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Carlos Alberto Santos

Publications and source records attributed to Carlos Alberto Santos.

18 recordsLinked to original sources
arXiv2026

Logistic elliptic and parabolic problem for the fractional $p$-Laplacian

In this paper we prove existence, uniqueness of weak solutions of the following nonlocal nonlinear logistic equation \begin{equation*} \begin{cases} (-Δ)_p^s u_λ=λu_λ^q - b(x)u_λ^r \quad \text{in} \;Ω,\\ u_λ=0 \quad \text{in} \; ( \mathbb{R}^d \backslash Ω), \\ u_λ>0 \text{ in} \; Ω. \end{cases}\ \end{equation*} We also prove behavior of $u_λ$ with respect to $λ,$ underlining the effect of the nonlocal operator. We then study the associated parabolic problem, proving local and global existence, uniqueness and global behavior such as stabilization, finite time extinction and blow up.

math.AP↗
arXiv2026

On a two-season faecal-oral model with impulsive intervention

Rainfall is associated with the outbreak of certain waterborne faecal-oral diseases, driving the implementation of various human interventions for their control and prevention. Taking into account human intervention and temporal variation in rainfall, this paper develops a two-season switching faecal-oral model with impulsive intervention and free boundaries. In this model, the infection fronts are represented by fixed boundaries during the dry season and by moving boundaries during the wet season, with impulsive intervention occurring at the end of each wet season. The simultaneous introduction of impulsive intervention and seasonal switching creates new difficulties for mathematical analysis. We overcome these challenges through novel analytical techniques, resulting in a spreading-vanishing dichotomy and a sharp criteria governing this dichotomy. Finally, numerical simulations are presented to validate the theoretical results and to visually illustrate the influence of seasonal switching and impulsive intervention. Our results mathematically explain that two factors, the duration of the dry season and the intensity of impulsive intervention are both positively correlated with effective disease control.

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arXiv2024

Interaction between harvesting intervention and birth perturbation in an age-structured model

An age-structured fish model with birth and harvesting pulses is established, where birth pulses are responsible for increasing the amount of fish due to the constant multiple placement of juveniles, and harvesting pulses describe the decrease of fish due to fishing activities. The principal eigenvalue as a threshold value depending on the harvesting and birth intensity is firstly investigated by three different ways. The asymptotic behavior of the population is fully investigated and sufficient conditions for the species to be extinct or persist are given. Numerical simulations suggest that interaction between negative harvesting intervention and positive birth perturbation decides extinction and persistence of the species. It is also shown that perturbation timing plays an important role.

q-bio.PE↗
arXiv2024

On an age-structured model in moving boundaries: The effects of nonlocal diffusion and harvesting pulse

In order to understand how nonlocal diffusion and pulse intervention affect dynamics of species, we focus on an age-structured nonlocal diffusion model in moving and heterogeneous environment, where nonlocal diffusion describes the long range dispersal of species itself and time-periodic harvesting pulse exacting on the adult reflects human intervention. A generalized principal eigenvalue involving harvesting rate used to identify the spreading and vanishing outcomes is firstly defined and the existence of the principal eigenvalue is given under some conditions. Subsequently, properties of the generalized principal eigenvalue and the principal eigenvalue related to harvesting rate and length of habitat interval are analyzed, respectively. The criteria to governing spreading or vanishing of the species are finally investigated, with sufficient conditions for spreading-vanishing established. Our results indicate that complexities can be induced by the internal long rang dispersal and expanding capacities of species, as well as external harvesting intervention of human. Specifically, appropriate harvesting rate and expanding capacities can even change the reciprocal outcomes of species from co-existence to co-extinction.

math.AP↗
arXiv2024

On an impulsive faecal-oral model in a periodically evolving environment

To understand how impulsive intervention and regional evolution jointly influence the spread of faecal-oral diseases, this paper develops an impulsive faecal-oral model in a periodically evolving environment. The well-posedness of the model is first checked. Then, the existence of the principal eigenvalue dependent on impulse intensity and evolving rate is proved based on Krein-Rutman theorem. With the help of this value, the threshold dynamical behaviours of the model are explored. More importantly, this paper also derives the monotonicity of the principal eigenvalue with respect to initial region and impulse intensity and estimates the principal eigenvalue in some special cases. Finally, numerical simulations are used to verify the correctness of the theoretical results and to explore the impact of regional evolution rate on the spread of the diseases. Our research shows that large impulsive intensity $1-g'(0)$ and small evolving rate $ρ(t)$ play a positive role in the prevention and control of the diseases.

