55,167 research outputs found
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
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
Asteroseismology and Magnetic Cycles
Small cyclic variations in the frequencies of acoustic modes are expected to
be a common phenomenon in solar-like pulsators, as a result of stellar magnetic
activity cycles. The frequency variations observed throughout the solar and
stellar cycles contain information about structural changes that take place
inside the stars as well as about variations in magnetic field structure and
intensity. The task of inferring and disentangling that information is,
however, not a trivial one. In the sun and solar-like pulsators, the direct
effect of the magnetic field on the oscillations might be significantly
important in regions of strong magnetic field (such as solar- / stellar-spots),
where the Lorentz force can be comparable to the gas-pressure gradient. Our aim
is to determine the sun- / stellar-spots effect on the oscillation frequencies
and attempt to understand if this effect contributes strongly to the frequency
changes observed along the magnetic cycle. The total contribution of the spots
to the frequency shifts results from a combination of direct and indirect
effects of the magnetic field on the oscillations. In this first work we
considered only the indirect effect associated with changes in the
stratification within the starspot. Based on the solution of the wave equation
and the variational principle we estimated the impact of these stratification
changes on the oscillation frequencies of global modes in the sun and found
that the induced frequency shifts are about two orders of magnitude smaller
than the frequency shifts observed over the solar cycle.Comment: 4 pages, 6 figures, ESF Conference: The Modern Era of Helio- and
Asteroseismology, to be published on 3 December 2012 at Astronomische
Nachrichten 333, No. 10, 1032-103
Evidence for an inflationary phase transition from the LSS and CMB anisotropy data
In the light of the recent Boomerang and Maxima observations of the CMB which
show an anomalously low second acoustic peak, we reexamine the prediction by
Adams et al (1997) that this would be the consequence of a 'step' in the
primordial spectrum induced by a spontaneous symmetry breaking phase transition
during primordial inflation. We demonstrate that a deviation from
scale-invariance around ~Mpc can simultaneously explain both
the feature identified earlier in the APM galaxy power spectrum as well the
recent CMB anisotropy data, with a baryon density consistent with the BBN
value. Such a break also allows a good fit to the data on cluster abundances
even for a critical density matter-dominated universe with zero cosmological
constant.Comment: 4 pages with 3 figures, LaTeX file using espcrc2.sty to appear on the
Proceedings of "Euroconference on Frontiers in Particle Astrophysics and
Cosmology",Sant Feliu de Guixols,Spain,30th September-5th October of 200
Massless and massive one-loop three-point functions in negative dimensional approach
In this article we present the complete massless and massive one-loop
triangle diagram results using the negative dimensional integration method
(NDIM). We consider the following cases: massless internal fields; one massive,
two massive with the same mass m and three equal masses for the virtual
particles. Our results are given in terms of hypergeometric and
hypergeometric-type functions of external momenta (and masses for the massive
cases) where the propagators in the Feynman integrals are raised to arbitrary
exponents and the dimension of the space-time D. Our approach reproduces the
known results as well as other solutions as yet unknown in the literature.
These new solutions occur naturally in the context of NDIM revealing a
promising technique to solve Feynman integrals in quantum field theories
On the functional form of the metallicity-giant planet correlation
It is generally accepted that the presence of a giant planet is strongly
dependent on the stellar metallicity. A stellar mass dependence has also been
investigated, but this dependence does not seem as strong as the metallicity
dependence. Even for metallicity, however, the exact form of the correlation
has not been established. In this paper, we test several scenarios for
describing the frequency of giant planets as a function of its host parameters.
We perform this test on two volume-limited samples (from CORALIE and HARPS). By
using a Bayesian analysis, we quantitatively compared the different scenarios.
We confirm that giant planet frequency is indeed a function of metallicity.
However, there is no statistical difference between a constant or an
exponential function for stars with subsolar metallicities contrary to what has
been previously stated in the literature. The dependence on stellar mass could
neither be confirmed nor be discarded.Comment: 5 pages, 2 figures, accepted in A&
Hydrogen storage in the form of metal hydrides
Reversible reactions between hydrogen and such materials as iron/titanium and magnesium/ nickel alloy may provide a means for storing hydrogen fuel. A demonstration model of an iron/titanium hydride storage bed is described. Hydrogen from the hydride storage bed powers a converted gasoline electric generator
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