2,296 research outputs found
Thermodynamics of hot dense H-plasmas: Path integral Monte Carlo simulations and analytical approximations
This work is devoted to the thermodynamics of high-temperature dense hydrogen
plasmas in the pressure region between and Mbar. In particular
we present for this region results of extensive calculations based on a
recently developed path integral Monte Carlo scheme (direct PIMC). This method
allows for a correct treatment of the thermodynamic properties of hot dense
Coulomb systems. Calculations were performed in a broad region of the
nonideality parameter and degeneracy parameter . We give a comparison with a few available results from
other path integral calculations (restricted PIMC) and with analytical
calculations based on Pade approximations for strongly ionized plasmas. Good
agreement between the results obtained from the three independent methods is
found.Comment: RevTex file, 21 pages, 5 ps-figures include
On anomalous diffusion in a plasma in velocity space
The problem of anomalous diffusion in momentum space is considered for
plasma-like systems on the basis of a new collision integral, which is
appropriate for consideration of the probability transition function (PTF) with
long tails in momentum space. The generalized Fokker-Planck equation for
description of diffusion (in momentum space) of particles (ions, grains etc.)
in a stochastic system of light particles (electrons, or electrons and ions,
respectively) is applied to the evolution of the momentum particle distribution
in a plasma. In a plasma the developed approach is also applicable to the
diffusion of particles with an arbitrary mass relation, due to the small
characteristic momentum transfer. The cases of an exponentially decreasing in
momentum space (including the Boltzmann-like) kernel in the PT-function, as
well as the more general kernels, which create the anomalous diffusion in
velocity space due to the long tail in the PT-function, are considered.
Effective friction and diffusion coefficients for plasma-like systems are
found.Comment: 18 pages, no figure
Sunyaev-Zeldovich effect in WMAP and its effect on cosmological parameters
We use multi-frequency information in first year WMAP data to search for the
Sunyaev-Zeldovich (SZ) effect. WMAP has sufficiently broad frequency coverage
to constrain SZ without the addition of higher frequency data: the SZ power
spectrum amplitude is expected to increase 50% from W to Q frequency band.
This, in combination with the low noise in WMAP, allows us to strongly
constrain the SZ contribution. We derive an optimal frequency combination of
WMAP cross-spectra to extract SZ in the presence of noise, CMB, and radio point
sources, which are marginalized over. We find that the SZ contribution is less
than 2% (95% c.l.) at the first acoustic peak in W band. Under the assumption
that the removed radio point sources are not correlated with SZ this limit
implies sigma_8<1.07 at 95% c.l. We investigate the effect on the cosmological
parameters of allowing an SZ component. We run Monte Carlo Markov Chains with
and without an SZ component and find that the addition of SZ does not affect
any of the cosmological conclusions. We conclude that SZ does not contaminate
the WMAP CMB or change cosmological parameters, refuting the recent claims that
they may be corrupted.Comment: 10 pages, 5 figures, 2 tables. Submitted to Phys. Rev.
Thirty-fold: Extreme gravitational lensing of a quiescent galaxy at
We report the discovery of eMACSJ1341-QG-1, a quiescent galaxy at
located behind the massive galaxy cluster eMACSJ1341.92442 (). The
system was identified as a gravitationally lensed triple image in Hubble Space
Telescope images obtained as part of a snapshot survey of the most X-ray
luminous galaxy clusters at and spectroscopically confirmed in
ground-based follow-up observations with the ESO/X-Shooter spectrograph. From
the constraints provided by the triple image, we derive a first, crude model of
the mass distribution of the cluster lens, which predicts a gravitational
amplification of a factor of 30 for the primary image and a factor of
6 for the remaining two images of the source, making eMACSJ1341-QG-1 by
far the most strongly amplified quiescent galaxy discovered to date. Our
discovery underlines the power of SNAPshot observations of massive, X-ray
selected galaxy clusters for lensing-assisted studies of faint background
populations
Reconstruction of a first-order phase transition from computer simulations of individual phases and subphases
We present a new method for investigating first-order phase transitions using
Monte Carlo simulations. It relies on the multiple-histogram method and uses
solely histograms of individual phases. In addition, we extend the method to
include histograms of subphases. The free energy difference between phases,
necessary for attributing the correct statistical weights to the histograms, is
determined by a detour in control parameter space via auxiliary systems with
short relaxation times. We apply this method to a recently introduced model for
structure formation in polypeptides for which other methods fail.Comment: 13 pages in preprint mode, REVTeX, 2 Figures available from the
authors ([email protected], [email protected]
On reaction-subdiffusion equations
To analyze possible generalizations of reaction-diffusion schemes for the
case of subdiffusion we discuss a simple monomolecular conversion A --> B. We
derive the corresponding kinetic equations for local A and B concentrations.
Their form is rather unusual: The parameters of reaction influence the
diffusion term in the equation for a component A, a consequence of the
nonmarkovian nature of subdiffusion. The equation for a product contains a term
which depends on the concentration of A at all previous times. Our discussion
shows that reaction-subdiffusion equations may not resemble the corresponding
reaction-diffusion ones and are not obtained by a trivial change of the
diffusion operator for a subdiffusion one
ROSAT PSPC Observations of the Richest () ACO Clusters
We have compiled an X-ray catalog of optically selected rich clusters of
galaxies observed by the PSPC during the pointed GO phase of the ROSAT mission.
This paper contains a systematic X-ray analysis of 150 clusters with an optical
richness classification of from the ACO catalog (Abell, Corwin, and
Olowin 1989). All clusters were observed within 45' of the optical axis of the
telescope during pointed PSPC observations. For each cluster, we calculate: the
net 0.5-2.0 keV PSPC count rate (or upper limit) in a 1 Mpc radius
aperture, 0.5-2.0 keV flux and luminosity, bolometric luminosity, and X-ray
centroid. The cluster sample is then used to examine correlations between the
X-ray and optical properties of clusters, derive the X-ray luminosity function
of clusters with different optical classifications, and obtain a quantitative
estimate of contamination (i.e, the fraction of clusters with an optical
richness significantly overestimated due to interloping galaxies) in the ACO
catalog
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