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In this paper, we use a class of finite state automata, called topology automaton, to study the metric classification of a special class of post-critically finite self-similar sets. As an application, we prove that the conformal dimension of post-critically finite self-similar dendrites and fractal gasket with connected component is 1., Comment: 38 pages, 11 figures, 27 references

The Fibonacci word is the fixed point beginning with the letter $a$ of morphism $\sigma(a)=ab$, $\sigma(b)=a$ defined over the alphabet $\{a,b\}$. In this paper, we get explicit expression of the number of distinct fractional powers in each factor of the Fibonacci word., Comment: 19 pages, 9 figures

We consider the infinite one-sided sequence over alphabet $\{a,b\}$ generated by the period-doubling substitution $\sigma(a)=ab$ and $\sigma(b)=aa$, denoted by $\mathbb{D}$. Let $r_p(\omega)$ be the $p$-th return word of factor $\omega$. The main result of this paper is twofold. (1) For any factor $\omega$ in $\mathbb{D}$, the return word sequence $\{r_p(\omega)\}_{p\geq1}$ is $\Theta_1$ or $\Theta_2$. Both of them are substitutive sequences and determined completely in this paper. (2) For any factor $\omega$ in $\Theta_1$ (resp. $\Theta_2$), the return word sequence $\{r_p(\omega)\}_{p\geq1}$ is still $\Theta_1$ or $\Theta_2$. We call it the reflexivity property of the return word sequence. As an application, we introduce a notion of spectrum for studying some typical combinatorial properties, such as separated, adjacent and overlapped., Comment: 17 pages, 3 figures. arXiv admin note: text overlap with arXiv:1606.05150 by other authors

The Tribonacci sequence $\mathbb{T}$ is the fixed point of the substitution $\sigma(a)=ab$, $\sigma(b)=ac$, $\sigma(c)=a$. The prefix of $\mathbb{T}$ of length $n$ is denoted by $\mathbb{T}[1,n]$. The main result is threefold, we give: (1) explicit expressions of the numbers of distinct squares and cubes in $\mathbb{T}[1,n]$; (2) algorithms for counting the numbers of repeated squares and cubes in $\mathbb{T}[1,n]$; (3) a discussion about $\alpha$-powers in $\mathbb{T}[1,n]$ for $\alpha\geq2$ and $n\geq1$., Comment: 17 pages, 4 figures

The irrationality exponent of an irrational number $\xi$, which measures the approximation rate of $\xi$ by rationals, is in general extremely difficult to compute explicitly, unless we know the continued fraction expansion of $\xi$. Results obtained so far are rather fragmentary, and often treated case by case. In this work, we shall unify all the known results on the subject by showing that the irrationality exponents of large classes of automatic numbers and Mahler numbers (which are transcendental) are exactly equal to $2$. Our classes contain the Thue--Morse--Mahler numbers, the sum of the reciprocals of the Fermat numbers, the regular paperfolding numbers, which have been previously considered respectively by Bugeaud, Coons, and Guo, Wu and Wen, but also new classes such as the Stern numbers and so on. Among other ingredients, our proofs use results on Hankel determinants obtained recently by Han., Comment: International Mathematics Research Notices 2015

In this paper, we introduce a class of fractals named homogeneous sets based on some measure versions of homogeneity, uniform perfectness and doubling. This fractal class includes all Ahlfors-David regular sets, but most of them are irregular in the sense that they may have different Hausdorff dimensions and packing dimensions. Using Moran sets as main tool, we study the dimensions, bilipschitz embedding and quasi-Lipschitz equivalence of homogeneous fractals.

Let $\alpha\in(0,1)$ be an irrational, and $[0;a_1,a_2,...]$ the continued fraction expansion of $\alpha$. Let $H_{\alpha,V}$ be the one-dimensional Schr\"odinger operator with Sturm potential of frequency $\alpha$. Suppose the potential strength $V$ is large enough and $(a_i)_{i\ge1}$ is bounded. We prove that the spectral generating bands possess properties of bounded distortion, bounded covariation and there exists Gibbs-like measure on the spectrum $\sigma(H_{\alpha,V})$. As an application, we prove that $$\dim_H \sigma(H_{\alpha,V})=s_*,\quad \bar{\dim}_B \sigma(H_{\alpha,V})=s^*,$$ where $s_*$ and $s^*$ are lower and upper pre-dimensions., Comment: 19 pages

Mandelbrot multiplicative cascades provide a construction of a dynamical system on a set of probability measures defined by inequalities on moments. To be more specific, beyond the first iteration, the trajectories take values in the set of fixed points of smoothing transformations (i.e., some generalized stable laws). Studying this system leads to a central limit theorem and to its functional version. The limit Gaussian process can also be obtained as limit of an `additive cascade' of independent normal variables.