• Korean Journal of Environmental Agriculture
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• v.23 no.4
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• pp.258-263
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• 2004

Bioassay was employed to assess toxicity of soil which had been treated with sewage sludges for seven years. The $Microtox^{(R)}$ and root elongation test of lettuce (Lactuca Sativa.) elucidated that the intensity of soil toxicity was closely related with the types and amount of sewage sludges applied. Both bioassay methods proved to be useful in an assessment of soil toxicity and were consistent to some extent with the conventional chemical analysis methods. $EC_{50}$ values resulted from $Microtox^{(R)}$ were highly correlated with concentration of heavy metals in soils amended with sewage sludges : Cu ($r^2=\;0.86^{**}$), Cr ($r^2\;=\;0.84^{**}$), Ni ($r^2\;=\;0.83^{**}$), and Zn ($r^2\;=\;0.69^{**}$). This demonstrated that both bioassay techniques could be employed as tools for soil toxicity assessment when the soil was exposed to solid wastes such as sewage sludge.

• Korean Journal of Ecology and Environment
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• v.40 no.3
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• pp.357-369
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• 2007

Water fleas are very important organisms in aquatic ecosystem because they are key constituents of food webs as either glazers or foods for predators. Daphnia magna is a representative test species and it has been extensively used in ecotoxicity evaluation. However, Daphnia magna has not been found yet in Korean water environment. There are limitations of using the foreign species such as Daphnia magna to reflect domestic situations in Korea. Consequently it is mandatory to find domestic species suitable for bioassay, and to develop corresponding toxicity test methods using the domestic species. In this study, we widely collected the domestic and foreign toxicity test methods performed by using domestic water fleas in Korea. The 58 test methods were collected from the standard methods (OECD, US EPA, ASTM), government reports, SCI papers and domestic papers. Ten domestic water fleas selected were Bosmina longirostris, Ceriodaphnia dubia, Ceriodaphnia reticulata, Daphnia obtusa, Daphnia puex, Moina macrocopa, Moina micrura, Simocephalus mixtus, Simocephalus serrulatus, and Simocephalus vetulus. We suggested the domestic ecotoxicity test methods using domestic water fleas in Korea through providing a range of test conditions, and future directions for toxicity test using water flea. This study could be a useful basis for establishing the aquatic toxicity test methods with domestic organisms in Korea.

• Journal of the Korean Society of Food Science and Nutrition
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• v.45 no.1
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• pp.61-67
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• 2016

An HPLC analysis method was developed for standard determinations of chlorogenic acid, 3,4-di-O-caffeoylquinic acid, 3,5-di-O-caffeoylquinic acid, and 4,5-di-O-caffeoylquinic acid as functional health materials in Ligularia fischeri extract. HPLC was performed on a $C_{18}$ Kromasil column ($4.6{\times}250mm$, $5{\mu}m$ column) with a gradient elution of 0.1% (v/v) trifluoroacetic acid and acetonitrile at a flow rate of 1.0 mL/min at $30^{\circ}C$. The analytes were detected at 330 nm. The HPLC method was validated in accordance with the International Conference on Harmonization guideline of analytical procedures with respect to specificity, precision, accuracy, and linearity. The limits of detection and quantitation for the four compounds were 3.0~14.6 and $9.2{\sim}44.4{\mu}g/mL$, respectively. Calibration curves showed good linearity ($r^2$ > 0.999), and the precision of analysis was satisfied (less than 0.9%). Recoveries of quantified compounds ranged from 98.96 to 101.81%. This result indicates that the established HPLC method is very useful for the determination of marker compounds in Ligularia fischeri leaf extracts.

