Past Seminars

Thu, 28/02
12:00 		Stefano Bianchini (SISSA-ISAS) OxPDE Lunchtime Seminar Add to calendar Gibson 1st Floor SR
Quadratic interaction functional and structure of solutions to hyperbolic conservation laws
The proof of several properties of solutions of hyperbolic systems of conservation laws in one space dimension (existence, stability, regularity) depends on the existence of a decreasing functional, controlling the nonlinear interactions of waves. In a special case (genuinely nonlinear systems) the interaction functional is quadratic, while in the general case it is cubic. Several attempts to prove the existence of a a quadratic functional also in the most general case have been done. I will present the approach we follow in order to prove this result, an some of its implication we hope to exploit.

Work in collaboration with Stefano Modena.
Wed, 27/02
16:00 		Andy Barwell (Heilbronn Institute) Analytic Topology in Mathematics and Computer Science Add to calendar L3
Symbolic dynamics: taking another look at complex quadratic maps
Complex dynamical systems have been very well studied in recent years, in particular since computer graphics now enable us to peer deep into structures such as the Mandlebrot set and Julia sets, which beautifully illustrate the intricate dynamical behaviour of these systems. Using new techniques from Symbolic Dynamics, we demonstrate previously unknown properties of a class of quadratic maps on their Julia sets.
Wed, 27/02
10:30 		Alessandro Sisto -- Queen's Lecture C ((Oxford University))) Algebra Kinderseminar Add to calendar Queen's College
Existence and construction of expanders (expanders are good for you)
Wed, 27/02
10:15 		Dr Peter Rashkov (Philipps-Universität Marburg) OCCAM Wednesday Morning Event Add to calendar OCCAM Common Room (RI2.28)
A model for a protein oscillator in Myxococcus xanthus
Cell polarity in the rod-shaped bacterium Myxococcus xanthus is crucial for the direction of movement of individual cells. Polarity is governed by a regulatory system characterized by a dynamic spatiotemporal oscillation of proteins between the opposite cell poles. A mathematical framework for a minimal macroscopic model is presented which produces self-sustained regular oscillations of the protein concentrations. The mathematical model is based on a reaction-diffusion PDE system and is independent of external triggers. Necessary conditions on the reaction terms leading to oscillating solutions are derived theoretically. Possible scenarios for protein interaction are numerically tested for robustness against parameter variation. Finally, possible extensions of the model will be addressed.
Tue, 26/02
17:00 		Alessandro Sisto (Oxford) Algebra Seminar Add to calendar L2
Relatively hyperbolic groups, mapping class groups and random walks

