Ulrik Enstad

activity

20182026

most citedHeisenberg modules as function spaces

16 citations · 60 across the 17 of their papers we have counts for

collaborators

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11 papers · 1 filter

math.FA2026

A Balian-Low theorem for nilpotent Lie groups

Ulrik Enstad, Jordy Timo van Velthoven

We prove strict necessary density conditions for smooth coherent frames and Riesz sequences in the orbit of a connected, simply connected, nilpotent Lie group. This extends previou…

math.FA2025

Bessel duality of Gabor systems: A von Neumann algebraic perspective

Ulrik Enstad, Franz Luef

Bessel duality of regular Gabor systems states that a Gabor system over a lattice is a Bessel sequence if and only if the corresponding Gabor system over the adjoint lattice is a B…

math.FA2024

Criteria for the existence of Schwartz Gabor frames over rational lattices

Ulrik Enstad, Hannes Thiel, Eduard Vilalta

We give an explicit criterion for a rational lattice in the time-frequency plane to admit a Gabor frame with window in the Schwartz class. The criterion is an inequality formulated…

math.FA2023

Linear independence of coherent systems associated to discrete subgroups

Ulrik Enstad, Jordy Timo van Velthoven

This note considers the finite linear independence of coherent systems associated to discrete subgroups. We show by simple arguments that such coherent systems of amenable groups a…

math.FA2022★ 2 cited

Coherent systems over approximate lattices in amenable groups

Ulrik Enstad, Jordy Timo van Velthoven

Let $G$ be a second-countable amenable group with a uniform $k$ -approximate lattice $Λ$ . For a projective discrete series representation $(π, H_{π})$ of $G$ of formal degre…

math.FA2022★ 2 cited

A dynamical approach to sampling and interpolation in unimodular groups

Ulrik Enstad, Sven Raum

We introduce a notion of covolume for point sets in locally compact groups that simultaneously generalizes the covolume of a lattice and the reciprocal of the Beurling density for…

math.FA2021★ 4 cited

On sufficient density conditions for lattice orbits of relative discrete series

Ulrik Enstad, Jordy Timo van Velthoven

This note provides new criteria on a unimodular group $G$ and a discrete series representation $(π, H_{π})$ of formal degree $d_{π} > 0$ under which any lattice $Γ \leq G$ wit…

math.FA2021★ 9 cited

Smooth lattice orbits of nilpotent groups and strict comparison of projections

Erik Bédos, Ulrik Enstad, Jordy Timo van Velthoven

This paper provides sufficient density conditions for the existence of smooth vectors generating a frame or Riesz sequence in the lattice orbit of a square-integrable projective re…

math.FA2020

Deformations and Balian-Low theorems for Gabor frames on the adeles

Ulrik Enstad, Mads S. Jakobsen, Franz Luef +1

We generalize Feichtinger and Kaiblinger's theorem on linear deformations of uniform Gabor frames to the setting of a locally compact abelian group $G$ . More precisely, we show tha…

math.FA2019★ 1 cited

The Balian-Low theorem for locally compact abelian groups and vector bundles

Ulrik Enstad

Let $Λ$ be a lattice in a second countable, locally compact abelian group $G$ with annihilator $Λ^{⊥} \subseteq G$ . We investigate the validity of the following state…

math.FA2018★ 12 cited

Time-frequency analysis on the adeles over the rationals

Ulrik B. R. Enstad, Mads S. Jakobsen, Franz Luef

We show that the construction of Gabor frames in $L^{2} (R)$ with generators in $S_{0} (R)$ and with respect to time-frequency shifts from a rectangular la…