368 research outputs found

    Topological pressure of simultaneous level sets

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    Multifractal analysis studies level sets of asymptotically defined quantities in a topological dynamical system. We consider the topological pressure function on such level sets, relating it both to the pressure on the entire phase space and to a conditional variational principle. We use this to recover information on the topological entropy and Hausdorff dimension of the level sets. Our approach is thermodynamic in nature, requiring only existence and uniqueness of equilibrium states for a dense subspace of potential functions. Using an idea of Hofbauer, we obtain results for all continuous potentials by approximating them with functions from this subspace. This technique allows us to extend a number of previous multifractal results from the C1+ϵC^{1+\epsilon} case to the C1C^1 case. We consider ergodic ratios Snϕ/SnψS_n \phi/S_n \psi where the function ψ\psi need not be uniformly positive, which lets us study dimension spectra for non-uniformly expanding maps. Our results also cover coarse spectra and level sets corresponding to more general limiting behaviour.Comment: 32 pages, minor changes based on referee's comment

    Statistical stability of equilibrium states for interval maps

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    We consider families of multimodal interval maps with polynomial growth of the derivative along the critical orbits. For these maps Bruin and Todd have shown the existence and uniqueness of equilibrium states for the potential ϕt:xtlogDf(x)\phi_t:x\mapsto-t\log|Df(x)|, for tt close to 1. We show that these equilibrium states vary continuously in the weak^* topology within such families. Moreover, in the case t=1t=1, when the equilibrium states are absolutely continuous with respect to Lebesgue, we show that the densities vary continuously within these families.Comment: More details given and the appendices now incorporated into the rest of the pape

    Ordering of magnetic impurities and tunable electronic properties of topological insulators

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    We study collective behavior of magnetic adatoms randomly distributed on the surface of a topological insulator. As a consequence of the spin-momentum locking on the surface, the RKKY-type interactions of two adatom spins depend on the direction of the vector connecting them, thus interactions of an ensemble of adatoms are frustrated. We show that at low temperatures the frustrated RKKY interactions give rise to two phases: an ordered ferromagnetic phase with spins pointing perpendicular to the surface, and a disordered spin-glass-like phase. The two phases are separated by a quantum phase transition driven by the magnetic exchange anisotropy. Ferromagnetic ordering occurs via a finite-temperature phase transition. The ordered phase breaks time-reversal symmetry spontaneously, driving the surface states into a gapped state, which exhibits an anomalous quantum Hall effect and provides a realization of the parity anomaly. We find that the magnetic ordering is suppressed by potential scattering. Our work indicates that controlled deposition of magnetic impurities provides a way to modify the electronic properties of topological insulators.Comment: 4+ pages, 2 figure

    The Lyapunov spectrum is not always concave

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    We characterize one-dimensional compact repellers having nonconcave Lyapunov spectra. For linear maps with two branches we give an explicit condition that characterizes non-concave Lyapunov spectra

    Press shaping of arched components by means of a mobile tool

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    The best tool motion in a press is considered, when producing U-shaped components from sheet. The elastoplastic properties of the deformed material are taken into account. © 2013 Allerton Press, Inc

    Typical Borel measures on [0,1]d[0,1]d satisfy a multifractal formalism

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    In this article, we prove that in the Baire category sense, measures supported by the unit cube of Rd\R^d typically satisfy a multifractal formalism. To achieve this, we compute explicitly the multifractal spectrum of such typical measures μ\mu. This spectrum appears to be linear with slope 1, starting from 0 at exponent 0, ending at dimension dd at exponent dd, and it indeed coincides with the Legendre transform of the LqL^q-spectrum associated with typical measures μ\mu.Comment: 17 pages. To appear in Nonlinearit

    Thermodynamic formalism for contracting Lorenz flows

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    We study the expansion properties of the contracting Lorenz flow introduced by Rovella via thermodynamic formalism. Specifically, we prove the existence of an equilibrium state for the natural potential ϕ^t(x,y,z):=tlogJ(x,y,z)cu\hat\phi_t(x,y, z):=-t\log J_{(x, y, z)}^{cu} for the contracting Lorenz flow and for tt in an interval containing [0,1][0,1]. We also analyse the Lyapunov spectrum of the flow in terms of the pressure

    Oseledets' Splitting of Standard-like Maps

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    For the class of differentiable maps of the plane and, in particular, for standard-like maps (McMillan form), a simple relation is shown between the directions of the local invariant manifolds of a generic point and its contribution to the finite-time Lyapunov exponents (FTLE) of the associated orbit. By computing also the point-wise curvature of the manifolds, we produce a comparative study between local Lyapunov exponent, manifold's curvature and splitting angle between stable/unstable manifolds. Interestingly, the analysis of the Chirikov-Taylor standard map suggests that the positive contributions to the FTLE average mostly come from points of the orbit where the structure of the manifolds is locally hyperbolic: where the manifolds are flat and transversal, the one-step exponent is predominantly positive and large; this behaviour is intended in a purely statistical sense, since it exhibits large deviations. Such phenomenon can be understood by analytic arguments which, as a by-product, also suggest an explicit way to point-wise approximate the splitting.Comment: 17 pages, 11 figure

    Delocalization of slowly damped eigenmodes on Anosov manifolds

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    We look at the properties of high frequency eigenmodes for the damped wave equation on a compact manifold with an Anosov geodesic flow. We study eigenmodes with spectral parameters which are asymptotically close enough to the real axis. We prove that such modes cannot be completely localized on subsets satisfying a condition of negative topological pressure. As an application, one can deduce the existence of a "strip" of logarithmic size without eigenvalues below the real axis under this dynamical assumption on the set of undamped trajectories.Comment: 28 pages; compared with version 1, minor modifications, add two reference