12,276 research outputs found
Analysis and Modeling of Two Flare Loops Observed by AIA and EIS
We analyze and model an M1.0 flare observed by SDO/AIA and Hinode/EIS to
investigate how flare loops are heated and evolve subsequently. The flare is
composed of two distinctive loop systems observed in EUV images. The UV 1600
\AA emission at the feet of these loops exhibits a rapid rise, followed by
enhanced emission in different EUV channels observed by AIA and EIS. Such
behavior is indicative of impulsive energy deposit and the subsequent response
in overlying coronal loops that evolve through different temperatures. Using
the method we recently developed, we infer empirical heating functions from the
rapid rise of the UV light curves for the two loop systems, respectively,
treating them as two big loops of cross-sectional area 5\arcsec by 5\arcsec,
and compute the plasma evolution in the loops using the EBTEL model (Klimchuk
et al. 2008). We compute the synthetic EUV light curves, which, with the
limitation of the model, reasonably agree with observed light curves obtained
in multiple AIA channels and EIS lines: they show the same evolution trend and
their magnitudes are comparable by within a factor of two. Furthermore, we also
compare the computed mean enthalpy flow velocity with the Doppler shift
measurements by EIS during the decay phase of the two loops. Our results
suggest that the two different loops with different heating functions as
inferred from their footpoint UV emission, combined with their different
lengths as measured from imaging observations, give rise to different coronal
plasma evolution patterns captured both in the model and observations.Comment: Accepted for publication in Ap
An Performance Study for Sectorised Antenna based Doppler Diversity in High-Speed Railway Communications
The wireless channel of High-Speed Railway communication system is rapidly time-varying. The orthogonal frequency division multiplexing transmitting over this channel will be exposed to the intercarrier interference caused by large Doppler spread. The sectorised antenna can be employed for Doppler mitigation and obtaining Doppler diversity gain. In this paper the performance of this directional antenna is analyzed. The preferable partition scheme for the omnidirectional antenna and the optimal Doppler compensation frequency are addressed firstly. And the uncorrelated property of the signal received from the different sectorised antennas is demonstrated originally which can be utilized for Doppler diversity gain. Finally, it is proved by the simulation results that this architecture will allows us to achieve remarkable performance under high mobility conditions
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