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We study projections onto non-degenerate one-dimensional families of lines and planes in $\mathbb{R}^{3}$. Using the classical potential theoretic approach of R. Kaufman, one can show that the Hausdorff dimension of at most…

Classical Analysis and ODEs · Mathematics 2014-11-27 Katrin Fässler , Tuomas Orponen

This paper extends some results of [M5] and [M3], in particular, removing assumptions of positive lower density. We give conditions on a general family $P_{\lambda}:\mathbb{R}^{n}\to\mathbb{R}^{m}, \lambda \in \Lambda,$ of orthogonal…

Classical Analysis and ODEs · Mathematics 2023-10-12 Pertti Mattila

For $S_g(x,y)=x-g(y), x,y\in\mathbb{R}^n, g\in O(n),$ we investigate the Lebesgue measure and Hausdorff dimension of $S_g(A)$ given the dimension of $A$, both for general Borel subsets of $\mathbb{R}^{2n}$ and for product sets.

Classical Analysis and ODEs · Mathematics 2020-09-28 Pertti Mattila

Intermediate dimensions were recently introduced to interpolate between the Hausdorff and box-counting dimensions of fractals. Firstly, we show that these intermediate dimensions may be defined in terms of capacities with respect to certain…

Classical Analysis and ODEs · Mathematics 2021-05-21 Stuart A. Burrell , Kenneth J. Falconer , Jonathan M. Fraser

\emph{Fractal percolation} or \emph{Mandelbrot percolation} is one of the most well studied families of random fractals. In this paper we study some of the geometric measure theoretical properties (dimension of projections and structure of…

Dynamical Systems · Mathematics 2015-06-16 Michal Rams , Károly Simon

Marstrand's celebrated projection theorem gives the Hausdorff dimension of the orthogonal projection of a Borel set in Euclidean space for almost all orthogonal projections. It is straightforward to see that sets for which the Fourier and…

Classical Analysis and ODEs · Mathematics 2024-06-21 Jonathan M. Fraser , Ana E. de Orellana

We prove a version of Bourgain's projection theorem for parametrized families of $C^2$ maps, that refines the original statement even in the linear case. As one application, we show that if $A$ is a Borel set of Hausdorff dimension close to…

Classical Analysis and ODEs · Mathematics 2024-08-19 Pablo Shmerkin

Let $F \subset \mathbb{R}^{2}$, and let $\dim_{\mathrm{A}}$ stand for Assouad dimension. I prove that $\dim_{\mathrm{A}} \pi_{e}(F) \geq \min\{\dim_{\mathrm{A}} F,1\}$ for all $e \in S^{1}$ outside of a set of Hausdorff dimension zero. This…

Classical Analysis and ODEs · Mathematics 2020-05-13 Tuomas Orponen

We obtain new lower bounds on the Hausdorff dimension of distance sets and pinned distance sets of planar Borel sets of dimension slightly larger than $1$, improving recent estimates of Keleti and Shmerkin, and of Liu in this regime. In…

Classical Analysis and ODEs · Mathematics 2018-11-09 Pablo Shmerkin

The behavior of the Hausdorff dimension of a set when projected onto a subspace is a fundamental question in fractal geometry. In this paper, we settle a question of Fassler and Orponen concerning the dimension of a set when projected onto…

Metric Geometry · Mathematics 2020-01-01 D. M. Stull

We examine the dimensions of the intersection of a subset $E$ of an $m$-ary Cantor space $\mathcal{C}^m$ with the image of a subset $F$ under a random isometry with respect to a natural metric. We obtain almost sure upper bounds for the…

Metric Geometry · Mathematics 2015-01-20 Casey Donoven , Kenneth Falconer

We establish the dimension version of Falconer's distance set conjecture for sets of equal Hausdorff and packing dimension (in particular, for Ahlfors-regular sets) in all ambient dimensions. In dimensions $d=2$ or $3$, we obtain the first…

Classical Analysis and ODEs · Mathematics 2024-08-14 Pablo Shmerkin , Hong Wang

This paper is concerned with restricted families of projections in $\mathbb{R}^{3}$. Let $K \subset \mathbb{R}^{3}$ be a Borel set with Hausdorff dimension $\dim K = s > 1$. If $\mathcal{G}$ is a smooth and sufficiently well-curved…

Classical Analysis and ODEs · Mathematics 2016-02-03 Tuomas Orponen

Let $1 \leq m < s \leq n$ and let $A \subseteq \mathbb{R}^n$ be a Borel set of with $s$-dimensional Hausdorff measure $\mathcal{H}^s(A) > 0$. The classical Marstrand slicing theorem states that, for almost every $m$-dimensional subspace $V…

Classical Analysis and ODEs · Mathematics 2025-10-14 Ryan E. G. Bushling

This is a survey on recent developments on the Hausdorff dimension of projections and intersections for general subsets of Euclidean spaces, with an emphasis on estimates of the Hausdorff dimension of exceptional sets and on restricted…

Classical Analysis and ODEs · Mathematics 2018-01-03 Pertti Mattila

It is shown that if $\gamma: [a,b] \to S^2$ is $C^3$ with $\det(\gamma, \gamma', \gamma'') \neq 0$, and if $A \subseteq \mathbb{R}^3$ is a Borel set, then $\dim \pi_{\theta} (A) \geq \min\left\{ 2,\dim A, \frac{ \dim A}{2} + \frac{3}{4}…

Classical Analysis and ODEs · Mathematics 2023-11-02 Terence L. J. Harris

We prove that for an arbitrary upper semi-continuous function $\phi\colon G(1,2) \to [0,1]$ there exists a compact set $F$ in the plane such that $\dim_{\textrm{A}} \pi F = \phi(\pi)$ for all $\pi \in G(1,2)$, where $\pi F$ is the…

Metric Geometry · Mathematics 2021-03-26 Jonathan M. Fraser , Antti Käenmäki

We consider the Assouad dimensions of orthogonal projections of planar sets onto lines. Our investigation covers both general and self-similar sets. For general sets, the main result is the following: if a set in the plane has Assouad…

Classical Analysis and ODEs · Mathematics 2017-05-04 Jonathan M. Fraser , Tuomas Orponen

We improve the best known lower bound for the dimension of radial projections of sets in the plane. We show that if $X,Y$ are Borel sets in $\R^2$, $X$ is not contained in any line and $\dim_H(X)>0$, then $$\sup\limits_{x\in X} \dim_H(\pi_x…

Classical Analysis and ODEs · Mathematics 2025-09-08 Marianna Csornyei , D. M. Stull

We provide exposition into the field of projection theory, which lies at the intersection of incidence geometry and geometric measure theory. We first give the necessary preliminaries in Chapter 2, focusing on incidences between points and…

Classical Analysis and ODEs · Mathematics 2025-09-30 Paige Bright