Seminars and Colloquia by Series

Friday, February 19, 2010 - 14:00 , Location: Skiles 269 , Anh Tran , Georgia Tech , Organizer:

This is part 1 of a two part talk.  The second part will continue next week. 

I will introduce the AJ conjecture (by Garoufalidis) which relates the A-polynomial and the colored Jones polynomial of a knot in the 3-sphere. Then I will verify it for the trefoil and the figure 8 knots (due to Garoufalidis) and torus knots (due to Hikami) by explicit calculations.
Friday, February 12, 2010 - 14:00 , Location: Skiles 269 , John Etnyre , Georgia Tech , Organizer:
After, briefly, recalling the definition of contact homology, a powerful but somewhat intractable and still largely unexplored invariant of Legendrian knots in contact structures, I will discuss various ways of constructing more tractable and computable invariants from it. In particular I will discuss linearizations, products, massy products, A_\infty structures and terms in a spectral sequence. I will also show examples that demonstrate some of these invariants are quite powerful. I will also discuss what is known and not known about the relations between all of these invariants.
Friday, February 5, 2010 - 14:00 , Location: Skiles 269 , Meredith Casey , Georgia Tech , Organizer:
Exact Topic TBA.  Talk will be a general survery of branched covers, possibly including covers from the algebraic geometry perspective.  In addition we will look at branched coveres in higher dimensions, in the contact world, and my current research interests.  This talk will be a general survery, so very little background is assumed. 
Friday, January 29, 2010 - 14:00 , Location: Skiles 269 , Mohammad Ghomi , School of Mathematics, Georgia Tech , Organizer:
We prove that convex hypersurfaces M in R^n which are level sets of functions f: R^n --> R are C^1-regular if f has a nonzero partial derivative of some order at each point of M. Furthermore, applying this result, we show that if f is algebraic and M is homeomorphic to R^(n-1), then M is an entire graph, i.e., there exists a line L in R^n such that M intersects every line parallel L at precisely one point. Finally we will give a number of examples to show that these results are sharp.
Friday, January 15, 2010 - 14:00 , Location: Skiles 269 , Mohammad Ghomi , Georgia Tech , Organizer:
We study the topology of the  space bd K^n of complete convex hypersurfaces of R^n which are homeomorphic to R^{n-1}. In particular, using Minkowski sums, we construct a deformation retraction of bd K^n onto the Grassmannian space of hyperplanes. So every hypersurface in bd K^n may be flattened in a canonical way. Further, the total curvature of each hypersurface evolves continuously and monotonically under this deformation. We also show that, modulo proper rotations, the subspaces of bd K^n consisting of smooth, strictly convex, or positively curved hypersurfaces are each contractible, which settles a question of H. Rosenberg.
Friday, December 4, 2009 - 14:00 , Location: Skiles 269 , Jim Krysiak , School of Mathematics, Georgia Tech , Organizer:
This talk will mostly be exposition on a result of M. Ghomi that any C^2 knot in R^n can be C^1 perturbed into a knot of constant curvature while preserving any smoothness properties.
Friday, November 6, 2009 - 15:00 , Location: Skiles 269 , Meredith Casey , Georgia Tech , Organizer:
The goal of this talk is to describe simple constructions by which we can construct any compact, orientable 3-manifold.  It is well-known that every orientable 3-manifold has a Heegaard splitting.  We will first define Heegaard splittings, see some examples, and go through a very geometric proof of this therem.  We will then focus on the Dehn-Lickorish Theorem, which states that any orientation-preserving homeomorphism of an oriented 2-manifold without boundary can by presented as the composition of Dehn twists and homeomorphisms isotopic to the identity.  We will prove this theorm, and then see some applications and examples.  With both of these resutls together, we will have shown that using only handlebodies and Dehn twists one can construct any compact, oriented 3-manifold.    
Friday, October 30, 2009 - 15:00 , Location: Skiles 269 , Shea Vela-Vick , Columbia University , Organizer: John Etnyre
In this talk I will discuss a generalizations and/oo applications of bordered Floer homology.  After reviewing the basic definitions and constructions, I will focus either on an application to sutured Floer homology developed by Rumen Zarev, or on applications of the theory to the knot Floer homology. (While it would be good to have attended the other two talks this week, this talk shoudl be independent of them.)  This is a 2 hour talk.
Wednesday, October 28, 2009 - 10:00 , Location: Skiles 255 , Shea Vela-Vick , Columbia University , Organizer: John Etnyre
Here we will introduce the basic definitions of bordered Floer homology.  We will discuss bordered Heegaard diagrams as well as the algebraic objects, like A_\infinity algebras and modules, involved in the theory.  We will also discuss the pairing theorem which states that if  Y = Y_1 U_\phi Y_2  is obtained by identifying the (connected) boundaries of  Y_1  and  Y_2, then the closed Heegaard Floer theory of  Y  can be obtained as a suitable tensor product of the bordered theories of  Y_1  and  Y_2.Note the different time and place!This is a 1.5 hour talk.
Monday, October 26, 2009 - 10:00 , Location: Skiles 255 , Shea Vela-Vick , Columbia University , Organizer: John Etnyre
We will focus on the "toy model" of bordered Floer homology.  Loosely speaking, this is bordered Floer homology for grid diagrams of knots.  While the toy model unfortunately does not provide us with any knot invariants, it highlights many of the key ideas needed to understand the more general theory. Note the different time and place!  This is a 1.5 hour talk.