Forthcoming Seminars

Tue, 23/02/2010
14:30 		Lowell Beineke (Purdue) Combinatorial Theory Seminar Add to calendar L3
Line Graphs and Beyond
The line graph operation, in which the edges of one graph are taken as the vertices of a new graph with adjacency preserved, is arguably the most interesting of graph transformations. In this survey, we will begin looking at characterisations of line graphs, focusing first on results related to our set of nine forbidden subgraphs. This will be followed by a discussion of some generalisations of line graphs, including our investigations into the Krausz dimension of a graph G, defined as the minimum, over all partitions of the edge-set of G into complete subgraphs, of the maximum number of subgraphs containing any vertex (the maximum in Krausz's characterisation of line graphs being 2).
Tue, 23/02/2010
15:45 		Kentaro Nagao (Oxford and Kyoto) Algebraic and Symplectic Geometry Seminar Add to calendar L3
(HoRSe seminar) Cluster category and applications
I will introduce the theory of cluster categories after Amiot and Plamondon. For a quiver with a potential, the cluster category is defined as the quotient of the category of perfect dg-modules by the category of dg-modules with finite dimensional cohomologies. We can show the existence of the equivalence in the first talk as an application of the cluster category. I will also propose a definition of a counting invariant for each element in the cluster category.
Tue, 23/02/2010
16:00 		David Hume (Oxford) Junior Geometric Group Theory Seminar Add to calendar SR1
Asymptotic cones
Tue, 23/02/2010
17:00 		Pierre-Emmanuel Caprace (Universite catholique de louvain) Algebra Seminar Add to calendar L2
Commensurators of profinite wreath branch groups
Tue, 23/02/2010
17:00 		John McCarthy (Washington Univ St Louis and Trinity College Dublin) Functional Analysis Seminar Add to calendar L3
Monotone Matrix functions in several variables
In 1934, K. Loewner characterized functions that preserve matrix inequalities, i.e. those f with the property that whenever A and B are self-adjoint matrices of the same dimension, with $ A \leq B $, then $ f(A) \leq f(B) $. In this talk, I shall discuss how to characterize monotone matrix functions of several variables, namely functions f with the property that if $ A = (A_1, \dots , A_n) $ is an n-tuple of commuting self-adjoint matrices, and $ B = (B_1, \dots, B_n) $ is another, with each $ A_i \leq B_i $, then $ f(A) \leq f(B) $.
Wed, 24/02/2010
10:10 		Rama Bhargava (IIT Roorkee) OCCAM Wednesday Morning Event Add to calendar OCCAM Common Room (RI2.28)
Can we sustain without Computational mathematics!!!!
Wed, 24/02/2010
11:30 		Jason Semeraro (University of Oxford) Algebra Kinderseminar Add to calendar ChCh, Tom Gate, Room 2
Topics in Fusion Systems
Thu, 25/02/2010
12:00 		Jessica Banks (Oxford) Junior Geometry and Topology Seminar Add to calendar SR1
Knots, graphs, and the Alexander polynomial
In 2008, Juhasz published the following result, which was proved using sutured Floer homology. Let $ K $ be a prime, alternating knot. Let $ a $ be the leading coefficient of the Alexander polynomial of $ K $. If $ |a|<4 $, then $ K $ has a unique minimal genus Seifert surface. We present a new, more direct, proof of this result that works by counting trees in digraphs with certain properties. We also give a finiteness result for these digraphs.
Thu, 25/02/2010
14:00 		Prof. Ekkehard Sachs (University of Trier) Computational Mathematics and Applications Add to calendar 3WS SR
Numerical Aspects of Optimization in Finance
