• 천문학회보
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• 제38권2호
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• pp.89.1-89.1
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• 2013

We present a multiwavelength study of the X-class flare, which occurred in active region (AR) NOAA 11339 on 3 November 2011. The EUV images recorded by SDO/AIA show the activation of a remote filament (located north of the AR) with footpoint brightenings about 50 min prior to the flare occurrence. The kinked filament rises-up slowly and after reaching a projected height of ~49 Mm, it bends and falls freely near the AR, where the X-class flare was triggered. Dynamic radio spectrum from the Green Bank Solar Radio Burst Spectrometer (GBSRBS) shows simultaneous detection of both positive and negative drifting pulsating structures (DPSs) in the decimetric radio frequencies (500-1200 MHz) during the impulsive phase of the flare. The global negative DPSs in solar flares are generally interpreted as a signature of electron acceleration related to the upward moving plasmoids in the solar corona. The EUV images from AIA $94{\AA}$ reveal the ejection of multiple plasmoids, which move simultaneously upward and downward in the corona during the magnetic reconnection. The estimated speeds of the upward and downward moving plasmoids are ~152-362 and ~83-254 km/s, respectively. These observations strongly support the recent numerical simulations of the formation and interaction of multiple plasmoids due to tearing of the current-sheet structure. On the basis of our analysis, we suggest that the simultaneous detection of both the negative and positive DPSs is most likely generated by the interaction/coalescence of the multiple plasmoids moving upward and downward along the current-sheet structure during the magnetic reconnection process. Moreover, the differential emission measure (DEM) analysis of the active region reveals presence of a hot flux-rope structure (visible in AIA 131 and $94{\AA}$) prior to the flare initiation and ejection of the multi-temperature plasmoids during the flare impulsive phase.

• 한국콘텐츠학회논문지
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• 제21권1호
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• pp.465-474
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• 2021

'심각한 급성 호흡기 증후군 코로나 바이러스 2(SARS-CoV-2)'에 의한 질병인 코로나-19는 2020년 3월 세계 보건기구에서 세계적인 전염병 대유행으로 선언되었고, 대부분의 나라에서 선별 및 확진을 위한 진단검사법으로 실시간 중합효소 연쇄반응 검사를 시행한다. 그러나 국가별 목표유전자 및 프로토콜이 다를 뿐만 아니라 진단결과의 판독절차도 다양해서 국가별로 확진자의 기준 역시 다르다. 이에 본 종설에서는 세계보건기구에서 고시한 국가별 목표유전자 및 검사기법, 진단기준을 비교하였고, 검사의 특이도와 민감도, 최소검출 한계, 양성 및 음성 대조군, 교차반응 후보군, 검체 대조군 설정 등의 특이사항도 함께 살펴보았다. 또한 각국의 검사기법과 한국의 검사기법의 특징을 고찰하였다. 마지막으로 향후 전세계가 '심각한 급성 호흡기 증후군 코로나 바이러스 2'에 대한 동일한 진단결과를 얻기 위하여 코로나-19 진단에 대한 표준화된 진단방법 및 결과판독 등을 제언하였다.

• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2005년도 춘계학술대회논문집
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• pp.57-60
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• 2005

This paper describes the experimental results of the pre-breakdown phenomena in $SF_6/CO_2$ mixtures under non-uniform electric fields caused by positive and negative lightning negative voltages. $SF_6/CO_2$ mixtures have an advantage of an environmental aspect and cost reduction, and safety aspects. In order to analyze the pre-breakdown processes in $SF_6/CO_2$ mixtures stressed by impulse voltages, pre-breakdown current and luminous signals were measured by a shunt and a photo-multiplier tube, respectively. Dielectric strengthes of $SF_6/CO_2$ mixtures were investigated. Additionally, characteristics of discharge channels were observed by high speed cameras and the physical properties were discussed. The pre-breakdown propagates with a stepwise process. The in to breakdown from the corona onset point in positive polarity was shorter than that in negative polarity. The time intervals of positive leaders are shorter than those of negative leaders, and the path of positive leader channel is zigzag.

