• Geomechanics and Engineering
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• v.19 no.1
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• pp.93-104
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• 2019

Anomalies and/or fractured grounds not detected by the surface geophysical and geological survey performed during design stage may cause significant problems during tunnel excavation. Many studies on prediction methods of the ground condition ahead of the tunnel face have been conducted and applied in tunneling construction sites, such as tunnel seismic profiling and probe drilling. However, most such applications have focused on the drill and blast tunneling method. Few studies have been conducted for mechanized tunneling because of the limitation in the available space to perform prediction tests. This study aims to predict the ground condition ahead of the tunnel face in TBM tunneling by using an electrical resistivity tomography survey. It compared the characteristics of each electrode array and performed an investigation on in-situ tunnel boring machine TBM construction site environments. Numerical simulations for each electrode array were performed, to determine the proper electrode array to predict anomalies ahead of the tunnel face. The results showed that the modified dipole-dipole array is, compared to other arrays, the best for predicting the location and condition of an anomaly. As the borehole becomes longer, the measured data increase accordingly. Therefore, longer boreholes allow a more accurate prediction of the location and status of anomalies and complex grounds.

• Journal of the Korean Geophysical Society
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• v.3 no.2
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• pp.77-90
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• 2000

Five electrical resistivity dipole-dipole and two seismic reflection surveys were performed in the southeastern margin of the Yongdong basin to delineate the shallow basin architecture. To investigate the intra-basin structure, twenty four resistivity sounding points and three dipole-dipole lines were selected especially in the vicinity of volcanic masses. The basin-fault boundaries are identified in electrical dipole-dipole resistivity section as high resistivity-contrast of approximately $1,500\;{\Omega}{\cdot}m$, characterized as a band of high standard-deviation. They are also effectively clarified in the seismic reflection data: amplitude and continuity contrasts in the common shot gather, first-arrival profiles, complex attribute plots. The intra-basin resistivity structures are constructed by interpolating vertical electrical sounding data and dipole-dipole profiles. The high-resistivity anomalies most likely originate from the northsouth-trending and northeast-dipping volcanic masses, which are to be further quantitatively investigated with geomagnetic and magnetotelluric surveys.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1996.11a
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• pp.44-48
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• 1996

We have investigated the influence of Ti/Ba mole ratio in the characteristics of the modified BaTiO$_3$systems with Ca addition. The specimens were fabricated with variations in Ti/Ba mole ratio between 0.995 and 1.01, and sintered in the temperature range between 13$25^{\circ}C$ and 1375$^{\circ}C$. The room temperature resistivity, PTCR effect and ac complex impedence characteristics were studied. It shows that the room temperature resistivity was increased with the increasing Ti/Ba mole ratio and sintering temperature. It was suggested that this result was mainly attributed to its grain-boundary properties

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.2
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• pp.178-183
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• 2002

The effects of Dy$_2$O$_3$and Er$_2$O$_3$addition on the electromagnetic properties of Mn-Zn ferrite were investigated in the doping concentration range from 0.05 wt% to 0.25 wt%. All samples were prepared by standard fabrication of ferrite ceramics. The XRD patterns of sample were observed spinel and secondary phase. The densities of sample were showed nearly constant values. As the increased additive, electrical resistivity, initial permeability and real component of the series complex permeability increased with setting limits each other. Excess doped with Dy$_2$O$_3$ and Er$_2$O$_3$, those values decreased. The maximum electrical resistivity was observed with 0.15 we% and initial permeability was observed with 0.05 wt%. Magnetic loss decreased with additive and then increased in proportion to increased.

• Journal of the Korean Ceramic Society
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• v.33 no.1
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• pp.35-40
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• 1996

The influence of grain boundary on the electrical properties of WO3-doped SrTiO3 ceramics has been investi-gated. From the result resistivity and capacitance of grains and boundaries were obtained by employing impedance spectrocopy. And the temperature dependance of capacitance of WO3-doped SrTiO3. was influenced directly by the variation of grain boundary capacitance. It was also found by impedance spectroscopy that the dispersion frequency characteristics showed discernibly that the resistivity of the specimen varied with WO3 content.

