Forthcoming Seminars
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Fri, 30/04/2010 10:00 |
Industrial and Interdisciplinary Workshops  |
DH 3rd floor SR | |
| NO WORKSHOP - 09:45 coffee in DH Common Room for those attending the OCIAM Meeting | |||
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Fri, 30/04/2010 12:00 |
Burt Ovrut (University of Pennsylvania) |
String Theory Seminar |
L3 |
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Fri, 30/04/2010 14:00 |
Dr Steven White (Wallingford) |
Mathematical Biology and Ecology Seminar |
L3 |
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Fri, 30/04/2010 14:15 |
Romuald Elie (Dauphine) |
Nomura Seminar |
DH 1st floor SR |
| Hamadène and Jeanblanc provided a BSDE representation for the resolution of bi-dimensional continuous time optimal switching problems. For example, an energy producer faces the possibility to switch on or off a power plant depending on the current price of electricity and corresponding comodity. A BSDE representation via multidimensional reflected BSDEs for this type of problems in dimension larger than 2 has been derived by Hu and Tang as well as Hamadène and Zhang [2]. Keeping the same example in mind, one can imagine that the energy producer can use different electricity modes of production, and switch between them depending on the commodity prices. We propose here an alternative BSDE representation via the addition of constraints and artificial jumps. This allows in particular to reinterpret the solution of multidimensional reflected BSDEs in terms of one-dimensional constrained BSDEs with jumps. We provide and study numerical schemes for the approximation of these two type of BSDEs | |||
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Mon, 03/05/2010 14:15 |
Christian Pauly (Montpellier) |
Geometry and Analysis Seminar |
L3 |
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Mon, 03/05/2010 17:00 |
Aaron N. K. Yip (Purdue) |
Partial Differential Equations Seminar |
Gibson 1st Floor SR |
| We investigate a dynamic model of two dimensional crystal growth described by a forward-backward parabolic equation. The ill-posed region of the equation describes the motion of corners on the surface. We analyze a fourth order regularized version of this equation and show that the dynamical behavior of the regularized corner can be described by a traveling wave solution. The speed of the wave is found by rigorous asymptotic analysis. The interaction between multiple corners will also be presented together with numerical simulations. This is joint work in progress with Fang Wan. | |||
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Tue, 04/05/2010 12:00 |
Chris Heunen (Comlab) |
Quantum Field Theory Seminar |
L3 |
| Topology can be generalised in at least two directions: pointless topology, leading ultimately to topos theory, or noncommutative geometry. The former has the advantage that it also carries a logical structure; the latter captures quantum settings, of which the logic is not well understood generally. We discuss a construction making a generalised space in the latter sense into a generalised space in the former sense, i.e. making a noncommutative C*-algebra into a locale. This construction is interesting from a logical point of view, and leads to an adjunction for noncommutative C*-algebras that extends Gelfand duality. | |||
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Tue, 04/05/2010 13:15 |
Guido Klingbeil (Oxford) |
Junior Applied Mathematics Seminar |
DH 1st floor SR |
| Graphics processing units (GPU) are well suited to decrease the computational in- tensity of stochastic simulation of chemical reaction systems. We compare Gillespie’s Direct Method and Gibson-Bruck’s Next Reaction Method on GPUs. The gain of the GPU implementation of these algorithms is approximately 120 times faster than on a CPU. Furthermore our implementation is integrated into the Systems Biology Toolbox for Matlab and acts as a direct replacement of its Matlab based implementation. | |||
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Tue, 04/05/2010 14:00 |
Maxim Kontsevich (IHES) |
Algebraic and Symplectic Geometry Seminar |
L2 |
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Tue, 04/05/2010 14:30 |
Leslie Goldberg (University of Liverpool) |
Combinatorial Theory Seminar |
L3 |
| This talk considers the problem of sampling an independent set uniformly at random from a bipartite graph (equivalently, the problem of approximately counting independent sets in a bipartite graph). I will start by discussing some natural Markov chain approaches to this problem, and show why these lead to slow convergence. It turns out that the problem is interesting in terms of computational complexity – in fact, it turns out to be equivalent to a large number of other problems, for example, approximating the partition function of the “ferromagnetic Ising model’’ (a 2-state particle model from statistical physics) in the presence of external fields (which are essentially vertex weights). These problems are all complete with respect to approximation-preserving reductions for a logically-defined complexity class, which means that if they can be approximated efficiently, so can the entire class. In recent work, we show some connections between this class of problems and the problem of approximating the partition function of the “ferromagnetic Potts model’’ which is a generalisation of the Ising model—our result holds for q>2 spins. (This corresponds to the approximation problem for the Tutte polynomial in the upper quadrant above the hyperbola q=2.) That result was presented in detail at a recent talk given by Mark Jerrum at Oxford’s one-day meeting in combinatorics. So I will just give a brief description (telling you what the Potts model is and what the result is) and then conclude with some more recently discovered connections to counting graph homomorphisms and approximating the cycle index polynomial. | |||
