College of Sciences (CoS)
http://hdl.handle.net/1853/6018
Since Georgia Tech first opened its doors in 1888, science has been used to drive Georgia Tech forward, endow students with the knowledge to lead in an increasingly technological world, and strengthen Georgia through interaction with industry.2016-12-04T18:37:17ZPerturbation problems in PDE dynamics
http://hdl.handle.net/1853/56057
Perturbation problems in PDE dynamics
Zeng, Chongchun
Issued as final report
2009-08-01T00:00:00ZZeng, ChongchunExploring the Inner Structure of Active Galactic Nuclei by Reverberation
http://hdl.handle.net/1853/56020
Exploring the Inner Structure of Active Galactic Nuclei by Reverberation
Peterson, Bradley M.
The innermost structure of active galactic nuclei (AGNs) consists of an accretion disk surrounding a supermassive black hole and, on somewhat larger scales, rapidly moving diffuse gas. The ultraviolet through near IR spectrum of AGNs is dominated by thermal continuum emission from the accretion disk and broad emission lines and absorption features from the diffuse gas. The continuum flux from the accretion disk varies with time, and the emission lines also change in brightness, or “reverberate,” in response to these variations, with a delay due to the light-travel time across the line-emitting region. Measurement of the emission-line time delay yields the size of the line-emitting region and by combining this with the emission-line Doppler width, the central black hole mass can be inferred. I will discuss results from recent “reverberation mapping” experiments, including a 179-orbit HST Cycle 21 program, that have been designed to explore the dynamics of the emission-line gas and are yielding a wealth of new and quite surprising information about AGN structure.
Presented on October 31, 2016 at 3:00 p.m. in the Marcus Nanotechnology Building, Room 1117; Bradley M. Peterson is the former Chair (2006-2015) of the Department of Astronomy at The Ohio State University. His research is directed towards determination of the physical nature of active galactic nuclei (AGNs). These are the most luminous discrete sources in the Universe, as bright as an entire giant galaxy of normal stars, but are nevertheless very compact, only about the size of the Solar System. The immediate goal of most of my recent research has been to probe the inner structure of AGNs on the smallest possible scales through studies of continuum and emission-line variability, a process known as "reverberation mapping." Reverberation mapping allows us to measure directly the masses of the black holes at the centers of active galactic nuclei.; Runtime: 59:18 minutes
2016-10-31T00:00:00ZPeterson, Bradley M.The innermost structure of active galactic nuclei (AGNs) consists of an accretion disk surrounding a supermassive black hole and, on somewhat larger scales, rapidly moving diffuse gas. The ultraviolet through near IR spectrum of AGNs is dominated by thermal continuum emission from the accretion disk and broad emission lines and absorption features from the diffuse gas. The continuum flux from the accretion disk varies with time, and the emission lines also change in brightness, or “reverberate,” in response to these variations, with a delay due to the light-travel time across the line-emitting region. Measurement of the emission-line time delay yields the size of the line-emitting region and by combining this with the emission-line Doppler width, the central black hole mass can be inferred. I will discuss results from recent “reverberation mapping” experiments, including a 179-orbit HST Cycle 21 program, that have been designed to explore the dynamics of the emission-line gas and are yielding a wealth of new and quite surprising information about AGN structure.New Applications of the Polynomial Method to Problems in Combinatorics
http://hdl.handle.net/1853/55993
New Applications of the Polynomial Method to Problems in Combinatorics
Croot, Ernie
Ernest Croot will discuss some new applications of the polynomial method to some classical problems in combinatorics, in particular the Cap-Set Problem. The Cap-Set Problem is to determine the size of the largest subset A of F_p^n having no three-term arithmetic progressions, which are triples of vectors x,y,z satisfying x+y=2z. I will discuss an analogue of this problem for Z_4^n and the recent progress on it due to myself, Seva Lev and Peter Pach; and will discuss the work of Ellenberg and Gijswijt, and of Tao, on the F_p^n version (the original context of the problem).
Presented on October 13, 2016 at the Skiles Building, Georgia Tech.; Ernest Croot is a Professor in the School of Mathematics at Georgia Tech.; Runtime: 51:26 minutes
2016-10-13T00:00:00ZCroot, ErnieErnest Croot will discuss some new applications of the polynomial method to some classical problems in combinatorics, in particular the Cap-Set Problem. The Cap-Set Problem is to determine the size of the largest subset A of F_p^n having no three-term arithmetic progressions, which are triples of vectors x,y,z satisfying x+y=2z. I will discuss an analogue of this problem for Z_4^n and the recent progress on it due to myself, Seva Lev and Peter Pach; and will discuss the work of Ellenberg and Gijswijt, and of Tao, on the F_p^n version (the original context of the problem).Thin film topological insulators: where do we stand and where are we headed?
http://hdl.handle.net/1853/55971
Thin film topological insulators: where do we stand and where are we headed?
Oh, Seongshik
About a decade ago, a little after graphene was discovered, a few theoretical physicists proposed that all solids can be grouped into different classes according to their band structure topologies: depending on which group of the topological families the solid belongs to, it is supposed to carry distinct electronic properties. This notion of topology applied to the band structure of materials gave rise to the birth of topological materials as a new paradigm of condensed matter physics. In particular, according to these theories, all insulators can be grouped into either of the two material classes: topological vs. trivial insulators. The conventional insulators we know are all trivial insulators but several materials such as Bi2Se3, Bi2Te3 and Sb2Te3 were proposed and later confirmed to be topological insulators (TIs), which are supposed to be insulating in the bulk but guaranteed to be metallic on their surfaces. Because of the strongly mathematical nature of the concept of topology, once the notion of topology started being applied to material systems, numerous theoretical proposals for various exotic functionalities have emerged. Nevertheless, only a very small set of those proposals have been realized, mostly due to various defect problems. In this talk, I will review and provide a perspective to the field, while discussing how to overcome these defect problems through thin film engineering schemes.
Presented on October 17, 2016 at 3:00 p.m. in the Marcus Nanotechnology Building, Room 1117; Seongshik Oh is a faculty member in the Department of Physics and Astronomy at Rutgers University. He is a member of the Condensed Matter Experiment Group.; Runtime: 67:32 minutes
2016-10-17T00:00:00ZOh, SeongshikAbout a decade ago, a little after graphene was discovered, a few theoretical physicists proposed that all solids can be grouped into different classes according to their band structure topologies: depending on which group of the topological families the solid belongs to, it is supposed to carry distinct electronic properties. This notion of topology applied to the band structure of materials gave rise to the birth of topological materials as a new paradigm of condensed matter physics. In particular, according to these theories, all insulators can be grouped into either of the two material classes: topological vs. trivial insulators. The conventional insulators we know are all trivial insulators but several materials such as Bi2Se3, Bi2Te3 and Sb2Te3 were proposed and later confirmed to be topological insulators (TIs), which are supposed to be insulating in the bulk but guaranteed to be metallic on their surfaces. Because of the strongly mathematical nature of the concept of topology, once the notion of topology started being applied to material systems, numerous theoretical proposals for various exotic functionalities have emerged. Nevertheless, only a very small set of those proposals have been realized, mostly due to various defect problems. In this talk, I will review and provide a perspective to the field, while discussing how to overcome these defect problems through thin film engineering schemes.