A. Alan Middleton

Self-organization and a dynamical transition in traffic-flow models.

A simple model that describes traffic flow in two dimensions is studied. A sharp jamming transition is found that separates between the low-density dynamical phase in which all cars move at maximal speed and the high-density jammed phase in which they are all stopped. Self-organization effects in both phases are studied and discussed.

Collective transport in arrays of small metallic dots

Collective charge transport is studied in one- and two-dimensional arrays of small normal-metal dots separated by tunneling barriers. At temperatures well below the charging energy of a dot, disorder leads to a threshold for conduction which grows linearly with the size of the array. For short-ranged interactions, one of the correlation length exponents near threshold is found from a novel argument based on interface growth. The dynamical exponent for the current above threshold is also predicted analytically, and the requirements for its experimental observation are described.

Three-dimensional random-field Ising magnet: Interfaces, scaling, and the nature of states

The nature of the zero-temperature ordering transition in the three-dimensional Gaussian random-field Ising magnet is studied numerically, aided by scaling analyses. Various numerical calculations are used to consistently infer the location of the transition to a high precision. A variety of boundary conditions are imposed on large samples to study the order of the transition and the number of states in the large volume limit. In the ferromagnetic phase, where the domain walls have fractal dimension

Vortex dynamics and defects in simulated flux flow.

{d}_{s}=2,

Self-Organized Criticality in Nonconserved Systems

the scaling of the roughness of the domain walls,

Possible description of domain walls in two-dimensional spin glasses by stochastic Loewner evolutions

w\ensuremath{\sim}{L}^{\ensuremath{\zeta}},

Numerical results for the ground-state interface in a random medium

is consistent with the theoretical prediction

Matching Kasteleyn Cities for Spin Glass Ground States

\ensuremath{\zeta}=2/3.

Viscoelastic depinning of driven systems: mean-field plastic scallops

As the randomness is increased through the transition, the probability distribution of the interfacial tension of domain walls scales in a manner that is clearly consistent with a single second-order transition. At the critical point, the fractal dimensions of domain walls and the fractal dimension of the outer surface of spin clusters are investigated: there are at least two distinct physically important fractal dimensions that describe domain walls. These dimensions are argued to be related by scaling to combinations of the energy scaling exponent

Ground-state roughness of the disordered substrate and flux lines in d = 2

\ensuremath{\theta},