• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.70.3-70.3
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• 2019

We present a method to estimate 3-component plasma velocity (Vx, Vy and Vz) at solar photosphere near solar disk center, using the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) called Space-weather HMI Active Region Patch (SHARP). In Heliocentric-Cartesian Coordinates, the component of Vz is obtained from Dopplergram while the components of Vx and Vy are derived from the relation of $B_z{\overrightarrow{u}}=B_z{\overrightarrow{{\nu}_t}}-{\nu}_z{\overrightarrow{B_t}}$ (Demoulin & Berger 2003) using a series of vector magnetograms by an optical flow technique NAVE (Nonlinear Affine Velocity Estimator). This velocity measurement method is applied to AR 12158 producing an X1.6 flare along with a coronal mass ejection. We find noticeable upflow motions at both ends of flux ropes which become a major eruption part, and strong transverse motions nearby them before the eruption. We will discuss the change of plasma motions and magnetic fields before and after the eruption.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.5 no.1
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• pp.27-32
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• 1996

This paper deals with the distributions of magnetic flux of an electro-magnetic chuck which is one of the most commonly used chucking attachments in a surface grinding machine. The measured results showed good correspondence with the theoretical results which were previously presented by the same author. The normal and tangential components of the magnetic flux density were measured using the gauss meter. The measured results indicated that the magnetic flux density was periodically changing over the transverse position to the magnetic pole. The normal component of magnetic flux decreases very rapidly for the increased z position.

• Journal of The Korean Astronomical Society
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• v.39 no.4
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• pp.129-138
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• 2006

A period study of the semi-detached eclipsing binary system W Delphini based on the extensive series of minimum timings covering more than a century(109 years) indicates a cyclic(O-C) variation of the system. This variation can be explained as due either to (1) stellar magnetic activity cycles of the cool subgiant G5 secondary component of the binary with a subsurface magnetic field equals to 3 kG, or (2) a long-term orbital period increases with a rate of $1.68{\times}10^{-8}$ day/cycle caused by a mass transfer rate of $4.9{\times}10^{-8}M_{\odot}yr^{-1}$ from the less to more massive component modulated by a light time effect due to a hypothetical third body with period of $53.4{\pm}1.06$ years. The former explanation is more recommended than the later one since the obtained third body mass value($M_3=1.58\;M_{\odot}$) is quite large but it can not manifest itself observationally and also it cannot be a white dwarf. In the contrary, from the magnetic activity point of view, the obtained characteristics are in good consistent when applying Applegate(1992) mechanism. However, further precise photometric and CCD observations for minima timings with brightness determinations are needed to confirm the present solution.

• Journal of Power Electronics
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• v.14 no.5
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• pp.815-826
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• 2014

An improved bridgeless interleaved boost power factor correction (PFC) rectifier to improve power efficiency and component utilization is proposed in this study. With combined conventional bridgeless PFC circuit and interleaved technology, the proposed rectifier consists of two interleaved and magnetic inter-coupling boost bridgeless converter cells. Each cell operates alternatively in the critical conduction mode, which can achieve the soft-switching characteristics of the switches and increase power capacity. Auxiliary blocking diodes are employed to eliminate undesired circulating loops and reduce current-sensing noise, which are among the serious drawbacks of a dual-boost PFC rectifier. Magnetic component utilization is improved by symmetrically coupling two inductors on a unique core, which can achieve independence from each other based on the auxiliary diodes. Through the interleaved approach, each switch can operate in the whole line cycle. A simple control scheme is employed in the circuit by using a conventional interleaved controller. The operation principle and theoretical analysis of the converter are presented. A 600 W experimental prototype is built to verify the theoretical analysis and feasibility of the proposed rectifier. System efficiency reaches 97.3% with low total harmonic distortion at full load.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.2
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• pp.282-288
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• 2007

Magnetization loss of high temperature superconductoring BSCCO tape and YBCO coated conductor(YBCOCC) is most important issue in the development of superconducting power devices. In this paper, the measured results of magnetization losses under various angles of external magnetic field in BSCCO tape stacked conductors and YBCO CC stacked conductors are presented and compared with each other. Also, we present the compared results of magnetization losses measured at arbitrary reaction magnetic fields and analyzed with perpendicular magnetic field components of those. The results show that magnetization losses of YBCO CC single and stacked conductors agree well with the analyzed value by it's perpendicular magnetic field component, but BSCCO single and stacked conductors are not.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1994.05a
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• pp.63-66
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• 1994

This paper describes the developed sensor for measuring the time-varying magnetic fields and presents the characteristics of the magnetic fields and presents the characteristics of the magnetic field generated by lighting a fluorescent lamp. The frequency bandwidth of magnetic field measurement system is kknown as 40 Hz∼100 kHz by means of calibration experiment. The magnetic field waveform which originates from the various lighting systems was measured and the frequency components were analyzed by fast Fourier transformation technique. The magnetic field generated during the operation of the fluorescent lamp mainly includes the odd harmonics, and in the case\ulcorner of push button switch and high frequency starter types the fast transient component is occurred in an instant of lighting.

• Current Applied Physics
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• v.18 no.11
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• pp.1196-1200
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• 2018

We have experimentally demonstrated circular polarization generation from linear polarized soft X-ray at synchrotron by adopting a thin magnetic film polarizer. Polarizer is composed of Co/Pt multilayer with a perpendicular magnetic anisotropy, which allows us to easily accommodate without needing any tilting angle into the measurement setup since the circular polarization is generated for the X-ray with normal incidence and transmission. Generated circular polarization is examined by observing magnetic domain features based on the X-ray magnetic circular dichroism, where~11% of circular component is estimated compared to the case of full circular polarization.

• Progress in Superconductivity and Cryogenics
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• v.8 no.2
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• pp.1-10
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• 2006

This paper reviews the magnetic refrigeration technology that is a novel cooling method utilizing magnetic field to obtain low temperature. The key component of the refrigeration is a novel magnetic refrigerant which should possess sufficiently large magneto-caloric effect so that a pseudo-Carnot magnetic refrigeration cycle can cover reasonably large temperature span. Otherwise, a regenerative concept should be employed to expand the temperature span of the refrigeration cycle. There is a growing interest in magnetic refrigeration as a viable refrigeration technology not only for cryogenics as well as room temperature range. This paper covers historical developments, fundamental concepts, key components, application classification, and recent research trend of magnetic refrigerators.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 2006.05a
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• pp.241-244
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• 2006

본 논문은 지구자계를 이용하여 3축 자계센서의 수직 성분자계를 보정하는 방법과 장치를 제안한다. 자계센서는 설치각도 및 이득오차에 의해 출력 특성이 변화한다. 따라서 자계센서를 사용하기에 앞서 보정이 필요하다. 지구에서 발생되는 지구자계를 이용하여 간편하게 센서의 설치각도 및 이득오차에 의한 영향을 보정하였으며 이를 위한 장치를 설계하였다. 제안한 방법은 실험을 통하여 실용성을 검증하였다.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.1510-1511
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• 2007

In this study quantifying techniques of ELF magnetic fields arising from currunt carrying indoor-conductor are proposed. These techniques can be applied to line-conductor with finite length and any configuration. Since each component of magnetic field in rectangular axes system is seperated, the resultant magnetic field can be caculated for multi-conductor system through these techniques.