• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.8
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• pp.2458-2467
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• 1996

The rigid-plastic finite element analysis was performed for analysis of ofhot forging and cold sizing of a bevel gear. Two dimensional analysis was carried out to investigate the defect occurrence on vertical symmetric planes during hot forging and three dimensional analysis was to understand the filling behavior on horizontal planes during cold sizing. The involute curve of a tooth was approximated by a circle for convenience in the present analysis. In order to estimate the elastic deformation of the gear and dies during cold sizing, linear elastic finite element analysis was performed. Results of the analysis can be used to predict grain flows and strength distributions in the forged gear, and to design dies and an appropriate preform for the cold sizing.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.22-25
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• 2009

Development of a curvic-coupling was presented in this paper. The research covers design, structural analysis, hot-temperature-torsion-test, curvic-coupling applied proto-type turbine disk manufacturing, and assembly test of a curvic-coupling rotor system for the turbopump application. Curvic-coupling was designed based on the Gleason-standard-tooth shape. The load capability of the designed curvic coupling was validated by the structural analysis and hot-temperature-torsion-test. A proto-type turbine disk which had adopted designed curvic-coupling was manufactured, assembled and tested to reveal that shaft-disk assembly run-outs in axial and radial directions were much smaller than the design requirements. The development will be finalized after spin test of shaft-disk assembly in near future.

• Restorative Dentistry and Endodontics
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• v.25 no.3
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• pp.321-337
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• 2000

Dental caries, one of the most frequent dental disease, become larger because it can be thought as a simple disease. Further more, it can progress to unexpected root canal therapy with fabrication of crown that needs reduction of tooth structure. Base is required in a large caries and ZOE, ZPC, glass ionomer are used frequently as base material. They, with restorative material, can affect the longevity of the restoration. In this study, we assume that the mandibular 1st molar has deep class I cavity. So, installing the 3 base material, 3 kinds of fillings were restored over the base as follows; 1) amalgam only, 2) amalgam with ZPC, 3) amalgam with ZOE, 4) amalgam with GI cement, 5) gold inlay with ZPC, 6) gold inlay with GI cement, 7) composite resin only, 8) composite resin with GI cement. After develop the 3-dimensional model for finite element analysis, we observe the distribution of stress and temperature with force of 500N to apical direction at 3 point on occlusal surface and temperature of 55 degree, 15 degree on entire surface. The analyzed results were as follow : 1. Principal stress produced at the interface of base, dentin, cavity wall was smallest in case of using GI cement as base material under the amalgam. 2. Principal stress produced at the interface of base, dentin, cavity wall was smaller in case of using GI cement as a base material than ZPC under gold inlay. 3. Composite resin-filled tooth showed stress distributed over entire tooth structure. In other words, there was little concentration of stress. 4. ZOE was the most effective base material against hot stimuli under the amalgam and GI cement was the next. In case of gold inlay, GI cement was more effective than ZPC. 5. Composite resin has the small coefficient of thermal conductivity. So, composite resin filling is the most effective insulating material.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.1 s.178
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• pp.185-192
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• 2006

A manufacturing process for a clutch gear which demands high strength and wear resistance, was developed by means of computer simulation. A preform was made by hot forging process and subsequent cold sizing process is applied to complete precise tooth part. Processes to obtain high dimensional accuracy and superior mechanical properties are analyzed and optimal heat treatment cycle to improve cold forgeability is introduced. Prototype was produced and the dimensional accuracy of the prototype was inspected to verify proposed process.

