PDE Seminar (Fall 2011 and Spring 2012)

08/23/2011

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08/30/2011

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09/06/2011

Speaker: Bernard Dacorogna, Ecole Polytechnique Federale de Lausanne

Title: On the pullback equation for differential forms.

Abstract: An important question in geometry and analysis is to know when two $k$-forms $f$ and $g$ are equivalent. The problem is therefore to find a map $\varphi$ such that $\varphi^*(g)=f$. We will mostly discuss the symplectic case $k=2$ and the case of volume forms $k=n$. We will give some results on the more difficult case where $3\leq k\leq n-2$, the case $k=n-1$ will also be considered.

09/13/2011

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09/20/2011

Speaker: Shigeaki Koike, Saitama University, Japan

Title: The ABP maximum principle for fully nonlinear PDE with unbounded coefficients.

Abstract: In this talk, I will show recent results on the Aleksandrov-Bakelman-Pucci (ABP for short) maximum principle for $L^p$-viscosity solutions of fully nonlinear, uniformly elliptic partial differential equations with unbounded inhomogeneous terms and coefficients. I will also discuss some cases when the PDE has superlinear terms in the first derivatives. This is a series of joint works with Andrzej Swiech.

09/27/2011

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10/04/2011

Speaker: Zhengping Wang, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, and Georgia Tech

Title: Ground state for nonlinear Schrodinger equation with sign-changing and vanishing potential.

Abstract: We consider the stationary nonlinear Schrodinger equation when the potential changes sign and may vanish at infinity. We prove that there exists a sign-changing ground state and the so called energy doubling property for sign-changing solutions does not hold. Furthermore, we find that the ground state energy is not equal to the infimum of energy functional over the Nehari manifold. These phenomena are quite different from the case of positive potential.

10/11/2011

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10/18/2011

Fall Break

10/25/2011

Speaker: Charles Smart, MIT

Title: The Fractal Nature of the Abelian Sandpile.

Abstract: I will discuss a natural elliptic obstacle problem that arises in the study of the Abelian sandpile. The Abelian sandpile is a deterministic growth model from statistical physics which produces beautiful fractal-like images. In recent joint work with Wesley Pegden, we characterize the continuum limit of the sandpile process using PDE techniques. In follow up work with Lionel Levine and Wesley Pegden, we partially describe the fractal structure of the stable sandpiles via a careful analysis of the limiting obstacle problem.

11/01/2011

Speaker: Pierre Germain, New York University, Courant Institute of Mathematical Sciences

Title: Global existence results for water waves.

Abstract: I will describe results of global existence and scattering for water waves (inviscid, irrotational), in the case of small data. I will examine two physical settings: gravity, but no capillarity; or capillarity, but no gravity. The proofs rely on the space-time resonance method, which I will briefly present. This is joint work with Nader Masmoudi and Jalal Shatah.

11/08/2011

Speaker: Hantaek Bae, University of Maryland

Title: Regularity and decay estimates of dissipative equations.

Abstract: We establish Gevrey class regularity of solutions to dissipative equations. The main tools are the Kato-Ponce inequality for Gevrey estimates in Sobolev spaces and the Gevrey estimates in Besov spaces using the paraproduct decomposition. As an application, we obtain temporal decay of solutions for a large class of equations including the Navier-Stokes equations, the subcritical quasi-geostrophic equations.

11/15/2011

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11/22/2011

Speaker: Toan T. Nguyen, Brown University

Title: On the stability of Prandtl boundary layers and the inviscid limit of the Navier-Stokes equations.

Abstract: In fluid dynamics, one of the most classical issues is to understand the dynamics of viscous fluid flows past solid bodies (e.g., aircrafts, ships, etc...), especially in the regime of very high Reynolds numbers (or small viscosity). Boundary layers are typically formed in a thin layer near the boundary. In this talk, I shall present various ill-posedness results on the classical Prandtl equation, and discuss the relevance of boundary-layer expansions and the vanishing viscosity limit problem of the Navier-Stokes equations. I will also discuss viscosity effects in destabilizing stable inviscid flows.

11/29/2011

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12/06/2011

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01/10/2012

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01/17/2012

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01/24/2012

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01/31/2012

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02/07/2012

Speaker: Jiahong Wu, Oklahoma State University

Title: The surface quasi-geostrophic equation and its generalizations.

