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Fractals deal with special sets that exhibit complicated patterns in every scale. Fractal sets usually have a Hausdorff dimension different from its topological dimension. Examples include Julia sets, the Sierpinski triangle, the Cantor set. Fractals naturally appear in dynamical system, such as iterations in the complex plane, or as strange attractors to continuous dynamical systems, (see Lorentz attractor).

3 votes
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Precise density estimates for Cantor sets

Upper densities In the following, I freely use the well known fact that $s_\lambda$-Hausdorff measure gives mass $2^{-k}$ to all intervals that make up the stage $k$ in the construction of $C_\lambda …
Pablo Shmerkin's user avatar
8 votes
Accepted

Dimensions of self-affine sets

Falconer's classical theorem from "The Hausdorff dimension of self-affine fractals" says that if $\alpha<1/2$, then for almost every choice of translations $v_1,v_2$, the Hausdorff and box counting dimensions …
Pablo Shmerkin's user avatar
1 vote

Isometrically-invariant measures and dilation of the Cantor set

This is too long for a comment. The following measure (defined on Borel sets) might be a counterexample to Question 1: let $\mathcal{I}_N$ be the collection of all left-closed, right-open intervals of …
Pablo Shmerkin's user avatar
6 votes

Iterated function system on the plane

Given the other (incorrect) answers, I think it is worth to give a detailed proof of the following partial negative answer: if the maps $f_i$ are only allowed to be homotheties, then there is no such …
Pablo Shmerkin's user avatar
12 votes
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Arithmetic products of Cantor sets.

The results my paper with M. Hochman yield the following result on the products of self-similar sets: Let $A=\bigcup_{i=1}^m r_i A + t_i$, $B=\bigcup_{i=1}^n s_i B+u_i$ be two self-similar sets on …
Pablo Shmerkin's user avatar
4 votes
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Measures of full Hausdorff dimension for self-affine sets

If $\beta^{-1}$ is Pisot, then there is an ergodic measure of maximal dimension. This is a special case of the rather difficult Theorem 2.15 in the paper Dimension Theory of iterated function systems …
Pablo Shmerkin's user avatar
5 votes

Fourier decay rate of Cantor measures

Edit in response to the editing of the second question: The central Cantor sets are never Salem (for any $\theta$). Here is a way to see this. If $A\subset \mathbb{R}$ is a Salem set, then $$ \dim(A+ …
Pablo Shmerkin's user avatar
20 votes
Accepted

Is there some known way to create the Mandelbrot set (the boundary), with an iterated functi...

I know very little about the Mandelbrot set or complex dynamics, but there are several features which strongly suggest that its boundary is not the attractor of an iterated function system, at least a …
Pablo Shmerkin's user avatar
20 votes
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Hausdorff dimension for invariant measure?

There are a wide variety of notions of dimension of a measure. Your basic intuition is completely correct: for a dynamical system, the dimension of a natural invariant measure provides more relevant i …
Pablo Shmerkin's user avatar
5 votes

local behavior of a finite Borel measure

I think in order to prove the sharp result you need to use a covering theorem. The best option seems to be Vitali's covering theorem for Radon measures, which says the following: let $\mu$ be a Radon …
Pablo Shmerkin's user avatar