• Membrane Journal
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• v.31 no.1
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• pp.16-34
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• 2021

Water supplies are decreasing in comparison to increasing clean water demands. Using nanofiltration is one of the most effective and economical methods to meet the need for clean water. Common methods for desalination are reverse osmosis and nanofiltration. However, pristine membranes lack the essential features which are, stability, economic efficiency, antibacterial and antifouling performances. To enhance the properties of the pristine membranes, graphene oxide (GO) is a promising and widely researched material for thin film composites (TFC) membrane due to their characteristics that help improve the hydrophilicity and anti-fouling properties. Modification of the membrane can be done on different layers. The thin film composite membranes are composed of three different layers, the top filtering active thin polyamide (PA) layer, supporting porous layer, and supporting fabric. Forward osmosis (FO) process is yet another energy efficient desalination process, but its efficiency is affected due to biofouling. Incorporation of GO enhance antibacterial properties leading to reduction of biofilm formation on the membrane surface. Pressure retarded osmosis (PRO) is an excellent process to generate clean energy from sea water and the biofouling of membrane is reduced by introduction of GO into the active layer of the TFC membrane. Different modifications on the membranes are being researched, each modification with its own advantages and disadvantages. In this review, modifications of nanofiltration membranes and their composites, characterization, and performances are discussed.

• Journal of Powder Materials
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• v.28 no.2
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• pp.143-149
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• 2021

In this study, (GaN)_1-x(ZnO)_x solid solution nanoparticles with a high zinc content are prepared by ultrasonic spray pyrolysis and subsequent nitridation. The structure and morphology of the samples are investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The characterization results show a phase transition from the Zn and Ga-based oxides (ZnO or ZnGa₂O₄) to a (GaN)_1-x(ZnO)_x solid solution under an NH3 atmosphere. The effect of the precursor solution concentration and nitridation temperature on the final products are systematically investigated to obtain (GaN)_1-x(ZnO)_x nanoparticles with a high Zn concentration. It is confirmed that the powder synthesized from the solution in which the ratio of Zn and Ga was set to 0.8:0.2, as the initial precursor composition was composed of about 0.8-mole fraction of Zn, similar to the initially set one, through nitriding treatment at 700℃. Besides, the synthesized nanoparticles exhibited the typical XRD pattern of (GaN)_1-x(ZnO)_x, and a strong absorption of visible light with a bandgap energy of approximately 2.78 eV, confirming their potential use as a hydrogen production photocatalyst.

• The Journal of Advanced Prosthodontics
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• v.13 no.6
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• pp.385-395
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• 2021

PURPOSE. To characterize the microstructure of three yttria partially stabilized zirconia ceramics and to compare their hardness, indentation fracture resistance (IFR), biaxial flexural strength (BFS), and fatigue flexural strength. MATERIALS AND METHODS. Disc-shaped specimens were obtained from 3Y-TZP (Vita YZ HT), 4Y-PSZ (Vita YZ ST) and 5Y-PSZ (Vita YZ XT), following the ISO 6872/2015 guidelines for BFS testing (final dimensions of 12 mm in diameter, 0.7 and 1.2 ± 0.1 mm in thicknesses). Energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were performed, and mechanical properties were assessed by Vickers hardness, IFR, quasi-static BFS and fatigue tests. RESULTS. All ceramics showed similar chemical compositions, but mainly differed in the amount of yttria, which was higher as the amount of cubic phase in the diffractogram (5Y-PSZ > 4Y-PSZ > 3Y-TZP). The 4Y- and 5Y-PSZ specimens showed surface defects under SEM, while 3Y-TZP exhibited greater grain uniformity on the surface. 5Y-PSZ and 3Y-TZP presented the highest hardness values, while 3Y-TZP was higher than 4Y- and 5Y-PSZ with regard to the IFR. The 5Y-PSZ specimen (0.7 and 1.2 mm) showed the worst mechanical performance (fatigue BFS and cycles until failure), while 3Y-TZP and 4Y-PSZ presented statistically similar values, higher than 5Y-PSZ for both thicknesses (0.7 and 1.2 mm). Moreover, 3Y-TZP showed the highest (1.2 mm group) and the lowest (0.7 mm group) degradation percentage, and 5Y-PSZ had higher strength degradation than 4Y-PSZ group. CONCLUSION. Despite the microstructural differences, 4Y-PSZ and 3Y-TZP had similar fatigue behavior regardless of thickness. 5Y-PSZ had the lowest mechanical performance.

