Forthcoming Seminars
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Thu, 14/10/2010 14:30 |
Daiva Pucinskaite (Kiel) |
Representation Theory Seminar  |
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Thu, 14/10/2010 16:00 |
Dr S Siksek (Dept. Mathematics, University of Warwick) |
Number Theory Seminar |
L3 |
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Let C be a smooth plane cubic curve over the rationals. The Mordell--Weil Theorem can be restated as follows: there is a finite subset B of rational points such that all rational points can be obtained from this subset by successive tangent and secant constructions. It is conjectured that a minimal such B can be arbitrarily large; this is indeed the well-known conjecture that there are elliptic curves with arbitrarily large ranks. This talk is concerned with the corresponding problem for cubic surfaces. |
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Thu, 14/10/2010 16:30 |
Julian Hunt |
Differential Equations and Applications Seminar |
L2 |
| The new model is that the universal small scale structure of high Reynolds number turbulence is determined by the dynamics of thin evolving shear layers, with thickness of the order of the Taylor micro scale,within which there are the familiar elongated vortices .Local quasi-linear dynamics shows how the shear layers act as barriers to external eddies and a filter for the transfer of energy to their interiors. The model is consistent with direct numerical simulations by Ishihara and Kaneda analysed in terms of conditional statistics relative to the layers and also with recent 4D measurements of lab turbulence by Wirth and Nickels. The model explains how the transport of energy into the layers leads to the observed inertial range spectrum and to the generation of intense structures, on the scale of the Kolmogorov micro-scale. But the modelling also explains the important discrepancies between data and the Kolmogorov-Richardson cascade concept ,eg larger amplitudes of the smallest scale motions and of the higher moments ,and why the latter are generally less isotropic than lower order moments, eg in thermal convection. Ref JCRHunt , I Eames, P Davidson,J.Westerweel, J Fernando, S Voropayev, M Braza J Hyd Env Res 2010 | |||
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Thu, 14/10/2010 17:00 |
Dr Koenigsmann (Oxford) |
Logic Seminar |
L3 |
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Fri, 15/10/2010 10:00 |
Industrial and Interdisciplinary Workshops |
DH 3rd floor SR | |
| 9:45 DH common room coffee | |||
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Fri, 15/10/2010 14:00 |
Prof Neil Ferguson (Public Health and Primary Care) |
Mathematical Biology and Ecology Seminar |
L1 |
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Mon, 18/10/2010 12:00 |
Luis Fernando Alday (Oxford) |
String Theory Seminar |
L3 |
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Mon, 18/10/2010 14:15 |
Tamas Hausel (Oxford) |
Geometry and Analysis Seminar |
L3 |
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Mon, 18/10/2010 14:15 |
Jeremie Unterberger |
Stochastic Analysis Seminar |
Eagle House |
| Rough path theory, invented by T. Lyons, is a successful and general method for solving ordinary or stochastic differential equations driven by irregular Hölder paths, relying on the definition of a finite number of substitutes of iterated integrals satisfying definite algebraic and regularity properties. Although these are known to exist, many questions are still open, in particular: (1) "how many" possible choices are there ? (2) how to construct one explicitly ? (3) what is the connection to "true" iterated integrals obtained by an approximation scheme ? In a series of papers, we (1) showed that "formal" rough paths (leaving aside regularity) were exactly determined by so-called "tree data"; (2) gave several explicit constructions, the most recent ones relying on quantum field renormalization methods; (3) obtained with J. Magnen (Laboratoire de Physique Theorique, Ecole Polytechnique) a Lévy area for fractional Brownian motion with Hurst index <1/4 as the limit in law of iterated integrals of a non-Gaussian interacting process, thus calling for a redefinition of the process itself. The latter construction belongs to the field of high energy physics, and as such established by using constructive field theory and renormalization; it should extend to a general rough path (work in progress). | |||
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Mon, 18/10/2010 15:45 |
Jason Behrstock (CUNY) |
Topology Seminar |
L3 |
| Abstract: We will explain a certain natural way to project elements of the mapping class to simple closed curves on subsurfaces. Generalizing a coordinate system on hyperbolic space, we will use these projections to describe a way to characterize elements of the mapping class group in terms of these projections. This point of view is useful in several applications; time permitting we shall discuss how we have used this to prove the Rapid Decay property for the mapping class group. This talk will include joint work with Kleiner, Minksy, and Mosher. | |||
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Mon, 18/10/2010 15:45 |
Nadia Sidorova |
Stochastic Analysis Seminar |
Eagle House |
| We consider a dilute stationary system of N particles uniformly distributed in space and interacting pairwise according to a compactly supported potential, which is repellent at short distances and attractive at moderate distances. We are interested in the large-N behaviour of the system. We show that at a certain scale there are phase transitions in the temperature parameter and describe the energy and ground states explicitly in terms of a variational problem | |||
