• Economic and Environmental Geology
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• v.41 no.2
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• pp.243-252
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• 2008

The Iho and Hamdeok beaches, the major coastal beaches in Jeju Island, have been studied through size analysis and using an experimental extension pole and sediment trap in beach profile, in order to understand their textural characteristics, migration patterns, and seasonal change in beach geometry. The Iho beach is composed of coarse and medium sands, 590 m in total length. The foreshore slope is 12.3$^{\circ}$ in summer and 10.8$^{\circ}$ in winter, which shows more steeper in summer. The Hamdeok beach consisting mostly of shell fragments is 950 m long, $5.7{\sim}7.4^{\circ}$ steep and 97.4${\sim}$114.5 m wide, respectively. The suspended load drift concentrations in the studied beaches showed 4.5 mg/l during the period of summer and 33.2 mg/l in winter, and those of fine-grained sediments are derived mostly from the marine of northeastward direction. The typical beach transformation of the Iho beach is resulting from the construction of jetties in the west side that built up the sand inside the jetties, whereas the erosion is occurring on the east side of beach. The center and berm sides of the sand in the Hamdeok beach drift into the dune side during the period of the stormy winter season.

• Geophysics and Geophysical Exploration
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• v.16 no.1
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• pp.6-17
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• 2013

Multicomponent seismic data including both P- and PS-waves have advantages in discriminating the type of pore fluid, characterizing the lithologic attributes and producing the high resolution image. However, multicomponent seismic data recorded at the vertical and horizontal component receivers contain both P- and PS-waves which have different features, simultaneously. Therefore, the wavefield separation of P- and PS-waves as a preprocessing is inevitable in order to use the multicomponent seismic data successfully. In this study, we analyzed the previous study of the wavefield separation method suggested by Jeong and Byun in 2011, where the approximated reflection angle calculated only from one refernce depth is used in rotation transform, and showed its limitation for seismic data containing various reflected events from the multi-layered structure. In order to overcome its limitation, we suggested a new effective wavefield separation method of P- and PS-waves. In new method, we calculate the reflection angles with various reference depths and apply rotation transforms to the data with those reflection angles. Then we stack all results to obtain the final separated data. To verify our new method, we applied it to the synthetic data sets from a multi-layered model, a fault model, and the Marmousi-2 model. The results showed that the proposed method separated successfully P- and PS-reflection events from the multicomponent data from mild dipping layered model as long as the dip is not too steep.

• 한국지구물리탐사학회:학술대회논문집
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• 2008.10a
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• pp.27-32
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• 2008

Detailed bathymetry and magnetic survey data for Esmeralda Bank obtained by R/V Onnuri of Korea Ocean Research & Development Institute in September 2007 were analyzed to estimate the locations of possible hydrothermal vents. The shape of Esmeralda Bank is caldera type opened in the western part. The summit is very shallow, about 50 meter b.s.l. and the bottom is about 1300 meter b.s.l. The western part of Esmeralda Bank is more steeper and topographic irregular than eastern part, and showed the valley made by erosion or collapse. The magnetic anomaly patterns of Esmeralda Bank located low anomalies over the north and high anomalies over the south. The magnetic anomalies are steep over the summits and gently smooth over the deep bottom. Two low magnetization zones are located in the summit and westside of Esmeralda Bank. The low magnetization zones of the summits of Esmeralda Bank suggest the possible existence of hydrothermal vent.

• Journal of Korean Ophthalmic Optics Society
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• v.17 no.4
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• pp.373-380
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• 2012

Purpose: The present study was performed to investigate a relationship between the stable centrations of spherical RGP lens and aspherical RGP lens on cornea and corneal eccentricity. Methods: Two RGP lenses with different designs were fitted in alignment, steep or flat on total 84 eyes having corneal eccentricity of 0.28~0.78. The stable centration of lenses on cornea was analyzed by taking photographs with a high-speed digital camera. Results: The stable centrations of spherical and aspherical RGP lenses in horizontal direction were decentrated to temporal side. More centration to median side was shown when corneal eccentricity was larger. The difference between the stable centrations of spherical and aspheric RGP lenses according to corneal eccentricity was bigger when the fitting state was flatter. The difference in the stable centrations of aspherical RGP lens was smaller than that of spherical RGP lens regardless of fitting status. The stable centrations of spherical and aspherical RGP lenses in vertical direction were located below corneal apex regardless of fitting status however, there was no significant difference analyzed by the variation of corneal eccentricity. However, there were many cases that RGP lenses were in upper eyelid with increasing corneal eccentricity. Conclusions: The consideration of corneal eccentricity is required for RGP lens fitting and manufacturing aspherical RGP lens since the stable centration of spherical RGP lens as well as aspherical RPG lens' centration was changed depending on corneal eccentricity.

• Geophysics and Geophysical Exploration
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• v.16 no.2
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• pp.71-78
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• 2013

The one-way wave equation migration is much more computationally efficient comparing with reverse time migration and it can provide better image than the migration algorithm based on the ray theory. We have developed the prestack depth migration module adopting (GS) propagator designed for vertical transverse isotropic media. Since GS propagator considers the higher-order term by expanding the Taylor series of the vertical slowness in the thin slab of the phase-screen propagator, the GS migration can offer more correct image for the complex subsurface with large lateral velocity variation or steep dip. To verify the validity of the developed GS migration module, we analyzed the accuracy with the order of the GS propagator for VTI media (GSVTI propagator) and confirmed that the accuracy of the wavefield propagation with the wide angles increases as the order of the GS propagator increases. Using the synthetic seismic data, we compared the migration results obtained from the isotropic GS migration module with the anisotropic GS migration module. The results show that the anisotropic GS migration provides better images and the improvement is more evident on steeply dipping structures and in a strongly anisotropic medium.

