182 research outputs found
Viscosity and thermal conductivity effects at first-order phase transitions in heavy-ion collisions
Effects of viscosity and thermal conductivity on the dynamics of first-order
phase transitions are studied. The nuclear gas-liquid and hadron-quark
transitions in heavy-ion collisions are considered. We demonstrate that at
non-zero thermal conductivity, , onset of spinodal instabilities
occurs on an isothermal spinodal line, whereas for instabilities
take place at lower temperatures, on an adiabatic spinodal.Comment: invited talk at 6th International Workshop on Critical Point and
Onset of Deconfinment (CPOD2010), Dubna, August 22-28, 201
Mapping the phase diagram of strongly interacting matter
We employ a conformal mapping to explore the thermodynamics of strongly
interacting matter at finite values of the baryon chemical potential .
This method allows us to identify the singularity corresponding to the critical
point of a second-order phase transition at finite , given information
only at . The scheme is potentially useful for computing thermodynamic
properties of strongly interacting hot and dense matter in lattice gauge
theory. The technique is illustrated by an application to a chiral effective
model.Comment: 5 pages, 3 figures; published versio
Net-proton probability distribution in heavy ion collisions
We compute net-proton probability distributions in heavy ion collisions
within the hadron resonance gas model. The model results are compared with data
taken by the STAR Collaboration in Au-Au collisions at sqrt(s_{NN})= 200 GeV
for different centralities. We show that in peripheral Au-Au collisions the
measured distributions, and the resulting first four moments of net-proton
fluctuations, are consistent with results obtained from the hadron resonance
gas model. However, data taken in central Au-Au collisions differ from the
predictions of the model. The observed deviations can not be attributed to
uncertainties in model parameters. We discuss possible interpretations of the
observed deviations.Comment: 4 pages, 2 figure
Magnetic properties of (FeCo)B alloys and the effect of doping by 5 elements
We have explored, computationally and experimentally, the magnetic properties
of \fecob{} alloys. Calculations provide a good agreement with experiment in
terms of the saturation magnetization and the magnetocrystalline anisotropy
energy with some difficulty in describing CoB, for which it is found that
both full potential effects and electron correlations treated within dynamical
mean field theory are of importance for a correct description. The material
exhibits a uniaxial magnetic anisotropy for a range of cobalt concentrations
between and . A simple model for the temperature dependence of
magnetic anisotropy suggests that the complicated non-monotonous temperature
behaviour is mainly due to variations in the band structure as the exchange
splitting is reduced by temperature. Using density functional theory based
calculations we have explored the effect of substitutional doping the
transition metal sublattice by the whole range of 5 transition metals and
found that doping by Re or W elements should significantly enhance the
magnetocrystalline anisotropy energy. Experimentally, W doping did not succeed
in enhancing the magnetic anisotropy due to formation of other phases. On the
other hand, doping by Ir and Re was successful and resulted in magnetic
anisotropies that are in agreement with theoretical predictions. In particular,
doping by 2.5~at.\% of Re on the Fe/Co site shows a magnetocrystalline
anisotropy energy which is increased by 50\% compared to its parent
(FeCo)B compound, making this system interesting, for
example, in the context of permanent magnet replacement materials or in other
areas where a large magnetic anisotropy is of importance.Comment: 15 pages 17 figure
Fluctuations as probe of the QCD phase transition and freeze-out in heavy ion collisions at LHC and RHIC
We discuss the relevance of higher order moments of net baryon number
fluctuations for the analysis of freeze-out and critical conditions in heavy
ion collisions at LHC and RHIC. Using properties of O(4) scaling functions, we
discuss the generic structure of these higher moments at vanishing baryon
chemical potential and apply chiral model calculations to explore their
properties at non-zero baryon chemical potential. We show that the ratios of
the sixth to second and eighth to second order moments of the net baryon number
fluctuations change rapidly in the transition region of the QCD phase diagram.
Already at vanishing baryon chemical potential they deviate considerably from
the predictions of the hadron resonance gas model which reproduce the second to
fourth order moments of the net proton number fluctuations at RHIC. We point
out that the sixth order moments of baryon number and electric charge
fluctuations remain negative at the chiral transition temperature. Thus, they
offer the possibility to probe the proximity of the thermal freeze-out to the
crossover line.Comment: 24 pages, 12 EPS files, revised version, to appear in EPJ
Hydrodynamical description of a hadron-quark first-order phase transition
Solutions of hydrodynamical equations are presented for the equation of state
of the Var der Waals type allowing for the first order phase transition.
Attention is focused on description of the hadron-quark phase transition in
heavy ion collisions. It is shown that fluctuations dissolve and grow as if the
fluid is effectively very viscous. Even in spinodal region germs are growing
slowly due to viscosity and critical slowing down. This prevents enhancement of
fluctuations in the near-critical region, which is frequently considered as a
signal of the critical point in heavy ion collisions.Comment: 4 pages, 4 figure
1/f noise from correlations between avalanches in self-organized criticality
We show that large, slowly driven systems can evolve to a self-organized
critical state where long range temporal correlations between bursts or
avalanches produce low frequency noise. The avalanches can occur
instantaneously in the external time scale of the slow drive, and their event
statistics are described by power law distributions. A specific example of this
behavior is provided by numerical simulations of a deterministic ``sandpile''
model.Comment: Completely revised version: 4 pages (revtex), 3 eps figure
Net-charge probability distributions in heavy ion collisions at chemical freeze-out
We explore net charge probability distributions in heavy ion collisions
within the hadron resonance gas model. The distributions for strangeness,
electric charge and baryon number are derived. We show that, within this model,
net charge probability distributions and the resulting fluctuations can be
computed directly from the measured yields of charged and multi-charged
hadrons. The influence of multi-charged particles and quantum statistics on the
shape of the distribution is examined. We discuss the properties of the net
proton distribution along the chemical freeze-out line. The model results
presented here can be compared with data at RHIC energies and at the LHC to
possibly search for the relation between chemical freeze-out and QCD cross-over
lines in heavy ion collisions.Comment: 21 pages, 6 figure
- …