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BUILDUP AND RELEASE OF MAGNETIC TWIST DURING THE X3.4 SOLAR FLARE OF 2006 DECEMBER 13
Inoue, S.,Shiota, D.,Yamamoto, T. T.,Pandey, V. S.,Magara, T.,Choe, G. S. IOP Publishing 2012 The Astrophysical journal Vol.760 No.1
<P>We analyze the temporal evolution of the three-dimensional magnetic structure of the flaring active region (AR) NOAA 10930 by using the nonlinear force-free fields extrapolated from the photospheric vector magnetic fields observed by the Solar Optical Telescope on board Hinode. This AR consisted mainly of two types of twisted magnetic field lines: one has a strong negative (left-handed) twist due to the counterclockwise motion of the positive sunspot and is rooted in the regions of both polarities in the sunspot at a considerable distance from the polarity inversion line (PIL). In the flare phase, dramatic magnetic reconnection occurs in those negatively twisted lines in which the absolute value of the twist is greater than a half-turn. The other type consists of both positively and negatively twisted field lines formed relatively close to the PIL between two sunspots. A strong Ca II image began to brighten in this region of mixed polarity, in which the positively twisted field lines were found to be injected within one day across the pre-existing negatively twisted region, along which strong currents were embedded. Consequently, the central region near the PIL contains a mix of differently twisted field lines and the strong currents may play a prominent role in flare onset.</P>
TWIST AND CONNECTIVITY OF MAGNETIC FIELD LINES IN THE SOLAR ACTIVE REGION NOAA 10930
Inoue, S.,Kusano, K.,Magara, T.,Shiota, D.,Yamamoto, T. T. IOP Publishing 2011 The Astrophysical journal Vol.738 No.2
<P>Twist and connectivity of magnetic field lines in the flare-productive active region NOAA 10930 are investigated in terms of the vector magnetograms observed by the Solar Optical Telescope on board the Hinode satellite and the nonlinear force-free field (NLFFF) extrapolation. First, we show that the footpoints of magnetic field lines reconstructed by the NLFFF correspond well to the conjugate pair of highly sheared flare ribbons on the Ca II images, which were observed by Hinode as an X3.4 class flare on 2006 December 13. This demonstrates that the NLFFF extrapolation may be used to analyze the magnetic field connectivity. Second, we find that the twist of magnetic field lines anchored on the flare ribbons increased as the ribbons moved away from the magnetic polarity inversion line in the early phase of the flare. This suggests that magnetic reconnection might commence from a region located below the most strongly twisted field. Third, we reveal that the magnetic flux twisted more than a half turn and gradually increased during the last one day prior to the onset of the flare, and that it quickly decreased for two hours after the flare. This is consistent with the store-and-release scenario of magnetic helicity. However, within this active region, only a small fraction of the flux was twisted by more than one full turn and the field lines that reconnected first were twisted less than one turn. These results imply that the kink mode instability could hardly occur, at least before the onset of flare. Based on our results, we discuss the trigger process of solar flares.</P>
PRACTICAL ACTIVE POWER FILTERS USING SI-THYRISTORS
S.ATOH,T.SHIOTA,T.YAMADA,S.ARAKI,M.KOHATA 전력전자학회 1989 ICPE(ISPE)논문집 Vol.- No.-
We have developed a practical active power filters using SI(Static Induction)-Thyristors, a self-turn-off device excellent in high speed switching characteristics. This active filter was applied to VVVF inverter-driven water distribution system and has operated in the best conditions since the end of the last year. The active filter we have developed uses the compensating algorithm based on the instantaneous spatial vector theory and achieves nig11 speed and high accuracy controls by performing the on-line arithmetic operation with a digital signal processor. As for compensating performances suppression effects within 2% have been a-chieved as compared with the fundamental components at the 5th to 19th harmonics components of inverter current contained in the input current of inverter system.<br/>
Encoderless Servo Drive with Adequately Designed IPMSM for Saliency-based Position Detection
K. Ide,M. Hisatsune,T. Shiota,S. Murakami,M. Ohto 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5
This paper presents a newly developed encoderless servo drive with an adequately designed interior permanent magnet synchronous motor (IPMSM). The motor for encoderless servo drive is designed to act like resolver incorporated with saliency-based position detection technique. The resolution of the position detection and sustainability against load are considered in the design. As the position detection a pulse voltage injection technique is employed to realize higher dynamics in the control performance than conventional technique. This paper mainly focuses on the technology fusion in between motor design and control design. Finally, the fast initial pole positioning, the high-dynamics performance in position and speed control, which are sufficient for servo drive applications, are shown in this paper. The net-resolution of the position detection is about 10 bits, and the accuracy of positioning is less than 1 mechanical degree in position control at steady state.
Encoderless Motor Design for Servo Drive Applications
S. Murakami,M. Ohto,M. Hisatsune,T. Shiota,K. Ide 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5
Improvement of output power of encoderless motor is desired in servo drive applications. However, as load on the encoderless motor increases, high frequency inductance distribution distorts so heavily that rotor position estimation becomes very difficult, which is a major technical problem hindering the improvement. This paper deals with a motor design aiming for high output power encoderless motor with concentrated winding and IPM configuration. First, reduction of armature reaction is referred to as the fundamental design concept. Next, a motor configuration realizing the concept is proposed. Then, motor design is conducted, and characteristics of a prototype motor is measured and evaluated. As a result, the prototype motor is verified to achieve basic servo motor performances and to have an almost sinusoidal high frequency inductance distribution feature without crucial distortion even when load increases. Output power of encoderless motor is enhanced by the design method presented in this paper.
MgO Overlayer Thickness Dependence of Perpendicular Magnetic Anisotropy in CoFeB Thin Films
D. D. Lam,F. Bonell,S. Miwa,Y. Shiota,K. Yakushiji,H. Kubota,T. Nozaki,A. Fukushima,S. Yuasa,Y. Suzuki 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.10
The dependence of the magnetization and perpendicular magnetic anisotropy (PMA) of Ta/CoFeB/MgO/Ta on the thicknesses of the CoFeB layer and the MgO overlayer was investigated by vibrating sample magnetometer. The magnetization is found to be small for samples with a thin MgO overlayer. The PMA strongly depends on the MgO overlayer (hereafter, MgO) thickness and its maximum value of 1.74 erg/cm2 is achieved for a 1.0 nm thick MgO overlayer with annealing at 300 ◦C. The volume anisotropy of the CoFeB layer is found to be independent of the MgO thickness,which suggest that only the interface anisotropy depends on the MgO thickness. The possible mechanisms that may influence the interface magnetization and anisotropy are discussed herein.