• Clean Technology
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• v.26 no.4
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• pp.286-292
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• 2020

This study confirmed the effect of the Cu/CeO2-X catalyst on the CO oxidation activity at low temperature through the catalyst's structure and reaction characteristics. The catalyst was prepared by the wet impregnation method. Cu/CeO2_X catalysts were manufactured by loading Cu (active metal) using CeO2 (support) formed at different calcination temperatures (300-600 ℃). Manufactured Cu/CeO2_X catalysts were evaluated for the low-temperature activity of carbon monoxide. The Cu/CeO2_300 catalyst showed an activity of 90% at 125 ℃, but the activity gradually decreased as the calcination temperature of the CeO2-X and Cu/CeO2_600 catalysts showed an activity of 65% at 125 ℃. Raman, XRD, H2-TPR, and XPS analysis confirmed the physicochemical properties of the catalysts. Based on the XPS analysis, the lower the calcination temperature of the CeO2 was, the higher the unstable Ce3+ species (non-stoichiometric species) ratio became. The increased Ce3+ species formed a solid solution bond between Cu and CeO2-X, and it was confirmed by the change of the CeO2 peak in Raman analysis and the reduction peak of the solid solution structure in H2-TPR analysis. According to the result, the formation of the solid solution bond between Cu and Ce has been enhanced by the redox properties of the catalysts and by CO oxidation activity at low temperatures.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.34 no.1
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• pp.1-7
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• 2021

This study investigated the structural, dielectric, ferroelectric, and strain properties of (0.98-x)Bi1/2Na1/2TiO3-0.02BiFeO3-xSrTiO3 (BNT-BF-100xST, x＝0.20, 0.22, 0.24, 0.26, and 0.28). All samples were successfully synthesized using the conventional solid-state reaction method and sintered at 1,175℃ for 2 h. The average grain size of the BNT-BF-100x ceramics decreased with increasing ST content. Furthermore, we observed that the ferroelectric- relaxor transition temperature (TF-R) decreased with increasing ST content, which eventually vanished in the BNT-BF-24ST ceramics. The results indicated that a ferroelectric to relaxor phase transition could be induced by ST modification. Consequently, a large electromechanical strain of 633 pm/V at 4 kV/mm was observed for the BNT-BF-26ST ceramics. These results imply that our materials have the competitive advantage of larger strain under lower operating field conditions compared with other BNT-based lead-free piezoelectric ceramics. We expect that BNT-BF-ST lead-free piezoelectric ceramics are promising candidates as a novel ternary BNT-based system and can find potential applications in actuators.

• Applied Chemistry for Engineering
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• v.33 no.3
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• pp.309-314
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• 2022

Carbon dots (CDs) are few nanometer-sized carbon-based nanoparticles and emerging candidate materials in various fields such as biosensors and bioimaging due to their excellent optical properties and high biocompatibility. However, most CDs, emitting blue light, have limited their application in biomedical fields due to the low penetration of short-wavelength lights into the biological system. Therefore, there has been enormous need to develop long-wavelength emitting CDs. In this study, red-emitting CDs were successfully synthesized through the hydrothermal reaction of p-phenylenediamine with hydrochloric acid. In addition, the effect of the amount of hydrochloric acid on the formation of carbon dots, resulting in the variation of the chemical structures of CDs, were investigated, which was confirmed with the intensive structural analyses using infrared and X-ray photoelectron spectroscopy. It was found that the chemical structure of CDs governed their optical properties and quantum yield. Therefore, this study provides an insight into the role of acid in forming red-emitting CDs as the optimal probe for biomedical application.

