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arXiv 1301.1827math.DSmath.CA
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具有可变折叠数的分形集稳定维数的上估计

Upper estimates for stable dimensions of fractal sets with variable number of foldings

Eugen Mihailescu, Bernd Stratmann

摘要:

对于鞍型分形λ上具有自相交的双曲映射f,λ中点x的f-原像数可能依赖于x。这使得估计的稳定尺寸更困难比的同胚或地图是常数。当f在局部稳定流形上共形时,我们利用热力学形式主义推导出λ上稳定的豪斯多夫维数函数delta^s的估计。这些估计是根据Lambda上的连续函数,其从下面限制原像计数函数。作为推论,我们得到,如果δ ^s在λ中达到其最大可能值,则稳定维数在整个λ中是恒定的,而原像计数函数至少在λ的开稠密子集上是恒定的。特别地,这表明,如果在λ中的某个点,稳定维数等于在该点稳定方向上的相似维数的模拟,则f的行为非常像λ上的同胚。最后,我们也得到了这类分形的稳定上盒维数的结果。最后,我们讨论了两个明确的例子。

英文摘要:

For a hyperbolic map f on a saddle type fractal Lambda with self-intersections, the number of f- preimages of a point x in Lambda may depend on x. This makes estimates of the stable dimensions more difficult than for diffeomorphisms or for maps which are constant-to-one. We employ the thermodynamic formalism in order to derive estimates for the stable Hausdorff dimension function delta^s on Lambda, in the case when f is conformal on local stable manifolds. These estimates are in terms of a continuous function on Lambda which bounds the preimage counting function from below. As a corollary we obtain that if delta^s attains its maximal possible value in Lambda, then the stable dimension is constant throughout Lambda, whereas the preimage counting function is constant on at least an open and dense subset of Lambda. In particular, this shows that if at some point in Lambda, the stable dimension is equal to the analogue of the similarity dimension in the stable direction at that point, then f behaves very much like a homeomorphism on Lambda. Finally we also obtain results about the stable upper box dimension for these type of fractals. We end the paper with a discussion of two explicit examples.

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