## Visiting address

Ullevål StadionSognsveien 77B

0855 OSLO

Norway

Time and place:
Dec. 13, 2017 11:00 AM - 12:00 PM,
Desolation Row, Sognsv. 77B

Abstract: Recently, Steve Kaliszewski, Tron Omland, and I have been investigating the following theorem of Pedersen: two actions of a compact abelian group on C*-algebras A and B are outer conjugate if and only if there is an equivariant isomorphism between the crossed products that respects the positions of A and B. We upgraded this to nonabelian groups (using coactions on the crossed products), and then searched for examples showing that the last condition (on the positions of A and B) is necessary. We failed. This lead us to formulate the "Pedersen Rigidity Problem": if the crossed products of A and B are equivariantly isomorphic, are the actions on A and B outer conjugate? We have been finding numerous "no-go theorems", which give various sufficient conditions for Pedersen Rigidity. Quite recently we have done this for ergodic actions of a compact group, assuming that the actions have "full spectrum". In fact, these actions are (not just outer) conjugate if and only if the dual coactions are. I will summarize our progress on the Pedersen Rigidity Problem and outline the proof of the no-go theorem for these compact ergodic full-spectrum actions.

Time and place:
Dec. 13, 2017 10:15 AM,
Gates of Eden, Ullevål stadion

M.Sc. Hannes Hagen Haferkorn ved Matematisk institutt avholder prøveforelesning over oppgitt emne: "Harmonic functions, Brownian motion and martingales".

Time and place:
Dec. 4, 2017 9:00 AM -
Dec. 8, 2017 12:00 PM,
Room 108, N.H. Abel's House

Time and place:
Nov. 30, 2017 2:30 PM - 3:30 PM,
Gates of Eden, Sognsv. 77B

NB! Coffee/Tea/Biscuits from 14.00.

Time and place:
Nov. 24, 2017 1:15 PM,
Ullevål Stadion: Gates of Eden

M.Sc. Espen Stokkereit ved Matematisk institutt vil forsvare sin avhandling for graden ph.d.:

**Essays on Stochastic Optimal Stopping and Control**

Time:
Nov. 24, 2017 11:30 AM - 12:00 PM

**Andreas Carlson og Jean Rabault**

Nature has invented ingenious aerodynamic design solutions, some of which are critical for plants as wind dispersal of seeds and fruits is coupled to their flight performance. This formulates into an optimization problem for plants: large seed wings can lead to increased lift and more efficient dispersion, but are costly for the tree to build and can more easily be trapped in the canopy. Double winged seeds/fruits separate from their tree when a specific level of dessication is reached, and autorotate as they descend to the ground. This leads to the question: how is the wing curvature of seeds/fruits linked to their flight performance? To answer this, we develop a theoretical model that suggests the existence of an optimal wing curvature that yields maximal lift. To further understand the interplay between the flow and the wing geometry, we perform a synthetic seed adaptation by deploying 3D printing of double winged fruits that we use in flight experiments, where we span the phase space of aerial dynamics by changing the of wing curvature and seed/fruit weight. Experiments confirm that there is a sweet-spot in curvature to maximise the flight time consisted with geometrical measurements from a wide range of seeds in Nature. Our results highlights the importance of not curving too much or too little for helicopter fruits to have an optimal flight performance.

Time:
Nov. 24, 2017 11:00 AM - 11:30 AM

Elisabeth Seland

In my job as research adviser, I receive a lot of questions about rights, possibilities and problems in connection with scientific publishing and open access. Both EU and the Norwegian Research Council have rules about this, and there is also a UiO policy in place that is relevant for all employees. I will give a short presentation to try to clear up what you have to, must, may, could and should related to Open access. In my experience many of you have the same questions about these issues, so I hope you bring your questions with you and we can address them in the seminar.

Time and place:
Nov. 22, 2017 2:15 PM - 4:00 PM,
Desolation Row, Sognsveien 77 B

I will discuss the differential structure in the mod 2 Adams spectral sequence for tmf, leading to its E_\infty-term. These calculations were known to Hopkins-Mahowald; in their current guise they are part of joint work with Bruner.

Time and place:
Nov. 15, 2017 2:30 PM - 4:00 PM,
Desolation Row, Sognveien 77 B

I will report on work in progress on calculations of the motivic homotopy groups of MGL (the algebraic cobordism spectrum) over number fields. It is known that pi_{2n,n}(MGL) is the Lazard ring, and pi_{-n,-n}(MGL) is Milnor K-theory of the base field. We will calculate all of pi_{*,*}(MGL) with the slice spectral sequence (motivic Atiyah-Hirzebruch spectral sequence) over a number field. I will give a brief review of the the tools and sketch the main parts of the calculation: The input from motivic cohomology, the use of C_2-equivariant Betti realization and comparison with Hill-Hopkins-Ravenel to determine the differentials, and settle most of the hidden extensions.

Time and place:
Nov. 8, 2017 3:00 PM - 4:00 PM,
Hurricane, Sognsveien 77 b

I will discuss the algebra structure of the E_2-term of the mod 2 Adams spectral sequence for tmf, given by the cohomology Ext_{A(2)}(F_2, F_2) of A(2). We (Bruner & Rognes) use Groebner bases to verify the presentation given by Iwai and Shimada, with 13 generators and 54 relations. Thereafter I will discuss the relationship between differentials and Steenrod operations in the Adams spectral sequence for E_\infty ring spectra.

