• Restorative Dentistry and Endodontics
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• v.31 no.6
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• pp.452-459
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• 2006

Competition will usually develop between the opposing walls as the restorative resin shrinks during polymerization. Magnitude of this phenomenon may be depended upon cavity configuration and volume. The purpose of this sturdy was to evaluate the effect of cavity configuration and volume on microleakage of composite resin restoration that has margins on the enamel site only. The labial enamel of forty bovine teeth was ground using a model trimmer to expose a flat enamel surface. Four groups with cylindrical cavities were defined, according to volume and configuration factor(Depth x Diameter / C-factor) - Group I : 1.5 mm ${\times}$ 2.0 mm / 4.0, Group II : 1.5 mm ${\times}$ 6.0 mm / 2.0, Group III : 2.Omm ${\times}$ 1.72 mm / 5.62, Group IV : 2.0 mm ${\times}$ 5.23 mm / 2.54. After treating with fifth-generation one-bottle adhesive - BC Plus$^{TM}$ (Vericom, AnYang, Korea), cavities were bulk flted with microhybrid composite resin - Denfill$^{TM}$ (Vericom). Teeth were stored in distilled water for one day at room temperature and were finished and polished with Sof-Lex system. Specimens were thermocycled 500 times between 5$^{\circ}$C and 55$^{\circ}$C for 30 second at each temperature. Teeth were isolated with two layers of nail varnish except the restoration surface and 1 mm surrounding margins. Electrical conductivity (${\mu}$A) was recorded in distilled water by electrochemical method. Microleakage scores were compared and analyzed using two-way ANOVA at 95% level. The results were as follows: 1. Small cavity volume showed lower microleakage score than large one, however, there was no statistically significant difference. 2. There was no relationship between cavity configuration and microleakage. Factors of cavity configuration and volume did not affect on microleakage of resin restorations with enamel margins only.

• Journal of Environmental Impact Assessment
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• v.30 no.1
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• pp.35-48
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• 2021

In this study, the assessment of field applicability of in-situ remediation of nitrate-contaminated groundwater located in Yesan-gun was performed. Zero-valent iron/bio composite media injected PRB (Permeable Reactive Barrier) and monitoring well were installed in the contaminated groundwater site and monitored main remediation indicators during the PRB operation. Nitrate, nitrite, ammonia, Fe ion, TOC, and turbidity were analyzed and the diversity and population of microorganism in the PRB installed site were investigated for the verification of effect of injected PRB. In the study site where is an agricultural area, a river flows from west to east that forms a river boundary and the southern area has an impermeable sector. It was found that nitrate flows into the river, which is similar as groundwater flow. Simulation result for the fate of nitrate in groundwater showed steady state of nitrate arrived after 3~5 years passed. However, it is just to consider current conditions with no additional input of contaminant source, if additional input of contaminant source occurs contamination dispersion and time for steady state are expected to be increased. The monitoring results showed that Fe ion, TOC and turbidity in groundwater were not clearly changed in concentration after PRB installation, which indicates adaptability of the injected PRB for remediation of groundwater with no additional harmful effect to water quality. The concentration of nitrate maintained less than 5mg/L until 42 days after PRB installation and recovered its initial concentration after 84 days passed and showed termination of reactivity of injected zero-valent iron/bio composite media for removal nitrate. Nitrite and ammonia ions found after installation of PRB indicates reductive removal of nitrate. And the outstanding increase of microorganism diversity and population of Betaproteobacteria Class which includes denitrification microorganism explains biologically reductive removal of nitrate in injected PRB.

• Journal of Astronomy and Space Sciences
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• v.22 no.4
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• pp.441-450
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• 2005

The organic material is one of the most popular material for the satellites and the spacecrafts in order to perform the thermal management, and to protect direct exposure from the space environment. The present paper observes material property changes of organic material under the space environment by using ground facilities. One of the representative organic thermal management material of satellites, 2 mil ITO(Indium Tin Oxide) coated aluminized KAPTON was selected for experiments. In order to investigate the single parametric effect of protons in space environment, MC-50 cyclotron system in KIRAMS(Korea Institute of Radiological and Medical Science) was utilized for the ion beam irradiation of protons and ion beam dose was set to the Very Large August 1972 EVENT model, the highest protons occurrence near the earth orbit in history. The energy of ion beam is fixed to 30MeV(mesa electron volt), observed average energy, and the equivalent irradiance time conditions were set to 1-year, 3-year, 5-year and 10-year exposure in space. The procedure of analyses includes the measurement of the ultimate tensile strength for the assessment of quantitative degradation in material properties, and the imaging analyses of crystalline transformation and damages on the exposed surface by FE-SEM(Field Emission Scanning Electron Spectroscopy) etc.

