• Korean Journal of Materials Research
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• v.5 no.5
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• pp.583-597
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• 1995

We investigated the effect of the oxygne partial pressure on the phase stability of B $i_{2}$S $r_{2}$Ca C $u_{2}$ $O_{8+x}$ and B $i_{2}$S $r_{2}$C $a_{2}$C $u_{3}$ $O_{10+x}$ at 82$0^{\circ}C$. As the oxygen pressure decreased, B $i_{2}$Sr/sb 2/CaC $u_{2}$ $O_{8+x}$ melted at 2.2$\times$10$^{-3}$ atm $O_{2}$. In the case of the B $i_{1.7}$P $b_{0.4}$S $r_{2}$C $a_{2}$ $O_{10+x}$, it started to decompose into theree phases of B $i_{2}$S $r_{2}$Cu $O_{6+y}$, $Ca_{2}$Cu $O_{3}$ and C $u_{4}$ $O_{3}$ and C $u_{4}$ $O_{3}$ at 8.0$\times$10$^{-3}$ atm $O_{2}$ and was completely decomposed at 4.3$\times$10$^{-3}$ atm $O_{2}$ B $i_{2}$S $r_{2}$C $a_{2}$C $u_{3}$ $O_{10+x}$ phase was not formed by the solid state reaction from the mixutre of $i_{2}$S $r_{2}$CaCu.sub 2/ $O_{8+x}$, $Ca_{2}$Cu $O_{3}$ and CuO down to 2.2$\times$10.sub -3/ atm O.sub 2/ but formed by the solidifciation of the formed from the mixture of the intermediate compounds in the Bi-Sr-Ca-Cu-O system and the fromation temperature of Bi.sub 2/S $r_{2}$C $a_{2}$Cu.$_{3}$ $O_{10+x}$ can be lowered by reducing oxygen partial pressure.e.e.ure.e.e.

• Journal of the Korean Ceramic Society
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• v.34 no.2
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• pp.123-130
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• 1997

In this study, (Sr.Pb.Ca)TiO3-Bi2O3.3TiO2(SPCT) systems were investigated to develop a new material which has a high dielectric constant, a low dielectric loss and a small TCC(Temperature Coefficient of Capa-citance), and are suitable for high voltage applications as a function of the additions of Bi2O3.3TiO2 from 5 mol.% to 9 mol.%. The result obtained from our investigation showed that up to 6 mol.% Bi2O3.3TiO ad-dition the dielectric constant increased and it deteriorated at higher concentrations with increasing amount of the acicular grains. As a result of some dopants (SiO2, Nb2O3, MnO2) addition to SPCT, the specimens with MnO2 showed good dielectric properties. The dielectric constant decreased, but the TCC was improved with the addition of MnO2 from 0.15 wt.% to 0.45 wt. %.

• Proceedings of the KIEE Conference
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• 1991.11a
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• pp.293-295
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• 1991

In this study, we investigated the possibilty that $Pb(Mg_{1/3}Nb_{2/3})O_3-PbTiO_3-PbZrO_3$ ceramics with strontium substitutions could be used for piezoelectric sounders. Piezoelectric buzzer is one of them. By partially substituting Sr for Ph, dielectric constants had values greater than 2000, the value proper piezoelectric buzzer, piezoelectric constant($d_{31}$) had a maximum value, 298 $[10^{-12}C/N]$, at the Sr 5 mol % substitution. Sound level of piezoelectric buzzer had the highest value of 91 dB at the Sr 5 mol % substitution.

• Progress in Superconductivity and Cryogenics
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• v.21 no.4
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• pp.9-12
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• 2019

We performed Raman spectroscopy on two different over-doped Bi₂Sr₂CaCu₂O_8+x (BSCCO), of which superconducting transition temperatures are 89 K and 77 K. Line-shape analysis of the Raman-spectrum was done, focused on B_1g bond buckling mode which have drawn a lot of attention, since photoemission studies showed an evidence for strong coupling between the mode and electron. The line-shapes show asymmetry and are well fitted by the Fano line-shape formula. Remarkably, we found that the peak line-widths from B_1g bond buckling mode in BSCCO show much broader than those in YBa₂Cu₃O_7-x. The broad line width can be attributed to the superstructure modulation of BSCCO. Our results imply that B_1g bond buckling mode may have close relation to the origin of superconductivity or to boosting the superconducting transition temperature in BSCCO.

• The Korean Journal of Ceramics
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• v.2 no.2
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• pp.95-101
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• 1996

Variations of the leakage current behaviors and interface potential barrier $({\Phi}_B)$ of rf-sputter deposited (Ba, Sr)$TiO_3$ (BST) thin films with thicknesses ranging from 20 nm to 150nm are investigated as a function of the thickness and bias voltages. The top and bottom electrodes are dc-sputter-deposited Pt films. ${\Phi}_B$ critically depends on the BST film deposition temperature, postannealing atmosphere and time after the annealing. The postannealing under $N_2$ atmosphere results in a high interface potential barrier height and low leakage current. Maintaining the BST capacitor in air for a long time reduces the ${\Phi}_B$ from about 2.4 eV to 1.6 eV due to the oxidation. ${\Phi}_B$ is not so dependent on the film thickness in this experimental range. The leakage conduction mechanism is very dependent on the BST film thickness; the 20 nm thick film shows tunneling current, 30 and 40 nm thick films show Shottky emission current.

