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João R. Santos Júnior

Publications and source records attributed to João R. Santos Júnior.

16 recordsLinked to original sources
arXiv2026

Characterizing the breakdown of the maximum principle in a class of nonlocal elliptic problems

In this paper, we consider a nonlocal elliptic equation involving a nonnegative parameter $a$ that quantifies the strength of the nonlocal term, posed in a smooth bounded domain with homogeneous Dirichlet boundary conditions and a given nonnegative source term $f$. This class of problems arises in several applications, including the modeling of thermistor behaviour and population dynamics with crowding effects. We focus on the breakdown of the maximum principle as the parameter $a$ increases. We characterize the two types of degeneracy that may occur, possibly simultaneously, at the critical parameter $a^*$: the solution may vanish at an interior point of the domain, possibly forming a dead-core region, or its normal derivative may vanish on the boundary. In particular, we obtain sufficient conditions for the emergence of dead-core solutions, thereby answering an open question raised in the recent literature. Several one- and two-dimensional examples are constructed to illustrate each possible scenario. Additionally, we study an optimization problem motivated by biological considerations, where the goal is to maximize the critical threshold $a^*$ over an admissible class of resource distributions. For sources with prescribed total mass, a uniform upper bound, and an interior-contact condition, we show that the critical threshold is unbounded and that the corresponding total population can be arbitrarily small. We also establish the existence of a maximizer in a class with a prescribed positive lower bound on the total population, a uniform bound on the sources, and the same interior-contact condition.

math.AP↗
arXiv2024

Quasilinear elliptic problems via nonlinear Rayleigh quotient

It is established existence and multiplicity of solution for the following class of quasilinear elliptic problems $$ \left\{ \begin{array}{lr} -Δ_Φu = λa(x) |u|^{q-2}u + |u|^{p-2}u, & x\inΩ, u = 0, & x \in \partial Ω, \end{array} \right. $$ where $Ω\subset \mathbb{R}^N, N \geq 2,$ is a smooth bounded domain, $1 < q < \ell \leq m < p < \ell^*$ and $Φ: \mathbb{R} \to \mathbb{R}$ is suitable $N$-function. The main feature here is to show whether the Nehari method can be applied to find the largest positive number $λ^* > 0$ in such way that our main problem admits at least two distinct solutions for each $λ\in (0, λ^*)$. Furthermore, using some fine estimates and some extra assumptions on $Φ$, we prove the existence of at least two positive solutions for $λ= λ^*$ and $λ\in (λ^*, \overlineλ)$ where $\overlineλ > λ^*$.

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arXiv2022

On a quasilinear elliptic problem involving the 1-laplacian operator and a discontinuous nonlinearity

In this work, we study a quasilinear elliptic problem involving the 1-laplacian operator, with a discontinuous, superlinear and subcritical nonlinearity involving the Heaviside function $H(\cdot - β)$. Our approach is based on an analysis of the associated p-laplacian problem, followed by a thorough analysis of the asymptotic behaviour or such solutions as $p \to 1^+$. We study also the asymptotic behaviour of the solutions, as $β\to 0^+$ and we prove that it converges to a solution of the original problem, without the discontinuity in the nonlinearity.

math.AP↗
arXiv2022

On asymptotically linear elliptic problems

In this paper we prove the existence of a signed ground state solution in the mountain pass level for a class of asymptotically linear elliptic problems, even when the nonlinearity is just continuous in the second variable. The (strongly) resonant and non-resonant cases are discussed. A multiplicity result is also proved when $f$ is odd with respect to the second variable.

math.AP↗
arXiv2022

The method of the energy function and applications

In this work, we establish a new method to find critical points of differentiable functionals defined in Banach spaces which belong to a suitable class ($\mathcal{J}$) of functionals. Once given a functional $J$ in the class ($\mathcal{J}$), the central idea of the referred method consists in defining a real function $ζ$ of a real variable, called {\it energy function}, which is naturally associated to $J$ in the sense that the existence of real critical points for $ζ$ guarantees the existence of critical points for the functional $J$. As a consequence, we are able to solve some variational elliptic problems, whose associated energy functional belongs to ($\mathcal{J}$) and provide a version of the mountain pass theorem for functionals in the class ($\mathcal{J}$) that allows us to obtain mountain pass solutions without the so-called Ambrosetti-Rabinowitz condition.

math.AP↗
arXiv2018

Study of a class of generalized Schrödinger equations

A class of generalized Schrödinger problems in bounded domain is studied. A complete overview of the set of solutions is provided, depending on the values assumed by parameters involved in the problem. In order to obtain the results, we combine monotony, bifurcation and variational methods.

math.AP↗
arXiv2018

Multiplicity of solutions for resonant and non-resonant asymptotically linear elliptic problems

Results about existence of a signed ground state solution and multiple solutions (if $f$ is odd with respect to the second variable) are proven for a class of asymptotically linear elliptic problems involving a Carathéodory type nonlinearity satisfying assumptions weaker than (fF) in \cite{GLZ} or $(F_{2})_{+}$ in \cite{CM}. A close relation between the behaviour of $\lim_{|t|\to \infty}f(x, t)/|t|$ and the number of solutions is stablished.

