• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.114.1-114.1
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• 2012

To measure the magnetic field strength in the solar corona, we examined 10 fast (>1000 km/s) limb coronal mass ejections (CMEs) that show clear shock structures in Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph images. By applying the piston-shock relationship to the observed CME's standoff distance and electron density compression ratio, we estimated the Mach number, Alfven speed, and magnetic field strength in the height range 3-15 solar radii (Rs). The main results from this study are as follows: (1) the standoff distance observed in the solar corona is consistent with those from a magnetohydrodynamic model and near-Earth observations; (2) the Mach number as a shock strength is in the range 1.49-3.43 from the standoff distance ratio, but when we use the density compression ratio, the Mach number is in the range 1.47-1.90, implying that the measured density compression ratio is likely to be underestimated owing to observational limits; (3) the Alfven speed ranges from 259 to 982 km/s and the magnetic field strength is in the range 6-105 mG when the standoff distance is used; (4) if we multiply the density compression ratio by a factor of two, the Alfven speeds and the magnetic field strengths are consistent in both methods; and (5) the magnetic field strengths derived from the shock parameters are similar to those of empirical models and previous estimates.

• Proceedings of the KIEE Conference
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• 2005.07c
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• pp.2140-2142
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• 2005

This paper presents the experimental results on the preliminary breakdown characteristics under a highly non-uniform electric field in $SF_6/CO_2$ gas mixtures. The impulse preliminary breakdown developments are investigated by the measurements of corona current and light emission images. As a result, the preliminary breakdown development mechanisms for both positive and negative polarities are same. The first streamer corona is initiated at the tip of needle electrode, and the leaders develop with a stepwise propagation and bridge the test gap. The pause time of leader pulses in the positive polarity is significantly shorter than that in the negative polarity. Also, the time interval between the first streamer corona onset and breakdown in the negative polarity was much longer than that in the positive polarity The discharge channel paths in the positive polarity were zigzag. On the other hands, the leader channel in the negative polarity was thicker than that in the positive polarity.

• Journal of Creative Information Culture
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• v.6 no.3
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• pp.149-158
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• 2020

Corona19 has experienced radical changes in teaching methods in primary and secondary schools and higher education institutions, and the Ministry of Education has continued various attempts and support to ensure the quality of teaching and to promote learning participation in distance education. In this study, the support policy of the Ministry of Education for the post-Corona era was reviewed, and the professors' experiences in remote education were investigated and analyzed through intensive interviews. As a way to utilize programs to support participation in learning in real-time distance education, first, consideration of the proper period of concentration of learning by learners, second, coping with unexpected problems during learning activities, and using small meeting rooms and chatting as a collaboration tool were presented.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.11
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• pp.2023-2026
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• 2008

Cooling technologies using natural and forced convection are limited and operated in very low efficiency. The corona discharge is utilized as the driving mechanism for an ionic pump, which allows for air flow control and generation with low noise and no moving parts. These ideal characteristics of ionic pump give rise to variety applications. However, all of these applications would benefit from maximizing the flow velocities and efficiencies of the pumps. In this study a needle-mesh type ionic pump, with a ring type third electrode installed just near the needle point, has been investigated by focusing on elevating the ionic wind velocity and efficiency. As a result, the enhanced ionic wind velocity and increased power yield can be obtained with the proposed ionic pump with the third electrode.

• Proceedings of the KIEE Conference
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• 2008.05a
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• pp.139-140
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• 2008

Cooling systems for electronic equipments are becoming more important. Cooling technologies using natural and forced convection are limited and operated in very low efficiency. A corona discharge is utilized as the driving mechanism for anair pump, which allows for airflow generation with low noise and no moving parts. However they do not enhance the flow rate and overcome the control mechanism of the pump. In this study a point-mesh type air pump, with a third electro de installed near the corona point, has been proposed and investigated by focusing on elevating the ionic wind velocity and power yield. As a result, the significantly enhanced ionic wind velocity and tremendously increased power yield can be obtained with the proposed air pump system.

