202,684 research outputs found
Propagating wave in active region-loops, located over the solar disk observed by the Interface Region Imaging Spectrograph
We aim to ascertain the physical parameters of a propagating wave over the
solar disk detected by the Interface Region Imaging Spectrograph (IRIS). Using
imaging data from the IRIS and the Solar Dynamic Observatory (SDO), we tracked
bright spots to determine the parameters of a propagating transverse wave in
active region (AR) loops triggered by activation of a filament. Deriving the
Doppler velocity of Si IV line from spectral observations of IRIS, we have
determined the rotating directions of active region loops which are relevant to
the wave. On 2015 December 19, a filament was located on the polarity inversion
line of the NOAA AR 12470. The filament was activated and then caused a C 1.1
two-ribbon flare. Between the flare ribbons, two rotation motions of a set of
bright loops were observed to appear in turn with opposite directions.
Following the end of the second rotation, a propagating wave and an associated
transverse oscillation were detected in these bright loops. In 1400 A channel,
there was bright material flowing along the loops in a wave-like manner, with a
period of ~128 s and a mean amplitude of ~880 km. For the transverse
oscillation, we tracked a given loop and determine the transverse positions of
the tracking loop in a limited longitudinal range. In both of 1400 A and 171 A
channels, approximately four periods are distinguished during the transverse
oscillation. The mean period of the oscillation is estimated as ~143 s and the
displacement amplitude as between ~1370 km and ~690 km. We interpret these
oscillations as a propagating kink wave and obtain its speed of ~1400 km s-1.
Our observations reveal that a flare associated with filament activation could
trigger a kink propagating wave in active region loops over the solar disk.Comment: Accepted for publication in A&
Tuning electronic structure of graphene via tailoring structure: theoretical study
Electronic structures of graphene sheet with different defective patterns are
investigated, based on the first principles calculations. We find that
defective patterns can tune the electronic structures of the graphene
significantly. Triangle patterns give rise to strongly localized states near
the Fermi level, and hexagonal patterns open up band gaps in the systems. In
addition, rectangular patterns, which feature networks of graphene nanoribbons
with either zigzag or armchair edges, exhibit semiconducting behaviors, where
the band gap has an evident dependence on the width of the nanoribbons. For the
networks of the graphene nanoribbons, some special channels for electronic
transport are predicted.Comment: 5 figures, 6 page
A Rate-Splitting Based Bound-Approaching Transmission Scheme for the Two-User Symmetric Gaussian Interference Channel with Common Messages
This paper is concerned with a rate-splitting based transmission strategy for the two-user symmetric Gaussian interference channel that contains common messages only. Each transmitter encodes its common message into multiple layers by multiple codebooks that drawn from one separate code book, and transmits the superposition of the messages corresponding to these layers; each receiver decodes the messages from all layers of the two users successively. Two schemes are proposed for decoding order and optimal power allocation among layers respectively. With the proposed decoding order scheme, the sum-rate can be increased by rate-splitting, especially at the optimal number of rate-splitting, using average power allocation in moderate and weak interference regime. With the two proposed schemes at the receiver and the transmitter respectively, the sum-rate achieves the inner bound of HK without time-sharing. Numerical results show that the proposed optimal power allocation scheme with the proposed decoding order can achieve significant improvement of the performance over equal power allocation, and achieve the sum-rate within two bits per channel use (bits/channel use) of the sum capacity
- …