• Restorative Dentistry and Endodontics
• /
• v.26 no.4
• /
• pp.263-272
• /
• 2001

The aim of this study was to investigate the influence of four different light curing modes on the marginal leakage of Class V composite resin restoration. Eighty extracted human premolars were used. Wedge-shaped class Y cavities were prepared on the buccal surface of the tooth with high-speed diamond bur without bevel. The cavities were positioned half of the cavity above and half beyond the cemento-enamel junction. The depth, height, and width of the cavity were 2 mm, 3 mm and 2 mm respectively. The specimens were divided into 4 groups of 20 teeth each. All the specimen cavities were treated with Prime & Bond$^{R}$ NT dental adhesive system (Dentsply DeTrey GmbH, Germany) according to the manufacturer's instructions and cured for 10 seconds except group VI which were cured for 3 seconds. All the cavities were restored with resin composite Spectrum$^{TM}$ TPH A2 (Dentsply DeTrey GmbH, Germany) in a bulk. Resin composites were light-cured under 4 different modes. A regular intensity group (600 mW/${cm}^2$, group I) was irradiated for 30 s, a low intensity group (300 mW/${cm}^2$, group II) for 60 s and a ultra-high intensity group (1930 mW/${cm}^2$, group IV) for 3 s. A pulse-delay group (group III) was irradiated with 400 mW/${cm}^2$ for 2 s followed by 800 mW/${cm}^2$ for 10 s after 5 minutes delay. The Spectrum$^{TM}$ 800 (Dentsply DeTrey GmbH, Germany) light-curing units were used for groups I, II and III and Apollo 95E (DMD, U.S.A.) was used for group IV. The composite resin specimens were finished and polished immediately after light curing except group III which were finished and polished during delaying time. Specimens were stored in a physiologic saline solution at 37$^{\circ}C$ for 24 hours. After thermocycling (500$\times$, 5-55$^{\circ}C$), all teeth were covered with nail varnish up to 0.5 mm from the margins of the restorations, immersed in 37$^{\circ}C$, 2% methylene blue solution for 24 hours, and rinsed with tap water for 24 hours. After embedding in clear resin, the specimens were sectioned with a water-cooled diamond saw (Isomet$^{TM}$, Buehler Co., Lake Bluff, IL, U.S.A.) along the longitudinal axis of the tooth so as to pass the center of the restorations. The cut surfaces were examined under a stereomicroscope (SZ-PT Olympus, Japan) at ${\times}$25 magnification, and the images were captured with a CCD camera (GP-KR222, Panasonic, Japan) and stored in a computer with Studio Grabber program. Dye penetration depth at the restoration/dentin and the restoration/enamel interfaces was measured as a rate of the entire depth of the restoration using a software (Scion image, Scion Corp., U.S.A.) The data were analysed statistically using One-way ANOVA and Tukey's method. The results were as follows : 1. Pulse-Delay group did not show any significant difference in dye penetration rate from other groups at enamel and dentin margins (p>0.05) 2. At dentin margin, ultra-high intensity group showed significantly higher dye penetration rate than both regular intensity group and low intensity group (p<0.05). 3. At enamel margin, there were no statistically significant difference among four groups (p>0.05). 4. Dentin margin showed significantly higher dye penetration rate than enamel margin in all groups (p<0.05).

• Journal of the Mineralogical Society of Korea
• /
• v.27 no.1
• /
• pp.31-40
• /
• 2014

In present study, we geochemically investigated the fresh coal ashes and the saline ash pond of an electric power plant in Korea, which burns imported bituminous coals. The goals are to see the chemical changes of the ash pond by reaction with coal ashes and to investigate the relative leachability of elements from the ashes by reaction with saline waters. For this study, one fresh fly ash, one fresh bottom ash, and 7 water samples were collected. All the ash samples and 2 water samples were analyzed for 55 elements. The results indicated that the fly ashes are enriched with chalcophilic elements such as Cu, Zn, Ga, Ge, Se, Cd, Sb, Au, Pb, and B relative to other elements. On the other hand, concentrations of As, Ba, Co, Ga, Li, Mn, Mo, Sb, U, V, W, and Zr are much higher in the ash pond than those dissolved in the seawater. Ag, Bi, Li, Mo, Rb, Sb, Sc, Se, Sn, Sr, and W show high ratios of elemental concentrations in pond water to those in the fly ash. Our results imply that the leaching of trace elements is regulated by geochemical controls such as solubility and adsorption even though the trace elements are relatively enriched on the ash surfaces after the coal combustion due to their volatilities.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.44 no.11
• /
• pp.15-19
• /
• 2007

This paper reports the effects of Ar ion beam surface treatment on a $SiO_2$ dielectric layer in organic thin film transistors. We compared the electrical properties of pentacene-based OTFTs, treated by $O_2$ plasma or Ar ion beam treatments and characterized the states of the surface of the dielectric by using atomic force microscopy and X-ray photoelectron spectroscopy. For the sample which received $O_2$ plasma treatment, the mobility increased significantly but the on/off current ratio was found very low. The Ar ion beam-treated sample showed a very high on/off current ratio as well as a moderately improved mobility. XPS data taken from the dielectric surfaces after each of treatments exhibit that the ratio of between Si-O bonds and O-Si-O bonds was much higher in the $O_2$ plasma treated surface than in the Ar ion beam treated surface. We believe that our surface treatment using an inert gas, Ar, carried out an effective surface cleaning while keeping surface damage very low, and also the improved device performances was achieved as a consequence of improved surface condition.

