## 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. GrÃ¶chenig). 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 SchrÃ¶dinger 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.