Seminars and Colloquia by Series

Thursday, March 10, 2011 - 15:00 , Location: Skiles 006 , Ka-Sing Lau , Hong Kong Chinese University , Organizer:
There is a large literature to study the behavior of the image curves f(\partial {\mathbb D}) of analytic functions f on the unit disc {\mathbb D}. Our interest is on the class of analytic functions f for which the image curves f(\partial {\mathbb D}) form infinitely many (fractal) loops. We formulated this as the Cantor boundary behavior (CBB). We develop a general theory of this property in connection with the analytic topology, the distribution of the zeros of f'(z) and the mean growth rate of f'(z) near the boundary. Among the many examples, we showed that the lacunary series such as the complex Weierstrass functions have the CBB, also the Cauchy transform F(z) of the canonical Hausdorff measure on the Sierspinski gasket, which is the original motivation of this investigation raised by Strichartz.
Wednesday, March 9, 2011 - 14:00 , Location: Skiles 005 , Michael Loss , School of Mathematics, Georgia Tech , Organizer: Jeff Geronimo
This talk is about a random Schroedinger operator describing the dynamics of an electron in a randomly deformed lattice. The periodic displacement configurations which minimize the bottom of the spectrum are characterized. This leads to an amusing problem about minimizing eigenvalues of a Neumann Schroedinger operator with respect to the position of the potential. While this configuration is essentially unique for dimension greater than one, there are infinitely many different minimizing configurations in the one-dimensional case. This is joint work with Jeff Baker, Frederic Klopp, Shu Nakamura and Guenter Stolz.
Wednesday, March 2, 2011 - 14:00 , Location: Skiles 005 , Camil Muscalu , Cornell , Organizer: Michael Lacey
 Calderon's algebra can be thought of as a world whichincludes singular integral operators and operators of multiplicationwith functions which grow at most linearly (more precisely, whose firstderivatives are bounded).The goal of the talk is to address and discuss in detail the followingnatural question: "Can one meaningfully extend it to include operatorsof multiplication with functions having polynomial growth as well ?".
Wednesday, February 16, 2011 - 14:00 , Location: Skiles 006 , Tim Ferguson , University of Michigan , Organizer: Michael Lacey
I will discuss linear extremal problems in the Bergman spaces $A^p$ ofthe unit disc and a theorem of Ryabykh about regularity of thesolutions to these problems.  I will also discuss extensions I havefound of Ryabykh's theorem in the case where $p$ is an even integer.The proofs of these extensions involve Littlewood-Paley theory and abasic characterization of extremal functions.
Wednesday, February 2, 2011 - 14:00 , Location: Skiles 006 , Yen Do , Georgia Tech , Organizer:
I will survey recent results about the convergence of the Wash-Fourier series near L1. Joint work with Michael Lacey.
Wednesday, January 26, 2011 - 14:00 , Location: Skiles 005 , Prof. Dany Leviatan , Tel Aviv University , Organizer: Doron Lubinsky
Let C[-1, 1] be the space of continuous functions on [-1, 1], and denote by \Delta^2 the set of convex functions f \in C[-1, 1]. Also, let E_n(f) and En^{(2)}_n(f) denote the degrees of best unconstrained and convex approximation of f \in \Delta^2 by algebraic polynomials of degree < n, respectively. Clearly, E_n(f) \le E^{(2)}_n (f), and Lorentz and Zeller proved that the opposite inequality E^{(2)}_n(f) \le CE_n(f) is invalid even with the constant C = C(f) which depends on the function f \in \Delta^2. We prove, for every \alpha > 0 and function f \in \Delta^2, that sup{n^\alpha E^{(2)}_n(f) : n \ge 1} \le c(\alpha)sup{n^\alpha E_n(f): n \ge 1}, where c(\alpha) is a constant depending only on \alpha. Validity of similar results for the class of piecewise convex functions having s convexity changes inside (-1,1) is also investigated. It turns out that there are substantial differences between the cases s \le 1 and s \ge 2.
Wednesday, January 19, 2011 - 14:00 , Location: Skiles 005 , Tim Nguyen , MIT , Organizer:
The Seiberg-Witten equations, introduced by Edward Witten in 1994, are a first-order semilinear geometric PDE that have led to manyimportant developments in low-dimensional topology. In this talk,we study these equations on cylindrical 4-manifolds with boundary, which we supplement with (Lagrangian) boundary conditions that have a natural Morse-Floer theoretic interpretation. These boundary conditions, however, are nonlinear and nonlocal, and so the resulting PDE is highlyunusual and nontrivial. After motivating and describing the underlying geometry for the Seiberg-Witten equations with Lagrangian boundary conditions, we discuss some of the intricate analysis involved in establishing elliptic regularity for these equations, including tools from the pseudodifferential analysis ofelliptic boundary value problems and nonlinear functional analysis.
Wednesday, December 8, 2010 - 14:00 , Location: Skiles 269 , Eyvindur Ari Palsson , Cornell University , Organizer:
When Calderón studied his commutators, in connection with the Cauchy integral on Lipschitz curves, he ran into the bilinear Hilbert transform by dropping an average in his first commutator. He posed the question whether this new operator satisfied any L^p estimates. Lacey and Thiele showed a wide range of L^p estimates in two papers from 1997 and 1999. By dropping two averages in the second Calderón commutator one bumps into the trilinear Hilbert transform. Finding L^p estimates for this operator is still an open question. In my talk I will discuss L^p estimates for a singular integral operator motivated by Calderón's second commutator by dropping one average instead of two. I will motivate this operator from a historical perspective and give some comments on potential applications to partial differential equations motivated by recent results on the water wave problem.
Wednesday, December 1, 2010 - 14:00 , Location: Skiles 269 , Svitlana Mayboroda , Purdue , Organizer: Michael Lacey
  The quest for a suitable geometric description of major analyticproperties of sets has largely motivated the development of GeometricMeasure Theory in the XXth theory. In particular, the 1880 Painlev\'eproblem and the closely related conjecture of Vitushkin remained amongthe central open questions in the field. As it turns out, their higherdimensional versions come down to the famous conjecture of G. Davidrelating the boundedness of the Riesz transform and rectifiability. Upto date, it remains unresolved in all dimensions higher than 2.However, we have recently showed with A. Volberg that boundedness ofthe square function associated to the Riesz transform indeed impliesrectifiability of the underlying set. Hence, in particular,boundedness of the singular operators obtained via truncations of theRiesz kernel is sufficient for rectifiability.  I will discuss thisresult, the major methods involved, and the connections with the G.David conjecture.
Wednesday, November 17, 2010 - 14:00 , Location: Skiles 269 , Guozhen Lu , Wayne State , Organizer: Michael Lacey
In this talk, we will discuss the theory of Hardy spacesassociated with a number of different multiparamter structures andboundedness of singular integral operators on such spaces. Thesemultiparameter structures include those arising from the Zygmunddilations, Marcinkiewcz multiplier. Duality and interpolation theoremsare also discussed.  These are joint works with Y. Han, E. Sawyer.