3,498 research outputs found
Cherenkov-like shock waves associated with surpassing the light velocity barrier
The effects arising from accelerated and decelerated motion of a point charge
inside a medium are studied. The motion is manifestly relativistic and may be
produced by a constant uniform electric field. It is shown that in addition to
the bremsstrahlung and Cherenkov shock waves, the electromagnetic shock wave
arises when the charge particle velocity coincides with the light velocity in
the medium. For the accelerated motion this shock wave forming an indivisible
entity with the Cherenkov shock wave arrives after the arrival of the
bremsstrahlung shock wave. For the decelerated motion the above shock wave
detaches from the charge at the moment when its velocity coincides with the
light velocity in the medium. This wave existing even after termination of the
charge motion of the charge propagates with the light velocity in the medium.
It has the same singularity as the Cherenkov shock and is more singular than
the bremsstrahlung shock wave. The space-time regions, where these shock waves
exist, and conditions under which they can be observed are determined.Comment: 15 pages, 4 figures, to be published in Canadian J. Phy
Fine structure of Vavilov-Cherenkov radiation near the Cherenkov threshold
We analyze the Vavilov-Cherenkov radiation (VCR) in a dispersive
nontransparent dielectric air-like medium both below and above the Cherenkov
threshold, in the framework of classical electrodynamics. It is shown that the
transition to the subthreshold energies leads to the destruction of
electromagnetic shock waves and to the sharp reduction of the frequency domain
where VCR is emitted. The fine wake-like structure of the Vavilov-Cherenkov
radiation survives and manifests the existence of the subthreshold radiation in
the domain of anomalous dispersion. These domains can approximately be defined
by the two phenomenological parameters of the medium, namely, the effective
frequency of oscillators and the damping describing an interaction with the
other degrees of freedom.Comment: 9 pages, 6 figure
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Calculation of the QED correction to the recoil proton polarization by the electron structure function method
Model independent radiative correction to the recoil proton polarization for the elastic electron-proton scattering is calculated within method of electron structure functions. The explicit expressions for the recoil proton polarization are represented as a contraction of the electron structure and the hard part of the polarization dependent contribution into cross-section. The calculation of the hard part with first order radiative correction is performed. The obtained representation includes the leading radiative corrections in all orders of perturbation theory and the main part of the second order next-to-leading ones. Numerical calculations illustrate our analytical results
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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