Gjesteforelesninger og seminarer - Side 25

Elizabeth Gillaspy, p.t. Münster (Germany) will give a talk with title "Wavelets and spectral triples for higher-rank graphs"  

Erik Bølviken (University of Oslo) gives a lecture with the title: Where models meet reality - The Solvency II regulation of  European insurance

The Oslo-Seminar in Mathematical Logic will take place at the same time and in the same location as in the previous terms.

Thursdays 10.15 - 12.00 in the meeting room of floor 9 in the computer science building.

The Barratt nerve BSd X of the Kan subdivision Sd X of a simplicial set X \in sSet is a triangulation. The Barratt nerve is defined as taking the poset of non-degenerate simplices, thinking of it as a small category and then finally taking the nerve.Waldhausen, Jahren and Rognes (Piecewise linear manifolds and categories of simple maps) named this construction 'the improvement functor' because of the homotopical properties and because its target is non-singular simplicial sets. A simplicial set is said to be 'non-singular' if its non-degenerate simplices are embedded. There is a least drastic way of making a simplicial set non-singular called 'desingularization', which is a functor D:sSet -> nsSet that is left adjoint to the inclusion. The functor DSd^{^2} is the left Quillen functor of a Quillen equivalence where the model structure on sSet is the standard one where the weak equivalences are those that induce weak homotopy equivalences and the fibrations are the Kan fibrations. I will talk about the main steps of the proof that the natural map DSd X -> BX is an isomorphism for regular X. This implies that DSd^{^2} is a triangulation and that the improvement functor is less ad hoc than it may seem. Furthermore, I will explain how the result provides evidence that any cofibrant non-singular simplicial set is the nerve of some poset.   

A conference celebrating the work of Ragni Piene on the occasion of her 70th birthday.

Triangulated categories of motives over schemes are sort of the "universal derived categories" among various derived categories obtained by various cohomology theories like l-adic cohomology. Ayoub constructed them using the A1-homotopy equivalences and étale topology. I will introduce the construction of triangulated categories of motives over fs log schemes. Fs log schemes are kinds of "schemes with toroidal boundary," and A1-homotopy equivalences and étale topology are not enough to obtain all homotopy equivalences between fs log schemes. I will explain what extra homotopy equivalences and topologies are neeeded. 

Daniel Roy (Department of Statistical Sciences, University of Toronto) will give a seminar in the lunch area, 8th floor Niels Henrik Abels hus at 14:15.

Ulrik Bo Rufus Enstad (Oslo) will give a talk with title: Connections between Gabor frames and Noncommutative Tori

Abstract: A Gabor frame is a special type of frame in the Hilbert space of square-integrable functions on the real line. Gabor frames provide robust, basis-like representations of functions, and have applications in a wide range of areas. They have a duality theory which is deeply linked to Rieffel’s work on imprimitivity bimodules over noncommutative tori. We explore several links between Gabor frames and noncommutative tori, and show how operator algebras can be used to give alternative proofs of theorems from time-frequency analysis.  This talk is based on my Master’s thesis written at NTNU, which reviews Franz Luef’s work on the connections between Gabor frames and modules over noncommutative tori, as well as some joint work with Franz Luef.

Nacira Agram (University of Oslo) gives a lecture with the title: Model Uncertainty Stochastic Mean-Field Control.

A continuation of part I.

John Quigg, Arizona State University (Tempe), USA, will give a talk with title "The Pedersen rigidity problem".

University of Abstract: If \alpha is an action of a locally compact abelian group G on a C*-algebra A, Takesaki-Takai duality recovers (A,\alpha) up to Morita equivalence from the dual action of \widehat{G} on the crossed product A\rtimes_\alpha G. Given a bit more information, Landstad duality recovers (A,\alpha) up to isomorphism. In between these, by modifying a theorem of Pedersen, (A,\alpha) is recovered up to outer conjugacy from the dual action and the position of A in M(A\rtimes_\alpha G). Our search (still unsuccessful, somehow irritating) for examples showing the necessity of this latter condition has led us to formulate the "Pedersen rigidity problem". We present numerous situations where the condition is redundant, including G discrete or A stable or commutative. The most interesting of these "no-go theorems" is for locally unitary actions on continuous-trace algebras. This is joint work with Steve Kaliszewski and Tron Omland. 

Riccardo De Bin (Department of Mathematics, University of Oslo) will give a seminar in the lunch area, 8th floor Niels Henrik Abels hus at 14:15.

Framed correspondences were invented and studied by Voevodsky in the early 2000-s, aiming at the construction of a new model for motivic stable homotopy theory. Joint with Ivan Panin we introduce and study framed motives of algebraic varieties basing on Voevodsky's framed correspondences. Framed motives allow to construct an explicit model for the suspension P¹-spectrum of an algebraic variety. Framed correspondences also give a kind of motivic infinite loop space machine. They also lead to several important explicit computations such as rational motivic homotopy theory or recovering the celebrated Morel theorem that computes certain motivic homotopy groups of the motivic sphere spectrum in terms of Milnor-Witt K-theory. In these lectures we shall discuss basic facts on framed correspondences and related constructions.  

Stereolithography - A Powerful Tool to Create almost Everything

Stereolithography or "SLA" printing is a powerful and widely used 3D printing technology for creating prototypes, models, and fully functional parts for production. This additive manufacturing process works by focusing an ultraviolet (UV) laser onto a vat of liquid resin. Layer by layer formation of a polymeric network allows printing parts that are almost impossible to create with other processes.At Formlabs, a startup that originated out of the MIT Media lab in 2011, we work on all aspects of SLA printing; we develop and manufacture 3D printers, resins, and software. In this talk, I will give a detailed overview of the printer technology, the chemistry of the materials, and how to use SLA for lots of exciting applications.

Abstract: We first discuss C*-simplicity and the unique trace property for discrete groups in light of recent years' development. In particular, we consider amalgamated free products, and give conditions for such to be (and fail to be) C*-simple. Then we define radical and residual classes of groups, and explain that there exists a radical detecting C*-simplicity, in a similar way as the amenable radical detects the unique trace property. The talk is based on joint work with Nikolay A. Ivanov from Sofia University, Bulgaria.

Hopkins, Kuhn, and Ravenel proved that, up to torsion, the Borel-equivariant  cohomology of a G-space with coefficients in a height n-Morava E-theory is  determined by its values on those abelian subgroups of G which are generated by  n or fewer elements. When n=1, this is closely related to Artin's induction  theorem for complex group representations. I will explain how to generalize the  HKR result in two directions. First, we will establish the existence of a  spectral sequence calculating the integral Borel-equivariant cohomology whose  convergence properties imply the HKR theorem. Second, we will replace Morava  E-theory with any L_n-local spectrum. Moreover, we can show, in some sense, a  partial converse to this result: if an HKR style theorem holds for an E_\infty  ring spectrum E, then K(n+j)_* E=0 for all j\geq 1. This partial converse has  applications to the algebraic K-theory of structured ring spectra.  

Peter Müller (University of Texas at Austin) will give a seminar in the lunch area, 8th floor Niels Henrik Abels hus at 14:15.

We compute the generalized slices (as defined by Spitzweck-Østvær) of the motivic spectrum KQ in terms of motivic cohomology and generalized motivic cohomology, obtaining good agreement with the situation in classical topology and the results predicted by Markett-Schlichting.