Forthcoming Seminars

Mon, 07/02/2011
15:45 		Roberto Frigerio (Universita di Pisa) Topology Seminar Add to calendar L3
Rigidity of manifolds without non-positive curvature
In this talk I describe some results obtained in collaboration with J.F. Lafont and A. Sisto, which concern rigidity theorems for a class of manifolds which are “mostly” non-positively curved, but may not support any actual non-positively curved metric. More precisely, we define a class of manifolds which contains non-positively curved examples. Building on techniques coming from geometric group theory, we show that smooth rigidity holds within our class of manifolds (in fact, they are also topologically rigid - i.e. they satisfy the Borel conjecture - but this fact won't be discussed in my talk). We also discuss some results concerning the quasi-isometry type of the fundamental groups of mostly non-positively curved manifolds.
Mon, 07/02/2011
15:45 		Malwina Luczak Stochastic Analysis Seminar Add to calendar Eagle House
Concentration of measure for degrees of vertices in web graphs

A very general model of evolving graphs was introduced by Cooper and Frieze in 2003, and further analysed by Cooper. At each stage of the process, either a new edge is added
between existing vertices, or a new vertex is added and joined to some number of existing vertices. Each vertex gaining a new neighbour may be chosen either uniformly, or by preferential attachment, i.e., with probability proportional to the current degree.
It is known that the degrees of vertices in any such model follow a ``power law''. Here we study in detail the degree sequence of a graph obtained from such a procedure, looking at the vertices of large degree as well as the numbers of vertices of each fixed degree.
This is joint work with Graham Brightwell.
Mon, 07/02/2011
16:00 		Damiano Testa (Oxford) Junior Number Theory Seminar Add to calendar SR1
The surface of cuboids
Mon, 07/02/2011
17:00 		Grigoris Pavliotis (Imperial College) Partial Differential Equations Seminar Add to calendar Gibson 1st Floor SR
Asymptotic analysis for the Generalized Langevin equation
In this talk we will present some recent results on the long time asymptotics of the generalized (non-Markovian) Langevin equation (gLE). In particular, we will discuss about the ergodic properties of the gLE and present estimates on the rate of convergence to equilibrium, we will present a homogenization result (invariance principle) and we will discuss about the convergence of the gLE dynamics to the (Markovian) Langevin dynamics, in some appropriate asymptotic limit. The analysis is based on the approximation of the gLE by a high (and possibly infinite) dimensional degenerate Markovian system, and on the analysis of the spectrum of the generator of this Markov process. This is joint work with M. Ottobre and K. Pravda-Starov.
Tue, 08/02/2011
11:00 		Hannah Arnold (AOPP (Oxford University)) Applied Dynamical Systems and Inverse Problems Seminar Add to calendar DH 3rd floor SR
Stochastic Parameterisation Part 2
Tue, 08/02/2011
14:00 		Nicolas Addington (Imperial College London) Algebraic and Symplectic Geometry Seminar Add to calendar SR1
Complete Intersections of Quadrics
There is a long-studied correspondence between intersections of two quadrics and hyperelliptic curves, first noticed by Weil and since used as a testbed for many fashionable theories: Hodge theory, motives, and moduli of vector bundles in the '70s and '80s, derived categories in the '90s, non-commutative geometry and mirror symmetry today. The story generalizes to three, four, and more quadrics, exhibiting new geometric behaviour at each step. The case of four quadrics nicely illustrates the modern theory of flops and derivced categories and, as a special case, gives a pair of derived-equivalent Calabi-Yau 3-folds.
Tue, 08/02/2011
15:45 		Nicolas Addington (Imperial College London) Algebraic and Symplectic Geometry Seminar Add to calendar L3
Derived Categories of Cubic 4-Folds
If $ X $ is a Fano variety with canonical bundle $ O(-k) $, its derived category has a semi-orthogonal decomposition (I will say what that means)
\[ D(X) = \langle O(-k+1), ..., O(-1), O, A \rangle, \]
where the subcategory $ A $ is the "interesting piece" of $ D(X) $. In the previous talk we saw that $ A $ can have very rich geometry. In this talk we will see a less well-understood example of this: when $ X $ is a smooth cubic in $ P^5 $, $ A $ looks like the derived category of a K3 surface. We will discuss Kuznetsov's conjecture that $ X $ is rational if and only if $ A $ is geometric, relate it to Hassett's earlier work on the Hodge theory of $ X $, and mention an autoequivalence of $ D(Hilb^2(K3)) $ that I came across while studying the problem.
Tue, 08/02/2011
16:30 		Lutz Warnke Combinatorial Theory Seminar Add to calendar SR2
"The C_ell -free process".
