Forthcoming Seminars

Wed, 02/11/2011
10:15 		Per Lotstedt OCCAM Wednesday Morning Event Add to calendar OCCAM Common Room (RI2.28)
Multiscale simulation of reaction-diffusion processes in molecular biology
In biological cells, molecules are transported actively or by diffusion and react with each other when they are close. The reactions occur with certain probability and there are few molecules of some chemical species. Therefore, a stochastic model is more accurate compared to a deterministic, macroscopic model for the concentrations based on partial differential equations. At the mesoscopic level, the domain is partitioned into voxels or compartments. The molecules may react with other molecules in the same voxel and move between voxels by diffusion or active transport. At a finer, microscopic level, each individual molecule is tracked, it moves by Brownian motion and reacts with other molecules according to the Smoluchowski equation. The accuracy and efficiency of the simulations are improved by coupling the two levels and only using the micro model when it is necessary for the accuracy or when a meso description is unknown. Algorithms for simulations with the mesoscopic, microscopic and meso-micro models will be described and applied to systems in molecular biology in three space dimensions.
Wed, 02/11/2011
11:30 		Alessandro Sisto (University College, Oxford) Algebra Kinderseminar Add to calendar
General relativity+cobordism= time machine (maybe) (St Hugh's, 80WR18)
We will start off with a crash course in General relativity, and then I'll describe a 'recipe' for a time machine. This will lead us to the question whether or not the topology of the universe can change. We will see that, in some sense, this is topologically allowed. However, the Einstein equation gives a certain condition on the Ricci tensor (which is violated by certain quantum effects) and meeting this condition is a more delicate problem.
Thu, 03/11/2011
12:00 		Benjamin Volk Junior Geometry and Topology Seminar Add to calendar SR2
Some Remarks on d-manifolds and d-bordism
We will give an introduction to the theory of d-manifolds, a new class of geometric objects recently/currently invented by Joyce (see http://people.maths.ox.ac.uk/joyce/dmanifolds.html). We will start from scratch, by recalling the definition of a 2-category and talking a bit about $ C^\infty $-rings, $ C^\infty $-schemes and d-spaces before giving the definition of what a d-manifold should be. We will then discuss some properties of d-manifolds, and say some words about d-manifold bordism and its applications.
Thu, 03/11/2011
13:00 		Greg Gyurko Mathematical Finance Internal Seminar Add to calendar DH 1st floor SR
Cubature on Wiener space and Multilevel Monte-Carlo
Cubature on Wiener space" is a numerical method for the weak approximation of SDEs. After an introduction to this method we present some cases when the method is computationally expensive, and highlight some techniques that improve the tractability. In particular, we adapt the Multilevel Monte-Carlo framework and extend the Milstein-scheme based version of Mike Giles to higher dimensional and higher degree cases.
Thu, 03/11/2011
14:00 		Dr Bora Ucar (ENS Lyon) Computational Mathematics and Applications Add to calendar Rutherford Appleton Laboratory, nr Didcot
On hypergraph partitioning based ordering methods for sparse matrix factorization
We will discuss the use of hypergraph-based methods for orderings of sparse matrices in Cholesky, LU and QR factorizations. For the Cholesky factorization case, we will investigate a recent result on pattern-wise decomposition of sparse matrices, generalize the result and develop algorithmic tools to obtain effective ordering methods. We will also see that the generalized results help us formulate the ordering problem in LU much like we do for the Cholesky case, without ever symmetrizing the given matrix $ A $ as $ A+A^{T} $ or $ A^{T}A $. For the QR factorization case, the use of hypergraph models is fairly standard. We will nonetheless highlight the fact that the method again does not form the possibly much denser matrix $ A^{T}A $. We will see comparisons of the hypergraph-based methods with the most common alternatives in all three cases.

This is joint work with Iain S. Duff.
Thu, 03/11/2011
16:00 		Jacob Tsimerman (Harvard) Logic Seminar Add to calendar
Number Theory Seminar Add to calendar 		L3
Lower bounds for CM points and torsion in class groups
Let $ x $ be a CM point in the moduli space $ \mathcal{A}_g(\mathbb{C}) $ of principally polarized complex abelian varieties of genus $ g $, corresponding to an Abelian variety $ A $ with complex multiplication by a ring $ R $. Edixhoven conjectured that the size of the Galois orbit of x should grow at least like a power of the discriminant $ {\rm Disc}(R) $ of $ R $. For $ g=1 $, this reduces to the classical Brauer-Siegel theorem. A positive answer to this conjecture would be very useful in proving the André-Oort conjecture unconditionally. We will present a proof of the conjectured lower bounds in some special cases, including $ g\le 6 $. Along the way we derive transfer principles for torsion in class groups of different fields which may be interesting in their own right.
Thu, 03/11/2011
16:00 		John King (University of Nottingham) Industrial and Applied Mathematics Seminar Add to calendar DH 1st floor SR
Wave propagation in heterogeneous reaction diffusion
The mechanisms for the selection of the propagation speed of waves connecting unstable to stable states will be discussed in the spatially non-homogeneous case, the differences from the very well-studied homogeneous version being emphasised.
Fri, 04/11/2011
10:00 		Various (Industry) Industrial and Interdisciplinary Workshops Add to calendar DH 1st floor SR
Industrial MSc project proposals

