Seminars and Colloquia by Series

Monday, November 20, 2017 - 14:00 , Location: Skiles 005 , Yat Tin Chow , Mathematics, UCLA , ytchow@math.ucla.edu , Organizer: Prasad Tetali
In this talk, we will introduce a family of stochastic processes on the Wasserstein space, together with their infinitesimal generators.  One of these processes is modeled after Brownian motion and plays a central role in our work.  Its infinitesimal generator defines a partial Laplacian on the space of Borel probability measures, taken as  a partial trace of a Hessian.  We study the eigenfunction of this partial Laplacian and develop a theory of Fourier analysis.  We also consider the heat flow generated by this partial Laplacian on the Wasserstein space, and discuss smoothing effect of this flow for a particular class of initial conditions.  Integration by parts formula, Ito formula and an analogous Feynman-Kac formula will be discussed. We note the use of the infinitesimal generators in the theory of Mean Field Games, and we expect they will play an important role in future studies of viscosity solutions of PDEs in the Wasserstein space.
Monday, November 20, 2017 - 11:15 , Location: Skiles 005 , Igor Belykh , Georgia State University , Organizer: Livia Corsi
Several modern footbridges around the world have experienced large lateral vibrations during crowd loading events. The onset of large-amplitude bridge wobbling has generally been attributed to crowd synchrony; although, its role in the initiation of wobbling has been challenged. In this talk, we will discuss (i) the contribution of a single pedestrian into overall, possibly unsynchronized, crowd dynamics, and (ii) detailed, yet analytically tractable, models of crowd phase-locking. The pedestrian models can be used as "crash test dummies" when numerically probing a specific bridge design. This is particularly important because the U.S. code for designing pedestrian bridges does not contain explicit guidelines that account for the collective pedestrian behavior. This talk is based on two recent papers: Belykh et al., Science Advances, 3, e1701512 (2017) and Belykh et al., Chaos, 26, 116314 (2016).
Friday, November 17, 2017 - 16:00 , Location: Skiles 001 , Maxie Schmidt , Georgia Tech , mschmidt34@gatech.edu , Organizer: Sudipta Kolay
Sage is widely considered to be the defacto open-source alternative to Mathematica that is freely available for download to users on most standard platforms at sagemath.org. New users to Sage are also able to use its capabilities from any webbrowser and other useful Linux-only software by registering for a free account on the Sage Math Cloud platform (SMC). In addition to providing users with excellent documentation, Sage allows its users to develop spohisticated mathematics applications using Python and other excellent open-source developer tools that are well tested under both Unix / Linux and Windows environments. In this two-week workshop we provide a user-friendly introduction to Sage for beginners starting from first principles in Python, though some coding experience in other languages will of course be helpful to participants. The main project we will be focusing on over the course of the workshop is an extension of the open-source library provided by the Tilings Gap Distributions and Pair Correlation Project developed by the workshop guide at the University of Washington this and last year. This application will allow participants in the workshop to hone their coding skills in Sage by working on an extension of a real-world computational mathematics application in statistics and geometry. Prospective participants can gain a heads-up on the workshop by visiting the syllabus webpage freely available for modification online at https://github.com/maxieds/WXMLTilingsHOWTO/wiki.  The workshop guide will also offer continued free technical support on Sage, Python programming, and Linux to participants in the workshop after the two-week session is complete. Future AMS workshop sessions focusing on other Sage programming topics may be run later based on feedback from this proto-session. Faculty and postdocs are welcome to attend. See you all there on Friday! 
Friday, November 17, 2017 - 15:00 , Location: Skiles 154 , Bhanu Kumar , GT Math , Organizer:
This lecture will discuss the stability of perturbations of integrable Hamiltonian systems. A brief discussion of history, integrability, and the Poincaré nonintegrability theorem will be followed by the proof of the theorem of Kolmogorov on persistence of invariant tori. Time permitting, the problem of small divisors may be briefly discussed. This lecture wIll follow the slides from the Satellite Dynamics and Space Missions 2017 summer school held earlier this semester in Viterbo, Italy.
