Forthcoming Seminars
|
Mon, 30/01/2012 17:00 |
Kewei Zhang (Swansea University) |
Partial Differential Equations Seminar  |
Gibson 1st Floor SR |
| In the first part, a variational model for composition of finitely many strongly elliptic homogenous elastic materials in linear elasticity is considered. The notion of`universal coercivity' for the variational integrals is introduced which is independent of particular compositions of materials involved. Examples and counterexamples for universal coercivity are presented. In the second part, some results of recent work with colleagues on image processing and feature extraction will be displayed. | |||
|
Tue, 31/01/2012 11:00 |
Dr Wonjung Lee (OCCAM) |
Applied Dynamical Systems and Inverse Problems Seminar |
DH 3rd floor SR |
| In this talk we aim to filter the Majda-McLaughlin-Tabak(MMT) model, which is a one-dimensional prototypical turbulence system. Due to its inherent high dimensionality, we first try to find a low dimensional dynamical system whose statistical property is similar to the original complexity system. This dimensional reduction, called stochastic parametrization, is clearly well-known method but the value of current work lies in the derivation of an analytic closure for the parameters. We then discuss the necessity of the accurate filtering algorithm for this effective dynamics, and introduce the particle filter using the cubature on Wiener space and the recombination skill. | |||
|
Tue, 31/01/2012 12:00 |
Malcolm Fairbairn (KCL) |
Quantum Field Theory Seminar |
L3 |
| We still don't know what dark matter is but a class of leading candidates are weakly interacting massive particles or WIMPs. These WIMP models are falsifiable, which is why we like them. However, the epoch of their falsifiability is upon us and a slew of data from different directions is placing models for WIMPs under pressure. I will try and present an updated overview of the different pieces of evidence, false (?) alarms and controversies that are making this such an active area of research at the moment. | |||
|
Tue, 31/01/2012 14:15 |
Prof. Victor Shrira (Keele University)) |
Geophysical and Nonlinear Fluid Dynamics Seminar |
Dobson Room, AOPP |
|
Tue, 31/01/2012 14:30 |
Lutz Warnke |
Combinatorial Theory Seminar |
L3 |
| In Achlioptas processes, starting from an empty graph, in each step two potential edges are chosen uniformly at random, and using some rule one of them is selected and added to the evolving graph. Although the evolution of such `local' modifications of the Erdös-Rényi random graph processes has received considerable attention during the last decade, so far only rather `simple' rules are well-understood. Indeed, the main focus has been on bounded size rules (where all component sizes larger than some constant B are treated the same way), and for more complex rules hardly any rigorous results are known. In this talk we will discuss a new approach that applies to many involved Achlioptas processes: it allows us to prove that certain key statistics are tightly concentrated during the early evolution of e.g. the sum and product rule. Joint work with Oliver Riordan. | |||
|
Tue, 31/01/2012 15:45 |
Andre Henriques (Utrecht) |
Algebraic and Symplectic Geometry Seminar |
L3 |
| There is a beautiful classification of full (rational) CFT due to Fuchs, Runkel and Schweigert. The classification says roughly the following. Fix a chiral algebra A (= vertex algebra). Then the set of full CFT whose left and right chiral algebras agree with A is classified by Frobenius algebras internal to Rep(A). A famous example to which one can successfully apply this is the case when the chiral algebra A is affine su(2): in that case, the Frobenius algebras in Rep(A) are classified by A_n, D_n, E_6, E_7, E_8, and so are the corresponding CFTs. Recently, Kapustin and Saulina gave a conceptual interpretation of the FRS classification in terms of 3-dimentional Chern-Simons theory with defects. Those defects are also given by Frobenius algebras in Rep(A). Inspired by the proposal of Kapustin and Saulina, we will (partially) construct the three-tier CFT associated to a given Frobenius algebra. | |||
|
Tue, 31/01/2012 17:00 |
Charles Batty (Oxford) |
Functional Analysis Seminar |
L3 |
|
Tue, 31/01/2012 17:00 |
Professor Martin Bridson (Oxford) |
Algebra Seminar |
L2 |
| In this talk I'll describe recent work with Henry Wilton (UCL) in which we prove that there does not exist an algorithm that can determine which finitely presented groups have a non-trivial finite quotient. | |||
|
Wed, 01/02/2012 14:00 |
Hilary Priestley (Oxford) |
Analytic Topology in Mathematics and Computer Science |
DH 1st floor SR |
|
Wed, 01/02/2012 16:00 |
Ramon Jansana (Barcelona) |
Analytic Topology in Mathematics and Computer Science |
L3 |
|
I will first present Priestley style topological dualities for |
|||
|
Wed, 01/02/2012 16:00 |
Chris Cashen |
Junior Geometric Group Theory Seminar |
SR2 |
|
Thu, 02/02/2012 12:30 |
Laura Caravenna (OxPDE, University of Oxford) |
OxPDE Lunchtime Seminar |
Gibson 1st Floor SR |
| In the talk I will mention two regularity results: the SBV regularity for strictly hyperbolic, genuinely nonlinear 1D systems of conservation laws and the characterization of intrinsic Lipschitz codimension 1 graphs in the Heisenberg groups. In both the contexts suitable scalar, 1D balance laws arise with very low regularity. I will in particular highlight the role of characteristics. This seminar will be based on joint works with G. Alberti, S. Bianchini, F. Bigolin and F. Serra Cassano, and the main previous literature. | |||
|
Thu, 02/02/2012 13:00 |
Sam Cohen |
Mathematical Finance Internal Seminar |
DH 1st floor SR |
