25 research outputs found
Information entropy in fragmenting systems
The possibility of facing critical phenomena in nuclear fragmentation is a
topic of great interest. Different observables have been proposed to identify
such a behavior, in particular, some related to the use of information entropy
as a possible signal of critical behavior. In this work we critically examine
some of the most widespread used ones comparing its performance in bond
percolation and in the analysis of fragmenting Lennard Jones Drops.Comment: 3 pages, 3 figure
Geometrical aspects of isoscaling
The property of isoscaling in nuclear fragmentation is studied using a simple
bond percolation model with ``isospin'' added as an extra degree of freedom. It
is shown analytically, first, that isoscaling is expected to exist in such a
simple model with the only assumption of fair sampling with homogeneous
probabilities. Second, numerical percolations of hundreds of thousands of grids
of different sizes and with different to ratios confirm this prediction
with remarkable agreement. It is thus concluded that isoscaling emerges from
the simple assumption of fair sampling with homogeneous probabilities, a
requirement which, if put in the nomenclature of the minimum information
theory, translates simply into the existence of equiprobable configurations in
maximum entropy states
Caloric Curves in two and three-dimensional Lennard-Jones-like systems including Long-range forces
We present a systematic study of the thermodynamics of two and
three-dimensional generalized Lennard-Jones () systems focusing on the
relationship between the range of the potential, the system density and its
dimension. We found that the existence of negative specific heats depends on
these three factors and not only on the potential range and the density of the
system as stated in recent contributions.Comment: LaTex, 12 pages, 7 figure
An Improved Quantum Molecular Dynamics Model and its Applications to Fusion Reaction near Barrier
An improved Quantum Molecular Dynamics model is proposed. By using this
model, the properties of ground state of nuclei from Li to Pb can
be described very well with one set of parameters. The fusion reactions for
Ca+Zr, Ca+Zr and Ca+Zr at energy near
barrier are studied by this model. The experimental data of the fusion cross
sections for Ca+Zr at the energy near barrier can be
reproduced remarkably well without introducing any new parameters. The
mechanism for the enhancement of fusion probability for fusion reactions with
neutron-rich projectile or target is analyzed.Comment: 20 pages, 12 figures, 3 table
Enhanced T-odd P-odd Electromagnetic Moments in Reflection Asymmetric Nuclei
Collective P- and T- odd moments produced by parity and time invariance
violating forces in reflection asymmetric nuclei are considered. The enhanced
collective Schiff, electric dipole and octupole moments appear due to the
mixing of rotational levels of opposite parity. These moments can exceed
single-particle moments by more than two orders of magnitude. The enhancement
is due to the collective nature of the intrinsic moments and the small energy
separation between members of parity doublets. In turn these nuclear moments
induce enhanced T- and P- odd effects in atoms and molecules. First a simple
estimate is given and then a detailed theoretical treatment of the collective
T-, P- odd electric moments in reflection asymmetric, odd-mass nuclei is
presented and various corrections evaluated. Calculations are performed for
octupole deformed long-lived odd-mass isotopes of Rn, Fr, Ra, Ac and Pa and the
corresponding atoms. Experiments with such atoms may improve substantially the
limits on time reversal violation.Comment: 28 pages, Revte
Lyapunov exponent, generalized entropies and fractal dimensions of hot drops
We calculate the maximal Lyapunov exponent, the generalized entropies, the
asymptotic distance between nearby trajectories and the fractal dimensions
for a finite two-dimensional system at different initial excitation
energies. We show that these quantities have a maximum at about the same
excitation energy. The presence of this maximum indicates the transition
from a chaotic regime to a more regular one. In the chaotic regime the
system is composed mainly of a liquid drop while the regular one corresponds
to almost freely flowing particles and small clusters. At the transitional
excitation energy the fractal dimensions are similar to those estimated from
the Fisher model for a liquid-gas phase transition at the critical point
Master Langevin equations: Origin of asymptotic diffusion
We extend the master-equation treatment of dynamical evolution of a system-plus-reservoir configuration including the propagation of initial correlations as a noise source. Specializing into the quantum harmonic oscillator coupled to a fermionic heat bath, we develop a model for the diffusion matrix in the space of diagonal density operators. It can be shown that mean values of observables undergo Langevin-like motion and, in particular, that the mean value and dispersion of the oscillator quanta approach the canonical equilibrium values. A final interpretation of the characteristics and role of the noise source is given. © 1993 The American Physical Society.Fil:Dorso, C.O. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Vega, J.L. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina
Local (in time) maximal Lyapunov exponents of fragmenting drops
Fil:Balenzuela, P. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Dorso, C.O. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina