We shall review recent progress obtained in the understanding of localization
properties of random Schrodinger operators. The hard issue of the Anderson
transition is stated in terms of the spreading and of the non spreading of a
wave-packet initially located at the origin. It particular it is shown that
slow transport cannot happen for ergodic random operators. As an application,
we study quantum Hall systems, that is the Hamiltonian of an electron confined
to a two dimensional plane and subjected to a constant transverse magnetic
field. We prove delocalization around each Landau level, and localization
outside a small neighborhood of these levels.
The total variation based image denoising model of Rudin, Osher,
and Fatemi
has been generalized and modified in many ways in the literature; one of
these modifications is to use the L1 norm as the fidelity term. We study the
interesting consequences of this modification, especially from the point of
view of geometric properties of its solutions. It turns out to have
interesting
new implications for data driven scale selection and multiscale image
decomposition.
This talk will describe the simulation, design and optimization of a qubit
for use in quantum communication or quantum computation. The qubit is
realized as the spin of a single trapped electron in a semi-conductor
quantum dot. The quantum dot and a quantum wire are formed by the
combination of quantum wells and gates. The design goal for this system is a
"double pinchoff", in which there is a single trapped electron in the dot
and a single (or small number of) conduction states in the wire. Because of
considerable experimental uncertainty in the system parameters, the optimal
design should be "robust", in the sense that it is far away from
unsuccessful designs. We use a Poisson-Schrodinger model for the
electrostatic potential and electron wave function and a semi-analytic
solution of this model. Through a Monte Carlo search, aided by an analysis
of singular points on the design boundary, we find successful designs and
optimize them to achieve maximal robustness.
In this talk, I will give a survey on
some of recent advances in orbifold theory and focus
on the application. It includes the computation for
cohomology of Hilbert scheme of points of algebraic surface,
symplectic resolution, twisted K-theory and many other stuff.
Tumor growth has been modeled at the macroscopic level by using established physical laws coup
led with biological processes which are described in a phenomenological fashion. Such model c
onsists of a system of PDEs in the tumor region; this region is changing in time, and thus its
boundary is a "free boundary." In this talk, I shall introduce basic material on free bounda
ry problems, and then proceed to describe models of tumor growth. I shall state results on exi
stence theorems, the shape of the free boundary, and on its asymptotic behavior as time goes t
o infinity.
I will discuss the proofs of some conjectural formulas
about Hodge integrals on moduli spaces of curves.
The generating series for all genera and all marked
points of such integrals are expressed in terms of
finite closed formulas from Chern-Simons knot invariants.
Such conjectures were made by string theorists based
on large N duality in string theory. I will explain
our proofs from localization techniques. Their relation
to toric Calabi-Yau manifolds and equivariant index
theory in gauge theory will also be discussed.
These are joint works with C.-C. Liu, J. Zhou and J. Li.
It is a classical problem to determine the span
of the theta series of a given quadraic space over
a small ring. In such a way, Jacobi proved his
famous formula of the number of ways of expressing
integers as sums of four squares.
For the norm form of a definite quaternion algebra B,
we determine the span integrally over very small ring
(for example, if B only ramifies at one prime p,
we shall determine the span over Z[1/(p-1)]).
The Diederich-Fornaess worm domain has proved to be of fundamental
importance in the understanding of the geometry of pseudoconvex domains in
multidimensional complex space. More recently, the worm has proved to be
an important example for the study of the inhomogeneous Cauchy-Riemann
equations in higher dimensions.
In forthcoming work, Krantz and Marco Peloso have done a complete
analysis of the Bergman kernel on a version of the worm domain.
We produce an asymptotic expansion for the kernel and calculate
its mapping properties. We can recover versions of the results
of Kiselman, Barrett, Christ, and Ligocka on the worm.
Many widely used statistical models of evolution are algebraic varieties, that is, solutions sets of polynomial equations. We discuss this algebraic representation and its implications for the construction of maximum likelihood trees in phylogenetics. The ensuing interaction between combinatorial algebraic geometry and computational biology works as a two-way street: biologists may benefit from new mathematical tools, while mathematicians will find a rich source of open problems concerning objects reminiscent of objects familiar from classical projective geometry.