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arXiv 1110.3192math.DS
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齐次Cantor集与Beta-展开式的交

Intersections of homogeneous Cantor sets and beta-expansions

Derong Kong, Wenxia Li, Michel Dekking

摘要:

设$Γ_{β,N}$是具有$β\in(1/(2N-1),1/N)$的$N$ -部分齐次Cantor集.任何带有$j_\ell\in\{0,\pm 1,...,\pm(N-1)\}$的字符串$(j_\ell)_{\ell=1}^\N$,使得$t=\sum_{\ell=1}^\N j_\ellβ^{\ell-1}(1-β)/(N-1)$被称为$t$的代码。令$\mathcal{U}_{β,\pm N}$是具有唯一码的$t\in[-1,1]$的集合,并且令$\mathcal{S}_{β,\pm N}$是使交集$Γ_{β,N}\cap(Γ_{β,N}+t)$成为自相似集合的$t\in\mathcal{U}_{β,\pm N}$的集合。本文用几何和代数的方法刻画了集合$\mathcal{U}_{β,\pm N}$,并给出了$t\in\mathcal{S}_{β,\pm N}$的一个充要条件.利用β-展开的技巧,证明了存在一个超越数$β_c\in(1/(2N-1),1/N)$的临界点,使得当$β\in(1/(2N-1),β_c)$时,$\mathcal{U}_{β,\pm N}$具有正的Hausdorff维数,当$β\in(β_c,1/N)$时,$\mathcal{U}_{β,\pm N}$包含可数无穷多个元素.此外,还存在第二个临界点$α_c=\big[N+1-\sqrt{(N-1)(N+3)}\,\big]/2\in(1/(2N-1),β_c)$,使得当$β\in(1/(2N-1),α_c)$时,$\mathcal{S}_{β,\pm N}$具有正的Hausdorff维数,当$β\in[α_c,1/N)$时,它包含可数无穷多个元素.

英文摘要:

Let $Γ_{β,N}$ be the $N$-part homogeneous Cantor set with $β\in(1/(2N-1),1/N)$. Any string $(j_\ell)_{\ell=1}^\N$ with $j_\ell\in\{0,\pm 1,...,\pm(N-1)\}$ such that $t=\sum_{\ell=1}^\N j_\ellβ^{\ell-1}(1-β)/(N-1)$ is called a code of $t$. Let $\mathcal{U}_{β,\pm N}$ be the set of $t\in[-1,1]$ having a unique code, and let $\mathcal{S}_{β,\pm N}$ be the set of $t\in\mathcal{U}_{β,\pm N}$ which make the intersection $Γ_{β,N}\cap(Γ_{β,N}+t)$ a self-similar set. We characterize the set $\mathcal{U}_{β,\pm N}$ in a geometrical and algebraical way, and give a sufficient and necessary condition for $t\in\mathcal{S}_{β,\pm N}$. Using techniques from beta-expansions, we show that there is a critical point $β_c\in(1/(2N-1),1/N)$, which is a transcendental number, such that $\mathcal{U}_{β,\pm N}$ has positive Hausdorff dimension if $β\in(1/(2N-1),β_c)$, and contains countably infinite many elements if $β\in(β_c,1/N)$. Moreover, there exists a second critical point $α_c=\big[N+1-\sqrt{(N-1)(N+3)}\,\big]/2\in(1/(2N-1),β_c)$ such that $\mathcal{S}_{β,\pm N}$ has positive Hausdorff dimension if $β\in(1/(2N-1),α_c)$, and contains countably infinite many elements if $β\in[α_c,1/N)$.

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