• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.41.3-42
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• 2016

No matter how intense magnetic flux it contains, a coronal magnetic structure has little free magnetic energy when a composing magnetic field is close to a potential field, or current-free field where no volume electric current flows. What kind of electric current system is developed is therefore a key to evaluating the activity of a coronal magnetic structure. Since the corona is a highly conductive medium, a coronal electric current tends to survive without being dissipated, so the free magnetic energy provided by a coronal electric current is normally hard to release in the corona. This work aims at clarifying how a coronal electric current system is structurally developed into a system responsible for producing a flare. Toward this end, we perform diffusive MHD simulations for the emergence of a magnetic flux tube with different twist applied to it, and go through the process of structuring a coronal electric current in a twisted flux tube emerging to form a coronal magnetic structure. Interestingly, when a strongly twisted flux tube emerges, there spontaneously forms a structure inside the flux tube, where a coronal electric current changes flow pattern from field-aligned dominant to cross-field dominant. We demonstrate that this structure plays a key role in releasing free magnetic energy via rapid dissipation of a coronal electric current, thereby producing a flare.

• Journal of The Korean Astronomical Society
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• v.54 no.5
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• pp.157-170
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• 2021

We investigate flow and magnetic structure of a solar prominence with a focus on how the magnetic field originally determined by subsurface dynamics gives rise to the structure. We perform a magnetohydrodynamic simulation that reproduces the self-consistent evolution of a flow and the magnetic field passing freely through the solar surface. By analyzing Lagrangian displacements of magnetized plasma elements, we demonstrate the flow structure that is naturally incorporated to the magnetic structure of the prominence formed via dynamic interaction between the flow and the magnetic field. Our results explain a diverging flow on a U-loop, a counterclockwise downdraft along a rotating field line, acceleration and deceleration of a downflow along an S-loop, and partial emergence of a W-loop, which may play key roles in determining structural properties of the prominence.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.8
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• pp.34-42
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• 2004

A new polishing technique for three dimensional micro/meso-scale parts is suggested using a micro quill and a magnetic chain structure. The principle of this method is to polish the target surface with the collected magnetic brushes at a micro tool by the non-uniform magnetic field generated around the tool. In a typical magnetic abrasive finishing process magnetic particles and abrasive particles are unbonded each other. But, to finish the three dimensional small parts bonded magnetic abrasive have to be used. Bonded magnetic abrasives are made from direct bonding, and their polishing characteristics are also examined. Alumina, silicon carbide and diamond micro powders are used as abrasives. Base metal matrix is carbonyl iron powder. It is found that bonded magnetic abrasives are superior to unbonded one by experiment. finally, the polished surface roughness is evaluated by atomic force microscope.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.102.1-102.1
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• 2011

In this study we use three-dimensional magnetohydrodynamic simulations to investigate how the dynamic state of emerging magnetic field is related to the twist of field lines. Emerging magnetic field forms a magnetic structure on the Sun where various kinds of activity such as solar flares, jets, and coronal mass ejections are observed. To understand the physical mechanism for producing such activity, we have to know the dynamic nature of this structure. Since flares are the manifestation of rapidly dissipating electric current in the corona, we also investigate the distribution of current density inside the structure and examine how it depends on the field-line twist. To demonstrate the dynamic structure of emerging magnetic field, we focus on the factors characterizing the geometric property and stratification of emerging magnetic field, such as the curvature of field line and the scale height of field strength. These two factors show that emerging field forms a two-part structure in which the central part is close to a force-free state while the outer marginal part is in a fairly dynamic state where magnetic pressure force is dominant. We discuss how the field-line twist affects the two-part structure and also explain a possible relation between electric current structure and sigmoid observed in a preflare phase.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.37-37
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• 2014

Magnetic fields appear to be ubiquitous in astrophysical environments. The existence of magnetic fields in the large-scale structure of the universe has been established through observations of Faraday rotation and synchrotron emission, as well as through recent gamma-ray observations. Yet, the nature and origin of the magnetic fields remains controversial and largely unknown. In this talk, I briefly summarize recent developments in our understanding of the nature and origin of magnetic fields. I also describe a plausible scenario for the origin of the magnetic fields; seed fields were created in the early universe and subsequently amplified during the formation of the large-scale structure of the universe. I then discuss the prospect of observation of magnetic fields in the large-scale structure of the universe.

