• Transactions of Materials Processing
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• v.25 no.5
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• pp.301-305
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• 2016

The manual modification of stamping die has widely been used in order to reduce springback after sheet metal forming. When UHSS (Ultra High Strength Steel) is used in sheet metal forming, the die design considering springback compensation is more difficult because higher strength sheet has more springback. In this study, the optimization method was used in order to design die geometry considering springback compensation after forming of 1.2GPa UHSS. Die geometries were defined as design variables and the springback distance from the die surface was conducted as object function in optimization process. The optimized die geometry considering springback compensation was performed using finite element and optimization analysis. The simulation results such as thickness distribution and springback amount were compared with measured data using 3D optical measurement system (GOM ARGUS, ATOS). And the prediction of springback amount showed a good agreement within test results.

• Journal of the Korean Society of Food Science and Nutrition
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• v.28 no.1
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• pp.107-112
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• 1999

Physicochemical properties and microflora of kimchi stew's sauce were investigated during 6 months at 13oC, 27oC and 37oC to study the changes of its quality. The final pH values in the sauce showed a slight decrease to 4.46, 4.38 and 4.21 during storage at 13oC, 27oC and 37oC, respectively. Color(L, a, b values), salinity, moisture and Aw in the sauce were decreased during storage. However, the values of brix and browning, and the amounts of total sugar, crude protein and crude fat in the sauce were increased during storage. All the reactions occurred more rapidly in the samples stored at 37oC than those stored at 27oC and 13oC. The viable cell counts of aerobic bacteria in the sauce were changed remarkably during storage, but viable cell counts of lactic acid bacteria were decreased. Yeast, mold and E. coli were not found in the above temperatures during storage. Regression analysis between sensory scores and quality characteristics showed that the ΔE value was a major quality index for the deterioration of kimchi stew's sauce. The shelf lives of sauces at 13oC, 27oC, 37oC were estimated to be 24 months, 6 months and 6 months, respectively.

• Journal of Environmental Science International
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• v.22 no.7
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• pp.837-845
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• 2013

This study was designed to synthesize mesoporous carbon, porous carbonic material and to characterize its surface in an attempt to adsorption methane gas($CH_4$). Synthesis of mesoporous carbon was carried out under two steps ; 1. forming a RF-silica complex with a mold using CTMABr, a surfactant, and TEOS, raw material of silica, and 2. eliminating silica through carbonization and HF treatment. The mesoporous carbon was synthesized under various conditions of synthesis time and calcination. Eight different types of mesoporous carbon, which were designated as MC1, MC2, MC3, MC4, MCT1, MCT2, MCT3, and MCT4, were prepared depending upon preparation conditions. The analysis of mesoporous carbon characteristics showed that the calcination of silica stabilized the mixed structure of silica and carbonic complex, and made the particle uniform. The results also showed that hydrothermal synthesis time did not have a strong influence on the size of pore. The bigger specific surface area was obtained as the hydrothermal synthesis time was extended. However, the specific surface area was getting smaller again after a certain period of time. In adsorption experiments, $CH_4$ was used as adsorbate. For the case of $CH_4$, MCT3 showed the highest adsorption efficiency.

• Journal of the Korean Society of Propulsion Engineers
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• v.5 no.1
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• pp.49-59
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• 2001

Functionally gradient materials(FGMs) generally consist of different material components, such as ceramics and metals. Continuous changes in their composition, microstructure, porositys, and so on result in gradients in the properties of FGMs. In this study AlN/Al-$Al_3$Ti FGM cubes were fabricated by the powder metallurgical process, and the characteristics of the FGMs were investigated. Powders of Mg and Ti mixed with Al in different ratios or the stack of the mixed powders having a stepwisely controlled compositional gradient from one plane to another were formed in a steel mold. The more the composition of Mg and sintering temperature are increased, the more the amount of AlN is formed. AlN and $Al_3$Ti distributed with continuously gradient composition were detected by XRD analysis and also revealed in optical microstructures, and microhardness tests.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2017.11a
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• pp.221-222
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• 2017

An analysis of the current water leak status of understand structure (underground parking lots, staircases, plumbing systems, water reservoirs, etc.) of multi-family housing in South Korea shows that water leaks are found from cracks in all areas of the underground structure caused by the degradation environment (water pressure by underground water, humidity, temperature, earth pressure, soil behaviour and vibration, etc.), which result in various problems, including mold, malodour, debonding of finishing materials, exfoliation, breakout, water leaks in electrical boxes, efflorescence, sedimentation of calcium hydroxide, decoloration, rusting, damages and pollution among others. Therefore, this study aims to analyse the current status of water leaks in underground structure and use the results as the basic data for developing a standard guideline for water leaks and maintenance by parts of the underground structure of multi-family housing.