| Decision making in the presence of uncertainty is a mathematically delicate topic. In this talk, we consider coherent sublinear expectations on a measurable space, without assuming the existence of a dominating probability measure. By considering discrete-time `martingale' processes, we show that the classical results of martingale convergence and the up/downcrossing inqualities hold in a `quasi-sure' sense. We also give conditions, for a general filtration, under which an `aggregation' property holds, generalising an approach of Soner, Touzi and Zhang (2011). From this, we extend various results on the representation of conditional sublinear expectations to general filtrations under uncertainty. | |||
|
Thu, 02/02/2012 13:00 |
Chris Hopper |
Junior Geometry and Topology Seminar |
SR2 |
| I will give an introduction to the variational characterisation of the Ricci flow that was first introduced by G. Perelman in his paper on "The entropy formula for the Ricci flow and its geometric applications" http://arxiv.org/abs/math.DG/0211159. The first in a series of three papers on the geometrisation conjecture. The discussion will be restricted to sections 1 through 5 beginning first with the gradient flow formalism. Techniques from the Calculus of Variations will be emphasised, notably in proving the monotonicity of particular functionals. An overview of the local noncollapsing theorem (Perelman’s first breakthrough result) will be presented with refinements from Topping [Comm. Anal. Geom. 13 (2005), no. 5, 1039–1055.]. Some remarks will also be made on connections to implicit structures seen in the physics literature, for instance of those seen in D. Friedan [Ann. Physics 163 (1985), no. 2, 318–419]. | |||
|
Thu, 02/02/2012 14:00 |
Dr Coralia Cartis (University of Edinburgh) |
Computational Mathematics and Applications |
Gibson Grd floor SR |
| We show that the steepest-descent and Newton's methods for unconstrained nonconvex optimization under standard assumptions may both require a number of iterations and function evaluations arbitrarily close to the steepest-descent's global worst-case complexity bound. This implies that the latter upper bound is essentially tight for steepest descent and that Newton's method may be as slow as the steepest-descent method in the worst case. Then the cubic regularization of Newton's method (Griewank (1981), Nesterov & Polyak (2006)) is considered and extended to large-scale problems, while preserving the same order of its improved worst-case complexity (by comparison to that of steepest-descent); this improved worst-case bound is also shown to be tight. We further show that the cubic regularization approach is, in fact, optimal from a worst-case complexity point of view amongst a wide class of second-order methods. The worst-case problem-evaluation complexity of constrained optimization will also be discussed. This is joint work with Nick Gould (Rutherford Appleton Laboratory, UK) and Philippe Toint (University of Namur, Belgium). | |||
|
Thu, 02/02/2012 16:00 |
Eugene Benilov (Limerick) |
Industrial and Applied Mathematics Seminar |
DH 1st floor SR |
| This work builds on the foundation laid by Benney & Timson (1980), who examined the flow near a contact line and showed that, if the contact angle is 180 degrees, the usual contact-line singularity does not arise. Their local analysis, however, does not allow one to determine the velocity of the contact line and their expression for the shape of the free boundary involves undetermined constants - for which they have been severely criticised by Ngan & Dussan V. (1984). As a result, the ideas of Benny & Timson (1980) have been largely forgotten. The present work shows that the criticism of Ngan & Dussan V. (1984) was, in fact, unjust. We consider a two-dimensional steady Couette flow with a free boundary, for which the local analysis of Benney & Timson (1980) can be complemented by an analysis of the global flow (provided the slope of the free boundary is small, so the lubrication approximation can be used). We show that the undetermined constants in the solution of Benney & Timson (1980) can all be fixed by matching their local solution to the global one. The latter also determines the contact line's velocity, which we compute among other characteristics of the global flow. | |||
|
Thu, 02/02/2012 17:00 |
Alessandro Berarducci (Pisa) |
Logic Seminar |
L3 |
|
Fri, 03/02/2012 10:30 |
Samson Abramsky (Oxford) |
Quantum Mathematics and Computation |
Comlab |
|
The seminar will take place in Lecture Theatre A, Department of Computer Science. ------------------- Contextuality and non-locality are features of quantum mechanics which stand in sharp contrast to the realistic picture underlying classical physics. We shall describe a unified geometric perspective on these notions in terms of *obstructions to the existence of global sections*. This allows general results and structural notions to be uncovered, with quantum mechanics appearing as a special case. The natural language to use here is that of sheaves and presheaves; and cohomological obstructions can be defined which witness contextuality in a number of salient examples. |
|||
|
Fri, 03/02/2012 14:00 |
Prof Bleddyn Jones (Gray Institute for Radiation Oncology & Biology University of Oxford) |
Mathematical Biology and Ecology Seminar |
L1 |
|
Fri, 03/02/2012 14:15 |
Stefan Gerold (TU Wien) |
Nomura Seminar |
DH 1st floor SR |
| In a market with one safe and one risky asset, an investor with a long horizon and constant relative risk aversion trades with constant investment opportunities and proportional transaction costs. We derive the optimal investment policy, its welfare, and the resulting trading volume, explicitly as functions of the market and preference parameters, and of the implied liquidity premium, which is identified as the solution of a scalar equation. For small transaction costs, all these quantities admit asymptotic expansions of arbitrary order. The results exploit the equivalence of the transaction cost market to another frictionless market, with a shadow risky asset, in which investment opportunities are stochastic. The shadow price is also derived explicitly. (Joint work with Paolo Guasoni, Johannes Muhle-Karbe, and Walter Schachermayer) | |||
