• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.150-153
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• 2007

Apply electromagnetic stirring system to making rheology slurry of Al7075. This experiment has important element which is the relation between solid fraction percent and melt temperature of Al7075. The rheology slurry of Al7075 eliminated liquid phase to include alloying element of copper and zinc by squeeze casting process. In result the most structure was composed entirely of globular primary $\alpha$. Used this material for this study. This study made a comparison of mechanical property according to heat treatment T6 at each melt temperature ($619^{\circ}C$ and $615^{\circ}C$). The microstructure and component are observed how heat treatment T6 weight with the mechanical property by SEM-EDS.

• Structural Engineering and Mechanics
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• v.16 no.1
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• pp.1-15
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• 2003

This paper proposes a new method for the preliminary design of cable-stayed bridges that belong to the radial system subjected to static loads (self weight, traffic loads, concentrated loads, etc). The method is based on the determination of the each time existing relation between the tension forces of the cables and the corresponding bridge-deck deformations, and can be extended on any type of cable layout (fan, parallel, or mixed system). Galerkin's method is used for the final determination of the cable stresses and the bridge deformation. The determination of the equation, which gives the forces of the cables in relation to the deck's configurations, permits us to convert the problem to the solving of a continuous beam without cables.

• Structural Engineering and Mechanics
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• v.10 no.3
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• pp.277-288
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• 2000

The present paper, deals with the dynamic analysis of a thin-walled tower with varying cross-section and additional masses. It, especially, deals with the effect of the rotary inertia of those masses, which have been neglected up to now. Using Galerkin's method, we can find the spectrum of the eigenfrequencies and, also, the shape functions. Finally, we can solve the equations of the problem of the forced vibrations, by using Carson-Laplace's transformation. Applying this method on a tall mast with 2 concentrated masses, we can examine the effect of the rotary inertia and the diaphragmatic operation of the above masses, on the 3 first eigenfrequencies.

• Korean Journal of Materials Research
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• v.31 no.11
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• pp.593-600
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• 2021

Herein, a series of g-C₃N₄ modified Bi₂MoO₆ nanocomposites using Bi₂MoO₆ and melamine as original materials are fabricated via sintering process. For presynthesis of Bi₂MoO₆ an ultrasonic-assisted hydrothermal technique is researched. The structure and composition of the nanocomposites are characterized by Raman spectroscopy, X-ray diffraction (XRD), and high-resolution field emission scanning electron microscopy (SEM). The improved photoelectrochemical properties are studied by photocurrent density, EIS, and amperometric i-t curve analysis. It is found that the structure of Bi₂MoO₆ nanoparticles remains intact, with good dispersion status. The as-prepared g-C₃N₄/Bi₂MoO₆ nanocomposites (BMC 5-9) are selected and investigated by SEM analysis, which inhibits special morphology consisting of Bi₂MoO₆ nanoparticles and some g-C₃N₄ nanosheets. The introduction of small sized g-C₃N₄ nanosheets in sample BMC 9 is effective to improve the charge separation and transfer efficiency, resulting in enhancing of the photoelectric behavior of Bi₂MoO₆. The improved photoelectronic behavior of g-C₃N₄/Bi₂MoO₆ may be attributed to enhanced charge separation efficiency, photocurrent stability, and fast electron transport pathways for some energy applications.

• The Journal of Korean Academy of Prosthodontics
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• v.29 no.3
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• pp.33-41
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• 1991

Cermic has been widely used because of its excellent esthetics and strength. The recently introduced castable ceramic system is regarded as the more esthetic and biocompatible restorative material. The purpose of this study was to compare the shear bond strength of Dicer & G-Cera porcelain laminate veneer according to the type of cement and surface treatment and to observe the surface of bonding failure with SEM. Total forty disks(3.5mm $diam.\times2.0mm$ thickness) were prepared. Forty extracted human maxillary central incisor teeth were stored in saline solution. Ten teeth were bonded to Dicer specimen with Dicer ZPC cement and ten teeth were bonded with Dicer resin cement. Ten silicoated G-Cera specimen and ten non-silicoated G-Cera specimen were bonded to teeth with G-Cera resin cement. Bonded units were mounted in a plastic tube with hard stone and stored in a humidor at $37^{\circ}C$ for 24 hours. Shear bond strength was measured by Instron Universal Testing Machine (Model 1125) and all the specimen were observed with SEM(JEOL, JSM-T2000)and modes of failure were recorded. The obtained results were as follows: 1. The mean shear bond strength of Dicer bonded with Dicer resin cement was 11.62 MPa and that bonded with Dicor ZPC cement was 0.88 MPa : Shear bond strength of Dicer bonded with Dicer resin cement was significantly increased(P<0.05). 2. The mean shear bond strength of silicoated G-Cera was 13.10 MPa and that of non silicoated G-Cera was 10.93 MPa : Shear bond strength of silicoated G-Cera was not significantly increased (P>0.05). 3. Shear bond strength of Dicer and G-Cera porcelain laminate veneer was not significantly different (P>0.05). 4. In observation of bond failure with SEM, Dicer bonded with Dicer ZPC cement exhibited adhesive failure. Dicer bonded with Dicer resin cement and silicoated and non silicoated G-Cera exhibited cohesive failure.