Abstract: Fundamental issues such as the global regularity problem concerning the surface quasi-geostrophic (SQG) and related equations have attracted a lot of attention recently. Significant progress has been made in the last few years. This talk summarizes some current results on the critical and supercritical SQG equations and presents very recent work on the generalized SQG equations. These generalized equations are active scalar equations with the velocity fields determined by the scalars through general Fourier multiplier operators. The SQG equation is a special case of these general models and it corresponds to the Riesz transform. We obtain global regularity for equations with velocity fields logarithmically singular than the 2D Euler and local regularity for equations with velocity fields more singular than those corresponding to the Riesz transform. The results are from recent papers in collaboration with D. Chae and P. Constantin, and with D. Chae, P. Constantin, D. Cordoba and F. Gancedo.

02/14/2012

Speaker: Ryan Hynd, Courant Institute of Mathematical Sciences, New York University

Title: Viscoelastic Navier-Stokes equations with damping.

Abstract: We prove an analog of the Caffarelli-Kohn-Nirenberg theorem for weak solutions of a system of PDE that model a viscoelastic fluid in the presence of an energy damping mechanism. The system was recently introduced in a method of establishing the global in time existence of weak solutions of the well known Oldroyd model, which remains an open problem.

02/21/2012

Speaker: Hermano Frid, IMPA, Brazil

Title: Remarks on the Theory of the Divergence-Measure Fields.

Abstract: We review the theory of the (extended) divergence-measure fields providing an up to date account of its basic results established by Chen and Frid (1999, 2002), as well as the more recent important contributions by Silhavy (2008, 2009). We include a discussion on some pairings that are important in connection with the definition of normal trace for divergence-measure fields. We also review its application to the uniqueness of Riemann solutions to the Euler equations in gas dynamics, as given by Chen and Frid (2002). While reviewing the theory, we simplify a number of proofs allowing an almost self-contained exposition.

02/28/2012

Speaker: Jin Feng, University of Kansas

Title: Stochastic Scalar Conservation Law.

Abstract: This talk considers a scalar conservation (balance) law equation with random (martingale measure) source term. A new notion of entropic solution is introduced as the underlying calculus for change of variable needs to be changed into Ito's calculus. This is due to irregularities in the trajectory of particles caused by randomness. In the new notion, entropy production has additional terms. We discuss ways to handle such term so that a uniqueness theory can still be established. Additionally, stochastic generalizations of compensated compactness will be given. This was a joint work with David Nualart. It appeared in Journal of Functional Analysis, Vol 255, Issue 2, 2008, pages 313-373.

03/06/2012

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03/13/2012

Speaker: John McCuan, Georgia Tech

Title: The stability of cylindrical pendant drops and soap films.

Abstract: The stability of a liquid drop of prescribed volume hanging from a circular cylindrical tube in a gravity field has been a problem of continuing interest. This problem was treated variationally in the late '70s by Henry Wente who showed there was a continuous family indexed by increasing volume which terminated in a final unstable equilibrium due to one or the other of two specific geometric mechanisms.

I will describe a similar problem arising in mathematical biology for drops at the bottom of a rectangular tube and explain, among other things, how the associated instability occurs through exactly three physical mechanisms.

03/20/2012

Spring Break

03/27/2012

Speaker: Cyril Roberto, University of Paris, Nanterre

Title: Hamilton-Jacobi equations on metric spaces and transport entropy inequalities.

Abstract: We will prove an Hopf-Lax-Oleinik formula for the solutions of some Hamilton-Jacobi equations on a general metric space. Then, we will present some consequences: in particular the equivalence of the log-Sobolev inequality and the hypercontractivity property of the Hamilton-Jacobi "semi-group", (and if time allows) that Talagrand’s transport-entropy inequalities in metric space are characterized in terms of log-Sobolev inequalities restricted to the class of c-convex functions (based on a paper in collaboration with N. Gozlan and P.M. Samson).

04/03/2012

Speaker: Phil Morrison, University of Texas at Austin

Title: A discontinuous Galerkin method for Vlasov-like systems.

