• Journal of Periodontal and Implant Science
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• v.38 no.2
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• pp.117-124
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• 2008

Purpose: The purpose of this study was to histomorphometrically evaluate the osteoconductivity of a new biphasic calcium phosphate ceramics with fully interconnected microporous structure. Material and Methods: Osseous defects created in the rabbit calvaria were filled with four different bone graft substitutes. Experimental sites were filled with a new fully interconnected microporous biphasic calcium phosphate with(BCP-2) or without(BCP-1) internal macropore of $4400\;{\mu}m$ in diameter. MBCP(Biomatlante, France) and Bio-Oss(Geistlich Pharma, Switzerland) were used as controls in this study. Histomorphometric evaluation was performed at 4 and 8 weeks after surgery. Result: In histologic evaluation, new bone formation and direct bony contact with the graft particles were observed in all four groups. At 4 weeks, BCP-1(15.5%) and BCP-2(15.5%) groups showed greater amount of newly formed mineralized bone area(NB%) compared to BO(11.4%) and MBCP(10.3%) groups. The amounts of NB% at 8 weeks were greater than those of 4 weeks in all four groups, but there was no statistically significant differences in NB% between the groups. Conclusion: These results indicate that new bone substitutes, BCP with interconnected microporous structure and with or without internal macroporous structures, have the osteoconductivity comparable to those of commercially available bone substitutes, MBCP and Bio-Oss.

• Progress in Superconductivity and Cryogenics
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• v.16 no.1
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• pp.36-41
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• 2014

Since glass microsphere has high crush strength, low density and small particle size, it becomes alternative thermal insulation material for cryogenic systems, such as storage and transportation tank for cryogenic fluids. Although many experiments have been performed to verify the effective thermal conductivity of microsphere, prediction by calculation is still inaccurate due to the complicated geometries, including wide range of powder diameter distribution and different pore sizes. The accurate effective thermal conductivity model for microsphere is discussed in this paper. There are four mechanisms which contribute to the heat transfer of the evacuated powder: gaseous conduction ($k_g$), solid conduction ($k_s$), radiation ($k_r$) and thermal contact ($k_c$). Among these components, $k_g$ and $k_s$ were calculated by Zehner and Schlunder model (1970). Other component values for $k_c$ and $k_r$, which were obtained from experimental data under high vacuum conditions were added. In this research paper, the geometry of microsphere was simplified as a homogeneous solid sphere. The calculation results were compared with previous experimental data by R. Wawryk (1988), H. S. Kim (2010) and the experiment of this paper to show good agreement within error of 46%, 4.6% and 17 % for each result.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.12 no.6
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• pp.142-151
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• 2013

This study develops an automation system for metallic mold design that is applicable in forging non-axial symmetric parts. The metallic mold design program is used to design the metallic mold using two-dimensional axial symmetric metallic molds and to predict the stress concentration using finite element analyses. Then, the program redesigns the metallic mold using variables such as the optimal split diameter, maximum allowable inner pressure, fit tolerance, and stress distribution, which are calculated using the metallic mold design program. When the involute spur gear is forged, stress concentration occurs on the tooth root bounded at the symmetric surface. The SCM4 material is suitable for metallic molds because the stress is less than the yield strength of the insert and it acts on the tooth root regardless of the inner pressure. The metallic mold for forging non-axial symmetric parts can be designed through adjusting the magnitude of the contact pressure. The program developed in this study can be applied to metallic mold designs in involute spur gears of forging, which is an ordinary non-axial symmetric part.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.11
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• pp.1183-1189
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• 2015

This study focuses on the design of the tapered joints of a wind power turbine. The main variables of the tapered joint are the transmitted torque, shaft diameter, contact area of the tapered ring, and tightening torque of the bolts, which applies a compressive pressure from the hub to the shaft. The stress distribution of the taper fit was calculated under axisymmetric plane strain conditions because of the small taper angle. The axial displacement of the clamp can be calculated from the radial elastic deformation and the taper angle. The stress field of each ring is obtained from the cylinder stress equation. To verify the accuracy of the calculation, finite element (FE) analysis was performed, and the results of the calculation and FE analysis were compared. The hoop stress of the tapered surface showed a discrepancy of approximately 10, but the trends of the stress distributions of each component and the relative movement obtained by FE analysis were in good agreement with the analytical calculation results.

• Journal of the Microelectronics and Packaging Society
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• v.26 no.4
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• pp.47-53
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• 2019

Stiffness-gradient stretchable electronic packages of the soft PDMS/hard PDMS/PTFE structure were processed using the polydimethylsiloxane (PDMS) as the base substrate and the more stiff polytetrafluoroethylene (PTFE) as the island substrate, and their stretchable deformation-resistance characteristics were characterized. The flip-chip joints, formed by bonding the chip bumps of 50 ㎛-diameter onto the PDMS/PTFE substrate pads, exhibited an average contact resistance of 96 mΩ. When the stretchable package of the soft PDMS/hard PDMS/PTFE structure was deformed to 30% elongation, the strain on the PTFE was restrained to 1%, resulting in a negligible resistance increase of 1% in the daisy-chain circuit formed on the PTFE island substrate. The circuit resistance increased for 1.7% after 2,500 cycles of 0~30% stretchable deformation.

