• Journal of the Mineralogical Society of Korea
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• v.22 no.4
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• pp.313-324
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• 2009

We explore the effect of particle shape and size on 3-dimensional (3D) network and pore structure of porous earth materials composed of glass beads and silica gel using NMR micro-imaging in order to gain better insights into relationship between structure and the corresponding hydrologic and seismological properties. The 3D micro-imaging data for the model porous networks show that the specific surface area, porosity, and permeability range from 2.5 to $9.6\;mm^2/mm^3$, from 0.21 to 0.38, and from 11.6 to 892.3 D (Darcy), respectively, which are typical values for unconsolidated sands. The relationships among specific surface area, porosity, and permeability of the porous media are relatively well explained with the Kozeny equation. Cube counting fractal dimension analysis shows that fractal dimension increases from ~2.5－2.6 to 3.0 with increasing specific surface area from 2.5 to $9.6\;mm^2/mm^3$, with the data also suggesting the effect of porosity. Specific surface area, porosity, permeability, and cube counting fractal dimension for the natural mongolian sandstone are $0.33\;mm^2/mm^3$, 0.017, 30.9 mD, and 1.59, respectively. The current results highlight that NMR micro-imaging, together with detailed statistical analyses can be useful to characterize 3D pore structures of various porous earth materials and be potentially effective in accounting for transport properties and seismic wave velocity and attenuation of diverse porous media in earth crust and interiors.

• Journal of the Korean Society of Combustion
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• v.1 no.1
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• pp.75-82
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• 1996

Laser induced incandescence, LII, recently developed technique for measuring soot concentration in flames, can overcome most of limitations of conventional laser extinction measurement. In this study, experiments were performed to investigate the effect of laser intensity, detection wavelength, and also laser beam quality on both LII signal at a particular position and peak-to-centerline LII signal ratio. The results of LII signal with increasing laser intensity shows its near-independence of laser intensity once threshold level of laser intensity has been reached. However, this near-independence depends on laser beam quality and the incident optical setup. The peak-to-centerline LII signal ratio slowly but continuously increases with laser power. This fact is due to the dependence of LII signal on particle mean diameter. LII signal is attenuated during it passes through the flame containing soot particles. The attenuation rate is inversely proportional to detection wavelength. In this study, LII signal at 680 nm band is 10% greater than the signal at 400 nm band.

• Explosives and Blasting
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• v.38 no.1
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• pp.23-29
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• 2020

The measurement technique with dynamic shock sensor was widely used in academic experiment for blasting and impact. However, most of dynamic sensors are expensive so that it needs to be protected by external housing structures or damping devices. In this study, the calibration method for dynamic shock sensor under the distortion by external structures. Hopkinson pressure bar system was adopted to measure the input acceleration to the sensor, and it was compared to the acceleration measured by accelerometer with customized damping device. Consequently, it is conclued that this method can be useful to calibrate the dynamic shock sensor under the linear distortion.

• Proceedings of the Korean Geotechical Society Conference
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• 1993.06a
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• pp.83-116
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• 1993

This article analyzed the dynamic compaction incuced vibration of man made waste landfill. General dynamic properties and compaction-condition-related dynamic properties were analyzed. from the results, it was turned out that the shear modulus G=17496-58320 t/m2, dannpln ratio D=14~58%, dominant frequency f=6-14Hz. Also, it was turned out that the propagation velocitis of low amplitude shear wave and compressive wave were increased as the number of impact increased, the relation between peak particle velocity, and impact distance was wpp=5.08.[D/r E]-1.4, the peak particle velocity was high at the lower part of the waste fill layer and the range of dynamically improved area was about 6-10m.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.10B
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• pp.1240-1245
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• 2011

In this paper, channel modeling and analysis of wireless visible light communication(VLC) were studied in indoor circumstance. Photons emitted from LED straightly moved and navigated within indoor, after that a part of photons reached on PD via LOS(Line Of Sight) or NLOS(None Line Of Sight). These received signals had characteristics of delay profile and attenuation, which was multiple-path fading. In this paper, computer simulation of VLC channel was executed under the condition that two LEDs were used for transmitter and three PDs were located at different positions of the 20*8*2.3m sized indoor. BER performance simulation was excuted based on the characteristics of each VLC channel.

• Journal of the Korean Geotechnical Society
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• v.25 no.12
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• pp.87-105
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• 2009

Nonlinear dynamic deformation characteristics, expressed in terms of normalized shear modulus reduction curve (G/$G_{max}-\log\gamma$, G/$G_{max}$ curve) and damping curve (D-$\log\gamma$), are important input parameters with shear wave velocity profile ($V_s$-profile) in the seismic analysis of (new or existing) fill dam. In this paper, the reasonable and economical methods to evaluate the nonlinear dynamic deformation characteristics for core zone and rockfill zone respectively are presented. For the core zone, 111 G/$G_{max}$ curves and 98 damping curves which meet the requirements of core material were compiled and representative curves and ranges were proposed for the three ranges of confining pressure (0~100 kPa, 100 kPa~200 kPa, more than 200 kPa). The reliability of the proposed curves for the core zone were verified by comparing with the resonant column test results of two kinds of core materials. For the rockfill zone, 135 G/$G_{max}$ curves and 65 damping curves were compiled from the test results of gravelly materials using large scale testing equipments. The representative curves and ranges for G/$G_{max}$ were proposed for the three ranges of confining pressure (0~50 kPa, 50 kPa~100 kPa, more than 100 kPa) and those for damping were proposed independently of confining pressure. The reliability of the proposed curves for the rockfill zone were verified by comparing with the large scale triaxial test results of rockfill materials in the B-dam which is being constructed.

