• Geomechanics and Engineering
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• v.8 no.1
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• pp.81-95
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• 2015

The permeability behavior of Ariake clays has been investigated by constant rate of strain (CRS) consolidation tests with vertical or radial drainage. Three types of Ariake clays, namely undisturbed Ariake clay samples from the Saga plain, Japan (aged Ariake clay), clay deposit in shallow seabed of the Ariake Sea (young Ariake clay) and reconstituted Ariake clay samples using the soil sampled from the Saga plain, were tested. The test results indicate that the deduced permeability in the horizontal direction ($k_h$) is generally larger than that in the vertical direction ($k_v$). Under odometer condition, the permeability ratio ($k_h/k_v$) increases with the vertical strain. It is also found that the development of the permeability anisotropy is influenced by the inter-particle bonds and clay content of the sample. The aged Ariake clay has stronger initial inter-particle bonds than the young and reconstituted Ariake clays, resulting in slower increase of $k_h/k_v$ with the vertical strain. The young Ariake clay has higher clay content than the reconstituted Ariake clay, resulting in higher values of $k_h/k_v$. The microstructure of the samples before and after the consolidation test has been examined qualitatively by scanning electron microscopy (SEM) image and semi-quantitatively by mercury intrusion porosimetry (MIP) tests. The SEM images indicate that there are more cut edges of platy clay particles on a vertical plane (with respect to the deposition direction) and there are more faces of platy clay particles on a horizontal plane. This tendency increases with the increase of one-dimensional (1D) deformation. MIP test results show that using a sample with a larger vertical surface area has a larger cumulative intruded pore volume, i.e., mercury can be intruded into the sample more easily from the horizontal direction (vertical plane) under the same pressure. Therefore, the permeability anisotropy of Ariake clays is the result of the anisotropic microstructure of the clay samples.

• Korean Journal of Remote Sensing
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• v.38 no.6_1
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• pp.1207-1217
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• 2022

Vegetation indices using the reflectance of selected wavelength, associating with the monitoring purpose such as identifying the progress of crop growth, on the vegetation canopy surface is widely used in the digital agriculture technology. However, the surface reflectance anisotropy can distort the true value of vegetation index related to the condition of surface, even though the surface property be unchanged. That causes difficulty to observe accurately crop growth on the monitoring system. In this study, a simple type goniometer was designed to measure the reflectance from the anisotropic surface according to various zeniths and azimuths of sun and viewing sensor in the field. On the tarp like as Lambertian surface, the reflectance of Blue, Green, Red, Near-Infrared band was similar to the tarps' reflectance properties. However, the reflectance was slightly overestimated in the cloudy day. The relative difference values of vegetation indices on grass were overestimated for the forward viewing and underestimated for the backward viewing. In addition, enhanced vegetation index (EVI) showed less sensitive according to the positions of sun and sensor viewing. Field observation with a goniometer will be helpful to understand the anisotropy characteristics on the vegetation surface.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.12
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• pp.889-898
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• 2022

In this paper, parallel computing method on the three-dimensional electromagnetic field is proposed. The present electromagnetic scattering analysis is conducted based on the time-harmonic vector wave equation and the finite element method. The edge-based element and 2^nd -order absorbing boundary condition are used. Parallelization of the elemental numerical integration and the matrix assemblage is accomplished by allocating the partitioned finite element subdomain for each processor. The graph partitioning library, METIS, is employed for the subdomain generation. The large sparse matrix computation is conducted by MUMPS, which is the parallel computing library based on the multi-frontal method. The accuracy of the present program is validated by the comparison against the Mie-series analytical solution and the results by ANSYS HFSS. In addition, the scalability is verified by measuring the speed-up in terms of the number of processors used. The present electromagnetic scattering analysis is performed for a perfect electric conductor sphere, isotropic/anisotropic dielectric sphere, and the missile configuration. The algorithm of the present program will be applied to the finite element and tearing method, aiming for the further extended parallel computing performance.

• Composites Research
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• v.36 no.1
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• pp.48-52
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• 2023

Fiber-reinforced composites have anisotropic material properties, so the mechanical properties of composite structures can vary depending on the stacking sequence. Therefore, it is essential to design the proper stacking sequence of composite structures according to the functional requirements. However, depending on the manufacturing condition or the shape of the structure, there are many cases where the designed stacking angle is out of range, which can affect structural performance. Accordingly, it is important to analyze the stacking angle in order to confirm that the composite structure is correctly fabricated as designed. In this study, the stacking angle was predicted from real cross-sectional images of fiber-reinforced composites using convolutional neural network (CNN)-based deep learning. Carbon fiber-reinforced composite specimens with several stacking angles were fabricated and their cross-sections were photographed on a micro-scale using an optical microscope. The training was performed for a CNN-based deep learning model using the cross-sectional image data of the composite specimens. As a result, the stacking angle can be predicted from the actual cross-sectional image of the fiber-reinforced composite with high accuracy.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.5D
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• pp.831-838
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• 2006

