Forthcoming Seminars

Wed, 25/01/2012
16:00 		Andrew Sale Junior Geometric Group Theory Seminar Add to calendar SR2
Horocyclic Products, the Geometry of Some Metabelian Groups and Short Conjugators
The lamplighter groups, solvable Baumslag-Solitar groups and lattices in SOL all share a nice kind of geometry. We'll see how the Cayley graph of a lamplighter group is a Diestel-Leader graph, that is a horocyclic product of two trees. The geometry of the solvable Baumslag-Solitar groups has been studied by Farb and Mosher and they showed that these groups are quasi-isometric to spaces which are essentially the horocyclic product of a tree and the hyperbolic plane. Finally, lattices in the Lie groups SOL can be seen to act on the horocyclic product of two hyperbolic planes. We use these spaces to measure the length of short conjugators in each type of group.
Thu, 26/01/2012
12:30 		Veronique Fischer (University of Padova and guest at King's College London) OxPDE Lunchtime Seminar Add to calendar Gibson 1st Floor SR
Global quantisation of pseudo-differential operators on Lie groups
Pseudo-differential operators (PDO's) are primarily defined in the familiar setting of the Euclidean space. For four decades, they have been standard tools in the study of PDE's and it is natural to attempt defining PDO's in other settings. In this talk, after discussing the concept of PDO's on the Euclidean space and on the torus, I will present some recent results and outline future work regarding PDO's on Lie groups as well as some of the applications to PDE's
Thu, 26/01/2012
13:00 		Christoph Reisinger Mathematical Finance Internal Seminar Add to calendar DH 1st floor SR
Some recent findings in the computation of American option prices
In this seminar, we discuss three questions related to the finite difference computation of early exercise options, one of which has a useful answer, one an interesting one, and one is open. We begin by showing that a simple iteration of the exercise strategy of a finite difference solution is efficient for practical applications and its convergence can be described very precisely. It is somewhat surprising that the method is largely unknown. We move on to discuss properties of a so-called penalty method. Here we show by means of numerical experiments and matched asymptotic expansions that the approximation of the value function has a very intricate local structure, which is lost in functional analytic error estimates, which are also derived. Finally, we describe a gap in the analysis of the grid convergence of finite difference approximations compared to empirical evidence. This is joint work with Jan Witte and Sam Howison.
Thu, 26/01/2012
13:00 		Jakob Blaavand Junior Geometry and Topology Seminar Add to calendar SR2
Geometric Quantization - an Introduction
In this talk we will discuss geometric quantization. First of all we will discuss what it is, but shall also see that it has relations to many other parts of mathematics. Especially shall we see how the Hitchin connection in geometric quantization can give us representations of a certain group associated to a surface, the mapping class group. If time permits we will discuss some recent results about these groups and their representations, results that are essentially obtained from geometrically quantizing a moduli space of flat connections on a surface."
Thu, 26/01/2012
14:00 		Dr Andreas Grothey (University of Edinburgh) Computational Mathematics and Applications Add to calendar Gibson Grd floor SR
Interior Point warmstarts and stochastic programming
We present progress on an Interior Point based multi-step solution approach for stochastic programming problems. Our approach works with a series of scenario trees that can be seen as successively more accurate discretizations of an underlying probability distribution and employs IPM warmstarts to "lift" approximate solutions from one tree to the next larger tree.
Thu, 26/01/2012
14:00 		Alexey Sevastyanov (Aberdeen) Representation Theory Seminar Add to calendar L3
De Concini-Kac-Procesi conjecture, Schubert cells and q-W algebras
De Concini-Kac-Procesi conjecture gives a good estimate for the dimensions of finite–dimensional non-restricted representations of quantum groups at m-th root of unity. According to De Concini, Kac and Procesi such representations can be split into families parametrized by conjugacy classes in an algebraic group G, and the dimensions of representations corresponding to a conjugacy class O are divisible by m^{dim O/2}. The talk will consist of two parts. In the first part I shall present an approach to the proof of De Concini-Kac-Procesi conjecture based on the use of q-W algebras and Bruhat decomposition in G. It turns out that properties of representations corresponding to a conjugacy class O depend on the properties of intersection of O with certain Bruhat cells. In the second part, which is more technical, I shall discuss q-W algebras and some related results in detail.
Thu, 26/01/2012
16:00 		Yichao Zhu (Oxford) Industrial and Applied Mathematics Seminar Add to calendar DH 1st floor SR
Modelling the Transition from Channel-Veins to PSBs in the Early Stage of Fatigue Tests
Understanding the fatigue of metals under cyclic loads is crucial for some fields in mechanical engineering, such as the design of wheels of high speed trains and aero-plane engines. Experimentally it has been found that metal fatigue induced by cyclic loads is closely related to a ladder shape pattern of dislocations known as a persistent slip band (PSB). In this talk, a quantitative description for the formation of PSBs is proposed from two angles: 1. the motion of a single dislocation analised by using asymptotic expansions and numerical simulations; 2. the collective behaviour of a large number of dislocations analised by using a method of multiple scales.
Thu, 26/01/2012
16:00 		Yu V Matiyasevich (Steklov Institute of Mathematics) Logic Seminar Add to calendar
Number Theory Seminar Add to calendar 		L3
New conjectures about zeros of Riemann’s zeta function
In http://logic.pdmi.ras.ru/~yumat/personaljournal/artlessmethod/artlessmethod.php the speaker described a surprising method for (approximate) calculation of the zeros of Riemann’s zeta function using terms of the divergent Dirichlet series.In the talk this method will be presented together with some heuristic “hints” explaining why the divergence of the series doesn’t spoil its use. Several conjectures about the zeros of Riemann’s zeta function will be stated including supposed new relationship between them and the prime numbers.
Fri, 27/01/2012
09:00 		Leonardo Cabrer (Bern) Analytic Topology in Mathematics and Computer Science Add to calendar L3
Admissibility and Unification through Natural Duality >