• 전자공학회논문지 IE
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• 제44권3호
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• pp.6-11
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• 2007

본 연구는 플라즈마 처리한 고분자 복합재료 표면의 접촉각, X-선광전자분광법(XPS) 및 코로나 대전에 의한 표면 정전특성을 분석하여 발생된 화학적 변화와 정전적 특성 변화를 고찰하여 열화 메커니즘을 도출하였다. 플라즈마 처리된 시료의 접촉각 및 표면전위는 표면에 카르복실기 라디칼을 포함하는 다량의 측쇄화가 집중적으로 발생되어 처리시간에 따라 급격한 친수화가 진행되었다. 플라즈마 처리로 인한 화학적 변화에서 표면에 carboxyl 라디칼이 주로 형성되면서 급격히 표면 친수화로 변화하였다. 정전변화를 분석한 전위감쇠 결과에서 미처리 시료는 부극성 표면을 나타내었으나, 친수화 표면은 carboxyl 라디칼(-COO*)을 포함하는 정극성 라디칼로 인해 정극성 표면으로 변화하여 부극성 전하가 빠르게 감소하였다.

• Journal of Electrical Engineering and Technology
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• 제1권4호
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• pp.528-533
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• 2006

Electrical discharges may occur in gas, liquid as well as solid insulating materials. This paper describes the investigation results on the discharges in air, silicone oil and low density polyethylene (LDPE) using needle plane electrode system under AC voltage of 50 Hz. The experimental results showed that for discharge in air (corona), discharge pulses were concentrated around the peak of applied voltage at negative half cycle. For silicone oil positive as well as negative discharges were observed which concentrated around the peak of applied voltage. The positive pulse number was smaller but the magnitude was higher than that of negative discharge. Discharges in void took place at wider range of phase of applied voltage. The unbalance in pulse number and magnitude similar to that of oil discharges were observed. For electrical treeing in LDPE, the discharges were spread before the zero cross of the applied voltage up to the peak at both positive and negative half cycles. The discharge pulse sequence analysis indicated that the PD occurrence in air, oil and void were strongly affected by the magnitude of applied voltage. However, for electrical treeing it was observed that the discharge occurrence was strongly affected by the time derivative of the applied voltage (dv/dt).

• 한국항공운항학회지
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• 제30권3호
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• pp.65-75
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• 2022

This study tried to confirm whether the public's negative emotions such as fear and anxiety about corona virus infection caused by the spatial nature of the aircraft were alleviated due to factors of in-flight services focusing on hygiene and quarantine and further had a positive effect on the formation of Rapport between cabin crews and passengers. We also investigated the impact on passengers' perceptions such as Reliability and Safety which can be viewed as a new measure and standard of customer satisfaction in the Pandemic era through Rapport. A survey was conducted online in December 2021 for passengers with experience in boarding aircraft after the COVID-19 outbreak, and a total of 211 responses were used for analysis. As a result of the analysis of the data, it was confirmed that aircraft in-flight service had a positive (+) effect on Rapport, and Rapport between passengers and cabin crews had a positive (+) effect on passenger Reliability and Safety.

• Journal of Electrical Engineering and Technology
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• 제5권2호
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• pp.329-336
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• 2010

The paper describes the electrical and optical properties of underwater discharges in highly inhomogeneous electric fields caused by 1.2/50 ${\mu}s$ impulse voltages as functions of the polarity and amplitude of the applied voltage, and various water conductivities. The electric fields are formed by a point-to-plane electrode system. The formation of air bubbles is associated with a thermal process of the water located at the tip of the needle electrode, and streamer coronas can be initiated in the air bubbles and propagated through the test gap with stepped leaders. The fastest streamer channel experiences the final jump across the test gap. The negative streamer channels not only have more branches but are also more widely spread out than the positive streamer channels. The propagation velocity of the positive streamer is much faster than that of the negative one and, in fact, both these velocities are independent of the water conductivity; in addition the time-lag to breakdown is insensitive to water conductivity. The higher the water conductivity the larger the pre-breakdown energy, therefore, the ionic currents do not contribute to the initiation and propagation of the underwater discharges in the test conditions considered.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제50권6호
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• pp.288-295
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• 2001

