Browsing NTNU Open by Author "Perfekt, KarlMikael"
Now showing items 120 of 24

Aspects of Dirichlet series: Composition operators, Bohr’s theorem and universality
Kouroupis, Athanasios (Doctoral theses at NTNU;2024:181, Doctoral thesis, 2024) 
Atomic decompositions, two stars theorems, and distances for the Bourgain–Brezis–Mironescu space and other big spaces
D'Onofrio, Luigi; Greco, Luigi; Sbordone, Carlo; Schiattarella, Roberta; Perfekt, KarlMikael (Peer reviewed; Journal article, 2020)Given a Banach space E with a supremumtype norm induced by a collection of operators, we prove that E is a dual space and provide an atomic decomposition of its predual. We apply this result, and some results obtained ... 
Biparameter Potential theory and Carleson measures for the Dirichlet space on the bidisc
Arcozzi, Nicola; Mozolyako, Pavel; Perfekt, KarlMikael; Sarfatti, Giulia (Journal article; Peer reviewed, 2023) 
Bohr's theorem for general Dirichlet series and different assumptions on frequencies
Eide, Jonas (Master thesis, 2023)Vi studerer generelle Dirichletrekker som antar forskjellige antakelser på frekvensen λ. Spesielt betrakter vi Dirichletrekker som tilhører rommet Dext∞ (λ) av alle noen steds konvergerende generelle Dirichletrekker som ... 
The ComplexScaled HalfSpace Matching Method
BONNETBEN DHIA, AnneSophie; ChandlerWilde, Simon; Fliss, Sonia; Hazard, Christophe; Perfekt, KarlMikael; TJANDRAWIDJAJA, Yohanes (Peer reviewed; Journal article, 2022)The halfspace matching (HSM) method has recently been developed as a new method for the solution of twodimensional scattering problems with complex backgrounds, providing an alternative to perfectly matched layers or ... 
Composition operators on weighted Hilbert spaces of Dirichlet series
Kouroupis, Athanasios; Perfekt, KarlMikael (Peer reviewed; Journal article, 2023) 
Contractive inequalities for Bergman spaces and multiplicative Hankel forms
Bayart, Frédéric; Brevig, Ole Fredrik; Haimi, Antti; OrtegaCerdà, Joaquim; Perfekt, KarlMikael (Journal article; Peer reviewed, 2019)We consider sharp inequalities for Bergman spaces of the unit disc, establishing analogues of the inequality in Carleman's proof of the isoperimetric inequality and of Weissler's inequality for dilations. By contractivity ... 
Cyclicity in the DruryArveson space and other weighted Besov spaces
Aleman, Alexandru; Perfekt, KarlMikael; Richter, Stefan; Sundberg, Carl; Sunkes, James (Peer reviewed; Journal article, 2023) 
Fourier series and Hilbert spaces
Kim, Jeongmin (Bachelor thesis, 2022)Denne bacheloroppgaven gir en oversikt over konvergensen av Fourierserier og dens anvendelse i Hilbertrom sammen med to kjerner, Dirichletkjernen og Fejérkjernen. Nødvendige teoremer som konvergenssetningen, Bessels ... 
Infinitely Many Embedded Eigenvalues for the NeumannPoincaré Operator in 3D
Li, Wei; Perfekt, KarlMikael; Shipman, Stephen (Peer reviewed; Journal article, 2022)This article constructs a surface whose NeumannPoincaré (NP) integral operator has infinitely many eigenvalues embedded in its essential spectrum. The surface is a sphere perturbed by smoothly attaching a conical ... 
The Nehari problem for the PaleyWiener space of a disc
Brevig, Ole Fredrik; Perfekt, KarlMikael (Peer reviewed; Journal article, 2023)There is a bounded Hankel operator on the Paley–Wiener space of a disc in R2 which does not arise from a bounded symbol. 
Nehari’s theorem for convex domain Hankel and Toeplitz operators in several variables
Carlsson, Marcus; Perfekt, KarlMikael (Peer reviewed; Journal article, 2021)We prove Nehari’s theorem for integral Hankel and Toeplitz operators on simple convex polytopes in several variables. A special case of the theorem, generalizing the boundedness criterion of the Hankel and Toeplitz operators ... 
Norms of composition operators on the $H^2$ space of Dirichlet series
Brevig, Ole Fredrik; Perfekt, KarlMikael (Journal article; Peer reviewed, 2020), generated by Dirichlet series symbols φ. We prove two different subordination principles for such operators. One concerns affine symbols only, and is based on an arithmetical condition on the coefficients of φ. The other ... 
A note on Bohr’s theorem for Beurling integer systems
Broucke, Frederik; Kouroupis, Athanasios; Perfekt, KarlMikael (Journal article; Peer reviewed, 2023)Given a sequence of frequencies , a corresponding generalized Dirichlet series is of the form . We are interested in multiplicatively generated systems, where each number arises as a finite product of some given ... 
On the spectrum of the doublelayer operator on locallydilationinvariant Lipschitz domains
ChandlerWilde, Simon N.; Hagger, Raffael; Perfekt, KarlMikael; Virtanen, Jani A. (Journal article; Peer reviewed, 2023) 
Orthogonal decomposition of composition operators on the $H^2$ space of Dirichlet series
Brevig, Ole Fredrik; Perfekt, KarlMikael (Peer reviewed; Journal article, 2022)Let denote the Hilbert space of Dirichlet series with squaresummable coefficients. We study composition operators on which are generated by symbols of the form , in the case that . If only a subset of prime numbers ... 
Picard's little theorem
Talgø, Nils Phillip (Bachelor thesis, 2024)Denne oppgaven gir et bevis av Picard's lille teorem ved å bruke en modulær funksjon, analytisk fortsettelse og Liouville's teorem. Etter noen nødvendige forberedelser, starter vi konstruksjonen av den modulære funksjonen ... 
Plasmonic eigenvalue problem for corners: limiting absorption principle and absolute continuity in the essential spectrum
Perfekt, KarlMikael (Peer reviewed; Journal article, 2021)We consider the plasmonic eigenvalue problem for a general 2D domain with a curvilinear corner, studying the spectral theory of the Neumann–Poincaré operator of the boundary. A limiting absorption principle is proved, valid ... 
The quasistatic plasmonic problem for polyhedra
de LeónContreras, Marta; Perfekt, KarlMikael (Peer reviewed; Journal article, 2022)We characterize the essential spectrum of the plasmonic problem for polyhedra in R3. The description is particularly simple for convex polyhedra and permittivities ϵ<−1. The plasmonic problem is interpreted as a spectral ... 
Rectangular Summation of Multiple Fourier Series and Multiparametric Capacity
Perfekt, KarlMikael (Peer reviewed; Journal article, 2021)We consider the class of multiple Fourier series associated with functions in the Dirichlet space of the polydisc. We prove that every such series is summable with respect to unrestricted rectangular partial sums, everywhere ...