• Journal of Life Science
• /
• v.24 no.5
• /
• pp.532-542
• /
• 2014

This study describe seasonal patterns in the variation of phytoplankton frequency in the water surface and basal layers and their spatial distributions at seven stations in Hwadang-ri, Goseng-gun in 2013. The phytoplankton community at Hwadang-ri was very diverse, with 60 taxa identified, representing three classes. Diatoms (Bacillariophyceae) exhibited the greatest diversity, with 41 taxa identified. These were followed by the dinoflagellates Dinophyceae, Cryptophyceae, and Eugenophyceae, with 16 taxa, two taxa, and one taxon, respectively. Water surfaces were shown with the relative individual density or abundance across areas. Except in January, Shannon-Weaver indices of diversity of the water surface layer were lower than those of the basal layer. In addition, evenness indices of the basal layer were higher than those of the water surface layer, except in January. For the community as a whole, the values of ${\beta}$-diversity were low for the seven stations: 1.125 for the water surface layer and 1.481 for the basal layer. Seasonal values for ${\beta}$-diversity were similar at the seven stations: 1.725 for the water surface layer and 1.347 for the basal layer. The phytoplankton community showed high taxonomic homogeneity in all four seasons, in addition to similar trends in seasonal development at depths in the same stations. However, the size distribution of the abundance and biomass showed a statistically significant west-east difference.

• Journal of the Mineralogical Society of Korea
• /
• v.17 no.1
• /
• pp.37-47
• /
• 2004

Sulfates such as alunite and schwertmannite formed under oxidation condition play a important role in geochemical processes taken place at waste dumps and a creek from Dalseong mine, Daegu. Water chemistry shows pH decreases from upstream toward downstream creek, mainly due to formation of schwertmannite that is the most abundant phase along the creek. The removal of Al from the creek is preferentially attributed to formation of Al-bearing minerals and Al-sulphates. Among them, alunite is the most important Al-sink phase that occurs at higher pH than $pK_1$, Al hydrolysis constant. With high saturation index, alunite formed at the creek has a spherical form, commonly associated with schwertmannite. Secondary minerals formed on the surface of altered or weathered surfaces of heavy metals from the wasted dump that underwent severe oxidation, where alunite has characteristic habits which are spheric, radiating, and botrytis-like aggregates. Natroalunite occurs in association with alunite, or as mixtures of both of them. Because the pH decreases with distance due to formation of schwertmannite, although total contents of dissolved ions slowly lessen at least in the AMD, it is expected that the minerals precipitated at the creek can be exposed to subsequent dissolution, which may induce possible environmental problems.

• Journal of the korean academy of Pediatric Dentistry
• /
• v.28 no.1
• /
• pp.45-53
• /
• 2001

Recently some studies have shown that low light intensity followed by final cure at high light intensity may result in a smaller marginal gap and may be no negative effect on material properties. The purpose of this study was to evaluate the influence of the initial cure with low intensity on the shear bond strength of dentin and the microhardness of composite resin. Twenty intact bovine teeth were prepared for shear bond strength test and each tooth sectioned to three specimens. The specimens were randomly divided into three groups according to the light intensity and curing time as follows; Group I. $450mmW/cm^2$ 40sec Group II. $300mmW/cm^2$ 20sec and $600mmW/cm^2$ 20sec Gropu III. $250mmW/cm^2$ 20sec and $450mmW/cm^2$ 20sec. Samples of each group were restored with light-cured composite resin after dentin bonding and then the shear bond strength of each specimen were measured using universal testing machine. Ten resin specimens per group were prepared. After 24 hours, the Vickers microhardness value was measured at the top and bottom surfaces. The result are as follows; 1. Mean value of low initial intensity groups(II, III) were higher than the control group(I) in shear bond strength, but no significant difference could be found. 2. No significant difference could be found between three groups in microhardness.

