Talks and events

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Upcoming talks

[oberseminar] Monday 27.03.2017, Math II (Lonza) at 16h00

Martin Kerin (Münster): Non-negative curvature on exotic spheres

Since their discovery, there has been much interest in the question of precisely which exotic spheres admit a metric with non-negative sectional curvature. In dimension 7, Gromoll and Meyer found the first such example. It was subsequently shown by Grove and Ziller that all of the Milnor spheres admit non-negative curvature. In this talk, it will be demonstrated that the remaining exotic 7-spheres also admit non-negative curvature. This is joint work with K. Shankar and S. Goette.

[colloque] Tue 28.03.2017, Phys 2.52 at 17h15

Martin Kerin (Univ. of Münster): Curvature and exotic spheres

The discovery by Milnor of spheres which admit exotic smooth structures has led to the development of much of modern topology. The geometry of exotic spheres, on the other hand, isn't very well understood at all. In dimension 7, however, there has been some success. In this talk, I will review some of the known results, starting with work of Gromoll and Meyer, and finishing with some recent developments.

[oberseminar] Wed 29.03.2017, Math II (Lonza)

Felix Günther (TU Berlin & Uni Genève): Smooth polyhedral surfaces

In modern architecture, facades and glass roofs often model smooth shapes but are realized as polyhedral surfaces. In the case of reflective surfaces it becomes apparent that the polyhedral surface is not smooth even though it is very close to a smooth reference surface. But how can we describe smoothness of polyhedral surfaces?
In this talk, we discuss a theory of smooth polyhedral surfaces. We start with a close investigation of the normal images of vertex neighborhoods and give first a complete proof of the widely believed fact that the discrete Gaussian curvature of a polyhedral vertex star embedded in three-space equals the algebraic area of the image of its Gauss map. We end up with a projectively invariant class of polyhedral surfaces that share several properties with their smooth counterparts. Smooth polyhedral surfaces are accompanied by suitable notions of normal vectors, tangent planes, asymptotic directions, and parabolic curves that are invariant under projective transformations.
This talk is based on joint works with Thomas Banchoff and with Caigui Jiang and Helmut Pottmann.

[oberseminar] Monday 03.04.2017, Math II (Lonza) at 16h00

Michael Wiemeler (Augsburg): Positively curved GKM manifolds

Let $T$ be a torus of dimension $\geq k$ and $M$ a $T$-manifold. $M$ is a GKM$_k$ manifold if the cohomology of $M$ is concentrated in even degrees, the $T$-action has only isolated fixed points, and any $k$ weights of the isotropy representation in the fixed points are linearly independent. In this talk I will report on joint work with Oliver Goertsches in which we computed the cohomology rings of GKM$_3$ and GKM$_4$ manifolds with invariant metrics of positive sectional curvature.

[colloque] Tue 4.4.2017, Phys 2.52 at 17h15

Prof. Armin Iske (Uni Hamburg): Kernel-based Scattered Data Approximation

Positive definite kernel functions are popular tools for multivariate scattered data approximation. In particular, the utility of kernel-based reconstructions from generalized Hermite-Birkhoff data has been demonstrated in many applications. The approximation of images from scattered Radon data is only one relevant example. As we show, however, standard kernel-based reconstruction methods fail to work for this particular application. Therefore, we first explain limitations of radial kernels, before we propose weighted positive definite kernels, which are symmetric but not radially symmetric. We discuss the characterization and construction of weighted positive definite kernels in general, before we provide concrete examples. This leads us to a larger class of flexible kernel-based approximation schemes, which work for image reconstruction from scattered Radon data and other relevant applications.

