• Journal of the Korean Geotechnical Society
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• 제21권8호
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• pp.63-72
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• 2005

Rocks are dumped to soft marine ground in order to improve trafficability and construction conditions in the tideland reclamation construction sites. Though this rock layer under earth fill has caused in a serious seepage problems after construction, seepage behaviors of this embankment structure is not correctly investigated. Water flow through rock layers is, in general, known as Non-Darcy's flow. However, the embedded rock layer under earth fill is not known whether its flow is governed by Darcy's or Non-Darcy's law. Therefore, a numerical analysis, laboratory model test and filed investigations were performed for analyzing the those seepage characteristics in this research. Results show that there is significance of $95\%$ of confidence between observed heads and seepage rates, and the calculated ones by SAMTLE which is developed under the assumption that the water flows through the two-layer system obey the Darcy's flow. And after operating the hydraulic gradient(i) of $0.10\~0.55$ upon laboratory model, these seepage characteristics of the embedded rock layer show that Reynolds Numbers are less than 10 and the relationship between these velocities of rock layer(v) and hydraulic gradients(i) is linearly proportional with more than 0.79 of the coefficient of correlation $(R^2)$. And the Reynolds Number of the velocity calculated by the relation of v=ki in the embedded rock layer of OO sea dike is $1\~6$. It shows also laminar flow. Based on these results, it is concluded that the seepage characteristics of embedded rock layer under earth fill can be laminar and Darcy's flow.

• Journal of the Computational Structural Engineering Institute of Korea
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• 제27권2호
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• pp.63-70
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• 2014

Design sensitivity analysis and topology design optimization for a piezoelectric crystal resonator are developed. The piezoelectric crystal resonator is deformed mechanically when subjected to electric charge on the electrodes, or vice versa. The Mindlin plate theory with higher-order interpolations along thickness direction is employed for analyzing the thickness-shear vibrations of the crystal resonator. Thin electrode plates are masked on the top and bottom layers of the crystal plate in order to enforce to vibrate it or detect electric signals. Although the electrode is very thin, its weight and shape could change the performance of the resonators. Thus, the design variables are the bulk material densities corresponding to the mass of masking electrode plates. An optimization problem is formulated to find the optimal topology of electrodes, maximizing the thickness-shear contribution of strain energy at the desired motion and restricting the allowable volume and area of masking plates. The necessary design gradients for the thickness-shear frequency(eigenvalue) and the corresponding mode shape(eigenvector) are computed very efficiently and accurately using the analytical design sensitivity analysis method using the eigenvector expansion concept. Through some demonstrative numerical examples, the design sensitivity analysis method is verified to be very efficient and accurate by comparing with the finite difference method. It is also observed that the optimal electrode design yields an improved mode shape and thickness-shear energy.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2001년도 정기총회 및 제3회 특별지포지움
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• pp.122-140
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• 2001

We have applied the geophysical survey, mainly electric and electromagnetic (EM) methods, to a test site contaminated by hydrocarbon waste disposal and local spill. The multi-frequency, moving source & receiver EM survey along with ground penetrating radar (GPR) showed a fairly good performance in detection of buried metal pipes and objects. Magnetic survey measuring vertical and horizontal gradients were so sensitive to the small metallic objects spread over the surface that it's hard to discriminate the buried pipe. We chose electrical resistivity, EM and GPR survey to examine the soil contamination. Depth slices of resistivity distribution as the results of the inversion of resistivity and EM data coincided each other and closely matched the contaminated area determined by chemical analysis of the soil samples. GPR images did not show the reflection events related with contamination plume since there are no distinct spill in this site. We inferred the contamination using the penetration depth of the GPR energy, which could be used as auxiliary information to the resistivity and EM results. We summarized the applicability of each survey methods based on this results and proposed a desirable survey scheme for the determination of hydrocarbon contaminated site.