• Journal of the korean academy of Pediatric Dentistry
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• v.26 no.2
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• pp.339-349
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• 1999

The dental structure substituted by restorative materials may produce discomfort resulting from hot or cold stimuli. To investigate the effects of this stimuli on the human teeth, thermal analysis was carried out by calculation of general heat conduction equation in a modeled tooth using numerical method. The method has been applied to axisymmetric and two-dimensional model, analyzing the effects of constant temperature $4^{\circ}C\;and\;60^{\circ}C$. That thermal shock was provided for 2 seconds and 4 seconds, respectively and recovered to normal condition of $20^{\circ}C$ until 10 seconds. The thermal behavior of tooth covered with a crown of gold or stainless steel was compared with that of tooth without crown. At the same time, the effects of restorative materials(amalgam, gold and zinc oxide-eugenol(ZOE)) on the temperature of PDJ(pulpo-dentinal junction) has been studied. The geometry used for thermal analysis so far has been limited to two-dimensional as well as axisymmetric tooth models. But the general restorative tooth forms a cross shaped cavity which is no longer two-dimensional and axisymmetric. Therefore, in this study, the three-dimensional model was developed to investigate the effect of shape and size of cavity. This three-dimensional model might be used for further research to investigate the effects of restorative materials and cavity design on the thermal behavior of the real shaped tooth. The results were as follows; 1. When cold temperature of $4^{\circ}C$ was applied to the surface of the restored teeth with amalgam for 2 seconds and recovered to ambient temperature of $20^{\circ}C$, the PDJ temperature decreased rapidly to $29^{\circ}C$ until 3 seconds and reached to $25^{\circ}C$ after 9 seconds. This temperature decreased rather slowly with stainless steel crown, but kept similar temperature within $1^{\circ}C$ differences. Using the gold as a restorative material, the PDJ temperature decreased very fast due to the high thermal conductivity and reached near to $25^{\circ}C$ but the temperature after 9 seconds was similar to that in the teeth without crown. The effects of coldness could be attenuated with the ZOE situated under the cavity. The low thermal conductivity caused a delay in temperature decrease and keeps $4^{\circ}C$ higher than the temperature of other conditions after 9 seconds. 2. The elapse time of cold stimuli was increased also until 4 seconds and recovered to $20^{\circ}C$ after 4 seconds to 9 seconds. The temperature after 9 seconds was about $2-3^{\circ}C$ lower than the temperature of 2 seconds stimuli, but in case of gold restoration, the high thermal conductivity of gold caused the minimum temperature of $21^{\circ}C$ after 5 seconds and got warm to $23^{\circ}C$ after 9 seconds. 3. The effects of hot stimuli was also investigated with the temperature of $60^{\circ}C$. For 2 seconds stimuli, the temperature increased to $40^{\circ}C$ from the initial temperature of $35^{\circ}C$ after 3 seconds of stimuli and decreased to $30^{\circ}C$ after 9 seconds in the teeth without crown. This temperature was sensitive to surface temperature in the teeth with gold restoration. It increased rapidly to $41^{\circ}C$ from the initial temperature of $35^{\circ}C$ after 2 seconds and decreased to $28^{\circ}C$ after 9 seconds, which showed $13^{\circ}C$ temperature variations for 9 seconds upon the surface temperature. This temperature variations were only in the range of $5^{\circ}C$ by using ZOE in the bottom of cavity and showed maximum temperature of $37^{\circ}C$ after 3 seconds of stimuli.

• Transactions of Materials Processing
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• v.13 no.8
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• pp.723-730
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• 2004

This paper describes the analysis of extrusion process and integrity for a condenser tube which is a component of the heat exchanger in automobile and all conditioning apparatus. Recently, according to the development of analysis method using the computer, the numerical simulation have been applied to the 3-dimensional hot extrusion process with complex section area of the non-steady statement and then results of the analysis have been applied to optimal die design and process design. In this paper, firstly, the die design was performed for a condenser tube with a multi-hole section and the rigid-plasticity FE analysis performed of extrusion process. Secondly, we estimated metal flow of billet, extrusion load, welding pressure in chamber etc. and evaluated the pressure and elastic strain of the die land and mandrel tooth profile through a stress analysis of the die. Finally, the extrusion test was performed to estimate the validity of FE analysis. This paper confirmed that the designed extrusion die of the research is satisfactorily designed fur integrity of condenser tube.

