The general conditions for the existence of a negative heat capacity branch in nonextensive finite systems are reviewed. Partial energy fluctuations are proposed as a directly measurable observable of such a phenomenon in Gibbs as well as Tsallis equilibria.

We examine a simple biologically motivated neural network, the three-layer version of the Chialvo–Bak ‘minibrain’ (Neurosci. 90 (1999) 1137), and present numerical results which indicate that a non-equilibrium phase transition between ordered and disordered phases occurs subject to the...

The critical behavior of a ferromagnetic spin-1 Ising superlattice in a transverse field is studied using the effective field theory with a probability distribution technique that accounts for the self-spin correlation functions. The critical temperature of the system is calculated as a function...

A prey–predator system with intelligent pursuit and evasion is studied by means of computer simulations. It is found that the model exhibits a coexistence state between prey and predators. In this state and depending on the parameters, the system may evolve toward two different regimes,...

We consider a three-component model of rodlike molecules AA, BB, and AB, confined to the bonds of the honeycomb or three-coordinated Bethe lattice, and with three-body interactions between the molecular ends near a common lattice site. The model is equivalent to an Ising model on an associated...

The work deals with the theoretical study of domain structures in a ferrofluid, filling a thin flat gap with hard non-magnetic walls, placed into magnetic field, perpendicular to the gap plane. Two experimentally observed types of these structures are considered. The first one is the direct...

A new notion of matrix order indices which relates the matrix norm and its trace is introduced. These indices can be defined for any given matrix. They are especially important for matrices describing many-body systems, equilibrium as well as nonequilibrium, for which the indices present a...

A surprising physical interpretation of the replica number n was unveiled in the study of the equilibrium properties of the coupled dynamics of fast Ising spins and slow interactions: n is the ratio of the characteristic temperatures of the spin and the interaction systems and can take on any...

We use a recently developed cluster algorithm for the Baxter–Wu model to study characteristic features of its behavior. Magnetic scaling properties of the model are investigated for second-order phase transitions. We improve significantly the accuracy of Monte Carlo simulation results and we...

In the present work we study the critical properties of the ferromagnetic three-color Ashkin–Teller model (3AT) by means of a Migdal–Kadanoff renormalization group approach on a diamond-like hierarchical lattice. The analysis of the fixed points and flux diagram of the recursion relations is...