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Mathematics Department Colloquium : Autumn 2011 schedule



   Monday, September 5, 1400-1500. (Obs! Unusual time)

SPEAKER : Vladimir Voevodsky, IAS Princeton.

TITLE : Univalent foundations of mathematics.

ABSTRACT : Univalent foundations is a new approach to formalization of mathematical knowledge which is proposed to replace the approach based on Zermelo-Fraenkel "set theory" ( ZFC ) . Unlike ZFC-based foundations which have never been intended for practical formalization of large bodies of complex mathematical knowledge the univalent foundations are being developed from the very beginning with a view towards the creation of usable computer verified libraries of mathematics . At the heart of the univalent foundations are two mathematical discoveries - the Grothendieck correspondence between homotopy types and infinity groupoids and the recently discovered connection between constructive type theories and homotopy theory . A library of formalized mathematics based on the univalent approach is currently being developed using "proof assistant" Coq.


   Monday, September 12, 1530-1630. (Obs! This is a promotion lecture)

SPEAKER : Maria Roginskaya, Chalmers.

TITLE : Travel notes from analysis.



   Monday, September 19, 1530-1630.

SPEAKER : Sophie Grivaux, Universite de Lille.

TITLE : Rigidity sequences for weakly mixing dynamical systems.

ABSTRACT : Let $(X,\mathcal{B},m)$ be a probability space, and $T$ a measure-preserving transformation of the space $X$. The transformation $T$ is said to be ergodic when, for any measurable sets $A$ and $B$ of $X$, there exists an integer $n$ such that $T^n A\cap B$ has positive measure, and weakly mixing when the product transformation $T \times T$ on $X \times X$ is ergodic. It is said to be rigid when there exists a sequence $(n_k)$ of integers such that $m(T^{n_k}A \bigtriangleup A)$ tends to $m(A)$ as $k$ tends to infinity. Given a sequence $(n_k)$, we will present a necessary and sufficient condition for the existence of a weakly dynamical system which is rigid with respect to $(n_k)$, and various examples of rigidity and non-rigidity sequences. This talk will be based in part on a joint work with Tanja Eisner.


   Monday, September 26, 1400-1500 (OBS! unusual time).

SPEAKER : Chengbo Zhu, National University of Singapore.

TITLE : Classical groups and branching laws.

ABSTRACT : A branching law from a group G to a subgroup H describes the restriction of an irreducible G-representation to H, namely H-irreducible representations and their multiplicities that occur in this restriction. In this talk, I will discuss some classical examples and some recent advances, with the emphasis on the most favorable circumstances when all multiplicities are at most one.

I will target the talk to a general audience.


   Monday, October 10, 1530-1630.

SPEAKER : Omer Egecioglu, UC Santa Barbara & currently on sabbatical at Chalmers.

TITLE : Monte-Carlo algorithms for comparison of voting methods.



   Monday, November 14, 1530-1630. (OBS! This is a promotion lecture)

SPEAKER : Hjalmar Rosengren, Chalmers/GU.

TITLE : Three-coloured chessboards.

ABSTRACT : I will discuss some mathematics and physics related to what I call three-coloured chessboards. These may seem like very simple combinatorial objects, but they turn out to have intriguing relations to topics such as elliptic functions and modular forms, solvable models of statistical mechanics, affine Lie algebras and Painlevé equations.

The lecture should be accessible to a wide audience.


   Monday, November 28, 1530-1630.

SPEAKER : Stellan Östlund, GU Physics Dept.

TITLE : An overview of quasicrystals.

ABSTRACT : This will be a repeat of Stellan's colloquium at the physics department on Nov. 24, which directly clashes with a Mathematics departmental meeting. For an abstract, see here.