• Journal of dental hygiene science
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• v.14 no.4
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• pp.597-609
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• 2014

To find out the effect of commercially available energy drinks on tooth enamel erosion, analyzed pH, buffering capacity, and the content of some of the inorganic components selecting 4 energy drinks that has high affinity of the products currently being sold. In addition, by observing the degree of erosion before and after immersion in energy drink by surface microhardness and scanning electron microscope (SEM) the results were as follows: Acidity of energy drink 'Burn Intense' was the lowest as $2.78{\pm}0.01$ highest on distilled water as $6.475{\pm}0.01$. 'Burn Intense' buffering capacity was $3.48{\pm}0.155$ at pH 5.5, $1.88{\pm}0.15$ at pH 7.0 which is the highest, and 'Hot6' was $1.71{\pm}0.37$, $1.23{\pm}0.35$ on each of it showing the lowest points. Ca content on energy drink was the highest at 'Volt Energy' as ($77.21{\pm}2.70mg/kg$), the lowest at 'Hot6' as ($0.98{\pm}0.05mg/kg$). P content was the highest on 'Hot6'($1.34{\pm}0.05mg/kg$) and detected at 'Red Bull'. Enamel surface hardness variation of the energy drinks before and after immersion showed rapid decrease at 'Red Bull' ($66.65{\pm}35.60$), and 'Volt Energy' ($61.96{\pm}31.42$), 'Burn Intense' ($58.53{\pm}24.84$), 'Hot6' ($53.99{\pm}60.26$) was in order. Distilled water, the control group, showed significant difference with the experimental group (p<0.05). But there was no significant difference between energy drinks. At SEM observation and analysis, 'Burn Intense' was the most severe demineralization, 'Volt Energy', 'Hot6', 'Red Bull', distilled water was in order. In the above results, taken together there were no statistically differences between energy drinks but significant difference in comparison with distilled water. In addition, at SEM observation and analysis all energy drink caused dental erosion, especially 'Burn Intense', has the lowest acidity, was serious. Thus, it is believed to provide a variety of oral health education and information about energy drinks that can affect the erosion of the teeth so public have the right to be recognized and reasonable dental care.

• The Korean Journal of Food And Nutrition
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• v.30 no.6
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• pp.1348-1358
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• 2017

To enhance the physiological activity of the Rhynchosia volubilis (RV), R. volubilis (RVHE-A) and R. volubilis-added herbal powder (RVHE-B) were fermented with a solid state culture of Hericium erinaceum mycelia (HE). The total isoflavone contents of the non-fermented RV-A ($489.9{\mu}g/g$) and RV-B ($571.1{\mu}g/g$) were remarkably increased in fermented RVHE-A ($1,836.4{\mu}g/g$) and RVHE-B ($1,276.7{\mu}g/g$). In particular, aglycone isoflavones such as daidzein and genistein were significantly higher in the RVHE-A than any other sample. When hot-water (HW) and EtOH extracts (E) were fractionated from the RV and RVHE, both extracts from the RVHE-A were higher than those from the RV-A in total polyphenol and flavonoid contents. However, the RVHE-B-HW showed a lower polyphenol and flavonoid content level than did RV-B-HW. RVHE-A-HW and -E also had more potent ABTS radical scavenging activity than any extract from the non-fermented RV and other ferments (RVHE-B). In the meanwhile, RVHE-A-HW potently stimulated the production of macrophage activation-related cytokines such as $TNF-{\alpha}$, IL-6 and IL-12 ($841.7{\pm}71.3pg/mL$, $3.9{\pm}0.1ng/mL$, $179.3{\pm}30.2pg/mL$) from peritoneal macrophage more than RV-A-HW ($92.5{\pm}1.5pg/mL$, $0.1{\pm}0.0ng/mL$, $37.4{\pm}5.4pg/mL$) as well as RVHE-B-HW ($557.0{\pm}21.3pg/mL$, $1.8{\pm}0.0ng/mL$, $90.0{\pm}10.0pg/mL$). However, all the EtOH extracts did not show significant activity. In addition, the RVHE-A-HW showed a significantly higher intestinal immune system modulating activity through Peyer's patch and GM-CSF production than did any other extract from RV and RVHE-B. In conclusion, these results suggest that the fermented R. volubilis with H. erinaceum mycelia possesses a possible use as an industrial application as functional food or material.

