• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.86.1-86.1
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• 2013

Observations of a filament showing an activated barb recorded from the at the Dutch Open Telescope (DOT) on 2010 August 20 are presented. The filament developed a barb in 10 minutes, which disappeared within the next 35 minutes. Such a rapid formation and disappearance of a filament barb is unusual, and has been seldom reported. Line-of-sight velocity maps were constructed from images in seven line positions along the H-alpha line. We observe flows in the filament spine towards the barb location prior to its formation, and flows in the barb towards the spine during its disappearance. Photospheric magnetograms from Helioseismic Magnetic Imager on board the Solar Dynamics Observatory were used to determine the changes in magnetic flux in the region surrounding the barb location. The variation of magnetic flux in this duration support the view that barbs are rooted in minor magnetic polarity.

• Economic and Environmental Geology
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• v.33 no.3
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• pp.217-228
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• 2000

We use spectral correlation method to analyze gravity and magnetic anomalies of Euiseong Sub-basin for distribution of rock facies and gelogic structures. The analysis reveals distinct polarity between gravity and magnetic anomaly correlation ; intermediate to mafic intrusives, extrusives, and the Tertiary basin shows positive gravity (+G) and positive magnetic (+M) correlation. Granitic gneiss and felsic volcanics negative gravity 9-G) and negative magnetic (-M) correlation. The Palgongsan granite, felsic to mafic extrusives and Mesozoic granites are characterized by -G and + M correlation. +G and -M correlations in the sedimentary formations are interpreted by uplift of pre-Cretaceous basement rocks . The + G and + M correlation characteristics in northeastern part of Euiseong Sub-basin including the Tertiary sedimentary basin result from the uplift of crustal materials. Major axes of spectrally correlated amomalies have mostly NW-SE or NE-SW directions. The former is due to the intrusives along strike-slip faults, and the latter which is observed in sedimentary formations is related to geological structures of basement associated new insight into the boundary between Euiseong and Milyang Sub-basin.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.83.2-83.2
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• 2011

The emergence of a magnetic flux tube (flux emergence) is a process of transporting magnetic field from the solar interior to the atmosphere. This process naturally produces bipolar structure at the surface, in which emerging field lines simply connect opposite polarities, while observations suggest that the surface distribution of magnetic field is more complicated than a simple bipole. This study is aimed at solving this apparent mismatch between the model and observations, showing how the surface distribution changes from a simple bipolar distribution to a quadrupolar-like one, where a half-turn rotation of the polarity inversion line plays an important role. We explain the physical reason of this half-turn rotation and also discuss a possible configuration of filament magnetic field in terms of the quadrupolar-like structure formed via flux emergence.

• Bulletin of the Korean Space Science Society
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• 2010.04a
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• pp.41.1-41.1
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• 2010

A bipolar magnetic field perturbation in the meridional plane was observed when the Polar spacecraft crossed the plasmapause near the midnight, which was identified by a clear jump in density and temperature, from the plasmasheet to the plasmasphere. The bipolar variation shows a negative-then-positive polarity. To examine the bipolar magnetic field perturbation at the plasmapause, we assume one-dimensional model with physical quantities varying along a direction normal to the plasmapause and employ two-fluid approach for the tangential plasmapause. That is, the magnetic fields on both sides are parallel. Considering Ampere's law and pressure balance relation, we have a perturbed magnetic field, which is consistent with the observation at the plasmapause.

• Journal of Astronomy and Space Sciences
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• v.28 no.2
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• pp.123-132
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• 2011

It is generally believed that the occurrence of a magnetic storm depends upon the solar wind conditions, particularly the southward interplanetary magnetic field (IMF) component. To understand the relationship between solar wind parameters and magnetic storms, variations in magnetic field polarity and solar wind parameters during magnetic storms are examined. A total of 156 storms during the period of 1997~2003 are used. According to the interplanetary driver, magnetic storms are divided into three types, which are coronal mass ejection (CME)-driven storms, co-rotating interaction region (CIR)-driven storms, and complicated type storms. Complicated types were not included in this study. For this purpose, the manner in which the direction change of IMF $B_y$ and $B_z$ components (in geocentric solar magnetospheric coordinate system coordinate) during the main phase is related with the development of the storm is examined. The time-integrated solar wind parameters are compared with the time-integrated disturbance storm time (Dst) index during the main phase of each magnetic storm. The time lag with the storm size is also investigated. Some results are worth noting: CME-driven storms, under steady conditions of $B_z$ < 0, represent more than half of the storms in number. That is, it is found that the average number of storms for negative sign of IMF $B_z$ (T1~T4) is high, at 56.4%, 53.0%, and 63.7% in each storm category, respectively. However, for the CIR-driven storms, the percentage of moderate storms is only 29.2%, while the number of intense storms is more than half (60.0%) under the $B_z$ < 0 condition. It is found that the correlation is highest between the time-integrated IMF $B_z$ and the time-integrated Dst index for the CME-driven storms. On the other hand, for the CIR-driven storms, a high correlation is found, with the correlation coefficient being 0.93, between time-integrated Dst index and time-integrated solar wind speed, while a low correlation, 0.51, is found between timeintegrated $B_z$ and time-integrated Dst index. The relationship between storm size and time lag in terms of hours from $B_z$ minimum to Dst minimum values is investigated. For the CME-driven storms, time lag of 26% of moderate storms is one hour, whereas time lag of 33% of moderate storms is two hours for the CIR-driven storms. The average values of solar wind parameters for the CME and CIR-driven storms are also examined. The average values of ${\mid}Dst_{min}{\mid}$ and ${\mid}B_{zmin}{\mid}$ for the CME-driven storms are higher than those of CIR-driven storms, while the average value of temperature is lower.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.38.2-38.2
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• 2012

