• 천문학회보
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• 제43권1호
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• pp.52.1-52.1
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• 2018

We investigate initial Fe/O enhancements for 44 large gradual solar energetic particles events from 2010 to 2014 and examine the associations of the Fe/O enhancements with the structures of the heliospheric current sheet (HCS). For this study, we use STEREO SIT Fe and O data in 0.32-0.45 MeV channel as well as ACE ULEIS Fe and O data in 0.32-0.64 MeV channel. We determine 1) the magnetic polarities of the SEP source regions using the potential field source surface (PFSS) model of the coronal field and 2) the spacecraft magnetic footpoints with Parker spiral approximation of interplanetary magnetic field using the in-situ measurements of STEREO and ACE. We find that 29 out of 44 events have initial Fe/O enhanced more than 5 times of the typical gradual event values. In the 6 events, the enhancements are simultaneously observed by two spacecraft. There is a tendency that the high Fe/O enhancements are observed near SEP source regions. It is also noted that the Fe/O enhancements are associated with the polarity of the magnetic footpoints. The high Fe/O enhancements are usually observed where their footpoints lie in the same polarity regions of SEP sources rather than the opposite polarity regions. Although Fe/O enhancements could be due to a transport effect and/or a flare contribution, our result implies that the structure of HCS is likely to affect particle propagations in the interplanetary space.

• 한국전기전자재료학회논문지
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• 제23권2호
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• pp.159-163
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• 2010

The superconducting fault current limiter (SFCL) plays a role in compensating the voltage sag of the sound feeder adjacent to the fault feeder as well as the fault current limiting operation of the fault feeder. Especially, the SFCL using magnetic coupling of two coils with parallel connection has different voltage sag compensating and current limiting characteristics due to the winding direction and the inductance ratio of two coils. In this paper, the current limiting and the voltage sag compensating characteristics of a SFCL using magnetic coupling of parallel connected two coils were analyzed. Through the analysis on the experimental results considering the winding direction of two coils, the SFCL designed with the additive polarity winding was shown to have the higher limited fault current than the SFCL designed with the subtractive polarity winding. In addition, it could be confirmed that the higher fault current limitation of the SFCL could be contributed to the higher load voltage sag compensation.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 하계학술대회 논문집
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• pp.86-88
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• 2002

The relationship between electrical properties of superconductor and externally allied magnetic field was studied to develop a magnetic field polarity sensor. The behavior was related to the magnetic flux trapped in the superconductor, which penetrates through the material by the external magnetic field. Electrical characteristics of the superconductor with trapped magnetic flux were extremely sensitive ta the external magnetic field and showed different responses depending on the direction of the magnetic field. Considering the observed properties of the superconductor with trapped magnetic flux, a magnetic sensor was fabricated to detect simultaneously both the intensity and the direction of the magnetic field.

• Journal of Astronomy and Space Sciences
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• 제31권2호
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• pp.145-148
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• 2014

There was a research on the prolongation of solar cycle 23 by the solar cyclic variation of solar, interplanetary geomagnetic parameters by Oh & Kim (2013). They also suggested that the sunspot number cannot typically explain the variation of total solar irradiance any more. Instead of the sunspot number, a new index is introduced to explain the degree of solar activity. We have analyzed the frequency of sunspot appearance, the length of solar cycle, and the rise time to a solar maximum as the characteristics of solar cycle. Then, we have examined the predictability of solar activity by the characteristics of preceding solar cycle. We have also investigated the hemispheric variation of flare index for the periods that the leading sunspot has the same magnetic polarity. As a result, it was found that there was a good correlation between the length of preceding solar cycle and spotless days. When the length of preceding solar cycle gets longer, the spotless days increase. It is also shown that the shorter rise time to a solar maximum is highly correlated with the increase of sunspots at a solar maximum. Therefore, the appearance frequency of spotless days and the length of solar cycle are more significant than the general sunspot number as an index of declining solar activity. Additionally, the activity of flares leads in the northern hemisphere and is stronger in the hemisphere with leading sunspots in positive polarity than in the hemisphere with leading sunspots in negative polarity. This result suggests that it is necessary to analyze the magnetic polarity's effect on the flares and to interpret the period from the solar maximum to solar maximum as the definition of solar cycle.