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arXiv2024

Extinction, persistence and growing in a degenerate logistic model with impulses

This paper deals with an impulsive degenerate logistic model, where pulses are introduced for modeling interventions or disturbances, and degenerate logistic term may describe refugees or protections zones for the species. Firstly, the principal eigenvalue depending on impulse rate, which is regarded as a threshold value, is introduced and characterized. Secondly, the asymptotic behavior of the population is fully investigated and sufficient conditions for the species to be extinct, persist or grow unlimitedly are given. Our results extend those of well-understood logistic and Malthusian models. Finally, numerical simulations emphanzise our theoretical results highlighting that medium impulse rate is more favorable for species to persist, small rate results in extinction and large rate leads the species to an unlimited growth.

q-bio.PE↗
arXiv2023

A competition model with impulsive interventions and environmental perturbations in moving environments

In order to understand how impulsive interventions and environmental perturbations affect dynamics of competitors, we focus on a diffusive competition model with free boundaries and periodic pulses in a temporally heterogeneous environment with upward or downward advection. The dependence of the principal eigenvalue of corresponding periodic impulsive eigenvalue problem on advection rates, habitat sizes and pulses is investigated, which gives precise conditions that classify the dynamics into four types of competition outcomes including coexistence, co-extinction, two different competition exclusions for small or negative advection rates. Some sufficient conditions on pulses or initial habitats for species spreading or vanishing, and spreading speeds are then established. Our results not only extend the existing ones to the case with pulses, but also reveal the effects of human and natural factors, that is, impulsive interventions factors including positive or negative impulsive effect, pulse intensity and timing can significantly affect and alter the competition outcomes. The different performances of the superior and inferior affected by environmental perturbations are also reflected in the simulations.

math.AP↗
arXiv2021

Existence of S-shaped type bifurcation curve with dual cusp catastrophe via variational methods

We discuss the existence of multiple positive solutions leading to the occurrence of an S-shaped bifurcation curve to the equations of the form $$ -Δ_p u= f(μ,λ, u)~ \mbox{in} ~Ω\subset \mathbb{R}^N $$ where $Δ_p$ is a $p$-Laplacian, $p>1$, $N\geq 1$, $μ, λ\in \mathbb{R}$. We deal with relatively unexplored cases when $f(μ,λ, u)$ is non-Lipschitz at $u=0$, $f(μ,λ, 0) = 0 $ and $ f(μ,λ, u) <0$, $u \in (0,r)$, for some $r<+\infty$. We develop the nonlinear generalized Rayleigh quotients method to find a range of parameters where the equation may have distinct branches of positive solutions. As a consequence, applying the Nehari manifold method and the mountain pass theorem, we prove that the equation for some range of values $μ, λ$, has at least three positive solutions with two linearly unstable solutions and one linearly stable. The results evidence that the bifurcation curve is S-shaped and exhibits the so-called dual cusp catastrophe which is characterized by the fact that the corresponding dynamic equation has stable states only within the cusp-shaped region in the control plane of parameters. Our results are new even in the one-dimensional case and $p=2$.

math.AP↗
arXiv2021

Multiplicity for a strongly singular quasilinear problem via bifurcation theory

A $p$-Laplacian elliptic problem in the presence of both strongly singular and $(p-1)$-superlinear nonlinearities is considered. We employ bifurcation theory, approximation techniques and sub-supersolution method to establish the existence of an unbounded branch of positive solutions, which is bounded in positive $λ-$direction and bifurcates from infinity at $λ=0$. As consequence of the bifurcation result, we determine intervals of existence, nonexistence and, in particular cases, global multiplicity.

math.AP↗
arXiv2019

Separating of critical points on the Nehari manifold via the nonlinear generalized Rayleigh quotients

In this paper, we deal with equations of variational form which Nahari manifolds can contain more than two different types of critical points. We introduce a method of separating critical points on the Nahari manifold, based on the use of nonlinear generalized Rayleigh quotients. The method is illustrated by establishing the existence of positive solutions, ground states and multiplicity results for a two-parameter nonlinear elliptic boundary problem with polynomial nonlinearities.

math.AP↗
arXiv2019

Equivalent conditions for existence of three solutions for a problem with discontinuous and strongly-singular terms

In this paper, we are concerned with a Kirchhoff problem in the presence of a strongly-singular term perturbed by a discontinuous nonlinearity of the Heaviside type in the setting of Orlicz-Sobolev space. The presence of both strongly-singular and non-continuous terms bring up difficulties in associating a differentiable functional to the problem with finite energy in the whole space $W_0^{1,Φ}(Ω)$. To overcome this obstacle, we established an optimal condition for the existence of $W_0^{1,Φ}(Ω)$-solutions to a strongly-singular problem, which allows us to constrain the energy functional to a subset of $W_0^{1,Φ}(Ω)$ to apply techniques of convex analysis and generalized gradient in Clarke sense.

math.AP↗
arXiv2018

Continuums of positive solutions for classes of non-autonomous and non-local problems with strong singular term

In this paper, we show existence of \textit{continuums} of positive solutions for non-local quasilinear problems with strongly-singular reaction term on a bounded domain in $\mathbb{R}^N$ with $N \geq 2$. We approached non-autonomous and non-local equations by applying the Bifurcation Theory to the corresponding $ε$-perturbed problems and using a comparison principle for $W_{\mathrm{loc}}^{1,p}(Ω)$-sub and supersolutions to obtain qualitative properties of the $ε$-\textit{continuum} limit. Moreover, this technique empowers us to study a strongly-singular and non-homogeneous Kirchhoff problem to get the existence of a \textit{continuum} of positive solutions.

