Let $M$ be a finite dimensional complex manifold. Its loop space
$LM$ is an infinite dimensional complex manifold consisting of
maps (loops) $S^1 \to M$ in some fixed $C^k$ or Sobolev $W^{k,p}$
space. It is a natural question to solve d-bar equation
and/or compute the Dolbeault cohomology groups on loop spaces. I
will talk about the joint work with L. Lempert to identify the
first Dolbeault cohomology group of the loop space of the Riemann
sphere. There are serious obstructions to applying techniques in
finite dimensions to an infinite dimensional setting. We introduced
a bag of tools to overcome the difficulties.
We define a new spectrum for compact length spaces and Riemannian manifolds called the ``covering spectrum" which roughly measures the size of the one dimensional holes in the space. More specifically, the covering spectrum is a set of real numbers $\delta>0$ which identify the distinct $\delta$ covers of the space. We investigate the relationship between this covering spectrum, the length spectrum, the marked length
spectrum and the Laplace spectrum. We analyze the behavior of the covering spectrum under Gromov-Hausdorff convergence and study its gap phenomenon. This is a joint work with Christina Sormani.
We present a new adaptive numerical scheme for solving parabolic PDEs in
cartesian geometry. Applying a finite volume discretization with explicit
time integration, both of second order, we employ a fully adaptive
multiresolution scheme to represent the solution on locally refined nested
grids. The fluxes are evaluated on the adaptive grid. A dynamical adaption
strategy to advance the grid in time and to follow the time evolution of
the solution directly explaoits the multiresolution representation.
Applying this new method to several test probelms in one, two and three
space dimensions, like convection-diffucion, viscous Burgers and
reaction-diffusion equations, we show its second order accuracy and
demonstrate its computational efficiency.
This work is joint work with Olivier Roussel.
I will consider a very natural class of functions,
called Hermitian algebraic, that generalize Hermitian polynomials. I will present a Hermitian analog, introduced by J. D'Angelo but already considered implicitly by D. Quillen, of Hilbert's 17th problem:
"When is a non-negative Hermitian algebraic function a quotient of squared norms of holomorphic mappings?" I will state a complete solution to the
problem, and then prove the result in a special (previously known) case. The proof I will present is new and simpler than the original proof. If time permits, I will indicate how one treats the general case.