Dynamical Systems

Local rules for planar tilings

Event Date: Mar 12, 2018 in Dynamical Systems, Seminars

  ABSTRACT:  The cut and project method is one of the prominent method to define quasiperiodic tilings. In order to model quasicrystals, where energetic interactions are only short range, it is important to know which of these tilings can be characterized by local configurations (in dynamical terms: which of these tiling spaces are of finite type or sofic). In this talk we shall review known results, in particular those obtained these last years with Nicolas Bedaride and Mathieu Sablik.

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Event Date: Jan 22, 2018 in Dynamical Systems, Seminars

ABSTRACT: In this work we characterize the class of continuous shift commuting maps between ultragraph shift spaces, proving a Curtis-Hedlund-Lyndon type theorem. Then we use it to characterize continuous, shift commuting, length preserving maps in terms of generalized sliding block codes. This is a joint work with Prof. Daniel Gon\c{c}alves (UFSC, Brazil)

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Equidistribution of dilated curves.

Event Date: Jul 10, 2017 in Dynamical Systems, Seminars

Resumen:    Consider a light source located in a polynomial room. It is a classic question whether the whole room is illuminated by the light. This question was recently settled by Lelievre, Monteil and Weiss. In this talk, we study the variation on the illumination problem introduced by Chaika and Hubert in the context of closed curves on nilmanifolds. We give necessary and sufficient conditions for a nilmanifold being illuminated by a curve.

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Quantitative multiple recurrence for two and three transformations.

Event Date: Apr 10, 2017 in Dynamical Systems, Seminars

Abstract:  In this talk I will provide some counter examples for quantitative multiple recurrence problems for systems with more than one transformation.  For instance, I will show that there exists an ergodic system $(X,\mathcal{X},\mu,T_1,T_2)$ with two commuting transformations such that for every $\ell < 4$ there exists $A\in \mathcal{X}$ such that  \[ \mu(A\cap T_1^n A\cap T_2^n A) < \mu(A)^{\ell} \]  for every $n \in \mathbb{N}$.   The construction of such a system is based on the study of “big” subsets of $\mathbb{N}^2$ and $\mathbb{N}^3$  satisfying...

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Event Date: Apr 17, 2017 in Dynamical Systems, Seminars

ABSTRACT: Let 0 < a < 1, 0 ≤ b < 1 and I = [0,1). We call contracted rotation the interval map φa,b : x ∈ I → ax+b mod1. Once a is fixed, we are interested in the dynamics of the one-parameter family φa,b, where b runs on the interval interval [0, 1). Any contracted rotation has a rotation number ρa,b which describes the asymptotic behavior of φa,b. In the first part of the talk, we analyze the numerical relation between the parameters a, b and ρa,b and discuss some applications of the map φa,b. Next, we introduce a generalization of contracted rotations. Let −1 < λ < 1 and f...

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The group of reversible Turing machines and the torsion problem for $\Aut(A^{\mathbb{Z})$ and related topological fullgroups.

Event Date: Dec 19, 2016 in Dynamical Systems, Seminars

Abstract:   We introduce the group $RTM(G,n,k)$ composed of abstract Turing machines which use the group $G$ as a tape, use an alphabet of $n$ symbols, $k$ states and act as a bijection on the set of configurations. These objects can be represented both as cellular automata and in terms of continous functions and cocycles. The study of this group structure yields interesting results concerning computability properties of some well studied groups such as $\Aut(A^{\mathbb{Z})$ and the topological full group of the two dimensional full shift. More precisely, given a finitely generated group $G...

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