Time and place:
Nov. 8, 2017 1:15 PM,
Ullevål Stadion: Gates of Eden

M.Sc. Fredrik Meyer ved Matematisk institutt vil forsvare sin avhandling for graden ph.d.:

**Join of hexagons and Calabi–Yau threefolds**

Time and place:
Nov. 8, 2017 12:00 PM -
Nov. 9, 2017 1:00 PM,
Seminar room: "Desolation Row" (3rd floor) on November 8 and "Gates of Eden" (2nd floor) on November 9, Matematisk Institutt, Sognsveien 77B, Ullevål Stadion

Welcome to the second FINEWSTOCH Networkshop. The workshop will bring together leading researchers in stochastics and probability theory to discuss recent developments with a particular focus on finance, insurance, energy and weather.

Time and place:
Nov. 8, 2017 10:15 AM,
Gates of Eden, Ullevål stadion

M.Sc. Fredrik Meyer ved Matematisk institutt avholder prøveforelesning over oppgitt emne: "Prym varieties: basic constructions and central results".

Time and place:
Nov. 8, 2017 10:15 AM,
Gates of Eden, Ullevål stadion

M.Sc. Espen Stokkereit ved Matematisk institutt avholder prøveforelesning over oppgitt emne: "Rough path theory".

Time and place:
Nov. 6, 2017 12:45 PM - 1:45 PM,
End of Line, Ullevål

Pawel Kasprzak (Warzaw) will give a talk with title " Quantum actions on discrete quantum spaces"

Abstract:

To any action of a compact quantum group on a von Neumann algebra which is a direct sum of factors we associate an equivalence relation corresponding to the partition of a space into orbits of the action. We show that in case all factors are finite-dimensional (i.e. when the action is on a discrete quantum space) the relation has finite orbits. We then apply this

i) to generalize the classical theory of Clifford, concerning the restrictions of representations to normal subgroups, to the framework of quantum subgroups of discrete quantum groups, itself extending the context of closed normal quantum subgroups of compact quantum groups; ii) to the context of idempotent states showing that the algebra of invariant elements is finite dimensional if and only if the corresponding state is normal. Joint work with K. De Commer, A. Skalski and P. Sołtan.

Time and place:
Nov. 2, 2017 2:30 PM - 3:30 PM,
Gates of Eden, Sognsv. 77 B

Professor Emeritus **Erling Størmer** will turn 80 on November 2, and he will use this occasion to give a Colloquium Talk with tittle:

POSITIVE LINEAR MAPS ON MATRIX ALGEBRAS

*Abstract: The first part of the talk will be an introduction to the theory of positive linear maps between matrix algebras, plus a few words on the operator algebra case. For the last 20 years, physicists working in quantum information theory have been active in the subject and I’ll devote the last half of the talk to a negative solution to a conjecture they had. *

Time and place:
Nov. 2, 2017 10:15 AM - 11:00 AM,
Gates of Eden

**When and how surface structure determines the dynamics of partial wetting**

Time and place:
Nov. 1, 2017 2:15 PM - 4:00 PM,
Desolation Row, Sognsveien 77 B

I will discuss machine computations in a finite range, using Bruner's ext-program, of Ext over A, the mod 2 Steenrod algebra, and over A(2), the subalgebra of A generated by Sq^{^1}, Sq^{^2} and Sq^{^4}. These are the E_2-terms of the mod 2 Adams spectral sequences for S and tmf, respectively.

Time and place:
Oct. 30, 2017 3:15 PM - 4:00 PM,
Hurricane

**Sedimentation-diffusion equilibrium of Quincke rollers**

Time and place:
Oct. 26, 2017 2:15 PM - 4:00 PM,
Ullevål

Time and place:
Oct. 23, 2017 12:45 PM - 1:45 PM,
Gates of Eden

Erik Bedos (UiO) will give a talk with title "On Exel-Pardo algebras as Cuntz-Pimsner algebras"

Abstract:

In a joint work with S. Kaliszweski and J. Quigg (https://arxiv.org/pdf/1512.07302.pdf, to appear in JOT), we consider a continuous action of a locally compact group G on a topological graph E, equipped with a G-valued continuous cocycle, and show how to construct a C*-correspondence from these data, giving rise to a Toeplitz algebra and a Cuntz-Pimsner algebra. In the talk we will sketch this construction, but restrict ourselves to the discrete case. We will also describe these algebras in terms of generators and relations when E is row-finite. As a corollary we get that the associated Cuntz-Pimsner algebra coincides with the C*-algebra recently introduced by Exel and Pardo when E is finite and sourceless.

Time and place:
Oct. 20, 2017 11:15 AM - 12:00 PM,
Hurricane

Reyna Ramirez

Time and place:
Oct. 19, 2017 2:15 PM - 4:00 PM,
Ullevål

Time and place:
Oct. 16, 2017 12:45 PM - 1:45 PM,
Gates of Eden, Ullevål

Nicolai Stammeier (Oslo) will give a talk with title: The inner structure of boundary quotients of right LCM semigroups

Abstract: In joint work with Roberto Conti, Stefano Rossi, and Valeriano Aiello, we use semidirect products built from algebraic dynamical systems to model right LCM semigroups to study various structural aspects in connection with a selection of distinguished subalgebras of the associated boundary quotients. Our two guiding examples are integral dynamics as considered in work of Barlak - Omland - Stammeier, and exact injective group endomorphisms of discrete abelian groups with finite cokernel as studied by Cuntz and Vershik.