• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.12
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• pp.791-797
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• 1999

Recently the ozone generation system is well used for cleaning the contaminated water by using the strong oxidization effects of ozone. In this paper the concentration, yield and generation quantity of the ozone by the Surface-Silent Discharge According to the Length of Coaxial Electrode is described. The electrodes composed of 3 electrodes-2 gaps are coaxial type and the ozone generation tube were designed and fabricated from the point of view of the energy efficiency, stability and easy control. To investigate the ozone generation dependency on electrode length, a few discharge tubes with different lengths were fabricated. The experimental equipments were provided with cooling system and dehumidifier for the many testing conditions. The main results show that the concentration, yield and generation quantity of ozone are improved by decreasing gas temperatures and increasing electrode lengths.

• Transactions of Materials Processing
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• v.22 no.1
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• pp.23-29
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• 2013

In this study, a micro/nano-random-pattern-structure surface was machined by electric discharge machining (EDM) followed by replicating the EDM surface with a silicone elastomer having low energy and greater hydrophobicity. The variation of hydrophobicity was of prime interest and was examined as a function of the surface roughness of the replicated silicone elastomer. The hydrophobicity was evaluated by the water contact angle (WCA) measured on the relevant surface. For the experiments, the original surfaces were machined by die sinking electric discharge machining (DS-EDM) and wire cutting electric discharge machining (WC-EDM). The ranges of surface roughness were Ra $0.8{\sim}19{\mu}m$ for the DS-EDM and Ra $0.5{\sim}4.7{\mu}m$ for the WC-EDM. In order to fabricate a hydrophobic surface, the EDM surfaces were directly replicated using a liquid-state silicone elastomer, which was thermally cured. The measured WCA on the replicated surfaces for DS-EDM was in the range of $115{\sim}130^{\circ}$ and for WC-EDM the WCA was in the range of $123{\sim}150^{\circ}$. Additionally, the dynamic hydrophobicity was evaluated by measuring an advancing and a receding WCA on the replicated silicone elastomer surfaces.

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.839-846
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• 2004

The objective of this study is the evaluation of the tunneling effect on the groundwater-surface water interaction. The designed tunnel line is laid beneath the Gapo-cheon, which runs throughout study area. And, the pre-evaluation of the tunnel-influence on the Gapo-cheon is urgently needed. However, it is very difficult to find out the similar domestic and/or foreign cases. In this study, we would exclude the numerical modeling technique with insufficient data. Instead of the evaluation of the tunneling effect on the groundwater-surface water interaction with the numerical modeling, we monitored the flow rate of surface water at various point. We measured the flow rate of surface water at 5 points. With the results of surface flow, we can conclude that 39% of flow rate in Gapo-cheon is contributed by the groundwater discharge, as baseflow.

• Journal of Korean Society on Water Environment
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• v.26 no.1
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• pp.28-34
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• 2010

This study was conducted to assess the validity of fecal coliforms to fecal streptococci ratio (FC/FS) for distinguishing the human from animal origin of fecal pollution in surface water. FC/FS ratio determined in effluent from municipal wastewater and human feces treatment plant (WWTP) and in downstream close to discharge of human feces was above 4 which indicates human origin. However FC/FS ratios determined seasonally in other water zones of the Nakdong River, even in the same sampling site, varied differently (above 4 or less than 0.7) due to different survival time of FC and FS and other environmental factors such as rainfall in watershed. Compared to other season, FC/FS ratios in winter were much lower regardless of the origin. It is concluded that the FC/FS ratio determined in surface water is not always valid for determining the origin of fecal pollution.

• Fire Science and Engineering
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• v.15 no.4
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• pp.41-48
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• 2001

Halogen-based fire suppressing agents have been the most effective fire suppressants and widely used for flammable liquid and electric fire. However they have environmental problems causing stratospheric ozone depletion and globe warming. As a substitution of halon, fire suppression system using fine water mist is one of an effective fire suppressant. Suffocating and cooling effects of water mist are increased by the evaporation characteristics because it has droplet size less than 1,000 $\mu{m}$ and very large surface area. In this study, the extinguishing characteristics of fire was measured with changing of water mist droplet size, flow density; discharge pressure, and fire size. As a result, the extinguishing time of pool fire was shortened with the increase of flow density and in case of low flow density less than 0.5$\pm$0.05 ml/$\textrm{cm}^2$ . min, the extinguishing time was shortened with the increase of droplet size. The cycling discharge was effective for $\eta$-heptane pool fire, and total amount of water mist required to extinguish fire was reduced to a quarter compare with continuous discharge.