• Proceedings of the KSR Conference
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• 2005.05a
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• pp.686-691
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• 2005

State of the art and current issues related with the RC and PSC structure system for the magnetic levitation train were investigated. The German and China magnetic levitation train adopted a new kind of a structure to enable high-speed transportation, which allows the use of the space over a ground. The loading from magnetic levitation trains is light-weight compared with a regular train due to load distribution to a supporting structure. Therefore, the magnetic levitation train is considered an economical and efficient transportation system, and is also an environmentally-sustainable structure. In this paper, the structural design and construction technology specific to a magnetic levitation train were discussed, and structural considerations related with an actual operation of the train were pointed out. In addition, the future research area of a magnetic levitation train was proposed

• Applied Science and Convergence Technology
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• v.23 no.3
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• pp.128-133
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• 2014

We study the ballistic spin transport properties in a two-dimensional electron gas system in the presence of magnetic barriers using a transfer matrix method. We concentrate on the size-effect of the magnetic barriers parallel to a two-dimensional electron gas plane. We calculate the transmission probability of the ballistic spin transport in the magnetic barrier structure while varying the width of the magnetic barriers. It is shown that resonant tunneling oscillation is affected by the width and height of the magnetic barriers sensitively as well as by the inter-spacing of the barriers. We also consider the effect of additional electrostatic modulation on the top of the magnetic barriers, which could enhance the current spin polarization. Because all-semiconductor-based devices are free from the resistance mismatch problem, a resonant tunneling structure using the two-dimensional electron gas system with electric-magnetic modulation would play an important role in future spintronics applications. From the results here, we provide information on the physical parameters of a device to produce well-defined spin-polarized current.

• Journal of Magnetics
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• v.2 no.2
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• pp.58-66
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• 1997

Recently, artificially modulated magnetic multilayer materials, for examples giant magnetoresistant magnetic head materials and magneto-optic recording materials in the wavelength of a blue laser beam, attract great attention in the electronics industry due to their unique properties derived from the modulated multilayer structure. Since the multilayer structure as well as amorphous structure, is non-equilibrium state in terms of free energy, an assessment of the thermal staibility in the multilayer structure is crucially importnat both for basic research and applications. In this review paper, effective microscopic interdiffusion process in the two dimensional multilayer structure will be described in terms of steep concentration gradient effect, strain effect and magnetic transition effect.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.1
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• pp.61-68
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• 2017

In this paper, we propose an improved magnetic field shielding structure to reducing the magnetic field generated in the wireless power transfer system operating at a low frequency band. The proposed structure consists of the magnetic material and the conductive material, magnetic field cancelling effect for power transfer is minimized while improving the leakage magnetic field cancelling effect by optimizing the various design parameters in the proposed structure. We analyzed and verified the efficiency of the wireless power transfer system and the reduction effect of the leakage magnetic field through computer simulation and measurement. Analysis results show that power transfer efficiency of the wireless power transfer system utilizing the proposed structure is 77 %, which is maintained at the conventional power transfer efficiency. In addition, compared with the structure maintaining high power transfer efficiency, leakage magnetic field strength is reduced to 29~37 % at the nearest point.

• Journal of Magnetics
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• v.2 no.4
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• pp.147-156
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• 1997

An artificially modulated magnetic Co/Pd multilayer is one of the promising candidates for high density magneto-optic (MO) recording media, due to a large Kerr rotation angle in the wavelength of a blue laser beam. However, since multilayer structure, as well as amorphous structure, is a non-equilibrium state in terms of free energy and a MO recording technology is a kind of thermal recording which is conducted around Curie temperature (Tc) of the recording media, when the Co/Pd mulilayer is used for the MO recording media, changes in the magnetic properties are occurred as the amorphous structure do. Therefore, the assessment of the magnetic properties in the Co/Pd multilayer during interdiffusion is crucially important both for basic research and applications. As the parameter of the magnetic properties in this research, saturation magnetization and perpendicular magnetic anisotropy energy of the Co/Pd multilayer are measured in terms of Ar sputtering pressure and heat treatment temperature. Form the results of the research, we find out that the magnetic exchange energy between Co and Pd sublayers strongly affects the changes in the magnetic properties of the Co/Pd multilayers during the interdiffusion in ferromagnetic state. This discovery will provide the understanding of the magnetic exchange energy in the Co/Pd multilayer structure and suggest the operating temperature range for MO recording in the Co/Pd multilayer for the basic research and applications, respectively.