• Geophysics and Geophysical Exploration
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• v.9 no.4
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• pp.304-315
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• 2006

We have examined the applicability of f-k analysis to the GPR direct wave measurement for water content to characterize vadose zone condition. When the vadose zone consists of a dry surface layer over wet substratum, we obtained f-k spectra where most of the energy is bounded by the air and dry soil velocities. In this case, dry soil velocity was successfully estimated by using high frequency data. On the other hands, when wet soil overlies dry substratum, the f-k spectra show a contrasting response where most of the energy travels with the velocity bounded by dry and wet soil velocities. In this case, the radar waves are trapped and guided within wet soil layer, exhibiting velocity dispersion. By adopting modal propagation theory, we could formulae a simple inversion code to find two layer's dielectric constants as well as layer thickness. By inverting the velocity dispersion curve obtained from f-k spectra of synthetic modeling data, we could obtain good estimates of dielectric constants of each layer as well as first layer thickness. Moreover, we could obtain more accurate results by including the higher mode data. We expect this method will be useful to get the quantitative property of real subsurface when the field condition is similar.

• Tunnel and Underground Space
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• v.22 no.5
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• pp.321-329
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• 2012

Laboratory tests for measuring absorption, porosity, P-wave velocity and uniaxial compressive strength (UCS) were performed to examine weathering characteristics of ilmenite by microorganism. Physical property changes were quantitatively estimated with comparing culture period on the condition of abiotic oxidation without microorganism and biooxidation with microorganism. As a result, the measured pH during 45 days was distributed in the range from 3.82 to 4.26, on the other hand, biooxidation showed the range from 2.20 to 2.57. The measured absorption according to microorganism and culture period represented 0.052% at final stage in the case of abiotic oxidation and 0.073% in the case of biooxidation. Porosity showed 0.206% at final stage in the case of abiotic oxidation and 0.281% in the case of biooxidation. In general, the values by biooxidation showed higher than that by abiotic oxidation. Change range of P-wave velocity with culture period showed that the measured value as 1410 m/s at final stage in the case of biooxidation was lower than 1886 m/s of that in the case of abiotic oxidation. The UCS was decreased with increasing culture period in all specimens and represented 241.1 MPa at final stage in the case of abiotic oxidation and 140.0 MPa in the case of bioxidation. In conclusion, it implies that influence of physical property on ilmenite by biooxidation related with microorganism was larger than that by abiotic oxidation.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.17 no.3
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• pp.138-148
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• 2005

Dynamic response of floating structures such as floating body and floating bridges subject to wave load is to be calculated in frequency domain. Added mass coefficient, damping coefficient and wave exciting force are obtained numerically from frequency domain formulation of linear potential theory and boundary element method for a floating body which is partially submerged into water and subjected to wave force. Next, the equation of motion for the dynamic behavior of a floating structure which is supported by the floating bodies and modeled with finite elements is written in frequency domain. hker a hemisphere is analyzed and compared with the published references as examples of floating bodies, the hydrodynamic coefficients for a pontoon type floating body which supports a floating bridge are determined. The dynamic response of the floating bridge subject to design wave load can be solved using the coefficients obtained for the pontoons and the results are plotted in the frequency domain. It can be seen from the example analysis that although the peak frequency of the incoming wave spectrum is near the natural frequency of the bridge, the response of the bridge is not amplified due to the effect that the peak frequency of wave exciting force is away from the natural frequency of the bridge.

• Geophysics and Geophysical Exploration
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• v.16 no.4
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• pp.250-256
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• 2013

Using shear wave velocity is more reasonable to estimate strength and integrity of rock compared with using compressional wave. It is often ambiguous to pick the dominant frequency caused by torsional wave when evaluating $V_S$ of rock specimen from FFRC method. It is also sometimes ambiguous to pick the first arrival point of S wave compared with P wave in the signals acquired from ultrasonic velocity method. Otherwise, the procedure of evaluating $V_P$ using ultrasonic velocity method and $V_L$ using FFRC method is relatively stable. Through the relationship between elastic modulus, poisson's ratio and $V_S$ can be obtained from $V_P$, $V_L$. Applicability was checked using model specimens having different material property and length and rock specimens sampled in mine area, and usefulness of proposed procedure was verified.

