• Journal of the Korean Society for Heat Treatment
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• v.35 no.2
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• pp.74-81
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• 2022

This study aims to mitigate the microstructural heterogeneity arising from the manufacture of magnesium alloy plates using the twin roll casting (TRC) process. Homogenization was introduced through hot rolling and heat treatment, followed by confirmation of observed changes in the microstructure. Following the TRC process, the hot rolled 2mm plate exhibited a dendritic cast structure tilted in the roll rotation direction, while central segregation were developed. This nonuniform structure and central segregation disappeared upon heat treatment, followed by recrystallization to form uniform and fine grains. Abnormal grain growth (AGG) was observed over the course of heat treatment; grains exhibiting AGG occupied up to 75% of the total area after having held the sample at 400℃ for 64 h. The formation of coarse grains was also observed during heat treatment at 340℃ over a relatively long duration, though the maximum grain size was significantly smaller than that corresponding to the heat treatment at 400℃. AGG in the 400℃ heat treatment occurred because of movement of the grain boundary, which had been fixed prior as a result of the grain boundary fixing effect of the precipitation phase. The re-dissolution of the Ca₂Mg₅Zn₅ precipitated phase over the long duration of the high-temperature annealing process caused the surrounding grains to disappear and regrow.

• Asian Pacific Journal of Cancer Prevention
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• v.15 no.24
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• pp.10659-10663
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• 2015

Background: Rapamycin is an effective anti-angiogenic drug. However, the mode of its action remains unclear. Therefore, in this study, we aimed to elucidate the antitumor mechanism of rapamycin, hypothetically via apoptotic promotion, using MCF-7 breast cancer cells. Materials and Methods: MCF-7 cells were plated at a density of $1{\times}10^5$ cells/well in 6-well plates. After 24h, cells were treated with a series of concentrations of rapamycin while only adding DMEM medium with PEG for the control regiment and grown at $37^{\circ}C$, 5% $CO_2$ and 95% air for 72h. Trypan blue was used to determine the cell viability and proliferation. Untreated and rapamycin-treated MCF-7 cells were also examined for morphological changes with an inverted-phase contrast microscope. Alteration in cell morphology was ascertained, along with a stage in the cell cycle and proliferation. In addition, cytotoxicity testing was performed using normal mouse breast mammary pads. Results: Our results clearly showed that rapamycin exhibited inhibitory activity on MCF-7 cell lines. The $IC_{50}$ value of rapamycin on the MCF-7 cells was determined as $0.4{\mu}g/ml$ (p<0.05). Direct observation by inverted microscopy demonstrated that the MCF-7 cells treated with rapamycin showed characteristic features of apoptosis including cell shrinkage, vascularization and autophagy. Cells underwent early apoptosis up to 24% after 72h. Analysis of the cell cycle showed an increase in the G0G1 phase cell population and a corresponding decrease in the S and G2M phase populations, from 81.5% to 91.3% and 17.3% to 7.9%, respectively. Conclusions: This study demonstrated that rapamycin may potentially act as an anti-cancer agent via the inhibition of growth with some morphological changes of the MCF-7 cancer cells, arrest cell cycle progression at G0/G1 phase and induction of apoptosis in late stage of apoptosis. Further studies are needed to further characterize the mode of action of rapamycin as an anti-cancer agent.

• Korean Journal of Applied Biomechanics
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• v.24 no.1
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• pp.1-9
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• 2014

The purpose of this study was to investigate the muscle mechanical properties of the pelvic axial pre-rotational movement for the Jireugi in the Taekwondo Juchumseogi stance. Eleven elite Taekwondo Poomsae athletes participated. Each participant performed 5 right hand Jireugi in Juchumseogi stance as fast and strong as possible while their motion was recorded by a 3D motion analysis system and the ground reaction forces by two force plates. The power and work of the muscular group surrounding the waist were analyzed to verify the effect of the stretch-shortening cycle (SSC) theory. The cause of the greater power seems to be the application of the SSC by the muscles surrounding the waist during the preparation phase of the pre-rotation group. For the none pre-rotation group, they only used the concentric contraction of the muscles surrounding the waist. Because the pre-rotation group used the SSC theory, they had the effect of shortening of the range of movement, creating a fast and more powerful rotation, thus anticipating the increase the magnitude of impact.