Dualities of various types have been used by different authors to 
describe free and projective objects in a large
  number of classes of algebras. Particularly, natural dualities provide a 
general tool to describe free objects. In
  this talk we present two interesting applications of this fact. 
  We first provide a combinatorial classification of unification problems 
by their unification type for the
varieties of Bounded Distributive Lattices, Kleene algebras, De Morgan 
algebras. Finally we provide axiomatizations forsingle
and multiple conclusion admissible rules for the varieties of Kleene 
algebras, De Morgan algebras, Stone algebras.
Fri, 27/01/2012
10:00 		Vallis, Cornelissen, Able (Oxford) Industrial and Interdisciplinary Workshops Add to calendar DH 1st floor SR
a kinetic–dynamic modeling approach to understand the effect of a new radiotherapeutic agent on DNA damage repair
DNA double strand breaks (DSB) are the most deleterious type of DNA damage induced by ionizing radiation and cytotoxic agents used in the treatment of cancer. When DSBs are formed, the cell attempts to repair the DNA damage through activation of a variety of molecular repair pathways. One of the earliest events in response to the presence of DSBs is the phosphorylation of a histone protein, H2AX, to form γH2AX. Many hundreds of copies of γH2AX form, occupying several mega bases of DNA at the site of each DSB. These large collections of γH2AX can be visualized using a fluorescence microscopy technique and are called ‘γH2AX foci’. γH2AX serves as a scaffold to which other DNA damage repair proteins adhere and so facilitates repair. Following re-ligation of the DNA DSB, the γH2AX is dephosphorylated and the foci disappear. We have developed a contrast agent, 111In-anti-γH2AX-Tat, for nuclear medicine (SPECT) imaging of γH2AX which is based on an anti-γH2AX monoclonal antibody. This agent allows us to image DNA DSB in vitro in cells, and in in vivo model systems of cancer. The ability to track the spatiotemporal distribution of DNA damage in vivo would have many potential clinical applications, including as an early read-out of tumour response or resistance to particular anticancer drugs or radiation therapy. The imaging tracer principle states that a contrast agent should not interfere with the physiology of the process being imaged. Therefore, we have investigated the influence of the contrast agent itself on the kinetics of DSB formation, repair and on γH2AX foci formation and resolution and now wish to synthesise these data into a coherent kinetic-dynamic model.
Fri, 27/01/2012
11:00 		André Henriques (Utrecht) Quantum Mathematics and Computation Add to calendar Comlab
Topological quantum field theories (TQFTs) and the cobordism hypothesis

Introductory talk on topological quantum field theories (TQFTs) and the cobordism hypothesis, focusing on the conceptual issues involved.

