Forschungskolloquium mit Frau Dr. Simona Nistor Barna ("Alexandru Ioan Cuza" University of Iasi, Romania)

"Stability for Energy-Type Functionals"

Abstract: Conformal-biharmonic maps arise as critical points of the conformal-bienergy functional, a second-order functional obtained by modifying the bienergy functional through curvature terms motivated by conformal geometry. In dimension four, this functional is conformally invariant, which makes it particularly relevant in variational problems in conformal geometry.

In this talk, I will focus on stability properties of conformal-biharmonic maps. In particular, I will discuss the conformal-biharmonic stability of the identity map on compact Einstein manifolds with non-negative scalar curvature, and show that its conformal-biharmonic index coincides with the classical harmonic index, with a notable exception in the case of the four-dimensional sphere. We will also present results on hypersurfaces in space forms, including computations of the index and nullity of great hyperspheres.
 
Mittwoch, 10.06.2026, 16:00 Uhr, Ulmenstr. 69, Haus 3, HS 326/327  
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Seminarleiter: Prof. Dr. Volker Branding

Forschungskolloquium mit Herrn Prof. Dr. Stefan Hoderlein (Emory University, Atlanta USA)

"Moment estimation in a correlated random coefficients linear panel data model: a functional fixed point approach to identification and estimation"

Abstract: We develop a linear regression panel data model allowing random coefficients to be correlated with regressors not only within periods but also across periods. The random coefficients are modeled as sums of independent possibly nonidentically distributed past and current shocks. This structure allows feedback, in the sense that future regressors can be correlated with all past shocks, and also allows all lagged dependent variables to be regressors. For each time period, we identify all marginal first moments of the random coefficients. These moments have causal interpretations. The identification results rest on a novel functional fixed point argument and lead to natural estimators of these moments. We provide simulation evidence of the usefulness of this approach.
 
Mittwoch, 10.06.2026, 16:00 Uhr, Ulmenstr. 69, Haus 3, HS 125 
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Seminarleiter: Prof. Dr. Alexander Meister

Forschungskolloquium mit Frau Kerrin Bielser (Europa-Universität Flensburg)

"Über eine Frage von Katona zu Familien von Paaren -- Ein kleines Problem aus der extremalen Kombinatorik"

Zusammenfassung: Klassischerweise wird in der extremalen Mengentheorie untersucht, wie groß ein Mengensystem unter gewissen Bedingungen höchstens sein kann. In diesem Vortrag werden wir uns nach einer kurzen Einführung mit Familien befassen, welche eng mit Semi-Antiketten verwandt sind. Bei verschiedenen Lösungsansätzen und Beweisen kommen sowohl elementare Operationen an Ketten als auch die Sperner-Eigenschaft gewisser Posets zum Einsatz. Dabei zeigt sich ein enger Zusammenhang zu Fragestellungen aus mathematischen Untersuchungen zu Datenbanken. 
Die vorgestellten Ergebnisse basieren auf gemeinsamer Arbeit mit Gyula O.H. Katona. 
 
Mittwoch, 03.06.2026, 15:00 Uhr, Ulmenstr. 69, Haus 3, SR 228
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Seminarleiter: Prof. Dr. Thomas Kalinowski

Forschungskolloquium mit Herrn Dr. Johannes Schmalz (Universität des Saarlandes)

"Bridging Automated Planning and Spectral Graph Theory"

Abstract: Automated planning concerns itself with combinatorial optimisation problems where an agent must navigate a state-space using a discrete set of actions -- a famous toy problem is to stack blocks on a table into a specific arrangement, only being allowed to lift one at a time. These problems are closely related to the shortest path problems on graphs. On the other hand, spectral graph theory considers different matrix representations of graphs, and studies what information can be read from their eigenvectors and eigenvalues, with applications to many areas of computer science, but surprisingly few relevant to automated planning. This talk will discuss an existing path-finding algorithm from spectral graph theory and its connections to automated planning, as a step in bridging the two disciplines. 
 
Donnerstag, 28.05.2026, 13:00 Uhr, Ulmenstr. 69, Haus 3, SR 228
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Seminarleiter: Prof. Dr. Thomas Kalinowski