Fall 2016

31st Aug. 14.15 in 734

Speaker: Eduard Ortega (NTNU).

Title: Cuntz-Krieger Uniqueness Theorem

Abstract: I will make a little survey about Cuntz-Krieger uniqueness theorems and how they help to the study of the ideal structure of the rings to which one can apply them. In certain classes of (C*-)algebras this is described as topologically freeness or condition (L). However they are important classes of algebras for which are not known Cuntz-Krieger type theorems. I will present a class of rings, that generalize Leavitt path algebras and Passman crossed products, for which I can totally characterize the Cuntz-Krieger uniqueness theorem. Later I will expose part of the recent progress of the on-going project with Carlsen and Kwasniewski about topologically freeness of C*-correspondences.

17th Aug. 10.15 in 734

Speaker: Anatoly N. Kochubei (Institute of Mathematics, National Academy of Sciences of Ukraine).

Title: Non-Archimedean Duality: Algebras, Groups, and Multipliers

Abstract: We develop a duality theory for multiplier Banach-Hopf algebras over a non-Archimedean field K. As examples, we consider algebras corresponding to discrete groups and zero-dimensional locally compact groups with K-valued Haar measure, as well as algebras of operators generated by regular representations of discrete groups.

Spring 2016

3rd May. 10.15 in 734

Speaker: Sayan Chakraborty

Title: K-theory of some noncommutative orbifolds

Abstract: I will consider noncommutative tori with finite group actions on those and compute K-theories of the crossed products. I will also talk about how one can produce projective modules over the tori and will compute the traces of these modules. If time permits, I will also talk about cyclic cohomology of these algebras and its pairing the K-theory elements.

19th Apr. 10.15 in 734

Speaker: Stuart White

Title: Amenability, Quasidiagonality and the UCT

Abstract: Quasidiagonality is a concept originating in work of Halmos in operator theory; it asks for block diagonal approximations of an operator algebra. It's a pretty mysterious property of a somewhat topological nature, and as noted by Rosenberg and Voiculescu quasidiagonality always entails some level of amenability. In this talk (based on joint work with Aaron Tikuisis and Wilhelm Winter) I'll discuss a kind of converse: how do we get quasidiagonality from amenability and what consequences does this have for group algebras and for simple amenable C*-algebras. No prior familiarity with quasidiagonality will be assumed.

12th Apr. 10.15 in 734

Speaker: Antoine Julien

Title: Spectral triples and wavelets associated to representations of Cuntz algebras

Abstract: I will survey some results on the construction of spectral triples and Laplace operators on Cantor sets (namely by Pearson and Bellissard). This construction, in some cases turns out to be related to wavelet bases associated to representations of Cuntz algebras. This is a joint work with C. Farsi, E. Gillaspy, S. Kang and J. Packer.

15th mar. 10.15 in 734

Speaker: Mads Sielemann Jakobsen

Title: The Feichtinger algebra S0.

Abstract: In this talk I will give an overview of the Feichtinger algebra. It is a function space which lies in the intersection of C_0 and L^{1} and it is a Wiener-Amalgam, Co-orbit, and Modulation space as well as a Segal algebra. As such, it enjoys a wealth of properties which makes it a very interesting (Banach) space of functions. In particular it is the smallest Banach space which is invariant under time- frequency shifts. It is heavily used in time-frequency analysis, and finds applications in generalized stochastic processes and is a good space of test-functions and provides a shortcut to the theory of distributions and Fourier analysis. The presentation is based on an ongoing project of mine where I try to make sense of the large body of litteratur on this subject (mostly by H.G. Feichtinger and K. Gröchenig). Among the results that will be presented in this talk many are known, however there are some details which are new.

23rd feb. 10.15 in 734

Speaker: Erik Bakken (NTNU)

Title: Stochastic Methods for Finite Approximations over Local Fields

Abstract: We show that over a local field a continuous-time random walk converges to a Brownian motion in the sense of weak convergence of probability measures. This is used to approximate the spectrum of a quantum Hamiltonian over a local field. The talk is based on joint work with Trond Digernes and David Weisbart.

12th january, kl. 10.15 in 734

Speaker: Siegfried Beckus

Title: Spectral Approximation of Schrödinger Operators: Continuous Behavior of the Spectra.

Abstract: I will speak about the work with Jean about the characterization of the continuous behavior of the spectra which is related to C*-algebras. The second part will be about Schroedinger operators and the application of the previous results.

2016-08-29, Eduard Ortega