• The Journal of Korean Academy of Prosthodontics
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• v.38 no.4
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• pp.427-437
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• 2000

Recently the 2nd generation laboratory composite resins were introduced. Although the mechanical properties of these composite resins have been improved, there were some disadvantages such as discoloration, low abrasion resistance and debonding between metal and resin. The purpose of this study was to evaluate the tensile bond strength between non-pecious dental alloy(verabond) and four veneering reinforced composite resins ; Targis(Ivoclar Co., U.S.A.), Artglass(Kulzer CO., Germany), Sculpture(Jeneric Pentron Co., U.S.A.), and Estonia(Kurary Co., Japan). All test metal specimens were polished with #1,000 SiC paper, and sandblasted with $250{\mu}m$ aluminum oxide. After then. according to manufacturer's instructions metal adhesive primer and veneering resins were applied. All test specimens were divided into two groups. One group was dried in a desiccator at $25^{\circ}C$ for 3 days, the other group was subjected to thermal cycling($2,000{\times}$) in water($5/55^{\circ}C$). Tensile bond strength was measured using Instron Universal Testing machine and the fractured surface was examined under the naked eyes and scanning electron microscope. Within the limitations imposed in this study, the following conclusions can be drawn: 1. In no-thermal cycling groups, there were no significant differences between Estenia and VMK68 but there were significant differences between Targis, Artglass, Sculpture and VMK68(p<0.05). 2. In no-thermal cycling resin groups, the highest tensile bond strength was observed in Estenia and there were significant differences between Estenia and the other resins(p<0.05). 3. Before and after thermal cycling, there were significant differences in tensile bond strength of Targis and Artglass(p<0.05). The tensile bond strength of Artglass was decreased and that of Targis was increased. 4. In no-thermal cycling groups, Artglass showed mixed fracture modes(95%), but after thermal cycling, Artglass showed adhesive fracture modes(75%).

• Particle and aerosol research
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• v.13 no.4
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• pp.151-158
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• 2017

Electrostatic precipitator is widely used to remove particulate matters in indoor air and industrial flue gas due to low pressure drop and high collection efficiency. However, it has a low collection efficiency for the submicrometer sized particles. Electrospraying is a potential method to increase the particle charging efficiency, which results in increased collection efficiency. Although particle charging efficiency is highly dependent upon droplet size, the effective measuring method of the droplets is still uncertain. Tap water was electrosprayed in this study, and the images of electrosprayed droplets were taken with a high speed camera coupled with several visualization methods in order to measure the droplets size. The droplet size distribution was determined by an image processing with an image-J program. As a result, a droplet measured by a laser visualization, had a half size of that by a Xenon light visualization. In addition, the experimentally measured droplet sizes were a good agreement with the predicted values suggested by $Fern{\acute{a}}ndez$ de la Mora and Loscertales(1994).

• Journal of the Korean GEO-environmental Society
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• v.13 no.4
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• pp.27-36
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• 2012

The water in surface of the earth is frozen under freezing point. The freezing phenomenon, which causes the volume change of soils, affects on the behavior of soils and causes the significant damage on the geotechnical structures. The purpose of this study is to investigate the characteristics of elastic waves in sand-silt mixtures using small size freezing cells, which reflect the frozen ground condition due to temperature change. Experiments are carried out in a nylon cell designed to freeze soils from top to bottom. Bender elements and piezo disk elements are used as the shear and compressional wave transducers. Three pairs of bender elements and piezo disk elements are placed on three locations along the depth. The specimen, which is prepared by mixing sand and silt, is frozen in the refrigerator. The temperature of soils changes from $20^{\circ}C$ to $-10^{\circ}C$. The velocities, resonant frequencies and amplitudes of the shear and compressional waves are continuously measured. Experimental results show that the shear and compressional wave velocities and resonant frequencies increase dramatically near the freezing points. The amplitudes of shear and compressional waves show the different tendency. The dominant factors that affect on the shear wave velocity change from the effective stress to the ice bonding due to freezing. This study provides basic information about the characteristics of elastic waves due to the soil freezing.

• Journal of the korean academy of Pediatric Dentistry
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• v.30 no.4
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• pp.593-599
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• 2003

The purposes of this study were to evaluate the microleakage of class V composite resin restorations utilizing the different curing lights, to assess the flowable resin, $Filtek^{TM}Flow$(3M Dental Products, USA) and composite resin, $Filtek^{TM}Z250$(3M Dental Products, USA) which need 20s curing time for halogen light could replace $Z100^{TM}$ Restorative(3M Dental Products, USA) for the microleakage, and to evaluate the effect of adhesive resin on marginal microleakage. Light curing units used in this study were conventional halogen light, XL3000(3M Dental Products, USA) and plasma arc light, Flipo(Lokki, France). Class V cavities were prepared and each cavity was filled with each composite resin. After being filled, the teeth were stored in distilled water, polished, thermocycled and soaked in 1% methylene blue solution. Following results were obtained from evaluation of the sectioned surface. 1. There was no statistically significant difference in microleakage of $Filtek^{TM}Flow$ and $Filk^{TM}Z250$ between two kinds of curing units(p>0.05). 2. Flowable resin, $Filtek^{TM}Flow$ showed more microleakage than Z100 and $Filtek^{TM}Z250$ regardless of curing units(p<0.05). 3. Adhesive resin reduced the microleakage of composite resin in both halogen light and plasma arc light(p<0.05).

