Tue, 16 Feb 2016

15:45 - 16:45
L4

The K3 category of a cubic fourfold

Daniel Huybrechts
(Bonn)
Abstract

Smooth cubic fourfolds are linked to K3 surfaces via their Hodge structures, due to work of Hassett, and via Kuznetsov's K3 category A. The relation between these two viewpoints has recently been elucidated by Addington and Thomas. 
We study both of these aspects further and extend them to twisted K3 surfaces, which in particular allows us to determine the group of autoequivalences of A for the general cubic fourfold. Furthermore, we prove finiteness results for cubics with equivalent K3 categories and study periods of cubics in terms of generalized K3 surfaces.

Mon, 22 Feb 2016
14:15
L4

The Gromoll filtration, Toda brackets and positive scalar curvature

OAC-manifolds meeting: Diarmuid Crowley
(Aberdeen)
Abstract
An exotic (n+1)-sphere has disc of origin D^k if k is the smallest integer such that some clutching diffeomorphism of the n-disc which builds the exotic sphere can be written as an (n-k)-parameter family of diffeomorphisms of the k-disc.
 
In this talk I will present a new method for constructing exotic spheres with small disc of origin via Toda brackets.  
 
This method gives exotic spheres in all dimensions 8j+1 and 8j+2 with disc of origin 6 and with Dirac operators of non-zero index (such spheres are often called "Hitchin spheres").
 
I will also briefly discuss implications of our results for the space of positive scalar curvature metrics on spin manifolds of dimension 6 and higher, and in particular the relationship of this project to the work of Botvinnik, Ebert and Randal-Williams.
 
This is part of joint work with Thomas Schick and Wolfgang Steimle.
Fri, 04 Mar 2016

10:00 - 11:00
L4

Fault prediction from time series data

Mike Newman
(Thales)
Abstract

On the railway network, for example, there is a large base of installed equipment with a useful life of many years.  This equipment has condition monitoring that can flag a fault when a measured parameter goes outside the permitted range.  If we can use existing measurements to predict when this would occur, preventative maintenance could be targeted more effectively and faults reduced.  As an example, we will consider the current supplied to a points motor as a function of time in each operational cycle.

Fri, 26 Feb 2016

10:00 - 11:00
L4

Ionic liquids - a challenge to our understanding of the liquid state

Susan Perkin
(Department of Chemistry)
Abstract
Ionic liquids are salts, composed solely of positive and negative ions, which are liquid under ambient conditions. Despite an increasing range of successful applications, there remain fundamental challenges in understanding the intermolecular forces and propagation of fields in ionic liquids. 
I am an experimental scientist, and in my laboratory we study thin films of liquids. The aim is to discover their molecular and surface interactions and fluid properties in confinement. In this talk I will describe the experiments and show some results which have led to better understanding of ionic liquids. I will then show some measurements which currently have no understanding attached! 
Fri, 29 Jan 2016

10:00 - 11:00
L4

Causal Calculus and Actionable Associations in Market-Basket Data

Marco Brambilla
(dunnhumby)
Abstract

“Market-Basket (MB) and Household (HH) data provide a fertile substrate for the inference of association between marketing activity (e.g.: prices, promotions, advertisement, etc.) and customer behaviour (e.g.: customers driven to a store, specific product purchases, joint product purchases, etc.). The main aspect of MB and HH data which makes them suitable for this type of inference is the large number of variables of interest they contain at a granularity that is fit for purpose (e.g.: which items are bought together, at what frequency are items bought by a specific household, etc.).

A large number of methods are available to researchers and practitioners to infer meaningful networks of associations between variables of interest (e.g.: Bayesian networks, association rules, etc.). Inferred associations arise from applying statistical inference to the data. In order to use statistical association (correlation) to support an inference of causal association (“which is driving which”), an explicit theory of causality is needed.

Such a theory of causality can be used to design experiments and analyse the resultant data; in such a context certain statistical associations can be interpreted as evidence of causal associations.

On observational data (as opposed to experimental), the link between statistical and causal associations is less straightforward and it requires a theory of causality which is formal enough to support an appropriate calculus (e.g.: do-calculus) of counterfactuals and networks of causation.

My talk will be focused on providing retail analytic problems which may motivate an interest in exploring causal calculi’s potential benefits and challenges.”

Mon, 01 Feb 2016
02:15
L4

Torelli theorems and integrable systems for parabolic Higgs bundles

Marina Logares
(Oxford)
Abstract

In the same way that the classical Torelli theorem determines a curve from its polarized Jacobian we show that moduli spaces of parabolic bundles and parabolic Higgs bundles over a compact Riemann surface X  also determine X. We make use of a theorem of Hurtubise on the geometry of algebraic completely integrable systems in the course of the proof. This is a joint work with I. Biswas and T. Gómez 

Tue, 02 Feb 2016

12:00 - 13:15
L4

Cutkosky rules and Outer Space

Dirk Kreimer (Berlin)
(HU Berlin)
Abstract

Amplitudes in quantum field theory have discontinuities when regarded as
functions of
the scattering kinematics. Such discontinuities can be determined from
Cutkosky rules.
We present a structural analysis of such rules for massive quantum field
theory which combines
algebraic geometry with the combinatorics of Karen Vogtmann's Outer Space.
This is joint work with Spencer Bloch (arXiv:1512.01705).

Subscribe to L4