Friday, November 17, 2017 - 15:00 , Location: Skiles 005 , Huseyin Acan , Rutgers University , Organizer: Lutz Warnke
A 1992 conjecture of Alon and Spencer says, roughly, that the ordinary random graph G_{n,1/2} typically admits a covering of a constant fraction of its edges by edge-disjoint, nearly maximum cliques. We show that this is not the case. The disproof is based on some (partial) understanding of a more basic question: for k ≪ \sqrt{n} and A_1, ..., A_t chosen uniformly and independently from the k-subsets of {1…n}, what can one say about P(|A_i ∩ A_j|≤1 ∀ i≠j)? Our main concern is trying to understand how closely the answers to this and a related question about matchings follow heuristics gotten by pretending that certain (dependent) choices are made independently. Joint work with Jeff Kahn.
Friday, November 17, 2017 - 15:00 , Location: Skiles 006 , Timo Weidl , Univ. Stuttgart , weidl@mathematik.uni-stuttgart.de , 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.
Friday, November 17, 2017 - 10:00 , Location: Skiles 114 , Timothy Duff , GA Tech , Organizer: Timothy Duff
Motivated by the general problem of polynomial system solving, we state and sketch a proof Kushnirenko's theorem. This is the simplest in a series of results which relate the number of solutions of a "generic" square polynomial system to an invariant of some associated convex bodies. For systems with certain structure (here, sparse coefficients), these refinements may provide less pessimistic estimates than the exponential bounds given by Bezout's theorem.
Thursday, November 16, 2017 - 13:30 , Location: Skiles 006 , Lotfi Hermi , Florida International University , lhermi@gmail.com , 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)
Thursday, November 16, 2017 - 13:30 , Location: Skiles 005 , Vijay Vazirani , UC Irvine , Organizer: Robin Thomas
Is matching in NC, i.e., is there a deterministic fast parallel algorithm for it? This has been an outstanding open question in TCS for over three decades, ever since the discovery of Random NC matching algorithms. Within this question, the case of planar graphs has remained an enigma: On the one hand, counting the number of perfect matchings is far harder than finding one (the former is #P-complete and the latter is in P),  and on the other, for planar graphs, counting has long been known to be in NC whereas finding one has resisted a solution!The case of bipartite planar graphs was solved by Miller and Naor in 1989 via a flow-based algorithm.  In 2000, Mahajan and Varadarajan gave an elegant way of using counting matchings to finding one, hence giving a different NC algorithm.However, non-bipartite planar graphs still didn't yield: the stumbling block being odd tight cuts.  Interestingly enough, these are also a key to the solution: a balanced odd tight cut leads to a straight-forward divide and conquer NC algorithm. The remaining task is to find such a cut in NC. This requires several algorithmic ideas, such as finding a point in the interior of the minimum weight face of the perfect matching polytope and uncrossing odd tight cuts.Joint work with Nima Anari.
Wednesday, November 15, 2017 - 13:55 , Location: Skiles 005 , Cristina Pereyra , University of New Mexico , Organizer: Michael Lacey
 t-Haar multipliers are examples of Haar multipliers were the symbol depends both on the frequency variable (dyadic intervals) and on the space variable, akin to pseudo differential operators. They were introduced more than 20 years ago, the corresponding multiplier when $t=1$ appeared first  in connection to the resolvent of the dyadic paraproduct, the cases $t=\pm 1/2$ is intimately connected to direct and reverse inequalities for the dyadic square function in $L^2$, the case $t=1/p$ naturally appears in the study of weighted inequalities in $L^p$. Much has happened in the theory of weighted inequalities in the last two decades, highlights are the resolution of the $A_2$ conjecture (now theorem) by Hyt\"onen in 2012 and the resolution of the two weight problem for the Hilbert transform by  Lacey, Sawyer, Shen and Uriarte Tuero in 2014. Among the competing methods used to prove these results were Bellman functions, corona decompositions, and domination by sparse operators. The later method has gained a lot of traction and is being widely used in contexts beyond what it was originally conceived for  in work of Lerner, several of these new applications have originated here at Gatech. In this talk I would like to tell you what I know about t-Haar multipliers (some work goes back to my PhD thesis and joint work with Nets Katz and with my former students Daewon Chung, Jean Moraes, and Oleksandra Beznosova), and what we ought to know in terms of sparse domination.

Pages