# PDE Seminar (Fall 2011 and Spring 2012)

## Organizer: Andrzej Swiech

### Meeting time and place: Tuesdays, 3:05 pm, Skiles 005.

### 08/23/2011

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### 08/30/2011

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### 09/06/2011

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### Speaker: Bernard Dacorogna, Ecole Polytechnique Federale de Lausanne

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### Title: On the pullback equation for differential forms.

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### 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.

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### 09/13/2011

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### 09/20/2011

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### Speaker: Shigeaki Koike, Saitama University, Japan

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

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### 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.

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### 09/27/2011

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### 10/04/2011

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

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

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### 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.

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### 10/11/2011

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### 10/18/2011

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### Fall Break

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### 10/25/2011

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### Speaker: Charles Smart, MIT

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### Title: The Fractal Nature of the Abelian Sandpile.

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### 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.

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### 11/01/2011

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

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### Title: Global existence results for water waves.

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### 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.

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### 11/08/2011

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### Speaker: Hantaek Bae, University of Maryland

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### Title: Regularity and decay estimates of dissipative equations.

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### 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.

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### 11/15/2011

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### 11/22/2011

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### Speaker: Toan T. Nguyen, Brown University

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

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### 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.

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### 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

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### Speaker: Jiahong Wu, Oklahoma State University

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

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### 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.

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### 02/14/2012

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

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### Title: Viscoelastic Navier-Stokes equations with damping.

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### 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.

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### 02/21/2012

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### Speaker: Hermano Frid, IMPA, Brazil

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

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### 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.

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### 02/28/2012

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### Speaker: Jin Feng, University of Kansas

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### Title: Stochastic Scalar Conservation Law.

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### 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.

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### 03/06/2012

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### 03/13/2012

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### Speaker: John McCuan, Georgia Tech

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

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### 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.

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### 03/20/2012

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### Spring Break

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### 03/27/2012

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### Speaker: Cyril Roberto, University of Paris, Nanterre

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

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### 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 Talagrandâ€™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).

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### 04/03/2012

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### Speaker: Phil Morrison, University of Texas at Austin

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

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### 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.

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### 04/05/2012

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### Speaker: Samuel Walsh, New York University

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### Title: Steady water waves in the presence of wind.

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### 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.

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### 04/10/2012

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### Speaker: Russell Schwab, Carnegie Mellon University

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

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### 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])

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### 04/12/2012

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

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

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### 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.

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### 04/17/2012

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### 04/24/2012

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### Speaker: Xiaoyi Zhang, University of Iowa

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

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### 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.

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### 05/01/2012

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### Speaker: Clement Mouhot, University of Cambridge

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### Title: Kac's program in Kinetic Theory.

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### 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.

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