arXiv subjects

Scott Zimmerman

Publications and source records attributed to Scott Zimmerman.

At least 19 recordsLinked to original sources

arXiv2026

A Lipschitz curve in a Carnot group that is purely unrectifiable by smooth horizontal curves

We construct a Lipschitz curve in the free Carnot group of step 3 with 2 generators that meets every $C^{1}$ horizontal curve in a set of measure zero. This shows that the $C^{1}_{H}$-Lusin property fails in a strong sense in this group, and we deduce that such a curve must be purely $C^1_H$ 1-unrectifiable. Hence 1-rectifiability in Carnot groups is wildly different to its counterpart in Euclidean spaces, wherein the Whitney Extension Theorem guarantees that Lipschitz rectifiability and $C^1$ rectifiability are equivalent.

math.MG↗

arXiv2025

Directional Pliability, Whitney Extension, and Lusin Approximation for Curves in Carnot Groups

We show that, in arbitrary Carnot groups, pliability in a subset of directions is sufficient to guarantee the existence of a Whitney-type extension and a Lusin approximation for curves with tangent vectors in the same set of directions. We apply this to show that every horizontal curve in the Engel group must intersect a $C^{1}$ horizontal curve in a set of positive measure.

math.DG↗

arXiv2024

On the equivalence of derivatives for maps between Carnot groups

This paper gives an alternate, elementary proof of a result of Magnani: maps between Carnot groups that preserve horizontal curves and are continuously differential in horizontal directions in the Euclidean sense are continuously Pansu differentiable. This proof contains primarily Euclidean arguments and also reproves a version of Magnani's mean value estimate for continuously Pansu differentiable maps.

math.MG↗

arXiv2023

Higher order Whitney extension and Lusin approximation for Horizontal curves in the Heisenberg group

In the setting of horizontal curves in the Heisenberg group, we prove a $C^{m,\omega}$ finiteness principle, a $C^{m,\omega}$ Lusin approximation result, a $C^{\infty}$ Whitney extension result, and a $C^{\infty}$ Lusin approximation result. Combined with previous work, this completes the study of Whitney extension and Lusin approximation for horizontal curves of class $C^{m}$, $C^{m,\omega}$, and $C^{\infty}$ in the Heisenberg group.

math.MG↗

arXiv2023

Bi-Lipschitz arcs in metric spaces with controlled geometry

We generalize a bi-Lipschitz extension result of David and Semmes from Euclidean spaces to complete metric measure spaces with controlled geometry (Ahlfors regularity and supporting a Poincar\'e inequality). In particular, we find sharp conditions on metric measure spaces $X$ so that any bi-Lipschitz embedding of a subset of the real line into $X$ extends to a bi-Lipschitz embedding of the whole line. Along the way, we prove that if the complement of an open subset $Y$ of $X$ has small Assouad dimension, then it is a uniform domain. Finally, we prove a quantitative approximation of continua in $X$ by bi-Lipschitz curves.

math.MG↗

arXiv2022

Methods to Simplify Object Tracking in Video Data

Recent years have seen an explosion of interest in analyzing the motion of objects in video data as a way for students to connect the concepts of physics to something tangible like a video recording of an experiment. A variety of software exists for students to look at individual frames and click on the object to infer the x,y position. Some of these tools include a capability to automatically identify the position of the object in the frame. But it is not unusual, especially when inexperienced users are recording the video and configuring the program, for these algorithms to struggle to "lock on" to the moving object. In this paper, we both include some general advice to help object tracking algorithms locate an object and we provide our own algorithms that are simpler and potentially more effective than the sophisticated image processing algorithms that are currently being used. These algorithms focus not on a "template image" of the moving object but instead distinguish between the object and the background by analyzing only the colors of individual pixels. These algorithms are built into a free and open source program called the STEMcoding Object Tracker (http://go.osu.edu/objecttracker) which works in the browser (without any downloads) and is compatible with a variety of operating systems including chromebooks.

physics.ed-ph↗

arXiv2022

A $C^{m,ω}$ Whitney Extension Theorem for Horizontal Curves in the Heisenberg Group

We characterize which mappings from a compact subset of $\mathbb{R}$ into the Heisenberg group can be extended to a $C^{m,ω}$ horizontal curve for a given modulus of continuity $ω$. We motivate our characterization by showing that the $C^{m,ω}$ extension property fails if we instead use a more direct analogue of the conditions from the $C^{m}$ case.

