• Economic and Environmental Geology
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• v.29 no.2
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• pp.183-192
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• 1996

Much computing time and large computer memory are needed to solve the wave equation in a large complex subsurface layer using finite difference method. The time and memory can be reduced by decreasing the number of grid per minimun wave length. However, decrease of grid may cause numerical dispersion and poor accuracy. In this study, we present 49 points weighted average method which save the computing time and memory and improve the accuracy. This method applies a new weighted average to the coordinate determined by transforming the coordinate of conventional 5 points finite difference stars to $0^{\circ}$ and $45^{\circ}$, 25 points finite differenc stars to $0^{\circ}$, $26.56^{\circ}$, $45^{\circ}$, $63.44^{\circ}$ and 49 finite difference stars to $0^{\circ}$, $18.43^{\circ}$, $33.69^{\circ}$, $45^{\circ}$, $56.30^{\circ}$, $71.56^{\circ}$. By this method, the grid points per minimum wave length can be reduced to 2.5, the computing time to $(2.5/13)^3$, and the required core memory to $(2.5/13)^4$ computing with the conventional method.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.7-13
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• 2008

To obtain a shear-wave velocity profile in geotechnical practice, various seismic investigation methods which have their own strength and weakness are being frequently used. Generally, geotechnical site have lateral variation of the properties, so it is needed to determine 2-dimensional shear wave velocity imaging of the site. In this study, harmonic wavelet analysis of wave (HWAW) method is applied to determination of 2-D $V_s$ imaging. HWAW method which is based on time-frequency analysis using harmonic wavelet transform have been developed to determine phase and group velocities of waves. HWAW method uses the signal portion of the maximum local signal/noise ratio to evaluate the phase velocity to minimize the effects of noise. HWAW method determine detailed local $V_s$ profile because one experimental setup which consists of one pair of receivers with spacing of 1~3m is used to determine the dispersion curve of the whole depth. So, 2-D Vs imaging with relatively high resolution can be determined through a series of HWAW test. In order to estimate the applicability of HWAW method, field tests were performed in 4 sites. Through field applications and comparison with other test results, the good accuracy and applicability of the proposed method were verified.

• International Journal of Concrete Structures and Materials
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• v.2 no.1
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• pp.15-19
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• 2008

The most typical capping method for concrete structures is a sulfur-mortar compound capping, provided it satisfied the standard criterion set forth by ASTM C 617, but this conventional bonded-type method has many problems. It exhibits relatively the smaller unreliable value of the strength of high-strength concrete due to the differences of elasticity and strength between the cylinder and the cap, and manifests poor serviceability such as dangerous working tasks or a waste of the working time. To prevent these problems, unbonded-type capping methods have taken the place of the conventional methods in recent years. One of the popular methods is the use of synthetic rubber like a neoprene pad. Serious problems still remain in this method, which include the consideration of its chemical characteristics in consideration of the selection, the safekeeping and the economy of the pads. Moreover, the synthetic rubber pads cannot be used in concrete cylinder with strength greater than 80 MPa according to ASTM C 1231-00. New 'sand-capping method' presented in this study, can be applicable to the compressive strength evaluation of the high strength concrete in the range of $70{\sim}100\;MPa$. This new method has better simplicity and reliability than those of existing 'sand-box', because usual materials such as standard sand and simply-devised apparatus are used for the capping system. The statistical analysis of the test results revealed that the new sand-capping method exhibited the smallest deviation and dispersion, attesting for its much better reliability than other methods specified in ASTM C 1231/1231M.

• Clean Technology
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• v.19 no.2
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• pp.128-133
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• 2013

Catalytic combustion of benzene over $CeO_2$-supported copper oxides has been investigated. The supported copper oxides catalysts were prepared using ball mill method and characterized by XRD, FT-IR, TEM and TPR. In the CuO/$CeO_2$ catalysts prepared using ball mill method, highly dispersed copper oxide species were shown at high loading ratio. The CuO/$CeO_2$ prepared using ball mill method showed the higher activity than those prepared using impregnation method. The catalytic activity increased with an increase in the CuO loading ratio, 10 wt% loaded CuO/$CeO_2$ catalyst giving the highest activity. In addition, the promoting of 10 wt% loaded CuO/$CeO_2$ catalyst with $Fe_2O_3$ and CoO enhanced the dispersion of CuO and then increased the catalytic activity.

