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Pablo Alvarez-Caudevilla

Publications and source records attributed to Pablo Alvarez-Caudevilla.

12 recordsLinked to original sources
arXiv2026

On countable subsets of solutions of nonlinear higher-order ODEs and elliptic PDEs with indefinite operators

Countable subsets of solutions of higher-order nonlinear ODEs and elliptic PDEs with indefinite non-coercive operators from the reaction-diffusion, thin film and dynamical system (DS) theories are obtained via a gluing/matching argument. In particular we study some classic and quasilinear degenerate ODEs in $\mathbb{R}$, with boundary conditions at infinity $F(\infty)=0$, with non-odd nonlinearities such as $$ \begin{matrix} F^{(4)} =-F+F^2,\, \,\, F^{(4)}=-F+F^2{\rm e}^{F-1}, \, (|F''|F'')''=-F + F^2, \\ F^{(4)} =-|F|F+F^2, \,\,\,F^{(4)} =-F^3+F^4, \,\,\, F^{(6)}=F-F^2, \end{matrix} $$ etc, as well as equations with odd and non-smooth nonlinearities like $$F^{(4)}=-F+F^3, \,F^{(4)}=-F-(|F|F-F)'', \,\, F^{(4)}=- \frac F{\sqrt{|F|}}-(F^3-F)'',\,\mbox{etc.}$$ Some of these ODEs are Hamiltonian and were studied in detail in the DS theory. On the basis of nonlinear operators, elliptic PDEs and variational theory, related polyharmonic elliptic equations in $\mathbb{R}^N$, $F(\infty)=0$, such as $$Δ^2 F=-F+F^2, \quad Δ^2 F=-F -Δ(F^2-F), \quad Δ^3 F=F-F^2, \quad \mbox{etc.};$$ are also shown to admit countable families of solutions. For such equations with non-odd functionals associated Lusternik--Schnirel'man (L--S) genus/category variational theory guaranteeing existence of a sequence of critical points does not apply. These ODEs and elliptic PDEs (e.g., in the radial setting) are shown to admit at least two basic countable families ${\mathcal F}_{1,2}$ of positively dominant solutions connected with two periodic orbits $Γ_{\rm max/min}$. Patterns obtained by gluing together via exponentially decaying tails of arbitrary finite samples from $Γ$'s form a countable subset of homoclinics in $\mathbb{R}^4$ of an arbitrary complexity.

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arXiv2024

A stationary population model with an interior interface-type boundary

We propose a stationary system that might be regarded as a migration model of some population abandoning their original place of abode and becoming part of another population, once they reach the interface boundary. To do so, we show a model where each population follows a logistic equation in their own environment while assuming spatial heterogeneities. Moreover, both populations are coupled through the common boundary, which acts as a permeable membrane on which their flow moves in and out. The main goal we face in this work will be to describe the precise interplay between the stationary solutions with respect to the parameters involved in the problem, in particular the growth rate of the populations and the coupling parameter involved on the boundary where the interchange of flux is taking place.

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arXiv2024

Asymptotic behaviour for a class of quasilinear cooperative eigenvalue problems

This work is devoted to the analysis of the asymptotic behaviour of a parameter dependent quasilinear cooperative eigenvalue system when a parameter in front of some non-negative potentials goes to infinity. In particular we consider operators of $p$-Laplacian type. We prove that the eigenfunctions concentrate on the subdomains where those potentials vanish at the limit, while the eigenvalue approaches to an upper bound that will depend on those subdomains as well. We also show several properties for the unusual limiting problems obtained here.

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arXiv2015

Towards optimal regularity for the fourth-order thin film equation in $\re^N$: Graveleau-type focusing self-similarity

An approach to some "optimal" (more precisely, non-improvable) regularity of solutions of the thin film equation u_{t} = -\nabla \cdot(|u|^{n} \nabla \D u) in \ren \times \re_+, u(x,0)=u_0(x) in \re^N, where n in (0,2) is a fixed exponent, with smooth compactly supported initial data u_0(x), in dimensions $N \geq 2$ is discussed. Namely, a precise exponent for the Hölder continuity with respect to the spatial radial variable $|x|$ is obtained by construction of a Graveleau-type focusing self-similar solution. As a consequence, optimal regularity of the gradient $\nabla u$ in certain $L^p$ spaces, as well as a Hölder continuity property of solutions with respect to x and t, are derived, which cannot be obtained by classic standard methods of integral identities-inequalities. Several profiles for the solutions in the cases n=0 and n>0 are also plotted. In general, we claim that, even for arbitrarily small n>0 and positive analytic initial data u_0(x), the solutions u(x,t) cannot be better than $C_x^{2-\e}$-smooth, where $\e(n)=O(n)$ as $n \to 0$.

