# Fine properties of the curvature of arbitrary closed sets

created by santilli on 21 Jul 2020
modified on 23 Jul 2020

[BibTeX]

Published Paper

Inserted: 21 jul 2020
Last Updated: 23 jul 2020

Journal: Ann. Mat. Pura Appl.
Volume: 199(2020)
Year: 2017
Doi: 10.1007/s10231-019-00926-w

Abstract:

Given an arbitrary closed set $A$ of $\mathbf{R}^n$, we establish the relation between the eigenvalues of the approximate differential of the spherical image map of $A$ and the principal curvatures of $A$ introduced by Hug–Last–Weil, thus extending a well-known relation for sets of positive reach by Federer and Zähle. Then, we provide for every $m=1,…,n−1$ an integral representation for the support measure $\mu_m$ of A with respect to the m-dimensional Hausdorff measure. Moreover, a notion of second fundamental form $Q_A$ for an arbitrary closed set $A$ is introduced so that the finite principal curvatures of $A$ correspond to the eigenvalues of $Q_A$. Finally, we establish the relation between $Q_A$ and the approximate differential of order 2 for sets introduced in a previous work of the author, proving that in a certain sense the latter corresponds to the absolutely continuous part of $Q_A$.

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