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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
Dynamical Dzyaloshinsky-Moriya interaction in KCuF3: Raman evidence for an antiferrodistortive lattice instability
In the orbitally ordered, quasi-one dimensional Heisenberg antiferromagnet
KCuF3 the low-energy Eg and B1g phonon modes show an anomalous softening (25%
and 13%) between room temperature and the characteristic temperature T_S = 50
K. In this temperature range a freezing-in of F ion dynamic displacements is
proposed to occur. In addition, the Eg mode at about 260 cm-1 clearly splits
below T_S. The width of the phonon lines above T_S follows an activated
behavior with an activation energy of about 50 K. Our observations clearly
evidence a reduction of the structural symmetry below T_S and indicate a strong
coupling of lattice and spin fluctuations for T>T_S.Comment: 7 pages, 9 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
On Tamm's problem in the Vavilov-Cherenkov radiation theory
We analyse the well-known Tamm problem treating the charge motion on a finite
space interval with the velocity exceeding light velocity in medium. By
comparing Tamm's formulae with the exact ones we prove that former do not
properly describe Cherenkov radiation terms. We also investigate Tamm's formula
cos(theta)=1/(beta n) defining the position of maximum of the field strengths
Fourier components for the infinite uniform motion of a charge. Numerical
analysis of the Fourier components of field strengths shows that they have a
pronounced maximum at cos(theta)=1/(beta n) only for the charge motion on the
infinitely small interval. As the latter grows, many maxima appear. For the
charge motion on an infinite interval there is infinite number of maxima of the
same amplitude. The quantum analysis of Tamm's formula leads to the same
results.Comment: 28 pages, 8 figures, to be published in J.Phys.D:Appl.Phy
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