Postdoctoral researcher
Department of Mathematical Analysis
Faculty of Mathematics and Physics
Charles University
Sokolovská 83
18675 Prague, Czech Republic
Email: stefanos.lappas@matfyz.cuni.cz
I am currently a postdoc at Charles University in Prague, Czech Republic, supervised by Dr. Lenka Slavíková. Before coming to Prague in 2024, I completed my PhD in August 2022 at University of Helsinki, Finland supervised by Dr. Tuomas Hytönen. Prior to Helsinki, I obtained my Masters degree from the University of Bonn, Germany. My master supervisors were Dr. Christoph Thiele and Dr. Pavel Zorin Kranich. Previously, I completed my Bachelor studies in Patras (Greece).
Research
My research interests lie in areas of harmonic analysis, operator theory and probability. In particular, during the years 2019-2022 I worked as a doctoral researcher at the University of Helsinki, Finland within the project ``Frontiers of singular integrals'' led by the Dr. Tuomas Hytönen. Moreover, I focused my research on dyadic harmonic analysis, wavelet theory, extrapolation of compactness on weighted spaces, Littlewood-Paley-Stein and semigroup theory.
Currently (January 2024-present) as a postdoctoral researcher at Charles University, Czechia, I am working within the Primus research programme ``Harmonic analysis, function spaces and their interaction'' led by Dr. Lenka Slavíková. Regarding the aforementioned research programme my research involves linear and multilinear singular integral operators, function spaces of various types, as well as applications of these subjects in ergodic theory and partial differential equations.
Papers and Preprints
All my research articles are available on Arxiv.
T. Hytönen and S. Lappas, Quantitative estimates for bounded holomorphic semigroups, (Published) In: Semigroup Forum, 108(1), pages 115–144, doi: 10.1007/s00233-024-10407-z, 2024.
T. Hytönen and S. Lappas, Extrapolation of compactness on weighted spaces, (Published) In: Revista Matemática Iberoamericana, 39(1), pages 91–122, doi: 10.4171/RMI/1325, 2023.
T. Hytönen and S. Lappas, The dyadic representation theorem using smooth wavelets with compact support, (Published) In: Journal of Fourier Analysis and Applications, 28(4), Paper No. 66, doi: 10.1007/s00041-022-09963-1, 2022.
T. Hytönen and S. Lappas, Extrapolation of compactness on weighted spaces: Bilinear operators, (Published) In: Indagationes Mathematicae, 33(2), pages 397-420, doi: 10.1016/j.indag.2021.09.007, 2022.
S. Lappas, Extrapolation of compactness on weighted Morrey spaces, (Published) In: Studia Mathematica, 265(2), pages 177–195, doi: 10.4064/sm210607-20-9, 2022.
P. Honzík, S. Lappas and L. Slavíková, Bilinear singular integral operators with kernels in weighted spaces, Preprint, arXiv:2412.07014, 2024.
T. Hytönen, S. Lappas and T. Oikari, Extrapolation of compactness on variable Lp(·) spaces, Preprint, arXiv2505.23300, 2025.
Past Invited Talks
January 2024: Charles University function spaces seminar, Prague Czech Republic.
May 2022: Discrete Harmonic and Harmonic Analysis seminar, University of Würzburg, Germany.
April 2022: Harmonic Analysis seminar, University of Helsinki, Finland.
April 2021: Analysis seminar, Clemson University, USA.
June 2020: Harmonic Analysis seminar, University of Helsinki, Finland.
Conferences
June 2025: 12th International Conference on Harmonic Analysis and Partial Differential Equations, El Escorial, Madrid, Spain, Participant.
June 2025: Conference on Modern trends in Fourier analysis, CRM (Centre de Recerca Matemàtica), Barcelona, Spain, Participant.
September 2024: Contemporary Harmonic Analysis and its Synergies, Conference in Warsaw, Poland, Participant and contributed speaker.
June 2024: Harmonic Analysis and Partial Differential Equations conference, CIRM (Centre International de Rencontres Mathematiques), Marseille, France, Participant.
May 2024: Madison Lectures in Harmonic Analysis conference, Madison, USA, Participant.
June 2022: Advances in Harmonic Analysis conference in honor of Michael Lacey's birthday, CRM (Centre de Recerca Matemàtica), Barcelona, Spain, Participant.
June 2021: Contemporary Analysis and its Applications, Satellite conference of the 8th European Congress of Mathematics, Portorož, Slovenia, Participant.
June 2019: Harmonic Analysis and Partial Differential Equations conference, Helsinki, Finland, Participant.
Spring and Summer Schools
May 2024: Spring school on Multilinear Singular and Oscillatory Integrals with Applications, Madison, USA, Participant and contributed speaker.
September-October 2019: Summer School on Sphere Packings and Optimal Configurations, Kopp, Germany, Participant and contributed speaker.
July 2019: 4th Summer school on Harmonic Analysis and Partial Differential Equations: Restriction theory, BCAM (Basque Center for Applied Mathematics), Bilbao, Spain, Participant and contributed speaker.
Current and Past Teaching
Winter 2024: Mathematical Analysis Elective 1-Topics in Harmonic Analysis (NMMA498), Teaching instructor, Charles University, Czech Republic.
Spring 2024: Selected Topics in Harmonic Analysis 2 (NMMA482), Co-teaching with Lenka Slavíková, Charles University, Czech Republic.
Spring 2022: Function Spaces (MAST30148), Teaching assistant, University of Helsinki, Finland.
Winter 2021: Linear Algebra and Complex Numbers (BSMA1001), Teaching assistant, University of Helsinki, Finland.
Spring 2021: Calculus IB: Integration (BSMA1003), Teaching assistant, University of Helsinki, Finland.
Winter 2020: Introduction to Real and Fourier Analysis (MAST30132), Teaching assistant, University of Helsinki, Finland.
Spring 2020: Fourier Analysis II (MAST31009), Teaching assistant, University of Helsinki, Finland.
Spring 2020: Fourier Analysis I (MAST31008), Teaching assistant, University of Helsinki, Finland.