math.AP↗
arXiv2018

Multiplicity of positive solutions for an equation with degenerate nonlocal diffusion

Even without a variational background, a multiplicity result of positive solutions with ordered $L^{p}(Ω)$-norms is provided to the following boundary value problem \begin{equation*} \left \{ \begin{array}{ll} -a(\int_Ωu^{p}dx)Δu = f(u) & \mbox{in $Ω$,}\\ u=0 & \mbox{on $\partialΩ$,} \end{array}\right. \end{equation*} where $Ω$ is a bounded domain and $a$, $f$ are continuous real functions with $a$ vanishing in many positive points.

math.AP↗
arXiv2018

Positive solutions for Kirchhoff problems with vanishing nonlocal term

In this paper we study the Kirchhoff problem \begin{equation*} \left \{ \begin{array}{ll} -m(\| u \|^{2})Δu = f(u) & \mbox{in $Ω$,} u=0 & \mbox{on $\partialΩ$,} \end{array}\right. \end{equation*} in a bounded domain, allowing the function $m$ to vanish in many different points. Under an appropriated {\sl area condition}, by using a priori estimates, truncation techniques and variational methods, we prove a multiplicity result of positive solutions which are ordered in the $H_{0}^{1}(Ω)$-norm.

math.AP↗
arXiv2017

Existence results of positive solutions for Kirchhoff type equations via bifurcation methods

In this paper we address the following Kirchhoff type problem \begin{equation*} \left\{ \begin{array}{ll} -Δ(g(|\nabla u|_2^2) u + u^r) = a u + b u^p& \mbox{in}~Ω, u>0& \mbox{in}~Ω, u= 0& \mbox{on}~\partialΩ, \end{array} \right. \end{equation*} in a bounded and smooth domain $Ω$ in ${\rm I}\hskip -0.85mm{\rm R}$. By using change of variables and bifurcation methods, we show, under suitable conditions on the parameters $a,b,p,r$ and the nonlinearity $g$, the existence of positive solutions.

math.AP↗
arXiv2017

On a generalized timoshenko-kirchhoff equation

In this paper we consider a generalized fourth order nonlinear Kirchhoff equation in a bounded domain in $\mathbb R^{N}, N\geq2$ under Navier boundary conditions and with sublinear nonlinearity. We employ a change of variable which reduces the problem to a semilinear one. Then variational and topological tools are used in order to prove the existence of a solution.

math.AP↗
arXiv2016

On a generalized Kirchhoff equation with sublinear nonlinearities

In this paper we consider a generalized Kirchhoff? equation in a bounded domain under the effect of a sublinear nonlinearity. Under suitable assumptions on the data of the problem we show that, with a simple change of variable, the equation can be reduced to a classical semilinear equation and then studied with standard tools.

math.AP↗
arXiv2013

Multiplicity and concentration behavior of positive solutions for a Schrodinger-Kirchhoff type problem via penalization method

In this paper we are concerned with questions of multiplicity and concentration behavior of positive solutions of the elliptic problem $$\left\{\begin{array}{rcl} \mathcal{L}_{\varepsilon}u = f(u) \ \ \mbox{in} \ \ \mathbb{R}^3,\\ u>0 \ \ \mbox{in} \ \ \mathbb{R}^3,\\ u \in H^1 (\mathbb{R}^3), \end{array} \right.$$ where $\varepsilon$ is a small positive parameter, $f:\mathbb{R}\rightarrow \mathbb{R}$ is a continuous function, $\mathcal{L}_{\varepsilon}$ is a nonlocal operator defined by $$ \mathcal{L}_{\varepsilon} u = M \left(\frac{1}{\varepsilon} \int_{\mathbb{R}^3} |\nabla u|^2 + \frac{1}{\varepsilon^3} \int_{\mathbb{R}^3} V(x) u^{2}\right) \left[-\varepsilon^2Δu + V(x)u \right],$$ $M:\mathbb{R}_+\to \mathbb{R}_+$ and $V:\mathbb{R}^3 \to \mathbb{R}$ are continuous functions which verify some hypotheses.

math.AP↗
arXiv2013

The effect of the domain topology on the number of positive solutions of an elliptic Kirchhoff problem

Using minimax methods and Lusternik-Schnirelmann theory, we study multiple positive solutions for the Schrödinger - Kirchhoff equation $$ M\left(\dis\int_{Ω_λ}|\nabla u|^{2}dx+\dis\int_{Ω_λ}u^{2}dx\right)\left[-Δu + u \right]= f(u) $$ in $Ω_λ = λΩ$. The set $Ω\subset \mathbb{R}^3$ is a smooth bounded domain, $λ>0$ is a parameter, $M$ is a general continuous function and $f$ is a superlinear continuous function with subcritical growth. Our main result relates, for large values of $λ$, the number of solutions with the least number of closed and contractible in $\barΩ$ which cover $\barΩ$.

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