23,144 research outputs found
Entropy gap and time asymmetry II
In this letter the paper [R. Aquilano, M. Castagnino, Mod. Phys. Lett A,11,
755 (1996)] is improved by considering that the main source of entropy
production are the stars photospheres
Addemdum to: ''The Mathematical Structure of Quantum Superspace as a Consequence of Time Asymmetry''
In this paper we improve the results of sec. VI of paper [M. Castagnino,
Phys. Rev. D 57, 750 (1998)] by considering that the main source of entropy
production are the photospheres of the stars
Molybdenum, Ruthenium, and the Heavy r-process Elements in Moderately Metal-Poor Main-Sequence Turnoff Stars
The ratios of elemental abundances observed in metal-poor stars of the
Galactic halo provide a unique present-day record of the nucleosynthesis
products of its earliest stars. While the heaviest elements were synthesized by
the r- and s-processes, dominant production mechanisms of light trans-ironic
elements were obscure until recently. This work investigates further our 2011
conclusion that the low-entropy regime of a high-entropy wind (HEW) produced
molybdenum and ruthenium in two moderately metal-poor turnoff stars that showed
extreme overabundances of those elements with respect to iron. Only a few, rare
nucleosynthesis events may have been involved.
Here we determine abundances for Mo, Ru, and other trans-Fe elements for 28
similar stars by matching spectral calculations to well-exposed near-UV Keck
HIRES spectra obtained for beryllium abundances. In each of the 26 turnoff
stars with Mo or Ru line detections and no evidence for s-process production
(therefore old), we find Mo and Ru to be three to six times overabundant. In
contrast, the maximum overabundance is reduced to factors of three and two for
the neighboring elements zirconium and palladium. Since the overproduction
peaks sharply at Mo and Ru, a low-entropy HEW is confirmed as its origin.
The overabundance level of the heavy r-process elements varies significantly,
from none to a factor of four, but is uncorrelated with Mo and Ru
overabundances. Despite their moderate metallicity, stars in this group trace
the products of different nucleosynthetic events: possibly very few events,
possibly events whose output depended on environment, metallicity, or time.Comment: Accepted April 2, 2013, for publication in the Astrophysical Journal
Letters (7 pages, 3 figures
Entropy Production of Main-Sequence Stars
The entropy production (inside the volume bounded by a photosphere) of main-sequence stars is calculated based on B–V photometry data. The entropy-production distribution function and the dependences of entropy production on temperature and luminosity are obtained for these stars for the first time. A very small range of variation of specific (per volume) entropy production discovered for main-sequence stars (only 0.5 to 1.8 solar magnitudes) is an interesting result that can be crucial for understanding thermodynamic processes of stars
Stars and statistical physics: a teaching experience
The physics of stars, their workings and their evolution, is a goldmine of
problems in statistical mechanics and thermodynamics. We discuss many examples
that illustrate the possibility of deepening student's knowledge of statistical
mechanics by an introductory study of stars. The matter constituting the
various stellar objects provides examples of equations of state for classical
or quantal and relativistic or non-relativistic gases. Maximum entropy can be
used to characterize thermodynamic and gravitational equilibrium which
determines the structure of stars and predicts their instability above a
certain mass. Contraction accompanying radiation induces either heating or
cooling, which explains the formation of stars above a minimum mass. The
characteristics of the emitted light are understood from black-body radiation
and more precisely from the Boltzmann-Lorentz kinetic equation for photons. The
luminosity is governed by the transport of heat by photons from the center to
the surface. Heat production by thermonuclear fusion is determined by
microscopic balance equations. The stability of the steady state of stars is
controlled by the interplay of thermodynamics and gravitation.Comment: latex gould_last.tex, 4 files, submitted to Am. J. Phy
Predicting the Cosmological Constant from the Causal Entropic Principle
We compute the expected value of the cosmological constant in our universe
from the Causal Entropic Principle. Since observers must obey the laws of
thermodynamics and causality, the principle asserts that physical parameters
are most likely to be found in the range of values for which the total entropy
production within a causally connected region is maximized. Despite the absence
of more explicit anthropic criteria, the resulting probability distribution
turns out to be in excellent agreement with observation. In particular, we find
that dust heated by stars dominates the entropy production, demonstrating the
remarkable power of this thermodynamic selection criterion. The alternative
approach - weighting by the number of "observers per baryon" - is less
well-defined, requires problematic assumptions about the nature of observers,
and yet prefers values larger than present experimental bounds.Comment: 38 pages, 9 figures, minor correction in Figure
Entropy Production of Stars
The entropy production (inside the volume bounded by a photosphere) of main-sequence stars, subgiants, giants, and supergiants is calculated based on B–V photometry data. A non-linear inverse relationship of thermodynamic fluxes and forces as well as an almost constant specific (per volume) entropy production of main-sequence stars (for 95% of stars, this quantity lies within 0.5 to 2.2 of the corresponding solar magnitude) is found. The obtained results are discussed from the perspective of known extreme principles related to entropy production
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