41 research outputs found
Collective excitations and universal broadening of cyclotron absorption in Dirac semimetals in a quantizing magnetic field
The spectrum of electromagnetic collective excitations in Dirac semimetals
placed in a quantizing magnetic field is considered. We have found the Landau
damping regions using the energy and momentum conservation law for allowed
transitions between one-particle states of electron excitations. Analysis of
dispersion equations for longitudinal and transverse waves near the window
boundaries in the Landau damping regions reveals different types of collective
excitations. We also indicate the features of universal broadening of cyclotron
absorption for a magnetic field variation in systems with linear dispersion of
the electron spectrum. The use of the obtained spectrum also allows us to
predict a number of oscillation and resonance effects in the field of
magneto-optical phenomena.Comment: 7 pages, 4 eps figure
3D Structure of Microwave Sources from Solar Rotation Stereoscopy vs Magnetic Extrapolations
We use rotation stereoscopy to estimate the height of a steady-state solar
feature relative to the photosphere, based on its apparent motion in the image
plane recorded over several days of observation. The stereoscopy algorithm is
adapted to work with either one- or two-dimensional data (i.e. from images or
from observations that record the projected position of the source along an
arbitrary axis). The accuracy of the algorithm is tested on simulated data, and
then the algorithm is used to estimate the coronal radio source heights
associated with the active region NOAA 10956, based on multifrequency imaging
data over 7 days from the Siberian Solar Radio Telescope near 5.7 GHz, the
Nobeyama Radio Heliograph at 17 GHz, as well as one-dimensional scans at
multiple frequencies spanning the 5.98--15.95 GHz frequency range from the
RATAN-600 instrument. The gyroresonance emission mechanism, which is sensitive
to the coronal magnetic field strength, is applied to convert the estimated
radio source heights at various frequencies, h(f), to information about
magnetic field vs. height B(h), and the results are compared to a magnetic
field extrapolation derived from photospheric magnetic field observations
obtained by Hinode and MDI. We found that the gyroresonant emission comes from
the heights exceeding location of the third gyrolayer irrespectively on the
magnetic extrapolation method; implications of this finding for the coronal
magnetography and coronal plasma physics are discussed.Comment: 26 pages, 13 figures, ApJ accepte