• Journal of the korean academy of Pediatric Dentistry
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• v.28 no.2
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• pp.261-270
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• 2001

This study was performed to evaluate wear characteristics of light-cured composites when opposed by human enamel. Seven light-cured restorative composites were selected and enamel cusps sectioned from premolars. All samples were stored in distilled water at $37^{\circ}C$ for 10 days. 68.6 N of weight was loaded during the test. The measurements of vertical loss of enamel cusps, weight loss and volume loss of composites, and SEM observations of the polished and abraded surfaces were made after 30,000 cycles. The results obtained were summarized as follows; 1. The highest hardness value of 70.4 was observed in the Spectrum group and the lowest value of 19.8 was observed in the Heliomolar group. Results of Tukey test showed that an overall significant difference was indicated except the Spectrum, Z100 and Clearfil AP-X groups(p<0.05). 2. Enamel showed the good abrasion resistance against the Heliomolar group of microfilled composite and the Palpique Toughwell group containing the submicron hybrid type spherical fillers. 3. The abrasive wear resistance of hybrid composites was improved with the decrease of mean particle size and hybrid of submicron particle fillers. 4. SEM observation of worn surfaces revealed the protrusion, attrition and missing of fillers, cracks developing and delamination in the matrix.

• Journal of Radiation Protection and Research
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• v.41 no.3
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• pp.245-252
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• 2016

Background: Ingestion of $^{210}Po$ laden seafood accounts for a substantial amount of the effective dose of $^{210}Po$. Among seafood items, mollusks, especially domestically produced oysters and mussels, are highly enriched in $^{210}Po$ and are consumed in large quantities in Korea. Materials and Methods: Oysters and mussels around the Korean coasts were collected from major farm areas in November 2013. Samples were spiked with an aliquot of $^{209}Po$ as a yield tracer, and they were digested with $6mol{\cdot}L^{-1}$ $HNO_3$ and $H_2O_2$. The $^{210}Po$ and $^{209}Po$ were spontaneously deposited onto a silver disc in an acidic solution of $0.5mol{\cdot}L^{-1}$ HCl and measured using an alpha spectrometer. The activity concentrations of $^{210}Pb$ and $^{210}Po$ were decay corrected to the sampling date, accounting for the possible in-growth and decay of $^{210}Po$. Results and Discussion: $^{210}Po$ activity concentrations in oysters were in a range from 41.3 to $206Bq{\cdot}(kg-ww)^{-1}$ and mussels in a range from 42.9 to $46.7Bq{\cdot}(kg-ww)^{-1}$. The $^{210}Po$ activity concentration of oysters in the turbid Western coast was higher than the Southern coast. The $^{210}Po$ activity concentration of the oysters was positively correlated ($R^2=0.89$) with those of the suspended particulate matter in the surface water. The calculated annual effective dose of $^{210}Po$ from oysters and mussels consumed by the Korean population was 21-104 and $5.01-5.46{\mu}Sv{\cdot}y^{-1}$. The combined effective dose due to the consumption of oysters and mussels appears to account for about $35{\pm}19%$ of that arising from seafood consumption in the Korean population. Conclusion: The annual effective dose of $^{210}Po$ for oysters in the Korean population was found to be higher than other countries. The total annual effective dose of $^{210}Po$ due to consumption of oysters and mussels consumed in Korea was found to be $76{\pm}42{\mu}Sv{\cdot}y^{-1}$, accounting for $28{\pm}16%$ of the total effective dose of $^{210}Po$ from food in Korea.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.585-588
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• 2008

To predict the service life of reinforced concrete structures exposed to chloride environment, quantitative measures of material properties such as the critical chloride content for corrosion in concrete and the diffusion coefficient of chloride ions of concrete and the surface chloride content of the concrete are essential. However, it should be noted that they are influenced by several factors such as concrete mix proportions, cement type, and environmental conditions, etc. Thus, the purpose of this research is to estimate more actually the critical chloride content for corrosion of the reinforcing steel in concrete by field exposure experiment. For this purpose, the prism concrete test specimens were made for water-cement(W/C) ratios of 31%, 42%, 50%, and 70%, and then the field exposure experiment for them were conducted at Youngduk of the east coast for about 3 years. During the test, corrosion monitoring by half cell potential method was carried out to detect the time to initiation of corrosion for test specimens and its chloride content was evaluated by breaking the concrete test specimens when corrosion of the reinforcing steel in concrete was perceived. It was observed from the test results that the critical chloride content for corrosion of reinforcing steel in concrete would be dependent on W/C ratio and almost irrespective of concrete cover.

