Forthcoming Seminars
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Tue, 09/06/2009 12:00 |
Marni Sheppeard (Computing Lab) |
Quantum Field Theory Seminar  |
L3 |
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Tue, 09/06/2009 16:30 |
Dr Xiaoming Zhai (University of Oxford) |
Geophysical and Nonlinear Fluid Dynamics Seminar |
Dobson Room, AOPP |
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Tue, 09/06/2009 17:00 |
Michael Collins (Oxford) |
Algebra Seminar |
L2 |
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Tue, 09/06/2009 17:00 |
Stephen Dilworth (South Carolina) |
Functional Analysis Seminar |
L3 |
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Wed, 10/06/2009 11:30 |
Tobias Barthel (University of Oxford) |
Algebra Kinderseminar |
ChCh, Tom Gate, Room 2 |
| Using the theory of formal groups, Landweber´s exactness theorem provides means to construct interesting invariants of topological spaces out of geometric objects. I will illustrate the resulting connection between algebraic geometry and stable homotopy theory in the special case of elliptic curves. | |||
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Wed, 10/06/2009 16:00 |
Dr.A.J. Ostaszewski (LSE) |
Analytic Topology in Mathematics and Computer Science |
L3 |
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Thu, 11/06/2009 11:00 |
Laura Campbell (Mathematical Institute) |
Applied Dynamical Systems and Inverse Problems Seminar |
DH 3rd floor SR |
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Thu, 11/06/2009 12:15 |
Frank Gounelas (Oxford) |
Junior Geometry and Topology Seminar |
SR1 |
In this talk I will outline the two constructions of the Brauer group Br( ) of a scheme , namely via etale cohomology and Azumaya algebras and briefly describe how one may compute this group using the Hochschild-Serre spectral sequence. In the early '70s Manin observed that one can use the Brauer group of a projective variety  to define an obstruction to the existence of rational points on . I will discuss this arithmetic application and time permitting, outline an example for a K3 surface. |
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Thu, 11/06/2009 12:30 |
João Lopes Costa (Lisbon and University of Oxford) |
OxPDE Lunchtime Seminar |
Gibson 1st Floor SR |
| I will address the celebrated and long standing “No-Hair” conjecture that aims for the classification of stationary, regular, electro-vacuum black hole space-times. Besides reviewing some of the necessary concepts from general relativity I will focus on the analysis of the singular harmonic map to which the source free Einstein-Maxwell equations reduce in the stationary and axisymmetric case. | |||
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Thu, 11/06/2009 13:00 |
Alison Etheridge |
Mathematical Finance Internal Seminar |
DH 1st floor SR |
| We take a leisurely look at some mathematical models from population genetics and the ways that they can be analysed. Some of the models have a very familiar form - for example diffusion models of population size look a lot like interest rate models. But hopefully there will also be something new. | |||
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Thu, 11/06/2009 14:00 |
Dr. Atsushi Suzuki (Czech Technical University in Prague / Kyushu University) |
Computational Mathematics and Applications |
Comlab |
| An iterative substructuring method with balancing Neumann-Neumann preconditioner is known as an efficient parallel algorithm for the elasticity equations. This method was extended to the Stokes equations by Pavarino and Widlund [2002]. In their extension, Q2/P0-discontinuous elements are used for velocity/pressure and a Schur complement system within "benign space", where incompressibility satisfied, is solved by CG method. For the construction of the coarse space for the balancing preconditioner, some supplementary solvability conditions are considered. In our algorithm for 3-D computation, P1/P1 elements for velocity/pressure with pressure stabilization are used to save computational cost in the stiffness matrix. We introduce a simple coarse space similar to the one of elasticity equations. Owing to the stability term, solvabilities of local Dirichlet problem for a Schur complement system, of Neumann problem for the preconditioner, and of the coarse space problem are ensured. In our implementation, local Dirichlet and Neumann problems are solved by a 4x4-block modified Cholesky factorization procedure with an envelope method, which leads to fast computation with small memory requirement. Numerical result on parallel efficiency with a shared memory computer will be shown. Direct use of the Stokes solver in an application of Earth's mantle convection problem will be also shown. | |||
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Thu, 11/06/2009 16:00 |
Laurent Moret-Bailly (Rennes) |
Number Theory Seminar |
L3 |
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Thu, 11/06/2009 16:00 |
Laurent Moret-Bailly (Rennes) |
Logic Seminar |
L3 |
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Thu, 11/06/2009 16:30 |
Rachel Kuske (UBC) |
Differential Equations and Applications Seminar |
