18,758 research outputs found
Wavelet-based Faraday Rotation Measure Synthesis
Faraday Rotation Measure (RM) Synthesis, as a method for analyzing
multi-channel observations of polarized radio emission to investigate galactic
magnetic fields structures, requires the definition of complex polarized
intensity in the range of the negative lambda square. We introduce a simple
method for continuation of the observed complex polarized intensity into this
domain using symmetry arguments. The method is suggested in context of magnetic
field recognition in galactic disks where the magnetic field is supposed to
have a maximum in the equatorial plane. The method is quite simple when applied
to a single Faraday-rotating structure on the line of sight. Recognition of
several structures on the same line of sight requires a more sophisticated
technique. We also introduce a wavelet-based algorithm which allows us to
consider a set of isolated structures. The method essentially improves the
possibilities for reconstruction of complicated Faraday structures using the
capabilities of modern radio telescopes.Comment: 5 pages, 5 figures, accepted for publication in MNRAS Letter
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The Diderot meteorite: The second chassignite
The Diderot meteorite is a dunite discovered in Sahara. The martian origin is unambiguous and Diderot shares strong petrographical similarities with Chassigny
Mixing and relaxation dynamics of the Henon map at the edge of chaos
The mixing properties (or sensitivity to initial conditions) and relaxation
dynamics of the Henon map, together with the connection between these concepts,
have been explored numerically at the edge of chaos. It is found that the
results are consistent with those coming from one-dimensional dissipative maps.
This constitutes the first verification of the scenario in two-dimensional
cases and obviously reinforces the idea of weak mixing and weak chaos.
Keywords: Nonextensive thermostatistics, Henon map, dynamical systemsComment: 10 pages with 3 fig
Reaction mechanisms for weakly-bound, stable nuclei and unstable, halo nuclei on medium-mass targets
An experimental overview of reactions induced by the stable, but weakly-bound
nuclei 6Li, 7Li and 9Be, and by the exotic, halo nuclei 6He, 8B, 11Be and 17F
on medium-mass targets, such as 58Ni, 59Co or 64Zn, is presented. Existing data
on elastic scattering, total reaction cross sections, fusion processes, breakup
and transfer channels are discussed in the framework of a CDCC approach taking
into account the breakup degree of freedom.Comment: 7 pages, 6 figures, Invited Talk given by C. Beck to the 10th
International Conference on Nucleus-Nucleus Collisions, August 16-21, 2009
Beijing, China; Paper submitted to the NN2009 Proceedings, Nuclear Physics A
(to be published
Properties of the warm magnetized ISM, as inferred from WSRT polarimetric imaging
We describe a first attempt to derive properties of the regular and turbulent
Galactic magnetic field from multi-frequency polarimetric observations of the
diffuse Galactic synchrotron background. A single-cell-size model of the thin
Galactic disk is constructed which includes random and regular magnetic fields
and thermal and relativistic electrons. The disk is irradiated from behind with
a uniform partially polarized background. Radiation from the background and
from the thin disk is Faraday rotated and depolarized while propagating through
the medium. The model parameters are estimated from a comparison with 350 MHz
observations in two regions at intermediate latitudes done with the Westerbork
Synthesis Radio Telescope. We obtain good consistency between the estimates for
the random and regular magnetic field strengths and typical scales of structure
in the two regions. The regular magnetic field strength found is a few
microGauss, and the ratio of random to regular magnetic field strength is 0.7
+/- 0.5, for a typical scale of the random component of 15 +/- 10 pc.
Furthermore, the regular magnetic field is directed almost perpendicular to the
line of sight. This modeling is a potentially powerful method to estimate the
structure of the Galactic magnetic field, especially when more polarimetric
observations of the diffuse synchrotron background at intermediate latitudes
become available.Comment: 12 pages, 6 figures, accepted by A&
Acousto-optical multiple interference devices
We present a new concept for waveguide acousto-optical devices based on coupled MachZehnder interferometers driven by acoustic waves. These acousto-optical multiple interference devices use the periodic refractive index modulation induced by the acoustic wave to realize functionalities such as ON/OFF switching for an arbitrary time interval, as well as for efficient light modulation at high harmonics of the acoustic frequency and pulse shaping for, e.g., integrated Q-switches. We also discuss application of the concepts to light modulation by very high acoustic frequencies, where the acoustic wavelengths become much shorter than the optical ones
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