• Korean Journal of Materials Research
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• v.31 no.6
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• pp.339-344
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• 2021

Composite materials offer distinct and unique properties that are not naturally inherited in the individual materials that make them. One of the most attractive composites to manufacture is the aluminum alloy matrix composite, because it usually combines easiness of availability, light weight, strength, and other favorable properties. In the current work, Powder Metallurgy Method (PMM) is used to prepare Al2024 matrix composites reinforced with different mixing ratios of yttrium oxide (Y₂O₃) particles. The tests performed on the composites include physical, mechanical, and tribological, as well as microstructure analysis via optical microscope. The results show that the experimental density slightly decreases while the porosity increases when the reinforcement ratio increases within the selected range of 0 ~ 20 wt%. Besides this, the yield strength, tensile strength, and Vickers hardness increase up to a 10 wt% Y₂O₃ ratio, after which they decline. Moreover, the wear results show that the composite follows the same paradigm for strength and hardness. It is concluded that this composite is ideal for application when higher strength is required from aluminum composites, as well as lighter weight up to certain values of Y₂O₃ ratio.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.557-560
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• 2008

This was done by analyzing the sandwich panels that are now widely used in construction work. Sandwich panels are used for diverse purposes in construction work worldwide. In Korea, polystyrene panels that have organic materials as their core material are used. These panels are thus very vulnerable to fire, with risks of core melting, sheet deformation, and hazardous gases. Accordingly, sandwich panels' fire-resistant or non-flammable properties must be secured. To solve these problems, the optimal mixing proportion of lightweight foamed concrete for the sandwich panel core was determined. A new method of doing this was introduced that is completely different from the existing method, wherein a foaming agent is added to realize lightweight concrete. For lightweight concrete, the foaming mechanisms via diverse chemical reactions were identified, H$_2$O$_2$ was added for heating in the reaction, and the concrete foaming was maximized. Through diverse experiments to determine the optimal mixing proportion of lightweight foamed concrete and to examine the filling characteristic of lightweight foamed concrete for sandwich panel cores using waste materials, the physical and mechanical properties of lightweight foamed concrete were examined.

• Composites Research
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• v.34 no.5
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• pp.330-336
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• 2021

Alumina powder is one of the widely used materials for industry, but there is a problem that the strength of the product changes depending on the powder packing state. To solve the above problem, previous studies have been conducted to increase the particle packing efficiency, but most of the existing studies analyzed the packing characteristics of millimeter-scale particles, so the physical properties are different from those of the micrometer scale. It is difficult to apply to the micrometer scale. In this paper, a three-step experiment was performed using a statistical method to increase packing using micrometer-scale alumina powder. First, a size combination with high packing and a mixing ratio were selected using the mixture test design method, and an appropriate excitation frequency was selected by analyzing the height change according to the frequency change in the vibration test apparatus. Finally, an alumina powder packing experiment was performed based on the experimental results mentioned above. As a result, it was confirmed that the maximum height variation was 42% higher than the maximum value of the 155 measurements performed when selecting the packing size combination. It is thought that this study will serve as basic data for processing and packing research using fine powder.

• The Journal of the Korean dental association
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• v.48 no.11
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• pp.813-818
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• 2010

Since MTA has many beneficial properties such as biocompatibility, great sealing capacity, antibacterial effects, low cytotoxicity, and stimulation of formation of mineralized tissue, it has been widely used as the material of choice in root-end filling, apexification, pulpotomy, perforation repair and so on. However, despite its favorable characteristics, MTA presents working properties which are less than ideal. The resulting cement from the mixing of powder and water is difficult to manipulate, and its setting time has been reported to be 2 h 45 min whereas the working time is <4 minutes. Additional moisture is also required to activate the setting of the cement. Moreover, according to recent studies, the physical properties of MT A may be hampered by acidic environment or blood contamination. Therefore, practitioners may have surprisingly worse results than they expected when they are not fully acquainted with the characteristics and manipulation method of MTA.

• Journal of Mechanical Science and Technology
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• v.14 no.6
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• pp.675-689
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• 2000

Rapid design and production techniques are indispensable for the custom-made production systems. For manufacturing custom-made shoes, the shoelast should be designed rapidly from the individual foot model. In this paper, we develop an integrated system for rapid design and manufacturing of custom-tailored shoes. The foot shape measurement sub-system allows scanning a standard shoelast and an individual foot and then extracts the three-dimensional crosssectional data of the shoelast and the human foot shape from the captured image data. The shoelast design sub-system uses the scanned data to design new customized shoelast curves or surfaces with the heeling and mixing algorithms built in this system. The pattern design subsystem provides a method, which transforms a shoe-upper surface designed by a stylist into a flat-pattern that can be manufactured. We also export the surface model to an NC machine to manufacture the physical shoelast model.

