## Seminars and Colloquia by Series

### Geometry and Topology in Fluid Mechanics

Series
School of Mathematics Colloquium
Time
Thursday, October 2, 2008 - 11:00 for 1 hour (actually 50 minutes)
Location
Skiles 269
Speaker
John EtnyreSchool of Mathematics, Georgia Tech
Describe the trajectories of particles floating in a liquid. This is a surprisingly difficult problem and attempts to understand it have involved many diverse techniques. In the 60's Arold, Marsden, Ebin and others began to introduce topological techniques into the study of fluid flows. In this talk we will discuss some of these ideas and see how they naturally lead to the introduction of contact geometry into the study of fluid flows. We then consider some of the results one can obtain from this contact geometry perspective. For example we will show that for a sufficiently smooth steady ideal fluid flowing in the three sphere there is always some particle whose trajectory is a closed loop that bounds an embedded disk, and that (generically) certain steady Euler flows are (linearly) unstable.

### Geometry and Topology in Fluid Mechanics

Series
School of Mathematics Colloquium
Time
Thursday, October 2, 2008 - 11:00 for 1 hour (actually 50 minutes)
Location
Skiles 269
Speaker
John EtnyreSchool of Mathematics, Georgia Tech
Describe the trajectories of particles floating in a liquid. This is a surprisingly difficult problem and attempts to understand it have involved many diverse techniques. In the 60's Arold, Marsden, Ebin and others began to introduce topological techniques into the study of fluid flows. In this talk we will discuss some of these ideas and see how they naturally lead to the introduction of contact geometry into the study of fluid flows. We then consider some of the results one can obtain from this contact geometry perspective. For example we will show that for a sufficiently smooth steady ideal fluid flowing in the three sphere there is always some particle whose trajectory is a closed loop that bounds an embedded disk, and that (generically) certain steady Euler flows are (linearly) unstable.

### A Friendly Introduction to Constraint Programming

Series
ACO Student Seminar
Time
Wednesday, October 1, 2008 - 13:30 for 2 hours
Location
ISyE Executive Classroom
Speaker
Constraint Programming is a powerful technique developed by the Computer Science community to solve combinatorial problems. I will present the model, explain constraint propagation and arc consistency, and give some basic search heuristics. I will also go through some illustrative examples to show the solution process works.

### Knots, continued fractions and DNA

Series
Research Horizons Seminar
Time
Wednesday, October 1, 2008 - 12:00 for 1 hour (actually 50 minutes)
Location
Skiles 255
Speaker
Roland van der VeenUniversity of Amsterdam
In this introduction to knot theory we will focus on a class of knots called rational knots. Here the word rational refers to a beautiful theorem by J. Conway that sets up a one to one correspondence between these knots and the rational numbers using continued fractions. We aim to give an elementary proof of Conway's theorem and discuss its application to the study of DNA recombination. No knowledge of topology is assumed.

### Demographic stochasticity and the Daphnia model

Series
Mathematical Biology Seminar
Time
Wednesday, October 1, 2008 - 11:00 for 1 hour (actually 50 minutes)
Location
Skiles 255
Speaker
John DrakeUGA

### Variational Principles and Partial Differential Equations for Some Model Problems in Polycrystal Plasticity

Series
PDE Seminar
Time
Tuesday, September 30, 2008 - 15:15 for 1.5 hours (actually 80 minutes)
Location
Skiles 255
Speaker
Marian BoceaNorth Dakota State University, Fargo
The yield set of a polycrystal may be characterized using variational principles associated to suitable supremal functionals. I will describe some model problems for which these can be obtained via Gamma-convergence of a class of "power-law" functionals acting on fields satisfying appropriate differential constraints, and I will indicate some PDEs which play a role in the analysis of these problems.

### Horn Conjecture for finite von Neumann algebras II

Series
Analysis Seminar
Time
Monday, September 29, 2008 - 14:00 for 1 hour (actually 50 minutes)
Location
Skiles 255
Speaker
Wing Suet LiSchool of Mathematics, Georgia Tech
The Horn inequalities give a characterization of eigenvalues of self-adjoint n by n matrices A, B, C with A+B+C=0. The proof requires powerful tools from algebraic geometry. In this talk I will talk about our recent result of these inequalities that are indeed valid for self-adjoint operators of an arbitrary finite factors. Since in this setting there is no readily available machinery from algebraic geometry, we are forced to look for an analysts friendly proof. A (complete) matricial form of our result is known to imply an affirmative answer to the Connes' embedding problem. Geometers especially welcome!

### Stable equivalence of manifolds

Series
Geometry Topology Seminar
Time
Monday, September 29, 2008 - 14:00 for 1 hour (actually 50 minutes)
Location
Skiles 269
Speaker
Igor BelegradekSchool of Mathematics, Georgia Tech
This is an expository talk. A classical theorem of Mazur gives a simple criterion for two closed manifolds M, M' to become diffeomorphic after multiplying by the Euclidean n-space, where n large. In the talk I shall prove Mazur's theorem, and then discuss what happens when n is small and M, M' are 3-dimensional lens spaces. The talk shall be accessible to anybody with interest in geometry and topology.

### Thin Elastic Materials Under Confinement

Series
Applied and Computational Mathematics Seminar
Time
Monday, September 29, 2008 - 13:00 for 1 hour (actually 50 minutes)
Location
Skiles 255
Speaker
Silas AlbenSchool of Mathematics, Georgia Tech
We discuss two problems. First: When a piece of paper is crumpled, sharp folds and creases form. These are distributed over the sheet in a complex yet fascinating pattern. We study experimentally a two-dimensional version of this problem using thin strips of paper confined within rings of shrinking radius. We find a distribution of curvatures which can be fit by a power law. We provide a physical argument for the power law using simple elasticity and geometry. The second problem considers confinement of charged polymers to the surface of a sphere. This is a generalization of the classical Thompson model of the atom and has applications in the confinement of RNA and DNA in viral shells. Using computational results and asymptotics we describe the sequence of configurations of a simple class of charged polymers.

### On "Near-ideal model selection by l_1 minimization" by E.Candes & Y.Plan

Series
Probability Working Seminar
Time
Friday, September 26, 2008 - 15:00 for 1 hour (actually 50 minutes)
Location
Skiles 168
Speaker
Stas MinskerSchool of Mathematics, Georgia Tech