• 한국지구물리탐사학회:학술대회논문집
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• 2007.12a
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• pp.53-62
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• 2007

Preliminary gas hydrate surveys were carried out From 2000 to 2004 in the East Sea. Research results showed the geophysical evidence of gas hydrate existence. In 2005, Gas Hydrate R&D Organization was established and 10 year gas hydrate development program was initiated. In the $1^{st}$ stage of the program from 2005 to 2007, 6,600 L-km 2-D seismic survey was conducted in the $1^{st}$ year 2005, and $400\;km^2$ 3D survey was conducted in the $2^{nd}$ year 2006. Acquired seismic data were processed and seismic section and 3D cube were produced. By geophysical interpretation and velocity analysis, prospective areas were mapped and candidate drilling sites were recommended. For the precise interpretation, velocity was analyzed using AVO method, and BSR signal was analyzed using deconvolution method. For the prospective area, OBS and high-resolution seismic surveys were conducted. This presentation shows the introduction and examples of the research results of the geophysical methods applied for the gas hydrate exploration in the East Sea.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.79.2-79.2
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• 2017

To dynamically and chemically understand how filaments, dense cores, and stars form under different environments, we are conducting a systematic mapping survey of nearby molecular clouds using the TRAO 14 m telescope with high ($N_2H^+$ 1-0, $HCO^+$ 1-0, SO 32-21, and $NH_2D$ v=1-0) and low ($^{13}CO$ 1-0, $C^{18}O$ 1-0) density tracers. The goals of this survey are to obtain the velocity distribution of low dense filaments and their dense cores for the study of their origin of the formation, to understand whether the dense cores form from any radial accretion or inward motions toward dense cores from their surrounding filaments, and to study the chemical differentiation of the filaments and the dense cores. Until the 2017A season, the real OTF observation time is ~760 hours. We have almost completed mapping observation with four molecular lines ($^{13}CO$ 1-0, $C^{18}O$ 1-0, $N_2H^+$ 1-0, and $HCO^+$ 1-0) on the six regions of molecular clouds (L1251 of Cepheus, Perseus West, Polaris South, BISTRO region of Serpens, California, and Orion B). The cube data for $^3CO$ and $C^{18}O$ lines were obtained for a total of 6 targets, 57 tiles, 676 maps, and $7.1deg^2$. And $N_2H^+$ and $HCO^+$ data were added for $2.2deg^2$ of dense regions. All OTF data were regridded to a cell size of 44 by 44 arcseconds. The $^{13}CO$ and $C^{18}O$ data show the RMS noise level of about (0.1-0.2) K and $N_2H^+$ and $HCO^+$ data show about (0.07-0.2) K at the velocity resolution of 0.06 km/s. Additional observations will be made on some regions that have not reached the noise level for analysis. To identify filaments, we are using and testing programs (DisPerSE, Dendrogram, FIVE) and visual inspection for 3D image of cube data. A basic analysis of the physical and chemical properties of each filament is underway.

• 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.

• The Journal of Engineering Geology
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• v.30 no.3
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• pp.327-345
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• 2020

The effects of ground vibration on lava tubes during construction were studied to aid design of management and preservation measures for lava tubes. Ground conditions were assessed by RMR (Rock mass rating) and Q-system classifications for the Geomunoreum lava tubes, and vibration velocity was measured during in situ blasting tests in the Manjanggul and Yongcheondonggul lava tubes. Results indicate that the higher the rock quality, the greater the effect of vibration, although there is no clear linear relationship due to ground heterogeneity. A relationship derived between vibration velocity (PPV) and intensity (dB(V)) on the basis of blasting tests indicates that a vibration level of < 0.285 cm/sec meets the regulatory limit of 0.371 cm/sec and 65 dB(V) during daytime, and 0.285 cm/sec and 60 dB(V) during night. For blasting vibrations, square- and cube-root scaled distances are linearly correlated, with R² ≥ 0.76. On the basis of this correlation, explosive-charge weights meeting the 0.2 cm/sec vibration criterion for cultural heritage were estimated to be 2.88 kg at 50 m distance, and 11.52 kg at 100 m.

• Advances in materials Research
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• v.9 no.3
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• pp.203-218
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• 2020

This research paper presents the outcomes in terms of mechanical and microstructural characteristics of binary and ternary concrete when exposed to elevated temperature. Three parameter were taken into account, (a) elevated temperature (i.e., 200, 400, 600 and 800℃) (b) binary concrete with cementitious material sugarcane bagasse ash (SCBA) and ground granulated blast furnace slag (GGBFS) replacement percentage (i.e., 0, 15, 20, 25 and 30%) and (c) ternary concrete with cementitious material SCBA and GGBFS replacement percentage (i.e., 0, 15, 20, 25 and 30%). A total of 285 standard cube specimens (150 mm × 150 mm × 150 mm) containing Ordinary Portland Cement (OPC), SCBA, and GGBFS were made. These specimens then exposed to several elevated temperatures for 2 h, afterword is allowed to cool at room temperature. The following basic physical, mechanical, and microstructural characteristics were then determined and discussed. (a) mass loss ratio, (b) ultrasonic pulse velocity (UPV) (c) physical behavior, (d) compressive strength, and (e) field emission scanning electron microscope (FESEM). It was found that compressive strength increases up to 400℃; beyond this temperature, it decreases. UPV value and massloss decrease with increase in temperature as well as the change in color and crack were observed at a higher temperature.

• Journal of The Korean Astronomical Society
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• v.41 no.6
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• pp.157-161
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• 2008

We have estimated the fractal dimension of the molecular clouds associated with the Hii region Sh 156 in the Outer Galaxy. We selected the $^{12}CO$ cube data from the FCRAO CO Survey of the Outer Galaxy. Using a developed code within IRAF, we identified slice-clouds (2-dimensional clouds in velocity-channel maps) with two threshold temperatures to estimate the fractal dimension. With the threshold temperatures of 1.8 K, and 3 K, we identified 317 slice-clouds and 217 slice-clouds, respectively. There seems to be a turn-over location in fractional dimension slope around NP (area; number of pixel) = 40. The fractal dimensions was estimated to be D = $1.5\;{\sim}\;1.53$ for $NP\;{\geq}\;40$, where $P\;{\propto}\;A^{D/2}$ (P is perimeter and A is area), which is slightly larger than other results. The sampling rate (spatial resolution) of observed data must be an important parameter when estimating fractal dimension. Fractal dimension is apparently invariant when varying the threshold temperatures applied to slice-clouds identification.