• Journal of the Korean Ceramic Society
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• v.39 no.1
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• pp.38-44
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• 2002

Dispersion stability of nano-sized rutile TiO$_2$powder with acicular typed primary particle produced by homogeneous precipitation process at low temperatures was studied in aqueous and non-aqueous media in the presence of various electrolytes. The zeta potential measurements have shown that the addition of electrolytes to aqueous and non-aqueous dispersion media leads to charge reversal on TiO$_2$particle surface. The electrostatic repulsive forces acting on between TiO$_2$particles dispersed in non-aqueous media were found to be significantly greater than that in aqueous media, which relate closely to the physical properties of the organic solvents, such as viscosities and dielectric constants. The pH values, the concentration of electrolytes and the valence of the ions have changed greatly the surface potential of TiO$_2$ particles and have governed the dispersion behavior of TiO$_2$particles virtually.

• Journal of the Korean Society of Radiology
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• v.13 no.3
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• pp.445-451
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• 2019

The fluorescence intensity and fluorescence lifetime of $Ba_2GdV_3O_{11}$, a vanadate compound based on $Ba^{2+}$ ion, were investigated by adding $Eu^{3+}$ as a rare earth ion which is an alkaline earth metal, which is distributed around active ions and has a large influence on fluorescent properties when used as a host in a phosphor. $Ba_2GdV_3O_{11}:Eu^{3+}$ phosphor was synthesized by solid state method and the crystallinity of the phosphor was confirmed by X - ray diffraction analysis. The fluorescence properties of the $Ba_2GdV_3O_{11}:Eu^{3+}$ phosphor were measured using optical and laser. The energy transfer and diffusion of the $Ba_2GdV_3O_{11}:Eu^{3+}$ phosphor are highly dependent on the concentration of $Eu^{3+}$. When the concentration of $Eu^{3+}$ is low, it shows strong fluorescence to the CT band. However, as the concentration of $Eu^{3+}$ increases, the fluorescence due to 4f - 4f transition is strong. The concentration of $Eu^{3+}$ ion increased and the energy between ions was diffused, and the lifetime of fluorescence decreased. Energy transfer occurs between two $Eu^{3+}$ ions at low $Eu^{3+}$ concentration and energy diffusion occurs at high $Eu^{3+}$ concentration.

• Proceedings of the Materials Research Society of Korea Conference
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• 1994.11a
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• pp.118-118
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• 1994

Processings of the P $b_2$S $r_2$( $Y_{1-x}$ C $a_{x}$) C $u_3$ $O_{8+{\delta}}$ (2213)system for x=0.4-0.6 to control deleterious oxidative decomposition have been studied. Our results show that comounds are stable at both low p $O_2$ and high p $O_2$ if they are suitably oxidized. Various oxidation and deoxidation procedures have been investigated in order tp determine the optimum hole concentration in the Cu $O_2$layers for the maximum $T_{c}$. In cases x=0.5 and x=0.6, the optimum hole concentration in the 2213-phase is achieved, but with accelerated oxidative decomposition. Destite this, the maximum $T_{c}$~80-83K for the 2213-phase can be deduced when x=0.5 to 0.6 to 0.6

• Bulletin of the Korean Chemical Society
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• v.12 no.5
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• pp.499-504
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• 1991

EPR spectra of the high $T_c$ superconductor $YBa_2Cu_3O_{7-y}$ (YBCO) doped with $Pd^{2+} or Zn^{2+}$ have been measured at several temperatures and dopant concentrations. The spectral intensity of $YBa_2({Cu_{1-x}}{Pd_x})_3O_{7-y}$ is proportional to the dopant concentration. The behavior of $YBa_2(Cu_{1-x}Zn_x)_3O_{7-y}$ is quite different: the spectral intensity remains almost constant up to x=0.10 and then increases rapidly above x=0.10. The results are interpreted in terms of localized and antiferromagnetically spin-paired d holes in both CuO chain and planes. The $Pd_{2+}$ ion substitutes on the CuO chain consisting of "CuOCu dimers", and a $Cu_{2+}$ ion with an unpaired spin is gene rated for each $Pd_{2+}$ ion substituted. On the other hand, $Zn_{2+}$ substitutes on the CuO planes, and all or most of the spins in the two-dimensional plane manage to pair up in the region of low dopant concentration. When the dopant concentration exceeds a certain limit, it becomes more difficult for the spins to find partners, and the number of unpaired spins increases rapidly with increasing dopant concentration. The $Zn_{2+}$ ion is more effective than the $Pd_{2+}$ ion in suppressing the superconductivity of YBCO. This is attributed to the fact that $Zn_{2+}$ substitutes on the CuO planes which are mainly responsible for the superconductivity, while $Pd_{2+}$ substitutes on the CuO chain which is of secondary importance in the superconductivity.

