Seminars Sorted by Series

We address the problem of building a body of specified shape and of specified mass, out of materials of varying density so as to minimize the first Dirichlet eigenvalue. It leads to a free boundary problem and many uniqueness questions, The...

In 1979, in collaboration with D. Bennequin, we started a direction of research around the study of periodic trajectories of the Reeb vector field $\xi$ on a contact manifold $(M^3, \alpha)$. We will describe in this talk where this direction of...

The de Rham complex is a prototype for a large class of sequences of differential operators often called (generalized) Bernstein-Gelfand-Gelfand BGG sequences. Conformal manifolds admit such sequences and on locally conformally flat manifolds the...

In this talk, we prove existence and uniqueness of vortexless solutions for Chern-Simons-Higgs equation in nonselfdual case.

In this talk we describe some recent result as well as the work in progress on the neck pinching of surfaces under under mean curvature flow.

Given two differential equations it is often useful to know invariants which guarantee that there exists a transformation of variables (independent, dependent or both) that transforms one of the equations into the other. Recently it has been...

In this talk, I will describe the blow-up profile for Q-curvature equations and related work.

If a solution (M,g(t)) of Ricci flow develops a local singularity at a finite time T , then there is a proper subset S of M on which the curvature becomes infinite as time approaches T . Existing approaches to Ricci-flow-with-surgery, due to...

We will discuss diffusion limits for linear Boltzmann equations. When the equilibrium distribution function is a Maxwellian distribution, it is well known that for an appropriate time scale, the small mean free path limit gives rise to a diffusion...

We discuss the local properties of the boundaries of sets whose indicator function is a local minimizer of a Sobolev norm of exponent strictly less than 1/2. It turns out that one devise a regularity that parallels very much that of de Giorgi for...

The first aim of Fefferman-Graham ambient metric construction was to write down all scalar invariants of conformal structures. For odd dimensions, the aim was achieved with the aid of the parabolic invariant theory by Bailey, Eastwood and Graham. In...

I shall explain how to obtain Strichartz estimates with no loss for Schrodinger equation in some cases where the geodesic flow has some trapped trajectories, but the flow is hyperbolic. (This is joint work with Burq and Hassell.)

In pioneering work Tian/Viaclovsky initiated the study of the moduli space of Bach-flat metrics. They showed C^0-orbifold regularity and, equivalently, ALE order zero of noncompact finite-energy solutions. By use of Kato inequalities, the full...

In recent years, fully nonlinear versions of the Yamabe problem have received much attention. In particular, for manifolds with boundary, $C^1$ and $C^2$a priori estimates have been proved for a large class of data. To get an existence result, it is...

In 1964 J. Serrin proposed the following conjecture. Let u be a weak solution (in W^{1,1}) of a second order elliptic equation in divergence form, with Holder continuous coefficients, then u is a "classical" solution ( i.e. u belongs to H^1). I will...

In this talk, I will discuss some characterizations of Sobolev spaces, BV spaces, and present some new inequalities in this context. As a consequence, I can improve classical properties of Sobolev spaces such as Sobolev inequality, Poincare...

Conditional on the scattering conjecture of the mass-critical nonlinear Schrodinger equation in spatial dimension one, we show that there exists a blow-up solution to the mass-critical generalized Korteweg de Vries equation (gKdV) with the minimal...

This talk is based on joint work with YanYan Li and Eduardo Teixeira. Some geometric problems in conformal geometry lead naturally to the study of singular solutions to certain PDEs that describe "canonical" conformal metrics. A good example is the...

In this talk, I will discuss the quadruple junction solutions in the entire three dimensional space to a vector-valued Allen-Cahn equation which models multiple phase separation. The solution is the basic profile of the local structure near a...

The "sigma_k Yamabe problem" is a fully nonlinear generalization of the Yamabe problem, in which one attempts to find a conformal multiple of a given metric to make constant the k-th elementary symmetric function of the eigenvalues of the Schouten...

The location of blowup points is often related to critical points of Green function. In fact, Green function plays a important role to understand the solutions structure of mean field equations. We will show how to use the elliptic function and the...

The talk is devoted to the homogenization of a stochastic evolution problem with non Lipschitz forcing. The problem is considered in a sequence of perforated cylindrical domains obtained from the removal of tiny cylinders from a fixed one (the...

We study a class of fully nonlinear metric flow on K\"ahler manifolds, which includes the J-flow as a special case. We provide a sufficient and necessary condition for the long time convergence of the flow, generalizing the result of Song-Weinkove...

Dislocations are line defects in crystals, and can be modeled using non-local operators. In this talk we will consider a related reaction-diffusion equation with a half-Laplacian. We show that the limit dynamics is characterized by a system of ODEs...