[colloque] Tue 25.4.2017, Phys 2.52 at 17h15

Prof. Antti Knowles (Uni Genève): tba

[colloque] Tue 2.5.2017, Phys 2.52 at 17h15

Prof. Gerhard Wanner (Uni Genève): tba

[colloque] Tue 16.5.2017, Phys 2.52 at 17h15

Prof. Pierre Nolin (ETHZ): tba

Archive:

Colloquia in the current semester

[colloque] Tue 1.3.2016, Phys 2.52 at 17h15 - Festvortrag zum 80. Geburtstag von Ernst Ruhmore

Prof. Dr. Ernst Heintze (Uni Augsburg): Affine root systems and submanifolds of Hilbert spaces

[colloque] Tue 8.3.2016, Phys 2.52 at 17h15more

Prof. Joan Porti (Barcelona): Reidemeister torsion and hyperbolic 3-manifolds

[colloque] Tue 22.3.2016, Phys 2.52 at 17h15more

Prof. Uwe Semmelmann (Uni. Stuttgart): Invariant 4-forms and exceptional Lie algebras

[colloque] Tue 12.4.2016, Phys 2.52 at 17h15more

Prof. Dr. Benjamin Sudakov (ETH Zürich): Induced matchings, arithmetic progressions and communication

[colloque] Tue 19.4.2016, Phys 2.52 at 17h15more

Prof. Christophe Bavard (Bordeaux): Points conjugués en géométrie riemannienne et lorentzienne

[colloque] Tue 26.4.2016, Phys 2.52 at 17h15more

Prof. Roman Sauer (KIT): Invariant random subgroups

[colloque] Tue 3.5.2016, Phys 2.52 at 17h15more

Prof. Hans Josef Pesch (Uni Bayreuth): Optimal Control of Dynamical Systems Governed by Partial Differential Equations

[colloque] Tue 10.5.2016, Phys 2.52 at 17h15more

Prof. Sergiu Moroianu (Bucharest): Renormalized volume in hyperbolic geometry

[colloque] Tue 17.5.2016, Phys 2.52 at 17h15more

Prof. Vincent Beffara (CNRS Grenoble): Introduction to the Schramm-Loewner Evolution

[colloque] Tue 24.5.2016, Phys 2.52 at 17h15more

Dr. Roger Zuest (Fribourg): Regularity theory for almost minimal surfaces

[colloque] Tue 31.5.2016, Phys 2.52 at 17h15more

Prof. Wolfgang Lück (Universität Bonn / HIM Bonn): Introduction to $L^2$-Betti numbers

[colloque] Tue 7.6.2016, Phys 2.52 at 15h30more

Prof. Alexandru Suciu (Northeastern University, Boston): Fundamental groups in algebraic geometry and three-dimensional topology

[colloque] Tue 20.9.2016, Phys 2.52 at 17h15more

Prof. Daniel Grieser (Universität Oldenburg): A look at triangles from elementary geometry, spectral theory and singular analysis

[colloque] Tue 27.9.2016, Phys 2.52 at 17h15more

Prof. Christoph Böhm (Universität Münster): Immortal homogeneous Ricci flows

[colloque] Tue 11.10.2016, Phys 2.52 at 17h15more

Prof. Gerhard Opfer (Universität Hamburg): Zeros of unilateral quaternionic and coquaternionic polynomials

[colloque] Tue, 25.10.2016, Phys 2.52 at 17h15more

Dr. Wim Hordijk (Konrad Lorenz Institut, Klosterneuburg): Autocatalytic Sets: The Origin and Organization of Life

[colloque] Tue 8.11.2016, Phys 2.52 at 17h15more

Prof. Manfred Lehn (JG Universität Mainz): The theorem of Grothendieck-Brieskorn-Slodowy and symplectic singularities

[colloque] Tue 15.11.2016, Phys 2.52 at 17h15more

Prof. Nicolas Curien (Université Paris-Sud Orsay): A panoramic introduction to random planar maps

[colloque] Tue 22.11.2016, Phys 2.52 at 17h15more

Prof. Masahiko Yoshinaga (Hokkaido University): Characteristic polynomials of hyperplane arrangements

[colloque] Tue 6.12.2016, Phys 2.52 at 17h15more

Prof. Priyam Patel (UCSB): Quantitative methods in hyperbolic geometry

[colloque] Tue 13.12.2016, Phys 2.52 at 17h15more

Prof. Christophe Soulé (IHES): La théorie d'Arakelov

[colloque] Tue 7.3.2017, Phys 2.52 at 17h15more

Prof. Sergei Tabachnikov (Pennsylvania State University): Skewers

[colloque] Tue 14.3.2017, Phys 2.52 at 17h15more

Prof. Philipp Habegger (Uni Basel): Complex Multiplication or is $e^{\pi \sqrt{163}}$ an Integer?