• Journal of Life Science
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• v.32 no.10
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• pp.778-783
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• 2022

This study isolated a new agarase-producing bacterium and characterized its agarase. A new agar-degrading strain was isolated from the seashore of Namhae in Gyeongnam province, Korea, and was purely cultured using the Marine Agar 2216 media. The isolated bacterium was identified as Simiduia sp. SH-2 after 16S rRNA gene sequencing. The crude agarase was obtained from the culture medium of the Simiduia sp. SH-2 strain, and the agar-degrading activity was measured. The highest level of activity of the Simiduia sp. SH-2-derived agar-degrading enzyme was 625 U/l. Agar degradation activity was most significant at 40℃ and pH 7.0. Compared to the activity at 40℃, the relative activity was 31% at 20℃ and 71% at 30℃. Compared to the activity at pH 7.0, the relative activity was 94% and 89% at pH 6.0 and pH 8.0, respectively. Residual activity was greater than 96% after exposure to 20℃ and 30℃ for 2 hr and more than 49% after exposure to 40℃ for 2 hr. Simiduia sp. SH-2 was identified as a strain producing β-agarase that creates neoagarooligosaccharides, such as neoagarotetraose and neoagarohexaose. Therefore, the Simiduia sp. SH-2 strain and its β-agarase are expected to be useful functional material producers in the food, cosmetic, and pharmaceutical industries.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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• v.29 no.1
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• pp.43-49
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• 2023

This study reports on the preparation of sodium caseinate-cardanol (CasNa/CL)-based papers coated with different amounts of bentonite (BN) for use as a sustainable packaging material. Their chemical and morphological structures, mechanical properties, water vapor permeability, surface properties, and antioxidant activity of coated papers was assessed as a function of the BN content. The drying of the CasNa/CL coated papers led to the formation of pinholes on their surfaces owing to the presence of trapped water resulting from the difference in the drying rate between the external surface and the inside of the coated layers. Increasing the BN content reduced the pinholes on surface of CasNa/CL/BN coated papers and highly decreased the water vapor transmittance rate of the papers from 387.3±1.9 g/m²·day to 269.25±4.5 g/m²·day. Free radical scavenging assays indicated the addition of CL to the CasNa exhibited the antioxidant activity and antioxidant activity of CasNa/CL/BN did not changed as increase of BN contents. The improved water vapor barrier property and antioxidant activity of CasNa/CL/BN coated papers can be promised for various packaging applications.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.3
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• pp.303-314
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• 2009

Image analyses for sheared joint specimens are performed to study asperity degradation characteristics with respect to the roughness mobilization of rock joints. Four different types of joint specimens, which are made of high-strength gypsum materials, are prepared by replicating the three-dimensional roughness of rock joints. About twenty jointed rock shear tests are performed at various normal stress levels. The characteristic and scale of asperity degradation on the sheared joint specimens are analyzed using the digital image analysis technique. The results show that the asperity degradation characteristic mainly depends on the normal stress level and can be defined by asperity failure and wear. The asperity degradation develops significantly around the peak shear displacement and the average amount of degraded asperities remains constant with further displacement because of new degradation of small scale asperities. The shear strength results using high-strength gypsum materials can not fully represent physical properties of each mineral particles of asperities on the natural rock joint surface. However the results of this quantitative estimation for the relationship between the peak shear displacement and the asperity degradation suggest that the characterization of asperity degradation provides an important insight into mechanical characteristics and shear models of rock joints.