math.MG↗

arXiv2022

Whitney's Extension Theorem and the finiteness principle for curves in the Heisenberg group

Consider the sub-Riemannian Heisenberg group $\mathbb{H}$. In this paper, we answer the following question: given a compact set $K \subseteq \mathbb{R}$ and a continuous map $f:K \to \mathbb{H}$, when is there a horizontal $C^m$ curve $F:\mathbb{R} \to \mathbb{H}$ such that $F|_K = f$? Whitney originally answered this question for real valued mappings, and Fefferman provided a complete answer for real valued functions defined on subsets of $\mathbb{R}^n$. We also prove a finiteness principle for $C^{m,\sqrtω}$ horizontal curves in the Heisenberg group in the sense of Brudnyi and Shvartsman.

math.MG↗

arXiv2021

Singular integrals on $C_{w^*}^{1,α}$ regular curves in Banach duals

The modern study of singular integral operators on curves in the plane began in the 1970's. Since then, there has been a vast array of work done on the boundedness of singular integral operators defined on lower dimensional sets in Euclidean spaces. In recent years, mathematicians have attempted to push these results into a more general metric setting particularly in the case of singular integral operators defined on curves and graphs in Carnot groups. Suppose $X = Y^*$ for a separable Banach space $Y$. Any separable metric space can be isometrically embedded in such a Banach space via the Kuratowski embedding. Suppose $Γ= γ([a,b])$ is a curve in $X$ whose $w^*$-derivative is Hölder continuous and bounded away from 0. We prove that any convolution type singular integral operator associated with a 1-dimensional Calderón-Zygmund kernel which is uniformly $L^2$-bounded on lines is $L^p$-bounded along $Γ$. We also prove a version of David's ``good lambda'' theorem for upper regular measures on doubling metric spaces.

math.CA↗

arXiv2021

Identifying 1-rectifiable measures in Carnot groups

We continue to develop a program in geometric measure theory that seeks to identify how measures in a space interact with canonical families of sets in the space. In particular, extending a theorem of the first author and R. Schul in Euclidean space, for an arbitrary locally finite Borel measure in an arbitrary Carnot group, we develop tests that identify the part of the measure that is carried by rectifiable curves and the part of the measure that is singular to rectifiable curves. Our main result is entwined with an extension of the Analyst's Traveling Salesman Theorem, which characterizes subsets of rectifiable curves in $\mathbb{R}^2$ (P. Jones, 1990), in $\mathbb{R}^n$ (K. Okikolu, 1992), or in an arbitrary Carnot group (the second author) in terms of local geometric least squares data called Jones' $\beta$-numbers. In a secondary result, we implement the Garnett-Killip-Schul construction of a doubling measure in $\mathbb{R}^n$ that charges a rectifiable curve in an arbitrary complete, doubling, locally quasiconvex metric space.

math.MG↗

arXiv2020

Singular integrals on $C^{1,α}$ regular curves in Carnot groups

Let $\mathbb{G}$ be any Carnot group. We prove that if a convolution type singular integral associated with a $1$-dimensional Calderón-Zygmund kernel is $L^2$-bounded on horizontal lines, with uniform bounds, then it is bounded in $L^p, p \in (1,\infty),$ on any compact $C^{1,α}, α\in (0,1],$ regular curve in $\mathbb{G}$.

math.CA↗

arXiv2019

An implicit function theorem for Lipschitz mappings into metric spaces

We prove a version of the implicit function theorem for Lipschitz mappings $f:\mathbb{R}^{n+m}\supset A \to X$ into arbitrary metric spaces. As long as the pull-back of the Hausdorff content $\mathcal{H}_{\infty}^n$ by $f$ has positive upper $n$-density on a set of positive Lebesgue measure, then, there is a local diffeomorphism $G$ in $\mathbb{R}^{n+m}$ and a Lipschitz map $π:X\to \mathbb{R}^n$ such that $π\circ f\circ G^{-1}$, when restricted to a certain subset of $A$ of positive measure, is a the orthogonal projection of $\mathbb{R}^{n+m}$ onto the first $n$-coordinates. This may be seen as a qualitative version of a similar result of Azzam and Schul. The main tool in our proof is the metric change of variables introduced in a paper of Hajlasz and Malekzadeh.