• Journal of the Korean Society for Precision Engineering
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• v.32 no.10
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• pp.885-890
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• 2015

Walking on split-belt treadmill has been applied to study walking disabilities, such as osteoarthritis (OA), to show asymmetric walking characteristics. In this study, we compared asymmetric walking in OA patients with healthy subjects under split-belt conditions and examined the reproduction of walking asymmetry in OA. Seven OA patients were instructed to walk at four frequencies, while four healthy subjects walked on a treadmill with tied-belt and split-belt conditions. To compare walking asymmetries, kinetic and kinematic measurements were made using force-plates and motion capture cameras, and subsequently center of mass (CoM) velocity, mechanical work and potential energy were calculated. Horizontal velocity change during split-belt walking of healthy subjects was similar to OA patients. Difference of mechanical work during single support phase occurred due to fall of CoM in fast belt. OA walking asymmetry could be reproduced by reducing differences of belt speeds to prevent rapid fall of CoM.

• Journal of the Korean Ceramic Society
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• v.53 no.4
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• pp.406-410
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• 2016

Carbon-coated sodium iron pyrophosphate ($Na_2FeP_2O_7$) was prepared by a simple and low-cost pyro-synthesis route for further use as the cathode for Na-ion batteries. The X-ray diffraction (XRD) pattern of the sample annealed at $650^{\circ}C$ confirmed the pure triclinic phase of $Na_2FeP_2O_7$. Electron microscopy studies revealed a cross linked plate shape morphology of the $Na_2FeP_2O_7$ sample. When tested for application in Na-ion battery, the $Na_2FeP_2O_7$ cathode showed two redox pairs in the potential window of 2.0-4.0 V. The cathode registered initial discharge and charge capacities of 80.85 and 90 mAh/g, respectively, with good cycling performance.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.59.1-59.1
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• 2015

In the Linford group at Brigham Young University we have recently developed three new sets of materials for three different areas of separations science: thin layer chromatography (TLC), high performance liquid chromatography (HPLC), and solid phase microextraction (SPME). First, via microfabrication we have grown patterned carbon nanotube (CNT) forests on planar substrates that we have infiltrated with inorganic materials such as silicon nitride. The coatings on the CNTs are conformal and typically deposited in a process like low pressure chemical vapor deposition. The resulting materials have high surface areas, are porous, and function as effective separation devices, where separations on our new TLC plates are typically significantly faster than on conventional devices. Second, we used the layer-by-layer (electrostatically driven) deposition of poly (allylamine) and nanodiamond onto carbonized poly (divinylbenzene) microspheres to create superficially porous particles for HPLC. Many interesting classes of molecules have been separated with these particles, including various cannabinoids, pesticides, tricyclic antidepressants, etc. Third, we have developed new materials for SPME by sputtering silicon onto cylindrical fiber substrates in a way that creates shadowing of the incoming flux so that materials with high porosity are obtained. These materials are currently outperforming their commercial counterparts. Throughout this work, the new materials we have made have been characterized by X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, scanning electron microscopy, transmission electron microscopy, etc.

• Journal of the Korean Ceramic Society
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• v.43 no.2 s.285
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• pp.69-73
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• 2006

A full retention of the tetragonal phase with coarse grains $(50\~60\;{\mu}m)$ was possible with the specimen $ZrO_2-1.9\;mol\%\;Y_2O_3$. In these coarse grains, $\{101\}_t$ annealing twins were frequently observed, although they do not exist in the usual fine grained specimens. The morphology and growth rate of the isothermally formed individual products are studied at an optical microscopic level. The habit planes of both products are also identified by performing two-surface trace analysis on the grains whose orientations are determined by the Electron Back Scattering Pattern (EBSP) method. The morphologies of isothermal martensite were well-defined thin plates and lenticular types. The growth rate in their longitudinal directions was quite slow and temperature-dependent. A two-surface trace analysis, incorporated with the EBSP method, identified the habit planes near $\{013\}_c$, in agreement with previous reports obtained from TEM works.