• Journal of Technologic Dentistry
• /
• v.36 no.2
• /
• pp.83-89
• /
• 2014

Purpose: This study is to evaluate the effect of modeling liquid on the shear-bond strength between zirconia core and veneering ceramic. Methods: Disk-shaped (diameter: 12.0mm; height: 3.0mm) zirconia were randomly divided into six groups according to the surface conditioning method and whether modeling liquid is used or not to be applied (N=60, n=10 per group): group 1-control group with distilled water(ZD); group 2-control group with modeling liquid(ZM); group 3-airborne particle abrasion with $110-{\mu}m$ $Al_2O_3$(AD) with distilled water; group 4-airborne particle abrasion with $110-{\mu}m$ $Al_2O_3$ with modeling liquid(AM); group 5-liner with distilled water(LD); group $6{\pounds}{\neq}liner$ with modeling liquid(LM). Contact angles were determined by the sessile drop method at room temperature using a contact angle measurement apparatus. The specimens were prepared using dentin veneering ceramics, veneered, 3mm high and 2.8mm in diameter, over the cores. The shear bond strength test was performed in a Shear bond test machine. Load was applied at a cross-head speed of 0.50mm/min until failure. The fractured zirconia surfaces were evaluated by using stereomicroscope (${\times}30$). Collected data were analyzed using SPSS(Statistical Package for Social Sciences) Win 12.0 statistics program. Results: ZD showed the highest contact angle($50.6{\pm}5.4^{\circ}$) and LD showed the lowest value($6.7{\pm}1.3^{\circ}$). Control groups and zirconia liner groups were significantly higher contact angle than liner groups(p<0.05). LD was the highest shear bond strength($43.9{\pm}3.8MPa$) and ZD was the lowest shear bond strength($24.8{\pm}4.9MPa$). Shear bond strengths of control groups and contact angle of liner groups were not significantly different((p>0.05). Liner groups presented adhesive failures. The others groups showed cohesive and adhesive failures. Conclusion: Modeling liquid groups showed lower contact angles and lower shear bond strength compared to those of distilled water groups.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.31 no.1B
• /
• pp.29-36
• /
• 2011

Evapotranspiration (ET) from the various surfaces needs to be understood because it is a crucial hydrological factor to grasp interaction between the land surface and the atmosphere. A traditional way of estimating it, which is calculating it empirically using lysimeter and pan evaporation observations, has a limitation that the measurements represent only point values. However, these measurements cannot describe ET because it is easily affected by outer circumstances. Thus, remote sensing technology was applied to estimate spatial distribution of ET. In this study, we estimated major components of energy balance method (i.e. net radiation flux, soil heat flux, sensible heat flux, and latent heat flux) and ET as a map using Mapping Evapo-Transpiration with Internalized Calibration (METRIC) satellite-based image processing model. This model was run using Landsat imagery of Gyeongan watershed in Korea on Feb 1, 2003 and Sep 13, 2006. Basic statistical analyses were also conducted. The estimated mean daily ETs had respectively 22% and 11% of errors with pan evaporation data acquired from the Suwon Weather Station. This result represented similar distribution compared with previous studies and confirmed that the METRIC algorithm had high reliability in the watershed. In addition, ET distribution of each land use type was separately examined. As a result, it was identified that vegetation density had dominant impacts on distribution of ET. Seasonally, ET in a growing season represented significantly higher than in a dormant season due to more active transpiration. The ET maps will be useful to analyze how ET behaves along with the circumstantial conditions; land cover classification, vegetation density, elevation, topography.

• Composites Research
• /
• v.29 no.5
• /
• pp.282-287
• /
• 2016

p-DCPD (poly dicyclopentadiene) is the resin that the versatile mechanical properties can be changeable via the control of inner monomer and catalysts. In this work, to improve the strength of composites, surface treated MGF (milled glass fiber) was used as an reinforcement in p-DCPD by molybdenum (Mo) catalyst matrix. The optimum concentration of surface treatment was obtained and the cohesion of MGF themselves increased with concentration. In case of 0.2 wt% silane concentration, the maximized mechanical properties of MGF/p-DCPD composite exhibited because of minimized MGF cohesion. When butyl silane showing minimizing cohesion was used as the optimized alkyl length, high tensile and flexure strength exhibited due to the steric hindrance effect among MGFs. Mechanical and their fractured surfaces of MGF/p-DCPD composites was compared for 4 different chemical functional groups. Norbornene functional groups containing similar chemical structure to DCPD matrix exhibited higher interfacial adhesion between MGFs and DCPD matrix.

• Korean Journal of Ecology and Environment
• /
• v.38 no.3 s.113
• /
• pp.393-402
• /
• 2005

The field scale experiment was performed to examine the effect of plant coverage on the constructed wetland performance and recommend the optimum development and management of macrophyte communities. Four sets (each set of 0.88 ha) of wetland (0.8 ha) and pond (0.08 ha) systems were used. Water flowing into the Seokmoon estuarine reservoir from the Dangjin stream was pumped into wetland system. Water depth was maintained at 0.3 ${\sim}$ 0.5 m and hydraulic retention time was managed to about 2 ${\sim}$ 5 days; emergent plants were allowed to grow in the wetlands. After three growing seasons of the construction of wetlands, plant coverage was about 90%, even with no plantation, from bare soil surfaces at the initial stage. During the start up period of constructed wetlands, lower water levels should be maintained to avoid flooding newly plants, if wetland plants are to be started from germinating seeds. Effluent T-N concentration in low plant coverage wetland was higher in winter than high plant coverage wetland, whereas no T-P effluent concentration and removal efficiency difference was observed within 15% plant coverage. Dead vegetation affected nitrogen removal during winter because it is a source of organic carbon which is an essential parameter in denitrification. Biomass harvesting is not a realistic management option for most constructed wetland systems because it could only slightly increase the removal rate and provide a minor nitrogen removal pathway due to lack of organic carbon.