DH 1st floor SR |
| Transient or unstable behavior is often ignored in considering long time dynamics in the deterministic world. However, stochastic effects can change the picture dramatically, so that the transients can dominate the long range behavior. Coherence resonance is one relatively simple example of this transformation, and we consider others such as noise-driven synchronization in networks, recurrence of diseases, and stochastic stabilization in systems with delay. The challenge is to identify common features in these phenomena, leading to new approaches for other systems of this type. Some recurring themes include the influence of multiple time scales, cooperation of both discrete and continuous aspects in the dynamics, and the remnants of underlying bifurcation structure visible through the noise. | |||
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Fri, 12/06/2009 10:00 |
Graeme Mackenzie and David Crosby (Oxford) |
Industrial and Interdisciplinary Workshops |
DH 1st floor SR |
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Fri, 12/06/2009 14:00 |
Dr Simon Preston (University of Nottingham) |
Mathematical Biology and Ecology Seminar |
L3 |
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Fri, 12/06/2009 14:15 |
Mike Teranchi (Cambridge) |
Nomura Seminar |
DH 1st floor SR |
| We consider the classical problem of forming portfolios of vanilla options in order to hedge more exotic derivatives. In particular, we focus on a model in which the agent can trade a stock and a family of variance swaps written on that stock. The market is only approximately complete in the sense that any submarket consisting of the stock and the variance swaps of a finite set of maturities is incomplete, yet every bounded claim is in the closure of the set of attainable claims. Taking a Hilbert space approach, we give a characterization of hedging portfolios for a certain class of contingent claims. (Joint work with Francois Berrier) | |||
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Mon, 15/06/2009 12:00 |
Sergei Dubovsky (Stanford) |
String Theory Seminar |
L3 |
| String theory suggests the simultaneous presence of many ultralight axions possibly populating each decade of mass down to the Hubble scale 10^-33eV. Conversely the presence of such a plenitude of axions (an "axiverse") would be evidence for string theory, since it arises due to the topological complexity of the extra-dimensional manifold and is ad hoc in a theory with just the four familiar dimensions. We investigate how upcoming astrophysical experiments will explore the existence of such axions over a vast mass range from 10^-33eV to 10^-10eV. Axions with masses between 10^-33eV to 10^-28eV cause a rotation of the CMB polarization that is constant throughout the sky. The predicted rotation angle is of order \alpha~1/137. Axions in the mass range 10^-28eV to 10^-18eV give rise to multiple steps in the matter power spectrum, that will be probed by upcoming galaxy surveys and 21 cm line tomography. Axions in the mass range 10^-22eV to 10^-10eV affect the dynamics and gravitational wave emission of rapidly rotating astrophysical black holes through the Penrose superradiance process. When the axion Compton wavelength is of order of the black hole size, the axions develop "superradiant" atomic bound states around the black hole "nucleus". Their occupation number grows exponentially by extracting rotational energy from the ergosphere, culminating in a rotating Bose-Einstein axion condensate emitting gravitational waves. This mechanism creates mass gaps in the spectrum of rapidly rotating black holes that diagnose the presence of axions. The rapidly rotating black hole in the X-ray binary LMC X-1 implies an upper limit on the decay constant of the QCD axion f_a<2*10^17GeV, much below the Planck mass. This reach can be improved down to the grand unification scale f_a<2*10^16GeV, by observing smaller stellar mass black holes. | |||
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Mon, 15/06/2009 14:15 |
Wilhelm Klingenberg (Durham) |
Geometry and Analysis Seminar |
L3 |
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Mon, 15/06/2009 14:15 |
Professor Andrew Stuart (University of Warwick) |
Stochastic Analysis Seminar |
Oxford-Man Institute |
| Diffusion limits of MCMC methods in high dimensions provide a useful theoretical tool for studying efficiency. In particular they facilitate precise estimates of the number of steps required to explore the target measure, in stationarity, as a function of the dimension of the state space. However, to date such results have only been proved for target measures with a product structure, severely limiting their applicability to real applications. The purpose of this talk is to desribe a research program aimed at identifying diffusion limits for a class of naturally occuring problems, found by finite dimensional approximation of measures on a Hilbert space which are absolutely continuous with respect to a Gaussian reference measure. The diffusion limit to a Hilbert space valued SDE (or SPDE) is proved. Joint work with Natesh Pillai (Warwick) and Jonathan Mattingly (Duke) | |||
