• 한국분말재료학회지
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• 제29권1호
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• pp.22-27
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• 2022

Conventionally, metal materials are produced by subtractive manufacturing followed by melting. However, there has been an increasing interest in additive manufacturing, especially metal 3D printing technology, which is relatively inexpensive because of the absence of complicated processing steps. In this study, we focus on the effect of varying powder size on the synthesis quality, and suggest optimum process conditions for the preparation of AlCrFeNi high-entropy alloy powder. The SEM image of the as-fabricated specimens show countless, fine, as-synthesized powders. Furthermore, we have examined the phase and microstructure before and after 3D printing, and found that there are no noticeable changes in the phase or microstructure. However, it was determined that the larger the powder size, the better the Vickers hardness of the material. This study sheds light on the optimization of process conditions in the metal 3D printing field.

• 대한방사성의약품학회지
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• 제6권2호
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• pp.102-115
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• 2020

In the state of Positronium (Ps), which is an unstable material created by the temporary combination of electrons and positrons, the imaging technology through photo-conversion methodology is emerging as a new research theme under resonance conditions through terahertz electromagnetic waves. Normally, Positronium can be observed in the positron emission computed tomography (PET) process when an unstable, separate state that remains after the pair annihilation of an electron and a positron remains. In this study, terahertz (THz) waves and Cherenkov radiation (CR) are generated using the principle of ponderomotive force in the plasma wake-field acceleration, and electrons and positrons are simultaneously generated by using a relativistic electron beam without using a PET device. We confirm the possibility of Positronium photoconversion technology in terahertz electromagnetic resonance conditions through experimental studies that generate an unstable state. Here, a relativistic electron beam (REB) energy of 0.5 MeV (γ=2) was used, and the terahertz wave frequencies is G-band. Meanwhile, a THz wave mode converting three-stepped axicon lens was used to apply the photoconversion technology. Through this, light emission in the form of a luminescence-converted Bessel beam can be verified. In the future, it can be used complementarily with PET in nuclear medicine in the field of medical imaging.

• 한국임상수의학회지
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• 제40권1호
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• pp.16-24
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• 2023

This study aimed to compare complete ruptured tendon healing between two different repair methods using the Achilles tendon of New Zealand white rabbits. Thoracolumbar fascia (TF) padded Kessler suture, polypropylene mesh (PM) padded Kessler suture, and Kessler suture only were performed on the completely transected lateral gastrocnemius tendon, and biomechanical and histologic characteristics were assessed after 8 weeks. For biomechanical assessment, the tensile strength of each repaired tendon was measured according to the established methods. For histomorphometric analysis, hematoxylin and eosin staining for general histology, and Masson's trichrome (MT) staining for collagen fibers, Alcian blue (AB) staining for proteoglycans were performed and analyzed. Significant increases in tensile strength with remarkable decreases in the abnormalities against nuclear roundness, cell density, fiber structure, and fiber alignment and significant decreases in the mean number of infiltrated inflammatory cells and AB-positive proteoglycan-occupied regions with increases in MT-positive collagen fiber-occupied regions were demonstrated in the Kessler suture with PM or TF padding groups as compared to those of the Kessler suture group. Both of PM and TF provided potent tensile strength and supported healing with the evidence of histological examinations. This means that augmentation with PM is useful for repairing a completely ruptured Achilles tendon, without additional surgery for autograft material harvesting.

• Journal of Microbiology and Biotechnology
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• 제33권4호
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• pp.463-470
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• 2023

This study confirmed the change in functional composition and alcohol-induced acute liver injury in Aloe arborescens after fermentation. An acute liver injury was induced by administration of ethanol (3 g/kg/day) to C57BL/6J mice for 5 days. A fermented A. arborescens Miller leaf (FAAL) extract was orally administered 30 minutes before ethanol treatment. After fermentation, the emodin content was approximately 13 times higher than that of the raw material. FAAL extract significantly attenuated ethanol-induced aspartate aminotransferase, alanine aminotransferase, and triglyceride increases in serum and liver tissue. Histological analysis revealed that FAAL extract inhibits inflammatory cell infiltration and fat accumulation in liver tissues. The cytochrome P450 2E1, superoxide dismutase, and glutathione (GSH), which involved in alcohol-induced oxidative stress, were effectively regulated by FAAL extract in serum and liver tissues, except for GSH. FAAL also maintained the antioxidant defense system by upregulating heme oxygenase 1 and nuclear factor erythroid 2-related factor 2 protein expression. In addition, FAAL extract inhibited the decrease in alcohol dehydrogenase and aldehyde dehydrogenase activity, which promoted alcohol metabolism and prevented the activation of inflammatory response. Our results suggest that FAAL could be used as a potential therapeutic agent for ethanol-induced acute liver injury.