• Proceedings of the KIEE Conference
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• 1994.07b
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• pp.1314-1316
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• 1994

$0.36[wtx]Sio_2$ and $0.1[wtx]H_3BO_3$ were added to strontium ferrite magnets of the magnetoplumbite phase SrO $5.7Fe_2O_3$. This experiment was carried out to investigate the effects of particle size distribution as a function of milling time(20,30,40,50,60,70 hours) on the magnetic properties of SrO $5.7Fe_2O_3$ ferrite magnet. The B-H Curve, density and the degree of orientation were measured. The optimal conditions of making magnets and properties of a typical sample are the following : The milling time was 60 hours. Magnetic and physical properties are $B_r$=4000[G], $_BH_c$=3330[Oe], $_IH_c$=3525[Oe], (BH)max=3.786 [MGOe], density= $5.0063g/cm^2$, orientation factor f=0.813.

• Electrical & Electronic Materials
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• v.9 no.1
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• pp.1-8
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• 1996

We investigated the effects of doping elements on the Bi-Sr-Ca-Cu-O ceramics. The doping elements can be classified into four groups depending on their supeconducting characteristics in the Bi-Sr-Ca-Cu-O structure. The first group of doping elements(Co, Fe, Ni and Zn) substitute into the copper site and can reduce the critical temperatures of the 2223 and 2212 phases. The second group of doping elements(Y and La) substitute into the Ca site and cause the disappearance of the 2223 phase and increase the critical temperatures in the 2212 phase. The third group of doping elements(P and K) have a tendency to decompose the superconducting phase and reduce the optimal sintering temperature. The fourth group of doping elements(B, Si, Sn and Ba) almost unaffected the superconductivity of the 2223 and 2212 phase.

• Korean Journal of Materials Research
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• v.33 no.11
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• pp.465-474
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• 2023

The effects of La³⁺ substitution for Sr²⁺-site on the crystal structure and the dielectric properties of (Ba_0.7Sr_0.3-3x/2La_x) (Ti_0.9Zr_0.1)O₃ (BSLTZ) (0.005 ≤ x ≤ 0.02) ceramics were investigated. The structural characteristics of the BSLTZ ceramics were quantitatively evaluated using the Rietveld refinement method from X-ray diffraction (XRD) data. For the specimens sintered at 1,550 ℃ for 6 h, a single phase with a perovskite structure and homogeneous microstructure were observed for the entire range of compositions. With increasing La³⁺ substitution (x), the unit cell volume decreased because the ionic size of La³⁺ (1.36 Å) ions is smaller than that of Sr²⁺ (1.44 Å) ions. With increasing La³⁺ substitution (x), the tetragonal phase fraction increased due to the A-site cation size mismatch effect. Dielectric constant (ε_r) increased with the La³⁺ substitution (x) due to the increase in tetragonality (c/a) and the average B-site bond valence of the ABO₃ perovskite. The BSLTZ ceramics showed a higher dielectric loss due to the smaller grain size than that of (Ba_0.7Sr_0.3)(Ti_0.9Zr_0.1)O₃ ceramics. BSLTZ (x = 0.02) ceramics met the X7R specification proposed by the Electronic Industries Association (EIA).

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.740-744
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• 1995

For the fabrication of a multi-pole anisotropic Sr-ferrite magnet by powder injection molding, it is important to control effectively the alignment of magnetic powders during the injection molding process. The effect of the fluidity of powder/binder mixture on the powder alignment was studied with changing the particle sizes and the volume fraction of Sr-ferrite magnetic powders. The critical volume fraction of Sr-ferrite powders increases from 58 vol.% to 64 vol.% as the mean powder size increases from $0.8\;\mu\textrm{m}$ to $1.2\;\mu\textrm{m}$. A Sr-ferrite powder alignment greater than 80 % is achieved at the conditions of an apparent viscosity lower than 1000 poise at $1600\;sec^{-1}$ shear rate, an applied magnetic field higher than 4 kOe, and a powder volume fraction 8 vol.% lower than the critical fraction. The powder alignment obtained during the injection molding process is not much affected by the subsequent processes of debinding and sintering, showing the magnetic properties of 3.8 kG of remanent flux density and 3.37 kOe of intrinsic coercivity.

• Journal of Life Science
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• v.32 no.2
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• pp.142-147
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• 2022

Oxysterols are known to be involved in the physiopathology of atherosclerosis. Since 7-ketocholesterol (7-KC) is found in large amounts in oxysterols and in atherosclerotic plaque, the study on how 7-KC may affect monocyte differentiation induced by phorbol myristate acetate (PMA) in the monocytic cell line, THP-1, is essential. 7-KC induced a dose-dependent reduction in cell proliferation without inducing cytotoxicity, and the substantial staining of Nile red demonstrates the increased absorption of intracellular lipids. Although 7-KC itself did not increase cell adhesion, it markedly decreased the adhesion of cells treated with PMA. Furthermore, by observing the effect of 7-KC on phagocytosis using fluorescent-labeled latex beads, 7-KC's ability to abolish phagocytosis in PMA-stimulated macrophages was illustrated. The effect of 7-KC on the expression of selected protein markers on the process of differentiation induced by PMA in THP-1 cells was also examined. 7-KC inhibited expression of ICAM-1, CD11a, SR-A1, and SR-B2 (CD36) in PMA-stimulated THP-1 cells. Conversely, 7-KC drastically increased the expression of SR-D1 (CD68)in PMA-stimulated THP-1 cells. In conclusion, these results suggest that 7-KC modulates monocyte differentiation and activation via the intracellular accumulation of lipid droplets.