• Journal of the Optical Society of Korea
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• 제13권1호
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• pp.8-14
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• 2009

In a laser-plasma wakefield accelerator, the ponderomotive force of an ultrashort high intensity laser pulse excites a longitudinal wave or plasma bubble in a way similar to the excitation of a wake wave behind a boat as it propagates on the water surface. Electric fields inside the plasma bubble can be several orders of magnitude higher than those available in conventional RF-based particle accelerator facilities which are limited by material breakdown. Therefore, if an electron bunch is properly phase-locked with the bubble's acceleration field, it can gain relativistic energies within an extremely short distance. Here, in the bubble regime we show the generation of stable and reproducible sub GeV, and GeV-class electron beams. Supported by three-dimensional particle-in-cell simulations, our experimental results show the highest acceleration gradients produced so far. Simulations suggested that the plasma bubble elongation should be minimized in order to achieve higher electron beam energies.

• Korean Journal of Environment and Ecology
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• 제15권3호
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• pp.213-223
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• 2001

This study was carried out to clarify the distribution pattern of Salicaceae species which are considered as obligatory riparian vegetation, and also the correspondence between their distribution and the environment factors. Eighty-three study sites by stratified sampling were selected from the upstream to the downstream of An-sung stream. Vegetation factors such as coverage by species, disturbance, etc., and environmental factors including microtopography, soil properties, etc., measured and analyzed. Salicaceae species were identified as total 2 genera, 11 species through all study area, and the average occurring species were 2.8 species.5. koreensis among other species showed highest occurring frequency at An-sung streams, and also it was distributed widely through study area. S. gracizistyla was mainly fecund at upstream sites, where sandy soil texture and high longitudinal slope were developed. S. purpurea vats. japonica was mostly observed in the sandy soil, the same as S. gracilistytu and however, was not dominant but rather mixed with S. gracitistyta and S. koreensis. On the other hand, distribution of S. glandulosa were closely related with littoral zone of the lake and the lower sea level with sandy loam and loamy sand Boils of high organic matter content. Under CCA, canonical correspondence analysis, distribution of Saticaceae species was positively correlated with environmental gradients such as soil properties along to topography.

• Korean Journal of Environment and Ecology
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• 제29권2호
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• pp.132-144
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• 2015

Yongneup wetland protected area, the only high moor in Korea, is a core area to conserve biodiversity. Even though the Yongneup wetland protected area is relatively small, various plant species are distributed in the Yongneup wetland protected area because it includes various habitats showing different environmental gradients. Vascular plants distributed in the Yongneup wetland protected area were identified as a total of 376 taxa that is composed of 73 families, 217 genera, 322 species, 3 subspecies, 44 varieties and 7 forms. For endangered plants designated by the Ministry of Environment, 5 species including Trientalis europaea var. arctica, Lilium dauricum, Halenia corniculata, Lychnis wilfordii and Menyanthes trifoliata were found and 34 taxa were confirmed to be distributed only in the mountainous wetland habitats. Regarding naturalized plants, a total of 11 taxa were distributed, but most of them were distributed in the areas where artificial interference has occurred. And in areas inside the wetlands that are relatively well preserved, 2 species of Bidens frondosa and Erigeron annuus were observed. In this study, the occurrence and distribution of Pseudostellaria baekdusanensis M. Kim, which was recently found in Mt. Baekdu and reported as a new species, were identified in the Yongneup wetland protected area. A wetland is a very vulnerable area to drastic environmental changes and damages to its ecosystem could cause the extinction of rare plant species which are distributed only in the wetlands. Therefore, it is mandatory that current status of the Yongneup wetland protected area is evaluated and actions to prevent rapid environmental changes are taken. Fourteen separate investigations were conducted in 2013 and another four in 2014, to evaluate current status of the Yongneup wetland protected area. These investigations have provided us the basic information for future actions of conservation and restoration.

