arXiv subjects

Raúl Ferreira

Publications and source records attributed to Raúl Ferreira.

6 recordsLinked to original sources

arXiv2026

Blow-up rates and sets for a quasilinear diffusion equation with weighted source

Blow-up rates are established for general solutions to the quasilinear diffusion equation $$ \partial_tu=Δu^m+|x|^σu^p, \quad (x,t)\in\mathbb{R}^N\times(0,T), $$ in the range of exponents $1 0$. More precisely, if we consider a compactly supported solution $u(x,t)$ with blow-up time $T=T(u)\in(0,\infty)$, we derive the blow-up rate $$ C_1(T-t)^{-α}\leq \|u(x,t)\|_{\infty}\leq C_2(T-t)^{-α}, \quad t\in(0,T), $$ for some positive constants $C_1$, $C_2$, and the upper rate of expansion of the support $$ \sup\{|x|:u(x,t)>0\}\leq C_0(T-t)^{-β}, \quad t\in(0,T), $$ for some constant $C_0>0$, where $$ α=\frac{σ+2}{L}, \quad β=\frac{m-p}{L}, \quad L=σ(m-1)+2(p-1). $$ We also analyze the blow-up sets of solutions $u$, showing, under a suitable condition, that either $B(u)=\mathbb{R}^N$ or blow-up takes place only as $|x|\to\infty$.

math.AP↗

arXiv2025

Quenching phenomena in a system of non-local diffusion equations

In this paper we study the quenching phenomena occurring in a non-local diffusion system of two equations with intertwined singular absorption terms of the type $u^{-p}$. We prove that there exists a range of multiplicative parameters for which every solution presents quenching, while outside this range there are both global and quenching solutions. We also characterize in terms of the exponents of the absorption terms when the quenching is simultaneous or non-simultaneous and obtain the quenching rates.

math.AP↗

arXiv2025

The Fujita exponent for finite difference approximations of nonlocal and local semilinear blow-up problems

We study monotone finite difference approximations for a broad class of reaction-diffusion problems, incorporating general symmetric Lévy operators. By employing an adaptive time-stepping discretization, we derive the discrete Fujita critical exponent for these problems. Additionally, under general consistency assumptions, we establish the convergence of discrete blow-up times to their continuous counterparts. As complementary results, we also present the asymptotic-in-time behavior of discrete heat-type equations as well as an extensive analysis of discrete eigenvalue problems.

math.NA↗

arXiv2024

Blow-up for a double nonlocal heat equation

We study the blow-up question for the diffusion equation involving a nonlocal derivative in time defined by convolution with a nonnegative and nonincreasing kernel, and a nonlocal operator in space driven by a nonnegative radial Lévy kernel. We show that the existence of solutions that blow up in finite time or exist globally depends only on the behaviour of the spatial kernel at infinity. A main difficulty of the work stems from estimating the fundamental pair defining the solution through a Duhamel formula, due to the generality of the setting, which includes singular or not, at the origin, spatial kernels, that can be either positive or compactly supported. As a byproduct we obtain that the Fujita exponent for the fractional type operators similar to the Caputo fractional derivative and the fractional Laplacian.

math.AP↗

arXiv2022

Blow-up for a fully fractional heat equation

We study the existence and behaviour of blowing-up solutions to the fully fractional heat equation $$ \mathcal{M} u=u^p,\qquad x\in\mathbb{R}^N,\;0 0$, where $\mathcal{M}$ is a nonlocal operator given by a space-time kernel $M(x,t)=c_{N,σ}t^{-\frac N2-1-σ}e^{-\frac{|x|^2}{4t}}{1}_{\{t>0\}}$, $0<σ<1$. This operator coincides with the fractional power of the heat operator, $\mathcal{M}=(\partial_t-Δ)^σ$ defined through semigroup theory. We characterize the global existence exponent $p_0=1$ and the Fujita exponent $p_*=1+\frac{2σ}{N+2(1-σ)}$, and study the rate at which the blowing-up solutions below $p_*$ tend to infinity, $\|u(\cdot,t)\|_\infty\sim (T-t)^{-\fracσ{p-1}}$.

math.AP↗

arXiv2021

A nonlinear diffusion equation with reaction localized to the half-line

We study the behaviour of the solutions to the quasilinear heat equation with a reaction restricted to a half-line $$ u_t=(u^m)_{xx}+a(x) u^p, $$ $m, p>0$ and $a(x)=1$ for $x>0$, $a(x)=0$ for $x<0$. We first characterize the global existence exponent $p_0=1$ and the Fujita exponent $p_c=m+2$. Then we pass to study the grow-up rate in the case $p\le1$ and the blow-up rate for $p>1$. In particular we show that the grow-up rate is different as for global reaction if $p>m$ or $p=1\neq m$.

math.AP↗