Forthcoming Seminars

Thu, 05/05/2011
17:00

Jamshid Derakhshan (Oxford)

"Model theory of local fields and counting problems in Chevalley groups"

This is joint with with Mark Berman, Uri Onn, and Pirita Paajanen.

Let K be a local field with valuation ring O and residue field of size q, and G a Chevalley group. We study counting problems associated with the group G(O). Such counting problems are encoded in certain zeta functions defined as Poincare series in q^{-s}. It turns out that these zeta functions are bounded sums of rational functions and depend only on q for all local fields of sufficiently large residue characteristic. We apply this to zeta functions counting conjugacy classes or dimensions of Hecke modules of interwining operators in congruence quotients of G(O). To prove this we use model-theoretic cell decomposition and quantifier-elimination to get a theorem on the values of 'definable' integrals over local fields as the local field varies.

Fri, 06/05/2011 10:00	OCIAM Meeting	Industrial and Interdisciplinary Workshops	DH 3rd floor SR
	Coffee in the Common Room 09:45

Fri, 06/05/2011 14:00	Dr J Krishnan (London))	Mathematical Biology and Ecology Seminar	L2
	Modelling and analysis of cellular signal processing underlying attractive and repulsive gradient sensing in eukaryotic systems
	Eukaryotic systems migrate in response to gradients in external signal concentrations, a process referred to as chemotaxis. This chemotactic behaviour may of either a chemoattractive or a chemorepulsive nature. Understanding such behaviour at the single cell level in terms of the underlying signal transduction networks is highly challenging for various reasons, including the strong non-linearity of the signal processing as well as other complicating factors. In this talk we will discuss modelling approaches which are aimed at trying to understand how signal transduction in the networks of eukaryotic cells can lead to appropriate internal signals to guide the cell motion either up-gradient or down-gradient. One part of the talk will focus on system-specific mechanistic modelling. This will be complemented by simplified models to address how signal transduction is organized in cells so that they may exhibit both attractive and repulsive gradient sensing.

Fri, 06/05/2011 14:15	Prof Emmanuel Gobet (Ecole Polytechnique)	Nomura Seminar	DH 1st floor SR
	Stochastic expansions for averaged diffusions and applications to pricing
	We derive a general methodology to approximate the law of the average of the marginal of diffusion processes. The average is computed w.r.t. a general parameter that is involved in the diffusion dynamics. Our approach is suitable to compute expectations of functions of arithmetic or geometric means. In the context of small SDE coefficients, we establish an expansion, which terms are explicit and easy to compute. We also provide non asymptotic error bounds. Applications to the pricing of basket options, Asian options or commodities options are then presented. This talk is based on a joint work with M. Miri.

Fri, 06/05/2011 14:30	Dirk Notz (Max Planck Inst)	Mathematical Geoscience Seminar	DH 3rd floor SR
	The Big Melt

Mon, 09/05/2011 12:00	Sara Pasquetti (QMUL)	String Theory Seminar	L3
	CANCELLED

Mon, 09/05/2011 14:15	Nigel Hitchin (Oxford)	Geometry and Analysis Seminar	L3
	Deformations of holomorphic Poisson manifolds

Mon, 09/05/2011 14:15	Mauro Mariani (Université Aix-Marseille III - Paul Cézanne)	Stochastic Analysis Seminar	Oxford-Man Institute
	Large Deviations for Stochastic Conservation Laws
	We consider parabolic scalar conservation laws perturbed by a (conservative) noise. Large deviations are investigated in the singular limit of jointly vanishing viscosity and noise. The model is supposed to feature the same behavior of "asymmetric" particles systems (e.g. TASEP) under Euler scaling. A first large deviations principle is obtained in a space of Young measures. A "second order" large deviations principle is then discussed, including connections with the Jensen and Varadhan functional. As time allows, more recent "long correlation" models will be treated.

Mon, 09/05/2011 15:45	Lukas Szpruch	Stochastic Analysis Seminar	Oxford-Man Institute
	Numerical Approximations of Non-linear Stochastic Systems.
	Numerical Approximations of Non-linear Stochastic Systems. Abstract: The explicit solution of stochastic differential equations (SDEs can be found only in a few cases. Therefore, there is a need fo accurate numerical approximations that could, for example, enabl Monte Carlo Simulations. Convergence and stability of these methods are well understood for SDEs with Lipschit continuous coefficients. Our research focuses on those situations wher the coefficients of the underlying SDEs are non-Lipschitzian It was demonstrated in the literature, that in this case using the classical methods we may fail t obtain numerically computed paths that are accurate for small step-sizes, or to obtain qualitative information about the behaviour of numerical methods over long time intervals. Our work addresses both of these issues, giving a customized analysis of the most widely used numerical methods.

