Mathematical Models and Methods in Applied Sciences

We study a model of population dynamics describing pregnancy: our model is composed by an equation describing the evolution of the total population, and an equation describing the evolution of pregnant individuals. These equations are of course coupled: one coupling expresses that the total population varies with the number of born people, and another coupling says that the number of fecundated individuals depends on the total population. We study three models of that type: a linear model without diffusion, a nonlinear model without diffusion and a linear model with diffusion. For these three models, we study precisely the qualitative properties and the asymptotic behavior of the solutions.

In this paper, we employ the fixed point index on cones to study the existence, multiplicity and nonexistence of positive periodic solutions to a system of infinite delay equations,

The time-harmonic Maxwell equations do not have an elliptic nature by themselves. Their regularization by a divergence term is a standard tool to obtain equivalent elliptic problems. Nodal finite element discretizations of Maxwell's equations obtained from such a regularization converge to wrong solutions in any non-convex polygon. Modification of the regularization term consisting in the introduction of a weight restores the convergence of nodal FEM, providing optimal convergence rates for the h version of finite elements. We prove exponential convergence of hp FEM for the weighted regularization of Maxwell's equations in plane polygonal domains provided the hp-FE spaces satisfy a series of axioms. We verify these axioms for several specific families of hp finite element spaces.

In this paper we study a nonlinear system of differential equations which arises from a stationary two-dimensional Ice-Sheet Model describing the ice-streaming phenomenon. The system consists of a multivalued nonlinear PDE of parabolic type coupled with a first-order PDE and an ODE involving a nonlocal term. We study the uniqueness of weak solution under suitable assumptions (physically reasonable). We also establish that the ice thickness collapses at a finite distance (by employing a comparison principle).

We thoroughly investigate a hierarchy of approximations to the radiative heat transfer equations which is intermediate between moment models and the direct solution. We discuss the modelling of this hierarchy, prove well-posedness and physically expected bounds, and show numerical results validating our approach.