[colloque] Tue 21.3.2017, Phys 2.52 at 17h15more

Prof. Jan Draisma (Uni Bern): Stabilisation in algebra and geometry

[colloque] Tue 28.03.2017, Phys 2.52 at 17h15more

Martin Kerin (Univ. of Münster): Curvature and exotic spheres

[colloque] Tue 4.4.2017, Phys 2.52 at 17h15more

Prof. Armin Iske (Uni Hamburg): Kernel-based Scattered Data Approximation

[colloque] Tue 25.4.2017, Phys 2.52 at 17h15more

Prof. Antti Knowles (Uni Genève): tba

[colloque] Tue 2.5.2017, Phys 2.52 at 17h15more

Prof. Gerhard Wanner (Uni Genève): tba

[colloque] Tue 16.5.2017, Phys 2.52 at 17h15more

Prof. Pierre Nolin (ETHZ): tba

Other talks and events in the current semester

[oberseminar] Oberseminar Geometrie, Wed 4.3.2015, Math II (Lonza) at 10:20more

Martin Herrmann (Fribourg): Almost nonnegative curvature operator, homogeneous spaces and a question of Karsten Grove

[oberseminar] Oberseminar Geometrie, Wed 11.3.2015, Math II (Lonza) at 10:20more

Mike Roberts (Durham): A methodical approach to the construction of Coxeter polytopes in hyperbolic n-space with n+3 facets

[oberseminar] Combinatorics seminar, Fri 13.3.2015, Math II (Lonza) at 13:15more

Ornella greco (KTH Stockholm): The Betti table of Veronese Modules

[oberseminar] Oberseminar Geometrie, Wed 18.3.2015, Math II (Lonza) at 10:20more

Kate Juschenko (Northwestern): Techniques and concepts of amenability of discrete groups

[oberseminar] Oberseminar Geometrie, Wed 26.3.2015, Math II (Lonza) at 10:20more

Stefan Rosemann (Jena): Kähler metrics with Hamiltonian 2-forms, their classification via projectively equivalent metrics and applications

[oberseminar] Oberseminar Geometrie, Wed 15.4.2015, Math II (Lonza) at 10:20more

Bernhard Mühlherr (Giessen): Tits-indices, affine Coxeter groups and buildings

[oberseminar] Oberseminar Geometrie, Wed 22.4.2015, Math II (Lonza) at 10:20more

Viktoriya Ozornova (Bremen / MPIM Bonn): Factorability structures

[oberseminar] Combinatorics seminar, Fri 24.04.2015, Time and place TBAmore

Matteo Varbaro (Genova): On dual graphs of complete intersections

[oberseminar] Oberseminar Geometrie, Wed 29.4.2015, Math II (Lonza) at 10:20more

Jordane Granier (Fribourg): Sous-groupe discret de PU(2,1) avec l'éponge de Menger pour ensemble limite

[oberseminar] Oberseminar Geometrie, Wed 6.5.2015, Math II (Lonza) at 10:20more

Vincent Emery (EPF Lausanne): Volumes des variétés hyperboliques et actions de Galois

[oberseminar] Oberseminar Geometrie, Wed 20.5.2015, Math II (Lonza) at 10:20more

Misha Wasem (ETHZ): Isometric extensions at low regularity and codimension

[oberseminar] Oberseminar Geometrie, Wed 27.5.2015, Math II (Lonza) at 10:20more

Martin Deraux (Grenoble): Groupes de triangles en géométrie hyperbolique complexe

Université de Fribourg - Mathématiques - Ch. du Musée 23, 1700 Fribourg - tél +41 26 / 300 9180      isabella.schmutz@unifr.ch
Last modified on Jun 27, 2016    Webmasters: Sophie Schneider, Michael Dougoud