Seminars and Colloquia by Series

Series: Other Talks
Monday, December 3, 2018 - 15:00 , Location: Howey N110 , Simon Berman , Georgia Tech (Physics) , Organizer: Rafael de la Llave
Thesis defense: Advisors: Turgay Uzer and Cristel Chandre Summary: Thirty years after the demonstration of the production of high laser harmonics through nonlinear laser-gas interaction, high harmonic generation (HHG) is being used to probe molecular dynamics in real time and is realizing its technological potential as a tabletop source of attosecond pulses in the XUV to soft X-ray range. Despite experimental progress, theoretical efforts have been stymied by the excessive computational cost of first-principles simulations and the difficulty of systematically deriving reduced models for the non-perturbative, multiscale interaction of an intense laser pulse with a macroscopic gas of atoms. In this thesis, we investigate first-principles reduced models for HHG using classical mechanics. On the microscopic level, we examine the recollision process---the laser-driven collision of an ionized electron with its parent ion---that drives HHG. Using nonlinear dynamics, we elucidate the indispensable role played by the ionic potential during recollisions in the strong-field limit. On the macroscopic level, we show that the intense laser-gas interaction can be cast as a classical field theory. Borrowing a technique from plasma physics, we systematically derive a hierarchy of reduced Hamiltonian models for the self-consistent interaction between the laser and the atoms during pulse propagation. The reduced models can accommodate either classical or quantum electron dynamics, and in both cases, simulations over experimentally-relevant propagation distances are feasible. We build a classical model based on these simulations which agrees quantitatively with the quantum model for the propagation of the dominant components of the laser field. Subsequently, we use the classical model to trace the coherent buildup of harmonic radiation to its origin in phase space. In a simplified geometry, we show that the anomalously high frequency radiation seen in simulations results from the delicate interplay between electron trapping and higher energy recollisions brought on by propagation effects.
Series: Other Talks
Thursday, November 29, 2018 - 09:00 , Location: Skiles, Room 114 , Hassan Attarchi , Georgia Institute of Technology , hattarchi@gatech.edu , Organizer: Hassan Attarchi

Oral Comprehensive Exam

<p>The purpose of this work is approximation of generic Hamiltonian dynamical systems by those with a finite number of islands. In this work, we will consider a Lemon billiard as our Hamiltonian dynamical system apparently with an infinitely many islands. Then, we try to construct a Hamiltonian dynamical system by deforming the boundary of our lemon billiard to have a finite number of islands which are the same or sub-islands of our original system. Moreover, we want to show elsewhere in the phase space of the constructed billiard is a chaotic sea. In this way, we will have a dynamical system which preserves some properties of our lemon billiards while it has much simpler structure.</p>
Series: Other Talks
Tuesday, November 27, 2018 - 13:05 , Location: Skiles Atrium , Cristobal Guzmanal Guzman , Universidad Católica de Chile, Chile , Organizer: Prasad Tetali
Cristobal Guzman will discuss his employment experience as an ACO alummus. The&nbsp;conversations will take place over coffee.
Series: Other Talks
Wednesday, November 14, 2018 - 04:00 , Location: Molecular Science and Engineering Building, Classroom G011 , Christopher Jarzynski , Director, Institute for Physical Science and Technology University of Maryland , Organizer: Rafael de la Llave
Thermodynamics provides a robust conceptual framework and set of laws that govern the exchange of energy and matter.&nbsp; Although these laws were originally articulated for macroscopic objects, it is hard to deny that nanoscale systems, as well, often exhibit “thermodynamic-like” behavior.&nbsp; To what extent can the venerable laws of thermodynamics be scaled down to apply to individual microscopic systems, and what new features emerge at the nanoscale?&nbsp; I will review recent progress toward answering these questions, with a focus on the second law of thermodynamics. I will argue that the inequalities ordinarily used to express the second law can be replaced by stronger equalities, known as fluctuation relations, which relate equilibrium properties to far-from-equilibrium fluctuations.&nbsp; The discovery and experimental validation of these relations has stimulated interest in the feedback control of small systems, the closely related Maxwell demon paradox, and the interpretation of the thermodynamic arrow of time.&nbsp; These developments have led to new tools for the analysis of non-equilibrium experiments and simulations, and they have refined our understanding of irreversibility and the second law. &nbsp; Bio Chris Jarzynski received an AB degree in physics from Princeton University in 1987, and a PhD in physics from the University of California, Berkeley in 1994. After postdoctoral positions at the University of Washington in Seattle and at Los Alamos National Laboratory in New Mexico, he became a staff member in the Theoretical Division at Los Alamos. In 2006, he moved to the University of Maryland, College Park, where he is now a Distinguished University Professor in the Department of Chemistry and Biochemistry, with joint appointments in the Institute for Physical Science and Technology and the Department of Physics. His research is primarily in the area of nonequilibrium statistical physics, where he has contributed to an understanding of how the laws of thermodynamics apply to nanoscale systems. He has been the recipient of a Fulbright Fellowship, the 2005 Sackler Prize in the Physical Sciences, and the 2019 Lars Onsager Prize in Theoretical Statistical Physics. He is a Fellow of the American Physical Society and the American Academy of Arts and Sciences. &nbsp; Contact:&nbsp;Professor Jennifer Curtis&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Email:&nbsp;<a rel="noopener noreferrer" href="mailto:jennifer.curtis@physics.gatech.edu" target="_blank">jennifer.curtis@physics.gatech.edu</a>&nbsp; &nbsp;
Series: Other Talks
Tuesday, November 6, 2018 - 12:30 , Location: Skiles 006 , Dantong Zhu , Georgia Tech , dantongzhu@gatech.edu , Organizer: Samantha Petti

