87,022 research outputs found
Bifurcations in the theory of current transfer to cathodes of dc discharges and observations of transitions between different modes
General scenarios of transitions between different spot patterns on
electrodes of dc gas discharges and their relation to bifurcations of
steady-state solutions are analyzed. In the case of cathodes of arc discharges,
it is shown that any transition between different modes of current transfer is
related to a bifurcation of steady-state solutions. In particular, transitions
between diffuse and spot modes on axially symmetric cathodes, frequently
observed in the experiment, represent an indication of the presence of
pitchfork or fold bifurcations of steady-state solutions. Experimental
observations of transitions on cathodes of dc glow microdischarges are analyzed
and those potentially related to bifurcations of steady-state solutions are
identified. The relevant bifurcations are investigated numerically and the
computed patterns are found to conform to those observed in the course of the
corresponding transitions in the experiment
Light elements in stars with exoplanets
It is well known that stars orbited by giant planets have higher abundances
of heavy elements when compared with average field dwarfs. A number of studies
have also addressed the possibility that light element abundances are different
in these stars. In this paper we will review the present status of these
studies. The most significant trends will be discussed.Comment: 10 pages, 6 figures. Submitted to the proceedings of IAU symposium
268: Light elements in the universe
Unified line profiles for hydrogen perturbed by collisions with protons: satellites and asymmetries
We present new calculations of unified line profiles for hydrogen perturbed
by collisions with protons. We report on new calculations of the potential
energies and dipole moments which allow the evaluation of profiles for the
lines of the Lyman series up to Lyman and the Balmer series up to
Balmer10. Unified calculations only existed for the lines Lyman to
Lyman and Balmer including the H quasi-molecule. These
data are available as online material accompanying this paper and should be
included in atmosphere models, in place of the Stark effect of protons, since
the quasi-molecular contributions cause not only satellites, but large
asymmetries that are unaccounted for in models that assume Stark broadening of
electrons and protons are equal.Comment: 13 pages, 25 figures. Accepted for publication in MNRA
Energy Conditions and Supernovae Observations
In general relativity, the energy conditions are invoked to restrict general
energy-momentum tensors on physical grounds. We show that in the standard
Friedmann-Lemaitre-Robertson-Walker approach to cosmological modelling where
the equation of state of the cosmological fluid is unknown, the energy
conditions provide model-independent bounds on the behavior of the distance
modulus of cosmic sources as a function of the redshift. We use both the gold
and the legacy samples of current type Ia supenovae to carry out a
model-independent analysis of the energy conditions violation in the context of
standard cosmology.Comment: 4 pages, 2 figures; v2: References added, misprints corrected,
published in Phys.Rev.D in the present for
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