• Journal of the korean academy of Pediatric Dentistry
• /
• v.24 no.2
• /
• pp.460-474
• /
• 1997

The purpose of this study was to evaluate and compare the effectiveness of various low-viscosity resin systems used as rebonding agents to prevent microleakage at the margins of class I composite resin restorations. Seventy sound human premolars were selected for experiment. Class I cavities were prepared and each cavity was conditioned with a 37% phosphoric acid for 15 sec, rinsed with water for 15 sec, and dried with compressed air. Bonding agent(Scotchbond Multipurpose, 3M Co.) was applied and a hybrid composite resin (Z-100, 3M Co.) was placed using an incremental technic. The excess cured composite resin was carefully removed with Sof-Lex discs(3M Co.) to expose the original margins of the cavity. The following seven groups were established : group 1 was not rebonded and used as control group ; group 2 was rebonded with a Scotchbond Multipurpose(3M Co.) and finished ; group 3 was rebonded with a Fortify(BISCO) and finished ; group 4 was rebonded with a Concise white sealant(3M Co.) and finished ; group 5 was rebonded with a Concise white sealant(3M Co.) and not finished ; group 6 was rebonded with a P&F sealant(BISCO) and finished; group 7 was rebonded with a P&F sealant(BISCO) and not finished. The specimens were then subjected to 500 thermocycles between 5 & 65 with a 10 see dwell time and immersed in 2% methylene blue dye solution for 24 hours and sectioned with low-speed diamond cutter into two part under water condition. The extent of microleakage at rebonded margins was evaluated microscopically and scored for dye penetration according to the following scale : 0=no dye penetration ; 1=dye penetration to half-way along axial wall between enamel surface and DEJ ; 2=dye penetration beyond halfway along axial wall between enamel surface and DEJ ; 3=dye penetration to the full depth of DEJ or beyond DEJ. Selected samples were prepared for SEM observation to determine the depth of penetration of the rebonding agent into the marginal interface. The obtained results were as follows: 1. In the group 2 and 3, which is rebonded with a Scotchbond Multipupose and Fortify, dye penetration score were decreased significantly than that of group 1 (P<0.05), but group 4 and 6 were not statistically different from group 1(P>0.05). 2. There were significant differences between group 4, 6 and group 5, 7 when compared by dye penetration score (P<0.05). 3. In the SEM observation, Scotchbond Multipurpose and Fortify were penetrated within $30-40{\mu}m$ depth of the outermost surface. However, both sealants were failed to penetrate into the debonded interface.

• The Journal of the Petrological Society of Korea
• /
• v.16 no.2 s.48
• /
• pp.47-58
• /
• 2007

This study examines the distribution of basement rocks in Gyochon-ri, Muan-eup, Muan-gun, Jeonnam where ground subsidence occurred in June 2005, and traces corrosion of limestone. Mica schist and rhyolite are distributed in the surface of the study area, but thick limestone layer with large and small caverns are distributed underground. A horizon of limestone with maximum width of 300 m and 4 km of length was found along the detour which is in the north of pound subsidence. Such identification of limestone presence would be very useful to predict potential ground subsidence. Limestone in this area was disturbed by fold and fault due to severe shearing deformation. Small caverns were frequently found in anticline part of folds formed in limestone layer. Schists with different thicknesses were intercalated in the limestone with shearing deformation and consist of sheet silicate minerals (chlorite and mica) and quartz. In sections of weathered specimen, it is shown that biotite of schist part was altered into chlorite and corrosion of calcite around the schist followed. This suggest that ground water permeated between intercalated sheet silicate minerals and corrosion of limestone began. And small caverns were generated where active corrosion occurred. This study suggests that because of many reasons (for instance, reclamation of the Bulmu reservior and excess pumping), cavern water level was lowered and cave sediments were removed, and it caused ground subsidence to occur.

