1,376 research outputs found
Relativistic approach to electromagnetic imaging
A novel imaging principle based on the interaction of electromagnetic waves
with a beam of relativistic electrons is proposed. Wave-particle interaction is
assumed to take place in a small spatial domain, so that each electron is only
briefly accelerated by the incident field. In the one-dimensional case the
spatial distribution of the source density can be directly observed in the
temporal spectrum of the scattered field. Whereas, in the two-dimensional case
the relation between the source and the spectrum is shown to be approximately
the Radon transform.Comment: 10 pages, 1 figur
Restoring the full velocity field in the gaseous disk ofthe spiral galaxy NGC 157
We analyse the line-of-sight velocity field of ionized gas in the spiral
galaxy NGC 157 which has been obtained in the H\alpha emission at the 6m
telescope of SAO RAS. The existence of systematic deviations of the observed
gas velocities from pure circular motion is shown. A detailed investigation of
these deviations is undertaken by applying a Fourier analysis of the azimuthal
distributions of the line-of-sight velocities at different distances from the
galactic center. As a result of the analysis, all the main parameters of the
wave spiral pattern are determined: the corotation radius, the amplitudes and
phases of the gas velocity perturbations at different radii, and the velocity
of circular rotation of the disk corrected for the velocity perturbations due
to spiral arms. At a high confidence level, the presence of the two giant
anticyclones in the reference frame rotating with the spiral pattern is shown;
their sizes and the localization of their centers are consistent with the
results of the analytic theory and of numerical simulations. Besides the
anticyclones, the existence of cyclones in residual velocity fields of spiral
galaxies is predicted. In the reference frame rotating with the spiral pattern
these cyclones have to reveal themselves in galaxies where a radial gradient of
azimuthal residual velocity is steeper than that of the rotation velocity
(abridged).Comment: 23 pages including 25 eps-figures. Accepted for publication in A&
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