5,554 research outputs found
Common pulse retrieval algorithm: a fast and universal method to retrieve ultrashort pulses
We present a common pulse retrieval algorithm (COPRA) that can be used for a
broad category of ultrashort laser pulse measurement schemes including
frequency-resolved optical gating (FROG), interferometric FROG, dispersion
scan, time domain ptychography, and pulse shaper assisted techniques such as
multiphoton intrapulse interference phase scan (MIIPS). We demonstrate its
properties in comprehensive numerical tests and show that it is fast, reliable
and accurate in the presence of Gaussian noise. For FROG it outperforms
retrieval algorithms based on generalized projections and ptychography.
Furthermore, we discuss the pulse retrieval problem as a nonlinear
least-squares problem and demonstrate the importance of obtaining a
least-squares solution for noisy data. These results improve and extend the
possibilities of numerical pulse retrieval. COPRA is faster and provides more
accurate results in comparison to existing retrieval algorithms. Furthermore,
it enables full pulse retrieval from measurements for which no retrieval
algorithm was known before, e.g., MIIPS measurements
Modeling and estimation of ambiguities in linear arrays
Published versio
Investigative study of planar array ambiguities based on "hyperhelical" parameterization
Published versio
Collaborative Beamforming for Distributed Wireless Ad Hoc Sensor Networks
The performance of collaborative beamforming is analyzed using the theory of
random arrays. The statistical average and distribution of the beampattern of
randomly generated phased arrays is derived in the framework of wireless ad hoc
sensor networks. Each sensor node is assumed to have a single isotropic antenna
and nodes in the cluster collaboratively transmit the signal such that the
signal in the target direction is coherently added in the far- eld region. It
is shown that with N sensor nodes uniformly distributed over a disk, the
directivity can approach N, provided that the nodes are located sparsely
enough. The distribution of the maximum sidelobe peak is also studied. With the
application to ad hoc networks in mind, two scenarios, closed-loop and
open-loop, are considered. Associated with these scenarios, the effects of
phase jitter and location estimation errors on the average beampattern are also
analyzed.Comment: To appear in the IEEE Transactions on Signal Processin
The intracluster magnetic field power spectrum in Abell 2382
The goal of this work is to put constraints on the strength and structure of
the magnetic field in the cluster of galaxies A2382. We investigate the
relationship between magnetic field and Faraday rotation effects in the
cluster, using numerical simulations as a reference for the observed
polarization properties. For this purpose we present Very Large Array
observations at 20 cm and 6 cm of two polarized radio sources embedded in
A2382, and we obtained detailed rotation measure images for both of them. We
simulated random three-dimensional magnetic field models with different power
spectra and thus produced synthetic rotation measure images. By comparing our
simulations with the observed polarization properties of the radio sources, we
can determine the strength and the power spectrum of intra-cluster magnetic
field fluctuations that best reproduce the observations. The data are
consistent with a power law magnetic field power spectrum with the Kolmogorov
index , while the outer scale of the magnetic field fluctuations is of
the order of 35 kpc. The average magnetic field strength at the cluster center
is about 3 G and decreases in the external region as the square root of
the electron gas density. The average magnetic field strength in the central 1
Mpc is about 1 G.Comment: Comments: 18 pages, 13 figures, accepted by A&A. For a version with
high quality figures, see http://erg.ca.astro.it/preprints/guidetti2007
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