There is a widespread use of mathematical tools in finance and its importance has grown over the last two decades. In this talk we concentrate on optimization problems in finance, in particular on numerical aspects. In this talk, we put emphasis on the mathematical problems and aspects, whereas all the applications are connected to the pricing of derivatives and are the outcome of a cooperation with an international finance institution. As one example, we take an in-depth look at the problem of hedging barrier options. We review approaches from the literature and illustrate advantages and shortcomings. Then we rephrase the problem as an optimization problem and point out that it leads to a semi-infinite programming problem. We give numerical results and put them in relation to known results from other approaches. As an extension, we consider the robustness of this approach, since it is known that the optimality is lost, if the market data change too much. To avoid this effect, one can formulate a robust version of the hedging problem, again by the use of semi-infinite programming. The numerical results presented illustrate the robustness of this approach and its advantages. As a further aspect, we address the calibration of models being used in finance through optimization. This may lead to PDE-constrained optimization problems and their solution through SQP-type or interior-point methods. An important issue in this context are preconditioning techniques, like preconditioning of KKT systems, a very active research area. Another aspect is the preconditioning aspect through the use of implicit volatilities. We also take a look at the numerical effects of non-smooth data for certain models in derivative pricing. Finally, we discuss how to speed up the optimization for calibration problems by using reduced order models.
Thu, 25/02/2010
14:30 		Anne Henke (Oxford) Representation Theory Seminar Add to calendar L3
Schur algebras of Brauer algebras
Thu, 25/02/2010
16:00 		Olivier Wittenberg (Paris) Number Theory Seminar Add to calendar L3
Sums of three cubes and the Brauer-Manin obstruction.
Thu, 25/02/2010
16:30 		Sam Howison (Oxford) Differential Equations and Applications Seminar Add to calendar DH 1st floor SR
Games with exhaustible resources
Thu, 25/02/2010
17:00 		Jonathan Pila (Bristol and Oxford) Logic Seminar Add to calendar L3
A Very Special Case of the Zilber-Pink Conjecture
Fri, 26/02/2010
10:00 		Jorn Dunkel (Physics, Oxford) Industrial and Interdisciplinary Workshops Add to calendar DH 1st floor SR
Microscopic and macroscopic modeling of active suspensions
Micron-sized bacteria or algae operate at very small Reynolds numbers. In this regime, inertial effects are negligible and, hence, efficient swimming strategies have to be different from those employed by fish or bigger animals. Mathematically, this means that, in order to achieve locomotion, the swimming stroke of a microorganism must break the time-reversal symmetry of the Stokes equations. Large ensembles of bacteria or algae can exhibit rich collective dynamics (e.g., complex turbulent patterns, such as vortices or spirals), resulting from a combination of physical and chemical interactions. The spatial extent of these structures typically exceeds the size of a single organism by several orders of magnitude. One of our current projects in the Soft and Biological Matter Group aims at understanding how the collective macroscopic behavior of swimming microorganisms is related to their microscopic properties. I am going to outline theoretical and computational approaches, and would like to discuss technical challenges that arise when one tries to derive continuum equations for these systems from microscopic or mesoscopic models.
Fri, 26/02/2010
11:45 		Heike Gramberg and Robert Whittaker Industrial and Interdisciplinary Workshops Add to calendar DH 1st floor SR
OCIAM internal seminar
Heike Gramberg - Flagellar beating in trypanosomes Robert Whittaker - High-Frequency Self-Excited Oscillations in 3D Collapsible Tube Flows
Fri, 26/02/2010
12:00 		Andrew Hodges (Oxford) Twistor Workshop Add to calendar Gibson 1st Floor SR
Twistor geometry of box functions II
Fri, 26/02/2010
14:30 		Dr Thibaut Putelat (Cambridge ITG) Mathematical Geoscience Seminar Add to calendar DH 3rd floor SR
To Be Announced
TBA
Fri, 26/02/2010
16:30 		Professor Pierre Cartier (IHES) (IHES) Colloquia Add to calendar L2
Algebraic Geometry and Feynman Amplitudes
We shall report on the use of algebraic geometry for the calculation of Feynman amplitudes (work of Bloch, Brown, Esnault and Kreimer). Or how to combine Grothendieck's motives with high energy physics in an unexpected way, radically distinct from string theory.

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

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