2,331 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
The influence of Pauli blocking effects on the properties of dense hydrogen
We investigate the effects of Pauli blocking on the properties of hydrogen at
high pressures, where recent experiments have shown a transition from
insulating behavior to metal-like conductivity. Since the Pauli principle
prevents multiple occupation of electron states (Pauli blocking), atomic states
disintegrate subsequently at high densities (Mott effect). We calculate the
energy shifts due to Pauli blocking and discuss the Mott effect solving an
effective Schroedinger equation for strongly correlated systems. The ionization
equilibrium is treated on the basis of a chemical approach. Results for the
ionization equilibrium and the pressure in the region 4.000 K < T < 20.000 K
are presented. We show that the transition to a highly conducting state is
softer than found in earlier work. A first order phase transition is observed
at T < 6.450 K, but a diffuse transition appears still up to 20.000 K.Comment: 8 pages, 4 figures, version accepted for publication in Journal of
Physics A: Mathematical and Theoretical, special issu
Directional motion of forced polymer chains with hydrodynamic interaction
We study the propulsion of a one-dimensional (1D) polymer chain under
sinusoidal external forces in the overdamped (low Reynolds number) regime. We
show that, when hydrodynamical interactions are included, the polymer presents
directional motion which depends on the phase differences of the external force
applied along the chain. Moreover, the velocity shows a maximum as a function
of the frequency. We discuss the relevance of all these results in light of
recent nanotechnology experiments.Comment: 5 pages, 6 figure
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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