2,959 research outputs found
Dynamical interpretation of chemical freeze-out in heavy ion collisions
It is demonstrated that there exists a direct correlation between chemical
freeze-out point and the softest point of the equation of state where the
pressure divided by the energy density, , has a minimum.
A dynamical model is given as an example where the passage of the softest point
coincides with the condition for chemical freeze-out, namely an average energy
per hadron 1 GeV. The sensitivity of the result to the equation of
state used is discussed.Comment: 10 pages, 2 figure
Thermodynamic limit and semi--intensive quantities
The properties of statistical ensembles with abelian charges close to the
thermodynamic limit are discussed. The finite volume corrections to the
probability distributions and particle density moments are calculated. Results
are obtained for statistical ensembles with both exact and average charge
conservation. A new class of variables (semi--intensive variables) which differ
in the thermodynamic limit depending on how charge conservation is implemented
in the system is introduced. The thermodynamic limit behavior of these
variables is calculated through the next to leading order finite volume
corrections to the corresponding probability density distributions.Comment: 11 pages, 2 figures In v2 figures are added and corresponding
editorial changes are done. Paper will be published in Journal of Physics
Vacuum fluctuations and the thermodynamics of chiral models
We consider the thermodynamics of chiral models in the mean-field
approximation and discuss the relevance of the (frequently omitted) fermion
vacuum loop. Within the chiral quark-meson model and its Polyakov loop extended
version, we show that the fermion vacuum fluctuations can change the order of
the phase transition in the chiral limit and strongly influence physical
observables. We compute the temperature-dependent effective potential and
baryon number susceptibilities in these models, with and without the vacuum
term, and explore the cutoff and the pion mass dependence of the
susceptibilities. Finally, in the renormalized model the divergent vacuum
contribution is removed using the dimensional regularization.Comment: 9 pages, 5 figure
The QCD equation of state for two flavours at non-zero chemical potential
We present results of a simulation of 2 flavour QCD on a
lattice using p4-improved staggered fermions with bare quark mass .
Derivatives of the thermodynamic grand canonical partition function
with respect to chemical potentials for
different quark flavours are calculated up to sixth order, enabling estimates
of the pressure and the quark number density as well as the chiral condensate
and various susceptibilities as functions of via Taylor series
expansion. Results are compared to high temperature perturbation theory as well
as a hadron resonance gas model. We also analyze baryon as well as isospin
fluctuations and discuss the relation to the chiral critical point in the QCD
phase diagram. We moreover discuss the dependence of the heavy quark free
energy on the chemical potential.Comment: 4 pages, 7 figures, talk presented at Quark Matter 2005, Budapes
Liver injury in workers exposed to dimethylformamide
An apparent epidemic cluster of toxic liver disease was reexamined among workers exposed to the solvent dimethylformamide. A demographically similar but unexposed group from a preemployment population was used for comparison. Analysis, after data transformation of the liver transaminases, revealed significant differences between the two populations with respect to the serum glutamic pyruvic transaminase and the ratio of serum glutaminic oxaloacetic transaminase to serum glutamic pyruvic transaminase. Thus a value of the ratio of serum glutamic oxaloacetic transaminase to serum glutamic pyruvic transaminase. Thus a value of the ratio less than 1 may be suggestive of toxic liver disease. Medical surveillance of the working population for 14 months revealed no further cases of toxic liver disease. Dimethylformamide was almost certainly the causative agent of the original epidemic. The use of preemployment populations as a source of unexposed subjects in the analysis of occupational clusters is recommended, especially in the scenario of relatively acute, and highly prevalent, occupational diseases
Conditions driving chemical freeze-out
We propose the entropy density as the thermodynamic condition driving best
the chemical freeze-out in heavy-ion collisions. Taking its value from lattice
calculations at zero chemical potential, we find that it is excellent in
reproducing the experimentally estimated freeze-out parameters. The two
characteristic endpoints in the freeze-out diagram are reproduced as well.Comment: 8 pages, 5 eps figure
Importance of reaction volume in hadronic collisions: Canonical enhancement
We study the canonical flavor enhancement arising from exact conservation of
strangeness, and charm flavor. Both the theoretical motivation, and the
practical consequences are explored. We argue using qualitative theoretical
arguments and quantitative evaluation, that this proposal to reevaluate
strangeness signature of quark--gluon plasma is not able to explain the
majority of available experimental results.Comment: 14 pages including 6 figures, submitted to Journal of Physics G
Presented at: Strange Quark Matter, September 2001, Frankfur
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