Mon, 26 Oct 2009
15:45
Eagle House

TBA

Alan Hammond
(New York University)
Abstract

Condition supercritical percolation so that the origin is enclosed by a dual circuit whose interior traps an area of n^2.

The Wulff problem concerns the shape of the circuit. We study the circuit's fluctuation. A well-known measure of this fluctuation is maximum local roughness (MLR), which is the greatest distance from a point on the circuit to the boundary of circuit's convex hull. Another is maximum facet length (MFL), the length of the longest line segment of which this convex hull is comprised.

In a forthcoming article, I will prove that

for various models including supercritical percolation, under the conditioned measure,

MLR = \Theta(n^{1/3}\log n)^{2/3}) and MFL = \Theta(n^{2/3}(log n)^{1/3}).

An important tool is a result establishing the profusion of regeneration sites in the circuit boundary. The talk will focus on deriving the main results with this tool

Mon, 26 Oct 2009

12:00 - 13:00
L3

Gauge Threshold Corrections for Local String Models

Joe Conlon
(Oxford)
Abstract
Local string models are those where Standard Model degrees of freedom arise on a small region inside a large bulk volume. I study threshold effects on gauge coupling running for such models. The Kaplunovsky-Louis formula for locally supersymmetric gauge theories predicts the unification scale should be the bulk winding mode scale, parametrically large than the string scale where divergences are naively cut off. Analysis of explicit string models on orbifold/orientifold geometries confirms this; the winding mode scale arises from the presence of tadpoles uncancelled in the local model. I briefly discuss phenomenological applications to supersymmetry breaking and gauge coupling unification.
Fri, 23 Oct 2009

16:30 - 17:00
DH 1st floor SR

Dislocation dynamics and instability

Yichao Zhu
(University of Oxford)
Abstract

Dislocation channel-veins and Persist Slip Band (PSB) structures are characteristic configurations in material science. To find out the formation of these structures, the law of motion of a single dislocation should be first examined. Analogous to the local expansion in electromagnetism, the self induced stress is obtained. Then combining the empirical observations, we give a smooth mobility law of a single dislocation. The stability analysis is carried our asymptotically based on the methodology in superconducting vortices. Then numerical results are presented to validate linear stability analysis. Finally, based on the evidence given by the linear stability analysis, numerical experiments on the non-linear evolution are carried out.

Fri, 23 Oct 2009
16:30
L2

*My Nonlinear Odyssey : Analytics*, * Simulation & Visualization *

Professor Norm Zabusky
(Weizmann Institute)
Abstract

An overview of the early history of the soliton (1960-1970) and equipartition in nonlinear 1D lattices : From Fermi-Pasta-Ulam to Korteweg de Vries, to Nonlinear Schrodinger*…., and recent developments .

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.