• Journal of the Korean Ceramic Society
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• v.35 no.6
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• pp.594-602
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• 1998

Titanium hydroxide (TiO({{{{ {OH }_{2 } }})) fine particles were produced by the reverse micelle technique. For the formation of titanium hydroxide (TiO({{{{ {OH }_{2 } }})) particles with the technique reversed micellar solution was prepared by solubilizing water into organic solvent (isooctane) with a surfactant and titanium alkoxide (tetraisopropyl orthotitanate) diluted with isopropyl alcohol was added to the reversed micellar solution. The hdrolyzed species (TiO({{{{ {OH }_{2 } }})) was formed by the hydrolysis of titanium alkoxide and titanium dioxide is then formed by the condensation of the hydrolyzed species. There are several process variables such as surfactants concentration of surface cosurfactant hydrolysis temperature and pH. In this work the ef-fects of process variables on paticle shapes particle size distribution and paticle agglomeration were bi-nodal for an anionic surfactant(AOT) in the whole range of temperature pH and surfactant concentration of this experiment. The addition of ethanol as a cosurfactant resulted in narrow particle size distribution of the experiment. The additiono of ethanol as a cosurfactant resulted in narrow particle size distribution and 0.12${\mu}{\textrm}{m}$ of smaller average particle diameter. FT-IR spectrum of particles shows the absorption peak of Ti-OH bonding and Ti-O bonding. An exothermic peak around 41$0^{\circ}C$ in TGA-DTA curve shows that crys- tallized anatase phase appears and completely transits to anatase around 45$0^{\circ}C$.

• Journal of Korean Society of Forest Science
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• v.89 no.2
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• pp.145-160
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• 2000

This study is focused to the national park of Korean typical Sea Hally$\check{o}$ Haesang, and its visual resources and practiced inspect course by the way of suppositions and tests, to show the visual resource management objectively, and that of qualitative basic data. Accordingly by measuring the physical amount spatial structure with the visual amount originated from the Mesh Analyzing Method and the Visual Preference from the Scenic Beauty Estimation(S.B.E.) method and analyzed the valuation of the visual resource by Iverson method. Spatial image structure measured by Semantic Differential(S.D.) Scale was shown through the factor analysis algorithm for the analyzing psychological amount and examined the flowing out of decisive factor and the objective importance related to the mutual factors by appling the measurement of the visual quality. As a national Park, the visual factors that have natural landscape harmonized with forest, sky, surface of the water, curious stones and rocks, and temples should be escalated their values affirmatively so as to be the scenery of pointed direction and enjoyable, and it is of more needed for visual resource and its' controlling technique to make artificial structures more intentional planning and systemical setting. When we are viewing the improvement for the national park along with the visual resource management, reasonable level of development is needed, because when men interference surpass plantations and leasts will be damaged and the quality of natural landscape can be lowered, so it is needed to set up a management end, tangibly or clearly; and it is permitted limit coming and going ablably by accounting the suitable number for availing. But the controling end should be set in every level, positive management, very actively within the permissive varcability. It is the main business for the national park to prevent the damage from human for their gay life or to prevent the damage of a land carpet, and to restorate for the visual resource management.

• Geotechnical Engineering
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• v.3 no.4
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• pp.41-54
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• 1987

A stochastic numerical analysis for predicting the groundswater fluctuations in hillside slopes is performed in this paper to account for the uncertainties associated with the rainfall and site characteristics. The effect of spatial variabilities of aquifer parameters and the effect of temporal variability of recharge on the groundwater fluctuations are studied in depth. The Kriging is used to account for the spatial tariabilities of aquifer parameters. This technique prolevides the best linear unbiased estimator of a parameter and its minimum variance from a litsitem number of measured data. A stochastic one-dimensional numerical model is delreloped b) combining the groundwater flow model, the Kriging, and the first-order second-moment analysis. In addition, a two dimensional detelministic groundwater model is developed to study the change of ground water surfas in the transverse direction as well as in the downslope direction. It is revealed that the undulations of the impervious bedrock in addition to the permeability and the specific yield have an important influence on the fluctuations of the groundwater surface. It is also found that th'e groundwater changes significantly in the transverse direction as well as in the downslope direction. The results obtained in this analysis may be used for evaluation of landslide risks due to high porewater pressure.