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$\DeclareMathOperator{\loc}{\mathrm{loc}}$This is from Lemarié-Rieusset's book "The Navier-Stokes problem in the 21st century", from the proof of a result about stationary solutions to Navier-Stokes ( …

Say, we're given smooth functions $f_n$, $n=1,2,3,...$ defined on a smooth bounded domain $\Omega\subset\mathbb{R}^d$ satisfying $\Delta f_n\ge 0$ (subharmonic) $f_n\ge 0$ $\int_\Omega f_n=I>0$ for a …

Consider the periodic strip $\Omega=\mathbb{T}\times[0,1]$ where $\mathbb{T}$ is the 1D torus with period 1. We consider the mixed Dirichlet/Neumann problem $$-\Delta u=f$$ with boundary conditions $$ …

Suppose $\Omega\subset\mathbb{R}^3$ is a bounded domain with smooth boundary. We note by $(-\Delta)^{-1}$ the inverse Laplacian i.e. $f\mapsto u$ where $u$ is the unique solution to $$-\Delta u=f,\qua …

Let $\Omega\subset\mathbb{R}^3$ be a bounded smooth domain. In general, for a Poincare inequality of the type $$\|u\|_{L^2}\le C \|\nabla u\|_{L^2}$$ to hold for all $u\in X\subset H^1(\Omega)$ and $C …