Let D=(\omega_n)_{n\ge0} be the multiplicative semi-group generated by the coprime integers q_1,\dotsc, q_\tau arranged in increasing order. If f is a real-valued 1-periodic function, we consider the sums S_nf(t)=\sum_{0\le k<n} f(\omega_kt). For a large class of functions, we prove the existence of a limiting variance \sigma^2 for the sequence \{S_nf/\sqrt n\}, we give a function characterization for the case when \sigma=0 and finally we prove a central limit theorem.

We show that the strong stable foliation of the canonical extension of an Axiom A flow to an Abelian cover of a compact manifold is ergodic with respect to the product of a Gibbs measure on the manifold times the Haar measure on the fiber, as soon as it is transitive on the support of the measure. This generalizes previous results of M. Babillot, F. Ledrappier, M. Pollicott and V. Kaimanovich.

We study continuous cocycles defined on the set of planar tilings with values in discrete groups. Following Schmidt we show that for generalized domino tilings, L-tiles, and some systems of paths there exists a fundamental cocycle, i.e. we find a cocycle cf, so that all other continuous cocycles c are cohomologous to a homomorphic image of cf.

We study the convergence of N^{-1} \sum f_1(T^{a_1n}x)f_2(T^{a_2n}x)f_3(T^{a_3n}x), for a measure-preserving system (X, \mathcal{B}, \mu, T) and f_{1}, f_{2}, f_{3} \in L^{\infty}(\mu). This generalizes the theorem of Conze and Lesigne on such expressions and simplifies the proof. We also obtain a description of the limit.

There are four Bowen–Franks groups associated to each shift of finite type. For an irreducible shift of finite type, we show that a 4-tuple of automorphisms corresponding to the four Bowen–Franks groups can be induced simultaneously by a specific path of flow equivalence from the shift to itself, if and only if it is F-compatible. The F-compatibleness defined in this paper describes completely the intrinsic relations among the four automorphisms induced by a flow equivalence. This result is one of the key ingredients in classifying reducible shifts of finite type up to flow equivalence. In the mean time, it also discloses a new and sharp difference between the invariants of flow equivalence for an irreducible shift of finite type, and the invariants of stable isomorphism for the associated simple Cuntz–Krieger algebra.

We consider measure-preserving diffeomorphisms of the two-dimensional torus with zero entropy. We prove that every ergodic C^3-diffeomorphism f of the two-dimensional torus with linear growth of the derivative (i.e. the sequence \{n^{-1}Df^n\}_{n\in{\mathbb N}} is uniformly separated from 0 and \infty and it is bounded in the C^2-norm) is algebraically conjugate to a skew product of an irrational rotation on the circle and a circle C^3-cocycle with non-zero topological degree.

We present a powerful approach to computing the Hausdorff dimension of certain conformally self-similar sets. We illustrate this method for the dimension \mathop{\rm dim}\nolimits_H(E_2) of the set E_2, consisting of those real numbers whose continued fraction expansions contain only the digits 1 or 2. A very striking feature of this method is that the successive approximations converge to \mathop{\rm dim}\nolimits_H(E_2) at a super-exponential rate

We estimate the decay of correlations for some Markov maps on a countable state space. A necessary and sufficient condition is given for the transfer operator to be quasi-compact on the space of locally Lipschitz functions. In the non-quasi-compact case, the decay of correlations depends on the contribution to the transfer operator of the complementary of finitely many cylinders. Estimates are given for some non-uniformly expanding maps and for maps with bounded jumps.

For a continuous circle map T, define the barycentre of any T-invariant probability measure \mu to be b(\mu)=\int_{S^1} z\, d\mu(z). The set \Omega of all such barycentres is a compact convex subset of \mathbb{C}. If T is conjugate to a rational rotation via a Möbius map, we prove \Omega is a disc. For every piecewise-onto expanding map we prove that the barycentre set has non-empty interior. In this case, each interior point is the barycentre of many invariant measures, but we prove that amongst these there is a unique one which maximizes entropy, and that this measure belongs to a distinguished two-parameter family of equilibrium states. This family induces a real-analytic radial foliation of int(\Omega), centred around the barycentre of the global measure of maximal entropy, where each ray is the barycentre locus of some one-parameter section of the family. We explicitly compute these rays for two examples. While developing this framework we also answer a conjecture of Z. Coelho [6] regarding limits of sequences of equilibrium states.

