Forthcoming Seminars
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Fri, 31/10/2008 14:00 |
Dr Mauricio Barahona (Imperial College London) |
Mathematical Biology and Ecology Seminar  |
L3 |
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Fri, 31/10/2008 14:15 |
Nizar Touzi (Polytechnique) |
Mathematical Finance Seminar |
DH 1st floor SR |
| Starting from the problem of perfect hedging under market illiquidity, as introduced by Cetin, Jarrow and Protter, we introduce a class of second order target problems. A dual formulation in the general non-Markov case is obtained by formulating the problem under a convenient reference measure. In contrast with previous works, the controls lie in the classical H2 spaces associated to the reference measure. A dual formulation of the problem in terms of a standard stochastic control problem is derived, and involves control of the diffusion component. | |||
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Mon, 03/11/2008 12:00 |
Lionel Mason (Oxford) |
String Theory Seminar |
L3 |
| Abstract: Recent developments in quantum field theory and twistor-string theory have thrown up surprising structures in the perturbative approach to gravity that cry out for a non-perturbative explanation. Firstly the MHV scattering amplitudes, those involving just two left handed and n-2 right handed outgoing gravitons are particularly simple, and a formalism has been proposed that constructs general graviton scattering amplitudes from these MHV amplitudes as building blocks. This formalism is chiral and suggestive of deep links with Ashtekar variables and twistor theory. In this talk, the MHV amplitudes are calculated ab initio by considering scattering of linear gravitons on a fully nonlinear anti-self-dual background using twistor theory, and a twistor action formulation is provided that produces the MHV formalism as its Feynman rules. | |||
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Mon, 03/11/2008 14:15 |
Prof. Tusheng Zhang (Manchester) |
Stochastic Analysis Seminar |
Oxford-Man Institute |
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Mon, 03/11/2008 14:15 |
Nigel Hitchin (Oxford) |
Geometry and Analysis Seminar |
L3 |
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Mon, 03/11/2008 15:45 |
Jonathan Hillman (Sydney and Durham) |
Topology Seminar |
L3 |
 -complexes model the homotopy theory of manifolds.
In dimension 3, the unique factorization theorem holds to the extent that a  -complex is a connected sum if and only if its fundamental group is a free product, and the indecomposables are aspherical or have virtually free fundamental group [Tura'ev,Crisp]. However in contrast to the 3-manifold case the group of an indecomposable may have infinitely many ends (i.e., not be virtually cyclic). We shall sketch the construction of one such example, and outline some recent work using only group theory that imposes strong restrictions on any other such examples. |
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Mon, 03/11/2008 15:45 |
Dr. Roger Tribe (University of Warwick) |
Stochastic Analysis Seminar |
Oxford-Man Institute |
| The system u_t = Delta u + buv - cu + u^{1/2} dW v_t = - uv models the evolution of a branching population and its usage of a non-renewable resource. A phase diagram in the parameters (b,c) describes its long time evolution. We describe this, including some results on asymptotics in the phase diagram for small and large values of the parameters. | |||
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Mon, 03/11/2008 16:00 |
Johan Bredberg (University of Oxford) |
Junior Number Theory Seminar |
SR1 |
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Mon, 03/11/2008 17:00 |
Philippe Laurençot (Toulouse) |
Partial Differential Equations Seminar |
Gibson 1st Floor SR |
| In space dimension 2, it is well-known that the Smoluchowski-Poisson system (also called the simplified or parabolic-elliptic Keller-Segel chemotaxis model) exhibits the following phenomenon: there is a critical mass above which all solutions blow up in finite time while all solutions are global below that critical mass. We will investigate the case of the critical mass along with the stability of self-similar solutions with lower masses. We next consider a generalization to several space dimensions which involves a nonlinear diffusion and show that a similar phenomenon takes place but with some different features. | |||
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Tue, 04/11/2008 09:00 |
Pras Pathmanathan and Yasemin Sengul |
OxMOS Workshop/Meeting/Lecture |
DH 3rd floor SR |
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Tue, 04/11/2008 15:45 |
Tom Coates (Imperial College London) |
Algebraic and Symplectic Geometry Seminar |
L3 |