We use two-dimensional high-resolution MHD simulations to investigate the effects of magnetic fields on the formation and evolution of such substructures as well as on the mass inflow rates to the galaxy center. We find that there exists an outermost x1-orbit relative to which gaseous responses to an imposed stellar bar potential are completely different between inside and outside. Inside this orbit, gas is shocked into dust lanes and infalls to form a nuclear ring. Magnetic fields are compressed in dust lanes, reducing their peak density. Magnetic stress removes further angular momentum of the gas at the shocks and leads to a smaller and more centrally distributed ring, resulting in the mass inflow rates larger, by more than two orders of magnitude, than in the unmagnetized counterparts. Outside the outermost x1-orbit, on the other hand, an MHD dynamo operates near the corotation and bar-end regions, efficiently amplifying magnetic fields. The amplified fields shape into trailing magnetic arms with strong fields and low density. The base of the magnetic arms have a thin layer in which magnetic fields with opposite polarity reconnect via a tearing-mode instability. This produces numerous magnetic islands with large density which propagate along the arms to turn the outer disk into a highly chaotic state.

• Ocean and Polar Research
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• v.24 no.3
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• pp.197-205
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• 2002

Total magnetic field and high-resolution bathymetric data were collected over nine seamounts to the northwest of the Marshall Islands in the western Pacific. Magnetic parameters including inclination and declination were calculated from the magnetic anomalies using inversion algorithm of Plouff (1976), and a corresponding paleomagnetic pole was determined with the magnetic parameters. The paleomagnetic poles determined in this study were compared with the previous apparent polar wander path (APWP) of Pacific plate. Most seamounts of the study area have normal polarity. The study reveals that all nine seamounts in the study area formed in the southern hemisphere during the Cretaceous based on their comparison with the APWP of Pacific plate. The ages estimated from paleomagnetic poles can be divided by age into three groups: the oldest (OSM1 and OSM3), middle age (OSM2, OSM4, and 6-2), and the youngest (OSM5-1, 5-2, 5-3, and 6-1). The fermer two groups and the latter seem to be coincident with two distinct pulses of Cretaceous volcanic activity (115-90 Ma and 83-65 Ma). As a whole the seamounts at southwest of the study area are older than at those northeast.

• The Transactions of the Korean Institute of Power Electronics
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• v.23 no.1
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• pp.72-75
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• 2018

An initial rotor position estimation method is proposed in this study for an interior permanent-magnet synchronous motor without a resolver or an absolute encoder. This method uses least squares approximation to estimate the initial rotor position. The magnetic polarity is identified by injection of short pulses. The proposed estimation process is robust because it does not require complex signal processing that depends on the performance of a digital filter. In addition, it can be applied to various servo systems because it does not require additional hardware. Experimental results validate the effectiveness of the proposed method using a standard industrial servomotor with interior-permanent magnets.

• 한국지구물리탐사학회:학술대회논문집
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• 2007.06a
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• pp.273-278
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• 2007

2-D MT surveys at the Century mine in Australia have been performed with very far remote reference in Esashi, Japan as well as Gregory Downs, which are roughly 6400 km and 80 km apart from the field site, respectively. Long period pulsations observed in this survey generally showed dominant $H_x$ polarization than $H_y$; $H_x$ component is more than 3 times stronger than $H_y$ component. Polarity reversal in magnetic field pointing east ($H_y$ component) has also been observed in long period pulsations, while $H_x$ component remain coherent between the hemispheres. Though $H_x$ component shows relatively good coherency than $H_y$ component between the hemispheres at frequencies lower than 0.01 Hz, it seems rather too far to be used as a remote reference for ordinary MT frequency band.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.21 no.10
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• pp.40-45
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• 2007

Lightning warning system plays an important role in protecting human life and other facilities from lightning return strokes. This paper dealt with lightning positioning algorithms and circuits as a main function of lightning warning system, which monitor movements and activities of thunderclouds. Electric field component produced by lightning discharge is detected by the configuration of a whip antenna and a narrow-band resonance amplifier with center frequency of 300[kHz]. Measurement circuit of magnetic field waveform consists of a crossed-loop coil and an integral amplifier, and its frequency bandwidth is ranges from 5[kHz] to 1.2[MHz]. The polarity of lightning discharge is discriminated by electric field component. After-fixing the polarity, we can calculate the direction and distance of lightning discharge by the peak and the zero-cross time of magnetic field waveform.