539 research outputs found
Nuclear Multifragmentation Critical Exponents
We show that the critical exponents of nuclear multi-fragmentation have not
been determined conclusively yet.Comment: 3 pages, LaTeX, one postscript figure appended, sub. to
Phys.Rev.Lett. as a commen
Liquid-Gas Phase Transition in Nuclear Equation of State
A canonical ensemble model is used to describe a caloric curve of nuclear
liquid-gas phase transition. Allowing a discontinuity in the freeze out density
from one spinodal density to another for a given initial temperature, the
nuclear liquid-gas phase transition can be described as first order. Averaging
over various freeze out densities of all the possible initial temperatures for
a given total reaction energy, the first order characteristics of liquid-gas
phase transition is smeared out to a smooth transition. Two experiments, one at
low beam energy and one at high beam energy show different caloric behaviors
and are discussed.Comment: 12 pages in Revtex including two Postscript figure
Geochemical indices allow estimation of heavy metal background concentration in soils
Defining background concentrations for heavy metals in soils is essential for recognizing and managing soil pollution. However, background concentrations of metals in soils can vary naturally by several orders of magnitude. Moreover, many soils have also been subject to unquantifiable anthropogenic inputs of metals, in some cases, for centuries. Hence determination of heavy metal background concentrations in soils has to date been fraught with difficulty. Here we demonstrate that there are associations between the background heavy metal and Fe or Mn contents in soils which appear to be consistent for seven important heavy metals of environmental concern. The relationships are remarkably independent of both soil type and climatic setting. These observations provide the basis for a series of general equations from which it is proposed Southeast Asian including Australian, and possibly worldwide background concentrations for As, Cr, Co, Cu, Ni, Pb, and Zn in soils can be derived.R. E. Hamon, M. J. McLaughlin, R. J. Gilkes, A. W. Rate, B. Zarcinas, A. Robertson, G. Cozens, N. Radford and L. Bettena
Universal Behavior of Lyapunov Exponents in Unstable Systems
We calculate the Lyapunov exponents in a classical molecular dynamics
framework. The system is composed of few hundreds particles interacting either
through Yukawa (Nuclear) or Slater-Kirkwood (Atomic) forces. The forces are
chosen to give an Equation of State that resembles the nuclear and the atomic
Equation Of State respectively near the critical point for liquid-gas
phase transition. We find the largest fluctuations for an initial "critical
temperature". The largest Lyapunov exponents are always positive and
can be very well fitted near this "critical temperature" with a functional form
, where the exponent is
independent of the system and mass number. At smaller temperatures we find that
, a universal behavior characteristic of an order
to chaos transition.Comment: 11 pages, RevTeX, 3 figures not included available upon reques
Event-by-Event Fluctuations in Heavy Ion Collisions and the QCD Critical Point
The event-by-event fluctuations of suitably chosen observables in heavy ion
collisions at SPS, RHIC and LHC can tell us about the thermodynamic properties
of the hadronic system at freeze-out. By studying these fluctuations as a
function of varying control parameters, it is possible to learn much about the
phase diagram of QCD. As a timely example, we stress the methods by which
present experiments at the CERN SPS can locate the second-order critical
endpoint of the first-order transition between quark-gluon plasma and hadron
matter. Those event-by-event signatures which are characteristic of freeze-out
in the vicinity of the critical point will exhibit nonmonotonic dependence on
control parameters. We focus on observables constructed from the multiplicity
and transverse momenta of charged pions. We first consider how the
event-by-event fluctuations of such observables are affected by Bose-Einstein
correlations, by resonances which decay after freeze-out and by fluctuations in
the transverse flow velocity. We compare our thermodynamic predictions for such
noncritical event-by-event fluctuations with NA49 data, finding broad
agreement. We then focus on effects due to thermal contact between the observed
pions and a heat bath with a given (possibly singular) specific heat, and due
to the direct coupling between the critical fluctuations of the sigma field and
the observed pions. We also discuss the effect of the pions produced in the
decay of sigma particles just above threshold after freeze-out on the inclusive
pion spectrum and on multiplicity fluctuations. We estimate the size of these
nonmonotonic effects which appear near the critical point, including
restrictions imposed by finite size and finite time, and conclude that they
should be easily observable.Comment: 58 pages, 2 figures; to appear in Phys. Rev.
The liquid to vapor phase transition in excited nuclei
For many years it has been speculated that excited nuclei would undergo a
liquid to vapor phase transition. For even longer, it has been known that
clusterization in a vapor carries direct information on the liquid- vapor
equilibrium according to Fisher's droplet model. Now the thermal component of
the 8 GeV/c pion + 197Au multifragmentation data of the ISiS Collaboration is
shown to follow the scaling predicted by Fisher's model, thus providing the
strongest evidence yet of the liquid to vapor phase transition.Comment: four pages, four figures, first two in color (corrected typo in Ref.
[26], corrected error in Fig. 4
Exactly Solvable Models: The Road Towards a Rigorous Treatment of Phase Transitions in Finite Systems
We discuss exact analytical solutions of a variety of statistical models
recently obtained for finite systems by a novel powerful mathematical method,
the Laplace-Fourier transform. Among them are a constrained version of the
statistical multifragmentation model, the Gas of Bags Model and the Hills and
Dales Model of surface partition. Thus, the Laplace-Fourier transform allows
one to study the nuclear matter equation of state, the equation of state of
hadronic and quark gluon matter and surface partitions on the same footing. A
complete analysis of the isobaric partition singularities of these models is
done for finite systems. The developed formalism allows us, for the first time,
to exactly define the finite volume analogs of gaseous, liquid and mixed phases
of these models from the first principles of statistical mechanics and
demonstrate the pitfalls of earlier works. The found solutions may be used for
building up a new theoretical apparatus to rigorously study phase transitions
in finite systems. The strategic directions of future research opened by these
exact results are also discussed.Comment: Contribution to the ``World Consensus Initiative III, Texas A & M
University, College Station, Texas, USA, February 11-17, 2005, 21
Equation of State, Spectra and Composition of Hot and Dense Infinite Hadronic Matter in a Microscopic Transport Model
Equilibrium properties of infinite relativistic hadron matter are
investigated using the Ultrarelativistic Quantum Molecular Dynamics (UrQMD)
model. The simulations are performed in a box with periodic boundary
conditions. Equilibration times depend critically on energy and baryon
densities. Energy spectra of various hadronic species are shown to be isotropic
and consistent with a single temperature in equilibrium. The variation of
energy density versus temperature shows a Hagedorn-like behavior with a
limiting temperature of 13010 MeV. Comparison of abundances of different
particle species to ideal hadron gas model predictions show good agreement only
if detailed balance is implemented for all channels. At low energy densities,
high mass resonances are not relevant; however, their importance raises with
increasing energy density. The relevance of these different conceptual
frameworks for any interpretation of experimental data is questioned.Comment: Latex, 20 pages including 6 eps-figure
Laying the groundwork at the AGS: Recent results from experiment E895
The E895 Collaboration at the Brookhaven AGS has performed a systematic
investigation of Au+Au collisions at 2-8 AGeV, using a large-acceptance Time
Projection Chamber. In addition to extensive measurements of particle flow,
spectra, two-particle interferometry, and strangeness production, we have
performed novel hybrid analyses, including azimuthally-sensitive pion HBT,
extraction of the six-dimensional pion phasespace density, and a first
measurement of the Lambda-proton correlation function.Comment: Presented at Quark Matter 2001, 8 pages, 5 figure
- …