Forthcoming Seminars

Tue, 08/11/2011
10:00 		Dmytro Arinkin (University of North Carolina & IAS Princeton) Special Lecture Add to calendar L3
Autoduality of Jacobians for singular curves I
Tue, 08/11/2011
12:00 		Dr Valiente-Kroon (Queen Mary) Relativity Seminar Add to calendar L3
Approximate twistors and positive mass
Tue, 08/11/2011
14:15 		Dr Chris Farmer (University of Oxford) Geophysical and Nonlinear Fluid Dynamics Seminar Add to calendar Dobson Room, AOPP
Bayesian parameter estimation in high dimensional systems
Tue, 08/11/2011
14:30 		Diana Piguet (Birmingham) Combinatorial Theory Seminar Add to calendar L3
Embedding trees in sparse graphs
An embedding of a graph H in a graph G is an injective mapping of the vertices of H to the vertices of G such that edges of H are mapped to edges of G. Embedding problems have been extensively studied. A very powerful tool in this area is Szemeredi's Regularity Temma. It approximates the host graph G by a quasirandom graph which inherits many of the properties of G. Unfortunately the direct use of Szemeredi's Regularity Lemma is useless if the host graph G is sparse. During the talk I shall expose a technique to deal with embedding trees in sparse graphs. This technique has been developed by Ajtai, Komlos,Simonovits and Szemeredi to solve the Erdos-Sos conjecture. Presently the author together with Hladky, Komlos, Simonovits, Stein and Szemeredi apply this method to solve the related conjecture of Loebl, Komlos and Sos (approximate version).
Tue, 08/11/2011
15:00 		John Mackay Advanced Class in Algebra Add to calendar SR2
Bass Serre Theory
Tue, 08/11/2011
15:45 		Vittoria Bussi (Oxford) Algebraic and Symplectic Geometry Seminar Add to calendar L3
Donaldson-Thomas theory: generalizations and related conjectures
Generalized Donaldson-Thomas invariants $ \bar{DT}^\alpha(\tau) $ defined by Joyce and Song are rational numbers which 'count' both $ \tau $-stable and $ \tau $-semistable coherent sheaves with Chern character $ \alpha $ on a Calabi-Yau 3-fold X, where $ \tau $ denotes Gieseker stability for some ample line bundle on X. The theory of Joyce and Song is valid only over the field $ \mathbb C $. We will extend it to algebraically closed fields $ \mathbb K $ of characteristic zero. We will describe the local structure of the moduli stack $ \mathfrak M $ of coherent sheaves on X, showing that an atlas for $ \mathfrak M $ may be written locally as the zero locus of an almost closed 1-form on an étale open subset of the tangent space of $ \mathfrak M $ at a point, and use this to deduce identities on the Behrend function $ \nu_{\mathfrak M} $ of $ \mathfrak M $. This also yields an extension of generalized Donaldson-Thomas theory to noncompact Calabi-Yau 3-folds. Finally, we will investigate how our argument might yield generalizations of the theory to a even wider context, for example the derived framework using Toen's theory and to motivic Donaldson-Thomas theory in the style of Kontsevich and Soibelman.
Tue, 08/11/2011
17:00 		Dr Justin McInroy (Oxford) Algebra Seminar Add to calendar L2
"Biaffine geometries, amalgams and group recognition"
A polar space $ \Pi $ is a geometry whose elements are the totally isotropic subspaces of a vector space $ V $ with respect to either an alternating, Hermitian, or quadratic form. We may form a new geometry $ \Gamma $ by removing all elements contained in either a hyperplane $ F $ of $ \Pi $, or a hyperplane $ H $ of the dual $ \Pi^* $. This is a biaffine polar space. We will discuss two specific examples, one with automorphism group $ q^6:SU_3(q) $ and the other $ G_2(q) $. By considering the stabilisers of a maximal flag, we get an amalgam, or "glueing", of groups for each example. However, the two examples have "similar" amalgams - this leads to a group recognition result for their automorphism groups.
Wed, 09/11/2011
10:15 		Simon Tavener (Colorado State University) OCCAM Wednesday Morning Event Add to calendar OCCAM Common Room (RI2.28)
A posteriori error analysis for a cut-cell finite-volume method

