24 research outputs found
Radio-wave propagation through a medium containing electron-density fluctuations described by an anisotropic Goldreich-Sridhar spectrum
We study the propagation of radio waves through a medium possessing density
fluctuations that are elongated along the ambient magnetic field and described
by an anisotropic Goldreich-Sridhar power spectrum. We derive general formulas
for the wave phase structure function, visibility, angular broadening,
diffraction-pattern length scales, and scintillation time scale for arbitrary
distributions of turbulence along the line of sight, and specialize these
formulas to idealized cases.Comment: 25 pages, 3 figures, submitted to Ap
Hot Jupiters and Hot Spots: The Short- and Long-term Chromospheric Activity on Stars with Giant Planets
We monitored the chromospheric activity in the Ca II H & K lines of 13
solar-type stars (including the Sun); 8 of them over three years at the CFHT
and 5 in a single run at the VLT. Ten of the 13 targets have close planetary
companions. All of the stars observed at the CFHT show long-term (months to
years) changes in H & K intensity levels. Four stars display short-term (days)
cyclical activity. For two, HD 73256 and kappa^1 Ceti, the activity is likely
associated with an active region rotating with the star, however, the flaring
in excess of the rotational modulation may be associated with a hot jupiter. A
planetary companion remains a possibility for kappa^1 Ceti. For the other two,
HD 179949 and upsilon And, the cyclic variation is synchronized to the hot
jupiter's orbit. For both stars this synchronicity with the orbit is clearly
seen in two out of three epochs. The effect is only marginal in the third epoch
at which the seasonal level of chromospheric activity had changed for both
stars. Short-term chromospheric activity appears weakly dependent on the mean
K-line reversal intensities for the sample of 13 stars. Also, a suggestive
correlation exists between this activity and the M_p sin(i) of the star's hot
jupiter. Because of their small separation (<= 0.1 AU), many of the hot
jupiters lie within the Alfv\'en radius of their host stars which allows a
direct magnetic interaction with the stellar surface. We discuss the conditions
under which a planet's magnetic field might induce activity on the stellar
surface and why no such effect was seen for the prime candidate, tau Boo. This
work opens up the possibility of characterizing planet-star interactions, with
implications for extrasolar planet magnetic fields and the energy contribution
to stellar atmospheres.Comment: Accepted to the Astrophysical Journal; 39 pages including 17 figure
Natural noise and external wake field seeding in a proton-driven plasma accelerator
We discuss the level of natural shot noise in a proton bunch-driven plasma
accelerator. The required seeding for the plasma wake field must be larger than
the cumulative shot noise. This is the necessary condition for the axial
symmetry of the generated wake and the acceleration quality. We develop an
analytical theory of the noise field and compare it with multi-dimensional
simulations. It appears that the natural noise wake field generated in plasma
by the available at CERN super-protons-synchrotron (SPS) bunches is very low,
at the level of a few 10 kV/m. This fortunate fact eases the requirements on
the seed. Our three dimensional simulations show that even a few tens MeV
electron bunch precursor of a very moderate intensity is sufficient to seed the
proton bunch self-modulation in plasma.Comment: 5 pages, 5 figure
ACTH-ectopic syndrome in a patient with a focus localization in the pancreas
The purpose of the study is to study diagnostic algorithms and therapy possibilities of this pathology using a clinical case example.Цель исследования – изучение алгоритмов диагностики и возможностей терапии данной патологии на примере клинического случая