math.AP↗
arXiv2018

Multiplicity of negative-energy solutions for singular-superlinear Schrödinger equations with indefinite-sign potential

We are concerned with the multiplicity of positive solutions for the singular superlinear and subcritical Schrödinger equation $$ \begin{array}{c} -Δu +V(x)u=λa(x)u^{-γ}+b(x)u^{p}~\mbox{in}~ \mathbb{R}^{N}, \end{array} $$ beyond the Nehari extremal value, as defined in Il'yasov [Topol. Methods Nonlinear Anal., 2017], when the potential $b \in L^{\infty}(\mathbb{R}^{N})$ may change its sign, $0 0$ is a real parameter. The main difficulties come from the non-differentiability of the energy functional and the fact that the intersection of the boundaries of the connected components of the Nehari set is non empty. We overcome these difficulties by exploring topological structures of that boundary to build non-empty sets whose boundaries have empty intersection and minimizing over them by controlling the energy level.

math.AP↗
arXiv2018

How to break the uniqueness of $W^{1,p}_{loc}(Ω)$-solutions for very singular elliptic problems by non-local terms

In this paper, we are going to show existence of branches of bifurcation for positive $W^{1,p}_{loc}(Ω)$-solutions for the very singular non-local $λ$-problem $$ -{\Big(\int_Ωg(x,u)dx\Big)^r}Δ_pu={λ} \Big(a(x)u^{-δ} + b(x)u^β\Big) \ \ \mbox{in} \ \ Ω, \ \ \ \ u > 0 \ \ \ \mbox{in} \ Ω\ \ \ \mbox{and} \ \ u=0 \ \ \mbox{on} \ \partial Ω, $$ where $Ω\subset \mathbb{R}^N $ is a smooth bounded domain, $δ>0$, $0 < β< p-1$, $a $ and $b$ are non-negative measurable functions and $g$ is a positive continuous function. Our approach is based on sub-supersolutions techniques, fixed point theory, in the study of $ W^{1,p}_{loc}(Ω)$-topology of a solution application and a new comparison principle for sub-supersolutions in $W^{1,p}_{loc}(Ω)$ to a problem with $p$-Laplacian operator perturbed by a very singular term at zero and sublinear at infinity.

math.AP↗
arXiv2017

Existence and regularity of positive solutions of quasilinear elliptic problems with singular semilinear term

This paper deals with existence and regularity of positive solutions of singular elliptic problems on a smooth bounded domain with Dirichlet boundary conditions involving the $Φ$-Laplacian operator. The proof of existence is based on a variant of the generalized Galerkin method that we developed inspired on ideas by Browder and a comparison principle. By using a kind of Moser iteration scheme we show $L^{\infty}(Ω)$-regularity for positive solutions

math.AP↗
arXiv2016

Infinite many Blow-up solutions for a Schrödinger quasilinear elliptic problem with a non-square diffusion term

In this paper, we consider existence of positive solutions for the Schrödinger quasilinear elliptic problem $$ \left\{ \begin{array}{l} Δ_pu+Δ_p(|u|^{2γ})|u|^{2γ-2}u = a(x)g(u)~ \mbox{on}~ \mathbb{R}^N,\\ u>0\ \mbox{in}~\mathbb{R}^N,\ u(x)\stackrel{\left|x\right|\rightarrow \infty}{\longrightarrow} \infty, \end{array} \right. $$ where $a(x), ~x\in \mathbb{R}^N$ and $g(s)~s>0$ are a nonnegative and continuous functions with $g$ being nonincreasing as well, $γ>{1}/{2}$, and $N \geq 1$. By a dual approach we establish sufficient conditions for existence and multiplicity of solutions for this problem.

math.AP↗
arXiv2016

Necessary and sufficient conditions for existence of Blow-up solutions for elliptic problems in Orlicz-Sobolev spaces

This paper is principally devoted to revisit the remarkable works of Keller and Osserman and generalize some previous results related to the those for the class of quasilinear elliptic problem $$ \left\{ \begin{array}{l} {\rm{div}} \left( ϕ(|\nabla u|)\nabla u\right) = a(x)f(u)\quad \mbox{in } Ω,\\ u\geq0\ \ \mbox{in}\ Ω,\ \ u=\infty\ \mbox{on}\ \partialΩ, \end{array} \right. $$ where either $Ω\subset \mathbb{R}^N$ with $N \geq 1$ is a smooth bounded domain or $Ω= \mathbb{R}^N$. The function $ϕ$ includes special cases appearing in mathematical models in nonlinear elasticity, plasticity, generalized Newtonian fluids, and in quantum physics. The proofs are based on comparison principle, variational methods and topological arguments on the Orlicz-Sobolev spaces.

math.AP↗