• Journal of the Korean Geographical Society
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• v.43 no.3
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• pp.392-411
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• 2008

The purpose of this paper is to develop a method for exploring hotspot patterns of house price volatility where there is a high fluctuation in price and homogeneity of direction of price volatility. These patterns are formed when the majority of householders in an area show an adaptive tendency in their decision making. This paper suggests a method that consists of two analytical parts. The first part uses spatial scan statistics to detect spatial clusters of houses with a positive range of price volatility. The second part utilizes local Moran's I to evaluate the homogeneity of direction of price volatility within each cluster. The method is applied to the areas of Gangnam-Gu, Seocho-Gu, and Songpa-Gu in Seoul from August to November of 2003; the Participatory Government of Korea designated these areas and this period as the most speculative. The results of the analysis show that the area around Gaepo-Dong was as a hotspot before the Government's anti-speculative 10.29 policy in 2003; the house prices in the same area stabilized in October, 2003 and the area was identified as a coldspot in December, 2003. This case study shows that the suggested method enables exploration of hotspot of house price volatility at micro spatial scales which had not been detected by visual analysis.

• The Journal of Engineering Geology
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• v.23 no.2
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• pp.149-160
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• 2013

Volcanic activity commonly creates a highly complicated volcanic complex due to the admixture of lava flow and sedimentation of volcanic ash. The Song-Gok site is composed of volcanic rocks that collapsed at the lower part of the slope, in combination with several discontinuities in and around a fault. The results of projection analysis indicated the possibility of plane, wedge, and toppling failure in the failure section. The results of discontinuity modeling using the Distinct Element Method (DEM) revealed a total displacement of 207 mm and a joint shear displacement of 114 mm. The yield surface zone was verified at the fault plane of the failure section. In geotechnical terms, volcanic rock slopes are characteristically vulnerable to failure because of differential weathering among the various rock types, the effect of groundwater based on the permeability of the rocks, and the presence of systematic joints generated by the cooling and contraction of lava. When considering the stability of a volcanic rock slope, it is necessary to consider data such as the geological features of the rock, as obtained through detailed geological survey, and variations in discontinuities and rock blocks.

• Journal of Korean Tunnelling and Underground Space Association
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• v.14 no.4
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• pp.293-308
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• 2012

The shear behavior at the particle/surface interface such as rock joint can determine the mechanical behavior of whole structure. Therefore, a fundamental understanding of the mechanisms governing its behavior and accurately estimation of the interface strength is essential. In this paper, PFC, a numerical analysis program of discrete element method was used to investigate the effects of the surface roughness on interface strength. The surface roughness was characterized by smooth, intermediate, and rough surface, respectively. In order to investigate the effects of particle shape and crushing on particle/surface interface behavior, one ball, clump, and cluster models were created and their results were compared. The shape of particle was characterized by circle, triangle, square, and rectangle, respectively. The results showed that as the surface roughness increases, interface strength and friction angle increase and the void ratio increases. The one ball model with smooth surface shows lower interface strength and friction angle than the clump model with irregular surface. In addition, a cluster model has less interface strength and friction angle than the clump model. The failure envelope of the cluster model shows non-linear characteristic. From these findings, it is verified that the surface roughness and particle shape effect on the particle/surface interface shear behavior.

• Journal of Korean Tunnelling and Underground Space Association
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• v.14 no.4
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• pp.321-336
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• 2012

The shear behavior at the particle/surface interface such as rock joint can determine the mechanical behavior of whole structure. Therefore, a fundamental understanding of the mechanisms governing its behavior and accurately estimation of the interface strength is essential. In this paper, PFC, a numerical analysis program of discrete element method was used to investigate the effects of the surface roughness crushing on interface strength. The surface roughness was characterized by smooth, intermediate, and rough surface, respectively. Particle shape was classified into one ball model of circular shape and 3 ball model of triangular shape. The surface shape was modelled by wall model of non-crushing surface and ball model of crushing surface. The results showed that as the bonding strength of ball model decreases, lower interface strength is induced. After the surface roughness crushing was occurred, the interface strength tended to converge and higher bonding strength induced lower surface roughness crushing. Higher friction angle was induced in wall model and higher surface roughness induced the higher friction angle. From these findings, it is verified that the surface roughness and surface roughness crushing effect on the particle/surface interface shear behavior.