10am Radius Health - Mark Evans

10:30am NAG - Mick Pont and Lawrence Mulholland

Please note, that Thales are also proposing several projects but the academic supervisors have already been allocated.
Fri, 04/11/2011
14:15 		Ulrich Horst (Berlin) Nomura Seminar Add to calendar DH 1st floor SR
Forward-backward systems for expected utility maximization
In this paper we deal with the utility maximization problem with a preference functional of expected utility type. We derive a new approach in which we reduce the utility maximization problem with general utility to the study of a fully-coupled Forward-Backward Stochastic Differential Equation (FBSDE). The talk is based on joint work with Ying Hu, Peter Imkeller, Anthony Reveillac and Jianing Zhang.
Fri, 04/11/2011
14:30 		Dr Frank Kwasniok (University of Exeter) Mathematical Geoscience Seminar Add to calendar DH 3rd floor SR
Data-based stochastic subgrid-scale parametrisation: an approach using cluster-weighted modelling
A new approach for data-based stochastic parametrisation of unresolved scales and processes in numerical weather and climate prediction models is introduced. The subgrid-scale model is conditional on the state of the resolved scales, consisting of a collection of local models. A clustering algorithm in the space of the resolved variables is combined with statistical modelling of the impact of the unresolved variables. The clusters and the parameters of the associated subgrid models are estimated simultaneously from data. The method is tested and explored in the framework of the Lorenz '96 model using discrete Markov processes as local statistical models. Performance of the scheme is investigated for long-term simulations as well as ensemble prediction. The present method clearly outperforms simple parametrisation schemes and compares favourably with another recently proposed subgrid scheme also based on conditional Markov chains.
Fri, 04/11/2011
16:30 		Professor John W.M Bush (Massachusetts Institute of Technology) Colloquia Add to calendar L2
Hydrodynamic quantum analogues

Yves Couder and co-workers have recently reported the results of a startling series of experiments in which droplets bouncing on a fluid surface exhibit several dynamical features previously thought to be peculiar to the microscopic realm. In an attempt to 

develop a connection between the fluid and quantum systems, we explore the Madelung transformation, whereby Schrodinger's equation is recast in a hydrodynamic form. New experiments are presented, and indicate the potential value of this hydrodynamic approach to both visualizing and understanding quantum mechanics.

 
Mon, 07/11/2011
12:00 		Davide Cassani (King's College London) String Theory Seminar Add to calendar L3
Landscape of consistent reductions with applications
Consistent truncations have proved to be powerful tools in the construction of new string theory solutions. Recently, they have been employed in the holographic description of condensed matter systems. In the talk, I will present a rich class of supersymmetric consistent truncations of higher-dimensional supergravity which are based on geometric structures, focusing on the tri-Sasakian case. Then I will discuss some applications, including a general result relating AdS backgrounds to solutions with non-relativistic Lifshitz symmetry.
Mon, 07/11/2011
14:15 		Dmytro Arinkin (University of North Carolina & IAS Princeton) Geometry and Analysis Seminar Add to calendar L3
Autoduality of Jacobians for singular curves
Let C be a (smooth projective algebraic) curve. It is well known that the Jacobian J of C is a principally polarized abelian variety. In otherwords, J is self-dual in the sense that J is identified with the space of topologically trivial line bundles on itself. Suppose now that C is singular. The Jacobian J of C parametrizes topologically trivial line bundles on C; it is an algebraic group which is no longer compact. By considering torsion-free sheaves instead of line bundles, one obtains a natural singular compactification J' of J. In this talk, I consider (projective) curves C with planar singularities. The main result is that J' is self-dual: J' is identified with a space of torsion-free sheaves on itself. This autoduality naturally fits into the framework of the geometric Langlands conjecture; I hope to sketch this relation in my talk.
Mon, 07/11/2011
14:15 		Anton Thalmaier (University of Luxembourg) Stochastic Analysis Seminar Add to calendar Oxford-Man Institute
Brownian measures on Jordan curves

We describe a construction of the Brownian measure on Jordan curves with respect to the Weil-Petersson metric. The step from Brownian motion on the diffeomorphism group of the circle to Brownian motion on Jordan curves in the complex plane requires probabilistic arguments well beyond the classical theory of conformal welding, due to the lacking quasi-symmetry of canonical Brownian motion on Diff(S1). A new key step in our construction is the systematic use of a Kählerian diffusion on the space of Jordan curves for which the welding functional gives rise to conformal martingales.
Mon, 07/11/2011
15:45 		Ric Wade (Oxford) Topology Seminar Add to calendar L3
Right-angled Artin groups and their automorphisms
Automorphisms of right-angled Artin groups interpolate between $ Out(F_n) $ and $ GL_n(\mathbb{Z}) $. An active area of current research is to extend properties that hold for both the above groups to $ Out(A_\Gamma) $ for a general RAAG. After a short survey on the state of the art, we will describe our recent contribution to this program: a study of how higher-rank lattices can act on RAAGs that builds on the work of Margulis in the free abelian case, and of Bridson and the author in the free group case.
Mon, 07/11/2011
15:45 		Simon Harris (University of Bath) Stochastic Analysis Seminar Add to calendar Oxford-Man Institute
Near-critical survival probability of branching Brownian motion with an absorbing barrier"

We will consider a branching Brownian motion where particles have a drift $-\rho$, binary branch at rate $\beta$ and are killed if they hit the origin. This process is supercritical  if $\beta>\rho^2/2$ and we will discuss the survival probability in the regime as criticality is approached. (Joint work with Elie Aidekon)
Mon, 07/11/2011
16:00 		Paul-James White Junior Number Theory Seminar Add to calendar SR1
The Local Langlands correspondence
Mon, 07/11/2011
17:00 		Tim Palmer (University of Oxford and European Centre for Medium-Range Weather Forecasts) Partial Differential Equations Seminar Add to calendar Gibson 1st Floor SR
The "real" butterfly effect: A study of predictability in multiscale systems, with implications for weather and climate.

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

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