Mon, 09/05/2011 15:45	Martin Bridson (Oxford)	Topology Seminar	L3
	Actions of mapping class groups and automorphism groups of free groups

Mon, 09/05/2011 16:00	Frank Gounelas (Oxford)	Junior Number Theory Seminar	SR1
	163
	I will describe why e^{\pi\sqrt{163}} is almost an integer and how this is related to Q(\sqrt{-163}) having class number one and why n^2-n+41 is prime for n=0,...,39. Bits and pieces about Gauss's class number problem, Heegner numbers, the j-invariant and complex multiplication on elliptic curves will be discussed along the way.

Mon, 09/05/2011 17:00	Giovanni Alberti (Universita di Pisa)	Partial Differential Equations Seminar	Gibson 1st Floor SR
	A uniqueness result for the continuity equation in dimension two
	We give a characterization of divergence-free vector fields on the plane such that the Cauchy problem for the associated continuity (or transport) equation has a unique bounded solution (in the sense of distribution). Unlike previous results in this directions (Di Perna-Lions, Ambrosio), the proof relies on a dimension-reduction argument, which can be regarded as a variant of the method of characteristics. Note that our characterization is not stated in terms of function spaces, but is based on a suitable weak formulation of the Sard property for the potential associated to the vector-field. This is a joint work with S. Bianchini (SISSA, Trieste) and Gianluca Crippa (Parma).

Tue, 10/05/2011 12:00	Dr Rutger Boels (DESY, Hamburg)	Relativity Seminar	L3
	Simple supersymmetric scattering amplitudes in higher dimensions
	In field theory simple forms of certain scattering amplitudes in four dimensional theories with massless particles are known. This has been shown to be closely related to underlying (super)symmetries and has been a source of inspiration for much development in the last years. Away from four dimensions much less is known with some concrete development only in six dimensions. I will show how to construct promising on-shell superspaces in eight and ten dimensions which permit suggestively simple forms of supersymmetric four point scattering amplitudes with massless particles. Supersymmetric on-shell recursion relations which allow one to compute in principle any amplitude are constructed, as well as the three point `seed' amplitudes to make these work. In the three point case I will also present some classes of supersymmetric amplitudes with a massive particle for the type IIB superstring in a flat background.

Tue, 10/05/2011 14:30	Penny Haxell (Waterloo)	Combinatorial Theory Seminar	L3
	Edge colouring multigraphs
	We highlight a technique for studying edge colourings of multigraphs, due to Tashkinov. This method is a sophisticated generalisation of the method of alternating paths, and builds upon earlier work by Kierstead and Goldberg. In particular we show how to apply it to a number of edge colouring problems, including the question of whether the class of multigraphs that attain equality in Vizing's classical bound can be characterised. This talk represents joint work with Jessica McDonald.

Tue, 10/05/2011 15:45	Maksim Maydanskiy (Cambridge)	Algebraic and Symplectic Geometry Seminar	L3
	Sections of Lefschetz fibrations, Lagrangian Floer homology, and empty manifolds

Tue, 10/05/2011 17:00	Dr Aditi Kar (Southampton)	Algebra Seminar	L2
	`Recent Advances in the Theory of Groups acting on Trees'

Tue, 10/05/2011 17:00	Bhishan Jacelon (Glasgow)	Functional Analysis Seminar	L3
	A projectionless C*-algebra related to the Elliott classification programme

Wed, 11/05/2011 10:10	Michael Shearer	OCCAM Wednesday Morning Event	OCCAM Common Room (RI2.28)
	Two phase flow in porous media and the Saffman-Taylor instability

Wed, 11/05/2011 11:30	Jan Grabowski (University of Oxford)	Algebra Kinderseminar	ChCh, Tom Gate, Room 2
	The hitchhiker's guide to quantum algebra

Wed, 11/05/2011 16:00	Alessandro Sisto (University of Oxford)	Junior Geometric Group Theory Seminar	SR1
	3-manifolds and their fundamental groups
	We'll discuss 2 ways to decompose a 3-manifold, namely the Heegaard splitting and the celebrated geometric decomposition. We'll then see that being hyperbolic, and more in general having (relatively) hyperbolic fundamental group, is a very common feature for a 3-manifold.