Thu, 08 Dec 2016

16:00 - 17:00
L2

Catastrophic Buckling Behavior of Shell Structures: A Brief History Followed by New Experiments and Theory on Spherical Shells

John Hutchinson
(Harvard University)
Abstract

The stability of structures continues to be scientifically fascinating and technically important.  Shell buckling emerged as one of the most challenging nonlinear problems in mechanics more than fifty years ago when it was intensively studied.  It has returned to life with new challenges motivated not only by structural applications but also by developments in the life sciences and in soft materials.  It is not at all uncommon for slightly imperfect thin cylindrical shells under axial compression or spherical shells under external pressure to buckle at 20% of the buckling load of the perfect shell.  A historical overview of shell buckling will be presented followed by a discussion of recent work by the speaker and his collaborators on the buckling of spherical shells.  Experimental and theoretical work will be described with a focus on imperfection-sensitivity and on viewing the phenomena within the larger context of nonlinear stability. 

Fri, 04 Mar 2016

15:30 - 16:30
L2

Hurricanes and Climate Change

Professor Kerry Emanuel
(MIT)
Abstract

In his talk, Kerry will explore the pressing practical problem of how hurricane activity will respond to global warming, and how hurricanes could in turn be influencing the atmosphere and ocean

Thu, 03 Mar 2016

16:00 - 17:00
L2

Hecke eigenvalue congruences and experiments with degree-8 L-functions

Neil Dummigan
(University of Sheffield)
Abstract

I will describe how the moduli of various congruences between Hecke eigenvalues of automorphic forms ought to show up in ratios of critical values of $\text{GSP}_2 \times \text{GL}_2$ L-functions. To test this experimentally requires the full force of Farmer and Ryan's technique for approximating L-values given few coefficients in the Dirichlet series.

Thu, 25 Feb 2016

16:00 - 17:00
L2

Badly approximable points

Victor Beresnevich
(University of York)
Abstract

I will discuss the notion of badly approximable points and recent progress and problems in this area, including Schmidt's conjecture, badly approximable points on manifolds and real numbers badly approximable by algebraic numbers.

Mon, 16 Nov 2015

15:00 - 16:00
L2

Magnitudes of compact sets in euclidean spaces: an application of analysis to the theory of enriched categories

Tony Carbery
(University of Edinburgh)
Abstract

Leinster and Willerton have introduced the concept of the magnitude of a metric space, as a special case as that of an enriched category. It is a numerical invariant which is designed to capture the important geometric information about the space, but concrete examples of ts values on compact sets in euclidean space have hitherto been lacking. We discuss progress in some conjectures of Leinster and Willerton.

Mon, 16 Nov 2015

16:00 - 17:00
L2

The Stokes-Fourier equations as scaling limit of the hard sphere dynamics

Laure Saint-Raymond
(Ecole Normale Superieure)
Abstract
In his sixth problem, Hilbert asked for an axiomatization of gas dynamics, and he suggested to use the Boltzmann equation as an intermediate description between the (microscopic) atomic dynamics and (macroscopic) fluid models. The main difficulty to achieve this program is to prove the asymptotic decorrelation between the local microscopic interactions, referred to as propagation of chaos, on a time scale much larger than the mean free time. This is indeed the key property to observe some relaxation towards local thermodynamic equilibrium.

 

This control of the collision process can be obtained in fluctuation regimes. In a recent work with I. Gallagher and T. Bodineau, we have established a long time convergence result to the linearized Boltzmann equation, and eventually derived the acoustic and incompressible Stokes equations in dimension 2. The proof relies crucially on symmetry arguments, combined with a suitable pruning procedure to discard super exponential collision trees.
Subscribe to L2