49,455 research outputs found
Uplink Multiuser MIMO Detection Scheme with Reduced Computational Complexity
The wireless communication systems with multiple antennas have recently received significant attention due to their higher capacity and better immunity to fading channels as compared to single antenna systems. A fast antenna selection scheme has been introduced for the uplink multiuser multiple-input multiple-output (MIMO) detection to achieve diversity gains, but the computational complexity of the fast antenna selection scheme in multiuser systems is very high due to repetitive pseudo-inversion computations. In this paper, a new uplink multiuser detection scheme is proposed adopting a switch-and-examine combining (SEC) scheme and the Cholesky decomposition to solve the computational complexity problem. K users are considered that each users is equipped with two transmit antennas for Alamouti space-time block code (STBC) over wireless Rayleigh fading channels. Simulation results show that the computational complexity of the proposed scheme is much lower than the systems with exhaustive and fast antenna selection, while the proposed scheme does not experience the degradations of bit error rate (BER) performances
Simultaneous EUV and Radio Observations of Bidirectional Plasmoids Ejection During Magnetic Reconnection
We present a multiwavelength study of the X-class flare, which occurred in
active region (AR) NOAA 11339 on 3 November 2011. The EUV images recorded by
SDO/AIA show the activation of a remote filament (located north of the AR) with
footpoint brightenings about 50 min prior to the flare occurrence. The kinked
filament rises-up slowly and after reaching a projected height of ~49 Mm, it
bends and falls freely near the AR, where the X-class flare was triggered.
Dynamic radio spectrum from the Green Bank Solar Radio Burst Spectrometer
(GBSRBS) shows simultaneous detection of both positive and negative drifting
pulsating structures (DPSs) in the decimetric radio frequencies (500-1200 MHz)
during the impulsive phase of the flare. The global negative DPSs in solar
flares are generally interpreted as a signature of electron acceleration
related to the upward moving plasmoids in the solar corona. The EUV images from
AIA 94 \AA reveal the ejection of multiple plasmoids, which move simultaneously
upward and downward in the corona during the magnetic reconnection. The
estimated speeds of the upward and downward moving plasmoids are ~152-362 and
~83-254 km/s, respectively. These observations strongly support the recent
numerical simulations of the formation and interaction of multiple plasmoids
due to tearing of the current-sheet structure. On the basis of our analysis, we
suggest that the simultaneous detection of both the negative and positive DPSs
is most likely generated by the interaction/coalescence of the multiple
plasmoids moving upward and downward along the current-sheet structure during
the magnetic reconnection process. Moreover, the differential emission measure
(DEM) analysis of the active region reveals presence of a hot flux-rope
structure (visible in AIA 131 and 94 \AA) prior to the flare initiation and
ejection of the multi-temperature plasmoids during the flare impulsive phase.Comment: A&A (accepted), 13 pages, 9 figure
Norm Estimates for the Difference Between Bochner's Integral and the Convex Combination of Function's Values
Norm estimates are developed between the Bochner integral of a vector-valued
function in Banach spaces having the Radon-Nikodym property and the convex
combination of function values taken on a division of the interval [a,b]
Color Reflection Invariance and Monopole Condensation in QCD
We review the quantum instability of the Savvidy-Nielsen-Olesen (SNO) vacuum
of the one-loop effective action of SU(2) QCD, and point out a critical defect
in the calculation of the functional determinant of the gluon loop in the SNO
effective action. We prove that the gauge invariance, in particular the color
reflection invariance, exclude the unstable tachyonic modes from the gluon loop
integral. This guarantees the stability of the magnetic condensation in QCD.Comment: 28 pages, 3 figures, JHEP styl
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