• The Journal of Korean Academy of Prosthodontics
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• v.61 no.3
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• pp.189-197
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• 2023

Purpose. This study aimed to compare and evaluate the shear bond strength between various temporary prostheses resin blocks fabricated by subtractive and additive manufacturing methods bonded to self-curing reline resin. Materials and methods. The experimental groups were divided into 4 groups according to the manufacturing methods of the resin block specimens and each specimen was fabricated by subtractive manufacturing (SM), additive manufacturing stereolithography apparatus manufacturing (AMS), additive manufacturing digital light processing manufacturing (AMD) and conventional self-curing (CON). To bond the resin block specimens and self-curing resin, the reline resin was injected and polymerized into the same location of each resin block using a silicone mold. The shear bond strength was measured using a universal testing machine, and the surface of the adhesive interface was examined by scanning electron microscopy. To compare between groups, one-way ANOVA was done followed by Tukey post hoc test (α = 0.05). Results. The shear bond strength showed higher values in the order of CON, SM, AMS, and AMD group. There were significant differences between CON and AMS groups, as well as between CON and AMD groups. but there were no significant differences between CON and SM groups (P > .05). There were significant differences between SM and AMD groups, but there were no significant differences between SM and AMS groups. The AMS group was significantly different from the AMD group (P < .001). The most frequent failure mode was mixed failures in CON and AMS groups, and adhesive failures in SM and AMD groups. Conclusion. The shear bond strength of SM group showed lower but not significant bond strength compared to the CON group. The additive manufacturing method groups (AMS and AMD) showed significantly lower bond strength than the CON group, with the AMD group the lowest. There was also a significant difference between the AMD and SM group.

• Membrane Journal
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• v.34 no.1
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• pp.50-57
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• 2024

In this experiment, Pd-Ag-Cu membrane was manufactured using electroless plating on an α-Al₂O₃ support. Pd, Ag and Cu were each coated on the surface of the support through electroless plating and heat treatment was performed for 18 h at 500℃ in H₂ in the middle of electroless plating to form Pd alloy. The surface of the Pd-Ag-Cu membrane was observed through Scanning Electron Microscopy (SEM), and the thickness of the Pd membrane was measured to be 7.82 ㎛ and the thickness of the Pd-Ag-Cu membrane was measured to be 3.54 ㎛. Energy dispersive X-ray spectroscopy and X-ray diffraction analysis confirmed the formation of a Pd-Ag-Cu alloy with a composition of Pd-78wt%, Ag-8.81wt% and Cu-13.19wt%. The gas permeation experiment was conducted under the conditions of 350~450℃ and 1~4 bar in H₂ single gas and H₂/N₂ mixed gas. The maximum H₂ flux of the hydrogen separation membrane measured in H₂ single gas is 74.16 ml/cm²·min at 450℃ and 4 bar for the Pd membrane and 113.64 ml/cm²·min at 450℃ and 4 bar for the Pd-Ag-Cu membrane. In the case of the separation factor measured in H₂/N₂ mixed gas, separation factors of 2437 and 11032 were measured at 450℃ and 4 bar.

• The Journal of Korean Academy of Prosthodontics
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• v.62 no.2
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• pp.95-103
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• 2024

Purpose. With the advancement of digital technology, 3D printing is being utilized in the fabrication of denture base. Nevertheless, increasing microbial adhesion to the surface of denture base has been reported as the disadvantage of 3D-printed denture base. The purpose of this study is to investigate the antifungal properties and flexural strength of 3D-printed denture base resin according to the different contents of titanium dioxide nanoparticles. Materials and methods. Titanium dioxide nanoparticles were mixed with the 3D printing resin at the ratios of 0.5, 1, 1.5, and 2 wt%. Twenty specimens per each group were printed in the form of cylindrical shape (diameter: 20 mm, height: 3 mm) to evaluate antifungal properties. Ten specimens from each group underwent polishing using autogrinder, while the remaining ten specimens did not. Candida albicans in hyphae form was inoculated onto each specimen, optical density and colony-forming unit were analyzed. The surface of the specimen was observed using scanning electron microscopy. To evaluate the flexural strength, twenty specimens per each group were 3D printed in the form of rectangular prism shape (length: 64 mm, height: 10 mm, width: 3 mm) and three-point bending tests were conducted using universal testing machine according to ISO 20795-1. Results. Colony-forming unit of C.albicans and optical density of culture medium showed no difference between non-polished groups, but decreased in the polished groups at concentration of 1, 1.5, 2 wt% titanium dioxide nanoparticles. Flexural strength increased with titanium dioxide nanoparticle at concentration of 0.5, 1, 1.5 wt%, but decreased at 2 wt% compared to 1.5 wt%. Conclusion. When 1.5 wt% of titanium dioxide nanoparticles were added to the 3D-printed denture base resin with polishing, antifungal properties were increased.