The $ C_\ell $-free process starts with the empty graph on $ n $ vertices and adds edges chosen uniformly at random, one at a time, subject to the condition that no copy of $ C_\ell $ is created. For every $ \ell \geq 4 $ we show that, with high probability as $ n \to \infty $, the maximum degree is $ O((n \log n)^{1/(\ell-1)}) $, which confirms a conjecture of Bohman and Keevash and improves on bounds of Osthus and Taraz. Combined with previous results this implies that the $ C_\ell $-free process typically terminates with $ \Theta(n^{\ell/(\ell-1)}(\log n)^{1/(\ell-1)}) $ edges, which answers a question of Erd\H{o}s, Suen and Winkler. This is the first result that determines the final number of edges of the more general $ H $-free process for a non-trivial class of graphs $ H $. We also verify a conjecture of Osthus and Taraz concerning the average degree, and obtain a new lower bound on the independence number. Our proof combines the differential equation method with a tool that might be of independent interest: we establish a rigorous way to `transfer' certain decreasing properties from the binomial random graph to the $ H $-free process.
Tue, 08/02/2011
17:00 		Bas Lemmens (Kent) Functional Analysis Seminar Add to calendar L3
One-complemented subspaces
Tue, 08/02/2011
17:00 		Dr Ehud Meir (Newton Institute) Algebra Seminar Add to calendar L2
On a conjecture of Moore
Abstract: this is joint work with Eli Aljadeff. Let G be a group, H a finite index subgroup. Moore's conjecture says that under a certain condition on G and H (which we call the Moore's condition), a G-module M which is projective over H is projective over G. In other words- if we know that a module is “almost projective”, then it is projective. In this talk we will survey cases in which the conjecture is known to be true. This includes the case in which the group G is finite and the case in which the group G has finite cohomological dimension. As a generalization of these two cases, we shall present Kropholler's hierarchy LHF, and discuss the conjecture for groups in this hierarchy. In the case of finite groups and in the case of finite cohomological dimension groups, the conjecture is proved by the same finiteness argument. This argument is straightforward in the finite cohomological dimension case, and is a result of a theorem of Serre in case the group is finite. We will show that inside Kropholler's hierarchy the conjecture holds even though this finiteness condition might fail to hold. We will also discuss some other cases in which the conjecture is known to be true (e.g. Thompson's group F).
Wed, 09/02/2011
11:30 		Maria Buzano (University of Oxford) Algebra Kinderseminar Add to calendar ChCh, Tom Gate, Room 2
Homogeneous Ricci flow
This talk will be divided into three parts. In the first part we will recall basic notions and facts of differential geometry and the Ricci flow equation. In the second part we will talk about singularities for the Ricci flow and Ricci flow on homogeneous spaces. Finally, in the third part of the talk, we will focus on the case of Ricci flow on compact homogeneous spaces with two isotropy summands.
Wed, 09/02/2011
16:00 		Alessandro Sisto (Oxford University) Junior Geometric Group Theory Seminar Add to calendar SR2
Nonstandard methods in geometry: asymptotic cones
After a quick-and-dirty introduction to nonstandard analysis, we will define the asymptotic cones of a metric space and we will play around with nonstandard tools to show some results about them. For example, we will hopefully prove that any separable asymptotic cone is proper and we will classify real trees appearing as asymptotic cones of groups.
Thu, 10/02/2011
11:00 		Bernhard Elsner (Oxford) Advanced Class Logic Add to calendar SR2
"Interpreting fields in stable theories using Zariski Types"
Thu, 10/02/2011
13:00 		Bahman Angoshtari Mathematical Finance Internal Seminar Add to calendar DH 1st floor SR
Portfolio choice with cointegrated assets
In portfolio management, there are specific strategies for trading between two assets that are cointegrated. These are commonly referred to as pairs-trading or spread-trading strategies. In this paper, we provide a theoretical framework for portfolio choice that justifies the choice of such strategies. For this, we consider a continuous-time error correction model to model the cointegrated price processes and analyze the problem of maximizing the expected utility of terminal wealth, for logarithmic and power utilities. We obtain and justify an extra no-arbitrage condition on the market parameters with which one obtains decomposition results for the optimal pairs-trading portfolio strategies.
Thu, 10/02/2011
13:00 		Imran Qureshi (University of Oxford) Junior Geometry and Topology Seminar Add to calendar SR1
Graded rings and polarised varieties
Many classes of polarised projective algebraic varieties can be constructed via explicit constructions of corresponding graded rings. In this talk we will discuss two methods, namely Basket data method and Key varieties method, which are often used in such constructions. In the first method we will construct graded rings corresponding to some topological data of the polarised varieties. The second method is based on the notion of weighted flag variety, which is the weighted projective analogue of a flag variety. We will describe this notion and show how one can use their graded rings to construct interesting classes of polarised varieties.
Thu, 10/02/2011
14:00 		Prof Mike Giles (University of Oxford) Computational Mathematics and Applications Add to calendar Gibson Grd floor SR
OP2 – an open-source parallel library for unstructured grid computations