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arXiv2014

Blow-up scaling and global behaviour of solutions of the bi-Laplace equation via pencil operators

As the main problem, the bi-Laplace equation $Δ^2u=0 (Δ=D_x^2+D_y^2)$ in a bounded domain $Ω\subset \re^2$, with inhomogeneous Dirichlet or Navier-type conditions on the smooth boundary $\partial Ω$ is considered. In addition, there is a finite collection of curves $$Γ= Γ_1\cup...\cupΓ_m \subset Ω, \quad \mbox{on which we assume homogeneous Dirichlet} \quad u=0,$$ focusing at the origin $0 \in Ω$ (the analysis would be similar for any other point). This makes the above elliptic problem overdetermined. Possible types of the behaviour of solution $u(x,y)$ at the tip $0$ of such admissible multiple cracks, being a singularity point, are described, on the basis of blow-up scaling techniques and spectral theory of pencils of non self-adjoint operators. Typical types of admissible cracks are shown to be governed by nodal sets of a countable family of harmonic polynomials, which are now represented as pencil eigenfunctions, instead of their classical representation via a standard Sturm--Liouville problem. Eventually, for a fixed admissible crack formation at the origin, this allows us to describe all boundary data, which can generate such a blow-up crack structure. In particular, it is shown how the co-dimension of this data set increases with the number of asymptotically straight-line cracks focusing at 0.

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arXiv2014

Countable families of solutions of a limit stationary semilinear fourth-order Cahn--Hilliard equation I. Mountain pass and Lusternik--Schnirel'man patterns in R^N

Solutions of the stationary semilinear Cahn--Hilliard equation -Δ^2 u - u -Δ(|u|^{p-1}u)=0 in R^N, with p>1, which are exponentially decaying at infinity, are studied. Using the Mounting Pass Lemma allows us the determination of two different solutions. On the other hand, the application of Lusternik--Schnirel'man (L--S) Category Theory shows the existence of, at least, a countable family of solutions. However, through numerical methods it is shown that the whole set of solutions, even in 1D, is much wider. This suggests that, actually, there exists, at least, a countable set of countable families of solutions, in which only the first one can be obtained by the L--S min-max approach.

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arXiv2014

The Cauchy problem for a tenth-order thin film equation II. Oscillatory source-type and fundamental similarity solutions

Fundamental global similarity solutions of the standard form u_\g(x,t)=t^{-\a_\g} f_\g(y), with the rescaled variable y= x/{t^{\b_\g}}, \b_\g= \frac {1-n \a_\g}{10}, where \a_\g>0 are real nonlinear eigenvalues (\g is a multiindex in R^N) of the tenth-order thin film equation (TFE-10) u_{t} = \nabla \cdot(|u|^{n} \n \D^4 u) in R^N \times R_+, n>0, are studied. The present paper continues the study began by the authors in the previous paper P. Alvarez-Caudevilla, J.D.Evans, and V.A. Galaktionov, The Cauchy problem for a tenth-order thin film equation I. Bifurcation of self-similar oscillatory fundamental solutions, Mediterranean Journal of Mathematics, No. 4, Vol. 10 (2013), 1759-1790. Thus, the following questions are also under scrutiny: (I) Further study of the limit n \to 0, where the behaviour of finite interfaces and solutions as y \to infinity are described. In particular, for N=1, the interfaces are shown to diverge as follows: |x_0(t)| \sim 10 \left( \frac{1}{n}\sec\left( \frac{4π}{9} \right) \right)^{\frac 9{10}} t^{\frac 1{10}} \to \infty as n \to 0^+. (II) For a fixed n \in (0, \frac 98), oscillatory structures of solutions near interfaces. (III) Again, for a fixed n \in (0, \frac 98), global structures of some nonlinear eigenfunctions \{f_\g\}_{|\g| \ge 0} by a combination of numerical and analytical methods.