• Korean Journal of Environmental Biology
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• v.34 no.2
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• pp.116-123
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• 2016

The ecotoxicity tests for metal plating wastewater were conducted using Daphnia magna (D. magna) and Euglena agilis (E. agilis). Evaluation for sources of toxicity was performed by 1) Correlation analysis between the concentration of individual metals in the metal plating wastewater and the toxic effects on D. magna, 2) Toxicant identification evaluation methods including graduated pH method, EDTA procedure and sodium thiosulfate procedure, 3) Comparison of toxic effect value ($EC_{50}$ or $LC_{50}$) of individual metal on D. magna and it's concentration in the metal plating wastewater. To evaluate the possibility of E. agilis, a Korean domestic organism, as a test model organism for metal plating waste water, E. agilis toxicity test was also assessed using on-line euglena ecotoxicity system (E-Tox system). Based on toxicant characterization test using D. magna, it was expected that SS, oxidants and heavy metals are responsible for toxicity of metal plating waste water. Especially Cu, Hg, and Ag were the major cationic metals that caused toxicity. E. agilis is less sensitive than D. magna based on the $EC_{50}$ value however it shows prompt response to toxic test substances. E. agilis shows even a significant effect on the cell swimming velocity within 2 min to toxic metal plating wastewater. Our study demonstrates that E. agilis test can be a putative ecotoxicity test for assessing the quality of metal plating waste water.

• Tunnel and Underground Space
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• v.11 no.2
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• pp.109-119
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• 2001

Up to now single large cavern was excavated for each undergroud hydraulic powerhouse in Korea. But the Yangyang underground hydraulic powerhouse consists of two large caverns; a powerhouse cavern and main transformer cavern. In this carte, the structural stability of the caverns, especially the rock pillar formed between two large caverns, should be guaranteed to be sound to make the caverns permanently sustainable. In this research, the Distinct Element Method(DEM) was used to analyze the structural stability of two caverns and the rock pillar. The Barton-Bandis joint model was used as a constitutive model. The moot significant parameters such as in-site stress, JRC of in-situ natural joints, and spatial distribution characteristics of discontinuities were acquired through field investigation. In addition, two different cases; 1) with no support system and 2) with a support system, were analysed to optimize a support system and to investigate reinforcing effects of a support system. The results of analysis horizontal displacement and joint shear displacement proved to be reduced with the support system. The relaxed zone in the rock pilar also proved to be reduced in conjunction with the support system. Having a support system in place provided the fact that the non zero minimum principal stresses were still acting in the rock pillar so that the pillar was not under uniaxial compressive condition but under triaxial compressive condition. The structural stability f an approximately 36 m wide rock pillar between two large caverns was assured with the appropriate support system.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.3
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• pp.16-20
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• 2018

Steel Fiber reinforced self-compacting concrete (SFRSCC) has been widely used in a number of structures, such as ordinary civil infrastructures, sky scrapers, nuclear power plants, hospitals, dams, channels and etc. Thanks to its short and discrete reinforcing fibers, its performance, including tensile strength, ductility, toughness and flexural strength gets much better in comparison with ordinary self-compacting concrete (SCC) without any reinforcing fibers. Despite all these aforementioned advantages of SFRSCC, its performance highly depends on fiber's orientation. In case of short discrete fibers, the orientation of fibers is completely random and cannot be controlled during pumping process. If fibers distribution inside hardened state concrete are randomly distributed, it leads to less resistance potential of concrete element, especially in terms of flexural and tensile strength. The maximum expected strength may not be achieved. Therefore, fiber alignment has been considered as one of the important factors in SFRSCC. To address this issue, this study investigates the effects of concrete matrix's density and inlet velocity on fiber alignment during the pumping process using a finite element method.