Fri, 23 Oct 2009
14:15
DH 1st floor SR

Stochastic version of the rule "Buy and Hold"

Albert Shiryaev
(Steklov)
Abstract

For a logarithmic utility function we extend our rezult with Xu and Zhou for case of the geometrical Brownian motion with drift term which depends of the some hidden parameter.

Fri, 23 Oct 2009

11:45 - 12:45
DH 1st floor SR

Anthony Lock and Becky Shipley

OCIAM Internal Seminar
(Oxford)
Abstract

Anthony Lock will speak on "A Column Model of Moist Convection".

Thu, 22 Oct 2009
17:00
L3

Canonical bases of types of finite SU-rank

Zoe Chatzidakis
(Université Paris 7)
Abstract

I will speak about the CBP (canonical base property) for types of finite SU-rank. This property first appears in a paper by Pillay and Ziegler, who show that it holds for types of finite rank in differentially closed fields of characteristic 0, as well as in existentially closed difference fields. It is unknown whether this property holds for all finite rank types in supersimple theories. I will first recall the definition of a canonical base, and give some natural examples. I will then  talk about a reduction of the problem (which allows one to extend the Pillay-Ziegler result to existentially closed fields of any characteristic), and finally derive some consequences of the CBP, in particular the UCBP, thus answering a question of Moosa and Pillay.  If time permits, I will show an application of these results to difference

 

fields.

 

 

 

Thu, 22 Oct 2009

14:00 - 15:00
3WS SR

Mesh redistribution algorithms and error control for time-dependent PDEs

Prof. Charalambos Makridakis
(University of Crete)
Abstract

Self adjusted meshes have important benefits approximating PDEs with solutions that exhibit nontrivial characteristics. When appropriately chosen, they lead to efficient, accurate and robust algorithms. Error control is also important, since appropriate analysis can provide guarantees on how accurate the approximate solution is through a posteriori estimates. Error control may lead to appropriate adaptive algorithms by identifying areas of large errors and adjusting the mesh accordingly. Error control and associated adaptive algorithms for important equations in Mathematical Physics is an open problem.

In this talk we consider the main structure of an algorithm which permits mesh redistribution with time and the nontrivial characteristics associated with it. We present improved algorithms and we discuss successful approaches towards error control for model problems (linear and nonlinear) of parabolic or hyperbolic type.

Thu, 22 Oct 2009

12:00 - 13:00
SR1

Degenerations of <2>-polarised K3 surfaces

Alan Thompson
(Oxford)
Abstract

A -polarised K3 surface admits an embedding into weighted projective space defined by its polarisation. Let X be a family of such surfaces, then one can construct a projective model W of X such that the map from X to W realises this embedding on the general fibre. This talk considers what happens to W when we allow the fibres of the family X to degenerate.

Wed, 21 Oct 2009

11:30 - 12:30
ChCh, Tom Gate, Room 2

On the Semisimplicity Problem for Group Rings

Peter Pappas
(Vassar College)
Abstract

The semisimplicity problem is the long-standing conjecture that the group algebra $KG$ of a $p'$-group $G$ over a field $K$ of characteristic $p\geqslant 0$ has zero Jacobson radical. We will discuss recent advances in connection with this problem.

Wed, 21 Oct 2009
10:10
OCCAM Common Room (RI2.28)

TBA

Mokhles Mnejja
Tue, 20 Oct 2009
16:00
DH 1st floor SR

Small cancellation complexes

Dawid Kielak
Abstract

We will discuss a connection between small cancellation conditions and isoperimetric inequalities. Additionally we shall look at a useful construction connecting small cancellation complexes and cube complexes.

Tue, 20 Oct 2009
12:00
L3

Relations between Gowdy and Bianchi spacetimes

Alan Rendall
(AEI Golm)
Abstract

Two classes of solutions of the Einstein equations with symmetry which

are frequently studied are the Bianchi and Gowdy models. The aim of this

talk is to explain certain relations between these two classes of

spacetimes which can provide insights into the dynamics of both. In

particular it is explained that the special case of the Gowdy models known as circular loop spacetimes are Bianchi models in disguise. Generalizations of Gowdy spacetimes which can be thought of as inhomogeneous perturbations of some of the Bianchi models are introduced.

Results concerning their dynamics are presented.

Mon, 19 Oct 2009

17:00 - 18:00
Gibson 1st Floor SR

Diffractive behavior of the wave equation in periodic media

Gr&eacute;goire Allaire
(Ecole Polytechnique)
Abstract

We study the homogenization and singular perturbation of the

wave equation in a periodic media for long times of the order

of the inverse of the period. We consider inital data that are

Bloch wave packets, i.e., that are the product of a fast

oscillating Bloch wave and of a smooth envelope function.

We prove that the solution is approximately equal to two waves

propagating in opposite directions at a high group velocity with

envelope functions which obey a Schr\"{o}dinger type equation.

Our analysis extends the usual WKB approximation by adding a

dispersive, or diffractive, effect due to the non uniformity

of the group velocity which yields the dispersion tensor of

the homogenized Schr\"{o}dinger equation. This is a joint

work with M. Palombaro and J. Rauch.

Mon, 19 Oct 2009

12:00 - 13:00
L3

A CY Manifold with 3 Generations and Small Hodge Numbers

Philip Candelas
(Oxford)
Abstract
I will discuss a Calabi-Yau manifold which admits free actions by Abelian and non-Abelian groups of order 12. The quotient manifolds have Euler number -6 and Hodge numbers (h^{11}, h^{21}) = (1,4). Apart from the various presentations of the Yau Manifold, that have Hodge numbers (6,9), this is the only other complete intersection CY manifold to admit a free quotient with Euler number -6 and hence three generations of particles with the standard embedding. I will discuss the spectrum of light particles and the possibility of a transgression to a heterotic vacuum on a manifold with Hodge numbers (2,2).