On arithmetic sums of Ahlfors-regular sets

Let $$A,B \subset \mathbb {R}$$ A , B ⊂ R be closed Ahlfors-regular sets with dimensions $$\dim _{\mathrm {H}}A =: \alpha $$ dim H A = : α and $$\dim _{\mathrm {H}}B =: \beta $$ dim H B = : β . I prove that $$\begin{aligned} \dim _{\mathrm {H}}[A + \theta B] \ge \alpha + \beta \cdot \tfrac{1 - \alpha }{2 - \alpha } \end{aligned}$$ dim H [ A + θ B ] ≥ α + β · 1 - α 2 - α for all $$\theta \in \mathbb {R}{\setminus } E$$ θ ∈ R \ E , where $$\dim _{\mathrm {H}}E = 0$$ dim H E = 0 .

Non-convex proximal pair and relatively nonexpansive maps with respect to orbits

Every non-convex pair $(C, D)$ ( C , D ) may not have proximal normal structure even in a Hilbert space. In this article, we use cyclic relatively nonexpansive maps with respect to orbits to show the presence of best proximity points in $C\cup D$ C ∪ D , where $C\cup D$ C ∪ D is a cyclic T-regular set and $(C, D)$ ( C , D ) is a non-empty, non-convex proximal pair in a real Hilbert space. Moreover, we show the presence of best proximity points and fixed points for non-cyclic relatively nonexpansive maps with respect to orbits defined on $C\cup D$ C ∪ D , where C and D are T-regular sets in a uniformly convex Banach space satisfying $T(C)\subseteq C$ T ( C ) ⊆ C , $T(D)\subseteq D$ T ( D ) ⊆ D wherein the convergence of Kranoselskii’s iteration process is also discussed.

Plenty of big projections imply big pieces of Lipschitz graphs

I prove that closed n-regular sets $$E \subset {\mathbb {R}}^{d}$$ E ⊂ R d with plenty of big projections have big pieces of Lipschitz graphs. In particular, these sets are uniformly n-rectifiable. This answers a question of David and Semmes from 1993.

The nonlocal-interaction equation near attracting manifolds

<p style='text-indent:20px;'>We study the approximation of the nonlocal-interaction equation restricted to a compact manifold <inline-formula><tex-math id="M1">\begin{document}$ {\mathcal{M}} $\end{document}</tex-math></inline-formula> embedded in <inline-formula><tex-math id="M2">\begin{document}$ {\mathbb{R}}^d $\end{document}</tex-math></inline-formula>, and more generally compact sets with positive reach (i.e. prox-regular sets). We show that the equation on <inline-formula><tex-math id="M3">\begin{document}$ {\mathcal{M}} $\end{document}</tex-math></inline-formula> can be approximated by the classical nonlocal-interaction equation on <inline-formula><tex-math id="M4">\begin{document}$ {\mathbb{R}}^d $\end{document}</tex-math></inline-formula> by adding an external potential which strongly attracts to <inline-formula><tex-math id="M5">\begin{document}$ {\mathcal{M}} $\end{document}</tex-math></inline-formula>. The proof relies on the Sandier–Serfaty approach [<xref ref-type="bibr" rid="b23">23</xref>,<xref ref-type="bibr" rid="b24">24</xref>] to the <inline-formula><tex-math id="M6">\begin{document}$ \Gamma $\end{document}</tex-math></inline-formula>-convergence of gradient flows. As a by-product, we recover well-posedness for the nonlocal-interaction equation on <inline-formula><tex-math id="M7">\begin{document}$ {\mathcal{M}} $\end{document}</tex-math></inline-formula>, which was shown [<xref ref-type="bibr" rid="b10">10</xref>]. We also provide an another approximation to the interaction equation on <inline-formula><tex-math id="M8">\begin{document}$ {\mathcal{M}} $\end{document}</tex-math></inline-formula>, based on iterating approximately solving an interaction equation on <inline-formula><tex-math id="M9">\begin{document}$ {\mathbb{R}}^d $\end{document}</tex-math></inline-formula> and projecting to <inline-formula><tex-math id="M10">\begin{document}$ {\mathcal{M}} $\end{document}</tex-math></inline-formula>. We show convergence of this scheme, together with an estimate on the rate of convergence. Finally, we conduct numerical experiments, for both the attractive-potential-based and the projection-based approaches, that highlight the effects of the geometry on the dynamics.</p>

Modeling of crowds in regions with moving obstacles

<p style='text-indent:20px;'>We present a model of crowd motion in regions with moving obstacles, which is based on the notion of measure sweeping process. The obstacle is modeled by a set-valued map, whose values are complements to <inline-formula><tex-math id="M1">\begin{document}$ r $\end{document}</tex-math></inline-formula>-prox-regular sets. The crowd motion obeys a nonlinear transport equation outside the obstacle and a normal cone condition (similar to that of the classical sweeping processes theory) on the boundary. We prove the well-posedness of the model, give an application to environment optimization problems, and provide some results of numerical computations.</p>

Main eigenvalues of a graph and its Hamiltonicity

The concept of (κ,τ)-regular vertex set appeared in 2004. It was proved that the existence of many classical combinatorial structures in a graph like perfect matchings, Hamiltonian cycles, effective dominating sets, etc., can be characterized by (κ,τ)-regular sets the definition whereof is equivalent to the determination of these classical combinatorial structures. On the other hand, the determination of (κ,τ)-regular sets is closely related to the properties of the main spectrum of a graph. This paper generalizes the well-known properties of (κ,κ)-regular sets of a graph to arbitrary (κ,τ)-regular sets of graphs with an emphasis on their connection with classical combinatorial structures. We also present a recognition algorithm for the Hamiltonicity of the graph that becomes polynomial in some classes of graphs, for example, in the class of graphs with a fixed cyclomatic number.