9,674 research outputs found
On the Maximal Invariant Statistic for Adaptive Radar Detection in Partially-Homogeneous Disturbance with Persymmetric Covariance
This letter deals with the problem of adaptive signal detection in
partially-homogeneous and persymmetric Gaussian disturbance within the
framework of invariance theory. First, a suitable group of transformations
leaving the problem invariant is introduced and the Maximal Invariant Statistic
(MIS) is derived. Then, it is shown that the (Two-step) Generalized-Likelihood
Ratio test, Rao and Wald tests can be all expressed in terms of the MIS, thus
proving that they all ensure a Constant False-Alarm Rate (CFAR).Comment: submitted for journal publicatio
Rational approximations of cosmography through Pad\'e polynomials
We consider high-redshift cosmography adopting the technique of
polynomial reconstruction. In lieu of considering Taylor treatments, which turn
out to be non-predictive as soon as , we take into account the Pad\'e
rational approximations which consist in performing expansions converging at
high redshift domains. Particularly, our strategy is to reconstruct
functions first, assuming the Ricci scalar to be invertible with respect to the
redshift . Having the thus-obtained functions, we invert them and we
easily obtain the corresponding terms. We minimize error propagation,
assuming no errors upon redshift data. The treatment we follow naturally leads
to evaluating curvature pressure, density and equation of state, characterizing
the universe evolution at redshift much higher than standard cosmographic
approaches. We therefore match these outcomes with small redshift constraints
got by framing the cosmology through Taylor series around .
This gives rise to a calibration procedure with small redshift that enables the
definitions of polynomial approximations up to . Last but not
least, we show discrepancies with the standard cosmological model which go
towards an extension of the CDM paradigm, indicating an effective dark
energy term evolving in time. We finally describe the evolution of our
effective dark energy term by means of basic techniques of data mining.Comment: 11 pages, 14 figures, accepted for publication in JCA
High-energy -ray emission from GRBs
GRBs are nowadays a rather well understood phenomenon in the soft (KeV-MeV)
-ray energy band, while only a few GRBs have been observed at high
photon energies (E_{\gamma} \ut > 1 GeV). It is also widely recognized that
GRBs accelerate protons to relativistic energies and that dense media are often
present nearby the sources. Within this framework we compute in detail the
high-energy -ray flux from the decay of neutral pions produced through
the interaction of accelerate protons with nucleons in the surrounding medium.
We also take into account the local and intergalactic -ray absorption.
The presence of magnetic fields around the GRB sources causes the deflection of
the accelerated protons and so a temporal spread of the produced high-energy
-rays with respect to the signal in the soft -ray band.
Moreover, we analyze the possibility to detect the -ray signal in the
GeV-TeV energy range by the ARGO detector under construction in Tibet.Comment: 9 pages, 7 figures, abstract shortened, to appear in Astronomy and
Astrophysic
Model Order Selection Rules For Covariance Structure Classification
The adaptive classification of the interference covariance matrix structure
for radar signal processing applications is addressed in this paper. This
represents a key issue because many detection architectures are synthesized
assuming a specific covariance structure which may not necessarily coincide
with the actual one due to the joint action of the system and environment
uncertainties. The considered classification problem is cast in terms of a
multiple hypotheses test with some nested alternatives and the theory of Model
Order Selection (MOS) is exploited to devise suitable decision rules. Several
MOS techniques, such as the Akaike, Takeuchi, and Bayesian information criteria
are adopted and the corresponding merits and drawbacks are discussed. At the
analysis stage, illustrating examples for the probability of correct model
selection are presented showing the effectiveness of the proposed rules
The Gauge-Bethe Correspondence and Geometric Representation Theory
The Gauge/Bethe correspondence of Nekrasov and Shatashvili relates the
spectrum of integrable spin chains to the ground states of supersymmetric gauge
theories. Up to now, this correspondence has been an observation; the
underlying reason for its existence remaining elusive. We argue here that
geometrical representation theory is the mathematical foundation of the
Gauge/Bethe correspondence, and it provides a framework to study families of
gauge theories in a unified way.Comment: 8 page
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