9,094,470 research outputs found
Spectrum Sensing for Cognitive Radio Systems Through Primary User Activity Prediction
Traditional spectrum sensing techniques such as energy detection, for instance, can sense the spectrum only when the cognitive radio (CR) is is not in operation. This constraint is relaxed recently by some blind source separation techniques in which the CR can operate during spectrum sensing. The proposed method in this paper uses the fact that the primary spectrum usage is correlated across time and follows a predictable behavior. More precisely, we propose a new spectrum sensing method that can be trained over time to predict the primary user's activity and sense the spectrum even while the CR user is in operation. Performance achieved by the proposed method is compared to classical spectrum sensing methods. Simulation results provided in terms of receiver operating characteristic curves indicate that in addition to the interesting feature that the CR can transmit during spectrum sensing, the proposed method outperforms conventional spectrum sensing techniques
Illustrative Model for Parity Doubling of Energy Levels
A one-dimensional quantum mechanical model possessing mass gap, a gapless
excitation, and an approximate parity doubling of energy levels is constructed
basing on heuristic QCD-inspired arguments. The model may serve for
illustrative purposes in considering the related dynamical phenomena in
particle and nuclear physics.Comment: 8 pages, 1 figur
Relation between quark and gluon condensates from QCD sum rules
A new relation between -meson mass, weak -meson decay constant,
quark and gluon condensates is derived from the QCD sum rules. As a byproduct
an explanation for the dominance of -decay for the -meson
is proposed.Comment: 7 pages, submitted to Phys. Lett.
Nature of the glassy magnetic state in CuMnAl shape memory alloy
The magnetic ground state of the ferromagnetic shape memory alloy of nominal
composition CuMnAl was investigated. The sample
shows reentry of a glassy magnetic phase below the martensitic transition
temperature, which is found to have complex character with two distinct
anomalies in the temperature dependent ac susceptibility data. The sample
retains its glassy phase even below the second transition as evident from the
magnetic memory measurements in different protocols. Existence of two
transitions along with their observed nature suggest that the system can be
described by the mean field Heisenberg model of reentrant spin glass as
proposed by Gabay and Toulous. \cite{rsg-GT1} The sample provides a fascinating
example where a Gabay-Toulous type spin glass state is triggered by a first
order magneto-structural transition
Wormholes and Off-Diagonal Solutions in f(R,T), Einstein and Finsler Gravity Theories
The aims of this work are 1) to sketch a proof that there are such
parameterizations of the local frame and canonical connection structures when
the gravitational field equations in f(R,T)-modified gravity, MG, can be
integrated in generic off-diagonal forms with metrics depending on all
spacetime coordinates and 2) to provide some examples of exact solutions.Comment: 4 pages, ERE2012-Proceedings macros, Contribution to the Spanish
Relativity Meeting in Portugal, Guimaraes, September 3-7, 201
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