• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.2
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• pp.267-277
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• 1993

A finite element method(FEM) is presented and applied to the two-dimensional bottom turbulent boundary layer. The time-dependent incompressible motion of a viscous fluid is formulated by using the well-known Navier-Stokes equations and vorticity equation in terms of the velocity and pressure fields. The general numerical formulation is based on Galerkin method and solved by introducing the mixing length theory of Prandtl for eddy kinematic viscosity of a turbulent flow field. Numerical computations of the transport of sediment on an arbitrary sea-bed due to wave motion in the turbulent boundary layer are carried out. The results obtained by the FEM made clear the difference in characteristic features between the boundary layer due to oscillatory flow and the boundary layer due to wave motion.

• Journal of Ecology and Environment
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• v.38 no.2
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• pp.271-279
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• 2015

After the reversion of Okinawa (Ryukyu Islands) to Japan in 1972, extensive urban and agricultural development resulted in a significant increase in sediment discharge to coastal waters. The release of sediment has caused the degradation of freshwater and coastal ecosystems and biodiversity. A consideration for catchment-to-reef continua, as well as agricultural (socioeconomic) factors is necessary to establish proper land-based management plans for the conservation of the island environment. We have set up a framework to integrate biophysics and socioeconomics: 1) setting a conservation target and threshold, 2) identifying the sources and processes, and 3) examining cost-effectiveness and management priorities. The framework may be applicable to other tropical and subtropical islands with similar characteristics.

• Journal of Korean Society for Geospatial Information Science
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• v.5 no.2 s.10
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• pp.145-152
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• 1997

A coupling of two-dimensional model and GIS technique is applied to simulate sediment transport analysis. Accurate transformations are performed for the data which have various reduced scales. Basic maps are discretized the mesh of true scale for the finite element model by using the digital map and the Traverse Mercator coordinate. Under $200m^3/s$ flow rate condition, velocity vectors, depth contours, velocity contours and deposition contours are Presented for the 5km reach of midstream of Keum River from confluence of Ji-chun to Baekche Bridge. The simulation results of the study agree well with those of one-dimensional varied flow analysis and observed data. The flow and deposition pattern revealed a meandering characteristics of the river qualitatively.

• The Journal of the Acoustical Society of Korea
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• v.22 no.1
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• pp.78-87
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• 2003

High-frequency (126-㎑) bottom backscattering measurements with various bottom types were conducted at the water tank in Ocean Acoustic Laboratory, Hanyang University. For the purpose of investigating the energy distribution of bottom scattering with various bottom types, the sediment was varied with gravel, sand, sandy mud and mixed bottoms. To examine the anisotropic nature of the scattering due to the orientations of bottom ripple, the footprints were made transverse and longitudinal to the direction of incident wave. The total scattering characteristics are that the larger grazing angles the larger backscattering strengths become and backscattering strengths for a transverse ripple case are higher than those of longitudinal ripple case. finally, the variations of scattering strength depend mainly on the ripple's orientation.

• 한국해양학회지
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• v.13 no.1
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• pp.9-18
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• 1978

The intertidal flat depositional environment of Southern Nam Yang Bay, west coast of Korea has been studied to understand textural, geochemical and mineralogical characteristics. The intertidal flat environment can be divided into two subenvironments, that is, the mud flat and the sand flat due to the sediment textures. From thd outer sand flat to the inner mud flat the grain size of the sediments decreases and the mud content increases. It is suggested that the intertidal flat environment is in the progradation of marsh deposits in the mud flat. The chemical composition of the sediments is related to the sediment textures. The chemical index of maturity of the mud flat sediments is higher than that of the sand flat sediments. The clay minerals of the sediments are chlorite, illite, montmorillonite and kaolinite.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.4 no.1
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• pp.25-32
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• 1999

In order to examine the degree of heavy metal pollutions around Samcheonpo and Youngkwang power plants, marine sediment samples were analyzed to determine heavy metal contents. Some of these sediment samples were also analyzed by using of a sequential extraction technique to know geochemical forms of the metals. The results showed that the spatial distribution of heavy metals coincided very well with those of mean grain size, carbonates and organic matters. The chemical speciation data using sequential extraction analysis also showed that a considerable amount of heavy metals except for Mn were bounded in the residual fraction, which mode of occurrence of heavy metals was generally interpreted as being the result of the lithogenic origin.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.2 no.3
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• pp.143-151
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• 1990

The sediment transport in shallow water regions has been studied in various ways and, accordingly, many formulas have been proposed. However, when these formulas are applied practically in the field, they are not sufficient to fully estimate the sediment transport rate yet. The primary reason is how to take into account the effect of irregularities of field waves : wave heights, periods and directions. Therefore, it is necessary to investigate stochastic and kinematic characteristics of waves in three dimensional random seas in order to more accurately estimate it. In particular, the asymmetrical properties of directional spectrum become significant and play an important role in various phenomena in a shallow water region. In this study, their effects of incident waves the joint distribution of wave heights, periods and directions are investigated through field measurements.

