Seminars and Colloquia by Series

Thursday, April 16, 2015 - 11:00 , Location: Skiles 005 , Prof. Vili Totik , Szeged University (Hungary) and University of South Florida , totik@mail.usf.edu , Organizer: Doron Lubinsky
Bernstein's inequality connecting the norms of a (trigonometric) polynomial with the norm of its derivative is 100 years old. The talk will discuss some recent developments concerning Bernstein's inequality: inequalities with doubling weights, inequalities on general compact subsets of the real line or on a system of Jordan curves. The beautiful Szego-Schaake–van der Corput generalization will also be mentioned along with some of its recent variants.
Thursday, April 9, 2015 - 11:00 , Location: Skiles 005 , Haynes Miller , MIT , Organizer: Kirsten Wickelgren
Much effort in the past several decades has gone into lifting various algebraic structures into a topological context. I will describe one such lifting: that of the arithmetic theory of elliptic curves. The result is a rich and highly structured family of cohomology theories collectively known as elliptic cohomology. By forming "global sections" one is led to a topological enrichment of the ring of modular forms. Geometric interpretations of these theories are enticing but still conjectural at best.
Thursday, February 19, 2015 - 11:00 , Location: Skiles 005 , Professor Izabella Laba , University of British Columbia , Organizer: Martin Short
Singular and oscillatory integral estimates, such as maximal theorems and restriction estimates for measures on hypersurfaces, have long been a central topic in harmonic analysis. We discuss the recent work by the speaker and her collaborators on the analogues of such results for singular measures supported on fractal sets. The common thread is the use of ideas from additive combinatorics. In particular, the additive-combinatorial notion of "pseudorandomness" for fractals turns out to be an appropriate substitute for the curvature of manifolds.
Thursday, February 12, 2015 - 11:00 , Location: Skiles 005 , Elizabeth Meckes , Case Western Reserve University , Organizer: Kirsten Wickelgren
Dvoretzky's theorem tells us that if we put an arbitrary norm on n-dimensional Euclidean space, no matter what that normed space is like, if we pass to subspaces of dimension about log(n), the space looks pretty much Euclidean.  A related measure-theoretic phenomenon has long been observed:the (one-dimensional) marginals of many natural high-dimensional probability distributions look about Gaussian. A natural question is whether this phenomenon persists for k-dimensional marginals for k growing with n, and if so, for how large a k? In this talk I will discuss a result showing that the phenomenon does indeed persist if k less than 2log(n)/log(log(n)), and that this bound is sharp (even the 2!).  The talk will not assume much background beyond basic probability and analysis; in particular, no prior knowledge of Dvoretzky's theorem is needed.
Friday, December 5, 2014 - 16:00 , Location: Skiles 006 , Danny Calegari , University of Chicago , Organizer: John Etnyre

Kick-off of the <a href="http://ttc.gatech.edu">Tech Topology Conference</a>, December 5-7, 2014

