55 research outputs found
On the calculation of equilibrium thermodynamic properties and the establishment of statistical-thermodynamically-consistent finite bound-state partition functions in nonideal multi-component plasma mixtures within the chemical model
The problem of the calculation of equilibrium thermodynamic properties and
the establishment of statistical-thermodynamically-consistent finite
bound-state partition functions in nonideal multi-component plasma systems is
revised within the chemical picture. The present exploration accompanied by the
introduction of a generalized accurate formulation, in terms of the solution of
the inverse problem, clears ambiguities and gives a better understanding of the
problem on top of pointing out weaknesses and inaccuracies/inconsistencies
buried in widely used models in the literature.Comment: 22 pages, 4 figure
Astrophysical implications of hypothetical stable TeV-scale black holes
We analyze macroscopic effects of TeV-scale black holes, such as could
possibly be produced at the LHC, in what is regarded as an extremely
hypothetical scenario in which they are stable and, if trapped inside Earth,
begin to accrete matter. We examine a wide variety of TeV-scale gravity
scenarios, basing the resulting accretion models on first-principles, basic,
and well-tested physical laws. These scenarios fall into two classes, depending
on whether accretion could have any macroscopic effect on the Earth at times
shorter than the Sun's natural lifetime. We argue that cases with such effect
at shorter times than the solar lifetime are ruled out, since in these
scenarios black holes produced by cosmic rays impinging on much denser white
dwarfs and neutron stars would then catalyze their decay on timescales
incompatible with their known lifetimes. We also comment on relevant lifetimes
for astronomical objects that capture primordial black holes. In short, this
study finds no basis for concerns that TeV-scale black holes from the LHC could
pose a risk to Earth on time scales shorter than the Earth's natural lifetime.
Indeed, conservative arguments based on detailed calculations and the
best-available scientific knowledge, including solid astronomical data,
conclude, from multiple perspectives, that there is no risk of any significance
whatsoever from such black holes.Comment: Version2: Minor corrections/fixed typos; updated reference
Iron and Nickel spectral opacity calculations in conditions relevant for pulsating stellar envelopes and experiments
Seismology of stars is strongly developing. To address this question we have
formed an international collaboration OPAC to perform specific experimental
measurements, compare opacity calculations and improve the opacity calculations
in the stellar codes [1]. We consider the following opacity codes: SCO,
CASSANDRA, STA, OPAS, LEDCOP, OP, SCO-RCG. Their comparison has shown large
differences for Fe and Ni in equivalent conditions of envelopes of type II
supernova precursors, temperatures between 15 and 40 eV and densities of a few
mg/cm3 [2, 3, 4]. LEDCOP, OPAS, SCO-RCG structure codes and STA give similar
results and differ from OP ones for the lower temperatures and for spectral
interval values [3]. In this work we discuss the role of Configuration
Interaction (CI) and the influence of the number of used configurations. We
present and include in the opacity code comparisons new HULLAC-v9 calculations
[5, 6] that include full CI. To illustrate the importance of this effect we
compare different CI approximations (modes) available in HULLAC-v9 [7]. These
results are compared to previous predictions and to experimental data.
Differences with OP results are discussed.Comment: 4 pages, 3 figures, conference Inertial Fusion Sciences and
Applications, Bordeaux, 12th to 16th September 2011; EPJ web of Conferences
201
Theoretical and experimental activities on opacities for a good interpretation of seismic stellar probes
Opacity calculations are basic ingredients of stellar modelling. They play a
crucial role in the interpretation of acoustic modes detected by SoHO, COROT
and KEPLER. In this review we present our activities on both theoretical and
experimental sides. We show new calculations of opacity spectra and comparisons
between eight groups who produce opacity spectra calculations in the domain
where experiments are scheduled. Real differences are noticed with real
astrophysical consequences when one extends helioseismology to cluster studies
of different compositions. Two cases are considered presently: (1) the solar
radiative zone and (2) the beta Cephei envelops. We describe how our
experiments are performed and new preliminary results on nickel obtained in the
campaign 2010 at LULI 2000 at Polytechnique.Comment: 6 pages, 4 figures, invited talk at SOHO2
Radiative properties of stellar plasmas and open challenges
The lifetime of solar-like stars, the envelope structure of more massive
stars, and stellar acoustic frequencies largely depend on the radiative
properties of the stellar plasma. Up to now, these complex quantities have been
estimated only theoretically. The development of the powerful tools of helio-
and astero- seismology has made it possible to gain insights on the interiors
of stars. Consequently, increased emphasis is now placed on knowledge of the
monochromatic opacity coefficients. Here we review how these radiative
properties play a role, and where they are most important. We then concentrate
specifically on the envelopes of Cephei variable stars. We discuss the
dispersion of eight different theoretical estimates of the monochromatic
opacity spectrum and the challenges we need to face to check these calculations
experimentally.Comment: 6 pages, 5 figures, in press (conference HEDLA 2010
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