• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.34 no.1
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• pp.56-62
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• 2021

In this study, we created a DBD plasma device and a MnO2 catalyst mesh filter for evaluating ozone reduction of devices via the catalyst method. The DBD plasma device was manufactured by applying Ag paste to soda lime glass via the screen-printing method. The MnO2 catalyst mesh filter was manufactured by mixing MnO2 powder with binder with a 10% difference in concentration from 10% to 50% and then applying it using the dip-coating method. Finally, we sintered a MnO2 catalyst mesh filter in an electric furnace. We evaluated the characteristics of ozone generation according to the Ar gas flow of DBD plasma devices, the opening ratio, and ozone reduction performance of the MnO2 catalyst filters. Ozone reduction performance was approximately 20.4% at MnO2 10 wt%, 37.8% at MnO2 30 wt% and 50% at MnO2 50 wt%.

• Journal of the Korean Society of Radiology
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• v.16 no.7
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• pp.825-833
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• 2022

In 3D printing technology, materials that can be printed are increasing along with the development of material engineering, and materials that can be used in the field of radiation are also increasing. Therefore, depending on the composition and density of the materials used, the applied field can be different and applied, so the composition and characteristics of the materials must also be considered. In this study, 10 filaments with different properties were selected using a 3D printer of the FDM (Fused Deposition Modeling) method, and the brightness change of each filament was checked using a diagnostic X-ray generator, and the CT number was measured through CT. I wanted to find a material similar to bone. As a result, a material called silicon carbide was found, which has a similar brightness and CT number to bone. It is thought that further research will be presented as basic data for various studies with a density similar to that of human bones.

• Tribology and Lubricants
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• v.38 no.5
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• pp.199-204
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• 2022

This paper presents a numerical investigation of the influence of water molecule thickness on frictional behavior at the nanoscale using molecular dynamics simulation. Three different models, comprising water thin films of various thicknesses, were built, and indentation and sliding simulations were performed using the models. Various normal loads were applied by indenting the Si tip on the water film for the sliding simulation to evaluate the interplay between the water thin film thickness and the normal load. The results of the simulations showed that the friction force generally increased with respect to the normal load and thickness of the water thin film. The friction coefficient varied with respect to the normal load and the water film thickness. The friction coefficient was the smallest under a moderate normal force and increased with decreasing or increasing normal loads. As the water film became thicker, the contact area between the tip and water film became larger. Under well-lubricated conditions, the friction force was proportional to the contact area regardless of the water film thickness. As the normal force increased above a critical condition, the water molecules beneath the Si tip spread out; thus, the film could not provide lubrication. Consequently, the substrate was permanently deformed by direct contact with the Si tip, while the friction force and friction coefficient significantly increased. The results suggest that a thin water film can effectively reduce friction under relatively low normal load and contact pressure conditions. In addition, the contact area between the contacting surfaces dominates the friction force.

• Journal of The Geomorphological Association of Korea
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• v.27 no.4
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• pp.53-70
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• 2020

Silgyeong sansuhwa (Realistic landscape paintings) are drawn in Korea since 17th century. It has characteristics of more realistic description of landscape than painting from previous periods. Kim Hong Do's 'Haedong Myeongsan docheop (The album of paintings of famous mountains in Korea)' has been recognized as fine example of realistic description of geomorphic landscapes. Kim Hong Do and Kim Eung hwan did official travel to Gwandong and Geumgangsan area by order of King Jeongjo in 1788. As a result of that travel they draw about 100 piece of landscape painting. About 60 pieces of the paintings are still remaining. These are open to public by Korea National Museum in 1996. 14 pieces of painting, Daegwanryeong and Gangneung, Gyeongpo-dae, Hohae-jeong, Gahak-jeong, Cheonggan-jeong, Mun-am, Mangyang-jeong, Wolsong-jeong, Neungpa-dae, Naksan-sa, Mureung-gye, Gyejo-gul, and Hyeonjong-am, are analysed in this study. Coastal depositional landforms, like lagoon, sand beach and spit or barriers, erosional forms, like sea stack, sea cliff and sea cave, depicted in the paintings are analysed. In addition, structural landforms, colluvial landform and bedrock incision form by the running water in mountain area were analysed and weathered forms of granite and excursion to karst cave also discussed. It is found that sea arch in the printing destroyed since 1788, though exact position and reason is still unknown. There are strong need for discovery and identification of geomorphic landscape resources, for applied geomorphological studies and for prepare educational materials for non-face-to-face education. It also be emphasized that it can be used of the course work materials for future education using augmented reality and virtual reality technology.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.6
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• pp.588-593
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• 2023