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Mon, 18/10/2010 17:00 |
Alexis Vasseur (University of Oxford) |
Partial Differential Equations Seminar |
Gibson 1st Floor SR |
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We develop a theory based on relative entropy to show stabilityand uniqueness of extremal entropic Rankine-Hugoniot discontinuities forsystems of conservation laws (typically 1-shocks, n-shocks, 1-contactdiscontinuities and n-contact discontinuities of big amplitude), amongbounded entropic weak solutions having an additional strong traceproperty. The existence of a convex entropy is needed. No BV estimateis needed on the weak solutions considered. The theory holds withoutsmallness condition. The assumptions are quite general. For instance, thestrict hyperbolicity is not needed globally. For fluid mechanics, thetheory handles solutions with vacuum. |
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Tue, 19/10/2010 10:00 |
Tim Adamo (Oxford) |
Twistor Workshop |
Gibson 1st Floor SR |
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Tue, 19/10/2010 12:00 |
Subir Sarkar (Theoretical Physics) |
Quantum Field Theory Seminar |
L3 |
| Much effort has been devoted to the study of weak scale particles, e.g. supersymmetric neutralinos, which have a relic abundance from thermal equilibrium in the early universe of order what is inferred for dark matter. This does not however provide any connection to the comparable abundance of baryonic matter, which must have a non-thermal origin. However "dark baryons" of mass ~5 GeV from a new strongly interacting sector would naturally provide dark matter and are consistent with recent putative signals in experiments such as CoGeNT and DAMA. Such particles would accrete in the Sun and affect heat transport in the interior so as to affect low energy neutrino fluxes and can possibly resolve the current conflict between helioseismological data and the Standard Solar Model. | |||
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Tue, 19/10/2010 13:15 |
Guido Klingbeil (Centre for Mathematical Biology) |
Junior Applied Mathematics Seminar |
DH 1st floor SR |
| We explore two different threading approaches on a graphics processing unit (GPU) exploiting two different characteristics of the current GPU architecture. The fat thread approach tries to minimise data access time by relying on shared memory and registers potentially sacrificing parallelism. The thin thread approach maximises parallelism and tries to hide access latencies. We apply these two approaches to the parallel stochastic simulation of chemical reaction systems using the stochastic simulation algorithm (SSA) by Gillespie. In these cases, the proposed thin thread approach shows comparable performance while eliminating the limitation of the reaction system's size.Link to paper: http://people.maths.ox.ac.uk/erban/papers/paperCUDA.pdf | |||
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Tue, 19/10/2010 14:15 |
Dr Andrew Prentice (School of Mathematical Sciences) |
Geophysical and Nonlinear Fluid Dynamics Seminar |
Dobson Room, AOPP |
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Tue, 19/10/2010 14:30 |
Jean Cardinal (Universite Libre de Bruxelles) |
Combinatorial Theory Seminar |
L3 |
| We revisit the problem of sorting under partial information: sort a finite set given the outcomes of comparisons between some pairs of elements. The input is a partially ordered set P, and solving the problem amounts to discovering an unknown linear extension of P, using pairwise comparisons. The information-theoretic lower bound on the number of comparisons needed in the worst case is log e(P), the binary logarithm of the number of linear extensions of P. In a breakthrough paper, Jeff Kahn and Jeong Han Kim (STOC 1992) showed that there exists a polynomial-time sorting algorithm achieving this bound up to a constant factor. They established a crucial link between the entropy of the input partial order and the information-theoretic lower bound. However, their algorithm invokes the ellipsoid algorithm at each iteration for determining the next comparison, making it unpractical. We develop efficient algorithms for sorting under partial information, derived from approximation and exact algorithms for computing the partial order entropy. This is joint work with S. Fiorini, G. Joret, R. Jungers, and I. Munro. | |||
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Tue, 19/10/2010 15:45 |
Andre Neves (Imperial) |
Algebraic and Symplectic Geometry Seminar |
L3 |
| I will show that given smooth embedded Lagrangian L in a Calabi-Yau, one can find a perturbation of L which lies in the same hamiltonian isotopy class and such that the correspondent solution to mean curvature flow develops a finite time singularity. This shows in particular that a simplified version of the Thomas-Yau conjecture does not hold. | |||
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Tue, 19/10/2010 16:00 |
Owen Cotton-Barratt (Oxford University) |
Junior Geometric Group Theory Seminar |
DH 3rd floor SR |
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Tue, 19/10/2010 17:00 |
Desi Kochloukova (UNICAMP) |
Algebra Seminar |
L2 |
| We discuss homological finiteness Bredon types FPm with respect to the class of finite subgroups and seperately with respect to the class of virtually cyclic subgroups. We will concentrate to the case of solubles groups and if the time allows to the case of generalized R. Thompson groups of type F. The results announced are joint work with Brita Nucinkis (Southampton) and Conchita Martinez Perez (Zaragoza) and will appear in papers in Bulletin of LMS and Israel Journal of Mathematics. | |||