• Journal of Korean Society on Water Environment
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• v.24 no.4
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• pp.465-472
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• 2008

Soil and Water Assessment Tool (SWAT) model was selected as a tool for assessing the effect of pollutant sources on the total loads from the Chungju Dam upstream watershed. The model was constructed through calibration of parameters related to nitrogen (N) and phosphorus (P), which was based on the runoff and sediment modeling performed in the previous research. Using this, the spatial and temporal pollutant loadings by source type were investigated. Results of this study indicated that in most forested upstream sub-watersheds, pollutant loadings from point sources were very low, and total loadings by point and non-point sources were also insignificant. On the other hand, in #14 sub-watershed including Jecheon city, the loadings by point source were relatively considerable. For the whole watershed, non-point sources accounted for 99% of sediment, 97% of N, and 93% of P loads. And monthly non-point source loadings were concentrated on rainy summer season, while point source loadings of N and P kept nearly constant throughout the year and were high on dry winter season relative to non-point source.

• Journal of Microbiology
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• v.44 no.2
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• pp.171-176
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• 2006

A strictly aerobic, non-motile, ovoid-shaped Alphaproteobacteria, designated strain $JC2049^T$ was isolated from a tidal flat sediment sample. The results of 16S rRNA gene sequence analysis indicated that this isolate belonged to the genus Thalassobius, with a sequence similarity of 96.9-97.3% to other valid Thalassobius spp. The cells required 1-7% NaCl for growth (optimum 2%) and accumulated $poly-\beta-hydroxybutyrate$. Nitrite was reduced to nitrogen, but nitrate was not reduced to nitrite. No genetic potential for aerobic anoxygenic photosynthesis was detected. The primary isoprenoid quinone (Ubiquinone-10), predominant cellular fatty acids $(C_{18:1}{\omega}7c,\;11\;methyl\;C_{18:1}\omega7c\;and\;C_{16:0})$ and DNA G+C content (61 mol %) were all consistent with the assignment of this isolate to the genus Thalassobius. Several phenotypic characteristics clearly distinguished our isolate from other Thalassobius species. The degree of genomic relatedness between strain $JC2049^T$ and other Thalassobius species was in a range of 20-43 %. The polyphasic data presented in this study indicates that our isolate should be classified as a novel species within the genus Thalassobius. The name Thalassobius aestuarii sp. novo is therefore proposed for this isolate; the type strain is $JC2049^T(=IMSNU\;14011^T=KCTC\;12049^T=DSM\;15283^T)$.

• Ocean and Polar Research
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• v.42 no.1
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• pp.1-13
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• 2020

We analyzed the characteristics of meiofaunal communities in the northern part of Jeju Island and the environmental factors affecting the meiofaunal communities. For the analysis of the communities, subtidal sediments containing meiofauna were collected from 6 sites (3 shallow sites and 3 deeper sites) on the northern coast of Jeju Island in April, June, August, and October 2017. The sediment samples were collected by SCUBA using a syringe. After isolating and counting meiofauna from the sediment using a series of sieves and centrifugation, the density of the meiofauna was expressed as individuals/10 ㎠. Density of meiofauna was lower in August compared to April and June, and the density determined in October was higher than August. During April and June, the meiofaunal communities at the shallow sites (i.e., ST 1, 2, and 3) were significantly different from the meiofaunal communities at deeper sites (ST 4, 5, and 6, p < 0.01). However, such spatial variation in the meiofaunal communities was not obvious in August and October. The most dominant meiofaunal taxa were harpacticoids, followed by nematodes and nauplius larvae. These three taxa accounted for 90% of the total meiofauna density. Abundance of harpacticoids and nematodes showed a significantly negative correlation with the water depth. BIO-ENV analysis indicated that the total organic nitrogen (TON) and the water temperature exerted a significant influence over the meiofaunal communities at the sampling sites.