2,891 research outputs found
Electronic structure and transport properties of CeNi9In2
We investigated CeNi9In2 compound, which has been considered as a mixed
valence (MV) system. Electrical resistivity vs. temperature variation was
analysed in terms of the model proposed by Freimuth for systems with unstable
4f shell. At low temperature the resistivity dependence is consistent with a
Fermi liquid state with a contribution characteristic of electron-phonon
interaction. Ultraviolet photoemission spectroscopy (UPS) studies of the
valence band did not reveal a Kondo peak down to 14 K. A difference of the
spectra obtained with photon energies of low and high photoionization cross
sections for Ce 4f electrons indicated that 4f states are located mainly close
to the Fermi energy. The peaks related to f_{5/2}^1 and f_{7/2}^1 final states
cannot be resolved but form a plateau between -0.3 eV and the Fermi energy.
X-ray photoemission spectroscopy (XPS) studies were realized for the cerium 3d
level. The analysis of XPS spectra within the Gunnarsson-Sh\"onhammer theory
yielded a hybridization parameter of 104 meV and non-integer f level
occupation, being close to 3. Calculations of partial densities of states were
realized by a full potential local orbital (FPLO) method. They confirm that the
valence band is dominated by Ni 3d states and are in general agreement with the
experiment except for the behavior of f-electrons.Comment: 10 pages, 5 figure
KIC7668647: a 14 day beaming sdB+WD binary with a pulsating subdwarf
The recently discovered subdwarf B (sdB) pulsator KIC7668647 is one of the 18
pulsating sdB stars detected in the Kepler field. It features a rich g-mode
frequency spectrum, with a few low-amplitude p-modes at short periods.
We use new ground-based low-resolution spectroscopy, and the near-continuous
2.88 year Kepler lightcurve, to reveal that KIC7668647 consists of a subdwarf B
star with an unseen white-dwarf companion with an orbital period of 14.2d. An
orbit with a radial-velocity amplitude of 39km/s is consistently determined
from the spectra, from the orbital Doppler beaming seen by Kepler at 163ppm,
and from measuring the orbital light-travel delay of 27 by timing of the many
pulsations seen in the Kepler lightcurve. The white dwarf has a minimum mass of
0.40 M_sun.
We use our high signal-to-noise average spectra to study the atmospheric
parameters of the sdB star, and find that nitrogen and iron have abundances
close to solar values, while helium, carbon, oxygen and silicon are
underabundant relative to the solar mixture.
We use the full Kepler Q06--Q17 lightcurve to extract 132 significant
pulsation frequencies. Period-spacing relations and multiplet splittings allow
us to identify the modal degree L for the majority of the modes. Using the
g-mode multiplet splittings we constrain the internal rotation period at the
base of the envelope to 46-48d as a first seismic result for this star. The few
p-mode splittings may point at a slightly longer rotation period further out in
the envelope of the star.
From mode-visibility considerations we derive that the inclination of the
rotation axis of the sdB in KIC7668647 must be around ~60 degrees.
Furthermore, we find strong evidence for a few multiplets indicative of
degree 3 <= L <= 8, which is another novelty in sdB-star observations made
possible by Kepler.Comment: arXiv admin note: text overlap with arXiv:1206.387
Free-streaming approximation in early dynamics of relativistic heavy-ion collisions
We investigate an approximation to early dynamics in relativistic heavy-ion
collisions, where after formation the partons are free streaming and around the
proper time of 1 fm/c undergo a sudden equilibration described in terms of the
Landau matching condition. We discuss physical and formal aspects of this
approach. In particular, we show that initial azimuthally asymmetric transverse
flow develops for non-central collisions as a consequence of the sudden
equilibration. Moreover, the energy-momentum tensor from the free-streaming
stage matches very smoothly to the form used in the transverse hydrodynamics,
whereas matching to isotropic hydrodynamics requires a more pronounced change
in the energy-momentum tensor. After the hydrodynamic phase statistical
hadronization is carried out with the help of THERMINATOR. The physical results
for the transverse-momentum spectra, the elliptic-flow, and the
Hanbury-Brown--Twiss correlation radii, including the ratio R_out/R_side as
well as the dependence of the radii on the azimuthal angle (azHBT), are
properly described within our approach. The agreement is equally good for a
purely hydrodynamic evolution started at an early proper time of 0.25 fm/c, or
for the free streaming started at that time, followed by the sudden
equilibration at tau ~1 fm/c and then by perfect hydrodynamics. Thus, the
inclusion of free streaming allows us to delay the start of hydrodynamics to
more realistic times of the order of 1 fm/c.Comment: 10 pages, 12 figure
The Neutron Halo in Heavy Nuclei Calculated with the Gogny Force
The proton and neutron density distributions, one- and two-neutron separation
energies and radii of nuclei for which neutron halos are experimentally
observed, are calculated using the self-consistent Hartree-Fock-Bogoliubov
method with the effective interaction of Gogny. Halo factors are evaluated
assuming hydrogen-like antiproton wave functions. The factors agree well with
experimental data. They are close to those obtained with Skyrme forces and with
the relativistic mean field approach.Comment: 13 pages in Latex and 17 figures in ep
Comparison of Chemical Freeze-Out Criteria in Heavy-Ion Collisions
One of the most remarkable results to emerge from heavy-ion collisions over
the past two decades is the striking regularity shown by particle yields at all
energies. This has led to several very successful proposals describing particle
yields over a very wide range of beam energies, reaching from 1 A GeV up to 200
A GeV, using only one or two parameters. A systematic comparison of these
proposals is presented here. The conditions of fixed energy per particle,
baryon+anti-baryon density, normalized entropy density as well as percolation
model are investigated. The results are compared with the most recent chemical
freeze-out parameters obtained in the thermal-statistical analysis of particle
yields. The sensitivity and dependence of the results on parameters is analyzed
and discussed. It is shown that in the energy range above the top AGS energy,
within present accuracies, all chemical freeze-out criteria give a fairly good
description of the particle yields. However, the low energy heavy-ion data
favor the constant energy per particle as a unified condition of chemical
particle freeze-out. This condition also shows the weakest sensitivity on model
assumptions and parameters.Comment: 15 pages 7 figures uses revte
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