Diffusive process with discontinuous coefficients provide significant computational challenges. We consider the solution of a diffusive process in a domain where the diffusion coefficient changes discontinuously across a curved interface. Rather than seeking to construct discretizations that match the interface, we consider the use of regularly-shaped meshes so that the interface "cuts'' through the cells (elements or volumes). Consequently, the discontinuity in the diffusion coefficients has a strong impact on the accuracy and convergence of the numerical method. We develop an adjoint based a posteriori error analysis technique to estimate the error in a given quantity of interest (functional of the solution). In order to employ this method, we first construct a systematic approach to discretizing a cut-cell problem that handles complex geometry in the interface in a natural fashion yet reduces to the well-known Ghost Fluid Method in simple cases. We test the accuracy of the estimates in a series of examples.
Wed, 09/11/2011
11:30 		David Hume Algebra Kinderseminar Add to calendar
Mathematical models of composition (St Hugh's, 80WR18)
We explore methods (deterministic and otherwise) of composing music using mathematical models. Musical examples will be provided throughout and the audience (with the speakers assistance) will compose a brand new piece.
Wed, 09/11/2011
16:00 		István Juhász (Renyi Institute, Budapest) Analytic Topology in Mathematics and Computer Science Add to calendar L3
Resolvability of topological spaces
Thu, 10/11/2011
11:00 		Adam Harris (Oxford) Advanced Class Logic Add to calendar SR2
"On the model theory of j-invariant" (continued)
Thu, 10/11/2011
12:00 		Tim Adamo Junior Geometry and Topology Seminar Add to calendar SR2
Holomorphic analogues of Chern-Simons gauge theory and Wilson operators
Chern-Simons theory is topological gauge theory in three dimensions that contains an interesting class of operators called Wilson lines/loops, which have connections with both physics and pure mathematics. In particular, it has been shown that computations with Wilson operators in Chern-Simons theory reproduce knot invariants, and are also related to Gauss linking invariants. We will discuss the complex generalizations of these ideas, which are known as holomorphic Chern-Simons theory, Wilson operators, and linking, in the setting of Calabi-Yau three-folds. This will (hopefully) include a definition of all three of these holomorphic analogues as well as an investigation into how these ideas can be translated into simple homological algebra, allowing us to propose the existence of "homological Feynman rules" for computing things like Wilson operators in a holomorphic Chern-Simons theory. If time permits I may say something about physics too.
Thu, 10/11/2011
13:00 		Hanqing Jin Mathematical Finance Internal Seminar Add to calendar DH 1st floor SR
Equilibrium of Time-Inconsistent Stochastic Linear–Quadratic Control
In this work, we study equilibrium solutions for a LQ control problem with state-dependent terms in the objective, which destroy the time-consisitence of a pre-commited optimal solution. We get a sufficient condition for equilibrium by a system of stochastic differential equations. When the coefficients in the problem are all deterministic, we find an explicit equilibrium for general LQ control problem. For the mean-variance portfolio selection in a complete financial market, we also get an explicit equilibrium with random coefficient of the financial.
Thu, 10/11/2011
14:00 		Dr Shahrokh Shahpar (Rolls Royce plc.) Computational Mathematics and Applications Add to calendar Gibson Grd floor SR
SOPHY: An Automated, Aerothermal Design and Optimisation System for Aero-Engine Components
Computational Fluid Dynamics (CFD) has become an indispensable tool in designing turbomachinery components in all sectors of Rolls-Royce business units namely, Aerospace, Industrial, Marine and Nuclear. Increasingly sophisticated search and optimisation techniques are used based on both traditional optimisation methods as well as, design of computer experiment techniques, advanced surrogate methods, and evolutionary optimisation techniques. Geometry and data representation as well as access, queuing and loading control of large high performance computing clusters are areas of research to establish the most efficient techniques for improving the performance of an already highly efficient modern jet engine.

This presentation focuses on a high fidelity design optimisation framework called SOPHY that is used in Rolls-Royce to provide parametric geometry, automatic meshing, advanced design-space search algorithms, accurate and robust CFD methodology and post-processing. The significance of including the so-called real geometry features and interaction of turbomachinery components in the optimisation cycle are discussed. Examples are drawn from real world applications of the SOPHY design systems in an engine project.
Thu, 10/11/2011
16:00 		Andrei Yafaev (UCL) Logic Seminar Add to calendar
Number Theory Seminar Add to calendar 		L3
A hyperbolic Ax-Lindemann theorem in the cocompact case
This is a joint work with Emmanuel Ullmo. This work is motivated by J.Pila's strategy to prove the Andre-Oort conjecture. One ingredient in the strategy is the following conjecture: Let S be a Shimura variety uniformised by a symmetric space X. Let V be an algebraic subvariety of S. Maximal algebraic subvarieties of the preimage of V in X are precisely the components of the preimages of weakly special subvarieties contained in V. We will explain the proof of this conjecture in the case where S is compact.
Thu, 10/11/2011
16:00 		Davide Ambrosi (Dipartimento di Matematica of the Politecnico di Milano) Industrial and Applied Mathematics Seminar Add to calendar DH 1st floor SR
Mathematical issues in modelling the contractility of the cardiac muscle

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

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