• Journal of Korea Water Resources Association
• /
• v.36 no.2
• /
• pp.285-300
• /
• 2003

An event-based, kinematic, infiltration-excess, and distributed rainfall-runoff model using weather radar and Geographic Information System(GIS) was developed to acknowledge and account lot the spatial variability and uncertainty of several parameters relevant to storm surface runoff and surface flow The developed model is compatible with raster GIS and spatially and temporally varied rainfall data. To calibrate the model, Monte Carlo simulation and a likelihood measure are utilized; allowing for a range of possible system responses from the calibrated model. Using rain gauge adjusted radar-rainfall estimates, the developed model was applied and evaluated to a limited number of historical events for the Ralston Creek and Goldsmith Gulch basins within the Denver Urban Drainage and Flood Control District (UDFCD) that contain mixed land use classifications. While based on a limited number of Monte Carlo simulations and considered flood events, Nash and Sutcliffe efficiency score ranges of -0.19∼0.95 / -0.75∼0.81 were obtained from the calibrated models for the Ralston Creek and Goldsmith Gulch basins, based on a comparison of observed and simulated hydrographs. For the Ralston Creek and Goldsmith Gulch basins, Nash and Sutcliffe efficiency scores of 0.88/0.10, 0.14/0.71, and 0.99/0.95 for runoff volume, peak discharge, and time to peak, respectively, were obtained from the model.

• Magazine of the Korean Society of Agricultural Engineers
• /
• v.21 no.2
• /
• pp.28-36
• /
• 1979

One of most important problems in the Monsoon Asia today is the production of rice paddy to meet the needs of the ever increasing population. Diversemeans are being employed to meet this demand, both by increasing productivity of existing farm land and by bringing further areas into cultivation. The primary step in either field is to ensure that there is sufficient moisture in the soil to suit the paddy, and at the same this means that excess moisture has to be drained off the land, while in others irrigat ion has to be employed to bring sufficient water to an area. In view of the fact that the project comprises a huge amount of earthwork, it can be carried out by extensive use of construction machinery in order to shorten the period. As farm ditch has a comparatively small section with shallow cutting depth, inaddition, there is lack of access road in the field, the excavation equipment with bulldozer or tracter-shovel (backhoe) type are not applicable because there are mostly adapted for the excavation of deep and wide section. Mini-backhoe with its bucket width not larger than 0. 3m, and width of blade not larger than 1. 00m seems to be more adaptable. About 80% of excavation of ditch section will be done by the machinery while the other 20% of excavation together with the finishing of the section are supposed to be done by man-power. The embankment of ditch section can be compacted by the crawler of backhoe when it is moving along the ditch for excavation. However, Lowland paddy field in the Monsoon Asia are made particulary in rain season, therefore, heavy machinery is not easy excavation for ditch. It is very important to know exact ground support power of the working site and select machines with corresponding ground pressure. Ground support power is variable subject to quality and water content of soil and therefore selection of machines should be made duly considering ground condition of the site at the time of construction works. Farm ditches dug and compacted by mannual labar are of poor quality and subject to destruction after one or two years of operation. On the other hand, excavation and compaction by bulldozer is not practical for ditches. Backboe is suitable for slope land, but this is required cycle time of bucket excavation and dumped out. If a small-scale farm ditch trencher adaptable to lowland paddy field is invented, such a machine could greatly accelerate the massive construction work envisaged in many countries and thus significantly speed up the most difficult part of irrigation development and management in Monsoon Asia.

• Polymer(Korea)
• /
• v.35 no.4
• /
• pp.363-369
• /
• 2011

To study the effect of incorporation of a surface crosslinking layer on a crosslinked poly (sodium acrylate) (cPSA) absorbent with ethylene glycol dimethacrylate CEGDMA), we synthesized several surface crosslinked cPSAs with EGDMA by an inverse emulsion polymerization method to delay the absorption of excess water in concrete, Liquid paraffin was used as a continuous phase. cPSA was synthesized with acrylic acid (AA) neutralized with aqueous 8 M sodium hydroxide solution as a monomer, N,N-methylene bisacrylamide (MBA) as crosslinking agent and ammonium persulfate (APS) and sodium metabisulfite (SMBS) as a redox initiator system by inverse emulsion polymerization. FTIR spectroscopy was used to characterize $Ca^{2+}$ ion interaction with cPSA and cPSA-EGDMAs. The swelling ratios of synthesized absorbents were evaluated from the absorption in deionized water, cement saturated aqueous solution and aqueous solution of calcium hydroxide (pH 12). Equilibrium swelling times for cPSA and surface crosslinked cPSA with EGDMA were 2 and 3 hrs, respectively. We also observed an increase in setting time of the cement and an increase in the compressive strength of mortar by addition of the synthesized cPSA-EGDMA.