• Journal of Advanced Marine Engineering and Technology
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• 제38권9호
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• pp.1146-1149
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• 2014

단자 표식이 불분명한 3상유도전동기에서 고정자 권선의 극성을 판별하는 데는 외부 여자전류에 의해 유도되는 기전력 특성에 기초하거나 또는 회전자의 잔류자기를 이용하는 방법이 가능하다. 회전자의 잔류자기로 유도되는 권선에서의 기전력은 자속 크기와 수동 구동의 회전자 속도 및 위상 관계에 따라 정해지며 이 같은 극성 판별이 작업현장에서 가능하려면 기전력의 크기가 멀티테스터로 확인될 수 있는 정도이어야 하고 또한, 코일 간 위상 특성이 극성 판별에 적합해야 한다. 잔류자기에 의한 기전력들이 3상 평형 관계에 있다면 전체 합성 전압은 권선들의 극성 연결 상태가 정상일 때 0이 되어야 하는 한편, 극성 연결의 오류 시에는 상대적으로 큰 출력 전압을 나타낸다는 점에서 본 연구에서는 각 경우에 대한 특성을 분석하였다. 또한, 잔류자기에 의한 판별 방식을 실험용 전동기에 적용하여 극성의 정상 및 이상 상태에서의 출력 파형을 비교함으로써 제시된 방식이 극성 판별 방법으로서 현장에서 용이하게 활용될 수 있는지를 확인한다.

• 자원환경지질
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• 제40권2호
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• pp.153-170
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• 2007

중력자료 및 자력자료를 이용하여 독도해산들의 지각평형 탄성판모델 및 VGP(Virtual Geomagnetic Pole)를 분석하여 해산들의 형성시기와 형성환경을 연구하였다. 후리에어중력이상은 독도와 이사부해산 최고치 사이에 약 50 mGal의 차이를 보이는데 이 두 화산체는 규모면에서 비슷하지만 후리에어중력이상에서 차이가 나는 것은 보상정도의 차이에 기인한다. 탄성판모델의 적용 결과는 해산 하부 지각의 강도(탄성두께)가 이사부해산에서 독도로 갈수록 강해짐(두꺼워짐)을 지시한다. 즉, 이사부해산이 생성될 당시의 해산 하부 지각의 연령이 가장 젊었고 독도가 생성될 때 하부 지각이 가장 오래 되었다는 것을 나타낸다. 자기이상은 독도해산들을 중심으로 복잡하게 나타난다. 고지자기 특성을 연구하기 위하여 자기 이상을 1500m 상향연속한 후 최소자승자화법 및 반놈자화법을 함께 이용하여 각 독도해산들의 VGP를 구하였다. 기존 독도암석의 연대측정, 탄성판 모델 및 VGP결과를 지자기 연대표와 비교하여 보면 울릉분지의 열개 종료 후에 이사부해산이 정자기극 시대에 가장 먼저 생성되었고 독도은 가장 후기에 생성되었으며 정자기극 시대에 첫 번째 대규모 분출이 있었고 그 후 역자기극 시대에 두 번째 대규모의 분출로 인하여 이루어졌을 것으로 생각된다. 심흥택 해산은 독도와 이사부해산의 생성시기 사이의 정자기극 시대에 형성되었을 것으로 사료된다. 이 해산들의 생성 시기는 동해 생성 후 압축응력이 작용하던 시기와 일치하며 이 압축력 시기의 화산활동에 의해 해산들이 생성되었을 가능성이 높은 것으로 판단된다.

