{\circ}C$ for 2 days are 12.3, 11.5, and 10.5, respectively. Gel aging for 24 h is essential for preparing high quality MCM-41. Longer aging causes a decrease of hexagonal phase.

• Journal of Korean Society of Water and Wastewater
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• v.12 no.3
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• pp.55-64
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• 1998

The degradation efficiency of chlorophenolic compounds in $TiO_2/H_2O_2$ combined system was compared with that of in $TiO_2$ sole system. As a result, the addition of hydrogen peroxide in photocatalytic oxidation reaction greatly enhanced the degradation efficiency of chlorophenolic compounds due to the availability of the hydroxyl radical formed on the $TiO_2$ surface. The hydrogen peroxide under UV illumination produces hydroxyl radicals that appear to be another source of hydroxyl radical formation. These results indicated the $TiO_2/H_2O_2$ combined system shows higher degradation efficiency than the $TiO_2$ sole system. Compared to another oxidation reaction, hydrogen peroxide assisted photocatalytic oxidation is more promising in practical aspect.