• Journal of Navigation and Port Research
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• v.28 no.2
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• pp.141-148
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• 2004

The observations of rapid motion of bubbles under water for approximately 50ms or less in high . magnetic fields of 10 T have been carried out successfully for the first time. The observation system constructed is composed of a high-speed video camera, a telescope, a cryostat with a split-type superconducting magnet, a light source, a mirror and a transparent sample cell. Using this system, the influence of magnetic field on the path and shape of single bubbles of $O_2$(paramagnetism) and $N_2$ (diamagnetism) has been examined carefully. Experimental values describing the path are in good agreement with theoretical values calculated on the basis of the magneto-Archimedes effect, despite the effect of magnetism on the bubble. However, no effect of magnetism on the shape of the bubble is observed In addition, the influence of magnetic field on drag coefficient of the bubble is discussed.

• Transactions on Electrical and Electronic Materials
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• v.1 no.3
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• pp.29-33
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• 2000

The crystallographic and high frequency characteristics of $Fe_{73.9}Cu_{1.0}Nb_{3.5}Si_{14.0}B_{7.6}$ soft magnetic alloys were investigated under magnetic field annealing, The crystallization fraction of annealed samples with longitudinal magnetic fields is higher than that of samples without magnetic field. When the transverse magnetic field is applied, the crystallization fraction does not increases but decreases until $500^{circ}C$. It is found that for samples, the saturation induction are all same with 1.3 T. The coercive field of as-cast samples is 1.03 A/cm, but in annealed samples it decrease from 0.56 to 0.1A/cm with increasing annealing temperature from 400 to $550^{circ}C$. The squareness of annealed samples under transverse magnetic field has a small value than that of both without field and with longitudinal field annealing. It is noted that the magnetic field annealing with transverse direction to amorphous $Fe_{73.9}Cu_{1.0}Nb_{3.5}Si_{14.0}B_{7.6}$ profoundly influenced on the Mossbauer spectra in contrast to that with longitudinal direction and without magnetic field.

• Proceedings of the KIEE Conference
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• 1997.11a
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• pp.19-21
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• 1997

This paper treated a new method that generates the dipole magnetic field for high speed machines by using Halbach array, which was suggested by Klaus Halbach. The Halbach array can produce the various field distribution without magnetic materials. Therefore, the iron losses can be reduced. This paper presented the magnetic characteristics on both linear and cylindrical Halbach array. And the Halbach array for dipole field was manufactured with Nd-Fe-B magnets having 1.17(T), the measured flux density was compared the theoretical values acquired by three dimensional FEM analysis. Finally, the magnetic characteristics of Halbach array were compared with those of other conventional dipole field systems.

• Proceedings of the KIEE Conference
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• 1989.11a
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• pp.87-90
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• 1989

The force acting on high Tc superconductors at 77K is measured and analyzed numerically. Both values are compared, and the difference between them is discussed. The forces, acting on a superconducting disk (thickness:1[mm], diameter:12[mm]) in an axially-symmetric magnetic field produced by a solenoid or a permanent magnet ring, are measured at 77K. The disk is an YBCO high Tc superconductor. The discrete surface current method(DSCM) is formalized for an axially-symmetric magnetic field. The forces of the superconducting disk in the magnetic field are analyzed using the DSCM, assuming that the disk is a perfect diamagnetic body. When the bottom side of the disk is separated 8[mm] from the top side of the solenoid, and the magnetic field applied on the center of the bottom side of the disk is 96[G], the measured value and the calculated value of the force are 96 and 496[mgf], respectively. The difference between them is caused by a non-perfect diamagnetism of the high Tc superconductor at 77K. It is proposed that a real force acting on high Tc superconductors at 77K can be estimated on the basis of a measured magnetic susceptibility of the high Tc superconductor at 77K and a calculated force of a perfect diamagnetic body.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.67.2-67.2
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• 2018

Magnetic fields play an important role in star-forming processes by regulating gravitational collapse. In filamentary structures of star-forming regions, magnetic fields are likely to be aligned with minor axes of filamentary molecular clouds because matter freely moves along magnetic field lines. Orion A region, one of the well-known high-mass star forming regions, has long filament structure. In order to study magnetic field directions with respect to the filamentary structure in Orion A, we have analyzed $850{\mu}m$ dust polarization observations obtained with the James Clerk Maxwell Telescope (JCMT). We found tight correlation of dust intensity gradients and magnetic field directions. It was estimated that 81% of magnetic field segments are aligned with density gradients within 40 degree. In conclusion, we confirmed most of magnetic field segments are perpendicular to the major axis of the filament in Orion A.