Abstract: This talk will be an amalgamation of aspects of scientific computing - development, verification, and interpretation - with application to the Vlasov- Poisson (VP) system, an important nonlinear partial differential equation containing the essential difficulties of collisionless kinetic theories. I will describe our development of a discontinuous Galerkin (DG) algorithm, its verification via convergence studies and comparison to known Vlasov results, and our interpretation of computational results in terms of dynamical systems ideas. The DG method was invented for solving a neutron transport model, successfully adapted to fluid motion including shock propagation, applied to the Boltzmann equation, and developed in the general context of conservation laws, and elliptic and parabolic equations. Our development for the VP system required the simultaneous approximation of the hyperbolic Vlasov equation with the elliptic Poisson equation, which created new challenges. I will briefy discuss advantages of the method and describe our error estimates and recurrence calculations for polynomial bases. Then, I will show results from a collection of benchmark computations of electron plasma dynamics, including i) convergence studies of high resolution linear and nonlinear Landau damping with a comparison to theoretical parameter dependencies ii) the nonlinear two-stream instability integrated out to (weak) saturation into an apparently stable equilibrium (BGK) state with detailed modeling of this state, and iii) an electric field driven (dynamically accessible) example that appears to saturate into various periodic solutions. I will interpret such final states, in analogy to finite-dimensional Hamiltonian theory, as Moser-Weinstein periodic orbits, and suggest a possible variational path for proof of their existence. Finally, I will comment briefly on recent progress on extensions to the Maxwell-Vlasov system, including estimates and computational results.

04/05/2012

Speaker: Samuel Walsh, New York University

Title: Steady water waves in the presence of wind.

Abstract: In large part, the waves that we observe in the open ocean are created by wind blowing over the water. The precise nature of this process occurs has been intensely studied, but is still not understood very well at a mathematically rigorous level. In this talk, we side-step that issue, somewhat, and consider the steady problem. That is, we prove the existence of small-amplitude traveling waves in a two phase air-water system that can be viewed as the eventual product of wind generation. This is joint work with Oliver Buhler and Jalal Shatah.

04/10/2012

Speaker: Russell Schwab, Carnegie Mellon University

Title: On Aleksandrov-Bakelman-Pucci type estimates for integro-differential equations.

Abstract: Despite much recent (and not so recent) attention to solutions of integro-differential equations of elliptic type, it is surprising that a result such as a comparison theorem which can deal with only measure theoretic norms (e.g. L-n and L-infinity) of the right hand side of the equation has gone unexplored. For the case of second order equations this result is known as the Aleksandrov-Bakelman-Pucci estimate (and dates back to circa 1960s), which says that for supersolutions of uniformly elliptic equation Lu=f, the supremum of u is controlled by the L-n norm of f (n being the underlying dimension of the domain). We will discuss this estimate in the context of fully nonlinear integro-differential equations and present a recent result in this direction. (Joint with Nestor Guillen, available at arXiv:1101.0279v3 [math.AP])

04/12/2012

Speaker: Guillaume Carlier, Universite de Paris IX (Paris-Dauphine)

Title: Variational problems and PDEs arising in congested transport models.

Abstract: In this talk, I will describe several models arising in congested transport problems. I will first describe static models which lead to some highly degenerate elliptic PDEs. In the second part of the talk, I will address dynamic models which can be seen as a generalization of the Benamou-Brenier formulation of the quadratic optimal transport problem and will discuss the existence and regularity of the adjoint state. The talk will be based on several joint works with Lorenzo Brasco, Pierre Cardaliaguet, Bruno Nazaret and Filippo Santambrogio.

04/17/2012

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04/24/2012

Speaker: Xiaoyi Zhang, University of Iowa

Title: On the global wellposedness and scattering for energy critical NLS outside a convex obstacle.

Abstract: In this talk, we consider 3d defocusing energy critical NLS on the exterior domain of a convex obstacle with Dirichlet boundary condition. We show that all solutions with finite energy exist globally and scatter.

05/01/2012

Speaker: Clement Mouhot, University of Cambridge

Title: Kac's program in Kinetic Theory.

Abstract: Mark Kac proposed in 1956 a program for deriving the spatially homogeneous Boltzmann equation from a many-particle jump collision process. The goal was to justify in this context the molecular chaos, as well as the H-theorem on the relaxation to equilibrium. We give answers to several questions of Kac concerning the connexion between dissipativity of the many-particle process and the limit equation; we prove relaxation rates independent of the number of particles as well as the propagation of entropic chaos. This crucially relies on a new method for obtaining quantitative uniform in time estimates of propagation of chaos. This is a joint work with S. Mischler.