• Advances in nano research
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• 제14권5호
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• pp.435-442
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• 2023

Sports activities, including playing tennis, are popular with many people. As this industry has become more professionalized, investors and those involved in sports are sure to pay attention to any tool that improves athletes' performance Tennis requires perfect coordination between hands, eyes, and the whole body. Consequently, to perform long-term sports, athletes must have enough muscle strength, flexibility, and endurance. Tennis rackets with new frames were manufactured because tennis players' performance depends on their rackets. These rackets are distinguished by their lighter weight. Composite rackets are available in many types, most of which are made from the latest composite materials. During physical exercise with a tennis racket, nanocomposite materials have a significant effect on reducing injuries. Materials as strong as graphite and thermoplastic can be used to produce these composites that include both fiber and filament. Polyamide is a thermoplastic typically used in composites as a matrix. In today's manufacturing process, materials are made more flexible, structurally more vital, and lighter. This paper discusses the production, testing, and structural analysis of a new polyamide/Multi-walled carbon nanotube nanocomposite. This polyamide can be a suitable substitute for other composite materials in the tennis racket frame. By compression polymerization, polyamide was synthesized. The functionalization of Multi-walled carbon nanotube (MWCNT) was achieved using sulfuric acid and nitric acid, followed by ultrasonic preparation of nanocomposite materials with weight percentages of 5, 10, and 15. Fourier transform infrared (FTIR) and Nuclear magnetic resonance (NMR) confirmed a synthesized nanocomposite structure. Nanocomposites were tested for thermal resistance using the simultaneous thermal analysis (DTA-TG) method. scanning electron microscopy (SEM) analysis was used to determine pores' size, structure, and surface area. An X-ray diffraction analysis (XRD) analysis was used to determine their amorphous nature.

• 한국초전도ㆍ저온공학회논문지
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• 제25권4호
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• pp.70-74
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• 2023

The Small Punch Test (SPT) was developed to evaluate the softening and embrittlement of materials such as power plants and nuclear fusion reactors by taking samples in the field. Specimens used in the SPT are very thin and small disk-shaped compared to specimens for general tensile test, and thus have economic advantages in terms of miniaturization and repeatability of the test. The cryogenic SPT can also be miniaturized and has a significantly lower heat capacity than conventional universal test machines. This leads to reduced cooling and warm-up times. In this study, the cryogenic SPT was developed by modifying the existing room temperature SPT to be cooled by liquid nitrogen using a super bellows and a thermal insulation structure. Since the cryogenic SPT was first developed, basic experiments were conducted to verify the effectiveness of it. For the validation, aluminum alloy 6061- T6 specimens were tested for mechanical properties at room and cryogenic temperature. The results of the corrected tensile properties from the SPT experiment results were compared with known room temperature and cryogenic properties. Based on the correction results, the effectiveness of the cryogenic SPT test was confirmed, and the surface fracture characteristics of the material were analyzed using a 3d image scanner. In the future, we plan to conduct property evaluation according to the development of various alloy materials.

• 한국표면공학회지
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• 제56권6호
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• pp.401-411
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• 2023

This study investigates the synthesis, characterization, and application of zinc oxide (ZnO) nanoparticles for corrosion resistance and stress corrosion cracking (SCC) mitigation in high-temperature and high-pressure environments. The ZnO nanoparticles are synthesized using plasma discharge in water, resulting in rod-shaped particles with a hexagonal crystal structure. The ZnO nanoparticles are applied to Alloy 600 tubes in simulated nuclear power plant atmospheres to evaluate their effectiveness. X-ray diffraction and X-ray photoelectron spectroscopy analysis reveals the formation of thermodynamically stable ZnCr₂O₄and ZnFe₂O₄ spinel phases with a depth of approximately 35 nm on the surface after 240 hours of treatment. Stress corrosion cracking (SCC) mitigation experiments reveal that ZnO treatment enhances thermal and mechanical stability. The ZnO-treated specimens exhibit increased maximum temperature tolerance up to 310 ℃ and higher-pressure resistance up to 60 bar compared to non-treated ZnO samples. Measurements of crack length indicate reduced crack propagation in ZnO-treated specimens. The formation of thermodynamically stable Zn spinel structures on the surface of Alloy 600 and the subsequent improvements in surface properties contribute to the enhanced durability and performance of the material in challenging high-temperature and high-pressure environments. These findings have significant implications for the development of corrosion-resistant materials and the mitigation of stress corrosion cracking in various industries.

