Tidligere arrangementer - Side 28

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.

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.

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.

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. 

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.  

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.

When and how surface structure determines the dynamics of partial wetting  

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.

Sedimentation-diffusion equilibrium of Quincke rollers  

Iceberg drift on dead water

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

Abstract:

Reyna Ramirez

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.

Eric Schaanning (Norges Bank) gives a lecture with the title: Interbank contagion and systemic risk: How robust are estimates?

Adam Sørensen (UiO) will give a talk with title: C*-stable groups.

Abstract: In this talk we will look at when group C*-algebra have stable relations, which loosely speaking means that any almost representation of the group in a C*-algebra will be close to an exact representation. A particularly interesting case is if we assume the C*-algebra is finite dimensional. I will mostly discuss a collection of examples. The talk is based on ongoing joint work with Søren Eilers and Tatiana Shulman.  

The seminar takes place in the meeting room, floor 9 of Ole Johan Dahls hus.

The room has been reserved Thursdays 10.15 - 12.00 from August 31 to November 30.

The program is subject to changes.

On the occasion of Professor Sylvia Richardson, University of Cambridge, receiving a Honorary Doctorate from the University of Oslo, we arrange a workshop in her honour. Please join us in the celebration of Sylvia and the statistics community at the University of Oslo, with presentations of some of the ongoing statistical research in the life sciences at our university!