Generalized xy lattice spin models consist of three-component unit vectors, associated with a D-dimensional lattice (say <InlineEquation ID="Equ1"> <EquationSource Format="TEX">${\mathbb{Z}}^D$</EquationSource> </InlineEquation>), parameterized by usual spherical angles (θ<Subscript>k</Subscript>,φ<Subscript>k</Subscript>), and interacting via a ferromagnetic potential restricted to nearest neighbours, of the form <InlineEquation ID="Equ2"> <EquationSource...</equationsource></inlineequation></subscript></subscript></equationsource></inlineequation>

An model of La<Subscript>2-x</Subscript>Sr<Subscript>x</Subscript>CuO<Subscript>4</Sub script> explaining the features of incommensurate spin textures without any assumption of stripe formation is proposed. The foundations of this model are the mechanism of negative-U center formation proposed earlier and the concept of specific ordering of doped ions. It is shown...<//sub></subscript></subscript></subscript>

We consider an inertial model of chemotactic aggregation generalizing the Keller-Segel model and we study the linear dynamical stability of an infinite and homogeneous distribution of cells (bacteria, amoebae, endothelial cells, ...) when inertial effects are accounted for. These inertial terms...

Parapatric speciation is studied using an individual-based model with sexual reproduction. We combine the theory of mutation accumulation for biological ageing with an environmental selection pressure that varies according to the individuals geographical positions and phenotypic traits....

For many infectious diseases, a small-world network on an underlying regular lattice is a suitable simplified model for the contact structure of the host population. It is well known that the contact network, described in this setting by a single parameter, the small-world parameter p, plays an...

A large deviation technique is used to calculate the microcanonical entropy function s(v,m) of the mean-field ϕ<Superscript>4</Superscript>-model as a function of the potential energy v and the magnetization m. As in the canonical ensemble, a continuous phase transition is found. An analytical expression is obtained for...</superscript>