• Journal of Korean Society on Water Environment
• /
• v.18 no.2
• /
• pp.201-212
• /
• 2002

The objective of this study was to investigate the treatment efficiency, kinetics, and morphological characteristics of biofilm in upflow $Biobead^{(R)}$ process, a kind of biological aerated filter(BAF). The $Biobead^{(R)}$ system showed high removal rates of $COD_{Mn}$(76~83%), $BOD_5$(67~88%) and SS(71~91%) for food wastewater with high salt concentration ($>4,000mg/{\ell}$) under short reaction times(2~3hrs). Even at aerobic condition, the system had high treatment efficiency for both T-N (51~63%) and T-P(62~81%). The removal kinetics of $COD_{Mn}$, $BOD_5$, T-N, T-P, and $Cl^-$ in the $Biobead^{(R)}$ system showed a plug-flow pattern with reaction rate constants($hr^{-1}$) of 0.58, 0.63, 0,30, 0.48, and 0.38 respectively. A backwashing process to remove excess biomass and filtered solids was needed at least once during 22-hour operation at $0.5kg\;BOD\;m^{-3}{\cdot}d^{-1}$ loading. At the higher loading($1.0kg\;BOD\;m^{-3}{\cdot}d^{-1}$) the backwashing interval was shorten by 8 hours. The COD, BOD, T-N, and T-P were removed from 43 to 66% only by aerobic biodegradation. The SS was removed over 70% by the filtering of $Biobead^{(R)}$ media in the treatment system. The first one of three serial Biobead reactors showed the highest removal values for $COD_{\alpha}$(52.3%), $COD_{Mn}$(38.8%), BOD(62.5%), and T-N(40.0%). The SS and T-P had the highest removal values(47.5% and 29.2%) at the second one of the serial reactors. The biofilm had non-homogeneous spatial distribution and the colonies were embedded in the sunk area of the Biobead. The thickness of the biofilm was very thin ($5.0{\sim}29.4{\mu}m$) compared to the biofilm thickness($200{\sim}300{\mu}m$) used in other BAF systems.

• Journal of fish pathology
• /
• v.23 no.3
• /
• pp.281-291
• /
• 2010

Crytocaryon irritans infection of rock bream was investigated in embankment fish farm from July to December 2009. Prevalence variation was 20.0~88.0% that was high in september and was low in July. While no mortality was found in July and August, it occurred after mid september. Environmental conditions during the survey period were water temperature $19.3{\sim}24.3^{\circ}C$, dissolved oxygen $5.0{\sim}7.1\;mg\;L^{-1}$ and salinity 31.9~33.7 psu, and the water temperature during mortality season was $24.0^{\circ}C$. External symptom of the rock bream was secretion mucus but swimming showed fine in the early infected period. While, the symptoms in the severe outbreak season were excess of mucus, falling off tail and congestion, bleeding spot the surface and weakened swimming. We observed free living and parasitic stages in the gills and body surface of rock bream. Hepato somatic index (HSI) was $1.9{\pm}1.1{\sim}3.5{\pm}1.7%$, which was low in the September being mortality season but was high in November. The percentages of hematocrit infected with Crytocaryon irritans were 37.3% and 41.0% in July and August, respectively while they gradually decreased to 32.1% and 24.2% in september and October, respectively. Total cholesterol and Triglyceride values rapidly decreased by October. After mortality, AST and ALT were 7 and 5 folds higher compared to non-mortality season.