• Solar Energy
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• v.12 no.3
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• pp.126-136
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• 1992

In this paper an EGD generator of small capacity with the operating gases of $O_2,\;N_2$ and air is made and the electric characteristics in relation to energy conversion range length, corona current and gas pressure are investigated. The results are as follows: 1. There is a critical value in conversion range length for maximum open voltage and the critical value increases with fluid velocity. 2. The open voltage increases approximately linearly with corona current. 3. There is a critical value in the gas pressure for maximum open voltage and this pressure of gas decreases with fluid velocity in constant conversion range length.

• Korean Association of Arts Management
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• no.58
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• pp.153-177
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• 2021

This study attempted to analyze language networks based on the theory of art policy in the New Normal era triggered by COVID-19 and domestic and foreign policy trends. For analysis, data containing key words of "Corona" and "Art" were collected from Google News and Web documents from March to September 2020 to extract 227 refined subject words, and the extracted subject words were analyzed as indicators of frequency and centrality of subject words through the Netminor program. In addition, visualization analysis of semantic networks has been attempted for the analysis of relationships between each topic languages. As a result of the semantic network analysis, the most frequent topic was "Corona," and "Culture and Art," "Art," "Performance," "Online" and "Support" were included in the group with the most frequencies. In the centrality analysis, "Corona" was the most popular, followed by "the era," "after," "post," "art," and "cultural arts," with high frequency, "Corona," "art," and "cultural arts" also dominated most centrality. In particular, the top-level key words in the analysis of frequency and centrality of the topic are 'online' and 'support' and 'policy'. This can be seen as indicating that the rapid rise of non-face-to-face and online content and support policies for the artistic communities are needed due to the dailyization of social distance due to COVID-19.

• Textile Coloration and Finishing
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• v.13 no.3
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• pp.155-164
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• 2001

Textile wet-processing industry usually five rise to environmental pollution problems caused by using chemical substance. The objective of this study is to apply enzymes for wool and reduce the environmental problems. Three commercial protein degradation enzymes and a cellulose degradation enzyme as a reference were treated to prevent the shrinkage of wool fabric on laundering. Shrink resistant effects used change with the kinds of enzyme, the amount of enzyme, assistant chemicals, and the pre-treatment condition of wool fabric. When pre-treated with corona before enzyme treatment under ultrasonic condition, the weight loss was increased and strength was decreased and elongation was increased. Both corona pre-treatment and the addition of $Na_2SO_4$ also decreased shrinkage of wool fabrics on laundering. The existence of assistant chemicals increased alkali solubility of wool fabrics.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1574-1575
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• 2011

The application of a pulsed power system is being extended to an environmental and industrial field. The non-destructive gaseous pollutants from industrial plants such as power generation plants and incinerators can be processed by applying high voltage pulses with a fast rising time (a few nanoseconds) and short duration (nano to microseconds) in a pulsed corona discharge reactor. The pulsed plasma generator with a triggered switch has been developed. Its corona current in load can be adjusted by applied voltage and repetition rate. We investigated the performance of the pulsed plasma generator by analyzing the concentration of ozone in small reactor. This paper describes the electrical characteristics of the pulse generator with a voltage of 30 kV at repetition rate of 50 PPS. In addition, we briefly discuss a configuration of the system and initial test results.

• Proceedings of the KIEE Conference
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• 2001.07c
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• pp.1738-1740
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• 2001

The occurrence of fires under transmission lines is responsible for a great number of power line outages. In this paper, the ac flashover voltages and the corona onset voltages of a model transmission line in the presence of flame were investigated. We found that the corona onset voltages and the flashover voltages were varied with the position of flames. Flashover voltages of vertical arranged electrodes with flame appeared to decrease 43[%] lower than those of same conditions with no flame.