Seminars and Colloquia by Series

Wednesday, November 8, 2017 - 13:55 , Location: Skiles 005 , Francisco Villarroya , UGA , , Organizer: Michael Lacey
In this talk I will introduce a Tb Theorem that characterizes all Calderón-Zygmund operators that extend compactly on L^p(R^n) by means of testing functions as general as possible. In the classical theory for boundedness, the testing functions satisfy a non-degeneracy property called accretivity, which essentially implies the existence of a positive lower bound for the absolute value of the averages of the testing functions over all dyadic cubes. However, in the setting of compact operators, due to their better properties, the hypothesis of accretivity can be relaxed to a large extend. As a by-product, the results also describe those Calderón-Zygmund operators whose boundedness can be checked with non-accretive testing functions.
Wednesday, November 8, 2017 - 12:10 , Location: Skiles 006 , Michael Worthington , GA Tech , Organizer: Timothy Duff
Series: PDE Seminar
Tuesday, November 7, 2017 - 15:00 , Location: Skiles 006 , Chun Liu , Illinois Institute of Technology , , Organizer: Yao Yao
Almost all biological activities involve transport and distribution of ions and charged particles. The complicated coupling and competition between different ionic solutions in various biological environments give the intricate specificity and selectivity in these systems. In this talk, I will introduce several extended general diffusion systems motivated by the study of ion channels and ionic solutions in biological cells. In particular, I will focus on the interactions between different species, the boundary effects and in many cases, the thermal effects.
Tuesday, November 7, 2017 - 13:00 , Location: Skiles 006 , Günter Stolz , University of Alabama, Birmingham , , Organizer: Michael Loss
Tuesday, November 7, 2017 - 10:00 , Location: Skiles 006 , Yulia Karpeshina , University of Alabama, Birmingham , , Organizer: Michael Loss
  Existence of ballistic transport for Schr ̈odinger operator with a quasi- periodic potential in dimension two is discussed. Considerations are based on the following properties of the operator: the spectrum of the operator contains a semiaxis of absolutely continuous spectrum and there are generalized eigenfunctions being close to plane waves ei⟨⃗k,⃗x⟩ (as |⃗k| → ∞) at every point of this semiaxis. The isoenergetic curves in the space of momenta ⃗k corresponding to these eigenfunctions have a form of slightly distorted circles with holes (Cantor type structure). 
Monday, November 6, 2017 - 15:00 , Location: Skiles 006 , Isabel Vogt , Massachusetts Institute of Technology , , Organizer: Padmavathi Srinivasan
In this talk we will discuss the following question: When does there exist a curve of degree d and genus g passing through n general points in P^r? We will focus primarily on what is known in the case of space curves (r=3).
Monday, November 6, 2017 - 14:30 , Location: Boyd 304 , Peter Lambert-Cole and Alex Zupan , Georgia Tech and Univ. Nebraska Lincoln , Organizer: Caitlin Leverson
Peter Lambert-Cole: Mutant knots are notoriously hard to distinguish. Many, but not all, knot invariants take the same value on mutant pairs. Khovanov homology with coefficients in Z/2Z is known to be mutation-invariant, while the bigraded knot Floer homology groups can distinguish mutants such as the famous Kinoshita-Terasaka and Conway pair. However, Baldwin and Levine conjectured that delta-graded knot Floer homology, a singly-graded reduction of the full invariant, is preserved by mutation. In this talk, I will give a new proof that Khovanov homology mod 2 is mutation-invariant. The same strategy can be applied to delta-graded knot Floer homology and proves the Baldwin-Levine conjecture for mutations on a large class of tangles.  -----------------------------------------------------------------------------------------------------------------------------------------------Alex Zupan: Generally speaking, given a type of manifold decomposition, a natural problem is to determine the structure of all decompositions for a fixed manifold. In particular, it is interesting to understand the space of decompositions for the simplest objects. For example, Waldhausen's Theorem asserts that up to isotopy, the 3-sphere has a unique Heegaard splitting in every genus, and Otal proved an analogous result for classical bridge splittings of the unknot. In both cases, we say that these decompositions are "standard," since they can be viewed as generic modifications of a minimal splitting. In this talk, we examine a similar question in dimension four, proving that -- unlike the situation in dimension three -- the unknotted 2-sphere in the 4-sphere admits a non-standard bridge trisection. This is joint work with Jeffrey Meier.
Monday, November 6, 2017 - 13:55 , Location: Skiles 005 , Prof. Kevin Lin , University of Arizona , , Organizer: Molei Tao
Weighted direct samplers, sometimes also called importance samplers, are Monte Carlo algorithms for generating independent, weighted samples from a given target probability distribution. They are used in, e.g., data assimilation, state estimation for dynamical systems, and computational statistical mechanics. One challenge in designing weighted samplers is to ensure the variance of the weights, and that of the resulting estimator, are well-behaved. Recently, Chorin, Tu, Morzfeld, and coworkers have introduced a class of novel weighted samplers called implicit samplers, which possess a number of nice empirical properties. In this talk, I will summarize an asymptotic analysis of implicit samplers in the small-noise limit and describe a simple method to obtain a higher-order accuracy. I will also discuss extensions to stochastic differential equatons. This is joint work with Jonathan Goodman, Andrew Leach, and Matthias Morzfeld.
Monday, November 6, 2017 - 11:15 , Location: Skiles 005 , Farshad Shirani , Georgia Institute of Technology , Organizer: Livia Corsi
We present a mean field model of electroencephalographic activity in the brain, which is composed of a system of coupled ODEs and PDEs. We show the existence and uniqueness of weak and strong solutions of this model and investigate the regularity of the solutions. We establish biophysically plausible semidynamical system frameworks and show that the semigroups of weak and strong solution operators possess bounded absorbing sets. We show that there exist parameter values for which the semidynamical systems do not possess a global attractor due to the lack of the compactness property. In this case, the internal dynamics of the ODE components of the solutions can create asymptotic spatial discontinuities in the solutions, regardless of the smoothness of the initial values and forcing terms.
Friday, November 3, 2017 - 16:00 , Location: Skiles 249 , Justin Lanier and Shane Scott , Georgia Tech , Organizer: Sudipta Kolay
All of us have seen talks where the speaker uses slides. Some are great, and some are awful. Come and learn how to make great slide decks and how to avoid making awful ones. We will share a number of pieces of software that are easy to use and that can help you to improve your slide decks. We will also discuss best practices and dissect several short slide decks together. Next week there will be a follow-up, hands-on workshop on using the software Inkscape to create mathematical figures for talks, posters, and papers.