This talk is organized by the Association for Women in Math (AWM). Everyone is welcome to attend.

In 1968, Mader showed that for every integer $p = 1, 2, …, 7$, agraph on $n \geq p$ vertices and at least $(p-2)n - \binom{p-1}{2} + 1$ edgeshas a $K_p$ minor. However, this result is false for $p = 8$ with the counter-example K2,2,2,2,2. In this talk, we will discuss this function presented byMader for $K_p$ where $p$ is bigger. We will also discuss related resultsproved using probabilistic methods and the relation of this problem toHadwiger’s conjecture.
Series: Other Talks
Tuesday, November 6, 2018 - 11:00 , Location: Howey N110 , Brian Swingle , Univ of Maryland , Organizer: Rafael de la Llave
&nbsp;&nbsp; I will discuss chaos in quantum many-body systems, specifically how it is relates to thermalization and how it fails in many-body localized states. I will conjecture a new universal form for the spreading of chaos in local systems, and discuss evidence for the conjecture from a variety of sources including new large-scale simulations of quantum dynamics of spin chains. &nbsp; &nbsp;
Series: Other Talks
Thursday, October 25, 2018 - 11:00 , Location: Skiles 006 , Lectures on Combinatorial Statistics , Pompeu Fabra University, Barcelona , gabor.lugosi@gmail.com , Organizer: Salvador Barone

Thanks are due to our colleague, Vladimir Koltchinskii, for arranging this visit. Please write to Vladimir if you would like to meet with Professor Gabor Lugosi during his visit, or for additional information.

In these lectures we discuss some statistical problems with an interesting combinatorial structure behind. We start by reviewing the "hidden clique" problem, a simple prototypical example with a surprisingly rich structure. We also discuss various "combinatorial" testing problems and their connections to high-dimensional random geometric graphs. Time permitting, we study the problem of estimating the mean of a random variable.
Series: Other Talks
Thursday, October 18, 2018 - 15:00 , Location: Skiles 006 , Lectures on Combinatorial Statistics , Pompeu Fabra University, Barcelona , gabor.lugosi@gmail.com , Organizer: Salvador Barone

Thanks are due to our colleague, Vladimir Koltchinskii, for arranging this visit. Please write to Vladimir if you would like to meet with Professor Gabor Lugosi during his visit, or for additional information.

In these lectures we discuss some statistical problems with an interesting combinatorial structure behind. We start by reviewing the "hidden clique" problem, a simple prototypical example with a surprisingly rich structure. We also discuss various "combinatorial" testing problems and their connections to high-dimensional random geometric graphs. Time permitting, we study the problem of estimating the mean of a random variable.
Series: Other Talks
Thursday, October 18, 2018 - 12:05 , Location: Skiles 006 , Boris Bukh , Carnegie Mellon University , Organizer: Lutz Warnke
What to do if the measurements that you took were corrupted by a malicious spy? We will see how the natural geometric approach to the problem leads to a geometry where lines are crooked, and triangles are square.
Series: Other Talks
Monday, October 15, 2018 - 12:00 , Location: Groseclose 402 , Lectures on Combinatorial Statistics , Pompeu Fabra University, Barcelona , gabor.lugosi@gmail.com , Organizer: Salvador Barone

Thanks are due to our colleague, Vladimir Koltchinskii, for arranging this visit. Please write to Vladimir if you would like to meet with Professor Gabor Lugosi during his visit, or for additional information. 

In these lectures we discuss some statistical problems with an interesting combinatorial structure behind. We start by reviewing the "hidden clique" problem, a simple prototypical example with a surprisingly rich structure. We also discuss various "combinatorial" testing problems and their connections to high-dimensional random geometric graphs. Time permitting, we study the problem of estimating the mean of a random variable.

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