• Korean Journal of Metals and Materials
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• v.56 no.12
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• pp.845-853
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• 2018

To understand the effect of microstructural factors (i.e., the size of ${\alpha}$ phase, equiaxed vs bimodal structure) on high cycle fatigue (HCF) and fatigue crack propagation (FCP) behaviors of mill-annealed Ti-6Al-4V (Ti64) alloy, three specimens of EQ (equiaxed)-8 (8 indicates the size of ${\alpha}$ grain), BM (bimodal)-8, and BM-16 were studied. The uniaxial HCF and FCP tests were conducted at an R ratio of 0.1 under sinusoidal fatigue loading. The microstructural influence (i.e., EQ vs BM) was not significant on the tensile properties of mill-annealed Ti64 alloy, and showed an increase in tensile strength and elongation with decreasing gauge thickness from 50 mm to 1.3 mm. The microstructure, on the other hand, affected the resistance to HCF substantially. It was found that the EQ structure in mill-annealed Ti64 has better resistance to HCF than the BM structure, as a result of different crack initiation mechanism. Unlike HCF behavior, the effect of microstructural features on the FCP behavior of mill-annealed Ti64 was not significant. Among the three specimens, BM-16 specimen showed the highest near-threshold ΔK value, probably because it had the greatest slip reversibility with large ${\alpha}$ grains. The effect of microstructural factors on the HCF and FCP behaviors of mill-annealed Ti64 alloy are discussed based on fractographic and micrographic observations.

• Biomedical Science Letters
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• v.24 no.3
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• pp.196-205
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• 2018

Reactive oxygen species (ROS) generated from metabolic reactions cause oxidative DNA damage, which results in oxidative tissue injury. Therefore, there is an increasing demand in the intake of high antioxidant sources in order to maintain a healthy environment in cells. In this study, we investigated the antioxidant and anti-inflammatory activities of Malus domestica (apple), Pyrus communis L. (pear), Daucus carota L. (carrot), Brassica oleracea var. (broccoli), Brassica oleracea var. capitata (cabbage), and Raphanus sativus L. (radish) obtained from the local market. Since these are common fruits and vegetables that are widely consumed, we aimed to investigate their beneficial properties, placing particular emphasis on their antioxidant and anti-inflammatory properties. The samples were processed via an indirect heating method and their properties were compared to their raw forms. Based on DPPH and ABTS assays, processed samples showed better antioxidant activities when compared to raw samples and processed pear samples exhibited the best antioxidant activity. The anti-inflammatory activities of the samples were also investigated in LPS-treated RAW 264.7 cells. mRNA expression of pro-inflammatory mediators and cytokines (iNOS, COX-2, $TNF-{\alpha}$, $IL-1{\beta}$, and IL-6) was assessed using RT-PCR. As expected, processed samples exhibited better iNOS inhibition when compared to their raw forms and processed broccoli and cabbage samples exhibited outstanding anti-inflammatory effects. The samples, up to 1 mg/mL concentration, did not exhibit cytotoxicity against RAW 264.7 cells as demonstrated by cell viability assays. Altogether, processed broccoli and cabbage samples exhibited the strongest anti-inflammatory properties.

• JSTS:Journal of Semiconductor Technology and Science
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• v.6 no.2
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• pp.119-123
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• 2006

This work presents the fabrication and characteristics of $Bi_2O_3/Si$ heterojunction prepared by rapid thermal oxidation technique without any postdeposition annealing condition. The bismuth trioxide film was deposited onto monocrystalline Si and glass substrates by rapid thermal oxidation of bismuth film with aid of halogen lamp at $500^{\circ}C/\;45$ s in static air. The structural, optical and electrical properties of $Bi_2O_3$ film were investigated and compared with other published results. The structural investigation showed that the grown films are polycrystalline and multiphase (${\alpha}-Bi_2O_3$ and ${\beta}-Bi_2O_3$). Optical properties revealed that these films having direct optical band gap of 2.55 eV at 300 K with high transparency in visible and NIR regions. Dark and illuminated I-V, CV, and spectral responsivity of $Bi_2O_3/Si$ heterojunction were investigated and discussed.

• Korean Journal of Materials Research
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• v.16 no.7
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• pp.416-421
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• 2006

The varistor properties of ZPCCL-based ceramics were investigated at different $La_2O_3$ contents in the range of $0{\sim}2.0$ mol%. As $La_2O_3$ content increased, the ceramic density greatly increased in the range of $4.71{\sim}5.77\;g/cm^3$ and the varistor voltage greatly decreased in the range of $503.5{\sim}9.4$ V. The varistor with 0.5 mol% $La_2O_3$ exhibited good nonlinearity, in which the nonlinear exponent is 81.6 and the leakage current is 0.2 ${\mu}A$. Furthermore, the varistors exhibited the high electrical stability, with $%{\Delta}V_{1mA}=-1.1%,%{\Delta}{\alpha}=-3.7%$, and $%{\Delta}I_L=+100%$ for DC accelerated aging stress condition of 0.95 $V_{1mA}/150^{\circ}C/24$ h.

