Francois Ledrappier, Michael Shub, Carles Simo, Amie Wilkinson
We study, both numerically and theoretically, the relationship between the random Lyapunov exponent of a family of area preserving diffeomorphisms of the 2-sphere and the mean of the Lyapunov exponents of the individual members.
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Robust transitivity versus trapping regions for partially hyperbolic diffeomorphisms
研究部分双曲微分同胚，通过仔细研究极小\(\mathcal{W}^u -\)饱和集，证明了在一维中心的部分双曲微分同胚中有\(C^1 -\)开且稠密子集，存在恰当拟吸引子或两个强叶状结构是极小的，保体积情形同理且有保守外的鲁棒传递性结果。
In this paper, we study the centralizer of a partially hyperbolic diffeomorphism on $\mathbb{T}^3$ which is homotopic to an Anosov automorphism, and we show that either its centralizer is virtually trivial or such diffeomorphism is smoothly conjugate to its linear part.
In this paper we investigate the relation between measure expansiveness and hyperbolicity. We prove that non atomic invariant ergodic measures with all of its Lyapunov exponents positive is positively measure-expansive. We also prove that local diffeomorphisms robustly positively measure-expansive is expanding. Finally, we prove that if a $C^1$ volume preserving diffeomorphism that. can not be accumulated by positively measure expansive diffeomorphis have a dominated sppliting.
A Conservative Partially Hyperbolic Dichotomy: Hyperbolicity versus Nonhyperbolic Measures
在保守部分双曲三维环境中，针对三类微分同胚建立双曲性与非双曲遍历测度的二分法，方法无需扰动，还独立于保守假设构造了非双曲遍历测度，可应用于更多情境。
We prove that, for $C^1$-generic diffeomorphisms, if a homoclinic class is not hyperbolic, then there is a non-hyperbolic ergodic measure supported on it. This proves a conjecture by Díaz and Gorodetski [28]. We also discuss the conjectured existence of periodic points with different stable dimension in the class.
We study two agent based models of opinion formation - one stochastic in nature and one deterministic. Both models are defined in terms of an underlying graph; we study how the structure of the graph affects the long time behavior of the models in all possible cases of graph topology. We are especially interested in the emergence of a consensus among the agents and provide a condition on the graph that is necessary and sufficient for convergence to a consensus in both models. This investigation reveals several contrasts between the models - notably the convergence rates - which are explored th…
We consider a family of planar systems introduced in 1991 by Benedicks and Carleson as a toy model for the dynamics of the so-called Hénon maps. We show that Smale's Axiom A property is $C^1$-dense among the systems in this family, despite the existence of $C^2$-open subsets (closely related to the so-called Newhouse phenomena) where Smale's Axiom A is violated. In particular, this provides some evidence towards Smale's conjecture that Axiom A is a $C^1$-dense property among surface diffeomorphisms. The basic tools in the proof of this result are: 1) a recent theorem of Moreira saying that sta…
Negative regularity mixing for random volume preserving diffeomorphisms
本文研究随机保体积微分同胚的负正则性指数混合，给出通用判据并应用于随机微分同胚、SDE 及随机不可压缩 Navier-Stokes 平流扩散，证明理想标量湍流存在唯一平稳测度。
Tail behaviour of stationary densities for one-dimensional random diffeomorphisms
研究一维随机微分同胚平稳密度在支撑边界处渐近行为，展示其依赖潜在噪声分布、边界点处极值微分同胚线性化或主导非线性项的情况。
We give a geometric proof, offering a new and quite different perspective on an earlier result of Ledrappier and Young on random transformations. We show that under mild conditions, sample measures of random diffeomorphisms are SRB measures. As sample measures are the limits of forward images of stationary measures, they can be thought of as the analog of physical measures for deterministic systems. Our results thus show the equivalence of physical and SRB measures in the random setting, a hoped-for scenario that is not always true for deterministic maps.
We propose a novel approach to generate chaotic business cycles in a deterministic setting. Rather than producing chaos endogenously, we consider aggregate economic models with limit cycles and equilibriums, subject them to chaotic exogenous shocks and obtain chaotic cyclical motions. Thus, we emphasize that chaotic cycles, which are inevitable in economics, are not only interior properties of economic models, but also can be considered as a result of interaction of several economical systems. This provides a comprehension of chaos (unpredictability, lack of forecasting) and control of chaos a…
Contraction versus Recurrence: An Exponential Separation in Observation-Based Prediction of Deterministic Dynamics
研究基于观测预测确定性动力学中收缩与递归方法的差异，通过形式化和实验验证两者指数分离，给出成本缩放规律及数值验证结果，还用准入协议补充定理，解释分形维数，在实际数据上验证了该方法。
Let X be a real algebraic surface. The comparison between the volume of real and complex loci of ample divisors D brings us to define the concordance, which is a number between 0 and 1. This number equals 1 when the Picard number is 1, and for some surfaces with a "quite simple" nef cone, e.g. Del Pezzo surfaces. For abelian surfaces, it is 1/2 or 1, depending on the existence or not of positive entropy automorphisms on X. In the general case, the existence of such an automorphism gives an upper bound for the concordance, namely the ratio of entropies in real and complex loci of X. Moreover th…
We consider a large class of 2D area-preserving diffeomorphisms that are not uniformly hyperbolic but have strong hyperbolicity properties on large regions of their phase spaces. A prime example is the Standard map. Lower bounds for Lyapunov exponents of such systems are very hard to estimate, due to the potential switching of "stable" and "unstable" directions. This paper shows that with the addition of (very) small random perturbations, one obtains with relative ease Lyapunov exponents reflecting the geometry of the deterministic maps.
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