• 한국식품영양학회지
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• 제37권1호
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• pp.17-29
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• 2024

To increase industrial applicability of Astragalus membranaceus (AM) as immunostimulating materials, hot-water extract (AME) was prepared from AM and fermented with Kimchi-lactic acid bacteria (Lactobacillus sakei & Leuconostoc mesenteroides) to prepare fermented AM-postbiotics (FAME). Although FAME prepared from AM-postbiotics did not show a significant enhancement in macrophage stimulating activity compared to non-fermented AME, crude polysaccharide (FAME-CP) fractionated by EtOH precipitation from FAME showed significantly higher macrophage stimulating activity than AME-CP. Compared to AME-CP, FAME-CP showed dramatic changes in component sugar and molecular weight distribution. FAME-CP was a polysaccharide with a major molecular weight distribution of 113.4 kDa containing Man (44.2%), Glc (19.3%), Gal (10.2%), GalA (10.2%), and Ara (7.4%) as sugar components. FAME-CP with enhanced macrophage stimulatory activity not only increased expression levels of mRNA genes encoding macrophage-activated factors (iNOS, TNF-α, MCP-1, IL-6, and COX-2), but also led the nuclear translocation of activated p65 and c-Jun. In conclusion, crude polysaccharide from AM-postbiotics fermented with lactic acid bacteria could increase industrial applicability as a functional material with enhanced immunostimulating activity than AME-CP.

• Advances in concrete construction
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• 제16권6호
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• pp.291-302
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• 2023

As the first part of the body that strikes the ground during running, sports shoes are especially important for improving performance and reducing injuries. The use of new nanotechnology materials in the shoe's sole that can affect the movement angle of the foot and the ground reaction forces during running has not been reported yet. It is important to consider the material of the sole of the shoe since it determines the long-term performance of sports shoes, including their comfort while walking, running, and jumping. Running performance can be improved by polymer foam that provides good support with low energy dissipation (low energy dissipation). Running shoes have a midsole made of ethylene propylene copolymer (EPP) foam. The mechanical properties of EPP foam are, however, low. To improve the mechanical performance of EPP, conventional mineral fillers are commonly used, but these fillers sacrifice energy return. In this study, to improve the magnificence of physical education training with nanotechnology, carbon nanotubes (CNTs) derived from recycled plastics were prepared by catalytic chemical vapor deposition and used as nucleating and reinforcing agents. As a result of the results, the physical, mechanical, and dynamic response properties of EPP foam combined with CNT and zinc oxide nanoparticles were significantly improved. When CNT was added to the nanocomposites with a weight percentage of less than 0.5 wt%, the wear resistance, physical properties, dynamic stiffness, compressive strength, and rebound properties of EPP foams were significantly improved.

• Tribology and Lubricants
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• 제40권3호
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• pp.97-102
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• 2024

The next-generation Molten Salt Reactor is known for its high safety because it uses nuclear fuel dissolved in high-temperature molten salt, unlike traditional solid atomic fuel methods. However, the high-temperature molten salt causes severe corrosion in internal structural materials, threatening the reactor's safety. Therefore, it is crucial to investigate the high-temperature corrosion resistance and wear performance of materials used in reactors to ensure safety. In this study, the high-temperature corrosion resistances and wear performances of corrosion samples in a NaCl-MgCl2-KCl (20-40-40 [wt%]) molten salt are investigated to evaluate the applicability of economically viable stainless steels, 316SS and 304SS. Hastelloy C276 and a new alloy containing a small amount of Nb are used as reference samples for comparative analysis. The mass loss, mass loss rate per unit volume, and surface roughness of each sample are measured to understand the corrosion mechanisms. Scanning electron microscopy and energy-dispersive spectroscopy analyses are employed to analyze the corrosion mechanisms. Wear tests on the corroded samples are also conducted to assess the extent of corrosion. Based on the experimental results, we predict the lifespans of the materials and evaluate their suitability as candidate materials for molten salt reactors. The data obtained from the experiments provide a valuable database for structural materials that can enhance the stability of molten salt reactors and recommend high-temperature corrosion-resistant materials suitable for next-generation reactors.