We construct new solutions to the $\sigma_k$-Yamabe problem on compact manifolds by considering the connected sum of two nondegenerate solutions $(M^n_1,g_1)$ and $(M^n_2,g_2)$, for any $2 \leq 2k < n$.

In this talk, I will first give an overview of recent progress on the scattering conjecture and rigidity conjecture for mass critical NLS. Then I will describe our recent results concerning both conjectures for L_2 initial data. I will also discuss...

We formulate several new boundary value problems for the 2D Navier-Stokes system. In all cases, we obtain quantitative decay estimates of the Fourier modes for both the vorticity and the velocity. In some special cases we found that the Fourier...

In this talk, I will discuss several topics related to transverse knots in contact 3-manifolds. I will introduce a conjecture on the maximal self-linking number of a topological knot in the standard contact 3-sphere. I will show how to apply braid...

Given a trivalent graph embedded in 3-space, we associate to it an instanton homology group, which is a finite-dimensional $\mathbf{Z}/2$ vector space. The main result about the instanton homology is a non-vanishing theorem, proved using techniques...

Given a trivalent graph embedded in 3-space, we associate to it an instanton homology group, which is a finite-dimensional $\mathbf{Z}/2$ vector space. The main result about the instanton homology is a non-vanishing theorem, proved using techniques...

We will discuss methods of decomposing knot and link complements into polyhedra. Using hyperbolic geometry, angled structures, and normal surface theory, we analyze geometric and topological properties of knots and links.

The non-orientable genus (a.k.a crosscap number) of a knot is the smallest genus over all non-orientable surfaces spanned by the knot. In this talk, I’ll describe joint work with Christine Lee, in which we obtain two-sided linear bound of the...

Sageev associated to a codimension 1 subgroup $H$ of a group $G$ a cube complex on which $G$ acts by isometries, and proved this cube complex is always CAT(0). Haglund and Wise developed a theory of special cube complexes, whose fundamental groups...

We prove that if a hyperbolic group $G$ acts cocompactly on a CAT(0) cube complexes and the cell stabilizers are quasiconvex and virtually special, then $G$ is virtually special. This generalizes Agol's Theorem (the case when the action is proper)...

We give a brief introduction to random walks on groups with hyperbolic properties.

Let $G$ be a group acting by isometries on a Gromov hyperbolic space, which need not be proper. If $G$ contains two hyperbolic elements with disjoint fixed points, then we show that a random walk on $G$ converges to the boundary almost surely. This...

In this first talk, we give an introduction to Penner’s construction of pseudo-Anosov mapping classes. Penner conjectured that all pseudo-Anosov maps arise from this construction up to finite power. We give an elementary proof (joint with Hyunshik...

We consider questions that arise naturally from the subject of the first talk. The have two main results: 1. In genus $g$, the algebraic degrees of pseudo-Anosov stretch factors include all even numbers between $2$ and $6g - 6$; 2. The Galois...

From a complex analytic perspective, Teichmüller spaces and symmetric spaces can be realised as contractible bounded domains, which have several features in common but also exhibit many differences. In this talk we will study isometric maps between...

For this talk I'll discuss uniformization of Riemann surfaces via Kleinian groups. In particular question of conformability by Hasudorff dimension spectrum. I'll discuss and pose some questions which also in particular will imply a conjecture due to...

A theorem of Borel's asserts that for any positive real number $V$, there are at most finitely many arithmetic lattices in ${\rm PSL}_2({\mathbb C})$ of covolume at most $V$, or equivalently at most finitely many arithmetic hyperbolid $3$-orbifolds...

A theorem of Borel's asserts that for any positive real number $V$, there are at most finitely many arithmetic lattices in ${\rm PSL}_2({\mathbb C})$ of covolume at most $V$, or equivalently at most finitely many arithmetic hyperbolid $3$-orbifolds...

I will discuss a proof that a complete, non-compact hyperbolic 3- manifold $M$ with finite volume contains an immersed, closed, quasi-Fuchsian surface that separates a given pair of points in the sphere at infinity. Joint with David Futer.

Thurston's hyperbolization of fibered 3-manifolds is based on his classification theorem for isotopy classes of surface homeomorphisms. This classification has also been extremely important to the study of dynamical systems on surfaces. The...

I will talk about bilipschitz geometry of complex algebraic sets, focusing on the local geometry in dimension 2 (complex surface singularities), where the topological classification has long been understood in terms of 3-manifolds, while the...

This talk will discuss the question: To what extent are the fundamental groups of compact 3-manifolds determined (amongst the fundamental groups of compact 3-manifolds) by their finite quotients. We will discuss work that provides a positive answer...