arXiv subjects

Jamil Abreu

Publications and source records attributed to Jamil Abreu.

3 recordsLinked to original sources

arXiv2017

Dirichlet-to-Neumann semigroup with respect to a general second order eigenvalue problem

In this paper we present a preliminary study on the Dirichlet-to-Neumann operator with respect to a second order elliptic operator with measurable coefficients, including first order terms, namely, the operator on $L^2(\partialΩ)$ given by $φ\mapsto \partial_νu$ where $u$ is a weak solution of \begin{equation} \left\{ \begin{aligned} -{\rm div}\, (a\nabla u) +b\cdot \nabla u -{\rm div}\, (cu)+du & =λu \ \ \text{on}\ Ω,\\ u|_{\partialΩ} & =φ. \end{aligned} \right. \end{equation} Under suitable assumptions on the matrix-valued function $a$, on the vector fields $b$ and $c$, and on the function $d$, we investigate positivity, sub-Markovianity, irreducibility and domination properties of the associated semigroups.

math.AP↗

arXiv2016

Generalized spectrum of the $\boldsymbol{(p,2)}$-Laplacian under a parametric boundary condition

In this paper we study an eigenvalue problem for the so called $(p,2)$-Laplace operator on a smooth bounded domain under a nonlinear Steklov type boundary condition, namely \begin{equation} \left\{ \begin{aligned} -Δ_pu-Δu & =λa(x)u \ \ \text{in}\ Ω,\\ (|\nabla u|^{p-2}+1)\dfrac{\partial u}{\partialν} & =λb(x)u \ \ \text{on}\ \partialΩ. \end{aligned} \right. \end{equation} Under suitable integrability and boundedness assumptions on the positive weight functions $a$ and $b$, we show that, for all $p>1$, the eigenvalue set consists of an isolated null eigenvalue plus a continuous family of eigenvalues located away from zero.

math.AP↗

arXiv2012

The stochastic Weiss conjecture for bounded analytic semigroups

Suppose -A admits a bounded H-infinity calculus of angle less than pi/2 on a Banach space E with Pisier's property (alpha), let B be a bounded linear operator from a Hilbert space H into the extrapolation space E_{-1} of E with respect to A, and let W_H denote an H-cylindrical Brownian motion. Let gamma(H,E) denote the space of all gamma-radonifying operators from H to E. We prove that the following assertions are equivalent: (i) the stochastic Cauchy problem dU(t) = AU(t)dt + BdW_H(t) admits an invariant measure on E; (ii) (-A)^{-1/2} B belongs to gamma(H,E); (iii) the Gaussian sum \sum_{n\in\mathbb{Z}} γ_n 2^{n/2} R(2^n,A)B converges in gamma(H,E) in probability. This solves the stochastic Weiss conjecture proposed recently by the second and third named authors.

math.FA↗