• Korean Journal of Environment and Ecology
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• v.20 no.2
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• pp.200-207
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• 2006

The objective of this study was to investigate the site and growth characteristics of Acer pictum var. mono growing in the deciduous stands at Mt. Joongwang area located in Pyungchanggun, Kangwon-do. A. pictum var. mono was mainly distributed at the rather steep slope and aspect facing from northeast to northwest, and altitudes ranging from 1,000 to 1,200m. It grew at relatively deep a soil layer with high moisture and nutrients. Major competing species in the upper stories were Betula costata, Acer mandshuricum, Quercus mongolica, Cornus controversa, and herb plants such as Meehania urtidfolia, Isodon excisus, Astilbe chinensis var. davidii, Dryopteris crassirhizoma and Ainsliaea acerifolia in the floor. The height growth was 0.25m in early time, decreased gradually and sustained growth of lower than 10cm. The diameter growth of A. pictum was under 1mm in early time, but increased to 0.3mm/yr and showed continuous growth of 2mm/yr recently. Annual volume growth showed rapid increased about age 120 and then showed stable growth, so the rotation period of A. pictum is expected more than 200 years without decay of heartwood.

• Korean journal of applied entomology
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• v.56 no.4
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• pp.351-356
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• 2017

For determining the insecticidal effect of Carbofuran on the Brown planthopper, Nilaparvata lugens, sucking toxicity by drenching application, sucking and contact toxicity by leaf dipping application, and contact toxicity by topical application were examined. Drenching caused two types of mortality patterns. One was logarithmic curve at a relatively high concentration (8~30 ppm) with over 40% mortality in 24 h, and the other was an S-shaped curve at low concentrations (1~4 ppm) with over 60% mortality on the fifth day after Carbofuran treatment. Leaf dipping application caused a rapid increase in mortality in a day, and this effect decreased steadily with time. Topical application showed steep increase in mortality in a day, and hardly increased thereafter. The best mortality evaluation time for the drenching application was the second day (42 h), and that for the leaf dipping and topical applications was the first or second day after Carbofuran application. When the insecticide has systemic effects, drench application provides the best efficacy and its insecticidal effects persist for a longer time than any other application method.

• Journal of the Korean Geographical Society
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• v.45 no.4
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• pp.431-443
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• 2010

The morphometric characteristics of 13 alluvial fans in the southern parts of the Korean Peninsula are studied and relationships between their distributions and causes are discussed by comparing them with 690 alluvial fans in Japan, Taiwan and the Philippines. The relationships between the surface gradient of alluvial fans and source basin area, the surface gradient and the relief ratio of the source basin, and the source basin area and the relief ratio were investigated. The alluvial fans in South Korea have typical characteristics of the Asian fans, although their frequency and density are relatively low, and the size and the relief ratio of their source basins are relatively small and steep, respectively. Moreover 36 major Korean river basins without alluvial fans tend to have lower altitude and relief ratios. Contrary to the argument by Blair and McPherson, the natural depositional gaps on the gradient of alluvial fans were not found. The Gyeongju alluvial fan is probably a fluvial fan with gentle gradient, whereas the other Korean fans seem to be debris-flow related on the base of their gradients.

• Journal of the Korean earth science society
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• v.35 no.2
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• pp.131-146
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• 2014

Multi-beam echosounder data and grain size analysis data of surface sediment were acquired and analyzed in order to investigate the shelf-to-slope morphology, geological character, and their geological controlling factors in the southwestern margin of the Ulleung Basin. According to the morphological character, the continental shelf can be divided into two parts: (1) shallow (~100 m) and steep ($0.5^{\circ}$) inner shelf, (2) deep (100-300 m) and gentle ($0.2^{\circ}$) outer shelf. The continental slope is featured with eight distinct topographic depressions of various spatial dimension (~121 $km^2$ in area) and head wall gradient (${\sim}24.3^{\circ}$). They are developed adjacent to each other and presumably formed by submarine landslides which have recurred under the strong influences of earthquakes and eustatic sea-level change. The inner continental shelf and the continental slope are dominated by fine-grained sediment, whereas the outer continental shelf is dominated by coarse-grained sediment. The surface sediment distribution seems dominantly influenced by eustatic sea-level change. The outer continental shelf is mostly covered by coarse relict sediment deposited during lowstand sea-level, while the inner shelf is covered with recent sediment during highstand sea-level. The surface of the continental slope is covered with fine-grained sediments which were supplied by hemipelagic advection process.

• Journal of the Korean GEO-environmental Society
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• v.9 no.4
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• pp.23-36
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• 2008

Soil nailing system can be mentioned to a method of supporting as the shear strength of in-situ soils is increased by passive inclusions. In the general soil nailing system, facing walls are used in two kind of a lattice concrete block or a cast in placed concrete wall. A case of lattice concrete blocks is used in slow slopes greater than 1(V):0.7(H). Also, a case of a cast in placed concrete wall is used in steep slopes less than 1(V):0.5(H). The cast in placed concrete walls are constructed to 30 cm thick together with a shotcrete facing. In this study, the assembling soil nailing method as a new soil nailing system will be proposed. This method is assembly construction using precast concrete panels with 20 cm thick. So, the ability of construction and the quality of facings can be improved more than a conventional soil nailing system. This method can be obtained the effects that a global slope stability increase, as precast concrete panels are immediately put on cutting face after excavating a slope. In this study, confining effects of concrete panels using the assembling soil nailing system were found out by large scaled load tests. In the tests, the load-settlement relationship to an assembling soil nailing system due to the stiff facings as concrete panels appeared to be better than a typical soil nailing system with shotcrete facings.