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Partial differential equations (PDEs): Existence and uniqueness, regularity, boundary conditions, linear and non-linear operators, stability, soliton theory, integrable PDEs, conservation laws, qualitative dynamics.

2 votes

Literature on Lateral cauchy problem

Victor Isakov's Inverse Problems for Partial Differential Equations has a quite extensive treatment of the Cauchy problem with lateral boundary data, see chapters 3, 7, 8.
Carlo Beenakker's user avatar
1 vote
Accepted

Exactly solvable examples of diffusion equation with variable diffusivity?

This would be the Schrödinger equation with a position dependent mass. Some exactly solvable examples are presented in Analytic results in the position-dependent mass Schrödinger problem Explicit s …
Carlo Beenakker's user avatar
1 vote

Finite speed of propagation of wave equation

The wave propagation speed can be infinite if your boundaries have a fractal shape, because of the different scaling of space and time. This idea is due to Strichartz, see Laplacians on fractals (2005 …
Carlo Beenakker's user avatar
5 votes

Scaling invariance for Hartree equation

substitution of $u_\mu(t,x)=\text{constant}\times u(\mu^\alpha t,\mu x)$ in the fractional GHE shows that this is a solution if $\text{constant}=\mu^{\frac{d-\gamma+\alpha}{2(p-1)}}$, so the scale inv …
Carlo Beenakker's user avatar
4 votes
Accepted

WKB expansion for NLS

A. Note that the time derivative $\partial u^\epsilon/\partial t$ and the spatial derivative $\partial u^\epsilon/\partial x$ are both of order $1/\epsilon$, since $u^\epsilon\propto e^{i\phi(t,x)/\ep …
Carlo Beenakker's user avatar
3 votes

How to find the associated conservation law from a given symmetry

You can find an overview of methods to obtain conservation laws from a wave equation in On the structure of conservation laws of (3+1)-dimensional wave equation. Noether's method requires that the PDE …
Carlo Beenakker's user avatar
4 votes
Accepted

What Morrey and Campanato space characterize

The lecture notes by Melanie Rupflin answer the question "What is a Morrey Space? What is a Campanato Space?" The Morrey space $L^{p,\lambda}$ is a subset of $L^p$ containing functions $f$ on a domai …
Carlo Beenakker's user avatar
3 votes

Nondimensionalization of Navier Stokes Equations

I think the count is off, because the unit of mass does not appear as an independent degree of freedom in the Navier-Stokes equation (unless you include gravitational effects). You have the independen …
Carlo Beenakker's user avatar
2 votes

Does there exist always an $L^2$ threshold below (or above) which a traveling waves of a non...

This addresses the case of a traveling wave (not a solitonic wave). If I consider the one-dimensional nonlinear Schrödinger equation $$i\partial_t\Psi+\partial_x^2\Psi+\Psi(f(|\Psi|^2)=0,$$ a travelli …
Carlo Beenakker's user avatar
2 votes

Regularity of stochastic heat equation

The presence of noise allows to exchange ("trade") time regularity for space regularity. For a simple example, consider the map $$(t,x)\mapsto \int_0^t b(s,x+W_s)\,ds,$$ with Gaussian noise $W_s$. If …
Carlo Beenakker's user avatar
3 votes

Conserved quantities for the Cauchy momentum equation

1) conserved quantity for incompressible flow: $$\frac{d\rho}{dt}=\frac{\partial\rho}{\partial t}+\bar{v}\cdot\nabla\rho=0$$ so if the flow is stationary, $\partial\rho/\partial t=0$, the density $\ …
Carlo Beenakker's user avatar
6 votes

Relativistic Control Theory

Maximum Mass of a Neutron Star (1974) Control theory and singular Riemannian geometry (1982) The Condition of Hydrostatic Equilibrium of Stellar Models Using Optimal Control (2002) Investigating a …
Carlo Beenakker's user avatar
4 votes

What to read for many-body problems in 3D Schrodinger equation

A question along these lines was asked recently to two eminent mathematical physicists, Mel Levy and Elliott Lieb, and here is their wish list of open problems in many-electron theory.
Carlo Beenakker's user avatar
2 votes
Accepted

semi-classical Green's function

The difference between the semiclassical approximations of the full Green's function and the trace is whether or not you restrict the sum over paths to closed orbits; for a treatment of the semiclassi …
Carlo Beenakker's user avatar
5 votes
Accepted

Stochastic methods for solving very high-dimensional PDE

It seems to me this question "has not received enough attention" because of the conflation of two issues: dimensional reduction of a high-dimensional PDE and stochastic (Monte Carlo) integration of th …
Carlo Beenakker's user avatar

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