arXiv subjects

M. J. Ison

Publications and source records attributed to M. J. Ison.

8 recordsLinked to original sources

arXiv2007

Expansion dynamics of Lennard-Jones systems

The dynamics of the expansion of a Lennard-Jones system, initially confined at high density and subsequently expanding freely in the vacuum, is confronted to an expanding statistical ensemble, derived in the diluted quasi-ideal Boltzmann approximation. The description proves to be fairly accurate at predicting average one-body global observables, but important deviations are observed in the configuration-space structure of the events. Possible implications for finite expanding physical systems are outlined.

cond-mat.stat-mech↗

arXiv2007

Extended Gibbs ensembles with flow

A statistical treatment of finite unbound systems in the presence of collective motions is presented and applied to a classical Lennard-Jones Hamiltonian, numerically simulated through molecular dynamics. In the ideal gas limit, the flow dynamics can be exactly re-casted into effective time-dependent Lagrange parameters acting on a standard Gibbs ensemble with an extra total energy conservation constraint. Using this same ansatz for the low density freeze-out configurations of an interacting expanding system, we show that the presence of flow can have a sizeable effect on the microstate distribution.

cond-mat.stat-mech↗

arXiv2005

Dynamical aspects of fragmentation

In this short communication we address the problem of reducibility in a highly excited Lennard-Jones system. We show that the probability of emitting $n$ fragments can be described in terms of a single probability through the binomial expression. However, the Arrhenius law does not hold and the process can be viewed as a mixture of sequential and simultaneous fragmentation events.

nucl-th↗

arXiv2005

Information theory of open fragmenting systems

An information theory description of finite systems explicitly evolving in time is presented. We impose a MaxEnt variational principle on the Shannon entropy at a given time while the constraints are set at a former time. The resulting density matrix contains explicit time odd components in the form of collective flows. As a specific application we consider the dynamics of the expansion in connection with heavy ion experiments. Lattice gas and classical molecular dynamics simulations are shown.

nucl-th↗

arXiv2004

Dynamics and thermodynamics of fragment emission from excited sources

In this paper we study the process of fragmentation of highly excited Lennard-Jones drops by introducing the concept of emitted fragments (clusters recognizable in configuration space which live more than a minimum lifetime). We focus on the dynamics and thermodynamics of the emitted sources, and show, among other things, that this kind of process can not be cast into a sequential or simultaneous one, and how a local equilibrium scenario comes up, allowing us to define and explore a local temperature, which turns out to be a strongly time-dependent quantity.

nucl-th↗

arXiv2004

Enhancement of kinetic energy fluctuations due to expansion

Global equilibrium fragmentation inside a freeze out constraining volume is a working hypothesis widely used in nuclear fragmentation statistical models. In the framework of classical Lennard Jones molecular dynamics, we study how the relaxation of the fixed volume constraint affects the posterior evolution of microscopic correlations, and how a non-confined fragmentation scenario is established. A study of the dynamical evolution of the relative kinetic energy fluctuations was also performed. We found that asymptotic measurements of such observable can be related to the number of decaying channels available to the system at fragmentation time.

nucl-th↗

arXiv2003

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 ($LJ$) 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.

cond-mat.stat-mech↗

arXiv2003

The role of Coulomb interaction in fragmentation

We examine the impact of adding a Coulomb term to a constrained system of 147 particles interacting via a Lennard-Jones (LJ) potential, finding that the inclusion of the coulombic interaction produces a shift, but no qualitative changes in the thermodynamical properties of the system. We also performed the systems characterization from a morphological point of view.

nucl-th↗