• Journal of Mechanical Science and Technology
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• v.17 no.1
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• pp.157-167
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• 2003

The exciplex fluorescence technique with the TMPD (tetamethyl-Ρ-phenylene-diamine) / naphthalene dopant system was applied in a combustion-type constant-volume spray chamber. A detailed set of calibration experiments has been performed in order to quantify the TMPD fluorescence signal. It has been demonstrated that the TMPD fluorescence intensity was directly proportional to concentration, was independent of the chamber pressure, and was not sensitive to quenching by either water vapor or carbon dioxide. Using a dual heated-jet experiment, the temperature dependence of TMPD fluorescence up to 1000 K was measured. The temperature field in the spray images was determined using a simple mixing model, and an iterative solution method was used to determine the concentration and temperature field including the additional effects of the laser sheet extinction. The integrated fuel vapor concentration compared favorably with the measured amount of injected fuel when all of the liquid fuel had evaporated.

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.703-710
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• 2003

In the sub-surface environments, detection of the movement of contaminant substances and recharge of groundwater by rainfall are very important factors which contain porosity and effective porosity of porous media. In this paper, the applicability of permittivity methods and proposed dielectric mixing models (DDMs) are discussed. This study showed that the ratio of effective porosity to porosity of Toyoura and River sands were 0.856 and 0.843. From the relationships between the relative porosity and effective porosity, all measured values can be confirmed to outside the range to about 0.800 for Toyoura and River sands under all experiments by FDR and FDR-V systems. In the study, this permittivity equipment can be considered to be good enough to measure determining the physical parameters of saturated soils. Consequently, this permittivity method can be contributed to estimate a porosity and effective porosity of saturated porous media because it is easy and instantaneous than previous in-situ methods.

• Journal of Microbiology and Biotechnology
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• v.7 no.2
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• pp.151-156
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• 1997

Two commercially available lipases, Lipase OF (non-specific lipase from Candida rugosa) and Lipolase 100T (1, 3-specific lipase from Aspergillus niger), were immobilized on insoluble hydrophobic support HDPE (high density polyethylene) by the physical adsorption method. Hydrolysis performance was enhanced by mixing a non-specific Lipase OF and a 1, 3-specific Lipolase 100T at a 2 : 1 ratio. The results also showed that the immobilized lipase maintained its activity at broader temperature ($25~55^{\circ}C$) and pH (4-8) ranges than soluble lipases. In the presence of organic solvent (isooctane), the immobilized lipase retained most of its activity in upto 12 runs of hydrolysis experiment. However, without organic solvent in the reaction mixture, the immobilized lipase maintained most of its activity even after 20 runs of hydrolysis experiment.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2017.11a
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• pp.126-127
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• 2017

This study investigates the effect of improving the heat resistance performance when carbon fiber is mixed in the polyurea coating material. A tensile strength test method was carried out with the carbon fiber mixed polyurea specimens at an interval of 7, 14, and 21 days after heat treatment at 140±2℃. The test results showed that there was a significant decrease in the tensile strength performance. While the elongation and tensile performance decreased greatly, it was confirmed nevertheless the overall performance was maintained. This study proposes that mixing carbon fiber to the polyurea resin can effectively secure long-term heat resistance, thereby solving the problem of deterioration of physical properties caused by exposure to ultraviolet rays.

• Elastomers and Composites
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• v.25 no.1
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• pp.13-19
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• 1990

The purpose of this study is to estabilish the synthetic condition of polyurhethane elastomer for excellent properties. Polyurethane elastomer which have different NCO percentage and hard segment contents was synthesized by casting method. And the effects of hard segment contents were investigated by analytical methods such as IR, DSC, etc. [NCO]/[OH] ratio was proper at the range $1.02{\sim}1.05$. By IR absorption peak($1250cm^{-1}$) which indicate interurethane hydrogen bond it was confirmed that hard segment were crystallized. Melting point that was determined by DSC showed the effects of hard segment contents, phase mixing and crystalline size.