• Journal of Navigation and Port Research
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• v.34 no.1
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• pp.15-19
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• 2010

Recently, the wireless LAN system is rapidly growing because of its convenience of high speed communication. However, the wireless LAN systems at indoor places occur multi-propagation path by reflected waves from walls, ceilings, floors, and desks. Multipath problems cause transmission errors and degradation of communication speed. These problems can be solved by using EM wave absorbers. In this paper, we analyzed property of Graphite and derived the optimum ratio of Graphite: CPE to develop EM wave absorber for the wireless LAN system. First, we fabricated several samples in different composition ratios of Graphite and CPE, and then measured the reflection coefficient of each samples. Material constants of permittivity and permeability were calculated using the measured data and designed EM wave absorber. Secondly, the EM wave absorber was fabricated and tested on the base of the simulation data. As a result, it showed that the EM wave absorber in 1.7 mm thickness with the ratio of Graphite: CPE=50:50 wt.% has excellent absorption ability more than 27 dB at 5.2 GHz.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.1
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• pp.171-175
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• 2006

In this paper, we have developed a retrodirective active array operating in the 2 GHz LS band. The retrodirective array has the property of redirecting any electromagnetic wave back to the incoming direction without any priory informations. The system is integrated with phase conjugators and antenna array. Microwave phase conjugators can be implemented by microwave mixers. In this research, 2-port gate mixers using pHEMT and $1{\times}4$ monopole array have been used to achieve the retrodirectivity. The measured results have been compared with the theoretical prediction, and it has been shown that there exists a reasonable agreement between them. The monopole array can be used easily in many areas for simplicity and cost-effective property, and the retrodirective array developed in this research can be applied directly in the base station facilities for the wireless mobile communications. indoor wireless LAN and RFID transponders.

• Analytical Science and Technology
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• v.24 no.6
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• pp.493-502
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• 2011

The catalyst works for visible-light region was characterized. Toluene, xylene, MEK and ammonia were used as reactants. The decomposition efficiency was compared between visible-light photocatalyst and UV-light one. UV-photocatalyst can be activated with UV-light wave length of 280~360 nm. However, visible-light photocatalyst can be activated with visible wave length of 400~750 nm. This result was found by using UV-Vis absorbance. A lot of materials were doped to visible light photocatalyst in order to increase its performance. Platinum was added to visible light photocatalyst with manganese in order to increase performance of the visible light photocatalyst. MTMS (Methyl tri methoxy silane) was used as a binder. Contact angle was analyzed varying with amount of binder. Contact angle was increased with increasing the amount of MTMS. As a result, the hydrophilic property of photocatalyst with MTMS binder was decreased due to its hydrophobic one. And Mn-$TiO_2$ catalyst had an excellent anti-bacterial property.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.6
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• pp.504-511
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• 2013

This paper proposes improved detection schemes for concealed micro-electronic devices using clustering and classification of radio frequency harmonics in order to protect intellectual property rights. In general, if a radio wave with a specific fundamental frequency is propagated from the transmitter of a classifier to a concealed object, the second and the third harmonics will be returned as the radio wave is reflected. Using this principle, we exploit the fuzzy c-means clustering and the ${\kappa}$-nearest neighbor classification for detecting diverse concealed objects. Simulation results indicate that the proposed scheme can detect electronic devices and metal devices in various learning environments by efficient classification. Thus, the proposed schemes can be utilized as an effective detection method for concealed micro-electronic device to protect intellectual property rights.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.6C
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• pp.221-229
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• 2011

A core zone of a fill dam is an important part of a dam for cutoff of water. Therefore, the material properties and behavior characteristics of a core zone are very important factors in an analysis of dam stability. However, the investigation on material properties of actual dam core is extremely rare so far. The material properties have been acquired or estimated by indirect methods like a surface wave surveying or empirical equation. In this research, in-situ and laboratory tests were conducted during dismantling an existing dam directly to investigate characteristics of the core zone in terms of the depth and transient variation of properties after construction of the dam. Dynamic material properties like shear wave velocity and shear modulus were measured and compared to other existing empirical correlations. In addition, aging characteristics of dynamic material properties were investigated by a series of laboratory tests.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.4
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• pp.308-315
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• 2009

Because the attenuation of AE signal in composite materials is relatively higher than that of metallic materials, it is required to develop a damage assessment technique less affected by the attenuation property of composite materials in order to use AE sensing as a damage detection method. In the signal processing procedure, it is profitable to use the leading wave that arrives first because the leading wave is less influenced by the boundary conditions. Using wavelet transform, we investigated the frequency characteristics of impact induced AE signals focused on the leading wave in advance and chose the key factors to discriminate the damaged condition quantitatively. In this research, we established a damage assessment technique using the sharing percentage of the wavelet detail components of AE signal, and conducted a low-velocity impact test on composite laminates to confirm the feasibility of the proposed signal processing method.