8,153 research outputs found

### Wakefield generation in magnetized plasmas

We consider wakefield generation in plasmas by electromagnetic pulses
propagating perpendicular to a strong magnetic field, in the regime where the
electron cyclotron frequency is equal to or larger than the plasma frequency.
PIC-simulations reveal that for moderate magnetic field strengths previous
results are re-produced, and the wakefield wavenumber spectrum has a clear peak
at the inverse skin depth. However, when the cyclotron frequency is
significantly larger than the plasma frequency, the wakefield spectrum becomes
broad-band, and simultaneously the loss rate of the driving pulse is much
enhanced. A set of equations for the scalar and vector potentials reproducing
these results are derived, using only the assumption of a weakly nonlinear
interaction.Comment: 6 pages, 8 figure

### Spin contribution to the ponderomotive force in a plasma

The concept of a ponderomotive force due to the intrinsic spin of electrons
is developed. An expression containing both the classical as well as the
spin-induced ponderomotive force is derived. The results are used to
demonstrate that an electromagnetic pulse can induce a spin-polarized plasma.
Furthermore, it is shown that for certain parameters, the nonlinear
back-reaction on the electromagnetic pulse from the spin magnetization current
can be larger than that from the classical free current. Suitable parameter
values for a direct test of this effect are presented.Comment: 4 pages, 2 figures, version accepted for publication in Physical
Review Letter

### Development of Speed-power Qualities of Young Sportsmen-Swimmers.

У статті обґрунтовано розвиток швидкісно-силових якостей залежно від віку, статі та рівня підготовленості юних спортсменів, узагальнено досвід теорії й практики з проблем підвищення ефективності швидкісно-силової підготовки юних плавців, дано науково-методичні рекомендації щодо використання вправ різного характеру з метою покращення спортивних результатів. In the article
obgruntovano development of speed-power qualities in dependence on age, floor and level of preparedness of young
sportsmen, the experience of theory and practice from the problems of increase of efficiency of speed-power
preparation of young swimmers is generalized,scientific-methodical recommendations are given after the use of
exercises of a different character with the purpose of improvement of sporting results

### The ponderomotive force due to the intrinsic spin in extended fluid and kinetic models

In this paper we calculate the contribution to the ponderomotive force in a
plasma from the electron spin using a recently developed model. The spin-fluid
model used in the present paper contains spin-velocity correlations, in
contrast to previous models used for the same purpose. Is its then found that
previous terms for the spin-ponderomotive force are recovered, but also that
additional terms appear. Furthermore, the results due to the spin-velocity
correlations are confirmed using the spin-kinetic theory. The significance of
our results is discussed.Comment: 6 page

### On the Minimal Model of Anyons

We present new geometric formulations for the fractional spin particle models
on the minimal phase spaces. New consistent couplings of the anyon to
background fields are constructed. The relationship between our approach and
previously developed anyon models is discussed.Comment: 17 pages, LaTex, no figure

### Radio holographic filtering, error estimation, and quality control of radio occultation data

Processing of radio occultation data requires filtering and quality control for the noise reduction and sorting out corrupted data samples. We introduce a radio holographic filtering algorithm based on the synthesis of canonical transform (CT2) and radio holographic focused synthesized aperture (RHFSA) methods. The field in the CT2-transformed space is divided by a reference signal to subtract the regular phase variation and to compress the spectrum. Next, it is convolved with a Gaussian filter window and multiplied by the reference signal to restore the phase variation. This algorithm is simple to implement, and it is numerically efficient. Numerical simulation of processing radio occultations with a realistic receiver noise indicates a good performance of the method. We introduce a new technique of the error estimation of retrieved bending angle profiles based on the width of the running spectra of the transformed wavefield multiplied with the reference signal. We describe a quality control method for the discrimination of corrupted samples in the L2 channel, which is most susceptible to signal tracking errors. We apply the quality control and error estimation techniques for the processing of data acquired by Challenging Minisatellite Payload (CHAMP) and perform a statistical comparison of CHAMP data with the analyses of the German Weather Service (DWD). The statistical analysis shows a good agreement between the CHAMP and DWD error estimates and the observed CHAMP–DWD differences. This corroborates the efficiency of the proposed quality control and error estimation techniques

### Instabilities for a relativistic electron beam interacting with a laser irradiated plasma

The effects of a radiation field (RF) on the unstable modes developed in
relativistic electron beam--plasma interaction are investigated assuming that
$\omega_{0} >\omega_{p}$, where $\omega_{0}$ is the frequency of the RF and
$\omega_{p}$ is the plasma frequency. These unstable modes are parametrically
coupled to each other due to the RF and are a mix between two--stream and
parametric instabilities. The dispersion equations are derived by the
linearization of the kinetic equations for a beam--plasma system as well as the
Maxwell equations. In order to highlight the effect of the radiation field we
present a comparison of our analytical and numerical results obtained for
nonzero RF with those for vanishing RF. Assuming that the drift velocity
$\mathbf{u}_{b}$ of the beam is parallel to the wave vector $\mathbf{k}$ of the
excitations two particular transversal and parallel configurations of the
polarization vector $\mathbf{E}_{0}$ of the RF with respect to $\mathbf{k}$ are
considered in detail. It is shown that in both geometries resonant and
nonresonant couplings between different modes are possible. The largest growth
rates are expected at the transversal configuration when $\mathbf{E}_{0}$ is
perpendicular to $\mathbf{k}$. In this case it is demonstrated that in general
the spectrum of the unstable modes in $\omega$--$k$ plane is split into two
distinct domains with long and short wavelengths, where the unstable modes are
mainly sensitive to the beam or the RF parameters, respectively. In parallel
configuration, $\mathbf{E}_{0} \parallel \mathbf{k}$, and at short wavelengths
the growth rates of the unstable modes are sensitive to both beam and RF
parameters remaining insensitive to the RF at long wavelengths.Comment: 23 pages, 5 figure

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