Forthcoming Seminars

Fri, 27/04/2012
10:00 		Industrial and Interdisciplinary Workshops Add to calendar DH 3rd floor SR
no workshop.
Fri, 27/04/2012
10:15 		Jimmy Moore (Texas A&M) OCCAM Special Seminar Add to calendar OCCAM Common Room (RI2.28)
Lymphatic system biomechanics and pumping
Mon, 30/04/2012
12:00 		Andrew Hodges (Oxford) String Theory Seminar Add to calendar L3
A simple formula for gravitational MHV amplitudes
A simple formula is given for the $ n $-field tree-level MHV gravitational amplitude, based on soft limit factors. It expresses the full $ S_n $ symmetry naturally, as a determinant of elements of a symmetric ($ n \times n $) matrix.
Mon, 30/04/2012
14:15 		MARTIN BARLOW (University of British Columbia) Stochastic Analysis Seminar Add to calendar Oxford-Man Institute
Energy of cut off functions and heat kernel upper bounds S Andres and M T Barlow*

It is well known that electrical resistance arguments provide (usually) the best method for determining whether a graph is transient or recurrent. In this talk I will discuss a similar characterization of 'sub-diffusive behaviour' -- this occurs in spaces with many obstacles or traps.

The characterization is in terms of the energy of functions in annuli.
Mon, 30/04/2012
15:45 		MISHA SODIN (Tel Aviv University) Stochastic Analysis Seminar Add to calendar Oxford-Man Institute
The number of connected components of zero sets of smooth Gaussian functions

 

We find the order of growth of the typical number of components of zero sets of smooth random functions of several real variables. This might be thought as a statistical version of the (first half of) 16th Hilbert problem. The primary examples are various ensembles of Gaussian real-valued polynomials (algebraic or trigonometric) of large degree, and smooth Gaussian functions on the Euclidean space with translation-invariant distribution.

Joint work with Fedor Nazarov.

                               

 
Mon, 30/04/2012
15:45 		Martin Palmer (Oxford) Topology Seminar Add to calendar L3
Configuration spaces and homological stability
For a fixed background manifold $ M $ and parameter-space $ X $, the associated configuration space is the space of $ n $-point subsets of $ M $ with parameters drawn from $ X $ attached to each point of the subset, topologised in a natural way so that points cannot collide. One can either remember or forget the ordering of the n points in the configuration, so there are ordered and unordered versions of each configuration space. It is a classical result that the sequence of unordered configuration spaces, as $ n $ increases, is homologically stable: for each $ k $ the degree-$ k $ homology is eventually independent of $ n $. However, a simple counterexample shows that this result fails for ordered configuration spaces. So one could ask whether it's possible to remember part of the ordering information and still have homological stability. The goal of this talk is to explain the ideas behind a positive answer to this question, using 'oriented configuration spaces', in which configurations are equipped with an ordering - up to even permutations - of their points. I will also explain how this case differs from the unordered case: for example the 'rate' at which the homology stabilises is strictly slower for oriented configurations. If time permits, I will also say something about homological stability with twisted coefficients.
Mon, 30/04/2012
16:00 		James Maynard Junior Number Theory Seminar Add to calendar SR1
Vinogradov's Three Prime Theorem
Vinogradov's three prime theorem resolves the weak Goldbach conjecture for sufficiently large integers. We discuss some of the ideas behind the proof, and discuss some of the obstacles to completing a proof of the odd goldbach conjecture.
Mon, 30/04/2012
17:00 		Jose L. Rodrigo (Warwick) Partial Differential Equations Seminar Add to calendar Gibson 1st Floor SR
On the existence of a Spine for SQG (and applications)
based on joint work with Charles Fefferman (Princeton) and Kevin Luli (Yale).
Tue, 01/05/2012
13:15 		Lucas Jeub Junior Applied Mathematics Seminar Add to calendar DH 1st floor SR
Overlapping Communities and Consensus Clustering
With the advent of powerful computers and the internet, our ability to collect and store large amounts of data has improved tremendously over the past decades. As a result, methods for extracting useful information from these large datasets have gained in importance. In many cases the data can be conveniently represented as a network, where the nodes are entities of interest and the edges encode the relationships between them. Community detection aims to identify sets of nodes that are more densely connected internally than to the rest of the network. Many popular methods for partitioning a network into communities rely on heuristically optimising a quality function. This approach can run into problems for large networks, as the quality function often becomes near degenerate with many near optimal partitions that can potentially be quite different from each other. In this talk I will show that this near degeneracy, rather than being a severe problem, can potentially allow us to extract additional information
Tue, 01/05/2012
15:45 		Jonathan Pridham (Cambridge) Algebraic and Symplectic Geometry Seminar Add to calendar L3
Representability of moduli stacks
Derived moduli stacks extend moduli stacks to give families over simplicial or dg rings. Lurie's representability theorem gives criteria for a functor to be representable by a derived geometric stack, and I will introduce a variant of it. This establishes representability for problems such as moduli of sheaves and moduli of polarised schemes.
Tue, 01/05/2012
17:00 		Professor R. Marsh (Leeds) Algebra Seminar Add to calendar L2
Reflection group presentations arising from cluster algebras