• Journal of the Computational Structural Engineering Institute of Korea
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• 제27권1호
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• pp.1-8
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• 2014

Using the level set and the meshfree methods, we develop a topological shape optimization method applied to linear elasticity problems. Design gradients are computed using an efficient adjoint design sensitivity analysis(DSA) method. The boundaries are represented by an implicit moving boundary(IMB) embedded in the level set function obtainable from the "Hamilton-Jacobi type" equation with the "Up-wind scheme". Then, using the implicit function, explicit boundaries are generated to obtain the response and sensitivity of the structures. Global nodal shape function derived on a basis of the reproducing kernel(RK) method is employed to discretize the displacement field in the governing continuum equation. Thus, the material points can be located everywhere in the continuum domain, which enables to generate the explicit boundaries and leads to a precise design result. The developed method defines a Lagrangian functional for the constrained optimization. It minimizes the compliance, satisfying the constraint of allowable volume through the variations of boundary. During the optimization, the velocity to integrate the Hamilton-Jacobi equation is obtained from the optimality condition for the Lagrangian functional. Compared with the conventional shape optimization method, the developed one can easily represent the topological shape variations.

• Journal of the Korean Geographical Society
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• 제45권4호
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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 Geotechnical Society
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• 제19권2호
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• pp.65-74
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• 2003

Most of land reclamation projects are being implemented along the south and west coastal lines of the Korean Peninsula. The earth structures and in-ground LNG tank, and buildings can be constructed using artificial freezing method on the reclaimed land to control the uplift pressure caused by capillary forces. In this study, upon freezing a saturated soil in a closed-system from the top, a considerable frost heaving pressure was developed. Decomposed granite soils, silty soil, and sandy soil were used in the laboratory freeze test which is sometimes subjected to thermal gradients under closed-systems. A major concern has been the ability to predict the frost heaving pressure over the results of relatively short-term laboratory tests. The frost heaving pressure arising within the soil samples and the temperature of the samples inside were monitored with time elapse. The degree of saturation versus heaving pressure curve is presented for each soil sample and the maximum pressure is closely related to this curve. TDR apparatus was used to measure the volumetric water content by the measurement of unfrozen water contents of frozen soils. Unfrozen water increased in soils containing a high percentage of fine-grained particles. In fine-grained soils with strong attractive farces between soil grains and water molecules, additional water is attracted into the pores leading to further volume changes and ice segregation.

• Journal of Environmental Science International
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• 제2권1호
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• pp.43-49
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• 1993

Concentrations of sulfate and 6-values of sulfate, $({\delta}^{34}SO_4_){pw}$, dissolved In pore waters were measured from the sediment cores of the two different marine environments : deep northeast Pacific (57-1) and coastal Kyunggi Bay of Yellow Sea (57-2) . Sulfate concentration in pore waters decreases with depth at both cores, reflecting sulfate reduction in the sediment columns. However, much higher gradient of pore water sulfate at 57-2 than 57-1 indicates more rapid sulfate reduction at 57-2, because of high sedimentation rate at the coastal area compared to the deep-sea. The measured 6-values, $({\delta}^{34}SO_4_){pw}$, follow extremely well the predicted trend of the Rayleigh fractionation equation. The range of 26.756 to 61.35% at the coastal core 57-2 is not so great as that of 32.4$\textperthousand$ to 97.8$\textperthousand$ at the deep-sea core 57-1. Despite greater graclient of pore water sulfate at 57-2, the 6-values become lower than those of the deep- sea core 57-1. This inverse relation between the 6-values and the gradients of pore water sulfate could be explained by the combination of the two subsequent factors : the kinetic effect by which the residual pore water sulfate becomes progressively enriched with respect to the heavy isotope of $^{34}S$ as sulfate reduction proceeds, and the intrinsic formulation effect of the Rayleigh fractionation equation in which the greater becomes the fractionation factor, the more diminished values of $({\delta}^{34}SO_4_){pw}$ are predicted.