The lecture will take place this Friday at 11am in Lecture Theatre A of the Department of Computer Science
Fri, 27/01/2012
14:15 		Jose Blanchet (Columbia) Nomura Seminar Add to calendar DH 1st floor SR
Modeling and Efficient Rare Event Simulation of Systemic Risk in Insurance-Reinsurance Networks (joint work with Yixi Shi).
We propose a dynamic insurance network model that allows to deal with reinsurance counter-party default risks with a particular aim of capturing cascading effects at the time of defaults. We capture these effects by finding an equilibrium allocation of settlements which can be found as the unique optimal solution of a linear programming problem. This equilibrium allocation recognizes 1) the correlation among the risk factors, which are assumed to be heavy-tailed, 2) the contractual obligations, which are assumed to follow popular contracts in the insurance industry (such as stop-loss and retro-cesion), and 3) the interconnections of the insurance-reinsurance network. We are able to obtain an asymptotic description of the most likely ways in which the default of a specific group of insurers can occur, by means of solving a multidimensional Knapsack integer programming problem. Finally, we propose a class of provably strongly efficient estimators for computing the expected loss of the network conditioning the failure of a specific set of companies. Strong efficiency means that the complexity of computing large deviations probability or conditional expectation remains bounded as the event of interest becomes more and more rare.
Fri, 27/01/2012
14:30 		Dr. Amos S. Lawless (University of Reading) Mathematical Geoscience Seminar Add to calendar DH 3rd floor SR
Variable transformations and preconditioning in variational data assimilation
Data assimilation aims to correct a forecast of a physical system, such as the atmosphere or ocean, using observations of that system, in order to provide a best estimate of the current system state. Since it is not possible to observe the whole state it is important to know how errors in different variables of the forecast are related to each other, so that all fields may be corrected consistently. In the first part of this talk we consider how we may impose constraints between different physical variables in data assimilation. We examine how we can use our knowledge of atmospheric physics to pose the assimilation problem in variables that are assumed to be uncorrelated. Using a shallow-water model we demonstrate that this is best achieved by using potential vorticity rather than vorticity to capture the balanced part of the flow. The second part of the talk will consider a further transformation of variables to represent spatial correlations. We show how the accuracy and efficiency with which we can solve the transformed assimilation problem (as measured by the condition number) is affected by the observation distribution and accuracy and by the assumed correlation lengthscales. Theoretical results will be illustrated using the Met Office variational data assimilation scheme.
Mon, 30/01/2012
11:00 		Andre Henriques (Utrecht) Topology Advanced Classes Add to calendar L3
Three-tier CFTs I: Modular invariance and the cobordism hypothesis
The idea of three-tier conformal field theory (CFT) was first proposed by Greame Segal. It is an extension of the functorial approach to CFT, where one replaces the bordism category of Riemann surfaces by a suitable bordism 2-category, whose objects are points, whose morphism are 1-manifolds, and whose 2-morphisms are pieces of Riemann surface. The Baez-Dolan cobordism hypothesis is a meta-mathematical principle. It claims that functorial quantum field theory (i.e. quantum field theory expressed as a functor from some bordism category) becomes simper once "you go all the way down to points", i.e., once you replace the bordism category by a higher category. Three-tier CFT is an example of "going all the way down to points". We will apply the cobordism hypothesis to the case of three-tier CFT, and show how the modular invariance of the partition function can be derived as a consequence of the formalism, even if one only starts with genus-zero data.
Mon, 30/01/2012
12:00 		Jihye Seo (McGill University) String Theory Seminar Add to calendar L3
Singularity structure and massless dyons of pure N = 2, d = 4 theories with SU(r+1) and Sp(2r) gauge groups
We study pure Seiberg-Witten theories with $ SU(r+1) $ and $ Sp(2r) $ gauge groups with no flavors. We study singularity loci of moduli space of the Seiberg-Witten curve. Using exterior derivative and discriminant operators, we can find Argyres-Douglas loci of the SW theory. We also compute BPS charges of the massless dyons of $ SU $ and $ Sp $ SW theory. In a detailed example of $ C_2=Sp(4) $, we find 6 points in the moduli space where we have 2 massless BPS dyons, and 3 of them give Argyres-Douglas loci. We show that BPS charges of the massless dyons jump as we go across Argyres-Douglas loci, giving an explicit example of Argyres-Douglas loci living inside the wall of marginal stability. (Based on work in progress with Keshav Dasgupta)
Mon, 30/01/2012
15:45 		Chris Cashen Topology Seminar Add to calendar L3
Line Patterns in Free Groups
I will discuss quasi-isometries of the free group that preserve an equivariant pattern of lines. There is a type of boundary at infinity whose topology determines how flexible such a line pattern is. For sufficiently complicated patterns I use this boundary to define a new metric on the free group with the property that the only pattern preserving quasi-isometries are actually isometries.
Mon, 30/01/2012
16:00 		Daniel Kotzen Junior Number Theory Seminar Add to calendar SR1
The Selberg Class - An Introduction
I will discuss the structure of the Selberg class - in which certain expected properties of Dirichlet series and L-functions are axiomatised - along with the numerous interesting conjectures concerning the Dirichlet series in the Selberg class. Furthermore, results regarding the degree of the elements in the Selberg class shall be explored, culminating in the recent work of Kaczorowski and Perelli in which they prove the absence of elements with degree between one and two.

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

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