• Journal of Surface Science and Engineering
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• v.34 no.5
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• pp.391-394
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• 2001

A new type plasma reactor is proposed to decompose CF4 diluted with N2 gas in atmospheric pressure. The arc plasmas is surrounded with a waterwall which acts as a source of water vapor, the solvent of HF, resultant product after decomposition, and conveyer to take away fluorine compound from exhaust gas. Abatement more than 99% is achieved by small size plasmas such as 1 cm in diameter, 25cm in length and 3.4KW of DC discharge power in such gas as the mixture of 100 sccm of CF4 and 15 slm of N2. Reactors of this type are to be expanded to such a system as Nitrogen flow of 50 slm with 200 sccm of CF4 and 7-8 KW discharge power.

• Korean Journal of Ecology and Environment
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• v.46 no.2
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• pp.205-214
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• 2013

In Yeongsan River estuary, located in the southern West Coast, a dike was constructed in December 1981. After the construction of a dike, discharge mechanism of fresh water has been changed, the water quality and chlorophyll-a are expected to be influenced by fresh water discharge. We investigated temporal and spatial variations and long-term trend of phytoplankton biomass (chlorophyll-a) and environmental factors. The concentrations of nutrient and chlorophyll-a were generally high in summer and the concentrations were increased toward downstream. Surface/bottom salinity difference was negatively correlated with salinity in surface water but positively with nutrient and chlorophyll-a. TN, TP and DIN concentrations were generally increased over 10 years. This study can provide information for better management of water quality for Youngsan River estuary.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.327-327
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• 2020

Increase in Earth's surface temperature, higher rainfall intensity rate, and rapid changes in land cover are just some of the most evident effects of climate change. Flooding, and river sedimentation are two inevitable natural processes in our environment, and both issues poses great risks in the dam industry when not addressed properly. River sedimentation is a significant issue that causes reservoir deposition, and thus causes the dam to gradually lose its ability to store water. In this study, the long-term effects of climate change on the sediment discharge in Yongdam Dam watershed is analyzed through the utilization of SWAT, a semi-distributed watershed model. Based from the results of this study, an abrupt increase on the annual sediment inflow trend in Yongdam Dam watershed was observed; which may suggests that due to the effects of climate change, higher rainfall intensity, land use and land cover changes, the sedimentation rate also increased. An efficient sedimentation management should consider the increasing trend in sedimentation rate due to the effects of climate change.

• Fisheries and Aquatic Sciences
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• v.3 no.2
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• pp.143-150
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• 2000

Assuming that summer surface waters in the South Sea (northern East China Sea) are formed mostly by a mixing of three source water (Changjiang Discharge Water; Kuroshio Water and Yellow Sea Surface Water) we apply optimum multiparameter (OMP) analysis to calculate the mixing ratio of each source water to a given surface water. Since OMP requires more parameters than the number of water types (three in this study), we utilize two radium isotopes of dissolved $^{226}Ra\;and\;^{228}Ra$ along with temperature and salinity. Parameter values of each source water are deduced from in situ and historical data. Results with three source of waters on the surface waters are quite promising with less than $1\%$ of unanswered portions. Results not only reproduce the measured temperature and salinity faithfully but also discern the water masses of similar T and S according to their source water mixing. Extending OMP analysis to a whole water column obviously requires more parameters because more source waters are involved in the water mass formation. Original OMP routine utilized dissolved oxygen and nutrients. However, they seem to be perturbed too much by biological activities in the case of shallow waters. We discussed the use of other potential parameters. Also the benefit of parameter substitution is briefly introduced for the future OMP application on shallow waters.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.51 no.10
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• pp.465-472
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• 2002

This paper presents a study on the aging and recovery of HTV (high temperature vulcanized) silicone rubber used for outdoor insulators. UV irradiation, corona discharge and water immersion were employed as factors of the artificial aging. The effects of changes derived from these stresses on the tracking and arc resistance of silicone rubber were examined. We have investigated the aging phenomena of HTV silicone rubber by the above stresses using the surface energy calculation with contact angle measurement, solvent-extraction, and surface/volume resistivity and so on. These results showed that UV irradiation and corona discharge lead to nearly the same surface oxidation, but the percentage change of mobile low molecular weight by these stresses was different. Furthermore, the oxidized layer induced under UV irradiation restricted the recovery of hydrophobic surface. Water immersion little lowered hydrophobicity level and leaded to a loss of tracking and arc resistance. The degradation mechanism based on our results was discussed.