• Korean Journal of Heritage: History & Science
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• v.57 no.3
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• pp.104-114
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• 2024

Sheet Music of the National Anthem of Korea with Lyrics in Korean, Chinese, and English is a four-sided sheet of paper folded in half. It was first introduced to Korea on November 12, 1945, by Kim Ku, the president of the Provisional Government. The sheet music was published in three languages and is a valuable document for researching the evolution of the anthem and its history. Although it was published in large quantities at the time, it is currently known as the only in Korea and has been designated and managed as a national registered heritage. The sheet music was not significantly damaged, but discoloration and physical damage suggested raised the need for conservation treatment. A pre-treatment examination of the conservation condition revealed that the artifact was received on archival film and had been folded in half for many years, leaving it vulnerable to tears at the top and bottom of the folds and partial wear and tear at the edges. In addition, the pigments used on both sides of the sheet had discolored and transferred to the opposite side. Portable X-ray fluorescence (XRF) analysis was conducted to investigate the pigments used in the sheet music cover, specifically focusing on red, black, and light blue pigments. Titanium (Ti) was detected in the light blue pigment, characterized by a powdery coloring layer. The remaining colors in the printed form were difficult to sample and could not be analyzed further. The light blue sample underwent additional analysis using X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), and Raman spectroscopy. Cross-validation of the results with the artifact's historical context suggested that the bright blue color observed in the 1945 sheet music is likely due to the use of anatase white pigment, rather than rutile. Furthermore, the bright blue pigment is believed to be a blend of phthalocyanine blue, a synthetic pigment introduced in 1936. Fiber analysis revealed longitudinal striations in the hemp fibers and twists in the cotton fibers, suggesting that the paper was made from a mixture of cotton and hemp fibers. Based on the findings of the condition survey, the conservation treatment for the artifact focused on minimizing moisture to avoid stressing the paper and reinforcing the physically vulnerable areas. The reinforcement paper was dyed to match the base of the artifacts, pre-coated repair paper was used for conservation, and appropriate folders and boxes were made for storage after treatment. This study is expected to serve as an important foundational resource on the materials used in modern and contemporary records.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.37 no.4
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• pp.225-232
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• 2024

This study focuses on the determination of the fracture mode in composite laminates using deep learning. With the increase in the use of laminated composites in numerous engineering applications, the insurance of their integrity and performance is of paramount importance. However, owing to the complex nature of these materials, the identification of fracture modes is often a tedious and time-consuming task that requires critical domain knowledge. Therefore, to alleviate these issues, this study aims to utilize modern artificial intelligence technology to automate the fractographic analysis of laminated composites. To accomplish this goal, scanning electron microscopy (SEM) images of fractured tensile test specimens are obtained from laminated composites to showcase various fracture modes. These SEM images are then categorized based on numerous fracture modes, including fiber breakage, fiber pull-out, mix-mode fracture, matrix brittle fracture, and matrix ductile fracture. Next, the collective data for all classes are divided into train, test, and validation datasets. Two state-of-the-art, deep learning-based pre-trained models, namely, DenseNet and GoogleNet, are trained to learn the discriminative features for each fracture mode. The DenseNet models shows training and testing accuracies of 94.01% and 75.49%, respectively, whereas those of the GoogleNet model are 84.55% and 54.48%, respectively. The trained deep learning models are then validated on unseen validation datasets. This validation demonstrates that the DenseNet model, owing to its deeper architecture, can extract high-quality features, resulting in 84.44% validation accuracy. This value is 36.84% higher than that of the GoogleNet model. Hence, these results affirm that the DenseNet model is effective in performing fractographic analyses of laminated composites by predicting fracture modes with high precision.

• The Journal of Engineering Geology
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• v.34 no.3
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• pp.403-413
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• 2024

This study aims to investigate the material properties of specimens made from pyrophyllite and pyrophyllite-aluminum mixed powders using high-speed, high-pressure dynamic compression technology. The aluminum powder exhibited a highly uniform particle size distribution ranging from 10 to 100 ㎛, whereas the pyrophyllite powder displayed four distinct particle size distributions: 0.1~1 ㎛, 1~10 ㎛, 80~100 ㎛, and 200~1,000 ㎛. Using high-speed, high-pressure dynamic compression technology with a drop time of approximately 0.34~0.4 seconds and a dynamic load of about 207 tonf, it was possible to fabricate pyrophyllite and pyrophyllite-aluminum mixed powder specimens with a volume of about 548 mm². The Shore hardness measurement results showed that specimen BG100 had an average of 43.7, BG90 had an average of 33.2, and BG85, BG80, BG75, and BG70 had an average of 31.0, indicating that the specimen with the least aluminum content exhibited the highest Shore hardness value. The thermogravimetric analysis revealed mass losses at two points: the first mass loss occurred at around 270℃ with a loss of approximately 1.45%, and the second mass loss occurred at around 600℃, where BG70 and BG80 showed a mass loss of about 2.53%, and BG75, BG85, and BG90 showed a mass loss of about 3.43%. Scanning electron microscopy analysis indicated that the microstructure of the specimens was similar regardless of the mixing ratio, with three elements-O, Si, and Al-being detected in all specimens. The mapping analysis of BG90 revealed an oxygen weight ratio of 50.80%, silicon weight ratio of 37.36%, and aluminum weight ratio of 11.85%. In the case of BG85, the results were 43.09% oxygen, 43.50% silicon, and 13.41% aluminum; for BG80, the results were 44.83% oxygen, 40.30% silicon, and 14.87% aluminum; for BG75, the results were 44.71% oxygen, 35.49% silicon, and 19.80% aluminum; and for BG70, the results were 34.95% oxygen, 35.73% silicon, and 29.32% aluminum.