• The Journal of Korean Academy of Prosthodontics
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• v.46 no.3
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• pp.227-237
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• 2008

STATEMENT OF PROBLEM: Zirconium oxide can be a substitute to titanium as implant materials to solve the esthetic problems of dark color in the gingival portion of implant restorations. PURPOSE: This study was performed to define attachment and growth behavior of osteoblast- like cells cultured on grooved surfaces of zirconium oxide and evaluate the genetic effect of zirconium oxide surfaces using the reverse transcriptase-polymerase chain reaction (RT-PCR). MATERIAL AND METHODS: MC3T3-E1 cells were cultured on (1) commercially pure titanium discs with smooth surface (T group), (2) yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) with machined surface (ZS group), and (3) Y-TZP with $100{\mu}m$ grooves (ZG group). Cell proliferation activity was evaluated through MTT assay and cell morphology was examined by SEM. The mRNA expression of Runx2, alkaline phosphatase, osteocalcin, TGF-${\beta}1$, IGF-1, G3PDH in E1 cells were evaluated by RT-PCR. RESULTS: From the MTT assay, after 48 hours of adhesion of MC3T3-E1 cells, the mean optical density value of T group and ZG group significantly increased compared to the ZS group. SEM images of osteoblast-like cells showed that significantly more cells were observed to attach to the grooves and appeared to follow the direction of the grooves. After 24 hours of cell adhesion, more spreading and flattening of cells with active filopodia formation occurred. Results of RT-PCR suggest that T group, ZS group, and ZG group showed comparable osteoblast-specific gene expression after 24 hours of cell incubation. CONCLUSION: Surface topography and material of implants can play an important role in expression of osteoblast phenotype markers. Zirconia ceramic showed comparable biological responses of osteoblast-like cells with titanium during a short-time cell culture period. Also, grooves influence cell spreading and guide the cells to be aligned within surface grooves.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.05a
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• pp.130-132
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• 2006

In this paper, the author describes a-C films grown in pure methane plasma without any diluent gas by using RF plasma-enhanced CVD, and the variations in their structural features and surface morphologies are examined as a function of substrate temperature. Raman spectroscopy and scanning electron microscopy were performed to characterize the properties of the film.

• Progress in Superconductivity
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• v.9 no.1
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• pp.111-114
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• 2007

We have investigated the effect of different heat treatment processes on electrical and magnetic properties of Bi2212/Ag ROSAT wire. The ROSAT wire was fabricated by stacking and arranging 12 filaments Bi2212/Ag tapes in triple rotation symmetry in a Ag tube. ROSAT wires have been prepared using a partial melting method with changing $T_{max}$ and $T_a$ in oxygen atmosphere. The highest critical current density($J_c$) at 65 K under 0 T was $21,158\;A/cm^2$ for wire prepared $890\;^{\circ}C(T_{max})$ and $840\;^{\circ}C(T_a)$, respectively. SEM results indicated that the wire prepared at $890\;^{\circ}C(T_{max})$ and $840\;^{\circ}C(T_a)$ showed better directional phases than the other samples. However the result of magnetic susceptibility measurement indicates that the wire prepared $890\;^{\circ}C(T_{max})$ and $835\;^{\circ}C(T_a)$ had better superconducting phases than the other samples. It was revealed that heat treatment temperature was important factor for superconducting properties of the ROSAT wire.

• Advances in nano research
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• v.6 no.2
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• pp.183-200
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• 2018

In the present study silver nanoparticles (AgNPs) were successfully synthesized using aqueous extract of Sargassum muticum. The aqueous extract (10%) treated with 1 mM silver nitrate solution resulted in the formation of AgNPs and the surface plasmon resonance (SPR) of the formed AgNPs was recorded at 360 nm using UV-Visible spectrophotometer. The molecules involved in the formation of AgNPs were identified by Fourier transform infrared spectroscopy (FT-IR), surface morphology was studied by using scanning electron microscopy (SEM), SEM micrograph clearly revealed the size of the AgNPs was in the range of 40-65 nm with spherical, hexagonal in shape and poly-dispersed nature, and X-ray diffraction spectroscopy (XRD) was used to determine the crystalline structure. High positive Zeta potential (36.5 mV) of formed AgNPs indicates the stability and XRD pattern revealed the crystal structure of the AgNPs by showing the Bragg's peaks corresponding to (111), (200), (311) and (222) planes of face-centered cubic crystal phase of silver. The synthesized AgNPs exhibited effective anticancerous activity (at doses 25 and $50{\mu}g/ml$ of AgNPs) against Breast cancer cell line (MCF7).

• Corrosion Science and Technology
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• v.21 no.1
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• pp.32-40
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• 2022

The o-Vanillin - Glutamine Schiff base [2-Hydroxy-3-Methoxy BenzylidineCarbomyl) -2-Butanoic Acid] was examined for low carbon steel corrosion inhibition in acid media. Weight loss studies were carried out at three different temperatures to determine the inhibition efficiency (IE). Electrochemical impedance spectroscopy revealed that the charge transfer resistance controlled the corrosion reaction and Tafel polarization indicated that the Schiff base acts as mixed mode of inhibitor. SEM images were recorded for the surface morphology of the low carbon steel surface. DFT studies revealed corrosion control mechanisms using quantum chemical parameters such as E_HOMO, E_LUMO, energy gap (∆E), chemical Hardness (η), chemical Softness (σ), Electronegativity (χ), and the fraction of electron transferred (∆N), which is calculated using Gaussian software 09. The gas-phase geometry was fully optimized in the Density Functional Theory (DFT/B3LYP-6-31G (d)).The DFT results are in good agreement with the experimental results. All the results proved that the Schiff Base (2-Hydroxy-3-Metoxy BenzylidineCarbomyl) -2-Butanoic is a suitable alternative for corrosion inhibition of low carbon steel in acid media.