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Reading along arithmetic progressions

T. Downarowicz — 1999

Colloquium Mathematicae

Given a 0-1 sequence x in which both letters occur with density 1/2, do there exist arbitrarily long arithmetic progressions along which x reads 010101...? We answer the above negatively by showing that a certain regular triadic Toeplitz sequence does not have this property. On the other hand, we prove that if x is a generalized binary Morse sequence then each block can be read in x along some arithmetic progression.

A non-regular Toeplitz flow with preset pure point spectrum

T. DownarowiczY. Lacroix — 1996

Studia Mathematica

Given an arbitrary countable subgroup σ 0 of the torus, containing infinitely many rationals, we construct a strictly ergodic 0-1 Toeplitz flow with pure point spectrum equal to σ 0 . For a large class of Toeplitz flows certain eigenvalues are induced by eigenvalues of the flow Y which can be seen along the aperiodic parts.

Almost 1-1 extensions of Furstenberg-Weiss type and applications to Toeplitz flows

T. DownarowiczY. Lacroix — 1998

Studia Mathematica

Let ( Z , T Z ) be a minimal non-periodic flow which is either symbolic or strictly ergodic. Any topological extension of ( Z , T Z ) is Borel isomorphic to an almost 1-1 extension of ( Z , T Z ) . Moreover, this isomorphism preserves the affine-topological structure of the invariant measures. The above extends a theorem of Furstenberg-Weiss (1989). As an application we prove that any measure-preserving transformation which admits infinitely many rational eigenvalues is measure-theoretically isomorphic to a strictly ergodic toeplitz...

Spontaneous clustering in theoretical and some empirical stationary processes

T. DownarowiczY. LacroixD. Léandri — 2010

ESAIM: Probability and Statistics

In a stationary ergodic process, clustering is defined as the tendency of events to appear in series of increased frequency separated by longer breaks. Such behavior, contradicting the theoretical “unbiased behavior” with exponential distribution of the gaps between appearances, is commonly observed in experimental processes and often difficult to explain. In the last section we relate one such empirical example of clustering, in the area of marine technology. In the theoretical part of the paper...

Spectral isomorphisms of Morse flows

T. DownarowiczJan KwiatkowskiY. Lacroix — 2000

Fundamenta Mathematicae

A combinatorial description of spectral isomorphisms between Morse flows is provided. We introduce the notion of a regular spectral isomorphism and we study some invariants of such isomorphisms. In the case of Morse cocycles taking values in G = p , where p is a prime, each spectral isomorphism is regular. The same holds true for arbitrary finite abelian groups under an additional combinatorial condition of asymmetry in the defining Morse sequence, and for Morse flows of rank one. Rank one is shown to...

A criterion for Toeplitz flows to be topologically isomorphic and applications

T. DownarowiczJ. KwiatkowskiY. Lacroix — 1995

Colloquium Mathematicae

A dynamical system is said to be coalescent if its only endomorphisms are automorphisms. The question whether there exist coalescent ergodic dynamical systems with positive entropy has not been solved so far and it seems to be difficult. The analogous problem in topological dynamics has been solved by Walters ([W]). His example, however, is not minimal. In [B-K2], a class of strictly ergodic (hence minimal) Toeplitz flows is presented, which have positive entropy and trivial topological centralizers...

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