• Geophysics and Geophysical Exploration
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• v.4 no.2
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• pp.34-44
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• 2001

Forward modeling by construction of synthetic data is usually practiced in a horizontal surface and a few subsurface structures. However, in-situ surveys often take place in such topographic changes that the corrupted field data always make it difficult to interpret the right signals. To examine the propagation characteristic of elastic waves on the irregular surface, a general mesh generation code for finite element method was modified to consider the topography. By implementing this algorithm, the time domain modeling was practiced in some models with surface topography such as mound, channel, etc. The synthetic data obtained by receivers placed on surface also agreed with the analytic solution. The snapshots showing the total wave-field revealed the propagation characteristic of the elastic waves through complex subsurface structures and helped to identify the signals on the time traces. The transmission of Rayleigh waves along the surface, compressive waves, and sheer waves was observed. Moreover, it turned out that the Rayleigh waves behave like a new source at the edge.

• Journal of the korean academy of Pediatric Dentistry
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• v.25 no.1
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• pp.76-92
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• 1998

The purpose of this study was to evaluate the possible efficacy of Nd-YAG laser as a dentin conditioner by observing the laser irradiation dentin surface under scanning electron micrograph and measuring shear bond strength of restored light-cured glass ionomer mold. Fifty intact premolars were prepared for shear bond strength tests. The teeth were randomly divided into five groups as follows; Group I. no treatment Group II. 10% poly acrylic acid, 20 sec Group III. laser treatment 2 w, 20 Hz, 2 sec Group IV. laser treatment 2 w, 20 Hz, 5 sec Group V. laser treatment 2 w, 20 Hz, 10 sec Samples of each group were restored with light-cured glass ionomer cement after dentin conditioning and then measuring the shear bond strength of each specimen were measured using universal testing machine. Additional ten premolars were prepared for SEM analysis The result from the this study can be summarized as follows. 1. Shear bond strength of polyacrylic acid-treated group (II) was significantly higher than other groups (p<0.05). 2. No statistically significant difference could be found between three laser-treated groups (III, IV, V) in shear bond strength(p>0.05) 3. According to the result of observation under SEM, Polyacrylic acid was shown to have removed the smear layer effectively and opened the dentinal tubules, whereas the laser has produced the irregular surface mainly composed of melted and fused structure. The microcracks found in laser-treated groups increased in number with irradiation time and formed the regular mesh-type in 10 sec-irradiation group. 4. The ultrastructural change of dentin surface created by laser irradiation was found to the improper for bonding of the glass ionomer restorative materials. And the lower shear bond strength of laser irradiated group might have been due to the failure to form the suit able dentin surface for the glass ionomer to penetrated into and form the proper micromechanical retention.

• Journal of the Korean Geotechnical Society
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• v.15 no.5
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• pp.217-228
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• 1999

The three methods of analysis (i) REV(representative elemental volume), (ii) non-REV and (iii) joint network analysis are introduced in this paper to analyze the groundwater flow in jointed rock mass and the inflow into underground excavations. The results from those methods are compared one another to reveal their characteristics by varying the number of joints and the diameter of the opening. The pre-processor, the so-called sequential analysis, is introduced to predict the equivalent hydraulic conductivity of a jointed rock mass having a number of intersecting joints. Using the finite element mesh, joint map and sequential analysis, the equivalent hydraulic conductivities are calculated for all 445 elements. The hydraulic inhomogeneity and the determination of the representative properties of jointed rock masses are discussed. In the REV analysis where the entire rock mass is homogenized through the representative properties, the inflow is increased regularly and consistently by increasing the joint density, the opening size and the conductivity contrast value. Though the non-REV analysis showed irregular variation of the inflow due to the local inhomogeneity allowed to individual elements, the inflow approached the REV results as the characteristic length increases. The joint network analysis showed the most sensitive reaction to the joint density, the opening size and the presence of the network crossing the opening. The reliability of the network analysis depends on the geometric data of individual joints. In view of the limited field data on joint geometry and possible uncertainty the REV and non-REV methods are considered more practical and rational than the joint network analysis.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.189-189
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• 2008

