Seminars and Colloquia by Series

A classical Hamiltonian model for high harmonic generation

Series
Dynamical Systems Working Seminar
Time
Friday, February 24, 2017 - 15:05 for 1 hour (actually 50 minutes)
Location
Skiles 254
Speaker
Simon Berman – School of Physics
In a high harmonic generation (HHG) experiment, an intense laser pulse is sent through an atomic gas, and some of that light is converted to very high harmonics through the interaction with the gas. The spectrum of the emitted light has a particular, nearly universal shape. In this seminar, I will describe my efforts to derive a classical reduced Hamiltonian model to capture this phenomenon. Beginning with a parent Hamiltonian that yields the equations of motion for a large collection of atoms interacting self-consistently with the full electromagnetic field (Lorentz force law + Maxwell's equations), I will follow a sequence of reductions that lead to a reduced Hamiltonian which is computationally tractable yet should still retain the essential physics. I will conclude by pointing out some of the still-unresolved issues with the model, and if there's time I will discuss the results of some preliminary numerical simulations.

Experimental Analysis of Combinatorial Sequences

Series
Combinatorics Seminar
Time
Friday, February 24, 2017 - 15:05 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Jay Pantone – Dartmouth College –
In enumerative combinatorics, it is quite common to have in hand a number of known initial terms of a combinatorial sequence whose behavior you'd like to study. In this talk we'll describe two techniques that can be used to shed some light on the nature of a sequence using only some known initial terms. While these methods are, on the face of it, experimental, they often lead to rigorous proofs. As we talk about these two techniques -- automated conjecturing of generating functions, and the method of differential approximation -- we'll exhibit their usefulness through a variety of combinatorial topics, including matchings, permutation classes, and inversion sequences.

Discrete excitable media

Series
Stochastics Seminar
Time
Thursday, February 23, 2017 - 15:05 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
David Sivakoff – Ohio State University –
Excitable media are characterized by a local tendency towards synchronization, which can lead to waves of excitement through the system. Two classical discrete, deterministic models of excitable media are the cyclic cellular automaton and Greenberg-Hastings models, which have been extensively studied on lattices, Z^d. One is typically interested in whether or not sites are excited (change states) infinitely often (fluctuation vs fixation), and if so, whether the density of domain walls between disagreeing sites tends to 0 (clustering). We introduce a new comparison process for the 3-color variants of these models, which allows us to study the asymptotic rate at which a site gets excited. In particular, for a class of infinite trees we can determine whether the rate is 0 or positive. Using this comparison process, we also analyze a new model for pulse-coupled oscillators in one dimension, introduced recently by Lyu, called the firefly cellular automaton (FCA). Based on joint works with Lyu and Gravner.

Braid and Knot Theory

Series
Geometry Topology Student Seminar
Time
Thursday, February 23, 2017 - 12:00 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Sudipta Kolay – Georgia Tech
Braid and knot theory in 3-dimensional Euclidean space are related by classical theorems of Alexander and Markov. We will talk about closed braids in higher dimensions, and generalizations of Alexander's theorem.

Sparse Signal Detection with Binary Outcomes

Series
Job Candidate Talk
Time
Thursday, February 23, 2017 - 11:00 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Rajarshi Mukherjee – Department of Statistics, Stanford University
In this talk, I will discuss some examples of sparse signal detection problems in the context of binary outcomes. These will be motivated by examples from next generation sequencing association studies, understanding heterogeneities in large scale networks, and exploring opinion distributions over networks. Moreover, these examples will serve as templates to explore interesting phase transitions present in such studies. In particular, these phase transitions will be aimed at revealing a difference between studies with possibly dependent binary outcomes and Gaussian outcomes. The theoretical developments will be further complemented with numerical results.

Variance-sensitive concentration inequalities and applications to convexity

Series
Stochastics Seminar
Time
Wednesday, February 22, 2017 - 14:05 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Grigoris Paouris – Texas A&M –

Please Note: Please note the special time! This is Stochastic & Analysis seminars joint.

Motivated by the investigation on the dependence on ``epsilon" in the Dvoretzky's theorem, I will show some refinements of the classical concentration of measure for convex functions. Applications to convexity will be presented if time permits. The talk will be based on joint works with Peter Pivovarov and Petros Valettas.

A Kirby calculus description of ribbon knots

Series
Geometry Topology Student Seminar
Time
Wednesday, February 22, 2017 - 14:05 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
Andrew McCullough – Georgia Tech
We will discuss a way of explicitly constructing ribbon knots using one-two handle canceling pairs. We will also mention how this is related to some recent work of Yasui, namely that there are infinitely many knots in (S^3, std) with negative maximal Thurston-Bennequin invariant for which Legendrian surgery yields a reducible manifold.

Video Slot Game Design

Series
Research Horizons Seminar
Time
Wednesday, February 22, 2017 - 12:00 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
Hua Xu – Gimmie Games
In this talk, we will have an overview of: the Gaming Industry, specifically on the Video Slot Machine segment; the top manufactures in the world; the game design studio Gimmie Games, who we are, what we do; what is the process of making a video slot game; what is the basic structure of the math model of a slot game; current strong math models in the market; what is the roll of a game designer in the game development process; the skill set needed to be a successful Game Designer. Only basic probability knowledge is required for this talk.

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