• The Journal of Advanced Prosthodontics
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• v.1 no.1
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• pp.10-18
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• 2009

STATEMENT OF PROBLEM. Despite an improved bone reactions of Mg-incorporated implants in the animals, little yet has been carried out by the experimental investigations in functional loading conditions. PURPOSE. This study investigated the clinical and histologic parameters of osseointegrated Mg-incorporated implants in early loading conditions. MATERIAL AND METHODS. A total of 36 solid screw implants(diameter 3.75 mm, length 10 mm) were placed in the mandibles of 6 beagle dogs. Test groups included 18 Mg-incorporated implants. Turned titanium implants served as control. Gold crowns were inserted 4 weeks after implant placement and the dogs were immediately put on a food diet. Implants were observed for 10 weeks after loading. Radiographic assessments and stability tests were performed at the time of fixture installation, $2^{nd}$ stage surgery, 4 weeks after loading, and 10 weeks after loading. Histological observations and morphometrical measurements were also performed. RESULTS. Of 36 implants, 33 displayed no discernible mobility, corresponding to successful clinical function. There was no statistically significant difference between test implants and controls in marginal bone levels(P=.46) and RFA values. The mean BIC % in the Mg-implants was $54.5{\pm}8.4%$. The mean BIC % in the turned implant was $45.3{\pm}12.2%$. These differences between the Mg-implant and control implant were statistically significant(P=.005). CONCLUSIONS. The anodized, Mg-incorporated implant demonstrated significantly more bone-to-implant contact(BIC) in early loading conditions. CLINICAL IMPLICATIONS. The results of this study in beagle dogs suggest the possibility of achieving predictable stability of early loaded free-standing dental implants with Mg-incorporated surface.

• Journal of Periodontal and Implant Science
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• v.39 no.1
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• pp.95-102
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• 2009

Purpose: The aim of this report is to investigate the efficacy of anorganic bovine bone xenograft(Bio-$Oss^{(R)}$) at maxillary sinus floor augmentation. Materials and methods: Two male patients who missed maxillary posterior teeth were included. They were performed maxillary sinus floor augmentation using anorganic bovine bone xenograft(Bio-$Oss^{(R)}$). After 10 or 13 months, the regenerated tissues were harvested using trephine drills with 2 or 4mm diameter and non-decalcified specimens were made. The specimens were examined histologically and histomorphometrically to investigate graft resorption and new bone formation. Results: Newly formed bone was in contact with Bio-$Oss^{(R)}$ particles directly without any gap between the bone and the particles. The proportions of newly formed bone were $23.4{\sim}25.3%$ in patient 1(Pt.1) and 28.8% in patient 2(Pt.2). And the proportions of remained Bio-$Oss^{(R)}$ were $29.7{\sim}30.2%$ in Pt.1 and 29.2% in Pt.2. The fixtures installed at augmented area showed good stability and the augmented bone height was maintained well. Conclusion: Anorganic bovine bone xenograft(Bio-$Oss^{(R)}$) has high osteoconductivity and helps new bone formation, so that it can be used in maxillary sinus floor augmentation.

• Korean Journal of Materials Research
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• v.5 no.6
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• pp.627-632
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• 1995

W-Cu composites utilize the high electrical conductivity of copper and arc erosion resistance of tungsten to provide properties better suited to electrical contact applications than either tungsten or copper alone. W-Cu composite materials were milled in an attritor with an impeller speed of 300rpm for various milling times. The milled powders were compacted at 300MPa into cylinders, 16m in diameter, and approximately 4m high. Sintering was performed in dry H$_2$at temperature ranging from 1200$^{\circ}C$ to 1400$^{\circ}C$. Samples were sectioned and were polished for scanning electron microscopy (SEM) of microstructures. Homogeneous W-Cu composites were formed after 10 hours mechanical alloying and could be attained 99% density at 1330$^{\circ}C$. As mechanical alloying time increased, Fe-concentration was increased linearly. Intermetallic compound formation interupted the growth of W particles Increased hardness.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.9 no.1
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• pp.45-48
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• 2016

The treatment of obesity have been developed various devices for the treatment of obesity, the ultrasound is to be made after the state changes to become easy fat decomposition by heat and vibrations to facilitate the flow of blood and lymph fatty acid released into the blood. There is such ultrasonic transducer array is used in obesity therapy focusing angle of the transducer array and the frequency may have a significant impact on the degradation of fat. In this paper, we set the frequency that reaches the shortest time to a set temperature 27kHz, 1MHz, by applying a transducer with a diameter of 5mm, 10mm, 16mm for the frequency of 3MHz, obtain the wavelength and near the stomach in order to set the frequency of the transducer array, which was set to the focusing angle of the transducer with three contact surfaces. As a result, the time to reach the set temperature was short days when 3MHz frequency, the focusing angle is titrated is $40^{\circ}$.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.2
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• pp.181-186
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• 2009

The objective of this study is ensuring safety of cabin when the blade impacts into a obstacle by verifying safety of the rotor mast and the transmission using impact loads calculated from the simulation. The rotor mast shall not fail and the transmission shall not be displaced into occupiable space when the main rotor composite blade impact into a 8 inch rigid cylinder in diameter on the outer 10% of the blade at operational rotor speed. To calculate the reaction loads at the spherical bearing and lead-lag damper, blade impact analysis was performed with FE model consist of composite blade, tree(or rigid cylinder) using elastic-plastic with damage material and several contact surfaces which were created to describe a progress of actual failure. Also, the reaction loads were investigated in change of blade rotation speed and pitch angle.