• The Journal of Korean Academy of Prosthodontics
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• v.35 no.1
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• pp.221-243
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• 1997

The objective of this study was to characterize the mechanical properties of $Y_{2}O_{3}$-containing glass infiltrated ceramic core material, which was made by pressureless powder packing method. A pure alumina powder with a grain size of about $4{\mu}m$ was packed without pressure is silicon mold to form a bar shaped sample, and applied PVA solution as a binder. Samples were sinterd at $1350^{\circ}C$ for 1 hour. After cooling, $Y_{2}O_{3}$-containing glass($SiO_{2},\;Y_{2}O_{3},\;B_{2}O_{3},\;Al_{2}O_{3}$, ect) was infiltrated to the sinterd samples at $1300^{\circ}C$ for 2 hours and cooled. Six different proportions $Y_{2}O_{3}$ of were used to know the effect of the mismatch of the thermal expansion coefficient between alumina powder and glass. The samples were ground to $3{\times}3{\times}30$ mm size and polished with $1{\mu}m$ diamond paste. Flexural strength, fracture toughness, hardness and other physical properties were obtained, and the fractured surface was examined with SEM and EPMA. Ten samples of each group were tested and compared with In-Ceram(tm) core materials of same size made in dental laboratory. The results were as follows : 1. The flexural strengths of group 1 and 3 were significantly not different with that of In-Ceram, but other experimental groups were lower than In-Ceram. 2. The shrinkage rate of samples was 0.42% after first firing, and 0.45% after glass infiltration. Total shrinkage rate was 0.87%. 3. After first firing, porosity rate of experimental groups was 50%, compared with 22.25% of In-Ceram. After glass infiltration, porosity rate of experimental groups was 2%, and 1% in In-Ceram. 4. There was no statistical difference in hardness between two materials tested, but in fracture toughness, group 2 and 3 were higher than In-Ceram. 5. The thermal expansion coefficients of experimental groups were varied to $4.51-5.35{\times}10^{-6}/^{\circ}C$ according to glass composition, also the flexural strengths of samples were varied. 6. In a view of SEM, many microparticles about $0.5{\mu}m$ diameter and $4{\mu}m$ diameter were observed in In-Ceram. But in experimental group, the size of most particles was about $4{\mu}m$, and a little microparticles was observed. The results obtained in this study showed that the mismatch of the thermal expansion coefficients between alumina powder and infiltrated glass affect the flexural strength of alumin/glass composite. The $Y_{2}O_{3}$-containing glass infiltrated ceramic core made by powder packing method will takes less time and cost with sufficient flexural strength similar to all ceramic crown made with slip casting technique.

• Journal of the Korean earth science society
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• v.42 no.3
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• pp.264-277
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• 2021

This study analyzed the relationship between the total precipitable water vapor in the atmosphere and the moving speed of recent typhoons. This study used ground observation data of air temperature, precipitation, and wind speed from the Korea Meteorological Administration (KMA) as well as total rainfall data and Red-Green-Blue (RGB) composite images from the U.S. Meteorological and Satellite Research Institute and the KMA's Cheollian Satellite 2A (GEO-KOMPSAT-2A). Using the typhoon location and moving speed data provided by the KMA, we compared the moving speeds of typhoon Bavi, Maysak, and Haishen from 2020, typhoon Tapah from 2019, and typhoon Kong-rey from 2018 with the average typhoon speed by latitude. Tapah and Kong-rey moved at average speed with changing latitude, while Bavi and Maysak showed a significant decrease in moving speed between approximately 25°N and 30°N. This is because a water vapor band in the atmosphere in front of these two typhoons induced frontogenesis and prevented their movement. In other words, when the water vapor band generated by the low-level jet causes frontogenesis in front of the moving typhoon, the high pressure area located between the site of frontogenesis and the typhoon develops further, inducing as a blocking effect. Together with the tropical night phenomenon, this slows the typhoon. Bavi and Maysak were accompanied by copious atmospheric water vapor; consequently, a water vapor band along the low-level jet induced frontogenesis. Then, the downdraft of the high pressure between the frontogenesis and the typhoon caused the tropical night phenomenon. Finally, strong winds and heavy rains occurred in succession once the typhoon landed.

• The Journal of Engineering Geology
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• v.27 no.3
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• pp.331-343
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• 2017

In this study to improve stability, workability and economics of the H-Pile+Earth plate or H-Pile+Earth plate+Cutoff grouting currently in use, we had developed HCS method belonging to the retaining wall which is consisting of a combination H-Pile, Plastic Sheet Pile and Steel Square Pipe for gap maintenance and reinforcement of flexible plastic Sheet Pile, and the behavior of each member composing HCS method is investigated by three-dimensional finite element analysis. To numerically analyze the behavior of the HCS method, we have performed extensive three-dimentional finite element analysis for three kinds of plastic Sheet Pile size, two kinds of H-Pile size and three kinds of H-Pile installation interval, one kinds of Steel Square Pipe and three kinds of Steel Square Pipe installation interval. After analyzing the numerical results, we found that the combinations of $P.S.P-460{\times}131.5{\times}7t$ (PS7) and H-Pile $250{\times}250{\times}9{\times}14$ (H250), $P.S.P473{\times}133.5{\times}9t$ (PS9) and H-Pile $300{\times}200{\times}9{\times}14$ (H300) is the most economical because these combinations are considered to have a stress ratio (=applied stress/allowable stress) close to that as the stiffness of H-Pile, plastic Sheet Pile and Steel Square Pipe composite increased, the horizontal displacement of the retaining wall and the vertical displacement of the upper ground decreased. Especially, due to the arching effects caused by the difference in stiffness between H-Pile and plastic Sheet Pile, a large part of the earth pressure acting on plastic Sheet Pile caused a stress transfer to H-Pile, and the stress and displacement of plastic Sheet Pile were small. Through this study, we can confirm the behavior of each member constituting the HCS method, and based on the confirmed results of this study, it can be used to apply HCS method in reasonable, stable and economical way in the future.