• Electrical & Electronic Materials
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• v.8 no.1
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• pp.40-47
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• 1995

Electrical properties of ZnO ceramics based on Bi oxide was investigated in relation to sintering temperature. In the temperature range >$1150^{\circ}C$ to >$1350^{\circ}C$ the grain size increased from 9.mu.m to 20.mu.m when the sintering temperature was raised. The leakage current in the low voltage range increased as the potential barrier decreases, which is caused by increasing the grain size at high temperature. The dielectric characteristics of the ZnO ceramics was also affected by sintering temperature. Large dielectric constant was attributed, to the grainboundary layer of polycrystalline ZnO ceramics and decreasing grainboundary width. The variation of breakdown voltage with sintering temperature was attributed to the change of the donor concentration in the ZnO grain and grain size. The results showed that breakdown voltage increased decreasing grain size and donor concentration. Nonohmic coefficient was associated with the lower breakdown voltage per grainboundary layer due to the grain growth and higher donor concentration.

• Journal of Environmental Science International
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• v.13 no.6
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• pp.537-542
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• 2004

$V_{2}O_{5}/TiO_{2}$ catalysts promoted with Mn were prepared and tested for selective catalytic reduction of NOx in $NH_3.$ The effects of promoter content, degree of catalyst loading were investigated for NOx activity while changing temperatures, mole ratio, space velocity and $O_2$ concentration. Among the various $V-{2}O_{5}$ catalysts having different metal loadings, $V-{2}O_{5}$(1 wt.%) catalyst showed the highest activity(98%) under wide temperature range of $200-250^{\circ}C.$ When the $V-{2}O_{5}$ catalyst was further modified with 5 wt.% Mn as a promoter, the highest activity(90-47%) was obtained over the low temperature windows of $100-200^{\circ}C.$ From Mn-$V_{2}O_{5}/TiO_{2}$, it was found that by addition of 5 wt.% Mn on $V_{2}O_{5}/TiO_{2}$ catalyst, reduction activity of catalyst was improved, which resulted in the increase of catalytic activity and NOx reduction. According to the results, NOx removal decreased for 10%, but the reaction temperature down to $100^{\circ}C.$

• The Journal of Korean Medicine
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• v.21 no.4
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• pp.193-203
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• 2000

Objectives : Hindered barrier function of vascular endothelium has been implicated in the initiation and progression of degenerative vascular diseases such as atherosclerosis. In this study, the effect of Sunghyangchungisan(SHCS) as a protectant against oxidant-induced destruction of endothelial barrier function was assessed. Methods : Toward this end, endothelial cells derived from the human umbilical vein were cultured as monolayers on permeable membrane filters. Endothelial permeability was monitored by measuring transendothelial electrical resistance and movement of low density lipoprotein (LDL) across the endothelial monolayer. Results : Along with increased movement of LDL, $H_2O_2$-induced increase in endothelial permeability was paralleled by a decrease in transendotheliaI electrical resistance. The effect of $H_2O_2$ was mimicked by phorbol 12-myristate 13-acetate (PMA), a potent activator of proteinkinase C. Calphostin-C, a protein kinase C inhibitor, effectively blocked the increase in endothelial permeability induced by $H_2O_2$ or PMA, indicating that activation of protein kinase C is associated with the $H_2O_2-induced$ permeability change. SHCS effectively protected the endothelial monolayer against $H_2O_2-induced$ increase in permeability, whereas, it did not affect PMA-induced change. Forskolin, a potent activator of adenylyl cyclase, antagonized $H_2O_2$ to increase endothelial permeability. In addition, in ${H_2O_2}-treated$ cens, intracenular cAMP concentration was significantly decreased, indicating that impaired cAMP production as well as activation of proteinkinase C is a mechanism underlying ${H_2O_2}>-induced$$H_2O_2$ with regard to its effect on intracellular cAMP content. However, SHCS itself did not affect resting cAMP concentration in endothelial cells. Conclusions : These results suggest that SHCS might operate as an effective protectant against oxidant-induced destruction of endothelial barrier function. The mechanism does not appear to involve direct interaction with protein kinase C- or cAMP-associated signaling mechanism.