• Journal of Korea Entertainment Industry Association
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• v.14 no.3
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• pp.431-442
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• 2020

This study examined the effect of the theratainment swiss ball exercise on the upper limb function, pain, and daily activities of a patient with axillary nerve injury. The research duration was from November 5^th, 2019 to February 25^th, 2020. The research subject was a 23-year-old female patient living in the metropolitan city of G in South Korea, and the A-B-A' type of single-subject experimental research design was used. In this study, repeated training was provided to the patient in the form of exercises employing different directions and gradually increased weights. The training increased the structural stability and mobility of the shoulder and was effective for pain relief as it strengthened shoulder function. The training helped the subject improve her posture change adaptability and reaction ability in different environments and ultimately enabled her to increase and maximize her performance of independent daily activities. This study thus demonstrated the positive effect of the Swiss ball exercise on the upper limb function, pain and disability, daily activities of a patient with axillary nerve injury and confirmed the potential of the exercise as an intervention method. Continued investigation to develop and test the effect of the Swiss ball exercise will be required for it to be used professionally as a therapeutic approach by occupational therapists in treating a variety of patients.

• Applied Chemistry for Engineering
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• v.34 no.1
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• pp.15-22
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• 2023

Recent studies have actively investigated ways to improve the economic feasibility and efficiency of the Fischer-Tropsch process by increasing the yields of the monocyclic aromatic compounds (BTEX). In this study, ethylene was selected as a model of F-T-derived hydrocarbons, and the ethylene-to-aromatics (ETA) reaction was investigated according to changes in acid characteristics, mesopores, and crystallinity of HZSM-5 (HZ5). Fluorinated HZ5 was prepared by calcination followed by impregnation of an aqueous NH₄F solution having different molar concentrations in HZ5, and the structural and chemical properties of F/HZ5 were investigated through Brunauer-Emmett-Teller (BET), solid-state nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), NH₃-temperature-programmed desorption (TPD), and pyridine-IR spectroscopy. The ETA reactions were performed at 673 K under 0.1 MPa, and fluorinating HZ5 by an aqueous NH₄F solution of 0.17 M improved ethylene conversion, BTEX selectivity, and catalytic stability due to acidity, mesopore fraction, and crystallinity.

• Journal of Marine Life Science
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• v.6 no.2
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• pp.73-79
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• 2021

Bisphenol A is a representative endocrine disruptor and continuously detected in aquatic environment due to wide use, resulting in adverse effects on growth, development, and reproduction in diverse organisms as well as human. Structural analogs have been developed to substitute BPA are also suspected to have endocrine disrupting effects. In the present study, the time-dependent expression patterns of ecdysteroid synthesis (nvd, cyp314a1), receptors (EcRA, EcRB, USP, ERR), and downstream signaling pathway - related genes (HR3, E75, Vtg, VtgR) were investigated using quantitative real time reverse transcription polymerase chain reaction (qRT-PCR) in the brackish water flea Diaphanosoma celebensis exposed to Bisphenol analogs (BPs; BPA, BPF, and BPS) for 6, 12, and 24 h. As results, the expression of nvd, cyp314a1, EcRs, USP, ERR and E75 mRNA was upregulated at 6 h exposure to BPF, which is earlier than BPA and BPS (12 h). On the other hand, HR3, E75 and VtgR mRNA levels were elevated at 6 h earlier at BPS and BPF than at BPA (12 h), but Vtg mRNA level was slightly changed within 24 h. These findings suggest that like BPA, BPF and BPS can also modulate the transcription of ecdysteroid pathway - related genes with different mechanisms, and have a potential as endocrine disruptors. This study will provide a better understanding the molecular mode of action of bisphenols on ecdysteroid pathway in the brackish water flea.

• Korean Journal of Optics and Photonics
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• v.33 no.2
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• pp.74-83
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• 2022

The entire process, from the raw material to the final system qualification test, has been developed to fabricate a large-diameter, lightweight reflective-telescope system for a satellite observation. The telescope with 3 anastigmatic mirrors has an aperture of 700 mm and a total mass of 66 kg. We baked a silicon carbide substrate body from a carbon preform using a reaction sintering method, and tested the structural and chemical properties, surface conditions, and crystal structure of the body. We developed the polishing and coating methods considering the mechanical and chemical properties of the silicon carbide (SiC) body, and we utilized a chemical-vapor-deposition method to deposit a dense SiC thin film more than 170 ㎛ thick on the mirror's surface, to preserve a highly reflective surface with excellent optical performance. After we made the SiC mirrors, we measured the wave-front error for various optical fields by assembling and aligning three mirrors and support structures. We conducted major space-environment tests for the components and final assembly by temperature-cycling tests and vibration-shock tests, in accordance with the qualifications for the space and launch environment. We confirmed that the final telescope achieves all of the target performance criteria.

