Mon, 26 Oct 2015
14:15
L4

The complex geometry of Teichmüller spaces and bounded symmetric domains.

Stergios Antonakoudis
(Cambridge)
Abstract

From a complex analytic perspective, both Teichmüller spaces and
symmetric spaces can be realised as contractible bounded domains, that
have several features in common but also exhibit many differences. In
this talk we will study isometric maps between these two important
classes of bounded domains equipped with their intrinsic Kobayashi metric.

Wed, 20 Jan 2016
15:00
L4

Multi Party Computation: Low Communication Protocols

Nigel Smart
(University of Bristol)
Abstract

In recent years there has been amazing progress in building
practical protocols for Multi-Party Computation (MPC).
So much progress in fact that there are now a number of
companies producing products utilizing this technology. A major issue with existing solutions is the high round
complexity of protocols involving more than two players. In this talk I will survey the main protocols for MPC
and recent ideas in how to obtain practical low round
complexity protocols.

Thu, 03 Dec 2015

12:00 - 13:00
L6

Weak solutions to the Navier-Stokes initial boundary value problem in exterior domains with initial data in L(3,∞)

Paolo Maremonti
(Seconda Università degli Studi di Napoli)
Abstract

We consider the Navier-Stokes initial boundary value problem (NS-IBVP) in a smooth exterior domain. We are interested in establishing existence of weak solutions (we mean weak solutions as synonym of solutions global in time) with an initial data in L(3,∞)

(Lorentz space). Apart from its own analytical interest, the research is connected with questions related to the space-time asymptotic properties of solutions to the NS-IBVP. However these questions are not discussed. The assumption on the initial data in L(3,∞) cuts the L2-theory out, which is the unique known for weak solutions. We find a simple strategy to bypass the difficulties of an initial data /∈ L2, and we take care to perform the same “regularity properties” of Leary’s weak solutions, hence to furnish a structure theorem of a weak solution.
Thu, 05 Nov 2015

12:00 - 13:00
L6

Ancient Solutions to Navier-Stokes Equations in Half Space

Tobias Barker
(University of Oxford)
Abstract

The relationship between the so-called ancient (backwards) solutions to the Navier-Stokes equations in the space or in a half space and the global well-posedness of initial boundary value problems for these equations will be explained. If time permits I will sketch details of an equivalence theorem and a proof of smoothness properties of mild bounded ancient solutions in the half space, which is a joint work with Gregory Seregin

Thu, 26 Nov 2015

12:00 - 13:00
L6

Non-orientable line defects in the Landau-de Gennes theory of nematic liquid crystals

Giacomo Canevari
(University of Oxford)
Abstract
Nematic liquid crystals are composed by rod-shaped molecules with long-range orientation order. These materials admit topological defect lines, some of which are associated with non-orientable configurations. In this talk, we consider the Landau-de Gennes variational theory of nematics. We study the asymptotic behaviour of minimizers as the elastic constant tends to zero. We assume that the energy of minimizers is of the same order as the logarithm of the elastic constant. This happens, for instance, if the boundary datum has finitely many singular points. We prove convergence to a locally harmonic map with singularities of dimension one (non-orientable line defects) and, possibly, zero (point defects).
Thu, 12 Nov 2015

12:00 - 13:00
L6

Energy decay in a 1D coupled heat-wave system

David Seifert
(University of Oxford)
Abstract

We study a simple one-dimensional coupled heat wave system, obtaining a sharp estimate for the rate of energy decay of classical solutions. Our approach is based on the asymptotic theory of $C_0$-semigroups and in particular on a result due to Borichev and Tomilov (2010), which reduces the problem of estimating the rate of energy decay to finding a growth bound for the resolvent of the semigroup generator. This technique not only leads to an optimal result, it is also simpler than the methods used by other authors in similar situations and moreover extends to problems on higher-dimensional domains. Joint work with C.J.K. Batty (Oxford) and L. Paunonen (Tampere).

Tue, 20 Oct 2015

14:00 - 15:00
L5

Simple unified convergence proofs for Trust Region and a new ARC variant, and implementation issues

Jean-Pierre Dussault
(Universite de Sherbrooke)
Abstract
We provide a simple convergence analysis unified for TR and a new ARC algorithms, which we name ARCq and which is very close in spirit to trust region methods, closer than the original ARC is. We prove global convergence to second order points. We also obtain as a corollary the convergence of the original ARC method. Since one of our aims is to achieve a simple presentation, we sacrifice some generality which we discuss at the end of our developments. In this simplified setting, we prove the optimal complexity property for the ARCq and identify the key elements which allow it. We then propose efficient implementations using a Cholesky like factorization as well as a scalable version based on conjugate gradients.
Wed, 14 Oct 2015
15:00
L4

The impact of quantum computing on cryptography

Steve Brierley
(University of Cambridge)
Abstract

This is an exciting time to study quantum algorithms. As the technological challenges of building a quantum computer continue to be met there is still much to learn about the power of quantum computing. Understanding which problems a quantum computer could solve faster than a classical device and which problems remain hard is particularly relevant to cryptography. We would like to design schemes that are secure against an adversary with a quantum computer. I'll give an overview of the quantum computing that is accessible to a general audience and use a recently declassified project called "soliloquy" as a case study for the development (and breaking) of post-quantum cryptography.

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