Dynamical Systems

SIR model: chaos, bifurcations and stability

This presentation is divided into three parts where we analyze three different epidemiological models.

In the first part we analyze a periodically-forced system SIR model. We prove that the condition R0 < 1 is not enough to guarantee the elimination of the disease. Using the Theory of rank-one attractors, we prove persistent strange attractors for an open subset in the space of parameters where R0 < 1.

Geometric and ergodic aspects of nonuniformly hyperbolic flows

The study of hyperbolic structures (uniform and nonuniform ones)
is a central subject in Dynamical Systems.
Nowadays, there are many notions of weak hyperbolicity, and
here I am interested in the setting of flows with singularities (e.g.,
Lorenz systems).
In this talk I am going to talk about some notions of (nonuniform)

Compound Poisson distributions for random dynamical systems

We show that quenched limiting hitting distributions are
compound Poisson distributed for certain random dynamical systems with
targets.
Targets are random and assumed to have well-defined return statistics
of certain type, which turn out to characterize the said compound
Poissonian limit.
Moreover, quenched and annealed polynomial decay of correlations are
assumed, whereas annealed Kac-time normalization is adopted.
Examples discussed are one-dimensional random piecewise expanding systems.

Dynamics near heteroclinic cycles and networks

A heteroclinic cycle is a structure in a dynamical system composed of a sequence of invariant sets---such as equilibria, periodic orbits, or even chaotic sets---and orbits which connect them in a cyclic manner. Near an attracting heteroclinic cycle, trajectories visit each invariant set in turn and, as time evolves, spend increasingly longer periods of time near each set, before making a rapid switch to the next one. A heteroclinic network is a connected union of heteroclinic cycles.

Bifurcation to a sink preserving the number of critical points and applications to statistical learning

We describe some results in dynamics, symmetry and geometric analysis which have applications to the theoretical study of machine learning.
Most of the first half of the talk will emphasise the mathematics and be introductory; at appropriate points, brief
indications will be made concerning the
motivating question from statistical learning.
 

Minimal distance between random orbits

We study the minimal distance between two orbit segments of length $n$, in
a random dynamical system with sufficiently good mixing properties. For the annealed version of this problem, the asymptotic behavior is given by a dimension-like quantity associated to the invariant measure, called its correlation dimension. We study the analogous quenched question, and show that the asymptotic behavior is more involved: two correlation dimensions show up, giving rise to a non-smooth behavior of the associated asymptotic exponent.

Topological synchronization or a simple attractor?

We present a skew system made of two unimodal maps of the interval coupled in a master-slave configuration. This system arises in the physics literature as an explanatory model of the so-called topological synchronization, i.e. the mechanism believed to be at the basis of emerging collective phenomena in coupled chaotic systems.