• Water for future
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• v.29 no.5
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• pp.139-150
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• 1996

This paper presents the effect of numerical parameters, such as grid size and grid ratio, on the outflow hydrograph of a unit-width plane in the linear Muskingum-Cunge method. The numerical results depend on Courant number C and cell Reynolds number D, two physically and numerically meaningful parameters. As C approache 1 and D increases, the numerical dispersion-relating oscillations are difficult to occur. The numerical oscillations occur in the front of a propagating wave for C < 1, while smaller oscillations occur behind the wave for C > 1 due to the numerical diffusion effect. For a plane with a small value of characteristic reach length L (e.g., a steep plane), the numerical solution of the Muskingum-Cunge method is similar to that of the kinematic wave method, which shows no wave attenuation. However, for a plane with a large value of L (e.g., a mild plane), the Muskingum-Cunge method leads to the diffusion waves which are essentially independent of the Courant number. Accordingly, the Muskingum-Cunge method will be suited for the routing of the catchment with relatively mild slopes.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.8 no.6
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• pp.46-54
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• 2009

This study deals with the effects on the accident reduction according to the installation of RLC (red light cameras). The objective is to analyze the effects on the accident reduction using EB (Empirical Bayes) method. In pursuing the above, the study uses the 728 accident data occurred at the 28 intersections which RLC are installed. The main results are as follows. First, the effects of accident reduction were analyzed to be 20.74% by simple before-after study method. Second, the safety performance functions (SPF) were developed by the Poisson and negative binominal regression models, and since the over-dispersion parameter was close to zero, Poisson model was evaluated to be more appropriate than the negative binominal model. Also, the Poisson model was analyzed to be statistically significant because its ${\rho}^2$ value was 0.409. Finally, the results of analysis using an EB method showed that the accidents were reduced by range from 3.89 to 29.23%.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.11
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• pp.3474-3490
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• 1996

A metal matrix composites(MMCs) for A16061 reinforced with silicon carbide particles is fabricated by melt-stirring method. The primary products of MMCs billets are prepared by volume fractions 5 vol% to 20 vol% and particle size $13\mu m$ to $22\mu m$.This paper will be made to examine the microstructure and mechanical properties of fabricated $SiC_p$/Al 6061 composite by melt-stirring and squeeze casting method. The MMC billets is extruded at $500^{\circ}C$ under the constant extrusion velocity $V_e$=2mm/min using curved shape die. Extrusion force, particle rearrangement, micro structure and mechanical properties of extruded composites will be investigated. The mechanical properties of primary billets manufactured by melt-stirring and squeeze casting method will be compared with extrusion specimen. The effect of volume fraction and size of the reinforcements will be studied. The increase in uniformity of particle dispersion is the major reason for an improvement in reliability due to hot extrusion with optimal shape die. Experimental Young's modulus and 0.2% offset yield strength for the extruded MMCs will be compared with theretical values calculated by the Eshelby method. A method will be proposed for the prediction of Young's modulus and yield strength in $SiC_p$ reinforced MMCs.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.2
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• pp.167-175
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• 2013

The wave propagation characteristics of an acoustic metamaterial composed of periodically repeated one-dimensional Helmholtz resonator array was investigated considering the effects of dimensional changes of the resonator geometry on the transmission coefficient and band gap. The effective impedance and transmission coefficient of the acoustic metamaterials are obtained based on the acoustic transmission line method. The designed acoustic metamaterials exhibit band gaps and negative bulk modulus that are non-existent properties in the nature. The band gap of the acoustic metamaterial is strongly dependent on the geometry parameters of Helmholtz resonators and lattice spacing. Also, a new type of metamaterial that is periodically constructed with two different resonators was designed to open the local resonance band gap without change of Bragg scattering.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.12
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• pp.1120-1131
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• 2011

Researches using time reversal acoustics(TRA) for impact localization have been paid attention to recently. Dispersion characteristics of Lamb waves, which restrict the utility of classical nondestructive evaluation based on time-of-flight information, can be compensated through the application of TRA to Lamb waves on a plate. This study investigates the spatial focusing performance of time reversal Lamb waves on a plate using finite element analysis. In particular, the virtual sensor effect caused by multiple wave reflections at the boundaries of a plate is shown to enable the spatial focusing of Lamb waves though a very small number of surface-bonded piezoelectric(PZT) sensors are available. The time window size of forward response signals, are normalized with respect to the number of virtual active sensors. Then their effects on the spatial focusing performance of Lamb waves are investigated.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.17 no.6
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• pp.272-276
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• 2007

The various colored cubic zirconia single crystals for jewelry were grown by skull melting method of excellent productivity. The cubic zirconia is similar to the character of diamond, which has high refractive index, large dispersion and high hardness. It is possible that the development of new colored cubic zirconia by doping 3d-transition elements or 4f-rare earth elements. The colored cubic zirconia is representative of synthetic gemstone which was grown up by mixing one or over two materials among $Pr_6O_{11},\;TiO_2,\;MnO_2\;and\;Er_2O_3$ as coloring agent. Subsequent heat treatment improves the quality of color and uniformity. This study is aimed the color reappearance of cubic zirconia such as natural peridot, smoky-quartz and red-tourmaline.