For a piecewise monotonic map T:X\to{\Bbb R}, where X is a finite union of closed intervals, define R(T)= \bigcap_{n=0}^{\infty}\overline{T^{-n}X}. The influence of small perturbations of T on the dynamical system (R(T),T) is investigated. If P is a finite and T-invariant subset of R(T), and if f_0:P\to{\Bbb R} is a non-negative continuous function, then it is proved that the infimum of the topological pressure p(R(T),T,f) over all non-negative continuous functions f:X\to{\Bbb R} with f|_P=f_0 equals the maximum of h_{\text{\rm top}}(R(T),T) and p(P,T,f_0). This result is used to obtain stability conditions, which are equivalent to the upper semi-continuity of the topological pressure for every continuous function f:X\to{\Bbb R}. In the case of a continuous piecewise monotonic map T:X\to{\Bbb R} one of these stability conditions is: there exists no endpoint of an interval of monotonicity of T which is periodic and contained in the interior of X. Furthermore, these results are applied to monotonic mod one transformations, another special case of piecewise monotonic maps.

We give stronger versions and alternative simple proofs of some results of Beardon, [Be1] and [Be2]. These results concern contractions of locally compact metric spaces and generalize the theorems of Wolff and Denjoy about the iteration of a holomorphic map of the unit disk. In the case of unbounded orbits, there are two types of statements which can sometimes be proven; first, about invariant horoballs, and second, about the convergence of the iterates to a point on the boundary. A few further remarks of similar type are made concerning certain random products of semicontractions and also concerning semicontractions of Gromov hyperbolic spaces.

We show that every real analytic action of a connected supersoluble Lie group on a compact surface with non-zero Euler characteristic has a fixed point. This implies that Lima's fixed point free C^{\infty} action on S^2 of the affine group of the line cannot be approximated by analytic actions. An example is given of an analytic, fixed point free action on S^2 of a solvable group that is not supersoluble.

This paper gives a simple proof of the well-known fact that a codimension-one Anosov diffeomorphism of a closed manifold is topologically conjugate to a hyperbolic toral automorphism.

We consider the problem of expressing the regularity of different objects which appear in Anosov systems in terms of Sobolev spaces. We show in examples that one cannot expect any improvements in the regularity of Anosov splitting from the classical results that give regularity in W^{r_0,\infty}. We also develop a Sobolev regularity theory for solutions of cohomology equations, both commutative and non-commutative, and the bootstrap of regularity arguments from Sobolev to other classes for a wide variety of functional equations involving Anosov systems.

Consider the conjugacy action of the unitary group of an infinite-dimensional separable Hilbert space on the unitary operators. A strong generic ergodicity property of this action is established, by showing that any conjugacy invariants assigned in a definable way to unitary operators, and taking as values countable structures up to isomorphism, generically trivialize. Similar results are proved for conjugacy of self-adjoint operators and for measure equivalence. The proofs make use of the theory of turbulence for continuous actions of Polish groups, developed by Hjorth. These methods are also used to give a new solution to a problem of Mauldin in measure theory, by showing that any analytic set of pairwise orthogonal measures on the Cantor space is orthogonal to a product measure.

Given an isolated fixed point p of index one, of an area- and orientation-preserving homeomorphism f of a surface, we define a type (positive, negative) for a lift of f to the universal cover of D\setminus \{p\}, where D is a small disc neighbourhood of p. Using this concept, we establish a new kind of fixed point theorem. Furthermore, a refinement of the Arnold conjecture for a surface homeomorphism is obtained.

C^*-algebras arising from directed graphs and their generalizations, Exel–Laca algebras \mathcal{O}_A of an infinite matrix A, are considered. Characterizations of pure infiniteness (in the sense of [11]) and of stability are given. In particular, these C^*-algebras admit no non-zero trace if and only if they are purely infinite. Stability is characterized by the absence of non-zero unital quotients and a bounded trace. Also, graph-theoretical analogues of pure infiniteness and stability are obtained.

On considère l'espace {\mathcal B}_2 des homéomorphismes du plan obtenus en recollant deux translations, muni de la topologie compacte-ouverte. On construit une famille dans {\mathcal B}_2, continûment indexée par les éléments du Cantor \{0,1\}^\mathbb{Z}, pour laquelle les classes de conjugaison correspondent aux orbites du décalage (ou “ shift ”) sur \{0,1\}^\mathbb{Z}. Ceci permet de montrer qu'il n'y a pas de classification borélienne de la relation de conjugaison sur {\mathcal B}_2.

We give an elementary proof of existence and uniqueness of Gibbs states for Hölder weight systems on subshifts of finite type. This uses a notion of duality for such subshifts. The approach of Paterson [2] is used to construct a measure with a prescribed Jacobian and the duality is used to produce an invariant measure from this

For a topologically mixing Anosov diffeomorphism on a compact manifold, the correlation function for two smooth functions is known to have exponential decay. As a generalization, higher correlation functions for several smooth functions are defined, and are shown to have exponential decay in the time variables. It is also proved that the higher derivatives of the pressure are equal to the summations of the higher correlations over the time variables.