• Korean Journal of Materials Research
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• v.33 no.8
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• pp.330-336
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• 2023

The effects of Ni²⁺ substitution for Mg²⁺-sites on the microwave dielectric properties of (Mg_1-xNi_x)(Ti_0.95(Mg_1/3Ta_2/3)_0.05)O₃ (0.01 ≤ x ≤ 0.05) (MNTMT) ceramics were investigated. MNTMT ceramics were prepared by conventional solid-state reaction. When the MgO / TiO₂ ratio was changed from 1.00 to 1.02, MgTi₂O₅ was detected as a secondary phase along with the MgTiO₃ main phase in the MNTMT specimens sintered at 1,400 ℃ for 4h. For the MNTMT specimens with MgO / TiO₂ = 1.07 sintered at 1,400 ℃ for 4h, a single phase of MgTiO₃ with an ilmenite structure was obtained from the entire range of compositions. The relative density of all the specimens sintered at 1,400 ℃ for 4h was higher than 95 %. The quality factor (Qf) of the sintered specimens depended strongly on the degree of covalency of the specimens, and the sintered specimens with x = 0.01 showed the maximum Qf value of 489,400 GHz. The dielectric constant (K) decreased with increasing Ni²⁺ content because Ni²⁺ had a lower dielectric polarizability (1.23ų) than Mg²⁺ (1.32ų). As Ni²⁺ content increased, the temperature coefficient of resonant frequency (TCF) improved, from -55.56 to -21.85 ppm/℃, due to the increase in tolerance factor (t) and the lower dielectric constant (K).

• Journal of the Microelectronics and Packaging Society
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• v.29 no.4
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• pp.9-14
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• 2022

Silica aerogel is a porous material with a very low density and high specific surface area. Still, its application is limited due to its weak mechanical properties due to structural features. To solve this problem, a method of complexing it with various polymers has been proposed. We synthesized polyimide cross-linked silica aerogel by the sol-gel process to obtain high mechanical properties. Tetraethyl orthosilicate (TEOS) was used as a precursor to make silica aerogel, and 3- aminopropyltriethoxysilane (APTES) was used as a coupling agent for cross-linking polyimide. Polyimide was synthesized using pyromellitic dianhydride and 3,5-diaminobenzoic acid, and mechanical properties were improved by crosslinking polyimide with 10 repeating units in the polyimide chain using the reaction formula ${\frac{n_1}{n_2}}={\frac{n}{n+1}}$ To realize silica aerogel, polyimide having various weight ratios was added before gelation, resulting in a 19-fold or greater increase in maximum compressive strength compared to pure silica aerogel. From this study, an enhancement of silica aerogel could be enhanced through polymer cross-linking bonds.

• Composites Research
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• v.36 no.6
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• pp.441-447
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• 2023

Recently, as demand for high-strength, lightweight materials has increased, there has been great interest in joining with metals. In the case of mechanical bonding, such as bolting and riveting, chemical bonding using adhesives is attracting attention as stress concentration, cracks, and peeling occur. In this paper, surface treatment was performed to improve the adhesive strength, and the change in adhesive strength was analyzed. For the adhesive strength test were conducted with Carbon Fiber Reinforced Plastic(CFRP), CR340(Steel), and Al6061(Aluminum), and laser and plasma surface treatment were used. After plasma surface treatment, the adhesive strength improved by 7.3% and 39.2% in CFRP-CR340 and CFRP-Al6061, respectively. CR340-Al6061 was improved by 56.2% in laser surface treatment. Surface free energy(SFE) was measured by contact angle after plasma treatment, and it is thought that the adhesion strength was improved by minimizing damage through a chemical reaction mechanism. For laser surface treatment, it is thought that creates a rough bonding surface and improves adhesive strength due to the mechanical interlocking effect. Therefore, surface treatment is effect to improve adhesive strength, and based on this paper, the long-term fatigue test will be conducted to prevent fatigue failure, which is a representative cause of actual structural damage.