• 한국전기전자재료학회논문지
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• 제24권2호
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• pp.141-146
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• 2011

When the current of the superconducting element exceeds its critical current by the fault occurrence, the quench of the high-$T_C$ superconducting fault current limiter (HTSC) comprising the flux-lock type superconducting fault current limiter (SFCL) occurs. Simultaneously, the magnetic flux in the iron core induces the voltage in each coil, which contributes to limit the fault current. In this paper, the fault current limiting characteristics of the flux-lock type SFCL as well as the load voltage sag suppressing characteristics according to the flux-lock type SFCL's winding direction were investigated. To confirm the fault current limiting and the voltage sag suppressing characteristics of the this SFCL, the short-circuit tests for the simulated power system with the flux-lock type SFCL were carried out. The flux-lock type SFCL designed with the additive polarity winding was shown to perform more effective fault current limiting and load voltage sag suppressing operations through the fast quench occurrence right after the fault occurs and the fast recovery operation after the fault removes than the flux-lock type SFCL designed with the subtractive polarity winding.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2008년도 한국우주과학회보 제17권2호
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• pp.25.2-25.2
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• 2008

Polar rain is a spatially uniform precipitation of electrons with energies around 100eV that penetrate into the polar cap region where geomagnetic field lines are connected to the Interplanetary Magnetic Fields (IMF). Since their occurrences depend on the IMF sector polarity, they are believed to originate from the field aligned component of the solar wind. However, statistically direct correlation between polar rain and solar wind has not been shown. In this presentation, we examined specifically the IMF strength influence on the polar rain flux variation by classifying of IMF sector polarities. For this study, we employed the polar rain flux data measured by STSAT-1 and compared them with the solar wind parameters obtained from the WIND and ACE satellites. We found the direct mutuality between polar rain flux and IMF strength with correlation coefficient above 0.5. This proportional tendency appears stronger when the northern hemisphere is in the away sector of the IMF, which could be associated with a favorable geometry for magnetic reconnection. Simple particle trajectory simulation clearly shows why polar rain intensity depends on the IMF sector polarity. These results are consistent with the direct entry model of Fairfield et al.(1985), while low correlation coefficient with solar wind density, the similarity between slops of both energy spectra shows that transport process occur without acceleration.

• 천문학회보
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• 제37권2호
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• pp.113.2-113.2
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• 2012

An innovative solar observing satellite, Hinode, has successfully observed the detailed evolution of a rapidly developing emerging flux region from the beginning of its appearance at the solar surface. The high spatial and temporal resolution provided by the satellite enables to capture the prominent dynamic processes such as the rotational motion of a polarity region with intense magnetic flux which is reminiscent of a cyclone on the Earth, and a running wave that spreads ahead of this rotating polarity region. This 'solar cyclone' is, on the other hand, generated differently from terrestrial cyclones, and a possible generating mechanism for it is demonstrated with a three-dimensional magnetohydrodynamic simulation of a twisted magnetic flux tube emerging from the solar interior into the solar atmosphere. The simulation shows that the rotational motion is caused by a strong downflow of plasma along the twisted field lines that form a helical pillar standing upright on the Sun.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제54권6호
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• pp.262-268
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• 2005

In this work, to obtain the detailed information about lightning electromagnetic field waveforms, the LabVIEW based-measurement system of time-changing magnetic fields was designed and constructed. The frequency bandwidth of the magnetic field measuring system ranges from 300 [Hz] to 1 [MHz], and the response sensitivity is 2.78 [mV/nT]. Data acquisition system with the resolution of 12 bits and memory capacity of 32 [Mbyte] was triggered by the magnetic field to be measured. The properties and parameters of the magnetic fields produced by cloud discharges were statistically investigated. The magnetic field waveforms radiated from cloud lighting discharges tend to be bipolar, with two or more narrow and several pulses superimposed on the initial front part. The recording length of the magnetic field measurement system is about 10 [ms]. The mean duration of cloud discharges is 1.3 [ms], and the number of outburst pulses for the period is 8 in average. The front times of the magnetic fields are 6.15 [$\mu$s] in average. The the zero-to-zero crossing times that is the initial half-cycle duration is widely dispersed and the mean value is 9.61 [$\mu$s], and the mean value of percentage depth of dip to opposite polarity is 41.1 [$\%$].