370 research outputs found
An improved MHD simulation of the 2006 December 13 coronal mass ejection of active region NOAA 10930
We present a magnetohydrodynamic (MHD) simulation of the coronal mass
ejection (CME) on 13 December 2006 in the emerging delta-sunspot active region
10930, improving upon a previous simulation by Fan (2016) as follows. (1)
Incorporate an ambient solar wind instead of using a static potential magnetic
field extrapolation as the initial state. (2) In addition to imposing the
emergence of a twisted flux rope, also impose at the lower boundary a random
electric field that represents the effect of turbulent convection, which drives
field-line braiding and produces resistive and viscous heating in the corona.
With the inclusion of this heating, which depends on the magnetic field
topology, we are able to model the synthetic soft X-ray images that would be
observed by the X-Ray Telescope (XRT) of the Hinode satellite, produced by the
simulated coronal magnetic field. We find that the simulated pre-eruption
magnetic field with the build up of a twisted magnetic flux rope, produces
synthetic soft X-ray emission that shows qualitatively similar morphology as
that observed by the Hinode/XRT for both the ambient coronal loops of the
active region and the central inverse-S shaped "sigmoid" that sharpens just
before the onset of the eruption. The synthetic post-flare loop brightening
also shows similar morphology as that seen in the Hinode/XRT image during the
impulsive phase of the eruption. It is found that the kinematics of the
erupting flux rope is significantly affected by the open magnetic fields and
fast solar wind streams adjacent to the active region.Comment: 17 pages, 14 figures, accepted for publication in the Astrophysical
Journa
Operating Measures, IPO Valuation, and After Market Performance-Perspective From Internet Bubble Period
Internet related firms experienced an extremely high degree of underpricing in the year 1999 and 2000; 40 percent more than underpricing of Non-Internet firms. Two explanations for this phenomenon are examined: the changing-risk composition hypothesis and overreaction hypothesis. Empirical tests are conducted in three stages: first trading day, short-term, and long-term performances. The results are consistent with both hypotheses, and the high initial returns for Internet firms are explainable by investors\u27 overreaction and the firm\u27s high uncertainties
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