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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.

1 vote
0 answers
97 views

Burgers' equation with viscosity: modulational analysis and energy estimates for large data

I think my question applies to many PDE that admit stationary solutions or travelling waves. I will simply describe the setting that I am more familiar with, but the technique is standard and applies …
Lorenzo Pompili's user avatar
3 votes

The integrability of $\widehat{e^{-|x|^a}}$, $a>0$

Heuristics Since $e^{-|x|^a}$ behaves like $1-|x|^a$ plus better behaved terms close to zero, and since formally the Fourier trasform of $|x|^a$ is proportional to $|\xi|^{-a-n}$, I would expect that …
Lorenzo Pompili's user avatar
1 vote

PDE: compactness vs blowup

One well-known example is Navier-Stokes' equation. It can be proved local well-posedness in any dimension $d\geq 2$ in suitable Lebesgue or Sobolev spaces (we call the solutions coming from the well-p …
Lorenzo Pompili's user avatar
5 votes
0 answers
222 views

Non-uniqueness of solutions to a simple nonlinear elliptic PDE in $\mathbb R^n$

My question is about non-uniqueness of solutions of an elliptic PDE in $\mathbb R^n$ with source term in a scaling-subcritical space (regular, but with too slow decay at infinity), and with some nice …
Lorenzo Pompili's user avatar
1 vote
0 answers
112 views

Global existence for large data in $H^{-1/2}(\mathbb R)$ of viscous Burgers' equation with e...

First, a quick summary of what to know about viscous (or dissipative) Burgers' equation $$ u_t-u_{xx}=(u^2)_x. \tag{1}\label{1}$$ Recall that $\dot H^{-1/2}(\mathbb R)$ is a scaling-critical Sobolev s …
Lorenzo Pompili's user avatar
3 votes

Looking for references to study $U^p$ and $V^p$ spaces

Here is one fairly recent paper of Sebastian Herr (the second author in the paper you linked) and Timothy Candy in which they use $U^p$ and $V^p$ spaces. During a winter school in Obergurgl in 2022, H …
Lorenzo Pompili's user avatar
5 votes
0 answers
404 views

All $L^pL^q$ estimates for the heat equation on $\mathbb R$ (with gain of derivatives)

I have asked this question on MSE, but this is a better place. The heat equation and the heat kernel. Consider the heat equation on $\mathbb R$: $$ \left\{\begin{aligned}u_t-\Delta u&=f\\u(0,x)&=0\qu …
Lorenzo Pompili's user avatar