• Journal of the Korean Magnetic Resonance Society
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• v.21 no.1
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• pp.7-12
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• 2017

The nuclear magnetic resonance (NMR) and atomic magnetic resonance (AMR) plays a fundamental role in achieving a high accuracy of magnetic field measurements. Magnetic field unit (T) was realized based on the shielded proton gyromagnetic ratio (${\gamma}^{\prime}_P$), helium-4 gyromagnetic ratio (${\gamma}_{4He}$) and related techniques. The magnetic field standard system has been disseminated by the NMR magnetometer and electromagnet, a Helmholtz coil system, and AMR magnetometer in the nonmagnetic laboratory. A magnetic field standard below 1 mT has been developed by using Cs and Cs- $^4He$ AMR with automatic compensation of an external magnetic field noise. The standards serve for the calibration of magnetometers and support the test of sensors and materials in the range from $5{\mu}T$ to 2.0 T with (1 to 50) ${\mu}T/T$ uncertainty (k=2).

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.52 no.3
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• pp.130-136
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• 2003

Crowbar system Vacuum switches, widely used In a pulsed power system, could use the magnetic force to prevent the electrode damage. Vacuum switches using the magnetic forces are classified roughly into RMF(Radial Magnetic Field) and AMF(Axial Magnetic Field) type. The RMF type switches restrain a main electrode from aging due to high temperature and high density arc by rotating the arc which is driven by the Lorenz force. The AMF type switches generate axial magnetic field which decreases the electrode damage by diffusing arc. In this paper, we present the energy loss characteristics of both RMF and AMF type switches which are made of CuCr(75:25 wt%) electrodes. The time-dependent dynamic arc resistance of high-current pulsed discharge in a high vacuum chamber(~10$^{-6}$ Torr). which occurs in RMF and AMF type switches, was obtained by solving the circuit equation using the measured values of the arc voltage and current. In addition, we compared energy loss characteristics of both switches. Based on our results, it was found that the arc voltage and the energy loss of an AMF type switch are lower than a RMF type switch.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1995.05a
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• pp.124-128
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• 1995

We have fabricated the vacuum magnetic device with a lateral field emitter arrays constructed on n-Si wafer, and investigated its magnetic characteristics. The device is consited to tip-arrayed emitter. gate and split-anode, The fabricated vacuum magnetic device has showed a good linearity of magnetic field and a high sensitivity compared with the conventional semiconductor magnetic device.

• Progress in Superconductivity and Cryogenics
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• v.23 no.4
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• pp.30-34
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• 2021

Superconducting magnets have paved the way for opening new horizons in designing an electromagnet of a high field magnetic resonance imaging (MRI) device. In the first phase of the superconducting MRI magnet era, low-temperature superconductor (LTS) has played a key role in constructing the main magnet of an MRI device. The highest magnetic resonance (MR) field of 11.7 T was indeed reached using LTS, which is generated by the well-known Iseult project. However, as the limit of current carrying capacity and mechanical robustness under a high field environment is revealed, it is widely believed that commercial LTS wires would be challenging to manufacture a high field (>10 T) MRI magnet. As a result, high-temperature superconductor together with the conducting cooling approach has been spotlighted as a promising alternative to the conventional LTS. In 2020, the Korean government launched a national project to develop an HTS magnet for a high field MRI magnet as an extent of this interest. We have performed a design study of a 7 T 320 mm winding bore HTS MRI magnet, which may be the ultimate goal of this project. Thus, in this paper, design study results are provided. Electromagnetic design and analysis were performed considering the requirements of central magnetic field and spatial field uniformity.

• Progress in Superconductivity and Cryogenics
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• v.14 no.3
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• pp.5-8
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• 2012

Superconducting windings of synchronous machine have to be operated in below the critical temperature, critical current density and critical magnetic field. If one of these characteristics does not satisfied, then the quench occurred in superconducting winding. Especially the armature current dramatically increased as the superconducting generator is short-circuited at the rated load condition and magnetic field in field winding increased due to the armature current. Therefore, damper is required to reduce the magnetic field of field winding which increases reliability of the superconducting generator. Damper dimension can be decided by time constant[1-2]. In this paper the basic model is high-power and low-speed superconducting generator. Damper time constant was calculated from the changed damper thickness and material. Magnetic flux of field coil at the basic model and changed damper time constant model is analyzed.