Non-equilibrium Statistical Mechanics
Dr M R Swift
My research interests lie in the broad area of statistical physics
and
some of my recent contributions are summarised below.
Driven Dissipative Systems: Granular media are ubiquitous
in nature and exhibit a wealth of intriguing physical properties,
ranging from the structural stability of sand piles to pattern formation
in vibrated granular layers. The key features that distinguish the
dynamical behaviour of granular systems from those of simple liquids
and gases are that thermal fluctuations are unimportant at the granular
scale, and inter-particle collisions dissipate energy. We investigated
the steady state properties of a randomly excited dissipative gas,
being a simple model for driven granular media[1]. We have shown
that the steady state is critical and exhibits long-range spatial
correlations. The exponents are found to be universal and can be
calculated from a single particle model which is amenable to exact
analysis. We have also demonstrated the existence of a novel, ergodicity
breaking transition exhibited by dissipative Brownian particles[2].
This
behaviour shows non-trivial scaling properties[3] and provides a
mechanism for ordering in a range of driven dissipative systems.
Lattice Boltzmann Hydrodynamics: We developed a scheme
for simulating hydrodynamics and phase separation in a non-ideal
fluid using lattice Boltzmann techniques[4]. The method relates
properties of the equilibrium pressure tensor of the inhomogeneous
fluid to the collision operator in the Boltzmann model and eliminates
many of the problems common to earlier numerical work in this field.
We extended these ideas to the case of a binary fluid mixture and
demonstrated that the two schemes are in different dynamical universality
classes[5]. We also investigated the effects of hydrodynamics on
spinodal decomposition, making a direct comparison between liquid-vapour
and binary-fluid systems[6]. The simulation method has now been
extended to describe the dynamics of complex fluid mixtures and
polymer solutions.
Interfaces and Fractality: We studied the spectral properties
of interfaces in random Ising ferromagnets for a range of distribution
functions characterising the bond disorder. As the width of the
distribution increases, the interface crosses over from a self affine
to a fractal object[7]. The measured fractal dimension indicates
the existence of a new universality class in strongly disordered
systems. Furthermore, we have shown that fractal interfaces arise
in Ising systems undergoing spinodal decomposition in the presence
of weak disorder[8], and that non-equilibrium states give rise to
a new universality class for percolation transitions[9]. Our findings
suggest that fractal structures observed in nature need not be related
to equilibrium properties of the system.
Contact:
Dr M R Swift
Michael.Swift@nottingham.ac.uk
Tel:
0115-9515134
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