| Let X be a Gorenstein orbifold and Y a crepant resolution of X. Suppose that the quantum cohomology algebra of Y is semisimple. We describe joint work with Iritani which shows that in this situation the genus-zero crepant resolution conjecture implies a higher-genus version of the crepant resolution conjecture. We expect that the higher-genus version in fact holds without the semisimplicity hypothesis. | |||
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Tue, 04/11/2008 16:30 |
Dr Greg King (Portugal and University of Warwick) |
Geophysical and Nonlinear Fluid Dynamics Seminar |
Dobson Room, AOPP |
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Tue, 04/11/2008 17:00 |
Charles Batty (Oxford) |
Functional Analysis Seminar |
L3 |
A number of results are known establishing exponential/polynomial/logarithmic decay of energy for (damped) wave equations. Typically the results have been obtained by estimating the resolvent of the generator of a certain bounded  -semigroup, and then showing that the estimates imply certain rates of decay for the smooth orbits of the semigroup. We shall present a result of this type, which is both general and sharp, and which has a simple proof thanks to a device of Newman and Korevaar. |
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Tue, 04/11/2008 17:00 |
Dan Segal (Oxford) |
Algebra Seminar |
L2 |
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Wed, 05/11/2008 11:30 |
Owen Cotton-Barratt |
Algebra Kinderseminar |
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Wed, 05/11/2008 13:30 |
Kaushik Bhattacharya (Caltech) |
OxPDE Lunchtime Seminar |
Gibson 1st Floor SR |
| This talk will review recent progress in understanding the effective behavior of free boundaries in heterogeneous media. Though motivated by the pinning of martensitic phase boundaries, we shall explain connections to other problems. This talk is based on joint work with Patrick Dondl. | |||
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Thu, 06/11/2008 12:00 |
Spiro Karigiannis (Oxford) |
Junior Geometry and Topology Seminar |
SR1 |
I will give a survey-type introduction to manifolds equipped with  structures, emphasizing the similarities and differences with Riemannian manifolds equipped with almost complex structures, and with oriented Riemannian 3-manifolds. Along the way I may discuss the Berger classification of Riemannian holonomy, the Calabi-Yau theorem, exceptional geometric structures arising from the algebra of the Octonions, and calibrated submanifolds. This talk will be in two parts. |
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Thu, 06/11/2008 12:30 |
Eugen Varvaruca (Imperial College) |
OxPDE Lunchtime Seminar |
Gibson 1st Floor SR |
| We present some recent results on singular solutions of the problem of travelling gravity water waves on flows with vorticity. We show that, for a certain class of vorticity functions, a sequence of regular waves converges to an extreme wave with stagnation points at its crests. We also show that, for any vorticity function, the profile of an extreme wave must have either a symmetric corner of 120 degrees or a horizontal tangent at any isolated stagnation point. Moreover, the profile necessarily has a symmetric corner of 120 degrees if the vorticity is nonnegative near the free surface. | |||
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Thu, 06/11/2008 14:00 |
Prof Divakar Viswanath (University of Michigan, USA) |
Computational Mathematics and Applications |
Comlab |
| The butterfly-shaped Lorenz attractor is a fractal set made up of infinitely many periodic orbits. Ever since Lorenz (1963) introduced a system of three simple ordinary differential equations, much of the discussion of his system and its strange attractor has adopted a dynamical point of view. In contrast, we allow time to be a complex variable and look upon such solutions of the Lorenz system as analytic functions. Formal analysis gives the form and coefficients of the complex singularities of the Lorenz system. Very precise (> 500 digits) numerical computations show that the periodic orbits of the Lorenz system have singularities which obey that form exactly or very nearly so. Both formal analysis and numerical computation suggest that the mathematical analysis of the Lorenz system is a problem in analytic function theory. (Joint work with S. Sahutoglu). | |||
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Thu, 06/11/2008 14:30 |
Max Neunhoeffer (St Andrews) |
Representation Theory Seminar |
L3 |
| In this talk we present a new construction of a Wedderburn basis for the generic q-Schur algebra using the Du-Kazhdan-Lusztig basis. We show that this gives rise to a new view on the Du-Lusztig homomorphism to the asymptotic algebra. At the end we explain a potential plan for an attack on James' conjecture using a reformulation by Meinolf Geck. The talk starts with a gentle recollection of facts about Iwahori-Hecke-Algebras of type A and q-Schur algebras and aims to be accessible to people who are not (yet) experts in the representation theory of q-Schur algebras. All this is joint work with Olivier Brunat (Bochum). | |||