• Journal of Radiation Protection and Research
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• v.29 no.4
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• pp.251-256
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• 2004

CsI(Tl), $CdWO_4(CWO),\;Bi_4Ge_3O_{12}(BGO)\;and\;Gd_2SiO_5:Ce(GSO)$ scintillators were studied to manufacture a phoswich detector. The maximum wavelengths of the CsI(Tl), CWO, BGO and GSO scintillators are 550 nm, 475 nm, 490 nm and 440 nm for the radioluminescence, and the absolute light outputs of the CsI(Tl), CWO, BGO and GSO scintillators are 54890 phonon/MeV, 17762 phonon/MeV, 8322 phonon/MeV and 8932 phonon/MeV with a neutral filter, and the decay time of the CsI(Tl), CWO, BGO and GSO scintillators is $1.3{\mu}s,\;8.17{\mu}s$, 213 ns and 37 ns by a single photon method. The phoswich detector which was manufactured with plastic and CsI(Tl) scintillators could separate the ${\beta}$ particle and ${\gamma}$ ray. The phoswich detector could also measure the pulse height spectra of the ${\beta}$ particle and ${\gamma}$ ray by a PSD method.

• Journal of the Korean Magnetics Society
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• v.18 no.3
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• pp.120-125
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• 2008

In this study, NiCoZn ferrites with the variation of sintering temperature and chemical composition were prepared by the coprecipitation. Microstructures Crystal structure of NiCoZn ferrites were analyzed by XRD and their electric magnetic characteristics were analyzed by LCR meter and their morphology observed by SEM. We identified that these powders have a typical NiCoZn spinel structure and nanoparticles average size of 40 nm. The impurity, the initial permeability and the Q factor value are the lowest of sintered NiCoZn ferrite at $1250^{\circ}C$. Also, we measured S-parameter for $(Ni_{0.4}Co_{0.1}Zn_{0.5})Fe_2O_4$ which showed a maximum reflection loss of -3.1 dB at 6 GHz for the 2 mm thick sample. From this result, we found that the NiCoZn ferrite can be used in ferrite microwave-absorbing application at a higher frequency region (> 6 GHz).

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.14 no.1
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• pp.22-29
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• 2000

This paper deals with the dielectric characteristics of $SF_6$ gas gap stressed by $\pm$1.2/44[$mutextrm{s}$] non-oscillating impulse and $\pm$0.4[$mutextrm{s}$]/1.14[MHz] oscillating impulse voltages in the presence of a needle-shape metallic particle in gas-insulated switchgear(GIS). Breakdown voltage-time (V-t) and breakdown voltage-gas pressure (V-p) characteristics were investigated and discussed. The experiments were carried out under highly inhomogeneous field geometry with a needle protrusion whose length and radius are 10[mm] and 0.5[mm], respectively. The gas pressure ranges from 0.1 to 0.5[㎫]. As a result, it was found that the electrical breakdown for both the positive and negative polarity develops with steplike pulses in leader mechanism, When subjected to the positive oscillating impulse voltage, the minimum breakdown voltages appeared in all the gas pressure ranges and the V-t curves have a pronounced upturning at short times to breakdown and give a little dependence of the gas pressure. On the other hand, in the case of the negative polarity the dependence of the V-t and V-p characteristics on the wave shape of the applied voltages is known to be appreciable.

• Journal of Korea Water Resources Association
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• v.47 no.3
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• pp.285-295
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• 2014

We applied the ISPSO-GLUE method, which integrates the Isolated-Speciation-based Particle Swarm Optimization (ISPSO) with the Generalized Likelihood Uncertainty Estimation (GLUE) method, to the uncertainty analysis of the Topography Model (TOPMODEL) and compared its performance with that of the GLUE method. When we performed the same number of model runs for the both methods, we were able to identify the point where the performance of ISPSO-GLUE exceeded that of GLUE, after which ISPSOGLUE kept improving its performance steadily while GLUE did not. When we compared the 95% uncertainty bounds of the two methods, their general shapes and trends were very similar, but those of ISPSO-GLUE enclosed about 5.4 times more observed values than those of GLUE did. What it means is that ISPSOGLUE requires much less number of parameter samples to generate better performing uncertainty bounds. When compared to ISPSO-GLUE, GLUE overestimated uncertainty in the recession limb following the maximum peak streamflow. For this recession period, GLUE requires to find more behavioral models to reduce the uncertainty. ISPSO-GLUE can be a promising alternative to GLUE because the uncertainty bounds of the method were quantitatively superior to those of GLUE and, especially, computationally expensive hydrologic models are expected to greatly take advantage of the feature.