Abstracts
(by order of
receipt):
Reverse
collaboration
Elena Geraci:
The Reverse experiment intends to study isospin
effects and cluster productions
in nuclear multifragmentation in heavy ion collisions as
a function of the mass
and the excitation energy of the colliding nuclear
systems in reverse
kinematics. The peculiarities of the experiment, isotopic
identification of the
nuclear clusters and good particle-particle correlation,
are important
requirements for studying phase transition in finite
nuclear system. The
experiment has been performed using the forward part of
Chimera
multidetector at Laboratori Nazionali del Sud using 112Sn
and 124Sn beams
impinging on 58Ni,64Ni and Al targets. Data analyses are
in progress.
DYNAMICS AND THERMODYNAMICS OF FINITE
SYSTEMS
J. Jellinek
Chemistry Division, Argonne National Laboratory,
Argonne, IL 60439, USA
The correspondence between dynamics and
thermodynamics/statistical
mechanics of finite systems will be examined, and a new
axiomatic
approach for introducing thermodynamic concepts and
quantities through
dynamics will be formulated. Illustrations will be given
through
analysis of phase changes in one- and two-component metal
clusters.
Caloric Curves for Atomic
Clusters.
Hellmut Haberland
Caloric curves of small, free and mass
selected sodium clusters are
measured by using the photofragmentation
pattern of thermalized and laser
excited clusters as a "nano-calorimeter".
The solid/liquid phase change is
studied for clusters containing between
50 and 200 atoms. The influence of
the finite size on the thermodynamics of
the clusters is investigated.
Ergodicity.
Pierre Labastie
MD simulation of quark system
or
Multifragmentation of expanding
nuclear matter.
Toshiki Maruyama
JAERI (staying in Catania for one year)
Hamiltonian dynamics, Geometrical
and Topological
concept in the study of phase
transitions
Marco Pettini
Osservatorio Astrofisico di Arcetri
and I.N.F.N. Sezione di Firenze
and I.N.F.M. UdR di Firenze
A reseach work performed with L. Casetti, R. Franzosi
and L.Spinelli during
the last years has made use of differential-geometric and
topological concepts
in the study of classical Hamiltonian dynamics and phase
transitions.
New important steps forward have been made for what
concerns the topological
hypothesis about the deep origin of phase transitions. In
this framework the
the main idea is to link the appearance of phase
transitions to some major
topology change of equipotential submanifolds of phase
space instead of
linking them to non-analyticity, as is usual in the
Yang-Lee and in the
Dobrushin-Ruelle theories. The implications are far
reaching because, in
principle, the thermodynamic limit dogma can be overcome
and from the
topological point of view a possibility appears of
properly defining a new
mathematical counterpart of phase transitions, also at
finite number of degrees
of freedom. This is of prospective interest to the study
of phase transitions
in finite N systems, like nano and mesoscopic systems,
nuclear or atomic
clusters and so on.
The results so far obtained concern: an analytic result
for a mean field XY
model; the numerical computation of the potential energy
dependence
of a topologic invariant (the Euler characteristic) of
the equipotential
surfaces of the configuration space of a lattice phi^4
model directly
confirming the tight link between topology and phase
transitions and suggesting
which kind of topology changes are involved; a first
successful attempt
at working out some sufficiency conditions, in order to
restrict the domain of
topology changes that can be responsible for the
appearance of a first or
second order thermodynamic phase transition, reported in;
finally,
the proof of a general theorem about the necessity of
topology changes of
equipotential submanifolds of the microscopic
configuration space for the
occurrence of first or second order phase
transitions.
Some Aspects of Ergodicity and
Chaos inGravitational systems
Harald A. Posch
Institut für Experimentalphysik, Universität
Wien, Boltzmanngasse 5, A-1090 Wien, Austria
E-mail: posch@ls.exp.univie.ac.at
Walter Thirring
Institut für Theoretische Physik,
Universität Wien, Boltzmanngasse 5, A-1090 Wien,
Austria
E-mail: fwagner@ap.univie.ac.at
Recently, we have studied many-body systems in $d$
dimensions interacting
with a purely attractive pair potential $\sim |{x}_i -
{x}_j|^{\nu}$, where $\nu$
is a positive parameter. The case $\nu = d = 1$
corresponds to the well-known
linear sheet model. We derive the temperature in
microcanonical equilibrium for
arbitrary $\nu$ and $d$ and, for $d=1$, the corresponding
velocity distribution
for a finite number $N$ of particles. We verified these
theoretical expressions by
comparing them to extensive computer simulation results
for various $\nu$. We
also computed full Lyapunov spectra and the
Kolmogorov-Sinai entropy and found
that the maximum exponent increases linearly as a
function of $|\nu - 2|$, where
$\nu = 2$ represents a regular harmonic oscillator chain
with vanishing expoents.
For the linear sheet model, we find indications for the
existence of sticky phase-space
regions and non ergodicity even if more than 16 particles
are involved.
We also studied some stability and ergodic properties
of the famous reduced three
body problem (``Sun, Jupiter, and a test particle''). We
propose a simple oscillator
model to understand the stability of orbits with small
eccentricity of the test particle.
It models the main short-time features for small mass
ratios of the other bodies. These
results are confronted with simulation results for bigger
mass ratios, where chaotic
features emerge. For larger energies, for which the test
particle may reach the
neighborhood of the Sun and of Jupiter, the density in
configuration space is nearly
homogeneous indicating almost ergodic behavior. In the
case of the more general problem
of three particles in a planar box (circular or square)
with reflecting boundaries, the
existence or lack of conserved quantities other than the
energy leads to a converging or
diverging kinetic energy, respectively.
What do we learn from the
Caloric curve ?
Walter F.J. Mueller
GSI, Abteilung KP3, D-64291 Darmstadt
Mail: W.F.J.Mueller@gsi.de
Critical behaviour and hydrogen
cluster multifragmentation
Michel FARIZON
IPNL, Lyon.
We report on a cluster fragmentation study involving
collisions of fast
(c/88) hydrogen cluster ions with atomic helium and
fullerenes. The
experimental characterization of cluster fragmentation by
a statistical
analysis of the fragmentation events, has become possible
because of a
multicoincidence technique in which all fragments are
detected on an event
by event basis. From the break-up in two fragments to the
complete
disintegration of the cluster, these molecular systems of
small size
exhibit a transition with an increase of the
fluctuations.
Statistical description of finite
systems
Philippe CHOMAZ
GANIL Caen France
Measurable observables of phase
coexistence.
Critical behaviour in first order
phase transition
Francesca GULMINELLI
LPC Caen FRANCE
Thermodynamics of hot drops at
fragmentation times
Claudio Dorso
Buenos Aires, Argentina