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Tue, 04/05/2010 15:45 |
Maxim Kontsevich (IHES) |
Algebraic and Symplectic Geometry Seminar |
L3 |
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Tue, 04/05/2010 16:00 |
Anne Thomas (Oxford) |
Junior Geometric Group Theory Seminar |
SR1 |
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Tue, 04/05/2010 16:30 |
Balázs Ráth (Budapest) |
Combinatorial Theory Seminar |
SR2 |
| We define the edge reconnecting model, a random multigraph evolving in time. At each time step we change one endpoint of a uniformly chosen edge: the new endpoint is chosen by linear preferential attachment. We consider a sequence of edge reconnecting models where the sequence of initial multigraphs is convergent in a sense which is a natural generalization of the Lovász-Szegedy notion of convergence of dense graph sequences. We investigate how the limit objects evolve under the edge reconnecting dynamics if we rescale time properly: we give the complete characterization of the time evolution of the limiting object from its initial state up to the stationary state using the theory of exchangeable arrays, the Pólya urn model, queuing and diffusion processes. The number of parallel edges and the degrees evolve on different timescales and because of this the model exhibits “aging”. | |||
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Wed, 05/05/2010 10:10 |
Xanthippi Markenscoff |
OCCAM Wednesday Morning Event |
OCCAM Common Room (RI2.28) |
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Wed, 05/05/2010 11:30 |
Plamen Kochloukov (Universidade Estadual de Campinas) |
Algebra Kinderseminar |
ChCh, Tom Gate, Room 2 |
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Wed, 05/05/2010 16:00 |
Dona Strauss (Hull) |
Analytic Topology in Mathematics and Computer Science |
L3 |
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Wed, 05/05/2010 17:00 |
Jackie Stedall (Oxford) |
Special Lecture |
L2 |
| What do historians of mathematics do? What sort of questions do they ask? What kinds of sources do they use? This series of four informal lectures will demonstrate some of the research on history of mathematics currently being done in Oxford. The subjects range from the late Renaissance mathematician Thomas Harriot (who studied at Oriel in 1577) to the varied and rapidly developing mathematics of the seventeenth century (as seen through the eyes of Savilian Professor John Wallis, and others) to the emergence of a new kind of algebra in Paris around 1830 in the work of the twenty-year old Évariste Galois. Each lecture will last about 40 minutes, leaving time for questions and discussion. No previous knowledge is required: the lectures are open to anyone from the department or elsewhere, from undergraduates upwards. | |||
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Thu, 06/05/2010 11:00 |
Jochen Koenigsmann (Oxford) |
Advanced Logic Class |
SR1 |
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Thu, 06/05/2010 12:00 |
Markus Roeser (Oxford) |
Junior Geometry and Topology Seminar |
SR1 |
| A Hyperkähler manifold is a riemannian manifold carrying three complex structures which behave like quaternions such that the metric is Kähler with respect to each of them. This means in particular that the manifold is a symplectic manifold in many different ways. In analogy to the Marsden-Weinstein reduction on a symplectic manifold, there is also a quotient construction for group actions that preserve the Hyperkähler structure and admit a moment map. In fact most known (non-compact) examples of hyperkähler manifolds arise in this way from an appropriate group action on a quaternionic vector space. In the first half of the talk I will give the definition of a hyperkähler manifold and explain the hyperkähler quotient construction. As an important application I will discuss the moduli space of solutions to the gauge-theoretic "Self-duality equations on a Riemann surface", the space of Higgs bundles, and explain how it can be viewed as a hyperkähler quotient in an infinite-dimensional setting. | |||
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Thu, 06/05/2010 14:00 |
Prof Roland Herzog (Chemnitz University of Technology) |
Computational Mathematics and Applications |
3WS SR |
| We consider saddle point problems arising as (linearized) optimality conditions in elliptic optimal control problems. The efficient solution of such systems is a core ingredient in second-order optimization algorithms. In the spirit of Bramble and Pasciak, the preconditioned systems are symmetric and positive definite with respect to a suitable scalar product. We extend previous work by Schoeberl and Zulehner and consider problems with control and state constraints. It stands out as a particular feature of this approach that an appropriate symmetric indefinite preconditioner can be constructed from standard preconditioners for those matrices which represent the inner products, such as multigrid cycles. Numerical examples in 2D and 3D are given which illustrate the performance of the method, and limitations and open questions are addressed. | |||
