2,626,405 research outputs found
Information Equation of State
Landauer's principle is applied to information in the universe. Once stars
began forming, the increasing proportion of matter at high stellar temperatures
compensated for the expanding universe to provide a near constant information
energy density. The information equation of state was close to the dark energy
value, w = -1, for a wide range of redshifts, 10> z >0.8, over one half of
cosmic time. A reasonable universe information bit content of only 10^87 bits
is sufficient for information energy to account for all dark energy. A time
varying equation of state with a direct link between dark energy and matter,
and linked to star formation in particular, is clearly relevant to the cosmic
coincidence problem.In answering the "Why now?" question we wonder "What next?"
as we expect the information equation of state to tend towards w = 0 in the
future.Comment: 10 pages, 2 figure
Thermal Equation of State of Tantalum
We have investigated the thermal equation of state of tantalum from first
principles using the Linearized Augmented Plane Wave (LAPW) and pseudopotential
methods for pressures up to 300 GPa and temperatures up to 10000 K. The
equation of state at zero temperature was computed using LAPW. For finite
temperatures, mixed basis pseudopotential computations were performed for 54
atom supercells. The vibrational contributions were obtained by computing the
partition function using the particle in a cell model, and the the finite
temperature electronic free energy was obtained from the LAPW band structures.
We discuss the behavior of thermal equation of state parameters such as the
Gr\"uneisen parameter , , the thermal expansivity , the
Anderson-Gr\"uneisen parameter as functions of pressure and
temperature. The calculated Hugoniot shows excellent agreement with shock-wave
experiments. An electronic topological transition was found at approximately
200 GPa
Interpolation of equation-of-state data
Aims. We use Hermite splines to interpolate pressure and its derivatives
simultaneously, thereby preserving mathematical relations between the
derivatives. The method therefore guarantees that thermodynamic identities are
obeyed even between mesh points. In addition, our method enables an estimation
of the precision of the interpolation by comparing the Hermite-spline results
with those of frequent cubic (B-) spline interpolation.
Methods. We have interpolated pressure as a function of temperature and
density with quintic Hermite 2D-splines. The Hermite interpolation requires
knowledge of pressure and its first and second derivatives at every mesh point.
To obtain the partial derivatives at the mesh points, we used tabulated values
if given or else thermodynamic equalities, or, if not available, values
obtained by differentiating B-splines.
Results. The results were obtained with the grid of the SAHA-S
equation-of-state (EOS) tables. The maximum difference lies in the range
from to , and difference varies from to
. Specifically, for the points of a solar model, the maximum
differences are one order of magnitude smaller than the aforementioned values.
The poorest precision is found in the dissociation and ionization regions,
occurring at K. The best precision is achieved at
higher temperatures, K. To discuss the significance of the
interpolation errors we compare them with the corresponding difference between
two different equation-of-state formalisms, SAHA-S and OPAL 2005. We find that
the interpolation errors of the pressure are a few orders of magnitude less
than the differences from between the physical formalisms, which is
particularly true for the solar-model points.Comment: Accepted for publication in A&
Equation of State and Collective Dynamics
This talk summarizes the present status of a program to quantitatively relate
data from the Relativistic Heavy Ion Collider (RHIC) on collective expansion
flow to the Equation of State (EOS) of hot and dense strongly interacting
matter, including the quark-gluon plasma and the quark-hadron phase transition.
The limits reached with the present state of the art and the next steps
required to make further progress will both be discussed.Comment: 8 pages, 6 two-part figures. Invited talk given at the 5th
International Conference on the Physics and Astrophysics of Quark-Gluon
Plasma (ICPAQGP 2005), Kolkata (India), Feb 8-12, 2005. Proceedings to be
published in Journal of Physics: Conference Series (Jan-E Alam et al., eds.
Kinetic equation consistent with the equation of state of nuclear matter
A kinetic equation which combines the quasiparticle drift of Landau's
equation with a dissipation governed by a nonlocal and noninstant scattering
integral in the spirit of Snider's equation for gases is derived. Consequent
balance equations for the density, momentum and energy include quasiparticle
contributions and the second order quantum virial corrections. The medium
effects on binary collisions are shown to mediate the latent heat, i.e., an
energy conversion between correlation and thermal energy. An implementation to
heavy ion collisions is discussed
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