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arXiv2014

Variational approach for a class of cooperative systems

The aim of this work is to ascertain the characterization of the existence of coexistence states for a class of cooperative systems supported by the study of an associated non--local equation through classical variational methods. Thanks to those results we are able to obtain the blow--up behaviour of the solutions in the whole domain for certain values of the main continuation parameter.

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arXiv2014

The p-Laplace equation in domains with multiple crack section via pencil operators

The p-Laplace equation $$ \n \cdot (|\n u|^n \n u)=0 \whereA n>0, $$ in a bounded domain $Ø\subset \re^2$, with inhomogeneous Dirichlet conditions on the smooth boundary $\p Ø$ is considered. In addition, there is a finite collection of curves $$Γ= Γ_1\cup...\cupΓ_m \subset Ø, \quad \{on which we assume homogeneous Dirichlet boundary conditions} \quad u=0, $$ modeling a multiple crack formation, focusing at the origin $0 \in Ø$. This makes the above quasilinear elliptic problem overdetermined. Possible types of the behaviour of solution $u(x,y)$ at the tip 0 of such admissible multiple cracks, being a "singularity" point, are described, on the basis of blow-up scaling techniques and a "nonlinear eigenvalue problem". Typical types of admissible cracks are shown to be governed by nodal sets of a countable family of nonlinear eigenfunctions, which are obtained via branching from harmonic polynomials that occur for $n=0$. Using a combination of analytic and numerical methods, saddle-node bifurcations in $n$ are shown to occur for those nonlinear eigenvalues/eigenfunctions.

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arXiv2014

Well-posedness of the Cauchy problem for a fourth-order thin film equation via regularization approaches

This paper is devoted to some aspects of well-posedness of the Cauchy problem for a quasilinear degenerate fourth-order parabolic thin film equation u_{t} = -\nabla \cdot(|u|^{n} \nabla\D u) in \ren \times \re_+, \quad u(x,0)=u_0(x) in \ren, where $n>0$ is a fixed exponent, with bounded smooth compactly supported initial data. Dealing with the CP (for, at least, $n \in (0, \frac 32)$) requires introducing classes of infinitely changing sign solutions that are oscillatory close to finite interfaces. The main goal of the paper is to detect proper solutions of the CP for the degenerate TFE--4 by uniformly parabolic analytic $\e$-regularizations at least for values of the parameter $n$ sufficiently close to 0.

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arXiv2013

Steady states, global existence and blow-up for fourth-order semilinear parabolic equations of Cahn--Hilliard type

Fourth-order semilinear parabolic equations of the Cahn--Hilliard-type (01) u_t + \D^2 u = \g u \pm \D (|u|^{p-1}u) in Ω\times \re_+, are considered in a smooth bounded domain $Ø\subset \ren$ with Navier-type boundary conditions on $\p Ø$, or $Ø= \ren$, where $p>1$ and $\g$ are given real parameters. The sign $``+"$ in the "diffusion term" on the right-hand side means the stable case, while $``-"$ reflects the unstable (blow-up) one, with the simplest, so called limit, canonical model for $\g=0$, (02) u_t + \D^2 u= \pm \D(|u|^{p-1}u) \inA. The following three main problems are studied: (i) for the unstable model (01), with the $- \D (|u|^{p-1}u)$, existence and multiplicity of classic steady states in $Ø\subset \ren$ and their global behaviour for large $\g>0$; (ii) for the stable model (02), global existence of smooth solutions $u(x,t)$ in $\ren \times \re_+$ for bounded initial data $u_0(x)$ in the subcritical case $p \le p_{*}= 1 + \frac {4}{(N-2)_+}$; and (iii) for the unstable model (02), a relation between finite time blow-up and structure of regular and singular steady states in the supercritical range. In particular, three distinct families of Type I and II blow-up patterns are introduced in the unstable case.

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