• Geophysics and Geophysical Exploration
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• v.15 no.1
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• pp.33-38
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• 2012

A resistivity method has been applied to wide range of engineering and environmental problems with the help of automatic and precise data acquisition. Thus, more accurate modeling and inversion of time-lapse monitoring data are required since resistivity monitoring has been introduced to quantitatively find out subsurface changes With respect to time. Here, we used the finite element method (FEM) for 3D resistivity modeling since the method is easy to realize complex topography and arbitrary shaped anomalous bodies. In the FEM, the linear elements, also referred to as first order elements, have certain advantages of simple formulation and narrow bandwidth of system equation. However, the linear elements show the poor accuracy and slow convergence of the solution with respect to the number of elements or nodes. To achieve the higher accuracy of finite element solution, high order elements are generally used. In this study, we developed a 3D resistivity modeling program using high order Serendipity elements. Comparing the Serendipity element solutions for a cube model with the linear element solutions, we assured that the Serendipity element solutions are more accurate than the linear element solutions in the 3D resistivity modeling.

• Journal of the Korean Vacuum Society
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• v.9 no.4
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• pp.321-327
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• 2000

Tungsten(W) thin films with good adhesion property and low resistivity (~10 $\mu$\Omega$$.cm) were deposited directly on $SiO_2$ by LPCVD. The adhesion property of W thin films on $SiO_2$ improves as the temperature and/or $SiH_4/WF_6$ gas ratio increase. Specifically tungsten thin films could be deposited on $SiO_2$ even at $350^{\circ}C$ if the gas ratio of 2 was employed. The resistivity of tungsten thin films deposited at $350^{\circ}C$ was high due to the presence of $\beta$-W. However, the resistivity can be minimized by increasing the amount of $H_2$ gas flow. Therefore, it is shown in this work that the adhesion of tungsten thin films on $SiO_2$ can be improved simply by controlling the process parameters (e.g., temperature, gas ratio and $H_2$ flow rate) without employing complex deposition methods or additional glue layers.

• Economic and Environmental Geology
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• v.29 no.3
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• pp.345-355
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• 1996

The effectiveness of various electrode configurations in horizontal mappings and 1-D inversions of vertical sounding data for delineating 2-D structures was studied. Apparent resistivity values of three point, dipole-dipole, Wenner, and Schlumberger mappings were simulated for such structures as vertical dyke, tabular prism, buried vertical fault, ramp and complex structure by finite difference method (FDM) and they were compared with each other. Also 2-D cross sections for three structures obtained by interpolation of 1-D inverted sounding data in terms of three layers were compared for Schlumberger and Wenner arrays. On these cross sections, horizontal and vertical resistivity interfaces of the 2-D structures are revealed relatively clearly. Apparent resistivity curves of Schlumberger mapping show vertical resistivity discontinuities very well. On the whole, Schlumberger array is superior to the other arrays in electric sounding as well as mapping. This study clearly indicates that interpretations of 2-D structures based on 1-D inversion are possible.

• Geophysics and Geophysical Exploration
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• v.20 no.2
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• pp.100-113
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• 2017

Induced polarization (IP) method is based on the measurement of a polarization effect known as overvoltage of the ground. IP techniques have been usually used to find mineral deposits, however, nowadays widely applied to hydrogeological investigations, surveys of groundwater pollution and foundation studies on construction sites. IP surveys can be classified by its source type, i.e., time-domain IP estimating chargeability, frequency-domain IP measuring frequency effect (FE), and complex resistivity (CR) and spectral IP (SIP) measuring complex resistivity. Recently, electromagnetic-based IP has been studied to avoid the requirement for spike electrodes to be placed in the ground. In order to understand IP methods in this study, we: 1) classify IP surveys by source type and measured data and illustrate their basic theories, 2) describe historical development of each IP forward modeling and inversion algorithm, and finally 3) introduce various case studies of IP measurements.

• Geophysics and Geophysical Exploration
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• v.25 no.3
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• pp.99-108
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• 2022

Among induced polarization (IP) methods, spectral IP (SIP) uses alternating current as a transmission source to measure amplitudes and phase of complex electrical resistivity at each source frequency, which disperse with respect to source frequencies. The frequency dependence, which can be explained by a relaxation model such as Cole-Cole model or equivalent models, is analyzed to estimate SIP parameters from dispersion curves of complex resistivity employing multi-objective optimization (MOO). The estimation uses a generic algorithm to optimize two objective functions minimizing data misfits of amplitude and phase based on Cole-Cole model, which is most widely used to explain IP relaxation effects. The MOO-based estimation properly recovered Cole-Cole model parameters for synthetic examples but hardly fitted for the real laboratory measures ones, which have relatively smaller values of phases (less than about 10 mrad). Discrepancies between scales for data misfits of amplitude and phase, used as parameters of MOO method, and it is in necessity to employ other methods such as machine learning, which can deal with the discrepancies, to estimate SIP parameters from dispersion curves of complex resistivity.