215 research outputs found

    Dynamical properties of the Pascal adic transformation

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    We study the dynamics of a transformation that acts on infinite paths in the graph associated with Pascal's triangle. For each ergodic invariant measure the asymptotic law of the return time to cylinders is given by a step function. We construct a representation of the system by a subshift on a two-symbol alphabet and then prove that the complexity function of this subshift is asymptotic to a cubic, the frequencies of occurrence of blocks behave in a regular manner, and the subshift is topologically weak mixing

    Modules with irrational slope over tubular algebras

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    Let AA be a tubular algebra and let rr be a positive irrational. Let Dr{\mathcal D}_r be the definable subcategory of AA-modules of slope rr. Then the width of the lattice of pp formulas for Dr{\mathcal D}_r is ∞\infty. It follows that if AA is countable then there is a superdecomposable pure-injective module of slope rr.Comment: minor corrections/improvements to argument

    Quantitative sheaf theory

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    We introduce a notion of complexity of a complex of ell-adic sheaves on a quasi-projective variety and prove that the six operations are "continuous", in the sense that the complexity of the output sheaves is bounded solely in terms of the complexity of the input sheaves. A key feature of complexity is that it provides bounds for the sum of Betti numbers that, in many interesting cases, can be made uniform in the characteristic of the base field. As an illustration, we discuss a few simple applications to horizontal equidistribution results for exponential sums over finite fields.Comment: v3, 68 pages; the key ideas of this paper are due to W. Sawin; A. Forey, J. Fres\'an and E. Kowalski drafted the current version of the text; revised after referee report

    Generalizations of Sturmian sequences associated with NN-continued fraction algorithms

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    Given a positive integer NN and xx irrational between zero and one, an NN-continued fraction expansion of xx is defined analogously to the classical continued fraction expansion, but with the numerators being all equal to NN. Inspired by Sturmian sequences, we introduce the NN-continued fraction sequences ω(x,N)\omega(x,N) and ω^(x,N)\hat{\omega}(x,N), which are related to the NN-continued fraction expansion of xx. They are infinite words over a two letter alphabet obtained as the limit of a directive sequence of certain substitutions, hence they are SS-adic sequences. When N=1N=1, we are in the case of the classical continued fraction algorithm, and obtain the well-known Sturmian sequences. We show that ω(x,N)\omega(x,N) and ω^(x,N)\hat{\omega}(x,N) are CC-balanced for some explicit values of CC and compute their factor complexity function. We also obtain uniform word frequencies and deduce unique ergodicity of the associated subshifts. Finally, we provide a Farey-like map for NN-continued fraction expansions, which provides an additive version of NN-continued fractions, for which we prove ergodicity and give the invariant measure explicitly.Comment: 23 pages, 2 figure

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