• Geophysics and Geophysical Exploration
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• v.19 no.4
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• pp.228-235
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• 2016

We investigated pre- and post- seismic total electron content (TEC) anomalies in ionosphere caused by recent large-scale earthquakes around the globe and additionally examined whether the similar phenomena are detected in connection with the earthquakes around the Korean Penisula. TEC anomalies associated with the large-scale earthquakes showed the similar results to previous studies. In addition, we newly found the similar TEC changes from the recent 2016 Ecuador earthquake (M7.8). However, the post-seismic TEC changes would be falsely interpreted as the pre-seismic TEC changes dependent on the post-processing of TEC observation. We also investigated the possibility of TEC responses from the recent domestic earthquakes including 2016 Gyeongju earthquake but could not find any anomalous TEC changes. This is probably because the domestic earthquakes release significantly smaller acoustic wave energy than that of large-scale earthquakes occurring in plate boundaries.

• Geomechanics and Engineering
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• v.24 no.2
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• pp.179-191
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• 2021

In this study, the strength and failure mechanism of red sandstones with combined defects were investigated by uniaxial compression tests on red sandstones with different crack angles using two-dimensional particle flow code numerical software, and their mechanical parameters and failure process were studied and analyzed. The results showed that the mechanical characteristics such as peak strength, peak strain, and elastic modulus of the samples with prefabricated combined defects were significantly inferior than those of the intact samples. With increasing crack angle from 15° to 60°, the weakening area of cracks increased, elastic modulus, peak strength, and peak strain gradually reduced, the total number of cracks increased, and more strain energy was released. In addition, the samples underwent initial brittle failure to plastic failure stage, and the failure form was more significant, leading to peeling phenomenon. However, with increasing crack angle from 75° to 90°, the crack-hole combination shared the stress concentration at the tip of the crack-crack combination, resulted in a gradual increase in elastic modulus, peak strain and peak strength, but a decrease in the number of total cracks, the release of strain energy reduced, the plastic failure state weakened, and the spalling phenomenon slowed down. On this basis, the samples with 30° and 45° crack-crack combination were selected for further experimental investigation. Through comparative analysis between the experimental and simulation results, the failure strength and final failure mode with cracks propagation of samples were found to be relatively similar.

• Journal of the Korean Society of Laryngology, Phoniatrics and Logopedics
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• v.17 no.2
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• pp.107-110
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• 2006

Background and Objeetives : There are few studies reported that specifically examined the voice onset time(VOT) in patients with bilateral vocal nodules. The purpose of this study was to study the characteristics of voice onset in patients with bilateral vocal nodules. Materials and Methods : 52 female patients with bilateral vocal nodules were examined, aged from 20 to 54 years, and were compared with 25 normal female control group. All subjects produced five repetitions of the voiceless stops $/p^h,\;t^h\;k^h/$ in vowel context /ai_a/. VOT was measured by the time between the release of the stops and the onset of voicing. Results : VOTs of the voiceless stops $/p^h/\;and\;/t^h/$ in patients with bilateral vocal nodules were significantly shorter than those of normal subjects. VOT of the $/k^h/$ in them was shorter than those of normals, but the difference was not significant. This results showed that VOTs of the voiceless stops in patients with bilateral vocal nodules were shorter than those of normal subjects. Conclusion : The rapid onset of voicing in patients with bilateral vocal nodules might be associated with increased laryngeal muscle tension by hard glottal attacks. We suggest that VOT can be a clinically useful acoustic parameter for evaluating voice in patients with bilateral vocal nodules.

• Journal of the Korean Institute of Gas
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• v.23 no.6
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• pp.1-7
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• 2019

Most oil refineries and chemical plants have flare systems designed to mitigate pressure rises in process facilities in case of emergencies that require the release of large amounts of gas due to sudden process shutdowns such as power outages. However, the rise of the flame of the flare system causes civil complaints from residents around the factory due to visible pollution, and economic loss occurs in the company, which requires constant management. In this study, two items were diagnosed and analyzed in order to derive the optimal operation method of flare system. First, to detect the cause of the rise in flame height, the acoustic leak detector was used to check gas leaks in safety valves and pressure control valves. Second, to identify the cause of flame instability, the pulsation phenomenon was diagnosed through the CFD simulation and modeling experiments of the sealing drum. By confirming the leak at 4.3% of the safety valve and 10% of the pressure control valve, the cause of abnormal sparking was derived. The information presented in this study can be easily applied to any company that has a flare system, and is expected to prevent complaints and product loss.