• Korean Journal of Breeding Science
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• v.51 no.4
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• pp.318-325
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• 2019

Salt stress is a significant factor limiting growth and productivity in crops. However, little is known about the response and resistance mechanism to salt stress in maize. The objective of this research was to develop an enhanced salt-tolerant silage maize by mutagenesis with gamma radiation. To generate gamma radiation-induced salt-tolerant silage maize, we irradiated a KS140 inbred line with 100 Gy gamma rays. Salt tolerance was determined by evaluating plant growth, morphological changes, and gene expression under NaCl stress. We screened 10 salt-tolerant maize inbred lines from 2,248 M₂ mutant populations and selected a line showing better growth under salt stress conditions. The selected 140RS516 mutant exhibited improved seed germination and plant growth when compared with the wild-type under salt stress conditions. Enhanced salt tolerance of the 140RS516 mutant was attributed to higher stomatal conductance and proline content. Using whole-genome re-sequencing analysis, a total of 328 single nucleotide polymorphisms and insertions or deletions were identified in the 140RS516 mutant. We found that the expression of the genes involved in salt stress tolerance, ABP9, CIPK21, and CIPK31, was increased by salt stress in the 140RS516 mutant. Our results suggest that the 140RS516 mutant induced by gamma rays could be a good material for developing cultivars with salt tolerance in maize.

• Journal of Practical Engineering Education
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• v.14 no.3
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• pp.479-489
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• 2022

In order to understand how to increase the use of virtual training content at K University's online lifelong education institute, this study examined the use experience, content recognition, field practice replacement, and requirements, focusing on the examples of operating institutions. To this end, 12 institutions that operated virtual training contents distributed by the K University Online Lifelong Education Center in 2020 were selected for in-depth interviews and qualitative analysis was conducted on the interviews of 11 institutions. As a result of the analysis, first, the experience of using the contents of the virtual training operating institution was aimed at changing the educational environment, supplementing theoretical learning, and improving the sense of practice. Second, according to a survey on the recognition of virtual training content, if the importance and utilization of the content are high, it can be replaced by on-site practice in non-face-to-face classes, such as experiences of facilities and equipment, attracting interest and attention. Third, in many cases, the perception of replacement for field practice is not unreasonable to use as a pre-training material for field practice, but it is difficult to replace field practice. Fourth, content quality improvements can be summarized as content quality improvement, content access and manipulation improvement, dedicated device development, training for instructors, and curriculum systematization. Fifth, institutional requirements include improving the quality of virtual training content itself, equipment support, curriculum systemization and characterization, systematic curriculum and detailed content sharing, detailed guidance on using virtual training content, introducing how to use content, and recruiting instructors. This study is meaningful in that it sought ways to improve the utilization of virtual training content based on the perception of virtual training content operating institutions.

• Membrane Journal
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• v.33 no.6
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• pp.362-368
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• 2023

This research article explores the application of Polymer of Intrinsic Microporosity (PIM-1) as a cutting-edge material for CO₂ gas separation membranes in response to the escalating global concern over climate change and the imperative to reduce greenhouse gas emissions. The study delves into the synthesis, molecular weight control, and fabrication of PIM-1 membranes, providing comprehensive insights through various characterization techniques. The intrinsic microporosity of PIM-1, arising from its unique crosslinked and rigid structure, is harnessed for selective gas permeation, particularly of carbon dioxide. The article emphasizes the tunable chemical properties of PIM-1, allowing for customization and optimization of gas separation membranes. By controlling the molecular weight, higher molecular weight (H-PIM-1) membranes are demonstrated to exhibit superior CO₂ permeability and selectivity compared to lower molecular weight counterparts (L-PIM-1). The study's findings highlight the critical role of molecular weight in tailoring PIM-1 membrane properties, contributing to the advancement of next-generation membrane technologies for efficient and selective CO₂ capture-an essential step in addressing the pressing global challenge of climate change.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.33 no.5
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• pp.167-173
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• 2023

Li₃V₂(PO₄)₃ and Li₃V₂(PO₄)₃/C composite with single phase monoclinic structure for the cathode materials are successfully synthesized by direct co-precipitation method using N₂H₄·H₂O as the reducing agent and alginic acid as the carbon source, and their electrochemical properties were compared. The particles with approximately 1~2 ㎛ size and the uniform spherical-like morphology of the narrow particle size distribution were obtained. In addition, the residual carbon can also improve the electrical conductivity. The Li₃V₂(PO₄)₃/C composite has improved initial specific discharge capacity and excellent cycle characteristics to maintain capacity stably than Li₃V₂(PO₄)₃. The results indicate that the reducing agent and carbon composite can affect the good crystallinity and electrochemical performance of the cathode materials.