Seminars

Speakers:
Filipa Soares de Almeida
Date: Thursday, 26 April, 2018 - 14:30
Abstract:

In this talk, we explore a notion that sits between the concept of locally finite variety and that of periodic variety, using the inescapable Green's relations. Namely, a variety is said to be K-finite, where K stands for any of the Green's relations, if every finitely generated semigroup in this variety has but finitely many K-classes. Our characterization uses the language of "forbidden objects".

Speakers:
António Girão
Date: Friday, 20 April, 2018 - 15:30
Abstract:

In 1975, Sheehan conjectured that every d-regular Hamiltonian graph contains a second Hamiltonian cycle. This conjecture has been verified for all d greater than 22. In the light of Sheehan’s conjecture, it is natural to ask if regularity is genuinely necessary to force the existence of a second Hamiltonian cycle, or if a minimum degree condition is enough.

Speakers:
Sebastian Perez
Date: Friday, 20 April, 2018 - 14:30
Abstract:

Os célebres resultados de S.Newhouse ([N]) mostram que a bifurcação de uma tangência homoclínica asociada a uma sela numa superfície gera tangências homoclínicas robustas (isto é, tangências homoclínicas que persistem por pequenas perturbações) associadas a um conjunto hiperbólico especial chamado ferradura espessa. Além disso, a continuação (hiperbólica) da sela inicial está contida nesse conjunto hiperbólico.

Speakers:
Luís Oliveira
Date: Friday, 20 April, 2018 - 14:30
Abstract:

Let X be a set, X' be a disjoint copy of X and $\bar{X}\wedge\bar{X}=\{(x\wedge y): x,y\in X\cup X'\}$. We look at $\hat{X}=X\cup X'\cup(\bar{X}\wedge \bar{X})$ as a set of letters and consider the free semigroup $\hat{X}^+$ on the set $\hat{X}$. Auinger [1] constructed a model for the bifree locally inverse semigroup on X as a quotient semigroup of $\hat{X}^+$. This result enables us to talk about presentations $\langle X;R\rangle$ of locally inverse semigroups (LI-presentations) where $R\subseteq \hat{X}^+\times\hat{X}^+$.

Speakers:
Alexandre Rodrigues
Date: Friday, 6 April, 2018 - 14:30
Abstract:

In this seminar, we explore the chaotic set near a homoclinic cycle to a hyperbolic bifocus at which the vector field has negative divergence. If the invariant manifolds of the bifocus satisfy a non-degeneracy condition, a sequence of hyperbolic suspended horseshoes arises near the cycle, with one expanding and two contracting directions.

Speakers:
Pavel Zalesskii
Date: Friday, 23 March, 2018 - 15:30
Abstract:

We shall  discuss  residual properties of  groups and their interpretation in connection with the profinite completion of groups of geometric nature.

Speakers:
​Theo Zapata
Date: Friday, 23 March, 2018 - 14:30
Abstract:

We present the result that, under a certain condition, free pro-$p$ products with procyclic amalgamation inherit from its free factors the property of each 2-generator pro-$p$ subgroup being free pro-$p$. This generalizes known pro-$p$ results, as well as some pro-$p$ analogues of classical results in Combinatorial Group Theory.

Speakers:
Dominik Kwietniak
Date: Friday, 23 March, 2018 - 14:30
Abstract:

A nonhyperbolic ergodic measure is an ergodic invariant measure with one Lyapunov exponent equal zero. Gorodetski, Ilyashenko, Kleptsyn, and Nalsky constructed a nonhyperbolic ergodic measure for a skew product diffeomorphism of the three-dimensional torus. Inspired by this construction, Bonatti, Diaz and Gorodetski gave sufficient condi- tions for weak convergence of a sequence of measures supported on periodic orbits to an ergodic measure. A royal measure is a measure obtained through this scheme.

Speakers:
Fagner Bernardini Rodrigues
Date: Friday, 23 March, 2018 - 11:30
Abstract:

In this talk we intend to present the denition of mean topological dimension for a topological dynamical system. It is a topological invariant which was introduced by M. Gromov and exploited by some authors. This invariant enables one to assign a meaningful quantity to a dynamical system of infinite topological entropy. Also is possible to obtain a kind of variational principle as we intend to show.

Speakers:
Paulo Varandas
Date: Friday, 16 March, 2018 (All day)
Abstract:

The celebrated Birkhoff's ergodic theorem asserts that from a probabilistic viewpoint the times averages of "almost all" points converge to a space average. Motivated by the application of iterated function systems (IFS) to model central dynamics of partially hyperbolic diffeomorphisms, we will describe mild conditions that ensure that Birkhoff non-typical points form a Baire generic subset. If time permits we will provide some applicationsof this result in a partial hyperbolicity context. This is a ongoing joint work with my postdoctoral student G. Ferreira (UFMA).