386 research outputs found
Energy-Efficient NOMA Enabled Heterogeneous Cloud Radio Access Networks
Heterogeneous cloud radio access networks (H-CRANs) are envisioned to be
promising in the fifth generation (5G) wireless networks. H-CRANs enable users
to enjoy diverse services with high energy efficiency, high spectral
efficiency, and low-cost operation, which are achieved by using cloud computing
and virtualization techniques. However, H-CRANs face many technical challenges
due to massive user connectivity, increasingly severe spectrum scarcity and
energy-constrained devices. These challenges may significantly decrease the
quality of service of users if not properly tackled. Non-orthogonal multiple
access (NOMA) schemes exploit non-orthogonal resources to provide services for
multiple users and are receiving increasing attention for their potential of
improving spectral and energy efficiency in 5G networks. In this article a
framework for energy-efficient NOMA H-CRANs is presented. The enabling
technologies for NOMA H-CRANs are surveyed. Challenges to implement these
technologies and open issues are discussed. This article also presents the
performance evaluation on energy efficiency of H-CRANs with NOMA.Comment: This work has been accepted by IEEE Network. Pages 18, Figure
Rapid Rotation of an Erupting Prominence and the Associated Coronal Mass Ejection on 13 May 2013
In this paper, we report the multiwavelength observations of an erupting
prominence and the associated CME on 13 May 2013. The event occurs behind the
western limb in the field of view of SDO/AIA. The prominence is supported by a
highly twisted magnetic flux rope and shows rapid rotation in the
counterclockwise direction during the rising motion. The rotation of the
prominence lasts for 47 minutes. The average period, angular speed, and
linear speed are 806 s, 0.46 rad min, and 355 km
s, respectively. The total twist angle reaches 7, which is
considerably larger than the threshold for kink instability. Writhing motion
during 17:4217:46 UT is clearly observed by SWAP in 174 {\AA} and EUVI on
board the behind STEREO spacecraft in 304 {\AA} after reaching an apparent
height of 405\,Mm. Therefore, the prominence eruption is most probably
triggered by kink instability. A pair of conjugate flare ribbons and post-flare
loops are created and observed by STA/EUVI. The onset time of writhing motion
is consistent with the commencement of the impulsive phase of the related
flare. The 3D morphology and positions of the associated CME are derived using
the graduated cylindrical shell (GCS) modeling. The kinetic evolution of the
reconstructed CME is divided into a slow-rise phase (330 km s) and
a fast-rise phase (1005 km s) by the writhing motion. The edge-on
angular width of the CME is a constant (60), while the face-on
angular width increases from 96 to 114, indicating a
lateral expansion. The latitude of the CME source region decreases slightly
from 18 to 13, implying an equatorward
deflection during propagation.Comment: 28 pages, 20 figures, accepted for publication in Solar Physics,
comments are welcom
Multi-thermal jet formation triggered by flux emergence
Flux emergence is responsible for various solar eruptions. Combining
observation and simulations, we investigate the influence of flux emergence at
one footpoint of an arcade on coronal rain as well as induced eruptions. The
emergence changes the pressure in the loops, and the internal coronal rain all
moves to the other side. The emerging flux reconnects with the overlying
magnetic field, forming a current sheet and magnetic islands. The plasma is
ejected outwards and heated, forming a cool jet ~ 6000 K and a hot X-ray jet ~
4 MK simultaneously. The jet dynamical properties agree very well between
observation and simulation. In the simulation, the jet also displays transverse
oscillations with a period of 8 minutes, a so-called whip-like motion. The
movement of the jet and dense plasmoids changes the configuration of the local
magnetic field, facilitating the occurrence of Kelvin--Helmholtz instability,
and vortex-like structures form at the boundary of the jet. Our simulation
clearly demonstrates the effect of emergence on coronal rain, the dynamical
details of reconnecting plasmoid chains, the formation of multi-thermal jets,
and the cycling of cool mass between the chromosphere and the corona.Comment: 11 pages, 5 figures, accepted for publication in The Astrophysical
Journal Letter
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