I will discuss similarities and differences between the geometry of
relatively hyperbolic groups and that of mapping class groups.
I will then discuss results about random walks on such groups that can
be proven using their common geometric features, namely the facts that
generic elements of (non-trivial) relatively hyperbolic groups are
hyperbolic, generic elements in mapping class groups are pseudo-Anosovs
and random paths of length $n$ stay $O(\log(n))$-close to geodesics in
(non-trivial) relatively hyperbolic groups and
$O(\sqrt{n}\log(n))$-close to geodesics in mapping class groups.
Tue, 26/02
17:00 		Derek Kitson (Lancaster) Functional Analysis Seminar Add to calendar L3
A Laman theorem for non-Euclidean bar-joint frameworks.
Laman's theorem characterises the minimally infinitesimally rigid frameworks in Euclidean space $ \mathbb{R}^2 $ in terms of $ (2,3) $-tight graphs. An interesting problem is to determine whether analogous results hold for bar-joint frameworks in other normed linear spaces. In this talk we will show how this can be done for frameworks in the non-Euclidean spaces $ (\mathbb{R}^2,\|\cdot\|_q) $ with $ 1\leq q\leq \infty $, $ q\not=2 $. This is joint work with Stephen Power.
Tue, 26/02
14:30 		Oleg Pikhurko (Warwick) Combinatorial Theory Seminar Add to calendar L3
Limit method in extremal combinatorics
Razborov's flag algebras provide a formal system for operating with asymptotic inequalities between subgraph densities, allowing to do extensive "book-keeping" by a computer. This novel use of computers led to progress on many old problems of extremal combinatorics. In some cases, finer structural information can be derived from a flag algebra proof by by using the Removal Lemma or graph limits. This talk will overview this approach.
Mon, 25/02
17:00 		Lars Andersson (Max Planck Institute for Gravitational Physics) Partial Differential Equations Seminar Add to calendar Gibson 1st Floor SR
Self-gravitating elastic bodies
Self-gravitating elastic bodies provide models for extended objects in general relativity. I will discuss constructions of static and rotating self-gravitating bodies, as well as recent results on the initial value problem for self-gravitating elastic bodies.
Mon, 25/02
16:00 		Paul-James White (undefined) Junior Number Theory Seminar Add to calendar SR1
Studying L-functions via the Trace formula
Mon, 25/02
15:45 		JOHANNES RUF (University of Oxford) Stochastic Analysis Seminar Add to calendar Oxford-Man Institute
Nonnegative local martingales, Novikow's and Kazamaki's criteria, and the distribution of explosion times
I will give a new proof for the famous criteria by Novikov and Kazamaki, which provide sufficient conditions for the martingale property of a nonnegative local martingale. The proof is based on an extension theorem for probability measures that can be considered as a generalization of a Girsanov-type change of measure. In the second part of my talk I will illustrate how a generalized Girsanov formula can be used to compute the distribution of the explosion time of a weak solution to a stochastic differential equation
Mon, 25/02
15:45 		Martin Bridson (Oxford) Topology Seminar Add to calendar L3
The complexity of group presentations, manifolds, and the Andrews-Curtis conjecture
Many natural problems concerning the geometry and topology of manifolds are intimately connected with the nature of presentations for the fundamental groups of the manifolds. I shall illustrate this theme with various specific results, then focus on balanced presentations. I'll explain the (open) Andrews-Curtis conjecture and it's relation to the smooth 4-dimensional Poincare conjecture, and I'll present a construction that gives (huge) lower bounds on how hard it is to distinguish a homology 4-sphere from a genuine sphere.
Mon, 25/02
14:15 		Hans-Joachim Hein (Imperial College) Geometry and Analysis Seminar Add to calendar L3
Calabi-Yau manifolds modelled on cones
Mon, 25/02
14:15 		SAM FINCH (University of Copenhagen) Stochastic Analysis Seminar Add to calendar Oxford-Man Institute
Poisson random forests and coalescents in expanding populations.
Let (V, ≥) be a finite, partially ordered set. Say a directed forest on V is a set of directed edges [x,y> with x ≤ y such that no vertex has indegree greater than one. Thus for a finite measure μ on some partially ordered measurable space D we may define a Poisson random forest by choosing a set of vertices V according to a Poisson point process weighted by the number of directed forests on V, and selecting a directed forest uniformly. We give a necessary and sufficient condition for such a process to exist and show that the process may be expressed as a multi-type branching process with type space D. We build on this observation, together with a construction of the simple birth death process due to Kurtz and Rodrigues [2011] to develop a coalescent theory for rapidly expanding populations.
Mon, 25/02
12:00 		Lotte Hollands (Oxford) String Theory Seminar Add to calendar L3
Fenchel-Nielsen coordinates from spectral networks
Fenchel-Nielsen coordinates play a central role in constructing partition functions for theories of class S with gauge group SU(2). Having an analogue of these coordinates for higher rank gauge groups is a first step in finding partition functions for strongly coupled gauge theories of the Minahan-Nemeschansky type. We find such a generalization through the formalism of spectral networks and the non-abelianization map, that was originally introduced by Gaiotto, Moore and Neitzke to find a better understanding of BPS states in the theories of class S. This is joint work with Andy Neitzke.
Fri, 22/02
16:30 		Professor Anand Pillay (University of Leeds) Colloquia Add to calendar L1
Recent applications of and trends in model theory.

There are many recent points of contact of model theory and other 
parts of mathematics: o-minimality and Diophantine geometry, geometric group 
theory, additive combinatorics, rigid geometry,...  I will probably 
emphasize  long-standing themes around stability, Diophantine geometry, and 
analogies between ODE's and bimeromorphic geometry.
Fri, 22/02
16:00 		Kathrin Glau (Technical University Munich) Nomura Seminar Add to calendar DH 1st floor SR
Cancelled

For any corrections/updates to these listings, please contact seminars [-at-] maths [dot] ox [dot] ac [dot] uk.

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