Predischarges in nonuniform electric field stressed by lightning impulse voltagesin SF(sub)6-$N_2$mixtures are initiated by streamer coronas. Due to field ehnancement at a protrusion point of electrodes new ionization processes occur and a precursor, which leads to a first leader, is created. The leader proceeds step by step to the opposite electrode and the final jump bridges the test gap. It was found that the predischarge is propagated with a leader mechanism of stepwise expansion from the predischarge current waveforms measured by a shunt. The predischarge current is closely related to the amplitude and polarity of applied voltages, the gas pressure and the gap geometry. The time intervals between step leaders for the positive and negative polarities were inversely proportional to V.P$^2$. When the gas pressure increases in the positive polarity, statistical time lag to statistical time lag to streamer corona inception increase slightly, but the formative time lag to flashover is significantly decreased.

• 전자공학회논문지T
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• 제35T권2호
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• pp.66-71
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• 1998

이단식 소형 전기 집진 장치는 작업 환경에서 오존 발생이 극히 적은 정극성 코로나를 널리 사용하고 있지만 이에 관한 과학적 연구보고는 적은 실정이다. 그러므로 이단식 소형전기 집진 장치의 기초 복성에 관하여 연구하였다. 모델 이단식 전기 집진 장치는 이론적 해석이 쉽고 하던부 집진부의 상대 위치를 이동시킬 수 있는 구조로 제작하여 다음의 실험적 결론을 얻었다. 하전부의 코로나 방전은 집진부 전극의 전체 강도에 영향을 받고, 집진부 후방에서의 입자 농도는 집진부의 고압전극과 접지전극 사이에서 크게 변화하고 있다. 집진효율은 집진부의 고압전극 후방이 집진전극 후방보다 높다. 측정 범위의 전 구간에서 입자농도를 적분하여 계산한 종합 접진 효율로부터 하전부의 방전극 바로 뒤에 집진부의 고압전극이 위치하는 구조가 접지전극이 위치하는 구조보다 높은 효율을 보이고 있다. 이것은 하전부와 접진부의 상대적 위치 관계가 집진 효율 특성에 영향을 미치고 있음을 알 수 있다.

• 천문학회지
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• 제36권spc1호
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• pp.37-44
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• 2003

In this paper, we review recent studies on the magnetic helicity changes of solar active regions by photospheric horizontal motions. Recently, Chae(200l) developed a methodology to determine the magnetic helicity change rate via photospheric horizontal motions. We have applied this methodology to four cases: (1) NOAA AR 8100 which has a series of homologous X-ray flares, (2) three active regions which have four eruptive major X-ray flares, (3) NOAA AR 9236 which has three eruptive X-class flares, and (4) NOAA AR 8668 in which a large filament was under formation. As a result, we have found several interesting results. First, the rate of magnetic helicity injection strongly depends on an active region and its evolution. Its mean rate ranges from 4 to $17 {\times} 10^{40}\;Mx^2\;h^{-1}$. Especially when the homologous flares occurred and when the filament was formed, significant rates of magnetic helicity were continuously deposited in the corona via photospheric shear flows. Second, there is a strong positive correlation between the magnetic helicity accumulated during the flaring time interval of the homologous flares in AR 8100 and the GOES X-ray flux integrated over the flaring time. This indicates that the occurrence of a series of homologous flares is physically related to the accumulation of magnetic helicity in the corona by photospheric shearing motions. Third, impulsive helicity variations took place near the flaring times of some strong flares. These impulsive variations whose time scales are less than one hour are attributed to localized velocity kernels around the polarity inversion line. Fourth, considering the filament eruption associated with an X1.8 flare started about 10 minutes before the impulsive variation of the helicity change rate, we suggest that the impulsive helicity variation is not a cause of the eruptive solar flare but its result. Finally, we discuss the physical implications on these results and our future plans.