Due to the environmental issue vast research is going on to replace the widely used lead contented piezoelectric materials. Bismuth sodium titanate (abbreviated as BNT) based bismuth sodium titanate-barium titanate (abbreviated as BNBT) ceramic was prepared by using modified method rather than conventional mixed oxide method. This modification was made to improve the properties of BNT based ceramic. In this procedure $BaTiO_3$ (abbreviated as BT) was prepared using conventional mixed oxide method. Analytical grade raw materials of $BaCO_3$ and $TiO_2$ were weighted and ball milled using ethanol medium. The mixed slurry was dried and sieved under 80 mesh. Then the powder was calcined at $1100^{\circ}C$ for 2 hours. This calcined BT powder was used in the preparation of BNBT. Stoichiometric amount of $Bi_2O_3$, $Na_2CO_3$, $TiO_2$ and BT were weighted and mixed by using ball mill. The used calcination temperature was $850^{\circ}C$ for 2 hours. Calcined powder was taken for another milling step. BNBT disks were pressed to 15 mm of diameter and then cold isostatical press (CIP) was used. Pressed samples were sintered at $1150^{\circ}C$ for 2 hours. The SEM microstructure analysis revealed that the grain shape of the sintered ceramic was polyhedral and grain boundary was well matched where as the sample prepared by conventional method showed irregular arrangement and grain boundary not well matched. And sintered density was better (5.78 g/cc) for the modified method. It was strongly observed that the properties of BNBT ceramic near MPB composition was found to be improved by the modified method compare to the conventional mixed oxide method. The piezoelectric constant dB of 177.33 pC/N, electromechanical coupling factor $k_p$ of 33.4%, dielectric constant $K_{33}^T$ of 688.237 and mechanical quality factor $Q_m$ of 109.37 was found.

• Journal of Korea Water Resources Association
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• v.46 no.6
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• pp.655-666
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• 2013

Lately, intensity and frequency of natural disasters such as flood are increasing because of abnormal climate. Casualties and property damages due to large-scale floods such as Typhoon Rusa in 2002 and Typhoon Maemi in 2003 rapidly increased, and these show the limits of the existing disaster prevention measures and flood forecasting systems regarding irregular climate changes. In order to efficiently respond to extraordinary flood, it is important to provide effective countermeasures through an inundation model that can accurately simulate flood inundation patterns. However, the existing flood inundation analysis model has problems such as excessive take of analysis time and accuracy of the analyzed results. Therefore, this study conducted a flood inundation analysis by using the Gerris flow solver that uses quadtree grid, targeting the Baeksan Levee in the Nakdong River Basin that collapsed because of a concentrated torrential rainfall in August, 2002. Through comparisons with the FLUMEN model that uses unstructured grid among the existing flood inundation models and the actual flooded areas, it determined the applicability and efficiency of the quadtree grid-based flood inundation model of the Gerris flow solver.

• Journal of Navigation and Port Research
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• v.34 no.1
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• pp.51-57
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• 2010

When estimating the calmness in a harbor, it is important that diffraction and reflection of irregular waves should be exactly calculated. The basic equation of the numerical model in this study was used Mild-slope equation, which has the advantage of which non-linearity with great influence for the wave behavior can be considered, and a triangular mesh was generated by using finite element method. So as to verify the nonlinear effects, the results of the numerical model developed in this study are compared with the experimental and numerical results by other researchers. As a result, it is shown that the results in case of considering nonlinear wave are more exact for wave analysis than in case of not considering nonlinear wave. In order to apply this model, wave height distributions in Jumunjin fishery port installed a seawater-exchange breakwater are computed. From the results of this numerical analysis, when abnormal waves are intruded through the seawater-exchange breakwater, the results of the wave height distributions in the harbor are highly presented. Therefore, in order to get wave height low in the harbor, it is considered that the facility with the ability to protect the inflow of abnormal waves is needed.