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Marstrand-type Theorems for the Counting and Mass Dimensions in ℤ

Published online by Cambridge University Press:  16 March 2016

DANIEL GLASSCOCK*
Affiliation:
Department of Mathematics, The Ohio State University, 231 W. 18th Avenue, Columbus, OH 43210, USA (e-mail: glasscock.4@buckeyemail.osu.edu)

Abstract

The counting and (upper) mass dimensions of a set A $\mathbb{R}^d$ are

$$D(A) = \limsup_{\|C\| \to \infty} \frac{\log | \lfloor A \rfloor \cap C |}{\log \|C\|}, \quad \smash{\overline{D}}\vphantom{D}(A) = \limsup_{\ell \to \infty} \frac{\log | \lfloor A \rfloor \cap [-\ell,\ell)^d |}{\log (2 \ell)},$$
where ⌊A⌋ denotes the set of elements of A rounded down in each coordinate and where the limit supremum in the counting dimension is taken over cubes C $\mathbb{R}^d$ with side length ‖C‖ → ∞. We give a characterization of the counting dimension via coverings:
$$D(A) = \text{inf} \{ \alpha \geq 0 \mid {d_{H}^{\alpha}}(A) = 0 \},$$
where
$${d_{H}^{\alpha}}(A) = \lim_{r \rightarrow 0} \limsup_{\|C\| \rightarrow \infty} \inf \biggl\{ \sum_i \biggl(\frac{\|C_i\|}{\|C\|} \biggr)^\alpha\ \bigg| \1 \leq \|C_i\| \leq r \|C\| \biggr\}$$
in which the infimum is taken over cubic coverings {Ci } of AC. Then we prove Marstrand-type theorems for both dimensions. For example, almost all images of A $\mathbb{R}^d$ under orthogonal projections with range of dimension k have counting dimension at least min(k, D(A)); if we assume D(A) = D (A), then the mass dimension of A under the typical orthogonal projection is equal to min(k, D(A)). This work extends recent work of Y. Lima and C. G. Moreira.

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Type
Paper
Copyright
Copyright © Cambridge University Press 2016 

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