math.GT↗

arXiv2018

Bi-Lipschitz embeddings of Heisenberg submanifolds into Euclidean spaces

The Heisenberg group $\mathbb{H}$ equipped with a sub-Riemannian metric is one of the most well known examples of a doubling metric space which does not admit a bi-Lipschitz embedding into any Euclidean space. In this paper we investigate which \textit{subsets} of $\mathbb{H}$ bi-Lipschitz embed into Euclidean spaces. We show that there exists a universal constant $L>0$ such that lines $L$-bi-Lipschitz embed into $\mathbb{R}^3$ and planes $L$-bi-Lipschitz embed into $\mathbb{R}^4$. Moreover, $C^{1,1}$ $2$-manifolds without characteristic points as well as all $C^{1,1}$ $1$-manifolds locally $L$-bi-Lipschitz embed into $\mathbb{R}^4$ where the constant $L$ is again universal. We also consider several examples of compact surfaces with characteristic points and we prove, for example, that Korányi spheres bi-Lipschitz embed into $\mathbb{R}^4$ with a uniform constant. Finally, we show that there exists a compact, porous subset of $\mathbb{H}$ which does not admit a bi-Lipschitz embedding into any Euclidean space.

math.MG↗

arXiv2018

A $C^m$ Whitney Extension Theorem for Horizontal Curves in the Heisenberg Group

We characterize those mappings from a compact subset of $\mathbb{R}$ into the Heisenberg group $\mathbb{H}^{n}$ which can be extended to a $C^{m}$ horizontal curve in $\mathbb{H}^{n}$. The characterization combines the classical Whitney conditions with an estimate comparing changes in the vertical coordinate with those predicted by the Taylor series of the horizontal coordinates.

math.MG↗

arXiv2018

The Traveling Salesman Theorem in Carnot Groups

Let $\mathbb{G}$ be any Carnot group. We prove that, if a subset of $\mathbb{G}$ is contained in a rectifiable curve, then it satisfies Peter Jones' geometric lemma with some natural modifications. We thus prove one direction of the Traveling Salesman Theorem in $\mathbb{G}$. Our proof depends on new Alexandrov-type curvature inequalities for the Hebisch-Sikora metrics. We also apply the geometric lemma to prove that, in every Carnot group, there exist $-1$-homogeneous Calderón-Zygmund kernels such that, if a set $E \subset \mathbb{G}$ is contained in a 1-regular curve, then the corresponding singular integral operators are bounded in $L^2(E)$. In contrast to the Euclidean setting, these kernels are nonnegative and symmetric.

math.MG↗

arXiv2017

Sobolev extensions of Lipschitz mappings into metric spaces

Wenger and Young proved that the pair $(\mathbb{R}^m,\mathbb{H}^n)$ has the Lipschitz extension property for $m \leq n$ where $\mathbb{H}^n$ is the sub-Riemannian Heisenberg group. That is, for some $C>0$, any $L$-Lipschitz map from a subset of $\mathbb{R}^m$ into $\mathbb{H}^n$ can be extended to a $CL$-Lipschitz mapping on $\mathbb{R}^m$. In this paper, we construct Sobolev extensions of such Lipschitz mappings with no restriction on the dimension $m$. We prove that any Lipschitz mapping from a compact subset of $\mathbb{R}^m$ into $\mathbb{H}^n$ may be extended to a Sobolev mapping on any bounded domain containing the set. More generally, we prove this result in the case of mappings into any Lipschitz $(n-1)$-connected metric space.

math.MG↗

arXiv2017

Weak BLD mappings and Hausdorff measure

We prove that if $Φ:X\to Y$ a mapping of weak bounded length distortion from a quasiconvex and complete metric space $X$ to any metric space $Y$, then for any Lipschitz mapping $f:\mathbb{R}^k\supset E\to X$ we have that ${\mathcal H}^k(f(E))=0$ in $X$ if and only if ${\mathcal H}^k(Φ(f(E)))=0$ in $Y$. This generalizes an earlier result of Hajłasz and Malekzadeh where the target space $Y$ was a Euclidean space $Y=\mathbb{R}^N$.

math.MG↗

arXiv2016

The Whitney Extension Theorem for $C^1$, horizontal curves in the Heisenberg group

For a real valued function defined on a compact set $K \subset \mathbb{R}^m$, the classical Whitney Extension Theorem from 1934 gives necessary and sufficient conditions for the existence of a $C^k$ extension to $\mathbb{R}^m$. In this paper, we prove a version of the Whitney Extension Theorem in the case of $C^1$, horizontal extensions for mappings defined on compact subsets of $\mathbb{R}$ taking values in the Heisenberg Group $\mathbb{H}^n$.

math.MG↗