Based on an MPI library written over 10 years ago, OP2 is a new open-source library which is aimed at application developers using unstructured grids. Using a single API, it targets a variety of HPC architectures, including both manycore GPUs and multicore CPUs with vector units. The talk will cover the API design, key aspects of the parallel implementation on the different platforms, and preliminary performance results on a small but representative CFD test code.

Project homepage: http://people.maths.ox.ac.uk/gilesm/op2/
Thu, 10/02/2011
16:00 		Ben Green (Cambridge) Number Theory Seminar Add to calendar L3
Applications of nilsequences to number theory
I will introduce the notion of a nilsequence, which is a kind of "higher" analogue of the exponentials used in classical Fourier analysis. I will summarise the current state of our understanding of these objects. Then I will discuss a variety of applications: to solving linear equations in primes (joint with T. Tao), to a version of Waring's problem for so-called generalised polynomials (joint with V. Neale and Trevor Wooley) and to solving certain pairs of diagonal quadratic equations in eight variables (joint work with L. Matthiesen). Some of the work to be described is a little preliminary!
Thu, 10/02/2011
16:00 		Simon Cox (Aberystwyth) Differential Equations and Applications Seminar Add to calendar DH 1st floor SR
Dynamics of aqueous foams
Predicting the dynamics of foams requires input from geometry and both Newtonian and non-Newtonian fluid mechanics, among many other fields. I will attempt to give a flavour of this richness by discussing the static structure of a foam and how it allows the derivation of dynamic properties, at least to leading order. The latter includes coarsening due to gas diffusion, liquid drainage under gravity, and the flow of the bubbles themselves.
Thu, 10/02/2011
17:00 		Philip Welch (Bristol) Logic Seminar Add to calendar L3
To Be Announced
Thu, 10/02/2011
17:00 		Philip Welch (Bristol) Logic Seminar Add to calendar L3
Games and Structures at aleph_2

Games are ubiquitous in set theory and in particular can be used to build models (often using some large cardinal property to justify the existence of strategies). As a reversal one can define large cardinal properties in terms of such games.

We look at some such that build models through indiscernibles, and that have recently had some effect on structures at aleph_2.

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

Syndicate content