• Korean Journal of Materials Research
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• v.16 no.8
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• pp.466-472
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• 2006

The electrical, dielectric properties, and its stability of ZPCCL-based varistors were investigated for different sintering temperatures in the range of $1230{\sim}1300^{\circ}C$. As the sintering temperatures increased, the varistor voltage decreased in the range of $777.9{\sim}108$ V/mm, the nonlinear coefficient decreased in the range of $77.9{\sim}7.1$, and the leakage current increased in the range of $0.3{\sim}50.6\;{\mu}A$. The stability of electrical and dielectric characteristics was obtained from sintering temperature of $1260^{\circ}C$. the varistors sintered at $1260^{\circ}C$ marked the high electrical and dielectric stability, with $%{\Delta}{V_{1mA}=+1.9%,\;%{\Delta}{\alpha}=-10.6%,\;%{\Delta}I_L=+20%\;and\;%{\Delta}tan\;{\delta}=+9.9%$ for DC accelerated aging stress state of $0.95V_{1mA}/150^{\circ}C$/24 h.

• Journal of the Korean Physical Society
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• v.73 no.11
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• pp.1691-1697
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• 2018

Employing the density functional theory, we have investigated the roles of Coulomb and Hund's interactions in the electronic and magnetic properties of newly discovered ${\alpha}-RuCl_3$ having the $R{\overline{3}}$ symmetry, which is in close proximity of the Kitaev system. We show that both the size and the direction of local magnetic moment are highly dependent on Coulomb and Hund's interactions, and the spin and orbital parts show different behaviors. The validity of the so-called $j^{eff}$ picture is accessed upon interaction parameters, and the explicit roles of Hund's interaction in the local electronic structures and magnetic properties are discussed.

• The Journal of Advanced Prosthodontics
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• v.7 no.1
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• pp.39-46
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• 2015

PURPOSE. The mechanical and interfacial characterization of laser welded Co-Cr alloy with two different joint designs. MATERIALS AND METHODS. Dumbbell cast specimens (n=30) were divided into 3 groups (R, I, K, n=10). Group R consisted of intact specimens, group I of specimens sectioned with a straight cut, and group K of specimens with a $45^{\circ}$ bevel made at the one welding edge. The microstructure and the elemental distributions of alloy and welding regions were examined by an SEM/EDX analysis and then specimens were loaded in tension up to fracture. The tensile strength (TS) and elongation (${\varepsilon}$) were determined and statistically compared among groups employing 1-way ANOVA, SNK multiple comparison test (${\alpha}$=.05) and Weibull analysis where Weibull modulus m and characteristic strength ${\sigma}_0$ were identified. Fractured surfaces were imaged by a SEM. RESULTS. SEM/EDX analysis showed that cast alloy consists of two phases with differences in mean atomic number contrast, while no mean atomic number was identified for welded regions. EDX analysis revealed an increased Cr and Mo content at the alloy-joint interface. All mechanical properties of group I (TS, ${\varepsilon}$, m and ${\sigma}_0$) were found inferior to R while group K showed intermediated values without significant differences to R and I, apart from elongation with group R. The fractured surfaces of all groups showed extensive dendritic pattern although with a finer structure in the case of welded groups. CONCLUSION. The K shape joint configuration should be preferred over the I, as it demonstrates improved mechanical strength and survival probability.

• YAKHAK HOEJI
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• v.32 no.4
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• pp.281-286
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• 1988

For the investigation of medicinal resources in Hydrocotyle species, the studies were conducted to evaluate the pharmaco-constituents in Hydrocotyle japonica MAKINO (Umbelliferae), which is used as folk medicine in Korea. From the methyl alcohol extract of the whole plant, $isorhamnetin-3-O-{\beta}-D-galactoside$ ($C_{22}H_{22}O_{12}{\cdot}1/3H_2O$, bright yellow needle crystal, mp $247{\sim}248^{\circ}C$, $[{\alpha}]_D^{28}^{\circ}=-52.27^{\circ}$ in pyridine), one of three flavonol substances in extrat, was isolated and identified by physicochemical properties and spectroscopic evidences (UV, IR, NMR and MS etc.,) in comparison with authentic sample. This flavonoid was appeared from Hydrocotyle japonica MAKINO through phytochemical approaches at the outset.

• Journal of the Korean Ceramic Society
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• v.29 no.6
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• pp.451-458
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• 1992

Dense glass-ceramics for low firing temperature substrate were prepared by addition of CeO2 flux to the glass of MgO-Al2O3-SiO2 system. Glass powders were fabricated by melting at 150$0^{\circ}C$ and ball milling. Glass powder compacts were sintered at 800~100$0^{\circ}C$ for 3h. The crystallization and the shrinkage behaviors of glass powder compacts were analyzed by XRD, DTA and TMA. The shrinkage of glass powder compact increased with increasing the amount of CeO2. Because the softening temperature decreased and the crystallization temperature increased with increasing the amount of CeO2. Apparently, addition of CeO2 prevented formation of $\mu$-cordierite phase from the glass-ceramics and improved formation of $\alpha$-cordierite phase. Therefore crystallization properties were enhanced.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.57-58
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• 2010

In this paper, direct tensile strength, $f_t$, and FR index, $F_i$, were considered, and factor ${\alpha}$ between and $f_t$ and $\sqrt{f'_c}$ was estimated through the results of preceding studies on the material properties of SHCCs in order to propose equation for evaluating shear strength of SHCC walls. Shear strength calculated by the proposed equation predicted shear strength of SHCC walls accurately, showing similar tendencies to experimental results.