An experimental/analytic study has been conducted to understand the adverse effects of low vehicle speed, high axle load and high tire pressure on the performance of asphalt pavements. Of 33 asphalt sections at KHC test road, two sections having different base layer thickness (180 mm versus 280 mm) are adopted for rollover tests. During the test, a standard three-axle dump truck maintains a steady state condition as moving along the wheel path of a passing lane, and lateral offsets and real travel speed are measured with a laser-based wandering system. Test results suggest that vehicle speed affects both longitudinal and transverse strains at the bottom of asphalt layer (290 mm and 390 mm below the surface), and even slightly influences the measured vertical stresses at the top of subbase and subgrade due to the dynamic effect of rolling vehicle. Since the anisotropic nature of asphalt-aggregate mixtures, the difference between longitudinal and transverse strains appears prominent throughout the measurements. As the thickness of asphalt pavement increases, the measured lateral strains become larger than its corresponding longitudinal strains. Over the limited testing conditions, it is concluded that higher axle weight and higher tire pressures induce more strains and vertical stresses, leading to a premature deterioration of pavements. Finally, a layered elastic analysis overestimates the maximum strains measured under the 1st axle load, while underestimating the maximum vertical stress in both pavement sections.

• The Journal of Korean Society for Radiation Therapy
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• v.31 no.1
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• pp.75-81
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• 2019

Purpose: Helmet type bolus for 3D printer is being manufactured because of the disadvantages of Bolus materials when photon beam is used for the treatment of scalp malignancy. However, PLA, which is a used material, has a higher density than a tissue equivalent material and inconveniences occur when the patient wears PLA. In this study, we try to treat malignant scalp tumors by using M3 wax helmet with 3D printer. Methods and materials: For the modeling of the helmet type M3 wax, the head phantom was photographed by CT, which was acquired with a DICOM file. The part for helmet on the scalp was made with Helmet contour. The M3 Wax helmet was made by dissolving paraffin wax, mixing magnesium oxide and calcium carbonate, solidifying it in a PLA 3D helmet, and then eliminated PLA 3D Helmet of the surface. The treatment plan was based on Intensity-Modulated Radiation Therapy (IMRT) of 10 Portals, and the therapeutic dose was 200 cGy, using Analytical Anisotropic Algorithm (AAA) of Eclipse. Then, the dose was verified by using EBT3 film and Mosfet (Metal Oxide Semiconductor Field Effect Transistor: USA), and the IMRT plan was measured 3 times in 3 parts by reproducing the phantom of the head human model under the same condition with the CT simulation room. Results: The Hounsfield unit (HU) of the bolus measured by CT was $52{\pm}37.1$. The dose of TPS was 186.6 cGy, 193.2 cGy and 190.6 cGy at the M3 Wax bolus measurement points of A, B and C, and the dose measured three times at Mostet was $179.66{\pm}2.62cGy$, $184.33{\pm}1.24cGy$ and $195.33{\pm}1.69cGy$. And the error rates were -3.71 %, -4.59 %, and 2.48 %. The dose measured with EBT3 film was $182.00{\pm}1.63cGy$, $193.66{\pm}2.05cGy$ and $196{\pm}2.16cGy$. The error rates were -2.46 %, 0.23 % and 2.83 %. Conclusions: The thickness of the M3 wax bolus was 2 cm, which could help the treatment plan to be established by easily lowering the dose of the brain part. The maximum error rate of the scalp surface dose was measured within 5 % and generally within 3 %, even in the A, B, C measurements of dosimeters of EBT3 film and Mosfet in the treatment dose verification. The making period of M3 wax bolus is shorter, cheaper than that of 3D printer, can be reused and is very useful for the treatment of scalp malignancies as human tissue equivalent material. Therefore, we think that the use of casting type M3 wax bolus, which will complement the making period and cost of high capacity Bolus and Compensator in 3D printer, will increase later.

• Tunnel and Underground Space
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• v.16 no.2 s.61
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• pp.109-134
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• 2006

Rocks undergo weathering processes influenced by changing in pressure-temperature condition, atmosphere, underground water, and rainfall. The weathering processes change physical and chemical characteristics of the rocks. Once the rocks are weathered, the characteristics of them are changed and, because of the changing, several disadvantages such as rock slope failures and underground water spouts are can occur. Before we cut a large rock slope, therefore, we must analyze current weathering conditions of rocks and predict weathering processes in the future. Through the results of such analyses, we can judge reinforcement works. In order to comply with such requests, chemical weathering sensitivity analysis which was analyzed from chemical weathering velocities and other characteristics of rocks has been applied in several prior construction works in Korea. But, It is defective to use directly in engineering fields because it was developed for soils(not rocks), it has too mny factors must be considered and the relationships between the factors are not clear, and it is hard to explain the weathering processes in engineering time range. Besides above, because it has been used for isotropic rocks, this method is hard to apply to anisotropic rocks such as sedimentary rocks. Acceding to studies from morphologists (e.g. Oguchi et al., 1994; Sunamura, 1996; Norwick and Dexter, 2002), time dependent strength reduction influenced by weathering shows a negative exponential function form. Appling this relation, one can synthesize the factors which influence the weathering processes to the strength reduction, and get meaningful estimates in engineering viewpoint. We suggest this weathering sensitivity characterization method as a technique that can explain time dependent weathering sensitivity characteristics through strength changes and can directly applied the rock slope design.