The advantage of OTFT technology is that large-area circuits can be manufactured on flexible substrates using a low-cost solution process such as inkjet printing. Compared to silicon-based inorganic semiconductor processes, the process temperature is lower and the process time is shorter, so it can be widely applied to fields that do not require high electron mobility. Materials that have utility as electrode materials include carbon that can be solution-processed, transparent carbon thin films, and metallic nanoparticles, etc. are being studied. Recently, a technology has been developed to facilitate charge injection by coating the surface of the Al electrode with solution-processable titanium oxide (TiOx), which can greatly improve the performance of OTFT. In order to commercialize OTFT technology, an appropriate method is to use a complementary circuit with excellent reliability and stability. For this, insulators and channel semiconductors using organic materials must have stability in the air. In this study, carbon-doped Mo (MoC) thin films were fabricated with different graphite target power densities via unbalanced magnetron sputtering (UBM). The influence of graphite target power density on the structural, surface area, physical, and electrical properties of MoC films was investigated. MoC thin films deposited by the unbalanced magnetron sputtering method exhibited a smooth and uniform surface. However, as the graphite target power density increased, the rms surface roughness of the MoC film increased, and the hardness and elastic modulus of the MoC thin film increased. Additionally, as the graphite target power density increased, the resistivity value of the MoC film increased. In the performance of an organic thin film transistor using a MoC gate electrode, the carrier mobility, threshold voltage, and drain current on/off ratio (I_on/I_off) showed 0.15 cm²/V·s, -5.6 V, and 7.5×10⁴, respectively.

• Journal of the Korean Society of Industry Convergence
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• v.27 no.3
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• pp.685-692
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• 2024

Currently used heating elements are metal and non-metal heating elements, including various types of heaters, and resistance line heating elements have a problem of decreasing thermal efficiency over time, so to solve this problem, a planar heating element using high-purity carbon materials and oxidation-resistant inorganic compounds was applied. Through the manufacture of planar heating elements using CNT, ruthenium composite materials, and ruthenium oxide, physicochemical performance and capacity were increased, and instantaneous responsiveness was increased. Through thick film technology applicable to various base bodies, fine patterns were formed by the screening method in consideration of the fact that the performance of the heat source depends on the viscosity and pattern shape. The heating element was manufactured by thick film printing technology by mixing ruthenium oxide, CNT, Ag, etc. The characteristics of each paste were analyzed through viscosity measurement, and STS 430 was used as a base. Surface temperature and efficiency were measured by testing heaters manufactured for small wind tunnels and real-vehicle experiments. The surface temperature decreased as the air volume increased, and the optimal system boundary was found to be about 200 mm. Among the currently used heating elements, this paper manufactured a planar heating element using thick film technology to find out the relationship between air volume and temperature, and to study the surface temperature.

• The korean journal of orthodontics
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• v.54 no.3
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• pp.160-170
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• 2024

Objective: Owing to the availability of 3D software, scanners, and printers, clinicians are encouraged to produce in-office aligners. Recently, a new direct-printing resin (Tera Harz TC-85DAC) has been introduced. Studies on its mechanical characteristics and biological effects have been published; however, evidence on its efficacy in orthodontic treatment remains scarce. This pilot study aimed to investigate the accuracy of teeth movement achieved with direct-printed aligners. Methods: Seventeen patients (eight males and nine females) with a mean age of 27.67 ± 8.95 years, presenting with dental rotations < 30° and spaces/crowding < 5 mm, were recruited for this study. The teeth movement was planned starting from a T0 digital dental cast. The 3D direct-printed aligners were produced using Tera Harz TC-85DAC resin. Once the orthodontic treatment was completed, a final digital cast was obtained (T1). The planned teeth positions were then superimposed onto the T0 and T1 digital models. The differences between the programmed movements and the achieved overall torque, tip, rotation, and transverse dimensions were assessed using the paired t test or Wilcoxon's signed rank test. Results: The overall accuracies for torque, tip, and rotation were 67.6%, 64.2%, and 72.0%, respectively. The accuracy of the change in transverse diameter was 99.6%. Conclusions: Within the limits of the present pilot study (difficulties with abnormally shaped teeth and use of attachments), it can be concluded that 3D printed aligners can be successfully printed in-house and utilized for mildly crowded cases, with a comparable accuracy of tooth movement to that of other aligners.