In 1985, Barnsley and Harrington defined a "Mandelbrot Set" M for pairs of similarities -- this is the set of complex numbers z with norm less than 1 for which the limit set of the semigroup generated by the similarities x -> zx and x -> z(x-1)+1 is connected. Equivalently, M is the closure of the set of roots of polynomials with coefficients in {-1,0,1}. Barnsley and Harrington already noted the (numerically apparent) existence of infinitely many small "holes" in M, and conjectured that these holes were genuine. These holes are very interesting, since they are "exotic" components of the space of (2 generator) Schottky semigroups. The existence of at least one hole was rigorously confirmed by Bandt in 2002, but his methods were not strong enough to show the existence of infinitely many holes; one difficulty with his approach was that he was not able to understand the interior points of M, and on the basis of numerical evidence he conjectured that the interior points are dense away from the real axis. We introduce the technique of traps to construct and certify interior points of M, and use them to prove Bandt's Conjecture. Furthermore, our techniques let us certify the existence of infinitely many holes in M. This is joint work with Sarah Koch and Alden Walker.
Thursday, December 4, 2014 - 11:00 , Location: Skiles 005 , Sybilla Beckman , Josiah Meigs Distinguished Teaching Professor of Mathematics, UGA , sybilla@math.uga.edu , Organizer:
In this presentation I will show some of the surprising depth and complexity of elementary- and middle-grades mathematics, much of which has been revealed by detailed studies into how students think about mathematical ideas. In turn, research into students' thinking has led to the development of teaching-learning paths at the elementary grades, which are reflected in the Common Core State Standards for Mathematics. These teaching-learning paths are widely used in mathematically high-performing countries but are not well understood in this country. At the middle grades, ideas surrounding ratio and proportional relationships are critical and central to all STEM disciplines, but research is needed into how students and teachers can reason about these ideas. Although research in mathematics education is necessary, it is not sufficient for solving our educational problems. For the mathematics teaching profession to be strong, we need a system in which all of us who teach mathematics, at any level, take collective ownership of and responsibility for mathematics teaching. 
Tuesday, November 18, 2014 - 11:00 , Location: Skiles 005 , Luis Vega , BCAM-Basque Center for Applied Mathematics (Scientific Director) and University of the Basque Country UPV/EHU , lvega@bcamath.org , Organizer:
In the first part of the talk I shall present a linear model based on the Schrodinger equation with constant coefficient and periodic boundary conditions that explains the so-called Talbot effect in optics. In the second part I will make a connection of this Talbot effect with turbulence through the Schrodinger map which is a geometric non-linear partial differential equation.
Thursday, November 13, 2014 - 11:00 , Location: Skiles 005 , Professor Andre Martinez-Finkelshtein , Universidad de Almería , Organizer: Martin Short
Random matrix theory (RMT) is a very active area of research and a greatsource of exciting and challenging problems for specialists in manybranches of analysis, spectral theory, probability and mathematicalphysics. The analysis of the eigenvalue distribution of many random matrix ensembles leads naturally to the concepts of determinantal point processes and to their particular case, biorthogonal ensembles, when the main object to study, the correlation kernel, can be written explicitly in terms of two sequences of mutually orthogonal functions.Another source of determinantal point processes is a class of stochasticmodels of particles following non-intersecting paths. In fact, theconnection of these models with the RMT is very tight: the eigenvalues of the so-called Gaussian Unitary Ensemble (GUE) and the distribution ofrandom particles performing a Brownian motion, departing and ending at the origin under condition that their paths never collide are, roughlyspeaking, statistically identical.A great challenge is the description of the detailed asymptotics of these processes when the size of the matrices (or the number of particles) grows infinitely large. This is needed, for instance, for verification of different forms of "universality" in the behavior of these models. One of the rapidly developing tools, based on the matrix Riemann-Hilbert characterization of  the correlation kernel, is the associated non-commutative steepest descent analysis of Deift and Zhou.Without going into technical details, some ideas behind this technique will be illustrated in the case of a model of squared Bessel nonintersectingpaths.
Thursday, November 6, 2014 - 11:00 , Location: Skiles 005 , Ken Ono , Emory University , Organizer: Kirsten Wickelgren
The speaker will discuss recent work on Moonshine and the Rogers-Ramanujan identities. The Rogers-Ramanujan identities are two peculiar identities which express two infinite product modular forms as number theoretic q-series. These identities give rise to the Rogers-Ramanujan continued fraction, whose values at CM points are algebraic integral units. In recent work with Griffin and Warnaar, the speaker has obtained a comprehensive framework of identities for infinite product modular forms in terms of Hall-Littlewood q-series. This work characterizes those integral units that arise from this theory. In a related direction, the speaker revisits the classical Moonshine Theorem which asserts that the coefficients of the modular j-functions are dimensions of virtual characters for the Monster, the largest of the simple sporadic groups. There are 194 irreducible representations of the Monster, and it has been a longstanding open problem to determine the distribution of these representations in Moonshine. In joint work with Griffin and Duncan, the speaker has obtained exact formulas for these distributions.
Thursday, October 30, 2014 - 11:00 , Location: Skiles 005 , Professor Albert Fathi , ENS-Lyon & IUF , Organizer: Martin Short
This is a joint work with Pierre Pageault. For a homeomorphism h of a compact space, a Lyapunov function is a real valued function that is non-increasing along orbits for h. By looking at simple dynamical systems(=homeomorphisms) on the circle, we will see that there are systems which are topologically conjugate and have Lyapunov functions with various regularity. This will lead us to define barriers analogous to the well known Peierls barrier or to the Maסי potential in Lagrangian systems. That will produce by analogy to Mather's theory of Lagrangian Systems an Aubry set which is the generalized recurrence set introduced in the 60's by Joe Auslander (via transfinite induction) and a Maסי set which is essentially Conley's chain recurrent set. No serious knowledge of Dynamical Systems is necessary to follow the lecture.

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