Seminars and Colloquia by Series

Knots, Heegaard Floer Homology and Contact Geometry

Series
Geometry Topology Seminar
Time
Friday, November 5, 2010 - 14:00 for 2 hours
Location
Skiles 171
Speaker
Vera VertesiMIT

Please Note: The talk is 1.5-2 hours long, and although some knowledge of HeegaardFloer homology and contact manifolds is useful I will spend some time inthe begining to review the basic notions. So the talk should be accessibleto everyone.

The first hour of this talk gives a gentle introduction to yet another version of Heegaard Floer homology; Sutured Floer homology. This is the generalization of Heegaard Floer homology, for 3-manifolds with decorations (sutures) on their boundary. Sutures come naturally for contact 3-manifolds. Later we will concentrate on invariants for contact 3--manifolds in Heegaard Floer homology. This can be defined both for closed 3--manifolds, in this case they live in Heegaard Floer homology and for 3--manifolds with boundary, when the invariant is in sutured Floer homology. There are two natural generalizations of these invariants for Legendrain knots. One can directly generalize the definition of the contact invariant $\widehat{\mathcal{L}}$, or one can take the complement of the knot, and compute the invariant for that:$\textrm{EH}$. At the end of this talk I would like to describe a map that sends $\textrm{EH}$ to$\widehat{\mathcal{L}}$. This is a joint work with Andr\'as Stipsicz.

Global Stability of Dynamical Networks

Series
SIAM Student Seminar
Time
Friday, November 5, 2010 - 13:00 for 1 hour (actually 50 minutes)
Location
Skiles 255
Speaker
Ben WebbSchool of Mathematics, Georgia Tech
In this talk we consider the collective dynamics of a network of interacting dynamical systems and show that under certain conditions such dynamical networks have a unique global attractor. This involves a combination of techniques from dynamical systems theory as well as newly devised methods in graph theory. However, this talk is intended to be an introduction to both areas of mathematics with a focus on how the combination of the two is yielding new results in graph and dynamical systems theory.

Commensurability classes of $(-2,3,n)$ pretzel knot complements

Series
Geometry Topology Seminar
Time
Friday, November 5, 2010 - 11:05 for 1 hour (actually 50 minutes)
Location
Skiles 255
Speaker
Thomas MattmanCalifornia State University, Chico
(joint work with M. Macasieb) Let $K$ be a hyperbolic $(-2, 3, n)$ pretzel knot and $M = S^3 \setminus K$ its complement. For these knots, we verify a conjecture of Reid and Walsh: there are at most three knotcomplements in the commensurability class of $M$. Indeed, if $n \neq 7$, weshow that $M$ is the unique knot complement in its class.

Plank problems - the discrete geometric side

Series
School of Mathematics Colloquium
Time
Thursday, November 4, 2010 - 11:00 for 1 hour (actually 50 minutes)
Location
Skiles 269
Speaker
Karoly BezdekUniversity of Calgary
In the 1930's, Tarski introduced his plank problem at a time when the field Discrete Geometry was about to born. It is quite remarkable that Tarski's question and its variants continue to generate interest in the geometric and analytic aspects of coverings by planks in the present time as well. The talk is of a survey type with some new results and with a list of open problems on the discrete geometric side of the plank problem.

Exit times of diffusions with incompressible drifts

Series
Analysis Seminar
Time
Wednesday, November 3, 2010 - 14:00 for 1 hour (actually 50 minutes)
Location
Skiles 269
Speaker
Andrej ZlatosUniversity of Wisconsin, Madison
We consider the influence of an incompressible drift on the expected exit time of a diffusing particle from a bounded domain. Mixing resulting from an incompressible drift typically enhances diffusion so one might think it always decreases the expected exit time. Nevertheless, we show that in two dimensions, the only simply connected domains for which the expected exit time is maximized by zero drift are the discs.

Markov Perfect Nash Equilibria: some considerations on Economic Models, Dynamical Systems and Statistical Mechanics.

Series
Research Horizons Seminar
Time
Wednesday, November 3, 2010 - 12:00 for 1 hour (actually 50 minutes)
Location
Skiles 171
Speaker
Federico BonettoSchool of Mathematics - Georgia Institute of Technology

Please Note: Hosts: Yao Li and Ricardo Restrepo

Modern Economic Theory is largely based on the concept of Nash Equilibrium. In its simplest form this is an essentially statics notion. I'll introduce a simple model for the origin of money (Kiotaki and Wright, JPE 1989) and use it to introduce a more general (dynamic) concept of Nash Equilibrium and my understanding of its relation to Dynamical Systems Theory and Statistical Mechanics.

On an analogue of Torelli's theorem for tropical curves

Series
Tropical Geometry Seminar
Time
Wednesday, November 3, 2010 - 10:05 for 1 hour (actually 50 minutes)
Location
Skiles 114
Speaker
Farbod ShokriehGeorgia Tech
In classical algebraic geometry,Torelli's theorem states that a complete smooth curve over an algebraically closed field is uniquely determined by its principally polarized Jacobian. We will investigate a tropical analogue of this theorem. Torelli's problem for tropical curves is intimately related to some basic combinatorial questions regarding the cycle space of a finite graph. Combinatorics of the Voronoi (or Delaunay) decomposition associated to the cycle lattice play an essential role. This talk will be self-contained. The talk next week (by Melody Chan) can be considered a natural sequel.

Persistence of a single phytoplankton species

Series
PDE Seminar
Time
Tuesday, November 2, 2010 - 15:00 for 1 hour (actually 50 minutes)
Location
Skiles 255
Speaker
Prof. Yuan LouOhio State University
We investigate a nonlocal reaction-diffusion-advection equation which models the growth of a single phytoplankton species in a water column where the species depends solely on light for its metabolism. We study the combined effect of death rate, sinking or buoyant coe±cient, water column depth and vertical turbulent diffusion rate on the persistence of a single phytoplankton species. This is based upon a joint work with Sze-Bi Hsu, National Tsing-Hua University.

Decimations of l-sequences and permutations of even residues mod p

Series
Combinatorics Seminar
Time
Friday, October 29, 2010 - 15:05 for 1 hour (actually 50 minutes)
Location
Skiles 255
Speaker
Todd CochraneMath, Kansas State University
\ell-sequences are periodic binary sequences {a_i} that arise from Feedback with Carry Shift Registers and in many other ways. A decimation of {a_i} is a sequence of the form {a_{di}}. Goresky and Klapper conjectured that for any prime p>13 and any \ell-sequence based on p, every pair of allowable decimations of {a_i} is cyclically distinct. If true this would yield large families of binary sequences with ideal arithmetic cross correlations. The conjecture is essentially equivalent to the statement that if p>13 then the mapping x \to Ax^d on \mathbb Z/(p) with (d,p-1)=1, p \nmid A, permutes the even residues only if it is the identity mapping. We will report on the progress towards resolving this conjecture, focussing on our joint work with Bourgain, Paulhus and Pinner.

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