• Korean Chemical Engineering Research
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• v.50 no.5
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• pp.923-928
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• 2012

Optimizing a water-phase suspending system is very important to manufacture high-quality suspension polymerized toners. Therefore, in this study, the effects of the molar ratio of calcium hydroxide ($CaOH_2$)/phosphoric acid ($H_3PO_4$)(Ca/P), which were used as inorganic suspending agents, and pH of the water-phase on the characteristics of styrene-based suspension polymerized toners were mainly investigated. At first, the water-phase was fixed to neutral condition (pH=7.5) and Ca/P molar ratio was changed from 1.5:1 to 1.76:1. As a result, an ideal calcium phosphate (hydroxyapatite) was prepared at the Ca/P molar ratio of 1.73:1 and polymerized toners prepared at this condition showed good particle size distribution, circularity and charging characteristic. Based on this result, Ca/P molar ratio was fixed to 1.73:1 and pH of the water-phase was changed to weak acidic (pH=5.5) and weak basic (pH=9.5) conditions. As a result, polymerized toners prepared under the weak acidic condition showed very good particle size distribution, circularity and charging characteristic along with excellent printing quality. High-quality suspension polymerized toners could be prepared via optimizing Ca/P molar ratio and pH of the water-phase.

• Journal of the Microelectronics and Packaging Society
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• v.24 no.3
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• pp.71-76
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• 2017

The electrical behavior and flexibility of the screen printed Ag circuits were investigated with infrared radiation sintering times and sintering temperatures. Electrical resistivity and radio frequency characteristics were evaluated by using the 4 point probe measurement and the network analyzer by using cascade's probe system, respectively. Electrical resistivity and radio frequency characteristics means that the direct current resistance and signal transmission properties of the printed Ag circuit. Flexibility of the screen printed Ag circuit was evaluated by measuring of electrical behavior during IPC sliding test. Failure mode of the Ag printed circuits was observed by using field emission scanning electron microscope and optical microscope. Electrical resistivity of the Ag circuits screen printed on Pl substrate was rapidly decreased with increasing sintering temperature and durations. The lowest electrical resistivity of Ag printed circuit was up to $3.8{\mu}{\Omega}{\cdot}cm$ at $250^{\circ}C$ for 45 min. The crack length arisen within the printed Ag circuit after $10{\times}10^4$ sliding numbers was 10 times longer than that of after $2.5{\times}10^4$ sliding numbers. Measured insertion loss and calculated insertion loss were in good agreements each other. Insertion loss of the printed Ag circuit was increased with increasing the number of sliding cycle.

• Journal of the Korean Institute of Gas
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• v.11 no.1 s.34
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• pp.29-33
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• 2007

This study investigates the use of $TiO_{2},\;Pd,\;Pt$, and In which greatly improves a sensitivity to trimethylamine gas. The metal-$SnO_{2}$ thick films were prepared by screen-printing method onto $Al_{2}O_{3}$ substrates with platinum electrode. The sensing characteristics were investigated by measuring the electrical resistance of each sensor in a test box as a function of detecting gas concentration. This was then used to detect trimethylamine, dimethylamine, and ammonia vapours within the concentration range of 100-1000ppm. The gas sensing properties of metal-$SnO_{2}$ mixed thick films depended on the content and variety of metal. It was found that sensitivity and selectivity of the films dopped with 1 wt% Pd and 10 wt% $TiO_{2}$ for trimethylamin gas showed the best result at $250^{\circ}C$.