Seminars and Colloquia by Series

Wednesday, May 30, 2018 - 14:00 , Location: Skiles 006 , Tongzhou Chen , GT Math , Organizer: Jiaqi Yang
We model and analyze the dynamics of religious group membership and size. A groups is distinguished by its strictness, which determines how much time group members are expected to spend contributing to the group. Individuals differ in their rate of return for time spent outside of their religious group. We construct a utility function that individ- uals attempt to maximize, then find a Nash Equilibrium for religious group participation with a heterogeneous population. We then model dynamics of group size by including birth, death, and switching of individuals between groups. Group switching depends on the strictness preferences of individuals and their probability of encountering members of other groups.
Friday, April 27, 2018 - 15:05 , Location: Skiles 271 , Bhanu Kumar , GTMath , Organizer: Jiaqi Yang
This talk follows Chapter 4 of the well known text by Guckenheimer and Holmes. It is intended to present the theorems on averaging for systems with periodic perturbation, but slow evolution of the solution. Also, a discussion of Melnikov’s method for finding persistence of homoclinic orbits and periodic orbits will also be given. Time permitting, an application to the circular restricted three body problem may also be included. 
Friday, April 20, 2018 - 15:05 , Location: Skiles 271 , Prof. Rafael de la Llave , GT Math , Organizer: Jiaqi Yang
A well known paper of H. Federer on Flat chains contains a remarkable example attributed  to F. Almgren. We intend to give a geometric exposition of the example and explain its relevance in the global theory of geodesic flows and some global problems such as homogenization in quasi-periodic media. This is part of an expository paper with X. Su.
Friday, April 20, 2018 - 15:05 , Location: Skiles 271 , Prof. Rafael de la Llave , GT Math , Organizer: Jiaqi Yang
A well known paper of H. Federer on Flat chains contains a remarkable example attributed  to F. Almgren. We intend to give a geometric exposition of the example and explain its relevance in the global theory of geodesic flows and some global problems such as homogenization in quasi-periodic media. This is part of an expository paper with X. Su.
Friday, March 16, 2018 - 15:05 , Location: Skiles 271 , Longmei Shu , GT Math , Organizer: Jiaqi Yang
Isospectral reductions decrease the dimension of the adjacency matrix while keeping all the eigenvalues. This is achieved by using rational functions in the entries of the reduced matrix. I will show how it's done through an example. I will also discuss about the eigenvectors and generalized eigenvectors before and after reductions.
Friday, March 2, 2018 - 15:05 , Location: Skiles 271 , Adrian P. Bustamante , Georgia Tech , Organizer:
Given a one-parameter family of maps of an interval to itself, one can observe period doubling bifurcations as the parameter is varied. The aspects of those bifurcations which are independent of the choice of a particular one-parameter family are called universal. In this talk we will introduce, heuristically, the so-called Feigenbaun universality and then we'll expose some rigorous results about it.
Friday, February 23, 2018 - 15:00 , Location: Skiles 271 , Jiaqi Yang , GT Math , Organizer: Jiaqi Yang
We will present a rigorous proof of non-existence of homotopically non-trivial invariant circles for standard map:x_{n+1}=x_n+y_{n+1}; y_{n+1}=y_n+\frac{k}{2\pi}\sin(2\pi x_n).This a work by J. Mather in 1984.
Friday, February 16, 2018 - 15:00 , Location: Skiles 271 , Yian Yao , GT Math , Organizer: Jiaqi Yang
I will report on the parameterization method for computing normally hyperbolic invariant tori(NHIT) for diffeomorphisms. To this end, a Newton-like method for solving the invariance equation based on the graph transform method will be presented with details. Some notes on numerical implementations will also be included if time allows.  This is a work by Marta Canadell and Alex Haro.
Friday, February 9, 2018 - 15:00 , Location: Skiles 271 , Joan Gimeno , BGSMath-UB , Organizer: Jiaqi Yang
We are going to explain how invariant dynamical objects, such as (quasi)periodic orbits, can numerically be computed for Delay Differential Equations as well as their stability. To this end, we will use Automatic Differentiation techniques and iterative linear solvers with appropiate preconditioners. Additionally some numerical experiments will be presented to illustrate the approaches for each of those objects.This is joint work with A. Jorba.
Friday, February 2, 2018 - 15:00 , Location: Skiles 271 , Gladston Duarte , University of Barcelona & GT , gladston@maia.ub.es , Organizer: Jiaqi Yang
In a given system of coordinates, the Restricted Three-Body Problem has some interesting dynamical objects, for instance, equilibrium points, periodic orbits, etc. In this work, some connections between the stable and unstable manifolds of periodic orbits of this system are studied. Such connections let one explain the movement of Quasi-Hilda comets, which describe an orbit that sometimes can be approximated by an ellipse of semi-major axis greater than Jupiter's one, sometimes smaller. Using a computer algebra system, one can compute an approximation to those orbits and its manifolds and investigate the above mentioned connections. In addition, the Planar Circular model is used as a base for the fitting of the orbit of comet 39P/Oterma, whose data were collected from the JPL Horizons system. The possibility of using other models is also discussed.  

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