Seminars and Colloquia by Series

Friday, April 6, 2018 - 17:53 , Location: Skiles 202 , Gunter Stolz , UAB , Organizer: Michael Loss
Friday, March 30, 2018 - 15:00 , Location: Skiles 202 , Rui Han , IAS , Organizer: Michael Loss
Friday, March 2, 2018 - 15:00 , Location: Skiles 202 , Predrag Cvitanovic , School of Physics, Georgia Tech , Organizer: Michael Loss
Recent advances in fluid dynamics reveal that the recurrent flows observed in moderate Reynolds number turbulence result from close passes to unstable invariant solutions of Navier-Stokes equations. By now hundreds of such solutions been computed for a variety of flow geometries, but always confined to small computational domains (minimal cells).Pipe, channel and plane flows, however, are flows on infinite spatial domains. We propose to recast the Navier-Stokes equations as a space-time theory, with the unstable invariant solutions now being the space-time tori (and not the 1-dimensional periodic orbits of the classical periodic orbit theory). The symbolic dynamics is likewise higher-dimensional (rather than a single temporal string of symbols). In this theory there is no time, there is only a repertoire of admissible spatiotemporal patterns.We illustrate the strategy by solving a very simple classical field theory on a lattice modelling many-particle quantum chaos, adiscretized screened Poisson equation, or the ``spatiotemporal cat.'' No actual cats, graduate or undergraduate, have showninterest in, or were harmed during this research.
Friday, February 16, 2018 - 15:00 , Location: Skiles 202 , Bharath Hebbe Madhusudhana , School of Physics, Georgia Tech , Organizer: Michael Loss
The expectation values of the first and second moments of the quantum mechanical spin operator can be used to define a spin vector and spin fluctuation tensor, respectively. The former is a vector inside the unit ball in three space, while the latter is represented by an ellipsoid in three space. They are both experimentally accessible in many physical systems. By considering transport of the spin vector along loops in the unit ball it is shown that the spin fluctuation tensor picks up geometric phase information. For the physically important case of spin one, the geometric phase is formulated in terms of an SO(3) operator. Loops defined in the unit ball fall into two classes: those which do not pass through the origin and those which pass through the origin. The former class of loops subtend a well defined solid angle at the origin while the latter do not and the corresponding geometric phase is non-Abelian. To deal with both classes, a notion of generalized solid angle is introduced, which helps to clarify the interpretation of the geometric phase information. The experimental systems that can be used to observe this geometric phase are also discussed.Link to arxiv:
Friday, February 9, 2018 - 15:00 , Location: Skiles 202 , Federico Bonetto , Georgia Tech , Organizer: Michael Loss
 I'll report on a project, developed in collaboration with Michael Loss, to extend a very simple model of rarefied gas due to Mark Kac and use it to understand some basic issues of Equilibrium and Non-Equilibrium Statistical Mechanics.
Friday, January 26, 2018 - 15:00 , Location: Skiles 202 , Evans Harrell , Georgia Tech , , Organizer: Michael Loss
Quantum theory includes many well-developed bounds for wave-functions, which can cast light on where they can be localized and where they are largely excluded by the tunneling effect.  These include semiclassical estimates, especially the technique of Agmon, the use of "landscape functions," and some bounds from the theory of ordinary differential equations.  With A. Maltsev of Queen Mary University I have been studying how these estimates of wave functions can be adapted to quantum graphs, which are by definition networks of one-dimensional Schrödinger equations joined at vertices.
Tuesday, November 28, 2017 - 13:00 , Location: Skiles 006 , Ian Jauslin , IAS, Princeton , , Organizer: Federico Bonetto
In 1979, O. Heilmann and E.H. Lieb introduced an interacting dimer model with the goal of proving the emergence of a nematic liquid crystal phase in it. In such a phase, dimers spontaneously align, but there is no long range translational order. Heilmann and Lieb proved that dimers do, indeed, align, and conjectured that there is no translational order. I will discuss a recent proof of this conjecture. This is joint work with Elliott H. Lieb.
Tuesday, November 28, 2017 - 11:00 , Location: Skiles 006 , Vieri Mastropietro , Universita' di Milano, Italy , , Organizer: Federico Bonetto
Abstract: A number of quantities in quantum many-body systems show remarkable universality properties, in the sense of exact independence from microscopic details. I will present some rigorous result establishing universality in presence of many body interaction in Graphene and in Topological Insulators, both for the bulk and edge transport. The proof uses Renormalization Group methods and a combination of lattice and emerging Ward Identities.
Friday, November 17, 2017 - 15:00 , Location: Skiles 006 , Timo Weidl , Univ. Stuttgart , , Organizer:

This is part of the 2017 Quolloquium series.

Starting from the classical Berezin- and Li-Yau-bounds onthe eigenvalues of the Laplace operator with Dirichlet boundaryconditions I give a survey on various improvements of theseinequalities by remainder terms. Beside the Melas inequalitywe deal with modifications thereof for operators with and withoutmagnetic field and give bounds with (almost) classical remainders.Finally we extend these results to the Heisenberg sub-Laplacianand the Stark operator in domains.
Thursday, November 16, 2017 - 13:30 , Location: Skiles 006 , Lotfi Hermi , Florida International University , , Organizer:

This is part of the 2017 Quolloquium series.

We use the weighted isoperimetric inequality of J. Ratzkin for a wedge domain in higher dimensions to prove new isoperimetric inequalities for weighted $L_p$-norms of the fundamental eigenfunction of a bounded domain in a convex cone-generalizing earlier work of Chiti, Kohler-Jobin, and Payne-Rayner. We also introduce relative torsional rigidity for such domains and prove a new Saint-Venant-type isoperimetric inequality for convex cones. Finally, we prove new inequalities relating the fundamental eigenvalue to the relative torsional rigidity of such a wedge domain thereby generalizing our earlier work to this higher dimensional setting, and show how to obtain such inequalities using the Payne interpretation in Weinstein fractional space. (Joint work with A. Hasnaoui)