We will be looking at the trace map of the discrete Schrodinger operator with potential given by the period doubling sequence. It is known that for any positive coupling constant the spectrum of the corresponding operator is a Cantor set of Lebesgue measure zero. We are interested in the structure of the spectrum for small coupling constant, specifically the Hausdorff dimension and thickness.
In this talk, we will begin with simple questions of the Diophantine Approximation Theory, for instance, how closely can a given irrational number x be approximated by a rational number r with denominator no larger than a fixed number? This will lead us to talk about the set known as the Lagrange Spectrum whose structure closely resembles the structure of the sum of dynamically defined Cantor sets, which are defined by an iterate system of expanding differentiable functions on intervals. We will construct two Cantor sets whose arithmetic sum is a uniformly contracting self-similar set. A local result on a sufficient condition for a uniformly contracting self-similar set to be of Lebesgue measure zero will be proven.
As one of the deepest and most beautiful theorems in geometry, the
Hodge theorem builds a bridge between Riemannian metric and
topological invariants. It gives an isomorphism between the space of
harmonic p forms on a Riemannian manifold and the pde Rham cohomology group of a smooth structure. By the de Rham theorem, we see the
isomorphism between the space of harmonic p forms and p real singular cohomology group.
The Hodge theorem is a good example of how PDEs help us understand geometric structure and even topological structure. In this talk, we
will give an introduction to this theorem, explain the idea behind it, and give some applications in Riemannian geometry.
The tree property at \kappa^+ states that every tree with height \kappa^+ and levels of size at most \kappa has an unbounded branch. There is a tension between the tree property and the Singular Cardinal Hypothesis (SCH). Woodin asked if the failure of SCH at a singular cardinal \kappa implies the tree property at \kappa^+. Recently Neeman answered this question in the negative. Here we show that this result can be obtained at small cardinals. In particular we will show that given \omega many supercompact cardinals there is a generic extension in which the tree property holds at \aleph_{\omega^2+1} and SCH fails at \aleph_{\omega^2}.
The theory of soliton equations has been an active research area for the past forty-five years, with applications to algebra, geometry, mathematical physics, and applied mathematics. In this talk, I will explain how many of these equations arise as geometric evolution equations for curves and as the governing equations for surfaces in 3-space. In particular, I will use Quicktime movies and pictures produced in Palais' 3D-XplorMath mathematical visualization program to demonstrate properties of soliton equations and their associated geometric objects.
Topologically all Cantor sets are the same. Nevertheless, thee are many ways to assign a quantitative characteristic to Cantor sets, and these notions play important role in applications to dynamical systems, number theory, spectral theory, and other areas of mathematics. We will describe some of the characteristics (e.g. fractal dimentions, thickness) of Cantor sets and the ways one can calculate and use them.
The structure of Anosov-Katok example (in fact, this is a series of examples that can be constructed using similar techniques) will be presented. This is a way to build a smooth realization for several classes of measure preserving transformations.
We will review the recent (and not so recent) results on dynamics of piecewise isometries (especially piecewise translations), both in one and in higher dimensional case. Some interesting results (by Suzuki, Goetz, Zhuravlev, Boshernitzan, Bruin, Troubetzkoy, Buzzi) are known, but most of natural questions are still open. The main goal of the talk is to expose these open questions to potential researchers.