• Journal of the Korean Geophysical Society
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• v.3 no.2
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• pp.99-112
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• 2000

The Iksan Jurassic Granite shows relatively less fractures and homogeneous rock fabrics, and is one of the most popular stone materials for architectures and sculptures. Almost mutually perpendicular rift, grain, and halfway in the Iksan Jurassic Granite are well known to quarrymen based on its splitting directions, and therefore it should exhibit orthorhombic symmetry. Theoretically, there are 9 independent elastic stiffness coefficients $(C_{1111},\;C_{2222},\;C_{3333},\;C_{2323},\;C_{1313},\;C_{1212},\;C_{1122},\;C_{2233},\;and\;C_{1133})$ for orthorhombic anisotropy. In order to characterize the static and dynamic elastic properties of the Iksan Jurassic Granite, triaxial strains under uniaxial compressive stresses and ultrasonic velocities of elastic waves in three different polarizations are measured. Both experiments are carried out with six directional core samples from massive rock body. Using the results of experiments and the densities measured independently, the static and dynamic elastic coefficients are computed by simple mathematical manipulation derived from the governing equations for general anisotropic media. The static elastic coefficients increase ar uniaxial compressive stress rises. Among those, the static elastic coefficients at uniaxial compressive stress of a 24.5 MPa appear to be similar to the dynamic elastic coefficients under ambient condition. Although some deviations are observed, the preferred orientations of microcracks appear to be parallel or subparallel to the rift, the grain, and the hardway from microscopic observation of thin sections. This indicates that the preferred orientations of microcracks cause the elastic anisotropy of the Iksan Jurassic Granite. The results are to be applied to the effective use of the Iksan Jurassic Granite as stone materials, and can be used for the non-destructive safety test.

• Journal of the Korean Geotechnical Society
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• v.23 no.10
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• pp.47-56
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• 2007

In this research, the effects of the gravel content on the liquefaction behavior for both of the isotropically and $K_0-anisotropically$ consolidated gravel-sand mixtures are investigated. for this purpose, the cyclic triaxial tests for the specimens with the same relative density (Dr=40%) and variations of gravel content were performed. On the other hand, a series of undrained cyclic triaxial tests were carried out on the isotropically consolidated gravel-sand mixtures with the same void ratio (e=0.7) and from 0% to 30% gravel contents. Void ratios of gravel-sand mixtures with the same relative density (Dr=40%) are found to decrease significantly with the increase of the gravel content from 0% to about 70% and increase thereafter. But the void ratio of the sand matrix among the gravel skeleton increases with the increase of the gravel contents. Test results are as follows : for the isotropically consolidated specimen with 40% of relative density and low gavel contents (GC=0%, 20%, 40%), pore water pressure development and axial strain behavior during undrained cyclic loading show similar behavior to those of the loose sand because of high void ratio, and the specimens with high gravel content (70%) both pore pressure and strata behaviors are similar to those of dense sand. And the isotropically consolidated specimens with the same void ratio (e=0.7) and higher gravel contents show the same behavior of pore water pressure and axial strain as that of the loose sand, but for the lower gravel content this behavior shows similar behavior to that of dense sand. The liquefaction strength of the isotropically consolidated specimens with the same relative density increases with gravel content up to 70%, and the strength decreases with the increase of the gravel content at the same void ratio. Thus, it is confirmed that the liquefaction strength of the gravel-sand mixtures depends both on relative density and void ratio of the whole mixture rather than the relative density of the sand matrix filled among gravels. On the other hand, the behavior of pore water pressure and axial strain for the $K_0-anisotropically$ consolidated gravel-sand mixtures shows almost the same cyclic behavior of the sand with no stress reversal even with some stress reversal of the cyclic loading. Namely, even the stress reversal of about 10% of cyclic stress amplitude, the permanent strain with small cyclic strain increases rapidly with the number of cycles, and the initial liquefaction does not occur always with less than maximum pore water pressure ratio of 1.0. The liquefaction resistance increases with the gravel contents between 0% and 40%, but tends to decrease beyond 40% of gravel content. In conclusion, the cyclic behavior of gravel-sand mixtures depends on factors such as gravel content, void ratio, relative density and consolidation condition.