• The Journal of Korean Academy of Prosthodontics
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• v.44 no.2
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• pp.157-164
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• 2006

Purpose: The purpose of this study was to compare the fracture strength of the zirconia monolithic all-ceramic crowns according to the thickness(0.5 mm, 0.8 mm, 1.1 mm) and IPS Empress II ceramic crown of 1.5 mm thickness. Material and method: Eight crowns for each of 3 zirconia crown groups were fabricated using CAD/CAM system(Kavo, Germany) and eight Empress II crowns were made from silicone mold and wax pattern. Each crown group was finished in accordance with the specific manufacturer s instruction. All crowns were luted to the metal dies using resin cement and mounted on the testing jig in a universal testing machine. The load was directed at the center of crown with perpendicular to the long axis of each specimen until catastrophic failure occurred. Analysis of variance and Tukey multiple comparison test(p<.05) were applied to the data. Results and Conclusion: 1. The fracture strength of the zirconia monolithic all-ceramic crown was higher thickness increased(p<.05). 2 The fracture strength of 1.1 mm thickness zirconia monolithic all-ceramic crown was higher than the fracture strength of 1.5 mm thickness IPS Empress II crown(p<.05). 3. The fracture strength of 0.5 mm thickness zirconia monolithic all-ceramic crown exceeded maximum occlusal forces.

• Restorative Dentistry and Endodontics
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• v.17 no.1
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• pp.181-190
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• 1992

The purpose of this study was to estimate the contents of the residual monomers, such as Bis-GMA and TEGDMA. In this study, materials used were six kinds of anterior and posterior visible light-cured resins. Resins were placed in disk-shaped Teflon mold (8.5mm in diameter, 2.0mm in thickness), and cured for 20 seconds with visible light source attached wide diameter lightguide. The specimens were immersed in 10ml ethanol and stored for 5 days at $37^{\circ}C$. The concentration of residual monomers in eluate solution was analysed by HPLC, and the following results are obtained. 1. The residual Bis-GMA and TEGDMA were detected in all materials used, and the ranges of quantity of the residual Bis-GMA was 0.101-1.236 wt% and that of TEGDMA was 0.230-5.794 wt%.2. The contents of residual TEGDMA was detected higher than that of residual Bis-GMA (P < 0.01). 3. The content of residual monomers was detected to be highest in Bis-Fil M as microfilled type. 4. In most of the materials used, there was no significant difference in the contents of residual monomers between anterior and posterior light-cured resins.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.274.1-274.1
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• 2013

We report the circumferential alignment of human aortic smooth muscle cells (HASMCs) in an orthogonally micropatterned circular microfluidic channel to form an in vivo-like smooth muscle cell layer. To realize a biomimetic smooth muscle cell layer which is aligned perpendicular to the axis of blood vessel, we first fabricated a half-circular polydimethylsiloxane (PDMS) microchannel by soft lithography using a convex PDMS mold. The orthogonally micro wrinkle patterns were generated inside the half-circular microchannel by stretching-releasing operation under UV irradiation. Upon UV treatment with uniaxial 40 % stretch of a PDMS substrate and releasing process, the microwrinkle patterns perpendicular to the axial direction of the circular microchannel were generated, which could guide the circumferential alignment of HASMCs successfully during cultivation. The analysis of orientation angle, shape index, and contractile protein marker expression indicates that the cultured HASMCs revealed the in vivo-like cell phenotype. Finally, we produced circular microchannels by bonding two half-circular microchannels, and cultured the HASMCs circumferentially with high alignment and viability for 5 days. These results are the first demonstration for constructing an in vivo-like 3D smooth muscle cell layer in the circular microfluidic channel which can provide novel bioassay platforms for in-depth study of HASMC biology and vascular function.

• Korean Journal of Materials Research
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• v.16 no.11
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• pp.668-675
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• 2006

In the partial squeeze casting process, the filling behavior of liquid metal and solidification pattern in thick area have significant influence on the quality of casting products and die life. For the optimal casting design of automobile transmission gear housing, various analyses were performed in this study by using computer simulation code, MAGMAsoft and the simulation results were compared and analyzed with experimental results. By air pressure criteria, internal porosities caused by air entrap during the mold filling were predicted and reduced remarkably by modification of gating system. Also, optimal squeeze-time lag to apply partial squeeze pin in thick area was calculated and the castings was free from shrinkage defects with the result of solidification analysis. Consequently, casting design for automobile transmission gear housing was optimized and approved by Computer Tomography.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.10
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• pp.1982-1988
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• 2002

Micro-injection molding and microfluidic devices with the help of MEMS technologies including the LIGA process are expected to play important roles in micro-system industries, in particular the bio-application industry, in the near future. Understanding fluid flows in micro-channels is important since micro-channels are typical geometry in various microfluidic devices and mold inserts for micro-injection molding. In the present study, Part 1, an experimental investigation has been carried out to understand the detailed flow phenomena in micro-channel filling process. Three sets of micro-channels of different thickness (40um,30um and 2011m) were fabricated using SU-8 on silicon wafer substrate. And a flow visualization system was developed to observe the filling flow into the micro-channels. Experimental flow observations are extensively made to find the effects of pressure, inertia force, viscous force and surface tension. A dimensional analysis for experimental results was carried out and several relationships A dimensionless parameters are obtained.