• Journal of Plant Biology
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• v.35 no.1
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• pp.1-8
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• 1992

The characteristic of Cyanophyte genus SG63 is similar to that of Aphanot hece sp. The optimal growth was found with the concentration of NaCI and $MgSO_4{\cdot}7H_2O$ on the culture medium. The most optimal condition is 56%0 of NaCl (S4 medium) and 20%0 of $MgSO_4{\cdot}7H_2O$ (M2 medium). The synthesis of chlorophyll a, phycocyanin and soluble proteins is affected by the concentration of the two mineral elements in culture. Especially, the content of chlorophyll a and phycocyanin decreases on the most highly saline medium. The identified principal carotenoids are ${\beta}-carotene$, echinenone, zeaxanthin and myxoxanthophyll. The rates of concentration of protein/chlorophyll a and phycocyanin/chlorophyll a are low on the S4 medium. Inversely, these rates are the highest on the M2 medium. Accordingly, the high concentration of $MgSO_4{\cdot}7H_2O$ provoke the synthesis of phycocyanin and total proteins.oteins.

• Nuclear Engineering and Technology
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• v.55 no.4
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• pp.1218-1224
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• 2023

We investigated the radiation shielding competence for TeO₂-V₂O₅-MoO₃ glasses. The Phy-X software was used to report the radiation shielding parameters for the present glasses. With an increase in TeO₂ and MoO₃ content, the samples' linear attenuation coefficient improves. However, at low energies, this change is more apparent. At low energy, the present samples have an effective atomic number (Z_eff) that is relatively high (in order of 16.17-24.48 at 0.347 MeV). In addition, the findings demonstrated that the density of the samples is a very critical factor in determining the half value layer (HVL). The minimal HVL for each sample can be found at 0.347 MeV and corresponds to 1.776, 1.519, 1.391, 1.210 and 1.167 cm for Te1 to Te5 respectively. However, the highest HVL of these glasses is recorded at 1.33 MeV, which corresponds to 3.773, 3.365, 3.218, 2.925 and 2.908 cm respectively. The tenth value layer results indicate that the thickness of the specimens needs to be increased in order to shield the photons that have a greater energy. Also, the TVL results demonstrated that the sample with the greatest TeO₂ and MoO₃ concentration has a higher capacity to attenuate photons.

• Journal of the Korean Vacuum Society
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• v.12 no.4
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• pp.269-274
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• 2003

The electrical, optical and structural properties of ZnNiO thin _ films deposited on Si substrates using rf-magnetron sputtering method have been investigated before and after the thermal annealing processes. The crystallinity of the ZnNiO thin film become degraded with increasing the Ni contents. This is mainly because the lattice of the thin film was expanded due to the oxygen-deficient conditions. Concerning the electrical properties of the thin film, the carrier concentration increases ($6.81\times10^{14}\textrm{cm}^{-2}$) and Hall mobility decreases (36.3 $\textrm{cm}^2$/Vㆍs) with higher doping concentration of Ni. However, the carrier concentration and Hall mobility became low ($1.10\times10^{14}\textrm{cm}^2$ and high (209.6 $\textrm{cm}^2$/Vㆍs), respectively, after the thermal annealing process at $1000 ^{\circ}C$. We also observed a strong luminescene center peaking at 546 nm in photoluminescence spectra, which was caused by a deep level center in the ZnO band gap with oxygen deficient ZnNiO structure.