• The korean journal of orthodontics
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• v.23 no.1 s.40
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• pp.75-88
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• 1993

Recent reports indicate that shorter etching times than 60 seconds can be adopted without affecting the bond strength and clinical disadvantages. The purpose of this in vitro study was to compare the shear bone strength and to measure depth of etch at different etching time length. One hundred and eight extracted bovine lower central incisors were embedded each in a tooth cup with cold-cure acrylic resin. The facial surfaces of the teeth were ground wet with 600-, 800-, 1000-, and 1200-grit Sic papers, and finally polished with a water slurry of extrafine silicon carbide powder, washed with tap water, and dried with hot air. Nine groups of nine prepared teeth were etched with a commercial($38\%$ phosphoric acid solution) for 0, 5, 10, 15, 20, 30, 60, 90, and 120 seconds, respectively, rinsed with tap water, and dried with hot air. One conditioned teeth from every group was selected randomly for the scanning electron microscopic examination, and the remaining eight teeth of the groups were used for measuring the push shear bond strength after bonding brackets and immensing them in the $36.5^{\circ}C$ water for 24 hours. Another nine groups of three teeth were used for measuring the depth of etch and surface roughness with a surface profilometer. after pieces of adhesive tape of 3mm inner diameter positioned on the ground enamel surfaces, and etched with the above mentioned. The data obtained form the above expeiments were analysed statistically with one way ANOVA and Dunkan's multiple range test with the $95\%$ confidence level. The results and conclusion of the study were as follows; 1. The results of shear bond strength for the given experimental etching times were not statistically different, but showed the tendency of decreasing shear bone strength after over 60 seconds etching times. 2. On the scanning election microscopic examination, it was observed that the morphological patterns of etched enamel surface for 5 to 20 seconds were similar and consitent, and those for 30 to 120 seconds showed increasing over-etched patterns depending on the length of etching times. 3. The depth of etch was increased almost proportionally by the length of etching times, but it was not associated with the shear bond strength. 4. The surface roughness increased depending on the length of etching times, but it was not associated with the shear bond strength. 5. This experiment indicated that proper etching time with $38\%$ phosphoric acid solution is in the range of 5 to 30 seconds.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.4
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• pp.1534-1539
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• 2010

This study carried out dental checkup targeting 251 students in the 1st grade of S middle school and 220 students in the 1st grade of S high school in Seoul Metropolis. The results are as follows. As for the experience of dental hypersensitivity to oral symptoms in middle-and-high school students, 23.2% of high school students had experience of painful tooth when drinking or eating cold and hot beverage or food, compared to 14.3% of middle school students, and showed significant difference($\chi^2=6.08$, p<.05). As for the experience of painful teeth, 9.1% of high school students had experience of being sore, aching, and painful in the teeth, compared to 4.4% of middle school students, and showed significant difference($\chi^2=4.23$, p<.05). As a result of the oral health behavior in middle-and-high school students, 48.6% of middle school students were indicated to be higher than 26.4% of high school students in the experience of having ever gone to dentist for the past 1 year, and showed statistically significant difference($\chi^2=24.56$, p<.001). As for the period of toothbrushing during one day, 68.5% of middle school students brushed teeth after having breakfast($\chi^2=6.39$, p<.05) more than 57.3% of high school students. After having lunch, 16.8% of high school students brushed teeth more than 7.2% of middle school students, and showed statistically significant difference($\chi^2=10.58$, p<.01). As a result of judging dental checkup in middle-and-high school students, 44.1% of high school students had dental caries($\chi^2=25.36$, p<.001) more than 22.3% of middle school students. 9.6% of middle school students had tooth loss more than 4.1% of high school students, and showed statistically significant difference($\chi^2=5.39$, p<.05).