• Journal of Nutrition and Health
• /
• v.5 no.2
• /
• pp.91-103
• /
• 1972

Zinc is one of the essential trace elements in the living organism for growth and health. The first identified metalloenzyme, carbonic anhydrase, is a zinc compound and several others have been described since. Among zinc deficiency syndromes in animals porcine parakeratosis has been successfully treated with zinc supplements, and in man a syndrome of anemia, hypogonadism, hepatosplenomegaly, and dwarfism, prevalent in parts of Iran and Egypt, has been ascribed to lack of zinc in the diet. Dietary zinc excess in the rat is manifested by a hypochromic, microcytic anemia, poor growth, reduction in liver catalase and cytochrome oxidase. The present study is an attempt to delineate the changes of tissue contents of trace elements, especially of iron, copper and zinc in liver and kidneys of the rats. Weanling albino rats, weighing 60 to 80gm. were used in this experiments. The rats were housed in cages with aluminum floors and received feed and distilled water ad libitum. Animals were divided into three groups, control, low zinc diet and high zinc diet groups. The high zinc diet group was subdivided into 0.5% Zn and 0.7%Zn groups. The supplementary copper or iron was added to the high dietary zinc groups. The animals were sacrificed and the tissues were washed several times with deionized water. The wet digested samples were analyzed by Hitachi Model 207 atomic absorption spectro-photometer for the determination of iron, copper and zinc in the liver and kidney. Hemoglobin level in the blood was measured by cyanmethemoglobin method. The results of this study are as follows: 1) All rats fed high zinc diets and low zinc diets gained less weight than control. Weight gain was not improved by the supplementary copper or iron and both. 2) Hemoglobin concentration was decreased significantly in the rats fed high zinc diets and less in the low zinc diet. Supplementary copper and iron to the higher zinc diet appeared to give some improvement of anemia. 3) The iron contents of the liver and kidneys were significantly decreased in the high zinc groups and the reduction was more significantly in the rats receiving higher zinc diet (0.7%). The supplementary copper caused a further depression of liver iron. On the other hand, the iron, added to the high zinc diet lessoned the severity of the decrease in liver iron and caused kidney iron to be maintained almost at the level found in the rats fed by zinc and supplementary copper diet. 4) High zinc diets did not change copper content of the liver and kidney. Supplementary copper elevated the concentration in the liver and kidney and added iron had no effect on the accumulation of copper in the liver and kidneys. 5) The high zinc diets caused marked increases of zinc content in the liver and kidney. Supplementary iron to the high zinc diet caused increases of zinc contents of liver and kidneys.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2019.05a
• /
• pp.294-294
• /
• 2019

The system for predicting flood of river at Flood Control Office is made up of a rainfall-runoff model and FLDWAV model. This system is mainly operating to predict the excess of the flood watch or warning level at flood forecast points. As the demand for information of the management and operation of riverside, which is being used as a waterfront area such as parks, camping sites, and bike paths, high-level forecasts of watch and warning at certain points are required as well as production of lowland flood forecast information that is used as a waterfront within the river. In this study, a technology to produce flood forecast information in lowland areas of the river used as a waterfront was developed. Based on the results of the 1D hydraulic analysis, a model for performing spatial operations based on high resolution grid was constructed. A model was constructed for Andong district, and the inundation conditions and level were analyzed through a virtual outflow scenarios of Andong and Imha Dam.

• Journal of Climate Change Research
• /
• v.8 no.4
• /
• pp.305-312
• /
• 2017

We aimed at investigating the difference in $N_2O$ emission factors of chemical and organic fertilizers and identifying the main factors influencing annual fluctuations in $N_2O$ emission. We conducted two-year experiments in 2016 and 2017 in an agricultural field planted with sweet potato (Ipomoea batatas). Treatments included chemical NPK fertilizer (NPK) and chicken compost application at $10\;ton\;ha^{-1}$, $20\;ton\;ha^{-1}$, and $30\;ton\;ha^{-1}$ rates (CK1, CK2 and CK3). Control was also employed with no addition. Results showed that $N_2O$ emission rates were significantly related with soil water status and soil available N contents. Significant correlation between % water filled pore space (WFPS) and $N_2O$ emission was observed only when the %WFPS was greater than 40% and during the initial stage of the experiment (<60 d). Comparison of the emission factors in 2016 and 2017 showed us that the emission factor was greater in 2016 when the %WFPS was maintained higher by 16.5% compared to that in 2017. In 2016, the emission factor of organic fertilizer was higher than that of chemical fertilizer, while in 2017, the pattern was reversed. Annual variability in $N_2O$ emission could also be originated from the available N contents remaining in soil after being taken up by plants. If we apply excessive N fertilizer, the soil would contain excess amount of N which was not uptaken by plants, leading to a huge increase in $N_2O$ emission. This case would overestimate emission factor, which was the case for the organic fertilizer in 2016. Over-fertilization should be avoided when we set up an experiment to determine $N_2O$ emission factor.