• The Plant Pathology Journal
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• v.16 no.4
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• pp.189-199
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• 2000

To search for the antifungal substances, various actino-mycete isolates were obtained from various soils of Korea using plate dilution method on the humic acid vitamin agar plates. In the screening procedures using a dual culture method, 32 actionomycete isolates were selected, which showed the inhibitory activity against mycelial growth of plant pathogenic fungi Altirnaria mali, Colletotrichum gloeosporides, Fusarium oxysporum f.sp. cucumerinum, Magnaporthe grisea, Phytophthora capsici, and Rhizoctonia solani. Bioassay of the crude extracts from culture filtrates and mycelial mets revealed that 12 antagonistic actionomycetes produced highly active antifungal substances. Actinomycete strain S5-55 which showed the substantial antifungal activity against the tested fungi was selected for production of the antifungal substances. Based on the cytochemical and morphological characteristics, strain S5-55 was identified as a Streptomyces species. The results of the numerical identification using the TAXON program confirmed that Streptomyces strain S5-55 was identical with Streptomyces humidus including in TAXON major cluster 19. The production of antifungal substance was most favorable when S. humidus strain S5-55 was cultivated for 10 dats on soluble starch broth supplemented with $K_2$HPO$_4$. The antifungal substances active against the plant pathogenic fungi P. capsici and M. grisea were partially purified using $\textrm{C}_{18}$ reversed-phase column chromatography.

• Restorative Dentistry and Endodontics
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• v.16 no.2
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• pp.1-17
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• 1991

The purpose of this study was to analyze the in vivo amalgam corrosion products qualitatively. 30 molars with large, intact amalgam restorations were selected. All the restorations were more than 5 years old. Twenty of the removed amalgams were embedded in acrylic resin block. The exposed surfaces of fifteen embedded amalgams were polished by amalgam polishing kit, and the rest were observed without polishing. The remaining 10 amalgams were fractured centrally and perpendiculary to the occlusal surface with a wire-cutter. After all specimens were cleaned ultrasonically in distilled water, each surface was examined under S.E.M. and E.D.A.X. (Energy Dispersive Micro X-ray Analyzer) to determine the morphology and chemical nature of the corrosion products. The following results were obtained: 1. The surfaces of the unpolished amalgam restorations were covered with thin amorphous layer of Sn-Ca-P-S complex with numerous cracks. 2. In the conventional amalgams, the major corrosion products were Sn-Cl phases however, tin oxide phases were also observed. 3. Only tin oxide phase was identified in the high copper amalgam, but it was less frequently observed than in the conventional amalgam. 4. It was easier to observe the corrosion product morphology in the fractured surfaces than in the polished ones. The morphologies of the corrosion product crystals looked like a stack of slightly bended plates in the Sn-Cl phases and polyhedra or polygonal prisms in the tin oxide phases.

• Journal of Power System Engineering
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• v.17 no.6
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• pp.122-129
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• 2013

The microstructure and deformation behavior in 22Cr-0.2N micro-duplex stainless steels with various Ni and Mn contents were compared using by OM, TEM, and XRD. The 22Cr-0.2N duplex stainless steel plates were fabricated and hot rolled, followed by annealing treatment at the temperature range of $1,000-1,100^{\circ}C$. All the samples showed the common strain hardening behaviour during the tensile test at a room temperature. The steels tested at the temperatures of $-30^{\circ}C$ or $-50^{\circ}C$ showed a distinct inflection point in the stress-strain curves, which should be resulted from the formation of strain-induced martensite(SIM) of austenite phase. This was confirmed by TEM observations. The onset strain of a inflection point in a stress-strain curve should be depended up the value of $M_d30$. With the decrease of the tensile test temperature, the inflection point appeared earlier, and the strength and fracture strain were higher. The tensile behaviour was discussed from the point of austenite stability of the micro-duplex stainless steels with the different Ni and Mn content.