2,337 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
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
A measurement of large-scale peculiar velocities of clusters of galaxies: results and cosmological implications
Peculiar velocities of clusters of galaxies can be measured by studying the
fluctuations in the cosmic microwave background (CMB) generated by the
scattering of the microwave photons by the hot X-ray emitting gas inside
clusters. While for individual clusters such measurements result in large
errors, a large statistical sample of clusters allows one to study cumulative
quantities dominated by the overall bulk flow of the sample with the
statistical errors integrating down. We present results from such a measurement
using the largest all-sky X-ray cluster catalog combined to date and the 3-year
WMAP CMB data. We find a strong and coherent bulk flow on scales out to at
least > 300 h^{-1} Mpc, the limit of our catalog. This flow is difficult to
explain by gravitational evolution within the framework of the concordance LCDM
model and may be indicative of the tilt exerted across the entire current
horizon by far-away pre-inflationary inhomogeneities.Comment: Ap.J. (Letters), in press. 20 Oct issue (Vol. 686
A measurement of large-scale peculiar velocities of clusters of galaxies: technical details
This paper presents detailed analysis of large-scale peculiar motions derived
from a sample of ~ 700 X-ray clusters and cosmic microwave background (CMB)
data obtained with WMAP. We use the kinematic Sunyaev-Zeldovich (KSZ) effect
combining it into a cumulative statistic which preserves the bulk motion
component with the noise integrated down. Such statistic is the dipole of CMB
temperature fluctuations evaluated over the pixels of the cluster catalog
(Kashlinsky & Atrio-Barandela 2000). To remove the cosmological CMB
fluctuations the maps are Wiener-filtered in each of the eight WMAP channels
(Q, V, W) which have negligible foreground component. Our findings are as
follows: The thermal SZ (TSZ) component of the clusters is described well by
the Navarro-Frenk-White profile expected if the hot gas traces the dark matter
in the cluster potential wells. Such gas has X-ray temperature decreasing
rapidly towards the cluster outskirts, which we demonstrate results in the
decrease of the TSZ component as the aperture is increased to encompass the
cluster outskirts. We then detect a statistically significant dipole in the CMB
pixels at cluster positions. Arising exclusively at the cluster pixels this
dipole cannot originate from the foreground or instrument noise emissions and
must be produced by the CMB photons which interacted with the hot intracluster
gas via the SZ effect. The dipole remains as the monopole component, due to the
TSZ effect, vanishes within the small statistical noise out to the maximal
aperture where we still detect the TSZ component. We demonstrate with
simulations that the mask and cross-talk effects are small for our catalog and
contribute negligibly to the measurements. The measured dipole thus arises from
the KSZ effect produced by the coherent large scale bulk flow motion.Comment: Minor changes to match the published version - Ap.J., 1 Feb 2009
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