We consider the topological category of various subsets of the set of expanding maps from a manifold to itself, and show in particular that a generic $C^1$ expanding map of the circle has no absolutely continuous invariant probability measure. This is in contrast with the situation for $C^2$ or $C^{1+\epsilon }$ expanding maps, for which it is known that there is always a unique absolutely continuous invariant probability measure.

Let Φ : H → R be a C2 function on a real Hilbert space and ∑ ⊂ H x R the manifold defined by ∑ := Graph (Φ). We study the motion of a material point with unit mass, subjected to stay on Σ and which moves under the action of the gravity force (characterized by g>0), the reaction force and the friction force ($\gamma >0$ is the friction parameter). For any initial conditions at time t=0, we prove the existence of a trajectory x(.) defined on R+. We are then interested in the asymptotic behaviour of...

Let $\Phi :H\to ℝ$ be a ${𝒞}^2$ function on a real Hilbert space and $\Sigma \subset H\times ℝ$ the manifold defined by $\Sigma :=$ Graph $\left(\Phi \right)$. We study the motion of a material point with unit mass, subjected to stay on $\Sigma$ and which moves under the action of the gravity force (characterized by $g\>0$), the reaction force and the friction force ($\gamma \>0$ is the friction parameter). For any initial conditions at time $t=0$, we prove the existence of a trajectory $x(.)$ defined on ${ℝ}_{+}$. We are then interested in the asymptotic behaviour of the trajectories when $t\to +\infty$. More precisely,...

In ergodic theory, certain sequences of averages $A_{k}f$ may not converge almost everywhere for all f ∈ L¹(X), but a sufficiently rapidly growing subsequence $A_{m_k}f$ of these averages will be well behaved for all f. The order of growth of this subsequence that is sufficient is often hyperexponential, but not necessarily so. For example, if the averages are $A_{k}f\left(x\right)=1/\left(2^k\right){\sum }_{j=4^k+1}^{4^k+2^k}f\left(T^{j}x\right)$, then the subsequence $A_{k²}f$ will not be pointwise good even on $L^{\infty }$, but the subsequence $A_{2^k}f$ will be pointwise good on L¹. Understanding when the hyperexponential...

In this paper we describe a non-local moving frame along a curve of pure spinors in $\mathrm{O}(2m,2m)/P$, and its associated basis of differential invariants. We show that the space of differential invariants of Schwarzian-type define a Poisson submanifold of the spinor Geometric Poisson brackets. The resulting restriction is given by a decoupled system of KdV Poisson structures. We define a generalization of the Schwarzian-KdV evolution for pure spinor curves and we prove that it induces a decoupled system of KdV...

En utilisant le théorème de Ruelle d'opérateur de transfert, nous démontrons que la moyenne 2-k Σn=02k-1 ||^wn||L1 de la localisation fréquentielle pour les paquets d'ondelettes admet un équivalent de la forme cρk (c > 0, 1 < ρ < √2). Cela améliore une inégalité antérieurement obtenue par Coifman, Meyer et Wickerhauser. Des estimations numériques de ρ sont obtenues pour des filtres de Daubechies.

Nous introduisons une notion de moyenne harmonique pour une marche aléatoire sur une relation d’équivalence mesurée graphée, qui généralise la notion classique de moyenne invariante. Pour les graphages à géométrie bornée, une telle moyenne existe toujours. Nous prouvons qu’une moyenne harmonique devient invariante lorsque la marche aléatoire sur presque toute orbite jouit de bonnes propriétés asymptotiques telles que la propriété de Liouville ou la récurrence.

Si dimostra l'esistenza di infinite soluzioni «multi-bump» - e conseguentemente il comportamento caotico - per una classe di sistemi Hamiltoniani del secondo ordine della forma $-\ddot{q}+q=\left(g_1\left(\omega t\right)+g_2\left(t/\omega \right)\right)V^{\prime }\left(q\right)$ per $\omega$ sufficientemente piccolo. Qui $q\in {\mathbb{R}}^n$ , $g_1$ e $g_2$ sono funzioni strettamente positive e periodiche e $V$ è un potenziale superquadratico (ad esempio $V\left(q\right)={\left|q\right|}^4$ ).

Let M be a d × d real contracting matrix. We consider the self-affine iterated function system Mv-u, Mv+u, where u is a cyclic vector. Our main result is as follows: if $\left|detM\right|\ge 2^{-1/d}$, then the attractor $A_M$ has non-empty interior. We also consider the set ${}_M$ of points in $A_M$ which have a unique address. We show that unless M belongs to a very special (non-generic) class, the Hausdorff dimension of ${}_M$ is positive. For this special class the full description of ${}_M$ is given as well. This paper continues our work begun...

We consider the multifractal analysis for Birkhoff averages of continuous potentials on a class of non-conformal repellers corresponding to the self-affine limit sets studied by Lalley and Gatzouras. A conditional variational principle is given for the Hausdorff dimension of the set of points for which the Birkhoff averages converge to a given value. This extends a result of Barral and Mensi to certain non-conformal maps with a measure dependent Lyapunov exponent.