59,184 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
Tensor-to-Scalar Ratio in Eddington-inspired Born-Infeld Inflation
We investigate the scalar perturbation of the inflation model driven by a
massive-scalar field in Eddington-inspired Born-Infeld gravity. We focus on the
perturbation at the attractor stage in which the first and the second slow-roll
conditions are satisfied. The scalar perturbation exhibits the corrections to
the chaotic inflation model in general relativity. We find that the
tensor-to-scalar ratio becomes smaller than that of the usual chaotic
inflation.Comment: 9 pages. revised version to appear in EPJC, with minor typo
corrections. arXiv admin note: text overlap with arXiv:1404.608
Light bottom squark and gluino confront electroweak precision measurements
We address the compatibility of a light sbottom (mass 2\sim 5.5 \gev) and a
light gluino (mass 12\sim 16 \gev) with electroweak precision measurements.
Such light particles have been suggested to explain the observed excess in the
quark production cross section at the Tevatron. The electroweak observables
may be affected by the sbottom and gluino through the SUSY-QCD corrections to
the vertex. We examine, in addition to the SUSY-QCD corrections, the
electroweak corrections to the gauge boson propagators from the stop which are
allowed to be light from the SU(2) symmetry. We find that this scenario is
strongly disfavored from electroweak precision measurements unless the heavier
sbottom mass eigenstate is lighter than 180\gev and the left-right mixing in
the stop sector is sufficiently large. This implies that one of the stops
should be lighter than about 98\gev.Comment: 4 pages, revtex, 2 figures. Reference added, version to appear in
Phys.Rev.Let
Sensor-Based Safety Performance Assessment of Individual Construction Workers
Over the last decade, researchers have explored various technologies and methodologies to enhance worker safety at construction sites. The use of advanced sensing technologies mainly has focused on detecting and warning about safety issues by directly relying on the detection capabilities of these technologies. Until now, very little research has explored methods to quantitatively assess individual workers’ safety performance. For this, this study uses a tracking system to collect and use individuals’ location data in the proposed safety framework. A computational and analytical procedure/model was developed to quantify the safety performance of individual workers beyond detection and warning. The framework defines parameters for zone-based safety risks and establishes a zone-based safety risk model to quantify potential risks to workers. To demonstrate the model of safety analysis, the study conducted field tests at different construction sites, using various interaction scenarios. Probabilistic evaluation showed a slight underestimation and overestimation in certain cases; however, the model represented the overall safety performance of a subject quite well. Test results showed clear evidence of the model’s ability to capture safety conditions of workers in pre-identified hazard zones. The developed approach presents a way to provide visualized and quantified information as a form of safety index, which has not been available in the industry. In addition, such an automated method may present a suitable safety monitoring method that can eliminate human deployment that is expensive, error-prone, and time-consuming
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