 Finite reflection groups are often presented as Coxeter groups. We give a
presentation of finite crystallographic reflection group in terms of an
arbitrary seed in the corresponding cluster algebra of finite type for which
the Coxeter presentation is a special case. We interpret the presentation in
terms of companion bases in the associated root system. This is joint work with 
Michael Barot (UNAM, Mexico)
Wed, 02/05/2012
10:15 		Stefan Hellander (University of Uppsala) OCCAM Wednesday Morning Event Add to calendar OCCAM Common Room (RI2.28)
Flexible and efficient simulation of stochastic reaction-diffusion processes in cells

The reaction-diffusion master equation (RDME) is a popular model in systems biology. In the RDME, diffusion is modeled as discrete jumps between voxels in the computational domain. However, it has been demonstrated that a more fine-grained model is required to resolve all the dynamics of some highly diffusion-limited systems.

In Greenʼs Function Reaction Dynamics (GFRD), a method based on the Smoluchowski model, diffusion is modeled continuously in space.

This will be more accurate at fine scales, but also less efficient than a discrete-space model.

We have developed a hybrid method, combining the RDME and the GFRD method, making it possible to do the more expensive fine-grained simulations only for the species and in the parts of space where it is required in order to resolve all the dynamics, and more coarse-grained simulations where possible. We have applied this method to a model of a MAPK-pathway, and managed to reduce the number of molecules simulated with GFRD by orders of magnitude and without an appreciable loss of accuracy.
Thu, 03/05/2012
12:00 		Henry Bradford Junior Geometry and Topology Seminar Add to calendar L3
Expander Graphs and Property $ \tau $
Expander graphs are sparse finite graphs with strong connectivity properties, on account of which they are much sought after in the construction of networks and in coding theory. Surprisingly, the first examples of large expander graphs came not from combinatorics, but from the representation theory of semisimple Lie groups. In this introductory talk, I will outline some of the history of the emergence of such examples from group theory, and give several applications of expander graphs to group theoretic problems.
Thu, 03/05/2012
12:30 		Beatrice Pelloni (University of Reading) OxPDE Lunchtime Seminar Add to calendar Gibson 1st Floor SR
The semigeostrophic equations: a survey of old and new results
In this talk I will survey the results on the existence of solutions of the semigeostrophic system, a fully nonlinear reduction of the Navier-Stokes equation that constitute a valid model when the effect of rotation dominate the atmospheric flow. I will give an account of the theory developed since the pioneering work of Brenier in the early 90's, to more recent results obtained in a joint work with Mike Cullen and David Gilbert.
Thu, 03/05/2012
14:00 		Dr Cécile Piret (Université catholique de Louvain.) Computational Mathematics and Applications Add to calendar Gibson Grd floor SR
The orthogonal gradients method: A radial basis functions method for solving partial differential equations on arbitrary surfaces
Although much work has been done on using RBFs for reconstructing arbitrary surfaces, using RBFs to solve PDEs on arbitrary manifolds is only now being considered and is the subject of this talk. We will review current methods and introduce a new technique that is loosely inspired by the Closest Point Method. This new technique, the Orthogonal Gradients Method (OGr), benefits from the advantages of using RBFs: the simplicity, the high accuracy but also the meshfree character, which gives the flexibility to represent the most complex geometries in any dimension.

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

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